Prefrontal cortex

Nrf2 Week #2: Neurons

gettingwell4 4-5 stars Advanced knowledge, Anterior cingulate cortex, Brain development, Cerebrum, Epigenetics, Hippocampus, Limbic system, Memory, Stress , , , , ,

To follow the Nrf2 Week #1 suggestion that Nrf2 target neurological disorders, this 2023 cell study investigated Nrf2 expression in neurons:

“Oxidative metabolism is inextricably linked to production of reactive oxygen species (ROS), which have the potential to damage all classes of macromolecules. Yet ROS are not invariably detrimental. Several properties make ROS useful signaling molecules, including their potential for rapid modification of proteins and close ties to cellular metabolism.

We used multiple single cell genomic datasets to explore Nrf2 expression and regulation in hundreds of neuronal and non-neuronal cell types in mouse and human. With few exceptions, Nrf2 is expressed at far lower levels in neurons than in non-neuronal support cells in both species.

This pattern is maintained in multiple disease states, and the chromatin accessibility landscape at the Nrf2 locus parallels these expression differences. These results imply that Nrf2 activity is limited in almost all neurons of the mouse and human central nervous system (CNS).

nrf2 expression

We separated cell types into neuron or non-neuronal ‘support’ cell categories. The general ‘support’ term is not meant to minimize the functional relevance of non-neuronal cells in the CNS, but is an umbrella term meant to cover everything from glial cell types (astrocytes, microglia, oligodendrocytes) to endothelial cells.

It is not clear why an important, near ubiquitous cytoprotective transcription factor like Nrf2 remains off in mature neurons, especially considering oxidative stress is a driver of many diseases. The simplest explanation is that Nrf2 activity also disrupts normal function of mature neurons.

ROS play a key role in controlling synaptic plasticity in mature neurons. These activity-dependent changes in synaptic transmission, which are important for learning and memory, are disrupted by antioxidants.

A subset of important Nrf2-targeted antioxidant genes (e.g., Slc3a2, Slc7a11, Nqo1, Prdx1) are also low in neurons. So it is likely that these and/or other Nrf2 targets must remain low or non-ROS-responsive in mature neurons. Future work exploring why this expression pattern persists in mature neurons will inform our models on roles of antioxidant genes in normal neuronal physiology and in neurological disorders.“

https://www.biorxiv.org/content/10.1101/2023.05.09.540014v1.full “Limited Expression of Nrf2 in Neurons Across the Central Nervous System”

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Don’t eat yourself into disease, Part 2

gettingwell4 4-5 stars Advanced knowledge, Dopamine, Epigenetics, Hippocampus, Hypothalamus, Immune system, Limbic system, Memory, Stress , , ,

This blog’s 1000th curation is a 2023 rodent study associating gut microbiota, behavior, memory, and food reward:

“Energy intake and energy expenditure is regulated by the hypothalamus, and is referred to as homeostatic regulation of food intake. The reward system is the non-homeostatic regulation of food intake – pleasure-related consumption of foods enriched in fat and sugar. The pleasure is encoded by dopamine release from dopaminergic neurons projecting from the ventral tegmental area to the striatum, the nucleus accumbens, and the prefrontal cortex.

Food reward can be divided into three components – liking, wanting, and learning:

  • Liking refers to food hedonic value;
  • Wanting to the motivational process to seek out and consume certain foods; and
  • Learning to reinforcing conditioning behavior associated with food intake stimulus.

We confirmed that obese mice have a dysregulation of the learning and the wanting components of  food reward. Our previous data showed that the liking component was transferable through fecal material transplantation.

We demonstrated that gut microbes play a role in the regulation of food reward, and could be responsible for compulsive behavior and excessive motivation to obtain sucrose pellets. Moreover, obese gut microbes affected dopaminergic and opioid markers involved in reward system.

We identified 33HPP (produced exclusively by gut bacteria) as particularly increased in mice recipients of gut microbes from obese mice. We were able to demonstrate its effects as key mediator of the gut-brain axis controlling the reward response to palatable food.”

https://microbiomejournal.biomedcentral.com/articles/10.1186/s40168-023-01526-w “Obese-associated gut microbes and derived phenolic metabolite as mediators of excessive motivation for food reward”

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Eat broccoli sprouts for depression, Part 3

gettingwell4 4-5 stars Advanced knowledge, Cerebrum, Epigenetics, Hippocampus, Hypothalamus, Limbic system, Memory, Stress , , , , ,

Here are two papers published after Part 2 that cited the Part 1 rodent study, starting with a 2023 rodent study performed by several Part 1 coauthors:

“We used a low-dose LPS-induced endotoxaemia model to mimic clinical characteristics of sepsis. We found that adolescent LPS treatment was sufficient to increase levels of inflammatory factor TNF-α in both the medial prefrontal cortex (mPFC) and hippocampus at post-natal day P22.

P21 LPS-treated mice were injected with sulforaphane (SFN) or saline intraperitoneally at P49 and then subjected to subthreshold social defeat stress (SSDS). We found that SFN preventative treatment significantly:

  • Decreased the social avoidance, anhedonia, and behavioural despair detected by the social interaction test, sucrose preference test, tail suspension test, and forced swim test, respectively.
  • Decreased anxiety-like behaviours without affecting locomotor activities.
  • Increased Nrf2 and brain-derived neurotrophic factor (BDNF) levels in the mPFC of P21 LPS-treated mice after SSDS compared with saline control mice.

The above results suggest that activation of the Nrf2-BDNF signalling pathway prevents the effect of adolescent LPS-induced endotoxaemia on stress vulnerability during adulthood.

sulforaphane and stress vulnerability

These results suggest that early adolescence is a critical period during which inflammation can promote stress vulnerability during adulthood. This might be due to increased inflammatory response in the mPFC, and mediated by decreased levels of Nrf2 and BDNF. These findings may shed light on the potential use of SFN as an alternative preventative intervention for inflammation-induced stress vulnerability.”

https://link.springer.com/article/10.1007/s00213-022-06285-4 “Lipopolysaccharide-induced endotoxaemia during adolescence promotes stress vulnerability in adult mice via deregulation of nuclear factor erythroid 2-related factor 2 in the medial prefrontal cortex” (not freely available)

This study demonstrated that adolescent diseases and stresses don’t necessarily develop into adult social problems. A timely intervention may even prevent future adult problems.

The one-time 10 mg/kg sulforaphane dose was the same as Part 1’s dose, a human equivalent of which is (10 mg x .081) x 70 kg = 57 mg.

I’d like to know more about how subjects’ memories of adverse events were retained, and subsequently affected their biology and behavior. Pretty sure limbic structures like the hypothalamus as well as lower brain structures played a part.

A 2022 review summarized what was known up to that time regarding Nrf2 and depression:

“Sulforaphane, an organosulfur compound isolated from Brassicaceae plants, is a potent natural NRF2 activator. Sulforaphane:

  • Exerts antidepressant- and anxiolytic-like activities and inhibits HPA axis and inflammatory response.
  • Has both therapeutic and prophylactic effects on inflammation-related depression.
  • Confers stress resilience.
  • Protects neurons via autophagy and promotes mitochondrial biogenesis by activating Nrf2.”

https://www.sciencedirect.com/science/article/pii/S2213231722002944 “Nrf2: An all-rounder in depression”

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Peripheral vs. brain epigenetic measurements

gettingwell4 2-3 stars Required further work, Epigenetics, Immune system , , ,

This 2023 human study investigated associations of peripheral and brain epigenetic measurements:

“Evaluating DNA methylation of brain tissue is challenging owing to the issue of tissue specificity. Consequently, peripheral surrogate tissues are used, resulting in limited progress compared with other epigenetic studies.

Averaging data for each CpG across individuals, saliva–brain correlation (r = 0.90) was higher than that for blood–brain (r = 0.87) and buccal–brain (r = 0.88) comparisons. Among individual CpGs, blood had the highest proportion of CpGs correlated to the brain at nominally significant levels (19.0%), followed by saliva (14.4%) and buccal (9.8%). However, cross-database correlations of correlation coefficients revealed relatively low brain vs. blood: r = 0.27, saliva: r = 0.18, and buccal: r = 0.24.

The majority of methylation in the brain is most likely not synchronized with methylation in the periphery. Despite this, variable CpGs that correlate in the brain and periphery, although in small numbers, may have biological relevance, and could be useful for inferring brain methylation from peripheral tissues.

This study has six major limitations.”

https://www.nature.com/articles/s41398-023-02370-0 “Cross-tissue correlations of genome-wide DNA methylation in Japanese live human brain and blood, saliva, and buccal epithelial tissues”

Real science is messy. Hypotheses are experimentally reevaluated many, many times under varying conditions. I skip over studies where researchers don’t provide meaningful limitation clauses.

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Broccoli sprouts activate the AMPK pathway, Part 4

gettingwell4 4-5 stars Advanced knowledge, Cerebrum, Dopamine, Epigenetics, Hippocampus, Immune system, Limbic system, Memory, Neurochemicals, Stress , , , , ,

Today someone viewed the 2020 Part 3 of Broccoli sprouts activate the AMPK pathway which lacked citations at the time. Checking again, here are three citing 2022 papers, starting with a review:

“Nrf2 is an important transcription factor that regulates expression of a large number of genes in healthy and disease states. Nrf2 regulates expression of several key components of oxidative stress, mitochondrial biogenesis, mitophagy, autophagy, and mitochondrial function in all organs of the human body, and in the peripheral and central nervous systems.

Overall, therapeutic drugs including sulforaphane that target Nrf2 expression and Nrf2/ARE pathway are promising. This article proposes additional research in Nrf2’s role within Parkinson’s disease, Huntington’s disease, and ischemic stroke in preclinical mouse models and humans with age-related neurodegenerative diseases.”

https://www.sciencedirect.com/science/article/pii/S1568163722001982 “Role of Nrf2 in aging, Alzheimer’s and other neurodegenerative diseases” (not freely available) Thanks to Dr. P. Hemachandra Reddy for providing a copy.

One of the Part 3 study’s coauthors contributed to this very detailed review:

“Due to observed overlapping cellular responses upon AMPK or NRF2 activation and common stressors impinging on both AMPK and NRF2 signaling, it is plausible to assume that AMPK and NRF2 signaling may interdepend and cooperate to readjust cellular homeostasis.

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The outcome and underlying signaling events of AMPK-NRF2 crosstalk may diverge between:

  1. in vitro and in vivo studies (one cell type in isolation vs inter-organ crosstalk in living organisms);
  2. Different cell types/organs/organisms of different cultivation conditions, genetic background, age or sex;
  3. Different stress-regimens (chronic vs acute, nature of stress (lipotoxicity, redox stress, xenobiotic, starvation, etc));
  4. Different modes of Nrf2 or AMPK activation and inhibition (genetic vs pharmacological, constitutive vs transient/intermittent, systemic vs organ-specific, electrophilic vs PPI, allosteric vs covalent, or pan vs subtype-specific);
  5. Different target genes with distinct promoter and enhancer structure; or
  6. Different timing of activation.

The latter should deserve increased attention as Nrf2 is one of the most cycling genes under control of the circadian clock. Feeding behavior, metabolism and hence AMPK activity follow and substantiate the biological clock, indicating an entangled circadian regulation of metabolic and redox homeostasis.”

https://www.sciencedirect.com/science/article/pii/S089158492200497X “AMPK and NRF2: Interactive players in the same team for cellular homeostasis?”

A third citing paper was a study of lens cells that provided an example of similar metformin effects noted in Part 2 of Broccoli sprouts activate the AMPK pathway:

“Loss of Nrf2 and Nrf2 antioxidant genes expression and activity in aging cells leads to an array of oxidative-induced deleterious responses, impaired function, and aging pathologies. This deterioration is proposed to be the primary risk factor for age-related diseases such as cataracts.

AMPK regulates energy at physiological levels during metabolic imbalance and stress. AMPK is a redox sensing molecule, and can be activated under cellular accumulation of reactive oxygen species, which are endogenously produced due to loss of antioxidant enzymes.

The therapeutic potential of AMPK activation has context-dependent beneficial effects, from cell survival to cell death. AMPK activation was a requisite for Bmal1/Nrf2-antioxidants-mediated defense, as pharmacologically inactivating AMPK impeded metformin’s effect.

Using lens epithelial cell lines (LECs) of human or mouse aging primary LECs along with lenses as model systems, we demonstrated that metformin could correct deteriorated Bmal1/Nrf2/ARE pathway by reviving AMPK-activation and transcriptional activities of Bmal1/Nrf2, resulting in increased antioxidants enzymatic activity and expression of Phase II enzymes. Results uncovered crosstalk between AMPK and Bmal1/Nrf2/antioxidants mediated by metformin for blunting oxidative/aging-linked pathobiology.”

https://www.mdpi.com/2073-4409/11/19/3021/htm “Obligatory Role of AMPK Activation and Antioxidant Defense Pathway in the Regulatory Effects of Metformin on Cellular Protection and Prevention of Lens Opacity”

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If you were given a lens to see clearly, would you accept it?

gettingwell4 4-5 stars Advanced knowledge, Amygdala, Brainstem, Cerebrum, Cortisol, Epigenetics, Hippocampus, Hypothalamus, Limbic system, Locus coeruleus, Lower brain, Memory, Neurochemicals, Primal Therapy, Serotonin, Stress , , , , , , , ,

Two papers, starting with a 2022 rodent study of maternal behaviors’ effects on offspring physiologies:

“Early life adversity (ELA) is a major risk factor for development of pathology. Predictability of parental care may be a distinguishing feature of different forms of ELA.

We tested the hypothesis that changes in maternal behavior in mice would be contingent on the type of ELA experienced, directly comparing predictability of care in the limited bedding and nesting (LBN) and maternal separation (MS) paradigms. We then tested whether predictability of the ELA environment altered expression of corticotropin-releasing hormone (Crh), a sexually-dimorphic neuropeptide that regulates threat-related learning.

MS was associated with increased expression of Crh-related genes in males, but not females. LBN primarily increased expression of these genes in females, but not males.”

https://www.sciencedirect.com/science/article/pii/S2352289522000595 “Resource scarcity but not maternal separation provokes unpredictable maternal care sequences in mice and both upregulate Crh-associated gene expression in the amygdala”

I came across this first study by it citing a republished version of 2005 epigenetic research from McGill University:

“Early experience permanently alters behavior and physiology. A critical question concerns the mechanism of these environmental programming effects.

We propose that epigenomic changes serve as an intermediate process that imprints dynamic environmental experiences on the fixed genome resulting in stable alterations in phenotype. These findings demonstrate that structural modifications of DNA can be established through environmental programming and that, in spite of the inherent stability of this epigenomic marker, it is dynamic and potentially reversible.”

https://www.tandfonline.com/doi/full/10.31887/DCNS.2005.7.2/mmeaney “Environmental programming of stress responses through DNA methylation: life at the interface between a dynamic environment and a fixed genome”

This post commemorates the five-year anniversary of Dr. Arthur Janov’s death. Its title is taken from my reaction to his comment on Beyond Belief: Symptoms of hopelessness. Search his blog for mentions of the second paper’s coauthors, Drs. Meaney and Szyf.

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Non-patentable boron benefits

gettingwell4 4-5 stars Advanced knowledge, Acetylcholine, Amygdala, Cerebellum, Cortisol, Dopamine, Epigenetics, Glutamate, Hippocampus, Hypothalamus, Immune system, Limbic system, Lower brain, Memory, Neurochemicals, Serotonin, Stress , , , , ,

To follow up Is boron important to health? I’ll highlight a 2022 review of boron intake:

“Boron is essential for activity of several metabolic enzymes, hormones, and micronutrients. It is important for growth and maintenance of bone, reduction in inflammatory biomarkers, and increasing levels of antioxidant enzymes.

The average person’s daily diet contains 1.5 to 3 milligrams of boron. Boron intakes of 1–3 mg/day have been shown to improve bone and brain health in adults when compared to intakes of 0.25–0.50 mg/day.

One week of 10 mg/d boron supplementation resulted in a 20% reduction in inflammatory biomarkers TNF-α, as well as significant reductions (nearly 50%) in plasma concentrations of hs-CRP and IL-6. Calcium fructoborate, a naturally occurring, plant-based boron-carbohydrate complex, had beneficial effects on osteoarthritis (OA) symptoms. A double-blind study in middle-aged patients with primary OA found that all groups except the placebo group saw a reduction in inflammatory biomarkers after 15 days of food supplementation with calcium fructoborate.

Dietary boron intake significantly improves brain function and cognitive functioning in humans. Electroencephalograms showed that boron pharmacological intervention after boron deficiency improved functioning in older men and women, such as less drowsiness and mental alertness, better psychomotor skills (for example, motor speed and dexterity), and better cognitive processing (e.g., attention and short-term memory). Boron compounds can help with both impaired recognition and spatial memory problems.

We discussed the role of boron-based diet in memory, boron and microbiome relation, boron as anti-inflammatory agents, and boron in neurodegenerative diseases. Boron reagents will play a significant role to improve dysbiosis.”

https://www.mdpi.com/1420-3049/27/11/3402/htm “The Role of Microbiome in Brain Development and Neurodegenerative Diseases”

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If you lose mobility, you lose cognitive function

gettingwell4 0-1 star Wasted resources, Cerebrum, Epigenetics, Memory , , ,

This 2022 human study used four epigenetic clocks to assess aging:

“This cohort study was a secondary analysis of 3 Women’s Health Initiative (WHI) ancillary studies among 1813 women eligible to survive to age 90 years by end of study period. The study found that increased epigenetic age acceleration (EAA) as measured by 4 epigenetic clocks was associated with lower odds of survival to age 90 years with intact mobility; results were similar when including intact cognitive functioning.

This study benefited from a large, racially and ethnically diverse sample of women who were followed up to at least age 90 years with detailed longitudinal data on a host of lifestyle and health history factors. This study is generalizable to WHI women owing to use of IPW weights, and may be generalizable to a large range of women in the United States.

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Among 1813 women, there were:

  • 464 women who survived to age 90 years with intact mobility and cognitive functioning;
  • 420 women who survived to age 90 years without intact mobility and cognitive functioning; and
  • 929 women who did not survive to age 90 years.

Only 29 women were reclassified from the healthy longevity group to surviving to age 90 years without intact mobility and cognitive functioning. Although it was of great interest to investigate the association between EAA and survival to age 90 years with intact cognitive function independently, this study population did not have sufficient numbers of women who experienced loss of cognitive function (without loss of mobility) to do so.”

https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2794706 “Analysis of Epigenetic Age Acceleration and Healthy Longevity Among Older US Women”

Early humans who lost mobility in our African savanna ancestral environment during the Pleistocene Epoch (approximately 2.6M to 12K years ago) were prey. I highly doubt that immobile individuals successfully became our ancestors.

I downgraded this study because these researchers misguidedly soiled worthwhile findings with BMI and education level non-causal associations. They intentionally did this, as several of them were coauthors of the execrable Epigenome-wide meta-analysis of BMI in nine cohorts: examining the utility of epigenetic BMI in predicting metabolic health.

See Findings, or fun with numbers? and Does a societal mandate cause DNA methylation? for opposing research.

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Non-CpG methylation

gettingwell4 4-5 stars Advanced knowledge, Amygdala, Cerebrum, Epigenetics, Hippocampus, Hypothalamus, Limbic system, Memory, Stress , , , , , , ,

Three 2022 papers on methylation epigenetic modifiers, starting with a human study focused on mitochondrial DNA non-CpG methylation involving nucleobases other than guanine (arginine, cytosine, or thymine):

“We collected brain tissue in the nucleus accumbens and prefrontal cortex from deceased individuals without (n = 39) and with (n = 14) drug use, and used whole-genome bisulfite sequencing to cover cytosine sites in the mitochondrial genome. Epigenetic clocks in illicit drug users, especially in ketamine users, were accelerated in both brain regions by comparison with nonusers.

Unlike the predominance of CpG over non-CpG methylation in the nuclear genome, the average CpG and non-CpG methylation levels in the mitochondrial genome were almost equal. The utility of non-CpG methylation was further illustrated by the three indices constructed in this study with non-CpG sites having better distinction between brain areas, age groups, and the presence or absence of drug use than indices consisting of CpG sites only. Results of previous studies on the mitochondrial genome that were solely based on CpG sites should be interpreted cautiously.

The epigenetic clock made up of age-related cytosine sites in mtDNA of the control group was consistently replicated in these two brain regions. One possibility for the correlation is the cycle theory that involves mitochondrial activity, mitochondrial DNA methylation, and alpha-ketoglutarate.

As mitochondrial activity fades with aging, mitochondria gradually lose the ability to eliminate methylation on cytosines through alpha-ketoglutarate. Further investigation of the underlying mechanisms is warranted.

To our knowledge, this is the first report that ketamine might change the mitochondrial epigenetic clock in human brain tissues. We believe this is the first report to elucidate comprehensively the importance of mitochondrial DNA methylation in human brain.”

https://clinicalepigeneticsjournal.biomedcentral.com/articles/10.1186/s13148-022-01300-z “Mitochondrial DNA methylation profiling of the human prefrontal cortex and nucleus accumbens: correlations with aging and drug use”

A second rodent study focused on RNA methylation:

“We investigated the role of RNA N6-methyladenosine (m6A) in improved resilience against chronic restraint stress. A combination of molecular, behavioral, and in vivo recording data demonstrates exercise-mediated restoration of m6A in the mouse medial prefrontal cortex, whose activity is potentiated to exert anxiolytic effects. To provide molecular explanations, it is worth noting that epigenetic regulation, such as histone modification, microRNA, and DNA methylation all participate in mental and cognitive rehabilitation following exercise.

To generalize these rodent data to humans, we recruited a small group of patients with major depressive disorder with prominent anxiety disorders. Compared to age- and sex-matched healthy individuals, patients displayed decreased circulating methyl donor S-adenosyl methionine (SAM) levels. Serum SAM levels were found to be inversely correlated with the Hamilton Anxiety Scale, suggesting the potential value of SAM as a biomarker for depression or anxiety disorders.

Hepatic biosynthesis of methyl donors is necessary for exercise to improve brain RNA m6A to counteract environmental stress. The dependence on hepatic-brain axis suggests the ineffectiveness of exercise training on people with hepatic dysfunctions.

This novel liver-brain axis provides an explanation for brain network changes upon exercise training, and provides new insights into diagnosis and treatment of anxiety disorders. Exercise-induced anxiolysis might be potentiated by further replenishment of RNA methylation donors, providing a strategy of exercise plus diet supplement in preventing anxiety disorders.”

https://onlinelibrary.wiley.com/doi/10.1002/advs.202105731 “Physical Exercise Prevented Stress-Induced Anxiety via Improving Brain RNA Methylation”

A third paper was a review of mitochondrial-to-nuclear epigenetic regulation. I’ll highlight one mitochondrial metabolite, alpha-ketoglutarate (α-KG):

“Apart from established roles in bioenergetics and biosynthesis, mitochondria are signaling organelles that communicate their fitness to the nucleus, triggering transcriptional programs to adapt homeostasis stress that is essential for organismal health and aging. Emerging studies revealed that mitochondrial-to-nuclear communication via altered levels of mitochondrial metabolites or stress signals causes various epigenetic changes, facilitating efforts to maintain homeostasis and affect aging.

Metabolites generated by the tricarboxylic acid (TCA) cycle, the electron transport chain (ETC), or one-carbon cycle within mitochondria can act as substrates or cofactors to control epigenetic modification, especially histone acetylation and methylation and DNA methylation. α-KG produced in the TCA cycle serves as an essential cofactor for the chromatin-modifying Jumonji C (JmjC) domain-containing lysine demethylases (JMJDs) and ten-eleven translocation (TETs) DNA demethylases. Changes in α-KG levels are capable of driving nuclear gene expression by affecting DNA and histone methylation profiles.

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α-KG deficiency in progenitor stem cells increases with age. For example, the level of α-KG is reduced in follicle fluids of aged humans, and supplementation with α-KG preserves ovarian function in mice.

α-KG extends lifespan in Drosophila by activating AMPK signaling and inhibiting the mTOR pathway. Supplementing α-KG in the form of a calcium salt promoted a longer and healthier life associated with decreased levels of inflammatory cytokines in old mice.

A human study showed a nearly 8-year reversal in DNA methylation clock biological ages of 42 individuals taking an α-KG based formulation for 4–10 months. α-KG supplementation leads to both demethylation and hypermethylation of some CpG sites in the genome, suggesting that α-KG may have a broader effect on methylation-based aging, such as metabolic functions.

Outstanding questions:

  1. How is production of mitochondrial metabolites regulated both spatially and temporally to elicit epigenetic changes in response to mitochondrial dysfunction?
  2. What are specific epigenetic factors involved in mitochondrial-to-nuclear communications, and how do they cooperate with transcription factors in response to various external and internal stimuli?
  3. Do various mitochondrial metabolites act alone or in concert on the epigenome to regulate the aging process?
  4. Are some organs or tissues more at risk than others in maintaining mitochondrial-to-nuclear communication during aging?
  5. Can intervention of mitochondrial-to-nuclear communications mimic beneficial epigenetic changes to delay aging or alleviate age-onset diseases?”

https://www.sciencedirect.com/science/article/pii/S0968000422000676 “Mitochondrial-to-nuclear communication in aging: an epigenetic perspective”

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Taurine week #7: Brain

gettingwell4 4-5 stars Advanced knowledge, Acetylcholine, Amygdala, Anterior cingulate cortex, Brain development, Cerebellum, Cerebrum, Dopamine, Epigenetics, Glutamate, Hippocampus, Hypothalamus, Immune system, Limbic system, Lower brain, Memory, Neurochemicals, Stress, Thalamus , , , , ,

Finishing a week’s worth of 2022 taurine research with two reviews of taurine’s brain effects:

“We provide a overview of brain taurine homeostasis, and review mechanisms by which taurine can afford neuroprotection in individuals with obesity and diabetes. Alterations to taurine homeostasis can impact a number of biological processes such as osmolarity control, calcium homeostasis, and inhibitory neurotransmission, and have been reported in both metabolic and neurodegenerative disorders.

Models of neurodegenerative disorders show reduced brain taurine concentrations. On the other hand, models of insulin-dependent diabetes, insulin resistance, and diet-induced obesity display taurine accumulation in the hippocampus. Given cytoprotective actions of taurine, such accumulation of taurine might constitute a compensatory mechanism that attempts to prevent neurodegeneration.

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Taurine release is mainly mediated by volume-regulated anion channels (VRAC) that are activated by hypo-osmotic conditions and electrical activity. They can be stimulated via glutamate metabotropic (mGluR) and ionotropic receptors (mainly NMDA and AMPA), adenosine A1 receptors (A1R), and metabotropic ATP receptors (P2Y).

Taurine mediates its neuromodulatory effects by binding to GABAA, GABAB, and glycine receptors. While taurine binding to GABAA and GABAB is weaker than to GABA, taurine is a rather potent ligand of the glycine receptor. Reuptake of taurine occurs via taurine transporter TauT.

Cytoprotective actions of taurine contribute to brain health improvements in subjects with obesity and diabetes through various mechanisms that improve neuronal function, such as:

  • Modulating inhibitory neurotransmission, which promotes an excitatory–inhibitory balance;
  • Stimulating antioxidant systems; and
  • Stabilizing mitochondria energy production and Ca2+ homeostasis.”

https://www.mdpi.com/2072-6643/14/6/1292/htm “Taurine Supplementation as a Neuroprotective Strategy upon Brain Dysfunction in Metabolic Syndrome and Diabetes”

A second review focused on taurine’s secondary bile acids produced by gut microbiota:

“Most neurodegenerative disorders are diseases of protein homeostasis, with misfolded aggregates accumulating. The neurodegenerative process is mediated by numerous metabolic pathways, most of which lead to apoptosis. Hydrophilic bile acids, particularly tauroursodeoxycholic acid (TUDCA), have shown important anti-apoptotic and neuroprotective activities, with numerous experimental and clinical evidence suggesting their possible therapeutic use as disease-modifiers in neurodegenerative diseases.

Biliary acids may influence each of the following three mechanisms through which interactions within the brain-gut-microbiota axis take place: neurological, immunological, and neuroendocrine. These microbial metabolites can act as direct neurotransmitters or neuromodulators, serving as key modulators of the brain-gut interactions.

The gut microbial community, through their capacity to produce bile acid metabolites distinct from the liver, can be thought of as an endocrine organ with potential to alter host physiology, perhaps to their own favour. Hydrophilic bile acids, currently regarded as important hormones, exert modulatory effects on gut microbiota composition to produce secondary bile acids which seem to bind a number of receptors with a higher affinity than primary biliary acids, expressed on many different cells.

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TUDCA regulates expression of genes involved in cell cycle regulation and apoptotic pathways, promoting neuronal survival. TUDCA:

  • Improves protein folding capacity through its chaperoning activity, in turn reducing protein aggregation and deposition;
  • Reduces reactive oxygen species production, leading to protection against mitochondrial dysfunction;
  • Ameliorates endoplasmic reticulum stress; and
  • Inhibits expression of pro-inflammatory cytokines, exerting an anti-neuroinflammatory effect.

Although Alzheimer’s disease, Huntington’s disease, Parkinson’s disease, amyotrophic lateral sclerosis (ALS), and cerebral ischemia have different disease progressions, they share similar pathways which can be targeted by TUDCA. This makes this bile acid a potentially strong therapeutic option to be tested in human diseases. Clinical evidence collected so far has reported comprehensive data on ALS only.”

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9166453/ “Tauroursodeoxycholic acid: a potential therapeutic tool in neurodegenerative diseases”

Taurine week #6: Stress

gettingwell4 4-5 stars Advanced knowledge, Cerebellum, Cerebrum, Cortisol, Epigenetics, Glutamate, Hippocampus, Immune system, Limbic system, Lower brain, Neurochemicals, Serotonin, Stress , , , , ,

Two 2022 rodent studies of taurine’s associations with long-term stress, starting with a chronic restraint stress model:

“We show that chronic restraint stress can lead to hyperalgesia accompanied by changes in gut microbiota that have significant gender differences. Corresponding changes of bacteria can further induce hyperalgesia and affect different serum metabolism in mice of the corresponding sex.

Different serum metabolites between pseudo-germ-free mice receiving fecal microbiota transplantation from the chronic restraint stress group and those from the control group were mainly involved in bile secretion and steroid hormone biosynthesis for male mice, and in taurine and hypotaurine metabolism and tryptophan metabolism for female mice.

Effects of gut microbiota transplantation on serum metabolomics of female host: Taurine and hypotaurine metabolism, tryptophan metabolism, serotonergic synapse, arachidonic acid metabolism, and choline metabolism in cancer were the five identified pathways in which these different metabolites were enriched.

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Taurine and hypotaurine play essential roles in anti-inflammation, anti-hypertension, anti-hyperglycemia, and analgesia. Taurine can be used as a diagnostic index for fibromyalgia syndrome and neuropathic pain.

These findings improve our understanding of sexual dimorphism in gut microbiota in stress-induced hyperalgesia and the effect of gut microbiota on blood metabolic traits. Follow-up research will investigate causal relationships between them.”

https://www.sciencedirect.com/science/article/pii/S1043661822000743 “Gut microbiota and its role in stress-induced hyperalgesia: Gender-specific responses linked to different changes in serum metabolites”

Human equivalents:

  • A 7-8 month-old mouse would be a 38-42 year-old human.
  • A 14-day stress period is about two years for humans.

A second study used a chronic social defeat stress model:

“The level of taurine in extracellular fluid of the cerebral medial prefrontal cortex (mPFC) was significantly reduced in mice with chronic social defeat stress (CSDS)-induced depression. We found that taurine supplementation effectively rescued immobility time during a tail suspension assay and improved social avoidance behaviors in CSDS mice.

Male C57BL/6 J mice (∼ 23 g) and male CD-1 mice aged 7–8 months (∼ 45 g) were used. CD-1 mice were screened for aggressive behavior during social interactions for three consecutive days before the start of the social defeat sessions. Experimental C57BL/6 J mice were subjected to physical interactions with a novel CD-1 mouse for 10 min once per day over 10 consecutive days.

We found significant reductions in taurine and betaine levels in mPFC interstitial fluid of CSDS mice compared with control mice.

csds taurine betaine

We additionally investigated levels of interstitial taurine in chronic restraint stress (CRS) mice, another depressive animal model. After 14 days of CRS treatment, mice showed typical depression-like behaviors, including decreased sucrose preference and increased immobility time. mPFC levels of interstitial taurine were also significantly decreased in CRS mice.

Taurine treatment protected CSDS mice from impairments in dendritic complexity, spine density, and proportions of different types of spines. Expression of N-methyl D-aspartate receptor subunit 2A, an important synaptic receptor, was largely restored in the mPFC of these mice after taurine supplementation.

These results demonstrated that taurine exerted an antidepressive effect by protecting cortical neurons from dendritic spine loss and synaptic protein deficits.”

https://link.springer.com/article/10.1007/s10571-022-01218-3 “Taurine Alleviates Chronic Social Defeat Stress-Induced Depression by Protecting Cortical Neurons from Dendritic Spine Loss”

Human equivalents:

  • A 7-8 month-old mouse would be a 38-42 year-old human.
  • A 500 mg/kg taurine dose injected intraperitoneally is (.081 x 500 mg) x 70KG = 2.835 g.
  • A 10-day stress period is about a year and a half for humans.

Don’t think aggressive humans would have to be twice as large to stress those around them. There may be choices other than enduring a year and a half of that.

The misnomer of nonessential amino acids

gettingwell4 4-5 stars Advanced knowledge, Amygdala, Brain development, Brainstem, Cerebellum, Cerebrum, Epigenetics, Glutamate, Hippocampus, Immune system, Limbic system, Lower brain, Memory, Neurochemicals, Stress , , , ,

Three papers, starting with a 2022 review:

“Ideal diets must provide all physiologically and nutritionally essential amino acids (AAs).

Proposed optimal ratios and amounts of true digestible AAs in diets during different phases of growth and production. Because dynamic requirements of animals for dietary AAs are influenced by a plethora of factors, data below as well as the literature serve only as references to guide feeding practices and nutritional research.

10.1177_15353702221082658-table5

Nutritionists should move beyond the ‘ideal protein’ concept to consider optimum ratios and amounts of all proteinogenic AAs in diets for mammals, birds, and aquatic animals, and, in the case of carnivores, also taurine. This will help formulate effectively low-protein diets for livestock (including swine and high-producing dairy cattle), poultry, fish, and crustaceans, as well as zoo and companion animals.”

https://journals.sagepub.com/doi/10.1177/15353702221082658 “The ‘ideal protein’ concept is not ideal in animal nutrition”

A second 2022 review focused on serine:

“The main dietary source of L-serine is protein, in which L-serine content ranges between 2 and 5%. At the daily intake of ~1 g protein per kg of body weight, the amount of serine obtained from food ranges between 1.4 and 3.5 g (13.2–33.0 mmol) per day in an adult.

Mechanisms of potential benefits of supplementing L-serine include increased synthesis of sphingolipids, decreased synthesis of 1-deoxysphingolipids, decrease in homocysteine levels, and increased synthesis of cysteine and its metabolites, including glutathione. L-serine supplementation has been suggested as a rational therapeutic approach in several disorders, particularly primary disorders of L-serine synthesis, neurodegenerative disorders, and diabetic neuropathy.

Unfortunately, the number of clinical studies evaluating dietary supplementation of L-serine as a possible therapy is small. Studies examining therapeutic effects of L-serine in CNS injury and chronic renal diseases, in which it is supposed that L-serine weakens glutamate neurotoxicity and lowers homocysteine levels, respectively, are missing.”

https://www.mdpi.com/2072-6643/14/9/1987/htm “Serine Metabolism in Health and Disease and as a Conditionally Essential Amino Acid”

A 2021 review subject was D-serine, L-serine’s D-isoform:

“The N-methyl-D-aspartate glutamate receptor (NMDAR) and its co-agonist D-serine are currently of great interest as potential important contributors to cognitive function in normal aging and dementia. D-serine is necessary for activation of NMDAR and in maintenance of long-term potentiation, and is involved in brain development, neuronal connectivity, synaptic plasticity, and regulation of learning and memory.

The source of D-amino acids in mammals was historically attributed to diet or intestinal bacteria until racemization of L-serine by serine racemase was identified as the endogenous source of D-serine. The enzyme responsible for catabolism (breakdown) of D-serine is D-amino acid oxidase; this enzyme is most abundant in cerebellum and brainstem, areas with low levels of D-serine.

Activation of the NMDAR co-agonist-binding site by D-serine and glycine is mandatory for induction of synaptic plasticity. D-serine acts primarily at synaptic NMDARs whereas glycine acts primarily at extrasynaptic NMDARs.

In normal aging there is decreased expression of serine racemase and decreased levels of D-serine and down-regulation of NMDARs, resulting in impaired synaptic plasticity and deficits in learning and memory. In contrast, in AD there appears to be activation of serine racemase, increased levels of D-serine and overstimulation of NMDARs, resulting in cytotoxicity, synaptic deficits, and dementia.”

https://www.frontiersin.org/articles/10.3389/fpsyt.2021.754032/full “An Overview of the Involvement of D-Serine in Cognitive Impairment in Normal Aging and Dementia”

PXL_20220518_093600487

Brain changes

gettingwell4 4-5 stars Advanced knowledge, Anterior cingulate cortex, Brain development, Brain hemispheres, Cerebrum, Epigenetics, Hippocampus, Limbic system, Memory , , ,

This 2022 human study investigated healthy young adult brain changes using MRI and epigenetic clock technologies:

“We aimed to characterize the association of epigenetic age (i.e. estimated DNA methylation age) and its acceleration with surface area, cortical thickness, and volume in healthy young adults. It is largely unknown how accelerated epigenetic age affects multiple cortical features among young adults from 19 to 49 years. Prior findings imply not only that these dynamic changes reveal different aspects of cortical aging, but also that chronological age itself is not a reliable factor to understand the process of cortical aging.

accelerated epigenetic age vs brain features

Seventy-nine young healthy individuals participated in this study. Findings of our study should be interpreted within the context of relatively small sample size, without older adults, and with epigenetic age assessed from saliva.

Additional and unique regional changes due to advanced and accelerated epigenetic age, compared to chronological age-related changes, suggest that epigenetic age could be a viable biomarker of cortical aging. Longitudinal and cross-sectional studies with a larger sample and wider age range are necessary to characterize ongoing effects of epigenetic cortical aging, not only for healthy but also for pathological aging.”

https://doi.org/10.1093/cercor/bhac043 “The effects of epigenetic age and its acceleration on surface area, cortical thickness, and volume in young adults” (not freely available) Thanks to Dr. Yong Jeon Cheong for providing a copy.

State-dependent memory

gettingwell4 4-5 stars Advanced knowledge, Amygdala, Anterior cingulate cortex, Cerebrum, Epigenetics, Hippocampus, Limbic system, Memory, Stress, Thalamus , , ,

This 2021 review by two coauthors of What can cause memories that are accessible only when returning to the original brain state? provided evidence for alternative interpretations of memory experiments:

“Memory consolidation hypotheses postulate a long series of various and time consuming elaborate processes that come to protect memory from disruption after various periods of time. For more than fifty years, consolidation hypotheses led to the idea that:

  1. Memories are fragile and can easily be disrupted; and
  2. Memories require several hours to be encoded (Cellular Consolidation), and extensive periods of time (days to weeks and even months and years), to be definitely stabilized (Systems Consolidation).

Although these views rely on well substantiated findings, their interpretation can be called into question.

An alternative position is that amnesia reflects retrieval difficulties due to contextual changes. This simple explanation is able to account for most, if not all, results obtained in consolidation studies.

memory state dependency

Systems Consolidation can be explained in terms of a form of state-dependency.

Recent memory remains detailed, context-specific (in animals), and vivid (in humans) and very susceptible to contextual changes. With the passage of time, memories become less precise, and retention performance less and less affected by contextual changes.”

https://www.sciencedirect.com/science/article/abs/pii/S0149763421005510 “Revisiting systems consolidation and the concept of consolidation” (not freely available)

I came across this review while trying to understand why a 2022 rodent study felt wrong. That study followed the standard memory paradigm, and I appreciate its lead author providing a copy since it wasn’t otherwise available.

But those researchers boxed themselves in with consolidation explanations for findings. They used drugs to change subjects’ memories’ contexts between training and testing. They didn’t see that tested memories were dependent on subjects’ initial brain states.

This review cited a paper abstracted in Resiliency in stress responses, namely Neurobiological mechanisms of state-dependent learning.

Crab for lunch

PXL_20220419_190655701

Are blood epigenetic clock measurements optimal?

gettingwell4 4-5 stars Advanced knowledge, Cerebellum, Epigenetics, Immune system, Lower brain , , , , ,

This 2022 human study investigated tissue-specific epigenetic clock measurements:

“We used DNA methylation data representing 11 human tissues (adipose, blood, bone marrow, heart, kidney, liver, lung, lymph node, muscle, spleen, and pituitary gland) to quantify the extent to which epigenetic age acceleration (EAA) in one tissue correlates with EAA in another tissue.

Epigenetic age was moderately correlated across tissues:

  • Blood had the greatest number and degree of correlation, most notably with spleen and bone marrow. Blood did not correlate with epigenetic age of liver.
  • EAA in liver was weakly correlated with EAA in kidney, adipose, lung, and bone marrow.
  • Hypertension was associated with EAA in several tissues, consistent with multiorgan impacts of this illness.
  • HIV infection was associated with positive age acceleration in kidney and spleen.
  • Men were found to exhibit higher EAA than women across all tissues when analyzed together. Significant results were also observed in individual tissues (muscle, spleen, and lymph nodes).

men age faster

Blood alone will often fail to detect EAA in other tissues. It will be advisable to profile several sources of DNA (including blood, buccal cells, adipose, and skin) to get a comprehensive picture of the epigenetic aging state of an individual.”

https://link.springer.com/article/10.1007/s11357-022-00560-0 “HIV, pathology and epigenetic age acceleration in different human tissues”

PXL_20220415_184720157