Epigenetic effects of diet, and reversing DNA methylation

This 2015 French review focused on:

“The role of maternal health and nutrition in the initiation and progression of metabolic and other disorders.

The effects of various in utero exposures and maternal nutritional status may have different effects on the epigenome. However, critical windows of exposure that seem to exist during development need to be better defined.

The epigenome can be considered as an interface between the genome and the environment that is central to the generation of phenotypes and their stability throughout the life course.”

The reviewer used the term “transgenerational” to refer to effects that were more appropriately termed parental or intergenerational. Per the definition in A review of epigenetic transgenerational inheritance of reproductive disease, for the term to apply there needed to be evidence in at least the next 2 male and/or 3 female generations of:

“Altered epigenetic information between generations in the absence of continued environmental exposure.”

The review had separate sections for animal and human studies.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4663595/ “Impact of Maternal Diet on the Epigenome during In Utero Life and the Developmental Programming of Diseases in Childhood and Adulthood”

I arrived at the above review as a result of it citing the 2014 Harvard Reversing DNA Methylation: Mechanisms, Genomics, and Biological Functions. I’ll quote a few items from that review’s informative “Role of DNA demethylation in neural development” section:

“Distinct parts of mammalian brains, including frontal cortex, hippocampus, and cerebellum, all exhibit age-dependent acquisition of 5hmC [an oxidized derivative of 5mC [methylation of the fifth position of cytosine]].

In fact, the genome of mature neurons in adult central nervous system contains the highest level of 5hmC of any mammalian cell-type (~40% as abundant as 5mC in Purkinje neurons in cerebellum). These observations indicate that 5mC oxidation and potentially DNA demethylation may be functionally important for neuronal differentiation and maturation processes.

A comprehensive base-resolution analyses of 5mC and 5hmC in mammalian frontal cortex in both fetal and adult stages indicate that non-CpG methylation (mCH) and CpG hydroxymethylation (hCG) drastically build up in cortical neurons after birth, coinciding with the peak of synaptogenesis and synaptic pruning in the cortex. This study demonstrated that mCH could become a dominant form of cytosine modifications in adult brains, accounting for 53% in adult human cortical neuronal genome.

In mature neurons, intragenic mCH is preferentially enriched at inactive non-neuronal lineage-specific genes, indicating a role in negative regulation of the associated transcripts. By contrast, genic hCG is positively correlated with gene expression levels.”

Brain-region-specific energy metabolism affected the social competitiveness of highly-anxious rats

This 2015 Swiss rodent study found:

Mitochondrial function in the nucleus accumbens, a brain region relevant for motivation and depression, is a critical mediating factor in the subordinate status displayed by high-anxious rats.

Treatment with nicotinamide, an amide form of vitamin B3 that boosts mitochondrial respiration, into the NAc [nucleus accumbens] of high-anxious rats at a time point before the social encounter and at a dose that increased accumbal mitochondrial respiration, abolished the disadvantage of high-anxious animals to become dominant against low-anxious animals.

Our findings highlight a key role for brain energy metabolism in social behavior and point to mitochondrial function in the nucleus accumbens as a potential marker and avenue of treatment for anxiety-related social disorders.”

The researchers handled individual differences of the outbred subjects by separating them into high-, intermediate-, and low-anxiety categories according to their responses on two tests. The high- and low-anxiety subjects were matched by weight, age, and social experience.

Here are a few examples of the researchers thoroughly ruling out confounding factors:

“Differences in social competitiveness are not related to overall differences in social motivation or sociability.

Although social competition did significantly increase corticosterone compared with baseline levels, there were no significant differences between anxiety groups at either time point.

Microinfusion of either ROT, MA, or 3NP [mitochondrial respiration inhibitors] reduced the success of treated animals to win the social contest.

Importantly, these treatments did not induce side effects on social investigation or auto-grooming during social competition, or alter locomotor activity, anxiety, or sociability in additional experiments.

Furthermore, these inhibitor treatments did not produce neurotoxic effects, as the drugs were infused at low doses and we confirmed the absence of lesion and neuronal death.

The effects of complex I or complex II inhibition on social competition were specific for the NAc, as infusions of the same inhibitors into the BLA [basolateral amygdala] had no effect on social dominance and did not affect general locomotor activity.

We further showed that, unlike infusion of muscimol [a GABA receptor agonist] in the BLA that interferes with BLA-dependent auditory fear conditioning, 3NP did not affect conditioning in this task, discarding that neuronal inactivation could be a general mechanism whereby impairing mitochondrial function would affect putative functions from the affected brain region.

The impact of mitochondrial function in social competition described here is not mediated by oxidative stress.”

http://www.pnas.org/content/112/50/15486.full “Mitochondrial function in the brain links anxiety with social subordination”

Assessing a mountain climber’s condition without noticing their empty backpack

A metaphor: for a mountain climber, which point has the most influence on their condition during the climb?

  • The path ahead?
  • The current situation?
  • The recent past?
  • The starting point?
  • The preparations?

Hard to say? Once the climb has started and until it’s finished, though, are there any points at which the preparations have no influence?

Let’s imagine that factors beyond the climber’s control ruined their preparations, leaving them with no reserves and a limited capability to adapt to environmental changes.

Let’s imagine further that researchers take initial physical and psychological measurements of the climber’s condition at an arbitrary point of the ascent or descent. Due to the design of their measurement system, however, they don’t discover that this climber has an empty backpack.

When the researchers interpret the results, will they understand how the climber’s measurements were influenced by the ruined preparations?  end metaphor

A 2014 Israeli study primary finding was of:

“Fear of terror-induced annual increases in resting heart rate.”

The researchers took 325 measurements each “of 17,380 apparently healthy volunteers” who had “consistent exposure to terror threats.”

The study was opaque in some areas. For example, what was the content and handling of a 4-item anxiety questionnaire?

The supplementary material showed that the headlined “fear of terror” term involved three disparate factors:

  • feeling unsafe;
  • fear of crowds; and
  • anxiety about future harm.

I’d like to understand the bases of why the researchers and the reviewer felt it was appropriate that:

“The scores on these items were averaged to yield a continuous FOT [fear-of-terror] score.”

The researchers probably had sufficient measurements of the subjects’ current conditions. They didn’t have a frame of reference that incorporated the present data with contextual information from each individual’s history back to the earliest parts of their life.

Lacking the links provided by such a framework, the researchers likely misassessed measurements that were influenced by how the subjects’ backpacks were packed.

http://www.pnas.org/content/112/5/E467.full “Fear and C-reactive protein cosynergize annual pulse increases in healthy adults”

Research that identified the source of generating gamma brain waves

This 2015 Harvard rodent study found that specific brain neurons trigger cortical band oscillations in the gamma wave length. The cell type:

“Has increased activity during waking and is involved in activating the cerebral cortex and generating gamma oscillations, enabling active cortical processing.

Cortical gamma band oscillations are correlated with conscious awareness.”

1. News coverage of the study misreported the research’s consciousness findings by regurgitating the Harvard press release word-for-word. Several speculations thrown in by the PR staff weren’t supported by the findings regarding:

  • “Awareness of consciousness;
  • Aware of the lower levels of consciousness and their contents.”

2. The researchers used optogenetic stimulation of neurons, similar to the Activation of brainstem neurons induces REM sleep study. The current study took the extra step of lesioning cholinergic neurons to ensure the activity studied was due to the target neurons.

3. The neurons generated gamma waves by simultaneously turning off all receptor neurons, then simultaneously switching them all back on. The researchers said:

“Our results are surprising and novel in indicating that this presumptively inhibitory”

neuron type acted this way.

http://www.pnas.org/content/112/11/3535.full “Cortically projecting basal forebrain parvalbumin neurons regulate cortical gamma band oscillations”

Activation of brainstem neurons induces REM sleep

This 2014 MIT/Harvard rodent study provided evidence that specific brainstem neurons (cholinergic, or containing acetylcholine) regulated dream sleep.

The researchers used a more exact technique that selectively activated just one neuron. They made the neurons in this study sensitive to light using an algae protein that responded to a specific light frequency. Once expressed in the neuron, the protein activated the neuron when that specific frequency of light was shown onto it.

“Interestingly, both manipulations resulted in a change in the number of REM [rapid eye movement] sleep episodes and did not change REM sleep episode duration, suggesting that the PPT [pedunculopontine tegmentumis part of the brainstem] involved in REM sleep initiation but not REM sleep maintenance.”

http://www.pnas.org/content/112/2/584.full “Optogenetic activation of cholinergic neurons in the PPT or LDT induces REM sleep”