Chronic pain causes epigenetic changes in the brain and immune system

This 2015 Canadian rodent study by McGill researchers found:

“The critical involvement of DNA methylation in chronic pain. We show that in the PFC [prefrontal cortex], a brain region strongly implicated in chronic pain, a stunning number of promoters [control gene expression] are differentially methylated 9 months after injury. These changes are distant both in time and space from the original injury.

The changes in DNA methylation are highly organized in functional pathways that have been implicated in pain such as dysregulation of dopaminergic, glutamatergic, opioid and serotoninergic systems and important signaling and inflammatory pathways.

Genome-wide DNA methylation modifications of T cells [circulating white blood cells that control immune response] are also associated with nerve injury.

Most of the promoters (72%) identified as differentially methylated in T cells after nerve injury were also affected in the brain. While the methylation profiles in some of these modules were affected in the same direction in the brain and the T cells, others went in opposite direction. This is consistent with the idea that the brain and the immune system play different roles in chronic pain.

These data suggest that persistent pain is associated with broad and highly organized organism-wide changes in DNA methylation, including two critical biological systems: the central nervous and immune systems. This work also provides a possible mechanistic explanation for commonly observed comorbidities observed in chronic pain (i.e anxiety, depression). Finally, the sheer magnitude of the impact of chronic pain, particularly in the prefrontal cortex, illustrates the profound impact that living with chronic pain exerts on an individual.”

The news coverage focused on how the study’s findings may lead to non-invasive DNA methylation measurements of chronic pain as well as treatments of the effects. I’d argue that the researchers’ concluding statement of the Discussion section deserved the most focus:

“Beyond the example of chronic pain, the robust and highly organized DNA methylation changes seen here in response to nerve injury provides some of the strongest evidence to date that experience effects DNA methylation landscapes at large distances in time and space.”

The study provided “some of the strongest evidence to date” that experiences caused widespread, long-lasting epigenetic changes. Given experiences’ etiologic functions, research with working hypotheses that experiences may potentially reverse epigenetic changes should be green-lighted.

“DNA methylation landscapes at large distances in time and space” warrant systematic examination of how experiential epigenetic changes during early life may be reversed by experiential therapies later in life. In 2016, there’s sufficient evidence for modifying research goals to primarily address causes, not just effects. “Overlapping signatures of chronic pain in the DNA methylation landscape of prefrontal cortex and peripheral T cells”

Outward expressions of inner truth

“Truth needs no defense except when that truth is more than the system can integrate; then it requires defenses.

Our merciful brain has found back-up ways to protect us. It keeps the truth from us even when we go on searching for the truth.

After patients have deep feelings they come up with many truths about their lives. It is buried and defended along with the pain. Thus no one has to give anyone insights; they are already there just waiting for the exit.” “The Act-out and More”

Epigenetics research that was designed to fall one step short of wonderful

This 2015 Edinburgh rodent study found:

“In utero exposure of rats to the analgesics indomethacin or acetaminophen, both of which target PG [prostaglandin] pathways, alters fetal germ cell number and development in both male and female fetuses. This results in modest but detrimental effects on F1 [first generation] female, but not F1 male, fertility in adulthood.

Fetal (F1) exposure of rats to either analgesic resulted in an effect in the second generation (F2 grand-daughters) that manifested as reduced ovarian size and markedly reduced follicle number in females but with evidence of increased follicle activation. The impact on F2 fertility (which was not studied) is unclear.

Our analgesic exposure regimen coincided with the period of chromatin/epigenetic remodelling of the (F1) fetal germ cells in both sexes, events which also occur in the human in the first trimester of pregnancy. The analgesic effects on F2 ovaries were transmitted via both paternal and maternal F1 lines.”

The limitations section showed that the rodents’ acetaminophen dosage was equivalent to a human overdose:

“We administered only a single dose of analgesics. The dose of acetaminophen which we used, resulted in blood levels of acetaminophen 2.5- to 8-fold higher than the levels reported in humans after normal therapeutic dosing (~60 mg/kg/day, divided into 4 doses) during pregnancy.”

I’m puzzled that the researchers didn’t take one more step, and design a great study. They knew what the additional effort would be, per statements such as:

“The impact on F2 fertility (which was not studied) is unclear.

The analgesic-induced reduction in fetal ovarian germ cell number was of particular concern, as the lifetime complement of oocytes is formed in utero at/around the time of birth in women and rodents.”

A F3 generation was needed at least to demonstrate “the impact on F2 fertility.” A F3 generation may have also provided evidence for or against transgenerational epigenetic inheritance, because those subjects’ cells would have had no direct exposure effects from analgesics.

Weren’t the researchers at the MRC Centre for Reproductive Health, The Queen’s Medical Research Institute University of Edinburgh, interested in understanding whether or not a pregnant woman who overdosed during her fetus’ early development on an analgesic available to billions of people, could potentially adversely affect not only her (F0) and her children’s (F1) and grandchildren’s (F2) reproductive health, but also her F3 great-grandchildren?

Weren’t the researchers interested in being a part of a great study, one that may have advanced science, one that may have shown whether or not epigenetic information was transmitted between generations in the absence of continued analgesic exposure? “Analgesic exposure in pregnant rats affects fetal germ cell development with inter-generational reproductive consequences”

Epigenetic memories of stress as therapeutic targets

This 2015 Swedish rodent study found:

Histone modifications induced by glucose are associated with activation of TXNIP gene [a proinflammatory gene involved in diabetic kidney disease] transcription.

Glucose-stimulated TXNIP gene expression can be

  • reversed by inhibition of histone acetyltransferase (HAT), or
  • enhanced by inhibition of histone deacetylase (HDAC).”

A 2016 Japanese commentary expounded on the study:

“Epigenetic changes accumulate as cell memory, and this epigenetic memory plays a crucial role in the long-term consequences of adult-onset diseases and aging.

The first stimulus, which might be high glucose levels or hypoxia, changes the condition of histone modification or chromosomal conformations. The changes are then memorized as epigenetic memory in the cells, which could help to maintain epigenetic status in response to the first stimulus.

Consequently, when a second stimulus occurs, cells with epigenetic memory respond to the stimulus promptly by the upregulation of downstream genes through binding transcriptional factors. The cells without epigenetic memory take longer to upregulate the expression of downstream target genes.

High glucose levels that are sustained for long periods appear to change histone modification, resulting in the prompt response of TXNIP gene upregulation. Considering that TXNIP is an important proinflammatory gene, this prompt response increases the likelihood of diabetic complications. TXNIP is reported to be augmented by high glucose levels and to promote oxidative stress.”

The study and commentary provided specific examples of the wide-ranging forms of physiological memory induced by stress. “Epigenetic regulation of the thioredoxin-interacting protein (TXNIP) gene by hyperglycemia in kidney”

Confusion may be misinterpreted as altruism and prosocial behavior

This 2015 Oxford human study of altruism found:

“Division of people into distinct social types relies on the assumption that an individual’s decisions in public-goods games can be used to accurately measure their social preferences. Specifically, that greater contributions to the cooperative project in the game reflect a greater valuing of the welfare of others, termed “prosociality.”

Individuals behave in the same way, irrespective of whether they are playing computers or humans, even when controlling for beliefs. Therefore, the previously observed differences in human behavior do not need to be explained by variation in the extent to which individuals care about fairness or the welfare of others.

Conditional cooperators, who approximately match the contributions of their groupmates, misunderstand the game. Answering the standard control questions correctly does not guarantee understanding.

We find no evidence that there is a subpopulation of players that understand the game and have prosocial motives toward human players.

These results cast doubt on certain experimental methods and demonstrate that a common assumption in behavioral economics experiments, that choices reveal motivations, will not necessarily hold.

When attempting to measure social behaviors, it is not sufficient to merely record decisions with behavioral consequences and then infer social preferences. One also needs to manipulate these consequences to test whether this affects the behavior.”

The researchers are evolutionary biologists who had made similar points in previous studies. They addressed possible confounders in the study and supporting information, and provided complete details in the appendix. For example, regarding reciprocity:

“Communication was forbidden, and we provided no feedback on earnings or the behavior of groupmates. This design prevents signaling, reciprocity, and learning and therefore minimizes any order effects.

It might also be argued that people playing with computers cannot help behaving as if they were playing with humans. Such ingraining of behavior would suggest a major problem for the way in which economic games have been used to measure social preferences. In particular, behavior would reflect everyday expectations from the real world, such as reputation concerns or the possibility of reciprocity, rather than the setup of the game and the true consequences of choices.”

Some of the news coverage missed the lead point of how:

“Economic experiments are often used to study if humans altruistically value the welfare of others.

These results cast doubt on certain experimental methods and demonstrate that a common assumption in behavioral economics experiments, that choices reveal motivations, will not necessarily hold.”

Here are several expressions of beliefs in one news coverage article where the author attempted to flip the discussion to cast doubt on the study. It was along the lines of “There’s something wrong with this study (that I haven’t thoroughly read) because [insert aspersion about sample size, etc.]” What motivates such reflexive behavior?

This study should inform social behavior studies that draw conclusions from flawed experimental designs. For example, both:

based their findings on a video game of popping balloons. Neither study properly interpreted their subjects’ decisions per the current study’s recommendation:

“When attempting to measure social behaviors, it is not sufficient to merely record decisions with behavioral consequences and then infer social preferences. One also needs to manipulate these consequences to test whether this affects the behavior.” “Conditional cooperation and confusion in public-goods experiments”

Lifelong effects of stress

A 2016 commentary A trilogy of glucocorticoid receptor actions on two 2015 French rodent studies started out:

“Glucocorticoids (GCs) belong to a class of endogenous, stress-stimulated steroid hormones..they have wide ranging physiologic effects capable of impacting metabolism, immunity, development, stress, cognition, and arousal.

GCs exert their cellular effects by binding to the GC receptor (GR), one of a 48-member (in humans) nuclear receptor superfamily of ligand-activated transcription factors.”

The French studies were exceedingly technical. The first GR SUMOylation and formation of an SUMO-SMRT/NCoR1-HDAC3 repressing complex is mandatory for GC-induced IR nGRE-mediated transrepression:

“GCs acting through binding to the GR are peripheral effectors of circadian and stress-related homeostatic functions fundamental for survival.

Unveils, at the molecular level, the mechanisms that underlie the GC-induced GR direct transrepression function mediated by the evolutionary conserved inverted repeated negative response element. This knowledge paves the way to the elucidation of the functions of the GR at the submolecular levels and to the future educated design and screening of drugs, which could be devoid of undesirable debilitating effects on prolonged GC therapy.”

The companion study Glucocorticoid-induced tethered transrepression requires SUMOylation of GR and formation of a SUMO-SMRT/NCoR1-HDAC3 repressing complex stated:

“GCs have been widely used to combat inflammatory and allergic disorders. However, multiple severe undesirable side effects associated with long-term GC treatments, as well as induction of glucocorticoid resistance associated with such treatments, limit their therapeutic usefulness.”

It’s funny that even when researchers study causes, they often justify their efforts in terms of outcomes that address effects. Is an etiologic advancement in science somehow unsatisfactory in and of itself?

Once in a while I get a series of personal revelations while reading scientific publications. Paradoxically, understanding aspects of myself has seldom been sufficient to address historical problems.

Thoughts are only where some of the effects of problems show up, and clarifying my understanding can – at most – tamp down these effects. The causes are elsewhere, and addressing them at the source is what ultimately needs to happen.

A few glucocorticoid-related items to ponder:

  • How has stress impacted my life? When and where did it start?
  • Why do I feel wonderful after taking prednisone or other anti-inflammatories? What may be the originating causes of such effects?
  • Why have prolonged periods of my life been characterized by muted responses to stress? How did I get that way?
  • Have I really understood why I put myself into stressful situations? What will break me out of that habit?
  • Why do the feelings I experience while under stressful situations feel familiar? Does my unconsciousness of their origins have something to do with “homeostatic functions fundamental for survival?”
  • Why haven’t I noticed that symptoms of stress keep showing up in my life? There are “physiologic effects capable of impacting metabolism, immunity,” etc. but I don’t do something about it?
  • How else may stress impact my biology? Brain functioning? Ideas? Behavior?

The purpose of many epigenetic processes is to control virus-like material

This 2016 Swiss human review’s subject was:

“Transposable elements (TEs) may account for up to two-thirds of the human genome, and as genomic threats they are subjected to epigenetic control mechanisms engaged from the earliest stages of embryonic development.

TEs are present in all organisms from bacteria to humans, and they constitute essential motors of evolution. TEs are phylogenetically and biologically related to viruses.

TEs can disrupt genes, provide novel coding activities, exert a wide range of transcriptional influences, and, because of their repetitive nature, create grounds for recombination events leading to genomic deletions and duplications, yet only a very small minority of TEs present in the human genome are still transposition-competent, accounting for one new germline integrant in 20 to 50 human births, and none is capable of horizontal transfer.

A vast majority of these DNA-binding proteins, including many of those expressed in human differentiated cells, primarily recognize sequences contained within TEs..controlling the transcriptional potential of their TE targets well beyond the early embryonic period..modulating the transcriptional impact of TE-residing sequences that are co-opted to regulate the expression of cellular genes.

A large fraction of the recognizable mobile elements in our genome are unique to humans or close relatives..The impact of this phenomenon on speciation might be particularly pronounced in organs subjected to environmental constraints that are not overly coercive, such as the brain..the central nervous system.”

The author presented evidence that the purpose of many ongoing epigenetic processes is to silence or otherwise “tame” TEs “to regulate the expression of cellular genes.” The author contrasted his view with the view that:

“Beyond this early embryonic period, TEs become permanently silenced, and that the evolutionary selection of TE controllers is the result of a simple evolutionary arms race between the host and these genetics invaders.” “Transposable Elements, Polydactyl Proteins, and the Genesis of Human-Specific Transcription Networks”