Epigenetic Regulation of Genes That Modulate Chronic Stress-Induced Visceral Pain in the Peripheral Nervous System

Abstract

BACKGROUNDS & AIMS Chronic stress alters the hypothalamic–pituitary–adrenal axis, increases gut motility, and increases perception of visceral pain. We investigated whether epigenetic mechanisms regulate chronic stress-induced visceral pain in the peripheral nervous systems of rats. METHODS Male rats were subjected to 1 hr water-avoidance stress each day, or given daily subcutaneous injections of corticosterone, for 10 consecutive days. L4–L5 and L6–S2 dorsal root ganglia (DRG) were collected and compared between stressed and control rats (placed for 1 hour each day in a tank without water). Levels of cannabinoid receptor 1 (CNR1), DNA (cytosine-5-)-methyltransferase 1 (DNMT1), transient receptor potential vanilloid type 1 (TRPV1), and EP300 were knocked down in DRG neurons in situ with small interfering RNAs. We measured DNA methylation and histone acetylation at genes encoding the glucocorticoid receptor (NR3C1), CNR1, and TRPV1. Visceral pain was measured in response to colorectal distention. RESULTS Chronic stress was associated with increased methylation of the Nr3c1 promoter and reduced expression of this gene in L6–S2, but not L4–L5, DRGs. Stress was also associated with upregulation in DNMT1-associated methylation of the Cnr1 promoter and downregulation of glucocorticoid receptor-mediated expression of CNR1 in L6–S2, but not L4–L5, DRGs. Concurrently, chronic stress increased expression of the histone acetyltransferase EP300 and increased histone acetylation at the Trpv1 promoter and expression of the TRPV1 receptor in L6–S2 DRG neurons. Knockdown of DNMT1 and EP300 in L6–S2 DRG neurons of rats reduced DNA methylation and histone acetylation, respectively, and prevented chronic stress-induced increases in visceral pain. CONCLUSIONS Chronic stress increases DNA methylation and histone acetylation of genes that regulate visceral pain sensation in the peripheral nervous system of rats. Blocking epigenetic regulatory pathways in specific regions of the spinal cord might be developed to treat patients with chronic abdominal pain.

Mechanisms of Stress-induced Visceral Pain

“…Subsequently, visceral hypersensitivity induced by a repeated stressor or by CORT was shown to modify histone acetylation in the brain and spinal cord, leading to specific changes in pro-and anti-nociceptive gene expression. 61,62,126 DNA methylation patterns within the brain and an increase in the expression of pronociceptive neurotransmitters have also been seen in a model of stress-induced visceral pain. 61 Through the use of currently available histone deacetylase inhibitors such as TSA and suberoylanilide hydroxamic acid (SAHA), in our laboratory, we showed that subjecting male rats to water avoidance stressinduced visceral hypersensitivity could be inhibited by intracerebroventricular infusions of TSA preceding the stress exposure.…”

“…The authors also found that exposing a male rat to the water avoidance stress had multiple additional effects on gene expression within the DRG including increased methylation of the cannabinoid receptor-1 promoter, causing decreased receptor expression and increased histone acetylation at the transient receptor potential cation channel subfamily V member 1 promoter, causing increased receptor expression. 126 The stress-induced visceral hypersensitivity could be reversed through targeted knockdown of the DNA methyltransferase or the histone acetyltransferase that regulated the change in receptor expression. 126 In a rodent model of chronic visceral hypersensitivity induced by neonatal maternal separation, a decrease in acetylation of histone 4 at lysine 12 in the lumbosacral spinal cord correlated with visceral hypersensitivity in adulthood.…”

“…126 The stress-induced visceral hypersensitivity could be reversed through targeted knockdown of the DNA methyltransferase or the histone acetyltransferase that regulated the change in receptor expression. 126 In a rodent model of chronic visceral hypersensitivity induced by neonatal maternal separation, a decrease in acetylation of histone 4 at lysine 12 in the lumbosacral spinal cord correlated with visceral hypersensitivity in adulthood. 127 Furthermore, in a model of visceral hypersensitivity induced by 17β-estradiol in female rats, SAHA infused on to the lumbosacral spinal cord lead to hyperacetylation of H3K9 at the promoter for the metabotropic glutamate receptor-2 (mGLuR2).…”

Impact of a folic acid-enriched diet on urinary tract function in mice treated with testosterone and estradiol

“…While we cannot speculate whether this change was specific to L6 and S1 DRG neurons, or occurred generally across all DRG neurons, these findings are significant since this is the first link between altered DNA methylation and TϩE2-mediated changes in urinary function. DNA methylation and histone acetylation are known regulators of gene expression in rat nociceptive DRG neurons (15). Environmental stressors increase DNA methyltransferase 1 (Dnmt1) abundance uniquely in rat L6-S2 DRG neurons, which increases promoter DNA methylation of cannabinoid receptor 1 and decreases its expression (15).…”

“…DNA methylation and histone acetylation are known regulators of gene expression in rat nociceptive DRG neurons (15). Environmental stressors increase DNA methyltransferase 1 (Dnmt1) abundance uniquely in rat L6-S2 DRG neurons, which increases promoter DNA methylation of cannabinoid receptor 1 and decreases its expression (15). This relieves repression of TRPV1 and thereby increases TRPV1 expression and visceral pain sensitivity (15).…”