Calcitonin gene‐related peptide induces the histone H3 lysine 9 acetylation in astrocytes associated with neuroinflammation in rats with neuropathic pain

Abstract

Aims Calcitonin gene‐related peptide (CGRP) as a regulator of astrocyte activation may facilitate spinal nociceptive processing. Histone H3 lysine 9 acetylation (H3K9ac) is considered an important regulator of cytokine and chemokine gene expression after peripheral nerve injury. In this study, we explored the relationship between CGRP and H3K9ac in the activation of astrocytes, and elucidated the underlying mechanisms in the pathogenesis of chronic neuropathic pain. Methods Astroglial cells (C6) were treated with CGRP and differentially enrichments of H3K9ac on gene promoters were examined using ChIP‐seq. A chronic constriction injury (CCI) rat model was used to evaluate the role of CGRP on astrocyte activation and H3K9ac signaling in CCI‐induced neuropathic pain. Specific inhibitors were employed to delineate the involved signaling. Results Intrathecal injection of CGRP and CCI increased the number of astrocytes displaying H3K9ac in the spinal dorsal horn of rats. Treatment of CGRP was able to up‐regulate H3K9ac and glial fibrillary acidic protein (GFAP) expression in astroglial cells. ChIP‐seq data indicated that CGRP significantly altered H3K9ac enrichments on gene promoters in astroglial cells following CGRP treatment, including 151 gaining H3K9ac and 111 losing this mark, which mostly enriched in proliferation, autophagy, and macrophage chemotaxis processes. qRT‐PCR verified expressions of representative candidate genes (ATG12, ATG4C, CX3CR1, MMP28, MTMR14, HMOX1, RET) and RTCA verified astrocyte proliferation. Additionally, CGRP treatment increased the expression of H3K9ac, CX3CR1, and IL‐1β in the spinal dorsal horn. CGRP antagonist and HAT inhibitor attenuated mechanical and thermal hyperalgesia in CCI rats. Such analgesic effects were concurrently associated with the reduced levels of H3K9ac, CX3CR1, and IL‐1β in the spinal dorsal horn of CCI rats. Conclusion Our findings highly indicate that CGRP is associated with the development of neuropathic pain through astrocytes‐mediated neuroinflammatory responses via H3K9ac in spinal dorsa horn following nerve injury. This study found that CGRP act on their astrocytic receptors and lead to H3K9 acetylation (H3K9ac), which are mainly associated with proliferation‐, autophagy‐, and inflammation‐related gene expression. The number of astrocytes with H3K9ac expression is increased after nerve injury. Inhibition of CGRP attenuates the development of neuropathic pain, which was accompanied by the suppression of H3K9ac, CX3CR1, and IL‐1β expression in CCI rats.

Astrocyte-microglia interaction through C3/C3aR pathway modulates neuropathic pain in rats model of chronic constriction injury

“…[36][37][38] Temporally, we found both C3 and C3aR get elevated between POD7-14, which is also an overlapped period of astrocyte and microglia activation. [39][40][41][42] Therefore, it is necessary for expanding our knowledge regarding the bridge role of C3-C3aR in crosstalk between astrocytes and microglia. It has been found that microglia can induce astrocytes to synthesize C3 by secreting cytokines, such as Il-1α, TNF, and C1q.…”

EZH2 Methyltransferase Regulates Neuroinflammation and Neuropathic Pain

“…In addition to causing vasodilation and sensitizing nociceptors [ 64 ], CGRP in the spinal cord induces microglial activation by acting on several microglial CGRP receptors [calcitonin receptor-like receptor (CRLR), receptor activity-modifying protein 1 (RAMP1), and receptor component protein (CRCP)] [ 65 , 66 ]. It has been known that enhanced CGRP signaling in the spinal dorsal horn is a crucial mechanism contributing to the genesis of neuropathic pain [ 67 , 68 , 69 ]. Increased expression of CGRP and microglial activation were temporally associated with increased EZH2 and H3K27me3 expression in the spinal cord in neuropathic rats induced by CCI on days 1 to 10 after nerve injury [ 10 ].…”

Potentials of Neuropeptides as Therapeutic Agents for Neurological Diseases

“…Interestingly, there is a convergence of the effects of small endogenous peptides such as VIP, substance P, and other cationic peptide drugs on mast cell activation via the Mas-related gene X2 receptor (MrgprX2) pathway [ 149 ], suggesting the presence of common pro-inflammatory pathways evoked by neuropeptides. Inflammatory processes have been reported to enhance tissue damage and accelerate the pathology of numerous neurological disorders including AD [ 150 , 151 , 152 , 153 ], stroke [ 154 , 155 ], Parkinson’s disease (PD) [ 156 , 157 ], amyotrophic lateral sclerosis (ALS) [ 158 ], Huntington’s disease (HD) [ 159 ], and neuropathic pain [ 160 ], as well as metabolic disorders such as obesity [ 161 , 162 ] and normal aging [ 163 ], all of which have been reported to display altered levels or function of neuropeptides. VIP has been heavily implicated in the regulation of the inflammatory response in the periphery (a comprehensive review can be found by Hooper and Kong (2015) [ 164 ]).…”