Abstract
Neuropathic pain is associated with hyperexcitability and intrinsic firing of dorsal root ganglia (DRG) neurons. These phenotypical changes can be long lasting, potentially spanning the entire life of animal models, and depend on altered expression of numerous proteins, including many ion channels. Yet, how DRGs maintain long-term changes in protein expression in neuropathic conditions remains unclear. DNA methylation is a well-known mechanism of epigenetic control of gene expression and is achieved by the action of three enzymes: DNA methyltransferase (DNMT) 1, 3a, and 3b, which have been studied primarily during development. We first performed immunohistochemical analysis to assess whether these enzymes are expressed in adult rat DRGs (L4–5) and found that DNMT1 is expressed in both glia and neurons, DNMT3a is preferentially expressed in glia and DNMT3b is preferentially expressed in neurons. A rat model of neuropathic pain was then used to determine whether nerve injury may induce epigenetic changes in DRGs at multiple time points after pain onset. Real-time RT PCR analysis revealed robust and time-dependent changes in DNMT transcript expression in ipsilateral DRGs from spared nerve injury (SNI) but not sham rats. Interestingly, DNMT3b transcript showed a robust upregulation that appeared already 1 week after surgery and persisted at 4 weeks (our endpoint); in contrast, DNMT1 and DNMT3a transcripts showed only moderate upregulation that was transient and did not appear until the second week. We suggest that DNMT regulation in adult DRGs may be a contributor to the pain phenotype and merits further study.
Highlights
Neuronal cell bodies located in the dorsal root ganglia (DRGs) generate the fibers that convey information from the skin, muscles and joints to the spinal cord (Gardner et al, 2000)
DNMT1 EXPRESSION IS ROBUST AND WIDESPREAD IN ADULT DRGs Immunochemical analysis was performed on 20 μm-thick slices obtained from L4 and L5 DRGs of 5–7 week old naïve rats to study the expression of the DNMT1, DNMT3a, and DNMT3b in L4 and L5 DRGs of adult rats
Immunostaining of DNMT1 demonstrated that expression is robust and is detected ubiquitously in the nuclei of DRG neurons as well as in Schwann cells (Figure 1)
Summary
Neuronal cell bodies located in the dorsal root ganglia (DRGs) generate the fibers that convey information from the skin, muscles and joints to the spinal cord (Gardner et al, 2000). In the presence of nerve injury or chronic pain, nociceptors become intrinsically firing and their intrinsic firing frequency correlates with spontaneous pain (Weng et al, 2012); DRG neurons become capable of ectopic (somatic) firing and this is considered a cause of neuropathic pain (Nordin et al, 1984; Sukhotinsky et al, 2004) These changes are often indicated as peripheral sensitization and they are not restricted to the injured nerve fibers but often include adjacent neurons, which may generate spontaneous firing (Michaelis et al, 1996). These aberrant electrophysiological phenotypes are the consequence of large changes in ion channel gene expression and distribution (Novakovic et al, 1998; Tanaka et al., 1998; Dib-Hajj et al, 1999; Tan et al, 2006; Xiang et al, 2008; Fan et al, 2011; Weng et al, 2012)
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call