Negative Evidence for a Functional Role of Neuronal DNMT3a in Persistent Pain

Abstract

Traditionally, neuroscience has had to rely on mixed tissue analysis to examine transcriptional and epigenetic changes in the context of nervous system function or pathology. However, particularly when studying chronic pain conditions, this approach can be flawed, since it neglects to take into account the shifting contribution of different cell types across experimental conditions. Here, we demonstrate this using the example of DNA methyltransferases (DNMTs) – a group of epigenetic modifiers consisting of Dnmt1, Dnmt3a, and Dnmt3b in mammalian cells. We used sensory neuron-specific knockout mice for Dnmt3a/3b as well as pharmacological blockade of Dnmt1 to study their role in nociception. In contrast to previous analyses on whole tissue, we find that Dnmt3a and 3b protein is not expressed in adult DRG neurons, that none of the DNA methyltransferases are regulated with injury and that interfering with their function has no effect on nociception. Our results therefore currently do not support a role for neuronal DNA methyltransferases in pain processing in adult animals.

Epigenetic control of hypersensitivity in chronic inflammatory pain by the de novo DNA methyltransferase Dnmt3a2

“…A recent study performed using sensory neuron-specific Dnmt3a knockout mice provided evidence against a role for Dnmt3a expression in dorsal root ganglia neurons in nociception. 34 These findings, in combination with our study – based instead on manipulation of the expression of Dnmt3a2 in the dorsal horn of the spinal cord – suggest that Dnmt3a2 contributes differentially to long-lasting hypersensitivity depending on the affected area.…”

The Role of DNA Methylation in Transcriptional Regulation of Pro-Nociceptive Genes in Rat Trigeminal Ganglia

“… 9 Interestingly, the role of DNMT3a in persistent pain remains controversial. 5 , 7 , 8 , 35 , 36 All of these factors prompted us to test whether DNMT3a-produced DNA methylation is involved in alteration of the 4 candidate genes above. Considering that 5-Aza-dC inhibits all known DNMTs, and DNMT3a-specific or isoform-specific inhibitors are still under development, 37 , 38 we addressed this question by overexpressing DNMT3a.…”

“…A series of studies from a lab showed that restoring global DNMT expression levels within a tissue following a nerve injury is sufficient to alter pain responses, 6 - 8 although the functional role of DNMT3a in mouse sensory neurons in persistent pain has recently been challenged. 36 Given that DNMTs could alter a multitude of genes that are either pro-nociceptive or anti-nociceptive, that DNMT expression levels are sensitive to changing tissue environments, and that DNMT is only one of many families enzymes involved in gene transcription, additional studies are warranted to confirm whether global changes in DNMT expression levels bear any functional relevance in pain modulation.…”

Granulocyte-Macrophage Colony Stimulating Factor As an Indirect Mediator of Nociceptor Activation and Pain

“…Brain, behavior, and immunity, 68, pp.248-260. Tanga, F.Y., Raghavendra, V. and DeLeo, J.A., 2004 TrpV1, which is well expressed in nociceptive neurons; Dnmt3a which is very lowly expressed if at all in neurons (Saunders et al, 2018); Nav1.8; CD40, a myeloid cell marker;…”

“…Calca, one of the most highly expressed genes in DRG; TrpV1 and Nav1.8, which are well expressed in nociceptive neurons; and Dnmt3a, which is very lowly expressed (Saunders et al, 2018). It is evident the two transcripts coding for the receptor chains of the GM-CSF receptor, namely CSF2Rα and CSF2Rβ, are expressed at levels below our negative control transcript in the DRG -the CSF2Rβ gene, in particular, appears to be undetectable, even by a technique as sensitive as RNA-seq.…”