Defective Branched-Chain Amino Acid Catabolism in Dorsal Root Ganglia Contributes to Mechanical Pain

Impaired branched-chain amino acid (BCAA) catabolism has recently been implicated in the development of mechanical pain, but the molecular mechanisms are unclear. Here we report that defective BCAA catabolism in dorsal root ganglia (DRG) neurons sensitizes mice to mechanical pain by increasing lactate production and Piezo2 expression, a mechanotransduction channel. In high-fat diet fed obese mice, we observed a downregulation of PP2Cm, a key regulator in BCAA catabolic pathway, in DRG neurons. Mice with conditional knockout of PP2Cm in DRG neurons (cKO) exhibited mechanical allodynia under normal or spare nerve injury (SNI)-induced neuropathic injury conditions. Further, in patients with peripheral neuropathic pain, we found that the Visual Analogue Scale (VAS) scores were positively correlated with BCAA contents in plasma, highlighting a link between peripheral neuropathic pain and dysregulated BCAA catabolism. Mechanistically, defective BCAA catabolism promotes the production of lactate through glycolysis in DRG neurons, which increases H3K18la modification and drives Piezo2 expression. Inhibition of lactate production or silencing of Piezo2 expression attenuated the pain phenotype of cKO to mechanical stimuli. Therefore, our study demonstrates a casual role of defective BCAA catabolism in mechanical pain by enhancing metabolite-mediated epigenetic regulation. Method: Fresh DRG samples (Ctrl and cKO) were frozen in liquid nitrogen. After thawing on ice, 10 mg tissue was homogenized in -80°C precooled labeled-solution (MeOH: H2O=4:1, v/v) for 30 s, 4 cycles, and placed at -80°C for 30 minutes. In ice water bath, ultrasonic wave was used for 10 min and centrifuged at 14000 rpm. The precipitated protein was dissolved in no labeled-liquid (MeOH: H2O=4:1), vortexed and centrifuged. After derivatization with N-methyl-N-(trimethylsilyl)tri-fluoroacetamide for 30 min, the supernatant was detected by LC-MS. Metabolites were identified by means of KEGG Metabolic pathways.