AAV-mediated overexpression of Prdm12 in knee-innervating afferents reduces inflammatory joint pain and neuronal hyperexcitability in mice

Inflammatory joint pain features in numerous musculoskeletal disorders that affect millions globally. The Prdm12 gene encodes a conserved zinc finger transcriptional regulator expressed selectively in the nervous system. In humans, PRDM12 mutations can cause congenital insensitivity to pain (CIP) or midface toddler excoriation syndrome (MiTES). Prdm12 is prominently expressed in developing somatosensory ganglia, where it plays a crucial role in nociceptive neuron development, its expression being maintained in mature C-LTMRs (C-low threshold mechanoreceptors) and nociceptive neurons. Despite enhanced understanding of Prdm12’s role in neuronal excitability and pain behavior, the impact of Prdm12 overexpression in mature nociceptive neurons has not been explored. Here, we conducted intravenous injection of AAV-PHP.S viral vectors encoding Prdm12-GFP (Prdm12-AAV) or GFP alone (Control-AAV), observing no overt changes in mouse behavior. When examining the properties of Prdm12 overexpressing sensory neurons in vitro, we observed an increase in rheobase alongside decreased neuronal responses to capsaicin and ATP, indicating a downregulation of TRPV1 and P2X ion channels activity, respectively. We next conducted intraarticular administration of viral constructs in female mice to determine how Prdm12 overexpression in knee-innervating sensory neurons alters their excitability and influences inflammatory joint pain induced by intraarticular administration of complete Freund’s adjuvant (CFA). Prdm12 overexpression in knee-innervating neurons decreased inflammation-induced changes in digging and weight bearing, prevented inflammation-induced neuronal hyperexcitability, and decreased macroscopic voltage-gated ion channel conductance. Our findings illustrate that Prdm12 overexpression strongly modulates neuronal excitability in adult animals, highlighting its importance in pain perception and its potential as an analgesic target.