(144) - Ischemia and reperfusion injury induces acute and chronic muscle pain-related behaviors through increased expression of the GFRα1 receptor

Abstract

Muscle pain is a common complication of conditions that produce ischemia/reperfusion injuries (I/R), like peripheral artery disease (PAD) or sickle cell anemia. Previously, we have found that I/R injury in mouse induces increased pain-related behaviors that correlate with group III/IV muscle afferent sensitization and increased gene expression in the affected muscles and the dorsal root ganglia (DRG). In particular, glial cell line-derived neurotrophic factor (GDNF) expression was increased in the injured muscle tissue, while its receptor, GDNF family receptor α1 (GFRα1) was upregulated in DRGs. Both GDNF and GFRα1 have been linked to behavioral changes as well as afferent sensitization in other models of muscle pain. We hypothesized that enhanced expression of GFRα1 in sensory neurons regulates the development of pain-related behaviors after I/R. To test this, we selectively knocked down GFRα1 in mice by median and ulnar nerve injection of Penetratin1-linked GFRα1-targeting siRNAs in vivo prior to unilateral I/R injury of the forelimb. We then performed pain-related behavioral tests and single unit recordings of group III/IV muscle afferents along with real-time PCR on the I/R affected DRGs. Selective knockdown of GFRα1 expression in the DRGs effectively decreased the I/R-induced pain related behaviors and the observed reduction in mechanical thresholds in group III/IV afferents. GFRα1 inhibition also specifically prevented I/R-induced upregulation of the purinergic receptor, P2X5 and acid sensing ion channel 3 (ASIC3). Finally, repetitive I/R injury induced prolonged spontaneous pain-like behaviors (paw guarding) compared to animals with a single injury. This also correlated with increased GFRα1 expression in DRGs. These results suggest that GFRα1 upregulation may play an important role in the development of pain-related behaviors via group III/IV muscle afferent sensitization. GFRα1 and the receptors downstream of its signaling, may provide potential targets for therapies aimed at patients experiencing acute or chronic pain from ischemia/reperfusion injuries.