Neuroimmune mechanisms of a mouse model of chronic back pain.

UNLABELLED: Chronic back pain (CBP) is the leading cause of disability affecting 1 in 10 people worldwide. Symptoms are marked by persistent lower back pain, reduced mobility, and heightened cold sensitivity. Here, we utilize a mouse model of CBP induced by injecting urokinase-type plasminogen activator (uPA), a proinflammatory agent in the fibrinolytic pathway, between the L2/L3 lumbar vertebrae. We identified neuroimmune interactions contributing to uPA-induced CBP (henceforth, uPA-CBP) in mouse dorsal root ganglia (DRG), where nociceptive neurons reside. Flow cytometric data reveal that uPA-CBP increases CD45+CD11b+ cells in the DRG, a population characteristically implicated in other chronic pain models 1 . Blocking colony stimulating factor 1 receptor (CSF1R) signaling using PLX5622 partially reduced pain, suggesting CD45+CD11b+ macrophage involvement. Whole-cell patch-clamp electrophysiology data indicated DRG neuron hyperexcitability in CBP mice compared to controls. RNA sequencing revealed upregulation of pain- and inflammation-related genes involved in leukocyte migration. Together, these findings underscore the importance of the DRG neuroimmune axis in mediating chronic back pain.

HIGHLIGHTS: uPA-CBP induces gait changes, mechanical and thermal sensitivity compared to shamsuPA-CBP mice show increased CD45+CD11b+ cells in DRG compared to shamsuPA-CBP mice show neuronal excitability in DRG neurons compared to shamsPain behaviors are alleviated by pharmacologically blocking CSF1R signalingDysregulation of inflammation- and ion channel-related genes in uPA-CBP DRG.