Reactive Neuroglia as a Central Regulator of Maladaptive Communication and Metabolic Stress in Neuropathic Pain

Neuropathic pain is a chronic and debilitating condition that persists well beyond tissue healing, severely impairing quality of life and remaining largely refractory to current pharmacological treatments. Despite progress in pain neurobiology, fewer than half of patients obtain meaningful relief with available therapies, underscoring the need for innovative approaches targeting the cellular and molecular mechanisms that drive pain chronification. This thesis explores how the transition from physiological to pathological intercellular signaling within the central nervous system (CNS) underlies maladaptive neuroinflammation, metabolic stress and neuronal hyperexcitability in neuropathic pain. Under physiological conditions, astrocytes and microglia maintain CNS homeostasis by regulating synaptic activity, metabolic coupling, redox balance and neurovascular integrity. Connexin (Cx)-forming gap junctions (GJs) and hemichannels (HCs) play a central role in this regulation, enabling glial networks to integrate neuronal and vascular compartments into functional syncytia. However, following nerve injury, astrocytes and microglia undergo profound phenotypic shift toward reactive states, characterized by aberrant Cx43 upregulation, excessive HC opening and uncontrolled release of ATP, glutamate and pro-inflammatory cytokines. Given the central role of glial reactivity in sustaining pain chronification and the need for non-opioid therapeutic alternatives, we investigated sigma-1 receptor (σ1R), a ligand-regulated chaperone enriched in sensory and pain-modulatory regions of the CNS expressed in both astrocytes and microglia. In our studies, we demonstrated that inhibition of σ1R with the novel antagonist (+)-MR200 not only alleviates mechanical allodynia in vivo, but also reduces glial activation and normalizes Cx43 expression, thereby disrupting pathological astrocyte-microglia coupling and limiting neuroinflammatory signaling. As reactive gliosis progressed into a chronic neuroinflammation, we further observed that metabolic and oxidative stress became key amplifiers of this maladaptive signaling. This led us to identify poly(ADP-ribose) polymerase 1 (Parp1) as a critical metabolic hub linking glial energy failure to neuroinflammation and mitochondrial dysfunction. Inhibition of Parp1 activity restored mitochondrial homeostasis, reduced central sensitization and reprogrammed microglia toward a neuroprotective phenotype, overall attenuating pain hypersensitivity in a neuropathic pain model. Altogether, this work uncovers converging roles for Cx43 and Parp1 in shaping maladaptive neuroglial signaling in neuropathic pain, pointing towards glial-centered strategies for future clinical applications in this field.