Local keratinocyte-nociceptor interactions enhance obesity-mediated small fiber neuropathy via NGF-TrkA-PI3K signaling axis.

The pathology of diabetic small fiber neuropathy, characterized by neuropathic pain and axon degeneration, develops locally within the skin during the stages of obesity and pre-diabetes. However, the initiation and progression of morphological and functional abnormalities in skin sensory nerves remains elusive. To address this, we utilized ear skin from mice with diet-induced obesity (DIO), the mouse models for obesity and pre-type 2 diabetes. We evaluated pain-associated wiping behavior and conducted live Ca imaging of the DIO ear skin to detect sensory hypersensitivity. Our findings reveal sensory hypersensitivity in skin nociceptive axons followed by axon degeneration. Further mechanistic analysis identified keratinocytes as a major source of nerve growth factor (NGF) in DIO skin, which locally sensitizes nociceptors through NGF-mediated signaling. Indeed, the local inactivation of NGF and its receptor TrkA-mediated downstream signaling, including the phosphoinositide 3-kinases (PI3K) pathway, suppresses sensory hypersensitivity in DIO skin. Thus, targeting these local interactions between keratinocytes and nociceptors offers a therapeutic strategy for managing neuropathic pain, avoiding the adverse effects associated with systemic interventions.