Dermal fibroblast mitochondrial profiles in painful diabetic neuropathy.

AIMS/HYPOTHESIS: Dermal fibroblasts have emerged as potential contributors to chronic pain, yet their role in diabetic polyneuropathy (DPN) and neuropathic pain remains poorly defined. Mitochondrial dysfunction and low-grade inflammation have been implicated in different pain conditions, but whether fibroblast mitochondrial health and cytokine secretion contribute to painful DPN is unknown. METHODS: We conducted an integrated cellular and molecular profiling of dermal fibroblasts and skin biopsies from 30 participants, grouped into control participants (n=5), diabetes without DPN (n=7), pain-free DPN (n=7) and painful DPN (n=11). Fibroblast cultures (n=24) were evaluated for morphology, growth rate, phenotype, inflammatory mediator secretion and mitochondrial function. Immunohistochemistry of skin biopsies was used to assess fibroblast density, mitochondrial markers and immune cell infiltration. RESULTS: Fibroblast morphology and proliferation did not differ significantly between groups. Flow cytometric profiling revealed no significant differences in fibroblast subtype distributions across groups. Inflammatory mediator secretion was limited. Mitochondrial mass, membrane potential, reactive oxygen species production and bioenergetic parameters were not different across groups. Skin biopsy analyses confirmed comparable fibroblast density and mitochondrial profiles across groups, regardless of neuropathy or pain. Notably, dermal macrophage infiltration was significantly elevated in the painful DPN group (mean ~8%; ANOVA p=0.02; painful DPN vs control participants p=0.02; painful DPN vs pain-free DPN p=0.07), consistent with prior findings from the same cohort, while Langerhans cell area fraction did not differ between groups. CONCLUSIONS/INTERPRETATION: Fibroblasts from participants with painful DPN did not differ in inflammatory and mitochondrial profiles compared with those from pain-free DPN. However, persistent dermal macrophage infiltration in painful DPN suggests a stable immune-activated microenvironment, potentially contributing to pain maintenance. Our results suggest that immune-related, rather than fibroblast-intrinsic, mechanisms could play a role in sustaining neuropathic pain in painful DPN.