Mitochondrial Bioenergetics\nof Functional Wound Closure\nis Dependent on Macrophage–Keratinocyte Exosomal Crosstalk

Tissue nanotransfection (TNT)-based fluorescent labeling\nof cell-specific\nexosomes has shown that exosomes play a central role in physiological\nkeratinocyte–macrophage (mϕ) crosstalk at the wound-site.\nHere, we report that during the early phase of wound reepithelialization,\nmacrophage-derived exosomes (Exo<sub>mϕ</sub>), enriched with\nthe outer mitochondrial membrane protein TOMM70, are localized in\nleading-edge keratinocytes. TOMM70 is a 70 kDa adaptor protein anchored\nin the mitochondrial outer membrane and plays a critical role in maintaining\nmitochondrial function and quality. TOMM70 selectively recognizes\ncytosolic chaperones by its tetratricopeptide repeat (TPR) domain\nand facilitates the import of preproteins lacking a positively charged\nmitochondrial targeted sequence. Exosomal packaging of TOMM70 in mϕ\nwas independent of mitochondrial fission. TOMM70-enriched Exo<sub>mϕ</sub> compensated for the hypoxia-induced depletion of epidermal\nTOMM70, thereby rescuing mitochondrial metabolism in leading-edge\nkeratinocytes. Thus, macrophage-derived TOMM70 is responsible for\nthe glycolytic ATP supply to power keratinocyte migration. Blockade\nof exosomal uptake from keratinocytes impaired wound closure with\nthe persistence of proinflammatory mϕ in the wound microenvironment,\npointing toward a bidirectional crosstalk between these two cell types.\nThe significance of such bidirectional crosstalk was established by\nthe observation that in patients with nonhealing diabetic foot ulcers,\nTOMM70 is deficient in keratinocytes of wound-edge tissues.