Mitochondria-melanosome crosstalk in pigmentary disorders: Implications for alopecia areata pathogenesis.

Organellar communication between mitochondria and melanosomes serves as a cornerstone of pigment cell biology, orchestrating bioenergetics, ion dynamics, and organelle remodeling during melanogenesis. Recent mechanistic insights reveal that melanosomal STIM1 engages mitochondrial Mitofusin-2 (Mfn2) upon calcium depletion to channel localized ATP for V-type ATPase-driven acidification, enabling PMEL amyloidogenesis. Concurrently, mitochondrial fission factor (MFF) translocates to melanosomes to assemble an ARP2/3-dependent actin network required for organelle scission and structural integrity. In Alopecia Areata (AA)-an autoimmune disorder classically characterized by hair follicle immune privilege collapse-active bulb melanocytes represent a primary vulnerable locus, as illustrated by clinical hallmarks such as the selective loss of pigmented hair ("canities sparing") and initial white hair regrowth (poliosis). Here, we synthesize how environmental or genetic stressors destabilize this mitochondria-melanosome axis: mitochondrial Ca2+ overload and respiratory uncoupling dismantle STIM1-Mfn2 tethers and disrupt MFF scission, resulting in bioenergetic crisis, "aborted" melanization, and melanosomal membrane peroxidation. The ensuing release of damage-associated molecular patterns (DAMPs) and carbonylated neoantigens activates the NLRP3 inflammasome and cGAS-STING pathway, driving ectopic MHC class I expression and recruiting autoreactive CD8+ T cells to execute targeted follicular destruction. By critically stratifying histopathologically proven AA endpoints from extrapolated vitiligo and epidermal melanocyte data, this review reframes AA within an organelle-centric pathogenic paradigm and highlights emerging therapeutic interventions targeting the mitochondria-melanosome axis.