Extracellular vesicles derived from the lactic acid bacterium Enterococcus rotai suppress melanogenesis by modulating the cAMP-MITF pathway

Enterococcus rotai CMTB-CA6-derived extracellular vesicles (CA6-ErEVs), isolated from a Centella asiatica-associated lactic acid bacterium, were investigated for their potential to modulate oxidative stress, inflammation, and melanogenesis in skin cells. CA6-ErEVs were purified and characterized using standardized nanoparticle analyses. Functional assays demonstrated that CA6-ErEVs displayed robust antioxidant activity by reducing free radical accumulation and intracellular reactive oxygen species levels. In tumor necrosis factor-α-stimulated dermal fibroblasts, CA6-ErEVs attenuated the secretion of proinflammatory cytokines and reduced matrix degradation while promoting procollagen synthesis. In α-melanocyte-stimulating hormone-activated murine and human melanocytes, CA6-ErEVs markedly suppressed melanin synthesis and tyrosinase activity, accompanied by the downregulation of microphthalmia-associated transcription factor (MITF) and key melanogenic enzymes including tyrosinase, tyrosinase-related protein 1, and tyrosinase-related protein 2. Mechanistically, CA6-ErEVs reduced intracellular cyclic adenosine monophosphate (cAMP) levels through intrinsic phosphodiesterase activity, thereby inhibiting the cAMP-MITF signaling axis and oxidative pathways involved in melanogenesis. Collectively, CA6-ErEVs exhibit integrated antioxidant, anti-inflammatory, and antimelanogenic effects through phosphodiesterase-mediated suppression of cAMP signaling and regulation of cellular redox balance. These findings highlight bacterial EVs derived from E. rotai as promising bioactive candidates for further development in the management of hyperpigmentation and improving cutaneous homeostasis.