Melanocyte differentiation and mechanosensation are differentially modulated by distinct extracellular matrix proteins

Abstract

Dysfunctions in melanocytes can lead to pigmentation disorders, such as albinism, or contribute to the development of melanoma, the most aggressive form of skin cancer. Epidermal melanocytes typically interact with the collagen IV-rich basement membrane, but upon injury or in pathological conditions, they can encounter environments rich in collagen I or fibronectin. While alterations in extracellular matrix (ECM) composition and stiffness are known to impact cell behavior, the specific roles of each of these cues for melanocyte functions remain unclear. To explore the impact of these extrinsic cues, we here exposed murine melanocytes to different ECM proteins as well as varying substrate stiffnesses. This study identified MITF, a key regulator of melanocyte differentiation and function, as an ECM- and mechanosensitive transcription factor. We further revealed that distinct ECM proteins and substrate stiffness engage a FAK/MEK/ERK/MITF signaling axis to control melanocyte functions. Exposure of melanocytes to collagen I restricted FAK and ERK activation, promoting high nuclear MITF levels associated with melanocyte proliferation and differentiation. Conversely, fibronectin elicited elevated FAK and ERK activation, leading to low nuclear MITF, correlating with a dedifferentiated and motile phenotype. Consistent with these observations, RNA sequencing revealed that collagen I supports a differentiated gene expression program, whereas fibronectin induces a dedifferentiated transcriptomic signature. Importantly, inhibiting MEK or ERK activity in melanocytes cultured on fibronectin led to increased MITF nuclear localization and enhanced melanogenesis. Additionally, on fibronectin FAK inhibition reduced ERK activation and enhanced melanogenesis, supporting a role for FAK upstream of ERK. Finally, we uncovered that melanocyte mechanoresponses differ depending on the specific ECM environment. Together, these findings reveal a substantial effect of extrinsic cues on melanocyte function, with a context-dependent MITF regulation downstream of ERK, offering new perspectives for our understanding of melanocyte-related pathologies.