TRPV4 mediates low-humidity responses in epidermal keratinocytes.

Environmental humidity is a key determinant of organismal physiology and homeostasis. Although the genetic basis of humidity-driven responses is well established in invertebrates, the molecular and genetic mechanisms by which mammals respond to low humidity remain unclear. Here, using reconstructed 3D epidermal equivalents and a mouse model, we identify transient receptor potential vanilloid 4 (TRPV4) as an important mediator of low-humidity-induced signaling and transcriptional responses in epidermal keratinocytes. In 3D skin models, low-humidity exposure induced rapid water movement, characterized by enhanced apical water loss and concomitant basal-side water uptake within 90 s, followed by TRPV4-dependent Ca2+ influx within 3 min. Pharmacological TRPV4 inhibition suppressed MAPK activation at 30 min and both early (3 h) and late (24 h) low-humidity-induced transcriptional changes. Ca2+ chelation reduced low-humidity-induced ERK and p38 activation, and ERK inhibition attenuated low-humidity-induced gene expression changes at 3 h. In vivo, acute low-humidity exposure in mice elicited epidermal MAPK activation within 15 min and early transcriptional changes at 3 h, with RNA-sequencing analysis showing enrichment of gene sets associated with cell adhesion or inflammatory responses. These signaling and transcriptomic responses were attenuated in the epidermis of keratinocyte-specific Trpv4 conditional knockout mice. Collectively, our findings identify TRPV4 as an important mediator of epidermalresponses to low-humidity stress, providing a molecular basis for low-humidity-driven signaling in the mammalian epidermis.