Salivary Nitrate Maintains Mucosal Homeostasis via the Sialin–Neuropeptide Axis

While saliva critically maintains oral homeostasis and accelerates mucosal repair, the molecular mediators driving this regenerative capacity remain unclear. Here, we identify salivary nitrate as a neuromodulatory signal coordinating oral mucosal regeneration through sensory neuron activation. In a palatal wound model, salivary nitrate depletion (via bilateral submandibular duct ligation or dietary restriction) impaired wound healing, characterized by reduced epithelial proliferation, aberrant collagen organization, and suppressed vascular endothelial growth factor (VEGF) and transforming growth factor-β (TGF-β) expression-phenotypes rescued by nitrate supplementation. Transcriptomic profiling revealed that both nitrate-dependent upregulation of Rnf112 and the enhancement of the mucin type O-glycan biosynthesis pathway were mechanistically linked to myelinated sensory nerve modulation. Crucially, salivary nitrate promoted the reinnervation of myelinated sensory nerve fibers, upregulated the nitrate transporter sialin (Slc17a5), and stimulated the secretion of regenerative neuropeptides including calcitonin gene-related peptide, vasoactive intestinal peptide, and neuropeptide Y. In vitro, sialin knockdown abolished nitrate-induced cell proliferation and neuropeptide release in H4 cells while disrupting O-glycosylation, a key posttranslational modification for mucosal barrier function. Sensory neuron-specific sialin knockout mice (Slc17a5^∆Trpv1, cKO) exhibited impaired neuropeptide release and failed to respond therapeutically to nitrate, confirming the indispensable role of sialin. These findings establish a sialin-dependent sensory neuropeptide axis wherein nitrate activates sensory neurons to drive mucosal regeneration, providing both mechanistic understanding of neuroepithelial crosstalk and a druggable target for tissue repair strategies.