Heat stress alters metabolic pathways and nitric oxide signaling in keratinocytes under hyperglycemia

BACKGROUND: Diabetic patients are particularly vulnerable to heat exposure due to impaired thermoregulation and reduced sweating ability. The impact of heat on skin cell function, particularly keratinocytes, is poorly understood. Recent studies highlight the critical role of nitric oxide (NO) in thermoregulation and heat stress responses, but its specific involvement in keratinocyte responses and metabolic profiles remains unexplored. OBJECTIVE: This proof-of-concept study investigates the metabolic profiles of HaCat keratinocytes under normal and high-glucose conditions during varied heat exposures. METHODS: We conducted experiments using a metabolomics approach, NO levels assessments, western blot analysis, and evaluations of mitochondrial morphology. RESULTS: Our findings indicate that acute heat exposure over 90 minutes significantly alters metabolic pathways, particularly amino acid metabolism (including arginine, valine, leucine, and serine), the pyrimidine metabolite uracil, and glycolysis, notably lactate production. Arginine metabolism was uniquely affected by high glucose combined with heat, aligning with previous clinical observations. Furthermore, we discovered that changes in NO production correlated with heat exposure duration, and that NO levels in extracellular vesicles (EVs) from HaCat cells were inversely related to intracellular NO levels. Additionally, we observed alterations in HSP-70 protein expression and mitochondrial morphology, supporting cellular adaptation to thermal stress. CONCLUSION: This study is the first to demonstrate heat-induced metabolic changes in keratinocytes involving arginine and NO, highlighting their potential as clinical biomarkers for thermal stress adaptation, with implications for both healthy individuals and diabetic patients.