Photoperiod-driven browning of white adipose tissue via the calcium signaling pathway in Brandt's voles

Seasonal fluctuations in energy pose major energetic challenges to temperate small mammals. Photoperiod is regarded as a highly reliable and anticipatory environmental cue, enabling animals to redistribute their energetic resources and prepare for upcoming seasonal stressors. However, the integrative mechanisms by which photoperiodic changes drive inguinal white adipose tissue (iWAT) browning to achieve this energetic redistribution remain poorly understood. Here, we investigated whether photoperiod alone can induce browning of iWAT and modulate thermogenic capacity in the Brandt's vole (Lasiopodomys brandtii). Combining field sampling across seasons and an 8-week controlled photoperiod experiment, we investigated how seasonal photoperiod regulates morphological and molecular remodeling of iWAT in Brandt's voles. In autumn, iWAT showed marked reductions in adipocyte size accompanied by increased expression of browning-related genes. Short-day exposure similarly decreased iWAT mass and adipocyte area while elevating UCP1 levels, indicating enhanced browning capacity in response to reduced day length. Transcriptomic analysis revealed that photoperiod-dependent molecular regulation was centered on the calcium signaling pathway, with Ca²+-mediated activation of CaMKII and CREB emerging as key drivers initiating the browning program. Our findings demonstrate that photoperiod alone is sufficient to induce functional browning of white adipose tissue, providing experimental evidence for a photoperiod-driven thermogenic program for the seasonality of physiological adaptation in temperate small mammals.