Plateau Hypoxia Influences Mouse Circadian Behavior by Remodeling the Hypothalamic Transcriptional Landscape

Hypoxia signaling and the circadian clock exhibit extensive molecular crosstalk, but how endogenous circadian timing influences behavioral responses during high-altitude exposure remains incompletely understood.

Male C57BL/6J mice were exposed to hypobaric hypoxia equivalent to an altitude of 6000 m. Wheel-running activity was continuously monitored under 12 h light/12 h dark (LD) cycle and constant-dark conditions to evaluate locomotor activity, rhythm amplitude, circadian phase, and free-running period. After 48 h of exposure, whole-hypothalamus samples were collected across the circadian cycle for time-series RNA sequencing, rhythmicity and pathway-enrichment analyses, and qPCR validation. In a separate experiment, hypoxia was initiated at ZT2 or ZT14 to assess circadian-phase-dependent behavioral responses.

High-altitude exposure acutely reduced locomotor activity and rhythm amplitude and subsequently delayed behavioral circadian phase under a LD cycle, whereas the free-running period under constant darkness remained unchanged. Transcriptomic analysis revealed extensive remodeling of rhythmic gene expression in the whole hypothalamus, involving multiple signaling and metabolic pathways. Relaxin-related signaling emerged as a candidate pathway associated with hypoxia-induced temporal transcriptional remodeling, and selected core clock genes and relaxin pathway-associated genes showed altered temporal expression profiles. Furthermore, exposure initiated at ZT14 produced greater locomotor suppression than exposure initiated at ZT2.

High-altitude exposure disrupts behavioral circadian organization and remodels hypothalamic rhythmic transcription. These findings suggest that endogenous circadian timing modulates behavioral sensitivity to hypoxic stress.