Severe burn disrupts tissue-specific clock gene expression in peripheral blood mononuclear cells and skeletal muscle in a rodent model.

INTRODUCTION: Severe burns cause systemic inflammation and a hypermetabolic response, yet their impact on biorhythms remains unclear. Clock gene-regulated circadian rhythms maintain physiologic homeostasis and are altered in disease. We posit that severe burn disrupts tissue-specific clock gene expression in peripheral blood mononuclear cells and is associated with molecular alterations in skeletal muscle. METHODS: Twenty-four adult male rats were randomized to 30% total body surface area (TBSA) scald burn or sham and euthanized sequentially at 12:00, 18:00, and 00:00 on post-burn day 2, and at 06:00 on day 3. RNA was extracted from both peripheral blood mononuclear cells (PBMCs) and gastrocnemius muscle. Per1, Per2, Cry1, Cry2, Clock, and Arntl expression was measured by TaqMan qPCR and expressed as fold change. Muscle LC3, Caspase-3, and PCNA were measured by immunoblotting (densitometry/GAPDH). 18S rRNA served as the housekeeping gene. Two-way ANOVAs were performed in SigmaPlot 15 and GraphPad Prism 11.0.0. RESULTS: Sham animals showed time-of-day variation in PBMC clock gene expression, whereas burned animals showed significantly reduced expression of Clock, Cry1, Cry2, Per1, and Per2 (p < 0.05). In gastrocnemius muscle, burn suppressed Cry1 and Per2 (p < 0.05); Fbxo32 and Trim63 expression increased, consistent with activation of muscle atrophy. LC3 was elevated at 12:00 and 00:00 in burn versus sham animals (p < 0.05); PCNA was reduced at 06:00 (p < 0.05), indicating time-dependent activation of autophagy and impairment of proliferative signaling. Caspase-3 and LC3 increased at 12:00 after burn (p < 0.05), consistent with transient apoptotic activation. Simple linear regression analyses did not reveal significant relationships between paired PBMC and gastrocnemius muscle gene expression for any of the analyzed clock genes (all p > 0.05). CONCLUSION: Severe burn alters tissue-specific clock gene expression in PBCMs and skeletal muscle without a significant inter-tissue relationship. These findings suggest distinct local circadian responses to burn and provide a foundation for future studies investigating the role of circadian regulation in post-burn pathophysiology and its potential as a therapeutic target, particularly in skin.