Selective Clock-Gene Responses to Photoperiodic and Glucocorticoid Exposure in Human Umbilical Cord-Derived Mesenchymal Stem Cells

Objective: Circadian rhythms regulate essential cellular functions, yet their presence and entrainment in human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) remain poorly defined.Methods: hUC-MSCs were cultured under 12-hour light/12-hour dark (light-dark [LD]) cycles or constant darkness (DD) for four days. Cell proliferation, senescence, and gene expression were assessed by Alamar Blue assay, senescence-associated β-galactosidase staining, fluorescence microscopy, and reverse transcription-quantitative polymerase chain reaction. Circadian rhythmicity was analyzed using Cosinor software. Dexamethasone (Dex; 100–500 nM, 2 hr) was applied to evaluate glucocorticoid-induced entrainment.Results: LD cycles were associated with increased cell proliferation and BMAL1 protein levels compared with DD conditions. Only PER3 showed evidence of rhythmic expression under LD exposure (Cosinor p<0.05), whereas other core clock genes did not show evidence of rhythmicity. Light exposure was not associated with a detectable increase in cellular senescence or changes in the expression of stemness markers (<i>OCT4, SOX2, NANOG, C-MYC)</i>. Short-term Dex treatment (100–500 nM, 2 hr) did not markedly impair cell proliferation or migration. Notably, treatment with 500 nM Dex was associated with rhythmic BMAL1 mRNA expression over the 24-hour observation period, whereas <i>CLOCK</i> expression did not show evidence of rhythmicity.Conclusion: hUC-MSCs show partial and selective clock-gene responses to photoperiodic and glucocorticoid exposure. Moderate LD exposure was associated with increased proliferation and <i>BMAL1</i> expression, while Dex was associated with rhythmic <i>BMAL1</i> expression and was relatively well tolerated in hUC-MSCs under the conditions tested. These findings provide preliminary insight into how circadian rhythmicity may influence mesenchymal stem cells culture conditions.