Circadian disruption impairs Leydig cell maturation and reproductive development in male rats.

Circadian desynchrony, caused by a misalignment between the internal biological clock and environmental light cues, is increasingly prevalent in adolescents due to irregular light exposure and social pressures. However, its impact on reproductive maturation remains poorly understood. In this study, the effects of chronic circadian disruption, induced by the 223 light regimen (two days of constant light, two days of constant darkness, and three days of a 14:10 h light-dark cycle), were examined in juvenile and peripubertal male rats (postnatal days 21-49). Gene expression profiles associated with Leydig cell maturation, including steroidogenic, mitochondrial, and clock-related genes, as well as markers of germ cell differentiation, were analyzed alongside functional mitochondrial parameters in Leydig cells. Under control conditions, Leydig cell maturation was marked by increased expression of core clock genes, steroidogenic enzymes (Star, Cyp11a1, Hsd3b1/2), and mitochondrial biogenesis and dynamics markers (Tfam, Nrf1, Cytc, Opa1, Mfn2). These transcriptional changes coincided with rising mitochondrial content, membrane potential, ATP levels, serum androgens, and progression of spermatogenesis. Conversely, the 223-regimen disrupted behavioral rhythms, reduced circulating melatonin, blunted expression of maturation-associated genes, and shifted the acrophase of key steroidogenic and circadian transcripts in 49-day-old rats, indicating altered Leydig cell rhythmicity. These molecular disruptions were accompanied by decreased testosterone levels, altered expression of spermatid differentiation genes (Tnp1 and Prm2), and a reduction in the number of elongated spermatids at stage VII of spermatogenesis. In conclusion, circadian misalignment disrupts endocrine and transcriptional coordination during Leydig cell development, underscoring the vulnerability of pubertal reproductive maturation to environmental light disturbances.