RNA-seq and ChIP-seq unveils thyroid hormone receptor α deficiency affects skeletal muscle myoblast proliferation and differentiation via Col6a1 during aging.

Primary sarcopenia, an age-related syndrome, is a serious threat to the health and longevity of the elderly. Our prior studies indicated that thyroid hormone (TH) activity within muscle tissue undergoes significant age-associated alterations, mainly evidenced by a reduction in thyroid hormone receptor α (TRα) expression over time. TRα regulates the transcription of downstream target genes to exert its biological effects. Although TH is essential for skeletal muscle growth and development, the specific regulatory mechanism and broader role of TH binding its receptors in skeletal muscle aging remain unclear. We used ChIP-seq and RNA-seq to explore the aging changes of TRα target genes in gastrocnemius muscle of natural aging mouse model. ChIP-seq analysis revealed that TRα target genes are involved in nutrient synthesis, energy production, hormone secretion, and ECM-related pathways, suggesting a potential role of TRα in muscle growth, metabolism and component regulation. Further integration of RNA-seq showed that a greater number of down-regulated TRα target genes are associated with skeletal muscle aging. Through GSEA analysis and RT-qPCR screening, Col6a1 was identified as a key target gene. Col6a1 encodes collagen VI which is an important component of the ECM, ECM disorders and abnormal expression of Col6a1 can affect cell proliferation and differentiation. We confirmed that knockdown of Col6a1 inhibited the proliferation and differentiation of C2C12 cells. ChIP-qPCR and TRα silencing in C2C12 cells showed that TRα positively regulates Col6a1 transcription, and TRα deficiency inhibits the proliferation and differentiation of myoblasts, which is probably associated with Col6a1. These findings provide new insights into the molecular mechanisms underlying skeletal muscle aging and the regulatory roles of TH-TRα interactions.