Thyroid-stimulating hormone stimulation downregulates autophagy and promotes apoptosis in chondrocytes

Subclinical hypothyroidism (SCH) patients have normal thyroid hormone levels but increased thyroid stimulating hormone (TSH) level in serum. It has been reported that high TSH is related to abnormal skeletal development in mice with hypothyroidism. However, the cellular mechanism is not fully understood. In the present study, we aim to investigate the direct effects of TSH stimulation on chondrocytes, and the putative role of autophagy in this process. By using EdU incorporation assay and flow cytometry for mitochondrial membrane potential assay, we demonstrated deceased proliferation and promoted apoptosis in TSH stimulated primary mouse chondrocytes. And the balance of Bcl-2 and BAX expression on protein level was broken. More interestingly, the expression of autophagic markers Beclin-1 and LC3II was reduced in TSH stimulated chondrocytes, accompanied by less autophagosomes and accumulated p62 protein, indicating an impaired autophagic flux. More interestingly, mTOR was upregulated and AMPK activity was decreased in TSH stimulated PMCs, suggesting that mTOR/AMPK pathway is get involved in the regulation of TSH on autophagy in PMCs. Collectively, we found an increased apoptosis and suppressed autophagy in TSH stimulated primary chondrocytes, which is meaningful in understanding the effects of increased TSH level on articular cartilage and the role of autophagy in this process, and thus provide a potential novel therapeutic target in related cartilage damages.