Thyrotropin aggravates insulin resistance by promoting macrophage inflammation in subclinical hypothyroidism.

In subclinical hypothyroidism (SH), serum thyroid-stimulating hormone (TSH) correlated positively with insulin resistance; however, the precise mechanism is now unclear. Except for thyroid follicular epithelial cells, macrophages exhibit the highest level of TSHR expression. Thus, we wondered if TSH leads to insulin resistance by macrophages. We established thyroid-stimulating hormone receptor (Tshr) myeloid-specific knockout (TshrMKO) C57BL6 mice, and observed that TshrMKO mice showed improvement on high-fat diet (HFD) induced obesity and insulin resistance, compared to WT mice. TshrMKO animals showed decreased macrophages infiltration and M1 polarization in liver, adipose, and skeletal muscles. Co-culture experiments proved that Tshr deficient macrophages decreased gluconeogenesis in primary hepatocytes but increased glucose uptake in 3T3L1 adipocytes and L6 skeletal muscle cells through improving insulin signaling, versus WT. TSH promoted the release of Il6, Il1a and Il1b cytokines, which upregulated Egr1, Lcn2 and Socs3, reversed by the inhibitors Il6st and Il1ra. Lastly, EGR1 transcriptionally activated LCN2 and SOCS3. In conclusion, TSH promotes the secretion of IL6, IL1A, and IL1B via activating macrophage M1 polarization, which leads to that the upregulation of EGR1, transcriptionally activating LCN2 and SOCS3 and inducing insulin resistance in liver, adipose, and skeletal muscle in SH.