Figure 6.

Actions of T₃ and TSH in skeletal cells. A, T₃ and TSH actions in osteocytes have not been investigated, and it is unknown whether osteocytes express thyroid hormone transporters, deiodinases, TRs, or the TSHR. B, Chondrocytes express MCT8, MCT10, and LAT1 transporters, DIO3 (D3), TRs (predominantly TRα), and TSHR. T₃ inhibits proliferation and stimulates prehypertrophic and hypertrophic chondrocyte differentiation, whereas TSH might inhibit proliferation and matrix synthesis. C, Osteoblasts express MCT8 and LAT1/2 transporters, the DIO2 (D2) and D3, TRs (predominantly TRα), and TSHR. Most studies indicate that T₃ stimulates osteoblast differentiation and bone formation. Contradictory data suggest that TSH may stimulate, inhibit, or have no effect on osteoblast differentiation and function. D, Osteoclasts express MCT8, D3, TRs and the TSHR. Currently, it is unclear whether T₃ acts directly in osteoclasts or whether indirect effects in the osteoblast lineage mediate its actions. Most studies indicate that TSH inhibits osteoclast differentiation and function.