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Osteoblasts mediate thyroid hormone stimulation of osteoclastic bone resorption
J M Britto1, A J Fenton, W R Holloway
1Department of Medicine, University of Melbourne, Geelong Hospital, Victoria, Australia.
Endocrinology
|January 1, 1994
Summary
Thyroid hormone (T3) indirectly stimulates bone resorption by acting on osteoblasts, not directly on osteoclasts. This finding clarifies the mechanism behind thyroid-associated osteoporosis.
Area of Science:
- Endocrinology
- Bone Biology
- Cell Biology
Background:
- Thyroid hormones influence bone turnover and resorption.
- Excess thyroid hormone levels are linked to osteoporosis.
- Understanding the precise mechanism of thyroid hormone action on bone is crucial.
Purpose of the Study:
- To investigate the direct and indirect effects of triiodothyronine (T3) on osteoclast bone resorption.
- To differentiate between thyroid hormone actions on osteoclasts versus osteoblasts.
Main Methods:
- Isolated rat osteoclast resorption assays with and without osteoblasts.
- Co-cultures of osteoclasts and osteoblasts (UMR 106-01 or rat calvarial cells).
- Pre-treatment experiments with osteoblasts before co-culture.
Main Results:
- T3 did not directly stimulate osteoclast resorption in osteoblast-poor cultures after 24 hours.
- T3 significantly increased resorption in osteoblast-osteoclast co-cultures within 24 hours.
- Pre-treating osteoblasts with T3 stimulated resorption in subsequent co-cultures, indicating an indirect effect.
Conclusions:
- Thyroid hormone (T3) primarily stimulates osteoclastic bone resorption indirectly through osteoblasts.
- Direct exposure of osteoclasts to T3 is not required for enhanced resorption.
- These findings elucidate a key pathway contributing to thyroid hormone-induced bone loss.