MiR-221-5p/Smad3 axis in osteoclastogenesis and its function: Potential therapeutic target for osteoporosis

To probe the role of miR-221-5p in osteoclastogenesis and the underlying mechanism.

Serum from patients with postmenopausal osteoporosis and healthy controls was collected for determination of miR-221-5p expression. For in vitro experiment, RAW264.7 macrophages, in which the expression of miR-221-5p and/or Smad3 was altered, were induced by RANKL to differentiate into osteoclasts. For in vivo experiment, ovariectomy was performed to construct osteoporosis mouse models, followed by tail vein injection of miR-221-5p agomir. qRT-PCR and/or western blot were applied to measure the expression of miR-221-5p, Smad3, and osteoclastogenesis-related genes (NFATc1 and TRAF6). TRAP staining was utilized for assessment of osteoclast formation, MTT assay for assessment of osteoclast viability, and H&E staining for observation of histomorphological changes. The targeting relationship between miR-221-5p and Smad3 was verified by dual-luciferase reporter gene assay.

Compared with healthy controls, patients with postmenopausal osteoporosis had decreased miR-221-5p expression and lower lumbar vertebra bone mineral density. MiR-221-5p expression was decreased and Smad3 level was increased during osteoclastogenesis. The osteoclastogenesis was suppressed by miR-221-5p and promoted by Smad3, as evidenced by diminished number and viability of osteoclasts following overexpression of miR-221-5p or knockdown of Smad3. MiR-221-5p negatively mediated Smad3 expression. Smad3 suppression nullified the pro-osteoclastogenesis effect of miR-221-5p inhibition. Consistent results were observed in osteoporosis mouse models.

MiR-221-5p may alleviate postmenopausal osteoporosis through suppressing osteoclastogenesis via Smad3, which provides new ideas for molecule-targeted therapy of osteoporosis.