Abstract
C1q/tumor necrosis factor‑related protein 3 (CTRP3) expression is markedly reduced in the serum of patients with osteoporosis. The present study aimed to investigate whether CTRP3 reduces bone loss in oophorectomy (OVX)‑induced mice via the AMP‑activated protein kinase (AMPK)/sirtuin 1 (SIRT1)/nuclear factor E2‑related factor 2 (Nrf2) signaling pathway. Female C57BL/6J mice and MC3T3‑E1 cells were used to construct in vivo and in vitro models of osteoporosis, respectively. The left femurs of mice were examined using micro‑computed tomography scans and bone‑related quantitative morphological evaluation was performed. Pathological changes and the number of osteoclasts in the left femurs of mice were detected using hematoxylin and eosin, and tartrate‑resistant acid phosphatase (TRAP) staining. Runt‑related transcription factor‑2 (RUNX2) expression in the left femurs was detected using immunofluorescence analysis, and the serum levels of bone resorption markers (C‑telopeptide of type I collagen and TRAP) and bone formation markers [osteocalcin (OCN) and procollagen type 1 N‑terminal propeptide] were detected. In addition, osteoblast differentiation and calcium deposits were examined in MC3T3‑E1 cells using alkaline phosphatase (ALP) and Alizarin red staining, respectively. Moreover, RUNX2, ALP and OCN expression levels were detected using reverse transcription‑quantitative PCR, and the expression levels of proteins associated with the AMPK/SIRT1/Nrf2 signaling pathway were detected using western blot analysis. The results revealed that globular CTRP3 (gCTRP3) alleviated bone loss and promoted bone formation in OVX‑induced mice. gCTRP3 also facilitated the osteogenic differentiation of MC3T3‑E1 cells through the AMPK/SIRT1/Nrf2 signaling pathway. The addition of an AMPK inhibitor (Compound C), SIRT1 inhibitor (EX527) or Nrf2 inhibitor (ML385) reduced the osteogenic differentiation of MC3T3‑E1 cells via inhibition of gCTRP3. In conclusion, gCTRP3 inhibits OVX‑induced osteoporosis by activating the AMPK/SIRT1/Nrf2 signaling pathway.