Strontium promotes osteogenic differentiation by activating autophagy via the the AMPK/mTOR signaling pathway in MC3T3‑E1 cells

Abstract

Strontium (Sr) is an alkaline earth metal that exerts the dual effect of improving bone formation and suppressing bone resorption, resulting in increased bone apposition rates and bone mineral density. However, the mechanisms through which Sr exerts these beneficial effects on bone have yet to be fully elucidated. The present study aimed to reveal the underlying molecular mechanisms associated with Sr-induced osteogenic differentiation. The effects of Sr on cell proliferation and osteogenic differentiation were analyzed by MTT assay, RT-qPCR, western blot analysis, alkaline phosphatase (ALP) and Alizarin red staining assays. The extent of autophagy was determined by monodansylca-daverine (MDC) staining and western blot analysis of two markers of cellular autophagic activity, the steatosis-associated protein, sequestosome-1 (SQSTM1/p62), and the two isoforms of microtubule-associated protein 1 light chain 3 (LC3), LC-3-I/II. The expression levels of AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) were also detected by western blot analysis. Sr at a concentration of 3 mM exerted the most pronounced effect on osteogenic differentiation, without any apparent cell toxicity. At the same time, cellular autophagy was active during this process. Subsequently, autophagy was blocked by 3-methyl-adenine, and the enhancement of osteogenic differentiation in response to Sr was abrogated. Additionally, the phosphorylation level of AMPK was significantly increased, whereas that of mTOR was significantly decreased, in the Sr-treated group. Taken together, the findings of the present study demonstrate that Sr stimulates AMPK-activated autophagy to induce the osteogenic differentiation of MC3T3-E1 cells.

FOXO3 is targeted by miR-223-3p and promotes osteogenic differentiation of bone marrow mesenchymal stem cells by enhancing autophagy

“…P62 is an adaptor protein that plays a vital role in selective autophagy [ 32 ]. Cheng et al revealed a relation between autophagy and osteogenic differentiation and suggested that the activation of AMPK-dependent autophagy might contribute to osteogenic differentiation [ 16 ]. The previous study also pointed out that the role of FOXO3 in autophagy suggested that FOXO3 could control autophagy in skeletal muscle in vivo [ 33 ].…”

“…Autophagy also acts as pro-survival or pro-death response under physiological or pathological conditions [ 14 , 15 ]. The previous studies suggested that the activation of autophagy might be related to the promotion of osteogenic differentiation [ 16 – 18 ]. However, the effects of miRNAs, miR-223-3p in particular, on enhancing MSCs autophagy to promote osteogenic differentiation remained to be fully understood.…”

Effects of ERK/p38 MAPKs signaling pathways on MTA-mediated osteo/odontogenic differentiation of stem cells from apical papilla: a vitro study

“…Recently, many studies have explored the effect of materials on osteogenic differentiation of mesenchymal stem cells and its related mechanism [14][15][16]. Mineral trioxide aggregate (MTA) is a biocompatible material and widely used in endodontic treatments, such as pulp capping, pulpotomy, perforation repair and apexification [17,18].…”

Ginsenoside Rg3 attenuates ovariectomy‐induced osteoporosis via AMPK/mTOR signaling pathway

“…Accumulating evidence has suggested that autophagy can stimulate differentiation and mineralization in MC3T3‐E1 cells (Kim et al, 2016; Li, Zhang, Liu, Liu, & Liang, 2019). Furthermore, AMPK‐/mTOR‐mediated autophagy has been reported to exhibit a marked effect on bone protection (Cheng et al, 2019; Kneissel et al, 2004). Thus, it was speculated that autophagy triggered by AMPK/mTOR signaling pathway might play a critical role in Rg3‐induced osteoblastic differentiation and mineralization.…”