Ca2+/Mg2+ homeostasis-related TRPM7 channel mediates chondrocyte hypertrophy via regulation of the PI3K-Akt signaling pathway

Abstract

Chondrocytes are specialized cells that form cartilage tissue, and are able to respond to their osmotic environment and exercise important roles in endochondral ossification via undergoing proliferation, hypertrophy and apoptosis. The transient receptor melastatin potential 7 (TRPM7) cation channel can modulate the intracellular and extracellular levels of Ca2+ and Mg2+, and therefore the cellular osmotic environment. However, the molecular pathways involved in TRPM7‑mediated signal transduction have yet to be elucidated. In the present study, the expression and functionality of TRPM7 were investigated during chondrocyte proliferation and hypertrophy. The ATDC5 mouse cell line was employed and cellular viability was evaluated using the MTT assay, whereas hypertrophy was monitored via evaluating the expression of chondrogenic marker genes and the activity of alkaline phosphatase (ALP). Gene expression of TRPM7 appeared slightly upregulated during the proliferative stages of chondrocyte development, and significantly upregulated during the hypertrophic stages, suggesting the importance of Ca2+/Mg2+ homeostasis for chondrocyte growth. Low extracellular Ca2+/Mg2+ levels significantly reduced the expression of type X collagen, Indian hedgehog homolog (Ihh) and matrix metalloproteinase (MMP)‑13 genes, as well as ALP activity; however, cell viability remained unaffected. Conversely, the gene expression levels of TRPM7 appeared upregulated in ATDC5 cells under low extracellular Ca2+ or Mg2+ conditions. Silencing TRPM7 expression during the chondrocyte differentiation period also reduced type X collagen, Ihh and MMP‑13 gene expression, and ALP activity. Furthermore, the phosphatidylinositol‑4,5‑bisphosphate 3‑kinase (PI3K)‑Akt signaling pathway was activated following TRPM7 overexpression, and inhibited following TRPM7 silencing. Notably, the actions of TRPM7 on chondrocyte hypertrophy were abolished through the inhibition of PI3K‑Akt signaling. The present results suggested that TRPM7 may be involved in Ca2+/Mg2+ homeostasis during chondrocyte hypertrophy, and contribute to endochondral ossification via interacting with the PI3K‑Akt signaling pathway.

TRPM7 channels mediate spontaneous Ca 2+ fluctuations in growth plate chondrocytes that promote bone development

“…6 and 8). Our conclusion is in accordance with a report that TRPM7 channels are involved in hypertrophic differentiation of cultured chondrogenic ATDC5 cells in vitro (13) and is further supported by the observation that bone outgrowth is systemically perturbed in zebrafish bearing a Trpm7 mutation (9). The bone phenotypes in this mutant zebrafish are consistent with the histological and cytological defects associated with the reduced bone outgrowth that we observed in cultured Trpm7-deficient metatarsals and in femurs from chondrocyte-specific Trpm7 knockout mice.…”

Magnesium transporter protein solute carrier family 41 member 1 suppresses human pancreatic ductal adenocarcinoma through magnesium-dependent Akt/mTOR inhibition and bax-associated mitochondrial apoptosis

“…It has been previously shown that Mg 2+ treatment could increase intracellular Mg 2+ concentrations and activate Akt phosphorylation [42], whereas decrease of intracellular Mg 2+ was observed during the mitochondrial apoptosis of colon cancer cells [43]. Mg 2+ was a necessary factor for stabilisation of the mitochondrial membrane [44], possibly due to the maintenance of intracellular Mg 2+ /calcium (Ca 2+ ) homeostasis [45]. Indeed, a previous study showed that Mg 2+ could inhibit the uptake of Ca 2+ by mitochondria, which was the initiating factor of MMP loss and Cytochrome C release [46].…”

TRPM7, Magnesium, and Signaling

“…The PI3K/AKT pathway is also affected by TRPM7. In mouse chondrocytes, overexpression of TRPM7 stimulated the AKT pathway, while TRPM7 silencing inhibited AKT signaling [136]. In human osteoblasts, Mg 2+ -induced increase in mRNA expression of chemotaxis-related genes was attenuated by TRPM7 siRNA and PI3K inhibition, suggesting a link between TRPM7 and PI3K activation mediated by Mg 2+ .…”