Department of Orthopedics and Trauma, Xi'an Honghui Hospital, Affiliated to School of Medicine, Xi'an Jiaotong University, Xi'an, Shaanxi 710054, P.R. China.
Mol Med Rep. 2017 Oct;16(4):5699-5705. doi: 10.3892/mmr.2017.7300. Epub 2017 Aug 21.
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.
软骨细胞是形成软骨组织的特化细胞，能够通过增殖、肥大和凋亡来响应其渗透环境，并在软骨内骨化过程中发挥重要作用。瞬时受体电位 melastatin 潜在 7 型 (TRPM7) 阳离子通道可调节细胞内外 Ca2+和 Mg2+的水平，从而调节细胞的渗透环境。然而，TRPM7 介导的信号转导所涉及的分子途径仍有待阐明。在本研究中，研究了 TRPM7 在软骨细胞增殖和肥大过程中的表达和功能。使用 ATDC5 小鼠细胞系评估细胞活力，采用 MTT 测定法，而通过评估软骨形成标志物基因的表达和碱性磷酸酶 (ALP) 的活性来监测肥大。TRPM7 的基因表达在软骨细胞发育的增殖阶段略有上调，在肥大阶段显著上调，表明 Ca2+/Mg2+ 稳态对软骨细胞生长的重要性。低细胞外 Ca2+/Mg2+水平显著降低了型 X 胶原、印度刺猬同源物 (Ihh) 和基质金属蛋白酶 (MMP)-13 基因的表达以及 ALP 活性；然而，细胞活力保持不变。相反，在低细胞外 Ca2+或 Mg2+条件下，ATDC5 细胞中的 TRPM7 基因表达上调。在软骨细胞分化期间沉默 TRPM7 表达也降低了型 X 胶原、Ihh 和 MMP-13 基因的表达以及 ALP 活性。此外，TRPM7 过表达后激活了磷脂酰肌醇-4,5-二磷酸 3-激酶 (PI3K)-Akt 信号通路，而沉默 TRPM7 后则抑制了该信号通路。值得注意的是，通过抑制 PI3K-Akt 信号通路，TRPM7 对软骨细胞肥大的作用被消除。本研究结果表明，TRPM7 可能参与软骨细胞肥大过程中的 Ca2+/Mg2+ 稳态，并通过与 PI3K-Akt 信号通路相互作用促进软骨内骨化。
