Lifeng Zheng1, Ximei Shen2, Junjian Ye1, Yun Xie1, Sunjie Yan3. 1. Department of Orthopedics, the First Affiliated Hospital of Fujian Medical University, Fuzhou 350005, Fujian, China. 2. Department of Endocrinology, the First Affiliated Hospital of Fujian Medical University, Fuzhou 350005, Fujian, China; Diabetes Research Institute of Fujian Province, Fuzhou 350005, Fujian, China. 3. Department of Endocrinology, the First Affiliated Hospital of Fujian Medical University, Fuzhou 350005, Fujian, China; Diabetes Research Institute of Fujian Province, Fuzhou 350005, Fujian, China. Electronic address: fjyansunjie@163.com.
Abstract
AIMS: Metformin was found to protect against hyperglycemia-induced injury in osteoblasts, but the cellular mechanisms involved remain unclear. Therefore, the aim of this study was to determine the effect of metformin on hyperglycemia-induced apoptosis and differentiation suppression in osteoblasts and to explore its relationships with the TLR4 signaling pathway. MAIN METHODS: A mouse osteoblast cell line, MC3T3-E1, and a diabetic rat model were used to survey the protective effects of metformin on hyperglycemia-induced injury. TLR4 expression was altered using small interfering (si)RNA and lentivirus-mediated TLR4 overexpression. LPS was used as a specific TLR4 activator, and CLI-095 was used as a TLR4 inhibitor. KEY FINDINGS: Metformin improved osteoblast differentiation, reduced apoptosis in hyperglycemic osteoblasts, and inhibited TLR4, MyD88 and NF-κB expression in a dose-dependent manner. Down-regulating the expression or inhibiting the activity of TLR4 enhanced these protective effects of metformin on osteoblast differentiation, cell viability and cell apoptosis in hyperglycemic conditions, whereas up-regulating the expression or activating the activity of TLR4 had the opposite effects. Activating NF-κB suppressed the protective effects of metformin, while inhibiting NF-κB activity had the opposite effects. Metformin increased ALP and OCN secretion, enhanced BMP-2 expression, improved bone mineral density (BMD), and decreased TLR4, MyD88 and NF-κB levels in the femur tissues of diabetic rats. SIGNIFICANCE: Taken together our experimentation support the hypothesis that metformin may alleviate hyperglycemia-induced apoptosis and differentiation suppression in osteoblasts by inhibiting the TLR4/MyD88/NF-κB signaling pathway.
AIMS: Metformin was found to protect against hyperglycemia-induced injury in osteoblasts, but the cellular mechanisms involved remain unclear. Therefore, the aim of this study was to determine the effect of metformin on hyperglycemia-induced apoptosis and differentiation suppression in osteoblasts and to explore its relationships with the TLR4 signaling pathway. MAIN METHODS: A mouse osteoblast cell line, MC3T3-E1, and a diabeticrat model were used to survey the protective effects of metformin on hyperglycemia-induced injury. TLR4 expression was altered using small interfering (si)RNA and lentivirus-mediated TLR4 overexpression. LPS was used as a specific TLR4 activator, and CLI-095 was used as a TLR4 inhibitor. KEY FINDINGS:Metformin improved osteoblast differentiation, reduced apoptosis in hyperglycemic osteoblasts, and inhibited TLR4, MyD88 and NF-κB expression in a dose-dependent manner. Down-regulating the expression or inhibiting the activity of TLR4 enhanced these protective effects of metformin on osteoblast differentiation, cell viability and cell apoptosis in hyperglycemic conditions, whereas up-regulating the expression or activating the activity of TLR4 had the opposite effects. Activating NF-κB suppressed the protective effects of metformin, while inhibiting NF-κB activity had the opposite effects. Metformin increased ALP and OCN secretion, enhanced BMP-2 expression, improved bone mineral density (BMD), and decreased TLR4, MyD88 and NF-κB levels in the femur tissues of diabeticrats. SIGNIFICANCE: Taken together our experimentation support the hypothesis that metformin may alleviate hyperglycemia-induced apoptosis and differentiation suppression in osteoblasts by inhibiting the TLR4/MyD88/NF-κB signaling pathway.
Authors: Elliot Ballato; Fnu Deepika; Mia Prado; Vittoria Russo; Virginia Fuenmayor; Siresha Bathina; Dennis T Villareal; Clifford Qualls; Reina Armamento-Villareal Journal: Front Endocrinol (Lausanne) Date: 2022-09-12 Impact factor: 6.055