17β-Estradiol Maintains Mitochondrial Homeostasis in Osteoblasts by Inhibiting MMP-8 and Activating the Ras Signaling Pathway in Postmenopausal Osteoporosis.

17β-estradiol is a potent endogenous estrogen used for postmenopausal osteoporosis treatment. Its osteoprotective role correlates with matrix metalloproteinase (MMP) and mitochondrial homeostasis. This research sought to examine the role of 17β-estradiol on MMP-8 in mitochondrial homeostasis and elucidate the potential regulatory pathways. We evaluated the effects of 17β-estradiol on MMP-8, bone loss, osteogenic differentiation, and mitochondrial homeostasis in bilateral ovariectomy (OVX)-induced mice and MC3T3-E1 cells. MMP-8 was overexpressed to validate its regulatory relationship with 17β-estradiol. Comprehensive analyses were further conducted to identify the potential pathways associated with MMP-8. The Ras pathway agonist ML-099 and inhibitor Lonafarnib were used for pathway validation. 17β-estradiol treatment attenuated bone loss and increased osteogenic Ca2+, osteoprotegerin (OPG), and osteocalcin (OC) levels. It inhibited reactive oxygen species (ROS) and malondialdehyde (MDA), promoted superoxide dismutase (SOD) activity, and restored mitochondrial homeostasis via upregulating the expression of dynamin-related protein 1 (DRP1), mitofusin 1 (MFN1), and peroxisome proliferator-activated receptor γ coactivator 1 alpha (PGC-1α), accompanied by increased adenosine triphosphate (ATP), mitochondrial membrane potential, and mitochondrial oxygen consumption. MMP-8 overexpression significantly reversed these protective effects. The Ras pathway was identified as a potential pathway associated with MMP-8-mediated osteoporosis regulation. ML-099 administration in 17β-estradiol + MMP-8 overexpression cells markedly restored mitochondrial homeostasis and rescued osteogenic differentiation. Conversely, the adverse impacts of MMP-8 overexpression on osteoblast differentiation, mitochondrial homeostasis, and Ras activation were further aggravated by Lonafarnib treatment. 17β-estradiol maintains mitochondrial homeostasis in osteoblasts via inhibiting MMP-8 and activating the Ras pathway, which provides novel potential targets for postmenopausal osteoporosis management.