cytochrome-c-t and Osteoporosis

Prolonged or overdose glucocorticoids (GCs) usage is the common cause of osteoporosis. In the present study, we studied the cellular mechanism of dexamethasone (Dex)-induce osteoblast cell death by focusing on the role of mitochondrial permeability transition pore (mPTP). In cultured osteoblastic MC3T3-E1 cells, Dex-induced mPTP opening, which was demonstrated by mitochondrial membrane potential (MPP) decrease, cyclophilin-D (CyPD)-adenine nucleotide translocator 1 (ANT-1) mitochondrial complexation and cytochrome C (cyto-C) release. The mPTP inhibitor sanglifehrin A (SfA) dramatically inhibited Dex-induced MPP loss, cyto-C release and MC3T3-E1 cell death. Dex-induced cell death requires mPTP composing protein CyPD, as CyPD inhibitor cyclosporin A (CsA) and CyPD siRNA knockdown inhibited Dex-induced MC3T3-E1 cell death, while CyPD overexpression aggravated Dex's cytotoxic effect. We found that Dex induced P53 phosphorylation and translocation to mitochondria, where it formed a complex with CyPD. Glucocorticoid receptor (GR) siRNA knockdown, or P53 inhibition (by its inhibitor pifithrin-α or shRNA silencing) suppressed Dex-induced CyPD-P53 mitochondrial association and subsequent MC3T3-E1 cell death. Finally, in primary cultured osteoblasts, Dex-induced cell death was inhibited by CsA, SfA or pifithrin-α. Together, our data suggest that Dex-induced osteoblast cell death is associated with GR-P53-regulated mPTP opening.

Topics: 3T3 Cells; Adenine Nucleotide Translocator 1; Animals; Apoptosis; Cell Line, Tumor; Cyclophilins; Cytochromes c; Dexamethasone; Dose-Response Relationship, Drug; Humans; Mice; Mitochondrial Membrane Transport Proteins; Mitochondrial Permeability Transition Pore; Osteoblasts; Osteoporosis; Peptidyl-Prolyl Isomerase F; Phosphorylation; Protein Transport; Receptors, Glucocorticoid; RNA Interference; Signal Transduction; Time Factors; Transfection; Tumor Suppressor Protein p53

Naringin, the primary active compound of the traditional Chinese medicine Rhizoma drynariae, possesses many pharmacological activities. The present study is an effort to explore the anti-osteoporosis potential of naringin in vivo and in vitro. In vivo, we used ovariectomized rats to clarify the mechanisms by which naringin anti-osteoporosis. In vitro, we used osteoclasts to investigate naringin promotes osteoclasts apoptosis. Naringin was effective at enhancing BMD, trabecular thickness, bone mineralization, and mechanical strength in a dose-dependent manner. The result of RT-PCR analysis revealed that naringin down-regulated the mRNA expression levels of BCL-2 and up-regulated BAX, caspase-3 and cytochrome C. In addition, naringin significantly reduced the bone resorption area in vitro. These findings suggest that naringin promotes the apoptosis of osteoclasts by regulating the activity of the mitochondrial apoptosis pathway and prevents OVX-induced osteoporosis in rats.

Topics: Animals; Apoptosis; Bone Density; Bone Density Conservation Agents; Bone Resorption; Calcification, Physiologic; Caspase 3; Cell Line; Cytochromes c; Dose-Response Relationship, Drug; Female; Flavanones; Gene Expression; Humans; Mitochondria; Osteoclasts; Osteoporosis; Ovariectomy; Plant Extracts; Proto-Oncogene Proteins c-bcl-2; Rats; Rats, Sprague-Dawley