Cyclophilin D Knock-Out Mice Show Enhanced Resistance to Osteoporosis and to Metabolic Changes Observed in Aging Bone

Metabolic alterations in the bone tissues of aged osteoporotic mice

Age-related osteoporosis is characterized by reduced bone mineralization and reduced bone strength, which increases the risk of fractures. We examined metabolic changes associated with age-related bone loss by profiling lipids and polar metabolites in tibia and femur bone tissues from young (5 months old) and old (28 months old) male C57BL/6J mice using ultra-performance liquid chromatography quadrupole-time-of-flight mass spectrometry. Partial least-squares discriminant analysis showed clear differences in metabolite levels in bone tissues of young and old mice. We identified 93 lipid species, including free fatty acids, sphingolipids, phospholipids, and glycerolipids, that were significantly altered in bone tissues of old mice. In addition, the expression of 26 polar metabolites differed significantly in bone tissues of old mice and young mice. Specifically, uremic toxin metabolite levels (p-cresyl sulfate, hippuric acid, and indoxylsulfate) were higher in bone tissues of old mice than in young mice. The increase in p-cresyl sulfate, hippuric acid, and indoxylsulfate levels were determined using targeted analysis of plasma polar extracts to determine whether these metabolites could serve as potential osteoporosis biomarkers. This study demonstrates that LC-MS-based global profiling of lipid and polar metabolites can elucidate metabolic changes that occur during age-related bone loss and identify potential biomarkers of osteoporosis.

Tanshinone‑IIA attenuates the deleterious effects of oxidative stress in osteoporosis through the NF‑κB signaling pathway

Osteoclasts are responsible for bone resorption caused by bone microstructural damage and bone-related disorders. Evidence shows that tanshinone IIA (Tan‑IIA), a traditional Chinese medicine, is used clinically as a drug for the treatment of cardiovascular and cerebrovascular diseases. However, the efficacy and mechanism underlying the effect of Tan‑IIA on the viability of osteoclasts remain to be fully elucidated. The present study investigated the therapeutic effects of Tan‑IIA on osteoblast differentiation and oxidative stress in vitro and in vivo. Cell viability was analyzed and oxidative stress was examined in the osteoblasts. Wnt1sw/sw mice were used to investigate the therapeutic effects of Tan‑IIA on spontaneous tibia fractures and severe osteopenia. The bone strength, collagen and mineral were examined in the tibia. Osteoblast activity was also analyzed in the experimental mice. The Tan‑IIA‑induced differentiation of osteoclasts and the mechanism of action were investigated in osteocytes. The data showed that Tan‑IIA treatment improved cell viability. The data also demonstrated that Tan‑IIA decreased the levels of H2O2, accumulation of reactive oxygen species and apoptosis of osteoblasts. Tan‑IIA inhibited the deleterious outcomes triggered by oxidative stress. In addition, Tan‑IIA inhibited the activation of nuclear factor (NF)‑κB and its target genes, tumor necrosis factor (TNF)‑α, inducible nitric oxide synthase and cyclooxygenase 2, and increased the levels of TNF receptor‑associated factor 1 and inhibitor of apoptosis protein‑1/2 in the osteocytes. Furthermore, it was shown that Tan‑IIA reduced the propensity to fractures and severe osteopenia in mice with osteoporosis. Tan‑IIA also exhibited improved bone strength, mineral and collagen in the bone matrix of the experimental mice. It was found that the Tan‑IIA‑mediated benefits on osteoblast activity and function were through the NF‑κB signaling pathway. Taken together, the data obtained in the present study suggested that Tan‑IIA had protective effects against oxidative stress in osteoblastic differentiation in mice with osteoporosis by regulating the NF‑κB signaling pathway.

Adrenomedullin inhibits osteoclast differentiation through the suppression of receptor activator of nuclear factor-κB ligand-induced nuclear factor-κB activation in glucocorticoid-induced osteoporosis

The current study aimed to improve the understanding on the association between adrenomedullin and osteoporosis in mice with glucocorticoid-induced osteoporosis. Bone resorption and osteoporosis-associated indexes, including maximum load, stiffness, energy to failure, ultimate strength, elastic modulus, post-yield displacement and post-yield displacement, in mice with osteoporosis were analyzed in order to evaluate the effect of adrenomedullin. The receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast differentiation was investigated subsequent to treatment with adrenomedullin in vitro. The results demonstrated that adrenomedullin significantly improved bone mass loss, density, bone strength and osteoporosis disease in the mice with glucocorticoid-induced osteoporosis. In addition, adrenomedullin markedly improved the osteoporosis-associated NFATc1, TRAP, OSCAR and c-Fos expression levels. Furthermore, the current findings indicated that RANKL-mediated osteoclast differentiation was suppressed in vitro and in vivo. Notably, the data revealed that adrenomedullin significantly improved the osteoporotic symptoms through inhibition of RANKL-induced NF-κB activation in glucocorticoid-induced osteoporosis. In conclusion, adrenomedullin serves an essential role in the progression of glucocorticoid-induced osteoporosis, regulating the bone mass loss, density and strength through the NF-κB signaling pathway.

Alendronate promotes osteoblast differentiation and bone formation in ovariectomy-induced osteoporosis through interferon-β/signal transducer and activator of transcription 1 pathway

Alendronate is commonly used for the treatment of postmenopausal osteoporosis; however, the underlying pathological molecular mechanisms of its action remain unclear. In the present study, the alendronate-treated signaling pathway in bone metabolism in rats with ovariectomy induced by osteoporosis was investigated. Rats with osteoporosis were orally administered alendronate or phosphate-buffered saline (control). In addition, the interferon-β (IFN-β)/signal transducer and activator of transcription 1 (STAT1) signaling pathway was investigated in osteoblasts following treatment with alendronate in vitro and in vivo. During the differentiation period, IFN-β (100 ng/ml) was used to treat the osteoblast cells, and the activity, viability and bone metabolism-associated gene expression levels (STAT1, p-STAT1, Fra1, TRAF6 and SOCS1) were analyzed in osteoblast cells. Histopathological changes were used to evaluate osteoblasts, osteoclasts, inflammatory phase of bone healing and osteonecrotic areas. The results demonstrated that alendronate significantly inhibited the activity of osteoporotic osteoclasts by stimulating expression of IFN-β, as well as markedly improved the viability and activity of osteoblasts compared with the control group. In addition, alendronate increased the expression and phosphorylation levels of STAT1 in osteoclasts, enhanced osteoblast differentiation, upregulated the expression levels of alkaline phosphatase and osteocalcin, and increased the expression of osteoblast differentiation-associated genes (osteocalcin, osterix and Runx2). Inhibition of IFN-β expression canceled the benefits of alendronate-mediated osteoblast differentiation. Notably, alendronate enhanced bone formation in rats with osteoporosis induced by ovariectomy. In conclusion, these findings suggest that alendronate can regulate osteoblast differentiation and bone formation in rats with osteoporosis induced by ovariectomy through upregulation of IFN-β/STAT1 signaling pathway.

The path from mitochondrial ROS to aging runs through the mitochondrial permeability transition pore

Excessive production of mitochondrial reactive oxygen species (mROS) is strongly associated with mitochondrial and cellular oxidative damage, aging, and degenerative diseases. However, mROS also induces pathways of protection of mitochondria that slow aging, inhibit cell death, and increase lifespan. Recent studies show that the activation of the mitochondrial permeability transition pore (mPTP), which is triggered by mROS and mitochondrial calcium overloading, is enhanced in aged animals and humans and in aging-related degenerative diseases. mPTP opening initiates further production and release of mROS that damage both mitochondrial and nuclear DNA, proteins, and phospholipids, and also releases matrix NAD that is hydrolyzed in the intermembrane space, thus contributing to the depletion of cellular NAD that accelerates aging. Oxidative damage to calcium transporters leads to calcium overload and more frequent opening of mPTP. Because aging enhances the opening of the mPTP and mPTP opening accelerates aging, we suggest that mPTP opening drives the progression of aging. Activation of the mPTP is regulated, directly and indirectly, not only by the mitochondrial protection pathways that are induced by mROS, but also by pro-apoptotic signals that are induced by DNA damage. We suggest that the integration of these contrasting signals by the mPTP largely determines the rate of cell aging and the initiation of cell death, and thus animal lifespan. The suggestion that the control of mPTP activation is critical for the progression of aging can explain the conflicting and confusing evidence regarding the beneficial and deleterious effects of mROS on health and lifespan.

Mitochondrial cyclophilin D ablation is associated with the activation of Akt/p70S6K pathway in the mouse kidney

The mitochondrial matrix protein cyclophilin D (CypD) is an essential component of the mitochondrial permeability transition pore (MPTP). Here we characterized the effects of CypD ablation on bioenergetics in the kidney. CypD loss triggers a metabolic shift in Ppif-/- male and female mouse kidneys towards glycolysis and Krebs cycle activity. The shift is accompanied by increased glucose consumption and a transcriptional upregulation of effectors of glucose metabolism in the kidney. These included activation of Akt, AMPK (only in males) and p70S6K kinases. Gender specific differences between the Ppif-/- male and female mouse kidneys were observed including activation of pro-surviving ERK1/2 kinase and inhibited expression of pro-apoptotic and pro-fibrotic JNK and TGFβ1 proteins in Ppif-/- females. They also showed the highest expression of phosphorylated-ERK1/2 and Akt S473 proteins of all four investigated animal groups. Furthermore, Ppif-/- females showed higher lactate concentrations and ATP/ADP-ratios in the kidney than males. These metabolic and transcriptional modifications could provide an additional level of protection to Ppif-/- females. In summary, loss of mitochondrial CypD results in a shift in bioenergetics and in activation of glucose-metabolism regulating Akt/AMPK/p70S6 kinase pathways that is expected to affect the capability of Ppif-/- mice kidneys to react to stimuli and injury.

PGE2 Receptor Subtype 1 (EP1) Regulates Mesenchymal Stromal Cell Osteogenic Differentiation by Modulating Cellular Energy Metabolism

Mesenchymal stromal cells (MSCs) are multipotent progenitors capable of differentiation into osteoblasts and can potentially serve as a source for cell-based therapies for bone repair. Many factors have been shown to regulate MSC differentiation into the osteogenic lineage such as the Cyclooxygenase-2 (COX2)/Prostaglandin E2 (PGE2) signaling pathway that is critical for bone repair. PGE2 binds four different receptors EP1-4. While most studies focus on the role PGE2 receptors EP2 and EP4 in MSC differentiation, our study focuses on the less studied, receptor subtype 1 (EP1) in MSC function. Recent work from our laboratory showed that EP1^-/- mice have enhanced fracture healing, stronger cortical bones, higher trabecular bone volume and increased in vivo bone formation, suggesting that EP1 is a negative regulator of bone formation. In this study, the regulation of MSC osteogenic differentiation by EP1 receptor was investigated using EP1 genetic deletion in EP1^-/- mice. The data suggest that EP1 receptor functions to maintain MSCs in an undifferentiated state. Loss of the EP1 receptor changes MSC characteristics and permits stem cells to undergo more rapid osteogenic differentiation. Notably, our studies suggest that EP1 receptor regulates MSC differentiation by modulating MSC bioenergetics, preventing the shift to mitochondrial oxidative phosphorylation by maintaining high Hif1α activity. Loss of EP1 results in inactivation of Hif1α, increased oxygen consumption rate and thus increased osteoblast differentiation. J. Cell. Biochem. 118: 4383-4393, 2017. © 2017 Wiley Periodicals, Inc.

Multiple Roles of Mitochondria in Aging Processes

Aging is a multifactorial process influenced by genetic factors, nutrition, and lifestyle. According to mitochondrial theory of aging, mitochondrial dysfunction is widely considered a major contributor to age-related processes. Mitochondria are both the main source and targets of detrimental reactions initiated in association with age-dependent deterioration of the cellular functions. Reactions leading to increased reactive oxygen species generation, mtDNA mutations, and oxidation of mitochondrial proteins result in subsequent induction of apoptotic events, impaired oxidative phosphorylation capacity, mitochondrial dynamics, biogenesis and autophagy. This review summarizes the major changes of mitochondria related to aging, with emphasis on mitochondrial DNA mutations, the role of the reactive oxygen species, and structural and functional changes of mitochondria.

Metabolomics and Its Application in the Development of Discovering Biomarkers for Osteoporosis Research

Osteoporosis is a progressive skeletal disorder characterized by low bone mass and increased risk of fracture in later life. The incidence and costs associated with treating osteoporosis cause heavy socio-economic burden. Currently, the diagnosis of osteoporosis mainly depends on bone mineral density and bone turnover markers. However, these indexes are not sensitive and accurate enough to reflect the osteoporosis progression. Metabolomics offers the potential for a holistic approach for clinical diagnoses and treatment, as well as understanding of the pathological mechanism of osteoporosis. In this review, we firstly describe the study subjects of osteoporosis and bio-sample preparation procedures for different analytic purposes, followed by illustrating the biomarkers with potentially predictive, diagnosis and pharmaceutical values when applied in osteoporosis research. Then, we summarize the published metabolic pathways related to osteoporosis. Furthermore, we discuss the importance of chronological data and combination of multi-omics in fully understanding osteoporosis. The application of metabolomics in osteoporosis could provide researchers the opportunity to gain new insight into the metabolic profiling and pathophysiological mechanisms. However, there is still much to be done to validate the potential biomarkers responsible for the progression of osteoporosis and there are still many details needed to be further elucidated.