Increased activity of osteocyte autophagy in ovariectomized rats and its correlation with oxidative stress status and bone loss

Quercetin potentiates the anti-osteoporotic effects of alendronate through modulation of autophagy and apoptosis mechanisms in ovariectomy-induced bone loss rat model

BACKGROUND

Osteoporosis is a bone disease leading to bone fracture and affects 200 million women worldwide. Autophagy and apoptosis are two fundamental mechanisms that are involved in the development of osteoporosis. In this study we aim to investigate the combined effects of quercetin and alendronate on the markers of osteoporosis, autophagy, and apoptosis in the bone of ovariectomized rats.

METHODS AND RESULTS

Fifty adult female Sprague-Dawley rats were ovariectomized and treated with alendronate alone (5 µg/kg/day) or alendronate (5 µg/kg/day) in combination with quercetin (15 mg/kg/day) for 12 weeks. Then, ELISA, stereological tests, Real-time PCR analysis, and immunofluorescence assay were used to measure the markers of osteoporosis, autophagy, and apoptosis in the serum and tibia of rats. The serum osteocalcin was significantly decreased in ovariectomized rats that received quercetin and alendronate compared with alendronate only. Stereological data showed that except for osteoclasts, the total trabecular volume, bone weight, bone volume, osteocyte, and osteoblast numbers were increased in an ovariectomized group that was treated with quercetin and alendronate compared with alendronate alone. Except for Bcl2, the autophagy markers (Beclin-1 and LC3B) and Caspase-3 were significantly downregulated in ovariectomized rats that received quercetin and alendronate compared with those treated with alendronate alone.

CONCLUSION

Our results show that quercetin enhances the anti-osteoporotic effects of alendronate, possibly through the regulation of autophagy and apoptosis mechanisms. These findings suggest that the combination of quercetin and alendronate could be a useful therapeutic strategy in the treatment of osteoporosis in postmenopausal women.

Resveratrol protects osteocytes against oxidative stress in ovariectomized rats through AMPK/JNK1-dependent pathway leading to promotion of autophagy and inhibition of apoptosis

A large number of studies in recent years indicate that osteocytes are the orchestrators of bone remodeling by regulating both osteoblast and osteoclast activities. Oxidative stress-induced osteocyte apoptosis plays critical roles in the pathological processes of postmenopausal osteoporosis. Resveratrol is a natural polyphenolic compound that ameliorates postmenopausal osteoporosis. However, whether resveratrol regulates osteocyte apoptosis via autophagy remains largely unknown. The effects of resveratrol on regulating osteocyte apoptosis and autophagy were analyzed both in vivo and in vitro. In vitro, cultured MLO-Y4 cells were exposed to H₂O₂ with or without resveratrol. In vivo, an ovariectomy-induced osteoporosis model was constructed in rats with or without daily intraperitoneal injection of 10 mg/kg body weight resveratrol. It was found that resveratrol attenuated H₂O₂-induced apoptosis through activating autophagy in cultured MLO-Y4 cells, which was mediated by the dissociation of Beclin-1/Bcl-2 complex in AMPK/JNK1-dependent pathway, ultimately regulating osteocytes function. Furthermore, it was shown that resveratrol treatment reduced osteocytes oxidative stress, inhibited osteocytes apoptosis and promoted autophagy in ovariectomized rats. Our study suggests that resveratrol protects against oxidative stress by restoring osteocytes autophagy and alleviating apoptosis via AMPK/JNK1 activation, therefore dissociating Bcl-2 from Beclin-1.

Monotropein: A comprehensive review of biosynthesis, physicochemical properties, pharmacokinetics, and pharmacology

Monotropein, a principal natural compound in iridoid glycosides extracted from Morindae officinalis radix, has potent pharmacological activities. To understand and utilize monotropein, we systematically summarized the studies on monotropein, including its biosynthetic pathway, physicochemical properties, pharmacokinetics, and pharmacology. Interestingly, we found that the multiple bioactivities of monotropein, such as anti-osteoporosis, anti-inflammation, anti-oxidation, anti-nociception, and hepatic or renal protection, are closely associated with its capability of downregulating the nuclear factor-κB signaling pathway, inhibiting the mitogen-activated protein kinase signaling pathway, attenuating the activation of nuclear factor E2-related factor 2/heme oxygenase-1 signaling pathway, and regulating the mammalian target of rapamycin/autophagy signaling pathway. However, the clinically therapeutic effects and the potential problems need to be addressed. This review highlights the current research progress on monotropein, which provides a reference for further investigation of monotropein.

Strategies of Macrophages to Maintain Bone Homeostasis and Promote Bone Repair: A Narrative Review

Bone homeostasis (a healthy bone mass) is regulated by maintaining a delicate balance between bone resorption and bone formation. The regulation of physiological bone remodeling by a complex system that involves multiple cells in the skeleton is closely related to bone homeostasis. Loss of bone mass or repair of bone is always accompanied by changes in bone homeostasis. However, due to the complexity of bone homeostasis, we are currently unable to identify all the mechanisms that affect bone homeostasis. To date, bone macrophages have been considered a third cellular component in addition to osteogenic spectrum cells and osteoclasts. As confirmed by co-culture models or in vivo experiments, polarized or unpolarized macrophages interact with multiple components within the bone to ensure bone homeostasis. Different macrophage phenotypes are prone to resorption and formation of bone differently. This review comprehensively summarizes the mechanisms by which macrophages regulate bone homeostasis and concludes that macrophages can control bone homeostasis from osteoclasts, mesenchymal cells, osteoblasts, osteocytes, and the blood/vasculature system. The elaboration of these mechanisms in this narrative review facilitates the development of macrophage-based strategies for the treatment of bone metabolic diseases and bone defects.

The Evaluation of Xiaozeng Qianggu Tablets for Treating Postmenopausal Osteoporosis via up-Regulated Autophagy

Objective. Postmenopausal osteoporosis (PMOP) is a common age-associated disease in the life course. Clinically, Xiaozeng Qianggu Tablets (XQT) have a potent therapeutic effect on the PMOP. However, the bioactive components and the mechanism of XQT underlying the PMOP treatment were unclear and it should be explored to discover the scientific connotation in traditional medical practice. Methods. The components in XQT were identified by UPLC-Q-TOF/MS. The animal model of PMOP was established by surgical ovariectomy in the female Sprague-Dawley rats. After treatment of XQT, the therapeutic effect was assessed by the determination of bone metabolism biomarkers in serum and histopathological examination. The effect of XQT on the autophagy and bone micro-situation were tested using western blot, RT-qPCR, and transmission electron microscope. Results. There were 27 compounds identified in XQT, including catalpol, monotropein, verbascoside, cryptochlorogenic acid, 5,7-dihydroxychromone 7-rutinoside, biorobin, and so on. The bone metabolism markers (alkaline phosphatase, bone alkaline phosphatase, procollagen type I intact N-terminal propeptide, cross-linked carboxy-terminal telopeptide of type I collagen, and tartrate-resistant acid phosphatase) were significantly increased in the PMOP rats and reversed by XQT administration. Moreover, the width of bone trabeculae and the ratio of the area of calcium deposition to bone trabeculae were also improved after treating the middle dose of XQT. Meanwhile, the bone micro-structure was improved by XQT. The mRNA and protein expression of unc-51 like kinase 1, beclin-1, and microtubule-associated protein 1B-light chain 3 in PMOP rats were down-regulated and up-regulated by XQT administration. Conclusions. The compounds in XQT, including catalpol, monotropein, verbascoside cryptochlorogenic acid, and so on, were valuable for further pharmacy evaluation. The pathological changes and bone micro-structure were improved by XQT, and the down-regulated autophagy level was also restored, which suggested a potent effect of XQT on treating PMOP, corresponding to its clinic use.

GSK 650394 Inhibits Osteoclasts Differentiation and Prevents Bone Loss via Promoting the Activities of Antioxidant Enzymes In Vitro and In Vivo

Osteoporosis (OP) is one of the most common bone disorders among the elderly, characterized by abnormally elevated bone resorption caused by formation and activation of osteoblast (OC). Excessive reactive oxygen species (ROS) accumulation might contribute to the formation process of OC as an essential role. Although accumulated advanced treatment target on OP have been proposed in recent years, clinical outcomes remain unexcellence attributed to severe side effects. The purpose of present study was to explore the underlying mechanisms of GSK 650394 (GSK) on inhibiting formation and activation of OC and bone resorption in vitro and in vivo. GSK could inhibit receptor activator of nuclear-κB ligand (RANKL-)-mediated Oc formation via suppressing the activation of NF-κB and MAPK signaling pathways, regulating intracellular redox status, and downregulate the expression of nuclear factor of activated T cells c1 (NFATc1). In addition, quantitative RT-PCR results show that GSK could suppress the expression of OC marker gene and antioxidant enzyme genes. Consistent with in vitro cellular results, GSK treatment improved bone density in the mouse with ovariectomized-induced bone loss according to the results of CT parameters, HE staining, and Trap staining. Furthermore, GSK treatment could enhance the capacity of antioxidant enzymes in vivo. In conclusion, this study suggested that GSK could suppress the activation of osteoclasts and therefore maybe a potential therapeutic reagent for osteoclast activation-related osteoporosis.

Membrane estrogen receptor ERα activation improves tau clearance via autophagy induction in a tauopathy cell model

Alzheimer's disease (AD) is the most prevalent aging-associated neurodegenerative disease, with a higher incidence in women than men. There is evidence that sex hormone replacement therapy, particularly estrogen, reduces memory loss in menopausal women. Neurofibrillary tangles are associated with tau protein aggregation, a characteristic of AD and other tauopathies. In this sense, autophagy is a promising cellular process to remove these protein aggregates. This study evaluated the autophagy mechanisms involved in neuroprotection induced by 17β-estradiol (E2) in a Tet-On inducible expression tauopathy cell model (EGFP-tau WT or with the P301L mutation, 0N4R isoform). The results indicated that 17β-estradiol induces autophagy by activating AMPK in a concentration-dependent manner, independent of mTOR signals. The estrogen receptor α (ERα) agonist, PPT, also induced autophagy, while the ERα antagonist, MPP, substantially attenuated the 17β-estradiol-mediated autophagy induction. Notably, 17β-estradiol increased LC3-II levels and phosphorylated and total tau protein clearance in the EGFP-tau WT cell line but not in EGPF-tau P301L. Similar results were observed with E2-BSA, a plasma membrane-impermeable estrogen, suggesting membrane ERα involvement in non-genomic estrogenic pathway activation. Furthermore, 17β-estradiol-induced autophagy led to EGFP-tau protein clearance. These results demonstrate that modulating autophagy via the estrogenic pathway may represent a new therapeutic target for treating AD.

Ovariectomy Affects Acute Pancreatitis in Mice

BACKGROUND

Serum estradiol levels in severe acute injury are correlated with in hospital mortality. In acute pancreatitis, serum estradiol levels are strong predictors of disease severity. Studies of whether changes in estradiol levels play a causative role in acute pancreatitis severity are limited. The ovariectomized mouse model has been used to study the effects of estradiol in health and disease.

AIMS

We assessed whether the ovariectomized mouse model could be used to assess the effects of estradiol on pancreatitis severity.

METHODS

C57BL/6 mice with their ovaries removed were used to simulate low circulating estradiol conditions. Ovariectomized mice were treated with six hourly injections of cerulein to induce mild acute pancreatitis and compared to ovariectomized mice pre-treated with subcutaneous estradiol injections.

RESULTS

Findings suggest ovariectomized model is a problematic preparation to study pancreatitis. At baseline, ovariectomy leads to prominent acinar cell ultrastructure changes as well as changes in other select morphologic and biomarkers of pancreatitis. In addition, ovariectomy changed select acute pancreatitis responses that were only partially rescued by estradiol pre-treatment.

CONCLUSIONS

These findings suggest that the ovariectomized mouse as a model of estradiol depletion should be used with caution in pancreatic studies. Future studies should explore whether derangements in other female hormones produced by the ovaries can lead to changes in pancreatic studies.

Geroprotectors and Skeletal Health: Beyond the Headlines

Osteoporosis and osteoarthritis are the most common age-related diseases of the musculoskeletal system. They are responsible for high level of healthcare use and are often associated with comorbidities. Mechanisms of ageing such as senescence, inflammation and autophagy are common drivers for both diseases and molecules targeting those mechanisms (geroprotectors) have potential to prevent both diseases and their co-morbidities. However, studies to test the efficacy of geroprotectors on bone and joints are scant. The limited studies available show promising results to prevent and reverse Osteoporosis-like disease. In contrast, the effects on the development of Osteoarthritis-like disease in ageing mice has been disappointing thus far. Here we review the literature and report novel data on the effect of geroprotectors for Osteoporosis and Osteoarthritis, we challenge the notion that extension of lifespan correlates with extension of healthspan in all tissues and we highlight the need for more thorough studies to test the effects of geroprotectors on skeletal health in ageing organisms.

Bisphenol A induces apoptosis and autophagy in murine osteocytes MLO-Y4: Involvement of ROS-mediated mTOR/ULK1 pathway

Bisphenol A (BPA) is a widely environmental endocrine disruptor. The accumulated BPA in humans is toxic to osteoblasts and osteoclasts, but few studies focused on the effects of BPA on osteocytes, the most abundant bone cell type, contributing to the development and metabolism of bone. Here, we reported that BPA (50, 100, 200 μmol/L) inhibited the cell viability of osteocytes MLO-Y4, promoted G0/G1 phase arrest and apoptosis in a dose-dependent manner. BPA treatment significantly increased the levels of autophagy-regulated proteins including Beclin-1 and LC3-II along with the decrease of p62, accompanied by the elevation of autophagy flux and the accumulation of acidic vacuoles, which was blocked by the autophagy inhibitor bafilomycin A1 (BafA1). Furthermore, BPA significantly inhibited the mammalian target of rapamycin (mTOR) and activated Unc-51 like autophagy activating kinase 1 (ULK1) signaling, leading to the decreased p-mTOR/mTOR ratio and the increased p-ULK1/ULK1 ratio. The mTOR activator MHY1485 (MHY) or the ULK1 inhibitor SBI-0206965 (SBI) prevented autophagy and enhanced apoptosis caused by BPA, respectively. In addition, BPA increased the levels of intracellular reactive oxygen species (ROS) and malondialdehyde (MDA) and decreased antioxidant enzymes nuclear factor E2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) levels, resulting in oxidative stress. The ROS scavenger N-acetylcysteine (NAC) attenuated BPA-induced the mTOR/ULK1 pathway activation, apoptosis and autophagy. Collectively, ROS-mediated mTOR/ULK1 signaling is involved in BPA-induced apoptosis and autophagy in osteocytes MLO-Y4. Our data first provide in vitro evidence that apoptosis and autophagy as cellular mechanisms for the toxic effect of BPA on osteocytes, thereby advancing our understanding of the potential role of osteocytes in the adverse effect of BPA on bone health.

Autophagy in Bone Remodeling: A Regulator of Oxidative Stress

Bone homeostasis involves bone formation and bone resorption, which are processes that maintain skeletal health. Oxidative stress is an independent risk factor, causing the dysfunction of bone homeostasis including osteoblast-induced osteogenesis and osteoclast-induced osteoclastogenesis, thereby leading to bone-related diseases, especially osteoporosis. Autophagy is the main cellular stress response system for the limination of damaged organelles and proteins, and it plays a critical role in the differentiation, apoptosis, and survival of bone cells, including bone marrow stem cells (BMSCs), osteoblasts, osteoclasts, and osteocytes. High evels of reactive oxygen species (ROS) induced by oxidative stress induce autophagy to protect against cell damage or even apoptosis. Additionally, pathways such as ROS/FOXO3, ROS/AMPK, ROS/Akt/mTOR, and ROS/JNK/c-Jun are involved in the regulation of oxidative stress-induced autophagy in bone cells, including osteoblasts, osteocytes and osteoclasts. This review discusses how autophagy regulates bone formation and bone resorption following oxidative stress and summarizes the potential protective mechanisms exerted by autophagy, thereby providing new insights regarding bone remodeling and potential therapeutic targets for osteoporosis.

Bioinformatics Analysis of Autophagy and Mitophagy Markers Associated with Delayed Cerebral Ischemia Following Subarachnoid Hemorrhage

Objective

To evaluate the interactions among differentially expressed autophagy and mitophagy markers in subarachnoid hemorrhage (SAH) patients with delayed cerebral ischemia (DCI).

Methods

The expression data of autophagy and mitophagy-related makers in the cerebrospinal fluid (CSF) cells was analyzed by real-time reverse transcription-polymerase chain reaction and Western blotting. The markers included death-associated protein kinase (DAPK)-1, BCL2 interacting protein 3 like (BNIP3L), Bcl-1 antagonist X, PINK, Unc-51 like autophagy activating kinase 1, nuclear dot protein 52, and p62. In silico functional analyses including gene ontology enrichment and the protein-protein interaction network were performed.

Results

A total of 56 SAH patients were included and 22 (38.6%) of them experienced DCI. The DCI patients had significantly increased mRNA levels of DAPK1, BNIP3L, and PINK1, and increased expression of BECN1 compared to the non-DCI patients. The most enriched biological process was the positive regulation of autophagy, followed by the response to mitochondrial depolarization. The molecular functions ubiquitin-like protein ligase binding and ubiquitin-protein ligase binding were enriched. In the cluster of cellular components, Lewy bodies and the phagophore assembly site were enriched. BECN1 was the most connected gene among the differentially expressed markers related to autophagy and mitophagy in the development of DCI.

Conclusion

Our study may provide novel insight into mitochondrial dysfunction in DCI pathogenesis.

Autophagy and bone diseases

Autophagy is a ubiquitous cellular process, allowing the removal and recycling of damaged proteins and organelles. At the basal level, this process plays a role in quality control, thus participating in cellular homeostasis. Autophagy can also be induced by various stresses, such as nutrient deprivation or hypoxia, to allow the cell to survive until conditions improve. In recent years, the role of this process has been widely studied in many pathologies such as neurodegenerative diseases or cancers. In bone tissue, various studies have shown that autophagy is involved in the survival, differentiation and activity of osteoblasts, osteocytes and osteoclasts. The evolution of this knowledge has led to the identification of new molecular pathophysiological mechanisms in bone pathologies. This review reports the current state of knowledge on the role of autophagy in 4 bone diseases: osteoporosis, which seems to be associated with a decrease in autophagy, osteopetrosis and Paget's disease where the course of the autophagic process is disturbed, and finally osteosarcoma where autophagy seems to play a protumoral role. A better understanding of the involvement of autophagy in these pathologies should eventually lead to the identification of new potential therapeutic targets.

Estrogen prevents cellular senescence and bone loss through Usp10-dependent p53 degradation in osteocytes and osteoblasts: the role of estrogen in bone cell senescence

Estrogens play multiple roles in maintaining skeletal homeostasis by regulating many physiological processes in bone cells. Recently, cellular senescence in bone cells, especially in osteocytes, has been demonstrated to be a pivotal factor in bone loss. However, whether and how estrogen mediates cellular senescence in bone cells remains unknown. Here, we show that estrogen is negatively correlated with p53-related cellular senescence, primarily through the regulation of p53 protein levels, both in vivo and in vitro. Further study confirmed that estrogen attenuated the nuclear import of p53 and accelerated p53 degradation in osteocyte-like MLO-Y4 cells and osteoblastic MC3T3-E1 cells. A screen of p53-related ubiquitinating/deubiquitinating enzymes indicated that estrogen induced the degradation of p53 through the regulation of Usp10, a deubiquitinase that is directly linked to p53. Usp10 inhibition attenuated H₂O₂-induced senescence in MLO-Y4 cells, as indicated by p53/p21 quantification, a senescence-associated β-galactosidase (SA-β-gal) assay, and p53 localization visualization with a confocal microscope. Usp10 overexpression abolished the estrogen-mediated regulation of p53 and the downstream transcriptional gene p21. The injection of ovariectomized (OVX) mice with Spautin-1, a Usp10 inhibitor, inhibited the expression of p53 and the transcription of downstream senescence markers, as well as promoted bone mass recovery. Taken together, our study unveils the regulatory function of estrogen in the prevention of cellular senescence through the regulation of Usp10, thereby accelerating the degradation of senescent factor p53 and inhibiting its nuclear import.

Quercetin and vitamin E alleviate ovariectomy-induced osteoporosis by modulating autophagy and apoptosis in rat bone cells

Osteoporosis is the most prevalent metabolic bone disease and one of the most important postmenopausal consequences. The aim of this study was to investigate the effects of quercetin (Q) and vitamin E (vitE) on ovariectomy-induced osteoporosis. Animals were ovariectomized and treated with Q (15 mg/kg/day), vitE (60 mg/kg/day), estradiol (10 µg/kg/day), and Q (7.5 mg/kg/day) + vitE (30 mg/kg/day) for 10 weeks by gavage, and osteoporosis markers and messenger RNA (mRNA) expression of autophagy and apoptosis-related genes were analyzed in serum and tibia of rats. Data indicated that ovariectomy resulted in development of osteoporosis as demonstrated by reduction in serum calcium, bone weight, bone volume, trabeculae volume, and the total number of osteocytes and osteoblasts, and increase in the total number of osteoclasts and serum osteocalcin. Total mRNA expressions of LC3, beclin1, and caspase 3 were also increased and bcl2 expression was decreased in the tibia. By reversing these changes, treatment with Q and vitE markedly improved osteoporosis. In conclusion, Q, and to a lesser extent, vitE, prevented osteoporosis by regulating the total number of bone cells, maybe through regulating autophagy and apoptosis.

Role of TRPA1 expressed in bone tissue and the antinociceptive effect of the TRPA1 antagonist repeated administration in a breast cancer pain model

AIMS

Breast cancer-induced chronic pain is usually treated with opioids, but these compounds cause various adverse effects. Transient receptor potential ankyrin 1 (TRPA1) is involved in cancer pain; also, endogenous TRPA1 agonists are associated with cancer pain development. The aim of this study was to observe the antinociceptive effect of a repeated-dose TRPA1 antagonist administration and the production of endogenous TRPA1 agonists and TRPA1 expression in bone tissue in a model of breast cancer pain in mice. Second, we used a sequence reading archive (SRA) strategy to observe the presence of this channel in the mouse bone and in mouse bone cell lines.

MAIN METHODS

We used BALB/c mice for experiments. The animals were subjected to the tumor cell inoculation (4 T1 strain). HC-030031 (a TRPA1 antagonist) treatment was done from day 11 to day 20 after tumor inoculation. TRPA1 expression and biochemical tests of oxidative stress were performed in the bone of mice (femur). SRA strategy was used to detect the TRPA1 presence.

KEY FINDINGS

Repeated treatment with the TRPA1 antagonist produced an antinociceptive effect. There was an increase in hydrogen peroxide levels, NADPH oxidase and superoxide dismutase activities, but the expression of TRPA1 in the bone tissue was not altered. SRA did not show TRPA1 residual transcription in the osteoblast and osteoclast cell lines, as well as for mice cranial tissue and in mouse osteoclast precursors.

SIGNIFICANCE

The TRPA1 receptor is a potential target for the development of new painkillers for the treatment of bone cancer pain.

Curcumin Ameliorates Palmitic Acid-Induced Saos-2 Cell Apoptosis Via Inhibiting Oxidative Stress and Autophagy

OBJECTIVES

We aimed to determine the effects of curcumin on palmitic acid- (PA-) induced human osteoblast-like Saos-2 cell apoptosis and to explore the potential molecular mechanisms in vitro level.

METHODS

Saos-2 cell were cultured with PA with or without curcumin, N-acetylcysteine (NAC, anti-oxidant), 3-methyladenine (3-MA, autophagy inhibitor) AY-22989 (autophagy agonist) or H2O2. Then, the effects of PA alone or combined with curcumin on viability, apoptosis, oxidative stress, and autophagy in were detected by CCK-8, flow cytometry assay and western blot.

RESULTS

We found that autophagy was induced, oxidative stress was activated, and apoptosis was promoted in PA-induced Saos-2 cells. Curcumin inhibited PA-induced oxidative stress, autophagy, and apoptosis in Saos-2 cells. NAC successfully attenuated oxidative stress and apoptosis, and 3-MA attenuated oxidative stress and apoptosis in palmitate-induced Saos-2 cells. Interestingly, NAC inhibited PA-induced autophagy, but 3-MA had no obvious effects on oxidative stress in PA-treated Saos-2 cells. In addition, curcumin inhibited H2O2 (oxidative stress agonist)-induced oxidative stress, autophagy, and apoptosis, but curcumin had no obvious effect on AY-22989 (autophagy agonist)-induced autophagy and apoptosis.

CONCLUSION

The present study demonstrated that oxidative stress is an inducer of autophagy and that curcumin can attenuate excess autophagy and cell apoptosis by inhibiting oxidative stress in PA-induced Saos-2 cells.

The role of autophagy in bone homeostasis

Autophagy is an evolutionarily conserved intracellular process and is considered one of the main catabolism pathways. In the process of autophagy, cells are digested nonselectively or selectively to recover nutrients and energy, so it is regarded as an antiaging process. In addition to the essential role of autophagy in cellular homeostasis, autophagy is a stress response mechanism for cell survival. Here, we review recent literature describing the pathway of autophagy and its role in different bone cell types, including osteoblasts, osteoclasts, and osteocytes. Also discussed is the mechanism of autophagy in bone diseases associated with bone homeostasis, including osteoporosis and Paget's disease. Finally, we discuss the application of autophagy regulators in bone diseases. This review aims to introduce autophagy, summarize the understanding of its relevance in bone physiology, and discuss its role and therapeutic potential in the pathogenesis of bone diseases such as osteoporosis.

Autophagy in spinal ligament fibroblasts: evidence and possible implications for ossification of the posterior longitudinal ligament

Background

The molecular mechanisms of ossification of the posterior longitudinal ligament (OPLL) remain to be elucidated. The aim of the present study was to investigate the autophagy of spinal ligament fibroblasts derived from patients with OPLL and to examine whether autophagy-associated gene expression was correlated with the expression of osteogenic differentiation genes.

Methods

Expression of autophagy-associated genes was detected in 37 samples from 21 OPLL patients and 16 non-OPLL patients. The correlation of autophagy-associated gene expression and the expression of osteogenic differentiation genes was analyzed by Pearson’s correlation. The expression of autophagy-associated genes of ligament fibroblasts was assessed by reverse transcription-quantitative polymerase chain reaction (RT-qPCR), western blotting, and immunofluorescence. The incidence of autophagy was assessed by flow cytometry. After knockdown using small interfering RNA targeting Beclin1, the expression of osteogenic differentiation genes were compared in spinal ligament fibroblasts.

Results

In clinical specimens, mRNA expression levels of microtubule-associated protein 1 light chain 3 and Beclin1 were higher in the OPLL group compared with the non-OPLL group. Pearson correlation analysis demonstrated that Beclin1 expression was positively correlated with expression of osteocalcin (OCN) (r = 0.8233, P < 0.001), alkaline phosphatase, biomineralization associated (ALP) (r = 0.7821, P < 0.001), and collagen type 1 (COL 1) (r = 0.6078, P = 0.001). Consistently, the upregulation of autophagy-associated genes in ligament fibroblasts from patients with OPLL were further confirmed by western blotting and immunofluorescence. The incidence of autophagy was also increased in ligament fibroblasts from patients with OPLL. Furthermore, knockdown of Beclin1 led to a decrease in the expression of OCN, ALP, and COL 1 by 63.2% (P < 0.01), 52% (P < 0.01), and 53.2% (P < 0.01) in ligament fibroblasts from patients with OPLL, respectively.

Conclusions

Beclin1-mediated autophagy was involved in the osteogenic differentiation of ligament fibroblasts and promoted the development of OPLL.

17α-Estradiol prevents ovariectomy-mediated obesity and bone loss

Menopause is a natural physiological process in older women that is associated with reduced estrogen production and results in increased risk for obesity, diabetes, and osteoporosis. 17α-estradiol (17α-E2) treatment in males, but not females, reverses several metabolic conditions associated with advancing age, highlighting sexually dimorphic actions on age-related pathologies. In this study we sought to determine if 17α-E2 could prevent ovariectomy (OVX)-mediated detriments on adiposity and bone parameters in females. Eight-week-old female C57BL/6J mice were subjected to SHAM or OVX surgery and received dietary 17α-E2 during a six-week intervention period. We observed that 17α-E2 prevented OVX-induced increases in body weight and adiposity. Similarly, uterine weight and luminal cell thickness were decreased by OVX and prevented by 17α-E2 treatment. Interestingly, 17α-E2 prevented OVX-induced declines in tibial metaphysis cancellous bone. And similarly, 17α-E2 improved bone density parameters in both tibia and femur cancellous bone, primarily in OVX mice. In contrast, to the effects on cancellous bone, cortical bone parameters were largely unaffected by OVX or 17α-E2. In the non-weight bearing lumbar vertebrae, OVX reduced trabecular thickness but not spacing, while 17α-E2 increased trabecular thickness and reduced spacing. Despite this, 17α-E2 did improve bone volume/tissue volume in lumbar vertebrae. Overall, we found that 17α-E2 prevented OVX-induced increases in adiposity and changes in bone mass and architecture, with minimal effects in SHAM-operated mice. We also observed that 17α-E2 rescued uterine tissue mass and lining morphology to control levels without inducing hypertrophy, suggesting that 17α-E2 could be considered as an adjunct to traditional hormone replacement therapies.

Targeting autophagy in osteoporosis: From pathophysiology to potential therapy

Osteoporosis is a highly prevalent disorder characterized by the loss of bone mass and microarchitecture deterioration of bone tissue, attributed to various factors, including menopause (primary), aging (primary) and adverse effects of relevant medications (secondary). In recent decades, knowledge regarding the etiological mechanisms underpinning osteoporosis emphasizes that bone cellular homeostasis, including the maintenance of cell functions, differentiation, and the response to stress, is tightly regulated by autophagy, which is a cell survival mechanism for eliminating and recycling damaged proteins and organelles. With the important roles in the maintenance of cellular homeostasis and organ function, autophagy has emerged as a potential target for the prevention and treatment of osteoporosis. In this review, we update and discuss the pathophysiology of autophagy in normal bone cell life cycle and metabolism. Then, the alternations of autophagy in primary and secondary osteoporosis, and the accompanied pathological process are discussed. Finally, we discuss current strategies, limitations, and challenges involved in targeting relevant pathways and propose strategies by which such hurdles may be circumvented in the future for their translation into clinical validations and applications for the prevention and treatment of osteoporosis.

Autophagy in fate determination of mesenchymal stem cells and bone remodeling

Mesenchymal stem cells (MSCs) have been widely exploited as promising candidates in clinical settings for bone repair and regeneration in view of their self-renewal capacity and multipotentiality. However, little is known about the mechanisms underlying their fate determination, which would illustrate their effectiveness in regenerative medicine. Recent evidence has shed light on a fundamental biological role of autophagy in the maintenance of the regenerative capability of MSCs and bone homeostasis. Autophagy has been implicated in provoking an immediately available cytoprotective mechanism in MSCs against stress, while dysfunction of autophagy impairs the function of MSCs, leading to imbalances of bone remodeling and a wide range of aging and degenerative bone diseases. This review aims to summarize the up-to-date knowledge about the effects of autophagy on MSC fate determination and its role as a stress adaptation response. Meanwhile, we highlight autophagy as a dynamic process and a double-edged sword to account for some discrepancies in the current research. We also discuss the contribution of autophagy to the regulation of bone cells and bone remodeling and emphasize its potential involvement in bone disease.

The roles of autophagy in osteogenic differentiation in rat ligamentum fibroblasts: Evidence and possible implications

Autophagy, a macromolecular degradation process, plays a pivotal role in cell differentiation and survival. This study was designed to investigate the role of autophagy in the osteogenic differentiation in ligamentum fibroblasts. Rat ligamentum fibroblasts were isolated from the posterior longitudinal ligament and cultured in osteogenic induction medium. Ultrastructural analysis, immunofluorescence assay, western blot, flow cytometry, and lysosomal activity assessment were performed to determine the presence and activity of autophagy in the cells. The mineralization deposit and osteogenic gene expressions were evaluated to classify the association between autophagy activity and the bone formation ability of the spinal ligament cells. The influence of leptin and endothelin-1 on the autophagy activity was also evaluated. Our study demonstrated that autophagy was present and increased in the ligament cells under osteogenic induction. Inhibition of autophagy with either pharmacologic inhibitors (Bafilomycin A and 3-methyladenine) or Belcin1 (BECN1) knocking down weakened the mineralization capacity, decreased the gene expressions of COL1A1, osteocalcin (Ocn), and runt-related transcription factor 2 (Runx2) in the ligamentum fibroblasts and increased cell apoptosis. The Adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK)-BECN1 autophagic pathway was activated in the osteogenic differentiating ligamentum fibroblasts. Leptin significantly increased the autophagy activity in the ligament cells under osteogenic induction. These discoveries might improve our understanding for the mechanism of ossification of the posterior longitudinal ligament (OPLL) and provide new approaches on the prevention and treatment of this not uncommon disease.

Dependence between estrogen sulfotransferase (SULT1E1) and nuclear transcription factor Nrf-2 regulations via oxidative stress in breast cancer

Human estrogen sulfotransferase (SULT1E1) and nuclear factor erythroid 2-related factor 2 (Nrf-2) expression influences each other in advanced human breast carcinogenesis. The difference in the metabolism of estradiol (E2) in pre- and post-menopausal women remains to be connected with post-menopausal breast cancer. A synergism between ROS production and E2 generation has been demonstrated. No definite mechanism for simultaneous functions of Nrf2, oxidative stress E2 regulating enzymes (SULT1E1) has been yet clarified. Our present review demonstrates that ROS dependent regulation of Nrf-2 is one of the most important determinants of E2 regulation by altering SULT1E1 expression. This study also focuses the idea that estrogen receptor cased subtypes of cancer may have different molecular environments which has an impact on the therapeutic efficacy.

Autophagy: A Promising Target for Age-related Osteoporosis

Autophagy is a process the primary role of which is to clear up damaged cellular components such as long-lived proteins and organelles, thus participating in the conservation of different cells. Osteoporosis associated with aging is characterized by consistent changes in bone metabolism with suppression of bone formation as well as increased bone resorption. In advanced age, not only bone mass but also bone strength decrease in both sexes, resulting in an increased incidence of fractures. Clinical and animal experiments reveal that age-related bone loss is associated with many factors such as accumulation of autophagy, increased levels of reactive oxygen species, sex hormone deficiency, and high levels of endogenous glucocorticoids. Available basic and clinical studies indicate that age-associated factors can regulate autophagy. Those factors play important roles in bone remodeling and contribute to decreased bone mass and bone strength with aging. In this review, we summarize the mechanisms involved in bone metabolism related to aging and autophagy, supplying a theory for therapeutic targets to rescue bone mass and bone strength in older people.

Evaluating the Correlations Between Osteoporosis and Lifestyle-Related Factors Using Transcriptome-Wide Association Study

Osteoporosis (OP) is a multi-factorial bone disease influenced by genetic factors, age, and lifestyles. The aim of this study is to evaluate the genetic correlations between OP and multiple lifestyle-related factors, and explore the genes underlying the detected genetic correlations. Linkage disequilibrium score regression (LDSC) analysis was applied to evaluate the genetic correlations of total body bone mineral density (TB-BMD) of different ages (including 15-30 years, 30-45 years, 45-60 years, and over 60 years) with four common lifestyle/environment-related factors (including serum 25-hydroxyvitamin D, cigarette smoking, alcohol dependence, and caffeine metabolites). Transcriptome-wide association studies (TWAS) of TB-BMD (30-45 years) and smoking were conducted in peripheral blood (PB), whole blood (WB), and adipose tissues. The identified candidate genes were also subjected to gene set enrichment analysis (GSEA). Genetic correlation was only observed between TB-BMD (30-45 years) and cigarette smoking status (P = 0.01, LD score = 0.11 ± 0.04). No significant genetic correlation was detected for other lifestyle/environmental factors, including serum 25-hydroxyvitamin D, alcohol dependence, and caffeine metabolites for TB-BMD within all of the four age groups. TWAS identified 85 genes in PB and 163 genes in WB for TB-BMD, as well as 123 genes in PB and 257 genes in WB for smoking. Multiple common candidate genes shared by both TB-BMD and smoking were detected, such as MAP1LC3B (P_TB-BMD-PB = 1.00 × 10^-3, P_smoking-PB = 9.62 × 10^-3, P_TB-BMD-WB = 2.99 × 10^-2) and SLC23A3 (P_TB-BMD-WB = 1.48 × 10^-2, P_smoking-WB = 8.76 × 10^-3). GSEA detected one GO terms for TB-BMD (cytosol) in WB, one GO term for smoking (mitochondrion) in PB, and one pathway (oocyte meiosis) for smoking in WB.

Aucubin exerts anti-osteoporotic effects by promoting osteoblast differentiation

Osteoporosis is a metabolic disease characterized by reduced osteoblast differentiation and proliferation. Oxidative stress plays a role in the pathogenesis of osteoporosis. Aucubin (AU), an iridoid glycoside, was previously shown to promote osteoblast differentiation. We investigated the effects of AU on MG63 human osteoblast-like cells treated with dexamethasone (Dex) or hydrogen peroxide (H₂O₂) to induce oxidative damage. AU protected MG63 cells against apoptosis, and promoted increased expression of cytokines associated with osteoblast differentiation, including collagen I, osteocalcin (OCN), osteopontin (OPN), and osterix. In Dex- and H₂O₂-treated MG63 cells, AU also enhanced the expression of anti-oxidative stress-associated factors in the nuclear respiratory factor 2 signaling pathway, including superoxide dismutases 1 and 2, heme oxygenases 1 and 2, and catalase. In vivo, using a Dex-induced mouse model of osteoporosis, AU promoted increased cortical bone thickness, increased bone density, and tighter trabecular bone. Additionally, it stimulated an increase in the expression of collagen I, OCN, OPN, osterix, and phosphorylated Akt and Smads in bone tissue. Finally, AU stimulated the expression of cytokines associated with osteoblast differentiation in bone tissue and serum. Our data indicate AU may have therapeutic efficacy in osteoporosis.

Are Oxidative Stress and Inflammation Mediators of Bone Loss Due to Estrogen Deficiency? A Review of Current Evidence

Osteoporosis is one of the major health issues associated with menopause-related estrogen deficiency. Various reports suggest that the hormonal changes related to menopausal transition may lead to the derangement of redox homeostasis and ultimately oxidative stress. Estrogen deficiency and oxidative stress may enhance the expression of genes involved in inflammation. All these factors may contribute, in synergy, to the development of postmenopausal osteoporosis. Previous studies suggest that estrogen may act as an antioxidant to protect the bone against oxidative stress, and as an antiinflammatory agent in suppressing pro-inflammatory and pro-osteoclastic cytokines. Thus, the focus of the current review is to examine the relationship between estrogen deficiency, oxidative stress and inflammation, and the impacts of these phenomena on skeletal health in postmenopausal women.

Autophagy in bone homeostasis and the onset of osteoporosis

Autophagy is an evolutionarily conserved intracellular process, in which domestic cellular components are selectively digested for the recycling of nutrients and energy. This process is indispensable for cell homeostasis maintenance and stress responses. Both genetic and functional studies have demonstrated that multiple proteins involved in autophagic activities are critical to the survival, differentiation, and functioning of bone cells, including osteoblasts, osteocytes, and osteoclasts. Dysregulation at the level of autophagic activity consequently disturbs the balance between bone formation and bone resorption and mediates the onset and progression of multiple bone diseases, including osteoporosis. This review aims to introduce the topic of autophagy, summarize the understanding of its relevance in bone physiology, and discuss its role in the onset of osteoporosis and therapeutic potential.

Effect of Ovariectomy and Ovarian Hormone Administration on Hepatic Autophagy in Female Rats

Autophagy is a major intracellular proteolytic process that contributes to the maintenance of protein homeostasis. Recent studies reported the induction of autophagy in the uterus and proximal tibias of ovariectomized (OVX) rodents, which was blocked by the injection of ovarian hormones. However, whether OVX and ovarian hormone treatment can regulate autophagy in the liver has not been clarified. Recently, it was revealed that autophagy is closely involved in hepatic lipid metabolism. The purpose of this study was to investigate the influence of OVX on autophagy in the rat liver as a first step to clarify the relationship between hepatic fat accumulation and the change in autophagy caused by OVX. We found that hepatic autophagy tended to be lower in OVX rats than in sham-operated rats. In addition, hepatic autophagy in OVX rats was induced by short-term exposure to ovarian hormones, especially progesterone. This study suggests that autophagy in the rat liver is suppressed by OVX and activated by progesterone. However, the autophagy-promoting effect of β-estradiol was not clarified.

The Role of Macrophage in the Pathogenesis of Osteoporosis

Osteoporosis is a systemic disease with progressive bone loss. The bone loss is associated with an imbalance between bone resorption via osteoclasts and bone formation via osteoblasts. Other cells including T cells, B cells, macrophages, and osteocytes are also involved in the pathogenesis of osteoporosis. Different cytokines from activated macrophages can regulate or stimulate the development of osteoclastogenesis-associated bone loss. The fusion of macrophages can form multinucleated osteoclasts and, thus, cause bone resorption via the expression of IL-4 and IL-13. Different cytokines, endocrines, and chemokines are also expressed that may affect the presentation of macrophages in osteoporosis. Macrophages have an effect on bone formation during fracture-associated bone repair. However, activated macrophages may secrete proinflammatory cytokines that induce bone loss by osteoclastogenesis, and are associated with the activation of bone resorption. Targeting activated macrophages at an appropriate stage may help inhibit or slow the progression of bone loss in patients with osteoporosis.

Loss of p27kip1 suppresses the myocardial senescence caused by estrogen deficiency

Estrogen deficiency accelerates the aging process and increases the risk of developing cardiovascular disease (CVD). Apoptosis is one of the important mechanisms of aging. p27^kip1 is a cyclin-dependent kinase inhibitor that can regulate cell cycle, apoptosis, and cell motility. p27^kip1 overexpression can inhibit cell cycle and increase apoptosis so it has been considered as a marker of aging. In the present study, bilateral ovariectomy (OVX) was performed as a model for menopause in wild-type (WT) and p27^kip1 knockout (KO) mice to assess the effects of p27^kip1 loss in myocardial aging caused by estrogen deficiency. We found that myocardial fibrosis and heart weight/body weight ratio of mice in the OVX group and p27^kip1 KO group were significantly increased. Echocardiography showed that the left ventricular diameter and volume of the WT OVX group increased significantly and the cardiac function decreased. However, there was no significant difference in the results of echocardiography between the two p27^kip1 KO groups. The aging and apoptosis indexes in OVX group were increased significantly, However, the indexes in p27^kip1 KO mice were decreased. The expression of antioxidant indexes in OVX group was decreased significantly and p27^kip1 KO can improve the antioxidant ability. These results provided that estrogen deficiency increased oxidative stress and apoptosis, accelerated aging of heart. p27^kip1 KO can partly delay the aging and apoptosis of heart through upregulated antioxidant enzymes.

Role of MicroRNA-141 in the Aging Musculoskeletal System: A Current Overview

MicroRNA's are small non-coding RNAs that regulate the expression of genes by targeting the 3' UTR's of mRNA. Studies reveal that miRNAs play a pivotal role in normal musculoskeletal function such as mesenchymal stem cell differentiation, survivability and apoptosis, osteogenesis, and chondrogenesis. Changes in normal miRNA expression have been linked to a number of pathological disease processes. Additionally, with aging, it is noted that there is dysregulation in the normal function of stem cell differentiation, bone formation/degradation, chondrocyte function, and muscle degeneration. Due to the change in expression of miRNA in degenerative musculoskeletal pathology, it is believed that these molecules may be at least partially responsible for cellular dysfunction. A number of miRNAs have already been identified to play a role in osteoarthritis, osteoporosis and sarcopenia. One miRNA that has become of interest recently is miRNA 141. The purpose of this article is to review the current literature available on miRNA 141 and how it could play a role in osteoporosis, osteoarthritis and musculoskeletal pathology overall.

Glucocorticoid-Induced Autophagy Protects Osteocytes Against Oxidative Stress Through Activation of MAPK/ERK Signaling

Autophagy confers protective or detrimental effects on cells depending on the cellular context. We showed here that oxidative stress‐induced cell death in osteocytic MLO‐Y4 cells coincided with decreased autophagy. Decreased autophagy was also observed in osteocytes of superoxide dismutase 1‐ (SOD1‐) deficient mice. Oxidative stress‐induced osteocyte death was exacerbated by an autophagy inhibitor, chloroquine, suggesting a protective function of basal autophagy levels against oxidative stress‐induced cell death. Pretreatment with dexamethasone reduced the susceptibility of osteocytes to oxidative stress‐induced cell death and conferred protection against TNFα/cycloheximide‐induced cell death. Inhibition of MAPK/ERK attenuated the formation of autophagosome, leading to increased osteocyte cell death. Taken together, our results suggest that autophagy, induced by moderate levels of glucocorticoids, leads to the preconditioning of osteocytes and conveys a novel cell‐protective function against cell death induced by oxidative stress and other insults. © 2018 The Authors. JBMR Plus is published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research.

How does estrogen work on autophagy?

Macroautophagy/autophagy is vital for intracellular quality control and homeostasis. Therefore, careful regulation of autophagy is very important. In the past 10 years, a number of studies have reported that estrogenic effectors affect autophagy. However, some results, especially those regarding the modulatory effect of 17β-estradiol (E2) on autophagy seem inconsistent. Moreover, several clinical trials are already in place combining both autophagy inducers and autophagy inhibitors with endocrine therapies for breast cancer. Not all patients experience benefit, which further confuses and complicates our understanding of the main effects of autophagy in estrogen-related cancer. In view of the importance of the crosstalk between estrogen signaling and autophagy, this review summarizes the estrogenic effectors reported to affect autophagy, subcellular distribution and translocation of estrogen receptors, autophagy-targeted transcription factors (TFs), miRNAs, and histone modifications regulated by E2. Upon stimulation with estrogen, there will always be opposing functional actions, which might occur between different receptors, receptors on TFs, TFs on autophagy genes, or even histone modifications on transcription. The huge signaling network downstream of estrogen can promote autophagy and reduce overstimulated autophagy at the same time, which allows autophagy to be regulated by estrogen in a restricted range. To help understand how the estrogenic regulation of autophagy affects cell fate, a hypothetical model is presented here. Finally, we discuss some exciting new directions in the field. We hope this might help to better understand the multiple associations between estrogen and autophagy, the pathogenic mechanisms of many estrogen-related diseases, and to design novel and efficacious therapeutics. Abbreviations: AP-1, activator protein-1; HATs, histone acetyltransferases; HDAC, histone deacetylases; HOTAIR, HOX transcript antisense RNA.

Effect of autophagy gene DRAM on proliferation, cell cycle, apoptosis, and autophagy of osteoblast in osteoporosis rats

OBJECTIVE

The research aimed at detecting the autophagy level of osteoblast in osteoporosis rat, and investigating the effect of autophagy gene damage-regulated autophagy modulator (DRAM) on osteoblast proliferation, cell cycle, apoptosis, and autophagy.

METHODS

The level of osteocalcin (OCN) and C-telopeptide (CTX) in serum of ovariectomized (OVX) rats was detected by enzyme-linked immunosorbent assay (ELISA). The Oil Red-O staining was used to observing bone histological changes. The messenger RNA level and protein expression level of Runt-related transcription factor 2 (Runx2; osteoblast markers) and other autophagy-related genes were revealed using quantitative real-time polymerase chain reaction (qRT-PCR) and western blot. The changes of autophagy in osteoblasts were detected by immunofluorescence staining. The following experiments were performed in osteoblasts of OVX rats through transfected with silencing DRAM to detecting cell proliferation, cell cycle, and apoptosis by Cell Counting Kit-8 assays and flow cytometry.

RESULTS

The result of ELISA showed a significantly elevated of OCN and CTX in OVX rats as well a high fat content compared with sham-operated rats. The expression of Runx2 in bone of proximal tibia was higher by qRT-PCR and western blot analysis. The immunofluorescence staining and transmission electron microscope observe revealed that pcDNA3-DRAM could promote the autophagy in OVX rats. Besides that, overexpression of DRAM inhibited cell proliferation, promoted apoptosis, and enhanced autophagy in osteoblasts. The results of Oil Red-O staining indicated that overexpression of DRAM enhanced lipid accumulation in osteoporosis rats.

CONCLUSIONS

The autophagy level of OVX rats was weakened, but overexpressed DRAM could increase the autophagy level of osteoblast, suppress proliferation, and induce apoptosis of osteoblast.

Cortical Thinning and Structural Bone Changes in Non-Human Primates after Single-Fraction Whole-Chest Irradiation

Stereotactic body radiation therapy (SBRT) is associated with an increased risk of vertebral compression fracture. While bone is typically considered radiation resistant, fractures frequently occur within the first year of SBRT. The goal of this work was to determine if rapid deterioration of bone occurs in vertebrae after irradiation. Sixteen male rhesus macaque non-human primates (NHPs) were analyzed after whole-chest irradiation to a midplane dose of 10 Gy. Ages at the time of exposure varied from 45-134 months. Computed tomography (CT) scans were taken 2 months prior to irradiation and 2, 4, 6 and 8 months postirradiation for all animals. Bone mineral density (BMD) and cortical thickness were calculated longitudinally for thoracic (T) 9, lumbar (L) 2 and L4 vertebral bodies; gross morphology and histopathology were assessed per vertebra. Greater mortality (related to pulmonary toxicity) was noted in NHPs <50 months at time of exposure versus NHPs >50 months ( P = 0.03). Animals older than 50 months at time of exposure lost cortical thickness in T9 by 2 months postirradiation ( P = 0.0009), which persisted to 8 months. In contrast, no loss of cortical thickness was observed in vertebrae out-of-field (L2 and L4). Loss of BMD was observed by 4 months postirradiation for T9, and 6 months postirradiation for L2 and L4 ( P < 0.01). For NHPs younger than 50 months at time of exposure, both cortical thickness and BMD decreased in T9, L2 and L4 by 2 months postirradiation ( P < 0.05). Regions that exhibited the greatest degree of cortical thinning as determined from CT scans also exhibited increased porosity histologically. Rapid loss of cortical thickness was observed after high-dose chest irradiation in NHPs. Younger age at time of exposure was associated with increased pneumonitis-related mortality, as well as greater loss of both BMD and cortical thickness at both in- and out-of-field vertebrae. Older NHPs exhibited rapid loss of BMD and cortical thickness from in-field vertebrae, but only loss of BMD in out-of-field vertebrae. Bone is sensitive to high-dose radiation, and rapid loss of bone structure and density increases the risk of fractures.

Sex Differences in Autophagy Contribute to Female Vulnerability in Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of dementia, with over 5. 4 million cases in the US alone (Alzheimer's Association, 2016). Clinically, AD is defined by the presence of plaques composed of Aβ and neurofibrillary pathology composed of the microtubule associated protein tau. Another key feature is the dysregulation of autophagy at key steps in the pathway. In AD, disrupted autophagy contributes to disease progression through the failure to clear pathological protein aggregates, insulin resistance, and its role in the synthesis of Aβ. Like many psychiatric and neurodegenerative diseases, the risk of developing AD, and disease course are dependent on the sex of the patient. One potential mechanism through which these differences occur, is the effects of sex hormones on autophagy. In women, the loss of hormones with menopause presents both a risk factor for developing AD, and an obvious example of where sex differences in AD can stem from. However, because AD pathology can begin decades before menopause, this does not provide the full answer. We propose that sex-based differences in autophagy regulation during the lifespan contribute to the increased risk of AD, and greater severity of pathology seen in women.

[Estradiol significantly increases the expression of antioxidant enzymes in osteoporotic rats and osteoblasts in vitro]

OBJECTIVE

To investigate the effect of estradiol on the expression of antioxidant enzymes in osteoblasts and its role in postmenopausal osteoporosis.

METHODS

Rat models of osteoporosis established by ovariectomy were treated with estradiol for 3 months, and the changes in serum levels of reactive oxygen species (H₂O₂) and antioxidant enzymes (γ -GCS, GSH-ST and GSH-px) were detected. The effects of estradiol on the expression of γ -GCS mRNA and protein in osteoblast-like cells MC3T3-E1, MG63 and OB were examined with PCR and Western blotting. Using a mRNA microarray, we analyzed the changes in the expressions of 84 antioxidant enzymes in the osteoblast cell line MC3T3-E1 following estradiol treatment, and the enzymes with significant changes were verified by PCR. CCK-8 kit was used to evaluate the effect of estradiol and antioxidant NAC on the proliferation of MC3T3-E1 cells.

RESULTS

Rat models of osteoporosis were successfully established with ovariectomy. The osteoporotic rats showed significantly increased serum level of reactive oxygen species (H2O2) and decreased levels of antioxidant enzymes. Estrogen treatment of the osteoporotic rats obviously reversed the phenotype of osteoporosis, lowered serum level of reactive oxygen species, and increased the level of γ -GCS. In MC3T3-E1, MG63 and OB cells, estradiol treatment significantly upregulated the expression levels of γ -GCS mRNA and protein. In MC3T3-E1 cells treated with estrogen, the mRNA chip identified 6 upregulated antioxidant enzymes (Gpx6, Gstk1, Nos2, Prdx2, Ngb and Ccs), and the results of PCR verified that estradiol upregulated Ccs and Ngb mRNAs in MC3T3-E1, MG63 and OB cells. Estradiol and antioxidant NAC obviously promoted the proliferation of MC3T3-E1 cells.

CONCLUSION

Estradiol significantly increases the expression of antioxidase γ -Gcs, Ccs and Ngb in osteoblasts in vitro. Postmenopausal osteoporosis is closely related with the increase of reactive oxygen species and the decrease of antioxidant levels. In osteoblasts, estrogen deficiency may increase the level of reactive oxygen species, decrease the level of antioxidant enzymes, activate the oxidative stress cascade, and consequently inhibit the proliferation of osteoblasts to aggravate the condition of osteoporosis.

Good, Bad, or Ugly: the Biological Roles of Bone Marrow Fat

PURPOSE OF REVIEW

Bone marrow fat expresses mixed characteristics, which could correspond to white, brown, and beige types of fat. Marrow fat could act as either energy storing and adipokine secreting white fat or as a source of energy for hematopoiesis and bone metabolism, thus acting as brown fat. However, there is also a negative interaction between marrow fat and other elements of the bone marrow milieu, which is known as lipotoxicity. In this review, we will describe the good and bad roles of marrow fat in the bone, while focusing on the specific components of the negative effect of marrow fat on bone metabolism.

RECENT FINDINGS

Lipotoxicity in the bone is exerted by bone marrow fat through the secretion of adipokines and free fatty acids (FFA) (predominantly palmitate). High levels of FFA found in the bone marrow of aged and osteoporotic bone are associated with decreased osteoblastogenesis and bone formation, decreased hematopoiesis, and increased osteoclastogenesis. In addition, FFA such as palmitate and stearate induce apoptosis and dysfunctional autophagy in the osteoblasts, thus affecting their differentiation and function. Regulation of marrow fat could become a therapeutic target for osteoporosis. Inhibition of the synthesis of FFA by marrow fat could facilitate osteoblastogenesis and bone formation while affecting osteoclastogenesis. However, further studies testing this hypothesis are still required.

Sex-specific autophagy modulation in osteoblastic lineage: a critical function to counteract bone loss in female

Age-related bone loss is associated with an increased oxidative stress which is worsened by estrogen fall during menauposis. This observation has drawn attention to autophagy, a major cellular catabolic process, able to alleviate oxidative stress in osteoblasts (OB) and osteocytes (OST), two key bone cell types. Moreover, an autophagy decline can be associated with aging, suggesting that an age-related autophagy deficiency in OB and/or OST could contribute to skeletal aging and osteoporosis onset.

In the present work, autophagy activity was analyzed in OST and OB in male and female mice according to their age and hormonal status. In OST, autophagy decreases with aging in both sexes. In OB, although a 95% decrease in autophagy is observed in OB derived from old females, this activity remains unchanged in males. In addition, while ovariectomy has no effect on OB autophagy levels, orchidectomy appears to stimulate this process. An inverse correlation between autophagy and the oxidative stress level was observed in OB derived from males or females. Finally, using OB-specific autophagy-deficient mice, we showed that autophagy deficiency aggravates the bone loss associated with aging and estrogen deprivation.

Taken together, our data indicate that autophagic modulation in bone cells differs according to sex and cell type. The lowering of autophagy in female OB, which is associated with an increased oxidative stress, could play a role in osteoporosis pathophysiology and suggests that autophagy could be a new therapeutic target for osteoporosis in women.

Effects of estrogen status in osteocyte autophagy and its relation to osteocyte viability in alveolar process of ovariectomized rats

Estrogen maintains osteocyte viability, whereas its deficiency induces osteocyte apoptosis. As autophagy is important for osteocyte viability, we hypothesized whether the anti-apoptotic effect of estrogen is related to autophagy in osteocytes. Thirty adult female rats were sham-operated (SHAM) or ovariectomized (OVX). After three weeks, twelve rats of SHAM and OVX groups were killed before treatment (basal period), whereas the remaining rats received estrogen (OVXE) or vehicle (OVX) for 45 days. Fragments of maxilla containing alveolar process of the first molars were embedded in paraffin or Araldite. Paraffin-sections were stained with hematoxylin/eosin for histomorphometry, or subjected to the silver impregnation method for morphological analysis of osteocyte cytoplasmic processes. Autophagy was analyzed by immunohistochemical detections of beclin-1, MAP-LC3α and p62, whereas apoptosis was evaluated by immunohistochemical detections of cleaved caspase-3 and BAX, TUNEL (Terminal deoxynucleotidyl transferase dUTP nick end labeling) method and by ultrastructural analysis. Araldite-semithin sections were subjected to the Sudan-black method for detection of lipids. OVX-basal group showed high frequency of caspase-3-, TUNEL- and p62-positive osteocytes accompanied with low frequency of beclin-1- and MAP-LC3α-positive osteocytes. At 45 days, OVXE group exhibited higher number of osteocytes, higher frequency of beclin-1- and MAP-LC3α-positive osteocytes, and lower frequency of caspase-3, BAX-, TUNEL- and p62-positive osteocytes than OVX group. Significant reduction in bone area was observed in the OVX compared to OVXE and SHAM groups. The highest frequency of Sudan-Black-positive osteocytes and osteocytes with scarce cytoplasmic processes, or showing apoptotic features were mainly observed in OVX groups. Our results indicate that estrogen deficiency decreases autophagy and increases apoptosis, whereas estrogen replacement enhances osteocyte viability by inhibiting apoptosis and maintaining autophagy in alveolar process osteocytes. These results suggest that the anti-apoptotic effect of estrogen may be, at least in part, related to autophagy regulation in osteocytes.

Osteoporosis and autophagy: What is the relationship?

Autophagy is a survival pathway wherein non-functional proteins and organelles are degraded in lysosomes for recycling and energy production. Therefore, autophagy is fundamental for the maintenance of cell viability, acting as a quality control process that prevents the accumulation of unnecessary structures and oxidative stress. Increasing evidence has shown that autophagy dysfunction is related to several pathologies including neurodegenerative diseases and cancer. Moreover, recent studies have shown that autophagy plays an important role for the maintenance of bone homeostasis. For instance, in vitro and animal and human studies indicate that autophagy dysfunction in bone cells is associated with the onset of bone diseases such as osteoporosis. This review had the purpose of discussing the issue to confirm whether a relationship between autophagy dysfunction and osteoporosis exits.

Osteomacs and Bone Regeneration

PURPOSE OF REVIEW

Mounting evidence supporting the critical contribution of macrophages, in particular osteal macrophages, to bone regeneration is reviewed. We specifically examine the potential role of macrophages in the basic multicellular units coordinating lifelong bone regeneration via remodelling and bone regeneration in response to injury. We review and discuss the distinctions between macrophage and osteoclast contributions to bone homeostasis, particularly the dichotomous role of the colony-stimulating factor 1-colony-stimulating factor 1 receptor axis.

RECENT FINDINGS

The impact of inflammation associated with aging and other hallmarks of aging, including senescence, on macrophage function is addressed in the context of osteoporosis and delayed fracture repair. Resident macrophages versus recruited macrophage contributions to fracture healing are also discussed. We identify some of the remaining knowledge gaps that will need to be closed in order to maximise benefits from therapeutically modulating or mimicking the function of macrophages to improve bone health and regeneration over a lifetime.

Autophagic regulation in steroid hormone-responsive systems

Two female sex steroid hormones, estrogen and progesterone, are crucial regulators of many physiological functions of reproductive organs. These two hormones are versatile factors linking growth, differentiation, metabolism, and death of cells in the uterus. In recent years, it has become evident that autophagy is involved in the effects of estrogen and progesterone on various cellular events in reproductive organs. Autophagy is the self-eating catabolic process which is linked to cell survival and death in many contexts. In this review, we focus on the new findings concerning the regulation of autophagic response by sex steroid hormones in responsive target organs. We also attempt to further expand our insight into intracellular signaling mediators governing this regulation.

High glucose induces autophagy of MC3T3-E1 cells via ROS-AKT-mTOR axis

In the present study, we investigate the function of ROS-AKT-mTOR axis on the apoptosis, proliferation and autophagy of MC3T3-E1 cells, and the proliferation of MC3T3-E1 cells after autophagy inhibition under high glucose conditions. MC3T3-E1 cells cultured in vitro were divided into the following groups: normal control group, N-acetylcysteine (NAC) group, 11.0 mM high glucose group, 11.0 mM high glucose + NAC group, 22.0 mM high glucose group, 22.0 mM high glucose + NAC group, CQ group, 22.0 mM high glucose + CQ group, 3-MA group and 3-MA + 22.0 mM high glucose group. ROS production was measured by DCFH-DA fluorescent probe. Cell proliferation was measured by MTT assay. Cells in different groups were stained with Annexin V-FITC/PI, and then apoptosis rate was detected by flow cytometry. Nucleus morphology was observed under fluorescence microscope after being incubated with Honchest33258. Protein expression was measured using Western blotting and immunofluorescence. Cell apoptosis and proliferation in high glucose group were increased and decreased, respectively, in a dose-dependent manner. Autophagy was significantly induced in high glucose group, even though different concentration of glucose induced autophagy in different stages of autophagy. ROS production in MC3T3-E1 cells was remarkably increased in high glucose group, but not in a dose-dependent manner. NAC, as an antioxidant, reduced ROS production and ameliorated cell apoptosis, proliferation abnormity and autophagy caused by high glucose. Expression of p-AKT and p-mTOR proteins were dramatically decreased in high glucose group, and NAC reversed their expression. In addition, 3-MA, an inhibitor of autophagy, significantly decreased the proliferation of MC3T3-E1 cells. When cocultured with 22.0 mM glucose that induced autophagy, proliferation of MC3T3-E1 cells was not affected compared to 22.0 mM high glucose group. Our present findings reveal that high glucose affects apoptosis, proliferation and autophagy of MC3T3-E1 cells through ROS-AKT-mTOR axis. In addition, autophagy inhibition does not affect the proliferation of MC3T3-E1 cells under high glucose conditions.