Intermittent injections of osteocalcin reverse autophagic dysfunction and endoplasmic reticulum stress resulting from diet-induced obesity in the vascular tissue via the NFκB-p65-dependent mechanism

Role of osteokines in atherosclerosis

Despite their diverse physiologies and roles, the heart, skeletal muscles, and smooth muscles all derive from a common embryonic source as bones. Moreover, bone tissue, skeletal and smooth muscles, and the heart share conserved signaling pathways. The maintenance of skeletal health is precisely regulated by osteocytes, osteoblasts, and osteoclasts through coordinated secretion of bone-derived factors known as osteokines. Increasing evidence suggests the involvement of osteokines in regulating atherosclerotic vascular disease. Therefore, this review aims to examine the evidence for the role of osteokines in atherosclerosis development and progression comprehensively. Specifically discussed are extensively studied osteokines in atherosclerosis such as osteocalcin, osteopontin, osteoprotegerin, and fibroblast growth factor 23. Additionally, we highlighted the effects of exercise on modulating these key regulators derived from bone tissue metabolism. We believe that gaining an enhanced understanding of how osteocalcin contributes to the process of atherosclerosis will enable us to develop targeted and comprehensive therapeutic strategies against diseases associated with its progression.

Current knowledge of bone-derived factor osteocalcin: its role in the management and treatment of diabetes mellitus, osteoporosis, osteopetrosis and inflammatory joint diseases

Osteocalcin (OC) is the most abundant non-collagenous and osteoblast-secreted protein in bone. It consists of two forms such as carboxylated OC (cOC) and undercarboxylated OC (ucOC). While cOC promotes bone mineralization and increases bone strength, ucOC is regarded an endocrinologically active form that may have several functions in multiple end organs and tissues. Total OC (tOC) includes both of these forms (cOC and ucOC) and is considered a marker of bone turnover in clinical settings. Most of the data on OC is limited to preclinical studies and therefore may not accurately reflect the situation in clinical conditions. For the stated reason, the aim of this review was not only to summarize current knowledge of all forms of OC and characterize its role in diabetes mellitus, osteoporosis, osteopetrosis, inflammatory joint diseases, but also to provide new interpretations of its involvement in the management and treatment of aforementioned diseases. In this context, special emphasis was placed on available clinical trials. Significantly lower levels of tOC and ucOC could be associated with the risk of type 2 diabetes mellitus. On the contrary, tOC level does not seem to be a good indicator of high bone turnover status in postmenopausal osteoporosis, osteoarthritis and rheumatoid arthritis. The associations between several pharmacological drugs used to treat all disorders mentioned above and OC levels have also been provided. From this perspective, OC may serve as a medium through which certain medications can influence glucose metabolism, body weight, adiponectin secretion, and synovial inflammation.

Osteocalcin inhibits myocyte aging through promotion of starvation-induced autophagy via IL-6/STAT3 signaling

This study aimed to investigate the effects and mechanisms of osteocalcin on autophagy in myoblasts, as well as its possible therapeutic effects in aging muscle. Starved murine myoblast C2C12 cells with or without interleukin (IL)-6 siRNA were treated with osteocalcin. Expression of the autophagy protein marker LC3, as well as IL-6 and phosphorylated STAT3 were detected by immunoblotting, immunofluorescence, or immunohistochemistry. Autophagosomes were observed with transmission electron microscopy. Levels of reactive oxygen species (ROS) were detected by flow cytometry. Fasted young mice were injected intraperitoneally with osteocalcin, with or without the JAK inhibitor CP-690550 to inhibit IL-6 signaling. Older mice were treated with osteocalcin and muscle mass, grip strength and muscle structure were assessed. The results revealed that compared to control and serum-starved cells, osteocalcin treatment significantly increased the relative expression of LC3-II/LC3-I protein, the numbers of autophagosomes, and levels of intracellular ROS. Osteocalcin injection in mice also resulted in increased relative LC3-II/LC3-I protein expression and autophagosome numbers. Osteocalcin treatment significantly increased the secretion of IL-6 in muscle cells and tissue, and activated STAT3 signaling. Moreover, knockdown of IL-6 or blocking IL-6 signaling inhibited the phosphorylation of STAT3, and further inhibited autophagy in starved myoblasts and fasting-treated murine muscle tissue. In addition, osteocalcin treatment significantly increased muscle mass and grip strength in both aged mice and aged fasting mice. In conclusion, the inhibition of osteocalcin on muscle cell aging is accompanied by the induction of IL-6-STAT3-dependent autophagy, indicating osteocalcin might be a promising therapeutic candidate for aging-related myopathies.

Osteocalcin association with vascular function in chronic kidney disease

Osteocalcin (OCN) is a bone‐derived and vitamin K dependent hormone that affects energy metabolism and vascular calcification. The relationship between serum OCN and vascular function in patients with chronic kidney disease (CKD) is uncertain. This study investigated the association between serum OCN and vascular function as expressed with reactive hyperemia index (RHI) and augmentation index (AIx) measured by Endo‐PAT 2000 device. This cross‐sectional analysis was based on 256 pre‐dialysis CKD patients who had completed the Endo‐PAT 2000 test and serum OCN at the First Center of Chinese PLA Hospital from November 2017 to December 2019. Based on whether the RHI was less than 1.67, the patients were divided into endothelial dysfunction and normal endothelial function groups. Multiple logistic and linear regression were used to analyze the association between OCN and vascular function. Subgroup analyses were performed to examine the effects of OCN on vascular function in different CKD populations. After multivariate adjustment, CKD with low OCN were more likely to have endothelial dysfunction (OR: 0.794; 95%CI: 0.674‐0.934; P = .006); on the contrary, patients with high OCN had a higher degree of arterial stiffness (standardized β: 0.174; P = .003). Subgroup analyses showed that higher OCN was associated with severe arterial stiffness but a better endothelial function in young (age < 65 years, P_RHI/P_AIx@75 = .027/.011), male (P_RHI/P_AIx@75 = .040/.016), patients with a history of hypertension (P_RHI/P_AIx@75 = .004/.009) or diabetes (P_RHI/P_AIx@75 = .005/.005), and in early CKD (P_RHI/P_AIx@75 = .014/.015). In conclusion, serum OCN correlates with vascular function in CKD patients: beneficial for endothelial function but detrimental to arterial stiffness.

Undercarboxylated, but not Carboxylated, Osteocalcin suppresses TNF-α induced inflammatory signaling pathway in Myoblast

Undercarboxylated osteocalcin (ucOCN) has been considered to be an important endocrine factor, especially to regulate bone and energy metabolism. Even with the mounting evidence showing the consistent inverse correlation of ucOCN levels in chronic inflammatory diseases, however, the mechanism underlying the involvement of ucOCN in the muscular inflammation has not been fully understood. In the present study, we explored 1) the endocrine role of ucOCN in the regulation of inflammation in C2C12 myoblasts and primary myoblasts and the underlying intracellular signaling mechanisms, and 2) whether G protein–coupled receptor family C group 6 member A (GPRC6A) is the ucOCN-sensing receptor associated with the ucOCN-mediated anti-inflammatory signaling pathway in myoblasts. ucOCN suppressed the tumor necrosis factor-α (TNF-α)–induced expressions of major inflammatory cytokines, including interleukin-1β (IL-1β) and inhibited the TNF-α–stimulated activities of transcription factors, including NF-κB, in C2C12 and primary myoblasts. Both knockdown and knockout of GPRC6A, by using siRNA or a CRISPR/CAS9 system, respectively, did not reverse the effect of ucOCN on IL-1β expression in myoblasts. Interestingly, TNF-α–induced IL-1β expression was inhibited by knockdown or deletion of GPRC6A itself, regardless of the ucOCN treatment. ucOCN was rapidly internalized into the cytoplasmic region via caveolae-mediated endocytosis, suggesting the presence of new target proteins in the cell membrane and/or in the cytoplasm for interaction with ucOCN in myoblasts. Taken together, these findings indicate that ucOCN suppresses the TNF-α–induced inflammatory signaling pathway in myoblasts. GPRC6A is not a sensing receptor associated with the ucOCN-mediated anti-inflammatory signaling pathway in myoblasts.

Sex Differences in Metabolic and Behavioral Responses to Exercise but Not Exogenous Osteocalcin Treatment in Mice Fed a High Fat Diet

Background

Exercise helps improve glucose handling in diabetes and has been shown to improve mood and cognition in other conditions. Osteocalcin, a protein produced by bone osteoblasts, was reported to have endocrine actions to improve both metabolism and also improve age-related cognitive deficits in mice.

Methods

This study was designed to compare the effects of daily treadmill running exercise with injection of osteocalcin in high fat diet (HFD) induced diabetes in male and female C57BL/6J mice. Following established glucose intolerance and treatment for 8 weeks, mice were assessed for anxiety on an elevated plus maze, motivation by tail suspension test and cognition and memory in a puzzle box. Endogenous osteocalcin was measured by ELISA.

Results

Mice on HFD had high weight gain, glucose intolerance and increased white fat. Exercise increased circulating osteocalcin levels in female mice but decreased them in male mice. Exercise also decreased weight gain and improved glucose tolerance in female but not male mice; however, treatment with osteocalcin made no metabolic improvements in either males or females. HFD induced anxiety only in female mice and this was not improved by osteocalcin. Exercise induced anxiety only in male mice. HFD also increased depressive-like behavior in both sexes, and this was improved by either exercise or osteocalcin treatment. Cognitive deficits were seen in both male and female mice on HFD. Exercise improved cognitive performance in female but not male mice, while osteocalcin treatment improved cognitive performance in both sexes.

Conclusion

There were sex differences in the effects of exercise on endogenous osteocalcin regulation that correlated with improvements in cognitive but not metabolic outcomes. Exogenous osteocalcin did not improve metabolism but was effective in improving HFD-induced cognitive deficits. Sex is an important variable in hormonal and cognitive responses to exercise in diabetes.

Osteocalcin and the Physiology of Danger

Bone biology has long been driven by the question as to what molecules affect cell differentiation or the functions of bone. Exploring this issue has been an extraordinarily powerful way to improve our knowledge of bone development and physiology. More recently, a second question has emerged: does bone have other functions besides making bone? Addressing this conundrum revealed that the bone-derived hormone osteocalcin affects a surprisingly large number of organs and physiological processes, including acute stress response. This review will focus on this emerging aspect of bone biology taking osteocalcin as a case study and will show how classical and endocrine functions of bone help to define a new functional identity for this tissue.

Explaining Divergent Observations Regarding Osteocalcin/GPRC6A Endocrine Signaling

A new schema proposes that the bone-derived osteocalcin (Ocn) peptide hormone activates the G-protein-coupled receptor GPRC6A to directly regulate glucose and fat metabolism in liver, muscle, and fat, and to stimulate the release of metabolism-regulating hormones, including insulin, fibroblast growth factor 21, glucagon-like peptide 1, testosterone, and interleukin 6. Ocn/GPRC6A activation has also been implicated in cancer progression. GPRC6A is activated by cations, amino acids, and testosterone. The multiligand specificity, the regulation of energy metabolism in diverse tissues, and the coordinated release of metabolically active hormones make the GPRC6A endocrine networks unique. Recently, the significance of Ocn/GPRCA has been questioned. There is a lack of metabolic abnormalities in newly created genetically engineered Ocn- and Gprc6a-deficient mouse models. There are also paradoxical observations that GPRC6A may function as a tumor suppressor. In addition, discordant published studies have cast doubt on the function of the most prevalent uniquely human GPRC6A-KGKY polymorphism. Explanations for these divergent findings are elusive. We provide evidence that the metabolic susceptibility of genetically engineered Ocn- and Gprc6a-deficient mice is influenced by environmental challenges and genetic differences in mouse strains. In addition, the GPRC6A-KGKY polymorphism appears to be a gain-of-function variant. Finally, alternatively spliced isoforms of GPRC6A may alter ligand specificity and signaling that modulate oncogenic effects. Thus, genetic, post-translational and environmental factors likely account for the variable results regarding the functions of GPRC6A in animal models. Pending additional information, GPRC6A should remain a potential therapeutic target for regulating energy and fat metabolism, hormone production, and cancer progression.

The effect of exercise training on osteocalcin, adipocytokines, and insulin resistance: a systematic review and meta-analysis of randomized controlled trials

Recently, it has been reported that osteocalcin (OC), in particular its undercarboxylated (ucOC) form, is not only a bone remodeling marker but also an active hormone that intercedes glucose metabolism in humans. This study aimed to determine the impact of an exercise intervention on ucOC, adiponectin, leptin, and insulin resistance (measured by HOMA-IR). PubMed, CINAHL, Medline, Google Scholar, and Scopus databases and reference lists of included studies were searched. Twenty-two randomized controlled trials (RCTs) of exercise training impact in adults were included in the analysis. Results showed an overall significant increase in serum ucOC (MD: 0.15 ng/ml; 95% CI: 0.05 to 0.25) and adiponectin (MD: 2.83 mg/ml; 95% CI: 1.67 to 3.98), a significant decline in leptin (MD: - 4.89 pg/ml; 95% CI: - 6.94 to - 2.84), fasting glucose (MD: - 2.29 mg/dl; 95% CI: - 4.04 to - 0.54), fasting insulin (MD, - 8.90 μIU/ml; 95% CI: - 13.81 to - 3.98), and HOMA-IR (MD: - 1.96; 95% CI: - 3.11 to - 0.80). However, after removal of studies that had prescribed a balanced diet along with exercise intervention, total OC (TOC) levels also increased in the exercise group compared with the control group (MD: 0.36 ng/ml; 95% CI: 0.07 to 0.65). Our findings demonstrate that exercise-induced increases in ucOC are the probable cause of increased adiponectin. Additionally, increases in ucOC itself are probably due to changes in leptin levels and other factors, rather than its direct impact on bone and its osteoblastic activity. Further studies are required to clarify the mechanisms underlying the impact of exercise training on ucOC, adipocytokines, and insulin resistance.

In vitro treatment of 3 T3-L1 adipocytes with recombinant Calcium/calmodulin-dependent Protein Kinase IV (CaMKIV) limits ER stress and improves insulin sensitivity through inhibition of autophagy via the mTOR/CREB signaling pathway

BACKGROUND

Recently, CaMKIV has been identified as a potential regulator of skeletal muscle glucose metabolism, it can also affect insulin gene expression in pancreas. However, its effects on adipose insulin resistance have yet to be explored. Autophagy has been shown as a potential therapeutic target for ER (endoplasmic reticulum) stress and insulin resistance. The purpose of this study is to investigate the effects of CaMKIV on ER stress, autophagic function and insulin signaling in tunicamycin-treated adipocytes.

METHODS

In this study, mature 3 T3-L1 adipocytes were treated with tunicamycin to induce ER stress. Tunicamycin-treated 3 T3-L1 adipocytes were treated with recombinant CaMKIV in the presence or absence of targeted-siRNA mediated down-regulation of CREB and mTOR. The ER stress markers, autophagy activation, mTOR/CREB signaling and insulin sensitivity were analyzed by western blotting or electron microscopy.

RESULTS

Treatment with CaMKIV significantly reversed tunicamycin-induced expression of p-PERK, cleaved-ATF6, Atg7 and LC3II. It also reduced p62 expression. In addition, levels of p-Akt and p-IRS-1 were increased. Moreover, CaMKIV inhibited activated ER stress and insulin resistance in Atg7 siRNA transfected adipocytes. However, the protective effects of CaMKIV on ER stress, insulin signaling, and autophagy function were nullified by suppression of mTOR or CREB in tunicamycin-treated adipocytes.

CONCLUSION

This study proves recombinant CaMKIV inhibits tunicamycin-induced ER stress and insulin resistance by regulating autophagy. The protective effect of CaMKIV in adipocytes is affected at least partly through mTOR/CREB signaling. Our finding may offer novel opportunities for treating obesity and type 2 diabetes.

Roles of bone-derived hormones in type 2 diabetes and cardiovascular pathophysiology

Background

Emerging evidence demonstrates that bone is an endocrine organ capable of influencing multiple physiological and pathological processes through the secretion of hormones. Recent research suggests complex crosstalk between the bone and other metabolic and cardiovascular tissues. It was uncovered that three of these bone-derived hormones—osteocalcin, lipocalin 2, and sclerostin—are involved in the endocrine regulations of cardiometabolic health and play vital roles in the pathophysiological process of developing cardiometabolic syndromes such as type 2 diabetes and cardiovascular disease. Chronic low-grade inflammation is one of the hallmarks of cardiometabolic diseases and a major contributor to disease progression. Novel evidence also implicates important roles of bone-derived hormones in the regulation of chronic inflammation.

Scope of review

In this review, we provide a detailed overview of the physiological and pathological roles of osteocalcin, lipocalin 2, and sclerostin in cardiometabolic health regulation and disease development, with a focus on the modulation of chronic inflammation.

Major conclusions

Evidence supports that osteocalcin has a protective role in cardiometabolic health, and an increase of lipocalin 2 contributes to the development of cardiometabolic diseases partly via pro-inflammatory effects. The roles of sclerostin appear to be complicated: It exerts pro-adiposity and pro-insulin resistance effects in type 2 diabetes and has an anti-calcification effect during cardiovascular disease. A better understanding of the actions of these bone-derived hormones in the pathophysiology of cardiometabolic diseases will provide crucial insights to help further research develop new therapeutic strategies to treat these diseases.

Undercarboxylated osteocalcin downregulates pancreatic lipase expression in an ATF4-dependent manner in pancreatic acinar cells

Osteocalcin is an osteoblast-specific secreted protein that has been associated with endocrine roles in multiple aspects of energy metabolism. We examined whether undercarboxylated osteocalcin (ucOC) downregulates pancreatic lipase (PNLIP) expression in pancreatic acinar cells and then identified the downstream signaling pathway involved. We previously demonstrated that β adrenergic blockade attenuates body weight/fat mass gain in high-fat diet-fed mice and that this effect is associated with decreased PNLIP expression in pancreatic acinar cells. In the present study, we first confirmed that the serum ucOC level is inversely correlated with PNLIP expression, i.e., mice exhibiting high serum levels of ucOC showed low PNLIP levels in the pancreas. In in vitro experiments using primary pancreatic acinar and 266-6 cells, ucOC downregulated PNLIP expression. cAMP/PKA signaling inhibitors significantly reversed ucOC-induced downregulation of PNLIP expression. ucOC promoted the phosphorylation of cAMP response element-binding protein 2 (ATF4). Overexpression of ATF4 significantly suppressed PNLIP expression. Knockdown of ATF4 by siRNA reversed the ucOC-induced downregulation of PNLIP expression. A luciferase reporter assay showed that ucOC suppressed PNLIP promoter transactivation. Chromatin immunoprecipitation and a luciferase reporter assay demonstrated that ATF4 directly bound to the CRE on the mouse PNLIP promoter and suppressed PNLIP transactivation. Knockdown of G-protein coupled receptor 6A (Gprc6a), a candidate receptor for mediating the response to ucOC in the bone-pancreas endocrine loop, by siRNA reversed the downregulating effect of ucOC on PNLIP expression. Taken together, ucOC downregulates pancreatic lipase expression in a cAMP/protein kinase A/ATF4-dependent manner. Gprc6a is a potential osteocalcin-sensing receptor that regulates PNLIP expression in pancreatic acinar cells.

Endoplasmic reticulum stress and NLRP3 inflammasome: Crosstalk in cardiovascular and metabolic disorders

When endoplasmic reticulum (ER) homeostasis is disrupted, known as ER stress (ERS), the ER generates an adaptive signaling pathway called the unfolded protein response to maintain the homeostasis of this organelle. However, if homeostasis is not restored, the ER initiates death signaling pathways, which contribute to the pathogenesis of various disorders. The activation of inflammatory mechanisms is also emerging as a crucial component of cardiovascular and metabolic disorders. Furthermore, the nucleotide-binding oligomerization domain-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome has attracted more attention than others and is the best-characterized member of the NLR family of inflammasomes to date. ERS intersects with many different inflammatory pathways, particularly the NLRP3 inflammasome. In this review, we focus on the interactions between ERS and the NLRP3 inflammasome. The pharmacologic and nonpharmaceutical manipulation of these two processes may offer novel opportunities for the treatment of cardiovascular and metabolic disorders.

Osteokines and the vasculature: a review of the in vitro effects of osteocalcin, fibroblast growth factor-23 and lipocalin-2

Bone-derived factors that demonstrate extra-skeletal functions, also termed osteokines, are fast becoming a highly interesting and focused area of cross-disciplinary endocrine research. Osteocalcin (OCN), fibroblast growth factor-23 (FGF23) and lipocalin-2 (LCN-2), produced in bone, comprise an important endocrine system that is finely tuned with other organs to ensure homeostatic balance and health. This review aims to evaluate in vitro evidence of the direct involvement of these proteins in vascular cells and whether any causal roles in cardiovascular disease or inflammation can be supported. PubMed, Medline, Embase and Google Scholar were searched for relevant research articles investigating the exogenous addition of OCN, FGF23 or LCN-2 to vascular smooth muscle or endothelial cells. Overall, these osteokines are directly vasoactive across a range of human and animal vascular cells. Both OCN and FGF23 have anti-apoptotic properties and increase eNOS phosphorylation and nitric oxide production through Akt signalling in human endothelial cells. OCN improves intracellular insulin signalling and demonstrates protective effects against endoplasmic reticulum stress in murine and human endothelial cells. OCN may be involved in calcification but further research is warranted, while there is no evidence for a pro-calcific effect of FGF23 in vitro. FGF23 and LCN-2 increase proliferation in some cell types and increase and decrease reactive oxygen species generation, respectively. LCN-2 also has anti-apoptotic effects but may increase endoplasmic reticulum stress as well as have pro-inflammatory and pro-angiogenic properties in human vascular endothelial and smooth muscle cells. There is no strong evidence to support a pathological role of OCN or FGF23 in the vasculature based on these findings. In contrast, they may in fact support normal endothelial functioning, vascular homeostasis and vasodilation. No studies examined whether OCN or FGF23 may have a role in vascular inflammation. Limited studies with LCN-2 indicate a pro-inflammatory and possible pathological role in the vasculature but further mechanistic data is required. Overall, these osteokines pose intriguing functions which should be investigated comprehensively to assess their relevance to cardiovascular disease and health in humans.

Vascular smooth muscle cell death, autophagy and senescence in atherosclerosis

In the present review, we describe the causes and consequences of loss of vascular smooth muscle cells (VSMCs) or their function in advanced atherosclerotic plaques and discuss possible mechanisms such as cell death or senescence, and induction of autophagy to promote cell survival. We also highlight the potential use of pharmacological modulators of these processes to limit plaque progression and/or improve plaque stability. VSMCs play a pivotal role in atherogenesis. Loss of VSMCs via initiation of cell death leads to fibrous cap thinning and promotes necrotic core formation and calcification. VSMC apoptosis is induced by pro-inflammatory cytokines, oxidized low density lipoprotein, high levels of nitric oxide and mechanical injury. Apoptotic VSMCs are characterized by a thickened basal lamina surrounding the cytoplasmic remnants of the VSMC. Inefficient clearance of apoptotic VSMCs results in secondary necrosis and subsequent inflammation. A critical determinant in the VSMC stress response and phenotypic switching is autophagy, which is activated by various stimuli, including reactive oxygen and lipid species, cytokines, growth factors and metabolic stress. Successful autophagy stimulates VSMC survival, whereas reduced autophagy promotes age-related changes in the vasculature. Recently, an interesting link between autophagy and VSMC senescence has been uncovered. Defective VSMC autophagy accelerates not only the development of stress-induced premature senescence but also atherogenesis, albeit without worsening plaque stability. VSMC senescence in atherosclerosis is likely a result of replicative senescence and/or stress-induced premature senescence in response to DNA damaging and/or oxidative stress-inducing stimuli. The finding that VSMC senescence can promote atherosclerosis further illustrates that normal, adequate VSMC function is crucial in protecting the vessel wall against atherosclerosis.

The Association Between Osteocalcin and Chronic Inflammation in Patients with Type 2 Diabetes Mellitus

Osteocalcin acts as an endocrine hormone to regulate energy homeostasis. Although several in vivo and in vitro studies suggest that osteocalcin is involved in chronic inflammation, the association between osteocalcin and chronic inflammation in humans is unknown. In this cross-sectional study, 246 patients with type 2 diabetes mellitus (T2DM) were recruited to investigate the association of bone turnover markers with chronic inflammation parameters such as high-sensitive C-reactive protein (hsCRP), ferritin, and leukocyte subtype counts. Bone-specific alkaline phosphatase (BAP), total osteocalcin (OC), undercarboxylated OC (ucOC), and urinary N-terminal cross-linked telopeptide of type-I collagen (uNTX) were measured. Multiple regression analysis adjusted for age, duration of diabetes, body mass index, estimated glomerular filtration rate, and hemoglobin A1c showed that serum OC levels were significantly and negatively associated with hsCRP, ferritin, basophil count, and monocyte count (β = - 0.18, p = 0.013; β = - 0.22, p = 0.031; β = - 0.14, p = 0.038; and β = - 0.17, p = 0.012, respectively). Moreover, serum ucOC levels were significantly and negatively associated with hsCRP, ferritin, total leukocyte count, neutrophil count, and monocyte count (β = - 0.24, p = 0.007; β =- 0.37, p = 0.003; β = - 0.21, p = 0.007; β = - 0.24, p = 0.002; and β = - 0.20, p = 0.011, respectively). The ratio of ucOC to OC was significantly and negatively associated with ferritin (β = - 0.31, p = 0.014). However, neither BAP nor uNTX was associated with any chronic inflammation parameters. This is the first study to show that serum OC and ucOC levels were negatively associated with chronic inflammation parameters such as hsCRP, ferritin, and leukocyte subtypes in patients with T2DM. Therefore, OC could be a therapeutic target for protecting against chronic inflammation.

Potential Role for Osteocalcin in the Development of Atherosclerosis and Blood Vessel Disease

There is increasing evidence for the involvement of the skeleton in the regulation of atherosclerotic vascular disease. Osteocalcin, an osteoblast derived protein, exists in two forms, carboxylated and undercarboxylated osteocalcin. Undercarboxylated osteocalcin has been linked to the regulation of metabolic functions, including glucose and lipid metabolism. Features of atherosclerosis have been associated with circulating osteocalcin; however, this association is often conflicting and unclear. Therefore, the aim of this review is to examine the evidence for a role of osteocalcin in atherosclerosis development and progression, and in particular endothelial dysfunction and vascular calcification. The current literature suggests that undercarboxylated osteocalcin stimulates the phosphoinositide 3-kinase/protein kinase B (PI3K/Akt) signaling pathway to upregulate nitric oxide and nuclear factor kappa β (NF-кβ) in vascular cells, possibly protecting endothelial function and preventing atherogenesis. However, this effect may be mediated by metabolic factors, such as improvements in insulin signaling, rather than through a direct effect on the vasculature. Total osteocalcin is frequently associated with vascular calcification, an association that may occur as a result of vascular cells eliciting an osteogenic phenotype. Whether osteocalcin acts as a mediator or a marker of vascular calcification is currently unclear. As such, further studies that examine each form of osteocalcin are required to elucidate if it is a mediator of atherogenesis, and whether it functions independently of metabolic factors.

Alpha-lipoic acid regulates the autophagy of vascular smooth muscle cells in diabetes by elevating hydrogen sulfide level

Dysfunctional vascular smooth muscle (VSM) plays a vital role in the process of atherosclerosis in patients with type 2 diabetes mellitus (T2DM). Alpha-lipoic acid (ALA) can prevent the altered VSM induced by diabetes. However, the precise mechanism underlying the beneficial effect of ALA is not well understood. This study aimed to determine whether ALA ameliorates VSM function by elevating hydrogen sulfide (H₂S) level in diabetes and whether this effect is associated with regulation of autophagy of VSM cells (VSMCs). We found decreased serum H₂S levels in Chinese patients and rats with type 2 diabetes mellitus (T2DM). ALA treatment could increase H₂S level, which reduced the autophagy-related index and activation of the 5'-monophosphate-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) pathway, thereby protecting vascular function in rats with T2DM. Propargylglycine (PPG), a cystathionine-γ-lyase inhibitor, could weaken the ALA effect. In cultured VSMCs, high glucose level also reduced H₂S level, upregulated the autophagy-related index and activated the AMPK/mTOR pathway, which were reversed by concomitant application of sodium hydrosulfide (NaHS, an H₂S donor) or ALA. The protective effect of NaHS or ALA was attenuated by rapamycin (an autophagy activator), 5-amino-1-β-d-ribofuranosyl-imidazole-4-carboxamide (an AMPK activator) or PPG. In contrast, Compound C (an AMPK inhibitor) enhanced the effect of ALA or NaHS. ALA may have a protective effect on VSMCs in T2DM by elevating H₂S level and downregulating autophagy via the AMPK/mTOR pathway. This study provides a new target for addressing diabetic macroangiopathy.

Undercarboxylated Osteocalcin: Experimental and Human Evidence for a Role in Glucose Homeostasis and Muscle Regulation of Insulin Sensitivity

Recent advances have indicated that osteocalcin, and in particular its undercarboxylated form (ucOC), is not only a nutritional biomarker reflective of vitamin K status and an indicator of bone health but also an active hormone that mediates glucose metabolism in experimental studies. This work has been supported by the putative identification of G protein-coupled receptor, class C, group 6, member A (GPRC6A) as a cell surface receptor for ucOC. Of note, ucOC has been associated with diabetes and with cardiovascular risk in epidemiological studies, consistent with a pathophysiological role for ucOC in vivo. Limitations of existing knowledge include uncertainty regarding the underlying mechanisms by which ucOC interacts with GPRC6A to modulate metabolic and cardiovascular outcomes, technical issues with commonly used assays for ucOC in serum, and a paucity of clinical trials to prove causation and illuminate the scope for novel health interventions. A key emerging area of research is the role of ucOC in relation to expression of GPRC6A in muscle, and whether exercise interventions may modulate metabolic outcomes favorably in part via ucOC. Further research is warranted to clarify potential direct and indirect roles for ucOC in human health and cardiometabolic diseases.

Regulation of Energy Metabolism by Bone-Derived Hormones

Like many other organs, bone can act as an endocrine organ through the secretion of bone-specific hormones or "osteokines." At least two osteokines are implicated in the control of glucose and energy metabolism: osteocalcin (OCN) and lipocalin-2 (LCN2). OCN stimulates the production and secretion of insulin by the pancreatic β-cells, but also favors adaptation to exercise by stimulating glucose and fatty acid (FA) utilization by the muscle. Both of these OCN functions are mediated by the G-protein-coupled receptor GPRC6A. In contrast, LCN2 influences energy metabolism by activating appetite-suppressing signaling in the brain. This action of LCN2 occurs through its binding to the melanocortin 4 receptor (MC4R) in the paraventricular nucleus of the hypothalamus (PVN) and ventromedial neurons of the hypothalamus.

Association of Bone Mineral Density, Bone Turnover Markers, and Vertebral Fractures with All-Cause Mortality in Type 2 Diabetes Mellitus

Patients with type 2 diabetes mellitus (T2DM) have an increased risk of fragility fracture. However, the association between diabetes-related osteoporosis and mortality in T2DM remains unknown. This historical cohort study assessed the endpoint of all-cause mortality in patients with T2DM. According to our hospital record, bone parameters were examined in 797 patients from 1997 to 2009. We excluded 78 because of diseases affecting bone metabolism and could not follow-up 308 patients. Finally, in 411 patients, the associations of bone turnover markers, bone mineral density (BMD), and the prevalence of vertebral fractures with mortality were investigated by Cox regression analyses adjusted for confounding factors. Of 411 patients, 56 died during the follow-up period of almost 7 years. Cox regression analyses showed that reduced BMD at the lumbar spine (LS) and femoral neck (FN) (T-score ≤ -2.5) and severe vertebral fractures were associated with higher mortality (hazard ratio [HR] 3.25, 95% confidence interval [CI] 1.48-7.16, p = 0.003 for LS-T score ≤ -2.5; HR 5.19, 95% CI 1.83-14.75, p = 0.002 for FN-T score ≤ -2.5; HR 2.93, 95% CI 1.42-6.02, p = 0.004 for multiple vertebral fractures; HR 7.64, 95% CI 2.13-27.42, p = 0.002 for grade 3 vertebral fracture). Separate analysis in men and women showed that decreased serum osteocalcin was associated with mortality in women (HR 3.82, 95% CI 1.01-14.46 per SD decrease, p = 0.048). The present study is the first to show the association of reduced BMD and severe vertebral fractures with increased all-cause mortality in patients with T2DM. Moreover, higher serum osteocalcin was significantly associated with decreased mortality in women with T2DM.

Undercarboxylated osteocalcin reverts insulin resistance induced by endoplasmic reticulum stress in human umbilical vein endothelial cells

Osteocalcin has been considered to be an important regulator of energy metabolism in type 2 diabetes mellitus (T2DM). However, the mechanism underlying the involvement of uncarboxylated osteocalcin in the vascular complications of T2DM is not fully understood. In the present study, we analyzed the potential correlations between uncarboxylated osteocalcin and macro- or microangiopathic complications in subjects with T2DM and tested the impact of uncarboxylated osteocalcin on insulin resistance in human umbilical vein endothelial cells (HUVECs). The results showed that the serum levels of uncarboxylated osteocalcin were lower in subjects with vascular complications of T2DM. Univariate correlation analyses revealed negative correlations between uncarboxylated osteocalcin and waist-to-hip ratio, HbA1c, and HOMA-IR. In in vitro experiments, insulin resistance was induced by applying tunicamycin to HUVECs. Uncarboxylated osteocalcin not only markedly reduced the phosphorylations of PERK and eIF2α, but also elevated the phosphorylations of IRS-1 and Akt, resulting in improvement of insulin signal transduction via PI3K/Akt/NF-κB signaling in HUVECs. Therefore, there is a possible relationship between uncarboxylated osteocalcin and the vascular complications of T2DM. Uncarboxylated osteocalcin partially improves insulin signal transduction via PI3K/Akt/NF-κB signaling in tunicamycin-induced HUVECs, suggesting osteocalcin as a potential treatment for the vascular complications of T2DM.

Endoplasmic Reticulum Stress in Arterial Smooth Muscle Cells: A Novel Regulator of Vascular Disease

Cardiovascular disease continues to be the leading cause of death in industrialised societies. The idea that the arterial smooth muscle cell (ASMC) plays a key role in regulating many vascular pathologies has been gaining importance, as has the realisation that not enough is known about the pathological cellular mechanisms regulating ASMC function in vascular remodelling. In the past decade endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) have been recognised as a stress response underlying many physiological and pathological processes in various vascular cell types. Here we summarise what is known about how ER stress signalling regulates phenotypic switching, trans/dedifferentiation and apoptosis of ASMCs and contributes to atherosclerosis, hypertension, aneurysms and vascular calcification.

Progranulin causes adipose insulin resistance via increased autophagy resulting from activated oxidative stress and endoplasmic reticulum stress

BACKGROUND

Progranulin (PGRN) has recently emerged as an important regulator for insulin resistance. However, the direct effect of progranulin in adipose insulin resistance associated with the autophagy mechanism is not fully understood.

METHODS

In the present study, progranulin was administered to 3T3-L1 adipocytes and C57BL/6 J mice with/without specific inhibitors of oxidative stress and endoplasmic reticulum stress, and metabolic parameters, oxidative stress, endoplasmic reticulum stress and autophagy markers were assessed.

RESULTS

Progranulin treatment increased iNOS expression, NO synthesis and ROS generation, and elevated protein expressions of CHOP, GRP78 and the phosphorylation of PERK, and caused a significant increase in Atg7 and LC3-II protein expression and a decreased p62 expression, and decreased insulin-stimulated tyrosine phosphorylation of IRS-1 and glucose uptake, demonstrating that progranulin activated oxidative stress and ER stress, elevated autophagy and induced insulin insensitivity in adipocytes and adipose tissue of mice. Interestingly, inhibition of iNOS and ER stress both reversed progranulin-induced stress response and increased autophagy, protecting against insulin resistance in adipocytes. Furthermore, the administration of the ER stress inhibitor 4-phenyl butyric acid reversed the negative effect of progranulin in vivo.

CONCLUSION

Our findings showed the clinical potential of the novel adipokine progranulin in the regulation of insulin resistance, suggesting that progranulin might mediate adipose insulin resistance, at least in part, by inducing autophagy via activated oxidative stress and ER stress.

4-PBA reverses autophagic dysfunction and improves insulin sensitivity in adipose tissue of obese mice via Akt/mTOR signaling

BACKGROUND

4-phenyl butyric acid (4-PBA) has been considered as a key regulator of insulin resistance in obesity. However the mechanism of 4-PBA involved in insulin resistance remains elusive.

METHODS

We evaluated the effect of 4-PBA on abnormal autophagy and endoplasmic reticulum (ER) stress in obese mice. 4-PBA was administered in obese mice and adipocyte models, and metabolic parameters, autophagy markers, ER stress indicators, Akt/mTOR signaling and insulin signaling molecular were assessed.

RESULTS

4-PBA treatment not only reversed autophagic dysfunction and ER stress, but also improved impaired insulin signaling in tunicamycin-induced adipocytes, and 4-PBA also inhibited activated ER stress and elevated insulin sensitivity in adipocytes with Atg7 siRNA. Additionally, administration of 4-PBA improves glucose tolerance and insulin sensitivity in obese mice via regulating abnormal autophagy and ER stress in adipose tissue. The protective effects of 4-PBA were nullified by suppression of Akt and mTOR in adipocytes, suggesting that 4-PBA inhibits autophagy and restores insulin sensitivity via Akt/mTOR signaling partially.

CONCLUSIONS

4-PBA reverses autophagic dysfunction and improves insulin sensitivity in adipose tissue of obese mice via Akt/mTOR signaling partly, which could be regarded as novel opportunities for treatment of insulin resistance.

Tunicamycin aggravates endoplasmic reticulum stress and airway inflammation via PERK-ATF4-CHOP signaling in a murine model of neutrophilic asthma

INTRODUCTION

Endoplasmic reticulum (ER) stress has been considered to be an important regulator of airway inflammation in the pathogenesis of bronchial asthma, but the mechanism of ER stress involved in neutrophilic asthma remain not fully understood.

METHODS

Tunicamycin is a mixture of homologous nucleoside antibiotics, which is used to induce ER stress. In the present study, Tunicamycin was administered to mouse bronchial epithelial cells and a neutrophilic asthma model (OVA_LPS-OVA mice), and ER stress indicators and inflammatory cytokines were measured by Western blotting and Elisa.

RESULTS

Tunicamycin not only induced ER stress in mouse bronchial epithelial cells, but also increased expression of inflammation indicators such as IL-6, IL-8, and TNF-α via PERK-ATF4-CHOP signaling. Additionally, the phosphorylation of PERK and the expression levels of ATF4 and CHOP proteins and inflammatory cytokines (IL-6, IL-8 and TNF-α) were elevated in the lung tissue of OVA_LPS-OVA mice. Administering tunicamycin further increased protein expression levels of ER stress indicators and inflammatory cytokines, and resulted in more severe asthma phenotypes in OVA_LPS-OVA mice, suggesting that PERK-ATF4-CHOP signaling is associated with airway inflammation in neutrophil-dominant asthma.

CONCLUSIONS

These data support the emerging notion that regulation of ER stress could be strongly associated with the development of neutrophilic asthma.

An overview of osteocalcin progress

An increasing amount of data indicate that osteocalcin is an endocrine hormone which regulates energy metabolism, male fertility and brain development. However, the detailed functions and mechanism of osteocalcin are not well understood and conflicting results have been obtained from researchers worldwide. In the present review, we summarize the progress of osteocalcin studies over the past 40 years, focusing on the structure of carboxylated and undercarboxylated osteocalcin, new functions and putative receptors, the role of osteocalcin in bone remodeling, specific expression and regulation in osteoblasts, and new indices for clinical studies. The complexity of osteocalcin in completely, uncompletely and non-carboxylated forms may account for the discrepancies in its tertiary structure and clinical results. Moreover, the extensive expression of osteocalcin and its putative receptor GPRC6A imply that there are new physiological functions and mechanisms of action of osteocalcin to be explored. New discoveries related to osteocalcin function will assist its potential clinical application and physiological theory, but comprehensive investigations are required.

miR-1273g-3p participates in acute glucose fluctuation-induced autophagy, dysfunction, and proliferation attenuation in human umbilical vein endothelial cells

Acute glucose fluctuations (AGF) often cause high mortality among critically ill patients, but the mechanisms induced by AGF are not clear. Recent studies suggest that endothelial dysfunction is a key factor that leads to high mortality among critically ill patients. Our goal is to evaluate the phenomenon and mechanisms of endothelial dysfunction induced by AGF. In this study, the functions of human umbilical vein endothelial cells (HUVECs) were compared after treatment with sustained high glucose (SHG), AGF in two groups (AGF1 fluctuations between 5 and 16 mM and AGF2 fluctuations between 5 and 25 mM), and normal glucose levels as a control group (CTR). The medium of the groups was changed every 4 h. The influence of AGF on wound healing was also tested on C57BL/6 mice. The results show that cell proliferation, angiogenesis, and migration functions were injured in the SHG and both AGF groups. AGF2 group shows the worse condition in vitro. In vivo, the wound healing was delayed after the AGF treatment. Furthermore, the markers of apoptosis and autophagy were analyzed. We observed that the autophagy changed in all treatment groups, but apoptosis showed no change. To get to know the mechanism of dysfunction and autophagy, we performed the microRNA chip assay and real-time PCR and found miR-1273g-3p remarkably changed in AGF2 group. After the mimic and inhibitor of miR-1273g-3p were transfected during the AGF2 treatment, we found that the dysfunction and autophagy were partially enhanced by miR-1273g-3p mimic and reversed by miR-1273g-3p inhibitor in AGF2 group. Thus, we conclude that AGF can induce more dysfunction and autophagy, and miR-1273g-3p is also an important factor that leads to the injury.

Administration of progranulin (PGRN) triggers ER stress and impairs insulin sensitivity via PERK-eIF2α-dependent manner

Progranulin (PGRN) has recently emerged as an important regulator for glucose metabolism and insulin sensitivity. However, the direct effects of PGRN in vivo and the underlying mechanisms between PGRN and impaired insulin sensitivity are not fully understood. In this study, mice treated with PGRN for 21 d exhibited the impaired glucose tolerance and insulin sensitivity, remarkable ER stress as well as attenuated insulin signaling in liver and adipose tissue but not in skeletal muscle. Furthermore, treatment of mice with phenyl butyric acid (PBA), a chemical chaperone alleviating ER stress, resulted in a significant restoration of systemic insulin sensitivity and recovery of insulin signaling induced by PGRN. Consistent with these findings in vivo, we also observed that PGRN treatment induced ER stress, impaired insulin signaling in cultured hepatocytes and adipocytes, with such effects being partially nullified by blockade of PERK. Whereas PGRN-deficient hepatocytes and adipocytes were more refractory to palmitate-induced insulin resistance, indicating the causative role of the PERK-eIF2α axis of the ER stress response in action of PGRN. Collectively, our findings supported the notion that PGRN is a key regulator of insulin resistance and that PGRN may mediate its effects, at least in part, by inducing ER stress via the PERK-eIF2α dependent pathway.

Lower uncarboxylated osteocalcin and higher sclerostin levels are significantly associated with coronary artery disease

Systemic roles for bone-derived proteins have emerged from recent studies. In particular, the serum concentration of osteocalcin (OCN) or sclerostin was found to be associated with altered glucose metabolism or atherosclerosis. The aims of this study were to evaluate OCN and sclerostin levels in subjects who underwent coronary artery bypass graft (CABG) surgery compared with those in normal controls and to analyze their relationships with atherosclerosis. This was an age- and sex-matched case-control study that included 61 male subjects who underwent CABG and 61 controls. Forty-six subjects (37.7%) with diabetes and 62 hypertensive subjects (50.8%) were included. Serum sclerostin, uncarboxylated OCN (ucOCN) and carboxylated OCN (cOCN) were measured. Coronary artery calcium (CAC) score was calculated according to Agatston's method, using a 64-slice multi-detector computed tomography scanner. The levels of serum ucOCN were significantly lower and sclerostin concentrations were higher in the CABG group than in the controls (p<0.05 for both), and these significances were maintained after adjusting for atherosclerotic risk factors in both diabetic and nondiabetic patients (p<0.05 in both groups). However, there was no difference in cOCN levels between CABG patients and controls. The group with abnormal CAC scores (CAC scores ≥100) had significantly higher levels of serum sclerostin (p<0.05). In multiple logistic regression analysis, both lower ucOCN and higher sclerostin levels were independently associated with CABG (odds ratio [OR] 0.43, 95% CI 0.22-0.84, p<0.05 for log(ucOCN); and OR 2.09, 95% CI 1.08-4.05, p<0.05 for log(sclerostin)). In subjects with CAD who underwent CABG, the serum ucOCN level was decreased and the sclerostin level was increased compared with those in the controls, regardless of diabetic status. Longitudinal studies are warranted to establish the precise roles of ucOCN and sclerostin in the pathogenesis of atherosclerosis.

New insights into the biology of osteocalcin

Osteocalcin is among the most abundant proteins in bone and is produced exclusively by osteoblasts. Initially believed to be an inhibitor of bone mineralization, recent studies suggest a broader role for osteocalcin that extends to the regulation of whole body metabolism, reproduction, and cognition. Circulating undercarboxylated osteocalcin, which is regulated by insulin, acts in a feed-forward loop to increase β-cell proliferation as well as insulin production and secretion, while skeletal muscle and adipose tissue respond to osteocalcin by increasing their sensitivity to insulin. Osteocalcin also acts in the brain to increase neurotransmitter production and in the testes to stimulate testosterone production. At least one putative receptor for osteocalcin, Gprc6a, is expressed by adipose, skeletal muscle, and the Leydig cells of the testes and appears to mediate osteocalcin's effects in these tissues. In this review, we summarize these new discoveries, which suggest that the ability of osteocalcin to function both locally in bone and as a hormone depends on a novel post-translational mechanism that alters osteocalcin's affinity for the bone matrix and bioavailability. This article is part of a Special Issue entitled Bone and diabetes.

Progranulin induces adipose insulin resistance and autophagic imbalance via TNFR1 in mice

Progranulin (PGRN) has recently emerged as an important regulator for insulin resistance. However, the direct effect of PGRN in vivo and the underlying role of progranulin in adipose insulin resistance involving the autophagy mechanism is not fully understood. In this study, mice treated with PGRN for 21 days exhibited the impaired glucose tolerance and insulin sensitivity, remarkable adipose autophagy as well as attenuated insulin signaling via inhibition of mammalian target of rapamycin (mTOR) pathway. Furthermore, blockade of tumor necrosis factor receptor 1 (TNFR1) by TNFR1BP-Fc injection resulted in the restoration of impaired insulin sensitivity and insulin signaling induced by PGRN. Consistent with these findings in vivo, PGRN treatment induced defective insulin signaling, abnormal autophagic and mitochondrial activity in cultured adipocytes, while such effects were nullified by the blockade of TNFR1. In addition, PGRN-deficient adipocytes were more refractory to tunicamycin- or dexamethasone-induced insulin resistance, indicating the causative role of the TNFR1 pathway in the action of PGRN. Collectively, our findings support the notion that PGRN is a key regulator of insulin resistance and that PGRN may mediate its effects, at least in part, by inducing autophagy via the TNFR1-dependent mechanism.

Searching for additional endocrine functions of the skeleton: genetic approaches and implications for therapeutics

Our knowledge of whole organism physiology has greatly advanced in the past decades through mouse genetics. In particular, genetic studies have revealed that most organs interact with one another through hormones in order to maintain normal physiological functions and the homeostasis of the entire organism. Remarkably, through these studies many unexpected novel endocrine means to regulate physiological functions have been uncovered. The skeletal system is one example. In this article, we review a series of studies that over the years have identified bone as an endocrine organ. The mechanism of action, pathological relevance, and therapeutic implications of the functions of the bone-derived hormone osteocalcin are discussed. In the last part of this review we discuss the possibility that additional endocrine functions of the skeleton may exist.

Acetylcholine ameliorates endoplasmic reticulum stress in endothelial cells after hypoxia/reoxygenation via M3 AChR-AMPK signaling

Endoplasmic reticulum (ER) stress is associated with various cardiovascular diseases. However, its pathophysiological relevance and the underlying mechanisms in the context of hypoxia/reoxygenation (H/R) in endothelial cells are not fully understood. Previous findings have suggested that acetylcholine (ACh), the major vagal nerve neurotransmitter, protected against cardiomyocyte injury by activating AMP-activated protein kinase (AMPK). This study investigated the role of ER stress in endothelial cells during H/R and explored the beneficial effects of ACh. Our results showed that H/R triggered ER stress and apoptosis in endothelial cells, evidenced by the elevation of glucose-regulated protein 78, cleaved caspase-12 and C/EBP homologous protein expression. ACh significantly decreased ER stress and terminal deoxynucleotidyl transferase mediated dUTP-biotin nick end labeling positive cells and restored ER ultrastructural changes induced by H/R, possibly via protein kinase-like ER kinase and inositol-requiring kinase 1 pathways. Additionally, 4-diphenylacetoxy-N-methylpiperidine methiodide, a type-3 muscarinic ACh receptor (M3 AChR) inhibitor, abolished ACh-mediated increase in AMPK phosphorylation during H/R. Furthermore, M3 AChR or AMPK siRNA abrogated the ACh-elicited the attenuation of ER stress in endothelial cells, indicating that the salutary effects of ACh were likely mediated by M3 AChR-AMPK signaling. Overall, ACh activated AMPK through M3 AChR, thereby inhibited H/R-induced ER stress and apoptosis in endothelial cells. We have suggested for the first time that AMPK may function as an essential intermediate step between M3 AChR stimulation and inhibition of ER stress-associated apoptotic pathway during H/R, which may help to develop novel therapeutic approaches targeting ER stress to prevent or alleviate ischemia/reperfusion injury.

The Ankyrin Repeat Domain 49 (ANKRD49) Augments Autophagy of Serum-Starved GC-1 Cells through the NF-κB Pathway

The ankyrin repeat domain 49 (ANKRD49) is an evolutionarily conserved protein highly expressed in testes. However, the function of ANKRD49 in spermatogenesis is unknown. In this study, we found that ANKRD49 resides primarily in nucleus of spermatogonia, spermatocytes and round spermatids. ANKRD49 overexpression augments starvation-induced autophagy in male germ GC-1 cells whereas shRNA knockdown of ANKRD49 attenuates the autophagy. Inhibition of NF-κB pathway by its inhibitors or p65 siRNA prevents the ANKRD49-dependent autophagy augmentation, demonstrating that ANKRD49 enhances autophagy via NF-κB pathway. Our findings suggest that ANKRD49 plays an important role in spermatogenesis via promotion of autophagy-dependent survival.

Glycolipid Metabolism Disorder in the Liver of Obese Mice Is Improved by TUDCA via the Restoration of Defective Hepatic Autophagy

Objective. Tauroursodeoxycholic acid (TUDCA) has been considered an important regulator of energy metabolism in obesity. However, the mechanism underlying how TUDCA is involved in insulin resistance is not fully understood. We tested the effects of TUDCA on autophagic dysfunction in obese mice. Material and Methods. 500 mg/kg of TUDCA was injected into obese mice, and metabolic parameters, autophagy markers, and insulin signaling molecular were assessed by Western blotting and real-time PCR. Results. The TUDCA injections in the obese mice resulted in a reduced body weight gain, lower blood glucose, and improved insulin sensitivity compared with obese mice that were injected with vehicle. Meanwhile, TUDCA treatment not only reversed autophagic dysfunction and endoplasmic reticulum stress, but also improved the impaired insulin signaling in the liver of obese mice. Additionally, the same results obtained with TUDCA were evident in obese mice treated with the adenoviral Atg7. Conclusions. We found that TUDCA reversed abnormal autophagy, reduced ER stress, and restored insulin sensitivity in the liver of obese mice and that glycolipid metabolism disorder was also improved via the restoration of defective hepatic autophagy.

Osteocalcin protects against nonalcoholic steatohepatitis in a mouse model of metabolic syndrome

Nonalcoholic fatty liver disease, particularly its more aggressive form, nonalcoholic steatohepatitis (NASH), is associated with hepatic insulin resistance. Osteocalcin, a protein secreted by osteoblast cells in bone, has recently emerged as an important metabolic regulator with insulin-sensitizing properties. In humans, osteocalcin levels are inversely associated with liver disease. We thus hypothesized that osteocalcin may attenuate NASH and examined the effects of osteocalcin treatment in middle-aged (12-mo-old) male Ldlr(-/-) mice, which were fed a Western-style high-fat, high-cholesterol diet for 12 weeks to induce metabolic syndrome and NASH. Mice were treated with osteocalcin (4.5 ng/h) or vehicle for the diet duration. Osteocalcin treatment not only protected against Western-style high-fat, high-cholesterol diet-induced insulin resistance but substantially reduced multiple NASH components, including steatosis, ballooning degeneration, and fibrosis, with an overall reduction in nonalcoholic fatty liver disease activity scores. Further, osteocalcin robustly reduced expression of proinflammatory and profibrotic genes (Cd68, Mcp1, Spp1, and Col1a2) in liver and suppressed inflammatory gene expression in white adipose tissue. In conclusion, these results suggest osteocalcin inhibits NASH development by targeting inflammatory and fibrotic processes.

Implications of autophagy for vascular smooth muscle cell function and plasticity

Vascular smooth muscle cells (VSMCs) are fundamental in regulating blood pressure and distributing oxygen and nutrients to peripheral tissues. They also possess remarkable plasticity, with the capacity to switch to synthetic, macrophage-like, or osteochondrogenic phenotypes when cued by external stimuli. In arterial diseases such as atherosclerosis and restenosis, this plasticity seems to be critical and, depending on the disease context, can be deleterious or beneficial. Therefore, understanding the mechanisms regulating VSMC phenotype and survival is essential for developing new therapies for vascular disease as well as understanding how secondary complications due to surgical interventions develop. In this regard, the cellular process of autophagy is increasingly being recognized as a major player in vascular biology and a critical determinant of VSMC phenotype and survival. Although autophagy was identified in lesional VSMCs in the 1960s, our understanding of the implications of autophagy in arterial diseases and the stimuli promoting its activation in VSMCs is only now being elucidated. In this review, we highlight the evidence for autophagy occurring in VSMCs in vivo, elaborate on the stimuli and processes regulating autophagy, and discuss the current understanding of the role of autophagy in vascular disease.