Modulation of bone morphogenetic protein-9 expression and processing by insulin, glucose, and glucocorticoids: possible candidate for hepatic insulin-sensitizing substance

Distinct signalling dynamics of BMP4 and BMP9 in brown versus white adipocytes

Adipocyte dysfunction contributes to lipotoxicity and cardiometabolic diseases. Bone morphogenetic protein 4 (BMP4) is expressed in white adipocytes and remodels white adipose tissue, while liver-derived BMP9, a key circulating BMP, influences adipocyte lipid metabolism. The gene sets regulated by BMP4 and BMP9 signalling in mature adipocytes remain unclear. Here, we directly compare BMP4 and BMP9 signalling in mature brown and white adipocytes. While both BMPs showed comparable potency across adipocyte types, RNA sequencing analysis revealed extensive gene regulation, with many more differentially expressed genes and suppression of critical metabolic pathways in white adipocytes. Although BMP4 and BMP9 induced inhibitors of BMP and GDF signalling in both adipocytes, they selectively upregulated several TGF-β family receptors and BMP4 expression only in white adipocytes. These findings underscore a central role of BMP signalling in adipocyte homeostasis and suggest both BMP4 and BMP9 as regulators of white adipocyte plasticity with potential therapeutic implications.

Unveiling the Impact of BMP9 in Liver Diseases: Insights into Pathogenesis and Therapeutic Potential

Bone morphogenetic proteins (BMPs) are a group of growth factors belonging to the transforming growth factor β(TGF-β) family. While initially recognized for their role in bone formation, BMPs have emerged as significant players in liver diseases. Among BMPs with various physiological activities, this comprehensive review aims to delve into the involvement of BMP9 specifically in liver diseases and provide insights into the complex BMP signaling pathway. Through an enhanced understanding of BMP9, we anticipate the discovery of new therapeutic options and potential strategies for managing liver diseases.

Elevated serum levels of bone morphogenetic protein-9 are associated with better outcome in AQP4-IgG seropositive NMOSD

Lymphatic drainage in the central nervous system is regulated by meningeal lymphatic vasculature, and recurrent neuroinflammation alters lymphatic vessel remodeling. Patients with aquaporin-4 antibody-positive neuromyelitis optica spectrum disorder (AQP4 + NMOSD) were reported to demonstrate worse outcomes compared with patients with anti-myelin oligodendrocyte glycoprotein-associated disorders (MOGAD). This study aimed to investigate the serum cytokines relevant to vascular remodeling after attacks and their prognostic role in patients with AQP4 + NMOSD. This study measured the serum levels of 12 cytokines relevant to vascular remodeling, including bone morphogenetic protein-9 (BMP-9) and leptin, in 20 patients with AQP4 + NMOSD and 17 healthy controls (HCs). Disease controls included 18 patients with MOGAD. Serum and cerebrospinal fluid interleukin-6 levels were also measured. Clinical severity was evaluated with Kurtzke's Expanded Disability Status Scale (EDSS). Compared with HCs, patients with AQP4 + NMOSD showed higher BMP-9 (median; 127 vs. 80.7 pg/mL; P = 0.0499) and leptin levels (median; 16,081 vs. 6770 pg/mL; P = 0.0224), but not those with MOGAD. Better improvement in EDSS at 6 months was associated with baseline BMP-9 levels in patients with AQP4 + NMOSD (Spearman's rho =  - 0.47; P = 0.037). Serum BMP-9 is upregulated at relapse and may contribute to vascular remodeling in AQP4 + NMOSD. Serum BMP-9 levels could predict clinical recovery 6 months after the attack.

Circulating Bone Morphogenetic Protein-9 is Decreased in Patients with Type 2 Diabetes and Non-Alcoholic Fatty Liver Disease

Objective

We aimed to examine the association between bone morphogenetic protein-9 (BMP-9) and type 2 diabetes mellitus (T2DM) in conjunction with non-alcoholic fatty liver disease (NAFLD) and insulin resistance (IR) and to identify evidence supporting the potential role of BMP-9 in the clinical prevention and treatment of T2DM in conjunction with NAFLD.

Methods

One hundred and twenty subjects were included in this study. We sorted all of the subjects into four groups of equal size (n=30 each). A trained expert assessed the height, weight, systolic blood pressure (SBP), and diastolic blood pressure (DBP) of the subjects and computed the body mass index (BMI). All subjects had their fasting blood glucose (FBG), fasting insulin (FINS), serum BMP-9, and biochemical indices assessed.

Results

Significant variations were observed in BMI, SBP, DBP, ALT, TC, TG, HDL-C, LDL-C, ApoB, FBG, FINS, HOMA-IR, and serum BMP-9 among the four groups (P<0.05). The level of serum BMP-9 was positively correlated with HDL-C, while the level of serum BMP-9 was negatively correlated with BMI, SBP, DBP, ALT, TC, TG, LDL-C, FBG, FINS, and HOMA-IR. Multiple stepwise regression analyses revealed that FINS, LDL-C, HDL-C, and BMI were independent factors impacting serum BMP-9 levels (P<0.05). Logistic regression analyses revealed that BMP-9 was a protective factor for T2DM paired with NAFLD, while HOMA-IR was a risk factor.

Conclusion

Serum BMP-9 levels are significantly lower in the T2DM+NAFLD group when compared to other groups, and BMP-9 is an independent risk factor for T2DM paired with NAFLD.

Bone morphogenic protein 9 is a novel thermogenic hepatokine secreted in response to cold exposure

OBJECTIVE

Maintaining a constant core body temperature is essential to homeothermic vertebrate survival. Adaptive thermogenesis in brown adipose tissue and skeletal muscle is the primary mechanism of adjustment to an external stimulus such as cold exposure. Recently, several reports have revealed that the liver can play a role as a metabolic hub during adaptive thermogenesis. In this study, we suggest that the liver plays a novel role in secreting thermogenic factors in adaptive thermogenesis. Bone morphogenetic protein 9 (BMP9) is a hepatokine that regulates many biological processes, including osteogenesis, chondrogenesis, hematopoiesis, and angiogenesis. Previously, BMP9 was suggested to affect preadipocyte proliferation and differentiation. However, the conditions and mechanisms underlying hepatic expression and secretion and adipose tissue browning of BMP9 remain largely unknown. In this study, we investigated the physiological conditions for secretion and the regulatory mechanism of hepatic Bmp9 expression and the molecular mechanism by which BMP9 induces thermogenic gene program activation in adipose tissue. Here, we also present the pharmacological effects of BMP9 on a high-fat-induced obese mouse model.

METHODS

To investigate the adaptive thermogenic role of BMP9 in vivo, we challenged mice with cold temperature exposure for 3 weeks and then examined the BMP9 plasma concentration and hepatic expression level. The cellular mechanism of hepatic Bmp9 expression under cold exposure was explored through promoter analysis. To identify the role of BMP9 in the differentiation of brown and beige adipocytes, we treated pluripotent stem cells and inguinal white adipose tissue (iWAT)-derived stromal-vascular (SV) cells with BMP9, and brown adipogenesis was monitored by examining thermogenic gene expression and signaling pathways. Furthermore, to evaluate the effect of BMP9 on diet-induced obesity, changes in body composition and glucose tolerance were analyzed in mice administered recombinant BMP9 (rBMP9) for 8 weeks.

RESULTS

Hepatic Bmp9 expression and plasma levels in mice were significantly increased after 3 weeks of cold exposure. Bmp9 mRNA expression in the liver was regulated by transcriptional activation induced by cAMP response-element binding protein (CREB) and CREB-binding protein (CBP) on the Bmp9 promoter. Treatment with BMP9 promoted the differentiation of multipotent stem cells and iWAT-derived SV cells into beige adipocytes, as indicated by the increased expression of brown adipocyte and mitochondrial biogenesis markers. Notably, activation of the mothers against decapentaplegic homolog 1 (Smad1) and p44/p42 mitogen-activated protein kinase (MAPK) pathways was required for the induction of uncoupling protein 1 (UCP1) and peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC1α) expression in BMP9-induced differentiation of SVs into beige adipocytes. The administration of rBMP9 in vivo also induced browning markers in white adipose tissue. In high-fat diet-induced obese mice, rBMP9 administration conferred protection against obesity and enhanced glucose tolerance.

CONCLUSIONS

BMP9 is a hepatokine regulated by cold-activated CREB and CBP and enhances glucose and fat metabolism by promoting the activation of the thermogenic gene program in adipocytes. These data implicate BMP9 as a potential pharmacological tool for protecting against obesity and type 2 diabetes.

Rethinking growth factors: the case of BMP9 during vessel maturation

Angiogenesis is an essential process for correct development and physiology. This mechanism is tightly regulated by many signals that activate several pathways, which are constantly interacting with each other. There is mounting evidence that BMP9/ALK1 pathway is essential for a correct vessel maturation. Alterations in this pathway lead to the development of hereditary haemorrhagic telangiectasias. However, little was known about the BMP9 signalling cascade until the last years. Recent reports have shown that while BMP9 arrests cell cycle, it promotes the activation of anabolic pathways to enhance endothelial maturation. In light of this evidence, a new criterion for the classification of cytokines is proposed here, based on the physiological objective of the activation of anabolic routes. Whether this activation by a growth factor is needed to sustain mitosis or to promote a specific function such as matrix formation is a critical characteristic that needs to be considered to classify growth factors. Hence, the state-of-the-art of BMP9/ALK1 signalling is reviewed here, as well as its implications in normal and pathogenic angiogenesis.

New insights into BMP9 signaling in liver diseases

Bone morphogenetic protein 9 (BMP9) is a recently discovered cytokine mainly secreted by the liver and is a member of the transforming growth factor β (TGF-β) superfamily. In recent years, an increasing number of studies have shown that BMP9 is associated with liver diseases, including nonalcoholic fatty liver disease (NAFLD), liver fibrosis and hepatocellular carcinoma (HCC), and BMP9 signaling may play dual roles in liver diseases. In this review, we mainly summarized and discussed the roles and potential mechanisms of BMP9 signaling in NAFLD, liver fibrosis and HCC. Specifically, this article will provide a better understanding of BMP9 signaling and new clues for the treatment of liver diseases.

Blockade of the interaction between BMP9 and endoglin on erythroid progenitors promotes erythropoiesis in mice

Bone morphogenetic protein‐9 (BMP9), a member of the transforming growth factor β (TGFβ) superfamily, plays important roles in the development and maintenance of various cell lineages via complexes of type I and type II TGFβ receptors. Endoglin is a coreceptor for several TGFβ family members, including BMP9, which is highly expressed in a particular stage of differentiation in erythroid cells as well as in endothelial cells. Although the importance of the interaction between BMP9 and endoglin for endothelial development has been reported, the contribution of BMP9 to endoglin‐expressing erythroid cells remains to be clarified. To address this point, we prepared an anti‐BMP9 antibody that blocks the BMP9‐endoglin interaction. Of note, challenge with the antibody promotes erythropoiesis in wild‐type mice but not in a mouse model of renal anemia in which erythropoietin (EPO) production in the kidneys is genetically ablated. While endoglin‐positive erythroid progenitors are mainly maintained as progenitors when bone marrow‐derived lineage‐negative and cKit‐positive cells are cultured in the presence of EPO and stem cell factor, the erythroid‐biased accumulation of progenitors is impeded by the presence of BMP9. Our findings uncover an unrecognized role for BMP9 in attenuating erythroid differentiation via its interaction with endoglin on erythroid progenitors.

BMP9 promotes methionine- and choline-deficient diet-induced nonalcoholic steatohepatitis in non-obese mice by enhancing NF-κB dependent macrophage polarization

Our previous study confirmed that bone morphogenetic protein 9 (BMP9) participated in the development of nonalcoholic steatohepatitis (NASH) by affecting macrophage polarization. The focus of this study was to further confirm the role of macrophages in BMP9-mediated NASH and to analyze the underlying mechanism. In vivo, mice that were administered adeno-associated viral (AAV) vectors containing a null transgene (AAV-null) or the BMP9 transgene (AAV-BMP9) were divided into methionine- and choline-deficient (MCD) and control diet (CD) groups, and they were administered either control liposomes or clodronate liposomes via tail vein injection, the latter to deplete macrophages. The mice were sacrificed after 4 weeks of MCD diet feeding. In vitro, RAW264.7 cells were pretreated with or without BAY11-7085 (an NF-κB inhibitor) and stimulated with recombinant human BMP9 (rh-BMP9). To explore the underlying mechanism of action of BMP9, primary human monocyte-derived macrophages were additionally investigated and immunohistochemistry, biochemical assays, qRT-PCR, and Western blotting were used. The characteristics of NASH-related inflammation were assessed by hepatic histological analysis. Serum AST and ALT and hepatic triglyceride were examined by biochemical assays. We found that the expression of M1 macrophage genes (including CD86, IL1β, IL6, MCP-1 and TNFα) and the number of M1 macrophages (iNOS+ macrophages) in the liver were significantly elevated after BMP9 overexpression and BMP9 directly upregulated TLR4 expression in MCD-induced NASH. These effects were eliminated by macrophage depletion. In vitro, we discovered that BMP9 enhanced the nuclear translocation of NF-κB to induce macrophage M1 polarization in RAW264.7 cells and it promoted LPS-mediated activation of the NF-κB pathway in primary human macrophages. Taken together, this study demonstrates that BMP9 promotes NASH development by directly acting on macrophages.

The Role of Bone Morphogenetic Protein 9 in Nonalcoholic Fatty Liver Disease in Mice

Background and Aims: It’s reported that bone morphogenetic protein 9 (BMP9) played an important role in lipid and glucose metabolism, but the role of BMP9 in nonalcoholic fatty liver disease (NAFLD) is unclear. Here, we evaluated the therapeutic efficacy of recombined BMP9 in NAFLD mice and investigated the potential mechanism.

Methods: The effects of recombinant BMP9 on NAFLD were assessed in HFD-induced NAFLD mice. C57BL/6 mice were administrated with high-fat diet (HFD) for 12 weeks. In the last 4 weeks, mice were treated with PBS or recombined BMP9 once daily. Insulin sensitivity was evaluated by glucose tolerance test (GTT) and insulin tolerance test (ITT) at the end of the 12th week. Then NAFLD related indicators were assessed by a variety of biological methods, including histology, western blotting, real-time PCR, RNA-seq and assay for transposase-accessible chromatin using sequencing (ATAC-seq) analyses.

Results: BMP9 reduced obesity, improved glucose metabolism, alleviated hepatic steatosis and decreased liver macrophages infiltration in HFD mice. RNA-seq showed that Cers6, Cidea, Fabp4 involved in lipid and glucose metabolism and Fos, Ccl2, Tlr1 involved in inflammatory response downregulated significantly after BMP9 treatment in HFD mouse liver. ATAC-seq showed that chromatin accessibility on promoters of Cers6, Fabp4, Ccl2 and Fos decreased after BMP9 treatment in HFD mouse liver. KEGG pathway analysis of dysregulated genes in RNA-seq and integration of RNA-seq and ATAC-seq showed that TNF signaling pathway and Toll-like receptor signaling pathway decreased in BMP9 treated HFD mouse liver.

Conclusion: Our data revealed that BMP9 might alleviate NAFLD via improving glucose and lipid metabolism, decreasing inflammatory response and reshaping chromatin accessibility in HFD mouse liver. BMP9 downregulate genes related to lipid metabolism, glucose metabolism and inflammation expression, at least partially via decreasing promoter chromatin accessibility of Cers6, Fabp4, Fos and Tlr1. BMP9 may also reduce the expression of liver Ccl2, thereby changing the number or composition of liver macrophages, and ultimately reducing liver inflammation. The effect of BMP9 on NAFLD might be all-round, and not limit to lipid and glucose metabolism. Therefore, the underlying mechanism needs to be studied in detail further.

Emerging Role of Bone Morphogenetic Protein 4 in Metabolic Disorders

Bone morphogenetic proteins (BMPs) are a group of signaling molecules that belong to the TGF-β superfamily. Initially discovered for their ability to induce bone formation, BMPs are known to play a diverse and critical array of biological roles. We here focus on recent evidence showing that BMP4 is an important regulator of white/beige adipogenic differentiation with important consequences for thermogenesis, energy homeostasis, and development of obesity in vivo. BMP4 is highly expressed in, and released by, human adipose tissue, and serum levels are increased in obesity. Recent studies have now shown BMP4 to play an important role not only for white/beige/brown adipocyte differentiation and thermogenesis but also in regulating systemic glucose homeostasis and insulin sensitivity. It also has important suppressive effects on hepatic glucose production and lipid metabolism. Cellular BMP4 signaling/action is regulated by both ambient cell/systemic levels and several endogenous and systemic BMP antagonists. Reduced BMP4 signaling/action can contribute to the development of obesity, insulin resistance, and associated metabolic disorders. In this article, we summarize the pleiotropic functions of BMP4 in the pathophysiology of these diseases and also consider the therapeutic implications of targeting BMP4 in the prevention/treatment of obesity and its associated complications.

SATB2: A versatile transcriptional regulator of craniofacial and skeleton development, neurogenesis and tumorigenesis, and its applications in regenerative medicine

SATB2 (special AT-rich sequence-binding protein 2) is a member of the special AT-rich binding protein family. As a transcription regulator, SATB2 mainly integrates higher-order chromatin organization. SATB2 expression appears to be tissue- and stage-specific, and is governed by several cellular signaling molecules and mediators. Expressed in branchial arches and osteoblast-lineage cells, SATB2 plays a significant role in craniofacial pattern and skeleton development. In addition to regulating osteogenic differentiation, SATB2 also displays versatile functions in neural development and cancer progression. As an osteoinductive factor, SATB2 holds great promise in improving bone regeneration toward bone defect repair. In this review, we have summarized our current understanding of the physiological and pathological functions of SATB2 in craniofacial and skeleton development, neurogenesis, tumorigenesis and regenerative medicine.

Potential roles of bone morphogenetic protein-9 in glucose and lipid homeostasis

Bone morphogenetic protein-9 (BMP-9) is a novel cytokine which is cloned from the fetal mouse liver cDNA library and belongs to the member of the transforming growth factor-β (TGF-β) superfamily. BMP-9 is mainly secreted by the liver and exerts a variety of physiological functions. In this review, we present the latest knowledge on the biochemistry of BMP-9 and its role in glucose metabolism and lipid homeostasis. We introduced the expression site, structure, synthesis, and secretion of BMP-9, as well as BMP-9 signaling pathway. We also discuss the effects of BMP-9 on glucose metabolism and lipid metabolism in different organs. BMP-9 can regulate glucose and lipid homeostasis in the body by inhibiting liver gluconeogenesis, transforming white adipose tissue to brown adipose tissue, promoting muscle glycogen synthesis, increasing the uptake and utilization of glucose by muscle tissue, increasing liver and adipose tissue insulin sensitivity, promoting insulin synthesis and secretion, inhibiting liver lipid deposition, and playing a leptin-like role. Finally, through the results of animal intervention studies and human clinical studies in the review, we deeply understand the association of BMP-9 with obesity, insulin resistance (IR), type 2 diabetes, and non-alcoholic fatty liver disease (NAFLD), which provides new ideas for the prevention and treatment of diseases.

Triiodothyronine Potentiates BMP9-Induced Osteogenesis in Mesenchymal Stem Cells Through the Activation of AMPK/p38 Signaling

Thyroid hormone (TH), triiodothyronine (T3), and thyroxine (T4), which are released from the thyroid, control many cellular processes in various cell types. It is worth noting that TH plays a complex role in skeletal metabolic balance, and few studies have investigated whether TH exerts any effects on osteogenesis in bone mesenchymal stem cells (MSCs). We explored the effects of T3 on bone morphogenetic protein 9 (BMP9)-induced osteogenesis, which process is considered the most important in the osteogenic differentiation of C3H10T1/2 cells. In vitro osteogenesis was analyzed by alkaline phosphatase (ALP) activity and staining, bone mineralisation, and osteocalcin and osteopontin expression. Fetal limb explant cultures and ectopic MSC implantation further confirmed the role of T3. Finally, we examined the effect of AMPK/p38 signaling on the osteoblastic differentiation. T3 synergizes with BMP9 to enhance osteogenic marker expression induced by BMP9. Furthermore, T3 promotes BMP9-induced bone formation by fetal limb explant cultures and ectopic MSC implantation. Co-treatment with BMP9 and T3 can promote AMPK and p38 phosphorylation, and pretreatment with the AMPK inhibitor compound C and siRNA can abolish phosphorylation of p38 and BMP9+T3-induced ALP activity. Our results suggest that BMP9 and T3 promote osteogenic differentiation at least partially via the activation of the AMPK/p38 signaling pathway.

Leptin Potentiates BMP9-Induced Osteogenic Differentiation of Mesenchymal Stem Cells Through the Activation of JAK/STAT Signaling

Mesenchymal stem cells (MSCs) are multipotent progenitors that have the ability to differentiate into multiple lineages, including bone, cartilage, and fat. We previously demonstrated that the least known bone morphogenetic protein (BMP)9 (also known as growth differentiation factor 2) is one of the potent osteogenic factors that can induce both osteogenic and adipogenic differentiation of MSCs. Nonetheless, the molecular mechanism underlying BMP9 action remains to be fully understood. Leptin is an adipocyte-derived hormone in direct proportion to the amount of body fat, and exerts pleiotropic functions, such as regulating energy metabolism, bone mass, and mineral density. In this study, we investigate the potential effect of leptin signaling on BMP9-induced osteogenic differentiation of MSCs. We found that exogenous leptin potentiated BMP9-induced osteogenic differentiation of MSCs both in vitro and in vivo, while inhibiting BMP9-induced adipogenic differentiation. BMP9 was shown to induce the expression of leptin and leptin receptor in MSCs, while exogenous leptin upregulated BMP9 expression in less differentiated MSCs. Mechanistically, we demonstrated that a blockade of JAK signaling effectively blunted leptin-potentiated osteogenic differentiation induced by BMP9. Taken together, our results strongly suggest that leptin may potentiate BMP9-induced osteogenesis by cross-regulating BMP9 signaling through the JAK/STAT signaling pathway in MSCs. Thus, it is conceivable that a combined use of BMP9 and leptin may be explored as a novel approach to enhancing efficacious bone regeneration and fracture healing.

Inhibition of MAPK and STAT3-SOCS3 by Sakuranetin Attenuated Chronic Allergic Airway Inflammation in Mice

Asthma allergic disease is caused by airway chronic inflammation. Some intracellular signaling pathways, such as MAPK and STAT3-SOCS3, are involved in the control of airway inflammation in asthma. The flavonoid sakuranetin demonstrated an anti-inflammatory effect in different asthma models. Our aim was to clarify how sakuranetin treatment affects MAPK and STAT3-SOCS3 pathways in a murine experimental asthma model. Mice were submitted to an asthma ovalbumin-induction protocol and were treated with vehicle, sakuranetin, or dexamethasone. We assayed the inflammatory profile, mucus production, and serum antibody, STAT3-SOCS3, and MAPK levels in the lungs. Morphological alterations were also evaluated in the liver. LPS-stimulated RAW 264.7 cells were used to evaluate the effects of sakuranetin on nitric oxide (NO) and cytokine production. In vivo, sakuranetin treatment reduced serum IgE levels, lung inflammation (eosinophils, neutrophils, and Th2/Th17 cytokines), and respiratory epithelial mucus production in ovalbumin-sensitized animals. Considering possible mechanisms, sakuranetin inhibits the activation of ERK1/2, JNK, p38, and STAT3 in the lungs. No alterations were found in the liver for treated animals. Sakuranetin did not modify in vitro cell viability in RAW 264.7 and reduced NO release and gene expression of IL-1β and IL-6 induced by LPS in these cells. In conclusion, our data showed that the inhibitory effects of sakuranetin on eosinophilic lung inflammation can be due to the inhibition of Th2 and Th17 cytokines and the inhibition of MAPK and STAT3 pathways, reinforcing the idea that sakuranetin can be considered a relevant candidate for the treatment of inflammatory allergic airway disease.

The wonders of BMP9: From mesenchymal stem cell differentiation, angiogenesis, neurogenesis, tumorigenesis, and metabolism to regenerative medicine

Although bone morphogenetic proteins (BMPs) initially showed effective induction of ectopic bone growth in muscle, it has since been determined that these proteins, as members of the TGF-β superfamily, play a diverse and critical array of biological roles. These roles include regulating skeletal and bone formation, angiogenesis, and development and homeostasis of multiple organ systems. Disruptions of the members of the TGF-β/BMP superfamily result in severe skeletal and extra-skeletal irregularities, suggesting high therapeutic potential from understanding this family of BMP proteins. Although it was once one of the least characterized BMPs, BMP9 has revealed itself to have the highest osteogenic potential across numerous experiments both in vitro and in vivo, with recent studies suggesting that the exceptional potency of BMP9 may result from unique signaling pathways that differentiate it from other BMPs. The effectiveness of BMP9 in inducing bone formation was recently revealed in promising experiments that demonstrated efficacy in the repair of critical sized cranial defects as well as compatibility with bone-inducing bio-implants, revealing the great translational promise of BMP9. Furthermore, emerging evidence indicates that, besides its osteogenic activity, BMP9 exerts a broad range of biological functions, including stem cell differentiation, angiogenesis, neurogenesis, tumorigenesis, and metabolism. This review aims to summarize our current understanding of BMP9 across biology and the body.

Role of bone morphogenetic protein-9 in the regulation of glucose and lipid metabolism

Bone morphogenetic protein (BMP)-9 has been reported to regulate energy balance in vivo. However, the mechanisms underlying BMP9-mediated regulation of energy balance remain incompletely understood. Here, we investigated the role of BMP9 in energy metabolism. In the current study, we found that hepatic BMP9 expression was down-regulated in insulin resistance (IR) mice and in patients who are diabetic. In mice fed a high-fat diet (HFD), the overexpression of hepatic BMP9 improved glucose tolerance and IR. The expression of gluconeogenic genes was down-regulated, whereas the level of insulin signaling molecule phosphorylation was increased in the livers of Adenovirus-BMP9-treated mice and glucosamine-treated hepatocytes. Furthermore, BMP9 overexpression ameliorated triglyceride accumulation and inhibited the expression of lipogenic genes in both human hepatocellular carcinoma HepG2 cells treated with a fatty acid mixture as well as the livers of HFD-fed mice. In hepatocytes isolated from sterol regulatory element-binding protein (SREBP)-1c knockout mice, the effects of BMP9 were ablated. Mechanistically, BMP9 inhibited SREBP-1c expression through the inhibition of liver X receptor response element 1 activity in the SREBP-1c promoter. Taken together, our results show that BMP9 is an important regulator of hepatic glucose and lipid metabolism.-Yang, M., Liang, Z., Yang, M., Jia, Y., Yang, G., He, Y., Li, X., Gu, H. F., Zheng, H., Zhu, Z., Li, L. Role of bone morphogenetic protein-9 in the regulation of glucose and lipid metabolism.

Circulating bone morphogenetic protein-9 levels are associated with hypertension and insulin resistance in humans

It has been demonstrated that bone morphogenetic protein-9 (BMP-9) may have an important role in vascular development and stability. However, the association of circulating BMP-9 with essential hypertension (HTN) has not been established in humans. The objective of this study is to observe the changes of circulating BMP-9 levels in patients with HTN and to investigate the association of circulation BMP-9 and insulin resistance (IR) in a cross-sectional study. Two hundred twenty-five individuals, including 132 patients with hypertension, and 93 healthy controls, were included in the present study. Circulating BMP-9 concentrations were measured with an ELISA kit. The association of circulating BMP-9 with other parameters was analyzed. When compared with healthy subjects, circulating BMP-9 concentrations were markedly lower in HTN patients (46.20 [31.85-62.80] vs. 77.21 [39.33-189.15], P < .01) and correlated negatively with blood pressure and the homeostasis model assessment of insulin resistance (P < .05 or P < .01). Decreasing levels of BMP-9 were independently and markedly related to HTN. In a multiple linear regression analysis, only systolic blood pressure and free fatty acid concentrations were independently associated with circulating BMP-9. Our findings suggest that BMP-9 may be a serum biomarker for HTN and IR.

Circulating bone morphogenetic protein-9 in relation to metabolic syndrome and insulin resistance

Our objective is to determine circulating Bone morphogenetic protein-9(BMP-9) levels in subjects with Metabolic Syndrome (MetS) and examine the relationship between BMP-9 and conventional markers for MetS and insulin resistance (IR). A total of 362 newly diagnosed patients with MetS along with healthy controls were recruited for this cross-sectional study. Circulating BMP-9 levels were measured by ELISA. Circulating BMP-9 levels were significantly lower in MetS patients compared to those of the healthy controls. BMP-9 was associated negatively with Waist hip ratio (WHR), fasting blood glucose (FBG), 2-hour blood glucose after glucose overload (2h-OGTT), HbA1c, triglyceride (TG) levels and HOMA-IR and positively with free fatty acid (FFA) and HDL after control for age and sex. In a multiple linear regression, BMP-9 was independently associated with type 2 diabetes mellitus (T2DM), HOMA-IR and FFA. Binary logistic regression showed that plasma BMP-9 concentrations were significantly associated with MetS even after controlling for anthropometric variables and lipid profiles. In addition, circulating BMP-9 levels reduced progressively with an increasing number of MetS components. The best cutoff values for circulating BMP-9 to predict MetS was 56.6 ng/L. Circulating BMP-9 levels were associated with the key components of MetS and IR.

Identification of novel biomarkers to monitor β-cell function and enable early detection of type 2 diabetes risk

A decline in β-cell function is a prerequisite for the development of type 2 diabetes, yet the level of β-cell function in individuals at risk of the condition is rarely measured. This is due, in part, to the fact that current methods for assessing β-cell function are inaccurate, prone to error, labor-intensive, or affected by glucose-lowering therapy. The aim of the current study was to identify novel circulating biomarkers to monitor β-cell function and to identify individuals at high risk of developing β-cell dysfunction. In a nested case-control study from the Relationship between Insulin Sensitivity and Cardiovascular disease (RISC) cohort (n = 1157), proteomics and miRNA profiling were performed on fasting plasma samples from 43 individuals who progressed to impaired glucose tolerance (IGT) and 43 controls who maintained normal glucose tolerance (NGT) over three years. Groups were matched at baseline for age, gender, body mass index (BMI), insulin sensitivity (euglycemic clamp) and β-cell glucose sensitivity (mathematical modeling). Proteomic profiling was performed using the SomaLogic platform (Colorado, USA); miRNA expression was performed using a modified RT-PCR protocol (Regulus Therapeutics, California, USA). Results showed differentially expressed proteins and miRNAs including some with known links to type 2 diabetes, such as adiponectin, but also novel biomarkers and pathways. In cross sectional analysis at year 3, the top differentially expressed biomarkers in people with IGT/ reduced β-cell glucose sensitivity were adiponectin, alpha1-antitrypsin (known to regulate adiponectin levels), endocan, miR-181a, miR-342, and miR-323. At baseline, adiponectin, cathepsin D and NCAM.L1 (proteins expressed by pancreatic β-cells) were significantly lower in those that progressed to IGT. Many of the novel prognostic biomarker candidates were within the epithelial-mesenchymal transition (EMT) pathway: for example, Noggin, DLL4 and miR-181a. Further validation studies are required in additional clinical cohorts and in patients with type 2 diabetes, but these results identify novel pathways and biomarkers that may have utility in monitoring β-cell function and/ or predicting future decline, allowing more targeted efforts to prevent and intercept type 2 diabetes.

Intranasal BMP9 Ameliorates Alzheimer Disease-Like Pathology and Cognitive Deficits in APP/PS1 Transgenic Mice

Alzheimer’s disease (AD) is the most common type of dementia and has no effective therapies. Previous studies showed that bone morphogenetic protein 9 (BMP9), an important factor in the differentiation and phenotype maintenance of cholinergic neurons, ameliorated the cholinergic defects resulting from amyloid deposition. These findings suggest that BMP9 has potential as a therapeutic agent for AD. However, the effects of BMP9 on cognitive function in AD and its underlying mechanisms remain elusive. In the present study, BMP9 was delivered intranasally to 7-month-old APP/PS1 mice for 4 weeks. Our data showed that intranasal BMP9 administration significantly improved the spatial and associative learning and memory of APP/PS1 mice. We also found that intranasal BMP9 administration significantly reduced the amyloid β (Aβ) plaques overall, inhibited tau hyperphosphorylation, and suppressed neuroinflammation in the transgenic mouse brain. Furthermore, intranasal BMP9 administration significantly promoted the expression of low-density lipoprotein receptor-related protein 1 (LRP1), an important membrane receptor involved in the clearance of amyloid β via the blood-brain barrier (BBB), and elevated the phosphorylation levels of glycogen synthase kinase-3β (Ser9), which is considered the main kinase involved in tau hyperphosphorylation. Our results suggest that BMP9 may be a promising candidate for treating AD by targeting multiple key pathways in the disease pathogenesis.

Decreased circulating BMP-9 levels in patients with Type 2 diabetes is a signature of insulin resistance

Bone morphogenetic protein 9 (BMP-9) has been demonstrated to improve glucose homoeostasis in diabetic mice. However, no report has demonstrated the relationship of circulating BMP-9 levels with insulin resistance (IR) or Type 2 diabetes mellitus (T2DM) in humans. The objective of the present study was to investigate the relationship between BMP-9 and IR in cross-sectional and interventional studies. Circulating BMP-9 levels were analysed by ELISA in 280 well-characterized individuals. Two-hour oral glucose tolerance test (OGTT) and euglycaemic-hyperinsulinaemic clamp (EHC) were performed in 20 healthy subjects. Acute IR was induced by lipid infusion for 4 h in 20 healthy volunteers. Real-time (RT)-PCR and Western blotting were used to assess mRNA and protein expression of BMP-9. The effect of a glucagon-like peptide-1 (GLP-1) receptor agonist (PEX168) on circulating BMP-9 was investigated in a 24-week treatment trial. Circulating BMP-9 levels were significantly higher in healthy subjects than in newly diagnosed patients with T2DM. Circulating BMP-9 negatively correlated with HbA1c, fasting blood glucose (FBG), OGTT, the area under the curve for glucose (AUC_glucose) and homoeostasis model assessment of insulin resistance (HOMA-IR). Multivariate regression analyses showed that BMP-9 levels were independently associated with non-esterified fatty acid (NEFA) and AUC_glucose Both hyperinsulinaemia and lipid infusion decreased circulating BMP-9 levels. BMP-9 mRNA and protein expressions were significantly decreased in muscle and adipose tissues of T2DM patients. In the placebo treated group, BMP-9 levels continued to decline over time, whereas in the PEX 168 treated groups BMP-9 levels remained stable. Our data suggest that BMP-9 is likely to play an important role in IR in humans.

Putative hormone with anti-obesogenic and insulin-sensitizing effect

It was confirmed that bone morphogenetic protein-9 (BMP-9), like insulin, improves glycemia in diabetic mice and regulates glucose metabolism in hepatocytes, which is why it is proposed as a candidate for the hepatic insulin-sensitizing substance (HISS). Regarding the fact that BMP-9 has a signaling pathway similar to other BMPs as well as insulin, it is expected that BMP-9 would also have certain effects on the liver. In our 2011 hypothesis, we aimed towards BMP-9 as a possible "hepatic insulin-sensitizing substance" (HISS) and in this article, we provide further evidence, derived from existing studies, suggesting that this putative hormone might in fact be none other than BMP-9.

The promise of recombinant BMP ligands and other approaches targeting BMPR-II in the treatment of pulmonary arterial hypertension

Human genetic discoveries offer a powerful method to implicate pathways of major importance to disease pathobiology and hence provide targets for pharmacological intervention. The genetics of pulmonary arterial hypertension (PAH) strongly implicates loss-of-function of the bone morphogenetic protein type II receptor (BMPR-II) signalling pathway and moreover implicates the endothelial cell as a central cell type involved in disease initiation. We and others have described several approaches to restore BMPR-II function in genetic and non-genetic forms of PAH. Of these, supplementation of endothelial BMP9/10 signalling with exogenous recombinant ligand has been shown to hold considerable promise as a novel large molecule biopharmaceutical therapy. Here, we describe the mechanism of action and discuss potential additional effects of BMP ligand therapy.

A flavanone from Baccharis retusa (Asteraceae) prevents elastase-induced emphysema in mice by regulating NF-κB, oxidative stress and metalloproteinases

Background

Pulmonary emphysema is characterized by irreversible airflow obstruction, inflammation, oxidative stress imbalance and lung remodeling, resulting in reduced lung function and a lower quality of life. Flavonoids are plant compounds with potential anti-inflammatory and antioxidant effects that have been used in folk medicine. Our aim was to determine whether treatment with sakuranetin, a flavonoid extracted from the aerial parts of Baccharis retusa, interferes with the development of lung emphysema.

Methods

Intranasal saline or elastase was administered to mice; the animals were then treated with sakuranetin or vehicle 2 h later and again on days 7, 14 and 28. We evaluated lung function and the inflammatory profile in bronchoalveolar lavage fluid (BALF). The lungs were removed to evaluate alveolar enlargement, extracellular matrix fibers and the expression of MMP-9, MMP-12, TIMP-1, 8-iso-PGF-2α and p65-NF-κB in the fixed tissues as well as to evaluate cytokine levels and p65-NF-κB protein expression.

Results

In the elastase-treated animals, sakuranetin treatment reduced the alveolar enlargement, collagen and elastic fiber deposition and the number of MMP-9- and MMP-12-positive cells but increased TIMP-1 expression. In addition, sakuranetin treatment decreased the inflammation and the levels of TNF-α, IL-1β and M-CSF in the BALF as well as the levels of NF-κB and 8-iso-PGF-2α in the lungs of the elastase-treated animals. However, this treatment did not affect the changes in lung function.

Conclusion

These data emphasize the importance of oxidative stress and metalloproteinase imbalance in the development of emphysema and suggest that sakuranetin is a potent candidate that should be further investigated as an emphysema treatment. This compound may be useful for counteracting lung remodeling and oxidative stress and thus attenuating the development of emphysema.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-015-0233-3) contains supplementary material, which is available to authorized users.

Pulmonary inflammation is regulated by the levels of the vesicular acetylcholine transporter

Acetylcholine (ACh) plays a crucial role in physiological responses of both the central and the peripheral nervous system. Moreover, ACh was described as an anti-inflammatory mediator involved in the suppression of exacerbated innate response and cytokine release in various organs. However, the specific contributions of endogenous release ACh for inflammatory responses in the lung are not well understood. To address this question we have used mice with reduced levels of the vesicular acetylcholine transporter (VAChT), a protein required for ACh storage in secretory vesicles. VAChT deficiency induced airway inflammation with enhanced TNF-α and IL-4 content, but not IL-6, IL-13 and IL-10 quantified by ELISA. Mice with decreased levels of VAChT presented increased collagen and elastic fibers deposition in airway walls which was consistent with an increase in inflammatory cells positive to MMP-9 and TIMP-1 in the lung. In vivo lung function evaluation showed airway hyperresponsiveness to methacholine in mutant mice. The expression of nuclear factor-kappa B (p65-NF-kB) in lung of VAChT-deficient mice were higher than in wild-type mice, whereas a decreased expression of janus-kinase 2 (JAK2) was observed in the lung of mutant animals. Our findings show the first evidence that cholinergic deficiency impaired lung function and produce local inflammation. Our data supports the notion that cholinergic system modulates airway inflammation by modulation of JAK2 and NF-kB pathway. We proposed that intact cholinergic pathway is necessary to maintain the lung homeostasis.

Effects of platycodins on liver complications of type 2 diabetes

The aim of the current study was to investigate the therapeutic effects and mechanism of platycodin in liver complications of type 2 diabetes. All rats were randomly divided into two groups: The control group (normal diet) and the model group (a high‑fat and high‑sugar diet). The model group was injected with 2% streptozocin (25 mg/kg body weight) through the tail vein following 4 weeks of dieting. After a total of 8 weeks of dieting, fasting blood glucose (FBG) and liver function were examined. The high‑fat and high‑sugar diet was continued in the successful model rats, which were randomly divided into four groups and treated with the following doses of platycodins: The untreated, and 50, 100 and 200 mg/kg body weight/day groups. Platycodins treatment lasted for 12 weeks. Platycodins treatment at a dose of 200 mg/kg body weight/day reduced the FBG, glutamate pyruvate transaminase (GPT), glutamic oxalacetic transaminase, triglycerides, total cholesterol (TC), low‑density lipoprotein (LDL) and liver index levels compared with the untreated group (P<0.05), while the high‑density lipoprotein levels increased (P<0.05). Furthermore, FBG, GPT, TC and LDL levels were returned to the normal level. This dose also increased the expression of BMP‑9 mRNA and BMP‑9 protein, and reduced the expression of Smad‑4 mRNA and Smad‑4 protein. These findings indicate that platycodins can rectify disorders of blood glucose and lipid metabolism, improve liver index and protect liver function in liver complications of type 2 diabetes. The current study suggests that this therapeutic effect is mediated through the BMP‑9/Smad‑4 pathway.

Potential roles of bone morphogenetic protein (BMP)-9 in human liver diseases

Bone morphogenetic proteins (BMP-2 to BMP-15) belong to the Transforming Growth Factor (TGF)-β superfamily and, besides their well-documented roles during embryogenesis and bone formation, some of them have recently been described to be involved in the pathogenesis of different organs, including the liver. The role of BMPs in liver damage responses including hepatocellular carcinoma (HCC) development has only begun to be addressed and strong evidence supports the concept of a pro-tumorigenic role of BMP signaling in HCC cells. BMP-9 (also termed Growth and Differentiation Factor (GDF)-2) represents the most recently discovered member of the BMP family. We have previously demonstrated that in HCC patient samples BMP-9 expression was positively associated with the tumor seize (“T stage”) and that it enhanced cell migration and induced epithelial to mesenchymal transition (EMT) in HCC cells in vitro. In another study we recently found that BMP-9 promotes growth in HCC cells, but not in non-transformed hepatocytes. Published as well as unpublished results obtained with primary hepatocytes support the concept of a dual function of BMP-9 in the liver: while in primary, non-malignant cells BMP-9 stabilizes the epithelial phenotype and inhibits proliferation, in HCC cells it induces cell growth and the acquisition of a migratory phenotype. In this review article we summarize current knowledge about BMPs in liver diseases, with special focus on the role of BMP-9 in HCC development and progression, that may provide new clues for a better understanding of the contribution of BMP-signaling to chronic liver diseases.

BMP signaling in mesenchymal stem cell differentiation and bone formation

Bone morphogenetic proteins (BMPs) are members of the TGF-β superfamily and have diverse functions during development and organogenesis. BMPs play a major role in skeletal development and bone formation, and disruptions in BMP signaling cause a variety of skeletal and extraskeletal anomalies. Several knockout models have provided insight into the mechanisms responsible for these phenotypes. Proper bone formation requires the differentiation of osteoblasts from mesenchymal stem cell (MSC) precursors, a process mediated in part by BMP signaling. Multiple BMPs, including BMP2, BMP6, BMP7 and BMP9, promote osteoblastic differentiation of MSCs both in vitro and in vivo. BMP9 is one of the most osteogenic BMPs yet is a poorly characterized member of the BMP family. Several studies demonstrate that the mechanisms controlling BMP9-mediated osteogenesis differ from other osteogenic BMPs, but little is known about these specific mechanisms. Several pathways critical to BMP9-mediated osteogenesis are also important in the differentiation of other cell lineages, including adipocytes and chondrocytes. BMP9 has also demonstrated translational promise in spinal fusion and bone fracture repair. This review will summarize our current knowledge of BMP-mediated osteogenesis, with a focus on BMP9, by presenting recently completed work which may help us to further elucidate these pathways.

Bone morphogenetic protein-9 induces epithelial to mesenchymal transition in hepatocellular carcinoma cells

Epithelial-mesenchymal transition (EMT) is an important mechanism to initiate cancer invasion and metastasis. Bone morphogenetic protein (BMP)-9 is a member of the transforming growth factor (TGF)-β superfamily. It has been suggested to play a role in cancer development in some non-hepatic tumors. In the present study, two hepatocellular carcinoma (HCC) lines, HLE and HepG2, were treated with BMP-9 in vitro, and phenotypic changes and cell motility were analyzed. In situ hybridization (ISH) and immunohistochemical analyses were performed with human HCC tissue samples in order to assess expression levels of BMP-9. In vivo, BMP-9 protein and mRNA were expressed in all the tested patients to diverse degrees. At the protein level, mildly positive (1 + ) BMP-9 staining could be observed in 25/41 (61%), and moderately to strongly positive (2 + ) in 16/41 (39%) of the patients. In 27/41 (65%) patients, the BMP-9 protein expression level was consistent with the mRNA expression level as measured by ISH. In those patients with 2 + protein level, nuclear pSmad1 expression in cancer cells was also significantly increased. Expression of BMP-9 was positively related to nuclear Snail expression and reversely correlated to cell surface E-cadherin expression, although this did not reach statistical significance. Expression levels of BMP-9 were significantly associated with the T stages of the investigated tumors and high levels of BMP-9 were detected by immunofluorescence especially at the tumor borders in samples from an HCC mouse model. In vitro, BMP-9 treatment caused a reduction of E-cadherin and ZO-1 and an induction of Vimentin and Snail expression. Furthermore, cell migration was enhanced by BMP-9 in both HCC cell lines. These results imply that EMT induced by BMP-9 is related to invasiveness of HCC.

The regulation of Rasd1 expression by glucocorticoids and prolactin controls peripartum maternal insulin secretion

The transition from gestation to lactation is characterized by a robust adaptation of maternal pancreatic β-cells. Consistent with the loss of β-cell mass, glucose-induced insulin secretion is down-regulated in the islets of early lactating dams. Extensive experimental evidence has demonstrated that the surge of prolactin is responsible for the morphofunctional remodeling of the maternal endocrine pancreas during pregnancy, but the precise molecular mechanisms by which this phenotype is rapidly reversed after delivery are not completely understood. This study investigated whether glucocorticoid-regulated expression of Rasd1/Dexras, a small inhibitory G protein, is involved in this physiological plasticity. Immunofluorescent staining demonstrated that Rasd1 is localized within pancreatic β-cells. Rasd1 expression in insulin-secreting cells was increased by dexamethasone and decreased by prolactin. In vivo data confirmed that Rasd1 expression is decreased in islets from pregnant rats and increased in islets from lactating mothers. Knockdown of Rasd1 abolished the inhibitory effects of dexamethasone on insulin secretion and the protein kinase A, protein kinase C, and ERK1/2 pathways. Chromatin immunoprecipitation experiments revealed that glucocorticoid receptor (GR) and signal transducer and activator of transcription 5b (STAT5b) cooperatively mediate glucocorticoid-induced Rasd1 expression in islets. Prolactin inhibited the stimulatory effect of GR/STAT5b complex on Rasd1 transcription. Overall, our data indicate that the stimulation of Rasd1 expression by glucocorticoid at the end of pregnancy reverses the increased insulin secretion that occurs during pregnancy. Prolactin negatively regulates this pathway by inhibiting GR/STAT5b transcriptional activity on the Rasd1 gene.

Maternal melatonin programs the daily pattern of energy metabolism in adult offspring

Background

Shift work was recently described as a factor that increases the risk of Type 2 diabetes mellitus. In addition, rats born to mothers subjected to a phase shift throughout pregnancy are glucose intolerant. However, the mechanism by which a phase shift transmits metabolic information to the offspring has not been determined. Among several endocrine secretions, phase shifts in the light/dark cycle were described as altering the circadian profile of melatonin production by the pineal gland. The present study addresses the importance of maternal melatonin for the metabolic programming of the offspring.

Methodology/Principal Findings

Female Wistar rats were submitted to SHAM surgery or pinealectomy (PINX). The PINX rats were divided into two groups and received either melatonin (PM) or vehicle. The SHAM, the PINX vehicle and the PM females were housed with male Wistar rats. Rats were allowed to mate and after weaning, the male and female offspring were subjected to a glucose tolerance test (GTT), a pyruvate tolerance test (PTT) and an insulin tolerance test (ITT). Pancreatic islets were isolated for insulin secretion, and insulin signaling was assessed in the liver and in the skeletal muscle by western blots. We found that male and female rats born to PINX mothers display glucose intolerance at the end of the light phase of the light/dark cycle, but not at the beginning. We further demonstrate that impaired glucose-stimulated insulin secretion and hepatic insulin resistance are mechanisms that may contribute to glucose intolerance in the offspring of PINX mothers. The metabolic programming described here occurs due to an absence of maternal melatonin because the offspring born to PINX mothers treated with melatonin were not glucose intolerant.

Conclusions/Significance

The present results support the novel concept that maternal melatonin is responsible for the programming of the daily pattern of energy metabolism in their offspring.

Mechanistic evaluation of the insulin response in H4IIE hepatoma cells: new endpoints for toxicity testing?

This study was designed to evaluate if the rat H4IIE hepatoma cell line is a physiologically relevant model to study hepatic insulin responses to hint at its prospective application in pollutant-related insulin resistance research. DNA microarray analysis, real-time PCR and flow cytometric cell cycle analysis were used to assess the relevance of the insulin response in H4IIE cells. Insulin dose dependently stimulated H4IIE growth and time dependently altered the expression of the known insulin responsive genes: Fasn, Pck1 and Irs2. Microarray analysis performed on cells exposed to insulin (100nM) for 6h and 24h showed that genes related to carbohydrate and lipid metabolism were most profoundly afflicted, in accordance with in vivo hepatic insulin action. Since changes in carbohydrate and lipid metabolism are pivotal in the pathogenesis of insulin resistance, the presence of a physiological relevant insulin response in H4IIE cells pleads for further testing of its potential use in research on pollutant-driven insulin resistance.

BMPs and their clinical potentials

Bone morphogenetic protein (BMP) signaling in diseases is the subject of an overwhelming array of studies. BMPs are excellent targets for treatment of various clinical disorders. Several BMPs have already been shown to be clinically beneficial in the treatment of a variety of conditions, including BMP-2 and BMP-7 that have been approved for clinical application in nonunion bone fractures and spinal fusions. With the use of BMPs increasingly accepted in spinal fusion surgeries, other therapeutic approaches targeting BMP signaling are emerging beyond applications to skeletal disorders. These approaches can further utilize next-generation therapeutic tools such as engineered BMPs and ex vivo- conditioned cell therapies. In this review, we focused to provide insights into such clinical potentials of BMPs in metabolic and vascular diseases, and in cancer. [BMB reports 2011; 44(10): 619-634].

Hepatoregenerative role of bone morphogenetic protein-9

Bone morphogenetic protein-9 (BMP-9) is a member of the transforming growth factor beta (TGF-β) superfamily of cytokines, which regulate cell growth and differentiation during embryogenesis. Apart of that, the hypoglycemic potential of BMP-9 is of great interest. It has been confirmed that BMP-9, like insulin, improves glycemia in diabetic mice and regulates directional glucose metabolism in hepatocytes; therefore it is proposed to be a candidate hepatic insulin-sensitizing substance (HISS). In liver fibrosis, due to the portocaval shunt, insulin bypasses the organ and the liver undergoes atrophy. Parenteral administration of insulin reverses atrophy by stimulating mitogenic activity of the hepatocytes. Because BMP-9 has a signaling pathway similar to other BMPs and insulin, it is to be expected that BMP-9 has a certain regenerative role in the liver, supporting the above-mentioned is evidence of BMP-9 expression in Dissè's spaces and BMP-7's mitogenic activity in mucosal cells. However, further studies are needed to confirm the possible regenerative role of BMP-9.

Absence of melatonin induces night-time hepatic insulin resistance and increased gluconeogenesis due to stimulation of nocturnal unfolded protein response

It is known that the circadian rhythm in hepatic phosphoenolpyruvate carboxykinase expression (a limiting catalytic step of gluconeogenesis) and hepatic glucose production is maintained by both daily oscillation in autonomic inputs to the liver and night feeding behavior. However, increased glycemia and reduced melatonin (Mel) levels have been recently shown to coexist in diabetic patients at the end of the night period. In parallel, pinealectomy (PINX) is known to cause glucose intolerance with increased basal glycemia exclusively at the end of the night. The mechanisms that underlie this metabolic feature are not completely understood. Here, we demonstrate that PINX rats show night-time hepatic insulin resistance characterized by reduced insulin-stimulated RAC-α serine/threonine-protein kinase phosphorylation and increased phosphoenolpyruvate carboxykinase expression. In addition, PINX rats display increased conversion of pyruvate into glucose at the end of the night. The regulatory mechanism suggests the participation of unfolded protein response (UPR), because PINX induces night-time increase in activating transcription factor 6 expression and prompts a circadian fashion of immunoglobulin heavy chain-binding protein, activating transcription factor 4, and CCAAT/enhancer-binding protein-homologous protein expression with Zenith values at the dark period. PINX also caused a night-time increase in Tribble 3 and regulatory-associated protein of mammalian target of rapamycin; both were reduced in liver of PINX rats treated with Mel. Treatment of PINX rats with 4-phenyl butyric acid, an inhibitor of UPR, restored night-time hepatic insulin sensitivity and abrogated gluconeogenesis in PINX rats. Altogether, the present data show that a circadian oscillation of UPR occurs in the liver due to the absence of Mel. The nocturnal UPR activation is related with night-time hepatic insulin resistance and increased gluconeogenesis in PINX rats.

Cross talk between insulin and bone morphogenetic protein signaling systems in brown adipogenesis

Both insulin and bone morphogenetic protein (BMP) signaling systems are important for adipocyte differentiation. Analysis of gene expression in BMP7-treated fibroblasts revealed a coordinated change in insulin signaling components by BMP7. To further investigate the cross talk between insulin and BMP signaling systems in brown adipogenesis, we examined the effect of BMP7 in insulin receptor substrate 1 (IRS-1)-deficient brown preadipocytes, which exhibit a severe defect in differentiation. Treatment of these cells with BMP7 for 3 days prior to adipogenic induction restored differentiation and expression of brown adipogenic markers. The high level of adipogenic inhibitor preadipocyte factor 1 (Pref-1) in IRS-1-null cells was markedly reduced by 3 days of BMP7 treatment, and analysis of the 1.3-kb pref-1 promoter revealed 9 putative Smad binding elements (SBEs), suggesting that BMP7 could directly suppress Pref-1 expression, thereby allowing the initiation of the adipogenic program. Using a series of sequential deletion mutants of the pref-1 promoter linked to the luciferase gene and chromatin immunoprecipitation, we demonstrate that the promoter-proximal SBE (-192/-184) was critical in mediating BMP7's suppressive effect on pref-1 transcription. Together, these data suggest cross talk between the insulin and BMP signaling systems by which BMP7 can rescue brown adipogenesis in cells with insulin resistance.

Smad5 regulates Akt2 expression and insulin-induced glucose uptake in L6 myotubes

Insulin-induced glucose uptake by skeletal muscle results from Akt2 activation and is severely impaired during insulin resistance. Recently, we and others have demonstrated that BMP9 improves glucose homeostasis in diabetic and non-diabetic rodents. However, the mechanism by which BMP9 modulates insulin action remains unknown. Here we demonstrate that Smad5, a transcription factor activated by BMP9, and Akt2, are upregulated in differentiated L6 myotubes. Smad5, rather than Smad1/8, is downregulated "in vivo" and "in vitro" by dexamethasone. Smad5 knockdown decreased Akt2 expression and serine phosphorylation and insulin-induced glucose uptake, and increased the expression of the lipid phosphatase Ship2. Additionally, binding of Smad5 to Akt2 gene is decreased in dexamethasone-treated rats and increased in L6 myotubes compared to myoblasts. The present study indicates that Smad5 regulates glucose uptake in skeletal muscle by controlling Akt2 expression and phosphorylation. These finding reveals Smad5 as a potential target for the therapeutic of type 2 diabetes.

Autocrine bone morphogenetic protein-9 signals through activin receptor-like kinase-2/Smad1/Smad4 to promote ovarian cancer cell proliferation

Bone morphogenetic proteins (BMPs) act as central regulators of ovarian physiology and may be involved in ovarian cancer development. In an effort to understand these processes, we characterized transforming growth factor beta/BMP receptor and Smad expression in immortalized ovarian surface epithelial cells and a panel of ovarian cancer cell lines. These studies prompted us to evaluate the potential role of BMP9 signaling in ovarian cancer. Using small interfering RNA, ligand trap, inhibitor, and ligand stimulation approaches, we show that BMP9 acts as a proliferative factor for immortalized ovarian surface epithelial cells and ovarian cancer cell lines, signaling predominantly through an ALK2/Smad1/Smad4 pathway rather than through ALK1, the major BMP9 receptor in endothelial cells. Importantly, we find that some ovarian cancer cell lines have gained autocrine BMP9 signaling that is required for proliferation. Furthermore, immunohistochemistry analysis of an ovarian cancer tissue microarray reveals that approximately 25% of epithelial ovarian cancers express BMP9, whereas normal human ovarian surface epithelial specimens do not. Our data indicate that BMP9 signaling through ALK2 may be a novel therapeutic target in ovarian cancer.

The RGM/DRAGON family of BMP co-receptors

The BMP signaling pathway controls a number of cell processes during development and in adult tissues. At the cellular level, ligands of the BMP family act by binding a hetero-tetrameric signaling complex, composed of two type I and two type II receptors. BMP ligands make use of a limited number of receptors, which in turn activate a common signal transduction cascade at the intracellular level. A complex regulatory network is required in order to activate the signaling cascade at proper times and locations, and to generate specific downstream effects in the appropriate cellular context. One such regulatory mechanism is the repulsive guidance molecule (RGM) family of BMP co-receptors. This article reviews the current knowledge regarding the structure, regulation, and function of RGMs, focusing on known and potential roles of RGMs in physiology and pathophysiology.