Transcriptional regulation of vascular bone morphogenetic protein by endothelin receptors in early autoimmune diabetes mellitus

A Supportive Role of Mesenchymal Stem Cells on Insulin-Producing Langerhans Islets with a Specific Emphasis on The Secretome

Type 1 Diabetes (T1D) is a chronic autoimmune disease characterized by a gradual destruction of insulin-producing β-cells in the endocrine pancreas due to innate and specific immune responses, leading to impaired glucose homeostasis. T1D patients usually require regular insulin injections after meals to maintain normal serum glucose levels. In severe cases, pancreas or Langerhans islet transplantation can assist in reaching a sufficient β-mass to normalize glucose homeostasis. The latter procedure is limited because of low donor availability, high islet loss, and immune rejection. There is still a need to develop new technologies to improve islet survival and implantation and to keep the islets functional. Mesenchymal stem cells (MSCs) are multipotent non-hematopoietic progenitor cells with high plasticity that can support human pancreatic islet function both in vitro and in vivo and islet co-transplantation with MSCs is more effective than islet transplantation alone in attenuating diabetes progression. The beneficial effect of MSCs on islet function is due to a combined effect on angiogenesis, suppression of immune responses, and secretion of growth factors essential for islet survival and function. In this review, various aspects of MSCs related to islet function and diabetes are described.

The role of bone morphogenetic protein signaling in vascular calcification

Vascular calcification is associated with atherosclerosis, chronic kidney disease, and diabetes, and results from processes resembling endochondral or intramembranous ossification, or from processes that are distinct from ossification. Bone morphogenetic proteins (BMP), as well as other ligands, receptors, and regulators of the transforming growth factor beta (TGFβ) family regulate vascular and valvular calcification by modulating the phenotypic plasticity of multipotent progenitor lineages associated with the vasculature or valves. While osteogenic ligands BMP2 and BMP4 appear to be both markers and drivers of vascular calcification, particularly in atherosclerosis, BMP7 may serve to protect against calcification in chronic kidney disease. BMP signaling regulators such as matrix Gla protein and BMP-binding endothelial regulator protein (BMPER) play protective roles in vascular calcification. The effects of BMP signaling molecules in vascular calcification are context-dependent, tissue-dependent, and cell-type specific. Here we review the current knowledge on mechanisms by which BMP signaling regulates vascular calcification and the potential therapeutic implications.

The Role of Bone Morphogenetic Proteins in Diabetic Complications

The prevalence of diabetes has reached epidemic proportions and is placing a significant burden on healthcare systems globally. Diabetes has a detrimental impact on many organs in the human body, including accelerating the development of micro- and macrovascular complications. Current therapeutic options to treat diabetic complications have their limitations. Importantly, many slow but fail to reverse the progression of diabetic complications. Bone morphogenetic proteins (BMPs) are a highly conserved subgroup of the transforming growth factor β (TGFβ) superfamily, signaling via serine/threonine kinase receptors, that have recently been implicated in glucose homeostasis and insulin resistance in the setting of diabetes. Downstream of the receptors, the signal can be transduced via the canonical Smad-dependent pathway or the noncanonical Smad-independent pathways. BMPs are essential in organ development, tissue homeostasis, and, as expected, disease pathogenesis. In fact, deletion of BMPs can be embryonically lethal or result in severe organ abnormalities. This review outlines the BMP signaling pathway and its relevance to diabetic complications, namely, diabetic nephropathy, diabetes-associated cardiovascular diseases, and diabetic retinopathy. Understanding the complexities of BMP signaling and particularly its tissue-, cellular-, and time-dependent actions will help delineate the underlying pathogenesis of the disease and may ultimately be harnessed in the treatment of diabetes-induced complications. This would replicate progress made in numerous other diseases, including cancer and atherosclerosis.

Inhibition of beta cell growth and function by bone morphogenetic proteins

AIMS/HYPOTHESIS

Impairment of beta cell mass and function is evident in both type 1 and type 2 diabetes. In healthy physiological conditions pancreatic beta cells adapt to the body's increasing insulin requirements by proliferation and improved function. We hypothesised that during the development of diabetes, there is an increase in the expression of inhibitory factors that prevent the beta cells from adapting to the increased need for insulin. We evaluated the effects of bone morphogenetic protein (BMP) 2 and -4 on beta cells.

METHODS

The effects of BMP2 and -4 on beta cell proliferation, apoptosis, gene expression and insulin release were studied in isolated islets of Langerhans from rats, mice and humans. The expression of BMPs was analysed by immunocytochemistry and real-time PCR. The role of endogenous BMP was investigated using a soluble and neutralising form of the BMP receptor 1A.

RESULTS

BMP2 and -4 were found to inhibit basal as well as growth factor-stimulated proliferation of primary beta cells from rats and mice. Bmp2 and Bmp4 mRNA and protein were expressed in islets and regulated by inflammatory cytokines. Neutralisation of endogenous BMP activity resulted in enhanced proliferation of rodent beta cells. The expression of Id mRNAs was induced by BMP4 in rat and human islets. Finally, glucose-induced insulin secretion was significantly impaired in rodent and human islets pre-treated with BMP4, and inhibition of BMP activity resulted in enhanced insulin release.

CONCLUSIONS/INTERPRETATION

These data show that BMP2 and -4 exert inhibitory actions on beta cells in vitro and suggest that BMPs exert regulatory roles of beta cell growth and function.

Boldine improves endothelial function in diabetic db/db mice through inhibition of angiotensin II-mediated BMP4-oxidative stress cascade

BACKGROUND AND PURPOSE

Boldine is a potent natural antioxidant present in the leaves and bark of the Chilean boldo tree. Here we assessed the protective effects of boldine on endothelium in a range of models of diabetes, ex vivo and in vitro.

EXPERIMENTAL APPROACH

Vascular reactivity was studied in mouse aortas from db/db diabetic and normal mice. Reactive oxygen species (ROS) production, angiotensin AT1 receptor localization and protein expression of oxidative stress markers in the vascular wall were evaluated by dihydroethidium fluorescence, lucigenin enhanced-chemiluminescence, immunohistochemistry and Western blot respectively. Primary cultures of mouse aortic endothelial cells, exposed to high concentrations of glucose (30 mmol L(-1) ) were also used.

KEY RESULTS

Oral treatment (20 mg kg(-1) day(-1) , 7 days) or incubation in vitro with boldine (1 μmol L(-1) , 12 h) enhanced endothelium-dependent aortic relaxations of db/db mice. Boldine reversed impaired relaxations induced by high glucose or angiotensin II (Ang II) in non-diabetic mouse aortas while it reduced the overproduction of ROS and increased phosphorylation of eNOS in db/db mouse aortas. Elevated expression of oxidative stress markers (bone morphogenic protein 4 (BMP4), nitrotyrosine and AT1 receptors) were reduced in boldine-treated db/db mouse aortas. Ang II-stimulated BMP4 expression was inhibited by boldine, tempol, noggin or losartan. Boldine inhibited high glucose-stimulated ROS production and restored the decreased phosphorylation of eNOS in mouse aortic endothelial cells in culture.

CONCLUSIONS AND IMPLICATIONS

Boldine reduced oxidative stress and improved endothelium-dependent relaxation in aortas of diabetic mice largely through inhibiting ROS overproduction associated with Ang II-mediated BMP4-dependent mechanisms.

The bone morphogenic protein inhibitor, noggin, reduces glycemia and vascular inflammation in db/db mice

Vascular diseases frequently accompany diabetes mellitus. Based on the current understanding of atherosclerosis as an inflammatory disorder of the vascular wall, it has been speculated that diabetes may accelerate atherosclerosis by inducing a proinflammatory milieu in the vasculature. ANG II and bone morphogenic proteins (BMPs) have been implicated in vascular inflammation. We evaluated the effect of angiotensin receptor blockade by valsartan and BMP inhibition by noggin on markers of vascular inflammation in a mouse model of diabetes. Noggin had no effect on blood pressure but decreased serum glucose levels, whereas valsartan significantly decreased blood pressure, but not serum glucose. Both inhibitors reduced reactive oxygen species production in the aorta. Additionally, noggin and valsartan diminish gene transcription and protein expression of various inflammatory molecules in the vascular wall. These observations indicate that although both inhibitors block superoxide production and have similar effects on inflammatory gene expression, glycemia and blood pressure may represent a secondary target differentially affected by noggin and valsartan. Our data clearly identify the BMP pathway as a potentially potent therapeutic target in diabetic inflammatory vascular disease.

MicroRNAs: Small but amazing, and their association with endothelin

MicroRNAs (miRNAs) are small non-coding RNA molecules involved in the expressional regulation of genes by inhibiting gene translation. MicroRNAs are recruited and incorporated into the miRISC, ribonucleoprotein complex, targeting specific mRNAs through mechanisms specific for a miRNA sequence. Here we review the biogenesis, regulation, and monitoring of miRNAs, as well as the current evidence for potential roles of miRNAs in human diseases associated with activation of the endothelin system. These diseases include cancer, kidney disease, cardiovascular diseases, inflammatory diseases, infectious diseases, and blood diseases, that may all be aggravated by aberrant miRNA expression. In this review we will also discuss regulatory mechanisms determining production of miRNA as well as measuring or targeting miRNAs as potential novel approaches for diagnosis and treatment. Targeting miRNAs possibly will allow one to detect diseases or to interfere with the progression of diseases associated with activation of the endothelin system.

The regulation of valvular and vascular sclerosis by osteogenic morphogens

Vascular calcification increasingly afflicts our aging, dysmetabolic population. Once considered only a passive process of dead and dying cells, vascular calcification has now emerged as a highly regulated form of biomineralization organized by collagenous and elastin extracellular matrices. During skeletal bone formation, paracrine epithelial-mesenchymal and endothelial-mesenchymal interactions control osteochondrocytic differentiation of multipotent mesenchymal progenitor cells. These paracrine osteogenic signals, mediated by potent morphogens of the bone morphogenetic protein and wingless-type MMTV integration site family member (Wnt) superfamilies, are also active in the programming of arterial osteoprogenitor cells during vascular and valve calcification. Inflammatory cytokines, reactive oxygen species, and oxylipids-increased in the clinical settings of atherosclerosis, diabetes, and uremia that promote arteriosclerotic calcification-elicit the ectopic vascular activation of osteogenic morphogens. Specific extracellular and intracellular inhibitors of bone morphogenetic protein-Wnt signaling have been identified as contributing to the regulation of osteogenic mineralization during development and disease. These inhibitory pathways and their regulators afford the development of novel therapeutic strategies to prevent and treat valve and vascular sclerosis.

An autonomous BMP2 regulatory element in mesenchymal cells

BMP2 is a morphogen that controls mesenchymal cell differentiation and behavior. For example, BMP2 concentration controls the differentiation of mesenchymal precursors into myocytes, adipocytes, chondrocytes, and osteoblasts. Sequences within the 3'untranslated region (UTR) of the Bmp2 mRNA mediate a post-transcriptional block of protein synthesis. Interaction of cell and developmental stage-specific trans-regulatory factors with the 3'UTR is a nimble and versatile mechanism for modulating this potent morphogen in different cell types. We show here, that an ultra-conserved sequence in the 3'UTR functions independently of promoter, coding region, and 3'UTR context in primary and immortalized tissue culture cells and in transgenic mice. Our findings indicate that the ultra-conserved sequence is an autonomously functioning post-transcriptional element that may be used to modulate the level of BMP2 and other proteins while retaining tissue specific regulatory elements.

Activation of vascular bone morphogenetic protein signaling in diabetes mellitus

RATIONALE

Diabetes mellitus is frequently complicated by cardiovascular disease, such as vascular calcification and endothelial dysfunction, which have been associated with bone morphogenetic proteins (BMPs).

OBJECTIVE

To determine whether hyperglycemia in vitro and diabetes in vivo promote vascular BMP activity and correlate with vascular calcification.

METHODS AND RESULTS

Increased glucose augmented expression of BMP-2 and BMP-4; the BMP inhibitors matrix Gla protein (MGP) and Noggin; activin-like kinase receptor (ALK)1, -2, -3 and -6; the BMP type 2 receptor; and the vascular endothelial growth factor in human aortic endothelial cells (HAECs). Diabetes induced expression of the same factors in the aortic wall of 3 animal models of diabetes, Ins2(Akita/+) mice, db/db mice, and HIP rats (rats transgenic for human islet amyloid polypeptide), representative of types 1 and 2 diabetes. Conditioned media from glucose-treated HAECs increased angiogenesis in bovine aortic endothelial cells, as mediated by BMP-4, and osteogenesis in calcifying vascular cells, as mediated by BMP-2. BMP-4, MGP, ALK1, and ALK2 were predominantly expressed on the endothelial side of the aorta, and small interfering RNA experiments showed that these genes were regulated as a group. Diabetic mice and rats showed a dramatic increase in aortic BMP activity, as demonstrated by SMAD1/5/8 phosphorylation. This was associated with increased osteogenesis and calcium accumulation. These changes were prevented in the Ins2(Akita/+) mice by breeding them with MGP transgenic mice, which increased aortic BMP inhibition.

CONCLUSIONS

Hyperglycemia and diabetes activate vascular BMP activity, which is instrumental in promoting vascular calcification and may be limited by increasing BMP inhibition.

Genetic and evolutionary analyses of the human bone morphogenetic protein receptor 2 (BMPR2) in the pathophysiology of obesity

OBJECTIVE

Human bone morphogenetic protein receptor 2 (BMPR2) is essential for BMP signalling and may be involved in the regulation of adipogenesis. The BMPR2 locus has been suggested as target of recent selection in human populations. We hypothesized that BMPR2 might have a role in the pathophysiology of obesity.

RESEARCH DESIGN AND METHODS

Evolutionary analyses (dN/dS, Fst, iHS) were conducted in vertebrates and human populations. BMPR2 mRNA expression was measured in 190 paired samples of visceral and subcutaneous adipose tissue. The gene was sequenced in 48 DNA samples. Nine representative single nucleotide polymorphisms (SNPs) were genotyped for subsequent association studies on quantitative traits related to obesity in 1830 German Caucasians. An independent cohort of 925 Sorbs was used for replication. Finally, relation of genotypes to mRNA in fat was examined.

RESULTS

The evolutionary analyses indicated signatures of selection on the BMPR2 locus. BMPR2 mRNA expression was significantly increased both in visceral and subcutaneous adipose tissue of 37 overweight (BMI>25 and <30 kg/m²) and 80 obese (BMI>30 kg/m²) compared with 44 lean subjects (BMI< 25 kg/m²) (P<0.001). In a case-control study including lean and obese subjects, two intronic SNPs (rs6717924, rs13426118) were associated with obesity (adjusted P<0.05). Combined analyses including the initial cohort and the Sorbs confirmed a consistent effect for rs6717924 (combined P = 0.01) on obesity. Moreover, rs6717924 was associated with higher BMPR2 mRNA expression in visceral adipose tissue.

CONCLUSION

Combined BMPR2 genotype-phenotype-mRNA expression data as well as evolutionary aspects suggest a role of BMPR2 in the pathophysiology of obesity.

Endothelin B receptor, a new target in cancer immune therapy

The endothelins and their G protein-coupled receptors A and B have been implicated in numerous diseases and have recently emerged as pivotal players in a variety of malignancies. Tumors overexpress the endothelin 1 (ET-1) ligand and the endothelin-A-receptor (ET(A)R). Their interaction induces tumor growth and metastasis by promoting tumor cell survival and proliferation, angiogenesis, and tissue remodeling. On the basis of results from xenograft models, drug development efforts have focused on antagonizing the autocrine-paracrine effects mediated by ET-1/ET(A)R. In this review, we discuss a novel role of the endothelin-B-receptor (ET(B)R) in tumorigenesis and the effect of its blockade during cancer immune therapy. We highlight key characteristics of the B receptor such as its specific overexpression in the tumor compartment; and specifically, in the tumor endothelium, where its activation by ET-1 suppresses T-cell adhesion and homing to tumors. We also review our recent findings on the effects of ET(B)R-specific blockade in increasing T-cell homing to tumors and enhancing the efficacy of otherwise ineffective immunotherapy.

Bone morphogenetic protein-2 antagonizes renal interstitial fibrosis by promoting catabolism of type I transforming growth factor-beta receptors

TGF-beta is a therapeutic target for renal fibrosis. Scientists have long sought ways to antagonize TGF-beta to ameliorate diabetic nephropathy. Bone morphogenetic protein (BMP-2) is a member of the TGF-beta superfamily and is highly regulated in the kidney. Thus, the role of BMP-2 was investigated in NRK-49F cells (rat fibroblasts). We showed that TGF-beta1 induces an increase in fibronectin. Treatment with exogenous BMP-2 or pCMV-BMP-2 significantly reversed the TGF-beta1-induced increase in fibronectin concomitant with a significant decrease in type I TGF-beta receptors (TGF-beta RI). Moreover, BMP-2 significantly shortened the half-life of TGF-beta RI. These results are related to proteosomal activation because MG132, a proteasome inhibitor, abolished BMP-2-mediated degradation of TGF-beta RI. This was confirmed because BMP-2 time course dependently enhanced the ubiquitination level of TGF-beta RI. In addition, Smads would seem to be involved in the interaction of BMP-2 and TGF-beta. We demonstrated that BMP-2 significantly reversed the TGF-beta1-induced increase in pSmad2/3 and reversed the TGF-beta1-induced decrease in inhibitory Smad7. Most importantly, Smad7 small interfering RNA abolished the BMP-2-induced decrease in TGF-beta RI. We evaluated the clinical efficacy of BMP-2 using unilateral ureteral obstruction rats. BMP-2 was administered ip for 7 d. In the unilateral ureteral obstruction kidneys, interstitial fibrosis was prominent. However, treatment with BMP-2 dramatically reduced Masson's trichrome staining (collagen) in the interstitial and tubular areas of the kidneys concomitantly with a reduction in TGF-beta RI. These results suggest that BMP-2 acts as a novel fibrosis antagonizing cytokine partly by down-regulating TGF-beta RI and Smads.

Bone morphogenetic proteins regulate osteoprotegerin and its ligands in human vascular smooth muscle cells

The bone-related protein osteoprotegerin (OPG) may be involved in the development of vascular calcifications, especially in diabetes, where it has been found in increased amounts in the arterial wall. Experimental studies suggest that members of the TGF-superfamily are involved in the transformation of human vascular smooth muscle cells (HVSMC) to osteoblast-like cells. In this study, we evaluated the effect of BMP-2, BMP-7 and transforming growth factor beta (TGF-beta1) on the secretion and mRNA expression of OPG and its ligands receptor activator of nuclear factor-kappabeta ligand (RANKL) and TNF-related apoptosis-inducing ligand (TRAIL) in HVSMC. All three growth factors decreased OPG protein production significantly; these results were paralleled by reduced OPG mRNA expression. TRAIL mRNA levels were also decreased. RANKL mRNA expression declined when treated with TGF-beta1 but were increased by both BMPs. Members of the TGF-superfamily, i.e. TGF-beta1, BMP-2 and BMP-7 exert effects on OPG and its ligands, indicating that these peptides may be involved in the development of vascular calcifications. The downregulation of OPG by these peptides does, however, not suggest that these factors are directly involved in OPG accumulation in diabetes.

Reactive oxygen species-selective regulation of aortic inflammatory gene expression in Type 2 diabetes

Vascular diseases are a major complication of diabetes mellitus (DM), although their etiology is poorly understood. NADPH oxidase-derived reactive oxygen species (ROS) production and inflammation are potential mediators of DM-associated vascular diseases. Using db/db mice as a Type 2 diabetes model, we examined the relationship between NADPH oxidase-derived ROS and vascular inflammation. When compared with control m+/+ mice, aortas from 4- and 12-wk-old db/db mice had higher NADPH oxidase activity and increased superoxide levels, leading to NADPH oxidase-dependent impaired vasodilation at 12 wk. Diabetes progression from 4 to 12 wk led to increased Nox1, Nox4, and p22(phox) subunit mRNAs and induced the expression of a group of matrix remodeling-related cytokines: connective tissue growth factor (CTGF), bone morphogenetic protein 4 (BMP-4), and osteopontin (OPN). After 8 wk of treatment with the superoxide scavenger Tempol, 12-wk-old db/db mice had lower superoxide production, reduced plasma glucose and lipids, and lower BMP-4 and OPN protein expression when compared with nontreated mice. No changes were observed with Tempol in CTGF or m+/+ mice. The ability of Tempol to reverse ROS production as well as OPN and BMP-4, but not CTGF, induction suggests that DM-induced vascular inflammation involves both ROS-sensitive and -insensitive pathways.