Deregulated Bone Morphogenetic Protein Receptor Signaling Underlies Fibrodysplasia Ossificans Progressiva

Signal transduction in aging related disease

Towards a cure for Fibrodysplasia ossificans progressiva

Cancer Signaling networks and Molecular Therapeutic

Biphasic Effects of Transforming Growth Factor beta on Bone Morphogenetic Protein-Induced Osteoblast Differentiation

Bone morphogenetic proteins (BMPs) exert an important role in skeletal development, adult bone homeostasis, and fracture healing and have demonstrated clinical utility for bone regeneration. However, BMPs fall short as regenerative agents because high doses need to be used to obtain therapeutic effects. Determining the molecular mechanisms controlling BMP-induced bone formation may lead to the development of more effective BMP-based therapies. To identify kinases mediating BMP-induced osteoblast differentiation, we performed an siRNA screen to find kinases modulating BMP-6-induced alkaline phosphatase (ALP) activity. Surprisingly, although transforming growth factor beta (TGF-beta) generally is considered to antagonize BMP-induced osteoblast differentiation, C2C12 cells transfected with siRNAs targeting TGF-beta receptors displayed reduced BMP-6-induced ALP activity. Furthermore, pharmacologic inhibitors blocking the TGF-beta type I receptor impaired BMP-induced ALP activity in KS483 and C2C12 cells and mineralization of KS483 cells. Consistently, costimulation with BMPs and TGF-beta further increased expression of osteoblast-specific genes, ALP activity, and mineralization of KS483 cells and primary mesenchymal stem cells compared with BMPs alone. The stimulatory and inhibitory effects of TGF-beta were found to depend on timing and duration of the costimulation. TGF-beta inhibited BMP-induced activation of a BMP-Smad-dependent luciferase reporter, suggesting that the stimulatory effect of TGF-beta is not due to increased BMP-Smad activity. TGF-beta also inhibited the BMP-induced expression of the BMP antagonist noggin and prolonged BMP activity. In conclusion, TGF-beta, besides acting as an inhibitor, also can, by dampening the noggin-mediated negative-feedback loop, enhance BMP-induced osteoblast differentiation, which might be beneficial in fracture healing. (C) 2011 American Society for Bone and Mineral Research.Signal transduction in aging related disease

MEASUREMENT OF CONSTITUTIVE ACTIVITY OF BMP TYPE I RECEPTORS

Bone morphogenetic proteins (BMPs) are pleiotropic cytokines controlling a multitude of processes, among which bone formation. BMPs function by binding and activating BMP type I and type II receptors, resulting in activation of Smad transcription factors and expression of BMP target genes. Mutations in the BMP type I receptor ALK2 were identified in patients suffering from Fibrodysplasia Ossificans Progressiva (FOP). The mutation found in all patients displaying classical FOP symptoms, the ALK2 R206H mutation, renders ALK2 constitutively active. Here, we provide a detailed description of how to determine whether other ALK2 mutations will confer constitutive activity to the receptor

Overactive bone morphogenetic protein signaling in heterotopic ossification and Duchenne muscular dystrophy

Signal transduction in aging related disease

ALK2 R206H Mutation Linked to Fibrodysplasia Ossificans Progressiva Confers Constitutive Activity to the BMP Type I Receptor and Sensitizes Mesenchymal Cells to BMP-Induced Osteoblast Differentiation and Bone Formation

Fibrodysplasia ossificans progressiva (FOP) is a rare disabling disease characterized by heterotopic ossification for which there is currently no treatment available. FOP has been linked recently to a heterozygous R206H mutation in the bone morphogenetic protein (BMP) type I receptor activin receptor-like kinase 2 (ALK2). Expression of the mutant ALK2-R206H receptor (FOP-ALK2) results in increased phosphorylation of the downstream Smad1 effector proteins and elevated basal BMP-dependent transcriptional reporter activity, indicating that FOP-ALK2 is constitutively active. FOP-ALK2-induced transcriptional activity could be blocked by overexpressing either of the inhibitory Smads, Smad6 or -7, or by treatment with the pharmacological BMP type I receptor inhibitor dorsomorphin. However, in contrast to wild-type ALK2, FOP-ALK2 is not inhibited by the negative regulator FKBP12. Mesenchymal cells expressing the FOP-ALK2 receptor are more sensitive to undergoing BMP-induced osteoblast differentiation and mineralization. In vivo bone formation was assessed by loading human mesenchymal stem cells (hMSCs) expressing the ALK2-R206H receptor onto calcium phosphate scaffolds and implantation in nude mice. Compared with control cells FOP-ALK2-expressing cells induced increased bone formation. Taken together, the R206H mutation in ALK2 confers constitutive activity to the mutant receptor, sensitizes mesenchymal cells to BMP-induced osteoblast differentiation, and stimulates new bone formation. We have generated an animal model that can be used as a stepping stone for preclinical studies aimed at inhibiting the heterotopic: ossification characteristic of FOP. (C) 2010 American Society for Bone and Mineral Research.Signal transduction in aging related disease

Cell-type specific regulation of myostatin signaling

The transforming growth factor (TGF)-β family member myostatin is an important regulator of myoblast, adipocyte, and fibroblast growth and differentiation, but the signaling mechanisms remain to be established. We therefore determined the contribution of myostatin type I receptors activin receptor-like kinase-4 (ALK4) and -5 (ALK5) and different coreceptors in C2C12 myoblasts, C3H10T1/2 mesenchymal stem cells, and 3T3-L1 fibroblasts, as well as in primary myoblast and fibroblasts. We performed siRNA-mediated knockdown of each receptor and measured signaling activity using Smad3-dependent luciferase and Smad2 phosphorylation assays with nontargeting siRNA as control. We find that myostatin utilizes ALK4 in myoblasts, whereas it has a preference for ALK5 in nonmyogenic cells. Notably, our results show that coreceptor Cripto is expressed in myoblasts but not in the nonmyogenic cells and that it regulates myostatin activity. More specifically, myostatin requires Cripto in myoblasts, whereas Cripto represses activin activity and TGF-β signaling is Cripto independent. Cripto-mediated myostatin signaling is dependent on both epidermal growth factor (EGF)-like and Cripto-FRL1-cryptic (CFC) domains, whereas activin signaling is solely conferred by the CFC domain. Furthermore, Cripto down-regulation enhances myoblast differentiation, showing its importance in myostatin signaling. Together, our results identify a molecular mechanism that explains the cell-type specific aspects of signaling by myostatin and other TGF-β family members.-Kemaladewi, D. U., de Gorter, D. J. J., Aartsma-Rus, A., van Ommen, G.-J. ten Dijke, P., 't Hoen, P. A., Hoogaars, W. M. Cell-type specific regulation of myostatin signaling.Genomics, epigenetics, population genetics and bioinformatic

BMP antagonists enhance myogenic differentiation and ameliorate the dystrophic phenotype in a DMD mouse model

Duchenne Muscular Dystrophy (DMD) is an X-linked lethal muscle wasting disease characterized by muscle fiber degeneration and necrosis. The progressive pathology of DMD can be explained by an insufficient regenerative response resulting in fibrosis and adipose tissue formation. BMPs are known to inhibit myogenic differentiation and in a previous study we found an increased expression of a BMP family member BMP4 in DMD myoblasts. The aim of the current study was therefore to investigate whether inhibition of BMP signaling could be beneficial for myoblast differentiation and muscle regeneration processes in a DMD context. All tested BMP inhibitors, Noggin, dorsomorphin and LDN-193189, were able to accelerate and enhance myogenic differentiation. However, dorsomorphin repressed both BMP and TG beta signaling and was found to be toxic to primary myoblast cell cultures. In contrast, Noggin was found to be a potent and selective BMP inhibitor and was therefore tested in vivo in a DMD mouse model. Local adenoviral-mediated overexpression of Noggin in muscle resulted in an increased expression of the myogenic regulatory genes Myog and Myod1 and improved muscle histology. In conclusion, our results suggest that repression of BMP signaling may constitute an attractive adjunctive therapy for DMD patients. (C) 2010 Elsevier Inc. All rights reserved.Genomics, epigenetics, population genetics and bioinformatic