Project description:Craniofacial and jaw bones have unique physiological specificities when compared to axial and appendicular bones. However, the molecular profile of the jaw osteoblast (OB) remains incomplete. The purpose of this study was to decipher the bone site-specific profile of transcription factors (TF) expressed in jaw osteoblasts in vivo. We accomplished this by performing RNA-seq analysis on flow-sorted osteoblasts isolated from jaw and tibial bones of 9-day-old (P9) transgenic Col1a1*2,3-GFP mice. This study demonstrated the feasibility of a new method to isolate pure OB populations and map their gene expression signature in the context of OB physiological environment, avoiding in vitro culture and its associated biases. Our results provided insights into the site-specific developmental pathways governing OB and identify new major OB regulators of bone physiology.
Project description:Craniofacial development involves regulation of a compendium of transcription factors, signaling molecules and epigenetic regulators. Histone deacetylases (HDACs) are involved in the regulation of cell proliferation, differentiation and homeostasis across a wide range of tissues, such as brain, cardiovascular system, muscular system, and skeletal system. However, functional role of Hdac4 during craniofacial development is still unclear. In this study, we investigated the effects of Hdac4 knockout in craniofacial skeletal development by conditionally disrupting the Hdac4 gene in cranial neural crest cells (CNCCs) using Cre-mediated recombination. Mice deficient in Hdac4 in CNCCs-derived osteoblasts demonstrated a dramatic decrease in bone formation in frontal bone. In vitro pre-osteoblasts (MC3T3-E1 cells) lacking Hdac4 exhibited reduced proliferation activity in association with dysregulation of cell cycle-related genes. These findings suggest that Hdac4 acts partially as a regulator of craniofacial skeletal development by positively regulating proliferation of CNCCs-derived osteoblasts.
Project description:Osteoarthritis (OA) is the most common joint disease and this is a major cause of joint pain and disability in the aging population. Its etiology is multifactorial (i.e., age, obesity, joint injury, genetic predisposition), and the pathophysiologic process affects the entirety of the joint (Martel-Pelletier J et al. Osteoarthritis. Nature reviews Disease primers. 2016;2:16072). Although it is not yet clear if it precedes or occurs subsequently to cartilage damage, subchondral bone sclerosis is an important feature in OA pathophysiology (Goldring SR et al. Changes in the osteochondral unit during osteoarthritis: structure, function and cartilage-bone crosstalk. Nat Rev Rheumatol. 2016;12:632-44). It is characterized by local bone resorption and the accumulation of weakly mineralized osteoid substance (Bailey AJ et al. Phenotypic expression of osteoblast collagen in osteoarthritic bone: production of type I homotrimer. Int J Biochem Cell Biol. 2002;34:176-82). Subchondral bone sclerosis is suspected to be linked to cartilage degradation, not only by modifying the mechanical stresses transmitted to the cartilage, but also by releasing biochemical factors with an activity on cartilage metabolism (Sanchez C et al. Osteoblasts from the sclerotic subchondral bone downregulate aggrecan but upregulate metalloproteinases expression by chondrocytes. This effect is mimicked by interleukin-6, -1beta and oncostatin M pre-treated non-sclerotic osteoblasts. Osteoarthritis Cartilage. 2005;13:979-87; Sanchez C et al. Subchondral bone osteoblasts induce phenotypic changes in human osteoarthritic chondrocytes. Osteoarthritis Cartilage. 2005;13:988-97; Westacott CI et al J. Alteration of cartilage metabolism by cells from osteoarthritic bone. Arthritis Rheum. 1997;40:1282-91. We have previously demonstrated that osteoblasts isolated from subchondral OA bone exhibited an altered phenotype. More precisely, we showed that osteoblasts coming from the thickening (called sclerotic, SC) of subchondral bone located just below a cartilage lesion produced higher levels of alkaline phosphatase, interleukin (IL)-6, IL-8, prostaglandinE2, vascular endothelial growth factor (VEGF), matrix metalloproteinase (MMP)-9 and transforming growth factor(TGF)-β1 and type I collagen than osteoblasts coming from the non-thickening neighboring area (called non-sclerotic area, NSC) (Sanchez C et al. Phenotypic characterization of osteoblasts from the sclerotic zones of osteoarthritic subchondral bone. Arthritis Rheum. 2008;58:442-55; Sanchez C et al. Regulation of subchondral bone osteoblast metabolism by cyclic compression. Arthritis Rheum. 2012;64:1193-203.) To compare secretome of cells living in different in vivo conditions is useful, not only to better understand the pathological mechanisms underlying changes in OA subchondral bone, but also to identify soluble biomarkers potentially reflecting these changes. Using our well-characterised human subchondral osteoblast culture model, we compared the secretome of osteoblasts coming from sclerotic and non sclerotic OA subchondral bone. This approach allowed to identify changes in secretome that contribute to explain some subchondral bone abnormalities in OA and to propose osteomodulin and fibulin-3 as potential biomarkers of OA subchondral bone remodelling.
Project description:Mucolipidosis type II (MLII) is a severe inherited multisystemic disorder caused by mutations in the GNPTAB gene. Skeletal abnormalities are a predominant feature of MLII. Here we investigate the gene expression in a knock-in mouse model for mucolipidosis type II, generated by the insertion of a cytosine in the murine Gnptab gene (c.3082insC) that is homologous to a homozygous mutation in an MLII patient. Since osteoblasts are critically involved in regulating bone development and remodeling, a genome-wide expression analysis was performed with RNA isolated from primary cultures of osteoblasts originating from MLII knock-in mice (KI) compared to RNA from wild-type (WT) osteoblasts to identify dysregulated genes involved in pathogenic mechanisms. Primary osteoblasts were isolated from calvaria of 5-day-old wild-type (WT) and MLII knock-in littermates (KI). RNA was extracted at day 10 of differentiation induced by ascorbic acid and beta-glycerophosphate and hybridization on Affymetrix microarrays. We used preparations of RNA from two individual primary cultures of osteoblasts for every genotype (WT_OB_I, WT_OB_II, KI_OB_I, KI_OB_II) and compared WT vs KI samples.
Project description:Osteoblasts are a key component of the endosteal hematopoietic stem cell (HSC) niche and have long been recognized with strong hematopoietic supporting activity. Osteoblast conditioned media (OCM) enhances the growth of hematopoietic progenitors in culture and modulate their engraftment activity. We aimed to characterize the hematopoietic supporting activity of OCM by comparing the secretome of immature osteoblasts to that of their precursor, mesenchymal stromal cells (MSC). Over 300 secreted proteins were quantified by mass spectroscopy in media conditioned with MSC or osteoblasts, with 47 being differentially expressed.