Osteoblast-Specific Expression of the Fibrous Dysplasia (FD)–Causing Mutation GsαR201C Produces a High Bone Mass Phenotype but Does Not Reproduce FD in the Mouse

Abstract

We recently reported the generation and initial characterization of the first direct model of human Fibrous Dysplasia (OMIM #174800), obtained through the constitutive systemic expression of one of the disease causing mutations, GsαR201C, in the mouse. To define the specific pathogenetic role(s) of individual cell types within the stromal/osteogenic system in FD, we generated mice expressing GsαR201C selectively in mature osteoblasts using the 2.3kb Col1a1 promoter. We show here that this results in a striking high bone mass phenotype, but not in a mimicry of human FD. The high bone mass phenotype involves specifically a deforming excess of cortical bone and prolonged and ectopic cortical bone remodeling. Expression of genes characteristic of late stages of bone cell differentiation/maturation is profoundly altered as a result of expression of GsαR201C in osteoblasts, and expression of the Wnt inhibitor, Sost, is reduced. While high bone mass is in fact a feature of some types/stages of FD lesions in humans, it is marrow fibrosis, localized loss of adipocytes and hematopoietic tissue, osteomalacia and osteolytic changes that together represent the characteristic pathological profile of FD, as well as the sources of specific morbidity. None of these features are reproduced in mice with osteoblast-specific expression of GsαR201C. We further show that hematopoietic progenitor/stem cells, as well as more mature cell compartments, and adipocyte development are normal in these mice. These data demonstrate that effects of Gsα mutations underpinning FD-defining tissue changes and morbidity do not reflect the effects of the mutations on osteoblasts proper.

Fibrous dysplasia of bone: craniofacial and dental implications

“…A second mouse model was subsequently developed by Remoli et al , using the 2.3 kb Col1a1 promoter to express Gs α R201C in mature osteoblasts. Despite developing postnatally and exhibiting the high bone mass phenotype, this mouse phenotype (similar to the Hsiao mouse model) did not represent the other characteristic pathologic changes seen in FD, such as marrow fibrosis, the loss of hematopoietic tissue, osteomalacia, and osteolytic changes (Remoli et al , ). This model supports the notion that the FD‐related tissue changes result from cells other than mature osteoblasts.…”

Induced Gnas R201H expression from the endogenous Gnas locus causes fibrous dysplasia by up-regulating Wnt/β-catenin signaling

“…Better understanding of FD is essential to providing new insights into marrow fibrosis and the regulation of osteoblast differentiation and maturation from bone marrow stromal cells (BMSCs, also called bone marrow-derived stem cells), but the lack of appropriate animal models has severely hampered research advancement and therapeutic development for FD. The existing in vivo models are either based on xenotransplantation of GNAS-mutated human skeletal progenitor cells into immunocompromised mice (11) or transgenic mouse models in which either an engineered Gα s -coupled receptor or a mutated rat Gnas transgene was driven by artificial promoters (13)(14)(15). As none of these models were able to accurately recapitulate pathophysiological characteristics of human FD, the development of a "knockin" (KI) mouse model in which the corresponding mouse mutant Gα s can be expressed from its endogenous locus is absolutely necessary.…”

Human AKTIP interacts with ESCRT proteins and functions at the midbody in cytokinesis

“…One-week post-transduction, cells were lysed by addition of TRIzol reagent (Invitrogen) and RNA extracted according to the manufacturer’s instructions. After DNase treatment (Invitrogen), RNA was reverse transcribed into cDNA as already described (30). q-PCR reactions were carried out as previously described (29), using the following primers: AKTIP Forward 5’-TCCACGCTTGGTGTTCGAT-3’; AKTIP Reverse 5’-TCACCTGAGGTGGGATCAACT-3’; GAPDH Forward 5’-TGGGCTACACTGAGCACCAG-3’; GAPDH Reverse 5’-GGGTGTCGCTGTTGAAGTCA-3’ and analyzed with the 2 −ΔΔCq method as previously described (31).…”