title: Heterozygous inactivation of Gnas in adipose-derived mesenchymal progenitor cells enhances osteoblast differentiation and promotes heterotopic ossification.
abstract: Human genetic disorders sharing the common feature of subcutaneous heterotopic ossification (HO) are caused by heterozygous inactivating mutations in GNAS, a gene encoding multiple transcripts including two stimulatory G proteins, the α subunit of the stimulatory G protein (G(s)α) of adenylyl cyclase, and the extralong form of G(s)α, XLαs. In one such disorder, progressive osseous heteroplasia (POH), bone formation initiates within subcutaneous fat before progressing to deeper tissues, suggesting that osteogenesis may involve abnormal differentiation of mesenchymal precursors that are present in adipose tissues. We determined by immunohistochemical analysis that GNAS protein expression is limited to G(s)α in bone-lining cells and to G(s)α and XLαs in osteocytes. By contrast, the GNAS proteins G(s)α, XLαs, and NESP55 are detected in adipocytes and in adipose stroma. Although Gnas transcripts, as assessed by quantitative RT-PCR, show no significant changes on osteoblast differentiation of bone-derived precursor cells, the abundance of these transcripts is enhanced by osteoblast differentiation of adipose-derived mesenchymal progenitors. Using a mouse knockout model, we determined that heterozygous inactivation of Gnas (by disruption of the G(s)α-specific exon 1) abrogates upregulation of multiple Gnas transcripts that normally occurs with osteoblast differentiation in wild-type adipose stromal cells. These transcriptional changes in Gnas(+/-) mice are accompanied by accelerated osteoblast differentiation of adipose stromal cells in vitro. In vivo, altered osteoblast differentiation in Gnas(+/-) mice manifests as subcutaneous HO by an intramembranous process. Taken together, these data suggest that Gnas is a key regulator of fate decisions in adipose-derived mesenchymal progenitor cells, specifically those which are involved in bone formation.
authors.affiliation: Department of Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA. pignolo@mail.med.upenn.edu
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Pignolo
authors.forename: Meiqi
authors.initials: M
authors.lastname: Xu
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Russell
authors.forename: Alec
authors.initials: A
authors.lastname: Richardson
authors.forename: Josef
authors.initials: J
authors.lastname: Kaplan
authors.forename: Paul C
authors.initials: PC
authors.lastname: Billings
authors.forename: Frederick S
authors.initials: FS
authors.lastname: Kaplan
authors.forename: Eileen M
authors.initials: EM
authors.lastname: Shore
mesh_terms: D000273:Adipose Tissue / Q000166:cytology; D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D001854:Bone Marrow Cells / Q000378:metabolism / Q000473:pathology; D002454:Cell Differentiation; D002864:Chromogranins; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation; D020868:Gene Silencing; D006579:Heterozygote; D006801:Humans; D007150:Immunohistochemistry; D059630:Mesenchymal Stem Cells / Q000378:metabolism*; D051379:Mice; D008954:Models, Biological; D009999:Ossification, Heterotopic / Q000378:metabolism / Q000473:pathology*; D010006:Osteoblasts / Q000378:metabolism / Q000473:pathology*; D010012:Osteogenesis; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D017154:Stromal Cells / Q000378:metabolism / Q000473:pathology
chemical_list: D015415:Biomarkers; D002864:Chromogranins; D012333:RNA, Messenger; C498642:Gnas protein, mouse; D019205:GTP-Binding Protein alpha Subunits, Gs