title: Endoglin promotes TGF-β/Smad1 signaling in scleroderma fibroblasts.
abstract: TGF-β is the primary inducer of extracellular matrix proteins in scleroderma (systemic sclerosis, SSc). Previous studies indicate that in a subset of SSc fibroblasts TGF-β signaling is activated via elevated levels of activin receptor-like kinase (ALK) 1 and phosphorylated Smad1 (pSmad1). The goal of this study was to determine the role of endoglin/ALK1 in TGF-β/Smad1 signaling in SSc fibroblasts. In SSc fibroblasts, increased levels of endoglin correlated with high levels of pSmad1, collagen, and connective tissue growth factor (CCN2). Endoglin depletion via siRNA in SSc fibroblasts inhibited pSmad1 but did not affect pSmad2/3. Following endoglin depletion mRNA and protein levels of collagen and CCN2 were significantly decreased in SSc fibroblasts but remained unchanged in normal fibroblasts. ALK1 was expressed at similar levels in SSc and normal fibroblasts. Depletion of ALK1 resulted in inhibition of pSmad1 and a moderate but significant reduction of mRNA and protein levels of collagen and CCN2 in SSc fibroblasts. Furthermore, constitutively high levels of endoglin were found in complexes with ALK1 in SSc fibroblasts. Overexpression of constitutively active ALK1 (caALK1) in normal and SSc fibroblasts led to a moderate increase of collagen and CCN2. However, caALK1 potently induced endothelin 1 (ET-1) mRNA and protein levels in SSc fibroblasts. Additional experiments demonstrated that endoglin and ALK1 mediate TGF-β induction of ET-1 in SSc and normal fibroblasts. In conclusion, this study has revealed an important profibrotic role of endoglin in SSc fibroblasts. The endoglin/ALK1/Smad1 pathway could be a therapeutic target in patients with SSc if appropriately blocked.
authors.affiliation: Medical University of South Carolina, Division of Rheumatology, Charleston, SC, USA.
authors.forename: Erin
authors.initials: E
authors.lastname: Morris
authors.forename: Izabela
authors.initials: I
authors.lastname: Chrobak
authors.forename: Andreea
authors.initials: A
authors.lastname: Bujor
authors.forename: Faye
authors.initials: F
authors.lastname: Hant
authors.forename: Christine
authors.initials: C
authors.lastname: Mummery
authors.forename: Peter
authors.initials: P
authors.lastname: Ten Dijke
authors.forename: Maria
authors.initials: M
authors.lastname: Trojanowska
mesh_terms: D030301:Activin Receptors, Type II / Q000235:genetics / Q000378:metabolism; D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism*; D003094:Collagen / Q000235:genetics / Q000378:metabolism; D055513:Connective Tissue Growth Factor / Q000235:genetics / Q000378:metabolism; D000071063:Endoglin; D019332:Endothelin-1 / Q000235:genetics / Q000378:metabolism; D004789:Enzyme Activation; D005347:Fibroblasts / Q000378:metabolism* / Q000473:pathology; D005355:Fibrosis; D057809:HEK293 Cells; D006801:Humans; D009154:Mutation; D010641:Phenotype; D010766:Phosphorylation; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D045743:Scleroderma, Diffuse / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D015398:Signal Transduction; D012867:Skin / Q000378:metabolism* / Q000473:pathology; D051898:Smad1 Protein / Q000378:metabolism*; D051899:Smad2 Protein / Q000378:metabolism; D051900:Smad3 Protein / Q000378:metabolism; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: D015703:Antigens, CD; C526317:CCN2 protein, human; C064206:ENG protein, human; D000071063:Endoglin; D019332:Endothelin-1; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; C497399:SMAD1 protein, human; C497782:SMAD2 protein, human; C497790:SMAD3 protein, human; D051898:Smad1 Protein; D051899:Smad2 Protein; D051900:Smad3 Protein; D016212:Transforming Growth Factor beta; D055513:Connective Tissue Growth Factor; D003094:Collagen; C425364:ACVRL1 protein, human; D030301:Activin Receptors, Type II