An increased transforming growth factor beta receptor type I:type II ratio contributes to elevated collagen protein synthesis that is resistant to inhibition via a kinase-deficient transforming growth factor beta receptor type II in scleroderma.
OBJECTIVE
Aberrant transforming growth factor beta (TGFbeta) signaling has been implicated in the pathogenesis of scleroderma (systemic sclerosis [SSc]), but the contribution of specific components in this pathway to SSc fibroblast phenotype remains unclear. This study was undertaken to delineate the role of TGFbeta receptor type I (TGFbetaRI) and TGFbetaRII in collagen overexpression by SSc fibroblasts.


METHODS
Primary dermal fibroblasts from SSc patients and healthy adults were studied (n = 10 matched pairs). Adenoviral vectors were generated for TGFbetaRI (AdTGFbetaRI), TGFbetaRII (AdTGFbetaRII), and kinase-deficient TGFbetaRII (AdDeltakRII). TGFbetaRI basal protein levels were analyzed by (35)S-methionine labeling/immunoprecipitation and immunohistochemistry. Type I collagen and TGFbetaRII basal protein levels were analyzed by Western blot and newly secreted collagen by (3)H-proline incorporation assay.


RESULTS
Analysis of endogenous TGFbetaRI and TGFbetaRII protein levels revealed that SSc TGFbetaRI levels were increased 1.7-fold (P = 0.008; n = 7) compared with levels in healthy controls, while TGFbetaRII levels were decreased by 30% (P = 0.03; n = 7). This increased TGFbetaRI:TGFbetaRII ratio correlated with SSc collagen overexpression. To determine the consequences of altered TGFbetaRI:TGFbetaRII ratio on collagen expression, healthy fibroblasts were transduced with AdTGFbetaRI or AdTGFbetaRII. Forced expression of TGFbetaRI in the range corresponding to elevated SSc TGFbetaRI levels increased basal collagen expression in a dose-dependent manner, while similar TGFbetaRII overexpression had no effect, although transduction of fibroblasts at higher multiplicities of infection led to a marked reduction of basal collagen levels. Blockade of TGFbeta signaling via AdDeltakRII resulted in approximately 50% inhibition of basal collagen levels in healthy fibroblasts and in 5 of 9 SSc cell lines. A subset of SSc fibroblasts (4 of 9 cell lines) was resistant to this treatment. SSc fibroblasts with the highest levels of TGFbetaRI were the least responsive to collagen inhibition via DeltakRII.


CONCLUSIONS
This study indicates that an increased TGFbetaRI:TGFbetaRII ratio may underlie aberrant TGFbeta signaling in SSc and contribute to elevated basal collagen production, which is insensitive to TGFbeta signaling blockade via DeltakRII.
Pannu
Jaspreet
J
Division of Rheumatology and Immunology, Medical University of South Carolina, 96 Jonathan Lucas Street, Charleston, SC 29425, USA.
Gore-Hyer
Elizabeth
E
Yamanaka
Masayoshi
M
Smith
Edwin A
EA
Rubinchik
Semyon
S
Dong
Jian-Yun
JY
Jablonska
Stefania
S
Blaszczyk
Maria
M
Trojanowska
Maria
M
D030201:Activin Receptors, Type I / Q000235:genetics* / Q000378:metabolism*; D000328:Adult; D000368:Aged; D003094:Collagen / Q000096:biosynthesis*; D020405:Dermis / Q000473:pathology; D005260:Female; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D016296:Mutagenesis; D010641:Phenotype; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D000077293:Receptor, Transforming Growth Factor-beta Type I; D000077294:Receptor, Transforming Growth Factor-beta Type II; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics* / Q000378:metabolism*; D012595:Scleroderma, Systemic / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D015398:Signal Transduction / Q000502:physiology
D018125:Receptors, Transforming Growth Factor beta; D003094:Collagen; D017346:Protein Serine-Threonine Kinases; D030201:Activin Receptors, Type I; D000077293:Receptor, Transforming Growth Factor-beta Type I; D000077294:Receptor, Transforming Growth Factor-beta Type II