Osteoblast gene expression is differentially regulated by TGF-beta isoforms.
The transforming growth factor beta (TGF-beta) superfamily encompasses a number of important growth factors including several TGF-beta isoforms, the bone morphogenetic proteins, activins, inhibins, and growth and differentiation factors. TGF-beta 1, -beta 2, and -beta 3 are three closely related isoforms that are widely expressed during skeletal morphogenesis and bone repair. Numerous studies suggest that each isoform has unique in vivo functions; however, the effects of these TGF-beta isoforms on osteoblast gene expression and maturation have never been directly compared. In the current study, we treated undifferentiated neonatal rat calvaria osteoblast-enriched cell cultures with 2.5 ng/ml of each TGF-beta isoform and analyzed gene expression at 0, 3, 6, and 24 hours. We demonstrated unique isoform-specific regulation of endogenous TGF-beta 1 and type I collagen mRNA transcription. To assess the effects of extended TGF-beta treatment on osteoblast maturation, we differentiated osteoblast cultures in the presence of 2.5 ng/ml of each TGF-beta isoform. Analysis of collagen I, alkaline phosphatase, and osteocalcin demonstrated that each TGF-beta isoform uniquely suppressed the transcription of these osteoblast differentiation markers. Interestingly, TGF-beta isoform treatment increased osteopontin expression in primary osteoblasts after 4 and 10 days of differentiation. To our knowledge, these data provide the first direct comparison of the effects of the TGF-beta isoforms on osteoblast gene expression in vitro. Furthermore, these data suggest that TGF-beta isoforms may exert their unique in vivo effects by differentially regulating osteoblast cytokine secretion, extracellular matrix production, and the rate of cellular maturation.
Fagenholz
P J
PJ
Laboratory of Developmental Biology and Repair, New York University Medical Center, New York, New York, USA.
Warren
S M
SM
Greenwald
J A
JA
Bouletreau
P J
PJ
Spector
J A
JA
Crisera
F E
FE
Longaker
M T
MT
D000469:Alkaline Phosphatase / Q000235:genetics; D000818:Animals; D000831:Animals, Newborn; D015415:Biomarkers; D002454:Cell Differentiation / Q000235:genetics; D002478:Cells, Cultured; D003094:Collagen / Q000235:genetics; D016207:Cytokines / Q000235:genetics / Q000378:metabolism; D005109:Extracellular Matrix / Q000378:metabolism; D005786:Gene Expression Regulation / Q000235:genetics*; D010006:Osteoblasts / Q000378:metabolism*; D015675:Osteocalcin / Q000235:genetics; D053495:Osteopontin; D010750:Phosphoproteins / Q000235:genetics; D020033:Protein Isoforms / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D012795:Sialoglycoproteins / Q000235:genetics; D012886:Skull / Q000166:cytology; D014158:Transcription, Genetic; D016212:Transforming Growth Factor beta / Q000235:genetics*
D015415:Biomarkers; D016207:Cytokines; D010750:Phosphoproteins; D020033:Protein Isoforms; D012333:RNA, Messenger; D012795:Sialoglycoproteins; C506897:Spp1 protein, rat; D016212:Transforming Growth Factor beta; D015675:Osteocalcin; D053495:Osteopontin; D003094:Collagen; D000469:Alkaline Phosphatase