Role of TGF-beta signaling in extracellular matrix production under high glucose conditions.
BACKGROUND
Hyperglycemia has been shown to play an important role in diabetic renal and vascular complications. Some studies show that high glucose may mediate diabetic complications by stimulating extracellular matrix (ECM) production. We hypothesize that this may be mediated by activating transforming growth factor-beta (TGF-beta)/Smads signaling.


METHODS
Renal and vascular cells were cultured under high glucose conditions in the presence or absence of a neutralizing TGF-beta antibody and examined for activation of Smad signaling and collagen production. The regulating role of Smad signaling in high glucose-induced collagen synthesis was determined by inducing overexpression of the inhibitory Smad7 in a stable Smad7-expressing tubular cell line.


RESULTS
Activation of Smad signaling, as evidenced by Smad2 and Smad3 nuclear translocation and phosphorylation, was found in renal and vascular cells at 24 hours after high glucose stimulation (up to 55% increased). This was associated with de novo synthesis of collagen I at day 3 by all cell types. High glucose-induced activation of Smad signaling and collagen synthesis were TGF-beta-dependent since these were associated with a significant increase in TGF-beta production at 24 hours (P < 0.01) and were blocked by a neutralizing TGF-beta antibody. Importantly, overexpression of Smad7 resulted in marked inhibition of high glucose-induced Smad2 and Smad3 activation and type I collagen synthesis, suggesting that Smad signaling is a key pathway in high glucose-mediated renal and vascular scarring.


CONCLUSIONS
High glucose acts by activating the TGF-beta dependent Smad signaling pathway to stimulate collagen synthesis by renal and vascular cells. Smad signaling plays a critical role in regulating high-glucose-mediated diabetic renal and vascular complications.
Li
Jin H
JH
Department of Medicine-Nephrology, Baylor College of Medicine, Houston, Texas 77030, USA.
Huang
Xiao R
XR
Zhu
Hong-Jian
HJ
Johnson
Richard
R
Lan
Hui Y
HY
D000818:Animals; D002460:Cell Line; D024042:Collagen Type I / Q000096:biosynthesis; D004268:DNA-Binding Proteins / Q000378:metabolism; D004730:Endothelium, Vascular / Q000166:cytology / Q000502:physiology; D005109:Extracellular Matrix / Q000378:metabolism*; D005920:Glomerular Mesangium / Q000166:cytology / Q000502:physiology*; D005947:Glucose / Q000494:pharmacology*; D006801:Humans; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000502:physiology; D010766:Phosphorylation; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D051899:Smad2 Protein; D051900:Smad3 Protein; D051906:Smad7 Protein; D015534:Trans-Activators / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000494:pharmacology / Q000502:physiology*
D024042:Collagen Type I; D004268:DNA-Binding Proteins; C497782:SMAD2 protein, human; C497790:SMAD3 protein, human; C497806:SMAD7 protein, human; D051899:Smad2 Protein; C497784:Smad2 protein, rat; D051900:Smad3 Protein; C497787:Smad3 protein, rat; D051906:Smad7 Protein; C497808:Smad7 protein, rat; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D005947:Glucose