Cultured tubule cells from TGF-beta1 null mice exhibit impaired hypertrophy and fibronectin expression in high glucose.
BACKGROUND
To firmly establish the role of the transforming growth factor-beta1 (TGF-beta1) isoform in the pathophysiology of diabetic tubulointerstitial hypertrophy and fibrosis, we examined how the total absence of TGF-beta1 would alter the effect of high glucose on cellular hypertrophy and matrix expression in tubuloepithelial cells cultured from TGF-beta1 null mice.


METHODS
Primary tubule cell cultures, obtained from kidneys of TGF-beta1 knockout mice and their wild-type littermates, were treated with exogenous TGF-beta1 or high glucose. The TGF-beta system was characterized at the ligand and receptor levels using Northern and Western blotting. Cellular hypertrophy and growth were assessed by thymidine incorporation, cell counting, leucine incorporation, and protein content. Fibronectin expression was assessed by Northern analysis and enzyme-linked immunosorbent assay (ELISA).


RESULTS
Knockout cells did not express TGF-beta1 but did express TGF-beta2, TGF-beta3, and TGF-beta type I and type II receptors. Exogenous TGF-beta1 down-regulated the ligand-binding type II receptor but up-regulated type I receptor expression. Knockout cells proliferated more rapidly than wild-type cells, but restoring TGF-beta1 to knockout cells slowed their proliferation. In wild-type cells, high glucose caused cellular hypertrophy, evidenced by greater leucine incorporation and protein content along with decreased thymidine incorporation. High glucose also increased fibronectin message and protein. However, in knockout cells, high glucose failed to induce hypertrophy and was severely limited in its capacity to stimulate fibronectin.


CONCLUSIONS
In tubular epithelial cells, TGF-beta1 mediates the hypertrophic and fibronectin-stimulatory effects of high glucose, confirming the role of the TGF-beta1 isoform in the pathogenesis of diabetic tubular hypertrophy and fibronectin overexpression.
Chen
Sheldon
S
Renal-Electrolyte and Hypertension Division, Department of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Hoffman
Brenda B
BB
Lee
Joseph S
JS
Kasama
Yuki
Y
Jim
Belinda
B
Kopp
Jeffrey B
JB
Ziyadeh
Fuad N
FN
D030201:Activin Receptors, Type I / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005353:Fibronectins / Q000378:metabolism*; D015870:Gene Expression / Q000187:drug effects; D005947:Glucose / Q000008:administration & dosage*; D006984:Hypertrophy; D007684:Kidney Tubules / Q000378:metabolism* / Q000473:pathology*; D051379:Mice; D018345:Mice, Knockout; D017346:Protein Serine-Threonine Kinases; 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; D016212:Transforming Growth Factor beta / Q000172:deficiency* / Q000378:metabolism / Q000494:pharmacology; D053773:Transforming Growth Factor beta1; D053781:Transforming Growth Factor beta2; D053782:Transforming Growth Factor beta3
D005353:Fibronectins; D018125:Receptors, Transforming Growth Factor beta; C508961:Tgfb1 protein, mouse; C509045:Tgfb3 protein, mouse; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D053781:Transforming Growth Factor beta2; D053782:Transforming Growth Factor beta3; 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; D005947:Glucose