Do changes in transglutaminase activity alter latent transforming growth factor beta activation in experimental diabetic nephropathy?
BACKGROUND
Diabetic nephropathy is the leading cause of end-stage kidney failure worldwide. It is characterized by excessive extracellular matrix accumulation. Transforming growth factor beta 1 (TGF-β1) is a fibrogenic cytokine playing a major role in the healing process and scarring by regulating extracellular matrix turnover, cell proliferation and epithelial mesanchymal transdifferentiation. Newly synthesized TGF-β is released as a latent, biologically inactive complex. The cross-linking of the large latent TGF-β to the extracellular matrix by transglutaminase 2 (TG2) is one of the key mechanisms of recruitment and activation of this cytokine. TG2 is an enzyme catalyzing an acyl transfer reaction leading to the formation of a stable ε(γ-glutamyl)-lysine cross-link between peptides.


METHODS
To investigate if changes in TG activity can modulate TGF-β1 activation, we used the mink lung cell bioassay to assess TGF-β activity in the streptozotocin model of diabetic nephropathy treated with TG inhibitor NTU281 and in TG2 overexpressing opossum kidney (OK) proximal tubular epithelial cells.


RESULTS
Application of the site-directed TG inhibitor NTU281 caused a 25% reduction in kidney levels of active TGF-β1. Specific upregulation of TG2 in OK proximal tubular epithelial cells increased latent TGF-β recruitment and activation by 20.7% and 19.7%, respectively, in co-cultures with latent TGF-β binding protein producing fibroblasts.


CONCLUSIONS
Regulation of TG2 directly influences the level of active TGF-β1, and thus, TG inhibition may exert a renoprotective effect by targeting not only a direct extracellular matrix deposition but also TGF-β1 activation and recruitment.
Academic Nephrology Unit (Sheffield Kidney Institute), University of Sheffield, Sheffield S10 2RX, UK.
Linghong
L
Huang
John L
JL
Haylor
Marie
M
Fisher
Zoe
Z
Hau
A Meguid
AM
El Nahas
Martin
M
Griffin
Timothy S
TS
Johnson
D000818:Animals; D018920:Coculture Techniques; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism* / Q000473:pathology; D003928:Diabetic Nephropathies / Q000378:metabolism* / Q000473:pathology; D004195:Disease Models, Animal; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005355:Fibrosis; D019204:GTP-Binding Proteins / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D008297:Male; D051379:Mice; D008907:Mink; D009893:Opossums; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D020033:Protein Isoforms / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013311:Streptozocin; D041701:Swiss 3T3 Cells; D014162:Transfection; D053773:Transforming Growth Factor beta1 / Q000378:metabolism*; D053781:Transforming Growth Factor beta2 / Q000378:metabolism; D053782:Transforming Growth Factor beta3 / Q000378:metabolism; D011503:Transglutaminases / Q000378:metabolism*
D004791:Enzyme Inhibitors; D020033:Protein Isoforms; C000717609:Tgm2 protein, rat; D053773:Transforming Growth Factor beta1; D053781:Transforming Growth Factor beta2; D053782:Transforming Growth Factor beta3; D013311:Streptozocin; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D019204:GTP-Binding Proteins