The role of transglutaminase in the rat subtotal nephrectomy model of renal fibrosis.

Abstract

Tissue transglutaminase is a calcium-dependent enzyme that catalyzes the cross-linking of polypeptide chains, including those of extracellular matrix (ECM) proteins, through the formation of ⑀ -( ␥ -glutamyl) lysine bonds. This crosslinking leads to the formation of protein polymers that are highly resistant to degradation. As a consequence, the enzyme has been implicated in the deposition of ECM protein in fibrotic diseases such as pulmonary fibrosis and atherosclerosis.In this study, we have investigated the involvement of tissue transglutaminase in the development of kidney fibrosis in adult male Wistar rats submitted to subtotal nephrectomy (SNx). Groups of six rats were killed on days 7, 30, 90, and 120 after SNx. As previously described, these rats developed progressive glomerulosclerosis and tubulo-interstitial fibrosis. The tissue level of ⑀ -( ␥ -glutamyl) lysine cross-link (as determined by exhaustive proteolytic digestion followed by cation exchange chromatography) increased from 3. 47

Increases in Renal ε-(γ-Glutamyl)-Lysine Crosslinks Result from Compartment-Specific Changes in Tissue Transglutaminase in Early Experimental Diabetic Nephropathy: Pathologic Implications

“…However, previous studies have reported increased tTg levels accompanying externalization (Johnson et al, 1997 rather than just the redistribution of enzyme observed in the tubulointerstitium, an observation comparable to one we find in the glomerulus. It remains a possibility that the increased presence of tTg in the ECM and the ability of the enzyme to crosslink itself into the ECM, making it a difficult protein to extract, may explain the marginally lower levels of detectable enzyme in the diabetic kidney.…”

“…In common with our previous studies in the subtotal nephrectomy model of renal scarring (Johnson et al, 1997, there is an increase in tTg crosslink product within diabetic kidneys that potentially has significant biochemical effects on ECM regulation and turnover, either directly or via TGF-␤1 activation (Nunes et al, 1997). It is quite conceivable that tTg can cause excess deposition of ECM components because it has been shown in vitro to cause fibril formation in the absence of lysyl oxidase (Kleman et al, 1995;Johnson et al, 1999), and when overexpressed in fibroblasts causes increased deposition of fibronectin and latent TGF-␤1 (Verderio et al, 1999).…”

“…The extent of mesangial and tubulointerstitial expansion after the induction of DM was determined by two of the authors (MF and MJ) blinded to the experimental code, using a morphometric analysis based on point counting (Johnson et al, 1997). For this, dewaxed sections stained with Masson's trichrome stain were used.…”

“…Perturbations in tTg have been noted in diseases including Alzheimer's, carcinogenesis, and celiac disease (Dudek and Johnson, 1993;Knight et al, 1991;Molberg et al, 2000). However, there are increasing reports of its involvement in fibrotic conditions including, heart (Small et al, 1999), liver (Mirza et al, 1997), lung (Griffin et al, 1979), and renal fibrosis (Johnson et al, 1997. tTg has also been linked to cell-matrix adhesion (Verderio et al, 1998) and cellular response to stress, as well as to apoptosis (Fesus et al, 1989;Mirza et al, 1997).…”

“…Increased ⑀-(␥-glutamyl)-lysine crosslink is found in both intracellular proteins and those of the surrounding peritubular ECM in remnant kidneys (Johnson et al, 1997. tTg action may therefore contribute toward renal fibrosis through at least three pathways.…”