Elevated ε-(γ-Glutamyl)lysine in Human Diabetic Nephropathy Results from Increased Expression and Cellular Release of Tissue Transglutaminase

Abstract

Introduction: Diabetic nephropathy (DN) is the leading cause of chronic kidney failure, however the mechanisms underlying the characteristic expansion of the extracellular matrix (ECM) in diabetic kidneys remain controversial and unclear. In non-diabetic kidney scarring the protein crosslinking enzyme tissue transglutaminase (tTg) has been implicated in this process by the formation of increased Ε-(γ-glutamyl)lysine bonds between ECM components in both experimental and human disease. Studies in db⁺/db⁺ diabetic mice and in streptozotocin-treated rats have suggested a similar mechanism, although the relevance of this to human disease has not been addressed. Methods: We have undertaken a retrospective analysis of renal biopsies from 16 DN patients with type 2 diabetes mellitus using an immunohistochemical and immunofluorescence approach, with tTg and Ε-(γ-glutamyl)lysine crosslink quantified by confocal microscopy. Results: Immunofluorescent analysis of human biopsies (confocal microscopy) showed increases in levels of tTg (+1,266%, p < 0.001) and Ε-(γ-glutamyl)lysine (+486%, p < 0.001) in kidneys with DN compared to normal. Changes were predominantly in the extracellular periglomerular and peritubular areas. tTg staining correlated with Ε-(γ-glutamyl)lysine (r = 0.615, p < 0.01) and renal scarring (Masson’s trichrome, r = 0.728, p < 0.001). Significant changes in Ε-(γ-glutamyl)lysine were also noted intracellularly in some (≤5%) tubular epithelial cells. This is consistent with cells undergoing a novel transglutaminase-mediated cell death process in response to Ca²⁺ influx and subsequent activation of intracellular tTg. Conclusion: Changes in tTg and Ε-(γ-glutamyl)lysine occur in human DN. Cellular export of tTg may therefore be a factor in the perpetuation of DN by crosslinking and stabilisation of the ECM, while intracellular activation may lead to cell death contributing towards tubular atrophy.

Microarray profiling of gene expression patterns in glomerular cells of astaxanthin-treated diabetic mice: A nutrigenomic approach

“…We observed increased expression of two probes of transglutaminase 2 (1433428_x_at, 1437277_x_at) in the db/db mice. It has been reported that tissue transglutaminase enzyme is implicated in protein crosslinking by the formation of increased ε-(Á-glutamyl) lysine bonds between extracellular matrix components in the diabetic kidneys of both db/db mice and human patients with diabetes (19). The present study revealed that this increased expression was markedly reversed by treatment with astaxanthin.…”

Chronic Cystamine Treatment Inhibits Small Artery Remodelling in Rats

“…The transglutaminase-specific bonds, N-ε-γ-glutamyl lysine chain cross-links, were stained with the mouse monoclonal 81D4 antibody (ab424 Abcam) [28, 29] on frozen artery sections. The staining was quantified with visual semiquantification.…”

Transglutaminase 2: A New Paradigm for NF‐κB Involvement in Disease

“…Morphologically, it is characterized by excessive renal ECM accumulation in the glomeruli and tubulointerstitial space, causing glomerulosclerosis and tubulointerstitial fibrosis. A role for TGase 2 in the pathogenesis of DN has been reported in both the streptozotocin (STZ)-induced model of type 1 diabetes [90] and human diabetic kidney disease [91]. Additionally, increased TGase 2-mediated ε-(␥ -glutamyl)lysine cross-link formation is tightly associated with both glomerular and tubulointerstitial ECM expansion in diabetic kidneys.…”