Abstract
Diabetic nephropathy (DN) is a complication of diabetes mellitus that can lead to proteinuria and a progressive decline in renal function. Endoglin, a co-receptor of TGF-β, is known primarily for regulating endothelial cell function; however, endoglin is also associated with hepatic, cardiac, and intestinal fibrosis. This study investigates whether endoglin contributes to the development of interstitial fibrosis in DN. Kidney autopsy material from 80 diabetic patients was stained for endoglin and Sirius Red and scored semi-quantitatively. Interstitial endoglin expression was increased in samples with DN and was correlated with Sirius Red staining (p < 0.001). Endoglin expression was also correlated with reduced eGFR (p = 0.001), increased creatinine (p < 0.01), increased systolic blood pressure (p < 0.05), hypertension (p < 0.05), and higher IFTA scores (p < 0.001). Biopsy samples from DN patients were also co-immunostained for endoglin together with CD31, CD68, vimentin, or α-SMA Endoglin co-localized with both the endothelial marker CD31 and the myofibroblast marker α-SMA. Finally, we used shRNA to knockdown endoglin expression in a human kidney fibroblast cell line. We found that TGF-β1 stimulation upregulated SERPINE1, CTGF, and ACTA2 mRNA and α-SMA protein, and that these effects were significantly reduced in fibroblasts after endoglin knockdown. Taken together, these data suggest that endoglin plays a role in the pathogenesis of interstitial fibrosis in DN.
Highlights
40% of patients with diabetes develop diabetic nephropathy (DN) [1], the leading cause of end-stage renal disease in the Western world; the incidence of DN continues to rise [2]
Semi-quantitative analysis of endoglin-stained sections revealed that the patients with histologically confirmed DN had significantly higher levels of endoglin in the interstitium compared to diabetic controls without DN (p < 0.05) (Figure 1A)
With respect to the clinical data, the endoglin-positive interstitial area negatively correlated with estimated glomerular filtration rate (p < 0.02), positively correlated with the presence of hypertension (p < 0.05), Interstitial fibrosis and tubular atrophy (IFTA) score (p < 0.001), and serum creatinine concentration (p < 0.001) (Figure 1C)
Summary
40% of patients with diabetes develop diabetic nephropathy (DN) [1], the leading cause of end-stage renal disease in the Western world; the incidence of DN continues to rise [2]. TGF-β induces the production of ECM proteins via connective tissue growth factor (CTGF) and/or plasminogen activator inhibitor-1 (PAI-1, encoded by the SERPINE1 gene) [7,8,9] and induces the differentiation of fibroblasts into myofibroblasts that express alpha smooth muscle actin (α-SMA) [10,11]. These myofibroblasts represent an activated fibroblast phenotype with the capacity to synthesize large amounts of ECM proteins [12,13]
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