Correlation of enhanced thrombospondin-1 expression, TGF-beta signalling and proteinuria in human type-2 diabetic nephropathy.

BACKGROUND: Activation of the thrombospondin-1 (TSP-1)-TGF-beta pathway by glucose and the relevance of TSP-1-dependent activation of TGF-beta for renal matrix expansion, renal fibrosis and sclerosis have previously been demonstrated by our group in in vivo and in vitro studies. Design and methods. We investigated renal biopsies (n = 40) and clinical data (n = 30) of patients with diabetic nephropathy. Ten kidneys without evidence of renal disease served as controls. Glomerular and cortical expression of TSP-1, p-smad2/3, fibrosis and glomerular sclerosis (PAS) were assessed by immunhistochemical staining and related with clinical data. RESULTS: Glomerular (g) and cortical (c) TSP-1 were increased during diabetic nephropathy (g: 2.62 +/- 2.65; c: 4.5 +/- 4.2) compared to controls (g: 0.67 +/- 0.7; c: 1.5 +/- 1.2). P-smad2/3 was significantly increased (g: 16.7 +/- 12.9; c: 148.7 +/- 92.8) compared to controls (g: 7.1 +/- 3.6; c: 55 +/- 25; P < 0.05). TSP-1 was coexpressed with p-smad2/3 as an indicator of TGF-beta activation. TSP-1 correlated with enhanced tubulointerstitial p-smad2/3 positivity (r = 0.39 and r = 0.4, P < 0.05) and glomerular p-smad2/3 correlated with proteinuria (r = 0.35, P < 0.05). CONCLUSIONS: In summary, the present study suggests a functional activity of the TSP-1/TGF-beta axis, especially in the tubulointerstitium of patients with diabetic nephropathy. The positive correlation of glomerular p-smad2/3 positivity with proteinuria further supports the importance of the TSP-1/TGF-beta system as a relevant mechanism for progression of human type-2 diabetic nephropathy.

Analysis of NO-synthase expression and clinical risk factors in human diabetic nephropathy.

BACKGROUND: Changes of renal nitric oxide (NO) production have been associated with glomerular hyperfiltration, vascular permeability, albuminuria, glomerulosclerosis and tubulointerstitial fibrosis. Several studies demonstrated an up- as well as downregulated expression of NO-synthases (NOS) in experimental diabetic nephropathy. It is still not yet specified whether the regulation and activity of NOS is changed in human diabetic nephropathy. METHODS: Renal biopsies and clinical data of 45 patients with diabetic nephropathy and of 10 control subjects were investigated. Glomerular and cortical endothelial NOS (eNOS) and inducible NOS (iNOS) expression were assessed by immunohistochemical staining and related to clinical data such as the duration of diabetes, insulin therapy and arterial hypertension, albuminuria/proteinuria, eGFR according to the formula modification of diet in renal disease (MDRD), presence of vascular complications or diabetic retinopathy. RESULTS: The mean age of patients at biopsy was 60.3 years and the mean duration of diabetes 12.9 years. Expression of cortical and glomerular eNOS was increased in type 2 diabetes (P < 0.05). Increased expression of glomerular and cortical eNOS correlated with more severe vascular complications (r = 0.44; P < 0.05). Glomerular eNOS was strongly increased among different degrees of proteinuria (P < 0.01). In contrast to expression levels of eNOS, the glomerular expression pattern of iNOS changed from an endothelial pattern in glomeruli with preserved morphology towards expression predominantly by inflammatory cells. CONCLUSIONS: Thus, increased eNOS expression by the renal endothelium could be demonstrated in type 2 diabetic nephropathy, whereas iNOS was unchanged but spatially differentially expressed. The eNOS expression was related to vascular lesions and the degree of proteinuria.