Markers of diabetic nephropathy

Glomerular type IV collagen in patients with diabetic nephropathy with and without additional glomerular disease

BACKGROUND

Type IV collagen is a constituent of mesangial matrix and is increased in amount in many forms of glomerular injury.

METHODS

We performed renal biopsies in patients who (1) were donating a kidney to a relative (LRD, N = 6), (2) had diabetic glomerulopathy with or without nephrosclerosis (DM, N = 6), or (3) had diabetic glomerulopathy with a superimposed glomerular lesion (DM+, N = 5). Glomerular collagen alpha2(IV) and control glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNAs were measured, and the former correlated with clinical and morphological data to assess its usefulness in reflecting glomerular injury.

RESULTS

Collagen alpha2(IV) mRNA levels were lowest in LRD (2.9 +/- 0.6 attomol/glomerulus), higher in DM (5.9 +/- 1.6, P = 0.05), and highest in DM+ (12.7 +/- 2.8 attm/glomerulus, P < 0.05 vs. LRD and vs. DM). Control GAPDH mRNA levels were not significantly different (P > 0.05). Levels of proteinuria, serum creatinine, and glomerular size did not correlate with collagen alpha2(IV) mRNA levels. The fractional mesangial area and the fractional mesangial area occupied by type IV collagen were higher in both diabetic groups than in LRD (P < 10-6), but the intensity of type IV collagen staining in the diabetic patients was significantly less than that seen in the LRD (P < 0.01). In DM+ patients, extramesangial type IV collagen was present. Fractional mesangial area and glomerular collagen alpha2(IV) mRNA levels correlated (r = 0.45, P < 0.05).

CONCLUSION

These data are consistent with a view of diabetic nephropathy as a lesion of increased alpha2 type IV collagen transcription, increased total amount of collagen present, but decreased mesangial density relative to other matrix molecules. These data further demonstrate that glomerular injury superimposed on diabetic nephropathy contributes to additional structural damage by inducing increased synthesis of type IV collagen at extramesangial sites.

Type IV collagen as an early marker for diabetic nephropathy in non-insulin-dependent diabetes mellitus

We measured urinary albumin (U-Alb) and type IV collagen (uIV.C) in spot urine collected from 82 patients with non-insulin-dependent diabetes mellitus (NIDDM) and 205 controls. Eighty-two NIDDM patients that had no increased excretion of either U-Alb or uIV.C were observed for 6 months. Prevalence of increased excretion of U-Alb and uIV.C at 6 months in these patients were 32.9%, and 62.2%, respectively. Increased excretion of uIV.C was detected in 27 patients without microalbuminuria. chi(2) analysis suggested that uIV.C was more sensitive than U-Alb, and that hypertension enhanced increased excretion of both U-Alb and uIV.C. uIV.C was significantly correlated (P<0.01) with U-Alb but not glycosylated hemoglobin A1C (HbA1C) in NIDDM patients. Taken together, uIV.C may be a useful marker for early diabetic nephropathy.

Relationship of serum N-acetyl-beta-glucosaminidase activity to oxidative stress in diabetes mellitus

Serum N-acetyl-beta-glucosaminidase activity was evaluated in 40 Type 1 and 40 Type 2 diabetic patients and compared with parameters of diabetes control and oxidative stress. Significantly increased mean serum N-acetyl-beta-glucosaminidase activity was found in both groups of diabetic patients as compared with the corresponding group of healthy persons (p < 0.01). Oxidative stress measured by plasma malondialdehyde concentration was significantly higher in Type 2 than in Type 1 diabetic patients (p < 0.01) but in comparison with control subjects it was higher only in Type 2 diabetes. Plasma malondialdehyde concentration positively correlated with body mass index (r=0.77, p<0.001) and with serum N-acetyl-beta-glucosaminidase activities (r=0.57, p <0.001). Treatment of 10 Type 2 diabetic patients with antioxidant alpha-tocopherol caused a significant decrease in malondialdehyde concentration (p < 0.001) which was accompanied by a decrease of N-acetyl-beta-glucosaminidase activity (p < 0.01). We conclude that serum N-acetyl-beta-glucosaminidase activity may be influenced by oxidative stress which is more pronounced in Type 2 than in Type 1 diabetic patients.

Suppression subtractive hybridization identifies high glucose levels as a stimulus for expression of connective tissue growth factor and other genes in human mesangial cells

Accumulation of mesangial matrix is a pivotal event in the pathophysiology of diabetic nephropathy. The molecular triggers for matrix production are still being defined. Here, suppression subtractive hybridization identified 15 genes differentially induced when primary human mesangial cells are exposed to high glucose (30 mM versus 5 mM) in vitro. These genes included (a) known regulators of mesangial cell activation in diabetic nephropathy (fibronectin, caldesmon, thrombospondin, and plasminogen activator inhibitor-1), (b) novel genes, and (c) known genes whose induction by high glucose has not been reported. Prominent among the latter were genes encoding cytoskeleton-associated proteins and connective tissue growth factor (CTGF), a modulator of fibroblast matrix production. In parallel experiments, elevated CTGF mRNA levels were demonstrated in glomeruli of rats with streptozotocin-induced diabetic nephropathy. Mannitol provoked less mesangial cell CTGF expression in vitro than high glucose, excluding hyperosmolality as the key stimulus. The addition of recombinant CTGF to cultured mesangial cells enhanced expression of extracellular matrix proteins. High glucose stimulated expression of transforming growth factor beta1 (TGF-beta1), and addition of TGF-beta1 to mesangial cells triggered CTGF expression. CTGF expression induced by high glucose was partially suppressed by anti-TGF-beta1 antibody and by the protein kinase C inhibitor GF 109203X. Together, these data suggest that 1) high glucose stimulates mesangial CTGF expression by TGFbeta1-dependent and protein kinase C dependent pathways, and 2) CTGF may be a mediator of TGFbeta1-driven matrix production within a diabetic milieu.