Glomerular mRNAs in human type 1 diabetes: Biochemical evidence for microalbuminuria as a manifestation of diabetic nephropathy

Background. In patients with type 1 diabetes, some consider microalbuminuri a to be a predictor of diabetic nephropathy while others believe it is an e arly feature of diabetic nephropathy. Methods. Levels of mRNAs that are of pathogenetic relevance in diabetic nep hropathy were compared in glomeruli isolated from microalbuminuric and over tly proteinuric subjects and in control normoalbuminuric diabetic subjects and living renal transplant donors. Results: In subjects with microalbuminuria and overt proteinuria, glomerula r mRNAs were virtually identical and approximately twofold higher for conne ctive tissue growth factor (CTGF; P < 0.01) and collagen alpha2(IV) (P < 0. 03) compared to living renal donors and normoalbuminuric patients. Glomerul ar glyceraldehyde-3-phosphate dehydrogenase (GAPDH) levels were not signifi cantly different among the groups (P = 0.4). Weak but statistically signifi cant correlations were noted between CTGF mRNA and albuminuria (assessed by rank), fractional mesangial surface area, and a composite renal biopsy ind ex. Glomerular CTGF mRNA correlated inversely with creatinine clearance. Gl omerular collagen alpha2(IV) mRNA levels correlated,with albuminuria (by ra nk) and less strongly with fractional mesangial area. Conclusion. To our knowledge, these data provide the first biochemical evid ence demonstrating that the glomeruli of microalbuminuric patients and thos e with avert proteinuria do not differ significantly. The data support the concept that microalbuminuria is not "predictive" of diabetic nephropathy, but rather is an earlier point in the spectrum of diabetic nephropathy.