['We reported that Smad1 is a key transcriptional factor for mesangial matrix expansion in diabetic nephropathy. In this study, we examined whether urinary Smad1 in an early phase of diabetes can predict later development of glomerulosclerosis in diabetic nephropathy and how an angiotensin II type 1 receptor blocker (ARB) can modulate structural changes and urinary markers.', 'Smad1 and albumin in the urine were examined 4 weeks after injection of streptozotocin in 48 rats or 6 weeks of diabetes in db/db mice. Their renal pathology was analyzed after 20 weeks in rats or 12 weeks in mice. Among 48 diabetic rats 7 rats were treated with olmesartan for 20 weeks.', 'Urinary Smad1 of diabetic rats at 4 weeks was nicely correlated with mesangial matrix expansion at 24 weeks (r = 0.70, P < 0.001), while albuminuria showed a weaker association (r = 0.31, P = 0.043). Olmesartan treatment significantly ameliorated glomerulosclerosis and dramatically decreased urinary Smad1 (from 3.9 +/- 2.9 to 0.3 +/- 0.3 ng/mg creatinine, P < 0.05). In db/db mice, urinary Smad1 at 6 weeks was also significantly correlated with mesangial expansion at 18 weeks. In contrast, there was no change in urinary Smad1 in control diabetic rats or mice.'] Is urinary Smad1 a novel marker to predict later onset of mesangial matrix expansion in diabetic nephropathy?