GLUCOSAMINYL N-DEACETYLASE IN CULTURED FIBROBLASTS - COMPARISON OF PATIENTS WITH AND WITHOUT DIABETIC NEPHROPATHY, AND IDENTIFICATION OF A POSSIBLE MECHANISM FOR DIABETES-INDUCED N-DEACETYLASE INHIBITION

Impaired heparan sulphate biosynthesis through diabetes-induced inhibi tion of glucosaminyl N-deacetylase may have a central role in the deve lopment of diabetic nephropathy, and genetic differences in the vulner ability of the N-deacetylase could influence the risk of developing ne phropathy. We studied N-deacetylase activity in fibroblast cultures fr om Type 1 (insulin-dependent) diabetic patients with (n = 14) or witho ut (n = 13) diabetic nephropathy, together with non-diabetic control s ubjects (n = 7). No difference in N-deacetylase activity was found (p = 0.13), and no inhibition of N-deacetylase was found in cultures grow n at 25 mmol/I glucose. N-deacetylase activity was inversely correlate d to growth rate (r = -0.59, p = 0.0008), and in patients with nephrop athy a negative correlation between HbA1c and fibroblast N-deacetylase activity (r = -0.72, p = 0.012) was found. Cell-cycle analysis reveal ed an increased fraction of S-phase cells in patients with nephropathy (28 % (21-52 %)) compared to healthy control subjects (17 % (9-24 %)) , p = 0.0008, but not between patients with and without nephropathy (l atter group 26 % (11-43 %)), p = 0.43. Forskolin, an activator of prot ein kinase A, specifically decreased N-deacetylase activity, whereas a ctivation of protein kinase C produced a combined reduction in N-deace tylase activity and total protein synthesis. In conclusion, no constit utive defects in N-deacetylase activity were found in fibroblasts from these patients. Further studies should consider possible associations between fibroblast characteristics and pre-biopsy environmental param eters related to cellular memory phenomena. Finally, activation of pro tein kinase A provides a potential general pathway for regulating N-de acetylase activity.