ENHANCED G-PROTEIN ACTIVATION IN IDDM PATIENTS WITH DIABETIC NEPHROPATHY

Genetic susceptibility contributes significantly to the risk of develo ping nephropathy in insulin-dependent diabetes mellitus (IDDM), The ce llular substrate for this has remained enigmatic. We investigated whet her afflicted IDDM patients display an enhanced activation of pertussi s toxin (PTX)-sensitive G proteins, a phenomenon which has been demons trated in patients with essential hypertension, We established immorta lised B lymphoblast cell lines from 10 IDDM patients; without nephropa thy (DC) and 15 IDDM patients with nephropathy (DN). Nephropathy was d efined as a persistent albumin excretion rate of more than 20 mu g/min (DC 3.9+/-5.8, DN 562.3+/-539.0 mu g/min, respectively). Subjects wer e matched with regard to age (DC 28.9+/-6.5, DN 35.9+/-9.9 years), dia betes duration (DC 19.3+/-6.9, DN 22.7+/-5.8 years) and HbA(1c), value s (DC 8.5+/-1.4, DN 8.8+/-1.6 %). Reactivity of PTX-sensitive G protei ns was quantified by measuring platelet-activating factor (PAF)-induce d Ca2+ mobilisation (fura 2 method) and by mastoparan-stimulated [S-35 ]GTP gamma S binding. Expression of G alpha(i) proteins was quantified by Western blot analysis. PAF-evoked Ca2+ increases above baseline av eraged 77.0+/-52.5 nmol/l in DC and 150.7+/-61.5 nmol/l in DN (p = 0.0 05). PAF-evoked Ca2+ increases correlated Faith stimulated [S-35]GTP g amma S binding (r(2) = 0.42, p = 0.012). From Western blot analysis an overexpression of G alpha(i) proteins could be excluded in DN. A cons equence of the altered metabolic milieu in diabetes is the increased r elease of vasoactive and proliferative agonists which promote glomerul ar hyperfiltration, hypertrophy, enhanced matrix deposition, and, fina lly, glomerulosclerosis. Many of these auto-and paracrine agonists bin d to G protein-coupled receptors. Therefore, their cellular effects ar e reinforced by the enhanced G protein reactivity and increase the pro pensity to nephropathy in IDDM.