Aims/hypothesis TNF-α levels are increased in obesity and type 2 diabetes. The regulation of TNF-α converting enzyme (TACE) and its inhibitor, tissue inhibitor of metalloproteinase 3 (TIMP3), in human type 2 diabetes is unknown. Methods We examined TACE/TIMP3 regulation: (1) in lean and obese normal glucose tolerant (NGT) individuals and in type 2 diabetes patients; (2) following 6 h of lipid/ saline infusion in NGT individuals; and (3) in cultured human myotubes from lean NGT individuals incubated with palmitate. Insulin sensitivity was assessed by a euglycaemic clamp and TACE/TIMP3 was evaluated by confocal microscopy, RT-PCR, western blotting and an in vitro activity assay. Circulating TNF-α, TNF-α-receptor 1 (TNFR1), TNF-α-receptor 2 (TNFR2), IL-6 receptor (IL-6R), vascular cell adhesion molecule (VCAM) and intercellular adhesion molecule (ICAM) levels were evaluated. Results TIMP3 levels were reduced and TACE enzymatic activity was increased in type 2 diabetes skeletal muscle. TACE expression, and TACE, TNF-α, TNFR1 and IL-6R levels were increased in type 2 diabetes, and positively correlated with insulin resistance. A 6 h lipid infusion into NGT individuals decreased insulin-stimulated glucose metabolism by 25% with increased TACE, decreased expression of the gene encoding TIMP3 and increased IL-6R release. Palmitate induced a dramatic reduction of TIMP3 and increased the TACE/TIMP3 ratio in cultured myotubes. Conclusions/interpretation TACE activity was increased in skeletal muscle of obese type 2 diabetes patients and in lipid-induced insulin resistance. We propose that dysregulation of membrane proteolysis by TACE/TIMP3 of TNF-α and IL-6R is an important factor for the development of skeletal muscle insulin resistance in obese type 2 diabetes patients by a novel autocrine/paracrine mechanism.

This study was funded by TAKEDA.

Summary Sera obtained at diagnosis from 273 children (0-14 years) with insulin-dependent diabetes mellitus (IDDM) were studied to compare different autoantibody levels. The subjects comprise 75 % of all incident cases in New South Wales, Australia, for a 2-year period (ascertainment > 99% complete). Antibodies against glutamate decarboxylase were measured by radioimmunoprecipitation, insulin autoantibodies (on 176 sera collected within 4 days of initiation of insulin therapy) by radioimmunoassay, thyroid peroxidase and antigliadin IgA antibodies by enzyme-linked immunoassay, and anti-endomysial IgA and islet cell antibodies by indirect immunofluorescence. Reference ranges for anti-glutamate decarboxylase and insulin autoantibodies were determined in a group of non-diabetic children. Of the sera 69 % were positive for anti-glutamate decarboxylase, 65 % for insulin autoantibodies, 71% for islet cell antibodies (>/20 Juvenile Diabetes Foundation units), 10 % for anti-thyroid peroxidase, 2.6 % for antigliadin and 3.0 % for anti-endomysial antibodies. Islet cell antibodies and insulin autoantibodies were both negative in 13.7 % of the sera, while only 5.8 % were negative for all three of islet cell antibodies, insulin autoantibodies and anti-glutamate decarboxylase. There was a higher frequency of anti-glutamate decarboxylase among girls than boys (75 % vs 63 %, p = 0.03) and a negative correlation between the level of insulin autoantibodies and age at diagnosis (r =-0.41, p < 0.0001). A higher frequency of antithyroid peroxidase was found with increasing age (p = 0.05). Higher titres of islet cell antibodies were associated with a higher frequency of both anti-glutamate decarboxylase (p < 0.0001) and insulin autoantibodies (p = 0.003). Five children (1.8 %) with clear elevations of antigliadin and anti-endomysial antibodies were found to have asymptomatic coeliac disease by small bowel biopsy. [Diabetologia (1994[Diabetologia ( ) 37: 1113[Diabetologia ( -1120

Summary Sera obtained at diagnosis from 273 children (0-14 years) with insulin-dependent diabetes mellitus (IDDM) were studied to compare different autoantibody levels. The subjects comprise 75 % of all incident cases in New South Wales, Australia, for a 2-year period (ascertainment > 99% complete). Antibodies against glutamate decarboxylase were measured by radioimmunoprecipitation, insulin autoantibodies (on 176 sera collected within 4 days of initiation of insulin therapy) by radioimmunoassay, thyroid peroxidase and antigliadin IgA antibodies by enzyme-linked immunoassay, and anti-endomysial IgA and islet cell antibodies by indirect immunofluorescence. Reference ranges for anti-glutamate decarboxylase and insulin autoantibodies were determined in a group of non-diabetic children. Of the sera 69 % were positive for anti-glutamate decarboxylase, 65 % for insulin autoantibodies, 71% for islet cell antibodies (>/20 Juvenile Diabetes Foundation units), 10 % for anti-thyroid peroxidase, 2.6 % for antigliadin and 3.0 % for anti-endomysial antibodies. Islet cell antibodies and insulin autoantibodies were both negative in 13.7 % of the sera, while only 5.8 % were negative for all three of islet cell antibodies, insulin autoantibodies and anti-glutamate decarboxylase. There was a higher frequency of anti-glutamate decarboxylase among girls than boys (75 % vs 63 %, p = 0.03) and a negative correlation between the level of insulin autoantibodies and age at diagnosis (r =-0.41, p < 0.0001). A higher frequency of antithyroid peroxidase was found with increasing age (p = 0.05). Higher titres of islet cell antibodies were associated with a higher frequency of both anti-glutamate decarboxylase (p < 0.0001) and insulin autoantibodies (p = 0.003). Five children (1.8 %) with clear elevations of antigliadin and anti-endomysial antibodies were found to have asymptomatic coeliac disease by small bowel biopsy. [Diabetologia (1994[Diabetologia ( ) 37: 1113[Diabetologia ( -1120

Short-term physiological increase in plasma FFA concentration in lean normal glucose tolerant subjects induces insulin resistance and impairs mitochondrial membrane potential but has no significant effects on mitochondrial content, gene expression, ATP content, or citrate synthase activity.