RESUMO
Glycogen synthase kinase-3 (GSK-3) protein levels and activity are elevated in skeletal muscle in type 2 diabetes, and inversely correlated with both glycogen synthase activity and insulin-stimulated glucose disposal. To explore this relationship, we have produced transgenic mice that overexpress human GSK-3beta in skeletal muscle. GSK-3beta transgenic mice were heavier, by up to 20% (P < .001), than their age-matched controls due to an increase in fat mass. The male GSK-3beta transgenic mice had significantly raised plasma insulin levels and by 24 weeks of age became glucose-intolerant as determined by a 50% increase in the area under their oral glucose tolerance curve (P < .001). They were also hyperlipidemic with significantly raised serum cholesterol (+90%), nonesterified fatty acids (NEFAs) (+55%), and triglycerides (+170%). At 29 weeks of age, GSK-3beta protein levels were 5-fold higher, and glycogen synthase activation (-27%), glycogen levels (-58%) and insulin receptor substrate-1 (IRS-1) protein levels (-67%) were significantly reduced in skeletal muscle. Hepatic glycogen levels were significantly increased 4-fold. Female GSK-3beta transgenic mice did not develop glucose intolerance despite 7-fold overexpression of GSK-3beta protein and a 20% reduction in glycogen synthase activation in skeletal muscle. However, plasma NEFAs and muscle IRS-1 protein levels were unchanged in females. We conclude that overexpression of human GSK-3beta in skeletal muscle of male mice resulted in impaired glucose tolerance despite raised insulin levels, consistent with the possibility that elevated levels of GSK-3 in type 2 diabetes are partly responsible for insulin resistance.
Assuntos
Intolerância à Glucose/genética , Quinase 3 da Glicogênio Sintase/biossíntese , Quinase 3 da Glicogênio Sintase/genética , Músculo Esquelético/fisiologia , Regiões Promotoras Genéticas/fisiologia , Animais , Western Blotting , Composição Corporal/fisiologia , Peso Corporal/fisiologia , Primers do DNA , DNA Complementar/biossíntese , DNA Complementar/genética , Feminino , Teste de Tolerância a Glucose , Glicogênio/metabolismo , Glicogênio Sintase Quinase 3 beta , Humanos , Proteínas Substratos do Receptor de Insulina , Resistência à Insulina/genética , Resistência à Insulina/fisiologia , Lipídeos/sangue , Fígado/metabolismo , Masculino , Camundongos , Camundongos Transgênicos , Músculo Esquelético/metabolismo , Fenótipo , Fosfoproteínas/biossíntese , Fosfoproteínas/genética , RNA Mensageiro/biossíntese , RNA Mensageiro/genética , Reação em Cadeia da Polimerase Via Transcriptase ReversaRESUMO
Peroxisome proliferator-activated receptor gamma (PPARgamma) is a critical regulator of adipocyte differentiation. Whilst 15-deoxy-delta(12,14)-prostaglandin J2 (15-d-PGJ2) has been identified as a putative endogenous ligand for this transcription factor, it is unclear whether the enzymes necessary for 15-d-PGJ2 biosynthesis are co-expressed with PPARgamma. Prostaglandin D2 synthase (PGDS) enzymes represent the terminal enzymatic components responsible for 15-d-PGJ2 production. Both glutathione (GSH)-dependent and GSH-independent PGDS isoenzymes exist. We have, therefore, examined the expression of PGDS isoenzymes in mouse 3T3-L1 adipocytes, and various human tissues. The GSH-independent PGDS was found to be expressed in 3T3-L1 cells both before and after their differentiation into adipocytes. By contrast, we were unable to detect expression of the GSH-dependent PGDS at any stage during the adipose conversion of 3T3-L1 cells. Quantitative analysis of mRNA levels for PPARgamma and each PGDS isoenzyme revealed their co-expression in a number of human tissues and cell types, including adipose tissue, placenta, prostate, and macrophages. These data reveal the potential for de novo 15-d-PGJ2 synthesis in the context of PPARgamma expression, suggesting that this prostaglandin may contribute to PPARgamma signalling in vivo.
