Abstract

Chronic hyperglycemia can alter pancreatic b-cell phenotype by decreasing expression of b-cell specific genes including insulin and GLUT2, while increasing expression of metabolic genes normally not abundantly expressed such as l-pyruvate kinase (l-PK), fatty acid synthase (FAS), acetyl-CoA carboxylase, and lactate dehydrogenase. Treatment of INS-1 pancreatic b-cells with high glucose (16.7 mM) for 48 hrs markedly suppressed insulin promoter activity [1] and induced l-PK promoter activity [1,2]. High glucose also elevated intracellular NAD levels 2-fold compared to control. PARP, an enzyme that uses NAD to poly(ADP-ribosy)late nuclear proteins [3], has been suggested to be involved in ß-cell cytotoxicity, regeneration and differentiation [2,4], and adipocyte differentiation [5]. Thus, we examined the ability of PARP inhibitors – nicotinamide (NAM), 3-aminobenzamide (3-AB), and PD128763 (PD) – to attenuate glucose-mediated changes in insulin and lipogenic gene expression and promoter activities in INS-1 cells. Incubation of INS-1 cells in high glucose for 48 hrs suppressed in suppressed insulin mRNA level >80% and induced l-PK, FAS, and SREBP-1c mRNA levels 4.4-, 12.6-, and 2.7-fold, respectively. Treatment with high glucose concentrations also repressed insulin (–327/+30) promoter activity >80%, and induced l-PK (–4.3 kb/+12) and FAS (–2.4 kb/+16) promoter activity 24- and 21-fold, respectively. Treatment of cells with high glucose plus 10 mM NAM, 10 mM 3-AB, or 500 KM PD, increased insulin mRNA levels and promoter activity 3.4- and 10-fold, respectively. PARP inhibitors also attenuated glucose-mediated induction of l-PK, FAS, and SREBP-1c mRNA levels by 55%, 69%, and 45%, respectively. Moreover, PARP inhibitors attenuated the ability of high glucose to activate l-PK and FAS promoters by 51% and 61%, respectively. These results indicate that PARP inhibitors can attenuate adverse changes in gene expression that occur when b-cells are exposed to elevated glucose concentrations.References: 1.Olson LK, Qian J, Poitout V: Mol Endocrinol, 1998; 12(2): 207-219 2.Newburg E, Qian J, Towle HC, Olson LK: Mol Cell Biochem, 2000; 210: 13-21 3.Virag L, Szabo C: Pharmacol Rev, 2002; 54(3): 375-429 4.Okamoto H, Takasawa S: Diabetes, 2002; 51(suppl. 3): S462-S473 5.Smulson ME, Kang VH, Ntambi JM et al: J Biol Chem, 1995; 270(1): 119-127

Keywords: PARP inhibitors, b-cell phenotype, islet of langerhans, Glucose, insulin gene, lipogenic genes