Oxidative stress has been implicated as a key trigger of neuronal apoptosis in stroke and neurodegenerative conditions such as Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis. The Bcl-2 homology 3 (BH3)-only subfamily of Bcl-2 genes consists of multiple members that can be activated in a cell-type-and stimulus-specific manner to promote cell death. In the present study, we demonstrate that, in cortical neurons, oxidative stress induces the expression of the BH3-only members Bim, Noxa, and Puma. Importantly, we have determined that Puma؊/؊ neurons, but not Bim؊/؊ or Noxa؊/؊ neurons, are remarkably resistant to the induction of apoptosis by multiple oxidative stressors. Furthermore, we have determined that Bcl-2-associated X protein (Bax) is also required for oxidative stress induced cell death and that Puma plays a dominant role in regulating Bax activation. Specifically, we have established that the induction of Puma, but not Bim or Noxa, is necessary and sufficient to induce a conformational change in Bax to its active state, its translocation to the mitochondria and mitochondrial membrane permeabilization. Finally, we demonstrate that whereas both Puma and Bim EL can bind to the antiapoptotic family member Bcl-X L , only Puma was found to associate with Bax. This suggests that in addition to neutralizing antiapoptotic members, Puma may play a dominant role by complexing with Bax and directly promoting its activation. Overall, we have identified Puma as a dominant regulator of oxidative stress induced Bax activation and neuronal apoptosis, and suggest that Puma may be an effective therapeutic target for the treatment of a number of neurodegenerative conditions.

The commonly occurring E23K and I337V Kir6.2 polymorphisms in the ATP-sensitive potassium (K ATP ) channel are more frequent in Caucasian type 2 diabetic populations. However, the underlying cellular mechanisms contributing to the pathogenesis of type 2 diabetes remain uncharacterized. Chronic elevation of plasma free fatty acids observed in obese and type 2 diabetic subjects leads to cytosolic accumulation of long-chain acyl CoAs (LC-CoAs) in pancreatic ␤-cells. We postulated that the documented stimulatory effects of LC-CoAs on K ATP channels might be enhanced in polymorphic K ATP channels. Patch-clamp experiments were performed on inside-out patches containing recombinant K ATP channels (Kir6.2/SUR1) to record macroscopic currents. K ATP channels containing Kir6.2 (E23K/I337V) showed significantly increased activity in response to physiological palmitoyl-CoA concentrations (100 -1,000 nmol/l) compared with wild-type K ATP channels. At physiological intracellular ATP concentrations (mmol/l), E23K/I337V polymorphic K ATP channels demonstrated significantly enhanced activity in response to palmitoyl-CoA. The observed increase in K ATP channel activity may result in multiple defects in glucose homeostasis, including impaired insulin and glucagon-like peptide-1 secretion and increased glucagon release. In summary, these results suggest that the E23K/I337V polymorphism may have a diabetogenic effect via increased K ATP channel activity in response to endogenous levels of LC-CoAs in tissues involved in the maintenance of glucose homeostasis. Diabetes 52: 2630 -2635, 2003 T ype 2 diabetes is a multifactorial disease with both genetic and environmental components contributing to its development. Despite the investigation of polymorphic variations in genes encoding for key components in pathways controlling insulin secretion, their precise roles in the etiology of type 2 diabetes are not well understood.Glucose homeostasis is maintained through the coordinated release of several hormones, including insulin, glucagon, and glucagon-like peptide-1 (GLP-1). A key component regulating the release of these hormones is the ATP-sensitive potassium (K ATP ) channel (1-3). Hormone secretion in the pancreatic ␤-and ␣-cell and in the intestinal L-cell is controlled through metabolic regulation of electrical activity, a process critically linked to glucose and fatty acid metabolism, which in turn regulates the activity of K ATP channels that control membrane potential (1-4).The K ATP channel is a hetero-octameric protein complex comprised of the pore-forming inward-rectifier Kir6.2 subunit coupled to the high-affinity sulfonylurea receptor SUR1 subunit (5,6) in a stoichiometry of (Kir6.2) 4 /(SUR1) 4 . Mutations that reduce K ATP channel activity can lead to the increased ␤-cell excitability and excessive insulin secretion that underlies the congenital disorder of persistent hyperinsulinemic hypoglycemia of infancy (7). In addition, transgenic animal models demonstrate that targeted overactivity of K ATP channels severely impair...

The ATP-sensitive potassium (KATP) channel couples membrane excitability to cellular metabolism and is a critical mediator in the process of glucose-stimulated insulin secretion. Increasing numbers of KATP channel polymorphisms are being described and linked to altered insulin secretion indicating that genes encoding this ion channel could be susceptibility markers for type-2 diabetes. Genetic variation of KATP channels may result in altered beta-cell electrical activity, glucose homeostasis, and increased susceptibility to type-2 diabetes. Of particular interest is the Kir6.2 E23K polymorphism, which is linked to increased susceptibility to type-2 diabetes in Caucasian populations and may also be associated with weight gain and obesity, both of which are major diabetes risk factors. This association highlights the potential contribution of both genetic and environmental factors to the development and progression of type-2 diabetes. In addition, the common occurrence of the E23K polymorphism in Caucasian populations may have conferred an evolutionary advantage to our ancestors. This review will summarize the current status of the association of KATP channel polymorphisms with type-2 diabetes, focusing on the possible mechanisms by which these polymorphisms alter glucose homeostasis and offering insights into possible evolutionary pressures that may have contributed to the high prevalence of KATP channel polymorphisms in the Caucasian population.