In pancreatic β-cells, glucose metabolism signals insulin secretion by altering the cellular array of messenger molecules. ATP is particularly important, given its role in regulating cation channel activity, exocytosis, and events dependent upon its hydrolysis. Uncoupling protein (UCP)-2 is proposed to catalyze a mitochondrial inner-membrane H⁺ leak that bypasses ATP synthase, thereby reducing cellular ATP content. Previously, we showed that overexpression of UCP-2 suppressed glucose-stimulated insulin secretion (GSIS) in isolated islets (1). The aim of this study was to identify downstream consequences of UCP-2 overexpression and to determine whether insufficient insulin secretion in a diabetic model was correlated with increased endogenous UCP-2 expression. In isolated islets from normal rats, the degree to which GSIS was suppressed was inversely correlated with the amount of UCP-2 expression induced. Depolarizing the islets with KCl or inhibiting ATP-dependent K⁺ (K_ATP) channels with glybenclamide elicited similar insulin secretion in control and UCP-2–overexpressing islets. The glucose-stimulated mitochondrial membrane (Ψ_m) hyperpolarization was reduced in β-cells overexpressing UCP-2. ATP content of UCP-2–induced islets was reduced by 50%, and there was no change in the efflux of Rb⁺ at high versus low glucose concentrations, suggesting that low ATP led to reduced glucose-induced depolarization, thereby causing reduced insulin secretion. Sprague-Dawley rats fed a diet with 40% fat for 3 weeks were glucose intolerant, and in vitro insulin secretion at high glucose was only increased 8.5-fold over basal, compared with 28-fold in control rats. Islet UCP-2 mRNA expression was increased twofold. These studies provide further strong evidence that UCP-2 is an important negative regulator of β-cell insulin secretion and demonstrate that reduced ΔΨ_m and increased activity of K_ATP channels are mechanisms by which UCP-2–mediated effects are mediated. These studies also raise the possibility that a pathological upregulation of UCP-2 expression in the prediabetic state could contribute to the loss of glucose responsiveness observed in obesity-related type 2 diabetes in humans.

Habitual physical activity is an important determinant of health, yet many people are considered to be inactive. Identification of the obstacles to greater participation is necessary for the development of strategies to overcome those obstacles. The weather has been identified as a perceived barrier to participation in physical activity, but exactly which adverse weather conditions are most important, and the extent to which they contribute to decreases in physical activity have rarely been quantified in populations. In the past decade, a small number of studies have used publicly available databases to examine the quantitative effects of weather (e.g., temperature, precipitation, wind) on physical activity in children, adolescents and adults. This review examines our historical, qualitative versus emerging, quantitative understanding of how specific weather conditions affect a population’s activity.

Uncoupling protein 2 (UCP-2) mRNA expression has been shown to be altered by metabolic conditions such as obesity in humans, but its functional significance is unknown. The expression of UCP-2 mRNA and protein in normal rat islets was established by reverse transcriptase-polymerase chain reaction and immunocytochemistry in pancreatic islets and tissue, respectively. Intense immunostaining of UCP-2 correlated with insulin-positive ,-cells. Overexpression of UCP-2 in normal rat islets was accomplished by infection with an adenovirus (AdEGI-UCP-2) containing the full-length human UCP-2 coding sequence. Induction of the AdEGI-UCP-2 gene resulted in severe blunting of glucose-stimulated insulin secretion (GSIS) without affecting islet insulin content or the ability of the calcium ionophore A23187 to increase insulin secretion from AdEGI-UCP-2-expressing islets. Therefore, UCP-2 overexpression affects signal transduction proximal to Ca2+-mediated steps, including exocytosis. Insulin secretion from single beta-cells to 16.5 mmol/l glucose examined by reverse hemolytic plaque assay was nearly ablated if UCP-2 was overexpressed. Thus, a direct, causal relationship between overexpression of UCP-2 and inhibition of GSIS in normal islets has been established. These data suggest that increased expression of UCP-2 has the potential to cause the lack of a glucose effect on insulin secretion in type 2 diabetes.