Toren Finkel

An increase in hepatic glucose production (HGP) is a key feature of type 2 diabetes. Excessive signaling through hepatic G_s–linked glucagon receptors critically contributes to pathologically elevated HGP. Here, we tested the hypothesis that this metabolic impairment can be counteracted by enhancing hepatic G_i signaling. Specifically, we used a chemogenetic approach to selectively activate G_i-type G proteins in mouse hepatocytes in vivo. Unexpectedly, activation of hepatic G_i signaling triggered a pronounced increase in HGP and severely impaired glucose homeostasis. Moreover, increased G_i signaling stimulated glucose release in human hepatocytes. A lack of functional G_i-type G proteins in hepatocytes reduced blood glucose levels and protected mice against the metabolic deficits caused by the consumption of a high-fat diet. Additionally, we delineated a signaling cascade that links hepatic G_i signaling to ROS production, JNK activation, and a subsequent increase in HGP. Taken together, our data support the concept that drugs able to block hepatic G_i–coupled GPCRs may prove beneficial as antidiabetic drugs.

The identification of the molecular composition of the mitochondrial calcium uniporter has allowed for the genetic manipulation of its components and the creation of various in vivo genetic models. Here, we review the initial attempts to modulate the expression of components of the calcium uniporter in a range of organisms from plants to mammals. This analysis has confirmed the strict requirement for the uniporter for in vivo mitochondrial calcium uptake and for maintaining mitochondrial calcium homeostasis. We further discuss the physiological effects following genetic manipulation of the uniporter on tissue bioenergetics and the threshold for cell death. Finally, we analyze the limited information regarding the role of various uniporter components in human disease.

The physiological role of autophagic flux within the vascular endothelial layer remains poorly understood. Here, we show that in primary endothelial cells, oxidized and native LDL stimulates autophagosome formation. Moreover, by both confocal and electron microscopy, excess native or modified LDL appears to be engulfed within autophagic structures. Transient knockdown of the essential autophagy gene ATG7 resulted in higher levels of intracellular (125) I-LDL and oxidized LDL (OxLDL) accumulation, suggesting that in endothelial cells, autophagy may represent an important mechanism to regulate excess, exogenous lipids. The physiological importance of these observations was assessed using mice containing a conditional deletion of ATG7 within the endothelium. Following acute intravenous infusion of fluorescently labeled OxLDL, mice lacking endothelial expression of ATG7 demonstrated prolonged retention of OxLDL within the retinal pigment epithelium (RPE) and choroidal endothelium of the eye. In a chronic model of lipid excess, we analyzed atherosclerotic burden in ApoE(-/-) mice with or without endothelial autophagic flux. The absence of endothelial autophagy markedly increased atherosclerotic burden. Thus, in both an acute and chronic in vivo model, endothelial autophagy appears critically important in limiting lipid accumulation within the vessel wall. As such, strategies that stimulate autophagy, or prevent the age-dependent decline in autophagic flux, might be particularly beneficial in treating atherosclerotic vascular disease.