A significant conceptual advance in our understanding of the molecular mechanism by which protein kinase C beta signaling is involved in obesity came from an earlier study linking oxidative stress, protein kinase C beta activation, phosphorylation of the redox enzyme p66shc and its translocation into the mitochondrial intermembrane space, and mitochondrial lifespan. Activation of protein kinase C beta by oxidative stress was shown to be required for phosphorylation of Ser36 on p66shc and its subsequent translocation to
mitochondria. Consistent with this signaling pathway, like protein kinase C beta−/−mice, p66shc−/− mice are also characterized by reduced triglyceride accumulation in adipocytes, increased metabolism, resistance to dietinduced
obesity, and reduced insulin resistance. Based on these findings, the following pathway has emerged: during oxidative
stress, protein kinase C beta is activated and induces p66shc phosphorylation, thus allowing p66shc to be recognized by Pin1 and isomerized for import into mitochondria after dephosphorylation by protein phosphatase-2A. The p66shc protein exhibits oxidoreductase activity,generating hydrogen peroxide and thus perturbing mitochondria structure and function. Importantly, our recent study emphasized the importance of the protein kinase C beta/p66shc mitochondrial axis in the regulation of autophagy. Activation of protein kinase C beta negatively regulates the mitochondrial energy status and inhibits autophagy. Cells treated with protein kinase C beta inhibitor and protein kinase C beta−/− mouse embryo fibroblasts show an increase in autophagy in vitro and in vivo, and increased mitochondrial membrane potential,suggesting a strong involvement of mitochondrial energy in modulation of the autophagy machinery. In view of the evolving role of autophagy in energy homeostasis, it is possible that a combination of adipose protein kinase C beta activation, mitochondrial dysfunction, and insufficient autophagy contributes to the diet-induced reduction in mitochondrial number and function (Fig. 2). Although the exact mechanism by which autophagy influences obesity is not clear, it has been suggested that a homeostatic low level of autophagy is critical to remove dysfunctional mitochondria, thus helping to reduce the production of mitochondria-derived ROS. Autophagy can also mitigate inflammation by inhibiting activation of NOD-like receptor family, pyrin domain
containing 3 (NLRP3) through the removal of permeabilized or ROSproducing mitochondria. A perturbed protein kinase C beta-mitochondrial axis may therefore be a cause of reduced mitochondrial number and capacity in obesity.
A significant conceptual advance in our understanding of the molecular mechanism by which protein kinase C beta signaling is involved in obesity came from an earlier study linking oxidative stress, protein kinase C beta activation, phosphorylation of the redox enzyme p66shc and its translocation into the mitochondrial intermembrane space, and mitochondrial lifespan. Activation of protein kinase C beta by oxidative stress was shown to be required for phosphorylation of Ser36 on p66shc and its subsequent translocation tomitochondria. Consistent with this signaling pathway, like protein kinase C beta−/−mice, p66shc−/− mice are also characterized by reduced triglyceride accumulation in adipocytes, increased metabolism, resistance to dietinducedobesity, and reduced insulin resistance. Based on these findings, the following pathway has emerged: during oxidativestress, protein kinase C beta is activated and induces p66shc phosphorylation, thus allowing p66shc to be recognized by Pin1 and isomerized for import into mitochondria after dephosphorylation by protein phosphatase-2A. The p66shc protein exhibits oxidoreductase activity,generating hydrogen peroxide and thus perturbing mitochondria structure and function. Importantly, our recent study emphasized the importance of the protein kinase C beta/p66shc mitochondrial axis in the regulation of autophagy. Activation of protein kinase C beta negatively regulates the mitochondrial energy status and inhibits autophagy. Cells treated with protein kinase C beta inhibitor and protein kinase C beta−/− mouse embryo fibroblasts show an increase in autophagy in vitro and in vivo, and increased mitochondrial membrane potential,suggesting a strong involvement of mitochondrial energy in modulation of the autophagy machinery. In view of the evolving role of autophagy in energy homeostasis, it is possible that a combination of adipose protein kinase C beta activation, mitochondrial dysfunction, and insufficient autophagy contributes to the diet-induced reduction in mitochondrial number and function (Fig. 2). Although the exact mechanism by which autophagy influences obesity is not clear, it has been suggested that a homeostatic low level of autophagy is critical to remove dysfunctional mitochondria, thus helping to reduce the production of mitochondria-derived ROS. Autophagy can also mitigate inflammation by inhibiting activation of NOD-like receptor family, pyrin domaincontaining 3 (NLRP3) through the removal of permeabilized or ROSproducing mitochondria. A perturbed protein kinase C beta-mitochondrial axis may therefore be a cause of reduced mitochondrial number and capacity in obesity.
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