BACKGROUND AND AIM:Diacylglycerol kinase (DGK) isoforms catalyze an enzymatic reaction that removes diacylglycerol (DAG) and thereby terminates protein kinase C signaling by converting DAG to phosphatidic acid. DGKδ (type II isozyme) downregulation causes insulin resistance, metabolic inflexibility, and obesity. Here we determined whether DGKδ overexpression prevents these metabolic impairments. METHODS:We generated a transgenic mouse model overexpressing human DGKδ2 under the myosin light chain promoter (DGKδ TG). We performed deep metabolic phenotyping of DGKδ TG mice and wild-type littermates fed chow or high-fat diet (HFD). Mice were also provided free access to running wheels to examine the effects of DGKδ overexpression on exercise-induced metabolic outcomes. RESULTS:DGKδ TG mice were leaner than wild-type littermates, with improved glucose tolerance and increased skeletal muscle glycogen content. DGKδ TG mice were protected against HFD-induced glucose intolerance and obesity. DGKδ TG mice had reduced epididymal fat and enhanced lipolysis. Strikingly, DGKδ overexpression recapitulated the beneficial effects of exercise on metabolic outcomes. DGKδ overexpression and exercise had a synergistic effect on body weight reduction. Microarray analysis of skeletal muscle revealed common gene ontology signatures of exercise and DGKδ overexpression that were related to lipid storage, extracellular matrix, and glycerophospholipids biosynthesis pathways. CONCLUSION:Overexpression of DGKδ induces adaptive changes in both skeletal muscle and adipose tissue, resulting in protection against HFD-induced obesity. DGKδ overexpression recapitulates exercise-induced adaptations on energy homeostasis and skeletal muscle gene expression profiles.

Group IIA secreted phospholipase A2 (PLA2G2A) hydrolyzes glycerophospholipids at the sn-2 position resulting in the release of fatty acids and lysophospholipids. C57BL/6 mice do not express Pla2g2a due to a frameshift mutation (wild-type [WT] mice). We previously reported that transgenic expression of human PLA2G2A in C57BL/6 mice (IIA+ mice) protects against weight gain and insulin resistance, in part by increasing total energy expenditure. Additionally, we found that brown and white adipocytes from IIA+ mice have increased expression of mitochondrial uncoupling markers, such as uncoupling protein 1 (UCP1), peroxisome proliferator-activated receptor-gamma coactivator, and PR domain containing 16, suggesting that the energy expenditure phenotype might be due to an increased thermogenic capacity in adipose tissue. Here, we further characterize the impact of PLA2G2A on thermogenic mechanisms in adipose tissue. Metabolic analysis of WT and IIA+ mice revealed that even when housed within their thermoneutral zone, IIA+ mice have elevated energy expenditure compared to WT littermates. Increased energy expenditure in IIA+ mice is associated with increased citrate synthase activity in brown adipose tissue (BAT) and increased mitochondrial respiration in both brown and white adipocytes. We also observed that direct addition of recombinant PLA2G2A enzyme to in vitro cultured adipocytes results in the marked induction of UCP1 protein expression. Finally, we report that PLA2G2A induces the expression of numerous transcripts related to energy substrate transport and metabolism in BAT, suggestive of an increase in substrate flux to fuel BAT activity. These data demonstrate that PLA2G2A enhances adipose tissue thermogenesis, in part, through elevated substrate delivery and increased mitochondrial content in BAT.

The phospholipases A 2 (PLA 2 ) superfamily encompasses enzymes commonly found in mammalian tissues and snake venom. Many of these enzymes have unique tissue distribution, function, and substrate specificity suggesting distinct biological roles. In the past, much of the research on secretory PLA 2 s has analyzed their roles in inflammation, anti-bacterial actions, and atherosclerosis. In recent studies utilizing a variety of mouse models, pancreatic islets, and clinical trials, a role for many of these enzymes in the control of metabolism and insulin action has been revealed. In this review, this research, and the unique contributions of the PLA 2 enzymes in insulin resistance and metabolism.

Secretory phospholipase A2 group IIA (PLA2G2A) is a member of a family of secretory phospholipases previously implicated in inflammation, atherogenesis, and antibacterial actions. These enzymes hydrolyze glycerophospholipids at the sn-2 position releasing lysophospholipids and fatty acids. Though studies have shown PLA2G2A is pro-inflammatory and promotes atherosclerosis, no research has analyzed the role of this enzyme in obesity and metabolism. Studies in the past 5-10 years utilizing various knockout or over-expression mouse models have analyzed the role of different secretory phospholipase A2s (sPLA2) in metabolic diseases. From these studies, it is known that at least seven of the 11 sPLA2 isozymes contribute to the prevention or causation of metabolic diseases such as obesity and Type 2 diabetes. Increased energy expenditure, insulin sensitivity, and glucose tolerance are common characteristics of a mouse with a beneficial metabolic phenotype. We studied the impact of a high-fat diet on wild-type C57BL/6 and C57BL/6 mice over-expressing the human PLA2G2A gene (IIA+ mice). Despite no differences in food intake, the IIA+ mice weighed less, had increased oxygen consumption and energy expenditure, increased glucose tolerance and insulin sensitivity, and significantly less fat mass. There was a significant induction of uncoupling protein 1 (UCP1) in the brown adipose tissue (BAT) of IIA+ mice, suggesting enhanced mitochondrial uncoupling in their adipose tissue to drive this metabolic phenotype. Previous work in Dr. Park’s laboratory suggested that hepatic PLA2G2A expression is negatively regulated by acute thyroid hormone administration. We also examined the regulation of PLA2G2A and the metabolic changes that occur in response to variations in thyroid status. The impact of PLA2G2A on brown adipose tissue thermogenic gene expression was explored. C57BL/6 and IIA+ mice were made hypothyroid over a 10-week period or treated with thyroid hormone (T3) for 5 weeks. There were no significant changes in PLA2G2A abundance in response to thyroid status. The hypothyroid IIA+ mice did not increase their energy expenditure even with T3 administration. However, the energy expenditure, substrate utilization, insulin sensitivity and glucose tolerance were all elevated in the IIA+ mice given T3. Moreover, white adipocytes from IIA+ mice were much more prone to ‘beiging,’ including increased expression of brown adipose thermogenic markers such as uncoupling protein 1 (UCP1), PR domain containing 16 (PRDM-16), and early B cell factor 2 (EBF2). Finally, the brown adipose tissue of IIA+ mice had increased UCP1. Further metabolic analysis of C57BL/6 and IIA+ mice revealed that even at thermoneutrality the IIA+ mice display elevated oxygen consumption and energy expenditure. Moreover, citrate synthase activity was increased in the brown adipose tissue but not muscle in IIA+ animals, suggesting that the elevated thermogenesis is adipose tissue-specific. Finally, RNA microarray analysis of brown adipose tissue from C57BL/6 and IIA+ mice showed induction of numerous genes related to fuel substrate transport and metabolism, indicating an increase in substrate flux to fuel brown adipose tissue activity the IIA+ mice. These data illustrate that PLA2G2A elevates thermogenesis in an adipose tissuespecific manner, in part through elevated fuel utilization and increased mitochondrial content in BAT.

Prevalence of obesity among infants and children below 5 years of age is rising dramatically, and early childhood obesity is a forerunner of obesity and obesity-associated diseases in adulthood. Childhood obesity is hence one of the most serious public health challenges today. Here, we have identified a mother-to-child lipid signaling that protects from obesity. We have found that breast milk-specific lipid species, so-called alkylglycerol-type (AKG-type) ether lipids, which are absent from infant formula and adult-type diets, maintain beige adipose tissue (BeAT) in the infant and impede the transformation of BeAT into lipid-storing white adipose tissue (WAT). Breast milk AKGs are metabolized by adipose tissue macrophages (ATMs) to platelet-activating factor (PAF), which ultimately activates IL-6/STAT3 signaling in adipocytes and triggers BeAT development in the infant. Accordingly, lack of AKG intake in infancy leads to a premature loss of BeAT and increases fat accumulation. AKG signaling is specific for infants and is inactivated in adulthood. However, in obese adipose tissue, ATMs regain their ability to metabolize AKGs, which reduces obesity. In summary, AKGs are specific lipid signals of breast milk that are essential for healthy adipose tissue development.

Background Patients with metabolic syndrome, who are characterized by co-existence of insulin resistance, hypertension, hyperlipidemia, and obesity, are also prone to develop non-alcoholic fatty liver disease (NAFLD). Although the prevalence and severity of NAFLD is significantly greater in men than women, the mechanisms by which gender modulates the pathogenesis of hepatic steatosis are poorly defined. The obese spontaneously hypertensive (SHROB) rats represent an attractive model of metabolic syndrome without overt type 2 diabetes. Although pathological manifestation caused by the absence of a functional leptin receptor has been extensively studied in SHROB rats, it is unknown whether these animals elicited sex-specific differences in the development of hepatic steatosis. Methods We compared hepatic pathology in male and female SHROB rats. Additionally, we examined key biochemical and molecular parameters of signaling pathways linked with hyperinsulinemia and hyperlipidemia. Finally, using methods of quantitative polymerase chain reaction (qPCR) and western blot analysis, we quantified expression of 45 genes related to lipid biosynthesis and metabolism in the livers of male and female SHROB rats. Results We show that all SHROB rats developed hepatic steatosis that was accompanied by enhanced expression of SREBP1, SREBP2, ACC1, and FASN proteins. The livers of male rats also elicited higher induction of Pparg , Ppara , Slc2a4 , Atox1 , Skp1 , Angptl3 , and Pnpla3 mRNAs. In contrast, the livers of female SHROB rats elicited constitutively higher levels of phosphorylated JNK and AMPK and enhanced expression of Cd36 . Conclusion Based on these data, we conclude that the severity of hepatic steatosis in male and female SHROB rats was mainly driven by increased de novo lipogenesis. Moreover, male and female SHROB rats also elicited differential severity of hepatic steatosis that was coupled with sex-specific differences in fatty acid transport and esterification.

Secretory phospholipase A(2) group IIA (PLA2G2A) is a phospholipase which has a role in inflammation, atherogenesis, and host defense. Previously, we found that PLA2G2A protects mice on high-fat diets from weight gain and insulin resistance. Here, we examined the regulation of PLA2G2A and the metabolic changes that occur in response to variations in thyroid status. In particular, the impact of PLA2G2A on the brown adipose tissue (BAT) thermogenic gene expression was explored. We induced hypothyroidism in C57BL/6 and PLA2G2A-overexpressing (IIA+) mice over a 10 wk period or treated them with thyroid hormone (T-3) for 5 wk. There were no significant changes in PLA2G2A abundance in response to thyroid status. The energy expenditure of hypothyroid IIA+ mice did not increase; however, the energy expenditure, substrate utilization, insulin sensitivity, and glucose tolerance were all elevated in the IIA+ mice given T-3. Moreover, white adipocytes from IIA+ mice were much more prone to beiging, including increased expression of brown adipose thermogenic markers such as uncoupling protein 1 (UCP1), PR domain containing 16, and early B cell factor 2. Finally, the BAT of IIA+ mice had increased UCP1 and other proteins indicative of mitochondrial uncoupling and nonshivering adaptive thermogenesis. These data reveal a novel role for PLA2G2A on adipose tissue thermogenesis depending on thyroid status.Kuefner, M. S., Deng, X., Stephenson, E. J., Pham, K., Park, E. A. Secretory phospholipase A(2) group IIA enhances the metabolic rate and increases glucose utilization in response to thyroid hormone.

Secretory phospholipase A2 group IIA (PLA2G2A) is a member of a family of secretory phospholipases that have been implicated in inflammation, atherogenesis, and antibacterial actions. Here, we evaluated the role of PLA2G2A in the metabolic response to a high fat diet. C57BL/6 (BL/6) mice do not express PLA2g2a due to a frameshift mutation. We fed BL/6 mice expressing the human PLA2G2A gene (IIA+ mice) a fat diet and assessed the physiologic response. After 10 weeks on the high fat diet, the BL/6 mice were obese, but the IIA+ mice did not gain weight or accumulate lipid. The lean mass in chow- and high fat-fed IIA+ mice was constant and similar to the BL/6 mice on a chow diet. Surprisingly, the IIA+ mice had an elevated metabolic rate, which was not due to differences in physical activity. The IIA+ mice were more insulin sensitive and glucose tolerant than the BL/6 mice, even when the IIA+ mice were provided the high fat diet. The IIA+ mice had increased expression of uncoupling protein 1 (UCP1), sirtuin 1 (SIRT1), and PPARγ coactivator 1α (PGC-1α) in brown adipose tissue (BAT), suggesting that PLA2G2A activates mitochondrial uncoupling in BAT. Our data indicate that PLA2G2A has a previously undiscovered impact on insulin sensitivity and metabolism.