Obesity has reached epidemic proportions worldwide, with some of the greatest severity in the United States. The most recent data reports ~70% of the American population is overweight (BMI ⥠25 kg/m2) and ~35% obese (BMI â¥30 kg/m2). Obesity is a metabolic disorder leading to increased risk for cardiovascular disease, type 2 diabetes, asthma, certain cancers, and various other diseases. A hallmark of obesity is adipose tissue (AT) inflammation and AT dysfunction. It is important to understand how immune cells accumulate in AT and regulate inflammation. We used CCR2-/- mice to study macrophage chemotaxis to AT, and also discovered CCR2-/- regulates chemotactic factors that upregulate AT eosinophil accumulation. Previous studies suggested that directly manipulating eosinophils (particularly in AT) could impart beneficial effects in obese subjects. Thus we developed an interventional treatment model of restoring obese AT eosinophils to higher levels of lean AT by injection of rIL5. AT eosinophils were successfully increased with rIL5, but there was no reduction in obesity and its comorbidities. Lastly, we discovered that repeated exposure to a foreign substance such as bovine serum albumin (BSA) could greatly increase AT eosinophils. While there were no metabolic improvements in mice chronically exposed to BSA, we have evidence to believe AT is capable of mounting a type 2 allergic response to antigens similar to the lung of an asthmatic, resulting in this large increase in AT eosinophils. Future studies will determine whether the AT eosinophilia following BSA exposure feeds back to the lung in allergic models, increasing both incidence and severity. Such studies will help in explaining the clinical link between obesity and allergic conditions such as asthma. In conclusion, we have found that restoring AT eosinophils to either physiological levels or super-physiological levels during obesity is not able to improve metabolic fitness (e.g. weight gain, glucose intolerance). Furthermore, we may have discovered a novel site of allergy that could offer insights and treatment opportunities for obese subjects that have increased difficulty with allergic disease.

Haploinsufficiency of the melanocortin-4 receptor (MC4R) is the most common monogenetic obesity syndrome in humans. This syndrome is associated with a reduction in autonomic tone, bradycardia, hyperinsulinemia and a reduced prevalence of obesity-associated hypertension. Thus, it has been assumed that melanocortin obesity syndrome may be protective with respect to obesity-associated cardiovascular disease. We show here that deletion of the Mc4r in mice causes a dilated cardiomyopathy characterized by reduced contractility and increased left ventricular diameter. This cardiomyopathy is independent of obesity as weight matched wild type mice are spared from systolic dysfunction. Mc4r-/- heart tissue further displays ultrastructural abnormalities in mitochondrial morphology and cardiomyocyte organization. Remarkably, mitochondrial function testing of myocardial tissue from Mc4r-/- mice revealed increased ADP stimulated respiration. This is in contrast to the reduction in O2 consumption seen in other models of cardiomyopathy, as well as the reduction in whole animal energy expenditure detected in MC4R knockout animals by indirect calorimetry. However, we show that this increase in respiration correlates with increased reactive oxygen species production â a canonical mediator of tissue damage. In keeping with this hypothesis, Mc4r-/- heart tissue displays a similar transcriptional profile to that of doxorubicin treatment â a free radical generating chemotherapy. Furthermore, Mc4r+/- mice are hypersensitive to both the cachexigenic and cardiac suppressive side effects of doxorubicin treatment. Together this study identifies MC4R deletion as a novel and potentially clinically important cause of heart failure.

The two-pore domain K⁺ (K2P) channel TALK-1 is highly expressed in the pancreatic islet and is linked to type 2 diabetes mellitus (T2DM) risk through a non-synonymous polymorphism (rs1535500). Here, we established that TALK-1 channels are functionally expressed in mouse and human β-cells where they modulate insulin secretion by limiting electrical excitability and cytosolic Ca²⁺ influx. We found that the rs1535500 polymorphism (encoding TALK-1 A277E) increases TALK-1 channel activity. When placed on a high-fat diet, mice lacking TALK-1 channels were protected from elevations in fasting glycemia. Therefore, rs1535500 may contribute to T2DM etiology by exacerbating hyperglycemia under diabetogenic conditions. We next determined that endoplasmic reticulum (ER)-localized TALK-1 channels conduct ER K⁺ countercurrents, facilitating β-cell and δ-cell ER Ca²⁺ leak. In β-cells, TALK-1 regulation of ER Ca²⁺ handling influences activation of K_slow, a Ca²⁺-dependent K⁺ current which repolarizes the plasma membrane potential, terminating each Ca²⁺ oscillation. K_slow is significantly reduced in KO β-cells, contributing to an elevated frequency of Ca²⁺ oscillations in TALK-1 KO islets. Furthermore, we determined that islets from mice lacking TALK-1 channels were resistant to ER stress induced by chronic exposure to a high-fat diet. Finally, we showed that TALK-1 channel regulation of δ-cell ER Ca²⁺ handling impacts δ-cell function. Somatostatin secretion is amplified by Ca²⁺-induced Ca²⁺ release (CICR) from the ER, and we found that TALK-1 regulates δ-cell Ca²⁺ handling and somatostatin secretion by modulating the ER Ca²⁺ stores which underlie CICR. Our data establish TALK-1 channels as key determinants of islet cell Ca²⁺ handling, and suggest that TALK-1 channels may be a therapeutic target to reduce islet cell ER Ca²⁺ defects during the pathogenesis of diabetes.

Type 2 diabetes is a major healthcare concern and is characterized by chronic hyperglycemia and low-grade inflammation. Hyperglycemia and systemic inflammation can induce the production of Prostaglandin E2 (PGE2) in islets. PGE2 signals through its four receptors, termed E-Prostanoid (EP) 1-4, to modulate many physiological functions, including insulin secretion and systemic inflammation. EP3 and EP4 often play opposing roles due to signaling through different G proteins, resulting in Gi inhibition (EP3) or Gs stimulation (EP4) of adenylyl cyclase. Previous work from our group revealed that Ptger4 (EP4) is increased while Ptger3 (EP3) is decreased in a mouse model of enhanced beta-cell proliferation and survival. Additional evidence from our lab suggests that EP3 inhibits mouse beta-cell proliferation in the setting of insulin resistance. Using ex vivo assays, we have determined that EP3 and EP4 play opposing roles in regulating beta-cell proliferation and survival in mouse and human islets: EP3 inhibits beta-cell proliferation via inhibition of PLC-gamma1 and enhances beta-cell death whereas EP4 activates beta-cell proliferation and promotes beta-cell survival in a PKA-dependent mechanism.

Type 2 diabetes (T2D) is characterized by hyperglycemia, which arises due to insulin resistance and beta cell failure and/or decreased beta cell mass. Genome-wide association studies have shown that single nucleotide polymorphisms in the SLC30A8 locus confer altered risk of T2D. Additional human genetic data show that SLC30A8 haploinsufficiency is protective against T2D development. Zinc transporter 8 (ZnT8), encoded by SLC30A8, is predominantly expressed in islet beta cells and localizes to insulin secretory vesicles. Studies of Slc30a8 KO mouse models observed a consistent decrease in islet zinc content, but no clear role for ZnT8 in glucose-stimulated insulin secretion (GSIS). We hypothesized that (i) ZnT8 is critical for the regulation of GSIS in mice, but this only becomes apparent in the absence of another zinc transporter, ZnT7; and (ii) Slc30a8 haploinsufficiency has beneficial effects on glucose metabolism in mice as in humans. To address these hypotheses, we generated several mouse models. A double KO (DKO) mouse lacking both ZnT7 and ZnT8 was generated, and the data demonstrated that deletion of ZnT7 alone had complex effects on glucose and insulin levels in vivo but no effect on GSIS in isolated islets. In contrast, GSIS was abolished in DKO islets. We also examined the protective effect of Slc30a8 haploinsufficiency in the context of diet-induced obesity (DIO). The results demonstrated a protection against DIO and improved glucose tolerance in ZnT8 heterozygous and KO mice compared to WT mice. Additionally, we examined the expression of Slc30a8 in Guinea pig pancreatic tissue and discovered that Slc30a8 is a pseudogene in Guinea pigs. Together, these data demonstrate that ZnT8 is not essential for beta cell function. Overall, the results of these studies suggest that altered ZnT8 function may affect T2D susceptibility through actions in other tissues where it is expressed at low levels rather than through effects on pancreatic islet function.

The pancreas is a dual function organ contributing to both blood glucose homeostasis and digestion. These functions are carried out by the endocrine and exocrine compartments of the pancreas, respectively, which derive from common multipotent progenitor cells (MPCs) during embryonic development. The differentiation process for the cells composing both the endocrine and exocrine compartments is highly orchestrated by regulatory transcription factors. Previous work from our lab showed that one such factor, Onecut 1 (Oc1), is essential for initiating endocrine development, proper duct development, and appears necessary for acinar cell development. Using gene expression and physiologic analyses of genetically altered mouse models we have determined that threshold-dependent cooperation between Oc1 and another transcription factor, Pancreatic and duodenal homeobox 1 (Pdx1) in MPCs is necessary for proper endocrine specification, differentiation, maturation, and function. Additionally, we have concluded that Oc1 is not necessary in differentiated acinar cells, however, we have identified novel targets of Oc1 in exocrine pancreas development.