Hepatic Glucagon-Receptor Signaling Enhances Insulin-Stimulated Glucose Disposal in Rodents

Glucagon receptor (GCGR) agonists cause hyperglycemia but also weight loss. However, GLP1R/GCGR mixed agonists do not exhibit the diabetogenic effects often attributed to GCGR activity. Thus, we sought to investigate the effect of glucagon agonism on insulin action and glucose homeostasis. Acute GCGR agonism induced immediate hyperglycemia, followed by improved glucose tolerance and enhanced glucose-stimulated insulin secretion. Moreover, acute GCGR agonism improved insulin tolerance in a dose-dependent manner in both lean and obese mice. Improved insulin tolerance was independent of GLP1R, FGF21, and hepatic glycogenolysis. Moreover, we observed increased glucose infusion rate, disposal, uptake, and suppressed endogenous glucose production during euglycemic clamps. Mice treated with insulin and GCGR agonist had enhanced phosphorylation of hepatic AKT at Ser473; this effect was reproduced in isolated mouse primary hepatocytes and resulted in increased AKT kinase activity. These data reveal that GCGR agonism enhances glucose tolerance in part, by augmenting insulin action, with implications for the use of GCGR agonism in therapeutic strategies for diabetes

High Prevalence of Natural Chlamydophila Species Infection in Calves

We investigated the acquisition and prevalence of Chlamydophila sp. infection in calves. Specimens were collected at weekly intervals from birth to week 12 postpartum from 40 female Holstein calf-dam pairs in a dairy herd. Real-time PCR detected, quantified, and differentiated Chlamydophila 23S rRNA gene DNA from vaginal cytobrush swabs and milk samples. Chemiluminescence enzyme-linked immunosorbent assay with lysed Chlamydophila abortus or Chlamydophila pecorum elementary body antigens quantified antibodies against Chlamydophila spp. in sera. Chlamydophila sp. DNA was found in 61% of calves and 20% of dams in at least one positive quantitative PCR. In calves, clinically inapparent C. pecorum infection with low organism loads was fivefold more prevalent than C. abortus infection and was most frequently detected by vaginal swabs compared to rectal or nasal swabs. In dams, C. abortus dominated in milk and C. pecorum dominated in the vagina. The group size of calves correlated positively (P < 0.01) with Chlamydophila infection in quadratic, but not linear, regression. Thus, a doubling of the group size was associated with a fourfold increase in frequency and intensity of Chlamydophila infection. For groups of 14 or 28 calves, respectively, logistic regression predicted a 9 or 52% probability of infection of an individual calf and a 52 or 99.99% probability of infection of the group. Anti-Chlamydophila immunoglobulin M antibodies in Chlamydophila PCR-positive calves and dams and in dams that gave birth to calves that later became positive were significantly higher than in PCR-negative animals (P ≤ 0.02). Collectively, crowding strongly enhances the frequency and intensity of highly prevalent Chlamydophila infections in cattle

The Role of beta-Hydroxybutyrate in Glucagon Receptor Stimulated Food Intake Suppression in Obese Mice

Glucagon’s counterregulatory role to insulin action is well known, but its broader therapeutic potential is an evolving research interest. We have reported that chronic glucagon receptor (GCGR) activation decreases body weight (BW) and food intake (FI) while increasing beta-Hydroxybutyrate (bHB), a known ketone body. Recent studies suggest that ketone esters similarly reduce food intake in mice. The primary objective of this study was to determine if decreases in FI seen in DIO mice treated with GCGR agonist (IUB288) are mediated by bHB. C57Bl6/J mice were fed High Fat Diet (HFD, 58% fat + sucrose) for 12 weeks, to stimulate diet induced obesity. Mice were assigned into groups matched for food intake; Vehicle-Vehicle, Vehicle-IUB288, Trimetazidine-Vehicle, Trimetazidine-IUB288, (n=3). Mice were treated with or without Trimetazidine, 15 mg/kg (TMZ), an inhibitor of ketogenesis, for two days prior to four days of IUB288 or vehicle injections. Following a ten-day wash out period, the study was repeated using 30 mg/kg. FI and BW were measured daily, and plasma bHB were measured at baseline and study conclusion. IUB288 reduced FI and BW in both TMZ and vehicle treated mice. Surprisingly bHB concentration was elevated post-treatment in both 15 mg/kg and 30 mg/kg TMZ treated mice. In both experiments, the administered dosage of TMZ was insufficient to block IUB288-stimulated bHB. The results provide neither evidence for, or against, bHB FI suppression in DIO mice. Future studies will utilize a larger dosage of TMZ, or administration of a different inhibitor of ketogenesis

Temporal Delay of Peak T-Cell Immunity Determines Chlamydia pneumoniae Pulmonary Disease in Mice▿ †

Severe chlamydial disease typically occurs after previous infections and results from a hypersensitivity response that is also required for chlamydial elimination. Here, we quantitatively dissected the immune and disease responses to repeated Chlamydia pneumoniae lung infection by multivariate modeling with four dichotomous effects: mouse strain (A/J or C57BL/6), dietary protein content (14% protein and 0.3% l-cysteine-0.9% l-arginine, or 24% protein and 0.5% l-cysteine-2.0% l-arginine), dietary antioxidant content (90 IU α-tocopherol/kg body weight versus 450 IU α-tocopherol/kg and 0.1% g l-ascorbate), and time course (3 or 10 days postinfection). Following intranasal C. pneumoniae challenge, C57BL/6 mice on a low-protein/low-antioxidant diet, but not C57BL/6 mice on other diets or A/J mice, exhibited profoundly suppressed early lung inflammatory and pan-T-cell (CD3δ+) and helper T-cell (CD45) responses on day 3 but later strongly exacerbated disease on day 10. Contrast analyses characterized severe C. pneumoniae disease as being a delayed-type hypersensitivity (DTH) response with increased lung macrophage and Th1 cell marker transcripts, increased Th1:Th2 ratios, and Th1 cytokine-driven inflammation. Results from functional analyses by DTH, enzyme-linked immunospot, and immunohistofluorescence assays were consistent with the results obtained by transcript analysis. Thus, chlamydial disease after secondary infection is a temporal dysregulation of the T-cell response characterized by a profoundly delayed T-helper cell response that results in a failure to eliminate the pathogen and provokes later pathological Th1 inflammation. This delayed T-cell response is under host genetic control and nutritional influence. The mechanism that temporally and quantitatively regulates the host T-cell population is the critical determinant in chlamydial pathogenesis

Antiretroviral therapy potentiates high-fat diet induced obesity and glucose intolerance

Objective: Breakthroughs in HIV treatment, especially combination antiretroviral therapy (ART), have massively reduced AIDS-associated mortality. However, ART administration amplifies the risk of non-AIDS defining illnesses including obesity, diabetes, and cardiovascular disease, collectively known as metabolic syndrome. Initial reports suggest that ART-associated risk of metabolic syndrome correlates with socioeconomic status, a multifaceted finding that encompasses income, race, education, and diet. Therefore, determination of causal relationships is extremely challenging due to the complex interplay between viral infection, ART, and the many environmental factors. Methods: In the current study, we employed a mouse model to specifically examine interactions between ART and diet that impacts energy balance and glucose metabolism. Previous studies have shown that high-fat feeding induces persistent low-grade systemic and adipose tissue inflammation contributing to insulin resistance and metabolic dysregulation via adipose-infiltrating macrophages. Studies herein test the hypothesis that ART potentiates the inflammatory effects of a high-fat diet (HFD). C57Bl/6J mice on a HFD or standard chow containing ART or vehicle, were subjected to functional metabolic testing, RNA-sequencing of epididymal white adipose tissue (eWAT), and array-based kinomic analysis of eWAT-infiltrating macrophages. Results: ART-treated mice on a HFD displayed increased fat mass accumulation, impaired glucose tolerance, and potentiated insulin resistance. Gene set enrichment and kinomic array analyses revealed a pro-inflammatory transcriptional signature depicting granulocyte migration and activation. Conclusion: The current study reveals a HFD-ART interaction that increases inflammatory transcriptional pathways and impairs glucose metabolism, energy balance, and metabolic dysfunction. Keywords: Antiretroviral therapy, Obesity, Glucose intolerance, Adipose tissue inflammation, Insulin resistance, Macrophage activatio

An early, reversible cholesterolgenic etiology of diet-induced insulin resistance

Objective: A buildup of skeletal muscle plasma membrane (PM) cholesterol content in mice occurs within 1 week of a Western-style high-fat diet and causes insulin resistance. The mechanism driving this cholesterol accumulation and insulin resistance is not known. Promising cell data implicate that the hexosamine biosynthesis pathway (HBP) triggers a cholesterolgenic response via increasing the transcriptional activity of Sp1. In this study we aimed to determine whether increased HBP/Sp1 activity represented a preventable cause of insulin resistance. Methods: C57BL/6NJ mice were fed either a low-fat (LF, 10% kcal) or high-fat (HF, 45% kcal) diet for 1 week. During this 1-week diet the mice were treated daily with either saline or mithramycin-A (MTM), a specific Sp1/DNA-binding inhibitor. A series of metabolic and tissue analyses were then performed on these mice, as well as on mice with targeted skeletal muscle overexpression of the rate-limiting HBP enzyme glutamine-fructose-6-phosphate-amidotransferase (GFAT) that were maintained on a regular chow diet. Results: Saline-treated mice fed this HF diet for 1 week did not have an increase in adiposity, lean mass, or body mass while displaying early insulin resistance. Consistent with an HBP/Sp1 cholesterolgenic response, Sp1 displayed increased O-GlcNAcylation and binding to the HMGCR promoter that increased HMGCR expression in skeletal muscle from saline-treated HF-fed mice. Skeletal muscle from these saline-treated HF-fed mice also showed a resultant elevation of PM cholesterol with an accompanying loss of cortical filamentous actin (F-actin) that is essential for insulin-stimulated glucose transport. Treating these mice daily with MTM during the 1-week HF diet fully prevented the diet-induced Sp1 cholesterolgenic response, loss of cortical F-actin, and development of insulin resistance. Similarly, increases in HMGCR expression and cholesterol were measured in muscle from GFAT transgenic mice compared to age- and weight-match wildtype littermate control mice. In the GFAT Tg mice we found that these increases were alleviated by MTM. Conclusions: These data identify increased HBP/Sp1 activity as an early mechanism of diet-induced insulin resistance. Therapies targeting this mechanism may decelerate T2D development