Excess circulating insulin is associated with obesity in humans and in animal models. However, the physiologic causality of hyperinsulinemia in adult obesity has rightfully been questioned because of the absence of clear evidence that weight loss can be induced by acutely reversing diet-induced hyperinsulinemia. Herein, we describe the consequences of inducible, partial insulin gene deletion in a mouse model in which animals have already been made obese by consuming a high-fat diet. A modest reduction in insulin production/secretion was sufficient to cause significant weight loss within 5 wk, with a specific effect on visceral adipose tissue. This result was associated with a reduction in the protein abundance of the lipodystrophy gene polymerase I and transcript release factor (Ptrf; Cavin) in gonadal adipose tissue. RNAseq analysis showed that reduced insulin and weight loss also associated with a signature of reduced innate immunity. This study demonstrates that changes in circulating insulin that are too fine to adversely affect glucose homeostasis nonetheless exert control over adiposity.—Page, M. M., Skovsø, S., Cen, H., Chiu, A. P., Dionne, D. A., Hutchinson, D. F., Lim, G. E., Szabat, M., Flibotte, S., Sinha, S., Nislow, C., Rodrigues, B., Johnson, J. D. Reducing insulin via conditional partial gene ablation in adults reverses diet-induced weight gain.

Insulin receptor (Insr) protein is present at higher levels in pancreatic β-cells than in most other tissues, but the consequences of β-cell insulin resistance remain enigmatic. Here, we use an Ins1cre knock-in allele to delete Insr specifically in β-cells of both female and male mice. We compare experimental mice to Ins1cre-containing littermate controls at multiple ages and on multiple diets. RNA-seq of purified recombined β-cells reveals transcriptomic consequences of Insr loss, which differ between female and male mice. Action potential and calcium oscillation frequencies are increased in Insr knockout β-cells from female, but not male mice, whereas only male βInsrKO islets have reduced ATP-coupled oxygen consumption rate and reduced expression of genes involved in ATP synthesis. Female βInsrKO and βInsrHET mice exhibit elevated insulin release in ex vivo perifusion experiments, during hyperglycemic clamps, and following i.p. glucose challenge. Deletion of Insr does not alter β-cell area up to 9 months of age, nor does it impair hyperglycemia-induced proliferation. Based on our data, we adapt a mathematical model to include β-cell insulin resistance, which predicts that β-cell Insr knockout improves glucose tolerance depending on the degree of whole-body insulin resistance. Indeed, glucose tolerance is significantly improved in female βInsrKO and βInsrHET mice compared to controls at 9, 21 and 39 weeks, and also in insulin-sensitive 4-week old males. We observe no improved glucose tolerance in older male mice or in high fat diet-fed mice, corroborating the prediction that global insulin resistance obscures the effects of β-cell specific insulin resistance. The propensity for hyperinsulinemia is associated with mildly reduced fasting glucose and increased body weight. We further validate our main in vivo findings using an Ins1-CreERT transgenic line and find that male mice have improved glucose tolerance 4 weeks after tamoxifen-mediated Insr deletion. Collectively, our data show that β-cell insulin resistance in the form of reduced β-cell Insr contributes to hyperinsulinemia in the context of glucose stimulation, thereby improving glucose homeostasis in otherwise insulin sensitive sex, dietary and age contexts.

Caloric restriction (CR) is the only environmental intervention with robust evidence that it extends lifespan and delays the symptoms of aging, but its mechanisms are incompletely understood. Based on the prolonged longevity of knockout models, it was hypothesized that the insulin-IGF pathway could be a target for developing a CR mimic. This study aimed to test whether CR has additive effects on glucose homeostasis and beta-cell function in mice with reduced insulin gene dosage. To study models with a range of basal insulin levels, wild-type C57BL/6J and mice on an background, were put on 8 weeks of 40% CR at various ages. Both male and female mice rapidly lost weight due to a reduced WAT mass. Glucose tolerance was improved and fasting glucose levels were reduced by CR in both wild type and 45- and 70-week-old mice. The effects of CR and reduced insulin on glucose tolerance were non-additive in 20-week-old mice. Interestingly, mice on CR generally exhibited an inability to further depress blood glucose after insulin injection, pointing to possible alterations in insulin sensitivity. In conclusion, our results demonstrate that CR can cause weight loss in the context of reduced insulin production, but that CR-improved glucose homeostasis does not occur near the 'insulin floor' in young mice. Collectively, these data shed further light on the relationships between CR, insulin and glucose homeostasis.

Introduction: Our goal in this study was to determine female representation on editorial boards of high-ranking emergency medicine (EM) journals. In addition, we examined factors associated with gender disparity, including board members' academic rank, departmental leadership position, h-index, total publications, total citations, and total publishing years. Methods: In this retrospective study, we examined EM editorial boards with an impact factor of 1 or greater according to the Clarivate Journal Citations Report for a total of 16 journals. All board members with a doctor of medicine or doctor of osteopathic medicine degree, or international equivalent were included, resulting in 781 included board members. We analyzed board members' gender, academic rank, departmental leadership position, h-index, total publications, total citations, and total publishing years. Results: Gender disparity was clearly notable, with men holding 87.3% (682/781) of physician editorial board positions and women holding 12.7% (99/781) of positions. Only 6.6% (1/15) of included editorial board chiefs were women. Male editorial board members possessed higher h-indices, total citations, and more publishing years than their female counterparts. Male board members held a greater number of departmental leadership positions, as well as higher academic ranks.