PI: Martin Fisher, Ph.D. ( Beth Israel Deaconess Medical Center )
Abstract: Defining the Role of the Thermogenic Adipocyte in Mediating the Pharmacologic Actions of Fgf21
Obesity is a substantial burden on the US population and rates of obesity are increasing at pandemic scale. Overweight individuals, even at sub-obese levels, enhance the risk of developing complications including type ii diabetes, cardio vascular disease and non-alcoholic fatty liver. Despite this, there remain few effective therapies for the treatment of weight gain and obesity. Fibroblast growth factor 21 (FGF21) is a hormone with pleotropic metabolic actions contributing to discrete, adaptive metabolic pathways. FGF21 has emerged as a potential metabolic therapy as systemic treatment leads to increased glucose tolerance, improved lipid profiles and weight loss. We described FGF21 as the first endocrine agent that induced browning when administered exogenously and demonstrated that FGF21 acts directly to activate brown adipocytes and brown white adipose depots, in vitro. Browning is a process whereby mitochondrial rich, multilocular 'beige' adipocytes appear in white adipose tissue and is associated with improved glucose tolerance and systemic insulin sensitivity. The studies outlined in this grant aim to progress this research by identifying the role of FGF21 signaling in either thermogenic or white adipocytes in vivo. In doing so we will validate and describe two mouse models which negate FGF21 signaling in either thermogenic adipocytes or all adipocytes and will be invaluable for future research on this topic. We believe that thermogenic adipocytes are critical to the glucose lowering and weight loss effects of FGF21 and that discovering the mechanisms that regulate this process will identify novel pathways for therapeutic intervention of metabolic diseases. Relevance: Diabetes and obesity are major problems confronting the US. FGF21 is a factor that improves glucose and weight in obese animals making it an extremely promising agent for treatment of these complications. We hope that interrogation of the biological action of FGF21 will help develop new treatments and strategies for diabetes and obesity management
PI: Elvira Isganaitis, MD, MPH (Joslin Diabetes Center)
Abstract: Novel Mediators of Excessive Fetal Growth in Type 1 Diabetes Pregnancy
Type 1 diabetes (T1D) incidence has risen sharply over the past 30 years, affecting increasing numbers of women of childbearing age. Unfortunately, infants of women with T1D are at high risk for life-threatening complications in the neonatal period. Over 40% of infants of diabetic mothers are admitted to neonatal intensive care units, as compared to 6% in the general population. Excessive fetal growth, or being "large for gestational age" (LGA), is among the most common and serious complications of diabetic pregnancy. LGA infants are at increased risk for birth trauma, asphyxia, jaundice, and hypoglycemia, each of which may cause lasting neurological impairments or death. Also of great concern is the recent discovery that LGA infants are at increased risk of obesity and type 2 diabetes later in life. Maintaining near-normal glucose levels during pregnancy can reduce risk of LGA, but the incidence remains high even in optimally managed pregnancies, with ~50% of infants born LGA. Thus, novel approaches for preventing LGA and its accompanying complications are urgently needed. In this grant, we will leverage the unique patient population of the Joslin Pregnancy Program together with state-of-the-art techniques, including continuous glucose monitoring and metabolomics analysis, to identify novel mechanisms for LGA in pregnancies complicated by T1D. In Aim 1, we will examine associations between maternal glycemic variability, as assessed by continuous glucose monitoring, and fetal glycemic exposure. In Aim 2, we will test whether lipids and other nutrients are associated with LGA risk in T1D pregnancy. We will perform global metabolomic analysis to comprehensively quantify lipids, metabolic intermediates, and other small molecules in (i) maternal plasma, and (ii) cord plasma. Because we are focusing on modifiable factors, including maternal glucose variability and nutrient metabolism, these studies will be readily translatable to the development of new clinical strategies to prevent LGA and its accompanying neonatal complications in the setting of T1D pregnancy.
PI: Anders M. Naar, Ph.D. ( Massachusetts General Hospital )
Abstract: Role of miR-128-1 in metabolic abnormalities underpinning type 2 diabetes
Abnormal regulation of cholesterol/lipid and energy homeostasis is associated with metabolic syndrome, type II diabetes, and cardiovascular disease. An improved understanding of the regulatory mechanisms governing cholesterol/lipid and energy homeostasis could yield novel therapeutic avenues to combat cardiometabolic disorders. We recently uncovered microRNAs (miR-33b/a) as key regulators of cholesterol/lipid and energy metabolism. We followed up this initial discovery with an unbiased and systematic meta-analysis of genome-wide association studies linking genomic loci to abnormal blood lipids to identify 69 microRNAs in proximity to signature single nucleotide polymorphisms. Two of these microRNAs (miR-128-1 and miR-148a) were validated as key regulators of cholesterol/lipid and energy homeostasis.both in vitro and in vivo. Intriguingly, miR-128-1 is located in a genomic region on human chromosome 2 that has been strongly linked to positive selection (last 5K years), type 2 diabetes, obesity and circulating cholesterol/lipid abnormalities. Based on strong preliminary data in diet-induced obese (DIO) mice showing that antisense treatment targeting miR-128-1 ameliorates excess adipocity, hepatic steatosis, hyperglycemia and insulin resistance, we posit that miR-128-1 dysregulation may contribute to all of these associations. Accordingly, miR-128-1 appears to directly control the expression of key metabolic proteins such as PGC1?, PPAR?, SIRT1, InsR, and IRS1 in white adipose tissue, liver, and skeletal muscle. We propose here to further investigate the functional role of miR-128-1 in insulin resistance/glucose abnormalities linked to cardiometabolic diseases using miR-128-1 KO mice fed a high-fat diet (DIO model) and miR-128-1 antisense targeting in leptin-deficient (ob/ob) mice. These studies will involve IP-GTT and ITT, echoMRI and melabolic cage studies, as well as in-depth tissue analysis by qRT-PCR, immunoblotting, IHC, and H&E staining to ascertain impact on miR-128-1 regulatory circuits and downstream effects on metabolic homeostasis. Data from these studies should provide further insights into metabolic control by miR-128-1 and whether it may represent anovel therapeutic target for the treatment or prevention of type 2 diabetes, and serve as support for an NIH R01 application to expand these studies.
PI: Vaibhav Saini, Ph.D. (Massachusetts General Hospital)
Abstract: Absence of Vitamin D Signaling Increases Lipolysis and Fatty acid Synthesis, Leading to NAFLD
Nonalcoholic fatty liver disease (NAFLD) afflicts 20-30% of the population in Western countries. Type II diabetes patients demonstrate NAFLD that worsens to hepatic fibrosis. In healthy individuals, adipose tissue is the primary source of free fatty acids (~70%) for liver triglyceride synthesis. In insulin resistance, insulin fails to inhibit lipolysis in adipocytes, causing excess free fatty acid supply to the liver, resulting in excess hepatic triglyceride synthesis and NAFLD. Therefore, molecular interventions to inhibit lipolysis could prevent or treat NAFLD. However, because the molecular mechanisms underlying adipose lipolysis in NAFLD remain poorly defined, no targeted therapies exist. Low vitamin D levels have been reported in obesity, Type II diabetes, prediabetes, and the metabolic syndrome. Vitamin D exerts its physiological effects by binding to the vitamin D receptor (VDR), a nuclear hormone receptor. While direct VDR actions in liver have been shown to suppress hepatic fibrosis, the role of impaired vitamin D signaling in adipocytes as a cause of NAFLD and hepatic fibrosis remains unknown. In this regard, our preliminary data in global VDR null mice show a fatty liver phenotype as well as increased PPAR??mRNA expression and increased expression of genes involved in fatty acid synthesis and lipolysis in gonadal white adipose tissue (gWAT). Therefore, we hypothesize that absence of vitamin D signaling increases adipose lipolysis and fatty acid synthesis, leading to NAFLD. Herein, we will use Adiponectin-Cre to conditionally knockout VDR expression in adipocytes. We will analyze lipolysis and fatty acid synthesis in gWAT; serum lipid profiles; and inflammation, steatosis, and fibrosis in the liver. mRNA expression of genes involved in lipolysis (LPL and its transcriptional regulator PPAR???and fatty acid synthesis (FASN) will be measured in gWAT. VDR and PPAR??co-recruitment to regulatory sites on the PPAR? and LPL genes will be evaluated by sequential ChIP-qPCR analysis in primary adipocytes. Interaction of VDR and PPAR??proteins will be examined by co-immunoprecipitation analysis in primary adipocytes. Our studies will define a role for the VDR in suppression of lipolysis and fatty acid synthesis and demonstrate that impaired vitamin D signaling in adipose tissue leads to NAFLD. Importantly, the results of the proposed studies are expected to identify the VDR as a therapeutic target in the prevention and treatment of NAFLD in Type II diabetes.
PI: Eric Sheu, MD., D Phil (Brigham and Women's Hospital)
Abstract: The Role of Gastrointestinal Mucosal Immunity in Diabetes
A person dies every 7 seconds from complications of type 2 diabetes (T2D). Fueled by the obesity epidemic, T2D affects 29 million people in the United States and 400 million worldwide. Aberrant systemic inflammation that develops in the obese contributes to insulin resistance and the development of T2D. Growing evidence suggest that the gastrointestinal (GI) tract may be an important organ that drives systemic inflammation and the pathogenesis of diabetes. Changes in intestinal permeability to inflammatory antigens derived from the microbiome have been shown to lead to insulin resistance and adipose tissue inflammation. Further supporting the importance of the GI tract in diabetes, alteration of intestinal anatomy with bariatric surgery reverse systemic markers of inflammation, alters the gut microbiome, and is the most effective current therapy for diabetes. We hypothesize that diabetes alters the GI mucosal immune response, leading to impaired intestinal metabolic and barrier function. To test this hypothesis, we propose the following specific aims: Aim 1. Quantify changes in GI leukocyte phenotype and function in diabetes. The mucosal immune system maintains homeostasis with the gut microbiota; therefore, we believe sustained changes in the GI immune response must occur that lead to altered intestinal permability and systemic inflammation. We will use the novel technique of mass cytometry to perform single cell immune profiles of gastric, small intestine, and colonic leukocytes in mouse models of diabetes and obesity. We will simultaneously collect human intestinal tissue for validation of animal results. Aim 2. Study the influence of mucosal immunity on intestinal glucose regulation. Intestinal inflammation has been linked to altered intestinal epithelial metabolic function. We will employ an unique portal-systemic catherization model to directly measure the impact of altered intestinal inflammation on intestinal glucose utilization, absorption, incretin hormone secretion, and gut permeability. The goal of this work is to identify targets in the gut immune system for the treatment of diabetes. This pilot study will also provide a foundation for future studies looking at the impact of bariatric surgery on mucosal and systemic immunity.
PI: Linus Tsai, MD, PhD ( Beth Israel Deaconess Medical Center)
Abstract: A Cellular and Molecular Atlas of the Arcuate Hypothalamus Using Dropseq
Obesity results from dysregulated energy homeostasis, governed by complex homeostatic interactions between peripheral tissues such as liver, the gastrointestinal tract, and adipose, and the central nervous system. The arcuate nucleus of the hypothalamus (ARH) is a key point of convergence for signals of energy balance and plays a fundamental role in body weight regulation. The arcuate is made up of a dense, heterogenous mix of cell types including multiple leptin receptor expressing neuronal subtypes, oligodendrocytes, microglia, astrocytes and given its proximity to the 3rd ventricle, a complex mix of ependymal cells and tanycytes. Many of these individual cell types are altered in number and/or function in the setting of obesity; however, mechanisms that underlie how these cells change and interact during development and maintenance of obesity are unclear. Previous attempts to assess gene expression within ARH have been limited by the difficulty of assessing cell type specific expression. We will overcome such limitations by generating tens of thousands of unbiased, untargeted transcriptional profiles from individual ARH cells across a variety of physiologic states relevant to energy balance and obesity. We will use a novel cost-efficient single cell transcriptional profiling technique (Dropseq) to determine the full complement of cell types within ARH in an unbiased fashion. By examining arcuates across a variety of metabolically relevant physiological conditions, we will determine transcriptional changes occurring in individual cell types as well as how cell types might interact with each other to cause or maintain the obese state. Relevance This proposal addresses the public health epidemic of obesity, a key driver of diabetes and metabolic syndrome. We will examine a key brain region involved in weight regulation in an unbiased and comprehensive manner, through simultaneous assessment of what RNAs are made in all cell subtypes. This study will provide an atlas of cell types in this brain region and will define molecular pathways that are altered and in what cell types, during development of obesity and diabetes.
PI: Walensky, Rochelle P. MD, MPH ( Massachusetts General Hospital )
Abstract: The Cost-effectiveness of Interventions to Promote Medication Adherence in Type 2 Diabetes
The goal of this project is to develop and validate a simulation model of diabetes prevention, care and treatment to evaluate clinical outcomes, costs, and cost-effectiveness of strategies for diabetes prevention and care. We propose an innovative approach to project the influence of long-term adherence with treatment and retention in care. Diabetes and its complications are amongst the leading causes of death in the U.S. and the growing economic burden, estimated to be $322 billion in 2012, is a major public health concern. The "cascade of diabetes care" reflects the continuum from diabetes diagnosis to linkage to care to medication adherence and retention; this cascade is a powerful illustration of the fact that of the estimated 28.4 million people living with diabetes only 20% receive treatment and achieve their targets, defined in terms of glucose, blood pressure, and lipid levels and smoking status (Figure, Ali et al., Ann Intern Med 2014). Poor adherence is the principal cause of development of complications of diabetes and their associated individual, societal and economic costs. This challenge highlights the critical impact of adherence toward achieving long-term glucose, lipid, and blood pressure control. Engagement in care is associated with better control of risk factors, which slows progression to clinical events. This emphasizes the need for economic evaluation of interventions and treatment strategies that consider important investments in mechanisms to promote engagement in care and adherence and their underlying behavioral mechanisms. Mathematical simulation models provide the necessary evidence to inform economic evaluation in comparative effectiveness research. They serve as a framework to synthesize the evidence from different sources for evidence-based medicine and allow considering all alternatives to make an informed decision. Especially important for diabetes as a chronic disease with long-term complications, simulation models enable adopting a sufficiently long time horizon to see the difference in cost and effectiveness between alternative treatments. Simulation models have long been used to inform guidelines and national policy in HIV disease, cardiovascular disease, and cancer, among others. The particular focus and novelty of the proposed research is the consideration of adherence, loss to follow up, and retention in the model formulation to project and compare the long-term cost-effectiveness of diabetes prevention and intervention programs. The main objective of the proposed research is to address the gaps in the continuum of care. Cohort data to populate the model will be based on published sources and will use health services data from the CDTR core for sensitivity analyses where published data is not available.