Jiandie Lin - US grants

[unreadable] DESCRIPTION (provided by applicant): Metabolic syndrome is emerging as a global epidemic. The profound metabolic dysregulation in this syndrome is typically manifested by clustering of several disorders, including obesity, type 2 diabetes, and dyslipidemia, and is associated with an increased risk for cardiovascular disease. Hepatic lipogenesis and lipoprotein metabolism are important in maintaining lipid homeostasis. There is increasing evidence that hepatic lipid metabolism plays an important role in the pathogenesis of key aspects of metabolic syndrome, including hyperlipidemia, hyperglycemia, and insulin resistance. We have recently demonstrated that transcriptional coactivator PGC-1? coordinately regulates lipogenesis, lipid trafficking, and lipoprotein metabolism in the liver. These data suggest that PGC-1? is a central component of the regulatory network in maintaining lipid homeostasis. The major goals of this proposal are to test the hypothesis that PGC-1? is involved in the pathogenesis of metabolic syndrome and serves as a molecular link between lipid metabolism and insulin resistance. In addition, molecular components of the PGC-1? pathway will be dissected and analyzed. Aim 1 is to determine evaluate the role of PGC-1? in the pathogenesis of metabolic dysregulation and in linking lipid metabolism to insulin resistance. Aim 2 is to define transcriptional components underlying PGC-1? regulation of triglyceride and lipoprotein metabolism. Aim 3 is to investigate the role of chromatin remodeling in lipid metabolism. Completion of this proposal will define the molecular details of a major regulatory network in the maintenance of lipid homeostasis. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Most living organisms exhibit behavioral and physiological rhythms, including sleep, activity, blood pressure as well as lipid and carbohydrate metabolism. This diurnal oscillation is regulated by circadian clock, which responds to light and feeding cycles. Perturbed clock function has been implicated in sleep disorders and it is associated with increased cardiovascular risk. Disruption of clock function in rodents leads to obesity and impaired glucose homeostasis, suggesting that energy homeostasis is linked to biological timing systems. The physiological and molecular mechanisms that integrate clock and energy metabolism, however, remain poorly defined. We have previously demonstrated that PGC-11, a transcriptional coactivator that regulates several major aspects of energy metabolism, including hepatic gluconeogenesis, fatty acid 2-oxidation, and mitochondrial oxidative metabolism, also controls clock gene expression. Mice deficient in PGC-11 have aberrant circadian rhythms of locomotor activity, body temperature, metabolic rate, and diurnal patterns of metabolic gene expression. Based on these findings, we hypothesize that the integration of clock and metabolism is achieved through reciprocal crosstalk between circadian pacemaker and metabolic regulatory networks. We will explore this hypothesis by evaluating the role of PGC-11 in tissue- autonomous integration of clock and metabolism. We will also explore molecular components involved in the crosstalk between the circadian pacemaker and PGC-11. Finally, we will investigate novel mechanisms through which the PGC-11 regulatory network controls circadian metabolic rhythms. How circadian pacemaker and energy metabolism are integrated in individual tissues remains a fundamental question. Our study has the potential to elucidate key molecular components that link the circadian timing system to energy homeostasis, and to gain insights into pathogenic mechanisms of metabolic and cardiovascular diseases. (End of Abstract)

DESCRIPTION (provided by applicant): Metabolic syndrome has become a global epidemic that significantly increases the risk for type 2 diabetes, cardiovascular disease, and non-alcoholic fatty liver disease (NAFLD). While hepatic steatosis often exists as a benign condition, a subset of NAFLD patients develop non-alcoholic steatohepatitic (NASH), which is characterized by progressive liver injury, inflammation, and fibrosis. The regulatory networks that control hepatic lipid metabolism have been a focus of research in the past two decades. These studies provide critical insights into the molecular and physiological mechanisms that contribute to the pathogenesis of hepatic steatosis. However, our understanding of the pathogenic mechanisms that drive the development of NASH from benign steatosis is remarkably limited. Further, a lack of appropriate animal models that recapitulate key aspects of NASH limits our ability to define the underlying pathogenic events and to evaluate their potential value in therapeutic development. Recent studies have shown that liver autophagy is impaired in insulin resistant states and its deficiency contributes to hepatic steatosis. The fundamental role of autophagy in hepatic lipid metabolism and liver function remains poorly understood. Here, we discovered a new molecular pathway that regulates the program of autophagy gene expression and autophagy in hepatocytes. Based on a body of new preliminary data, we hypothesize that impaired autophagy in the liver perturbs hepatic lipid metabolism and exacerbates liver injury, inflammation, and fibrosis. In this proposal, we will first define the molecular mechanisms that regulate autophagy in hepatocytes. We will assess the role of autophagy in lipid metabolism using a mouse strain with conditional autophagy deficiency in the liver. Finally, we will use genetic and chemical approaches to evaluate whether activation of autophagy improves hepatic lipid homeostasis and ameliorates the progression of NASH pathologies. Successful completion of this project will provide novel insights into the fundamental crosstalk between autophagy and lipid metabolic pathways, and shift the current paradigm on the pathogenesis of NASH.

DESCRIPTION (provided by applicant): Metabolic syndrome has become a global epidemic that dramatically increases the risk for type 2 diabetes, cardiovascular disease, and non-alcoholic steatohepatitis. Skeletal muscle insulin resistance is a hallmark of the metabolic derangements in this syndrome that has been associated with impaired mitochondrial oxidative capacity and a shift from oxidative to glycolytic myofiber types. However, the cause and effect relationship between the metabolic properties of skeletal myofibers and insulin sensitivity remains unclear. While the PGC-1 coactivators and their transcriptional partners are emerging as core regulators of mitochondrial biogenesis and the oxidative fiber program, our understanding of the regulatory cascade that controls the development and function of fast-twitch glycolytic muscle is remarkably limited. The overall goal of this proposal is to explore novel mechanisms that regulate glycolytic muscle formation and investigate their role in the pathogenesis of insulin resistance during chronic caloric excess. In preliminary studies, we have identified BAF60c, a subunit of the SWI/SNF chromatin- remodeling complexes that interacts with other transcription factors, as a novel regulator of fast glycolytic muscle formation. Further we have delineated key molecular components of this regulatory cascade. In this proposal, we will first use gain- and loss- of-function mouse models to establish the physiological role of this pathway in the regulation of metabolic and contractile specification of fast glycolytic muscle. We will dissect the core molecular components involved, and assess the role of glycolytic muscle in the development of diet-induced insulin resistance. Successful completion of this project will provide novel insights into the mechanistic basis of glycolytic muscle development and plasticity, and shift the current paradigm on interrelationship between muscle fiber types and the pathogenesis of insulin resistance. PUBLIC HEALTH RELEVANCE: Metabolic syndrome is linked to increased risk for type 2 diabetes, cardiovascular disease, and non-alcoholic steatohepatitis, and has become a serious public health challenge for the US and the rest of the world. While it has been recognized that insulin resistance is an early pathogenic event in disease progression, the mechanisms that regulate tissue and systemic insulin sensitivity remain poorly understood. We propose to use state-of-the-art molecular, genetic, and metabolic tools to establish the significance of this new pathway in muscle function, dissect novel regulatory components, and assess the cause and effect relationship between muscle metabolism and insulin resistance.

? DESCRIPTION (provided by applicant): Metabolic syndrome has become a global epidemic that dramatically increases the risk for type 2 diabetes, cardiovascular disease, and non-alcoholic fatty liver disease. Brown fat plays an important role in the defense against cold and contributes to whole body energy balance. To date, the metabolic action of brown fat has been primarily attributed to its unique ability to stimulate uncoupled mitochondrial respiration. Secreted factors exert diverse effects on carbohydrate and lipid metabolism in peripheral tissues and the maintenance of systemic energy homeostasis. Adipose tissue hormones, such as leptin and adiponectin, gut-derived fibroblast growth factors, and myokines sense nutrient status and coordinate key aspects of cellular metabolism. Whether brown adipocytes engage other metabolic tissues through secreted factors to regulate nutrient and energy metabolism in the body is unknown. In preliminary studies, we identified a novel brown fat-enriched secreted factor that is highly inducible during brown adipocyte differentiation. Using gain and loss of function mouse models, we established that this brown adipokine regulates whole body glucose and lipid metabolism. In this proposal, we will test our central hypothesis that brown fat secreted factors play a central role in metabolic crosstalk. In Aim 1, we plan to define the role of brown adipokine in metabolic adaptation during thermogenesis and in obesity. In Aim 2, we will evaluate the mechanisms underlying the metabolic action of this secreted factor. In Aim 3, we will assess the extent to which elevated adipokine expression protects mice from diet-induced metabolic derangements. Our proposed work will provide insights into a previously unrecognized role of brown fat in endocrine signaling and generate critical preclinical data for future therapeutic development.

Skeletal muscle is a major site of postprandial glucose disposal. Impaired muscle glucose metabolism contributes to insulin resistance and glucose intolerance in type 2 diabetes. Whether glucose directly engages nutrient signaling pathways in skeletal myocytes to maintain homeostasis under physiological and metabolic stress conditions remains largely unexplored. Skeletal myofibers are remarkably heterogeneous in their metabolic properties, ranging from highly oxidative to highly glycolytic types. We recently demonstrated that Baf60c, a subunit of the SWI/SNF chromatin-remodeling complex, is enriched in glycolytic muscles and regulates a program of gene expression that promotes glycolytic metabolism. Muscle-specific transgenic activation of this pathway improved whole body glucose metabolism in obesity. Despite its strong effects on myocyte metabolism, the physiological signals that engage this pathway and the mechanisms through which Baf60c regulates muscle and systemic glucose metabolism remain to be established. A body of preliminary data has been obtained to support our hypothesis that Baf60c is a key target of myocyte nutrient sensing that controls muscle and systemic glucose metabolism. In this proposal, we will first assess the role of Baf60c in skeletal muscle nutrient signaling and glycolytic metabolism and whole body glucose homeostasis. We will dissect the molecular events that lead to the activation of the Baf60c/Deptor pathway. Finally, we will investigate the significance of a muscle-derived secreted factor in the regulation of systemic glucose metabolism. Successful completion of this project will provide novel insights into the physiological and mechanistic basis of glycolytic muscle metabolism and its role in glucose homeostasis.

ABSTRACT Aging is associated with a progressive decline of metabolic health and represents a unique risk factor for the development of type 2 diabetes, cardiovascular disease, and non-alcoholic fatty liver disease in the elderly. The biology underlying age-related metabolic disease is likely multifaceted, and conceptually, may involve intrinsic changes in tissue metabolism and perturbations of inter-tissue metabolic crosstalk. Endocrine factors play a critical role in modulating carbohydrate and lipid metabolism and maintaining systemic energy homeostasis. Perturbations of endocrine signaling are commonly observed during mammalian aging. However, the nature of endocrine signals that govern metabolic homeostasis during mammalian aging remains poorly defined. In preliminary studies, we identified Neuregulin 4 (Nrg4) as a novel adipocyte-derived secreted factor that protects mice from insulin resistance and hepatic fat accumulation in an age-dependent manner. The expression of Nrg4 in mouse adipose tissues was elevated by caloric restriction. These findings form the basis for our central hypothesis that endocrine signaling by adipokines plays a uniquely important role in preserving metabolic homeostasis during aging. In this proposal, we plan to evaluate the physiological role of this factor in age-dependent metabolic regulation using gain- and loss-of-function mouse models. We will delineate its regulation during aging and explore the molecular and metabolic mechanisms involved.

Abstract The mammalian liver functions as a hub for nutrient and energy metabolism that helps maintain systemic homeostasis. Hepatic metabolism is highly responsive to physiological signals and undergoes drastic reprogramming in insulin resistant state. The liver also provides an important source of secreted proteins in circulation, including lipoproteins, coagulation factors, and endocrine factors (hepatokines). Upon release into circulation, hepatokines may act locally or on other peripheral tissues and the central nervous system to exert pleiotropic metabolic effects, as illustrated by recent studies on FGF21. Despite the expanding role of liver-derived secreted factors in systemic energy metabolism, the molecular nature and physiological action of the endocrine liver remains an important unsolved problem in molecular metabolism. Addressing this challenge provides a significant opportunity for the discovery of novel therapeutic targets and approaches for the treatment of metabolic disease. In preliminary studies, we identified Tsukushin (TSKU) as a novel liver-derived endocrine factor that exhibits markedly elevated levels in plasma from diet-induced and genetic obese mice. Genetic inactivation of this hepatokine stimulates thermogenesis and energy expenditure and protects mice from high-fat diet-induced obesity and metabolic disorders. Based on these exciting findings, we hypothesize that TSKU exacerbates diet-induced deterioration of metabolic health through attenuating thermogenesis and energy expenditure. We will test this hypothesis using a combination of in vivo and in vitro gain- and loss-of-function model systems. In Aim 1, we will examine the association of plasma TSKU levels with obesity in obese patients and establish the causative role of TSKU in diet-induced metabolic disorders. In Aim 2, we will dissect the role of TSKU in physiological regulation of adipose thermogenesis. In Aim 3, we will dissect the mechanisms through which TSKU modulates adipose sympathetic innovation using a combination of 3D imaging and molecular cellular tools. Successful completion of this highly innovative project will generate high-impact discoveries of significant scientific and translational value.

Inter-organ crosstalk via endocrine hormones is a fundamental feature of mammalian metabolic physiology. Disruptions of hormonal signaling have been linked to the development of insulin resistance, type 2 diabetes, and non-alcoholic steatohepatitis (NASH). We recently discovered Neuregulin 4 (NRG4) as a fat-derived hormone that is reduced in mouse and human obesity. Using gain- and loss-of-function mouse models, we demonstrated that NRG4 preserves metabolic health by acting on the liver to attenuate hepatic lipogenesis and stress-induced liver injury. These findings illustrate a novel adipose-hepatic hormonal axis mediated by NRG4 in metabolic signaling and disease pathogenesis. The non-parenchymal cells (NPCs) of the liver represent approximately 30% of total liver cells and play an important role in tissue homeostasis, hepatic metabolism, and disease progression. To delineate the landscape and regulation of liver cell heterogeneity, we performed single-cell RNA sequencing on NPCs isolated from healthy and diet-induced NASH mouse livers. This single-cell analysis revealed unprecedented insights into transcriptomic reprogramming of liver cells during NASH pathogenesis. Based on a body of preliminary data, we hypothesize that NRG4 signaling shapes the liver microenvironment to impinge on the progression of NASH and its associated liver disease. In this proposal, we plan to delineate how NRG4 regulates the transcriptomic and functional properties of liver cells at single-cell resolution. We will determine the mechanisms and significance of the regulation of hepatic immune cell landscape by NRG4 in mediating its effects on NASH pathogenesis. Finally, we plan to assess the therapeutic potential of targeting NRG4 for the treatment of metabolic liver disease.