Mechanisms by which Metaflammation and Adiponectin Regulates Glucose and Lipid Metabolism

Obesity and Type 2 Diabetes mellitus (T2DM) are among the most serious global health problems as they are increasing in prevalence and related to many chronic diseases, including cardiovascular and cerebrovascular diseases, cancer and other metabolic disorders. Obesity increases the risk for T2DM through the development of low-grade inflammation and insulin resistance. Specifically, studies have shown that enhanced inflammation in adipose tissue is an essential player in the progression of insulin resistance and T2DM in obese individuals. However, how immune cells sense nutritional status and contribute to whole-body metabolism are largely unknown. In addition, most of the currently available therapies do not address the root cause of T2DM: insulin resistance. Pharmacological agents that improve diabetes have limited success due to side effects and decline in efficacy as most patients develop resistance over time. As such, understanding the pathogenesis of T2DM and finding new interventions to ameliorate insulin resistance are of great interest. In this doctoral dissertation, I describe work that elucidates the nutritional regulation of macrophage function and its contribution to whole-body metabolism, as well as the mechanisms by which a new potential treatment, adiponectin, ameliorates insulin resistance. Protein O-GlcNAcylation is thought to be a metabolic sensor that modulates cell signaling. I showed that overnutrition stimulated nutrient-sensing O-linked β-N-acetylglucosamine (O-GlcNAc) signaling in macrophages and O-GlcNAc signaling was down-regulated during macrophage pro-inflammatory polarization. Further, mice with O-GlcNAc transferase (Ogt) deletion in macrophages and other myeloid cells displayed enhanced macrophage pro-inflammatory activation in adipose tissue and lipolysis, increased ectopic lipid accumulation in peripheral tissues, and exacerbated tissue-specific and whole-body insulin resistance in diet-induced obese mice. O-GlcNAc signaling inhibited macrophage pro-inflammatory polarization by catalyzing ribosomal protein S6 kinase beta-1 (S6K1) serine 489 O-GlcNAcylation and suppressing S6K1 phosphorylation. These studies uncovered O-GlcNAc signaling as a novel homeostatic regulator at the interface of inflammation and metabolism and suggested that O-GlcNAc signaling may serve as a therapeutic target for obesity, diabetes, and other immune-related diseases. Finally, I examined the mechanisms for the anti-diabetic effect of adiponectin. Adiponectin has emerged as a promising insulin-sensitizing adipokine and a potential therapy to treat T2DM; however, the mechanisms by which adiponectin administration improves insulin sensitivity were unclear. To address this question, I examined the effects of a 2-week continuous subcutaneous infusion of globular adiponectin (gAcrp30) or saline on glucose and lipid metabolism in a high-fat diet (HFD) fed mouse model. Whole-body and tissue-specific insulin action was assessed by a hyperinsulinemic-euglycemic clamp (HEC). gAcrp30-treated mice displayed reduced fasting plasma glucose and insulin concentrations and increased glucose infusion rate during the HEC, reflecting increased whole-body insulin sensitivity. Increased insulin sensitivity could be attributed to reduced endogenous glucose production and increased glucose uptake in muscle and adipose tissues. We found that these liver and muscle sensitivity improvements were associated with reductions in the plasma membrane-associated diacylglycerol (DAG) content, and contrary to prior studies, were independent of reductions in total ceramide content. These effects in turn led to decreased protein kinase Cε (PKCε) activation in liver, decreased PKCε/PKCθ activity in muscle, and improved insulin signaling in these tissues. I further demonstrated that globular adiponectin (gAcrp30) and full-length adiponectin (Acrp30) reverse insulin resistance in HFD-fed mice through reductions in ectopic lipid in liver and muscle likely by stimulation of lipoprotein lipase (LPL) activity in white adipose tissue and increased epithelial nitric oxide synthase (eNOS)/ 5\u27 AMP-activated protein kinase (AMPK) activation and fat oxidation in muscle. Taken together, the work presented in the dissertation provides novel mechanistic insight into the regulation and function of O-GlcNAc signaling in the immunometabolism and the mechanisms by which adiponectin reverses HFD-induced liver and muscle insulin resistance in mice. As such, adiponectin and O-GlcNAc signaling activators, such as glutamine and glucosamine, could serve as viable treatment options for T2DM, insulin resistance and other obesity-associated morbidities

Short-term overnutrition induces white adipose tissue insulin resistance through sn-1,2-diacylglycerol/PKCε/insulin receptor Thr1160 phosphorylation

White adipose tissue (WAT) insulin action has critical anabolic function and is dysregulated in overnutrition. However, the mechanism of short-term high-fat diet–induced (HFD-induced) WAT insulin resistance (IR) is poorly understood. Based on recent evidences, we hypothesize that a short-term HFD causes WAT IR through plasma membrane (PM) sn-1,2-diacylglycerol (sn-1,2-DAG) accumulation, which promotes protein kinase C-ε (PKCε) activation to impair insulin signaling by phosphorylating insulin receptor (Insr) Thr1160. To test this hypothesis, we assessed WAT insulin action in 7-day HFD–fed versus regular chow diet–fed rats during a hyperinsulinemic-euglycemic clamp. HFD feeding caused WAT IR, reflected by impaired insulin-mediated WAT glucose uptake and lipolysis suppression. These changes were specifically associated with PM sn-1,2-DAG accumulation, higher PKCε activation, and impaired insulin-stimulated Insr Tyr1162 phosphorylation. In order to examine the role of Insr Thr1160 phosphorylation in mediating lipid-induced WAT IR, we examined these same parameters in InsrT1150A mice (mouse homolog for human Thr1160) and found that HFD feeding induced WAT IR in WT control mice but not in InsrT1150A mice. Taken together, these data demonstrate the importance of the PM sn-1,2-DAG/PKCε/Insr Thr1160 phosphorylation pathway in mediating lipid-induced WAT IR and represent a potential therapeutic target to improve WAT insulin sensitivity

Data_Sheet_1_Muscarinic receptor regulation of chronic pain-induced atrial fibrillation.xlsx

Atrial fibrillation (AF), one of the most common arrhythmias, is associated with chronic emotional disorder. Chronic pain represents a psychological instability condition related to cardiovascular diseases, but the mechanistic linkage connecting chronic pain to AF occurrence remains unknown. Wild-type C57BL/6J male mice were randomly divided into sham and chronic pain groups. Autonomic nerve remodeling was reflected by the increased atrial parasympathetic tension and muscarinic acetylcholine receptor M2 expression. AF susceptibility was assessed through transesophageal burst stimulation in combination with electrocardiogram recording and investigating AERP in Langendorff perfused hearts. Our results demonstrated the elevated protein expression of muscarinic acetylcholine receptor M2 in the atria of mice subjected to chronic pain stress. Moreover, chronic pain induced the increase of atrial PR interval, and atrial effective refractory periods as compared to the sham group, underlying the enhanced susceptibility of AF. Thus, autonomic cholinergic nerve may mediate mice AF in the setting of chronic pain.</p

Image_3_Muscarinic receptor regulation of chronic pain-induced atrial fibrillation.JPEG

Atrial fibrillation (AF), one of the most common arrhythmias, is associated with chronic emotional disorder. Chronic pain represents a psychological instability condition related to cardiovascular diseases, but the mechanistic linkage connecting chronic pain to AF occurrence remains unknown. Wild-type C57BL/6J male mice were randomly divided into sham and chronic pain groups. Autonomic nerve remodeling was reflected by the increased atrial parasympathetic tension and muscarinic acetylcholine receptor M2 expression. AF susceptibility was assessed through transesophageal burst stimulation in combination with electrocardiogram recording and investigating AERP in Langendorff perfused hearts. Our results demonstrated the elevated protein expression of muscarinic acetylcholine receptor M2 in the atria of mice subjected to chronic pain stress. Moreover, chronic pain induced the increase of atrial PR interval, and atrial effective refractory periods as compared to the sham group, underlying the enhanced susceptibility of AF. Thus, autonomic cholinergic nerve may mediate mice AF in the setting of chronic pain.</p

Image_1_Muscarinic receptor regulation of chronic pain-induced atrial fibrillation.JPEG

Atrial fibrillation (AF), one of the most common arrhythmias, is associated with chronic emotional disorder. Chronic pain represents a psychological instability condition related to cardiovascular diseases, but the mechanistic linkage connecting chronic pain to AF occurrence remains unknown. Wild-type C57BL/6J male mice were randomly divided into sham and chronic pain groups. Autonomic nerve remodeling was reflected by the increased atrial parasympathetic tension and muscarinic acetylcholine receptor M2 expression. AF susceptibility was assessed through transesophageal burst stimulation in combination with electrocardiogram recording and investigating AERP in Langendorff perfused hearts. Our results demonstrated the elevated protein expression of muscarinic acetylcholine receptor M2 in the atria of mice subjected to chronic pain stress. Moreover, chronic pain induced the increase of atrial PR interval, and atrial effective refractory periods as compared to the sham group, underlying the enhanced susceptibility of AF. Thus, autonomic cholinergic nerve may mediate mice AF in the setting of chronic pain.</p

Image_2_Muscarinic receptor regulation of chronic pain-induced atrial fibrillation.JPEG

Atrial fibrillation (AF), one of the most common arrhythmias, is associated with chronic emotional disorder. Chronic pain represents a psychological instability condition related to cardiovascular diseases, but the mechanistic linkage connecting chronic pain to AF occurrence remains unknown. Wild-type C57BL/6J male mice were randomly divided into sham and chronic pain groups. Autonomic nerve remodeling was reflected by the increased atrial parasympathetic tension and muscarinic acetylcholine receptor M2 expression. AF susceptibility was assessed through transesophageal burst stimulation in combination with electrocardiogram recording and investigating AERP in Langendorff perfused hearts. Our results demonstrated the elevated protein expression of muscarinic acetylcholine receptor M2 in the atria of mice subjected to chronic pain stress. Moreover, chronic pain induced the increase of atrial PR interval, and atrial effective refractory periods as compared to the sham group, underlying the enhanced susceptibility of AF. Thus, autonomic cholinergic nerve may mediate mice AF in the setting of chronic pain.</p

Data_Sheet_2_Muscarinic receptor regulation of chronic pain-induced atrial fibrillation.docx

Atrial fibrillation (AF), one of the most common arrhythmias, is associated with chronic emotional disorder. Chronic pain represents a psychological instability condition related to cardiovascular diseases, but the mechanistic linkage connecting chronic pain to AF occurrence remains unknown. Wild-type C57BL/6J male mice were randomly divided into sham and chronic pain groups. Autonomic nerve remodeling was reflected by the increased atrial parasympathetic tension and muscarinic acetylcholine receptor M2 expression. AF susceptibility was assessed through transesophageal burst stimulation in combination with electrocardiogram recording and investigating AERP in Langendorff perfused hearts. Our results demonstrated the elevated protein expression of muscarinic acetylcholine receptor M2 in the atria of mice subjected to chronic pain stress. Moreover, chronic pain induced the increase of atrial PR interval, and atrial effective refractory periods as compared to the sham group, underlying the enhanced susceptibility of AF. Thus, autonomic cholinergic nerve may mediate mice AF in the setting of chronic pain.</p