Biology subjects

Shannon, C. E.

Publications and source records attributed to Shannon, C. E..

4 recordsLinked to original sources

bioRxiv2024

Sex-dependent adipose glucose partitioning by the mitochondrial pyruvate carrier

ObjectiveThe mitochondrial pyruvate carrier (MPC) occupies a critical node in intermediary metabolism, prompting interest in its utility as a therapeutic target for the treatment of obesity and cardiometabolic disease. Dysregulated nutrient metabolism in adipose tissue is a prominent feature of obesity pathophysiology, yet the functional role of adipose MPC has not been explored. We investigated whether the MPC shapes the adaptation of adipose tissue to dietary stress in female and male mice. MethodsThe impact of pharmacological and genetic disruption of the MPC on mitochondrial pathways of triglyceride assembly (lipogenesis and glyceroneogenesis) was assessed in 3T3L1 adipocytes and murine adipose explants, combined with analyses of adipose MPC expression in metabolically compromised humans. Whole-body and adipose-specific glucose metabolism were subsequently investigated in male and female mice lacking adipocyte MPC1 (Mpc1AD-/-) and fed either standard chow, high-fat western style, or high-sucrose lipid restricted diets for 24 weeks, using a combination of radiolabeled tracers and GC/MS metabolomics. ResultsTreatment with UK5099 or siMPC1 impaired the synthesis of lipids and glycerol-3-phosphate from pyruvate and blunted triglyceride accumulation in 3T3L1 adipocytes, whilst MPC expression in human adipose tissue was negatively correlated with indices of whole-body and adipose tissue metabolic dysfunction. Mature adipose explants from Mpc1AD-/- mice were intrinsically incapable of incorporating pyruvate into triglycerides. In vivo, MPC deletion restricted the incorporation of circulating glucose into adipose triglycerides, but only in female mice fed a zero fat diet, and this associated with sex-specific reductions in tricarboxylic acid cycle pool sizes and compensatory transcriptional changes in lipogenic and glycerol metabolism pathways. However, whole-body adiposity and metabolic health were preserved in Mpc1AD-/- mice regardless of sex, even under conditions of zero dietary fat. ConclusionThese findings highlight the greater capacity for mitochondrially driven triglyceride assembly in adipose from female versus male mice and expose a reliance upon MPC-gated metabolism for glucose partitioning in female adipose under conditions of dietary lipid restriction.

physiology↗

bioRxiv2022

Persistent Inflammatory Lipotoxicity Impedes Pancreatic β-cell Function in Diet-Induced Obese Mice Despite Correction of Glucotoxicity

Insulin resistance is a hallmark feature of Type 2 Diabetes (T2D), but the progression of the disease is closely linked to a deterioration in {beta}-cell mass and function. While the precise mechanisms of {beta}-cell failure are unclear, chronic hyperglycemia (glucotoxicity) and dyslipidemia (lipotoxicity) are considered contributing factors; however, the relative importance of these insults on {beta}-cell function remains controversial. To examine this, we dissociated glucotoxicity from lipotoxicity using a high-fat diet (HFD)-fed mouse model of T2D and the glucose-lowering SGLT2 inhibitor, canagliflozin (CANA). As expected, HFD-feeding impaired glucose tolerance and isolated islet function. However, despite improvements in glucose tolerance and indices of {beta}-cell insulin secretory function in vivo, CANA failed to restore isolated {beta}-cell function. Shotgun lipidomics analysis of isolated islets revealed that HFD-feeding induced glycerophospholipid remodeling with a persistent increase in arachidonic acid (20:4)-enriched molecular species. Further analysis revealed that lysophosphatidylcholine (LPC) was the predominant lipid class elevated in HFD islets following correction of glucotoxicity with CANA. In follow-up experiments, LPC stimulations acutely and dose-dependently impaired glucose-stimulated insulin secretion (GSIS) in isolated wild-type islets, mechanistically linking this lipid class to {beta}-cell dysfunction. Our findings indicate that persistent inflammatory lipotoxicity impedes {beta}-cell function in diet-induced obese (DIO) rodents even after normalization of hyperglycemia. If replicated in humans, these data suggest that interventions targeting lipotoxicity may be beneficial for the long-term protection of pancreatic {beta}-cell function in T2D.

physiology↗

bioRxiv2020

Pioglitazone rescues mitochondrial lipid remodeling and pyruvate dehydrogenase hyperactivation in hepatic insulin resistance

Insulin resistance and altered hepatic mitochondrial function are central features of type 2 diabetes (T2D) and non-alcoholic fatty liver disease (NAFLD), but the etiological role of these processes in disease progression remains unclear. We investigated the molecular links between insulin resistance, mitochondrial remodeling, and hepatic lipid accumulation in a rodent model of T2D / NAFLD. Livers from obese, insulin resistant mice displayed augmented mitochondrial content and increased TCA cycle and pyruvate dehydrogenase (PDH) activities. Insulin sensitization with pioglitazone mitigated pyruvate-driven TCA cycle activity and PDH activation via both covalent (PDK4 and PDP2) and allosteric (intracellular pyruvate availability) mechanisms. Interestingly, improvements in insulin sensitivity and mitochondrial function were entirely dissociated from changes in hepatic triglycerides, diacylglycerides or fatty acids. Instead, we show that the mitochondrial phospholipid cardiolipin undergoes pathological remodeling in livers from obese mice and that this is reversed by insulin sensitization. Our findings identify targetable mitochondrial features of T2D and NAFLD and highlight the benefit of insulin sensitization in managing the clinical burden of obesity-associated disease.

biochemistry↗

bioRxiv2019

The Metabolic Effects of Angiopoietin-like protein 8 (ANGPLT8) are Differentially Regulated by Insulin and Glucose in Adipose Tissue and Liver and are Controlled by AMPK Signaling

ObjectiveThe angiopoietin-like protein (ANGPTL) family represents a promising therapeutic target for dyslipidemia, which is a feature of obesity and type 2 diabetes (T2DM). The aim of the present study was to determine the metabolic role of ANGPTL8 and to investigate its nutritional, hormonal and molecular regulation in key metabolic tissues.\n\nMethodsThe metabolism of ANGPTL8 knockout mice (ANGPTL8-/-) was examined in mice following chow and high-fat diets (HFD). The regulation of ANGPTL8 expression by insulin and glucose was quantified using a combination of in vivo insulin clamp experiments in mice and in vitro experiments in hepatocytes and adipocytes. The role of AMPK signaling was examined, and the transcriptional control of ANGPTL8 was determined using bioinformatic and luciferase reporter approaches.\n\nResultsThe ANGPTL8-/-mice had improved glucose tolerance and displayed reduced fed and fasted plasma triglycerides. However, there was no reduction in steatosis in ANGPTL8-/-mice after the HFD. Insulin acutely activated ANGPTL8 expression in liver and adipose tissue, which was mediated by C/EBP{beta}. Using insulin clamp experiments we observed that glucose further enhanced ANGPTL8 expression in the presence of insulin in adipocytes only. The activation of AMPK signaling potently suppressed the effect of insulin on ANGPTL8 expression in hepatocytes.\n\nConclusionThese data show that ANGPTL8 plays an important metabolic role in mice that may extend beyond triglyceride metabolism. The finding that insulin and glucose have distinct roles in regulating ANGPTL8 expression in liver and adipose tissue may provide important clues about the function of ANGPTL8 in these tissues.

physiology↗