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The Journal of Clinical Investigation Jan 2022The dysregulation of energy homeostasis in obesity involves multihormone resistance. Although leptin and insulin resistance have been well characterized, catecholamine...
The dysregulation of energy homeostasis in obesity involves multihormone resistance. Although leptin and insulin resistance have been well characterized, catecholamine resistance remains largely unexplored. Murine β3-adrenergic receptor expression in adipocytes is orders of magnitude higher compared with that of other isoforms. While resistant to classical desensitization pathways, its mRNA (Adrb3) and protein expression are dramatically downregulated after ligand exposure (homologous desensitization). β3-Adrenergic receptor downregulation also occurs after high-fat diet feeding, concurrent with catecholamine resistance and elevated inflammation. This downregulation is recapitulated in vitro by TNF-α treatment (heterologous desensitization). Both homologous and heterologous desensitization of Adrb3 were triggered by induction of the pseudokinase TRIB1 downstream of the EPAC/RAP2A/PI-PLC pathway. TRIB1 in turn degraded the primary transcriptional activator of Adrb3, CEBPα. EPAC/RAP inhibition enhanced catecholamine-stimulated lipolysis and energy expenditure in obese mice. Moreover, adipose tissue expression of genes in this pathway correlated with body weight extremes in a cohort of genetically diverse mice and with BMI in 2 independent cohorts of humans. These data implicate a signaling axis that may explain reduced hormone-stimulated lipolysis in obesity and resistance to therapeutic interventions with β3-adrenergic receptor agonists.
Topics: 3T3-L1 Cells; Adipocytes; Animals; Catecholamines; Down-Regulation; Drug Resistance; Energy Metabolism; Lipolysis; Male; Mice; Obesity; Receptors, Adrenergic, beta-3; Signal Transduction
PubMed: 34847077
DOI: 10.1172/JCI153357 -
Cell Reports Jun 2022In hepatocytes, peroxisome proliferator-activated receptor α (PPARα) orchestrates a genomic and metabolic response required for homeostasis during fasting. This...
In hepatocytes, peroxisome proliferator-activated receptor α (PPARα) orchestrates a genomic and metabolic response required for homeostasis during fasting. This includes the biosynthesis of ketone bodies and of fibroblast growth factor 21 (FGF21). Here we show that in the absence of adipose triglyceride lipase (ATGL) in adipocytes, ketone body and FGF21 production is impaired upon fasting. Liver gene expression analysis highlights a set of fasting-induced genes sensitive to both ATGL deletion in adipocytes and PPARα deletion in hepatocytes. Adipose tissue lipolysis induced by activation of the β-adrenergic receptor also triggers such PPARα-dependent responses not only in the liver but also in brown adipose tissue (BAT). Intact PPARα activity in hepatocytes is required for the cross-talk between adipose tissues and the liver during fat mobilization.
Topics: Adipose Tissue; Adipose Tissue, Brown; Adipose Tissue, White; Hepatocytes; Ketone Bodies; Lipolysis; PPAR alpha
PubMed: 35675775
DOI: 10.1016/j.celrep.2022.110910 -
Developmental Cell Mar 2015Fatty acids (FAs) provide cellular energy under starvation, yet how they mobilize and move into mitochondria in starved cells, driving oxidative respiration, is unclear....
Fatty acids (FAs) provide cellular energy under starvation, yet how they mobilize and move into mitochondria in starved cells, driving oxidative respiration, is unclear. Here, we clarify this process by visualizing FA trafficking with a fluorescent FA probe. The labeled FA accumulated in lipid droplets (LDs) in well-fed cells but moved from LDs into mitochondria when cells were starved. Autophagy in starved cells replenished LDs with FAs, increasing LD number over time. Cytoplasmic lipases removed FAs from LDs, enabling their transfer into mitochondria. This required mitochondria to be highly fused and localized near LDs. When mitochondrial fusion was prevented in starved cells, FAs neither homogeneously distributed within mitochondria nor became efficiently metabolized. Instead, FAs reassociated with LDs and fluxed into neighboring cells. Thus, FAs engage in complex trafficking itineraries regulated by cytoplasmic lipases, autophagy, and mitochondrial fusion dynamics, ensuring maximum oxidative metabolism and avoidance of FA toxicity in starved cells.
Topics: Animals; Autophagy; Biological Transport; Cell Line; Fatty Acids; Fibroblasts; Fluorescent Dyes; Lipase; Lipid Droplets; Lipid Metabolism; Lipolysis; Mice; Mitochondria; Mitochondrial Dynamics; Oxidation-Reduction; Respiration; Starvation
PubMed: 25752962
DOI: 10.1016/j.devcel.2015.01.029 -
Nature Mar 2020Although it is well-established that reductions in the ratio of insulin to glucagon in the portal vein have a major role in the dysregulation of hepatic glucose...
Although it is well-established that reductions in the ratio of insulin to glucagon in the portal vein have a major role in the dysregulation of hepatic glucose metabolism in type-2 diabetes, the mechanisms by which glucagon affects hepatic glucose production and mitochondrial oxidation are poorly understood. Here we show that glucagon stimulates hepatic gluconeogenesis by increasing the activity of hepatic adipose triglyceride lipase, intrahepatic lipolysis, hepatic acetyl-CoA content and pyruvate carboxylase flux, while also increasing mitochondrial fat oxidation-all of which are mediated by stimulation of the inositol triphosphate receptor 1 (INSP3R1). In rats and mice, chronic physiological increases in plasma glucagon concentrations increased mitochondrial oxidation of fat in the liver and reversed diet-induced hepatic steatosis and insulin resistance. However, these effects of chronic glucagon treatment-reversing hepatic steatosis and glucose intolerance-were abrogated in Insp3r1 (also known as Itpr1)-knockout mice. These results provide insights into glucagon biology and suggest that INSP3R1 may represent a target for therapies that aim to reverse nonalcoholic fatty liver disease and type-2 diabetes.
Topics: Acetyl Coenzyme A; Adipose Tissue; Animals; Diabetes Mellitus, Type 2; Enzyme Activation; Glucagon; Gluconeogenesis; Inositol 1,4,5-Trisphosphate Receptors; Lipase; Lipolysis; Liver; Mice, Knockout; Mitochondria; Non-alcoholic Fatty Liver Disease; Oxidation-Reduction
PubMed: 32132708
DOI: 10.1038/s41586-020-2074-6 -
TheScientificWorldJournal 2022Hormone-sensitive lipase (HSL) is a pivotal enzyme that mediates triglyceride hydrolysis to provide free fatty acids and glycerol in adipocytes in a hormonally... (Review)
Review
Hormone-sensitive lipase (HSL) is a pivotal enzyme that mediates triglyceride hydrolysis to provide free fatty acids and glycerol in adipocytes in a hormonally controlled lipolysis process. Elevated plasma-free fatty acids were accompanied by insulin resistance, type-2 diabetes, and obesity. Inhibition of lipolysis through HSL inhibition may provide a mechanism to prevent the accumulation of free fatty acids and to improve the affectability of insulin and blood glucose handling in type II diabetes. The published studies that examine the structure, regulation, and function of HSL and major inhibitors were reviewed in this paper.
Topics: Humans; Sterol Esterase; Fatty Acids, Nonesterified; Diabetes Mellitus, Type 2; Lipase; Lipolysis
PubMed: 36530555
DOI: 10.1155/2022/1964684 -
Autophagy Mar 2021The autophagic degradation of lipid droplets (LDs), termed lipophagy, is a major mechanism that contributes to lipid turnover in numerous cell types. While numerous...
The autophagic degradation of lipid droplets (LDs), termed lipophagy, is a major mechanism that contributes to lipid turnover in numerous cell types. While numerous factors, including nutrient deprivation or overexpression of PNPLA2/ATGL (patatin-like phospholipase domain containing 2) drive lipophagy, the trafficking of fatty acids (FAs) produced from this pathway is largely unknown. Herein, we show that PNPLA2 and nutrient deprivation promoted the extracellular efflux of FAs. Inhibition of autophagy or lysosomal lipid degradation attenuated FA efflux highlighting a critical role for lipophagy in this process. Rather than direct transport of FAs across the lysosomal membrane, lipophagy-derived FA efflux requires lysosomal fusion to the plasma membrane. The lysosomal Ca2+ channel protein MCOLN1/TRPML1 (mucolipin 1) regulates lysosomal-plasma membrane fusion and its overexpression increased, while inhibition blocked FA efflux. In addition, inhibition of autophagy/lipophagy or MCOLN1, or sequestration of extracellular FAs with BSA attenuated the oxidation and re-esterification of lipophagy-derived FAs. Overall, these studies show that the well-established pathway of lysosomal fusion to the plasma membrane is the primary route for the disposal of FAs derived from lipophagy. Moreover, the efflux of FAs and their reuptake or subsequent extracellular trafficking to adjacent cells may play an important role in cell-to-cell lipid exchange and signaling. ACTB: beta actin; ADRA1A: adrenergic receptor alpha, 1a; ALB: albumin; ATG5: autophagy related 5; ATG7: autophagy related 7; BafA1: bafilomycin A1; BECN1: beclin 1; BHBA: beta-hydroxybutyrate; BSA: bovine serum albumin; CDH1: e-cadherin; CQ: chloroquine; CTSB: cathepsin B; DGAT: diacylglycerol O-acyltransferase; FA: fatty acid; HFD: high-fat diet; LAMP1: lysosomal-associated membrane protein 1; LD: lipid droplet; LIPA/LAL: lysosomal acid lipase A; LLME: Leu-Leu methyl ester hydrobromide; MAP1LC3B/LC3: microtubule associated protein 1 light chain 3 beta; MCOLN1/TRPML1: mucolipin 1; MEF: mouse embryo fibroblast; PBS: phosphate-buffered saline; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; PLIN: perilipin; PNPLA2/ATGL patatin-like phospholipase domain containing 2; RUBCN (rubicon autophagy regulator); SM: sphingomyelin; TAG: triacylglycerol; TMEM192: transmembrane protein 192; VLDL: very low density lipoprotein.
Topics: Animals; Autophagosomes; Autophagy; Biological Transport; Exocytosis; Fatty Acids; Homeostasis; Lipolysis; Lysosomes; Mice, Inbred C57BL; Mice
PubMed: 32070194
DOI: 10.1080/15548627.2020.1728097 -
The FEBS Journal Dec 2022The white adipose tissues (WAT) are located in distinct depots throughout the body. They serve as an energy reserve, providing fatty acids for other tissues via... (Review)
Review
The white adipose tissues (WAT) are located in distinct depots throughout the body. They serve as an energy reserve, providing fatty acids for other tissues via lipolysis when needed, and function as an endocrine organ to regulate systemic metabolism. Their activities are coordinated through intercellular communications among adipocytes and other cell types such as residential and infiltrating immune cells, which are collectively under neuronal control. The adipocytes and immune subtypes including macrophages/monocytes, eosinophils, neutrophils, group 2 innate lymphoid cells (ILC2s), T and B cells, dendritic cells (DCs), and natural killer (NK) cells display cellular and functional diversity in response to the energy states and contribute to metabolic homeostasis and pathological conditions. Accumulating evidence reveals that neuronal innervations control lipid deposition and mobilization via regulating lipolysis, adipocyte size, and cellularity. Vice versa, the neuronal innervations and activity are influenced by cellular factors in the WAT. Though the literature describing adipose tissue cells is too extensive to cover in detail, we strive to highlight a selected list of neuronal and immune components in this review. The cell-to-cell communications and the perspective of neuroimmune regulation are emphasized to enlighten the potential therapeutic opportunities for treating metabolic disorders.
Topics: Immunity, Innate; Lymphocytes; Adipose Tissue, White; Adipose Tissue; Adipocytes; Lipolysis
PubMed: 34564950
DOI: 10.1111/febs.16213 -
Nature Communications Jul 2022β-Adrenergic signaling is a core regulator of brown adipocyte function stimulating both lipolysis and transcription of thermogenic genes, thereby expanding the capacity...
β-Adrenergic signaling is a core regulator of brown adipocyte function stimulating both lipolysis and transcription of thermogenic genes, thereby expanding the capacity for oxidative metabolism. We have used pharmacological inhibitors and a direct activator of lipolysis to acutely modulate the activity of lipases, thereby enabling us to uncover lipolysis-dependent signaling pathways downstream of β-adrenergic signaling in cultured brown adipocytes. Here we show that induction of lipolysis leads to acute induction of several gene programs and is required for transcriptional regulation by β-adrenergic signals. Using machine-learning algorithms to infer causal transcription factors, we show that PPARs are key mediators of lipolysis-induced activation of genes involved in lipid metabolism and thermogenesis. Importantly, however, lipolysis also activates the unfolded protein response and regulates the core circadian transcriptional machinery independently of PPARs. Our results demonstrate that lipolysis generates important metabolic signals that exert profound pleiotropic effects on transcription and function of cultured brown adipocytes.
Topics: Adipocytes, Brown; Adipose Tissue, Brown; Adrenergic Agents; Lipolysis; Peroxisome Proliferator-Activated Receptors; Thermogenesis
PubMed: 35803907
DOI: 10.1038/s41467-022-31525-8 -
Biomedicine & Pharmacotherapy =... Apr 2023Fatty acids (FAs), as part of lipids, are involved in cell membrane composition, cellular energy storage, and cell signaling. FAs can also be toxic when their... (Review)
Review
Fatty acids (FAs), as part of lipids, are involved in cell membrane composition, cellular energy storage, and cell signaling. FAs can also be toxic when their concentrations inside and/or outside the cell exceed physiological levels, which is called "lipotoxicity", and steatosis is a form of lipotoxity. To facilitate the storage of large quantities of FAs in cells, they undergo a process called lipolysis or lipophagy. This review focuses on the effects of lipolytic enzymes including cytoplasmic "neutral" lipolysis, lysosomal "acid" lipolysis, and lipophagy. Moreover, the impact of related lipolytic enzymes on lipid metabolism homeostasis and energy conservation, as well as their role in lipid-related metabolic diseases. In addition, we describe how they affect lipid metabolism homeostasis and energy conservation in lipid-related metabolic diseases with a focus on hepatic steatosis and cancer and the pathogenesis and therapeutic targets of AMPK/SIRTs/FOXOs, PI3K/Akt, PPARs/PGC-1α, MAPK/ERK1/2, TLR4/NF-κB, AMPK/mTOR/TFEB, Wnt/β-catenin through immune inflammation, oxidative stress and autophagy-related pathways. As well as the current application of lipolytic enzyme inhibitors (especially Monoacylglycerol lipase (MGL) inhibitors) to provide new strategies for future exploration of metabolic programming in metabolic diseases.
Topics: Humans; Lipolysis; AMP-Activated Protein Kinases; Phosphatidylinositol 3-Kinases; Lipid Metabolism; Metabolic Diseases; Fatty Acids; Fatty Liver; Autophagy
PubMed: 36764133
DOI: 10.1016/j.biopha.2023.114311 -
Current Opinion in Gastroenterology Sep 2017The obesity pandemic poses a unique set of problems for acute pancreatitis - both by increasing acute pancreatitis incidence, and worsening acute pancreatitis severity.... (Review)
Review
PURPOSE OF REVIEW
The obesity pandemic poses a unique set of problems for acute pancreatitis - both by increasing acute pancreatitis incidence, and worsening acute pancreatitis severity. This review explores these associations, underlying mechanisms, and potential therapies.
RECENT FINDINGS
We review how the obesity associated increase in gallstones, surgical, and endoscopic interventions for obesity management, diabetes, and related medications such as incretin-based therapies and hypertriglyceridemia may increase the incidence of acute pancreatitis. The mechanism of how obesity may increase acute pancreatitis severity are discussed with a focus on cytokines, adipokines, damage-associated molecular patterns and unsaturated fatty acid-mediated lipotoxicity. The role of obesity in exacerbating pancreatic necrosis is discussed; focusing on obesity-associated pancreatic steatosis. We also discuss how peripancreatic fat necrosis worsens organ failure independent of pancreatic necrosis. Last, we discuss emerging therapies including choice of intravenous fluids and the use of lipase inhibitors which have shown promise during severe acute pancreatitis.
SUMMARY
We discuss how obesity may contribute to increasing acute pancreatitis incidence, the role of lipolytic unsaturated fatty acid release in worsening acute pancreatitis, and potential approaches, including appropriate fluid management and lipase inhibition in improving acute pancreatitis outcomes.
Topics: Enzyme Inhibitors; Fatty Acids, Unsaturated; Humans; Hypertriglyceridemia; Incretins; Lipase; Lipolysis; Obesity; Pancreatitis; Severity of Illness Index
PubMed: 28719397
DOI: 10.1097/MOG.0000000000000386