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Banks, Alexander

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Banks

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Alexander

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Banks, Alexander
Author's Publications: search.filters.isAuthorOfPublication.78c63044-57f3-4cdb-bc7b-9843cb08dad0

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Now showing 1 - 6 of 6
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    Phosphorylation of Beta-3 adrenergic receptor at serine 247 by ERK MAP kinase drives lipolysis in obese adipocytes
    (Elsevier, 2018) Hong, Shangyu; Song, Wei; Zushin, Peter-James H.; Liu, Bingyang; Jedrychowski, Mark; Mina, Amir I.; Deng, Zhaoming; Cabarkapa, Dimitrije; Hall, Jessica; Palmer, Colin J.; Aliakbarian, Hassan; Szpyt, John; Gygi, Steven; Tavakkoli, Ali; Lynch, Lydia; Perrimon, Norbert; Banks, Alexander
    Objective: The inappropriate release of free fatty acids from obese adipose tissue stores has detrimental effects on metabolism, but key molecular mechanisms controlling FFA release from adipocytes remain undefined. Although obesity promotes systemic inflammation, we find activation of the inflammation-associated Mitogen Activated Protein kinase ERK occurs specifically in adipose tissues of obese mice, and provide evidence that adipocyte ERK activation may explain exaggerated adipose tissue lipolysis observed in obesity. Methods and Results: We provide genetic and pharmacological evidence that inhibition of the MEK/ERK pathway in human adipose tissue, mice, and flies all effectively limit adipocyte lipolysis. In complementary findings, we show that genetic and obesity-mediated activation of ERK enhances lipolysis, whereas adipose tissue specific knock-out of ERK2, the exclusive ERK1/2 protein in adipocytes, dramatically impairs lipolysis in explanted mouse adipose tissue. In addition, acute inhibition of MEK/ERK signaling also decreases lipolysis in adipose tissue and improves insulin sensitivity in obese mice. Mice with decreased rates of adipose tissue lipolysis in vivo caused by either MEK or ATGL pharmacological inhibition were unable to liberate sufficient White Adipose Tissue (WAT) energy stores to fuel thermogenesis from brown fat during a cold temperature challenge. To identify a molecular mechanism controlling these actions, we performed unbiased phosphoproteomic analysis of obese adipose tissue at different time points following acute pharmacological MEK/ERK inhibition. MEK/ERK inhibition decreased levels of adrenergic signaling and caused de-phosphorylation of the β3-adrenergic receptor (β3AR) on serine 247. To define the functional implications of this phosphorylation, we showed that CRISPR/Cas9 engineered cells expressing wild type β3AR exhibited β3AR phosphorylation by ERK2 and enhanced lipolysis, but this was not seen when serine 247 of β3AR was mutated to alanine. Conclusion: Taken together, these data suggest that ERK activation in adipocytes and subsequent phosphorylation of the β3AR on S247 are critical regulatory steps in the enhanced adipocyte lipolysis of obesity.
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    An Erk/Cdk5 axis controls the diabetogenic actions of PPARγ
    (2014) Banks, Alexander; McAllister, Fiona E.; Camporez, João Paulo G.; Zushin, Peter-James H.; Jurczak, Michael J.; Laznik-Bogoslavski, Dina; Shulman, Gerald I.; Gygi, Steven; Spiegelman, Bruce
    Obesity-linked insulin resistance is a major precursor to the development of type 2 diabetes. Previous work has shown that phosphorylation of PPARγ at serine 273 by Cdk5 stimulates diabetogenic gene expression in adipose tissues1. Inhibition of this modification is a key therapeutic mechanism for anti-diabetic PPARγ ligand drugs, such as the thiazolidinediones and PPARγ partial/non-agonists2. To better understand the importance of this obesity-linked PPARγ phosphorylation, we created mice that ablated Cdk5 specifically in adipose tissues. Surprisingly, these mice have both a paradoxical increase in PPARγ phosphorylation at S273 and worsened insulin resistance. Unbiased proteomic studies show that ERK kinases are activated in these KO animals. We show here that ERK directly phosphorylates S273 of PPARγ in a robust manner and that Cdk5 suppresses ERKs through direct action on a novel site in MEK, the ERK kinase. Importantly, pharmacological MEK and ERK inhibition markedly improves insulin resistance in both obese wild type and ob/ob mice, and also completely reverses the deleterious effects of the Cdk5 ablation. These data show that an ERK/Cdk5 axis controls PPARγ function and suggest that MEK/ERK inhibitors may hold promise for the treatment of type 2 diabetes.
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    Deficiency of FcεR1 increases body weight gain but improves glucose tolerance in diet-induced obese mice
    (Endocrine Society, 2015) Lee, Yun-Jung; Liu, Conglin; Liao, Mengyang; Sukhova, Galina; Shirakawa, Jun; Abdennour, Meriem; Iamarene, Karine; Andre, Sebastien; Inouye, Karen; Clement, Karine; Kulkarni, Rohit; Banks, Alexander; Libby, Peter; Shi, Guo-Ping
    Prior studies demonstrated increased plasma immunoglobulin E (IgE) in diabetic patients, but the direct participation of IgE in diabetes or obesity remains unknown. This study found that plasma IgE levels correlated inversely with body weight, body mass index, and body fat mass among a population of randomly selected obese women. IgE receptor FcεR1-deficient (Fcer1a–/–) mice and diet-induced obesity (DIO) mice demonstrated that FcεR1 deficiency in DIO mice increased food intake, reduced energy expenditure, and increased body weight gain, but improved glucose tolerance and glucose-induced insulin secretion. White adipose tissue (WAT) from Fcer1a–/– mice showed increased expression of phospho-AKT, C/EBPα, PPARγ, Glut4, and Bcl-2, but reduced UCP1 and phospho-JNK expression, tissue macrophage accumulation, and apoptosis, suggesting that IgE reduces adipogenesis and glucose uptake, but induces energy expenditure, adipocyte apoptosis, and WAT inflammation. In 3T3-L1 cells, IgE inhibited the expression of C/EBPα and PPARγ, and preadipocyte adipogenesis, and induced adipocyte apoptosis. IgE reduced 3T3-L1 cell expression of Glut4, phospho-AKT, and glucose uptake, which concurred with improved glucose tolerance in Fcer1a–/– mice. This study established two novel pathways of IgE in reducing body weight gain in DIO mice by suppressing adipogenesis and inducing adipocyte apoptosis, while worsening glucose tolerance by reducing Glut4 expression, glucose uptake, and insulin secretion.
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    Thioesterase superfamily member 1 suppresses cold thermogenesis by limiting the oxidation of lipid droplet-derived fatty acids in brown adipose tissue
    (Elsevier, 2016) Okada, Kosuke; LeClair, Katherine B.; Zhang, Yongzhao; Li, Yingxia; Ozdemir, Cafer; Krisko, Tibor I.; Hagen, Susan; Betensky, Rebecca; Banks, Alexander; Cohen, David E.
    Objective: Non-shivering thermogenesis in brown adipose tissue (BAT) plays a central role in energy homeostasis. Thioesterase superfamily member 1 (Them1), a BAT-enriched long chain fatty acyl-CoA thioesterase, is upregulated by cold and downregulated by warm ambient temperatures. Them1−/− mice exhibit increased energy expenditure and resistance to diet-induced obesity and diabetes, but the mechanistic contribution of Them1 to the regulation of cold thermogenesis remains unknown. Methods: Them1−/− and Them1+/+ mice were subjected to continuous metabolic monitoring to quantify the effects of ambient temperatures ranging from thermoneutrality (30 °C) to cold (4 °C) on energy expenditure, core body temperature, physical activity and food intake. The effects of Them1 expression on O2 consumption rates, thermogenic gene expression and lipolytic protein activation were determined ex vivo in BAT and in primary brown adipocytes. Results: Them1 suppressed thermogenesis in mice even in the setting of ongoing cold exposure. Without affecting thermogenic gene transcription, Them1 reduced O2 consumption rates in both isolated BAT and primary brown adipocytes. This was attributable to decreased mitochondrial oxidation of endogenous but not exogenous fatty acids. Conclusions: These results show that Them1 may act as a break on uncontrolled heat production and limit the extent of energy expenditure. Pharmacologic inhibition of Them1 could provide a targeted strategy for the management of metabolic disorders via activation of brown fat.
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    Forkhead Transcription Factors (FoxOs) Promote Apoptosis of Insulin-Resistant Macrophages During Cholesterol-Induced Endoplasmic Reticulum Stress
    (American Diabetes Association, 2008) Senokuchi, Takafumi; Liang, Chien-Ping; Seimon, Tracie A.; Han, Seongah; Matsumoto, Michihiro; Accili, Domenico; Tabas, Ira; Tall, Alan R.; Banks, Alexander; Paik, Ji-Hye; DePinho, Ronald A.
    OBJECTIVE—Endoplasmic reticulum stress increases macrophage apoptosis, contributing to the complications of atherosclerosis. Insulin-resistant macrophages are more susceptible to endoplasmic reticulum stress–associated apoptosis probably contributing to macrophage death and necrotic core formation in atherosclerotic plaques in type 2 diabetes. However, the molecular mechanisms of increased apoptosis in insulin-resistant macrophages remain unclear. RESEARCH DESIGN AND METHODS—The studies were performed in insulin-resistant macrophages isolated from insulin receptor knockout or ob/ob mice. Gain- or loss-of-function approaches were used to evaluate the roles of forkhead transcription factors (FoxOs) in endoplasmic reticulum stress–associated macrophage apoptosis. RESULTS—Insulin-resistant macrophages showed attenuated Akt activation and increased nuclear localization of FoxO1 during endoplasmic reticulum stress induced by free cholesterol loading. Overexpression of active FoxO1 or FoxO3 failed to induce apoptosis in unchallenged macrophages but exacerbated apoptosis in macrophages with an active endoplasmic reticulum stress response. Conversely, macrophages with genetic knockouts of FoxO1, -3, and -4 were resistant to apoptosis in response to endoplasmic reticulum stress. FoxO1 was shown by chromatin immunoprecipitation and promoter expression analysis to induce inhibitor of κBɛ gene expression and thereby to attenuate the increase of nuclear p65 and nuclear factor-κB activity during endoplasmic reticulum stress, with proapoptotic and anti-inflammatory consequences. CONCLUSIONS—Decreased Akt and increased FoxO transcription factor activity during the endoplasmic reticulum stress response leads to increased apoptosis of insulin-resistant macrophages. FoxOs may have a dual cellular function, resulting in either proapoptotic or anti-inflammatory effects in an endoplasmic reticulum stress–modulated manner. In the complex plaque milieu, the ultimate effect is likely to be an increase in macrophage apoptosis, plaque inflammation, and destabilization.
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    Foxo1 Links Hyperglycemia to LDL Oxidation and Endothelial Nitric Oxide Synthase Dysfunction in Vascular Endothelial Cells
    (American Diabetes Association, 2009) Tanaka, Jun; Qiang, Li; Banks, Alexander; Welch, Carrie L.; Matsumoto, Michihiro; Kitamura, Tadahiro; Ido-Kitamura, Yukari; DePinho, Ronald A.; Accili, Domenico
    OBJECTIVE: Atherosclerotic cardiovascular disease is the leading cause of death among people with diabetes. Generation of oxidized LDLs and reduced nitric oxide (NO) availability because of endothelial NO synthase (eNOS) dysfunction are critical events in atherosclerotic plaque formation. Biochemical mechanism leading from hyperglycemia to oxLDL formation and eNOS dysfunction is unknown. RESEARCH DESIGN AND METHODS: We show that glucose, acting through oxidative stress, activates the transcription factor Foxo1 in vascular endothelial cells. RESULTS: Foxo1 promotes inducible NOS (iNOS)-dependent NO-peroxynitrite generation, which leads in turn to LDL oxidation and eNOS dysfunction. We demonstrate that Foxo1 gain-of-function mimics the effects of hyperglycemia on this process, whereas conditional Foxo1 knockout in vascular endothelial cells prevents it. CONCLUSIONS: The findings reveal a hitherto unsuspected role of the endothelial iNOS-NO-peroxynitrite pathway in lipid peroxidation and eNOS dysfunction and suggest that Foxo1 activation in response to hyperglycemia brings about proatherogenic changes in vascular endothelial cell function.