Search

Therapeutic potential of metformin in obese/diabetic patients has been associated to its ability to combat insulin resistance. However, it remains largely unknown the signaling pathways involved and whether some cell types are particularly relevant for its beneficial effects. M1-activation of macrophages by bacterial lipopolysaccharide (LPS) promotes a paracrine activation of hypoxia-inducible factor-1α (HIF1α) in brown adipocytes which reduces insulin signaling and glucose uptake, as well as β-adrenergic sensitivity. Addition of metformin to M1-polarized macrophages blunted these signs of brown adipocyte dysfunction. At the molecular level, metformin inhibits an inflammatory program executed by HIF1α in macrophages by inducing its degradation through the inhibition of mitochondrial complex I activity, thereby reducing oxygen consumption in a reactive oxygen species (ROS)-independent manner. In obese mice, metformin reduced inflammatory features in brown adipose tissue (BAT) such as macrophage infiltration, proinflammatory signaling and gene expression, and restored the response to cold exposure. In conclusion, the impact of metformin on macrophages by suppressing a HIF1α-dependent proinflammatory program is likely responsible for a secondary beneficial effect on insulin-mediated glucose uptake and β-adrenergic responses in brown adipocytes., Graphical abstract Image 1, Highlights • Macrophage-mediated inflammation in brown adipocytes stabilizes HIF1α. • Stabilization of HIF1α reduces brown adipocyte hormonal responses. • Metformin attenuates inflammation and BAT dysfunction in obese mice. • Mitochondrial complex I inhibition by metformin reduces HIF1α in macrophages. • Targeting macrophages HIF1α by metformin alleviates brown adipocyte inflammation.

ARS Open., [Aims]: Sirtuin 1 (SIRT1) is a key player in liver physiology and a therapeutic target against hepatic inflammation. We evaluated the role of SIRT1 in the proinflammatory context and oxidative stress during acetaminophen (APAP)-mediated hepatotoxicity., [Results]: SIRT1 protein levels decreased in human and mouse livers following APAP overdose. SIRT1-Tg mice maintained higher levels of SIRT1 on APAP injection than wild-type mice and were protected against hepatotoxicity by modulation of antioxidant systems and restrained inflammatory responses, with decreased oxidative stress, proinflammatory cytokine messenger RNA levels, nuclear factor kappa B (NFκB) signaling, and cell death. Mouse hepatocytes stimulated with conditioned medium of APAP-treated macrophages (APAP-CM) showed decreased SIRT1 levels; an effect mimicked by interleukin (IL)1β, an activator of NFκB. This negative modulation was abolished by neutralizing IL1β in APAP-CM or silencing p65-NFκB in hepatocytes. APAP-CM of macrophages from SIRT1-Tg mice failed to downregulate SIRT1 protein levels in hepatocytes. In vivo administration of the NFκB inhibitor BAY 11-7082 preserved SIRT1 levels and protected from APAP-mediated hepatotoxicity., [Inovation]: Our work evidenced the unique role of SIRT1 in APAP hepatoprotection by targeting oxidative stress and inflammation., [Conclusion]: SIRT1 protein levels are downregulated by IL1β/NFκB signaling in APAP hepatotoxicity, resulting in inflammation and oxidative stress. Thus, maintenance of SIRT1 during APAP overdose by inhibiting NFκB might be clinically relevant., [Rebound Track]: This work was rejected during standard peer review and rescued by Rebound Peer Review (Antioxid Redox Signal 16:293-296, 2012) with the following serving as open reviewers: Rafael de Cabo, Joaquim Ros, Kalervo Hiltunen, and Neil Kaplowitz. Antioxid. Redox Signal. 28, 1187-1208., This work was funded by SAF2015-65267-R (MINECO/FEDER), CIBERdem (ISCIII, Spain), and INFLAMES (ISCIII PIE14/00045, cofunded by ERDF, ‘‘Investing in your future’’) to A.M.V.; IJCI-2014-19381 (MINECO/FEDER) to P.R. and A.M.V.; SAF2014-52009-R (MINECO/FEDER) to S.A.; SAF2015-63904-R (MINECO/FEDER) to M.M.; CP14/00181 (ISCIII/FEDER) to A.G.-R.; and PI13/00021 (ISCIII/FEDER) to J.M. CIBERehd (ISCIII) to A.G.-R. and J.M.; Grant 37/371 from Al Jouf University to M.A.M. We also acknowledge H2020 Marie Sklodowska-Curie ITNTREATMENT (Grant Agreement No. 721236) (European Commission).

Schizophrenia is a mental disease that results in decreased life expectancy and wellbeing, by promoting obesity and sedentary lifestyles. Schizophrenia is treated by antipsychotic drugs. While the second generation of antipsychotics (SGA), Olanzapine and Aripiprazole are more effective in treating schizophrenia, they display a higher risk of metabolic side effects, mostly by development of diabetes and insulin resistance, weight gain as well as dyslipidemia. Endoplasmic reticulum (ER) stress is induced when ER homeostasis of lipid biosynthesis and protein folding is impaired. This leads to the activation of the unfolded protein response (UPR), a signaling cascade that aims to restore ER homeostasis or initiate cell death. Chronic conditions of ER stress in the liver are associated with diabetes and perturbed lipid metabolism. These metabolic dysfunctions resemble the pharmacological side effects of SGAs. We, therefore, investigated whether SGAs promote the UPR in human and mouse hepatocytes. We observed full-fledged activation of ER stress by Aripiprazole, not by Olanzapine. This occurred at low micromolar concentrations and to variable intensities in different cell types, such as hepatocellular carcinoma, melanoma and glioblastoma. Mechanistically, Aripiprazole caused depletion of ER calcium, leading to activation of IRE1 and PERK, two major transducers of the UPR. Cells underwent apoptosis upon Aripiprazole treatment, which coincided with UPR induction, and this effect was reduced by adding glutathione without affecting UPR itself. Deletion of IRE1 from HepG2 cells protected cells from Aripiprazole toxicity. Our study reveals for the first time a cytotoxic effect of Aripiprazole that involves the induction of ER stress., FF, PD and VF are Marie Curie fellows [Treatment H2020-MSCA-ITN721236]. AMV, PR and IGM were supported by grants [RTI2018-094052-B-100] (MCIU/AEI/FEDER, UE)) and [S2017/BMD-3684] MOIR2-CM (Comunidad de Madrid, Spain) and CIBERdem (ISCIII, Spain).