Increased oxidative stress and abundance of reactive oxygen species (ROS) are positively correlated with a variety of pathophysiologies, including cardiovascular disease, type 2 diabetes, Alzheimer's disease, and neuroinflammation. In adipose biology, diabetic obesity is correlated with increased ROS in an ageand depot-specific manner and is mechanistically linked to mitochondrial dysfunction, endoplasmic reticulum (ER) stress, potentiated lipolysis, and insulin resistance. The cellular quality control systems that homeostatically regulate oxidative stress in the lean state are down-regulated in obesity as a consequence of inflammatory cytokine pressure leading to the accumulation of oxidized biomolecules. New findings have linked protein, DNA, and lipid oxidation at the biochemical level, and the structures and potential functions of protein adducts such as carbonylation that accumulate in stressed cells have been characterized. The sum total of such regulation and biochemical changes results in alteration of cellular metabolism and function in the obese state relative to the lean state and underlies metabolic disease progression. In this review, we discuss the molecular mechanisms and events underlying these processes and their implications for human health and disease. Adipose oxidative stress is a major contributor to insulin resistance and cellular dysfunction (1) and is regulated in an ageand depot-specific manner. Adipose oxidative stress increases with age in both humans and experimental mice and varies between depots. For example, in contrast to younger mice (6 months), aged C57BL/6 mice (23 months) exhibit increased ROS 2 in the visceral adipose depot (epididymal) as compared with the subcutaneous depot (inguinal) (2). Similar experiments on human tissue have revealed that subcutaneous adipose tissue from obese diabetic subjects exhibit increased H 2 O 2 production compared with that from age-matched obese, nondiabetic subjects or to lean controls (3). Moreover, ROS levels are higher in epicardial fat as compared with subcutaneous adipose tissue (4). Furthermore, oxidized lipids and proteins accumulate to a greater extent in visceral depots compared with subcutaneous depots (5, 6). These observations point out the complexity of linking oxidative stress to disease and the molecular mechanisms that drive dysfunction and dysregulation. Major challenges exist in defining the specifics of reactive oxygen species-driven pathology and its connectivity to human health and disease.

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Obesity-linked diabetes is associated with accumulation of pro-inflammatory macrophages into adipose tissue leading to inflammasome activation and pyroptotic secretion of IL-1β and IL-18. Targeting fatty acid binding protein 4 (FABP4) uncouples obesity from inflammation, attenuates characteristics of type II diabetes and is mechanistically linked to the cellular accumulation of monounsaturated fatty acids in macrophages. Herein we show that pharmacologic inhibition or genetic deletion of FABP4 activates SIRT1 and deacetylates its downstream targets p53 and STAT3. Pharmacologic inhibition of fatty acid synthase or stearoyl CoA desaturase inhibits, whereas exogenous addition of C16:1 or C18:1 but not their saturated acyl chain counterparts, activates SIRT1 and p53/STAT3 signaling and IL-1β/IL-18 release. Expression of the p53 target gene ASC required for assembly of the NLRP3 inflammasome is down regulated in FABP4 null mice and macrophage cell lines leading to loss of pro-caspase 1 activation and pyroptosis. Concomitant with loss of ASC expression in FABP4 -/- macrophages, inflammasome activation, gasdermin D processing and functional activation of pyroptosis are all diminished in FABP4 null macrophages but can be rescued by silencing SIRT1 or exogenous expression of ASC. Taken together, these results reveal a novel lipid-regulated pathway linking to SIRT1-p53-ASC signaling and activation of inflammasome action and pyroptosis.

Besides the secretion of fatty acids, lipolytic stimulation of adipocytes results in the secretion of triglyceride-rich extracellular vesicle (AdEVs) and some free proteins (e.g., Fatty Acid Binding Protein 4) that in sum affect adipose homeostasis as well as the development of metabolic disease. At the mechanistic level, lipolytic signals activate p53 in an ATGL-dependent manner and pharmacologic inhibition of p53 attenuates AdEV protein and FABP4 secretion. Mass spectrometry analyses of the lipolytic secretome identified proteins involved in glucose and fatty acid metabolism, translation, chaperone activities as well as redox control. Consistent with a role for p53 in adipocyte protein secretion, activation of p53 by the MDM2 antagonist nutlin potentiated AdEV particles and non-AdEV protein secretion from cultured 3T3-L1 or OP9 adipocytes while the levels of FABP4 and AdEV proteins were significantly reduced in serum from p53-/- mice compared to wild-type controls. The genotoxin doxorubicin increased AdEV protein and FABP4 secretion in a p53-dependent manner and DNA repair-depleted ERCC1-/Δ haploinsufficient mice expressed elevated p53 in adipose depots, along with significantly increased serum FABP4. In sum, these data suggest that lipolytic signals, and cellular stressors such as DNA damage, facilitate AdEV protein and FABP4 secretion by adipocytes in a p53-dependent manner.

<p>Besides the secretion of fatty acids, lipolytic stimulation of adipocytes results in the secretion of triglyceride-rich extracellular vesicle (AdEVs) and some free proteins (e.g., Fatty Acid Binding Protein 4) that in sum affect adipose homeostasis as well as the development of metabolic disease. At the mechanistic level, lipolytic signals activate p53 in an ATGL-dependent manner and pharmacologic inhibition of p53 attenuates AdEV protein and FABP4 secretion. Mass spectrometry analyses of the lipolytic secretome identified proteins involved in glucose and fatty acid metabolism, translation, chaperone activities as well as redox control. Consistent with a role for p53 in adipocyte protein secretion, activation of p53 by the MDM2 antagonist nutlin potentiated AdEV particles and non-AdEV protein secretion from cultured 3T3-L1 or OP9 adipocytes while the levels of FABP4 and AdEV proteins were significantly reduced in serum from p53-/- mice compared to wild-type controls. The genotoxin doxorubicin increased AdEV protein and FABP4 secretion in a p53-dependent manner and DNA repair-depleted ERCC1-/D haploinsufficient mice expressed elevated p53 in adipose depots, along with significantly increased serum FABP4. In sum, these data suggest that lipolytic signals, and cellular stressors such as DNA damage, facilitate AdEV protein and FABP4 secretion by adipocytes in a p53-dependent manner.</p>