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On September 7 and 8, 2022, Healthy Environment and Endocrine Disruptors Strategies, an Environmental Health Sciences program, convened a scientific workshop of relevant stakeholders involved in obesity, toxicology, or obesogen research to review the state of the science regarding the role of obesogenic chemicals that might be contributing to the obesity pandemic. The workshops objectives were to examine the evidence supporting the hypothesis that obesogens contribute to the etiology of human obesity; to discuss opportunities for improved understanding, acceptance, and dissemination of obesogens as contributors to the obesity pandemic; and to consider the need for future research and potential mitigation strategies. This report details the discussions, key areas of agreement, and future opportunities to prevent obesity. The attendees agreed that environmental obesogens are real, significant, and a contributor at some degree to weight gain at the individual level and to the global obesity and metabolic disease pandemic at a societal level; moreover, it is at least, in theory, remediable.

Mitochondria associate with lipid droplets (LDs) in fat-oxidizing tissues, but the functional role of these peridroplet mitochondria (PDM) is unknown. Microscopic observation of interscapular brown adipose tissue reveals that PDM have unique protein composition and cristae structure and remain adherent to the LD in the tissue homogenate. We developed an approach to isolate PDM based on their adherence to LDs. Comparison of purified PDM to cytoplasmic mitochondria reveals that (1) PDM have increased pyruvate oxidation, electron transport, and ATP synthesis capacities; (2) PDM have reduced β-oxidation capacity and depart from LDs upon activation of brown adipose tissue thermogenesis and β-oxidation; (3) PDM support LD expansion as Perilipin5-induced recruitment of mitochondria to LDs increases ATP synthase-dependent triacylglyceride synthesis; and (4) PDM maintain a distinct protein composition due to uniquely low fusion-fission dynamics. We conclude that PDM represent a segregated mitochondrial population with unique structure and function that supports triacylglyceride synthesis.

BAT-controlled thermogenic activity is thought to be required for its capacity to prevent the development of insulin resistance. This hypothesis predicts that mediators of thermogenesis may help prevent diet-induced insulin resistance. We report that the mitochondrial fusion protein Mitofusin 2 (Mfn2) in BAT is essential for cold-stimulated thermogenesis, but promotes insulin resistance in obese mice. Mfn2 deletion in mice through Ucp1-cre (BAT-Mfn2-KO) causes BAT lipohypertrophy and cold intolerance. Surprisingly however, deletion of Mfn2 in mice fed a high fat diet (HFD) results in improved insulin sensitivity and resistance to obesity, while impaired cold-stimulated thermogenesis is maintained. Improvement in insulin sensitivity is associated with a gender-specific remodeling of BAT mitochondrial function. In females, BAT mitochondria increase their efficiency for ATP-synthesizing fat oxidation, whereas in BAT from males, complex I-driven respiration is decreased and glycolytic capacity is increased. Thus, BAT adaptation to obesity is regulated by Mfn2 and with BAT-Mfn2 absent, BAT contribution to prevention of insulin resistance is independent and inversely correlated to whole-body cold-stimulated thermogenesis.

The proapoptotic BCL-2 family member BAD resides in a glucokinase-containing complex that regulates glucose-driven mitochondrial respiration. Here, we present genetic evidence of a physiologic role for BAD in glucose-stimulated insulin secretion by beta cells. This novel function of BAD is specifically dependent upon the phosphorylation of its BH3 sequence, previously defined as an essential death domain. We highlight the pharmacologic relevance of phosphorylated BAD BH3 by using cell- permeable, hydrocarbon-stapled BAD BH3 helices that target glucokinase, restore glucose-driven mitochondrial respiration and correct the insulin secretory response in Bad-deficient islets. Our studies uncover an alternative target and function for the BAD BH3 domain and emphasize the therapeutic potential of phosphorylated BAD BH3 mimetics in selectively restoring beta cell function. Furthermore, we show that BAD regulates the physiologic adaptation of beta cell mass during high-fat feeding. Our findings provide genetic proof of the bifunctional activities of BAD in both beta cell survival and insulin secretion., The BCL-2 family of proteins constitutes a key control point in apoptosis by regulating the release of apoptogenic factors from mitochondria (1). Recent studies have assigned new roles to certain [...]

Aging is associated with metabolic syndrome, tissue damage by cytotoxic lipids, and altered fatty acid handling. Fat tissue dysfunction may contribute to these processes. This could result, in part, from age-related changes in preadipocytes, since they give rise to new fat cells throughout life. To test this hypothesis, preadipocytes cultured from rats of different ages were exposed to oleic acid, the most abundant fatty acyl moiety in fat tissue and the diet. At fatty acid concentrations at which preadipocytes from young animals remained viable, cells from old animals accumulated lipid in multiple small lipid droplets and died, with increased apoptotic index, caspase activity, BAX, and p53. Rather than inducing apoptosis, oleic acid promoted adipogenesis in preadipocytes from young animals, with appearance of large lipid droplets. CCAAT/enhancer-binding protein-[alpha] (C/EBP[alpha]) and peroxisome proliferator-activated receptor-[gamma] (PPAR[gamma]) increased to a greater extent in cells from young than old animals after oleate exposure. Oleic acid, but not glucose, oxidation was impaired in preadipocytes and fat cells from old animals. Expression of carnitine palmitoyltransferase (CPT)-1, which catalyzes the rate-limiting step in fatty acid [beta]-oxidation, was not reduced in preadipocytes from old animals. At lower fatty acid levels, constitutively active CPT I expression enhanced [beta]-oxidation. At higher levels, CPT I was not as effective in enhancing [beta]-oxidation in preadipocytes from old as young animals, suggesting that mitochondrial dysfunction may contribute. Consistent with this, medium-chain acyl-CoA dehydrogenase expression was reduced in preadipocytes from old animals. Thus preadipocyte fatty acid handling changes with aging, with increased susceptibly to lipotoxicity and impaired fatty acid-induced adipogenesis and [beta]-oxidation. fatty acid metabolism; oleic acid; peroxisome proliferator-activated receptor-[gamma]; CCAAT/enhancer-binding protein-[alpha]; [beta]-oxidation

We examined the effects of different physiological concentrations of glucose on cytoplasmic [Ca.sup.2+] handling and mitochondrial membrane potential ([DELTA][[psi].sub.m]) and insulin secretion in single mouse islet cells. The threshold for both glucose-induced changes in [Ca.sup.2+] and [DELTA][[psi].sub.m] ranged from 6 to 8 mM. Glucose step-jumps resulted in sinusoidal oscillations of cytoplasmic [Ca.sup.2+], whereas [DELTA][[psi].sub.m] reached sustained plateaus with oscillations interposed on the top of these plateaus. The amplitude of the [Ca.sup.2+] rise (height of the peak) did not vary with glucose concentration, suggesting a 'digital' rather than 'analog' character of this aspect of the oscillatory [Ca.sup.2+] response. The average glucose-dependent elevation of cytoplasmic [Ca.sup.2+] concentration during glucose stimulation reached saturation at 8 mM stimulatory glucose, whereas [DELTA][[psi].sub.m] showed a linear glucose dose-response relationship over the range of stimulatory glucose concentrations (4-16 mM). Glucose-dependent increases in insulin secretion correlated well with [DELTA][[psi].sub.m], but not with average [Ca.sup.2+] concentration. These data show that an ATP-dependent [K.sup.+] channel-independent pathway is operative at the single cell level and suggest mitochondrial metabolism may be a determining factor in explaining graded, glucose concentration-dependent increases in insulin secretion.

Intracellular lipolysis is a major pathway of lipid metabolism that has roles, not only in the provision of free fatty acids as energy substrate, but also in intracellular signal transduction. The latter is likely to be particularly important in the regulation of insulin secretion from islet [beta]-cells. The mechanisms by which lipolysis is regulated in different tissues is, therefore, of considerable interest. Here, the effects of long-chain acyl-CoA esters (LC-CoA) on lipase activity in islets and adipocytes were compared. Palmitoyl-CoA (Pal-CoA, 1-10 [micro]M) stimulated lipase activity in islets from both normal and hormone-sensitive lipase (HSL)-null mice and in phosphatase-treated islets, indicating that the stimulatory effect was neither on HSL nor phosphorylation dependent. In contrast, we reproduced the previously published observations showing inhibition of HSL activity by LC-CoA in adipocytes. The inhibitory effect of LC-CoA on adipocyte HSL was dependent on phosphorylation and enhanced by acyl-CoA-binding protein (ACBP). In contrast, the stimulatory effect on islet lipase activity was blocked by ACBP, presumably due to binding and sequestration of LC-CoA. These data suggest the following intertissue relationship between islets and adipocytes with respect to fatty acid metabolism, LC-CoA signaling, and lipolysis. Elevated LC-CoA in islets stimulates lipolysis to generate a signal to increase insulin secretion, whereas elevated LC-CoA in adipocytes inhibits lipolysis. Together, these opposite actions of LC-CoA lower circulating fat by inhibiting its release from adipocytes and promoting fat storage via insulin action. acyl-coenzyme A-binding protein; free fatty acid; hormone-sensitive lipase; lipid signaling

To understand how medium-chain fatty acids (FA) influence lipid metabolism in adipocytes, we studied the effects of octanoate on the oxidation of glucose and endogenous palmitate, cellular [O.sub.2] consumption, mitochondrial membrane potential, lipid synthesis from long-chain FA, glucose and lactate. We found that octanoate significantly suppressed the esterification of oleate into triglycerides (TG) in both 3T3-L1 and human adipocytes. Octanoate also significantly suppressed de novo FA synthesis. These effects were associated with octanoate-mediated reductions in the activities of acyl CoA:1,2-diacylglycerol acyltransferase (DGAT) and acetyl CoA carboxylase (ACC). Cells pretreated with octanoate had reduced mRNA levels for a number of lipid metabolism genes, including of DGAT, ACC and stearoyl CoA desaturase-1. On the other hand, octanoate did not acutely perturb cellular [O.sub.2] consumption or mitochondrial membrane potential. Together, these results suggest that octanoate affected adipocyte function by reducing TG synthesis but not by enhancing oxidation. KEY WORDS: * medium-chain fatty acids * triglyceride synthesis * adipocytes

Culturing clonal [beta]-cells (HIT-T15) overnight in the presence of phorbol ester [phorbol myristate acetate (PMA)] enhanced insulin secretion while causing downregulation of some protein kinase C (PKC) isoforms and most PKC activity. We show here that this enhanced secretion required the retention of PMA in the cell. Hence, it could not be because of long-lived phosphorylation of cellular substrates by the isoforms that were downregulated, namely PKC-[alpha], -[beta]II, and -[epsilon], but could be because of the continued activation of the two remaining diacylglycerol-sensitive isoforms [delta] and [mu]. The enhanced secretion did not involve changes in glucose metabolism, cell membrane potential, or intracellular [Ca.sup.2+] handling, suggesting a distal effect. PMA washout caused the loss of the enhanced response, but secretion was then stimulated by acute readdition of PMA or bombesin. The magnitude of this restimulation appeared dependent on the mass of PKC-[alpha], which was rapidly resynthesized during PMA washout. Therefore, stimulation of insulin secretion by PMA, and presumably by endogenous diacylglycerol, involves the activation of PKC isoforms [delta] and/or [mu], and also PKC-[alpha]. insulin secretion; protein kinase C isoforms; phorbol 12-myristate 13-acetate; bombesin