Phospholipid isotope tracing suggests ß-catenin-driven suppression of phosphatidylcholine metabolism in hepatocellular carcinoma.

Activating mutations in the CTNNB1 gene encoding ß-catenin are among the most frequently observed oncogenic alterations in hepatocellular carcinoma (HCC). Profound alterations in lipid metabolism, including increases in fatty acid oxidation and transformation of the phospholipidome, occur in HCC with CTNNB1 mutations, but it is unclear what mechanisms give rise to these changes. We employed untargeted lipidomics and targeted isotope tracing to measure phospholipid synthesis activity in an inducible human liver cell line expressing mutant ß-catenin, as well as in transgenic zebrafish with activated ß-catenin-driven HCC. In both models, activated ß-catenin expression was associated with large changes in the lipidome including conserved increases in acylcarnitines and ceramides and decreases in triglycerides. Lipid isotope tracing analysis in human cells revealed a reduction in phosphatidylcholine (PC) production rates as assayed by choline incorporation. We developed lipid isotope tracing analysis for zebrafish tumors and observed reductions in phosphatidylcholine synthesis by both the CDP-choline and PEMT pathways. The observed changes in the ß-catenin-driven HCC phospholipidome suggest that zebrafish can recapitulate conserved features of HCC lipid metabolism and may serve as a model for identifying future HCC-specific lipid metabolic targets.

The mechanism of covalent inhibition of LAR phosphatase by illudalic acid.

Leukocyte antigen-related (LAR) phosphatase is a receptor-type protein tyrosine phosphatase involved in cellular signaling and associated with human disease including cancer and metabolic disorders. Selective inhibition of LAR phosphatase activity by well characterized and well validated small molecules would provide key insights into the roles of LAR phosphatase in health and disease, but identifying selective inhibitors of LAR phosphatase activity has been challenging. Recently, we described potent and selective inhibition of LAR phosphatase activity by the fungal natural product illudalic acid. Here we provide a detailed biochemical characterization of the adduct formed between LAR phosphatase and illudalic acid. A mass spectrometric analysis indicates that two cysteine residues are covalently labeled by illudalic acid and a related analog. Mutational analysis supports the hypothesis that inhibition of LAR phosphatase activity is due primarily to the adduct with the catalytic cysteine residue. A computational study suggests potential interactions between the illudalic acid moiety and the enzyme active site. Taken together, these data offer novel insights into the mechanism of inhibition of LAR phosphatase activity by illudalic acid.

Sedentary behavior in mice induces metabolic inflexibility by suppressing skeletal muscle pyruvate metabolism.

Carbohydrates and lipids provide the majority of substrates to fuel mitochondrial oxidative phosphorylation (OXPHOS). Metabolic inflexibility, defined as an impaired ability to switch between these fuels, is implicated in a number of metabolic diseases. Here we explore the mechanism by which physical inactivity promotes metabolic inflexibility in skeletal muscle. We developed a mouse model of sedentariness, small mouse cage (SMC) that, unlike other classic models of disuse in mice, faithfully recapitulated metabolic responses that occur in humans. Bioenergetic phenotyping of skeletal muscle mitochondria displayed metabolic inflexibility induced by physical inactivity, demonstrated by a reduction in pyruvate-stimulated respiration (JO2) in absence of a change in palmitate-stimulated JO2. Pyruvate resistance in these mitochondria was likely driven by a decrease in phosphatidylethanolamine (PE) abundance in the mitochondrial membrane. Reduction in mitochondrial PE by heterozygous deletion of phosphatidylserine decarboxylase (PSD) was sufficient to induce metabolic inflexibility measured at the whole-body level, as well as at the level of skeletal muscle mitochondria. Low mitochondrial PE in C2C12 myotubes was sufficient to increase glucose flux towards lactate. We further implicate that resistance to pyruvate metabolism is due to attenuated mitochondrial entry via mitochondrial pyruvate carrier (MPC). These findings suggest a mechanism by which mitochondrial PE directly regulates MPC activity to modulate metabolic flexibility in mice.

The phospholipids cardiolipin and phosphatidylethanolamine differentially regulate MDC biogenesis.

Cells utilize multiple mechanisms to maintain mitochondrial homeostasis. We recently characterized a pathway that remodels mitochondria in response to metabolic alterations and protein overload stress. This remodeling occurs via the formation of large membranous structures from the mitochondrial outer membrane called mitochondrial-derived compartments (MDCs), which are eventually released from mitochondria and degraded. Here, we conducted a microscopy-based screen in budding yeast to identify factors that regulate MDC formation. We found that two phospholipids, cardiolipin (CL) and phosphatidylethanolamine (PE), differentially regulate MDC biogenesis. CL depletion impairs MDC biogenesis, whereas blocking mitochondrial PE production leads to constitutive MDC formation. Additionally, in response to metabolic MDC activators, cellular and mitochondrial PE declines, and overexpressing mitochondrial PE synthesis enzymes suppress MDC biogenesis. Altogether, our data indicate a requirement for CL in MDC biogenesis and suggest that PE depletion may stimulate MDC formation downstream of MDC-inducing metabolic stress.

Zinc Alpha-2-Glycoprotein (ZAG/AZGP1) secreted by triple-negative breast cancer promotes tumor microenvironment fibrosis.

Obesity is a predisposition factor for breast cancer, suggesting a localized, reciprocal interaction between breast cancer cells and the surrounding mammary white adipose tissue. To investigate how breast cancer cells alter the composition and function of adipose tissue, we screened the secretomes of ten human breast cancer cell lines for the ability to modulate the differentiation of adipocyte stem and progenitor cells (ASPC). The screen identified a key adipogenic modulator, Zinc Alpha-2-Glycoprotein (ZAG/AZGP1), secreted by triple-negative breast cancer (TNBC) cells. TNBC-secreted ZAG inhibits adipogenesis and instead induces the expression of fibrotic genes. Accordingly, depletion of ZAG in TNBC cells attenuates fibrosis in white adipose tissue and inhibits tumor growth. Further, high expression of ZAG in TNBC patients, but not other clinical subtypes of breast cancer, is linked to poor prognosis. Our findings suggest a role of TNBC-secreted ZAG in promoting the transdifferentiation of ASPCs into cancer-associated fibroblasts to support tumorigenesis.

Acute activation of adipocyte lipolysis reveals dynamic lipid remodeling of the hepatic lipidome.

Adipose tissue is the site of long-term energy storage. During the fasting state, exercise, and cold exposure, the white adipose tissue mobilizes energy for peripheral tissues through lipolysis. The mobilization of lipids from white adipose tissue to the liver can lead to excess triglyceride accumulation and fatty liver disease. Although the white adipose tissue is known to release free fatty acids, a comprehensive analysis of lipids mobilized from white adipocytes in vivo has not been completed. In these studies, we provide a comprehensive quantitative analysis of the adipocyte-secreted lipidome and show that there is interorgan crosstalk with liver. Our analysis identifies multiple lipid classes released by adipocytes in response to activation of lipolysis. Time-dependent analysis of the serum lipidome showed that free fatty acids increase within 30 min of ß3-adrenergic receptor activation and subsequently decrease, followed by a rise in serum triglycerides, liver triglycerides, and several ceramide species. The triglyceride composition of liver is enriched for linoleic acid despite higher concentrations of palmitate in the blood. To further validate that these findings were a specific consequence of lipolysis, we generated mice with conditional deletion of adipose tissue triglyceride lipase exclusively in adipocytes. This loss of in vivo adipocyte lipolysis prevented the rise in serum free fatty acids and hepatic triglycerides. Furthermore, conditioned media from adipocytes promotes lipid remodeling in hepatocytes with concomitant changes in genes/pathways mediating lipid utilization. Together, these data highlight critical role of adipocyte lipolysis in interorgan crosstalk between adipocytes and liver.

Inhibition of the skeletal muscle Lands cycle ameliorates weakness induced by physical inactivity.

BACKGROUND: Lipid hydroperoxides (LOOH) have been implicated in skeletal muscle atrophy with age and disuse. Lysophosphatidylcholine acyltransferase 3 (LPCAT3), an enzyme of the Lands cycle, conjugates a polyunsaturated fatty acyl chain to a lysophospholipid to form a polyunsaturated fatty acid containing phospholipid (PUFA-PL) molecule, providing substrates for LOOH propagation. Previous studies suggest that inhibition of the Lands cycle is an effective strategy to suppress LOOH. Mice with skeletal muscle-specific tamoxifen-inducible knockout of LPCAT3 (LPCAT3-MKO) were utilized to determine if muscle-specific attenuation of LOOH may alleviate muscle atrophy and weakness with disuse. METHODS: LPCAT3-MKO and control mice underwent 7 days of sham or hindlimb unloading (HU model) to study muscle mass and force-generating capacity. LOOH was assessed by quantifying 4-hydroxynonenal (4-HNE)-conjugated peptides. Quantitative PCR and lipid mass spectrometry were used to validate LPCAT3 deletion. RESULTS: Seven days of HU was sufficient to induce muscle atrophy and weakness concomitant to a ~2-fold increase in 4-HNE (P = 0.0069). Deletion of LPCAT3 reversed HU-induced increase in muscle 4-HNE (P = 0.0256). No difference was found in body mass, body composition, or caloric intake between genotypes. The soleus (SOL) and plantaris (PLANT) muscles of the LPCAT3-MKO mice experienced ~15% and ~40% less atrophy than controls, respectively. (P = 0.0011 and P = 0.0265). Type I and IIa SOL myofibers experienced a ~40% decrease in cross sectional area (CSA), which was attenuated to only 15% in the LPCAT3-MKO mice (P = 0.0170 and P = 0.0411, respectively). Strikingly, SOL muscles were fully protected and extensor digitorum longus (EDL) muscles experienced a ~35% protection from HU-induced reduction in force-generating capacity in the LPCAT3-MKO mice compared with controls (P < 0.0001 for both muscles). CONCLUSIONS: Our findings demonstrate that attenuation of skeletal muscle lipid hydroperoxides is sufficient to restore its function, in particular a protection from reduction in muscle specific force. Our findings suggest muscle lipid peroxidation contributes to atrophy and weakness induced by disuse in mice.

Phospholipid isotope tracing reveals ß-catenin-driven suppression of phosphatidylcholine metabolism in hepatocellular carcinoma.

Background and Aims: Activating mutations in the CTNNB1 gene encoding ß-catenin are among the most frequently observed oncogenic alterations in hepatocellular carcinoma (HCC). HCC with CTNNB1 mutations show profound alterations in lipid metabolism including increases in fatty acid oxidation and transformation of the phospholipidome, but it is unclear how these changes arise and whether they contribute to the oncogenic program in HCC. Methods: We employed untargeted lipidomics and targeted isotope tracing to quantify phospholipid production fluxes in an inducible human liver cell line expressing mutant ß-catenin, as well as in transgenic zebrafish with activated ß-catenin-driven HCC. Results: In both models, activated ß-catenin expression was associated with large changes in the lipidome including conserved increases in acylcarnitines and ceramides and decreases in triglycerides. Lipid flux analysis in human cells revealed a large reduction in phosphatidylcholine (PC) production rates as assayed by choline tracer incorporation. We developed isotope tracing lipid flux analysis for zebrafish and observed similar reductions in phosphatidylcholine synthesis flux accomplished by sex-specific mechanisms. Conclusions: The integration of isotope tracing with lipid abundances highlights specific lipid class transformations downstream of ß-catenin signaling in HCC and suggests future HCC-specific lipid metabolic targets.

Animal FAS-like polyketide synthases produce diverse polypropionates.

Animal cytoplasmic fatty acid synthase (FAS) represents a unique family of enzymes that are classically thought to be most closely related to fungal polyketide synthase (PKS). Recently, a widespread family of animal lipid metabolic enzymes has been described that bridges the gap between these two ubiquitous and important enzyme classes: the animal FAS-like PKSs (AFPKs). Although very similar in sequence to FAS enzymes that produce saturated lipids widely found in animals, AFPKs instead produce structurally diverse compounds that resemble bioactive polyketides. Little is known about the factors that bridge lipid and polyketide synthesis in the animals. Here, we describe the function of EcPKS2 from Elysia chlorotica, which synthesizes a complex polypropionate natural product found in this mollusc. EcPKS2 starter unit promiscuity potentially explains the high diversity of polyketides found in and among molluscan species. Biochemical comparison of EcPKS2 with the previously described EcPKS1 reveals molecular principles governing substrate selectivity that should apply to related enzymes encoded within the genomes of photosynthetic gastropods. Hybridization experiments combining EcPKS1 and EcPKS2 demonstrate the interactions between the ketoreductase and ketosynthase domains in governing the product outcomes. Overall, these findings enable an understanding of the molecular principles of structural diversity underlying the many molluscan polyketides likely produced by the diverse AFPK enzyme family.

Inhibition of skeletal muscle Lands cycle ameliorates weakness induced by physical inactivity.

Background: Lipid hydroperoxides (LOOH) have been implicated in skeletal muscle atrophy with age and disuse. Lysophosphatidylcholine acyltransferase 3 (LPCAT3), an enzyme of Lands cycle, conjugates a polyunsaturated fatty acyl chain to a lysophospholipid (PUFA-PL) molecule, providing substrates for LOOH propagation. Previous studies suggest that inhibition of Lands cycle is an effective strategy to suppress LOOH. Mice with skeletal muscle-specific tamoxifen-inducible knockout of LPCAT3 (LPCAT3-MKO) were utilized to determine if muscle-specific attenuation of LOOH may alleviate muscle atrophy and weakness with disuse. Methods: LPCAT3-MKO and control mice underwent 7 days of sham or hindlimb unloading (HU model) to study muscle mass and force-generating capacity. LOOH was assessed by quantifying 4-hydroxynonenal (4-HNE)-conjugated peptides. Quantitative PCR and lipid mass spectrometry were used to validate LPCAT3 deletion. Results: 7 days of HU was sufficient to induce muscle atrophy and weakness concomitant to an increase in 4-HNE. Deletion of LPCAT3 reversed HU-induced increase in muscle 4HNE. No difference was found in body mass, body composition, or caloric intake between genotypes. The soleus (SOL) and plantaris (PLANT) muscles of the LPCAT3-MKO mice were partially protected from atrophy compared to controls, concomitant to attenuated decrease in cross-sectional areas in type I and IIa fibers. Strikingly, SOL and extensor digitorum longus (EDL) were robustly protected from HU-induced reduction in force-generating capacity in the LPCAT3-MKO mice compared to controls. Conclusion: Our findings demonstrate that attenuation of muscle LOOH is sufficient to restore skeletal muscle function, in particular a protection from reduction in muscle specific force. Thus, muscle LOOH contributes to atrophy and weakness induced by HU in mice.

Postnatal growth restriction impairs rat lung structure and function.

The negative impact of nutritional deficits in the development of bronchopulmonary dysplasia is well recognized, yet mechanisms by which nutrition alters lung outcomes and nutritional strategies that optimize development and protect the lung remain elusive. Here, we use a rat model to assess the isolated effects of postnatal nutrition on lung structural development without concomitant lung injury. We hypothesize that postnatal growth restriction (PGR) impairs lung structure and function, critical mediators of lung development, and fatty acid profiles at postnatal day 21 in the rat. Rat pups were cross-fostered at birth to rat dams with litter sizes of 8 (control) or 16 (PGR). Lung structure and function, as well as serum and lung tissue fatty acids, and lung molecular mediators of development, were measured. Male and female PGR rat pups had thicker airspace walls, decreased lung compliance, and increased tissue damping. Male rats also had increased lung elastance, increased lung elastin protein abundance, and lysol oxidase expression, and increased elastic fiber deposition. Female rat lungs had increased conducting airway resistance and reduced levels of docosahexaenoic acid in lung tissue. We conclude that PGR impairs lung structure and function in both male and female rats, with sex-divergent changes in lung molecular mediators of development.

Loss of the mitochondrial protein Abcb10 results in altered arginine metabolism in MEL and K562 cells and nutrient stress signaling through ATF4.

Abcb10 is a mitochondrial membrane protein involved in hemoglobinization of red cells. Abcb10 topology and ATPase domain localization suggest it exports a substrate, likely biliverdin, out of mitochondria that is necessary for hemoglobinization. In this study, we generated Abcb10 deletion cell lines in both mouse murine erythroleukemia and human erythroid precursor human myelogenous leukemia (K562) cells to better understand the consequences of Abcb10 loss. Loss of Abcb10 resulted in an inability to hemoglobinize upon differentiation in both K562 and mouse murine erythroleukemia cells with reduced heme and intermediate porphyrins and decreased levels of aminolevulinic acid synthase 2 activity. Metabolomic and transcriptional analyses revealed that Abcb10 loss gave rise to decreased cellular arginine levels, increased transcripts for cationic and neutral amino acid transporters with reduced levels of the citrulline to arginine converting enzymes argininosuccinate synthetase and argininosuccinate lyase. The reduced arginine levels in Abcb10-null cells gave rise to decreased proliferative capacity. Arginine supplementation improved both Abcb10-null proliferation and hemoglobinization upon differentiation. Abcb10-null cells showed increased phosphorylation of eukaryotic translation initiation factor 2 subunit alpha, increased expression of nutrient sensing transcription factor ATF4 and downstream targets DNA damage inducible transcript 3 (Chop), ChaC glutathione specific gamma-glutamylcyclotransferase 1 (Chac1), and arginyl-tRNA synthetase 1 (Rars). These results suggest that when the Abcb10 substrate is trapped in the mitochondria, the nutrient sensing machinery is turned on remodeling transcription to block protein synthesis necessary for proliferation and hemoglobin biosynthesis in erythroid models.

Weight loss increases skeletal muscle mitochondrial energy efficiency in obese mice.

Weight loss from an overweight state is associated with a disproportionate decrease in whole-body energy expenditure that may contribute to the heightened risk for weight regain. Evidence suggests that this energetic mismatch originates from lean tissue. Although this phenomenon is well documented, the mechanisms have remained elusive. We hypothesized that increased mitochondrial energy efficiency in skeletal muscle is associated with reduced expenditure under weight loss. Wildtype (WT) male C57BL6/N mice were fed with high fat diet for 10 weeks, followed by a subset of mice that were maintained on the obesogenic diet (OB) or switched to standard chow to promote weight loss (WL) for additional 6 weeks. Mitochondrial energy efficiency was evaluated using high-resolution respirometry and fluorometry. Mass spectrometric analyses were employed to describe the mitochondrial proteome and lipidome. Weight loss promoted ~50% increase in the efficiency of oxidative phosphorylation (ATP produced per O2 consumed, or P/O) in skeletal muscle. However, weight loss did not appear to induce significant changes in mitochondrial proteome, nor any changes in respiratory supercomplex formation. Instead, it accelerated the remodeling of mitochondrial cardiolipin (CL) acyl-chains to increase tetralinoleoyl CL (TLCL) content, a species of lipids thought to be functionally critical for the respiratory enzymes. We further show that lowering TLCL by deleting the CL transacylase tafazzin was sufficient to reduce skeletal muscle P/O and protect mice from diet-induced weight gain. These findings implicate skeletal muscle mitochondrial efficiency as a novel mechanism by which weight loss reduces energy expenditure in obesity.

Metaboverse enables automated discovery and visualization of diverse metabolic regulatory patterns.

Metabolism is intertwined with various cellular processes, including controlling cell fate, influencing tumorigenesis, participating in stress responses and more. Metabolism is a complex, interdependent network, and local perturbations can have indirect effects that are pervasive across the metabolic network. Current analytical and technical limitations have long created a bottleneck in metabolic data interpretation. To address these shortcomings, we developed Metaboverse, a user-friendly tool to facilitate data exploration and hypothesis generation. Here we introduce algorithms that leverage the metabolic network to extract complex reaction patterns from data. To minimize the impact of missing measurements within the network, we introduce methods that enable pattern recognition across multiple reactions. Using Metaboverse, we identify a previously undescribed metabolite signature that correlated with survival outcomes in early stage lung adenocarcinoma patients. Using a yeast model, we identify metabolic responses suggesting an adaptive role of citrate homeostasis during mitochondrial dysfunction facilitated by the citrate transporter, Ctp1. We demonstrate that Metaboverse augments the user's ability to extract meaningful patterns from multi-omics datasets to develop actionable hypotheses.

Macrophage metabolic rewiring improves heme-suppressed efferocytosis and tissue damage in sickle cell disease.

Sickle cell disease (SCD) is hallmarked by an underlying chronic inflammatory condition, which is contributed by heme-activated proinflammatory macrophages. Although previous studies addressed heme ability to stimulate macrophage inflammatory skewing through Toll-like receptor4 (TLR4)/reactive oxygen species signaling, how heme alters cell functional properties remains unexplored. Macrophage-mediated immune cell recruitment and apoptotic cell (AC) clearance are relevant in the context of SCD, in which tissue damage, cell apoptosis, and inflammation occur owing to vaso-occlusive episodes, hypoxia, and ischemic injury. Here we show that heme strongly alters macrophage functional response to AC damage by exacerbating immune cell recruitment and impairing cell efferocytic capacity. In SCD, heme-driven excessive leukocyte influx and defective efferocytosis contribute to exacerbated tissue damage and sustained inflammation. Mechanistically, these events depend on heme-mediated activation of TLR4 signaling and suppression of the transcription factor proliferator-activated receptor γ (PPARγ) and its coactivator peroxisome proliferator-activated receptor γ coactivator 1α (PGC1α). These changes reduce efferocytic receptor expression and promote mitochondrial remodeling, resulting in a coordinated functional and metabolic reprogramming of macrophages. Overall, this results in limited AC engulfment, impaired metabolic shift to mitochondrial fatty acid ß-oxidation, and, ultimately, reduced secretion of the antiinflammatory cytokines interleukin-4 (IL-4) and IL-10, with consequent inhibition of continual efferocytosis, resolution of inflammation, and tissue repair. We further demonstrate that impaired phagocytic capacity is recapitulated by macrophage exposure to plasma of patients with SCD and improved by hemopexin-mediated heme scavenging, PPARγ agonists, or IL-4 exposure through functional and metabolic macrophage rewiring. Our data indicate that therapeutic improvement of heme-altered macrophage functional properties via heme scavenging or PGC1α/PPARγ modulation significantly ameliorates tissue damage associated with SCD pathophysiology.

Lipid hydroperoxides promote sarcopenia through carbonyl stress.

Reactive oxygen species (ROS) accumulation is a cardinal feature of skeletal muscle atrophy. ROS refers to a collection of radical molecules whose cellular signals are vast, and it is unclear which downstream consequences of ROS are responsible for the loss of muscle mass and strength. Here, we show that lipid hydroperoxides (LOOH) are increased with age and disuse, and the accumulation of LOOH by deletion of glutathione peroxidase 4 (GPx4) is sufficient to augment muscle atrophy. LOOH promoted atrophy in a lysosomal-dependent, proteasomal-independent manner. In young and old mice, genetic and pharmacological neutralization of LOOH or their secondary reactive lipid aldehydes robustly prevented muscle atrophy and weakness, indicating that LOOH-derived carbonyl stress mediates age- and disuse-induced muscle dysfunction. Our findings provide novel insights for the role of LOOH in sarcopenia including a therapeutic implication by pharmacological suppression.

Protein-metabolite interactomics of carbohydrate metabolism reveal regulation of lactate dehydrogenase.

Metabolic networks are interconnected and influence diverse cellular processes. The protein-metabolite interactions that mediate these networks are frequently low affinity and challenging to systematically discover. We developed mass spectrometry integrated with equilibrium dialysis for the discovery of allostery systematically (MIDAS) to identify such interactions. Analysis of 33 enzymes from human carbohydrate metabolism identified 830 protein-metabolite interactions, including known regulators, substrates, and products as well as previously unreported interactions. We functionally validated a subset of interactions, including the isoform-specific inhibition of lactate dehydrogenase by long-chain acyl-coenzyme A. Cell treatment with fatty acids caused a loss of pyruvate-lactate interconversion dependent on lactate dehydrogenase isoform expression. These protein-metabolite interactions may contribute to the dynamic, tissue-specific metabolic flexibility that enables growth and survival in an ever-changing nutrient environment.

Mitochondrial phosphatidylethanolamine modulates UCP1 to promote brown adipose thermogenesis.

Thermogenesis by uncoupling protein 1 (UCP1) is one of the primary mechanisms by which brown adipose tissue (BAT) increases energy expenditure. UCP1 resides in the inner mitochondrial membrane (IMM), where it dissipates membrane potential independent of adenosine triphosphate (ATP) synthase. Here, we provide evidence that phosphatidylethanolamine (PE) modulates UCP1-dependent proton conductance across the IMM to modulate thermogenesis. Mitochondrial lipidomic analyses revealed PE as a signature molecule whose abundance bidirectionally responds to changes in thermogenic burden. Reduction in mitochondrial PE by deletion of phosphatidylserine decarboxylase (PSD) made mice cold intolerant and insensitive to ß3 adrenergic receptor agonist-induced increase in whole-body oxygen consumption. High-resolution respirometry and fluorometry of BAT mitochondria showed that loss of mitochondrial PE specifically lowers UCP1-dependent respiration without compromising electron transfer efficiency or ATP synthesis. These findings were confirmed by a reduction in UCP1 proton current in PE-deficient mitoplasts. Thus, PE performs a previously unknown role as a temperature-responsive rheostat that regulates UCP1-dependent thermogenesis.

An evolutionary trade-off between host immunity and metabolism drives fatty liver in male mice.

Adaptations to infectious and dietary pressures shape mammalian physiology and disease risk. How such adaptations affect sex-biased diseases remains insufficiently studied. In this study, we show that sex-dependent hepatic gene programs confer a robust (~300%) survival advantage for male mice during lethal bacterial infection. The transcription factor B cell lymphoma 6 (BCL6), which masculinizes hepatic gene expression at puberty, is essential for this advantage. However, protection by BCL6 protein comes at a cost during conditions of dietary excess, which result in overt fatty liver and glucose intolerance in males. Deleting hepatic BCL6 reverses these phenotypes but markedly lowers male survival during infection, thus establishing a sex-dependent trade-off between host defense and metabolic systems. Our findings offer strong evidence that some current sex-biased diseases are rooted in ancient evolutionary trade-offs between immunity and metabolism.

Following Roux-en-Y gastric bypass surgery, serum ceramides demarcate patients that will fail to achieve normoglycemia and diabetes remission.

BACKGROUND: Obesity is a prevalent health threat and risk factor for type 2 diabetes. In this study, we evaluate the relationship between ceramides, which inhibit insulin secretion and sensitivity, and markers of glucose homeostasis and diabetes remission or recursion in patients who have undergone a Roux-en-Y gastric bypass (RYGB). METHODS: The Utah Obesity Study is a prospective cohort study, with targeted ceramide and dihydroceramide measurements performed on banked serum samples. The Utah Obesity Study consists of 1,156 participants in three groups: a RYGB surgery group, a non-surgery group denied insurance coverage, and severely obese population controls. Clinical examinations and ceramide assessments were performed at baseline and 2 and 12 years after RYGB surgery. FINDINGS: Surgery patients (84% female, 42.2 ± 10.6 years of age at baseline) displayed lower levels of several serum dihydroceramides and ceramides at 2 and 12 years after RYGB. By contrast, neither the control group (77% female, 48.7± 6.4 years of age at baseline) nor the non-surgery group (95% female, 43.0± 11.4 years of age at baseline) experienced significant decreases in any species. Using a linear mixed effect model, we found that multiple dihydroceramides and ceramides positively associated with the glycemic control measures HOMA-IR and HbA1c. In surgery group participants with prevalent diabetes, ceramides inversely predict diabetes remission, independent of changes in weight. CONCLUSIONS: Ceramide decreases may explain the insulin sensitization and diabetes resolution observed in most RYGB surgery patients. FUNDING: Funded by the National Institutes of health (NIH), The Juvenile Diabetes Research Foundation, and the American Heart Association.