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Context We have recently shown that the secreted isoform of endoplasmic reticulum membrane complex subunit 10 (scEMC10) is upregulated in human obesity and that overexpression of scEMC10 promotes, whereas antibody neutralization of circulating scEMC10 prevents diet-induced obesity in mice. Objective To explore associations of serum scEMC10 with body mass index (BMI), resting metabolism rate (RMR), and age in humans. Design A cross-sectional study. Setting and Patients A total of 833 participants from a Chinese physical examination cohort and 191 participants from the Leipzig Obesity Biobank cohort. Main Outcome Measures Serum scEMC10 concentrations are measured using chemiluminescent immunoassay. RMR is calculated based on measurements from indirect calorimetry with an open-circuit ventilated-hood system. Results In the Chinese physical examination cohort, a J-shaped nonlinear correlation between BMI and serum scEMC10 was identified in participants where underweight, overweight, and obese people all presented higher serum scEMC10 levels than normal weight people. Participants younger than age 30 years old exhibited significantly higher serum scEMC10 levels than those older than 50 years of age. In addition, participants aged 30 to 40 years also had significantly higher serum scEMC10 levels than those aged 50 to 60 years. In the Leipzig Obesity Biobank cohort, we observed a significantly negative correlation between serum scEMC10 and resting energy expenditure after adjusting for BMI. Participants in the highest quartile of serum scEMC10 levels had significantly lower RMR than those in the first quartile. RMR had an independently inverse association with serum scEMC10. Conclusions Serum scEMC10 levels are negatively associated with age and RMR in humans.

Long-term ad libitum dietary restrictions, such as low-protein diets (LPDs), improve metabolic health and extend the life span of mice and humans. However, most studies conducted thus far have focused on the preventive effects of LPDs on metabolic syndromes. To test the therapeutic potential of LPD, we treated a lipodystrophy mouse model IRFKO (adipose-specific insulin receptor knockout) in this study. We have previously shown that IRFKO mice have profound insulin resistance, hyperglycemia, and whitenng of interscapular brown adipose tissue (BAT), closely mimicking the phenotypes in lipoatrophic diabetic patients. Here, we demonstrate that 14-day of LPD (5.1% kcal from protein) feeding is sufficient to reduce postprandial blood glucose, improve insulin resistance, and normalize glucose tolerance in the IRFKO mice. This profound metabolic improvement is associated with BAT activation and increase in whole body energy expenditure. To confirm, we showed that surgical denervation of BAT attenuated the beneficial metabolic effects of LPD feeding in IRFKO mice, including the ‘browning’ effects on BAT and the glucose-ameliorating results. However, BAT denervation failed to affect the body weight-lowering effects of LPD. Together, our results imply a therapeutic potential to use LPD for the treatment of lipoatrophic diabetes.

Long-term ad libitum dietary restriction such as low-protein diet (LPD) improves metabolic health and extends the life span of mice and possibly humans. However, most studies conducted thus far have focused on the preventive, but not therapeutic, potential of LPDs. Previously we shown that LPD (5.1% kcal from protein) was able to improve postprandial blood glucose values of the lipodystrophic IRFKO (adipose-specific insulin receptor knockout) mice after 14 days with strong activation of interscapular brown adipose tissue (iBAT) and increase energy expenditure. To determine whether iBAT activation was responsible for the hyperglycemia normalization after the LPD treatment, we surgically denervated iBAT of IRFKO mice before LPD treatment. Blood glucose were measured twice a week for up to 4 weeks, at the end of the monitoring mice were subjected to indirect calorimetry assessment (Promethion, Sable Systems) . Our data showed that surgical denervation of iBAT abolished the hyperglycemia normalization effect of LPD in the IRFKO mice. Morphologically, surgical denervation also prevented the ‘browning’ effect of LPD on the whitening iBAT observed in IRFKO mice. In line with the morphological data, LPD failed to induce thermogenic markers including UCP1 and BMP8b in denervated iBAT. In contrast, iBAT denervation has lesser effects on the LPD-induced energy expenditure and circulating FGF21 level, possibly due to compensation by beige fat formation in the inguinal WAT. Together, our data confirms that hyperglycemia normalization caused by LPD on IRFKO is iBAT activation dependent. Our observation suggests that blood glucose could be utilized to fuel LPD-induced iBAT activation as a mechanism for amino acid homeostasis. Further experimentation needs to be done in order to narrow down the mechanism driving this phenomenon. Taken together, our data suggest that short-term LPD could be a potential strategy for the treatment of metabolic syndrome. Disclosure M.D.Munoz: None. A.Zamudio: None. M.A.Mccann: None. C.Liew: None. Funding NIH RDK109015A1

FoxO1 is a major target of insulin action and regulates expression of ATGL and its inhibitor, G0S2, in the liver (Cell Rep 15:349, 2016) . Here, we asked whether ATGL mediates effects of FoxO1 in liver-specific insulin receptor knockout (LIRKO) mice. Studies in LIRKO and IR/FoxO1 double knockout (LIRFKO) mice show ATGL expression is increased and G0S2 is suppressed in a FoxO1-dependent fashion when insulin signaling is disrupted in the liver. ATGL knockdown (KD) reduces high plasma glucose and insulin concentrations, HOMA-IR and fatty acid oxidation, and improves glucose tolerance in LIRKO mice. Hyperinsulinemic-euglycemic clamp studies show ATGL KD improves insulin sensitivity due to effects on both HGP and glucose utilization, reflecting changes in WAT lipolysis, BAT metabolism and hepatic gene expression. The expression of FoxO1-regulated gluconeogenic genes (PEPCK, G6Pase, PCO, PGC-1α) , hepatokines (e.g., follistatin) and IGFBP-1 is increased in LIRKO mice and reduced by ATGL KD, reflecting changes in acetylation of FoxO1 and its co-activator, PGC-1α (decreased in LIRKO, increased by ATGL KD) . Rictor acetylation, which promotes activation of Akt and phosphorylation of FoxO1, also is increased by ATGL KD in LIRKO mice and isolated hepatocytes. Since ATGL promotes activation of Sirt1 (Mol Cell 77:810, 2020) and Sirt1 deacetylates FoxO1, PGC-1α and rictor, these studies suggest FoxO1 promotes increased ATGL and Sirt1 activity, and that Sirt1 activation enhances the effects of FoxO1 on gene expression and glucose homeostasis in a feed forward fashion (FoxO1 -> ATGL -> Sirt1 -> FoxO1) . Targeting the FoxO1/ATGL/Sirt1 pathway may provide a useful strategy for improving glucose homeostasis when insulin signaling is impaired in the liver. Disclosure I.O-sullivan: None. S.Bhattacharyya: None. C.Liew: None. S.M.Lee: None. J.Cordoba-chacon: None. R.J.Perry: None. G.I.Shulman: Advisory Panel; 89bio, Inc., AstraZeneca, Equator Therapeutics, Inc., Janssen Research & Development, LLC, Merck & Co., Inc., Consultant; DiCerna Pharmaceuticals, Inc., Novo Nordisk, Other Relationship; Generian Pharmaceuticals, iMetabolic Biopharma Corporation, Maze Therapeutics, The Liver Company, Stock/Shareholder; Levels Health, Inc. . T.Unterman: None. Funding Department of Veterans Affairs (5I01BX001968)

Obesity is a consequence of chronic disruption in energy homeostasis. This phenomenon is controlled by systemic and local signals such as leptin, a nutrient-sensitive signal secreted primarily by the white adipose tissue (WAT) . In contrast, interscapular brown adipose tissue (iBAT) has been shown to express undetectable or very low levels of leptin. In this study, unexpectedly, we observed overnight fasting decreased leptin expression in iBAT, and 2-hour refeeding was able to restore the iBAT leptin levels. This nutritional status-dependent fluctuation suggests a vital role of iBAT leptin in the acute regulation of energy homeostasis. Consistently, we found that mice with leptin selectively overexpressed in the UCP1-positive cells of iBAT (LEP-OEiBAT/UCP1) showed reduced fast-induced food intake. This hypophagia phenotype was associated with increased satiation as reflected by decreased meal numbers and increase postmeal interval. Notably, LEP-OEiBAT/UCP1 selectively increased the mRNA expression of leptin in the iBAT without affecting circulating leptin levels, indicating a possible paracrine role of iBAT leptin. In supporting this point of view, we showed that chemical ablation of sensory nerves (SS) in iBAT significantly increased fast-induced food intake, associated with altered meal frequency. Additionally, we also found that iBAT-specific infusion of leptin increased Stat3 phosphorylation (pStat3) in the upstream iBAT-innervating sensory neurons, suggesting leptin-mediated sensory detection. Notably, the increased pStat3 was associated with neural activation in the arcuate nucleus of the hypothalamus in the brain, and chemical ablation of iBAT SS blunted this stimulation. Our results support a model that feeding-induced iBAT leptin modulates iBAT-specific sensory inputs to the brain to regulate food intake and feeding patterns. Disclosure M.D.Munoz: None. V.C.Torres irizarry: None. P.Xu: None. C.Liew: None. Funding RDK109015A1

Purpose Z-spectrum imaging, defined as the consecutive collection of images after saturating over a range of frequency offsets, has been recently proposed as a method to measure the fat-water fraction by the simultaneous detection of fat and water resonances. By incorporating a binomial pulse irradiated at each offset before the readout, the spectral selectivity of the sequence can be further amplified, making it possible to monitor the subtle proton resonance frequency shift that follows a change in temperature. Methods We tested the hypothesis in aqueous and cream phantoms and in healthy mice, all under thermal challenge. The binomial module consisted of 2 sinc-shaped pulses of opposite phase separated by a delay. Such a delay served to spread out off-resonance spins, with the resulting excitation profile being a periodic function of the delay and the chemical shift. Results During heating experiments, the water resonance shifted downfield, and by fitting the curve to a sine function it was possible to quantify the change in temperature. Results from Z-spectrum imaging correlated linearly with data from conventional MRI techniques like T1 mapping and phase differences from spoiled GRE. Conclusion Because the measurement is performed solely on magnitude images, the technique is independent of phase artifacts and is therefore applicable in mixed tissues (e.g., fat). We showed that Z-spectrum imaging can deliver reliable temperature change measurement in both muscular and fatty tissues.

Secreted isoform of endoplasmic reticulum membrane complex subunit 10 (scEMC10) is a poorly characterised secreted protein of largely unknown physiological function. Here we demonstrate that scEMC10 is upregulated in humans with obesity and is positively associated with insulin resistance. Consistent with a causal role for scEMC10 in obesity, Emc10-/- mice are resistant to diet-induced obesity due to an increase in energy expenditure. Furthermore, neutralization of circulating scEMC10 using a monoclonal antibody reduces body weight and enhances insulin sensitivity in obese mice. Mechanistically, we provide evidence that scEMC10 binds to the catalytic subunit of PKA and inhibits its stimulatory action on CREB while ablation of EMC10 promotes thermogenesis in adipocytes via activation of the PKA signalling pathway and its downstream targets. Taken together, our data identify scEMC10 as a novel circulating inhibitor of thermogenesis and a potential therapeutic target for obesity and its cardiometabolic complications.

Secreted isoform of endoplasmic reticulum membrane complex subunit 10 (scEMC10) is a poorly characterized secreted protein of largely unknown physiological function. Here we demonstrate that scEMC10 is upregulated in people with obesity and is positively associated with insulin resistance. Consistent with a causal role for scEMC10 in obesity, Emc10-/- mice are resistant to diet-induced obesity due to an increase in energy expenditure, while scEMC10 overexpression decreases energy expenditure, thus promoting obesity in mouse. Furthermore, neutralization of circulating scEMC10 using a monoclonal antibody reduces body weight and enhances insulin sensitivity in obese mice. Mechanistically, we provide evidence that scEMC10 can be transported into cells where it binds to the catalytic subunit of PKA and inhibits its stimulatory action on CREB while ablation of EMC10 promotes thermogenesis in adipocytes via activation of the PKA signalling pathway and its downstream targets. Taken together, our data identify scEMC10 as a circulating inhibitor of thermogenesis and a potential therapeutic target for obesity and its cardiometabolic complications.