Hepatic lipid-associated macrophages mediate the beneficial effects of bariatric surgery against MASH

For patients with obesity and metabolic syndrome, bariatric procedures such as vertical sleeve gastrectomy (VSG) have a clear benefit in ameliorating metabolic dysfunction-associated steatohepatitis (MASH). While the effects of bariatric surgeries have been mainly attributed to nutrient restriction and malabsorption, whether immuno-modulatory mechanisms are involved remains unclear. Here we report that VSG ameliorates MASH progression in a weight loss-independent manner. Single-cell RNA sequencing revealed that hepatic lipid-associated macrophages (LAMs) expressing the triggering receptor expressed on myeloid cells 2 (TREM2) increase their lysosomal activity and repress inflammation in response to VSG. Remarkably, TREM2 deficiency in mice ablates the reparative effects of VSG, suggesting that TREM2 is required for MASH resolution. Mechanistically, TREM2 prevents the inflammatory activation of macrophages and is required for their efferocytotic function. Overall, our findings indicate that bariatric surgery improves MASH through a reparative process driven by hepatic LAMs, providing insights into the mechanisms of disease reversal that may result in new therapies and improved surgical interventions.

Lipid Droplet Signaling in Metabolic Health and Aging

Lipid droplets (LDs) are neutral lipid rich organelles involved in lipid storage, fatty acid trafficking, and signaling. Emerging evidence from our laboratory and others suggests that the specific LD resident proteins couple/uncouple cells and tissues from inflammation and metabolic dysfunction. However, the mechanism by which LD proteins influences these critical pathways remains unknown. We will present data delving into the role of LD proteins Perilipin (PLIN) 2 and 5 in balancing cellular energy metabolism, mitochondrial function, and inflammation. Data will be presented defining novel mechanisms through which PLIN2 orchestrates eicosanoid production as a means to promote inflammation. We will contrast these findings to PLIN5, which uncouples LD accumulation from metabolic dysfunction and inflammation, in part due to its promotion of SIRT1 signaling. Overall, these studies will highlight a crucial role of LD metabolism and signaling in regulating cellular energy homeostatic processes known to be key players in governing healthspan.

Hepatic Lysosomal Acid Lipase Overexpression Worsens Hepatic Inflammation in Mice Fed a Western Diet

Nonalcoholic fatty liver disease (NAFLD) is characterized by the accumulation of lipid droplets in hepatocytes. NAFLD development and progression is associated with an increase in hepatic cholesterol levels and decreased autophagy and lipophagy flux. Previous studies have shown that the expression of lysosomal acid lipase (LAL), encoded by the gene LIPA, which can hydrolyze both triglyceride and cholesteryl esters, is inversely correlated with the severity of NAFLD. In addition, ablation of LAL activity results in profound NAFLD. Based on this, we predicted that overexpressing LIPA in the livers of mice fed a Western diet would prevent the development of NAFLD. As expected, mice fed the Western diet exhibited numerous markers of NAFLD, including hepatomegaly, lipid accumulation, and inflammation. Unexpectedly, LAL overexpression did not attenuate steatosis and had only minor effects on neutral lipid composition. However, LAL overexpression exacerbated inflammatory gene expression and infiltration of immune cells in mice fed the Western diet. LAL overexpression also resulted in abnormal phagosome accumulation and lysosomal lipid accumulation depending upon the dietary treatment. Overall, we found that hepatic overexpression of LAL drove immune cell infiltration and inflammation and did not attenuate the development of NAFLD, suggesting that targeting LAL expression may not be a viable route to treat NAFLD in humans.

MON-606 Changes in Eating Frequency but Not in Food Quality During Time Restricted Eating: Analysis from the See Food Study

Time-restricted eating (TRE) is a form of intermittent fasting that has gained interest in nutrition research and interventions as one of the dietary patterns to promote weight loss and other metabolic benefits. TRE is an eating pattern in which all nutrient intakes occur within a few hours (< 12 hours) every day, with no overt attempt to alter nutrient quality or quantity. The “See Food” study was a randomized, unblinded, controlled, behavioral interventional pilot clinical trial conducted from 2017-2018, that aimed to study the effect of a TRE intervention on metabolic health of overweight and obese participants, using the help of novel digital mobile technology. The objective of the current study is to analyze changes in diet quality among participants of the “See Food” study. Specifically, food intake patterns (frequency and type of meals, snacks and beverages) were compared between subjects in the 8-hour TRE intervention group, versus the unrestricted intake control group. Inclusion criteria included age 18-65, BMI >25 kg/m², had stable sleep and work schedule and owned a smartphone. Participants with diabetes, cardiovascular disease, uncontrolled pulmonary disease, pregnancy and nursing were excluded. A total of 20 participants with overweight or obesity (9 in control group and 11 in TRE group) were enrolled. Participants were instructed to use the “myCircadianClock” smartphone application to document their time of eating, type of meal and food images at baseline and during the intervention period of 14 weeks. The TRE group was instructed to consume calories within 8 hours each day. We compared the data between 14 days at baseline and 14 days at the end of the intervention. An eating occasion (EO) as defined as an occasion when a food or beverage (other than water) was consumed, and was separate from another EO by at least 15 minutes. Compared to baseline, both the TRE (3.8±0.4 vs 5.3±0.4, p<0.0001) and control group (4.9±0.4 vs 5.6±0.5, p=0.007) had less eating frequency. The TRE group had less eating frequency compared to control group (-1.5±0.2 vs -0.6±0.2, p=0.01) at the end of the study. Meal quality was classified by meal or snack type using a food-based classification system, and included 6 Eos ranging from a complete meal, to a low-quality snack. Beverages were classified separately by type. There were no differences in meal quality between the TRE and control group. The TRE group had less frequency of high-quality snack (-0.5±0.1 vs 0.05±0.1, p=0.008), mixed quality snack (-0.03±0.06 vs -0.3±0.07, p=0.01) and caffeinated beverage (-0.6±0.09 vs -0.008±0.1) compared to the control group. Conclusions: There was a reduction in eating frequency but no change in food quality when following an 8-hour TRE. Estimation of calories intake was limited in this study. A strength of the study is the use of a novel mobile app to track timing of meals. This would be feasible to implement in a real life setting.

New lipid-producing, cold-tolerant yellow-green alga isolated from the Rocky Mountains of Colorado

A new strain of yellow-green algae (Xanthophyceae, Heterokonta), tentatively named Heterococcus sp. DN1 (UTEX accession number UTEX ZZ885), was discovered among snow fields in the Rocky Mountains. Axenic cultures of H. sp. DN1 were isolated and their cellular morphology, growth, and composition of lipids were characterized. H. sp. DN1 was found to grow at temperatures approaching freezing to accumulate large intracellular stores of lipids. H. sp. DN1 produces the highest quantity of lipids when grown undisturbed with high light in low temperatures. Of particular interest was the accumulation of eicosapentaenoic acid, known to be important for human nutrition, and palmitoleic acid, known to improve biodiesel feedstock properties.