Postnatal Deletion of Fat Storage-inducing Transmembrane Protein 2 (FIT2/FITM2) Causes Lethal Enteropathy.

Lipid droplets (LDs) are phylogenetically conserved cytoplasmic organelles that store neutral lipids within a phospholipid monolayer. LDs compartmentalize lipids and may help to prevent cellular damage caused by their excess or bioactive forms. FIT2 is a ubiquitously expressed transmembrane endoplasmic reticulum (ER) membrane protein that has previously been implicated in LD formation in mammalian cells and tissue. Recent data indicate that FIT2 plays an essential role in fat storage in an in vivo constitutive adipose FIT2 knock-out mouse model, but the physiological effects of postnatal whole body FIT2 depletion have never been studied. Here, we show that tamoxifen-induced FIT2 deletion using a whole body ROSA26CreER(T2)-driven FIT2 knock-out (iF2KO) mouse model leads to lethal intestinal pathology, including villus blunting and death of intestinal crypts, and loss of lipid absorption. iF2KO mice lose weight and die within 2 weeks after the first tamoxifen dose. At the cellular level, LDs failed to form in iF2KO enterocytes after acute oil challenge and instead accumulated within the ER. Intestinal bile acid transporters were transcriptionally dysregulated in iF2KO mice, leading to the buildup of bile acids within enterocytes. These data support the conclusion that FIT2 plays an essential role in regulating intestinal health and survival postnatally.

Fat storage-inducing transmembrane protein 2 is required for normal fat storage in adipose tissue.

Triglycerides within the cytosol of cells are stored in a phylogenetically conserved organelle called the lipid droplet (LD). LDs can be formed at the endoplasmic reticulum, but mechanisms that regulate the formation of LDs are incompletely understood. Adipose tissue has a high capacity to form lipid droplets and store triglycerides. Fat storage-inducing transmembrane protein 2 (FITM2/FIT2) is highly expressed in adipocytes, and data indicate that FIT2 has an important role in the formation of LDs in cells, but whether FIT2 has a physiological role in triglyceride storage in adipose tissue remains unproven. Here we show that adipose-specific deficiency of FIT2 (AF2KO) in mice results in progressive lipodystrophy of white adipose depots and metabolic dysfunction. In contrast, interscapular brown adipose tissue of AF2KO mice accumulated few but large LDs without changes in cellular triglyceride levels. High fat feeding of AF2KO mice or AF2KO mice on the genetically obese ob/ob background accelerated the onset of lipodystrophy. At the cellular level, primary adipocyte precursors of white and brown adipose tissue differentiated in vitro produced fewer but larger LDs without changes in total cellular triglyceride or triglyceride biosynthesis. These data support the conclusion that FIT2 plays an essential, physiological role in fat storage in vivo.

The lipid droplet as a potential therapeutic target in NAFLD.

Nonalcoholic fatty liver disease (NAFLD) is a growing problem worldwide. Nonalcoholic fatty liver disease is characterized by an abnormal accumulation of triglyceride-rich lipid droplets (LDs) in the liver, which can lead to liver inflammation and metabolic disturbances. Lipid droplets are dynamic organelles that have recently gained considerable scientific interest. Their formation and growth are regulated processes requiring the participation of many endoplasmic reticulum- (ER-) and LD-associated proteins, which may serve as potential therapeutic targets for NAFLD. Protein families such as fat-inducing transmembrane proteins 1 and 2 (FITM1/FIT1 and FITM2/FIT2), the CIDE family of proteins, and the perilipin family, play important roles in LD biology. In this review, the authors discuss current views on LD formation and growth, and how various proteins may affect LD metabolism and lipoprotein assembly in the pathogenesis of NAFLD.

Prevalence, clinical correlates, and outcomes of anaemia in multi-ethnic Asian patients with heart failure with reduced ejection fraction.

AIMS: Recent international heart failure (HF) guidelines recognize anaemia as an important comorbidity contributing to poor outcomes in HF, based on data mainly from Western populations. We sought to determine the prevalence, clinical correlates, and prognostic impact of anaemia in patients with HF with reduced ejection fraction across Asia. METHODS AND RESULTS: We prospectively studied 3886 Asian patients (60 ± 13 years, 21% women) with HF (ejection fraction ≤40%) from 11 regions in the Asian Sudden Cardiac Death in Heart Failure study. Anaemia was defined as haemoglobin <13 g/dL (men) and <12 g/dL (women). Ethnic groups included Chinese (33.0%), Indian (26.2%), Malay (15.1%), Japanese/Korean (20.2%), and others (5.6%). Overall, anaemia was present in 41%, with a wide range across ethnicities (33-54%). Indian ethnicity, older age, diabetes, and chronic kidney disease were independently associated with higher odds of anaemia (all P < 0.001). Ethnicity modified the association of chronic kidney disease with anaemia (Pinteraction  = 0.045), with the highest adjusted odds among Japanese/Koreans [2.86; 95% confidence interval (CI) 1.96-4.20]. Anaemic patients had lower Kansas City Cardiomyopathy Questionnaire scores (P < 0.001) and higher risk of all-cause mortality and HF hospitalization at 1 year (hazard ratio = 1.28, 95% CI 1.08-1.50) compared with non-anaemic patients. The prognostic impact of anaemia was modified by ethnicity (Pinteraction  = 0.02), with the greatest hazard ratio in Japanese/Koreans (1.82; 95% CI 1.14-2.91). CONCLUSIONS: Anaemia is present in a third to more than half of Asian patients with HF and adversely impacts quality of life and survival. Ethnic differences exist wherein prevalence is highest among Indians, and survival is most severely impacted by anaemia in Japanese/Koreans.

Novel Index of Maladaptive Myocardial Remodeling in Hypertension.

BACKGROUND: Hypertensive left ventricular hypertrophy (HTN-LVH) is a leading cause of heart failure. Conventional patterns of cardiac geometry do not adequately risk-stratify patients with HTN-LVH. Using cardiovascular magnetic resonance, we developed a novel Remodeling Index (RI) that was designed to detect an exaggerated hypertrophic response to hypertension and tested its potential to risk-stratify hypertensive patients. METHODS AND RESULTS: The RI was derived using LaPlace's Law (), and normal RI ranges were established in 180 healthy volunteers. The utility of the RI was examined in 256 asymptomatic hypertensive patients and 10 patients with heart failure with preserved ejection fraction. Hypertensive patients underwent multimodal cardiac assessment: contrast-enhanced cardiovascular magnetic resonance, echocardiograms, 24-hour blood pressure monitoring, and cardiac biomarkers (high-sensitivity cardiac troponins, NT-proBNP [N-terminal pro-B-type natriuretic peptide], and galectin-3). Blood pressure accounted for only 20% of the variance observed in LV mass. Although there was no association between blood pressure and myocardial fibrosis, LV mass was independently associated with fibrosis. Compared with hypertensive patients without LVH (n=191; 74.6%) and those with HTN-LVH and normal RI (n=50; 19.5%), patients with HTN-LVH and low RI (HTN-LVH/low RI; n=15, 5.9%) had an amplified myocardial response: elevated indexed LV masses (83±24 g/m2), more fibrosis (73%), and higher biomarkers of myocardial injury and dysfunction (P<0.05 for all). RI was similar in HTN-LVH/low RI and heart failure with preserved ejection fraction (4.1 [3.4-4.5] versus 3.7 [3.4-4.0], respectively; P=0.15). CONCLUSIONS: We suggest that RI provides an approach for stratifying hypertensive patients and is suitable for testing in other disease cohorts to assess its clinical utility. CLINICAL TRIAL REGISTRATION: URL: https://clinicaltrials.gov. Unique identifier: NCT02670031.

Recent advances in understanding proteins involved in lipid droplet formation, growth and fusion.

Lipid droplets (LDs) were once viewed as simple, inert lipid micelles. However, they are now known to be organelles with a rich proteome involved in a myriad of cellular processes. LDs are heterogeneous in nature with different sizes and compositions of phospholipids, neutral lipids and proteins. This review takes a focused look at the roles of proteins involved in the regulation of LD formation, expansion, and morphology. The related proteins are summarized such as the fat-specific protein (Fsp27), fat storage-inducing transmembrane (FIT) proteins, seipin and ADP-ribosylation factor 1-coat protein complex I (Arf-COPI). Finally, we present important challenges in LD biology for a deeper understanding of this dynamic organelle to be achieved.

MicroRNAs are required for the feature maintenance and differentiation of brown adipocytes.

Brown adipose tissue (BAT) is specialized to burn lipids for heat generation as a natural defense against cold and obesity. Previous studies established microRNAs (miRNAs) as essential regulators of brown adipocyte differentiation, but whether miRNAs are required for the feature maintenance of mature brown adipocytes remains unknown. To address this question, we ablated Dgcr8, a key regulator of the miRNA biogenesis pathway, in mature brown as well as in white adipocytes. Adipose tissue-specific Dgcr8 knockout mice displayed enlarged but pale interscapular brown fat with decreased expression of genes characteristic of brown fat and were intolerant to cold exposure. Primary brown adipocyte cultures in vitro confirmed that miRNAs are required for marker gene expression in mature brown adipocytes. We also demonstrated that miRNAs are essential for the browning of subcutaneous white adipocytes in vitro and in vivo. Using this animal model, we performed miRNA expression profiling analysis and identified a set of BAT-specific miRNAs that are upregulated during brown adipocyte differentiation and enriched in brown fat compared with other organs. We identified miR-182 and miR-203 as new regulators of brown adipocyte development. Taken together, our study demonstrates an essential role of miRNAs in the maintenance as well as in the differentiation of brown adipocytes.