adipocyte ͉ Cide ͉ diabetes ͉ fat droplet ͉ fat metabolism

Fat-specific protein (FSP)27/Cidec is most highly expressed in white and brown adipose tissues and increases in abundance by over 50-fold during adipogenesis. However, its function in adipocytes has remained elusive since its discovery over 15 years ago. Here we demonstrate that FSP27/Cidec localizes to lipid droplets in cultured adipocytes and functions to promote lipid accumulation. Ectopically expressed FSP27-GFP surrounds lipid droplets in 3T3-L1 adipocytes and colocalizes with the known lipid droplet protein perilipin. Immunostaining of endogenous FSP27 in 3T3-L1 adipocytes also confirmed its presence on lipid droplets. FSP27-GFP expression also markedly increases lipid droplet size and enhances accumulation of total neutral lipids in 3T3-L1 preadipocytes as well as other cell types such as COS cells. Conversely, RNA interference-based FSP27/Cidec depletion in mature adipocytes significantly stimulates lipolysis and reduces the size of lipid droplets. These data reveal FSP27/Cidec as a novel adipocyte lipid droplet protein that negatively regulates lipolysis and promotes triglyceride accumulation.Adipose tissue is a major determinant of whole body glucose homeostasis and insulin sensitivity, as evidenced by its ability to secrete bioactive peptides and control lipid storage (1-6). The nuclear receptor peroxisome proliferator-activated receptor-␥ promotes adipogenesis and enhances these functions, acting in mice and humans to increase insulin signaling and glucose tolerance (7-12). Several proteins that are highly and selectively expressed in adipocytes, such as the secreted proteins adiponectin and leptin as well as adipsin, are under the control of peroxisome proliferator-activated receptor-␥ (3-5, 13, 14). These and other adipocyte proteins are highly up-regulated during adipogenesis and confer unique characteristics to these cells, including high capacity to store triglyceride and release fatty acids.Fat-specific protein (FSP)27, also denoted as CIDEC for the human homolog (15), was discovered over 15 years ago to be strikingly up-regulated during adipogenesis and is highly expressed in both white and brown adipose tissues (15-18). However, the question of FSP27/Cidec function has remained unsolved. The results we present here demonstrate FSP27/Cidec to be a novel lipid droplet protein that shares many features characteristic of the lipid droplet protein perilipin (19,20), including the ability to enhance neutral lipid accumulation when expressed in 3T3-L1 preadipocytes or even COS cells. Our data also reveal that a mechanism whereby FSP27/Cidec functions to promote triglyceride deposition in adiocytes is by inhibiting lipolysis. FSP27 is thus a major new modulator of lipid droplet function that is required for optimal storage of triglycerides by adipocytes. EXPERIMENTAL PROCEDURESMaterials-C57BL/6J (male, 10 weeks old) mice were obtained from The Jackson Laboratory. Human insulin was obtained from Lilly. Fetal bovine serum was purchased from Atlanta Biologicals, Inc. (Lawrenceville, GA). Other reagents ...

Storing excess energy for future use during starvation is critical for the survival of mammals. Much of this energy is stored in the form of triacylglycerol (TAG) within lipid droplets, which are present most abundantly in adipocytes and which, in turn, accumulate in depots such as subcutaneous and visceral adipose tissue in mice and humans. TAG in lipid droplets is mobilized during starvation by lipase-catalyzed hydrolysis (lipolysis) to release energy in the forms of glycerol and free fatty acids, providing fuel to other cell types such as muscle and liver. Previous work investigating formation of lipid droplets and regulation of lipolysis has elucidated the importance of lipid dropletassociated proteins for these processes ( 1, 2 ). Based on shared sequence homology, one set of lipid droplet proteins is grouped as the perilipin-adipophilin-tail interacting protein 47 (PAT/TIP47) family of proteins ( 3 ). PAT-related proteins are functionally conserved from mammals to lower organisms such as Drosophila and Dictyostelium spp ( 4 ). In Drosophila , two PAT domain proteins are encoded by the Lsdp1 and Lsd2 genes. Drosophila loss-of-function Lsd2 mutants are lean, whereas Lsd2 overexpression causes obesity ( 5 ). In mammals, PAT proteins can be divided into exchangeable TAG-associated PAT proteins (EPATs) or constitutively TAG-associated PAT proteins (CPATs). EPATs include the TIP47/perilipin-3 (PLIN3), S3-12/PLIN4, and Abstract The lipid droplet-associated fat specifi c protein 27 (FSP27) suppresses lipolysis and thereby enhances triglyceride accumulation in adipocytes. We and others have recently found FSP27 to be a remarkably short-lived protein (half-life, 15 min) due to its rapid ubiquitination and proteasomal degradation. Thus, we tested the hypothesis that lipolytic agents such as tumor necrosis factor-␣ (TNF-␣ ) and isoproterenol modulate FSP27 levels to regulate FFA release. Consistent with this concept, we showed that the lipolytic actions of TNF-␣ , interleukin-1 ␤ (IL-1 ␤ ), and IFN-␥ are accompanied by marked decreases in FSP27 expression and lipid droplet size in mouse adipocytes. Similar depletion of FSP27 using short interfering RNA (siRNA) mimicked the lipolysis-enhancing effect of TNF-␣ , while maintaining stable FSP27 levels using expression of hemagglutinin epitopetagged FSP27 blocked TNF-␣ -mediated lipolysis. In contrast, we show the robust lipolytic action of isoproterenol is paradoxically associated with increases in FSP27 levels and a delayed degradation rate corresponding to decreased ubiquitination. This catecholamine-mediated increase in FSP27 abundance, probably a feedback mechanism for restraining excessive lipolysis by catecholamines, is mimicked by forskolin or 8-bromo-cAMP treatment and is prevented by the protein kinase A (PKA) inhibitor KT5720 or by PKA depletion using siRNA. Taken together, these data identify the regulation of FSP27 as an important intermediate in the mechanism of lipolysis in adipocytes in response to TNF-␣ and isoproterenol. -Ranjit, S

Activation-induced cytidine deaminase (AID) is essential for class switch recombination (CSR) and somatic hypermutation (SHM) of Ig genes. The AID C terminus is required for CSR but not for S region DNA DSBs during CSR, and it is not required for SHM. AID lacking the C terminus (ΔAID) is a dominant negative (DN) mutant, as human patients heterozygous for this mutant fail to undergo CSR. In agreement, we show that ΔAID is a DN mutant when expressed in AID-sufficient mouse splenic B cells. In order to have DN function,ΔAID must have deaminase activity, suggesting that its ability to induce DSBs is important for the DN function. Supporting this hypothesis, Msh2-Msh6 have previously been shown to contribute to DSB formation in S regions, and here we find that Msh2 is required for the DN activity, as ΔAID is not a DN mutant in msh2−/− cells. Our results suggest that the DNA DSBs induced by ΔAID are unable to participate in CSR, and might interfere with the ability of full-length AID to participate in CSR. We propose thatΔAID is impaired in its ability to recruit non-homologous end joining (NHEJ) repair factors, resulting in accumulation of DSBs that undergo aberrant resection. Supporting this hypothesis, we find that the S-S junctions induced by ΔAID have longer microhomologies than those induced by full-length AID. In addition, our data suggest that AID binds Sµ regions in vivo as a monomer.

Introduction: Bloodstream Infection is one of the leading causes of mortality and morbidity among various groups of patients in a developing country like Nepal. Identification of the bacteria and their susceptibility to commonly used antibiotics is very essential for the treatment of the patients. Aims: This study aims to analyze current trends in bloodstream infection by accessing their bacteriological profile and antibiotic susceptibility. Methods: This is a hospital-based retrospective analysis of blood cultures of patients suspected with bloodstream infection. We conducted a three years (January 2018 to January 2021) retrospective analysis of blood culture reports from patients suspected with bloodstream infection. Data of the laboratory reports were used to determine bloodstream infection, blood culture contamination, pathogen profile and antimicrobial resistance patterns. Results: Out of 12811 blood samples that were sent to microbiology laboratory for culture, 438 were positive cultures. The most common etiological agent causing Bloodstream Infection was found to be Salmonella Typhi with129 isolates (29.6%) followed by Escherichia coli (21.9%). There was a significant rise in resistance to most of the frequently used antibiotics. Conclusion: Salmonella Typhi is the most frequent bacteria to be isolated in Bloodstream Infection. Resistance towards different etiological agents of Bloodstream Infection is alarmingly increasing every year. Resistance to frequently prescribed drugs should be of concern to the clinicians prescribing the drugs.