Micro RNA-124a regulates lipolysis via adipose triglyceride lipase and comparative gene identification 58.

Lipolysis is the biochemical pathway responsible for the catabolism of cellular triacylglycerol (TG). Lipolytic TG breakdown is a central metabolic process leading to the generation of free fatty acids (FA) and glycerol, thereby regulating lipid, as well as energy homeostasis. The precise tuning of lipolysis is imperative to prevent lipotoxicity, obesity, diabetes and other related metabolic disorders. Here, we present our finding that miR-124a attenuates RNA and protein expression of the major TG hydrolase, adipose triglyceride lipase (ATGL/PNPLA2) and its co-activator comparative gene identification 58 (CGI-58/ABHD5). Ectopic expression of miR-124a in adipocytes leads to reduced lipolysis and increased cellular TG accumulation. This phenotype, however, can be rescued by overexpression of truncated Atgl lacking its 3'UTR, which harbors the identified miR-124a target site. In addition, we observe a strong negative correlation between miR-124a and Atgl expression in various murine tissues. Moreover, miR-124a regulates the expression of Atgl and Cgi-58 in murine white adipose tissue during fasting as well as the expression of Atgl in murine liver, during fasting and re-feeding. Together, these results point to an instrumental role of miR-124a in the regulation of TG catabolism. Therefore, we suggest that miR-124a may be involved in the regulation of several cellular and organismal metabolic parameters, including lipid storage and plasma FA concentration.

Macrophage CGI-58 deficiency activates ROS-inflammasome pathway to promote insulin resistance in mice.

Overnutrition activates a proinflammatory program in macrophages to induce insulin resistance (IR), but its molecular mechanisms remain incompletely understood. Here, we show that saturated fatty acid and lipopolysaccharide, two factors implicated in high-fat diet (HFD)-induced IR, suppress macrophage CGI-58 expression. Macrophage-specific CGI-58 knockout (MaKO) in mice aggravates HFD-induced glucose intolerance and IR, which is associated with augmented systemic/tissue inflammation and proinflammatory activation of adipose tissue macrophages. CGI-58-deficient macrophages exhibit mitochondrial dysfunction due to defective peroxisome proliferator-activated receptor (PPAR)γ signaling. Consequently, they overproduce reactive oxygen species (ROS) to potentiate secretion of proinflammatory cytokines by activating NLRP3 inflammasome. Anti-ROS treatment or NLRP3 silencing prevents CGI-58-deficient macrophages from oversecreting proinflammatory cytokines and from inducing proinflammatory signaling and IR in the cocultured fat slices. Anti-ROS treatment also prevents exacerbation of inflammation and IR in HFD-fed MaKO mice. Our data thus establish CGI-58 as a suppressor of overnutrition-induced NLRP3 inflammasome activation in macrophages.

An engineered E.coli strain for the production of glycoglycerolipids.

The glycolipid synthase MG517 from Mycoplasma genitalium catalyzes the glucosyl transfer from UDPGlc to diacylglycerol producing glycoglycerolipids (GGL) (Andrés et al., 2011). The enzyme was functional in E. coli accumulating GGL in the plasma membrane. A metabolic engineering strategy for GGL production was evaluated using this microorganism. To increase the levels of GGL precursors, UDPGlc and diacylglycerol, GalU and PlsC enzymes involved in their biosynthesis were overexpressed. Seven engineered strains were obtained containing different combinations of the mg517 with galU and plsC genes. Diacylglycerol synthesis showed to be limiting and the strain overexpressing MG517 and PlsC achieved the highest GGL yield. The new lipids were mono, di- and triglucosyldiacylglycerol with different acyl combinations in each compound. It indicates that the successive glucosyl transferase activities of MG517 have different acyl chain specificity for the acceptor substrate. GGL represented up to 6 mg per g of dry weight.

Expression and regulation of 1-acyl-sn-glycerol- 3-phosphate acyltransferases in the epidermis.

Phospholipids are a major class of lipids in epidermis, where they serve as a source of free fatty acids that are important for the maintenance of epidermal permeability barrier function. The phospholipid biosynthetic enzyme, 1-acyl-sn-glycerol-3-phosphate acyltransferase (AGPAT), catalyzes the acylation of lysophosphatidic acid to form phosphatidic acid, the major precursor of all glycerolipids. We identified an expression pattern of AGPAT isoforms that is unique to epidermis, with relatively high constitutive expression of mouse AGPAT (mAGPAT) 3, 4, and 5 but low constitutive expression of mAGPAT 1 and 2. Localization studies indicate that all five isoforms of AGPAT were expressed in all nucleated layers of epidermis. Furthermore, rat AGPAT 2 and 5 mRNAs increased in parallel with both an increase in enzyme activity and permeability barrier formation late in rat epidermal development. Moreover, after two methods of acute permeability barrier disruption, mAGPAT 1, 2, and 3 mRNA levels increased rapidly and were sustained for at least 24 h. In parallel with the increase in mRNA levels, an increase in AGPAT activity also occurred. Because upregulation of mAGPAT mRNAs after tape-stripping could be partially reversed by artificial barrier restoration by occlusion, these studies suggest that an increase in the expression of AGPATs is linked to barrier requirements.