Microglia become progressively activated and seemingly dysfunctional with age, and genetic studies have linked these cells to the pathogenesis of a growing number of neurodegenerative diseases. Here we report a striking buildup of lipid droplets in microglia with aging in mouse and human brains. These cells, which we call lipid droplet-accumulating microglia (LDAM), are defective in phagocytosis, produce high levels of reactive oxygen species, and secrete pro-inflammatory cytokines. RNA sequencing analysis of LDAM revealed a transcriptional profile driven by innate inflammation distinct from previously reported microglial states. An unbiased CRISPR-Cas9 screen identified genetic modifiers of lipid droplet formation; surprisingly, variants of several of these genes, including progranulin, are causes of autosomal dominant forms of human neurodegenerative diseases. We thus propose that LDAM contribute to age-related and genetic forms of neurodegeneration.

Storage and degradation of triglycerides are essential processes to ensure energy homeostasis and availability of precursors for membrane lipid synthesis. Recent evidence suggests that an emerging class of enzymes containing a conserved patatin domain are centrally important players in lipid degradation. Here we describe the identification and characterization of a major triglyceride lipase of the adipose triglyceride lipase/Brummer family, Tgl4, in the yeast Saccharomyces cerevisiae. Elimination of Tgl4 in a tgl3 background led to fat yeast, rendering growing cells unable to degrade triglycerides. Tgl4 and Tgl3 lipases localized to lipid droplets, independent of each other. Serine 315 in the GXSXG lipase active site consensus sequence of the patatin domain of Tgl4 is essential for catalytic activity. Mouse adipose triglyceride lipase (which also contains a patatin domain but is otherwise highly divergent in primary structure from any yeast protein) localized to lipid droplets when expressed in yeast, and significantly restored triglyceride breakdown in tgl4 mutants in vivo. Our data identify yeast Tgl4 as a functional ortholog of mammalian adipose triglyceride lipase. Triglycerides (TG)2 serve different functions in a cell. First, they represent a most efficient way to store energy in the form of fatty acids (FA). Second, diglycerides (DG) liberated from TG by cleavage of a single fatty acyl ester bond, may serve as precursors for re-esterification to membrane phospholipids. Third, TG synthesis may also function as a sink to remove excess free fatty acids from the cellular milieu, in order to prevent FA-induced lipotoxicity. Because TG precursors or degradation products, such as phosphatidic acid or DG species, are also potential second messengers involved in multiple signaling processes, both TG synthesis and breakdown obviously require a stringent spatial and temporal control (1). Fueled by the epidemic dimensions of lipid-associated disorders, such as obesity and type 2 diabetes (2-4), numerous research strategies are focused toward understanding the genetic basis and molecular mechanisms that regulate uptake, synthesis, deposition, and mobilization of lipids, in the context of energy homeostasis (5-7). Because of the complexity of the problem, major input in this endeavor comes from the use of model systems, including mice, flies (Drosophila), worms (Caenorhabditis elegans) or yeast.In yeast, mobilization of fat depots occurs as a consequence of at least three different metabolic stimuli: in stationary phase, upon nutrient depletion, fatty acids are released from TG depots rather slowly and are subjected to peroxisomal ␤-oxidation, providing the metabolic energy for cellular maintenance (8). Alternatively, lipid depots are degraded very rapidly in cells that exit starvation conditions, e.g. from the stationary phase, and enter a vegetative growth cycle upon supplementation with carbohydrates (9). Because peroxisomes are repressed under these conditions, storage lipid compounds including steryl esters (SE) a...

For over 140 years, lichens have been regarded as a symbiosis between a single fungus, usually an ascomycete, and a photosynthesizing partner. Other fungi have long been known to occur as occasional parasites or endophytes, but the one lichen-one fungus paradigm has seldom been questioned. Here we show that many common lichens are composed of the known ascomycete, the photosynthesizing partner, and, unexpectedly, specific basidiomycete yeasts. These yeasts are embedded in the cortex, and their abundance correlates with previously unexplained variations in phenotype. Basidiomycete lineages maintain close associations with specific lichen species over large geographical distances and have been found on six continents. The structurally important lichen cortex, long treated as a zone of differentiated ascomycete cells, appears to consistently contain two unrelated fungi.

Lipid droplet formation and degradation are pivotal processes in preventing lipotoxicity and providing energy sources and signaling molecules. This is the first demonstration of lipid droplet turnover in yeast by microautophagy. Lipophagy is distinct from ER-phagy, mitophagy, and pexophagy and contributes to neutral lipid homeostasis by vacuolar lipolysis.

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SUMMARY Biofilms are a preferred mode of survival for many microorganisms including Vibrio cholerae, the causative agent of the severe secretory diarrheal disease cholera. The ability of the facultative human pathogen V. cholerae to form biofilms is a key factor for persistence in aquatic ecosystems and biofilms act as a source for new outbreaks. Thus, a better understanding of biofilm formation and transmission of V. cholerae is an important target to control the disease. So far the Vibrio exopolysaccharide was the only known constituent of the biofilm matrix. In this study we identify and characterize extracellular DNA as a component of the Vibrio biofilm matrix. Furthermore, we show that extracellular DNA is modulated and controlled by the two extracellular nucleases Dns and Xds. Our results indicate that extracellular DNA and the extracellular nucleases are involved in diverse processes including the development of a typical biofilm architecture, nutrient acquisition, detachment from biofilms and the colonization fitness of biofilm clumps after ingestion by the host. This study provides new insights into biofilm development and transmission of biofilm-derived V. cholerae.

Triacylglycerols (TGs) serve essential cellular functions as reservoirs for energy substrates (fatty acids) and membrane lipid precursors (diacylglycerols and fatty acids). Here we show that the major yeast TG lipase Tgl4, the functional ortholog of murine adipose TG lipase ATGL, is phosphorylated and activated by cyclin-dependent kinase 1 (Cdk1/Cdc28). Phospho-Tgl4-catalyzed lipolysis contributes to early bud formation in late G1 phase of the cell cycle. Conversely, lack of lipolysis delays bud formation and cell-cycle progression. In the absence of beta-oxidation, lipolysis-derived metabolites are thus required to support cellular growth. TG homeostasis is the only metabolic process identified as yet that is directly regulated by Cdk1/Cdc28-dependent phosphorylation of key anabolic and catabolic enzymes, highlighting the importance of FA storage and mobilization during the cell cycle. Our data provide evidence for a direct link between cell-cycle-regulatory kinases and TG degradation and suggest a general mechanism for coordinating membrane synthesis with cell-cycle progression.

Storage triacylglycerols (TAG) and membrane phospholipids share common precursors, i.e. phosphatidic acid and diacylglycerol, in the endoplasmic reticulum. In addition to providing a biophysically rather inert storage pool for fatty acids, TAG synthesis plays an important role to buffer excess fatty acids (FA). The inability to incorporate exogenous oleic acid into TAG in a yeast mutant lacking the acyltransferases Lro1p, Dga1p, Are1p, and Are2p contributing to TAG synthesis results in dysregulation of lipid synthesis, massive proliferation of intracellular membranes, and ultimately cell death. Carboxypeptidase Y trafficking from the endoplasmic reticulum to the vacuole is severely impaired, but the unfolded protein response is only moderately up-regulated, and dispensable for membrane proliferation, upon exposure to oleic acid. FA-induced toxicity is specific to oleic acid and much less pronounced with palmitoleic acid and is not detectable with the saturated fatty acids, palmitic and stearic acid. Palmitic acid supplementation partially suppresses oleic acid-induced lipotoxicity and restores carboxypeptidase Y trafficking to the vacuole. These data show the following: (i) FA uptake is not regulated by the cellular lipid requirements; (ii) TAG synthesis functions as a crucial intracellular buffer for detoxifying excess unsaturated fatty acids; (iii) membrane lipid synthesis and proliferation are responsive to and controlled by a balanced fatty acid composition.In the aqueous cellular environment, fatty acyl chains esterified in glycerophospholipids constitute the hydrophobic barrier of biological membranes. Thus, fatty acid (FA) 3 composition is a crucial determinant of cellular membrane function. Establishment of the specific FA profiles in lipid species of various organelle membranes (1) relies on an intricate balance between endogenous FA synthesis, recycling of FA from lipid breakdown, and perhaps uptake from the exterior. Glycerophospholipids and triacylglycerols (TAG), which serve as the major storage form of FA, share the similar precursors phosphatidic acid (PA) and diacylglycerol (DAG), both generated in the endoplasmic reticulum (ER) membrane. TAG are packaged into lipid droplets and are thus sequestered away from the ER membrane by a mechanism not yet understood. In addition, membranes and lipid storage pools (2, 3) undergo significant turnover and intracellular flux, e.g. during secretion or endocytosis and cellular growth, which must be accounted for by mechanisms that establish and maintain lipid homeostasis in these dynamic membrane systems (4). We have recently shown that TAG degradation provides metabolites that are critical for efficient cell cycle progression at the G 1