Ovarian yolk formation in fishes: Molecular mechanisms underlying formation of lipid droplets and vitellogenin-derived yolk proteins

AbstractIn yeast, the selective autophagy of intracellular lipid droplets (LDs) or lipophagy can be induced by either nitrogen (N) starvation or carbon limitation (e.g. in the stationary (S) phase). We developed the yeast, Komagataella phaffii (formerly Pichia pastoris), as a new lipophagy model and compared the N-starvation and S-phase lipophagy in over 30 autophagy-related mutants using the Erg6-GFP processing assay. Surprisingly, two lipophagy pathways had hardly overlapping stringent molecular requirements. While the N-starvation lipophagy strictly depended on the core autophagic machinery (Atg1-Atg9, Atg18 and Vps15), vacuole fusion machinery (Vam7 and Ypt7) and vacuolar proteolysis (proteinases A and B), only Atg6 and proteinases A and B were essential for the S-phase lipophagy. The rest of the proteins were only partially required in the S-phase. Moreover, we isolated the prl1 (for positive regulator of lipophagy 1) mutant affected in the S-phase lipophagy but not N-starvation lipophagy. The prl1 defect was at a stage of delivery of the LDs from the cytoplasm to the vacuole further supporting mechanistically different nature of the two lipophagy pathways. Taken together, our results suggest that N-starvation and S-phase lipophagy have distinct molecular mechanisms.

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Pathophysiology of Lipid Droplets in Neuroglia

Antioxidants ◽

10.3390/antiox11010022 ◽

2021 ◽

Vol 11 (1) ◽

pp. 22

Author(s):

Tina Smolič ◽

Robert Zorec ◽

Nina Vardjan

Keyword(s):

Energy Production ◽

Lipid Droplets ◽

Molecular Mechanisms ◽

Cell Function ◽

Ependymal Cells ◽

Potential Contribution ◽

Neurologic Disorders ◽

Lipid Turnover ◽

The Central Nervous System ◽

Development And Aging

In recent years, increasing evidence regarding the functional importance of lipid droplets (LDs), cytoplasmic storage organelles in the central nervous system (CNS), has emerged. Although not abundantly present in the CNS under normal conditions in adulthood, LDs accumulate in the CNS during development and aging, as well as in some neurologic disorders. LDs are actively involved in cellular lipid turnover and stress response. By regulating the storage of excess fatty acids, cholesterol, and ceramides in addition to their subsequent release in response to cell needs and/or environmental stressors, LDs are involved in energy production, in the synthesis of membranes and signaling molecules, and in the protection of cells against lipotoxicity and free radicals. Accumulation of LDs in the CNS appears predominantly in neuroglia (astrocytes, microglia, oligodendrocytes, ependymal cells), which provide trophic, metabolic, and immune support to neuronal networks. Here we review the most recent findings on the characteristics and functions of LDs in neuroglia, focusing on astrocytes, the key homeostasis-providing cells in the CNS. We discuss the molecular mechanisms affecting LD turnover in neuroglia under stress and how this may protect neural cell function. We also highlight the role (and potential contribution) of neuroglial LDs in aging and in neurologic disorders.

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PxdA interacts with the DipA phosphatase to regulate endosomal hitchhiking of peroxisomes

Molecular Biology of the Cell ◽

10.1091/mbc.e20-08-0559 ◽

2021 ◽

pp. mbc.E20-08-0559

Author(s):

John Salogiannis ◽

Jenna R. Christensen ◽

Livia D. Songster ◽

Adriana Aguilar-Maldonado ◽

Nandini Shukla ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Lipid Droplets ◽

Molecular Mechanisms ◽

Ustilago Maydis ◽

Adaptor Proteins ◽

Early Endosome ◽

Alternative Mode ◽

Ribonucleoprotein Complexes ◽

Early Endosomes ◽

Mode Of Transport

In canonical microtubule-based transport, adaptor proteins link cargos to dynein and kinesin motors. Recently, an alternative mode of transport known as ‘hitchhiking’ was discovered, where cargos achieve motility by hitching a ride on already-motile cargos, rather than attaching to a motor protein. Hitchhiking has been best-studied in two filamentous fungi, Aspergillus nidulans and Ustilago maydis. In U. maydis, ribonucleoprotein complexes, peroxisomes, lipid droplets, and endoplasmic reticulum hitchhike on early endosomes. In A. nidulans, peroxisomes hitchhike using a putative molecular linker, PxdA, which associates with early endosomes. However, whether other organelles use PxdA to hitchhike on early endosomes is unclear, as are the molecular mechanisms that regulate hitchhiking. Here we find that the proper distribution of lipid droplets, mitochondria and pre-autophagosomes do not require PxdA, suggesting that PxdA is a peroxisome-specific molecular linker. We identify two new pxdA alleles, including a point mutation (R2044P) that disrupts PxdA's ability to associate with early endosomes and reduces peroxisome movement. We also identify a novel regulator of peroxisome hitchhiking, the phosphatase DipA. DipA co-localizes with early endosomes and its early endosome-association relies on PxdA. Together, our data suggest that PxdA and the DipA phosphatase are specific regulators of peroxisome hitchhiking on early endosomes. [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text]

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Loss of CIB2 causes non-canonical autophagy deficits and visual impairment

10.1101/2020.09.18.302174 ◽

2020 ◽

Author(s):

Saumil Sethna ◽

Patrick A. Scott ◽

Arnaud P.J. Giese ◽

Todd Duncan ◽

T. Michael Redmond ◽

...

Keyword(s):

Retinal Pigment Epithelium ◽

Lipid Droplets ◽

Molecular Mechanisms ◽

Pigment Epithelium ◽

Retinal Pigment ◽

Photoreceptor Outer Segments ◽

Impaired Ability ◽

Age Related ◽

Retinal Pathology ◽

Marked Accumulation

SUMMARYNon-canonical autophagy or LC3-associated phagocytosis (LAP) is essential for the maintenance and functioning of the retinal pigment epithelium (RPE) and photoreceptors. Although molecular mechanisms still remain elusive, deficits in LAP have been found to be associated with age-related retinal pathology in both mice and humans. In this study, we found that calcium and integrin-binding protein 2 (CIB2) regulates LAP in the RPE. Mice lacking CIB2, both globally and specifically within RPE, have an impaired ability to process the engulfed photoreceptor outer segments due to reduced lysosomal capacity, which leads to marked accumulation of improperly digested remnants, lipid droplets, fused phago-melanosomes in RPE, and impaired visual function. In aged mice, we also found marked accumulation of drusen markers APOE, C3, and Aβ, along with esterified cholesterol. Intriguingly, we were able to transiently rescue the photoreceptor function in Cib2 mutant mice by exogenous retinoid delivery. Our study links LAP and phagocytic clearance with CIB2, and their relevance to the sense of sight.

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Yeast Cells Exposed to Exogenous Palmitoleic Acid Either Adapt to Stress and Survive or Commit to Regulated Liponecrosis and Die

Oxidative Medicine and Cellular Longevity ◽

10.1155/2018/3074769 ◽

2018 ◽

Vol 2018 ◽

pp. 1-11 ◽

Cited By ~ 4

Author(s):

Karamat Mohammad ◽

Paméla Dakik ◽

Younes Medkour ◽

Mélissa McAuley ◽

Darya Mitrofanova ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Cell Death ◽

Lipid Metabolism ◽

Lipid Droplets ◽

Palmitoleic Acid ◽

Molecular Mechanisms ◽

Neutral Lipids ◽

Yeast Cells ◽

Cellular Processes ◽

Regulated Cell Death

A disturbed homeostasis of cellular lipids and the resulting lipotoxicity are considered to be key contributors to many human pathologies, including obesity, metabolic syndrome, type 2 diabetes, cardiovascular diseases, and cancer. The yeast Saccharomyces cerevisiae has been successfully used for uncovering molecular mechanisms through which impaired lipid metabolism causes lipotoxicity and elicits different forms of regulated cell death. Here, we discuss mechanisms of the “liponecrotic” mode of regulated cell death in S. cerevisiae. This mode of regulated cell death can be initiated in response to a brief treatment of yeast with exogenous palmitoleic acid. Such treatment prompts the incorporation of exogenously added palmitoleic acid into phospholipids and neutral lipids. This orchestrates a global remodeling of lipid metabolism and transfer in the endoplasmic reticulum, mitochondria, lipid droplets, and the plasma membrane. Certain features of such remodeling play essential roles either in committing yeast to liponecrosis or in executing this mode of regulated cell death. We also outline four processes through which yeast cells actively resist liponecrosis by adapting to the cellular stress imposed by palmitoleic acid and maintaining viability. These prosurvival cellular processes are confined in the endoplasmic reticulum, lipid droplets, peroxisomes, autophagosomes, vacuoles, and the cytosol.

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A novel function of lipid droplets in regulating longevity

Biochemical Society Transactions ◽

10.1042/bst0371050 ◽

2009 ◽

Vol 37 (5) ◽

pp. 1050-1055 ◽

Cited By ~ 38

Author(s):

Alexander A. Goldberg ◽

Simon D. Bourque ◽

Pavlo Kyryakov ◽

Tatiana Boukh-Viner ◽

Christopher Gregg ◽

...

Keyword(s):

Lipid Droplets ◽

Aging Process ◽

Essential Role ◽

Molecular Mechanisms ◽

Neutral Lipids ◽

Intracellular Signalling ◽

Eukaryotic Cells ◽

Eukaryotic Organisms

Growing evidence supports the view that LDs (lipid droplets) are dynamic organelles that can serve both as an intracellular signalling compartment and as an organizing platform orchestrating many vital processes in eukaryotic cells. It has become clear that the LDs-confined deposition and lipolytic degradation of neutral lipids define longevity in multicellular eukaryotic organisms and yeast. We summarize the evidence in support of the essential role that LDs play in longevity regulation and propose several molecular mechanisms by which these dynamic organellar compartments control the aging process in multicellular eukaryotes and yeast.

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The FATP1–DGAT2 complex facilitates lipid droplet expansion at the ER–lipid droplet interface

The Journal of Cell Biology ◽

10.1083/jcb.201201139 ◽

2012 ◽

Vol 198 (5) ◽

pp. 895-911 ◽

Cited By ~ 151

Author(s):

Ningyi Xu ◽

Shaobing O. Zhang ◽

Ronald A. Cole ◽

Sean A. McKinney ◽

Fengli Guo ◽

...

Keyword(s):

Electron Microscopy ◽

Endoplasmic Reticulum ◽

Lipid Droplet ◽

Mammalian Cells ◽

Lipid Droplets ◽

Molecular Mechanisms ◽

Diacylglycerol Acyltransferase ◽

Present Evidence ◽

Evolutionarily Conserved ◽

Subcellular Level

At the subcellular level, fat storage is confined to the evolutionarily conserved compartments termed lipid droplets (LDs), which are closely associated with the endoplasmic reticulum (ER). However, the molecular mechanisms that enable ER–LD interaction and facilitate neutral lipid loading into LDs are poorly understood. In this paper, we present evidence that FATP1/acyl-CoA synthetase and DGAT2/diacylglycerol acyltransferase are components of a triglyceride synthesis complex that facilitates LD expansion. A loss of FATP1 or DGAT2 function blocked LD expansion in Caenorhabditis elegans. FATP1 preferentially associated with DGAT2, and they acted synergistically to promote LD expansion in mammalian cells. Live imaging indicated that FATP1 and DGAT2 are ER and LD resident proteins, respectively, and electron microscopy revealed FATP1 and DGAT2 foci close to the LD surface. Furthermore, DGAT2 that was retained in the ER failed to support LD expansion. We propose that the evolutionarily conserved FATP1–DGAT2 complex acts at the ER–LD interface and couples the synthesis and deposition of triglycerides into LDs both physically and functionally.

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Komagataella phaffii Cue5 Piggybacks on Lipid Droplets for Its Vacuolar Degradation During Stationary Phase Lipophagy

10.20944/preprints202112.0271.v1 ◽

2021 ◽

Author(s):

Ravinder Kumar ◽

Ankit Shroff ◽

Taras Y. Nazarko

Keyword(s):

Lipid Droplets ◽

Molecular Mechanisms ◽

S Phase ◽

Ubiquitinated Protein ◽

Selective Autophagy ◽

Komagataella Phaffii ◽

Ubiquitin Binding ◽

N Starvation ◽

Relationship Of ◽

The Relationship

Recently, we developed Komagataella phaffii (formerly Pichia pastoris) as a model for lipophagy, the selective autophagy of lipid droplets (LDs). We found that lipophagy pathways induced by acute nitrogen (N) starvation and in stationary (S) phase have different molecular mechanisms. Moreover, both types of lipophagy are independent of Atg11, the scaffold protein that interacts with most autophagic receptors and, therefore, is essential for most types of selective autophagy in yeast. Since yeast aggrephagy, the selective autophagy of ubiquitinated protein aggregates, is also independent of Atg11 and utilizes the ubiquitin-binding receptor, Cue5, we studied the relationship of K. phaffii Cue5 with differentially induced LDs and lipophagy. While there was no relationship of Cue5 with LDs and lipophagy under N-starvation conditions, Cue5 accumulated on LDs in S-phase and degraded together with LDs via S-phase lipophagy. The accumulation of Cue5 on LDs and its degradation by S-phase lipophagy strongly depended on the ubiquitin-binding CUE domain and Prl1, the positive regulator of lipophagy 1. However, unlike Prl1, which is required for S-phase lipophagy, Cue5 was dispensable for it suggesting that Cue5 is rather a new substrate of this pathway. We propose that a similar mechanism (Prl1-dependent accumulation on LDs) might be employed by Prl1 to recruit another ubiquitin-binding protein that is essential for S-phase lipophagy.

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Lipid Droplets and Ferritin Heavy Chain: a Devilish Liaison in Cancer Radioresistance

10.1101/2021.05.11.443559 ◽

2021 ◽

Author(s):

Luca Tirinato ◽

Maria Grazia Marafioti ◽

Francesca Pagliari ◽

Jeanette Jansen ◽

Ilenia Aversa ◽

...

Keyword(s):

Lung Cancer ◽

Cancer Cells ◽

Heavy Chain ◽

Lipid Droplets ◽

Molecular Mechanisms ◽

X Ray ◽

Ferritin Heavy Chain ◽

Clonogenic Potential ◽

Radiation Treatments ◽

Made In

Although much progress has been made in cancer treatment, the molecular mechanisms underlying cancer radioresistance (RR) as well as the biological characteristic of radioresistant cancer cells still need to be clarified. In this regard, we discovered that breast, bladder, lung, neuroglioma and prostate 6 Gy X-ray resistant cells were characterized by an increase of Lipid Droplet (LD) number and that the cells containing highest LDs showed the highest clonogenic potential after irradiation. Moreover, we observed that LD content was tightly connected with the iron metabolism and in particular with the presence of the ferritin heavy chain (FTH1). In fact, breast and lung cancer cells silenced for the FTH1 gene showed a reduction in the LD numbers and, by consequence, became radiosensitive. FTH1 restoration as well as iron-chelating treatment by Deferoxamine were able to restore the LD amount and RR. Overall, these results provide evidence of a novel molecular mechanism behind RR in which LDs and FTH1 are tightly connected to each other, a synergistic effect which might be worth deeply investigating in order to make cancer cells more radiosensitive and improve the efficacy of radiation treatments.

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Hypertrophied human adipocyte spheroids as in vitro model of weight gain and adipose tissue dysfunction

10.1101/2021.01.06.425629 ◽

2021 ◽

Author(s):

Anna Ioannidou ◽

Shemim Alatar ◽

Matilda Ahlander ◽

Amanda Hornell ◽

Rachel M Fisher ◽

...

Keyword(s):

Weight Gain ◽

Lipid Droplets ◽

Molecular Mechanisms ◽

Metabolic Dysfunction ◽

Obesity Prevalence ◽

Human Adipocytes ◽

Human Adipocyte ◽

Vitro Model

The rise in obesity prevalence has created an urgent need for new and improved methods to study human adipocytes and the pathogenic effects of weight gain in vitro. Despite numerous studies showing the advantages of culturing adipocyte progenitors as 3D structures, the majority continue using traditional 2D cultures which result in small, multilocular adipocytes with poor representability. We hypothesized that providing differentiating pre-adipocytes with a vascular growth niche would mimic in vivo adipogenesis and improve the differentiation process. Here we present a simple, easily applicable culture protocol that allows for the differentiation and culturing of human adipocytes with a more unilocular morphology and larger lipid droplets than previous protocols. We moreover offer a protocol for inducing adipocyte enlargement in vitro, resulting in larger lipid droplets and the development of several key features of adipocyte dysfunction, including altered adipokine secretions and impaired lipolysis. Taken together, our hypertrophied human adipocyte spheroids offer an improved culture system for studying the cellular and molecular mechanisms causing metabolic dysfunction and inflammation during weight gain.

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