The CYP71 clan comprises the majority of Arabidopsis thaliana P450s. The functional role of the great majority of CYP71 clan enzymes remains unknown hitherto. Some Arabidopsis CYP71B subfamily proteins, such as AtCYP71B23, exhibit primary structural similarities to CYP74 enzymes and prostacyclin synthase (CYP8A1). Particularly, AtCYP71B23 and some related CYP71B proteins, along with the CYP74s and CYP8A1, exhibit a critical substitution of the D/E residue, which is conserved in monooxygenases, in the centre of the I-helix groove motif, with an asparagine (N) residue. This substitution may result in a nonclassical behaviour of these P450s. These observations prompted us to prepare the recombinant AtCYP71B23 and examine its behaviour towards the fatty acid hydroperoxides. AtCYP71B23 was active towards the linoleic acid 9(S)-hydroperoxides of linoleic (9-HPOD) and α-linolenic (9-HPOT) acids, as well as the 13(S)-hydroperoxide of linoleic acid (13-HPOD). α-Linolenic acid 13(S)-hydroperoxide was an inefficient substrate. Major products were the divinyl ethers (1'Z)-colneleic (9-HPOD), (1'Z)-colnelenic (9-HPOT), and (11Z)-etheroleic (13-HPOD) acids. Thus, AtCYP71B23 is an unprecedented CYP71 clan enzyme of fatty acid hydroperoxide metabolism and behaves primarily as a divinyl ether synthase.

Bile Salt Export Pump (BSEP) deficiency is a rare genetic cholestatic liver disease, often necessitating liver transplantation. The p.E297G missense mutation is associated with residual BSEP function in vitro and delayed need for transplantation in patients. We aimed to generate a p.E297G BSEP knock-in (BSEP) mouse model to evaluate interventions to improve residual BSEP function.

Excessive lipid accumulation within the liver is a main factor inducing non-alcoholic fatty liver diseases (NAFLD). Chitosan coated selenium nanoparticles (CS-SeNPs), a new kind of selenium supplement. In vitro study, CS-SeNPs remarkably decreased FFA-induced lipid accumulation. CS-SeNPs could reverse the inhibition effects of FFA on the autophagy process. Inhibition of autophagy increased lipid accumulation and TC and TG levels, and decreased the expression levels of fat metabolism-related genes. In vivo analysis, CS-SeNPs administration apparently improved the pathological changes in NAFLD, including body weight, liver function, serum lipids, and liver histopathological changes. Additionally, autophagy levels in the liver were also increased, oxidative stress and inflammation were reduced after CS-SeNPs treatment. In summary, CS-SeNPs showed protective effects on NAFLD both in vivo and in vitro, likely through a mechanism involving promotion of lipid degradation and reduction of fat accumulation in hepatocytes by inducing lipid autophagy.

Palmitoyl-protein thioesterase 1 (PPT1), a key depalmitoylating enzyme, modulates substrate protein function and lipid metabolism through enzymatic thioester bond hydrolysis of the palmitoyl-thioester bond. While PPT1 may regulate lipid metabolism through dynamic palmitoylation, its fundamental regulatory pathways require further elucidation. In this study, PPT1 was homologously overexpressed in Mucor circinelloides to investigate the mechanism of PPT1-mediated lipid metabolism. The results showed that the cell dry weight (CDW) did not differ significantly between the strains. However, the total fatty acids (TFA) content, expressed as a percentage of CDW, was significantly higher in the recombinant strain (34.7 % of CDW) than in the control strain (25.9 % of CDW), representing a 34.0 % increase. Concurrently, the proportion of C16:0 in TFA increased significantly by 32.1 %. To determine the effects of PPT1 overexpression on lipid accumulation in M. circinelloides, the lipid composition was analyzed by using thin-layer chromatography coupled with gas chromatography. The results revealed that the content of free fatty acids (FFA) exhibited a significant increase of 128.2 %, with the percentages of C16:0 and C18:0 in FFA increasing by 64.7 % and 24.8 %, respectively. The analysis of the mRNA level of key genes involved in lipid synthesis indicated that PPT1 overexpression enhances the flux of acyl-CoA towards FFA. This study reveals the mechanism by which PPT1 regulates lipid synthesis in oleaginous fungi through depalmitoylation, providing novel insights for engineering lipid metabolism.

Fibroblast growth factor 19 (FGF19) is a key intestinally secreted factor in mammals, its physiological role in teleost remains largely unclear. This study aimed to investigate the function and underlying mechanisms of FGF19 in the regulation of lipid metabolism in large yellow croaker. Results revealed that FGF19 was predominantly expressed in the liver. Treatment with recombinant FGF19 protein significantly reduced triglyceride (TG) levels in hepatocytes in a dose-dependent manner. Both in vitro treatment and in vivo injection of FGF19 significantly downregulated lipogenic genes and upregulated lipolytic genes expression in hepatocytes and liver tissue. Further investigation demonstrated that FGFR1 inhibition attenuated the TG-lowering effects of FGF19 and reversed the suppression of lipogenic gene expression. Additionally, FGF19 treatment enhanced the phosphorylation of ERK, P38, AMPK, and AKT. Inhibition of P38, AMPK, or AKT significantly increased triglyceride levels which were reduced by FGF19. Inhibition of ERK, P38, and AKT impaired the FGF19-mediated regulation of lipolysis-related genes, whereas AMPK inhibition predominantly affected the regulation of lipogenic genes. Moreover, results showed that high linoleic acid (LA) intake induced endoplasmic reticulum stress and elevated expression of FGF19. The expression of XBP1s protein was significantly increased by LA treatment, while co-expression of XBP1s significantly induced the promoter activity of FGF19. In summary, these results suggest that FGF19 is primarily expressed in the liver and plays a crucial role in regulating lipid metabolism to prevent excessive lipid accumulation in large yellow croaker, while high LA intake can increase FGF19 expression through ER stress-induced XBP1s. This study will enhance the understanding of FGF19 in lipid metabolism, offering insights into the evolution of these processes in vertebrates.

α/β-hydrolase domain-containing-6 (ABHD6) hydrolyzes various lipids, including monoacylglycerols (MAGs). Pharmacological inhibition of ABHD6 with WWL70 is anti-inflammatory in animal models. However, because of the multiple substrates of ABHD6 and the off-target effects of WWL70, the precise role of ABHD6 in inflammation remains to be clarified. Here, we investigated the role of ABHD6 in lipopolysaccharide (LPS)-mediated inflammatory response, employing a more specific ABHD6 inhibitor, KT203, and ABHD6-KO mice. ABHD6-KO mice showed lower susceptibility to LPS-mediated systemic endotoxemia. Inhibition by KT203 or deletion of ABHD6 in LPS-stressed macrophages reduced the pro-inflammatory and elevated the anti-inflammatory markers. In RAW 264.7 macrophages, KT203 reduced LPS-induced morphological changes, migration and cytokine release. In vivo, KT203 treatment of LPS-exposed wild-type mice markedly curtailed circulating TNF-α levels. Analysis of cellular and secreted bioactive lipids in the LPS-treated RAW 264.7 macrophages revealed that KT203 markedly elevated the levels of various lipid species, in particular secreted docosahexaenoic acid (DHA)-derived MAG (1/2-docosahexaenoylglycerol (DHG)) and DHA-containing N-acylethanolamines and oxylipins. We further observed that 1-DHG, 2-arachidonoylglycerol, docosahexaenoylethanolamide and 17-hydroxydocosahexaenoic acid showed anti-inflammatory effects and PPARα agonism in LPS-treated RAW 264.7 macrophages. The data suggest that ABHD6 suppression results in the accumulation of various bioactive lipids, in particular DHA-containing MAG, N-acylethanolamines and oxylipins, which activate PPARα signaling pathway to curtail the inflammatory response of macrophages to LPS. Overall, the findings provide evidence for a mechanism involving MAG and possibly other lipid species/PPARα signaling, for the anti-inflammatory effects of ABHD6 suppression during endotoxemia. Thus, the inhibition of ABHD6 is a promising approach to mitigate inflammation.

Sphinganine (SA), a fundamental sphingolipid whose cytotoxicity remains incompletely characterized, has received less attention compared to other sphingoid bases. Here, we demonstrate that SA predominantly triggers cell death via lysosomal membrane permeabilization (LMP) resulting from pH dysregulation and osmotic imbalance, rather than through direct ROS-mediated mechanisms, although mitochondrial ROS contribute to oxidative stress. SA-induced mitochondrial fragmentation significantly increased hydrogen peroxide levels in both the mitochondrial matrix and intermembrane space (IMS). Strikingly, lysosomes exhibited spatial colocalization with elevated hydrogen peroxide microdomains under SA exposure, suggesting a redox-dependent mechanism governing organelle repositioning. The cysteine protease inhibitor E64D attenuated SA-induced apoptosis through suppressing cathepsin B/L release, confirming lysosomal membrane permeabilization as an executor of apoptotic signaling. These findings unveil SA's dual-targeting organelle toxicity mechanism. Our study not only elucidates key aspects of sphingolipid-mediated cytotoxicity but also provides therapeutic rationale for counteracting fumonisin B1 (FB1)-induced pathologies and related sphingolipid disorders, potentially through lysosomal stabilization or targeted ROS modulation.

Oxidized low-density lipoprotein (ox-LDL) has been shown to induce significant lipid accumulation and disrupt cholesterol homeostasis in vascular smooth muscle cells (VSMCs), which may contribute to the development of atherosclerosis (AS). In this study, we investigated the effects of ox-LDL on lipid accumulation, and the expression of key proteins involved in cholesterol transport, such as ATP-binding cassette transporter A family member 1 (ABCA1). Our results demonstrated that ox-LDL treatment led to a concentration-dependent increase in intracellular lipid content, as evidenced by Oil Red O and BODIPY staining. Additionally, ox-LDL elevated intracellular calcium (Ca) levels and activated the Ca-Calpain signaling pathway, which in turn suppressed the expression of ABCA1, a critical protein responsible for cholesterol efflux. We further explored the therapeutic potential of melatonin (MLT) in mitigating the harmful effects of ox-LDL. Treatment with MLT significantly improved cell viability and reduced lipid accumulation in VSMC. Moreover, MLT, along with specific inhibitors of the TRPV1-Ca-Calpain pathway (Capsazepine, EGTA, and Calpeptin), successfully lowered intracellular Ca levels and calpain activity, while restoring ABCA1 expression at protein levels but not mRNA. These findings suggest that MLT exerts a protective effect by inhibiting the TRPV1-Ca-Calpain signaling pathway, thereby promoting cholesterol efflux and reducing lipid accumulation in VSMCs. To validate these findings in vivo, ApoE mice were fed a high-fat diet (HFD) for 12 weeks to induce atherosclerotic lesions, with MLT administered via intraperitoneal injection during the final 6 weeks. Histological analyses of the aortic root revealed that MLT treatment significantly reduced atherosclerotic plaque areas compared to untreated HFD-fed mice. Furthermore, Western blot analyses demonstrated that MLT increased ABCA1 expression and decreased TRPV1 expression in aortic tissues, aligning with our in vitro observations. In conclusion, our study highlights the role of the TRPV1-Ca-Calpain signaling pathway in ox-LDL-induced lipid dysregulation and identifies MLT as a potential therapeutic agent for reversing these effects, offering new insights into the molecular mechanisms underlying lipid accumulation in VSMCs.

Defects in Adipose tissue TriGlyceride Lipase (ATGL)-mediated myocellular lipid droplet (LD) lipolysis results in mitochondrial dysfunction of unknown origin, which can be rescued by PPAR agonists. Here we examine if ATGL-mediated lipolysis is required to maintain mitochondrial network connectivity and function. Moreover, we explored if the functional implications of ATGL deficiency for mitochondrial network dynamics and function can be alleviated by promoting PPARα and/or PPARδ transcriptional activity. To this end, we cultured human primary myotubes from patients with neutral lipid storage disease with myopathy (NLSDM), a rare metabolic disorder caused by a mutation in the gene encoding for ATGL. These myotubes possess dysfunctional ATGL and compromised LD lipolysis. In addition, mitochondria-LD contact, mitochondrial network connectivity, and mitochondrial membrane potential were affected. Using a humanized ATGL inhibitor in myotubes (cultured form healthy donors) revealed similar results. Upon stimulating PPARδ transcriptional activity, mitochondrial respiration improved by more than 50 % in human primary myotubes from healthy lean individuals. This increase in respiration was dampened in myotubes with dysfunctional ATGL. Stimulation of PPARδ transcriptional activity had no effect on mitochondria-LD contacts, mitochondrial network connectivity, and mitochondrial membrane potential. Our results demonstrate that dysfunctional ATGL results in compromised mitochondrial-LD contacts and mitochondrial network connectivity, and that functional ATGL is required to improve mitochondrial respiratory capacity upon stimulation of PPARδ transcriptional activity.

In mammals, plasmalogens are enriched in the brain, kidney, and heart, while the lowest amounts of plasmalogens are found in the liver. The physiological significance of the low level of plasmalogens in the liver remains unknown. Here, we used alkylglycerol, a precursor that is readily converted to plasmalogen upon exogenous administration, to study the effects of elevated liver plasmalogens on fatty acyl-CoA reductase (FAR1), a rate-limiting enzyme in plasmalogen biosynthesis. Indeed, oral administration of alkylglycerol in wild-type mice augmented plasmalogen levels in the liver and resulted in reduced FAR1 protein levels. Vice versa, we determined increased FAR1 levels in mice with diminished plasmalogen levels due to a genetic defect in plasmalogen biosynthesis. Together, these findings suggest a role of FAR1-mediated regulation of plasmalogen biosynthesis in liver physiology. Further experiments indicated that elevation of plasmalogens in the liver of wild-type mice reduces the protein level of squalene epoxidase, and further suppresses a liver X receptor-mediated transcription of genes encoding ATP-binding cassette transporters such as Abca1, Abcg5, and Abcg8. In the livers of plasmalogen-deficient mice, the expression of Abca1 appears to be reduced due to the suppressed function of the nuclear receptor protein hepatocyte nuclear factor 4. These aberrant expression of transporters causes reduced levels of high-density lipoprotein cholesterol in plasma derived from wild-type mice administered alkylglycerol and plasmalogen synthesis-deficient mice. Taken together, the present results suggest that the homeostasis of plasmalogens, mediated by the regulation of FAR1 protein levels in the liver, plays a physiologically important role in the synthesis of high-density lipoprotein.

Intrahepatic cholestasis of pregnancy (ICP) is associated with adverse fetal outcomes, while current biomarkers such as total bile acid remain suboptimal. This study aimed to identify novel biomarkers and clarify metabolic pathways underlying ICP through integrated metabolomic and proteomic analyses. Placental profiles were obtained from ICP model rats and healthy controls, with differential metabolites and proteins validated in human placental and serum samples. Multiomics integration revealed prominent dysregulation of lipid metabolism, particularly fatty acid degradation and biosynthesis, highlighting lipids as central players in ICP. Palmitic acid and acyl-CoA synthetase long chain family member 1 (ACSL1) were central to these pathways, markedly elevated in ICP, and showed high diagnostic value (area under the curve 0.794 and 0.825), with combined detection reaching 0.894. Both markers also stratified patients by disease severity, suggesting their potential use for disease monitoring and risk classification. Moreover, ferroptosis was implicated in ICP pathophysiology, supported by validations in both patient placental tissues and taurocholic acid (TCA)-treated trophoblast cells, showing reduced glutathione peroxidase 4 (GPX4) and solute carrier family 7 member 11 (SLC7A11) together with increased six-transmembrane epithelial antigen of prostate 3 (STEAP3), transferrin receptor protein 1 (CD71), and acyl-CoA synthetase long-chain family member 4 (ACSL4). In summary, palmitic acid and ACSL1 represent promising biomarkers for ICP diagnosis and classification, while ferroptosis contributes to ICP-related placental dysfunction. These findings provide comprehensive evidence linking altered lipid metabolism and ferroptosis to ICP, offering new insights for clinical diagnosis and potential therapeutic strategies.

This review provides an integrated overview of the current understanding of class II PI3Ks, with particular attention to their structural and enzymatic properties, lipid substrate specificity, and emerging roles in membrane trafficking, cellular signaling, and disease. Class II phosphoinositide 3-kinases (PI3Ks) are lipid kinases that regulate membrane identity and intracellular signaling by generating phosphatidylinositol 3-phosphate [PI(3)P] and phosphatidylinositol (3,4)-bisphosphate [PI(3,4)P] at distinct subcellular compartments. Advances over the past decade have clarified the structural organization, regulatory principles, and lipid output of all the three mammalian isoforms (PI3K-C2α, PI3K-C2β, and PI3K-C2γ). These studies have revealed that class II PI3K function is highly context-dependent, governed by compartment-specific cues and the spatial restriction of lipid products. Dysregulation of class II PI3Ks has been implicated in diverse pathological conditions, including cancer, metabolic disorders, epilepsy, congenital myopathies, vascular dysfunction, and premature aging. These findings establish a framework for understanding how localized phosphoinositide synthesis contributes to cellular homeostasis and disease, and underscore the therapeutic potential of selectively targeting class II PI3K isoforms.

Phosphoinositides are regulators of key cell biological processes such as plasma membrane function, vesicular transport, cytoskeletal and nuclear organization. In turn, their levels are tightly controlled by the function of lipid kinases and phosphatases that modify specific hydroxyl groups on the inositol ring. Phosphatidylinositol 5 phosphate 4-kinase (PIP4K) is one such lipid kinase. Although initially discovered as an enzyme that phosphorylates the 4th hydroxyl on the inositol ring of phosphatidylinositol 5 phosphate (PI5P) with exquisite specificity, it has recently emerged that PIP4K may also work on other substrates. Interestingly, recent studies have also proposed functions for this enzyme that do not require its catalytic activity. Although most elements of phosphoinositide signalling are conserved across all eukaryota, a limited number of phosphoinositide kinases and phosphatases including PIP4K seem to be a unique feature of the genomes of organisms that exist in a multicellular state but not unicellular eukaryotes. Genetic studies in model organisms implicate PIP4K function in key processes such as hormone regulated metabolic control as well as cell division and growth. Consequently, PIP4K function has important biomedical implications in the context of cancer, metabolic syndrome and autoimmune disorders. In this review, we analyze emerging findings on PIP4K function and reflect on the biochemical raison d'être of how this protein regulates cell physiology in metazoans.

Rheumatoid arthritis (RA) is associated with increased cardiovascular disease (CVD) risk, partly attributed to altered lipid metabolism. Apolipoprotein C-III (ApoC-III), a key regulator of triglyceride-rich lipoproteins in the plasma, has been implicated in both dyslipidemia and inflammation. In this study, we investigated the role of hypertriglyceridemia in RA using a transgenic mouse model overexpressing the human ApoC-III gene (ApoC-III Tg). Using a protocol of antigen-induced arthritis (AIA), we show that ApoC-III Tg mice exhibited significantly greater joint swelling, inflammatory infiltration and cartilage destruction compared to non-transgenic controls. These changes were accompanied by altered lipoprotein distribution in serum and High Density Lipoprotein (HDL) dysfunction including reduced antioxidant function. Furthermore, HDL isolated from arthritic ApoC-III Tg mice had pro-inflammatory properties on macrophages as demonstrated by the increased expression of iNOS and IL1β as well as increased mitochondrial respiration. Treatment of arthritic ApoC-III Tg mice with fenofibrate, a triglyceride-lowering drug, reduced triglyceride levels and increased ApoA-I content in HDL fractions. Importantly, fenofibrate significantly ameliorated arthritis severity, restored HDL antioxidant function and reduced macrophage activation. These findings highlight a mechanistic link between dyslipidemia, HDL dysfunction, and inflammatory exacerbation in RA and suggest that targeting ApoC-III-associated pathways may offer therapeutic benefit in patients with coexisting metabolic and inflammatory disorders.

Barth Syndrome (BTHS) is an ultra-rare, X-linked mitochondrial disorder caused by a variety of different mutations in the cardiolipin remodeling gene TAFAZZIN that results in cardiac and skeletal myopathy, as well as immunological deficits. Epstein-Barr virus-mediated transformation of B-lymphocytes has been used to generate B-lymphoblastoid cells that retain many of the characteristics of the initial cell line, but can be propagated extensively in culture to generate biological materials enabling study of the basic, natural function of this enzyme in cells, as well as disease-relevant effects and interventions. Notably, these model lines from individual donors are of particular value for understanding a disease with variable penetrance such as BTHS, where variation in genetic background can alter symptom severity considerably, even among closely-related individuals with the same mutation. Here, we review the generation, benefits, and limitations of the B-lymphoblastoid cell model in BTHS research, and provide an overview of recent advances in understanding the role of TAFAZZIN in mitochondrial biology from this model. Implications of these findings for understanding the pathology of BTHS, and determining future directions, are also provided, along with a review of recent advances in our understanding of the mechanism of TAFAZZIN function in cardiolipin degradation, remodeling and stability.

Phosphoinositides (PIs) have been at the center of cell signaling and membrane biology since Michell's proposal of the PI-cycle in 1975. Over the past fifty years, these quantitatively minor lipids have emerged as versatile molecular organizers, defining membrane identity, generating spatial cues, coordinating cytoskeletal dynamics and thus playing pivotal role in polarity. Studies in yeast, amoebae, and neutrophils demonstrated how localized PI pools regulate polarity and chemotaxis, providing a conceptual advance to tissue-level organization. In epithelia, PIs now stand as central determinants of apico-basal polarity and lumen morphogenesis through their cooperation with Rho GTPases, polarity complexes, and septins. This review highlights how these lipids shape our understanding of membrane dynamics and epithelial tissue organization. To conclude, this review underscores how alterations in the activities of these polarity regulators lead to abnormal epithelial morphogenesis and severe diseases such as cancer.

Phosphoinositides (PPIn) are low-abundance phospholipids that define membrane identity and direct compartment-specific signaling across eukaryotic cells. Marking fifty years since Michell's seminal 1975 review, we re-evaluate how the subcellular localization of these lipids informs their function. Using a historical and mechanistic framework, we survey evidence for the steady-state distribution of all eight PPIn species and their key precursor, phosphatidic acid, emphasizing live-cell biosensor studies and kinase localization. We conclude that PI(4,5)P₂ and PIP₃ signaling remain largely confined to the plasma membrane, whereas PI4P and PI3P occupy distinct but complementary domains of the Golgi and endosomal systems, and PI(3,5)P₂ marks specialized late endosomal compartments. Together, these patterns reveal PPIn as spatial rather than purely temporal signaling molecules-an ATP-derived currency maintaining the ordered heterogeneity of eukaryotic membranes. Understanding how these pathways self-regulate will define the next generation of phosphoinositide biology.

Synaptojanin 1 (Synj1) is a protein highly enriched in the nervous system which comprises tandemly arranged inositol 4-phosphatase and 5-phosphatase domains. Since its discovery as a synaptically enriched binding partner of SH3 domain containing proteins, Synj1 has been shown to be a key player in synaptic vesicle recycling via its property to couple the endocytic reaction to dephosphorylation of PI(4,5)P, a determinant of plasma membrane identity. Beyond its well established role in synaptic vesicle traffic, Synj1 has housekeeping roles at the interface of endocytosis, receptor signaling and regulation of actin nucleation. It is essential for postnatal life, while partial loss-of-function mutations are responsible for early-onset Parkinsonism and epilepsy. Conversely Synj1 overexpression, such as due to gene duplication in Down syndrome, may also have a pathogenic role. Here I review current knowledge about Synj1's molecular and physiological functions and the role of its dysfunction in disease.

Phospholipids play crucial roles in autophagy; however, the underlying mechanisms remain elusive. We previously found that the phosphatidylserine (PtdSer) transporter Osh5 is critical for autophagosome formation. Therefore, in this study, we aimed to investigate the impact of the knockout of cho1, which encodes PtdSer synthase, on autophagy. Green fluorescent protein-autophagy-related gene 8 (GFP-Atg8) processing assay revealed a significant defect in the macroautophagic activity of the cho1∆ mutant, regardless of the presence or absence of ethanolamine (Etn). Notably, autophagosomes were absent in the cytosol, and macroautophagic bodies were not observed in the vacuoles of the starved cho1∆ mutant, underscoring the essential role of PtdSer synthesized using Cho1 in autophagosome biogenesis. In contrast, numerous microautophagic vesicles containing lipid droplets were observed in the vacuoles of cho1∆ mutants starved in the presence of Etn, suggesting the crucial role of phosphatidylethanolamine (PtdEtn) synthesized via the Kennedy pathway in microautophagic lipophagy when PtdSer synthesis using Cho1 is disrupted. Given recent evidence pointing to the involvement of the ubiquitination system in various autophagy-related processes, we also examined the role of ubiquitin-conjugating enzyme E2 gene ubc4. In addition, deletion of ubc4 gene led to a pronounced reduction in microautophagic lipophagy in starved cho1∆ cells, but not in wild-type cells. Together, these observations highlight an essential role for Ubc4-mediated ubiquitination in driving vacuolar microautophagic lipophagy specifically under Cho1-deficient conditions.