Explore the vast range of titles available.

Summary Variation in thermal tolerance among ectotherms has often been associated with a set of structural modifications in their cell membrane that modify the membrane's physical properties to secure appropriate fluidity at different temperatures. These adaptive mechanisms have been found in some insects, including some Drosophila species, but adaptation in phospholipid fatty acid (PLFA) composition has never been examined comprehensively in a large multispecies approach that includes appropriate phylogenetic analysis. Drosophila species are found in tropical, subtropical and temperate environments and display considerable interspecific variation in thermal tolerance. Here, we measured the PLFA composition of 55 Drosophila species that have previously been characterized for their critical thermal minima (CTmin) which represents a powerful correlate of drosophilids' distribution across thermal clines. All species were reared under common garden conditions, and interspecific variance in CTmin could therefore be related to the metrics of membrane PLFA composition without confounding effects of acclimation or rearing. We hypothesized that cold‐adapted species would have PLFA's with (i) shorter chain length; (ii) higher proportion of unsaturated fatty acid; (iii) higher degree of unsaturation and (iv) lower mean melting point than warm‐adapted species. Following phylogenetic correction, the data support a highly significant correlation between cold tolerance and both the proportion of unsaturated fatty acid and the degree of unsaturation. Accordingly, we also found a highly significant negative correlation with the estimated mean melting point of PLFAs. Although there was no significant correlation between PLFA length and cold tolerance, the phylogenetically corrected model found PLFA parameters to explain >20% of the variation in cold tolerance when PLFA melting point and length were included. However, further functional assays are still needed to establish how these differences in chemical composition translate into functional differences of cells at low temperature. The tropical to subpolar gradient in PLFA composition found in this study suggests adaptive tuning of biological membrane function. It is noteworthy that a single measure such as PLFA composition explains more than 20% of the interspecific variance in cold tolerance. Even though PLFA composition is only one of several important physiological characteristics that relate to interspecific differences in cold tolerance, modification of membrane composition is likely an important adaptive trait in insects and perhaps invertebrates in general. Lay Summary

Therapy resistance and metastasis, the most fatal steps in cancer, are often triggered by a (partial) activation of the epithelial–mesenchymal transition (EMT) programme. A mesenchymal phenotype predisposes to ferroptosis, a cell death pathway exerted by an iron and oxygen-radical-mediated peroxidation of phospholipids containing polyunsaturated fatty acids. We here show that various forms of EMT activation, including TGFβ stimulation and acquired therapy resistance, increase ferroptosis susceptibility in cancer cells, which depends on the EMT transcription factor Zeb1. We demonstrate that Zeb1 increases the ratio of phospholipids containing pro-ferroptotic polyunsaturated fatty acids over cyto-protective monounsaturated fatty acids by modulating the differential expression of the underlying crucial enzymes stearoyl-Co-A desaturase 1 (SCD), fatty acid synthase (FASN), fatty acid desaturase 2 (FADS2), elongation of very long-chain fatty acid 5 (ELOVL5) and long-chain acyl-CoA synthetase 4 (ACSL4). Pharmacological inhibition of selected lipogenic enzymes (SCD and FADS2) allows the manipulation of ferroptosis sensitivity preferentially in high-Zeb1-expressing cancer cells. Our data are of potential translational relevance and suggest a combination of ferroptosis activators and SCD inhibitors for the treatment of aggressive cancers expressing high Zeb1. Schwab, Rao et al. report that Zeb1 mediates enhanced ferroptosis sensitivity in cancer cells after EMT activation, associated with altered expression of selected lipogenic enzymes and an subsequent increase in the PUFA:MUFA ratio.

Lipid droplets (LDs) and peroxisomes are ubiquitous organelles with central roles in eukaryotic cells. Although the mechanisms involved in biogenesis of these organelles remain elusive, both seem to require the endoplasmic reticulum (ER). Here we show that in yeast the ER budding of these structurally unrelated organelles has remarkably similar requirements and involves cooperation between Pex30 and the seipin complex. In the absence of these components, budding of both LDs and peroxisomes is inhibited, leading to the ER accumulation of their respective constituent molecules, such as triacylglycerols and peroxisomal membrane proteins, whereas COPII vesicle formation remains unaffected. This phenotype can be reversed by remodeling ER phospholipid composition highlighting a key function of these lipids in organelle biogenesis. We propose that seipin and Pex30 act in concert to organize membrane domains permissive for organelle budding, and that may have a lipid composition distinct from the bulk ER. Lipid droplets (LDs) and peroxisomes both emerge from the endoplasmic reticulum (ER). Here, the authors show that yeast Seipin and Pex30 proteins act together to regulate budding of these organelles from the same subdomain of the ER.

The outer membrane of gram-negative bacteria is a barrier to chemical and physical stress. Phospholipid transport between the inner and outer membranes has been an area of intense investigation and, in E . coli K-12, it has recently been shown to be mediated by YhdP, TamB, and YdbH, which are suggested to provide hydrophobic channels for phospholipid diffusion, with YhdP and TamB playing the major roles. However, YhdP and TamB have different phenotypes suggesting distinct functions. It remains unclear whether these functions are related to phospholipid metabolism. We investigated a synthetic cold sensitivity caused by deletion of fadR , a transcriptional regulator controlling fatty acid degradation and unsaturated fatty acid production, and yhdP , but not by Δ tamB Δ fadR or Δ ydbH Δ fadR . Deletion of tamB recuses the Δ yhdP Δ fadR cold sensitivity further demonstrating the phenotype is related to functional diversification between these genes. The Δ yhdP Δ fadR strain shows a greater increase in cardiolipin upon transfer to the non-permissive temperature and genetically lowering cardiolipin levels can suppress cold sensitivity. These data also reveal a qualitative difference between cardiolipin synthases in E . coli , as deletion of clsA and clsC suppresses cold sensitivity but deletion of clsB does not. Moreover, increased fatty acid saturation is necessary for cold sensitivity and lowering this level genetically or through supplementation of oleic acid suppresses the cold sensitivity of the Δ yhdP Δ fadR strain. Together, our data clearly demonstrate that the diversification of function between YhdP and TamB is related to phospholipid metabolism. Although indirect regulatory effects are possible, we favor the parsimonious hypothesis that YhdP and TamB have differential phospholipid-substrate transport preferences. Thus, our data provide a potential mechanism for independent control of the phospholipid composition of the inner and outer membranes in response to changing conditions based on regulation of abundance or activity of YhdP and TamB.

The protein complexes of the mitochondrial electron transport chain exist in isolation and in higher order assemblies termed supercomplexes (SCs) or respirasomes (SC I+III 2 +IV). The association of complexes I, III and IV into the respirasome is regulated by unknown mechanisms. Here, we designed a nanoluciferase complementation reporter for complex III and IV proximity to determine in vivo respirasome levels. In a chemical screen, we found that inhibitors of the de novo pyrimidine synthesis enzyme dihydroorotate dehydrogenase (DHODH) potently increased respirasome assembly and activity. By-passing DHODH inhibition via uridine supplementation decreases SC assembly by altering mitochondrial phospholipid composition, specifically elevated peroxisomal-derived ether phospholipids. Cell growth rates upon DHODH inhibition depend on ether lipid synthesis and SC assembly. These data reveal that nucleotide pools signal to peroxisomes to modulate synthesis and transport of ether phospholipids to mitochondria for SC assembly, which are necessary for optimal cell growth in conditions of nucleotide limitation. A chemical screen identifies DHODH inhibitors as robust activators of mitochondrial respirasome assembly. Lipidomics reveal that peroxisomal-derived ether phospholipids accumulate in mitochondria during nucleotide deprivation to drive proliferation.

Heterozygous mutations in NADP‐dependent isocitrate dehydrogenases (IDH) define the large majority of diffuse gliomas and are associated with hypermethylation of DNA and chromatin. The metabolic dysregulations imposed by these mutations, whether dependent or not on the oncometabolite D‐2‐hydroxyglutarate (D2HG), are less well understood. Here, we applied mass spectrometry imaging on intracranial patient‐derived xenografts of IDH‐mutant versus IDH wild‐type glioma to profile the distribution of metabolites at high anatomical resolution in situ . This approach was complemented by in vivo tracing of labeled nutrients followed by liquid chromatography–mass spectrometry (LC‐MS) analysis. Selected metabolites were verified on clinical specimen. Our data identify remarkable differences in the phospholipid composition of gliomas harboring the IDH1 mutation. Moreover, we show that these tumors are characterized by reduced glucose turnover and a lower energy potential, correlating with their reduced aggressivity. Despite these differences, our data also show that D2HG overproduction does not result in a global aberration of the central carbon metabolism, indicating strong adaptive mechanisms at hand. Intriguingly, D2HG shows no quantitatively important glucose‐derived label in IDH‐mutant tumors, which suggests that the synthesis of this oncometabolite may rely on alternative carbon sources. Despite a reduction in NADPH, glutathione levels are maintained. We found that genes coding for key enzymes in de novo glutathione synthesis are highly expressed in IDH‐mutant gliomas and the expression of cystathionine‐β‐synthase ( CBS ) correlates with patient survival in the oligodendroglial subtype. This study provides a detailed and clinically relevant insight into the in vivo metabolism of IDH1‐mutant gliomas and points to novel metabolic vulnerabilities in these tumors. Synopsis Oncogenic isocitrate dehydrogenase (IDH) mutations are a major glioma subtype determinant. Mass spectrometry imaging (MSI) and LC‐MS on patient‐derived orthotopic IDH‐mutated glioma xenografts reveal IDH‐specific adaptive mechanisms in metabolic pathways. Altered phospholipid metabolism is a major abnormality associated with IDH‐mutant gliomas. IDH‐mutant gliomas display a low energy potential as shown by a reduced ATP/ADP ratio. Potential compensatory pathways to maintain glutathione levels and thus redox balance are established. Cystathionine‐β‐synthase (CBS) expression is a novel prognostic factor in the oligodendroglial glioma subtype. Graphical Abstract Oncogenic isocitrate dehydrogenase (IDH) mutations are a major glioma subtype determinant. Mass spectrometry imaging (MSI) and LC‐MS on patient‐derived orthotopic IDH‐mutated glioma xenografts reveal IDH‐specific adaptive mechanisms in metabolic pathways.

The breakdown of toll-like receptor (TLR) tolerance results in tissue damage, and hyperactivation of the TLRs and subsequent inflammatory consequences have been implicated as risk factors for more severe forms of disease and poor outcomes from various diseases including COVID-19 and metabolic (dysfunction) associated fatty liver disease (MAFLD). Here we provide evidence that membrane bound O-acyltransferase domain containing 7 (MBOAT7) is a negative regulator of TLR signalling. MBOAT7 deficiency in macrophages as observed in patients with MAFLD and in COVID-19, alters membrane phospholipid composition. We demonstrate that this is associated with a redistribution of arachidonic acid toward proinflammatory eicosanoids, induction of endoplasmic reticulum stress, mitochondrial dysfunction, and remodelling of the accessible inflammatory-related chromatin landscape culminating in macrophage inflammatory responses to TLRs. Activation of MBOAT7 reverses these effects. These outcomes are further modulated by the MBOAT7 rs8736 (T) MAFLD risk variant. Our findings suggest that MBOAT7 can potentially be explored as a therapeutic target for diseases associated with dysregulation of the TLR signalling cascade. Hyperactivation of the toll-like receptors (TLRs) have been implicated as risk factors for more severe forms of disease in COVID-19 and metabolic (dysfunction) associated fatty liver disease (MAFLD). Here the authors report that MBOAT7 is reduced in macrophages of patients with MAFLD and COVID-19, and acts as a negative regulator of TLR signalling.

The β 2 adrenergic receptor (β 2 AR) signals through both G s and G i in cardiac myocytes, and the G i pathway counteracts the G s pathway. However, G i coupling is much less efficient than G s coupling in most cell-based and biochemical assays, making it difficult to study β 2 AR−G i interactions. Here we investigate the role of phospholipid composition on G s and G i coupling. While negatively charged phospholipids are known to enhance agonist affinity and stabilize an active state of the β 2 AR, we find that they impair coupling to G i3 and facilitate coupling to G s . Positively charged Ca 2+ and Mg 2+ , known to interact with the negative charge on phospholipids, facilitates G i3 coupling. Mutational analysis suggests that Ca 2+ coordinates an interaction between phospholipid and the negatively charged EDGE motif on the amino terminal helix of G i3 . Taken together, our observations suggest that local membrane charge modulates the interaction between β 2 AR and competing G protein subtypes. In the healthy heart, the β 2 adrenergic receptor (β 2 AR) signals through G s and G i proteins but the mechanism underlying G protein selectivity is not fully understood. Here, the authors show that membrane charge and intracellular cations modulate the β 2 AR−G i3 interaction.

Mitochondria form a dynamic network that responds to physiological signals and metabolic stresses by altering the balance between fusion and fission. Mitochondrial fusion is orchestrated by conserved GTPases MFN1/2 and OPA1, a process coordinated in yeast by Ugo1, a mitochondrial metabolite carrier family protein. We uncovered a homozygous missense mutation in SLC25A46 , the mammalian orthologue of Ugo1 , in a subject with Leigh syndrome. SLC25A46 is an integral outer membrane protein that interacts with MFN2, OPA1, and the mitochondrial contact site and cristae organizing system (MICOS) complex. The subject mutation destabilizes the protein, leading to mitochondrial hyperfusion, alterations in endoplasmic reticulum (ER) morphology, impaired cellular respiration, and premature cellular senescence. The MICOS complex is disrupted in subject fibroblasts, resulting in strikingly abnormal mitochondrial architecture, with markedly shortened cristae. SLC25A46 also interacts with the ER membrane protein complex EMC, and phospholipid composition is altered in subject mitochondria. These results show that SLC25A46 plays a role in a mitochondrial/ER pathway that facilitates lipid transfer, and link altered mitochondrial dynamics to early‐onset neurodegenerative disease and cell fate decisions. Synopsis Whole‐exome sequencing in a Leigh syndrome patient identified mutations in SLC25A46, a degenerate member of the mitochondrial metabolite transport family, linking altered mitochondrial dynamics to early‐onset neurodegenerative disease. Loss of SLC25A46 results in mitochondrial hyperfusion and striking changes in mitochondrial architecture. SLC25A46 is an outer membrane protein that interacts with MFN2, OPA1, the MICOS complex, and the EMC complex in the ER. Loss of SLC25A46 results in altered ER morphology and marked changes in the phospholipid composition of the mitochondrial membranes. Loss of SLC25A46 results in premature cellular senescence in dividing cells. Graphical Abstract Whole‐exome sequencing in a Leigh syndrome patient identified mutations in SLC25A46, a degenerate member of the mitochondrial metabolite transport family, linking altered mitochondrial dynamics to early‐onset neurodegenerative disease.

Virtually all integral outer membrane proteins (OMPs) produced by Gram-negative bacteria contain a unique ‘β barrel’ structure that serves as a membrane spanning domain. The universal b arrel a ssembly m achine (BAM) catalyzes OMP assembly (folding and membrane insertion) in vivo, and purified Escherichia coli BAM that is reconstituted into proteoliposomes catalyzes OMP assembly in vitro. Here we show that BAM also catalyzes the assembly of OMPs into outer membrane fractions (‘native OMs’) that are purified by optimized conventional methods. Interestingly, we found that OMP assembly was moderately impaired when native OMs were isolated from a mlaA - strain that is deficient in maintaining OM lipid homeostasis but was strongly reduced when native OMs were isolated from a pldA - strain that is deficient in a parallel pathway. We also found that the mlaA and pldA deletions altered the OM phospholipid profile to different degrees that correlated with the degree to which the mutations impaired OMP assembly. Taken together, our results provide direct evidence that the mla and pldA pathways play distinct roles in maintaining OM homeostasis and strongly suggest that OM phospholipids play a more significant role in OMP biogenesis than previously appreciated. The BAM protein complex catalyzes the integration of newly made proteins into the outer membrane of Gram-negative bacteria. Here, Nilaweera et al. provide evidence that outer-membrane lipids also play an important role in this process.