Elovl2-Ablation Leads to Mitochondrial Membrane Fatty Acid Remodeling and Reduced Efficiency in Mouse Liver Mitochondria

The fatty acid elongase ELOngation of Very-Long-chain fatty acids protein 2 (ELOVL2) controls the elongation of polyunsaturated fatty acids (PUFA) producing precursors for omega-3, do-cosahexaenoic acid (DHA), and omega-6, docosapentaenoic acid (DPAn6) in-vivo. Expectedly, Elovl2-ablation drastically reduced the DHA and DPAn6 in liver mitochondrial membranes. Unexpectedly, however, total PUFAs levels decreased further than could be explained by Elovl2 ablation. The lipid peroxidation process was not involved in PUFAs reduction since malondial-dehyde-lysine (MDAL) and other oxidative stress biomarkers were not enhanced. The content of mitochondrial respiratory chain proteins remained unchanged. Still, membrane remodeling was associated with high voltage-dependent anion channel (VDAC) and adenine nucleotide trans-locase 2 (ANT2), a possible reflection of the increased demand on phospholipid transport to the mitochondria. Mitochondrial function was impaired despite preserved content of the respiratory chain proteins and the absence of oxidative damage. Oligomycin-insensitive oxygen consumption increased, and coefficients of respiratory control were reduced by 50%. The mitochondria became very sensitive to fatty acid-induced uncoupling and permeabilization, where ANT2 is involved. Mitochondrial volume and number of peroxisomes increased as revealed by transmission elec-tron microscopy. In conclusion, the results imply that endogenous DHA production is vital for the normal function of mouse liver mitochondria and could be relevant not only for mice but also for human metabolism.

Modifying the yeast very long chain fatty acid biosynthetic machinery by the expression of plant 3-ketoacyl CoA synthase isozymes

Eukaryotes express a multi-component fatty acid elongase to produce very long chain fatty acids (VLCFAs), which are building blocks of diverse lipids. Elongation is achieved by cyclical iteration of four reactions, the first of which generates a new carbon-carbon bond, elongating the acyl-chain. This reaction is catalyzed by either ELONGATION DEFECTIVE LIKE (ELO) or 3-ketoacyl-CoA synthase (KCS) enzymes. Whereas plants express both ELO and KCS enzymes, other eukaryotes express only ELOs. We explored the KCS and ELO enzymatic redundancies by expressing the former in yeast strains that lacked endogenous ELO isozymes. Expression of the 26 maize KCS isozymes in wild-type, scelo2 or scelo3 single mutants did not affect VLCFA profiles. However, five of these KCSs were capable of complementing the lethal scelo2; scelo3 double mutant. These rescued strains express novel VLCFA profiles reflecting the different catalytic capabilities of the KCS isozymes. These novel strains offer a platform to explore the relationship between VLCFA profiles and cellular physiology.

PUFA synthase-independent DHA synthesis pathway in Parietichytrium sp. and its modification to produce EPA and n-3DPA

The demand for n-3 long-chain polyunsaturated fatty acids (n-3LC-PUFAs), such as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), will exceed their supply in the near future, and a sustainable source of n-3LC-PUFAs is needed. Thraustochytrids are marine protists characterized by anaerobic biosynthesis of DHA via polyunsaturated fatty acid synthase (PUFA-S). Analysis of a homemade draft genome database suggested that Parietichytrium sp. lacks PUFA-S but possesses all fatty acid elongase (ELO) and desaturase (DES) genes required for DHA synthesis. The reverse genetic approach and a tracing experiment using stable isotope-labeled fatty acids revealed that the ELO/DES pathway is the only DHA synthesis pathway in Parietichytrium sp. Disruption of the C20 fatty acid ELO (C20ELO) and ∆4 fatty acid DES (∆4DES) genes with expression of ω3 fatty acid DES in this thraustochytrid allowed the production of EPA and n-3docosapentaenoic acid (n-3DPA), respectively, at the highest level among known microbial sources using fed-batch culture.

Polymorphisms of Fatty Acid Elongase 2 Gene Afftects Risk of Pulmonary Tuberculosis in China Han Population

Background: As an infectious disease closely related to Mycobacterium tuberculosis, autoimmunity, inflammation, environment and heredity, the relationship between the single nucleotide polymorphism of elongase 2 gene and the susceptibility to tuberculosis is still unknown. Methods: Between January 2016 and November 2018, a hospital-based case-control study was conducted. This epidemiological survey was conducted in both hospitals every three months. rs3798719, rs1570069, and rs2236212 in ELOVL2 gene were detected by Sanger sequencing. Results: Stratified by gender, the genotypes and allele frequencies of rs3798719, rs1570069 and rs2236212 showed significant differences between the two groups (χ2 = 6.987, P = 0.030), Genetic modeling showed that rs3798719 was statistically different in the overdominance model (χ2 = 4.784, OR = 1.414, 95% CI: 1.036-1.929, P < 0.05). The polymorphism of rs2236212 between male TB patients and healthy controls was statistically different in the dominance model. (χ2 = 4.192, OR = 0.507; 95% CI: 0.262-0.981, P < 0.05). Conclusion: The rs3798719 of ELOVL2 gene may be associated with susceptibility to TB in female population and the rs2236212 of ELOVL2 gene may be associated with TB incidence in male patients.

Saturated very long chain fatty acid configures glycosphingolipid for lysosome homeostasis in long-lived C. elegans

The contents of numerous membrane lipids change upon ageing. However, it is unknown whether and how any of these changes are causally linked to lifespan regulation. Acyl chains contribute to the functional specificity of membrane lipids. In this study, working with C. elegans, we identified an acyl chain-specific sphingolipid, C22 glucosylceramide, as a longevity metabolite. Germline deficiency, a conserved lifespan-extending paradigm, induces somatic expression of the fatty acid elongase ELO-3, and behenic acid (22:0) generated by ELO-3 is incorporated into glucosylceramide for lifespan regulation. Mechanistically, C22 glucosylceramide is required for the membrane localization of clathrin, a protein that regulates membrane budding. The reduction in C22 glucosylceramide impairs the clathrin-dependent autophagic lysosome reformation, which subsequently leads to TOR activation and longevity suppression. These findings reveal a mechanistic link between membrane lipids and ageing and suggest a model of lifespan regulation by fatty acid-mediated membrane configuration.

TMEM120A is a coenzyme A-binding membrane protein with structural similarities to ELOVL fatty acid elongase

TMEM120A, also named as TACAN, is a novel membrane protein highly conserved in vertebrates and was recently proposed to be a mechanosensitive channel involved in sensing mechanical pain. Here we present the single particle cryo-EM structure of human TMEM120A which forms a tightly packed dimer with extensive interactions mediate by the N-terminal coiled coil domain (CCD), the C-terminal transmembrane domain (TMD), and the re-entrant loop between the two domains. The TMD of each TMEM120A subunit contains six transmembrane helices (TMs) and has no clear structural feature of a channel protein. Instead, the six TMs form an α-barrel with a deep pocket where a coenzyme A (CoA) molecule is bound. Intriguingly, some structural features of TMEM120A resemble those of elongase for very long-chain fatty acid (ELOVL) despite low sequence homology between them, pointing to the possibility that TMEM120A may function as an enzyme for fatty acid metabolism, rather than a mechanosensitive channel.

Analysis of the Mechanosensor Channel Functionality of TACAN

Mechanosensitive ion channels mediate transmembrane ion currents activated by mechanical forces. A mechanosensitive ion channel called TACAN was recently reported. We began to study TACAN with the intent to understand how it senses mechanical forces and functions as an ion channel. Using cellular patch-recording methods we failed to identify mechanosensitive ion channel activity. Using membrane reconstitution methods we found that TACAN, at high protein concentrations, produces heterogeneous conduction levels that are not mechanosensitive and are most consistent with disruptions of the lipid bilayer. We determined the structure of TACAN using single particle cryo-EM and observe that it forms a symmetrical dimeric transmembrane protein. Each protomer contains an intracellular-facing cleft with a coenzyme-A cofactor, confirmed by mass spectrometry. The TACAN protomers are related in 3-dimensional structure to a fatty acid elongase, ELOVL. Whilst its physiological function remains unclear, we anticipate that TACAN is not a mechanosensitive ion channel.

Modulation of fatty acid elongation in cockroaches sustains sexually dimorphic hydrocarbons and female attractiveness

Insect cuticular hydrocarbons (CHCs) serve as important intersexual signaling chemicals and generally show variation between the sexes, but little is known about the generation of sexually dimorphic hydrocarbons (SDHCs) in insects. In this study, we report the molecular mechanism and biological significance that underlie the generation of SDHC in the German cockroach Blattella germanica. Sexually mature females possess more C29 CHCs, especially the contact sex pheromone precursor 3,11-DimeC29. RNA interference (RNAi) screen against the fatty acid elongase family members combined with heterologous expression of the genes in yeast revealed that both BgElo12 and BgElo24 were involved in hydrocarbon (HC) production, but BgElo24 is of wide catalytic activities and is able to provide substrates for BgElo12, and only the female-enriched BgElo12 is responsible for sustaining female-specific HC profile. Repressing BgElo12 masculinized the female CHC profile, decreased contact sex pheromone level, and consequently reduced the sexual attractiveness of female cockroaches. Moreover, the asymmetric expression of BgElo12 between the sexes is modulated by sex differentiation cascade. Specifically, male-specific BgDsx represses the transcription of BgElo12 in males, while BgTra is able to remove this effect in females. Our study reveals a novel molecular mechanism responsible for the formation of SDHCs and also provide evidences on shaping of the SDHCs by sexual selection, as females use them to generate high levels of contact sex pheromone.