Monomethyl Branched-chain Fatty Acids Research Articles

Quantifying acyl-chain diversity in isobaric compound lipids containing monomethyl branched-chain fatty acids.

Compound lipids comprise a diverse group of metabolites present in living systems, and metabolic- and environmentally-driven structural distinctions across this family is increasingly linked to biological function. However, methods for deconvoluting these often isobaric lipid species are lacking or require specialized instrumentation. Notably, acyl-chain diversity within cells may be influenced by nutritional states, metabolic dysregulation, or genetic alterations. Therefore, a reliable, validated method of quantifying structurally similar even-, odd-, and branched-chain acyl groups within intact compound lipids will be invaluable for gaining molecular insights into their biological functions. Here we demonstrate the chromatographic resolution of isobaric lipids containing distinct combinations of straight-chain and branched-chain acyl groups via ultra-high-pressure liquid chromatography (UHPLC)-mass spectrometry (MS) using a C30 liquid chromatography column. Using metabolically-engineered adipocytes lacking branched-keto acid dehydrogenase A (Bckdha), we validate this approach through a combination of fatty acid supplementation and metabolic tracing using monomethyl branched-chain fatty acids and valine. We observe resolution of numerous isobaric triacylglycerols and other compound lipids, demonstrating the resolving utility of this method. This approach strengthens our ability to quantify and characterize the inherent diversity of acyl chains across the lipidome.

Auto-mmBCFAs: A swift precision approach for determination of monomethyl branched-chain fatty acids

Monomethyl-branched chain fatty acids (mmBCFAs) are prevalent in diverse food sources, garnering significant interest owing to their distinctive branched structure and biological activity. However, the conventional analytical methods suffer from the time consumption and lower accuracy. In this study, we developed a method named Auto-mmBCFAs integrated GC-MS and algorithms for rapid and accurate measuring mmBCFAs. This method utilizes a multivariate matching approach, significantly enhancing detection efficiency. Compared to NIST database, Auto-mmBCFAs exhibits higher detection rates and accuracy. The developed method was validated in terms of precision, sensitivity, and linearity, and further evaluated mmBCFAs profile in sheep milk from different regions and breeds. Our results demonstrated that Auto-mmBCFAs methods is a rapid and reliable method for the determination of mmBCFAs in complex biological matrices.

Alkaline wet oxidative pretreatment and acid hydrolysis of wheat straw for squalene and monomethyl branched chain fatty acids rich lipid production in Lentibacillus salarius BPIITR

Lignocellulosic biomass has high potential for use as a carbon substrate in microbial fermentation. However, the generation of various lignin-derived phenolic compounds, benzoic acids, and carbohydrate-derived furan aldehydes poses a major bottleneck. In this study, wheat straw was subjected to sequential alkaline wet oxidative pretreatment (AWOP) and acid hydrolysis to extract hemicellulose sugars. After statistical optimization, 251.50 mg/g total sugar (228.57 mg/g pentose, 22.93 mg/g hexose) and 19.64 mg/g hydrolysis by-products were achieved, with a theoretical pentose recovery of 89.57% and residual cellulose of 72.1%. The lignin-rich and carbohydrate-rich liquids from the AWOP treatment and acid hydrolysis, respectively, were valorised to produce squalene and branched chain fatty acid rich lipid using Lentibacillus salarius BPIITR. The lipid of 100.9 ± 3.53 and 235.75 ± 10.39 mg/g of dcw rich in squalene up to 3121.17 ± 25.49 and 676.41 ± 134.27 μg/g of lipid was produced in AWOP and acid hydrolysate, respectively. In the AWOP hydrolysate, lignin content was reduced by 63.78%, compared to a 40.18% reduction in the acid hydrolysate. GC-MS analysis of the lignin monomer and metabolites suggests the potential influence of lignin monomers on the biosynthetic pathway of squalene and carbohydrate content on the branched chain fatty acids accumulation in the halophilic bacterial lipid of L. salarius BPIITR.

Amino acid and protein specificity of protein fatty acylation in Caenorhabditis elegans

Protein lipidation plays critical roles in regulating protein function and localization. However, the chemical diversity and specificity of fatty acyl group utilization have not been investigated using untargeted approaches, and it is unclear to what extent structures and biosynthetic origins of S-acyl moieties differ from N- and O-fatty acylation. Here, we show that fatty acylation patterns in Caenorhabditis elegans differ markedly between different amino acid residues. Hydroxylamine capture revealed predominant cysteine S-acylation with 15-methylhexadecanoic acid (isoC17:0), a monomethyl branched-chain fatty acid (mmBCFA) derived from endogenous leucine catabolism. In contrast, enzymatic protein hydrolysis showed that N-terminal glycine was acylated almost exclusively with straight-chain myristic acid, whereas lysine was acylated preferentially with two different mmBCFAs and serine was acylated promiscuously with a broad range of fatty acids, including eicosapentaenoic acid. Global profiling of fatty acylated proteins using a set of click chemistry-capable alkyne probes for branched- and straight-chain fatty acids uncovered 1,013 S-acylated proteins and 510 hydroxylamine-resistant N- or O-acylated proteins. Subsets of S-acylated proteins were labeled almost exclusively by either a branched-chain or a straight-chain probe, demonstrating acylation specificity at the protein level. Acylation specificity was confirmed for selected examples, including the S-acyltransferase DHHC-10. Last, homology searches for the identified acylated proteins revealed a high degree of conservation of acylation site patterns across metazoa. Our results show that protein fatty acylation patterns integrate distinct branches of lipid metabolism in a residue- and protein-specific manner, providing a basis for mechanistic studies at both the amino acid and protein levels.

Long chain monomethyl branched-chain fatty acid levels in human milk vary with gestational weight gain

Breastfeeding is an important determinant of infant health and there is immense interest in understanding its metabolite composition so that key beneficial components can be identified. The aim of this research was to measure the fatty acid composition of human milk in an Irish cohort where we examined changes depending on lactation stage and gestational weight gain trajectory. Utilizing a chromatography approach optimal for isomer separation, we identified 44 individual fatty acid species via GCMS and showed that monomethyl branched-chain fatty acids(mmBCFA's), C15:0 and C16:1 are lower in women with excess gestational weight gain versus low gestational weight gain. To further explore the potential contribution of the activity of endogenous metabolic pathways to levels of these fatty acids in milk, we administered D2O to C57BL/6J dams fed a purified lard based high fat diet (HFD) or low-fat diet during gestation and quantified the total and de novo synthesized levels of fatty acids in their milk. We found that de novo synthesis over three days can account for between 10 and 50 % of mmBCFAs in milk from dams on the low-fat diet dependent on the branched-chain fatty acid species. However, HFD fed mice had significantly decreased de novo synthesized fatty acids in milk resulting in lower total mmBCFAs and medium chain fatty acid levels. Overall, our findings highlight the diverse fatty acid composition of human milk and that human milk mmBCFA levels differ between gestational weight gain phenotypes. In addition, our data indicates that de novo synthesis contributes to mmBCFA levels in mice milk and thus may also be a contributory factor to mmBCFA levels in human milk. Given emerging data indicating mmBCFAs may be beneficial components of milk, this study contributes to our knowledge around the phenotypic factors that may impact their levels.

Enhanced production of anteiso-branched chain fatty acids rich bacterial oil using Lentibacillus salarius strain BPIITR under furan aldehydes induced oxidative stress

Monomethyl branched-chain fatty acids (mBCFAs) are highly valuable compounds in the oleochemical industry, with diverse industrial applications including pharmaceuticals, biofuels and lubricants. In the current study, the medium components of L. salarius BPIITR were statistically optimized to produce mBCFAs-rich lipid, yielding up to 227.16 ± 16.2 mg/g dcw. The supplementation of 2-methyl butyric acid increased the lipid content to 276.42 ± 7.46 mg/g dcw, with anteiso fatty acids up to 87.59 ± 1.56 % w/w of the total lipid. The addition of 5-hydroxymethyl furfural (5-HmF) and furfural induced oxidative stress, resulting in the synthesis of lipids rich in anteiso-mBCFAs. Furfural supplementation led to a lipid accumulation of 256.49 ± 7.91 mg/g dcw, whereas with 5-HmF, it increased to 284.75 ± 8.98 mg/g dcw. Furthermore, the elongation of mBCFAs from C15:0 to C17:0 was significantly affected during oxidative stress. This study suggests that under oxidative stress conditions, the synthesis of anteiso fatty acids is favored over iso-fatty acids in L. salarius BPIITR. Additionally, value-added products such as trehalose and furan carboxylic acids were identified as potential co-products in this study, with trehalose reaching up to 255.84 ± 8.04, 163.65 ± 20.94, and 217.46 mg/g dcw in the presence of 2-methylbutyric acid, furfural, and 5-HmF, respectively. The concentration of 2-furan carboxylic acid and 2,5-furan dicarboxylic acids in the fermentation broth reached up to 4.37 ± 0.28 g/L and 2.48 ± 0.35 g/L, respectively. The utilization of short-chain fatty acids and furan aldehydes not only provided a cost-effective carbon source but also modulated the metabolic flux towards specific mBCFAs rich bacterial oil production.

Fasting and non-fasting plasma levels of monomethyl branched chain fatty acids: Implications for maple syrup urine disease.

The branched-chain amino acids (BCAA) leucine, valine, and isoleucine provide precursors for monomethyl branched-chain fatty acids (BCFA). Established reference ranges for BCFAs are lacking. In maple syrup urine disease (MSUD), a rare inborn error of BCAA metabolism, the endogen production is impaired and MSUD patients are treated with a low protein (low BCAA) diet. The protein restriction may affect the dietary intake of BCFA, depending on the dietary choices made. Patients with MSUD are prescribed a more or less protein-restricted diet depending on the severity of the disease. The combination of a protein-restricted diet and subsequent impaired endogenous synthesis may render MSUD patients sensitive to BCFA deficiency, with yet unknown implications. To investigate the possibility of lower circulatory BCFA levels in MSUD that favors dietary BCFA supplementation, we first established fasting-state reference ranges for selected BCFAs and saturated/unsaturated fatty acids in plasma. Then, the effect of fasting on BCFA levels was evaluated by comparing the distribution in a fasting versus a non-fasting cohort. To test the hypothesis that BCFA deficiency could contribute to MSUD pathophysiology, we recruited patients with intermittent, intermediate, and classical form of MSUD and analyzed the corresponding BCFA z-scores. None of the BCFA species had |z-scores| > 2 relative to the reference range. Our findings do not support the requirement of BCFA supplementation in MSUD patients. The origin of BCFAs is discussed. Impaired capacity to synthesize BCFA do not manifest as reduced plasma levels in MSUD, suggesting that endogenous synthesis is dispensable for plasma levels.

Targeted lipidomics reveals a novel role for glucosylceramides in glucose response

The addition of excess glucose to the diet drives a coordinated response of lipid metabolism pathways to tune the membrane composition to the altered diet. Here, we have employed targeted lipidomic approaches to quantify the specific changes in the phospholipid and sphingolipid populations that occur in elevated glucose conditions. The lipids within wild-type Caenorhabditis elegans are strikingly stable with no significant changes identified in our global mass spectrometry–based analysis. Previous work has identified ELO-5, an elongase that is critical for the synthesis of monomethyl branched-chain fatty acids (mmBCFAs), as essential for surviving elevated glucose conditions. Therefore, we performed targeted lipidomics on elo-5 RNAi-fed animals and identified several significant changes in these animals in lipid species that contain mmBCFAs as well as in species that do not contain mmBCFAs. Of particular note, we identified a specific glucosylceramide (GlcCer 17:1;O2/22:0;O) that is also significantly upregulated with glucose in wild-type animals. Furthermore, compromising the production of the glucosylceramide pool with elo-3 or cgt-3 RNAi leads to premature death in glucose-fed animals. Taken together, our lipid analysis has expanded the mechanistic understanding of metabolic rewiring with glucose feeding and has identified a new role for the GlcCer 17:1;O2/22:0;O.

Monomethyl branched-chain fatty acids enriched bacterial oil production by furan aldehydes tolerant halophile Lentibacillus salarius strain BPIITR using non-detoxified sugarcane bagasse

The structural diversity of monomethyl branched-chain fatty acids (mBCFAs) expanded their application in biolubricants, biofuels for enhancing cold flow and thermo-oxidative properties. Current study focuses on mBCFAs production from sugarcane bagasse hydrolysate in biorefinery approach with halophilic Lentibacillus salarius BPIITR. Halophilic bacterium exhibited tolerance towards furan aldehydes up to 150 mM in minimal medium and produced 3.40 ± 0.13 and 2.47 ± 0.15 gL−1 lipid rich in mBCFAs, in xylose and glucose rich non-detoxified hydrolysate, respectively at bench-scale bioreactor. In addition, 2,5-furandicarboxylic acid and 2-furancarboxylic acids were co-produced as value-added products up to 41.34 ± 4.73 and 59.84 ± 5.17 mM, respectively. The biosynthesized bacterial oil exhibited onset oxidation temperature of 319.5 °C and low temperature viscosity ratio of 2.92. The accumulated lipid was rich in triacylglycerol content more than 67 % with 12-methyl tetradecanoic acid as major fatty acid.

Monomethyl branched-chain fatty acids are critical for Caenorhabitis elegans survival in elevated glucose conditions

The maintenance of optimal membrane composition under basal and stress conditions is critical for the survival of an organism. High-glucose stress has been shown to perturb membrane properties by decreasing membrane fluidity, and the membrane sensor PAQR-2 is required to restore membrane integrity. However, the mechanisms required to respond to elevated dietary glucose are not fully established. In this study, we used a 13C stable isotope-enriched diet and mass spectrometry to better understand the impact of glucose on fatty acid dynamics in the membrane of Caenorhabditis elegans. We found a novel role for monomethyl branched-chain fatty acids (mmBCFAs) in mediating the ability of the nematodes to survive conditions of elevated dietary glucose. This requirement of mmBCFAs is unique to glucose stress and was not observed when the nematode was fed elevated dietary saturated fatty acid. In addition, when worms deficient in elo-5, the major biosynthesis enzyme of mmBCFAs, were fed Bacillus subtilis (a bacteria strain rich in mmBCFAs) in combination with high glucose, their survival rates were rescued to wild-type levels. Finally, the results suggest that mmBCFAs are part of the PAQR-2 signaling response during glucose stress. Taken together, we have identified a novel role for mmBCFAs in stress response in nematodes and have established these fatty acids as critical for adapting to elevated glucose.

MmBCFA C17iso ensures endoplasmic reticulum integrity for lipid droplet growth.

In eukaryote cells, lipid droplets (LDs) are key intracellular organelles that dynamically regulate cellular energy homeostasis. LDs originate from the ER and continuously contact the ER during their growth. How the ER affects LD growth is largely unknown. Here, we show that RNAi knockdown of acs-1, encoding an acyl-CoA synthetase required for the biosynthesis of monomethyl branched-chain fatty acids C15iso and C17iso, remarkably prevented LD growth in Caenorhabditis elegans. Dietary C17iso, or complex lipids with C17iso including phosphatidylcholine, phosphatidylethanolamine, and triacylglycerol, could fully restore the LD growth in the acs-1RNAi worms. Mechanistically, C17iso may incorporate into phospholipids to ensure the membrane integrity of the ER so as to maintain the function of ER-resident enzymes such as SCD/stearoyl-CoA desaturase and DGAT2/diacylglycerol acyltransferase for appropriate lipid synthesis and LD growth. Collectively, our work uncovers a unique fatty acid, C17iso, as the side chain of phospholipids for determining the ER homeostasis for LD growth in an intact organism, C. elegans.

Monomethyl branched-chain fatty acid mediates amino acid sensing upstream of mTORC1

Animals have developed various nutrient-sensing mechanisms for survival under fluctuating environmental conditions. Although extensive cell-culture-based analyses have identified diverse mediators of amino acid sensing upstream of mTOR, studies using animal models to examine intestine-initiated amino acid sensing mechanisms under specific physiological conditions are lacking. Here, we developed a Caenorhabditis elegans model to examine the impact of amino acid deficiency on development. We discovered a leucine-derived monomethyl branched-chain fatty acid and its downstream metabolite, glycosphingolipid, which critically mediates the overall amino acid sensing by intestinal and neuronal mTORC1, which in turn regulates postembryonic development at least partly by controlling protein translation and ribosomal biogenesis. Additional data suggest that a similar mechanism may operate in mammals. This study uncovers an amino-acid-sensing mechanism mediated by a lipid biosynthesis pathway.

Dairy Fat Intake, Plasma Pentadecanoic Acid, and Plasma Iso-heptadecanoic Acid Are Inversely Associated With Liver Fat in Children.

We sought to evaluate the relevance of pediatric dairy fat recommendations for children at risk for nonalcoholic fatty liver disease (NAFLD) by studying the association between dairy fat intake and the amount of liver fat. The effects of dairy fat may be mediated by odd chain fatty acids (OCFA), such as pentadecanoic acid (C15:0), and monomethyl branched chain fatty acids (BCFA), such as iso-heptadecanoic acid (iso-C17:0). Therefore, we also evaluated the association between plasma levels of OCFA and BCFA with the amount of liver fat. Observational, cross-sectional, community-based sample of 237 children ages 8 to 17. Dairy fat intake was assessed by 3 24-hour dietary recalls. Plasma fatty acids were measured by gas chromatography-mass spectrometry. Main outcome was hepatic steatosis measured by whole liver magnetic resonance imaging proton density fat fraction (MRI-PDFF). Median dairy fat intake was 10.6 grams/day (range 0.0--44.5 g/day). Median liver MRI-PDFF was 4.5% (range 0.9%-45.1%). Dairy fat intake was inversely correlated with liver MRI-PDFF (r = -0.162; P = .012). In multivariable log linear regression, plasma C15:0 and iso-C17:0 were inverse predictors of liver MRI-PDFF (B = -0.247, P = 0.048; and B = -0.234, P = 0.009). Dairy fat intake, plasma C15:0, and plasma iso-C17:0 were inversely correlated with hepatic steatosis in children. These hypothesis-generating findings should be tested through clinical trials to better inform dietary guidelines.

Branched-Chain Fatty Acids as Mediators of the Activation of Hepatic Peroxisome Proliferator-Activated Receptor Alpha by a Fungal Lipid Extract.

The study aimed to test the hypothesis that monomethyl branched-chain fatty acids (BCFAs) and a lipid extract of Conidiobolus heterosporus (CHLE), rich in monomethyl BCFAs, are able to activate the nuclear transcription factor peroxisome proliferator-activated receptor alpha (PPARalpha). Rat Fao cells were incubated with the monomethyl BCFAs 12-methyltridecanoic acid (MTriA), 12-methyltetradecanoic acid (MTA), isopalmitic acid (IPA) and 14-methylhexadecanoic acid (MHD), and the direct activation of PPARalpha was evaluated by reporter gene assay using a PPARalpha responsive reporter gene. Furthermore, Fao cells were incubated with different concentrations of the CHLE and PPARalpha activation was also evaluated by using the reporter gene assay, and by determining the mRNA concentrations of selected PPARalpha target genes by real-time RT-PCR. The reporter gene assay revealed that IPA and the CHLE, but not MTriA, MHD and MTA, activate the PPARalpha responsive reporter gene. CHLE dose-dependently increased mRNA concentrations of the PPARalpha target genes acyl-CoA oxidase (ACOX1), cytochrome P450 4A1 (CYP4A1), carnitine palmitoyltransferase 1A (CPT1A) and solute carrier family 22 (organic cation/carnitine transporter), member 5 (SLC22A5). In conclusion, the monomethyl BCFA IPA is a potent PPARalpha activator. CHLE activates PPARalpha-dependent gene expression in Fao cells, an effect that is possibly mediated by IPA.

The Antiglycation Effect of Monomethyl Branched Chained Fatty Acid and Phytochemical Compounds and their Synergistic Effect on Obesity Related Colorectal Cancer Cell Panel

Abstract Background and aims: monomethyl branched chain fatty acids (mmBCFA) and phytochemicals including: Hydroxycitric Acid, Chlorogenic Acid and Piperine have been considered as an interesting agent for researches due to their role in diabetes and cancer. The present study examines the antiglycation effect of mmBCFA and phytochemicals and investigate their Synergistic effect on different colorectal cancer cell lines. Methods: This study was carried out by using murine monocyte-macrophage cell line and Methylglyoxal (MGO) to enhance the glycation process, furthermore to examine the antiproliferative effect of both the mmBCFA and phytochemicals we use Sulforhodamine B (SRB) assay against obesity related-colorectal cancer cell line panel. Results: Both phytochemicals and mmBCFA have a higher antiglycation effect than Aminoguanidine (AMG) significantly, moreover, all of the phytochemicals and mmBCFA have antiproliferative against SW620, CACO2 and SW480, nevertheless none of these agents was equipotent to Cisplatin, furthermore, the synergetic effect observed only when we co-incubate Piperine with mmBCFA. Conclusions: phytochemicals such as Hydroxycitric Acid, Chlorogenic Acid and Piperine and mmBCFA could be used as treatment to prevents the accumulation of advanced glycation end-products (AGEs) in diabetes. Furthermore, the co-incubation between these compounds can inhibit cancer growth, as alternative therapeutic strategy against obesity related-colorectal cancer.

Engineering Streptomyces coelicolor for production of monomethyl branched chain fatty acids

Branched chain fatty acids (BCFA) are an appealing biorefinery-driven target of fatty acid (FA) production. BCFAs typically have lower melting points compared to straight chain FAs, making them useful in lubricants and biofuels. Actinobacteria, especially Streptomyces species, have unique secondary metabolism that are capable of producing not only antibiotics, but also high percentage of BCFAs in their membrane lipids. Since biosynthesis of polyketide (PK) and FA partially share common pathways to generate acyl-CoA precursors, in theory, Streptomyces sp. with high levels of PK antibiotics production can be easily manipulated into strains producing high levels of BCFAs. To increase the percentage of the BCFA moieties in lipids, we redirected acyl-CoA precursor fluxes from PK into BCFAs using S. coelicolor M1146 (M1146) as a host strain. In addition, 3-ketoacyl acyl carrier protein synthase III and branched chain α-keto acid dehydrogenase were overexpressed to push fluxes of branched chain acyl-CoA precursors towards FA synthesis. The maximum titer of 354.1 mg/L BCFAs, 90.3% of the total FA moieties, was achieved using M1146dD-B, fadD deletion and bkdABC overexpression mutant of M1146 strain. Cell specific yield of 64.4 mg/L/gcell was also achieved. The production titer and specific yield are the highest ever reported in bacterial cells, which provides useful insights to develop an efficient host strain for BCFAs.

Enzyme promiscuity drives branched-chain fatty acid synthesis in adipose tissues.

SummaryFatty acid synthase (FASN) predominantly generates straight-chain fatty acids using acetyl-CoA as the initiating substrate. However, monomethyl branched-chain fatty acids (mmBCFAs) are also present in mammals but thought to be primarily diet-derived. Here we demonstrate that mmBCFAs are de novo synthesized via mitochondrial BCAA catabolism, exported to the cytosol by adipose-specific expression of carnitine acetyltransferase (CrAT), and elongated by FASN. Brown fat exhibits the highest BCAA catabolic and mmBCFA synthesis fluxes, whereas these lipids are largely absent from liver and brain. mmBCFA synthesis is also sustained in the absence of microbiota. We identify hypoxia as a potent suppressor of BCAA catabolism that decreases mmBCFA synthesis in obese adipose tissue, such that mmBCFAs are significantly decreased in obese animals. These results identify adipose tissue mmBCFA synthesis as a novel link between BCAA metabolism and lipogenesis, highlighting roles for CrAT and FASN promiscuity that influence acyl-chain diversity in the lipidome.

Monomethyl Branched Chain Fatty Acids link Mitochondrial Amino Acid Metabolism and Adipose Tissue Lipogenesis to Fatty Acid Diversity

BCAA's are important substrates for protein synthesis and bioenergetics in mammals, and this metabolic pathway is dysregulated in various disease states. Fatty acid biosynthesis occurs in many tissues, but the balance of lipogenesis in liver and adipose tissue is disturbed in the context of obesity and metabolic syndrome. Here, using in vitro and in vivo stable isotope tracing we demonstrate that these pathways are linked within adipose tissue, where mammalian FAS produces monomethyl branched chain fatty acids (mmBCFAs). BCAA catabolic flux and short chain fatty acids from the gut microbiome initiate fatty acid synthesis in brown and beige adipocytes to influence the diversity of fatty acids present in the body. Diet‐induced obesity decreases BCAA catabolism and adipose tissue de novo lipogenesis such that mmBCFAs are the most reduced fatty acid species detected and mmBCFA abundance correlates negatively with markers of non‐alcoholic steatohepatitis. These results highlight the origin and regulation of mmBCFAs in mammals, which may play functional roles in metabolic homeostasis, nutrient sensing, and membrane function in human disease.Support or Funding InformationAjinomoto Innovation Alliance Program Grant.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Developmental Defects of Caenorhabditis elegans Lacking Branched-chain α-Ketoacid Dehydrogenase Are Mainly Caused by Monomethyl Branched-chain Fatty Acid Deficiency

Branched-chain α-ketoacid dehydrogenase (BCKDH) catalyzes the critical step in the branched-chain amino acid (BCAA) catabolic pathway and has been the focus of extensive studies. Mutations in the complex disrupt many fundamental metabolic pathways and cause multiple human diseases including maple syrup urine disease (MSUD), autism, and other related neurological disorders. BCKDH may also be required for the synthesis of monomethyl branched-chain fatty acids (mmBCFAs) from BCAAs. The pathology of MSUD has been attributed mainly to BCAA accumulation, but the role of mmBCFA has not been evaluated. Here we show that disrupting BCKDH in Caenorhabditis elegans causes mmBCFA deficiency, in addition to BCAA accumulation. Worms with deficiency in BCKDH function manifest larval arrest and embryonic lethal phenotypes, and mmBCFA supplementation suppressed both without correcting BCAA levels. The majority of developmental defects caused by BCKDH deficiency may thus be attributed to lacking mmBCFAs in worms. Tissue-specific analysis shows that restoration of BCKDH function in multiple tissues can rescue the defects, but is especially effective in neurons. Taken together, we conclude that mmBCFA deficiency is largely responsible for the developmental defects in the worm and conceivably might also be a critical contributor to the pathology of human MSUD.

Intestinal apical polarity mediates regulation of TORC1 by glucosylceramide in C. elegans.

TORC1 (target of rapamycin complex 1) plays a central role in regulating growth, development, and behavior in response to nutrient cues. We previously showed that leucine-derived monomethyl branched-chain fatty acids (mmBCFAs) and derived glucosylceramide promote intestinal TORC1 activity for post-embryonic development and foraging behavior in Caenorhabditis elegans. Here we show that clathrin/adaptor protein 1 (AP-1)-dependent intestinal apical membrane polarity and polarity-dependent localization of the vacuolar-type H(+)-ATPase (V-ATPase) mediate the impact of the lipid pathway on intestinal TORC1 activation. Moreover, NPRL-3 represses mmBCFA-dependent intestinal TORC1 activity at least partly by regulating apical membrane polarity. Our results provide new insights into TORC1 regulation by lipids and membrane polarity in a specific tissue.