The unique catalytic properties of PSAT1 mediate metabolic adaptation to glutamine blockade.

Cultured cancer cells frequently rely on the consumption of glutamine and its subsequent hydrolysis by glutaminase (GLS). However, this metabolic addiction can be lost in the tumour microenvironment, rendering GLS inhibitors ineffective in the clinic. Here we show that glutamine-addicted breast cancer cells adapt to chronic glutamine starvation, or GLS inhibition, via AMPK-mediated upregulation of the serine synthesis pathway (SSP). In this context, the key product of the SSP is not serine, but α-ketoglutarate (α-KG). Mechanistically, we find that phosphoserine aminotransferase 1 (PSAT1) has a unique capacity for sustained α-KG production when glutamate is depleted. Breast cancer cells with resistance to glutamine starvation or GLS inhibition are highly dependent on SSP-supplied α-KG. Accordingly, inhibition of the SSP prevents adaptation to glutamine blockade, resulting in a potent drug synergism that suppresses breast tumour growth. These findings highlight how metabolic redundancy can be context dependent, with the catalytic properties of different metabolic enzymes that act on the same substrate determining which pathways can support tumour growth in a particular nutrient environment. This, in turn, has practical consequences for therapies targeting cancer metabolism.

Characterization, Structure, and Inhibition of the Human Succinyl-CoA:glutarate-CoA Transferase, a Putative Genetic Modifier of Glutaric Aciduria Type 1.

Glutaric Aciduria Type 1 (GA1) is a serious inborn error of metabolism with no pharmacological treatments. A novel strategy to treat this disease is to divert the toxic biochemical intermediates to less toxic or nontoxic metabolites. Here, we report a putative novel target, succinyl-CoA:glutarate-CoA transferase (SUGCT), which we hypothesize suppresses the GA1 metabolic phenotype through decreasing glutaryl-CoA and the derived 3-hydroxyglutaric acid. SUGCT is a type III CoA transferase that uses succinyl-CoA and glutaric acid as substrates. We report the structure of SUGCT, develop enzyme- and cell-based assays, and identify valsartan and losartan carboxylic acid as inhibitors of the enzyme in a high-throughput screen of FDA-approved compounds. The cocrystal structure of SUGCT with losartan carboxylic acid revealed a novel pocket in the active site and further validated the high-throughput screening approach. These results may form the basis for the future development of new pharmacological intervention to treat GA1.

Characterization, structure and inhibition of the human succinyl-CoA:glutarate-CoA transferase, a genetic modifier of glutaric aciduria type 1.

Glutaric Aciduria Type 1 (GA1) is a serious inborn error of metabolism with no pharmacological treatments. A novel strategy to treat this disease is to divert the toxic biochemical intermediates to less toxic or non-toxic metabolites. Here, we report a novel target, SUGCT, which we hypothesize suppresses the GA1 metabolic phenotype through decreasing glutaryl-CoA. We report the structure of SUGCT, the first eukaryotic structure of a type III CoA transferase, develop a high-throughput enzyme assay and a cell-based assay, and identify valsartan and losartan carboxylic acid as inhibitors of the enzyme validating the screening approach. These results may form the basis for future development of new pharmacological intervention to treat GA1.

A genetically encoded tool to increase cellular NADH/NAD+ ratio in living cells.

Impaired redox metabolism is a key contributor to the etiology of many diseases, including primary mitochondrial disorders, cancer, neurodegeneration and aging. However, mechanistic studies of redox imbalance remain challenging due to limited strategies that can perturb redox metabolism in various cellular or organismal backgrounds. Most studies involving impaired redox metabolism have focused on oxidative stress; consequently, less is known about the settings where there is an overabundance of NADH reducing equivalents, termed reductive stress. Here we introduce a soluble transhydrogenase from Escherichia coli (EcSTH) as a novel genetically encoded tool to promote reductive stress in living cells. When expressed in mammalian cells, EcSTH, and a mitochondrially targeted version (mitoEcSTH), robustly elevated the NADH/NAD+ ratio in a compartment-specific manner. Using this tool, we determined that metabolic and transcriptomic signatures of the NADH reductive stress are cellular background specific. Collectively, our novel genetically encoded tool represents an orthogonal strategy to promote reductive stress.

Mouse sperm energy restriction and recovery (SER) revealed novel metabolic pathways.

Mammalian sperm must undergo capacitation to become fertilization-competent. While working on mice, we recently developed a new methodology for treating sperm in vitro, which results in higher rates of fertilization and embryo development after in vitro fertilization. Sperm incubated in media devoid of nutrients lose motility, although they remain viable. Upon re-adding energy substrates, sperm resume motility and become capacitated with improved functionality. Here, we explore how sperm energy restriction and recovery (SER) treatment affects sperm metabolism and capacitation-associated signaling. Using extracellular flux analysis and metabolite profiling and tracing via nuclear magnetic resonance (NMR) and mass spectrometry (MS), we found that the levels of many metabolites were altered during the starvation phase of SER. Of particular interest, two metabolites, AMP and L-carnitine, were significantly increased in energy-restricted sperm. Upon re-addition of glucose and initiation of capacitation, most metabolite levels recovered and closely mimic the levels observed in capacitating sperm that have not undergone starvation. In both control and SER-treated sperm, incubation under capacitating conditions upregulated glycolysis and oxidative phosphorylation. However, ATP levels were diminished, presumably reflecting the increased energy consumption during capacitation. Flux data following the fate of 13C glucose indicate that, similar to other cells with high glucose consumption rates, pyruvate is converted into 13C-lactate and, with lower efficiency, into 13C-acetate, which are then released into the incubation media. Furthermore, our metabolic flux data show that exogenously supplied glucose is converted into citrate, providing evidence that in sperm cells, as in somatic cells, glycolytic products can be converted into Krebs cycle metabolites.

Capacitation induces changes in metabolic pathways supporting motility of epididymal and ejaculated sperm.

Mammalian sperm require sufficient energy to support motility and capacitation for successful fertilization. Previous studies cataloging the changes to metabolism in sperm explored ejaculated human sperm or dormant mouse sperm surgically extracted from the cauda epididymis. Due to the differences in methods of collection, it remains unclear whether any observed differences between mouse and human sperm represent species differences or reflect the distinct maturation states of the sperm under study. Here we compare the metabolic changes during capacitation of epididymal versus ejaculated mouse sperm and relate these changes to ejaculated human sperm. Using extracellular flux analysis and targeted metabolic profiling, we show that capacitation-induced changes lead to increased flux through both glycolysis and oxidative phosphorylation in mouse and human sperm. Ejaculation leads to greater flexibility in the ability to use different carbon sources. While epididymal sperm are dependent upon glucose, ejaculated mouse and human sperm gain the ability to also leverage non-glycolytic energy sources such as pyruvate and citrate.

Distinct metabolic requirements regulate B cell activation and germinal center responses.

Following infection or vaccination, activated B cells at extrafollicular sites or within germinal centers (GCs) undergo vigorous clonal proliferation. Proliferating lymphocytes have been shown to undertake lactate dehydrogenase A (LDHA)-dependent aerobic glycolysis; however, the specific role of this metabolic pathway in a B cell transitioning from a naïve to a highly proliferative, activated state remains poorly defined. Here, we deleted LDHA in a stage-specific and cell-specific manner. We find that ablation of LDHA in a naïve B cell did not profoundly affect its ability to undergo a bacterial lipopolysaccharide-induced extrafollicular B cell response. On the other hand, LDHA-deleted naïve B cells had a severe defect in their capacities to form GCs and mount GC-dependent antibody responses. In addition, loss of LDHA in T cells severely compromised B cell-dependent immune responses. Strikingly, when LDHA was deleted in activated, as opposed to naïve, B cells, there were only minimal effects on the GC reaction and in the generation of high-affinity antibodies. These findings strongly suggest that naïve and activated B cells have distinct metabolic requirements that are further regulated by niche and cellular interactions.

Acyl-CoA dehydrogenase substrate promiscuity: Challenges and opportunities for development of substrate reduction therapy in disorders of valine and isoleucine metabolism.

Toxicity of accumulating substrates is a significant problem in several disorders of valine and isoleucine degradation notably short-chain enoyl-CoA hydratase (ECHS1 or crotonase) deficiency, 3-hydroxyisobutyryl-CoA hydrolase (HIBCH) deficiency, propionic acidemia (PA), and methylmalonic aciduria (MMA). Isobutyryl-CoA dehydrogenase (ACAD8) and short/branched-chain acyl-CoA dehydrogenase (SBCAD, ACADSB) function in the valine and isoleucine degradation pathways, respectively. Deficiencies of these acyl-CoA dehydrogenase (ACAD) enzymes are considered biochemical abnormalities with limited or no clinical consequences. We investigated whether substrate reduction therapy through inhibition of ACAD8 and SBCAD can limit the accumulation of toxic metabolic intermediates in disorders of valine and isoleucine metabolism. Using analysis of acylcarnitine isomers, we show that 2-methylenecyclopropaneacetic acid (MCPA) inhibited SBCAD, isovaleryl-CoA dehydrogenase, short-chain acyl-CoA dehydrogenase and medium-chain acyl-CoA dehydrogenase, but not ACAD8. MCPA treatment of wild-type and PA HEK-293 cells caused a pronounced decrease in C3-carnitine. Furthermore, deletion of ACADSB in HEK-293 cells led to an equally strong decrease in C3-carnitine when compared to wild-type cells. Deletion of ECHS1 in HEK-293 cells caused a defect in lipoylation of the E2 component of the pyruvate dehydrogenase complex, which was not rescued by ACAD8 deletion. MCPA was able to rescue lipoylation in ECHS1 KO cells, but only in cells with prior ACAD8 deletion. SBCAD was not the sole ACAD responsible for this compensation, which indicates substantial promiscuity of ACADs in HEK-293 cells for the isobutyryl-CoA substrate. Substrate promiscuity appeared less prominent for 2-methylbutyryl-CoA at least in HEK-293 cells. We suggest that pharmacological inhibition of SBCAD to treat PA should be investigated further.

MAIT and Vδ2 unconventional T cells are supported by a diverse intestinal microbiome and correlate with favorable patient outcome after allogeneic HCT.

Microbial diversity is associated with improved outcomes in recipients of allogeneic hematopoietic cell transplantation (allo-HCT), but the mechanism underlying this observation is unclear. In a cohort of 174 patients who underwent allo-HCT, we demonstrate that a diverse intestinal microbiome early after allo-HCT is associated with an increased number of innate-like mucosal-associated invariant T (MAIT) cells, which are in turn associated with improved overall survival and less acute graft-versus-host disease (aGVHD). Immune profiling of conventional and unconventional immune cell subsets revealed that the prevalence of Vδ2 cells, the major circulating subpopulation of γδ T cells, closely correlated with the frequency of MAIT cells and was associated with less aGVHD. Analysis of these populations using both single-cell transcriptomics and flow cytometry suggested a shift toward activated phenotypes and a gain of cytotoxic and effector functions after transplantation. A diverse intestinal microbiome with the capacity to produce activating ligands for MAIT and Vδ2 cells appeared to be necessary for the maintenance of these populations after allo-HCT. These data suggest an immunological link between intestinal microbial diversity, microbe-derived ligands, and maintenance of unconventional T cells.

MYC-mediated early glycolysis negatively regulates proinflammatory responses by controlling IRF4 in inflammatory macrophages.

MYC activates different metabolic programs in a cell-type- and cell-status-dependent manner. However, the role of MYC in inflammatory macrophages has not yet been determined. Metabolic and molecular analyses reveal that MYC, but not hypoxia inducible factor 1 (HIF1), is involved in enhancing early glycolytic flux during inflammatory macrophage polarization. Ablation of MYC decreases lactate production by regulating lactate dehydrogenase (LDH) activity and causes increased inflammatory cytokines by regulating interferon regulatory factor 4 (IRF4) in response to lipopolysaccharide. Moreover, myeloid-specific deletion of MYC and pharmacological inhibition of the MYC/LDH axis enhance inflammation and the bacterial clearance in vivo. These results elucidate the potential role of the MYC/LDH/IRF4 axis in inflammatory macrophages by connecting early glycolysis with inflammatory responses and suggest that modulating early glycolytic flux mediated by the MYC/LDH axis can be used to open avenues for the therapeutic modulation of macrophage polarization to fight against bacterial infection.

Murine deficiency of peroxisomal L-bifunctional protein (EHHADH) causes medium-chain 3-hydroxydicarboxylic aciduria and perturbs hepatic cholesterol homeostasis.

Peroxisomes play an essential role in the ß-oxidation of dicarboxylic acids (DCAs), which are metabolites formed upon ω-oxidation of fatty acids. Genetic evidence linking transporters and enzymes to specific DCA ß-oxidation steps is generally lacking. Moreover, the physiological functions of DCA metabolism remain largely unknown. In this study, we aimed to characterize the DCA ß-oxidation pathway in human cells, and to evaluate the biological role of DCA metabolism using mice deficient in the peroxisomal L-bifunctional protein (Ehhadh KO mice). In vitro experiments using HEK-293 KO cell lines demonstrate that ABCD3 and ACOX1 are essential in DCA ß-oxidation, whereas both the bifunctional proteins (EHHADH and HSD17B4) and the thiolases (ACAA1 and SCPx) have overlapping functions and their contribution may depend on expression level. We also show that medium-chain 3-hydroxydicarboxylic aciduria is a prominent feature of EHHADH deficiency in mice most notably upon inhibition of mitochondrial fatty acid oxidation. Using stable isotope tracing methodology, we confirmed that products of peroxisomal DCA ß-oxidation can be transported to mitochondria for further metabolism. Finally, we show that, in liver, Ehhadh KO mice have increased mRNA and protein expression of cholesterol biosynthesis enzymes with decreased (in females) or similar (in males) rate of cholesterol synthesis. We conclude that EHHADH plays an essential role in the metabolism of medium-chain DCAs and postulate that peroxisomal DCA ß-oxidation is a regulator of hepatic cholesterol biosynthesis.

Lactate dehydrogenase A-dependent aerobic glycolysis promotes natural killer cell anti-viral and anti-tumor function.

Natural killer (NK) cells are cytotoxic lymphocytes capable of rapid cytotoxicity, cytokine secretion, and clonal expansion. To sustain such energetically demanding processes, NK cells must increase their metabolic capacity upon activation. However, little is known about the metabolic requirements specific to NK cells in vivo. To gain greater insight, we investigated the role of aerobic glycolysis in NK cell function and demonstrate that their glycolytic rate increases rapidly following viral infection and inflammation, prior to that of CD8+ T cells. NK cell-specific deletion of lactate dehydrogenase A (LDHA) reveals that activated NK cells rely on this enzyme for both effector function and clonal proliferation, with the latter being shared with T cells. As a result, LDHA-deficient NK cells are defective in their anti-viral and anti-tumor protection. These findings suggest that aerobic glycolysis is a hallmark of NK cell activation that is key to their function.

Translation in amino-acid-poor environments is limited by tRNAGln charging.

An inadequate supply of amino acids leads to accumulation of uncharged tRNAs, which can bind and activate GCN2 kinase to reduce translation. Here, we show that glutamine-specific tRNAs selectively become uncharged when extracellular amino acid availability is compromised. In contrast, all other tRNAs retain charging of their cognate amino acids in a manner that is dependent upon intact lysosomal function. In addition to GCN2 activation and reduced total translation, the reduced charging of tRNAGln in amino-acid-deprived cells also leads to specific depletion of proteins containing polyglutamine tracts including core-binding factor α1, mediator subunit 12, transcriptional coactivator CBP and TATA-box binding protein. Treating amino-acid-deprived cells with exogenous glutamine or glutaminase inhibitors restores tRNAGln charging and the levels of polyglutamine-containing proteins. Together, these results demonstrate that the activation of GCN2 and the translation of polyglutamine-encoding transcripts serve as key sensors of glutamine availability in mammalian cells.

Bacterial metabolism of bile acids promotes generation of peripheral regulatory T cells.

Intestinal health relies on the immunosuppressive activity of CD4+ regulatory T (Treg) cells1. Expression of the transcription factor Foxp3 defines this lineage, and can be induced extrathymically by dietary or commensal-derived antigens in a process assisted by a Foxp3 enhancer known as conserved non-coding sequence 1 (CNS1)2-4. Products of microbial fermentation including butyrate facilitate the generation of peripherally induced Treg (pTreg) cells5-7, indicating that metabolites shape the composition of the colonic immune cell population. In addition to dietary components, bacteria modify host-derived molecules, generating a number of biologically active substances. This is epitomized by the bacterial transformation of bile acids, which creates a complex pool of steroids8 with a range of physiological functions9. Here we screened the major species of deconjugated bile acids for their ability to potentiate the differentiation of pTreg cells. We found that the secondary bile acid 3ß-hydroxydeoxycholic acid (isoDCA) increased Foxp3 induction by acting on dendritic cells (DCs) to diminish their immunostimulatory properties. Ablating one receptor, the farnesoid X receptor, in DCs enhanced the generation of Treg cells and imposed a transcriptional profile similar to that induced by isoDCA, suggesting an interaction between this bile acid and nuclear receptor. To investigate isoDCA in vivo, we took a synthetic biology approach and designed minimal microbial consortia containing engineered Bacteroides strains. IsoDCA-producing consortia increased the number of colonic RORγt-expressing Treg cells in a CNS1-dependent manner, suggesting enhanced extrathymic differentiation.

Proline biosynthesis is a vent for TGFß-induced mitochondrial redox stress.

The production and secretion of matrix proteins upon stimulation of fibroblasts by transforming growth factor-beta (TGFß) play a critical role in wound healing. How TGFß supports the bioenergetic cost of matrix protein synthesis is not fully understood. Here, we show that TGFß promotes protein translation at least in part by increasing the mitochondrial oxidation of glucose and glutamine carbons to support the bioenergetic demand of translation. Surprisingly, we found that in addition to stimulating the entry of glucose and glutamine carbon into the TCA cycle, TGFß induced the biosynthesis of proline from glutamine in a Smad4-dependent fashion. Metabolic manipulations that increased mitochondrial redox generation promoted proline biosynthesis, while reducing mitochondrial redox potential and/or ATP synthesis impaired proline biosynthesis. Thus, proline biosynthesis acts as a redox vent, preventing the TGFß-induced increase in mitochondrial glucose and glutamine catabolism from generating damaging reactive oxygen species (ROS) when TCA cycle activity exceeds the ability of oxidative phosphorylation to convert mitochondrial redox potential into ATP. In turn, the enhanced synthesis of proline supports TGFß-induced production of matrix proteins.

Vitamin B6 Addiction in Acute Myeloid Leukemia.

Cancer cells rely on altered metabolism to support abnormal proliferation. We performed a CRISPR/Cas9 functional genomic screen targeting metabolic enzymes and identified PDXK-an enzyme that produces pyridoxal phosphate (PLP) from vitamin B6-as an acute myeloid leukemia (AML)-selective dependency. PDXK kinase activity is required for PLP production and AML cell proliferation, and pharmacological blockade of the vitamin B6 pathway at both PDXK and PLP levels recapitulated PDXK disruption effects. PDXK disruption reduced intracellular concentrations of key metabolites needed for cell division. Furthermore, disruption of PLP-dependent enzymes ODC1 or GOT2 selectively inhibited AML cell proliferation and their downstream products partially rescued PDXK disruption induced proliferation blockage. Our work identifies the vitamin B6 pathway as a pharmacologically actionable dependency in AML.

Stable Isotope Tracers for Metabolic Pathway Analysis.

Stable isotope tracing allows a metabolic substrate to be followed through downstream biochemical reactions, thereby providing unparalleled insights into the metabolic wiring of cells. This approach stops short of modeling absolute fluxes but is relatively straightforward and has become increasingly accessible due to the widespread adoption of high-resolution mass spectrometers. Analysis of both dynamic and steady-state labeling patterns in downstream metabolites provides valuable qualitative information as to their origin and relative rates of production. Stable isotope tracing is, therefore, a powerful way to understand the impact of genetic alterations and defined perturbations on metabolism. In this chapter, we describe a liquid chromatography-mass spectrometry (LC-MS) protocol for stable isotope tracing using 13C-L-arginine in a macrophage cell line. A similar approach can be used to follow other stable isotope tracers, and notes are provided with advice on how this protocol can be generalized for use in other settings.

Mild inborn errors of metabolism in commonly used inbred mouse strains.

Inbred mouse strains are a cornerstone of translational research but paradoxically many strains carry mild inborn errors of metabolism. For example, α-aminoadipic acidemia and branched-chain ketoacid dehydrogenase deficiency are known in C57BL/6J mice. Using RNA sequencing, we now reveal the causal variants in Dhtkd1 and Bckdhb, and the molecular mechanism underlying these metabolic defects. C57BL/6J mice have decreased Dhtkd1 mRNA expression due to a solitary long terminal repeat (LTR) in intron 4 of Dhtkd1. This LTR harbors an alternate splice donor site leading to a partial splicing defect and as a consequence decreased total and functional Dhtkd1 mRNA, decreased DHTKD1 protein and α-aminoadipic acidemia. Similarly, C57BL/6J mice have decreased Bckdhb mRNA expression due to an LTR retrotransposon in intron 1 of Bckdhb. This transposable element encodes an alternative exon 1 causing aberrant splicing, decreased total and functional Bckdhb mRNA and decreased BCKDHB protein. Using a targeted metabolomics screen, we also reveal elevated plasma C5-carnitine in 129 substrains. This biochemical phenotype resembles isovaleric acidemia and is caused by an exonic splice mutation in Ivd leading to partial skipping of exon 10 and IVD protein deficiency. In summary, this study identifies three causal variants underlying mild inborn errors of metabolism in commonly used inbred mouse strains.

PLPHP deficiency: clinical, genetic, biochemical, and mechanistic insights.

Biallelic pathogenic variants in PLPBP (formerly called PROSC) have recently been shown to cause a novel form of vitamin B6-dependent epilepsy, the pathophysiological basis of which is poorly understood. When left untreated, the disease can progress to status epilepticus and death in infancy. Here we present 12 previously undescribed patients and six novel pathogenic variants in PLPBP. Suspected clinical diagnoses prior to identification of PLPBP variants included mitochondrial encephalopathy (two patients), folinic acid-responsive epilepsy (one patient) and a movement disorder compatible with AADC deficiency (one patient). The encoded protein, PLPHP is believed to be crucial for B6 homeostasis. We modelled the pathogenicity of the variants and developed a clinical severity scoring system. The most severe phenotypes were associated with variants leading to loss of function of PLPBP or significantly affecting protein stability/PLP-binding. To explore the pathophysiology of this disease further, we developed the first zebrafish model of PLPHP deficiency using CRISPR/Cas9. Our model recapitulates the disease, with plpbp-/- larvae showing behavioural, biochemical, and electrophysiological signs of seizure activity by 10 days post-fertilization and early death by 16 days post-fertilization. Treatment with pyridoxine significantly improved the epileptic phenotype and extended lifespan in plpbp-/- animals. Larvae had disruptions in amino acid metabolism as well as GABA and catecholamine biosynthesis, indicating impairment of PLP-dependent enzymatic activities. Using mass spectrometry, we observed significant B6 vitamer level changes in plpbp-/- zebrafish, patient fibroblasts and PLPHP-deficient HEK293 cells. Additional studies in human cells and yeast provide the first empirical evidence that PLPHP is localized in mitochondria and may play a role in mitochondrial metabolism. These models provide new insights into disease mechanisms and can serve as a platform for drug discovery.

Peroxisomes can oxidize medium- and long-chain fatty acids through a pathway involving ABCD3 and HSD17B4.

Peroxisomes are essential organelles for the specialized oxidation of a wide variety of fatty acids, but they are also able to degrade fatty acids that are typically handled by mitochondria. Using a combination of pharmacological inhibition and clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR associated protein 9 genome editing technology to simultaneously manipulate peroxisomal and mitochondrial fatty acid ß-oxidation (FAO) in HEK-293 cells, we identified essential players in the metabolic crosstalk between these organelles. Depletion of carnitine palmitoyltransferase (CPT)2 activity through pharmacological inhibition or knockout (KO) uncovered a significant residual peroxisomal oxidation of lauric and palmitic acid, leading to the production of peroxisomal acylcarnitine intermediates. Generation and analysis of additional single- and double-KO cell lines revealed that the D-bifunctional protein (HSD17B4) and the peroxisomal ABC transporter ABCD3 are essential in peroxisomal oxidation of lauric and palmitic acid. Our results indicate that peroxisomes not only accept acyl-CoAs but can also oxidize acylcarnitines in a similar biochemical pathway. By using an Hsd17b4 KO mouse model, we demonstrated that peroxisomes contribute to the plasma acylcarnitine profile after acute inhibition of CPT2, proving in vivo relevance of this pathway. We summarize that peroxisomal FAO is important when mitochondrial FAO is defective or overloaded.-Violante, S., Achetib, N., van Roermund, C. W. T., Hagen, J., Dodatko, T., Vaz, F. M., Waterham, H. R., Chen, H., Baes, M., Yu, C., Argmann, C. A., Houten, S. M. Peroxisomes can oxidize medium- and long-chain fatty acids through a pathway involving ABCD3 and HSD17B4.