SummarySeveral mouse models for mitochondrial fatty acid β-oxidation (FAO) defects have been developed. So far, these models have contributed little to our current understanding of the pathophysiology. The objective of this study was to explore differences between murine and human FAO. Using a combination of analytical, biochemical and molecular methods, we compared fibroblasts of long chain acyl-CoA dehydrogenase knockout (LCAD −/− ), very long chain acyl-CoA dehydrogenase knockout (VLCAD −/− ) and wild type mice with fibroblasts of VLCAD-deficient patients and human controls. We show that in mice, LCAD and VLCAD have overlapping and distinct roles in FAO. The absence of VLCAD is apparently fully compensated, whereas LCAD deficiency is not. LCAD plays an essential role in the oxidation of unsaturated fatty acids such as oleic acid, but seems redundant in the oxidation of saturated fatty acids. In strong contrast, LCAD is neither detectable at the mRNA level nor at the protein level in men, making VLCAD indispensable in FAO. Our findings open new avenues to employ the existing mouse models to study the pathophysiology of human FAO defects.Keywords cellular metabolism; inborn errors of metabolism; fatty acid oxidation; mouse models; long chain acyl-CoA dehydrogenase; very long chain acyl-CoA dehydrogenase

Vaz, McDermott et al. identify variants in PCYT2, which encodes a key gene in phospholipid biosynthesis, in five individuals with a new complex hereditary spastic paraplegia. Functional studies in fibroblasts and a zebrafish model confirm the pathogenic nature of the variants, while lipidomic analysis reveals potential treatment strategies and plasma biomarkers.

Mitochondrial complex I deficiency is the most common oxidative phosphorylation defect. Mutations have been detected in mitochondrial and nuclear genes, but the genetics of many patients remain unresolved and new genes are probably involved. In a consanguineous family, patients presented easy fatigability, exercise intolerance and lactic acidosis in blood from early childhood. In muscle, subsarcolemmal mitochondrial proliferation and a severe complex I deficiency were observed. Exercise intolerance and complex I activity was improved by a supplement of riboflavin at high dosage. Homozygosity mapping revealed a candidate region on chromosome three containing six mitochondria-related genes. Four genes were screened for mutations and a homozygous substitution was identified in ACAD9 (c.1594 C>T), changing the highly conserved arginine-532 into tryptophan. This mutation was absent in 188 ethnically matched controls. Protein modelling suggested a functional effect due to the loss of a stabilizing hydrogen bond in an α-helix and a local flexibility change. To test whether the ACAD9 mutation caused the complex I deficiency, we transduced fibroblasts of patients with wild-type and mutant ACAD9. Wild-type, but not mutant, ACAD9 restored complex I activity. An unrelated patient with the same phenotype was compound heterozygous for c.380 G>A and c.1405 C>T, changing arginine-127 into glutamine and arginine-469 into tryptophan, respectively. These amino acids were highly conserved and the substitutions were not present in controls, making them very probably pathogenic. Our data support a new function for ACAD9 in complex I function, making this gene an important new candidate for patients with complex I deficiency, which could be improved by riboflavin treatment.

SummaryActivation of macrophages by inflammatory stimuli induces reprogramming of mitochondrial metabolism to support the production of pro-inflammatory cytokines and nitric oxide. Hallmarks of this metabolic rewiring are downregulation of α-ketoglutarate formation by isocitrate dehydrogenase (IDH) and accumulation of glutamine-derived succinate, which enhances the inflammatory response via the activity of succinate dehydrogenase (SDH). Here, we identify the nuclear receptor Nur77 (Nr4a1) as a key upstream transcriptional regulator of this pro-inflammatory metabolic switch in macrophages. Nur77-deficient macrophages fail to downregulate IDH expression and accumulate higher levels of succinate and other TCA cycle-derived metabolites in response to inflammatory stimulation in a glutamine-independent manner. Consequently, these macrophages produce more nitric oxide and pro-inflammatory cytokines in an SDH-dependent manner. In vivo, bone marrow Nur77 deficiency exacerbates atherosclerosis development and leads to increased circulating succinate levels. In summary, Nur77 induces an anti-inflammatory metabolic state in macrophages that protects against chronic inflammatory diseases such as atherosclerosis.

BackgroundOver 80% of women with X-linked adrenoleukodystrophy (ALD) develop spinal cord disease in adulthood for which treatment is supportive only. For future clinical trials quantitative data on disease progression rates are essential. Moreover, diagnosis can be challenging in ALD women, as the most important diagnostic biomarker is normal in 15–20%. Better biomarkers are needed. The purpose of this single centre cross-sectional follow-up study in women with ALD was to assess whether Expanded Disability Status Scale (EDSS), AMC Linear Disability Scale (ALDS) and Short Form (36) Health Survey (SF-36) can detect disease progression and to model the effect of age and duration of symptoms on the rate of progression. Moreover, we performed a pilot study to assess if a semi-targeted lipidomics approach can identify possible new diagnostic biomarkers.ResultsIn this study 46 women (baseline clinical data published by our group previously) were invited for a follow-up visit. Newly identified women at our center were also recruited. We analysed 65 baseline and 34 follow-up assessments. Median time between baseline and follow-up was 7.8 years (range 6.4–8.7). Mean age at baseline was 49.2 ± 14.2 years, at follow-up 55.4 ± 10.1. EDSS increased significantly (+ 0.08 points/year), but the other outcome measures did not. Increasing age and duration of symptoms were associated with more disability. For the pilot study we analysed plasma of 20 ALD women and 10 controls with ultra-high performance liquid chromatography coupled to high-resolution mass spectrometry, which identified 100 potential biomarker ratios with strong differentiating properties and non-overlapping data distributions between ALD women and controls.ConclusionsProgression of spinal cord disease can be detected with EDSS, but not with ALDS or SF-36 after a follow-up period of almost 8 years. Moreover, age and the duration of symptoms seem positively associated with the rate of progression. Although a significant progression was measurable, it was below the rate generally conceived as clinically relevant. Therefore, EDSS, ALDS and SF-36 are not suitable as primary outcome measures in clinical trials for spinal cord disease in ALD women. In addition, a semi-targeted lipidomics approach can identify possible new diagnostic biomarkers for women with ALD.Electronic supplementary materialThe online version of this article (10.1186/s13023-019-1008-6) contains supplementary material, which is available to authorized users.

Slowing down mRNA translation in either the cytoplasm or the mitochondria are conserved longevity mechanisms. Here, we found a non-interventional natural correlation of mitochondrial and cytoplasmic ribosomal proteins (RPs) in mouse population genetics, suggesting a translational balance between these two compartments. Inhibiting mitochondrial translation in C. elegans through mrps-5 RNAi repressed overall cytoplasmic translation. Transcriptomics integrated with proteomics revealed that this inhibition specifically reduced the translational efficiency (TE) of mRNAs required in growth pathways while increasing the TE of stress response mRNAs. The coordinated repression of cytoplasmic translation is dependent on atf-5/Atf4 and is conserved in mammalian cells upon inhibiting mitochondrial translation pharmacologically with the antibiotic doxycycline. Lastly, extending this in vivo, doxycycline repressed cytoplasmic translation and RP expression in the livers of germ-free mice. These data demonstrate that inhibiting mitochondrial translation initiates an atf-5/Atf4-dependent cascade leading to coordinated repression of cytoplasmic translation, which could be targeted to promote longevity. Keywords longevity / ribosomes / mitochondrial translation / cytoplasmic translation / translational balance Highlights • Mitochondrial and cytoplasmic RP levels balance in a natural stoichiometric ratio • Blocking mitochondrial ribosomes in worms and mice reduces cytoplasmic translation • This translational balance is ATF4/atf-5 dependent and conserved in human cells • Translational efficiency of RP transcripts changes in response to ratio requirement

Macrophages represent a major immune cell population in atherosclerotic plaques and play central role in the progression of this lipid-driven chronic inflammatory disease. Targeting immunometabolism is proposed as a strategy to revert aberrant macrophage activation to improve disease outcome. Here, we show ATP citrate lyase (Acly) to be activated in inflammatory macrophages and human atherosclerotic plaques. We demonstrate that myeloid Acly deficiency induces a stable plaque phenotype characterized by increased collagen deposition and fibrous cap thickness, along with a smaller necrotic core. In-depth functional, lipidomic, and transcriptional characterization indicate deregulated fatty acid and cholesterol biosynthesis and reduced liver X receptor activation within the macrophages in vitro. This results in macrophages that are more prone to undergo apoptosis, whilst maintaining their capacity to phagocytose apoptotic cells. Together, our results indicate that targeting macrophage metabolism improves atherosclerosis outcome and we reveal Acly as a promising therapeutic target to stabilize atherosclerotic plaques.

Background-Lipotoxicity may be a key contributor to the pathogenesis of cardiac abnormalities in mitochondrial long-chain fatty acid ␤-oxidation (FAO) disorders. Few data are available on myocardial lipid levels and cardiac performance in FAO deficiencies. The purpose of this animal study is to assess fasting-induced changes in cardiac morphology, function, and triglyceride (TG) storage as a consequence of FAO deficiency in a noninvasive fashion. Methods and Results-MRI and proton magnetic resonance spectroscopy ( 1 H-MRS) were applied in vivo in long-chain acyl-CoA dehydrogenase (LCAD) knockout (KO) mice and wild-type (WT) mice (nϭ8 per genotype). Fasting was used to increase the heart's dependency on FAO for maintenance of energy homeostasis. In vivo data were complemented with ex vivo measurements of myocardial lipids. Left ventricular (LV) mass was higher in LCAD KO mice compared with WT mice (PϽ0.05), indicating LV myocardial hypertrophy. Myocardial TG content was higher in LCAD KO mice at baseline (PϽ0.001) and further increased in fasted LCAD KO mice (PϽ0.05). Concomitantly, LV ejection fraction (PϽ0.01) and diastolic filling rate (PϽ0.01) decreased after fasting, whereas these functional parameters did not change in fasted WT mice. Myocardial ceramide content was higher in fasted LCAD KO mice compared with fasted WT mice (PϽ0.05). Conclusions-Using