Lipid-induced endoplasmic reticulum stress in X-linked adrenoleukodystrophy.

X-linked adrenoleukodystrophy (ALD) is a progressive neurodegenerative disease that is caused by mutations in the ABCD1 gene and characterized by elevated levels of very long-chain fatty acids (VLCFA) in plasma and tissues, with the most pronounced increase in the central nervous system. Virtually all male patients develop adrenal insufficiency and myelopathy (adrenomyeloneuropathy), but a subset develops a fatal cerebral demyelinating disease (known as cerebral ALD). Female patients may also develop myelopathy, but adrenal insufficiency or leukodystrophy are very rare. ALD has been associated with mitochondrial dysfunction, oxidative stress and bioenergetic failure, but the mechanism by which VLCFA accumulation triggers these effects has not been resolved thus far. In this study, we used primary human fibroblasts from normal subjects and ALD patients to investigate whether VLCFA can induce endoplasmic reticulum stress. We show that saturated VLCFA (C26:0) induce endoplasmic reticulum stress in fibroblasts from ALD patients, but not in controls. Furthermore, there is a clear correlation between the chain-length of the fatty acid and the induction of endoplasmic reticulum stress. Exposure of ALD fibroblasts to C26:0, resulted in increased expression of additional endoplasmic reticulum stress markers (EDEM1, GADD34 and CHOP) and in lipoapoptosis. This new insight into the underlying mechanism of VLCFA-induced toxicity is of great importance for the development of a disease modifying treatment for ALD aimed at the normalization of VLCFA levels in tissues.

Comparison of C26:0-carnitine and C26:0-lysophosphatidylcholine as diagnostic markers in dried blood spots from newborns and patients with adrenoleukodystrophy.

X-linked adrenoleukodystrophy (ALD) is the most common leukodystrophy with a birth incidence of 1:14,700 live births. The disease is caused by mutations in ABCD1 and characterized by very long-chain fatty acids (VLCFA) accumulation. In childhood, male patients are at high-risk to develop adrenal insufficiency and/or cerebral demyelination. Timely diagnosis is essential. Untreated adrenal insufficiency can be life-threatening and hematopoietic stem cell transplantation is curative for cerebral ALD provided the procedure is performed in an early stage of the disease. For this reason, ALD is being added to an increasing number of newborn screening programs. ALD newborn screening involves the quantification of C26:0-lysoPC in dried blood spots which requires a dedicated method. C26:0-carnitine, that was recently identified as a potential new biomarker for ALD, has the advantage that it can be added as one more analyte to the routine analysis of amino acids and acylcarnitines already in use. The first objective of this study was a comparison of the sensitivity of C26:0-carnitine and C26:0-lysoPC in dried blood spots from control and ALD newborns both in a case-control study and in newborns included in the New York State screening program. While C26:0-lysoPC was elevated in all ALD newborns, C26:0-carnitine was elevated only in 83%. Therefore, C26:0-carnitine is not a suitable biomarker to use in ALD newborn screen. In women with ALD, plasma VLCFA analysis results in a false negative result in approximately 15-20% of cases. The second objective of this study was to compare plasma VLCFA analysis with C26:0-carnitine and C26:0-lysoPC in dried blood spots of women with ALD. Our results show that C26:0-lysoPC was elevated in dried blood spots from all women with ALD, including from those with normal plasma C26:0 levels. This shows that C26:0-lysoPC is a better and more accurate biomarker for ALD than plasma VLCFA levels. We recommend that C26:0-lysoPC be added to the routine biochemical array of diagnostic tests for peroxisomal disorders.

Metabolic rerouting via SCD1 induction impacts X-linked adrenoleukodystrophy.

X-linked adrenoleukodystrophy (ALD) is a progressive neurodegenerative disease caused by mutations in ABCD1, the peroxisomal very long-chain fatty acid (VLCFA) transporter. ABCD1 deficiency results in accumulation of saturated VLCFAs. A drug screen using a phenotypic motor assay in a zebrafish ALD model identified chloroquine as the top hit. Chloroquine increased expression of stearoyl-CoA desaturase-1 (scd1), the enzyme mediating fatty acid saturation status, suggesting that a shift toward monounsaturated fatty acids relieved toxicity. In human ALD fibroblasts, chloroquine also increased SCD1 levels and reduced saturated VLCFAs. Conversely, pharmacological inhibition of SCD1 expression led to an increase in saturated VLCFAs, and CRISPR knockout of scd1 in zebrafish mimicked the motor phenotype of ALD zebrafish. Importantly, saturated VLCFAs caused ER stress in ALD fibroblasts, whereas monounsaturated VLCFA did not. In parallel, we used liver X receptor (LXR) agonists to increase SCD1 expression, causing a shift from saturated toward monounsaturated VLCFA and normalizing phospholipid profiles. Finally, Abcd1-/y mice receiving LXR agonist in their diet had VLCFA reductions in ALD-relevant tissues. These results suggest that metabolic rerouting of saturated to monounsaturated VLCFAs may alleviate lipid toxicity, a strategy that may be beneficial in ALD and other peroxisomal diseases in which VLCFAs play a key role.

Adult mouse eIF2Bε Arg191His astrocytes display a normal integrated stress response in vitro.

Vanishing white matter (VWM) is a genetic childhood white matter disorder, characterized by chronic as well as episodic, stress provoked, neurological deterioration. Treatment is unavailable and patients often die within a few years after onset. VWM is caused by recessive mutations in the eukaryotic initiation factor 2B (eIF2B). eIF2B regulates protein synthesis rates in every cell of the body. In normal cells, various types of cellular stress inhibit eIF2B activity and induce the integrated stress response (ISR). We have developed a VWM mouse model homozygous for the pathogenic Arg191His mutation in eIF2Bε (2b5 ho ), representative of the human disease. Neuropathological examination of VWM patient and mouse brain tissue suggests that astrocytes are primarily affected. We hypothesized that VWM astrocytes are selectively hypersensitive to ISR induction, resulting in a heightened response. We cultured astrocytes from wildtype and VWM mice and investigated the ISR in assays that measure transcriptional induction of stress genes, protein synthesis rates and cell viability. We investigated the effects of short- and long-term stress as well as stress recovery. We detected congruent results amongst the various assays and did not detect a hyperactive ISR in VWM mouse astrocytes.

Method for Measurement of Peroxisomal Very Long-Chain Fatty Acid Beta-Oxidation and De Novo C26:0 Synthesis Activity in Living Cells Using Stable-Isotope Labeled Docosanoic Acid.

Peroxisomes are present in virtually every eukaryotic cell type with the exception of the mature erythrocyte. In higher eukaryotes, one of the main functions of peroxisomes is lipid metabolism by means of beta-oxidation of very long-chain fatty acids (VLCFA; ≥22 carbon atoms). A dysfunction in peroxisomal VLCFA beta-oxidation results in elevated VLCFA levels in cells, tissue, and plasma. Here, we describe a straightforward and sensitive method to measure peroxisomal beta-oxidation capacity in living cells using stable-isotope labeled docosanoic acid (D3-C22:0).

C26:0-Carnitine Is a New Biomarker for X-Linked Adrenoleukodystrophy in Mice and Man.

X-linked adrenoleukodystrophy (ALD), a progressive neurodegenerative disease, is caused by mutations in ABCD1 and characterized by very-long-chain fatty acids (VLCFA) accumulation. Virtually all males develop progressive myelopathy (AMN). A subset of patients, however, develops a fatal cerebral demyelinating disease (cerebral ALD). Hematopoietic stem cell transplantation is curative for cerebral ALD provided the procedure is performed in an early stage of the disease. Unfortunately, this narrow therapeutic window is often missed. Therefore, an increasing number of newborn screening programs are including ALD. To identify new biomarkers for ALD, we developed an Abcd1 knockout mouse with enhanced VLCFA synthesis either ubiquitous or restricted to oligodendrocytes. Biochemical analysis revealed VLCFA accumulation in different lipid classes and acylcarnitines. Both C26:0-lysoPC and C26:0-carnitine were highly elevated in brain, spinal cord, but also in bloodspots. We extended the analysis to patients and confirmed that C26:0-carnitine is also elevated in bloodspots from ALD patients. We anticipate that validation of C26:0-carnitine for the diagnosis of ALD in newborn bloodspots may lead to a faster inclusion of ALD in newborn screening programs in countries that already screen for other inborn errors of metabolism.