LC-MS Based Platform Simplifies Access to Metabolomics for Peroxisomal Disorders

Peroxisomes are central hubs for cell metabolism and their dysfunction is linked to devastating human disorders, such as peroxisomal biogenesis disorders and single peroxisomal enzyme/protein deficiencies. For decades, biochemical diagnostics have been carried out using classical markers such as very long-chain fatty acids (VLCFA), which can be inconspicuous in milder and atypical cases. Holistic metabolomics studies revealed several potentially new biomarkers for peroxisomal disorders for advanced laboratory diagnostics including atypical cases. However, establishing these new markers is a major challenge in routine diagnostic laboratories. We therefore investigated whether the commercially available AbsoluteIDQ p180 kit (Biocrates Lifesciences), which utilizes flow injection and liquid chromatography mass spectrometry, may be used to reproduce some key results from previous global metabolomics studies. We applied it to serum samples from patients with mutations in peroxisomal target genes PEX1, ABCD1, and the HSD17B4 gene. Here we found various changes in sphingomyelins and lysophosphatidylcholines. In conclusion, this kit can be used to carry out extended diagnostics for peroxisomal disorders in routine laboratories, even without access to a metabolomics unit.

Msp1/ATAD1 restores mitochondrial function in Zellweger Spectrum Disease

Peroxisomal Biogenesis Disorders (PBDs) are a class of inherited metabolic disorders with profound neurological and other phenotypes. The most severe PBDs are caused by mutations in peroxin genes, which result in nonfunctional peroxisomes typically through impaired protein import. In order to better understand the molecular causes of Zellweger Spectrum Disease (ZSD) - the most severe PBDs -, we investigated the fate of peroxisomal mRNAs and proteins in ZSD model systems. We found that loss of peroxisomal import has no effect on peroxin mRNA expression or translational efficiency. Instead, peroxin proteins -still produced at high levels- aberrantly accumulate on the mitochondrial membrane, impairing respiration and ATP generation. Finally, we rescued mitochondrial function in fibroblasts derived from human patients with ZSD by overexpressing ATAD1, an AAA-ATPase that functions in mitochondrial quality control. These findings might provide a new focus of PBD therapies in supporting quality control pathways that protect mitochondrial function.

The Peroxisomal PTS1-Import Defect of PEX1- Deficient Cells Is Independent of Pexophagy in Saccharomyces cerevisiae

The important physiologic role of peroxisomes is shown by the occurrence of peroxisomal biogenesis disorders (PBDs) in humans. This spectrum of autosomal recessive metabolic disorders is characterized by defective peroxisome assembly and impaired peroxisomal functions. PBDs are caused by mutations in the peroxisomal biogenesis factors, which are required for the correct compartmentalization of peroxisomal matrix enzymes. Recent work from patient cells that contain the Pex1(G843D) point mutant suggested that the inhibition of the lysosome, and therefore the block of pexophagy, was beneficial for peroxisomal function. The resulting working model proposed that Pex1 may not be essential for matrix protein import at all, but rather for the prevention of pexophagy. Thus, the observed matrix protein import defect would not be caused by a lack of Pex1 activity, but rather by enhanced removal of peroxisomal membranes via pexophagy. In the present study, we can show that the specific block of PEX1 deletion-induced pexophagy does not restore peroxisomal matrix protein import or the peroxisomal function in beta-oxidation in yeast. Therefore, we conclude that Pex1 is directly and essentially involved in peroxisomal matrix protein import, and that the PEX1 deletion-induced pexophagy is not responsible for the defect in peroxisomal function. In order to point out the conserved mechanism, we discuss our findings in the context of the working models of peroxisomal biogenesis and pexophagy in yeasts and mammals.

TRIM37, a novel E3 ligase for PEX5-mediated peroxisomal matrix protein import

Most proteins destined for the peroxisomal matrix depend on the peroxisomal targeting signals (PTSs), which require the PTS receptor PEX5, whose deficiency causes fatal human peroxisomal biogenesis disorders (PBDs). TRIM37 gene mutations cause muscle–liver–brain–eye (mulibrey) nanism. We found that TRIM37 localizes in peroxisomal membranes and ubiquitylates PEX5 at K464 by interacting with its C-terminal 51 amino acids (CT51), which is required for PTS protein import. PEX5 mutations (K464A or ΔCT51), or TRIM37 depletion or mutation, reduce PEX5 abundance by promoting its proteasomal degradation, thereby impairing its functions in cargo binding and PTS protein import in human cells. TRIM37 or PEX5 depletion induces apoptosis and enhances sensitivity to oxidative stress, underscoring the cellular requirement for functional peroxisomes. Therefore, TRIM37-mediated ubiquitylation stabilizes PEX5 and promotes peroxisomal matrix protein import, suggesting that mulibrey nanism is a new PBD.

Zellweger syndrome: Depiction of MRI findings in early infancy at 3.0 Tesla

Zellweger syndrome, also referred to as cerebrohepatorenal syndrome, is a rare autosomal recessive disease representing the most severe form of the peroxisomal biogenesis disorders. Neuroanatomical sequelae include impaired neuronal migration, diffuse hypomyelination, and sensorineural degeneration. Due to the rare and severe nature of this disorder, early mortality, and comorbidities that place the patient at risk for sedated imaging, high-resolution magnetic resonance imaging findings of Zellweger syndrome are scarce in the literature. Presented here is a case of this rare disease imaged at 3.0 Tesla.