PEX13 deficiency in mouse brain as a model of Zellweger syndrome: abnormal cerebellum formation, reactive gliosis and oxidative stress

Abstract

SUMMARYDelayed cerebellar development is a hallmark of Zellweger syndrome (ZS), a severe neonatal neurodegenerative disorder. ZS is caused by mutations in PEX genes, such as PEX13, which encodes a protein required for import of proteins into the peroxisome. The molecular basis of ZS pathogenesis is not known. We have created a conditional mouse mutant with brain-restricted deficiency of PEX13 that exhibits cerebellar morphological defects. PEX13 brain mutants survive into the postnatal period, with the majority dying by 35 days, and with survival inversely related to litter size and weaning body weight. The impact on peroxisomal metabolism in the mutant brain is mixed: plasmalogen content is reduced, but very-long-chain fatty acids are normal. PEX13 brain mutants exhibit defects in reflex and motor development that correlate with impaired cerebellar fissure and cortical layer formation, granule cell migration and Purkinje cell layer development. Astrogliosis and microgliosis are prominent features of the mutant cerebellum. At the molecular level, cultured cerebellar neurons from E19 PEX13-null mice exhibit elevated levels of reactive oxygen species and mitochondrial superoxide dismutase-2 (MnSOD), and show enhanced apoptosis together with mitochondrial dysfunction. PEX13 brain mutants show increased levels of MnSOD in cerebellum. Our findings suggest that PEX13 deficiency leads to mitochondria-mediated oxidative stress, neuronal cell death and impairment of cerebellar development. Thus, PEX13-deficient mice provide a valuable animal model for investigating the molecular basis and treatment of ZS cerebellar pathology.

Mitochondria are targets for peroxisome-derived oxidative stress in cultured mammalian cells

“…Over the years, an increasing number of observations have lent support to the concept that a loss of peroxisome function makes cells more vulnerable to oxidative stress [68][69][70]76]. In this study, we confirm and extend these findings by showing that cells lacking either GNPAT or peroxisomes are more sensitive toward KR-induced oxidative stress than the corresponding control cells.…”

“…Note that (i) C11-Bodipy 581/591 is a lipophilic compound that rapidly incorporates into phospholipids of all cellular membranes; (ii) the emission spectra of the nonoxidized (red) and oxidized (green) forms of C11-Bodipy 581/591 display spectral overlap with KR (red) and (roGFP2-tagged) po-GSTK1 (green), respectively; (iii) the peroxisomal staining pattern of (I, J, K) po-GSTK1 (green) can be easily distinguished from that observed for (D, F, N) the oxidized Bodipy probe (green); and (iv) the green signal in (L) represents a mixture of po-GSTK1 and oxidized C11-Bodipy 581/591. and apoptosis [69], and (iii) mouse fibroblasts lacking GNPAT (EC 2.3.1.42), a peroxisomal enzyme catalyzing the first step in ether phospholipid biosynthesis, are more susceptible to 2,2′-azobis(2-methylpropionamidine) dihydrochloride-induced oxidative stress [70]. Note that, as (i) human fibroblasts are less sensitive to KR-induced cell death than mouse fibroblasts (data not shown) and (ii) the phototoxic effects of c-KR are relatively weak (see above), the light dose for the human cells expressing c-KR was increased to 72 J/cm 2 to facilitate the detection of potential differences between the control and the peroxisome-deficient cells.…”

Peroxisomes Are Required for Lipid Metabolism and Muscle Function in Drosophila melanogaster

“…If so, then longer acyl chain lipids may accumulate in muscle lacking peroxisome, which could lead to toxicity, specifically to mitochondria. Such FA toxicity could explain the defects in mitochondrial morphology and activity that have been observed in PBD patients and PBD mouse models [25]–[27], [53], [56]–[60]. Other peroxisomal substrates, such as bile acid intermediates and phytanic acid, can induce mitochondrial damage [61], [62].…”

Hepatic dysfunction in peroxisomal disorders

“…Engraftment was successful and for both type of operation, clinical and biochemical parameters improved (decrease in phytanic acid, VLCFA and abnormal bile acids in serum), and cholestasis resolved [137,139]. Although the liver-derived metabolites normalized in these patients, it is unlikely that brain defects can be restored by liver transplantation given the detrimental phenotype of brain selective Pex knockout mice [140,141]. Unfortunately, as far as we know, follow up studies were not published on these patients.…”