Defective Sphingosine-1-phosphate metabolism is a druggable target in Huntington's disease

Huntington's disease is characterized by a complex and heterogeneous pathogenic profile. Studies have shown that disturbance in lipid homeostasis may represent a critical determinant in the progression of several neurodegenerative disorders. The recognition of perturbed lipid metabolism is only recently becoming evident in HD. In order to provide more insight into the nature of such a perturbation and into the effect its modulation may have in HD pathology, we investigated the metabolism of Sphingosine-1-phosphate (S1P), one of the most important bioactive lipids, in both animal models and patient samples. Here, we demonstrated that S1P metabolism is significantly disrupted in HD even at early stage of the disease and importantly, we revealed that such a dysfunction represents a common denominator among multiple disease models ranging from cells to humans through mouse models. Interestingly, the in vitro anti-apoptotic and the pro-survival actions seen after modulation of S1P-metabolizing enzymes allows this axis to emerge as a new druggable target and unfolds its promising therapeutic potential for the development of more effective and targeted interventions against this incurable condition

Supplementary Material for: Dysregulation of the Expression of Asparagine-Linked Glycosylation 13 Short Isoform 2 Affects Nephrin Function by Altering Its N-Linked Glycosylation

<p><b><i>Background:</i></b> N-linked glycosylation, which is a post-translational modification process, plays an important role in protein folding, intracellular trafficking and membrane targeting, as well as in regulating the protein function. Recently, we identified a missense variant (p.T141L) in the short isoform 2 of the X-linked gene asparagine-linked glycosylation 13 (<i>ALG13-is2</i>), which segregated with focal segmental glomerulosclerosis and PCCD in a large Australian pedigree; however, any evidence of its pathogenicity was demonstrated. <i>ALG13</i> gene encodes, through alternative splicing, 2 glycosyltransferase isoforms, which catalyse the second sugar addition of the highly conserved oligosaccharide precursor in the endoplasmic reticulum (ER). Mutations in the long isoform 1 were associated with epilepsy. <b><i>Methods and Results:</i></b> Here, we show a different expression of the 2 isoforms depending on the tissue. Specifically, the long isoform is highly expressed in lungs, ovaries, testes, cerebellum, cortex, retina, pituitary gland, and olfactory bulbs, while the short isoform is highly expressed in mouse podocytes and in human podocyte cell lines, at both mRNA and protein levels. The silencing of ALG13-is2 by specific siRNAs induces an altered N-linked glycosylation pattern of nephrin, as demonstrated by the presence of an additional immunostaining band of about 130 kD. In knock-down cells, immunofluorescence analysis shows perturbed organization of the cytoskeleton and altered localization of nephrin on the cellular membrane. We also demonstrated that the altered pattern of N-linked glycosylation induces an over-expression of binding immunoglobulin protein and calreticulin, suggesting ER stress. <b><i>Conclusions:</i></b> These results provide preliminary evidence that ALG13-is2 could be an important modifier of renal filtration defects.</p

Oxidative brain damage in Mecp2-mutant murine models of Rett syndrome.

Rett syndrome (RTT) is a rare neurodevelopmental disorder affecting almost exclusively females, caused in the overwhelming majority of the cases by loss-of-function mutations in the gene encoding methyl-CpG binding protein 2 (MECP2). High circulating levels of oxidative stress (OS) markers in patients suggest the involvement of OS in the RTT pathogenesis. To investigate the occurrence of oxidative brain damage in Mecp2 mutant mouse models, several OS markers were evaluated in whole brains of Mecp2-null (pre-symptomatic, symptomatic, and rescued) and Mecp2-308 mutated (pre-symptomatic and symptomatic) mice, and compared to those of wild type littermates. Selected OS markers included non-protein-bound iron, isoprostanes (F2-isoprostanes, F4-neuroprostanes, F2-dihomo-isoprostanes) and 4-hydroxy-2-nonenal protein adducts. Our findings indicate that oxidative brain damage 1) occurs in both Mecp2-null (both -/y and stop/y) and Mecp2-308 (both 308/y males and 308/+ females) mouse models of RTT; 2) precedes the onset of symptoms in both Mecp2-null and Mecp2-308 models; and 3) is rescued by Mecp2 brain specific gene reactivation. Our data provide direct evidence of the link between Mecp2 deficiency, oxidative stress and RTT pathology, as demonstrated by the rescue of the brain oxidative homeostasis following brain-specifically Mecp2-reactivated mice. The present study indicates that oxidative brain damage is a previously unrecognized hallmark feature of murine RTT, and suggests that Mecp2 is involved in the protection of the brain from oxidative stress

Abnormal N-glycosylation pattern for brain nucleotide pyrophosphatase-5 (NPP-5) in Mecp2-mutant murine models of Rett syndrome

Neurological disorders can be associated with protein glycosylation abnormalities. Rett syndrome is a devastating genetic brain disorder, mainly caused by de novo loss-of-function mutations in the methyl-CpG binding protein 2 (MECP2) gene. Although its pathogenesis appears to be closely associated with a redox imbalance, no information on glycosylation is available. Glycoprotein detection strategies (i.e., lectin-blotting) were applied to identify target glycosylation changes in the whole brain of Mecp2 mutant murine models of the disease. Remarkable glycosylation pattern changes for a peculiar 50kDa protein, i.e., the N-linked brain nucleotide pyrophosphatase-5 were evidenced, with decreased N-glycosylation in the presymptomatic and symptomatic mutant mice. Glycosylation changes were rescued by selected brain Mecp2 reactivation. Our findings indicate that there is a causal link between the amount of Mecp2 and the N-glycosylation of NPP-5