The V471A polymorphism in autophagy-related gene ATG7 modifies age at onset specifically in Italian Huntington disease patients

The cause of Huntington disease (HD) is a polyglutamine repeat expansion of more than 36 units in the huntingtin protein, which is inversely correlated with the age at onset of the disease. However, additional genetic factors are believed to modify the course and the age at onset of HD. Recently, we identified the V471A polymorphism in the autophagy-related gene ATG7, a key component of the autophagy pathway that plays an important role in HD pathogenesis, to be associated with the age at onset in a large group of European Huntington disease patients. To confirm this association in a second independent patient cohort, we analysed the ATG7 V471A polymorphism in additional 1,464 European HD patients of the “REGISTRY” cohort from the European Huntington Disease Network (EHDN). In the entire REGISTRY cohort we could not confirm a modifying effect of the ATG7 V471A polymorphism. However, analysing a modifying effect of ATG7 in these REGISTRY patients and in patients of our previous HD cohort according to their ethnic origin, we identified a significant effect of the ATG7 V471A polymorphism on the HD age at onset only in the Italian population (327 patients). In these Italian patients, the polymorphism is associated with a 6-years earlier disease onset and thus seems to have an aggravating effect. We could specify the role of ATG7 as a genetic modifier for HD particularly in the Italian population. This result affirms the modifying influence of the autophagic pathway on the course of HD, but also suggests population-specific modifying mechanisms in HD pathogenesis

Monitoring RIPK1 phosphorylation in the TNFR1 signaling complex

Receptor-interacting protein kinase 1 (RIPK1) is a component of the TNFR1 signaling complex (also known as complex I or TNFR-SC), where its ubiquitylation by cIAP1/2 and LUBAC serves to initiate prosurvival and proinflammatory responses through activation of the MAPK and NF-κB pathways. IKKα/β-mediated phosphorylation of RIPK1 in complex I was shown to maintain RIPK1 in a prosurvival modus. Consequently, conditions affecting proper IKKα/β activation perturb IKKα/β-phosphorylation of RIPK1 and switch the TNF response toward RIPK1 kinase-dependent cell death. Methods to study the posttranslational modifications of RIPK1 in complex I are therefore of great value. Here, we describe a detailed protocol to isolate complex I-associated RIPK1 from cells and provide different tools to study the phosphorylation status of RIPK1 in TNFR1 complex I