Alpha-synuclein-glucocerebrosidase interactions in pharmacological Gaucher models: a biological link between Gaucher disease and parkinsonism

The role of glucocerebrosidase mutations in Parkinson disease and Lewy body disorders

Mutations in the gene encoding glucocerebrosidase (GBA), the enzyme deficient in the lysosomal storage disorder Gaucher disease, are associated with the development of Parkinson disease and other Lewy body disorders. In fact, GBA variants are currently the most common genetic risk factor associated with parkinsonism, and identified subjects with Parkinson disease are more than five times more likely to carry mutations in GBA. The mechanisms underlying this association are not known, but proposed theories include enhanced protein aggregation, alterations in lipid levels, and autophagy-lysosomal dysfunction promoting the retention of undegraded proteins. We review the genetic studies linking GBA to parkinsonism, as well as several of the mechanisms postulated to explain the association of GBA mutations and the synucleinopathies, which demonstrate how studies of a rare mendelian disease may provide insights into our understanding of a common complex disorder.

The ceramide transporter and the Goodpasture antigen binding protein: one protein--one function?

The Goodpasture antigen-binding protein (GPBP) and its splice variant the ceramide transporter (CERT) are multifunctional proteins that have been found to play important roles in brain development and biology. However, the function of GPBP and CERT is controversial because of their involvement in two apparently unrelated research fields: GPBP was initially isolated as a protein associated with collagen IV in patients with the autoimmune disease Goodpasture syndrome. Subsequently, a splice variant lacking a serine-rich domain of 26 amino acids (GPBPDelta26) was found to mediate the cytosolic transport of ceramide and was therefore (re)named CERT. The two splice forms likely carry out different functions in specific sub-cellular localizations. Selective GPBP knockdown induces extensive apoptosis and tissue loss in the brain of zebrafish. GPBP/GPBPDelta26 knock-out mice die as a result of structural and functional defects in endoplasmic reticulum and mitochondria. Because both mitochondria and ceramide play an important role in many biological events that regulate neuronal differentiation, cellular senescence, proliferation and cell death, we propose that GPBP and CERT are pivotal in neurodegenerative processes. In this review, we discuss the current state of knowledge on GPBP and CERT, including the molecular and biochemical characterization of GPBP in the field of autoimmunity as well as the fundamental research on CERT in ceramide transport, biosynthesis, localization, metabolism and cell homeostasis.

Glucocerebrosidase as a genetic modifier influencing susceptibility and phenotype of Parkinson’s disease

Evaluation of: Sidransky E, Nalls MA, Aasly JO et al.: Multicenter analysis of glucocerebrosidase mutations in Parkinson’s disease. N. Engl. J. Med. 361, 1651–1661 (2009). This study aimed to substantiate the role of glucocerebrosidase (GBA) mutations in Parkinson’s disease (PD) by pooling clinical and genotypic data for 5691 PD patients and 4898 unaffected individuals from 16 international centers. Genotyping was performed for either two mutations (N370S and L444P) or for three to eight GBA mutations. One of the N370S and L444P mutations was found in 15 and 3% of PD patients of Ashkenazi and non-Ashkenazi Jewish origin, respectively. Whole gene sequencing performed in a subgroup of these patients revealed a combined odds ratio of carrying any GBA mutation of 5.43. Genotype–phenotype correlations verified that GBA mutation carriers were more likely to develop PD at an earlier age, have affected relatives and show increased incidence of cognitive changes compared with PD patients without mutations. This study provides evidence that heterozygosity for GBA mutations is the most common susceptibility factor for the onset of PD symptoms to date. It also highlights the need for further studies using large numbers of patients and controls in order to elucidate the effect(s) of GBA mutations on PD clinical manifestations and their role in the molecular mechanisms of PD pathogenesis.