Targeting lipids in CLN8-associated NCL diseases: structural and functional interaction of CLN8 with vesicle-associated membrane protein-associated protein A (VAPA), and genotype-phenotype correlations

The neuronal ceroid lipofuscinoses (NCLs) are a clinical and genetic heterogeneous group of autosomal recessive neurodegenerative diseases, which manifest mainly in childhood. Symptoms generally include progressive mental and motor deterioration, epilepsy, ataxia, in some cases also visual loss. Basic mechanisms of these diseases are unknown, because functions of the involved genes and their protein products remain to be determined, and this represents a serious obstacle to developing effective therapies. The investigators have recently found that the protein encoded by CLN8 gene, whose defects associate with two different clinical forms of these diseases, interacts with the VAPA protein, which significantly contributes to neural cell functions by regulating sphingolipid metabolism. In the present project, they intend to further investigate the interaction between CLN8 and VAPA proteins in order to: (i) define CLN8 function in sphingolipids and (ii) establish whether CLN8 defects affect this function, and therefore be relevant to the development of CLN8-associated NCL diseases. To this purpose, new technological approaches for genomic manipulation and high-throughput will be developed, aimed at large-scale loss of function screening; moreover, cells will be treated with specific vectors co-expressing both CLN8 and VAPA proteins to verify their interaction and function. Sphingolipidomic technology will be applied for the analysis of sphingolipid patterns, metabolism and function. The study will be extended to investigation of fibroblast cells from patients with CLN8-associated diseases provided by collaborations with institutions in Italy, Finland and Germany. The overall objective of this project is to provide a comprehensive molecular understanding of CLN8 function, bringing to a closer definition of pathogenic mechanisms of CLN8 diseases. These diseases are characterized by diverse CLN8 gene defects (genotype variants) and clinical symptoms (phenotype variants), therefore analyses of fibroblasts of patients with CLN8 could shed lights on possible different pathogenic mechanisms. Finally, the results may lay the foundation for future research on more appropriate targets helping diagnosis and targeted therapy.