An induced pluripotent stem cell line (TRNDi006-A) from a MPS IIIB patient carrying homozygous mutation of p.Glu153Lys in the NAGLU gene

Disease modeling for Mucopolysaccharidosis type IIIB using patient derived induced pluripotent stem cells

Mucopolysaccharidosis type IIIB (MPS IIIB) is a lysosomal disease caused by mutations in the NAGLU gene encoding α-N-acetylglucosaminidase (NAGLU) which degrades heparan sulfate in lysosomes. Deficiency in NAGLU results in lysosomal accumulation of glycosaminoglycans (GAGs) and neurological symptoms. Currently, there is no effective treatment or cure for this disease. In this study, induced pluripotent stem cell lines were established from two MPS IIIB patient fibroblast lines and differentiated into neural stem cells and neurons. MPS IIIB neural stem cells exhibited NAGLU deficiency accompanied with GAG accumulation, as well as lysosomal enlargement and secondary lipid accumulation. Treatments with recombinant NAGLU, δ-tocopherol, and 2-hydroxypropyl-b-cyclodextrin significantly reduced the disease phenotypes in these cells. These results indicate the MPS IIIB neural stem cells and neurons have the disease relevant phenotype and can be used as a cell-based disease model system for evaluation of drug efficacy and compound screening for drug development.

Genome editing in mucopolysaccharidoses and mucolipidoses

Mucopolysaccharidoses (MPS) and mucolipidoses (ML) are disorders that alter lysosome function. While MPS are caused by mutation in enzymes that degrade glycosaminoglycans, the ML are disorders characterized by reduced function in the phosphotransferase enzyme. Multiple clinical features are associated with these diseases and the exact mechanisms that could explain such different clinical manifestations in patients are still unknown. Furthermore, there are no curative treatment for any of MPS and ML conditions so far. Gene editing holds promise as a tool for the creation of cell and animal models to help explain disease pathogenesis, as well as a platform for gene therapy. In this chapter, we discuss the main studies involving genome editing for MPS and the prospect applications for ML.

Sanfilippo Syndrome: Molecular Basis, Disease Models and Therapeutic Approaches

Sanfilippo syndrome or mucopolysaccharidosis III is a lysosomal storage disorder caused by mutations in genes responsible for the degradation of heparan sulfate, a glycosaminoglycan located in the extracellular membrane. Undegraded heparan sulfate molecules accumulate within lysosomes leading to cellular dysfunction and pathology in several organs, with severe central nervous system degeneration as the main phenotypical feature. The exact molecular and cellular mechanisms by which impaired degradation and storage lead to cellular dysfunction and neuronal degeneration are still not fully understood. Here, we compile the knowledge on this issue and review all available animal and cellular models that can be used to contribute to increase our understanding of Sanfilippo syndrome disease mechanisms. Moreover, we provide an update in advances regarding the different and most successful therapeutic approaches that are currently under study to treat Sanfilippo syndrome patients and discuss the potential of new tools such as induced pluripotent stem cells to be used for disease modeling and therapy development.

Role of induced pluripotent stem cells in lysosomal storage diseases

Lysosomal storage diseases (LSDs) are a group of metabolism inborn errors caused by defective enzymes in the lysosome, resulting in the accumulation of undegraded substrates. Many characteristic cell features have been revealed in LSDs, including abnormal autophagy and mitochondrial dysfunction. The development of induced pluripotent stem cells (iPSCs) dramatically boosted research on LSDs, particularly regarding novel opportunities to clarify the disease etiology based on the storage of macromolecules, such as sphingolipids in lysosomes. iPSCs made from LSD patients (LSD-iPSCs) have been differentiated into neurons, endothelial cells, cardiomyocytes, hepatocytes, and macrophages, with each cell type closely resembling the primary disease phenotypes, providing new tools to probe the disease pathogenesis and to test therapeutic strategies. Abnormally accumulated substrates impaired autophagy and mitochondrial and synapse functions in LSD-iPSC-derived neurons. Reducing the accumulation with the treatment of drug candidates improved LSD-iPSC-derived neuron functions. Additionally, iPSC technology can help probe the gene expressions, proteomics, and metabolomics of LSDs. Further, gene repair and the generation of new mutations in causative genes in LSD-iPSCs can be used to understand both the specific roles of causative genes and the contributions of other genetic factors to these phenotypes. Moreover, the development of iPSC-derived organoids as disease models has bridged the gap between studies using cell lines and in vivo animal models. There are some reproducibility issues in iPSC research, however, including genetic and epigenetic abnormalities, such as chromosomal abnormalities, DNA mutations, and gene modifications via methylation. In this review, we present the disease and treatment concepts gathered using selected LSD-iPSCs, discuss iPSC research limitations, and set our future research visions. Such studies are expected to further inform and generate insights into LSDs and are important in research and clinical practice.