iPSCs, CRISPR/Cas9 y protocolos de diferenciación basados en factores de transcripción para generar nuevos modelos neuronales y astrocíticos del síndrome de Sanfilippo

[spa] El objetivo general de esta tesis doctoral ha sido la generación de nuevos modelos celulares para el síndrome de Sanfilippo y su utilización para ensayar una aproximación terapéutica para esta enfermedad basada en el uso de siRNAs como terapia de reducción de sustrato. Los objetivos concretos han sido: 1) Generación de modelos celulares • Obtención y caracterización de líneas isogénicas con mutaciones en el gen HGSNAT derivadas de células madre pluripotentes inducidas de donantes sanos, mediante la tecnología de edición génica CRISPR/Cas9. • Diferenciación de las células madre pluripotentes inducidas con mutaciones en el gen HGNSAT a neuronas y astrocitos, utilizando un protocolo optimizado. • Obtención y caracterización de líneas isogénicas con mutaciones en el gen NAGLU derivadas de células madre pluripotentes inducidas de donantes sanos, mediante la tecnología de edición génica CRISPR/Cas9. 2) Aproximación terapéutica basada en siRNAs • Evaluación del efecto de diferentes siRNAs contra los genes EXTL2 y EXTL3, como terapia de reducción de sustrato, en fibroblastos de pacientes de Sanfilippo C. • Evaluación del efecto terapéutico de siRNAs contra el gen EXTL2, como terapia de reducción de sustrato, en neuronas derivadas de células madre pluripotentes inducidas con mutaciones en HGSNAT

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

EXTL2 and EXTL3 inhibition with siRNAs as a promising substrate reduction therapy for Sanfilippo C syndrome

Sanfilippo syndrome is a rare lysosomal storage disorder caused by an impaired degradation of heparan sulfate (HS). It presents severe and progressive neurodegeneration and currently there is no effective treatment. Substrate reduction therapy (SRT) may be a useful option for neurological disorders of this kind, and several approaches have been tested to date. Here we use different siRNAs targeting EXTL2 and EXTL3 genes, which are important for HS synthesis, as SRT in Sanfilippo C patients' fibroblasts in order to decrease glycosaminoglycan (GAG) storage inside the lysosomes. The results show a high inhibition of the EXTL gene mRNAs (around 90%), a decrease in GAG synthesis after three days (30-60%) and a decrease in GAG storage after 14 days (up to 24%). Moreover, immunocytochemistry analyses showed a clear reversion of the phenotype after treatment. The in vitro inhibition of HS synthesis genes using siRNAs shown here is a first step in the development of a future therapeutic option for Sanfilippo C syndrome

Generation of two NAGLU-mutated homozygous cell lines from healthy induced pluripotent stem cells using CRISPR/Cas9 to model Sanfilippo B syndrome

Mutations in the NAGLU gene cause Sanfilippo B syndrome (mucopolysaccharidosis IIIB), a rare lysosomal storage disorder whose main symptom is a severe and progressive neurodegeneration for which no treatment is still available. Here, we generated two homozygous NAGLU-mutated cell lines using CRISPR/Cas9 editing in a healthy human induced pluripotent stem cell (hiPSC) line. These novel cell lines express pluripotency specific markers and maintain their capability to differentiate into all three germ layers in vitro while exhibit a normal karyotype. These mutated lines in combination with the isogenic control line will be useful to model in vitro Sanfilippo B syndrome

Neuronal and astrocytic differentiation from Sanfilippo C syndrome iPSCs for disease modeling and drug development

Sanfilippo syndrome type C (mucopolysaccharidosis IIIC) is an early-onset neurodegenerative lysosomal storage disorder, which is currently untreatable. The vast majority of studies focusing on disease mechanisms of Sanfilippo syndrome were performed on non-neural cells or mouse models, which present obvious limitations. Induced pluripotent stem cells (iPSCs) are an efficient way to model human diseases in vitro. Recently developed transcription factor-based differentiation protocols allow fast and efficient conversion of iPSCs into the cell type of interest. By applying these protocols, we have generated newneuronal and astrocyticmodels of Sanfilippo syndrome using our previously established disease iPSC lines. Moreover, our neuronal model exhibits disease-specific molecular phenotypes, such as increase in lysosomes and heparan sulfate. Lastly, we tested an experimental, siRNA-based treatment previously shown to be successful in patients' fibroblasts and demonstrated its lack of efficacy in neurons. Our findings highlight the need to use relevant human cellular models to test therapeutic interventions and shows the applicability of our neuronal and astrocyticmodels of Sanfilippo syndrome for future studies on disease mechanisms and drug development

Genome Editing Using Cas9-gRNA Ribonucleoprotein in Human Pluripotent Stem Cells for Disease Modeling

The discovery that the CRISPR/Cas9 system could be used for genome editing purposes represented a major breakthrough in the field. This advancement has notably facilitated the introduction or correction of disease-specific mutations in healthy or disease stem cell lines respectively; therefore, easing disease modeling studies in combination with differentiation protocols. For many years, variability in the genetic background of different stem cell lines has been a major burden to specifically identify phenotypes arising uniquely from the presence of the mutation and not from differences in other genomic regions. Here, we provide a complete protocol to introduce random indels in human wild type pluripotent stem cells using CRISPR/Cas9 in order to generate clonal lines with potential pathogenic alterations in any gene of interest. In this protocol, we use transfection of a ribonucleoprotein complex to diminish the risk of off-target effects, and select clonal lines with promising indels to obtain disease induced pluripotent stem cell lines

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

Generation of two compound heterozygous HGSNAT-mutated lines from healthy induced pluripotent stem cells using CRISPR/Cas9 to model Sanfilippo C syndrome

Sanfilippo C syndrome (Mucopolysaccharidosis IIIC) is a rare lysosomal storage disorder caused by mutations in the HGSNAT gene. It is characterized by a progressive and severe neurodegeneration, for which there is no treatment available. Here, we report the generation of two HGSNAT-mutated cell lines from a healthy human induced pluripotent stem cell (hiPSC) line using CRISPR/Cas9 editing. These novel cell lines have a normal karyotype, express pluripotency specific markers and have the capability to differentiate into all three germ layers in vitro. These hiPSC lines will be useful for the generation of in vitro models of Sanfilippo C syndrome

Therapeutic Strategies Targeting Mitochondrial Calcium Signaling: A New Hope for Neurological Diseases?

Calcium (Ca2+) is a versatile secondary messenger involved in the regulation of a plethora of different signaling pathways for cell maintenance. Specifically, intracellular Ca2+ homeostasis is mainly regulated by the endoplasmic reticulum and the mitochondria, whose Ca2+ exchange is mediated by appositions, termed endoplasmic reticulum–mitochondria-associated membranes (MAMs), formed by proteins resident in both compartments. These tethers are essential to manage the mitochondrial Ca2+ influx that regulates the mitochondrial function of bioenergetics, mitochondrial dynamics, cell death, and oxidative stress. However, alterations of these pathways lead to the development of multiple human diseases, including neurological disorders, such as amyotrophic lateral sclerosis, Friedreich’s ataxia, and Charcot–Marie–Tooth. A common hallmark in these disorders is mitochondrial dysfunction, associated with abnormal mitochondrial Ca2+ handling that contributes to neurodegeneration. In this work, we highlight the importance of Ca2+ signaling in mitochondria and how the mechanism of communication in MAMs is pivotal for mitochondrial maintenance and cell homeostasis. Lately, we outstand potential targets located in MAMs by addressing different therapeutic strategies focused on restoring mitochondrial Ca2+ uptake as an emergent approach for neurological diseases