A stress-free strategy to correct point mutations in patient iPS cells

Advances in modeling the Charcot-Marie-Tooth disease: Human induced pluripotent stem cell-derived Schwann cells harboring SH3TC2 variants

Human induced pluripotent stem cells (hiPSCs) represent a powerful tool for investigating neuropathological disorders, such as Charcot-Marie-Tooth disease (CMT), the most prevalent inherited peripheral neuropathy, where the cells of interest are hardly accessible. Advancing the development of appropriate cellular models is crucial for studying the disease's pathophysiology. In this study, we present the first two isogenic hiPSC-derived Schwann cell models for studying CMT4C, also known as AR-CMTde-SH3TC2. This subtype of CMT is associated with alterations in SH3TC2 and is the most prevalent form of autosomal recessive demyelinating CMT. We aimed to study the impact of two nonsense mutations in SH3TC2. To achieve this, we used two CRISPR hiPSC clones, one carrying a homozygous nonsense mutation: c.211C>T, p.Gln71*, and the other one, carrying the most common AR-CMTde-SH3TC2 alteration, c.2860G>A, p.Arg954*. To study the endogenous expression of SH3TC2 in the cells mainly altered in AR-CMTde-SH3TC2, we initiated the differentiation of both our CMT clones and their isogenic control into Schwann cells (SCs). This study represents the first in vitro investigation of human endogenous SH3TC2 expression in AR-CMTde-SH3TC2 hiPSC-derived SC models, allowing for the examination of its expression and of its cellular impact. By comparing this AR-CMTde-SH3TC2 models to the control one, we observed disparities in RNA and protein expression of SH3TC2. Additionally, our RNA and coculture experiments with hiPSC-derived motor neurons (MNs) revealed delayed maturation of SCs and a reduced ability of SH3TC2-deficient SCs to sustain motor neuron culture. Our findings also demonstrated a disability in receptor recycling in SH3TC2-deficient cells, depending on the AR-CMTde-SH3TC2 alteration. These hiPSC-derived-SC models further provide a new modelling tool for studying Schwann cell contribution to CMT4C.

From in vivo models to in vitro bioengineered neuromuscular junctions for the study of Charcot-Marie-Tooth disease

Peripheral neuropathies are disorders affecting the peripheral nervous system. Among them, Charcot-Marie-Tooth disease is an inherited sensorimotor neuropathy for which no effective treatment exists yet. Research on Charcot-Marie-Tooth disease has been hampered by difficulties in accessing relevant cells, such as sensory and motor neurons, Schwann cells, and myocytes, which interact at the neuromuscular junction, the specialized synapses formed between nerves and skeletal muscles. This review first outlines the various in vivo models and methods used to study neuromuscular junction deficiencies in Charcot-Marie-Tooth disease. We then explore novel in vitro techniques and models, including complex hiPSC-derived cultures, which offer promising isogenic and reproducible neuromuscular junction models. The adaptability of in vitro culture methods, including cell origin, cell-type combinations, and choice of culture format, adds complexity and excitement to this rapidly evolving field. This review aims to recapitulate available tools for studying Charcot-Marie-Tooth disease to understand its pathophysiological mechanisms and test potential therapies.

CRISPR Base Editing to Create Potential Charcot-Marie-Tooth Disease Models with High Editing Efficiency: Human Induced Pluripotent Stem Cell Harboring SH3TC2 Variants

Human induced pluripotent stem cells (hiPSCs) represent a powerful tool to investigate neuropathological disorders in which the cells of interest are inaccessible, such as in the Charcot-Marie-Tooth disease (CMT), the most common inherited peripheral neuropathy. Developing appropriate cellular models becomes crucial in order to both study the disease's pathophysiology and test new therapeutic approaches. The generation of hiPS cellular models for disorders caused by a single nucleotide variation has been significantly improved following the development of CRISPR-based editing tools. In this study, we efficiently and quickly generated, by CRISPR editing, the two first hiPSCs cellular models carrying alterations involved in CMT4C, also called AR-CMTde-SH3TC2. This subtype of CMT is associated with alterations in the SH3TC2 gene and represents the most prevalent form of autosomal recessive demyelinating CMT. We aimed to develop models for two different SH3TC2 nonsense variants, c.211C>T, p.Gln71* and the most common AR-CMTde-SH3TC2 alteration, c.2860C>T, p.Arg954*. First, in order to determine the best CRISPR strategy to adopt on hiPSCs, we first tested a variety of sgRNAs combined with a selection of recent base editors using the conveniently cultivable and transfectable HEK-293T cell line. The chosen CRISPR base-editing strategy was then applied to hiPSCs derived from healthy individuals to generate isogenic CMT disease models with up to 93% editing efficiency. For point mutation generation, we first recommend to test your strategies on alternative cell line such as HEK-293T before hiPSCs to evaluate a variety of sgRNA-BE combinations, thus boosting the chance of achieving edited cellular clones with the hard-to-culture and to transfect hiPSCs.

CRISPR Del/Rei: a simple, flexible, and efficient pipeline for scarless genome editing

Scarless genome editing of induced pluripotent stem cells (iPSCs) is crucial for the precise modeling of genetic disease. Here we present CRISPR Del/Rei, a two-step deletion-reinsertion strategy with high editing efficiency and simple PCR-based screening that generates isogenic clones in ~ 2 months. We apply our strategy to edit iPSCs at 3 loci with only rare off target editing.

On the Road from Phenotypic Plasticity to Stem Cell Therapy

In 1981, I published a paper in the first issue of The Journal of Neuroscience with my postdoctoral mentor, Richard Bunge. At that time, the long-standing belief that each neuron expressed only one neurotransmitter, known as Dale's Principle (Dale, 1935), was being hotly debated following a report by French embryologist Nicole Le Douarin showing that neural crest cells destined for one transmitter phenotype could express characteristics of another if transplanted to alternate sites in the developing embryo (Le Douarin, 1980). In the Bunge laboratory, we were able to more directly test the question of phenotypic plasticity in the controlled environment of the tissue culture dish. Thus, in our paper, we grew autonomic catecholaminergic neurons in culture under conditions which promoted the acquisition of cholinergic traits and showed that cells did not abandon their inherited phenotype to adopt a new one but instead were capable of dual transmitter expression. In this Progressions article, I detail the path that led to these findings and how this study impacted the direction I followed for the next 40 years. This is my journey from phenotypic plasticity to the promise of a stem cell therapy.