Differentiation of lymphoblastoid-derived iPSCs into functional cardiomyocytes, neurons and myoblasts

Enriching iPSC research diversity: Harnessing human biobank collections for improved ethnic representation

Biobanks of human biosamples and cell lines are indispensable for biomedical research on human health and disease and for drug development projects. Many human cell line biobanks worldwide hold collections of lymphoblastoid cell lines (LCLs), representing thousands of affected and control donors from diverse ethnic/ancestry groups. In recent years, induced human pluripotent stem cells (iPSCs) and differentiated human cells derived from these iPSCs have become indispensable for applied biomedical research. Establishing iPSCs remains a laborious and costly step towards generating differentiated human cells. To address this research need, several non-profit and commercial biobanks have established iPSC collections for distribution to researchers, thereby serving as a resource for generating differentiated human cells. The most common starting materials for generation of iPSCs are a skin biopsy for harvesting fibroblasts, or a blood sample for collection of peripheral blood mononuclear cells. However untapped resources include the large established collections of biobanked human LCLs which can be reprogrammed to iPSCs using a variety of published protocols including the use of non-integrating episomal vectors. Many biobanks curate LCLs from diverse ethnic/ancestry populations, an aspect largely absent in most established iPSC biobanks which tend to primarily reflect populations from developed countries. Here, we call upon researchers across the breadth of iPSC research to tap the unique resource of existing and diverse human LCL collections for establishing biobanked iPSC panels that better represent the varied human ethnic (and hence genomic) diversity, thereby benefiting precision medicine and drug development research on a global scale.

Exchange of subtelomeric regions between chromosomes 4q and 10q reverts the FSHD genotype and phenotype

The most common form of facioscapulohumeral dystrophy (FSHD1) is caused by a partial loss of the D4Z4 macrosatellite repeat array in the subtelomeric region of chromosome 4. Patients with FSHD1 typically carry 1 to 10 D4Z4 repeats, whereas nonaffected individuals have 11 to 150 repeats. The ~150-kilobyte subtelomeric region of the chromosome 10q exhibits a ~99% sequence identity to the 4q, including the D4Z4 array. Nevertheless, contractions of the chr10 array do not cause FSHD or any known disease, as in most people D4Z4 array on chr10 is flanked by the nonfunctional polyadenylation signal, not permitting the DUX4 expression. Here, we attempted to correct the FSHD genotype by a CRISPR-Cas9-induced exchange of the chr4 and chr10 subtelomeric regions. We demonstrated that the induced t(4;10) translocation can generate recombinant genotypes translated into improved FSHD phenotype. FSHD myoblasts with the t(4;10) exhibited reduced expression of the DUX4 targets, restored PAX7 target expression, reduced sensitivity to oxidative stress, and improved differentiation capacity.

Optimized protocol for the generation of functional human induced-pluripotent-stem-cell-derived dopaminergic neurons

Generation of functional human dopaminergic (DA) neurons from human induced pluripotent stem cells (hiPSCs) is a crucial tool for modeling dopamine-related human diseases and cell replacement therapies. Here, we present a protocol to combine neuralizing transcription factor (NGN2) programming and DA patterning to differentiate hiPSCs into mature and functional induced DA (iDA) neurons. We describe steps from transduction of hiPSCs and neural induction through to differentiation and maturation of near-pure, fully functional iDA neurons within 3 weeks. For complete details on the use and execution of this protocol, please refer to Sheta et al. (2022).1.

Optical Mapping of Cardiomyocytes in Monolayer Derived from Induced Pluripotent Stem Cells

Optical mapping is a powerful imaging technique widely adopted to measure membrane potential changes and intracellular Ca2+ variations in excitable tissues using voltage-sensitive dyes and Ca2+ indicators, respectively. This powerful tool has rapidly become indispensable in the field of cardiac electrophysiology for studying depolarization wave propagation, estimating the conduction velocity of electrical impulses, and measuring Ca2+ dynamics in cardiac cells and tissues. In addition, mapping these electrophysiological parameters is important for understanding cardiac arrhythmia mechanisms. In this review, we delve into the fundamentals of cardiac optical mapping technology and its applications when applied to hiPSC-derived cardiomyocytes and discuss related advantages and challenges. We also provide a detailed description of the processing and analysis of optical mapping data, which is a crucial step in the study of cardiac diseases and arrhythmia mechanisms for extracting and comparing relevant electrophysiological parameters.

Antisense oligonucleotides as a potential treatment for brain deficits observed in myotonic dystrophy type 1

Myotonic dystrophy, or dystrophia myotonica type 1 (DM1), is a multi-systemic disorder and is the most common adult form of muscular dystrophy. It affects not only muscles but also many organs, including the brain. Cerebral impairments include cognitive deficits, daytime sleepiness, and loss of visuospatial and memory functions. The expression of mutated transcripts with CUG repeats results in a gain of toxic mRNA function. The antisense oligonucleotide (ASO) strategy to treat DM1 brain deficits is limited by the fact that ASOs do not cross the blood-brain barrier after systemic administration, indicating that other methods of delivery should be considered. ASO technology has emerged as a powerful tool for developing potential new therapies for a wide variety of human diseases, and its potential has been proven in a recent clinical trial. Targeting DMPK mRNA in neural cells derived from human induced pluripotent stem cells obtained from a DM1 patient with the IONIS 486178 ASO abolished CUG-expanded foci, enabled nuclear redistribution of MBNL1/2, and corrected aberrant splicing. Intracerebroventricular injection of the IONIS 486178 ASO in DMSXL mice decreased the levels of mutant DMPK mRNAs by up to 70% throughout different brain regions. It also reversed behavioral abnormalities following neonatal administration. The present study indicated that the IONIS 486178 ASO targets mutant DMPK mRNAs in the brain and strongly supports the feasibility of a therapy for DM1 patients based on the intrathecal injection of an ASO.

Combining NGN2 programming and dopaminergic patterning for a rapid and efficient generation of hiPSC-derived midbrain neurons

The use of human derived induced pluripotent stem cells (hiPSCs) differentiated to dopaminergic (DA) neurons offers a valuable experimental model to decorticate the cellular and molecular mechanisms of Parkinson's disease (PD) pathogenesis. However, the existing approaches present with several limitations, notably the lengthy time course of the protocols and the high variability in the yield of DA neurons. Here we report on the development of an improved approach that combines neurogenin-2 programming with the use of commercially available midbrain differentiation kits for a rapid, efficient, and reproducible directed differentiation of hiPSCs to mature and functional induced DA (iDA) neurons, with minimum contamination by other brain cell types. Gene expression analysis, associated with functional characterization examining neurotransmitter release and electrical recordings, support the functional identity of the iDA neurons to A9 midbrain neurons. iDA neurons showed selective vulnerability when exposed to 6-hydroxydopamine, thus providing a viable in vitro approach for modeling PD and for the screening of small molecules with neuroprotective proprieties.

High-throughput optical action potential recordings in hiPSC-derived cardiomyocytes with a genetically encoded voltage indicator in the AAVS1 locus

Cardiomyocytes (CMs) derived from human induced pluripotent stem cells (hiPSCs) represent an excellent in vitro model in cardiovascular research. Changes in their action potential (AP) dynamics convey information that is essential for disease modeling, drug screening and toxicity evaluation. High-throughput optical AP recordings utilizing intramolecular Förster resonance energy transfer (FRET) of the voltage-sensitive fluorescent protein (VSFP) have emerged as a substitute or complement to the resource-intensive patch clamp technique. Here, we functionally validated our recently generated voltage indicator hiPSC lines stably expressing CAG-promoter-driven VSFP in the AAVS1 safe harbor locus. By combining subtype-specific cardiomyocyte differentiation protocols, we established optical AP recordings in ventricular, atrial, and nodal CMs in 2D monolayers using fluorescence microscopy. Moreover, we achieved high-throughput optical AP measurements in single hiPSC-derived CMs in a 3D context. Overall, this system greatly expands the spectrum of possibilities for high-throughput, non-invasive and long-term AP analyses in cardiovascular research and drug discovery.

Deciphering the mechanisms underlying brain alterations and cognitive impairment in congenital myotonic dystrophy

Myotonic dystrophy type 1 (DM1) is a multisystemic and heterogeneous disorder caused by the expansion of CTG repeats in the 3' UTR of the myotonic dystrophy protein kinase (DMPK) gene. There is a congenital form (CDM1) of the disease characterized by severe hypotonia, respiratory insufficiency as well as developmental delays and intellectual disabilities. CDM1 infants manifest important brain structure abnormalities present from birth while, in contrast, older patients with adult-onset DM1 often present neurodegenerative features and milder progressive cognitive deficits. Promising therapies targeting central molecular mechanisms contributing to the symptoms of adult-onset DM1 are currently in development, but their relevance for treating cognitive impairment in CDM1, which seems to be a partially distinct neurodevelopmental disorder, remain to be elucidated. Here, we provide an update on the clinical presentation of CDM1 and review recent in vitro and in vivo models that have provided meaningful insights on its consequences in development, with a particular focus on the brain. We discuss how enhanced toxic gain-of-function of the mutated DMPK transcripts with larger CUG repeats and the resulting dysregulation of RNA-binding proteins may affect the developing cortex in utero. Because the methylation of CpG islets flanking the trinucleotide repeats has emerged as a strong biomarker of CDM1, we highlight the need to investigate the tissue-specific impacts of these chromatin modifications in the brain. Finally, we outline promising potential therapeutic treatments for CDM1 and propose future in vitro and in vivo models with great potential to shed light on this disease.

R1617Q epilepsy mutation slows NaV 1.6 sodium channel inactivation and increases the persistent current and neuronal firing

KEY POINTS

A human Na_V 1.6 construct was established to study the biophysical consequences of the R1617Q mutation on Na_V 1.6 identified in patients with unclassified epileptic encephalopathy and severe intellectual disability. The R1617Q mutation disrupts the inactivation process of the channel, and more specifically, slows the current decay, increases the persistent sodium current that was blocked by tetrodotoxin and riluzole, and disrupts the inactivation voltage-dependence and increases the kinetics of recovery. In native hippocampal neurons, the R1617Q mutation exhibited a significant increase in action potentials triggered in response to stimulation and a significant increase in the number of neurons that exhibited spontaneous activity compared to neurons expressing WT channels that were inhibited by riluzole. The abnormally persistent current activity caused by the disruption of the channel inactivation process in Na_V 1.6/R1617Q may result in epileptic encephalopathy in patients.

ABSTRACT

The voltage-gated sodium channel Na_V 1.6 is the most abundantly expressed sodium channel isoform in the central nervous system. It plays a critical role in saltatory and continuous conduction. Although over 40 Na_V 1.6 mutations have been linked to epileptic encephalopathy, only a few have been functionally analysed. In the present study, we characterized a Na_V 1.6 mutation (R1617Q) identified in patients with epileptic encephalopathy and intellectual disability. R1617Q substitutes an arginine for a glutamine in the S4 segment of domain IV, which plays a major role in coupling the activation and inactivation of sodium channels. We used patch-clamp to show that R1617Q is a gain-of-function mutation. It is typified by slower inactivation kinetics and a loss of inactivation of voltage-dependence, which result in a 2.5-fold increase in the window current. In addition, sodium currents exhibited an enhanced rate of recovery from inactivation, most likely due to the destabilization of the inactivation state. The alterations in the fast inactivation caused a significant increase in the persistent sodium current. Overexpression of R1617Q in rat hippocampal neurons resulted in an increase in action potential firing activity that was inhibited by riluzole, consistent with the gain-of-function observed. We conclude that the R1617Q mutation causes neuronal hyperexcitability and may result in epileptic encephalopathy.

Preseeding of Mesenchymal Stem Cells Increases Integration of an iPSC-Derived CM Sheet into a Cardiac Matrix

Cell sheet technology has demonstrated great promise in delivering a large amount of therapeutic cells for tissue repair, including in the myocardium. However, the lack of host integration remains one of the key challenges in using cell sheets for cardiac repair. Paracrine factors secreted by mesenchymal stem cells (MSCs) have been reported to facilitate tissue repair and regeneration in a variety of ways. It has been demonstrated that paracrine factors from MSCs could enhance scaffold recellularization and vascularization. In this study, we used an in vitro cardiac matrix mimic platform to examine the effects of hMSCs preseeding on the interactions between cell sheets and cardiac matrix. The fabricated human induced pluripotent stem cells-derived cardiomyocyte sheets were attached to a decellularized porcine myocardium slice with or without preseeding of hMSCs. The hMSCs preseeding significantly enhanced the interactions between cardiomyocyte sheets and cardiac matrix in terms of cell migration distance, cell distribution, and mature vascular and cardiomyocyte marker expressions in the matrix. Growth factor and matrix metalloproteinases array analysis suggested that hMSCs- induced vascularization and MMPs regulation are the two possible mechanisms that lead to the improved CMs and cardiac matrix interactions. Further examination of these two mechanisms will enable the development of new approaches to facilitate transplanted cells for tissue repair.