Disease Modeling Using Induced Pluripotent Stem Cells

Authors: Donna R. Trollinger and Priyanka Swamynathan

Introduction to iPSC Technology

Since their original discovery in the 1960s, stem cells have been a key player in biology research.¹ Stem cells are defined by their ability to differentiate into other cell types and self-renew indefinitely without senescence. Of particular utility are pluripotent stem cells, which can differentiate into any cell type in the adult body, making them highly useful for generating cells that are difficult to obtain from primary tissues, such as neurons. Pluripotent stem cells are only found in the developing embryo during its pre-implantation stage, after which time their potency and self-renewing properties decrease.

Despite their usefulness, the isolation of embryonic stem cells (ESCs) poses both technical and ethical challenges. These problems were circumvented in 2006, when a landmark paper by Takahashi and Yamanaka described a method to generate induced pluripotent stem cells (iPSCs).²By exposing fully differentiated cells to a cocktail of reprogramming factors, the authors were able to generate iPSCs with very similar properties to ESCs. Since then, numerous other reprogramming factors, as well as alternative technologies such as viral vectors, have been developed for this purpose. In addition, the advent of CRISPR-Cas9 technology has enabled the generation of iPSCs with practically any known genetic mutation.

iPSCs are a valuable tool for disease modeling, even enabling the generation of patient-specific models to facilitate research in personalized medicine. This article will focus on two prominent examples of iPSC disease modeling: Parkinson’s disease and cardiomyopathy.

iPSC Models of Parkinson’s Disease

Parkinson’s disease (PD) is a neurodegenerative disorder characterized by tremors and rigidity, in addition to a range of cognitive issues. PD affects approximately 1% of individuals over age 60. The disease is characterized by the buildup of a toxic protein called alpha-synuclein into aggregates known as Lewy bodies. This buildup is particularly prevalent in dopaminergic neurons within a part of the brain called the substantia nigra, resulting in the motor defects seen with this disease.³

The features of PD have proven difficult to model in the laboratory.⁴ Because most PD cases are sporadic, genetic animal models do not fully recapitulate the course of the disease. In particular, the progressive loss of dopaminergic neurons and the development of Lewy bodies are typically not observed in PD animal models. Furthermore, the drug candidates developed using these models have failed to translate into clinical success.

More recently, iPSCs have been introduced as a model for PD. These models avoid the possibility of species-specific differences between humans and mice. In addition, since they’re derived from PD patients, iPSCs can capture the full myriad of genetic risk factors that contribute to sporadic PD, in contrast to the relative simplicity of the animal and cellular models that alter one or a small number of specific genes. Creating iPSC lines from a diverse group of PD patients can allow researchers to understand the genetic heterogeneity of the disease.

An additional benefit of iPSCs is their ability to be differentiated into other cell types, such as the dopaminergic neurons that are directly affected in PD. This enables a far greater supply of disease-relevant cells than postmortem samples can provide. Digging deeper into the phenotypic changes brought about by such differentiation with the help of cellular markers or by observing changes in signature proteins, can help elucidate underlying mechanisms that bring about PD. Several such markers and proteins that are important to PD were highlighted in a recent article.

Brochure: 5 Steps to model Parkinson’s disease

Overcover the challenges of genome editing in human pluripotent stem cells for building tissue-relevant disease models.

In this proven guide, validated steps are provided to facility generation of your new iPSC-derived neurodegenerative disease model.

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Learn more about Parkinson’s Disease Genetics and Related Antibody Targets

iPSC models have been increasing in popularity within the PD research community. One intriguing example was published in 2017 in Nature. The authors of the study showed that dopaminergic progenitor cells derived from human iPSCs could both survive and function after being grafted into a primate model of PD, Macaca fascicularis. The grafted cells differentiated into mature dopaminergic neurons, which extended neurites into the host. Furthermore, the animals who received grafts from a non-PD human donor showed gradual improvements in spontaneous movement. This example highlights the utility of stem cells for disease modeling and their emerging potential as a clinical treatment for PD.⁵

Find antibodies that can be used to study Parkinson’s Disease

iPSC Models of Cardiomyopathy

Cardiomyopathy is another condition where iPSCs have become a critical research tool. Cardiomyopathy encompasses several diseases of the heart muscle that impair its ability to pump blood. The heart becomes enlarged and its muscle is thick or rigid, which can result in heart failure or arrhythmia.

Rodent models for cardiomyopathy are limited due to considerable differences from humans in their electrophysiology and calcium handling. For example, the cardiac action potential lasts 10 times longer in humans than in mice. Thus, human cells are a more reliable model for studying cardiac diseases. Because cardiac muscle cells (cardiomyocytes, CM) have limited regeneration potential, the process of generating large quantities of cells for research purposes relies heavily on stem cells.

A recent application of iPSC derived CMs has been for hypertrophic cardiomyopathy (HCM). HCM is a genetic cardiomyopathy that affects up to 1 in 200 people. The disease is typically inherited in an autosomal dominant manner, and more than 1500 causal variants have been identified. Studies from rodent models suggest that in HCM, CMs enlarge and switch to a more fetal-like gene expression pattern. iPSC-derived CM models of HCM recapitulate many pathological hallmarks of the condition.

Brochure: 5 Steps to model cardiac disease

Overcome the challenges of genome editing in human pluripotent stem cells for building tissue-relevant disease models.

In this proven guide, see the steps our scientist took to model Parkinson’s disease sing human iPSCs.

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Download this free guide

One example of using iPSCs to study HCM was published last year in the Journal of Molecular and Cellular Cardiology. The authors were investigating the role of a protein called troponin T (TnT). Mutations in this gene frequently result in myofilament hypersensitivity to calcium, which is a risk factor for arrhythmia. The authors used CRISPR-Cas9 to generate iPSCs with a missense mutation in the TnT gene. CMs derived from these cells showed myofibrillar disarray, in addition to several physiological characteristics of HCM including enhanced contraction, impaired relaxation, and myofibrillar hypersensitivity to calcium. The study established a useful model for the TnT-mutant variety of HCM and highlighted the utility of gene editing technology for developing specific disease models.

Conclusion

The field of stem cell biology has advanced considerably in the past six decades. iPSCs now allow researchers to use somatic cells to generate practically any differentiated cell type in large quantities. The applications of iPSC technology include disease modeling, regenerative medicine, and drug screening. Advancements in the field are continuing to improve these models and show potential to bring iPSCs further into the forefront of biomedical research.

As mentioned above, studying alterations in protein expression can decode causes and mechanisms of diseases and laboratory tools like antibodies further assist such research. Antibodies are considered workhorses of biological experiments and can be used in a variety of applications including western blotting, live/fixed cell visualization using immunofluorescence, ELISA, flow cytometry and immunoprecipitation to study protein interactions and functions, qualitatively and quantitatively. Some helpful resources to find antibodies crucial to stem cells and neurodegenerative disorders are linked below.

Download these posters to find antibodies useful to stem cell and neuroscience research.

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