A Novel Isogenic Human Cell-Based System for MEN1 Syndrome Generated by CRISPR/Cas9 Genome Editing

Multiple endocrine neoplasia type 1 (MEN1) is a rare tumor syndrome that manifests differently among various patients. Despite the mutations in the MEN1 gene that commonly predispose tumor development, there are no obvious phenotype-genotype correlations. The existing animal and in vitro models do not allow for studies of the molecular genetics of the disease in a human-specific context. We aimed to create a new human cell-based model, which would consider the variability in genetic or environmental factors that cause the complexity of MEN1 syndrome. Here, we generated patient-specific induced pluripotent stem cell lines carrying the mutation c.1252G>T, D418Y in the MEN1 gene. To reduce the genetically determined variability of the existing cellular models, we created an isogenic cell system by modifying the target allele through CRISPR/Cas9 editing with great specificity and efficiency. The high potential of these cell lines to differentiate into the endodermal lineage in defined conditions ensures the next steps in the development of more specialized cells that are commonly affected in MEN1 patients, such as parathyroid or pancreatic islet cells. We anticipate that this isogenic system will be broadly useful to comprehensively study MEN1 gene function across different contexts, including in vitro modeling of MEN1 syndrome.

Immortalized murine fibroblast cell lines are refractory to reprogramming to pluripotent state

To date different cell types of various mammalian species have been reprogrammed to induced pluripotent stem cells (iPSCs) using Yamanaka's cocktail of transcription factors (Oct4, Klf4, Sox2, and cMyc). It has been shown that several primary human cancer cell lines could be reprogrammed to iPSCs. We sought if immortalized mouse fibroblast cell lines could also be reprogrammed to iPSCs. The approach of generating iPSCs from such cells should be valuable in different experimental settings as it allows clonally derive cell lines carrying mutations whose impact on reprogramming could be next evaluated. Therefore, we investigated reprogramming of widely used immortalized cell lines (NIH3T and STO), as well as of de novo immortalized fibroblast line (tKM) with the use of highly effective lentiviral polycistronic OKSM expression system. Our reprogramming experiments have shown that in contrast to mouse embryonic fibroblasts (MEFs), none of the immortalized cell lines can be reprogrammed to pluripotent state. Contrary to colonies derived from MEFs, those derived from the immortalized cells lines (1) developed much later, (2) contained large round cells, not typical for iPSCs, and (3) were negative for trusted markers of matured iPSCs, Nanog and SSEA1. Immortalized cell lines NIH3T and STO are known to be mostly aneuploid, whereas tKM population includes cells with normal karyotype, however, neither cell type can be reprogrammed. Thus our data argue that aneuploidy per se is not a reason for the observed refractoriness of mouse immortalized cells to reprogramming to pluripotent state.

Reprogramming of HUVECs into induced pluripotent stem cells (HiPSCs), generation and characterization of HiPSC-derived neurons and astrocytes

Neurodegenerative diseases are characterized by chronic and progressive structural or functional loss of neurons. Limitations related to the animal models of these human diseases have impeded the development of effective drugs. This emphasizes the need to establish disease models using human-derived cells. The discovery of induced pluripotent stem cell (iPSC) technology has provided novel opportunities in disease modeling, drug development, screening, and the potential for “patient-matched” cellular therapies in neurodegenerative diseases. In this study, with the objective of establishing reliable tools to study neurodegenerative diseases, we reprogrammed human umbilical vein endothelial cells (HUVECs) into iPSCs (HiPSCs). Using a novel and direct approach, HiPSCs were differentiated into cells of central nervous system (CNS) lineage, including neuronal, astrocyte and glial cells, with high efficiency. HiPSCs expressed embryonic genes such as nanog, sox2 and Oct-3/4, and formed embryoid bodies that expressed markers of the 3 germ layers. Expression of endothelial-specific genes was not detected in HiPSCs at RNA or protein levels. HiPSC-derived neurons possess similar morphology but significantly longer neurites compared to primary human fetal neurons. These stem cell-derived neurons are susceptible to inflammatory cell-mediated neuronal injury. HiPSC-derived neurons express various amino acids that are important for normal function in the CNS. They have functional receptors for a variety of neurotransmitters such as glutamate and acetylcholine. HiPSC-derived astrocytes respond to ATP and acetylcholine by elevating cytosolic Ca²⁺ concentrations. In summary, this study presents a novel technique to generate differentiated and functional HiPSC-derived neurons and astrocytes. These cells are appropriate tools for studying the development of the nervous system, the pathophysiology of various neurodegenerative diseases and the development of potential drugs for their treatments.