Human Pluripotent Stem Cells as In Vitro Models of Neurodegenerative Diseases

Abstract

My main research focused in the last years has been the reprogramming of differentiated cell types, such as human fibroblasts, into pluripotent stem cells called induced pluripotent stem cells (iPSCs) and the application of this technology to studies of the nervous system and the diseases that affect it. We have been working on the generation of iPSC lines from Alzheimer’s disease (AD) patients using recent developments in reprogramming strategies such as non-integrating episomal vectors to produce virus-free, clinical safe hiPSC. Our study shows that neurons differentiated from these cells display important disease properties and, thus, have the potential to serve as cellular models to explore various aspects of Alzheimer’s pathogenesis. One of the lab’s scientific goal is to use lines of familial Alzheimer’s disease (FAD)-derived induced pluripotent stem cells (iPSCs) to generate brain-like structures (“organoids”) mimicking native brains. Three-dimensional (3D) systems, called cerebral organoids, can recapitulate distinct architectures of the human brain, such as fluid-filled cavities resembling brain ventricles and tissues organized in layers including progenitor ventricular and subventricular zones present in the native brain. Recently, we have extended our research interests in the rapidly emerging field of exosomes and micro-vesicles (called as EMVs). Extracellular vesicles of either 50–200 nm in size (called exosomes) or 200 nm–1 μm in size (called micro-vesicles) are membrane-bounded vesicles that can carry RNAs, proteins, and other metabolites and are secreted from all cell types and are present in biological fluids such as serum and plasma. We have examined properties and functions of EMVs from human iPSCs that can be cultured infinitely under a chemically defined medium and compared them with the ones secreted by human mesenchymal stem cells (MSCs). Purified EVs produced by both stem cell types have similar sizes, but human iPSCs produced 16-fold more EVs than MSCs. When iPSC-EMVs were applied in culture to senescent MSCs, they reduced their elevated cellular ROS levels and alleviated aging phenotypes. We are currently exploring the potential application of EMVs in diagnostics, pathology, and therapeutics of AD. Extracellular vesicles secreted from AD patient derived neurons contain a relatively low amount of Aβ but have an increased Aβ42/ Aβ40 ratio; the majority of Aβ is located on the surface of the EVs. The results of our research can contribute substantially to the successful translation of stem cell biology into clinical therapy by improving our understanding of the pathogenesis and treatment of Alzheimer’s disease.