Induced pluripotent stem cells: applications in regenerative medicine, disease modeling, and drug discovery

Abstract

Recent progresses in the field of Induced Pluripotent Stem Cells (iPSCs) have opened up many gateways for the research in therapeutics. iPSCs are the cells which are reprogrammed from somatic cells using different transcription factors. iPSCs possess unique properties of self renewal and differentiation to many types of cell lineage. Hence could replace the use of embryonic stem cells (ESC), and may overcome the various ethical issues regarding the use of embryos in research and clinics. Overwhelming responses prompted worldwide by a large number of researchers about the use of iPSCs evoked a large number of peple to establish more authentic methods for iPSC generation. This would require understanding the underlying mechanism in a detailed manner. There have been a large number of reports showing potential role of different molecules as putative regulators of iPSC generating methods. The molecular mechanisms that play role in reprogramming to generate iPSCs from different types of somatic cell sources involves a plethora of molecules including miRNAs, DNA modifying agents (viz. DNA methyl transferases), NANOG, etc. While promising a number of important roles in various clinical/research studies, iPSCs could also be of great use in studying molecular mechanism of many diseases. There are various diseases that have been modeled by uing iPSCs for better understanding of their etiology which maybe further utilized for developing putative treatments for these diseases. In addition, iPSCs are used for the production of patient-specific cells which can be transplanted to the site of injury or the site of tissue degeneration due to various disease conditions. The use of iPSCs may eliminate the chances of immune rejection as patient specific cells may be used for transplantation in various engraftment processes. Moreover, iPSC technology has been employed in various diseases for disease modeling and gene therapy. The technique offers benefits over other similar techniques such as animal models. Many toxic compounds (different chemical compounds, pharmaceutical drugs, other hazardous chemicals, or environmental conditions) which are encountered by humans and newly designed drugs may be evaluated for toxicity and effects by using iPSCs. Thus, the applications of iPSCs in regenerative medicine, disease modeling, and drug discovery are enormous and should be explored in a more comprehensive manner.

Keywords: differentiation; disease modeling; drug discovery; gene therapy; iPSC; pluripotency; reprogramming.

Figure 1

Historical timeline showing events that led to the development of iPSCs and the recent advances that have occurred in the field.

Figure 2

An overview of the methodology for the generation of iPSCs. (1) Establishment of culture: the source cells are cultured for further use as host cells for the delivery of reprogramming proteins. (2) The cultured source cells are then transfected with the four factors from Yamanaka's cocktail and incubated on feeder layers that provide the nourishment to host cells and are responsible for the formation of extra cellular matrix, under suitable conditions of media. Two types of methods for the delivery of reprogramming factors into the somatic cells can be used- Integrating viral vector systems and Non-Integrating methods. (3) After the formation of iPSCs, they are characterized by different morphological and physicochemical analyses, which is followed by the expansion of iPSCs.

Figure 3

Introduction of the four transcription factors (Oct-4, Sox-2, Klf-4, and c-Myc) leads to reprogramming of a somatic cell to an Induced Pluripotent Stem Cell (iPSC) which can further differentiate into different types of cells. Many factors or chemicals are able to replace one of the factors from the basic four factors required for reprogramming, and for the enhancement many other small molecule chemicals or factor are also used.

Figure 4

There are many applications of iPSCs in the fields of gene therapy, disease modeling and drug discovery. Somatic cells from the patient are used for the generation of diseased iPSCs. These diseased iPSCs may be repaired by Gene Therapy and further used for the generation of healthy somatic cells to be transplanted to the patient, or they may be used to produce unrepaired somatic cells for disease modeling or drug screening.