RESEARCH
IN VIVO REPROGRMMING FOR TISSUE REPAIR
Research
In vivo Reprogramming and Tissue Regeneration
The induction of cellular plasticity and dedifferentiation in somatic cells to pluripotency can be achieved through prolonged expression of the 'Yamanaka factors' - Oct4, Sox2, Klf4, and c-Myc (referred to as OSKM). This process involves epigenetic reprogramming, including progressive and consistent erasure of DNA methylation. OSKM-driven cellular reprogramming serves as the standard method for generating induced pluripotent stem cells (iPSCs) and finds extensive applications. More recently, studies have shown that OSKM-induced partial reprogramming not only rejuvenates aged mice but also triggers fetal-like dedifferentiation in various tissues such as the eye, muscle, heart, and liver. This rejuvenation is achieved by establishing youthful DNA methylation patterns and transcriptomes while activating muscle stem cells and cardiomyocytes. However, the specific mechanisms underlying the regenerative effects of partial reprogramming in diverse tissues remain unclear. Given the similarity between the characteristics of transiently dedifferentiated repair stem cells post-injury and reprogrammed stem cells through OSKM, researchers are exploring common molecular mechanisms that could explain these phenomena
PLURIPOTENT STEM CELLS AND DISEASE MODELING
The breakthrough of inducing pluripotent stem cells (iPSCs) from human somatic cells had significant implications for regenerative medicine and drug discovery. This advancement allowed the creation of patient iPSCs with disease-causing mutations, serving two primary purposes: understanding disease mechanisms and conducting drug screening based on disease phenotypes. This approach, referred to as "diseases-in-a-dish," employs patient-derived iPSCs to uncover pathogenic characteristics. However, variations in cellular traits stemming from individual genetic differences often outweigh disease-related effects, complicating comparative analysis. To facilitate precise comparisons, genome editing techniques that target specific sequences are crucial for generating isogenic pairs of disease and control human pluripotent stem cells (hPSCs). Moreover, the success of the first autologous stem cell therapy using iPSC-derived cells for Parkinson's disease has opened new avenues for personalized regenerative therapies. In addition to autologous stem cell therapy for degenerative disorders, using genetically corrected cells obtained from edited iPSCs offers promise for treating various genetic diseases through ex vivo cell therapies. Consequently, the efficacy and safety of novel genome editing techniques have been extensively validated in hPSCs shortly after their development, demonstrating potential for translational applications.
Genetic alteration of PLURIPOTENT STEM CELLS
Human pluripotent stem cells (hPSCs) possess unique cellular and molecular properties that safeguard genomic integrity, setting them apart from somatic cells. Particularly, human embryonic stem cells (hESCs) exhibit robust DNA repair mechanisms and heightened vulnerability to genotoxic stressors. These attributes prompt swift cell death via mitochondria-mediated apoptosis upon DNA damage, preventing the passage of mutations to subsequent generations. The phenomenon of 'high mitochondrial priming' in hESCs contributes to rapid cell death upon DNA damage. Consequently, hPSCs tend to accumulate fewer mutations than somatic stem cells during in vitro culture. However, during in vitro maintenance, hPSCs often experience genetic abnormalities like recurrent copy number variations (CNVs), chromosomal abnormalities, and irregular mitosis. These anomalies pose risks to the safety of hPSC-based cell therapies. Nonetheless, the exact clinical implications and underlying mechanisms of these culture-induced (epi)genetic irregularities in hPSCs remain unclear.
MOLECULAR CONTROL of PLURIPOTENCY
Pluripotent stem cells (PSCs) display two primary states: naïve (or ground) and primed, denoting their condition prior to and after implantation. These pluripotency states (naïve vs. primed) influence diverse attributes of embryonic stem cells, including metabolic variations, signaling disparities, and epigenetic patterns. Grasping the unique qualities of these pluripotent states is essential to address lingering queries regarding early embryo development and the regulation of the transition from totipotency to pluripotency.
