RESUMO
BACKGROUND: Hepatocyte-like cells (iHEPs) generated by transcription factor-mediated direct reprogramming of somatic cells have been studied as potential cell sources for the development of novel therapies targeting liver diseases. The mechanisms involved in direct reprogramming, stability after long-term in vitro expansion, and safety profile of reprogrammed cells in different experimental models, however, still require further investigation. METHODS: iHEPs were generated by forced expression of Foxa2/Hnf4a in mouse mesenchymal stromal cells and characterized their phenotype stability by in vitro and in vivo analyses. RESULTS: The iHEPs expressed mixed hepatocyte and liver progenitor cell markers, were highly proliferative, and presented metabolic activities in functional assays. A progressive loss of hepatic phenotype, however, was observed after several passages, leading to an increase in alpha-SMA+ fibroblast-like cells, which could be distinguished and sorted from iHEPs by differential mitochondrial content. The resulting purified iHEPs proliferated, maintained liver progenitor cell markers, and, upon stimulation with lineage maturation media, increased expression of either biliary or hepatocyte markers. In vivo functionality was assessed in independent pre-clinical mouse models. Minimal engraftment was observed following transplantation in mice with acute acetaminophen-induced liver injury. In contrast, upon transplantation in a transgenic mouse model presenting host hepatocyte senescence, widespread engraftment and uncontrolled proliferation of iHEPs was observed, forming islands of epithelial-like cells, adipocyte-like cells, or cells presenting both morphologies. CONCLUSION: The results have significant implications for cell reprogramming, suggesting that iHEPs generated by Foxa2/Hnf4a expression have an unstable phenotype and depend on transgene expression for maintenance of hepatocyte-like characteristics, showing a tendency to return to the mesenchymal phenotype of origin and a compromised safety profile.
Assuntos
Células-Tronco Mesenquimais , Animais , Diferenciação Celular , Reprogramação Celular , Hepatócitos , Fígado , Camundongos , FenótipoRESUMO
Aging is associated with a progressive increase in the incidence of neurodegenerative diseases, with Alzheimer's (AD) and Parkinson's (PD) disease being the most conspicuous examples. Within this context, the absence of efficacious therapies for most age-related brain pathologies has increased the interest in regenerative medicine. In particular, cell reprogramming technologies have ushered in the era of personalized therapies that not only show a significant potential for the treatment of neurodegenerative diseases but also promise to make biological rejuvenation feasible. We will first review recent evidence supporting the emerging view that aging is a reversible epigenetic phenomenon. Next, we will describe novel reprogramming approaches that overcome some of the intrinsic limitations of conventional induced-pluripotent-stem-cell technology. One of the alternative approaches, lineage reprogramming, consists of the direct conversion of one adult cell type into another by transgenic expression of multiple lineage-specific transcription factors (TF). Another strategy, termed pluripotency factor-mediated direct reprogramming, uses universal TF to generate epigenetically unstable intermediates able to differentiate into somatic cell types in response to specific differentiation factors. In the third part we will review studies showing the potential relevance of the above approaches for the treatment of AD and PD.
Assuntos
Envelhecimento/metabolismo , Encéfalo/metabolismo , Reprogramação Celular/fisiologia , Medicina Regenerativa/métodos , Rejuvenescimento/fisiologia , Envelhecimento/patologia , Animais , Encéfalo/patologia , Diferenciação Celular/fisiologia , Humanos , Células-Tronco Pluripotentes Induzidas/fisiologia , Células-Tronco Pluripotentes Induzidas/transplante , Doenças Neurodegenerativas/metabolismo , Doenças Neurodegenerativas/patologia , Medicina Regenerativa/tendências , Fatores de Transcrição/metabolismoRESUMO
After the demonstration that somatic cells could be reprogrammed to a pluripotent state, exciting new prospects were opened for the cardiac regeneration field. It did not take long for the development of strategies to convert somatic cells directly into cardiomyocytes. Despite the intrinsic difficulties of cell reprogramming, such as low efficiency, the therapeutic possibilities created by the ability to turn scar into muscle are enormous. Here, we discuss some of the major advances and strategies used in direct cardiac reprogramming and examine discrepancies and concerns that still need to be resolved in the field.