Regenerative Medicine for the Aging Brain

In the central nervous system, cholinergic and dopaminergic (DA) neurons are among the cells most susceptible to the deleterious effects of age. Thus, the basal forebrain cholinergic system is known to undergo moderate neurodegenerative changes during normal aging as well as severe atrophy in Alzheimer’s disease (AD). Parkinson’s disease (PD), a degeneration of nigro-striatal DA neurons is the most conspicuous reflection of the vulnerability of DA neurons to age. In this context, cell reprogramming offers novel therapeutic possibilities for the treatment of these devastating diseases. In effect, the generation of induced pluripotent stem cells (iPSCs) from somatic cells demonstrated that adult mammalian cells can be reprogrammed to a pluripotent state by the overexpression of a few embryonic transcription factors (TF). This discovery fundamentally widened the research horizon in the fields of disease modeling and regenerative medicine. Although it is possible to re-differentiate iPSCs to specific somatic cell types, the tumorigenic potential of contaminating iPSCs that failed to differentiate, increases the risk for clinical application of somatic cells generated by this procedure. Therefore, reprogramming approaches that bypass the pluripotent stem cell state are being explored. A method called lineage reprogramming has been recently documented. It consists of the direct conversion of one adult cell type into another by transgenic expression of multiple lineage-specific TF or microRNAs. Another approach, termed direct reprogramming, features several advantages such as the use of universal TF system and the ability to generate a rejuvenated multipotent progenitor cell population, able to differentiate into specific cell types in response to a specific differentiation factors. These novel approaches offer a new promise for the treatment of pathologies associated with the loss of specific cell types as for instance, nigral DA neurons (in PD) or basal forebrain cholinergic neurons in the early stages of AD. The above topics are reviewed here.Fil: López León, Micaela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Bioquímicas de La Plata ; ArgentinaFil: Reggiani, Paula Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Bioquímicas de La Plata ; ArgentinaFil: Hereñú, Claudia Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Bioquímicas de La Plata ; ArgentinaFil: Goya, Rodolfo Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Bioquímicas de La Plata ; Argentin

Rationale and Methodology of Reprogramming for Generation of Induced Pluripotent Stem Cells and Induced Neural Progenitor Cells.

Great progress has been made regarding the capabilities to modify somatic cell fate ever since the technology for generation of induced pluripotent stem cells (iPSCs) was discovered in 2006. Later, induced neural progenitor cells (iNPCs) were generated from mouse and human cells, bypassing some of the concerns and risks of using iPSCs in neuroscience applications. To overcome the limitation of viral vector induced reprogramming, bioactive small molecules (SM) have been explored to enhance the efficiency of reprogramming or even replace transcription factors (TFs), making the reprogrammed cells more amenable to clinical application. The chemical induced reprogramming process is a simple process from a technical perspective, but the choice of SM at each step is vital during the procedure. The mechanisms underlying cell transdifferentiation are still poorly understood, although, several experimental data and insights have indicated the rationale of cell reprogramming. The process begins with the forced expression of specific TFs or activation/inhibition of cell signaling pathways by bioactive chemicals in defined culture condition, which initiates the further reactivation of endogenous gene program and an optimal stoichiometric expression of the endogenous pluri- or multi-potency genes, and finally leads to the birth of reprogrammed cells such as iPSCs and iNPCs. In this review, we first outline the rationale and discuss the methodology of iPSCs and iNPCs in a stepwise manner; and then we also discuss the chemical-based reprogramming of iPSCs and iNPCs

The lens as a model for fibrotic disease

Fibrosis affects multiple organs and is associated with hyperproliferation, cell transdifferentiation, matrix modification and contraction. It is therefore essential to discover the key drivers of fibrotic events, which in turn will facilitate the development of appropriate therapeutic strategies. The lens is an elegant experimental model to study the processes that give rise to fibrosis. The molecular and cellular organization of the lens is well defined and consequently modifications associated with fibrosis can be clearly assessed. Moreover, the avascular and non-innervated properties of the lens allow effective in vitro studies to be employed that complement in vivo systems and relate to clinical data. Using the lens as a model for fibrosis has direct relevance to millions affected by lens disorders, but also serves as a valuable experimental tool to understand fibrosis per se

Cell divisions are not essential for the direct conversion of fibroblasts into neuronal cells

Direct lineage conversion is a promising approach for disease modeling and regenerative medicine. Cell divisions play a key role in reprogramming of somatic cells to pluripotency, however their role in direct lineage conversion is not clear. Here we used transdifferentiation of fibroblasts into neuronal cells by forced expression of defined transcription factors as a model system to study the role of cellular division in the direct conversion process. We have shown that conversion occurs in the presence of the cell cycle inhibitors aphidicolin or mimosine. Moreover, overexpression of the cell cycle activator cMyc negatively influences the process of direct conversion. Overall, our results suggest that cell divisions are not essential for the direct conversion of fibroblasts into neuronal cells

Cardiomyocyte generation from somatic sources — current status and future directions

Transdifferentiation of one cell type to another has garnered significant research efforts in recent years. As cardiomyocyte loss following myocardial infarction becomes debilitating for cardiac patients, the option of an autologous source of cardiomyocytes not derived from multi/pluripotent stem cell sources is an attractive option. Such direct programming has been clearly realized with the use of transcription factors, microRNAs and more recently small molecule delivery to enhance epigenetic modifications, all albeit with low efficiencies in vitro. In this review, we aim to present a brief overview of the current in vitro and in vivo transdifferentiation strategies in the generation of cardiomyocytes from somatic sources. The interdisciplinary fields of tissue, cell, material and regenerative engineering offer many opportunities to synergistically achieve directly programmed cardiac tissue in vitro and enhance transdifferentiation in vivo. This review aims to present a concise outlook on this topic with these fields in mind

Role of galectin-3 in bone cell differentiation, bone pathophysiology and vascular osteogenesis

Galectin-3 is expressed in various tissues, including the bone, where it is considered a marker of chondrogenic and osteogenic cell lineages. Galectin-3 protein was found to be increased in the differentiated chondrocytes of the metaphyseal plate cartilage, where it favors chondrocyte survival and cartilage matrix mineralization. It was also shown to be highly expressed in differentiating osteoblasts and osteoclasts, in concomitance with expression of osteogenic markers and Runt-related transcription factor 2 and with the appearance of a mature phenotype. Galectin-3 is expressed also by osteocytes, though its function in these cells has not been fully elucidated. The effects of galectin-3 on bone cells were also investigated in galectin-3 null mice, further supporting its role in all stages of bone biology, from development to remodeling. Galectin-3 was also shown to act as a receptor for advanced glycation endproducts, which have been implicated in age-dependent and diabetes-associated bone fragility. Moreover, its regulatory role in inflammatory bone and joint disorders entitles galectin-3 as a possible therapeutic target. Finally, galectin-3 capacity to commit mesenchymal stem cells to the osteoblastic lineage and to favor transdifferentiation of vascular smooth muscle cells into an osteoblast-like phenotype open a new area of interest in bone and vascular pathologies

microRNA induced transdifferentiation

Recent months have seen rapid advances in the field of transdifferentiation, specifically in the conversion of fibroblasts to neurons. Most surprising is the observation that the ability to drive these transitions is not limited to transcription factors, but that they can be promoted by microRNAs as well. Indeed, in one case, microRNAs alone induced the transdifferentiation of fibroblasts to neuron-like cells, albeit at a low efficiency. Here, we review this rapidly advancing field, discuss possible mechanisms underlying microRNA-induced transdifferentiation and the potential for microRNAs to drive such transitions to any cell type of interest in vitro and in vivo

Induced Stem Cells as a Novel Multiple Sclerosis Therapy.

Stem cell replacement is providing hope for many degenerative diseases that lack effective therapeutic methods including multiple sclerosis (MS), an inflammatory demyelinating disease of the central nervous system. Transplantation of neural stem cells or mesenchymal stem cells is a potential therapy for MS thanks to their capacity for cell repopulation as well as for their immunomodulatory and neurotrophic properties. Induced pluripotent stem cell (iPSC), an emerging cell source in regenerative medicine, is also being tested for the treatment of MS. Remarkable improvement in mobility and robust remyelination have been observed after transplantation of iPSC-derived neural cells into demyelinated models. Direct reprogramming of somatic cells into induced neural cells, such as induced neural stem cells (iNSCs) and induced oligodendrocyte progenitor cells (iOPCs), without passing through the pluripotency stage, is an alternative for transplantation that has been proved effective in the congenital hypomyelination model. iPSC technology is rapidly progressing as efforts are being made to increase the efficiency of iPSC therapy and reduce its potential side effects. In this review, we discuss the recent advances in application of stem cells, with particular focus on induced stem/progenitor cells (iPSCs, iNSC, iOPCs), which are promising in the treatment of MS