Direct reprogramming of adult somatic cells into other lineages: past evidence and future perspectives

The transdifferentiation of human dedifferentiated fat cells into fibroblasts: An in vitro experimental pilot study

BACKGROUND

Skin grafting is a common method of treating damaged skin; however, surgical complications may arise in patients with poor health. Currently, no effective conservative treatment is available for extensive skin loss. Mature adipocytes, which constitute a substantial portion of adipose tissue, have recently emerged as a potential source of stemness. When de-lipidated, these cells exhibit fibroblast-like characteristics and the ability to redifferentiate, offering homogeneity and research utility as "dedifferentiated fat cells."

METHODS AND RESULTS

We conducted an in vitro study to induce fibroblast-like traits in the adipose tissue by transdifferentiating mature adipocytes for skin regeneration. Human subcutaneous fat tissues were isolated and purified from mature adipocytes that underwent a transformation process over 14 days of cultivation. Microscopic analysis revealed lipid degradation over time, ultimately transforming cells into fibroblast-like forms. Flow cytometry was used to verify their characteristics, highlighting markers such as CD90 and CD105 (mesenchymal stem cell markers) and CD56 and CD106 (for detecting fibroblast characteristics). Administering dedifferentiated fat cells with transforming growth factor-β at the identified optimal differentiation concentration of 5 ng/mL for a span of 14 days led to heightened expression of alpha smooth muscle actin and fibronectin, as evidenced by RNA and protein analysis. Meanwhile, functional validation through cell sorting demonstrated limited fibroblast marker expression in both treated and untreated cells after transdifferentiation by transforming growth factor-β.

CONCLUSION

Although challenges remain in achieving more effective transformation and definitive fibroblast differentiation, our trial could pave the way for a novel skin regeneration treatment strategy.

Transcription Factors in Brain Regeneration: A Potential Novel Therapeutic Target

Transcription factors play a crucial role in providing identity to each cell population. To maintain cell identity, it is essential to balance the expression of activator and inhibitor transcription factors. Cell plasticity and reprogramming offer great potential for future therapeutic applications, as they can regenerate damaged tissue. Specific niche factors can modify gene expression and differentiate or transdifferentiate the target cell to the required fate. Ongoing research is being carried out on the possibilities of transcription factors in regenerating neurons, with neural stem cells (NSCs) being considered the preferred cells for generating new neurons due to their epigenomic and transcriptome memory. NEUROD1/ASCL1, BRN2, MYTL1, and other transcription factors can induce direct reprogramming of somatic cells, such as fibroblasts, into neurons. However, the molecular biology of transcription factors in reprogramming and differentiation still needs to be fully understood.

Advances in Genetic Reprogramming: Prospects from Developmental Biology to Regenerative Medicine

The foundations of cell reprogramming were laid by Yamanaka and co-workers, who showed that somatic cells can be reprogrammed into pluripotent cells (induced pluripotency). Since this discovery, the field of regenerative medicine has seen advancements. For example, because they can differentiate into multiple cell types, pluripotent stem cells are considered vital components in regenerative medicine aimed at the functional restoration of damaged tissue. Despite years of research, both replacement and restoration of failed organs/ tissues have remained elusive scientific feats. However, with the inception of cell engineering and nuclear reprogramming, useful solutions have been identified to counter the need for compatible and sustainable organs. By combining the science underlying genetic engineering and nuclear reprogramming with regenerative medicine, scientists have engineered cells to make gene and stem cell therapies applicable and effective. These approaches have enabled the targeting of various pathways to reprogramme cells, i.e., make them behave in beneficial ways in a patient-specific manner. Technological advancements have clearly supported the concept and realization of regenerative medicine. Genetic engineering is used for tissue engineering and nuclear reprogramming and has led to advances in regenerative medicine. Targeted therapies and replacement of traumatized , damaged, or aged organs can be realized through genetic engineering. Furthermore, the success of these therapies has been validated through thousands of clinical trials. Scientists are currently evaluating induced tissue-specific stem cells (iTSCs), which may lead to tumour-free applications of pluripotency induction. In this review, we present state-of-the-art genetic engineering that has been used in regenerative medicine. We also focus on ways that genetic engineering and nuclear reprogramming have transformed regenerative medicine and have become unique therapeutic niches.

Osteogenic Response to Polysaccharide Nanogel Sheets of Human Fibroblasts After Conversion Into Functional Osteoblasts by Direct Phenotypic Cell Reprogramming

Human dermal fibroblasts (HDFs) were converted into osteoblasts using a ALK inhibitor II (inhibitor of transforming growth factor-β signal) on freeze-dried nanogel-cross-linked porous (FD-NanoClip) polysaccharide sheets or fibers. Then, the ability of these directly converted osteoblasts (dOBs) to produce calcified substrates and the expression of osteoblast genes were analyzed in comparison with osteoblasts converted by exactly the same procedure but seeded onto a conventional atelocollagen scaffold. dOBs exposed to FD-NanoClip in both sheet and fiber morphologies produced a significantly higher concentration of calcium deposits as compared to a control cell sample (i.e., unconverted fibroblasts), while there was no statistically significant difference in calcification level between dOBs exposed to atelocollagen sheets and the control group. The observed differences in osteogenic behaviors were interpreted according to Raman spectroscopic analyses comparing different polysaccharide scaffolds and Fourier transform infrared spectroscopy analyses of dOB cultures. This study substantiates a possible new path to repair large bone defects through a simplified transplantation procedure using FD-NanoClip sheets with better osteogenic outputs as compared to the existing atelocollagen scaffolding material.

The effect of liver donors' age, gender and metabolic state on pancreatic lineage activation

Autologous cells replacement therapy by liver to pancreas transdifferentiation (TD) allows diabetic patients to be also the donors of their own therapeutic tissue. Aim: To analyze whether the efficiency of the process is affected by liver donors' heterogeneity with regard to age, gender and the metabolic state. Materials & methods: TD of liver cells derived from nondiabetic and diabetic donors at different ages was characterized at molecular and cellular levels, in vitro. Results: Neither liver cells proliferation nor the propagated cells TD efficiency directly correlate with the age (3-60 years), gender or the metabolic state of the donors. Conclusion: Human liver cells derived from a wide array of ages and metabolic states can be used for autologous cells therapies for diabetics.

Acquisition of functional neurons by direct conversion: Switching the developmental clock directly

Identifying approaches for treating neurodegeneration is a thorny task but is important for a growing number of patients. Researchers have focused on discovering the underlying molecular mechanisms of reprogramming and optimizing the technologies for acquiring neurons. Direct conversion is one of the most important processes for treating neurological disorders. Induced neurons derived from direct conversion, which bypass the pluripotency stage, are more effective, more quickly obtained, and are safer than those produced via induced pluripotent stem cells (iPSCs). Based on iPSC strategies, scientists have derived methods to obtain functional neurons by direct conversion, such as neuron-related transcriptional factors, small molecules, microRNAs, and epigenetic modifiers. In this review, we discuss the present strategies for direct conversion of somatic cells into functional neurons and the potentials of direct conversion for producing functional neurons and treating neurodegeneration.

Impelling force and current challenges by chemicals in somatic cell reprogramming and expansion beyond hepatocytes

In the field of regenerative medicine, generating numerous transplantable functional cells in the laboratory setting on a large scale is a major challenge. However, the in vitro maintenance and expansion of terminally differentiated cells are challenging because of the lack of specific environmental and intercellular signal stimulations, markedly hindering their therapeutic application. Remarkably, the generation of stem/progenitor cells or functional cells with effective proliferative potential is markedly in demand for disease modeling, cell-based transplantation, and drug discovery. Despite the potent genetic manipulation of transcription factors, integration-free chemically defined approaches for the conversion of somatic cell fate have garnered considerable attention in recent years. This review aims to summarize the progress thus far and discuss the advantages, limitations, and challenges of the impact of full chemicals on the stepwise reprogramming of pluripotency, direct lineage conversion, and direct lineage expansion on somatic cells. Owing to the current chemical-mediated induction, reprogrammed pluripotent stem cells with reproducibility difficulties, and direct lineage converted cells with marked functional deficiency, it is imperative to generate the desired cell types directly by chemically inducing their potent proliferation ability through a lineage-committed progenitor state, while upholding the maturation and engraftment capacity posttransplantation in vivo. Together with the comprehensive understanding of the mechanism of chemical drives, as well as the elucidation of specificity and commonalities, the precise manipulation of the expansion for diverse functional cell types could broaden the available cell sources and enhance the cellular function for clinical application in future.

Making NSC and Neurons from Patient-Derived Tissue Samples

The human brain and mechanisms underlying its functioning has been a field of intense research due to its complexity, inaccessibility, and the large numbers of debilitating disorders affecting this organ. Model organisms have provided great insight into the functioning of the mammalian brain; however, there exist many features unique to humans which need detailed understanding. In this context, human pluripotent stem cells (HPSCs) have emerged as a promising resource.In the developing brain, cortical diversification is achieved by neural stem cells/neural progenitor cells (NSCs/NPCs) by altering its potency (from multipotent to unipotent) and differentiation capacity (from neurogenesis to gliogenesis). Recent development in tissue reprogramming allows for derivation of NSCs/NPCs from either healthy control subjects manipulated to carry disease mutations or affected individuals carrying specific disease-causing mutations allowing for detailed evaluation of cellular phenotype, pharmacological manipulation, and/or toxicological screening.In this chapter, we will discuss HPSC differentiation into neural stem cells (NSCs) and neurons. We will review the mechanism underlying in vivo neural differentiation and methods which recapitulate this in vitro. We describe a method of deriving NSCs and differentiated mature neurons highlighting key steps of the core protocol. We also provide detailed information of the transcription factor and morphogen map of the developing brain which can be used as a guide to derive region- and lineage-specific NSCs and differentiated neurons.

Direct phenotypic conversion of human fibroblasts into functional osteoblasts triggered by a blockade of the transforming growth factor-β signal

A procedure to generate functional osteoblasts from human somatic cells may pave the way to a novel and effective transplantation therapy in bone disorders. Here, we report that human fibroblasts were induced to show osteoblast phenotypes by culturing with ALK5 i II, which is a specific inhibitor for activin-like kinase 5 (ALK5) (tumor growth factor-β receptor 1 (TGF-β R1)). Cells cultured with ALK5 i II expressed osteoblast-specific genes and massively produced calcified bone matrix, similar to the osteoblasts induced from mesenchymal stem cells (MSC-OBs). Treatment with vitamin D3 in addition to ALK5 i II induced more osteoblast-like characters, and the efficiency of the conversion reached approximately 90%. The chemical compound-mediated directly converted osteoblasts (cOBs) were similar to human primary osteoblasts in terms of expression profiles of osteoblast-related genes. The cOBs abundantly produced bone matrix in vivo and facilitated bone healing after they were transplanted into immunodeficient mice at an artificially induced defect lesion in femoral bone. The present procedure realizes a highly efficient direct conversion of human fibroblasts into transgene-free and highly functional osteoblasts, which might be applied in a novel strategy of bone regeneration therapy in bone diseases.

Adult Stem Cell-Based Strategies for Peripheral Nerve Regeneration

Peripheral nerve injuries (PNI) occur as the result of sudden trauma and can lead to life-long disability, reduced quality of life, and heavy economic and social burdens. Although the peripheral nervous system (PNS) has the intrinsic capacity to regenerate and regrow axons to a certain extent, current treatments frequently show incomplete recovery with poor functional outcomes, particularly for large PNI. Many surgical procedures are available to halt the propagation of nerve damage, and the choice of a procedure depends on the extent of the injury. In particular, recovery from large PNI gaps is difficult to achieve without any therapeutic intervention or some form of tissue/cell-based therapy. Autologous nerve grafting, considered the "gold standard" is often implemented for treatment of gap formation type PNI. Although these surgical procedures provide many benefits, there are still considerable limitations associated with such procedures as donor site morbidity, neuroma formation, fascicle mismatch, and scarring. To overcome such restrictions, researchers have explored various avenues to improve post-surgical outcomes. The most commonly studied methods include: cell transplantation, growth factor delivery to stimulate regenerating axons and implanting nerve guidance conduits containing replacement cells at the site of injury. Replacement cells which offer maximum benefits for the treatment of PNI, are Schwann cells (SCs), which are the peripheral glial cells and in part responsible for clearing out debris from the site of injury. Additionally, they release growth factors to stimulate myelination and axonal regeneration. Both primary SCs and genetically modified SCs enhance nerve regeneration in animal models; however, there is no good source for extracting SCs and the only method to obtain SCs is by sacrificing a healthy nerve. To overcome such challenges, various cell types have been investigated and reported to enhance nerve regeneration.In this review, we have focused on cell-based strategies aimed to enhance peripheral nerve regeneration, in particular the use of mesenchymal stem cells (MSCs). Mesenchymal stem cells are preferred due to benefits such as autologous transplantation, routine isolation procedures, and paracrine and immunomodulatory properties. Mesenchymal stem cells have been transplanted at the site of injury either directly in their native form (undifferentiated) or in a SC-like form (transdifferentiated) and have been shown to significantly enhance nerve regeneration. In addition to transdifferentiated MSCs, some studies have also transplanted ex-vivo genetically modified MSCs that hypersecrete growth factors to improve neuroregeneration.

Hypothesis about Transdifferentiation As Backbone of Malignancy

Background

Cancer is mainly watched through the prism of random mutations and related corruption of signaling pathways. However, it would seem puzzling to explain the tumor organization, pugnacity and steady evolution of the tumorous disease and, moreover, a systematic ascendancy over the healthy tissues, only through stochastic genomic alterations.

Malignancy specific properties

Considering the core characteristics of cancer cells, it appears that two major sets of properties are emerging, corresponding to well-identified physiological phenotypes, i.e., (1) the trophoblastic logistical functions for cell survival, protection, expansion, migration, and host-tissue conditioning for angiogenesis and immune tolerance and (2) the sexual functions for genome maintenance. To explain the resurgence of these trophoblastic and sexual phenotypes, a particular cell reprogramming, to be called “malignant transdifferentiation” in view of its key role in the precancer-to-cancer shift, appears to be a convincing hypothesis.

Perspectives

The concept of malignant transdifferentiation, in addition to oncogenic mutations, would determine a more rational approach of oncogenesis and would open so far unexplored ways of therapeutic actions. Indeed, the trophoblastic phenotype would be a good candidate for therapeutic purposes because, on the one hand, it covers numerous properties that all are vital for the tumor, and on the other hand, it can be targeted with potentially no risk of affecting the healthy tissues as it is not expressed there after birth.

A review of induced pluripotent stem cell, direct conversion by trans-differentiation, direct reprogramming and oligodendrocyte differentiation

Rapid progress in the field of stem cell therapy and cellular reprogramming provides convincing evidence of its feasibility in treating a wide range of pathologies through autologous cell replacement therapy. This review article describes in detail on three widely used approaches of somatic cell reprogramming: induced pluripotent stem cells, direct conversion and direct reprogramming, in the context of demyelination in the CNS. The potential limitations of each reprogramming technique are reviewed along with their distinct molecular approach to reprogramming. This is followed by an analysis on the scopes and challenges of its translational applications in deriving oligodendrocyte progenitor cells and oligodendrocytes for cell replacement treatment of demyelinating conditions in the CNS.

New approaches for direct conversion of patient fibroblasts into neural cells

Recent landmark studies have demonstrated the production of disease-relevant human cell types by two different methods; differentiation of stem cells using external morphogens or lineage conversion using genetic factors. Directed differentiation changes embryonic stem cells (ESCs) or induced pluripotent stem cells (iPSCs) into a desired cell type by providing developmental cues in an in vitro environment. Direct reprogramming is achieved by the introduction of exogenous lineage specific transcription factors to convert any somatic cell type into another, thereby bypassing an intermediate pluripotent stage. A variety of somatic cell types such as blood, keratinocytes and fibroblasts can be used to derive iPSC cells. However, the process is time consuming,laborious, expensive and gives rise to cells with reported epigenetic heterogeneity even amongst different iPSC lines from same patient which could propagate phenotypic variability. A major concern with the use of pluripotent cells as starting material for cell replacement therapy is their incomplete differentiation and their propensity to form tumors following transplantation. In comparison, transcription factor mediated reprogramming offers a direct route to target cell types. This could allow for rapid comparison of large cohorts of patient and control samples at a given time for disease modeling. Additionally, transcription factors that drive maturation may yield more functionally mature cells than directed differentiation. Several studies have demonstrated the feasibility of generating of cell types such as cardiomyocytes, hepatocytes, and neurons from fibroblasts. Here, we will discuss recent advances and key challenges regarding direct reprogramming of somatic cell types into diverse neural cells. This article is part of a Special Issue entitled SI: Exploiting human neurons.