Transcription Factors in Regulatory and Protein Subnetworks during Generation of Neural Stem Cells and Neurons from Direct Reprogramming of Non-fibroblastic Cell Sources

Stem cell therapies: a new era in the treatment of multiple sclerosis

Multiple Sclerosis (MS) is an immune-mediated condition that persistently harms the central nervous system. While existing treatments can slow its course, a cure remains elusive. Stem cell therapy has gained attention as a promising approach, offering new perspectives with its regenerative and immunomodulatory properties. This article reviews the application of stem cells in MS, encompassing various stem cell types, therapeutic potential mechanisms, preclinical explorations, clinical research advancements, safety profiles of clinical applications, as well as limitations and challenges, aiming to provide new insights into the treatment research for MS.

Generation and Application of Directly Reprogrammed Endothelial Cells

Cell-based therapy has emerged as a promising option for treating advanced ischemic cardiovascular disease by inducing vascular regeneration. However, clinical trials with adult cells turned out disappointing in general. As a newer approach, direct reprogramming has emerged to efficiently generate endothelial cells (ECs), which can promote neovascularization and vascular regeneration. This review provides recent updates on the direct endothelial reprogramming. In general, directly reprogrammed ECs can be generated by two approaches: one by transitioning through a plastic intermediate state and the other in a one-step transition without any intermediate states toward pluripotency. Moreover, the methods to deliver reprogramming factors and chemicals for the fate conversion are highlighted. Next, the therapeutic effects of the directly reprogrammed ECs on animal models are reviewed in detail. Other applications using directly reprogrammed ECs, such as tissue engineering and disease modeling, are also discussed. Lastly, the remaining questions and foremost challenges are addressed.

Gene regulatory networks of epidermal and neural fate choice in a chordate

Neurons are a highly specialized cell type only found in metazoans. They can be scattered throughout the body or grouped together, forming ganglia or nerve cords. During embryogenesis, centralized nervous systems develop from the ectoderm, which also forms the epidermis. How pluripotent ectodermal cells are directed toward neural or epidermal fates, and to which extent this process is shared among different animal lineages, are still open questions. Here, by using micromere explants, we were able to define in silico the putative gene regulatory networks (GRNs) underlying the first steps of the epidermis and the central nervous system formation in the cephalochordate amphioxus. We propose that although the signal triggering neural induction in amphioxus (i.e., Nodal) is different from vertebrates, the main transcription factors implicated in this process are conserved. Moreover, our data reveal that transcription factors of the neural program seem to not only activate neural genes but also to potentially have direct inputs into the epidermal GRN, suggesting that the Nodal signal might also contribute to neural fate commitment by repressing the epidermal program. Our functional data on whole embryos support this result and highlight the complex interactions among the transcription factors activated by the signaling pathways that drive ectodermal cell fate choice in chordates.

Induced Neurons for Disease Modeling and Repair: A Focus on Non-fibroblastic Cell Sources in Direct Reprogramming

Direct cellular reprogramming exhibits distinct advantages over reprogramming from an induced pluripotent stem cell intermediate. These include a reduced risk of tumorigenesis and the likely preservation of epigenetic data. In vitro direct reprogramming approaches primarily aim to model the pathophysiological development of neurological disease and identify therapeutic targets, while in vivo direct reprogramming aims to develop treatments for various neurological disorders, including cerebral injury and cancer. In both approaches, there is progress toward developing increased control of subtype-specific production of induced neurons. A majority of research primarily utilizes fibroblasts as the donor cells. However, there are a variety of other somatic cell types that have demonstrated the potential for reprogramming into induced neurons. This review highlights studies that utilize non-fibroblastic cell sources for reprogramming, such as astrocytes, olfactory ensheathing cells, peripheral blood cells, Müller glia, and more. We will examine benefits and obstructions for translation into therapeutics or disease modeling, as well as efficiency of the conversion. A summary of donor cells, induced neuron types, and methods of induction is also provided.

Neuronal Reprogramming for Tissue Repair and Neuroregeneration

Stem cell and cell reprogramming technology represent a rapidly growing field in regenerative medicine. A number of novel neural reprogramming methods have been established, using pluripotent stem cells (PSCs) or direct reprogramming, to efficiently derive specific neuronal cell types for therapeutic applications. Both in vitro and in vivo cellular reprogramming provide diverse therapeutic pathways for modeling neurological diseases and injury repair. In particular, the retina has emerged as a promising target for clinical application of regenerative medicine. Herein, we review the potential of neuronal reprogramming to develop regenerative strategy, with a particular focus on treating retinal degenerative diseases and discuss future directions and challenges in the field.

miR-155 increases stemness and decitabine resistance in triple-negative breast cancer cells by inhibiting TSPAN5

Effective therapeutic targets for triple-negative breast cancer (TNBC), a special type of breast cancer (BC) with rapid metastasis and poor prognosis, are lacking, especially for patients with chemotherapy resistance. Decitabine (DCA) is a Food and Drug Administration-approved DNA methyltransferase inhibitor that has been proven effective for the treatment of tumors. However, its antitumor effect in cancer cells is limited by multidrug resistance. Cancer stem cells (CSCs), which are thought to act as seeds during tumor formation, regulate tumorigenesis, metastasis, and drug resistance through complex signaling. Our previous study found that miR-155 is upregulated in BC, but whether and how miR-155 regulates DCA resistance is unclear. In this study, we demonstrated that miR-155 was upregulated in CD24^- CD44⁺ BC stem cells (BCSCs). In addition, the overexpression of miR-155 increased the number of CD24^- CD44⁺ CSCs, DCA resistance and tumor clone formation in MDA-231 and BT-549 BC cells, and knockdown of miR-155 inhibited DCA resistance and stemness in BCSCs in vitro. Moreover, miR-155 induced stemness and DCA resistance by inhibiting the direct target gene tetraspanin-5 (TSPAN5). We further confirmed that overexpression of TSPAN5 abrogated the effect of miR-155 in promoting stemness and DCA resistance in BC cells. Our data show that miR-155 increases stemness and DCA resistance in BC cells by targeting TSPAN5. These data provide a therapeutic strategy and mechanistic basis for future possible clinical applications targeting the miR-155/TSPAN5 signaling axis in the treatment of TNBC.

Direct cell-fate conversion of somatic cells: Toward regenerative medicine and industries

Cells of multicellular organisms have diverse characteristics despite having the same genetic identity. The distinctive phenotype of each cell is determined by molecular mechanisms such as epigenetic changes that occur throughout the lifetime of an individual. Recently, technologies that enable modification of the fate of somatic cells have been developed, and the number of studies using these technologies has increased drastically in the last decade. Various cell types, including neuronal cells, cardiomyocytes, and hepatocytes, have been generated using these technologies. Although most direct reprogramming methods employ forced transduction of a defined sets of transcription factors to reprogram cells in a manner similar to induced pluripotent cell technology, many other strategies, such as methods utilizing chemical compounds and microRNAs to change the fate of somatic cells, have also been developed. In this review, we summarize transcription factor-based reprogramming and various other reprogramming methods. Additionally, we describe the various industrial applications of direct reprogramming technologies.

Next-generation disease modeling with direct conversion: a new path to old neurons

Within just over a decade, human reprogramming-based disease modeling has developed from a rather outlandish idea into an essential part of disease research. While iPSCs are a valuable tool for modeling developmental and monogenetic disorders, their rejuvenated identity poses limitations for modeling age-associated diseases. Direct cell-type conversion of fibroblasts into induced neurons (iNs) circumvents rejuvenation and preserves hallmarks of cellular aging. iNs are thus advantageous for modeling diseases that possess strong age-related and epigenetic contributions and can complement iPSC-based strategies for disease modeling. In this review, we provide an overview of the state of the art of direct iN conversion and describe the key epigenetic, transcriptomic, and metabolic changes that occur in converting fibroblasts. Furthermore, we summarize new insights into this fascinating process, particularly focusing on the rapidly changing criteria used to define and characterize in vitro-born human neurons. Finally, we discuss the unique features that distinguish iNs from other reprogramming-based neuronal cell models and how iNs are relevant to disease modeling.

Chemical modulation of transcriptionally enriched signaling pathways to optimize the conversion of fibroblasts into neurons

Direct conversion of human somatic fibroblasts into induced neurons (iNs) allows for the generation of functional neurons while bypassing any stem cell intermediary stages. Although iN technology has an enormous potential for modeling age-related diseases, as well as therapeutic approaches, the technology faces limitations due to variable conversion efficiencies and a lack of thorough understanding of the signaling pathways directing iN conversion. Here, we introduce a new all-in-one inducible lentiviral system that simplifies fibroblast transgenesis for the two pioneer transcription factors, Ngn2 and Ascl1, and markedly improves iN yields. Further, our timeline RNA-Seq data across the course of conversion has identified signaling pathways that become transcriptionally enriched during iN conversion. Small molecular modulators were identified for four signaling pathways that reliably increase the yield of iNs. Taken together, these advances provide an improved toolkit for iN technology and new insight into the mechanisms influencing direct iN conversion.

Methyl 3,4-Dihydroxybenzoate Induces Neural Stem Cells to Differentiate Into Cholinergic Neurons in vitro

Neural stem cells (NSCs) have been shown as a potential source for replacing degenerated neurons in neurodegenerative diseases. However, the therapeutic potential of these cells is limited by the lack of effective methodologies for controlling their differentiation. Inducing endogenous pools of NSCs by small molecule can be considered as a potential approach of generating the desired cell types in large numbers. Here, we reported the characterization of a small molecule (Methyl 3,4-dihydroxybenzoate; MDHB) that selectively induces hippocampal NSCs to differentiate into cholinergic motor neurons which expressed synapsin 1 (SYN1) and postsynaptic density protein 95 (PSD-95). Studies on the mechanisms revealed that MDHB induced the hippocampal NSCs differentiation into cholinergic motor neurons by inhibiting AKT phosphorylation and activating autophosphorylation of GSK3β at tyrosine 216. Furthermore, we found that MDHB enhanced β-catenin degradation and abolished its entering into the nucleus. Collectively, this report provides the strong evidence that MDHB promotes NSCs differentiation into cholinergic motor neurons by enhancing gene Isl1 expression and inhibiting cell cycle progression. It may provide a basis for pharmacological effects of MDHB directed on NSCs.