Progress and Challenges of Cell Replacement Therapy for Neurodegenerative Diseases Based on Direct Neural Reprogramming

Caffeic acid activates Nrf2 enzymes, providing protection against oxidative damage induced by ionizing radiation

Caffeic acid (CA) is a prevalent polyphenolic compound commonly found in various plant-derived foods. Due to its diverse pharmacological properties, including antioxidant activity, cardiovascular protection, and immune regulation, CA has garnered significant attention. Ionizing radiation (IR) is extensively utilized across industrial sectors, agriculture, defense applications, scientific research, and clinical medicine; however, the detrimental effects of radiation on human health cannot be ignored. IR can directly damage the DNA, proteins, and lipids within macromolecules or ionize water molecules to generate substantial quantities of free radicals that indirectly harm cells, especially those in the brain which are highly susceptible to radiation exposure. Consequently, effective strategies for preventing and treating IR-induced neurological damage represent an urgent medical challenge that necessitates resolution. Our study aims to investigate the protective effects of CA against IR-induced neuronal cell damage along with elucidating its potential mechanisms of action. The results indicate that CA can covalently modify active cysteine residues on Keap1 protein altering its conformation; this modification disrupts the interaction between Keap1 and Nrf2 while facilitating Nrf2's translocation into the nucleus where it activates downstream expression of cellular protective factors such as heme oxygenase-1 (HO-1), NAD(P)H: quinone oxidoreductase 1 (NQO1), Thioredoxin Reductase-1 (TrxR1) and other cellular protective factors to play a role in countering radiation-induced neurological damage. In conclusion, CA emerges as an effective radioprotective agent capable of exerting antiradiation effects. Our findings provide valuable insights for developing novel therapeutic agents aimed at preventing and treating IR-induced neurological impairment.

Recent advances in mRNA-based therapeutics for neurodegenerative diseases and brain tumors

Messenger RNA (mRNA) therapy is an innovative approach that delivers specific protein-coding information. By promoting the ribosomal synthesis of target proteins within cells, it supplements functional or antigenic proteins to treat diseases. Unlike traditional gene therapy, mRNA does not need to enter the cell nucleus, reducing the risks associated with gene integration. Moreover, protein expression levels can be regulated by adjusting the dosage and degradation rates of mRNA. As a new generation gene therapy strategy, mRNA therapy represents the latest advancements and trends in the field. It offers advantages such as precision, safety, and ease of modification. It has been widely used in the prevention of COVID-19. Unlike acute conditions such as cerebral hemorrhage and stroke that often require immediate surgical or interventional treatments, neurodegenerative diseases (NDs) and brain tumors progress relatively slowly and face challenges such as the blood-brain barrier and complex pathogenesis. These characteristics make them particularly suitable for mRNA therapy. With continued research, mRNA-based therapeutics are expected to play a significant role in the prevention and treatment of NDs and brain tumors. This paper reviews the preparation and delivery of mRNA drugs and summarizes the research progress of mRNA gene therapy in treating NDs and brain tumors. It also discusses the current challenges, providing a theoretical basis and reference for future research in this field.

Reprogramming Glioblastoma Cells into Non-Cancerous Neuronal Cells as a Novel Anti-Cancer Strategy

Glioblastoma Multiforme (GBM) is an aggressive brain tumor with a high mortality rate. Direct reprogramming of glial cells to different cell lineages, such as induced neural stem cells (iNSCs) and induced neurons (iNeurons), provides genetic tools to manipulate a cell's fate as a potential therapy for neurological diseases. NeuroD1 (ND1) is a master transcriptional factor for neurogenesis and it promotes neuronal differentiation. In the present study, we tested the hypothesis that the expression of ND1 in GBM cells can force them to differentiate toward post-mitotic neurons and halt GBM tumor progression. In cultured human GBM cell lines, including LN229, U87, and U373 as temozolomide (TMZ)-sensitive and T98G as TMZ-resistant cells, the neuronal lineage conversion was induced by an adeno-associated virus (AAV) package carrying ND1. Twenty-one days after AAV-ND1 transduction, ND1-expressing cells displayed neuronal markers MAP2, TUJ1, and NeuN. The ND1-induced transdifferentiation was regulated by Wnt signaling and markedly enhanced under a hypoxic condition (2% O2 vs. 21% O2). ND1-expressing GBM cultures had fewer BrdU-positive proliferating cells compared to vector control cultures. Increased cell death was visualized by TUNEL staining, and reduced migrative activity was demonstrated in the wound-healing test after ND1 reprogramming in both TMZ-sensitive and -resistant GBM cells. In a striking contrast to cancer cells, converted cells expressed the anti-tumor gene p53. In an orthotopical GBM mouse model, AAV-ND1-reprogrammed U373 cells were transplanted into the fornix of the cyclosporine-immunocompromised C57BL/6 mouse brain. Compared to control GBM cell-formed tumors, cells from ND1-reprogrammed cultures formed smaller tumors and expressed neuronal markers such as TUJ1 in the brain. Thus, reprogramming using a single-factor ND1 overcame drug resistance, converting malignant cells of heterogeneous GBM cells to normal neuron-like cells in vitro and in vivo. These novel observations warrant further research using patient-derived GBM cells and patient-derived xenograft (PDX) models as a potentially effective treatment for a deadly brain cancer and likely other astrocytoma tumors.

Progress in direct reprogramming of dopaminergic cell replacement therapy

Parkinson's disease (PD) is a gradual neurodegenerative disease. While drug therapy and surgical treatments have been the primary means of addressing PD, they do not offer a cure, and the risks associated with surgical treatment are high. Recent advances in cell reprogramming have given rise to new prospects for the treatment of Parkinson's disease (PD), with induced pluripotent stem cells (iPSCs), induced dopamine neurons (iDNs), and induced neural stem cells (iNSCs) being created. These cells can potentially be used in the treatment of Parkinson's disease. On the other hand, this article emphasizes the limits of iPSCs and iNSCs in the context of Parkinson's disease treatment, as well as approaches for direct reprogramming of somatic cells into iDNs. The paper will examine the benefits and drawbacks of directly converting somatic cells into iDNs.

Reprogramming of Rat Fibroblasts into Induced Neurons by Small-Molecule Compounds In Vitro and In Vivo

Cell replacement is a promising approach for neurodegenerative disease treatment. Somatic cells such as fibroblasts can be induced to differentiate into neurons by specific transcription factors; however, the potential of viral vectors used for reprogramming to integrate into the genome raises concerns about the potential clinical applications of this approach. Here, we directly reprogrammed rat embryonic skin fibroblasts into induced neurons (iNs) via six small-molecule compounds (SMs) (VPA, CHIR99021, forskolin, Y-27632, Repsox, and P7C3-A20). iNs exhibit typical neuronal morphology, and immunofluorescence showed that more than 96% of the iNs expressed the early neuronal marker class III beta-tubulin (TUJ1) and that more than 91% of iNs expressed the mature neuronal marker neuron-specific enolase (NSE) after 10 days of reprogramming. Quantitative real-time polymerase chain reaction also showed that most iNs expressed the dopaminergic neuron marker tyrosine hydroxylase, the neural marker Nur correlation factor 1, the (γ-aminobutyric acid, GABA) GABAergic neuronal marker GABA, and the cholinergic neuron marker choline acetyltransferase. In addition, we found that cell proliferation decreased during reprogramming and that protein synthesis increased initially and then decreased. SMs were mixed with hydrogels, and the hydrogels were implanted subcutaneously into the backs of rats. After 7 days, the TUJ1 and NSE proteins were expressed in surrounding tissues, indicating that SMs caused reprogramming in vivo. In summary, rat skin fibroblasts can be efficiently reprogrammed into iNs by SMs in vitro and in vivo.

Direct conversion of mouse astrocytes into neural progenitor cells and specific lineages of neurons

BACKGROUND

Cell replacement therapy has been envisioned as a promising treatment for neurodegenerative diseases. Due to the ethical concerns of ESCs-derived neural progenitor cells (NPCs) and tumorigenic potential of iPSCs, reprogramming of somatic cells directly into multipotent NPCs has emerged as a preferred approach for cell transplantation.

METHODS

Mouse astrocytes were reprogrammed into NPCs by the overexpression of transcription factors (TFs) Foxg1, Sox2, and Brn2. The generation of subtypes of neurons was directed by the force expression of cell-type specific TFs Lhx8 or Foxa2/Lmx1a.

RESULTS

Astrocyte-derived induced NPCs (AiNPCs) share high similarities, including the expression of NPC-specific genes, DNA methylation patterns, the ability to proliferate and differentiate, with the wild type NPCs. The AiNPCs are committed to the forebrain identity and predominantly differentiated into glutamatergic and GABAergic neuronal subtypes. Interestingly, additional overexpression of TFs Lhx8 and Foxa2/Lmx1a in AiNPCs promoted cholinergic and dopaminergic neuronal differentiation, respectively.

CONCLUSIONS

Our studies suggest that astrocytes can be converted into AiNPCs and lineage-committed AiNPCs can acquire differentiation potential of other lineages through forced expression of specific TFs. Understanding the impact of the TF sets on the reprogramming and differentiation into specific lineages of neurons will provide valuable strategies for astrocyte-based cell therapy in neurodegenerative diseases.

Nanomaterials in Neural-Stem-Cell-Mediated Regenerative Medicine: Imaging and Treatment of Neurological Diseases

Patients are increasingly being diagnosed with neuropathic diseases, but are rarely cured because of the loss of neurons in damaged tissues. This situation creates an urgent clinical need to develop alternative treatment strategies for effective repair and regeneration of injured or diseased tissues. Neural stem cells (NSCs), highly pluripotent cells with the ability of self-renewal and potential for multidirectional differentiation, provide a promising solution to meet this demand. However, some serious challenges remaining to be addressed are the regulation of implanted NSCs, tracking their fate, monitoring their interaction with and responsiveness to the tissue environment, and evaluating their treatment efficacy. Nanomaterials have been envisioned as innovative components to further empower the field of NSC-based regenerative medicine, because their unique physicochemical characteristics provide unparalleled solutions to the imaging and treatment of diseases. By building on the advantages of nanomaterials, tremendous efforts have been devoted to facilitate research into the clinical translation of NSC-based therapy. Here, recent work on emerging nanomaterials is highlighted and their performance in the imaging and treatment of neurological diseases is evaluated, comparing the strengths and weaknesses of various imaging modalities currently used. The underlying mechanisms of therapeutic efficacy are discussed, and future research directions are suggested.

Drug Discovery in Fish, Flies, and Worms

Nonmammalian model organisms such as the nematode Caenorhabditis elegans, the fruit fly Drosophila melanogaster, and the zebrafish Danio rerio provide numerous experimental advantages for drug discovery including genetic and molecular tractability, amenability to high-throughput screening methods and reduced experimental costs and increased experimental throughput compared to traditional mammalian models. An interdisciplinary approach that strategically combines the study of nonmammalian and mammalian animal models with diverse experimental tools has and will continue to provide deep molecular and genetic understanding of human disease and will significantly enhance the discovery and application of new therapies to treat those diseases. This review will provide an overview of C. elegans, Drosophila, and zebrafish biology and husbandry and will discuss how these models are being used for phenotype-based drug screening and for identification of drug targets and mechanisms of action. The review will also describe how these and other nonmammalian model organisms are uniquely suited for the discovery of drug-based regenerative medicine therapies.

Effects of Neuropeptide Y on Stem Cells and Their Potential Applications in Disease Therapy

Neuropeptide Y (NPY), a 36-amino acid peptide, is widely distributed in the central and peripheral nervous systems and other peripheral tissues. It takes part in regulating various biological processes including food intake, circadian rhythm, energy metabolism, and neuroendocrine secretion. Increasing evidence indicates that NPY exerts multiple regulatory effects on stem cells. As a kind of primitive and undifferentiated cells, stem cells have the therapeutic potential to replace damaged cells, secret paracrine molecules, promote angiogenesis, and modulate immunity. Stem cell-based therapy has been demonstrated effective and considered as one of the most promising treatments for specific diseases. However, several limitations still hamper its application, such as poor survival and low differentiation and integration rates of transplanted stem cells. The regulatory effects of NPY on stem cell survival, proliferation, and differentiation may be helpful to overcome these limitations and facilitate the application of stem cell-based therapy. In this review, we summarized the regulatory effects of NPY on stem cells and discussed their potential applications in disease therapy.