Identification and Successful Negotiation of a Metabolic Checkpoint in Direct Neuronal Reprogramming

Identifying similar populations across independent single cell studies without data integration

Supervised and unsupervised methods have emerged to address the complexity of single cell data analysis in the context of large pools of independent studies. Here, we present ClusterFoldSimilarity (CFS), a novel statistical method design to quantify the similarity between cell groups across any number of independent datasets, without the need for data correction or integration. By bypassing these processes, CFS avoids the introduction of artifacts and loss of information, offering a simple, efficient, and scalable solution. This method match groups of cells that exhibit conserved phenotypes across datasets, including different tissues and species, and in a multimodal scenario, including single-cell RNA-Seq, ATAC-Seq, single-cell proteomics, or, more broadly, data exhibiting differential abundance effects among groups of cells. Additionally, CFS performs feature selection, obtaining cross-dataset markers of the similar phenotypes observed, providing an inherent interpretability of relationships between cell populations. To showcase the effectiveness of our methodology, we generated single-nuclei RNA-Seq data from the motor cortex and spinal cord of adult mice. By using CFS, we identified three distinct sub-populations of astrocytes conserved on both tissues. CFS includes various visualization methods for the interpretation of the similarity scores and similar cell populations.

The Chromatin Accessibility Landscape in Cell Plasticity and Reprogramming: Understanding and Overcoming the Barriers

Cell plasticity enables the dynamic changes in cell identities necessary for normal development and tissue repair. Induced cell reprogramming, which leverages this plasticity, holds great promise for regenerative medicine and personalized therapies. However, the success of cell reprogramming is often impeded by various molecular barriers, such as epigenetic marks, cell senescence, and the activation of alternative or refractory routes. In this review, we examine the cell reprogramming events that occur within or between germ layers and adult stem cell lineages and propose that the overall similarity in the pre-existing chromatin accessibility landscape is a major determinant of reprogramming efficiency from one cell type to another. A better understanding of the regulation and control of chromatin accessibility should facilitate the development of new methods and strategies to improve cell reprogramming efficiency and advance translational research.

Characteristic changes in astrocyte properties during astrocyte-to-neuron conversion induced by NeuroD1/Ascl1/Dlx2

JOURNAL/nrgr/04.03/01300535-202506000-00030/figure1/v/2024-08-05T133530Z/r/image-tiff Direct in vivo conversion of astrocytes into functional new neurons induced by neural transcription factors has been recognized as a potential new therapeutic intervention for neural injury and degenerative disorders. However, a few recent studies have claimed that neural transcription factors cannot convert astrocytes into neurons, attributing the converted neurons to pre-existing neurons mis-expressing transgenes. In this study, we overexpressed three distinct neural transcription factors--NeuroD1, Ascl1, and Dlx2--in reactive astrocytes in mouse cortices subjected to stab injury, resulting in a series of significant changes in astrocyte properties. Initially, the three neural transcription factors were exclusively expressed in the nuclei of astrocytes. Over time, however, these astrocytes gradually adopted neuronal morphology, and the neural transcription factors was gradually observed in the nuclei of neuron-like cells instead of astrocytes. Furthermore, we noted that transcription factor-infected astrocytes showed a progressive decrease in the expression of astrocytic markers AQP4 (astrocyte endfeet signal), CX43 (gap junction signal), and S100β. Importantly, none of these changes could be attributed to transgene leakage into pre-existing neurons. Therefore, our findings suggest that neural transcription factors such as NeuroD1, Ascl1, and Dlx2 can effectively convert reactive astrocytes into neurons in the adult mammalian brain.

Neuroferroptosis in health and diseases

Ferroptosis is a type of cell death process defined by iron-dependent peroxidation of phospholipids leading to the destruction of cellular membranes and death of the cell. Ferroptosis occurs throughout the body, but a considerable research focus on ferroptosis in the brain - neuroferroptosis - has been driven by the rich lipid and iron content of the brain as well as its high oxygen consumption. Neurons also have an exceptionally large surface area and metabolic demand, which necessitates specific mechanisms (such as lipid antioxidants) to engage constantly to protect the plasma membrane against lipid peroxidation. Ferroptosis has been extensively linked to neurodegeneration and ischaemia and is increasingly implicated in physiological processes such as neuronal reprogramming. Astrocytes provide metabolic support to neurons, enabling them to defend against ferroptosis, yet ferroptotic signals in microglia can propagate damage to astrocytes and neurons, highlighting the complex intercellular (patho)physiology of neuroferroptosis.

Compromised retinoic acid receptor beta expression accelerates the onset of motor, cellular and molecular abnormalities in a mouse model of Huntington's disease

The mechanisms underlying detrimental effects of mutant Huntingtin on striatal dysfunction in Huntington's disease (HD) are not well understood. Although retinoic acid receptor beta (RARβ) emerged recently as one of the top regulators of transcriptionally downregulated genes in the striatum of HD patients and mouse models, its involvement in disease progression remains elusive. Here we challenged functional relevance of RARβ dysregulation in HD onset and progression. Using a series of genetic mouse models, we investigated whether genetically reduced Rarβ expression synergizes with disease- causing mutant huntingtin (mHTT) fragment in R6/1 mice to accelerate HD-like behavioral, cellular and molecular striatal deregulations. We report that genetically compromised Rarβ signaling accelerates onset of motor abnormalities in the R6/1 HD mouse model. Transcriptional profiling revealed that downregulation of Rarβ expression in Rarβ+/-; R6/1 mice also accelerates transcriptional signature of disease progression and aging by emergence of a cluster of upregulated genes related to cell-cycle, stem cell maintenance and telencephalon development, contributing thereby to degradation of striatal cell-identity. Reactivation of proliferative activity in the neurogenic niche and development-related transcriptional programs in the striatum prompt an attempt of lineage infidelity in HD striatum which may lead as a consequence to disease-driving energy crisis, as suggested by downregulation of oxidative phosphorylation genes, a well-accepted correlate of HD physiopathology, and a metabolic condition required for maintenance of proliferative activity and differentiation but not compatible with high energetic demand of differentiated and active neurons. Overall, our data indicate that RARβ delays disease progression, perhaps by delaying aging process.

Characterization and neurogenic responses of primary and immortalized Müller glia

Primary Müller glia (MG) have been reported to exhibit a neurogenic capacity induced by small molecules. However, whether immortalized mouse MG cell lines exhibit neurogenic capacities similar to those of primary mouse MG remains unclear. In this study, we examined the morphology, proliferation rate, and marker profile of primary MG cells isolated from postnatal mouse pups with two immortalized mouse MG cell lines, QMMuC-1 and ImM10, in a standard growth medium. After chemical induction, we compared the morphology, markers, direct neuronal reprogramming efficiency, and axon length of these cell types in two culture media: Neurobasal and DMEM/F12. Our results showed that in standard growth medium, QMMuC-1 and ImM10 cells displayed similar morphology and marker profiles as primary MG cells, with the only differences observed in nestin expression. However, QMMuC-1 and ImM10 cells exhibited much higher proliferation rates than the primary MG cells. Following chemical treatment in both Neurobasal and DMEM/F12 media, a subset of primary MG, QMMuC-1, and ImM10 cells was induced to differentiate into immature neuron-like cells by day 7. While primary MG cells showed similar neuronal reprogramming efficiency and axon length extension in both media, QMMuC-1 and ImM10 cells displayed variations between the two culture media. Moreover, some of the induced neuronal cells derived from primary MG cells expressed HuC/D and Calbindin markers, whereas none of the cells derived from QMMuC-1 and ImM10 cells expressed these markers. Subsequent observations revealed that induced immature neuron-like cells derived from primary MG cells in both types of media and those derived from ImM10 cells cultured in DMEM/F12 survived until day 14. Taken together, our findings suggest that the two immortalized cell lines, QMMuC-1 and ImM10, exhibited neurogenic capacities similar to those of primary MG cells to some extent but did not fully recapitulate all their characteristics. Therefore, careful consideration should be given to culture conditions and the validation of key results when using immortalized cells as a substitute for primary MG cells.

Hmgb2 improves astrocyte to neuron conversion by increasing the chromatin accessibility of genes associated with neuronal maturation in a proneuronal factor-dependent manner

BACKGROUND

Direct conversion of reactive glial cells to neurons is a promising avenue for neuronal replacement therapies after brain injury or neurodegeneration. The overexpression of neurogenic fate determinants in glial cells results in conversion to neurons. For repair purposes, the conversion should ideally be induced in the pathology-induced neuroinflammatory environment. However, very little is known regarding the influence of the injury-induced neuroinflammatory environment and released growth factors on the direct conversion process.

RESULTS

We establish a new in vitro culture system of postnatal astrocytes without epidermal growth factor that reflects the direct conversion rate in the injured, neuroinflammatory environment in vivo. We demonstrate that the growth factor combination corresponding to the injured environment defines the ability of glia to be directly converted to neurons. Using this culture system, we show that chromatin structural protein high mobility group box 2 (HMGB2) regulates the direct conversion rate downstream of the growth factor combination. We further demonstrate that Hmgb2 cooperates with neurogenic fate determinants, such as Neurog2, in opening chromatin at the loci of genes regulating neuronal maturation and synapse formation. Consequently, early chromatin rearrangements occur during direct fate conversion and are necessary for full fate conversion.

CONCLUSIONS

Our data demonstrate novel growth factor-controlled regulation of gene expression during direct fate conversion. This regulation is crucial for proper maturation of induced neurons and could be targeted to improve the repair process.

Enhanced fatty acid oxidation via SCD1 downregulation fuels cardiac reprogramming

Direct cardiac reprogramming has emerged as a promising therapeutic strategy to remuscularize injured myocardium. This approach converts non-contractile fibroblasts to induced cardiomyocytes (iCMs) that spontaneously contract, yet the intrinsic metabolic requirements driving cardiac reprogramming are not fully understood. Using single-cell metabolic flux estimation and flux balance analysis, we characterized the metabolic heterogeneity of iCMs and identified fatty acid oxidation (FAO) as a critical factor in iCM conversion. Both pharmacological and genetic inhibition of FAO impairs iCM generation. We further identified stearoyl-coenzyme A desaturase 1 (SCD1) as a metabolic switch that suppresses iCM reprogramming. Mechanistically, Scd1 knockdown activates PGC1α and PPARβ signaling, enhancing FAO-related gene expression and mitochondrial biogenesis, thereby improving reprogramming efficacy. Pharmacological manipulations targeting SCD1, PGC1α, and the PPARβ signaling axis further improved iCM generation and mitochondrial function. Our findings collectively highlight FAO as a key determinant of iCM fate and offer new therapeutic avenues for advancing reprogramming strategies.

Investigating Müller glia reprogramming in mice: a retrospective of the last decade, and a look to the future

Müller glia, as prominent glial cells within the retina, plays a significant role in maintaining retinal homeostasis in both healthy and diseased states. In lower vertebrates like zebrafish, these cells assume responsibility for spontaneous retinal regeneration, wherein endogenous Müller glia undergo proliferation, transform into Müller glia-derived progenitor cells, and subsequently regenerate the entire retina with restored functionality. Conversely, Müller glia in the mouse and human retina exhibit limited neural reprogramming. Müller glia reprogramming is thus a promising strategy for treating neurodegenerative ocular disorders. Müller glia reprogramming in mice has been accomplished with remarkable success, through various technologies. Advancements in molecular, genetic, epigenetic, morphological, and physiological evaluations have made it easier to document and investigate the Müller glia programming process in mice. Nevertheless, there remain issues that hinder improving reprogramming efficiency and maturity. Thus, understanding the reprogramming mechanism is crucial toward exploring factors that will improve Müller glia reprogramming efficiency, and for developing novel Müller glia reprogramming strategies. This review describes recent progress in relatively successful Müller glia reprogramming strategies. It also provides a basis for developing new Müller glia reprogramming strategies in mice, including epigenetic remodeling, metabolic modulation, immune regulation, chemical small-molecules regulation, extracellular matrix remodeling, and cell-cell fusion, to achieve Müller glia reprogramming in mice.

Brain-Wide Neuroregenerative Gene Therapy Improves Cognition in a Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is a progressive and irreversible brain disorder with extensive neuronal loss in the neocortex and hippocampus. Current therapeutic interventions focus on the early stage of AD but lack effective treatment for the late stage of AD, largely due to the inability to replenish the lost neurons and repair the broken neural circuits. In this study, by using engineered adeno-associated virus vectors that efficiently cross the blood-brain-barrier in the mouse brain, a brain-wide neuroregenerative gene therapy is developed to directly convert endogenous astrocytes into functional neurons in a mouse model of AD. It is found that ≈500 000 new neurons are regenerated and widely distributed in the cerebral cortex and hippocampus. Importantly, it is demonstrated that the converted neurons can integrate into pre-existing neural networks and improve various cognitive performances in AD mice. Chemogenetic inhibition of the converted neurons abolishes memory enhancement in AD mice, suggesting a pivotal role for the newly converted neurons in cognitive restoration. Together, brain-wide neuroregenerative gene therapy may provide a viable strategy for the treatment of AD and other brain disorders associated with massive neuronal loss.

Single-cell RNA sequencing provides new insights into the interaction between astrocytes and neurons after spinal cord injury in mice

Background

Spinal cord injury (SCI) is a devastating neurological disease in which astrocytes play a central role. Understanding the relationship between different subtypes of astrocytes and neuron subtypes during the progression of SCI is critical to understanding the disease.

Methods and results

In this study, single-cell RNA sequencing (scRNA-seq) was used to analyze the transcriptome data of acute, subacute and intermediate stages of SCI in mice as well as normal tissues. Different subtypes of astrocytes and neuronal cells were identified and their dynamic changes and functionalities during the development of SCI. An intriguing discovery was the identification of a specific subtype of astrocytes characterized by unique expression of Gap43, Vim, Aldoc, and Mt1. This subtype of cells shows similarities in gene expression with neurons and potentially transitioned into neurons during the course of SCI. Furthermore, we have uncovered the important role of the glycolytic pathway in this cellular transformation process. Furthermore, through cellular interaction analysis, we validated pathways (mdk-ptprz1,ptn-ptprz1,ptn-sdc3) associated with the potential conversion of these specific cell subsets into neurons. Finally, these cells were observed by fluorescence microscopy and critical gene expressions were validated by Western blot.

Conclusions

The results of this study not only deepen our understanding of the mechanisms underlying SCI, but also provide new insights and opportunities for the development of novel therapeutic strategies and interventions.

Direct fibroblast reprogramming: an emerging strategy for treating organic fibrosis

Direct reprogramming has garnered considerable attention due to its capacity to directly convert differentiated cells into desired cells. Fibroblasts are frequently employed in reprogramming studies due to their abundance and accessibility. However, they are also the key drivers in the progression of fibrosis, a pathological condition characterized by excessive extracellular matrix deposition and tissue scarring. Furthermore, the initial stage of reprogramming typically involves deactivating fibrotic pathways. Hence, direct reprogramming offers a valuable method to regenerate target cells for tissue repair while simultaneously reducing fibrotic tendencies. Understanding the link between reprogramming and fibrosis could help develop effective strategies to treat damaged tissue with a potential risk of fibrosis. This review summarizes the advances in direct reprogramming and reveals their anti-fibrosis effects in various organs such as the heart, liver, and skin. Furthermore, we dissect the mechanisms of reprogramming influenced by fibrotic molecules including TGF-β signaling, mechanical signaling, inflammation signaling, epigenetic modifiers, and metabolic regulators. Innovative methods for fibroblast reprogramming like small molecules, CRISPRa, modified mRNA, and the challenges of cellular heterogeneity and senescence faced by in vivo direct reprogramming, are also discussed.

Direct Neural Reprogramming in situ: Existing Approaches and Their Optimization

Direct in situ neuronal reprogramming (transdifferentiation) of glial cells (astrocytes and microglia) has attracted a significant interest as a potential approach for the treatment of a wide range of neurodegenerative diseases and damages of the central nervous system (CNS). The nervous system of higher mammals has a very limited capacity for repair. Disruption of CNS functioning due to traumatic injuries or neurodegenerative processes can significantly affect the quality of patients' life, lead to motor and cognitive impairments, and result in disability and, in some cases, death. Restoration of lost neurons in situ via direct reprogramming of glial cells without the intermediate stage of pluripotency seems to be the most attractive approach from the viewpoint of translational biomedicine. The ability of astroglia to actively proliferate in response to the damage of neural tissue supports the idea that these neuron-like cells, which are already present at the lesion site, are good candidates for transdifferentiation into neurons, considering that the possibility of direct neuronal reprogramming of astrocytes both in vitro and in vivo have demonstrated in many independent studies. Overexpression of proneuronal transcription factors, e.g., neurogenic differentiation factors 1-4 (NeuroD1-4), Neurogenin 2 (NeuroG2), Ascl1 (Achaete-Scute homolog 1), and Dlx2 (distal-less homeobox 2), including pioneer transcription factors that recognize target sequences in the compacted chromatin and activate transcription of silent genes, has already been proven as a potential therapeutic strategy. Other strategies, such as microRNA-mediated suppression of activity of PTB and REST transcription factors and application of small molecules or various biomaterials, are also utilized in neuronal reprogramming. However, the efficiency of direct in situ reprogramming is limited by a number of factors, including cell specificity of transgene delivery systems and promoters, brain regions in which transdifferentiation occurs, factors affecting cell metabolism, microenvironment, etc. Reprogramming in situ, which takes place in the presence of a large number of different cell types, requires monitoring and precise phenotypic characterization of subpopulations of cells undergoing transdifferentiation in order to confirm the reprogramming of the astroglia into neurons and subsequent integration of these neurons into the CNS. Here, we discussed the most efficient strategies of neuronal reprogramming and technologies used to visualize the transdifferentiation process, with special focus on the obstacles to efficient neuronal conversion, as well as approaches to overcome them.

Copper and iron orchestrate cell-state transitions in cancer and immunity

Whereas genetic mutations can alter cell properties, nongenetic mechanisms can drive rapid and reversible adaptations to changes in their physical environment, a phenomenon termed 'cell-state transition'. Metals, in particular copper and iron, have been shown to be rate-limiting catalysts of cell-state transitions controlling key chemical reactions in mitochondria and the cell nucleus, which govern metabolic and epigenetic changes underlying the acquisition of distinct cell phenotypes. Acquisition of a distinct cell identity, independently of genetic alterations, is an underlying phenomenon of various biological processes, including development, inflammation, erythropoiesis, aging, and cancer. Here, mechanisms that have been uncovered related to the role of these metals in the regulation of cell plasticity are described, illustrating how copper and iron can be exploited for therapeutic intervention.

Fate erasure logic of gene networks underlying direct neuronal conversion of somatic cells by microRNAs

Neurogenic microRNAs 9/9∗ and 124 (miR-9/9∗-124) drive the direct reprogramming of human fibroblasts into neurons with the initiation of the fate erasure of fibroblasts. However, whether the miR-9/9∗-124 fate erasure logic extends to the neuronal conversion of other somatic cell types remains unknown. Here, we uncover that miR-9/9∗-124 induces neuronal conversion of multiple cell types: dura fibroblasts, astrocytes, smooth muscle cells, and pericytes. We reveal the cell-type-specific and pan-somatic gene network erasure induced by miR-9/9∗-124, including cell cycle, morphology, and proteostasis gene networks. Leveraging these pan-somatic gene networks, we predict upstream regulators that may antagonize somatic fate erasure. Among the predicted regulators, we identify TP53 (p53), whose inhibition is sufficient to enhance neuronal conversion even in post-mitotic cells. This study extends miR-9/9∗-124 reprogramming to alternate somatic cells, reveals the pan-somatic gene network fate erasure logic of miR-9/9∗-124, and shows a neurogenic role for p53 inhibition in the miR-9/9∗-124 signaling cascade.

Challenges and Efficacy of Astrocyte-to-Neuron Reprogramming in Spinal Cord Injury: In Vitro Insights and In Vivo Outcomes

Traumatic spinal cord injury (SCI) leads to the disruption of neural pathways, causing loss of neural cells, with subsequent reactive gliosis and tissue scarring that limit endogenous repair. One potential therapeutic strategy to address this is to target reactive scar-forming astrocytes with direct cellular reprogramming to convert them into neurons, by overexpression of neurogenic transcription factors. Here we used lentiviral constructs to overexpress Ascl1 or a combination of microRNAs (miRs) miR124, miR9/9*and NeuroD1 transfected into cultured and in vivo astrocytes. In vitro experiments revealed cortically-derived astrocytes display a higher efficiency (70%) of reprogramming to neurons than spinal cord-derived astrocytes. In a rat cervical SCI model, the same strategy induced only limited reprogramming of astrocytes. Delivery of reprogramming factors did not significantly affect patterns of breathing under baseline and hypoxic conditions, but significant differences in average diaphragm amplitude were seen in the reprogrammed groups during eupneic breathing, hypoxic, and hypercapnic challenges. These results show that while cellular reprogramming can be readily achieved in carefully controlled in vitro conditions, achieving a similar degree of successful reprogramming in vivo is challenging and may require additional steps.

Lactoferrin Attenuates Pro-Inflammatory Response and Promotes the Conversion into Neuronal Lineages in the Astrocytes

Neurodegenerative diseases are characterized by progressive loss of neurons and persistent inflammation. Neurons are terminally differentiated cells, and lost neurons cannot be replaced since neurogenesis is restricted to only two neurogenic niches in the adult brain, whose neurogenic potential decreases with age. In this regard, the astrocytes reprogramming into neurons may represent a promising strategy for restoring the lost neurons and rebuilding neural circuits. To date, many anti-inflammatory agents have been shown to reduce neuroinflammation; however, their potential to restore neuronal loss was poorly investigated. This study investigates the anti-inflammatory effects of lactoferrin on DI-TNC1 astrocyte cell line and its ability to induce astrocyte reprogramming in a context of sustained inflammation. For this purpose, astrocytes were pre-treated with lactoferrin (4 μg/mL) for 24 h, then with lipopolysaccharide (LPS) (400 ng/mL), and examined 2, 9 and 16 days from treatment. The results demonstrate that lactoferrin attenuates astrocyte reactivity by reducing Toll-like receptor 4 (TLR4), Glial fibrillary acidic protein (GFAP) and IL-6 expression, as well as by upregulating Interleukin-10 (IL-10) cytokine and NRF2 expression. Moreover, lactoferrin promotes the reprogramming of reactive astrocytes into proliferative neuroblasts by inducing the overexpression of the Sex determining region Y/SRY-box 2 (SOX2) reprogramming transcription factor. Overall, this study highlights the potential effects of lactoferrin to attenuate neuroinflammation and improve neurogenesis, suggesting a future strategy for the treatment of neurodegenerative disorders.

From Physiology to Pathology of Astrocytes: Highlighting Their Potential as Therapeutic Targets for CNS Injury

In the mammalian central nervous system (CNS), astrocytes are the ubiquitous glial cells that have complex morphological and molecular characteristics. These fascinating cells play essential neurosupportive and homeostatic roles in the healthy CNS and undergo morphological, molecular, and functional changes to adopt so-called 'reactive' states in response to CNS injury or disease. In recent years, interest in astrocyte research has increased dramatically and some new biological features and roles of astrocytes in physiological and pathological conditions have been discovered thanks to technological advances. Here, we will review and discuss the well-established and emerging astroglial biology and functions, with emphasis on their potential as therapeutic targets for CNS injury, including traumatic and ischemic injury. This review article will highlight the importance of astrocytes in the neuropathological process and repair of CNS injury.

Retrovirus-Mediated Reprogramming of Endogenous Hippocampal Glia into GABAergic Induced Neurons

Lineage reprogramming of glial cells into induced neurons (iNs) has emerged as an innovative strategy to replace neurons lost due to injury or neurological diseases. Here, we describe a step-by-step protocol to induce in vivo conversion of reactive glial cells, proliferating within the injured hippocampus, into mature and functional GABAergic iNs through retrovirus-mediated expression of two neurogenic fate determinants (Ascl1 and Dlx2). We have previously applied this method to study the integration and functional impact of GABAergic iNs in epileptic mice (Lentini et al., Cell Stem Cell 28:2104-2121.e10, 2021). We successfully generated GABAergic iNs that exhibited substantial integration within pathological circuits, leading to a significant reduction in epileptic seizures.

Recent progress of principal techniques used in the study of Müller glia reprogramming in mice

In zebrafish, Müller glia (MG) cells retain the ability to proliferate and de-differentiate into retinal progenitor-like cells, subsequently differentiating into retinal neurons that can replace those damaged or lost due to retinal injury. In contrast, the reprogramming potential of MG in mammals has been lost, with these cells typically responding to retinal damage through gliosis. Considerable efforts have been dedicated to achieving the reprogramming of MG cells in mammals. Notably, significant advancements have been achieved in reprogramming MG cells in mice employing various methodologies. At the same time, some inevitable challenges have hindered identifying accurate MG cell reprogramming rather than the illusion, let alone improving the reprogramming efficiency and maturity of daughter cells. Recently, several strategies, including lineage tracking, multi-omics techniques, and functional analysis, have been developed to investigate the MG reprogramming process in mice. This review summarizes both the advantages and limitations of these novel strategies for analyzing MG reprogramming in mice, offering insights into enhancing the reliability and efficiency of MG reprogramming.

A multiplexed, single-cell sequencing screen identifies compounds that increase neurogenic reprogramming of murine Muller glia

Retinal degeneration in mammals causes permanent loss of vision, due to an inability to regenerate naturally. Some non-mammalian vertebrates show robust regeneration, via Muller glia (MG). We have recently made significant progress in stimulating adult mouse MG to regenerate functional neurons by transgenic expression of the proneural transcription factor Ascl1. While these results showed that MG can serve as an endogenous source of neuronal replacement, the efficacy of this process is limited. With the goal of improving this in mammals, we designed a small molecule screen using sci-Plex, a method to multiplex up to thousands of single-nucleus RNA-seq conditions into a single experiment. We used this technology to screen a library of 92 compounds, identified, and validated two that promote neurogenesis in vivo. Our results demonstrate that high-throughput single-cell molecular profiling can substantially improve the discovery process for molecules and pathways that can stimulate neural regeneration and further demonstrate the potential for this approach to restore vision in patients with retinal disease.

PRDX6 dictates ferroptosis sensitivity by directing cellular selenium utilization

Selenium-dependent glutathione peroxidase 4 (GPX4) is the guardian of ferroptosis, preventing unrestrained (phospho)lipid peroxidation by reducing phospholipid hydroperoxides (PLOOH). However, the contribution of other phospholipid peroxidases in ferroptosis protection remains unclear. We show that cells lacking GPX4 still exhibit substantial PLOOH-reducing capacity, suggesting a contribution of alternative PLOOH peroxidases. By scrutinizing potential candidates, we found that although overexpression of peroxiredoxin 6 (PRDX6), a thiol-specific antioxidant enzyme with reported PLOOH-reducing activity, failed to prevent ferroptosis, its genetic loss sensitizes cancer cells to ferroptosis. Mechanistically, we uncover that PRDX6, beyond its known peroxidase activity, acts as a selenium-acceptor protein, facilitating intracellular selenium utilization and efficient selenium incorporation into selenoproteins, including GPX4. Its physiological significance was demonstrated by reduced GPX4 expression in Prdx6-deficient mouse brains and increased sensitivity to ferroptosis in PRDX6-deficient tumor xenografts in mice. Our study highlights PRDX6 as a critical player in directing cellular selenium utilization and dictating ferroptosis sensitivity.

ETV2 transcriptionally activates Rig1 gene expression and promotes reprogramming of the endothelial lineage

ETV2 is an essential transcription factor as Etv2 null murine embryos lack all vasculature, blood and are lethal early during embryogenesis. Previous studies have established that ETV2 functions as a pioneer factor and directly reprograms fibroblasts to endothelial cells. However, the underlying molecular mechanisms regulating this reprogramming process remain incompletely defined. In the present study, we examined the ETV2-RIG1 cascade as regulators that govern ETV2-mediated reprogramming. Mouse embryonic fibroblasts (MEFs) harboring an inducible ETV2 expression system were used to overexpress ETV2 and reprogram these somatic cells to the endothelial lineage. Single-cell RNA-seq from reprogrammed fibroblasts defined the induction of the transcriptional network involved in Rig1-like receptor signaling pathways. Studies using ChIP-seq, electrophoretic mobility shift assays, and transcriptional assays demonstrated that ETV2 was a direct upstream activator of Rig1 gene expression. We further demonstrated that the knockdown of Rig1 and separately, Nfκb1 using shRNA significantly reduced the efficiency of endothelial cell reprogramming. These results highlight that ETV2 reprograms fibroblasts to endothelial cells by directly activating RIG1. These findings extend our current understanding of the molecular mechanisms underlying ETV2-mediated reprogramming and will be important in the design of revascularization strategies for the treatment of ischemic tissues such as ischemic heart disease.

In situ chemical reprogramming of astrocytes into neurons: A new hope for the treatment of central neurodegenerative diseases?

Central neurodegenerative disorders (e.g. Alzheimer's disease (AD) and Parkinson's disease (PD)) are tightly associated with extensive neuron loss. Current therapeutic interventions merely mitigate the symptoms of these diseases, falling short of addressing the fundamental issue of neuron loss. Cell reprogramming, involving the transition of a cell from one gene expression profile to another, has made significant strides in the conversion between diverse somatic cell types. This advancement has been facilitated by gene editing techniques or the synergistic application of small molecules, enabling the conversion of glial cells into functional neurons. Despite this progress, the potential for in situ reprogramming of astrocytes in treating neurodegenerative disorders faces challenges such as immune rejection and genotoxicity. A novel avenue emerges through chemical reprogramming of astrocytes utilizing small molecules, circumventing genotoxic effects and unlocking substantial clinical utility. Recent studies have successfully demonstrated the in situ conversion of astrocytes into neurons using small molecules. Nonetheless, these findings have sparked debates, encompassing queries regarding the origin of newborn neurons, pivotal molecular targets, and alterations in metabolic pathways. This review succinctly delineates the background of astrocytes reprogramming, meticulously surveys the principal classes of small molecule combinations employed thus far, and examines the complex signaling pathways they activate. Finally, this article delves into the potential vistas awaiting exploration in the realm of astrocytes chemical reprogramming, heralding a promising future for advancing our understanding and treatment of neurodegenerative diseases.

Reprogramming astroglia into neurons with hallmarks of fast-spiking parvalbumin-positive interneurons by phospho-site-deficient Ascl1

Cellular reprogramming of mammalian glia to an induced neuronal fate holds the potential for restoring diseased brain circuits. While the proneural factor achaete-scute complex-like 1 (Ascl1) is widely used for neuronal reprogramming, in the early postnatal mouse cortex, Ascl1 fails to induce the glia-to-neuron conversion, instead promoting the proliferation of oligodendrocyte progenitor cells (OPC). Since Ascl1 activity is posttranslationally regulated, here, we investigated the consequences of mutating six serine phospho-acceptor sites to alanine (Ascl1SA6) on lineage reprogramming in vivo. Ascl1SA6 exhibited increased neurogenic activity in the glia of the early postnatal mouse cortex, an effect enhanced by coexpression of B cell lymphoma 2 (Bcl2). Genetic fate-mapping revealed that most induced neurons originated from astrocytes, while only a few derived from OPCs. Many Ascl1SA6/Bcl2-induced neurons expressed parvalbumin and were capable of high-frequency action potential firing. Our study demonstrates the authentic conversion of astroglia into neurons featuring subclass hallmarks of cortical interneurons, advancing our scope of engineering neuronal fates in the brain.

Programmed cell death and melatonin: A comprehensive review

Melatonin (MLT), a main product of pineal gland, recently has attracted the attention of scientists due to its benefits in various diseases and also regulation of cellular homeostasis. Its receptor scares widely distributed indicating that it influences numerous organs. Programmed cell death (PCD), of which there several types, is a regulated by highly conserved mechanisms and important for development and function of different organs. Enhancement or inhibition of PCDs could be a useful technique for treatment of different diseases and MLT, due to its direct effects on these pathways, is a good candidate for this strategy. Many studies investigated the role of MLT on PCDs in different diseases and in this review, we summarized some of the most significant studies in this field to provide a better insight into the mechanisms of modulation of PCD by MLT modulation.

Ferroptosis in health and disease

Ferroptosis is a pervasive non-apoptotic form of cell death highly relevant in various degenerative diseases and malignancies. The hallmark of ferroptosis is uncontrolled and overwhelming peroxidation of polyunsaturated fatty acids contained in membrane phospholipids, which eventually leads to rupture of the plasma membrane. Ferroptosis is unique in that it is essentially a spontaneous, uncatalyzed chemical process based on perturbed iron and redox homeostasis contributing to the cell death process, but that it is nonetheless modulated by many metabolic nodes that impinge on the cells' susceptibility to ferroptosis. Among the various nodes affecting ferroptosis sensitivity, several have emerged as promising candidates for pharmacological intervention, rendering ferroptosis-related proteins attractive targets for the treatment of numerous currently incurable diseases. Herein, the current members of a Germany-wide research consortium focusing on ferroptosis research, as well as key external experts in ferroptosis who have made seminal contributions to this rapidly growing and exciting field of research, have gathered to provide a comprehensive, state-of-the-art review on ferroptosis. Specific topics include: basic mechanisms, in vivo relevance, specialized methodologies, chemical and pharmacological tools, and the potential contribution of ferroptosis to disease etiopathology and progression. We hope that this article will not only provide established scientists and newcomers to the field with an overview of the multiple facets of ferroptosis, but also encourage additional efforts to characterize further molecular pathways modulating ferroptosis, with the ultimate goal to develop novel pharmacotherapies to tackle the various diseases associated with - or caused by - ferroptosis.

Two-photon live imaging of direct glia-to-neuron conversion in the mouse cortex

JOURNAL/nrgr/04.03/01300535-202408000-00032/figure1/v/2023-12-16T180322Z/r/image-tiff Over the past decade, a growing number of studies have reported transcription factor-based in situ reprogramming that can directly convert endogenous glial cells into functional neurons as an alternative approach for neuroregeneration in the adult mammalian central nervous system. However, many questions remain regarding how a terminally differentiated glial cell can transform into a delicate neuron that forms part of the intricate brain circuitry. In addition, concerns have recently been raised around the absence of astrocyte-to-neuron conversion in astrocytic lineage-tracing mice. In this study, we employed repetitive two-photon imaging to continuously capture the in situ astrocyte-to-neuron conversion process following ectopic expression of the neural transcription factor NeuroD1 in both proliferating reactive astrocytes and lineage-traced astrocytes in the mouse cortex. Time-lapse imaging over several weeks revealed the step-by-step transition from a typical astrocyte with numerous short, tapered branches to a typical neuron with a few long neurites and dynamic growth cones that actively explored the local environment. In addition, these lineage-converting cells were able to migrate radially or tangentially to relocate to suitable positions. Furthermore, two-photon Ca2+ imaging and patch-clamp recordings confirmed that the newly generated neurons exhibited synchronous calcium signals, repetitive action potentials, and spontaneous synaptic responses, suggesting that they had made functional synaptic connections within local neural circuits. In conclusion, we directly visualized the step-by-step lineage conversion process from astrocytes to functional neurons in vivo and unambiguously demonstrated that adult mammalian brains are highly plastic with respect to their potential for neuroregeneration and neural circuit reconstruction.

Decoding single-cell molecular mechanisms in astrocyte-to-iN reprogramming via Ngn2- and Pax6-mediated direct lineage switching

BACKGROUND

The limited regenerative capacity of damaged neurons in adult mammals severely restricts neural repair. Although stem cell transplantation is promising, its clinical application remains challenging. Direct reprogramming, which utilizes cell plasticity to regenerate neurons, is an emerging alternative approach.

METHODS

We utilized primary postnatal cortical astrocytes for reprogramming induced neurons (iNs) through the viral-mediated overexpression of the transcription factors Ngn2 and Pax6 (NP). Fluorescence-activated cell sorting (FACS) was used to enrich successfully transfected cells, followed by single-cell RNA sequencing (scRNA-seq) using the 10 × Genomics platform for comprehensive transcriptomic analysis.

RESULTS

The scRNA-seq revealed that NP overexpression led to the differentiation of astrocytes into iNs, with percentages of 36% and 39.3% on days 4 and 7 posttransduction, respectively. CytoTRACE predicted the developmental sequence, identifying astrocytes as the reprogramming starting point. Trajectory analysis depicted the dynamic changes in gene expression during the astrocyte-to-iN transition.

CONCLUSIONS

This study elucidates the molecular dynamics underlying astrocyte reprogramming into iNs, revealing key genes and pathways involved in this process. Our research contributes novel insights into the molecular mechanisms of NP-mediated reprogramming, suggesting avenues for optimizing the efficiency of the reprogramming process.

Controlling the Expression Level of the Neuronal Reprogramming Factors for a Successful Reprogramming Outcome

Neuronal reprogramming is a promising approach for making major advancement in regenerative medicine. Distinct from the approach of induced pluripotent stem cells, neuronal reprogramming converts non-neuronal cells to neurons without going through a primitive stem cell stage. In vivo neuronal reprogramming brings this approach to a higher level by changing the cell fate of glial cells to neurons in neural tissue through overexpressing reprogramming factors. Despite the ongoing debate over the validation and interpretation of newly generated neurons, in vivo neuronal reprogramming is still a feasible approach and has the potential to become clinical treatment with further optimization and refinement. Here, we discuss the major neuronal reprogramming factors (mostly pro-neurogenic transcription factors during development), especially the significance of their expression levels during neurogenesis and the reprogramming process focusing on NeuroD1. In the developing central nervous system, these pro-neurogenic transcription factors usually elicit distinct spatiotemporal expression patterns that are critical to their function in generating mature neurons. We argue that these dynamic expression patterns may be similarly needed in the process of reprogramming adult cells into neurons and further into mature neurons with subtype identities. We also summarize the existing approaches and propose new ones that control gene expression levels for a successful reprogramming outcome.

Generation of functional neurons from adult human mucosal olfactory ensheathing glia by direct lineage conversion

A recent approach to promote central nervous system (CNS) regeneration after injury or disease is direct conversion of somatic cells to neurons. This is achieved by transduction of viral vectors that express neurogenic transcription factors. In this work we propose adult human mucosal olfactory ensheathing glia (hmOEG) as a candidate for direct reprogramming to neurons due to its accessibility and to its well-characterized neuroregenerative capacity. After induction of hmOEG with the single neurogenic transcription factor NEUROD1, the cells under study exhibited morphological and immunolabeling neuronal features, fired action potentials and expressed glutamatergic and GABAergic markers. In addition, after engraftment of transduced hmOEG cells in the mouse hippocampus, these cells showed specific neuronal labeling. Thereby, if we add to the neuroregenerative capacity of hmOEG cultures the conversion to neurons of a fraction of their population through reprogramming techniques, the engraftment of hmOEG and hmOEG-induced neurons could be a procedure to enhance neural repair after central nervous system injury.

Direct neuronal reprogramming of mouse astrocytes is associated with multiscale epigenome remodeling and requires Yy1

Direct neuronal reprogramming is a promising approach to regenerate neurons from local glial cells. However, mechanisms of epigenome remodeling and co-factors facilitating this process are unclear. In this study, we combined single-cell multiomics with genome-wide profiling of three-dimensional nuclear architecture and DNA methylation in mouse astrocyte-to-neuron reprogramming mediated by Neurogenin2 (Ngn2) and its phosphorylation-resistant form (PmutNgn2), respectively. We show that Ngn2 drives multilayered chromatin remodeling at dynamic enhancer-gene interaction sites. PmutNgn2 leads to higher reprogramming efficiency and enhances epigenetic remodeling associated with neuronal maturation. However, the differences in binding sites or downstream gene activation cannot fully explain this effect. Instead, we identified Yy1, a transcriptional co-factor recruited by direct interaction with Ngn2 to its target sites. Upon deletion of Yy1, activation of neuronal enhancers, genes and ultimately reprogramming are impaired without affecting Ngn2 binding. Thus, our work highlights the key role of interactors of proneural factors in direct neuronal reprogramming.

Neuronal conversion from glia to replenish the lost neurons

ABSTRACT

Neuronal injury, aging, and cerebrovascular and neurodegenerative diseases such as cerebral infarction, Alzheimer's disease, Parkinson's disease, frontotemporal dementia, amyotrophic lateral sclerosis, and Huntington's disease are characterized by significant neuronal loss. Unfortunately, the neurons of most mammals including humans do not possess the ability to self-regenerate. Replenishment of lost neurons becomes an appealing therapeutic strategy to reverse the disease phenotype. Transplantation of pluripotent neural stem cells can supplement the missing neurons in the brain, but it carries the risk of causing gene mutation, tumorigenesis, severe inflammation, and obstructive hydrocephalus induced by brain edema. Conversion of neural or non-neural lineage cells into functional neurons is a promising strategy for the diseases involving neuron loss, which may overcome the above-mentioned disadvantages of neural stem cell therapy. Thus far, many strategies to transform astrocytes, fibroblasts, microglia, Müller glia, NG2 cells, and other glial cells to mature and functional neurons, or for the conversion between neuronal subtypes have been developed through the regulation of transcription factors, polypyrimidine tract binding protein 1 (PTBP1), and small chemical molecules or are based on a combination of several factors and the location in the central nervous system. However, some recent papers did not obtain expected results, and discrepancies exist. Therefore, in this review, we discuss the history of neuronal transdifferentiation, summarize the strategies for neuronal replenishment and conversion from glia, especially astrocytes, and point out that biosafety, new strategies, and the accurate origin of the truly converted neurons in vivo should be focused upon in future studies. It also arises the attention of replenishing the lost neurons from glia by gene therapies such as up-regulation of some transcription factors or down-regulation of PTBP1 or drug interference therapies.

Reflections on the complex mechanisms of endometriosis from the perspective of ferroptosis

Ferroptosis is a novel type of iron-dependent programmed cell death characterised by intracellular iron overload, increased lipid peroxidation and abnormal accumulation of reactive oxygen species.It has been implicated in the progression of several diseases including cancer, ischaemia-reperfusion injury, neurodegenerative diseases and liver disease. The etiology of endometriosis (EMS) is still unclear and is associated with multiple factors, often accompanied by various forms of cell death and a complex microenvironment. In recent decades, the role of non-traditional forms of cell death, represented by ferroptosis, in endometriosis has come to the attention of researchers. This article reviews the transitional role of iron homeostasis in the development of ferroptosis, the characteristics and regulatory mechanisms of ferroptosis, and focuses on summarising the links between iron death and various pathogenic mechanisms of EMS, including oxidative stress, dysregulation of lipid metabolism, inflammation, autophagy and epithelial-mesenchymal transition. The possible applications of ferroptosis in the treatment of EMS, future research directions and current issues are discussed with the aim of providing new ideas for further understanding of EMS.

Recent advancements in nanomaterial-mediated ferroptosis-induced cancer therapy: Importance of molecular dynamics and novel strategies

Ferroptosis is a novel type of controlled cell death resulting from an imbalance between oxidative harm and protective mechanisms, demonstrating significant potential in combating cancer. It differs from other forms of cell death, such as apoptosis and necrosis. Molecular therapeutics have hard time playing the long-acting role of ferroptosis induction due to their limited water solubility, low cell targeting capacity, and quick metabolism in vivo. To this end, small molecule inducers based on biological factors have long been used as strategy to induce cell death. Research into ferroptosis and advancements in nanotechnology have led to the discovery that nanomaterials are superior to biological medications in triggering ferroptosis. Nanomaterials derived from iron can enhance ferroptosis induction by directly releasing large quantities of iron and increasing cell ROS levels. Moreover, utilizing nanomaterials to promote programmed cell death minimizes the probability of unfavorable effects induced by mutations in cancer-associated genes such as RAS and TP53. Taken together, this review summarizes the molecular mechanisms involved in ferroptosis along with the classification of ferroptosis induction. It also emphasized the importance of cell organelles in the control of ferroptosis in cancer therapy. The nanomaterials that trigger ferroptosis are categorized and explained. Iron-based and noniron-based nanomaterials with their characterization at the molecular and cellular levels have been explored, which will be useful for inducing ferroptosis that leads to reduced tumor growth. Within this framework, we offer a synopsis, which traverses the well-established mechanism of ferroptosis and offers practical suggestions for the design and therapeutic use of nanomaterials.

Directed differentiation of functional corticospinal-like neurons from endogenous SOX6+/NG2+ cortical progenitors

Corticospinal neurons (CSN) centrally degenerate in amyotrophic lateral sclerosis (ALS), along with spinal motor neurons, and loss of voluntary motor function in spinal cord injury (SCI) results from damage to CSN axons. For functional regeneration of specifically affected neuronal circuitry in vivo , or for optimally informative disease modeling and/or therapeutic screening in vitro , it is important to reproduce the type or subtype of neurons involved. No such appropriate in vitro models exist with which to investigate CSN selective vulnerability and degeneration in ALS, or to investigate routes to regeneration of CSN circuitry for ALS or SCI, critically limiting the relevance of much research. Here, we identify that the HMG-domain transcription factor Sox6 is expressed by a subset of NG2+ endogenous cortical progenitors in postnatal and adult cortex, and that Sox6 suppresses a latent neurogenic program by repressing inappropriate proneural Neurog2 expression by progenitors. We FACS-purify these genetically accessible progenitors from postnatal mouse cortex and establish a pure culture system to investigate their potential for directed differentiation into CSN. We then employ a multi-component construct with complementary and differentiation-sharpening transcriptional controls (activating Neurog2, Fezf2 , while antagonizing Olig2 with VP16:Olig2 ). We generate corticospinal-like neurons from SOX6+/NG2+ cortical progenitors, and find that these neurons differentiate with remarkable fidelity compared with corticospinal neurons in vivo . They possess appropriate morphological, molecular, transcriptomic, and electrophysiological characteristics, without characteristics of the alternate intracortical or other neuronal subtypes. We identify that these critical specifics of differentiation are not reproduced by commonly employed Neurog2 -driven differentiation. Neurons induced by Neurog2 instead exhibit aberrant multi-axon morphology and express molecular hallmarks of alternate cortical projection subtypes, often in mixed form. Together, this developmentally-based directed differentiation from genetically accessible cortical progenitors sets a precedent and foundation for in vitro mechanistic and therapeutic disease modeling, and toward regenerative neuronal repopulation and circuit repair.

Targeting ferroptosis as a potential strategy to overcome the resistance of cisplatin in oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) is a crucial public health problem, accounting for approximately 2% of all cancers globally and 90% of oral malignancies over the world. Unfortunately, despite the achievements in surgery, radiotherapy, and chemotherapy techniques over the past decades, OSCC patients still low 5-year survival rate. Cisplatin, a platinum-containing drug, serves as one of the first-line chemotherapeutic agents of OSCC. However, the resistance to cisplatin significantly limits the clinical practice and is a crucial factor in tumor recurrence and metastasis after conventional treatments. Ferroptosis is an iron-based form of cell death, which is initiated by the intracellular accumulation of lipid peroxidation and reactive oxygen species (ROS). Interestingly, cisplatin-resistant OSCC cells exhibit lower level of ROS and lipid peroxidation compared to sensitive cells. The reduced ferroptosis in cisplatin resistance cells indicates the potential relationship between cisplatin resistance and ferroptosis, which is proved by recent studies showing that in colorectal cancer cells. However, the modulation pathway of ferroptosis reversing cisplatin resistance in OSCC cells still remains unclear. This article aims to concisely summarize the molecular mechanisms and evaluate the relationship between ferroptosis and cisplatin resistance OSCC cells, thereby providing novel strategies for overcoming cisplatin resistance and developing new therapeutic approaches.

A multiplexed, single-cell sequencing screen identifies compounds that increase neurogenic reprogramming of murine Muller glia

Retinal degeneration in mammals causes permanent loss of vision, due to an inability to regenerate naturally. Some non-mammalian vertebrates show robust regeneration, via Muller glia (MG). We have recently made significant progress in stimulating adult mouse MG to regenerate functional neurons by transgenic expression of the proneural transcription factor Ascl1. While these results showed that MG can serve as an endogenous source of neuronal replacement, the efficacy of this process is limited. With the goal of improving this in mammals, we designed a small molecule screen using sci-Plex, a method to multiplex up to thousands of single nucleus RNA-seq conditions into a single experiment. We used this technology to screen a library of 92 compounds, identified, and validated two that promote neurogenesis in vivo. Our results demonstrate that high-throughput single-cell molecular profiling can substantially improve the discovery process for molecules and pathways that can stimulate neural regeneration and further demonstrate the potential for this approach to restore vision in patients with retinal disease.

Direct neuronal reprogramming of NDUFS4 patient cells identifies the unfolded protein response as a novel general reprogramming hurdle

Mitochondria account for essential cellular pathways, from ATP production to nucleotide metabolism, and their deficits lead to neurological disorders and contribute to the onset of age-related diseases. Direct neuronal reprogramming aims at replacing neurons lost in such conditions, but very little is known about the impact of mitochondrial dysfunction on the direct reprogramming of human cells. Here, we explore the effects of mitochondrial dysfunction on the neuronal reprogramming of induced pluripotent stem cell (iPSC)-derived astrocytes carrying mutations in the NDUFS4 gene, important for Complex I and associated with Leigh syndrome. This led to the identification of the unfolded protein response as a major hurdle in the direct neuronal conversion of not only astrocytes and fibroblasts from patients but also control human astrocytes and fibroblasts. Its transient inhibition potently improves reprogramming by influencing the mitochondria-endoplasmic-reticulum-stress-mediated pathways. Taken together, disease modeling using patient cells unraveled novel general hurdles and ways to overcome these in human astrocyte-to-neuron reprogramming.

Ignorance is bliss: Inhibition of proteomic stress sensing improves direct neuronal conversion

Direct conversion of non-neuronal cells to neurons offers opportunities for disease modeling and therapy. In this issue of Neuron, Sonsalla et al.1 reveal the unfolded protein response (UPR) pathway as a "proteomic roadblock" to direct neuronal conversion; overcoming this roadblock enhances reprogramming.

Putative Molecular Mechanisms Underpinning the Inverse Roles of Mitochondrial Respiration and Heme Function in Lung Cancer and Alzheimer's Disease

Mitochondria are the powerhouse of the cell. Mitochondria serve as the major source of oxidative stress. Impaired mitochondria produce less adenosine triphosphate (ATP) but generate more reactive oxygen species (ROS), which could be a major factor in the oxidative imbalance observed in Alzheimer's disease (AD). Well-balanced mitochondrial respiration is important for the proper functioning of cells and human health. Indeed, recent research has shown that elevated mitochondrial respiration underlies the development and therapy resistance of many types of cancer, whereas diminished mitochondrial respiration is linked to the pathogenesis of AD. Mitochondria govern several activities that are known to be changed in lung cancer, the largest cause of cancer-related mortality worldwide. Because of the significant dependence of lung cancer cells on mitochondrial respiration, numerous studies demonstrated that blocking mitochondrial activity is a potent strategy to treat lung cancer. Heme is a central factor in mitochondrial respiration/oxidative phosphorylation (OXPHOS), and its association with cancer is the subject of increased research in recent years. In neural cells, heme is a key component in mitochondrial respiration and the production of ATP. Here, we review the role of impaired heme metabolism in the etiology of AD. We discuss the numerous mitochondrial effects that may contribute to AD and cancer. In addition to emphasizing the significance of heme in the development of both AD and cancer, this review also identifies some possible biological connections between the development of the two diseases. This review explores shared biological mechanisms (Pin1, Wnt, and p53 signaling) in cancer and AD. In cancer, these mechanisms drive cell proliferation and tumorigenic functions, while in AD, they lead to cell death. Understanding these mechanisms may help advance treatments for both conditions. This review discusses precise information regarding common risk factors, such as aging, obesity, diabetes, and tobacco usage.

Research progress on ferroptosis in the pathogenesis and treatment of neurodegenerative diseases

Globally, millions of individuals are impacted by neurodegenerative disorders including Huntington's disease (HD), amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD), and Alzheimer's disease (AD). Although a great deal of energy and financial resources have been invested in disease-related research, breakthroughs in therapeutic approaches remain elusive. The breakdown of cells usually happens together with the onset of neurodegenerative diseases. However, the mechanism that triggers neuronal loss is unknown. Lipid peroxidation, which is iron-dependent, causes a specific type of cell death called ferroptosis, and there is evidence its involvement in the pathogenic cascade of neurodegenerative diseases. However, the specific mechanisms are still not well known. The present article highlights the basic processes that underlie ferroptosis and the corresponding signaling networks. Furthermore, it provides an overview and discussion of current research on the role of ferroptosis across a variety of neurodegenerative conditions.

In Vivo Reprogramming Using Yamanaka Factors in the CNS: A Scoping Review

Central nervous system diseases, particularly neurodegenerative disorders, pose significant challenges in medicine. These conditions, characterized by progressive neuronal loss, have remained largely incurable, exacting a heavy toll on individuals and society. In recent years, in vivo reprogramming using Yamanaka factors has emerged as a promising approach for central nervous system regeneration. This technique involves introducing transcription factors, such as Oct4, Sox2, Klf4, and c-Myc, into adult cells to induce their conversion into neurons. This review summarizes the current state of in vivo reprogramming research in the central nervous system, focusing on the use of Yamanaka factors. In vivo reprogramming using Yamanaka factors has shown promising results in several animal models of central nervous system diseases. Studies have demonstrated that this approach can promote the generation of new neurons, improve functional outcomes, and reduce scar formation. However, there are still several challenges that need to be addressed before this approach can be translated into clinical practice. These challenges include optimizing the efficiency of reprogramming, understanding the cell of origin for each transcription factor, and developing methods for reprogramming in non-subventricular zone areas. Further research is needed to overcome the remaining challenges, but this approach has the potential to revolutionize the way we treat central nervous system disorders.

Next-generation direct reprogramming

Tissue repair is significantly compromised in the aging human body resulting in critical disease conditions (such as myocardial infarction or Alzheimer's disease) and imposing a tremendous burden on global health. Reprogramming approaches (partial or direct reprogramming) are considered fruitful in addressing this unmet medical need. However, the efficacy, cellular maturity and specific targeting are still major challenges of direct reprogramming. Here we describe novel approaches in direct reprogramming that address these challenges. Extracellular signaling pathways (Receptor tyrosine kinases, RTK and Receptor Serine/Theronine Kinase, RSTK) and epigenetic marks remain central in rewiring the cellular program to determine the cell fate. We propose that modern protein design technologies (AI-designed minibinders regulating RTKs/RSTK, epigenetic enzymes, or pioneer factors) have potential to solve the aforementioned challenges. An efficient transdifferentiation/direct reprogramming may in the future provide molecular strategies to collectively reduce aging, fibrosis, and degenerative diseases.

A promise for neuronal repair: reprogramming astrocytes into neurons in vivo

Massive loss of neurons following brain injury or disease is the primary cause of central nervous system dysfunction. Recently, much research has been conducted on how to compensate for neuronal loss in damaged parts of the nervous system and thus restore functional connectivity among neurons. Direct somatic cell differentiation into neurons using pro-neural transcription factors, small molecules, or microRNAs, individually or in association, is the most promising form of neural cell replacement therapy available. This method provides a potential remedy for cell loss in a variety of neurodegenerative illnesses, and the development of reprogramming technology has made this method feasible. This article provides a comprehensive review of reprogramming, including the selection and methods of reprogramming starting cell populations as well as the signaling methods involved in this process. Additionally, we thoroughly examine how reprogramming astrocytes into neurons can be applied to treat stroke and other neurodegenerative diseases. Finally, we discuss the challenges of neuronal reprogramming and offer insights about the field.

Effects of small molecules on neurogenesis: Neuronal proliferation and differentiation

Neurons are believed to be non-proliferating cells. However, neuronal stem cells are still present in certain areas of the adult brain, although their proliferation diminishes with age. Just as with other cells, their proliferation and differentiation are modulated by various mechanisms. These mechanisms are foundational to the strategies developed to induce neuronal proliferation and differentiation, with potential therapeutic applications for neurodegenerative diseases. The most common among these diseases are Parkinson's disease and Alzheimer's disease, associated with the formation of β -amyloid (Aβ ) aggregates which cause a reduction in the number of neurons. Compounds such as LiCl, 4-aminothiazoles, Pregnenolone, ACEA, harmine, D2AAK1, methyl 3,4-dihydroxybenzoate, and shikonin may induce neuronal proliferation/differentiation through the activation of pathways: MAPK ERK, PI3K/AKT, NFκ B, Wnt, BDNF, and NPAS3. Moreover, combinations of these compounds can potentially transform somatic cells into neurons. This transformation process involves the activation of neuron-specific transcription factors such as NEUROD1, NGN2, ASCL1, and SOX2, which subsequently leads to the transcription of downstream genes, culminating in the transformation of somatic cells into neurons. Neurodegenerative diseases are not the only conditions where inducing neuronal proliferation could be beneficial. Consequently, the impact of pro-proliferative compounds on neurons has also been researched in mouse models of Alzheimer's disease.

Programming of neural progenitors of the adult subependymal zone towards a glutamatergic neuron lineage by neurogenin 2

Although adult subependymal zone (SEZ) neural stem cells mostly generate GABAergic interneurons, a small progenitor population expresses the proneural gene Neurog2 and produces glutamatergic neurons. Here, we determined whether Neurog2 could respecify SEZ neural stem cells and their progeny toward a glutamatergic fate. Retrovirus-mediated expression of Neurog2 induced the glutamatergic lineage markers TBR2 and TBR1 in cultured SEZ progenitors, which differentiated into functional glutamatergic neurons. Likewise, Neurog2-transduced SEZ progenitors acquired glutamatergic neuron hallmarks in vivo. Intriguingly, they failed to migrate toward the olfactory bulb and instead differentiated within the SEZ or the adjacent striatum, where they received connections from local neurons, as indicated by rabies virus-mediated monosynaptic tracing. In contrast, lentivirus-mediated expression of Neurog2 failed to reprogram early SEZ neurons, which maintained GABAergic identity and migrated to the olfactory bulb. Our data show that NEUROG2 can program SEZ progenitors toward a glutamatergic identity but fails to reprogram their neuronal progeny.

Overexpression of miR-124 in astrocyte improves neurological deficits in rat with ischemic stroke via DLL4 modulation

BACKGROUND

Astrocytes have been demonstrated to undergo conversion into functional neurons, presenting a promising approach for stroke treatment. However, the development of small molecules capable of effectively inducing this cellular reprogramming remains a critical challenge.

METHODS

Initially, we introduced a glial cell marker gene, GFaABC1D, as the promoter within an adeno-associated virus vector overexpressing miR-124 into the motor cortex of an ischemia-reperfusion model in rats. Additionally, we administered NeuroD1 as a positive control. Lentiviral vectors overexpressing miR-124 were constructed and transfected into primary rat astrocytes. We assessed the cellular distribution of GFAP, DCX, and NeuN on days 7, 14, and 28, respectively.

RESULTS

In rats with ischemic stroke, miR-124-transduced glial cells exhibited positive staining for the immature neuron marker doublecortin (DCX) and the mature neuron marker NeuN after 4 weeks. In contrast, NeuroD1-overexpressing model rats only expressed NeuN, and the positive percentage was higher in co-transfection with miR-124 and NeuroD1. Overexpression of miR-124 effectively ameliorated neurological deficits and motor functional impairment in the model rats. In primary rat astrocytes transduced with miR-124, DCX was not observed after 7 days of transfection, but it appeared at 14 days, with the percentage further increasing to 44.6% at 28 days. Simultaneously, 15.1% of miR-124-transduced cells exhibited NeuN positivity, which was not detected at 7 and 14 days. In vitro, double fluorescence assays revealed that miR-124 targeted Dll4, and in vivo experiments confirmed that miR-124 inhibited the expression of Notch1 and DLL4.

CONCLUSIONS

The overexpression of miR-124 in astrocytes demonstrates significant potential for improving neurological deficits following ischemic stroke by inhibiting DLL4 expression, and it may facilitate astrocyte-to-neuronal transformation.