Role of Mitochondrial Metabolism in the Control of Early Lineage Progression and Aging Phenotypes in Adult Hippocampal Neurogenesis

Mitochondrial regulation of adult hippocampal neurogenesis: Insights into neurological function and neurodevelopmental disorders

Mitochondria are essential regulators of cellular energy metabolism and play a crucial role in the maintenance and function of neuronal cells. Studies in the last decade have highlighted the importance of mitochondrial dynamics and bioenergetics in adult neurogenesis, a process that significantly influences cognitive function and brain plasticity. In this review, we examine the mechanisms by which mitochondria regulate adult neurogenesis, focusing on the impact of mitochondrial function on the behavior of neural stem/progenitor cells and the maturation and plasticity of newborn neurons in the adult mouse hippocampus. In addition, we explore the link between mitochondrial dysfunction, adult hippocampal neurogenesis and genes associated with cognitive deficits in neurodevelopmental disorders. In particular, we provide insights into how alterations in the transcriptional regulator NR2F1 affect mitochondrial dynamics and may contribute to the pathophysiology of the emerging neurodevelopmental disorder Bosch-Boonstra-Schaaf optic atrophy syndrome (BBSOAS). Understanding how genes involved in embryonic and adult neurogenesis affect mitochondrial function in neurological diseases might open new directions for therapeutic interventions aimed at boosting mitochondrial function during postnatal life.

Mitochondrial regulation in stem cells

Stem cells persist throughout the lifespan to repair and regenerate tissues due to their unique ability to self-renew and differentiate. Here we reflect on the recent discoveries in stem cells that highlight a mitochondrial metabolic checkpoint at the restriction point of the stem cell cycle. Mitochondrial activation supports stem cell proliferation and differentiation by providing energy supply and metabolites as signaling molecules. Concomitant mitochondrial stress can lead to loss of stem cell self-renewal and requires the surveillance of various mitochondrial quality control mechanisms. During aging, a mitochondrial protective program mediated by several sirtuins becomes dysregulated and can be targeted to reverse stem cell aging and tissue degeneration, giving hope for targeting the mitochondrial metabolic checkpoint for treating tissue degenerative diseases.

The therapeutic potential of curculigoside in poststroke depression: a focus on hippocampal neurogenesis and mitochondrial function

OBJECTIVES

To investigate the effects and mechanism of curculigoside against poststroke depression (PSD).

METHODS

In vivo, a PSD rat model was created by combining bilateral common carotid artery occlusion and chronic unpredictable mild stress stimulations. After 4-week modeling and intragastrically administration of curculigoside, the effects of curculigoside on behavior, hippocampal neurogenesis, and hippocampal mitochondrial oxidative phosphorylation (OxPhos) were investigated. In vitro, PSD-like primary neural stem cells (NSCs) model was established by oxygen-glucose deprivation/recovery (OGD/R) combing high-corticosterone (CORT) concentration, followed by treatment with curculigoside. The investigation subsequently examined the impact of curculigoside on mitochondrial OxPhos, proliferation, and differentiation of NSCs under OGD/R + CORT conditions.

KEY FINDINGS

In vivo, PSD rats showed significantly depressive behaviors, dysfunctional neurogenesis in hippocampus, as well as decreased hippocampus adenosine triphosphate (ATP) levels, reduced electron transport chain complexes activity, and downregulates mitochondrial transcription factor A (TFAM) and PPAR-gamma coactivator 1 alpha (PGC-1α) expression in hippocampus. In vitro, OGD/R +CORT significantly injured the proliferation and differentiation, as well as impaired the mitochondrial OxPhos in NSCs. Curculigoside treatment was effective in improving these abnormal changes.

CONCLUSION

Curculigoside may repair hippocampal neurogenesis in PSD rats by enhancing hippocampal mitochondrial OxPhos, and has shown a great potential for anti-PSD.

Cross-species analysis uncovers the mitochondrial stress response in the hippocampus as a shared mechanism in mouse early life stress and human depression

Depression, or major depressive disorder, poses a significant burden for both individuals and society, affecting approximately 10.8% of the general population. This psychiatric disorder leads to approximately 800,000 deaths per year. A combination of genetic and environmental factors such as early life stress (ELS) increase the risk for development of depression in humans, and a clear role for the hippocampus in the pathophysiology of depression has been shown. Nevertheless, the underlying mechanisms of depression remain poorly understood, resulting in a lack of effective treatments. To better understand the core mechanisms underlying the development of depression, we used a cross-species design to investigate shared hippocampal pathophysiological mechanisms in mouse ELS and human depression. Mice were subjected to ELS by a maternal separation paradigm, followed by RNA sequencing analysis of the adult hippocampal tissue. This identified persistent transcriptional changes linked to mitochondrial stress response pathways, with oxidative phosphorylation and protein folding emerging as the main mechanisms affected by maternal separation. Remarkably, there was a significant overlap between the pathways involved in mitochondrial stress response we observed and publicly available RNAseq data from hippocampal tissue of depressive patients. This cross-species conservation of changes in gene expression of mitochondria-related genes suggests that mitochondrial stress may play a pivotal role in the development of depression. Our findings highlight the potential significance of the hippocampal mitochondrial stress response as a core mechanism underlying the development of depression. Further experimental investigations are required to expand our understanding of these mechanisms.

Lineage-specific changes in mitochondrial properties during neural stem cell differentiation

Neural stem cells (NSCs) reside in discrete regions of the adult mammalian brain where they can differentiate into neurons, astrocytes, and oligodendrocytes. Several studies suggest that mitochondria have a major role in regulating NSC fate. Here, we evaluated mitochondrial properties throughout NSC differentiation and in lineage-specific cells. For this, we used the neurosphere assay model to isolate, expand, and differentiate mouse subventricular zone postnatal NSCs. We found that the levels of proteins involved in mitochondrial fusion (Mitofusin [Mfn] 1 and Mfn 2) increased, whereas proteins involved in fission (dynamin-related protein 1 [DRP1]) decreased along differentiation. Importantly, changes in mitochondrial dynamics correlated with distinct patterns of mitochondrial morphology in each lineage. Particularly, we found that the number of branched and unbranched mitochondria increased during astroglial and neuronal differentiation, whereas the area occupied by mitochondrial structures significantly reduced with oligodendrocyte maturation. In addition, comparing the three lineages, neurons revealed to be the most energetically flexible, whereas astrocytes presented the highest ATP content. Our work identified putative mitochondrial targets to enhance lineage-directed differentiation of mouse subventricular zone-derived NSCs.

Nlrp6 protects from corticosterone-induced NSPC ferroptosis by modulating RIG-1/MAVS-mediated mitophagy

Hippocampal neural stem/progenitor cells (NSPCs) are highly vulnerable to different stress stimuli, resulting in adult neurogenesis decline and eventual cognitive defects. Our previous study demonstrated that NOD-like receptor family pyrin domain-containing 6 (Nlrp6) highly expressed in NSPCs played a critical role in sustaining hippocampal neurogenesis to resist stress-induced depression, but the underlying mechnistms are still unclear. Here, we found that Nlrp6 depletion led to cognitive defects and hippocampal NSPC loss in mice. RNA-sequencing analysis of the primary NSPCs revealed that Nlrp6 deficiency altered gene expression profiles of mitochondrial energy generation and ferroptotic process. Upon siNlrp6 transfection, as well as corticosterone (CORT) exposure, downregulation of Nlrp6 suppressed retinoic acid-inducible gene I (RIG-1)/mitochondrial antiviral signaling proteins (MAVS)-mediated autophagy, but drove NSPC ferroptotic death. More interesting, short chain fatty acids (SCFAs) upregulated Nlrp6 expression and promoted RIG-1/MAVS-mediated mitophagy, preventing CORT-induced NSPC ferroptosis. Our study further demonstrates that Nlrp6 should be a sensor for RIG-1/MAVS-mediated mitophagy and play a critical role in maintain mitochondrial homeostasis of hippocampal NSPCs. These results suggests that Nlrp6 should be a potential drug target to combat neurodegenerative diseases relative with chronic stress.

Molecular cascade reveals sequential milestones underlying hippocampal neural stem cell development into an adult state

Quiescent adult neural stem cells (NSCs) in the mammalian brain arise from proliferating NSCs during development. Beyond acquisition of quiescence, an adult NSC hallmark, little is known about the process, milestones, and mechanisms underlying the transition of developmental NSCs to an adult NSC state. Here, we performed targeted single-cell RNA-seq analysis to reveal the molecular cascade underlying NSC development in the early postnatal mouse dentate gyrus. We identified two sequential steps, first a transition to quiescence followed by further maturation, each of which involved distinct changes in metabolic gene expression. Direct metabolic analysis uncovered distinct milestones, including an autophagy burst before NSC quiescence acquisition and cellular reactive oxygen species level elevation along NSC maturation. Functionally, autophagy is important for the NSC transition to quiescence during early postnatal development. Together, our study reveals a multi-step process with defined milestones underlying establishment of the adult NSC pool in the mammalian brain.

Enhanced mitochondrial fusion during a critical period of synaptic plasticity in adult-born neurons

Integration of new neurons into adult hippocampal circuits is a process coordinated by local and long-range synaptic inputs. To achieve stable integration and uniquely contribute to hippocampal function, immature neurons are endowed with a critical period of heightened synaptic plasticity, yet it remains unclear which mechanisms sustain this form of plasticity during neuronal maturation. We found that as new neurons enter their critical period, a transient surge in fusion dynamics stabilizes elongated mitochondrial morphologies in dendrites to fuel synaptic plasticity. Conditional ablation of fusion dynamics to prevent mitochondrial elongation selectively impaired spine plasticity and synaptic potentiation, disrupting neuronal competition for stable circuit integration, ultimately leading to decreased survival. Despite profuse mitochondrial fragmentation, manipulation of competition dynamics was sufficient to restore neuronal survival but left neurons poorly responsive to experience at the circuit level. Thus, by enabling synaptic plasticity during the critical period, mitochondrial fusion facilitates circuit remodeling by adult-born neurons.

Hippocampal mitophagy contributes to spatial memory via maintaining neurogenesis during the development of mice

BACKGROUND

Impaired mitochondrial dynamics have been identified as a significant contributing factor to reduced neurogenesis under pathological conditions. However, the relationship among mitochondrial dynamics, neurogenesis, and spatial memory during normal development remains unclear. This study aims to elucidate the role of mitophagy in spatial memory mediated by neurogenesis during development.

METHODS

Adolescent and adult male mice were used to assess spatial memory performance. Immunofluorescence staining was employed to evaluate levels of neurogenesis, and mitochondrial dynamics were assessed through western blotting and transmission electron microscopy. Pharmacological interventions further validated the causal relationship among mitophagy, neurogenesis, and behavioral performance during development.

RESULTS

The study revealed differences in spatial memory between adolescent and adult mice. Diminished neurogenesis, accompanied by reduced mitophagy, was observed in the hippocampus of adult mice compared to adolescent subjects. Pharmacological induction of mitophagy in adult mice with UMI-77 resulted in enhanced neurogenesis and prolonged spatial memory retention. Conversely, inhibition of mitophagy with Mdivi-1 in adolescent mice led to reduced hippocampal neurogenesis and impaired spatial memory.

CONCLUSION

The observed decline in spatial memory in adult mice is associated with decreased mitophagy, which affects neurogenesis in the dentate gyrus. This underscores the therapeutic potential of enhancing mitophagy to counteract age- or disease-related cognitive decline.

Characteristics of quiescent adult neural stem cells induced by the bFGF/BMP4 combination or BMP4 alone in vitro

Bone morphogenetic protein-4 (BMP4) is involved in regulation of neural stem cells (NSCs) proliferation, differentiation, migration and survival. It was previously thought that the treatment of NSCs with BMP4 alone induces astrocytes, whereas the treatment of NSCs with the bFGF/BMP4 combination induces quiescent neural stem cells (qNSCs). In this study, we performed bulk RNA sequencing (RNA-Seq) to compare the transcriptome profiles of BMP4-treated NSCs and bFGF/BMP4-treated NSCs, and found that both NSCs treated by these two methods were Sox2 positive qNSCs which were able to generate neurospheres. However, NSCs treated by those two methods exhibited different characteristics in state and the potential for neuronal differentiation based on transcriptome analysis and experimental results. We found that BMP4-treated NSCs tended to be in a deeper quiescent state than bFGF/BMP4-treated NSCs as the percentage of ki67-positive cells were lower in BMP4-treated NSCs. And after exposure to differentiated environment, bFGF/BMP4-treated NSCs generated more DCX-positive immature neurons and MAP2-positive neurons than BMP4-treated NSCs. Our study characterized qNSCs treated with BMP4 alone and bFGF/BMP4 combination, providing a reference for the scientific use of BMP4 and bFGF/BMP4-induced qNSCs models.

Quiescent Adult Neural Stem Cells: Developmental Origin and Regulatory Mechanisms

The existence of neural stem cells (NSCs) in the adult mammalian nervous system, although small in number and restricted to the sub-ventricular zone of the lateral ventricles, the dentate gyrus of the hippocampus, and the olfactory epithelium, is a gift of evolution for the adaptive brain function which requires persistent plastic changes of these regions. It is known that most adult NSCs are latent, showing long cell cycles. In the past decade, the concept of quiescent NSCs (qNSCs) has been widely accepted by researchers in the field, and great progress has been made in the biology of qNSCs. Although the spontaneous neuronal regeneration derived from adult NSCs is not significant, understanding how the behaviors of qNSCs are regulated sheds light on stimulating endogenous NSC-based neuronal regeneration. In this review, we mainly focus on the recent progress of the developmental origin and regulatory mechanisms that maintain qNSCs under normal conditions, and that mobilize qNSCs under pathological conditions, hoping to give some insights for future study.

Prosaposin maintains adult neural stem cells in a state associated with deep quiescence

In most vertebrates, adult neural stem cells (NSCs) continuously give rise to neurons in discrete brain regions. A critical process for maintaining NSC pools over long periods of time in the adult brain is NSC quiescence, a reversible and tightly regulated state of cell-cycle arrest. Recently, lysosomes were identified to regulate the NSC quiescence-proliferation balance. However, it remains controversial whether lysosomal activity promotes NSC proliferation or quiescence, and a finer influence of lysosomal activity on NSC quiescence duration or depth remains unexplored. Using RNA sequencing and pharmacological manipulations, we show that lysosomes are necessary for NSC quiescence maintenance. In addition, we reveal that expression of psap, encoding the lysosomal regulator Prosaposin, is enriched in quiescent NSCs (qNSCs) that reside upstream in the NSC lineage and display a deep/long quiescence phase in the adult zebrafish telencephalon. We show that shRNA-mediated psap knockdown increases the proportion of activated NSCs (aNSCs) as well as NSCs that reside in shallower quiescence states (signed by ascl1a and deltaA expression). Collectively, our results identify the lysosomal protein Psap as a (direct or indirect) quiescence regulator and unfold the interplay between lysosomal function and NSC quiescence heterogeneities.

Spinal Cord Injury Model Mitochondria Connect Altered Function with Defects of Mitochondrion Morphology: an Ultrastructural Study

The key role of mitochondria in neurodegenerative disease patients is well documented. Recent studies claimed that mitochondrial regulatory dysfunction might play a role in ongoing cell death and dysfunction. In the present study, we characterized ultrastructural morphometry of mitochondrial alterations occurring at the level of motor neuron cell bodies in SCI-induced rats. We applied 17β-estradiol (E2) to determine whether it can improve mitochondria structural integrity of motor neurons. We used a rat model of acute SCI generated by spinal cord contusion at the T9-T10 level, followed by tissue processing 21 days post-SCI. Samples were divided into five groups: laminectomy, SCI, vehicle, SCI + 25 µg/kg E2, and SCI + 10 µg/kg E2. Assessments included analysis of hind limb motor recovery, quantifying tissue repair, and evaluation of morphological changes in the ultrastructure of mitochondria in motor neurons by transmission electron microscopy. In the E2-treated groups, especially the group receiving 25 µg/kg E2, less irregular mitochondria were observed, as there was a significant reduction in swelling or vacuolization, or fragmentation compared to the SCI group. Furthermore, E2 significantly reduced membrane rupture in the SCI group. E2 could be a proper therapeutic agent to relieve mitochondrial deleterious effects on neurons in neurodegenerative diseases.

High OXPHOS efficiency in RA-FUdr-differentiated SH-SY5Y cells: involvement of cAMP signalling and respiratory supercomplexes

Neurons are highly dependent on mitochondria to meet their bioenergetic needs and understanding the metabolic changes during the differentiation process is crucial in the neurodegeneration context. Several in vitro approaches have been developed to study neuronal differentiation and bioenergetic changes. The human SH-SY5Y cell line is a widely used cellular model and several differentiation protocols have been developed to induce a neuron-like phenotype including retinoic acid (RA) treatment. In this work we obtained a homogeneous functional population of neuron-like cells by a two-step differentiation protocol in which SH-SY5Y cells were treated with RA plus the mitotic inhibitor 2-deoxy-5-fluorouridine (FUdr). RA-FUdr treatment induced a neuronal phenotype characterized by increased expression of neuronal markers and electrical properties specific to excitable cells. In addition, the RA-FUdr differentiated cells showed an enrichment of long chain and unsaturated fatty acids (FA) in the acyl chain composition of cardiolipin (CL) and the bioenergetic analysis evidences a high coupled and maximal respiration associated with high mitochondrial ATP levels. Our results suggest that the observed high oxidative phosphorylation (OXPHOS) capacity may be related to the activation of the cyclic adenosine monophosphate (cAMP) pathway and the assembly of respiratory supercomplexes (SCs), highlighting the change in mitochondrial phenotype during neuronal differentiation.

Xinshubao tablet rescues cognitive dysfunction in a mouse model of vascular dementia: Involvement of neurogenesis and neuroinflammation

Vascular dementia (VaD) represents a severe cognitive dysfunction syndrome closed linked to cardiovascular function. In the present study, we assessed the potential of Xinshubao tablet (XSB), a traditional Chinese prescription widely used for cardiovascular diseases, to mitigate neuropathological damage in a mouse model of VaD and elucidated the underlying mechanisms. Our findings revealed that oral administration of XSB rescued the cardiac dysfunction resulting from bilateral common carotid artery stenosis (BCAS), improved the cerebral blood flow (CBF) and cognitive function, reduced white matter injury, inhibited excessive microglial and astrocytic activation, stimulated hippocampal neurogenesis, and reduced neural apoptosis in the brains of BCAS mice. Mechanistically, RNA-seq analysis indicated that XSB treatment was significantly associated with neuroinflammation, vasculature development, and synaptic transmission, which were further confirmed by q-PCR assays. Western blot results revealed that XSB treatment hindered the nuclear translocation of nuclear factor-κB (NF-κB), thereby suppressing the NF-κB signaling pathway. These results collectively demonstrated that XSB could ameliorate cognitive dysfunction caused by BCAS through regulating CBF, reducing white matter lesions, suppressing glial activation, promoting neurogenesis, and mitigating neuroinflammation. Notably, the NF-κB signaling pathway emerged as a pivotal player in this mechanism.

Emerging Functional Connections Between Metabolism and Epigenetic Remodeling in Neural Differentiation

Stem cells possess extraordinary capacities for self-renewal and differentiation, making them highly valuable in regenerative medicine. Among these, neural stem cells (NSCs) play a fundamental role in neural development and repair processes. NSC characteristics and fate are intricately regulated by the microenvironment and intracellular signaling. Interestingly, metabolism plays a pivotal role in orchestrating the epigenome dynamics during neural differentiation, facilitating the transition from undifferentiated NSC to specialized neuronal and glial cell types. This intricate interplay between metabolism and the epigenome is essential for precisely regulating gene expression patterns and ensuring proper neural development. This review highlights the mechanisms behind metabolic regulation of NSC fate and their connections with epigenetic regulation to shape transcriptional programs of stemness and neural differentiation. A comprehensive understanding of these molecular gears appears fundamental for translational applications in regenerative medicine and personalized therapies for neurological conditions.

Significance of quantitative analyses of the impact of heterogeneity in mitochondrial content and shape on cell differentiation

Mitochondria, classically known as the powerhouse of cells, are unique double membrane-bound multifaceted organelles carrying a genome. Mitochondrial content varies between cell types and precisely doubles within cells during each proliferating cycle. Mitochondrial content also increases to a variable degree during cell differentiation triggered after exit from the proliferating cycle. The mitochondrial content is primarily maintained by the regulation of mitochondrial biogenesis, while damaged mitochondria are eliminated from the cells by mitophagy. In any cell with a given mitochondrial content, the steady-state mitochondrial number and shape are determined by a balance between mitochondrial fission and fusion processes. The increase in mitochondrial content and alteration in mitochondrial fission and fusion are causatively linked with the process of differentiation. Here, we critically review the quantitative aspects in the detection methods of mitochondrial content and shape. Thereafter, we quantitatively link these mitochondrial properties in differentiating cells and highlight the implications of such quantitative link on stem cell functionality. Finally, we discuss an example of cell size regulation predicted from quantitative analysis of mitochondrial shape and content. To highlight the significance of quantitative analyses of these mitochondrial properties, we propose three independent rationale based hypotheses and the relevant experimental designs to test them.

Ganglioside GD3 regulates neural stem cell quiescence and controls postnatal neurogenesis

The postnatal neural stem cell (NSC) pool hosts quiescent and activated radial glia-like NSCs contributing to neurogenesis throughout adulthood. However, the underlying regulatory mechanism during the transition from quiescent NSCs to activated NSCs in the postnatal NSC niche is not fully understood. Lipid metabolism and lipid composition play important roles in regulating NSC fate determination. Biological lipid membranes define the individual cellular shape and help maintain cellular organization and are highly heterogeneous in structure and there exist diverse microdomains (also known as lipid rafts), which are enriched with sugar molecules, such as glycosphingolipids. An often overlooked but key aspect is that the functional activities of proteins and genes are highly dependent on their molecular environments. We previously reported that ganglioside GD3 is the predominant species in NSCs and that the reduced postnatal NSC pools are observed in global GD3-synthase knockout (GD3S-KO) mouse brains. The specific roles of GD3 in determining the stage and cell-lineage determination of NSCs remain unclear, since global GD3S-KO mice cannot distinguish if GD3 regulates postnatal neurogenesis or developmental impacts. Here, we show that inducible GD3 deletion in postnatal radial glia-like NSCs promotes NSC activation, resulting in the loss of the long-term maintenance of the adult NSC pools. The reduced neurogenesis in the subventricular zone (SVZ) and the dentate gyrus (DG) of GD3S-conditional-knockout mice led to the impaired olfactory and memory functions. Thus, our results provide convincing evidence that postnatal GD3 maintains the quiescent state of radial glia-like NSCs in the adult NSC niche.

Mitochondrial, cell cycle control and neuritogenesis alterations in an iPSC-based neurodevelopmental model for schizophrenia

Schizophrenia is a severe psychiatric disorder of neurodevelopmental origin that affects around 1% of the world's population. Proteomic studies and other approaches have provided evidence of compromised cellular processes in the disorder, including mitochondrial function. Most of the studies so far have been conducted on postmortem brain tissue from patients, and therefore, do not allow the evaluation of the neurodevelopmental aspect of the disorder. To circumvent that, we studied the mitochondrial and nuclear proteomes of neural stem cells (NSCs) and neurons derived from induced pluripotent stem cells (iPSCs) from schizophrenia patients versus healthy controls to assess possible alterations related to energy metabolism and mitochondrial function during neurodevelopment in the disorder. Our results revealed differentially expressed proteins in pathways related to mitochondrial function, cell cycle control, DNA repair and neuritogenesis and their possible implication in key process of neurodevelopment, such as neuronal differentiation and axonal guidance signaling. Moreover, functional analysis of NSCs revealed alterations in mitochondrial oxygen consumption in schizophrenia-derived cells and a tendency of higher levels of intracellular reactive oxygen species (ROS). Hence, this study shows evidence that alterations in important cellular processes are present during neurodevelopment and could be involved with the establishment of schizophrenia, as well as the phenotypic traits observed in adult patients. Neural stem cells (NSCs) and neurons were derived from induced pluripotent stem cells (iPSCs) from schizophrenia patients and controls. Proteomic analyses were performed on the enriched mitochondrial and nuclear fractions of NSCs and neurons. Whole-cell proteomic analysis was also performed in neurons. Our results revealed alteration in proteins related to mitochondrial function, cell cycle control, among others. We also performed energy pathway analysis and reactive oxygen species (ROS) analysis of NSCs, which revealed alterations in mitochondrial oxygen consumption and a tendency of higher levels of intracellular ROS in schizophrenia-derived cells.

Mitochondrial OPA1 Deficiency Is Associated to Reversible Defects in Spatial Memory Related to Adult Neurogenesis in Mice

Mitochondria are integrative hubs central to cellular adaptive pathways. Such pathways are critical in highly differentiated postmitotic neurons, the plasticity of which sustains brain function. Consequently, defects in mitochondria and in their dynamics appear instrumental in neurodegenerative diseases and may also participate in cognitive impairments. To directly test this hypothesis, we analyzed cognitive performances in a mouse mitochondria-based disease model, because of haploinsufficiency in the mitochondrial optic atrophy type 1 (OPA1) protein involved in mitochondrial dynamics. In males, we evaluated adult hippocampal neurogenesis parameters using immunohistochemistry. We performed a battery of tests to assess basal behavioral characteristics and cognitive performances, and tested putative treatments. While in dominant optic atrophy (DOA) mouse models, the known main symptoms are late onset visual deficits, we discovered early impairments in hippocampus-dependent spatial memory attributable to defects in adult neurogenesis. Moreover, less connected adult-born hippocampal neurons showed a decrease in mitochondrial content. Remarkably, voluntary exercise or pharmacological treatment targeting mitochondrial dynamics restored spatial memory in DOA mice. Altogether, our study identifies a crucial role for OPA1-dependent mitochondrial functions in adult neurogenesis, and thus in hippocampal-dependent cognitive functions. More generally, our findings show that adult neurogenesis is highly sensitive to mild mitochondrial defects, generating impairments in spatial memory that can be detected at an early stage and counterbalanced by physical exercise and pharmacological targeting of mitochondrial dynamics. Thus, amplification of mitochondrial function at an early stage appears beneficial for late-onset neurodegenerative diseases.

Therapeutic Effects of Mesenchymal Stromal Cells Require Mitochondrial Transfer and Quality Control

Due to their beneficial effects in an array of diseases, Mesenchymal Stromal Cells (MSCs) have been the focus of intense preclinical research and clinical implementation for decades. MSCs have multilineage differentiation capacity, support hematopoiesis, secrete pro-regenerative factors and exert immunoregulatory functions promoting homeostasis and the resolution of injury/inflammation. The main effects of MSCs include modulation of immune cells (macrophages, neutrophils, and lymphocytes), secretion of antimicrobial peptides, and transfer of mitochondria (Mt) to injured cells. These actions can be enhanced by priming (i.e., licensing) MSCs prior to exposure to deleterious microenvironments. Preclinical evidence suggests that MSCs can exert therapeutic effects in a variety of pathological states, including cardiac, respiratory, hepatic, renal, and neurological diseases. One of the key emerging beneficial actions of MSCs is the improvement of mitochondrial functions in the injured tissues by enhancing mitochondrial quality control (MQC). Recent advances in the understanding of cellular MQC, including mitochondrial biogenesis, mitophagy, fission, and fusion, helped uncover how MSCs enhance these processes. Specifically, MSCs have been suggested to regulate peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC1α)-dependent biogenesis, Parkin-dependent mitophagy, and Mitofusins (Mfn1/2) or Dynamin Related Protein-1 (Drp1)-mediated fission/fusion. In addition, previous studies also verified mitochondrial transfer from MSCs through tunneling nanotubes and via microvesicular transport. Combined, these effects improve mitochondrial functions, thereby contributing to the resolution of injury and inflammation. Thus, uncovering how MSCs affect MQC opens new therapeutic avenues for organ injury, and the transplantation of MSC-derived mitochondria to injured tissues might represent an attractive new therapeutic approach.

Metabolic switches during development and regeneration

Metabolic switches are a crucial hallmark of cellular development and regeneration. In response to changes in their environment or physiological state, cells undergo coordinated metabolic switching that is necessary to execute biosynthetic demands of growth and repair. In this Review, we discuss how metabolic switches represent an evolutionarily conserved mechanism that orchestrates tissue development and regeneration, allowing cells to adapt rapidly to changing conditions during development and postnatally. We further explore the dynamic interplay between metabolism and how it is not only an output, but also a driver of cellular functions, such as cell proliferation and maturation. Finally, we underscore the epigenetic and cellular mechanisms by which metabolic switches mediate biosynthetic needs during development and regeneration, and how understanding these mechanisms is important for advancing our knowledge of tissue development and devising new strategies to promote tissue regeneration.

Caveolin-1 Autonomously Regulates Hippocampal Neurogenesis Via Mitochondrial Dynamics

The mechanisms underlying adult hippocampal neurogenesis (AHN) are not fully understood. AHN plays instrumental roles in learning and memory. Understanding the signals that regulate AHN has implications for brain function and therapy. Here we show that Caveolin-1 (Cav-1), a protein that is highly enriched in endothelial cells and the principal component of caveolae, autonomously regulates AHN. Conditional deletion of Cav-1 in adult neural progenitor cells (nestin +) led to increased neurogenesis and enhanced performance of mice in contextual discrimination. Proteomic analysis revealed that Cav-1 plays a role in mitochondrial pathways in neural progenitor cells. Importantly, Cav-1 was localized to the mitochondria in neural progenitor cells and modulated mitochondrial fission-fusion, a critical process in neurogenesis. These results suggest that Cav-1 is a novel regulator of AHN and underscore the impact of AHN on cognition.

Generation of mouse hippocampal brain organoids from primary embryonic neural stem cells

Here we present a protocol to generate standardized cerebral organoids with hippocampal regional specification using morphogen WNT3a. We describe steps for isolating mouse embryonic (E14.5) neural stem cells from the brain subgranular zone, preparing organoids samples for immunofluorescence, calcium imaging, and metabolic profiling. This protocol can be used to generate mouse brain organoids for developmental studies, modeling disease, and drug screening. Organoids can be obtained in one month, thus providing a rapid tool for high-throughput data validation. For complete details on the use and execution of this protocol, please refer to Ciarpella et al. "Murine cerebral organoids develop network of functional neurons and hippocampal brain region identity".1.

Mitochondrial proteins encoded by the 22q11.2 neurodevelopmental locus regulate neural stem and progenitor cell proliferation

Microdeletion of a 3Mb region encompassing 45 protein-coding genes at chromosome 22q11.2 (22q11.2DS) predisposes individuals to multiple neurodevelopmental disorders and is one of the greatest genetic risk factors for schizophrenia. Defective mitochondrial function has been hypothesized to contribute to 22q11.2DS pathogenesis; however, which of the six mitochondrial genes contribute to neurodevelopmental phenotypes and their underlying mechanisms remain unresolved. To systematically test 22q11.2DS genes for functional roles in neurodevelopment and behavior, we generated genetic mutants for each of the 37 conserved zebrafish orthologs and performed high throughput behavioral phenotyping using seven behavioral assays. Through this unbiased approach, we identified five single-gene mutants with partially overlapping behavioral phenotypes. Two of these genes, mrpl40 and prodha, encode for mitochondrial proteins and, similar to what we observed in mrpl40 and prodha mutants, pharmacologic inhibition of mitochondrial function during development results in microcephaly. Single mutant analysis shows that both mrpl40 and prodha mutants display aberrant neural stem and progenitor cell proliferation, with each gene regulating distinct cell populations. Finally, double mutants for both mrpl40 and prodha display aggravated behavioral phenotypes and neural stem and progenitor cell analysis reveals a previously unrecognized partially redundant role for mrpl40 and prodha in regulating radial glia-like cell proliferation. Combined, our results demonstrate a critical role for mitochondrial function in neural stem and progenitor cell populations in the developing vertebrate brain and provide compelling evidence that mitochondrial dysfunction during neurodevelopment is linked to brain volume and behavioral phenotypes observed in models of 22q11.2DS.

Catapol reduced the cognitive and mood dysfunctions in post-stroke depression mice via promoting PI3K-mediated adult neurogenesis

Adult hippocampal neurogenesis provides a regenerative resource for neural tissue and enhances neural plasticity, which is beneficial for brain functional rehabilitation post stroke. Recently, an increasing number of metabolic drugs have been reported to attenuate behavioral symptoms in neurodegeneration or psychiatric disorders via promoting adult hippocampal neurogenesis. Bioeffects of catapol show its potential as an antidiabetic though it has been previously widely indicated to perform the neuroprotective functions. However, the systematic evidence to support the behavioral effects of catapol to PSD model and what is the role of adult neurogenesis in such effects remains unexplored. In current study, we created the PSD model by combining MCAO procedure and CORT feeding. The treatment of catapol strikingly reduced the depressive/anxiety behavior in PSD model. Moreover, treatment of catapol also improved the cognitive functions. Immunofluorescence indicates that catapol could promote adult hippocampal neurogenesis in PSD model, and TMZ treatment further confirmed the role of the hippocampal neurogenesis in catapol's therapeutic effects to PSD. Cultural neurons also indicates that PI3K is the key signal in regulating catapol mediated neurogenesis. By administrating the PI3K specific inhibitor, we found that PI3K is the key to mediate the behavioral effects of catapol to PSD. In conclusion, catapol could perform as the effective drug to treat PSD via the PI3K mediated adult hippocampal neurogenesis.

From Youthful Vigor to Aging Decline: Unravelling the Intrinsic and Extrinsic Determinants of Hippocampal Neural Stem Cell Aging

Since Joseph Altman published his pioneering work demonstrating neurogenesis in the hippocampus of adult rats, the number of publications in this field increased exponentially. Today, we know that the adult hippocampus harbors a pool of adult neural stem cells (NSCs) that are the source of life-long neurogenesis and plasticity. The functions of these NSCs are regulated by extrinsic cues arising from neighboring cells and the systemic environment. However, this tight regulation is subject to imbalance with age, resulting in a decline in adult NSCs and neurogenesis, which contributes to the progressive deterioration of hippocampus-related cognitive functions. Despite extensive investigation, the mechanisms underlying this age-related decline in neurogenesis are only incompletely understood, but appear to include an increase in NSC quiescence, changes in differentiation patterns, and NSC exhaustion. In this review, we summarize recent work that has improved our knowledge of hippocampal NSC aging, focusing on NSC-intrinsic mechanisms as well as cellular and molecular changes in the niche and systemic environment that might be involved in the age-related decline in NSC functions. Additionally, we identify future directions that may advance our understanding of NSC aging and the concomitant loss of hippocampal neurogenesis and plasticity.

Neural stem cell metabolism revisited: a critical role for mitochondria

Metabolism has emerged as a key regulator of stem cell behavior. Mitochondria are crucial metabolic organelles that are important for differentiated cells, yet considered less so for stem cells. However, recent studies have shown that mitochondria influence stem cell maintenance and fate decisions, inviting a revised look at this topic. In this review, we cover the current literature addressing the role of mitochondrial metabolism in mouse and human neural stem cells (NSCs) in the embryonic and adult brain. We summarize how mitochondria are implicated in fate regulation and how substrate oxidation affects NSC quiescence. We further explore single-cell RNA sequencing (scRNA-seq) data for metabolic signatures of adult NSCs, highlight emerging technologies reporting on metabolic signatures, and discuss mitochondrial metabolism in other stem cells.

Preserving and enhancing mitochondrial function after stroke to protect and repair the neurovascular unit: novel opportunities for nanoparticle-based drug delivery

The neurovascular unit (NVU) is composed of vascular cells, glia, and neurons that form the basic component of the blood brain barrier. This intricate structure rapidly adjusts cerebral blood flow to match the metabolic needs of brain activity. However, the NVU is exquisitely sensitive to damage and displays limited repair after a stroke. To effectively treat stroke, it is therefore considered crucial to both protect and repair the NVU. Mitochondrial calcium (Ca²⁺) uptake supports NVU function by buffering Ca²⁺ and stimulating energy production. However, excessive mitochondrial Ca²⁺ uptake causes toxic mitochondrial Ca²⁺ overloading that triggers numerous cell death pathways which destroy the NVU. Mitochondrial damage is one of the earliest pathological events in stroke. Drugs that preserve mitochondrial integrity and function should therefore confer profound NVU protection by blocking the initiation of numerous injury events. We have shown that mitochondrial Ca²⁺ uptake and efflux in the brain are mediated by the mitochondrial Ca²⁺ uniporter complex (MCU_cx) and sodium/Ca²⁺/lithium exchanger (NCLX), respectively. Moreover, our recent pharmacological studies have demonstrated that MCU_cx inhibition and NCLX activation suppress ischemic and excitotoxic neuronal cell death by blocking mitochondrial Ca²⁺ overloading. These findings suggest that combining MCU_cx inhibition with NCLX activation should markedly protect the NVU. In terms of promoting NVU repair, nuclear hormone receptor activation is a promising approach. Retinoid X receptor (RXR) and thyroid hormone receptor (TR) agonists activate complementary transcriptional programs that stimulate mitochondrial biogenesis, suppress inflammation, and enhance the production of new vascular cells, glia, and neurons. RXR and TR agonism should thus further improve the clinical benefits of MCU_cx inhibition and NCLX activation by increasing NVU repair. However, drugs that either inhibit the MCU_cx, or stimulate the NCLX, or activate the RXR or TR, suffer from adverse effects caused by undesired actions on healthy tissues. To overcome this problem, we describe the use of nanoparticle drug formulations that preferentially target metabolically compromised and damaged NVUs after an ischemic or hemorrhagic stroke. These nanoparticle-based approaches have the potential to improve clinical safety and efficacy by maximizing drug delivery to diseased NVUs and minimizing drug exposure in healthy brain and peripheral tissues.

Talk to Me-Interplay between Mitochondria and Microbiota in Aging

The existence of mitochondria in eukaryotic host cells as a remnant of former microbial organisms has been widely accepted, as has their fundamental role in several diseases and physiological aging. In recent years, it has become clear that the health, aging, and life span of multicellular hosts are also highly dependent on the still-residing microbiota, e.g., those within the intestinal system. Due to the common evolutionary origin of mitochondria and these microbial commensals, it is intriguing to investigate if there might be a crosstalk based on preserved common properties. In the light of rising knowledge on the gut-brain axis, such crosstalk might severely affect brain homeostasis in aging, as neuronal tissue has a high energy demand and low tolerance for according functional decline. In this review, we summarize what is known about the impact of both mitochondria and the microbiome on the host's aging process and what is known about the aging of both entities. For a long time, bacteria were assumed to be immortal; however, recent evidence indicates their aging and similar observations have been made for mitochondria. Finally, we present pathways by which mitochondria are affected by microbiota and give information about therapeutic anti-aging approaches that are based on current knowledge.

Epigenetic aging in adult neurogenesis

Neural stem cells (NSCs) in the hippocampus generate new neurons throughout life, which functionally contribute to cognitive flexibility and mood regulation. Yet adult hippocampal neurogenesis substantially declines with age and age-related impairments in NSC activity underlie this reduction. Particularly, increased NSC quiescence and consequently reduced NSC proliferation are considered to be major drivers of the low neurogenesis levels in the aged brain. Epigenetic regulators control the gene expression programs underlying NSC quiescence, proliferation and differentiation and are hence critical to the regulation of adult neurogenesis. Epigenetic alterations have also emerged as central hallmarks of aging, and recent studies suggest the deterioration of the NSC-specific epigenetic landscape as a driver of the age-dependent decline in adult neurogenesis. In this review, we summarize the recently accumulating evidence for a role of epigenetic dysregulation in NSC aging and propose perspectives for future research directions.

L-arginine homeostasis governs adult neural stem cell activation by modulating energy metabolism in vivo

Neurogenesis in the developing and adult brain is intimately linked to remodeling of cellular metabolism. However, it is still unclear how distinct metabolic programs and energy sources govern neural stem cell (NSC) behavior and subsequent neuronal differentiation. Here, we found that adult mice lacking the mitochondrial urea metabolism enzyme, Arginase-II (Arg-II), exhibited NSC overactivation, thereby leading to accelerated NSC pool depletion and decreased hippocampal neurogenesis over time. Mechanistically, Arg-II deficiency resulted in elevated L-arginine levels and induction of a metabolic shift from glycolysis to oxidative phosphorylation (OXPHOS) caused by impaired attachment of hexokinase-I to mitochondria. Notably, selective inhibition of OXPHOS ameliorated NSC overactivation and restored abnormal neurogenesis in Arg-II deficient mice. Therefore, Arg-II-mediated intracellular L-arginine homeostasis directly influences the metabolic fitness of neural stem cells that is essential to maintain neurogenesis with age.

Ganglioside GD3 regulates neural stem cell quiescence and controls postnatal neurogenesis

The postnatal neural stem cell (NSC) pool hosts quiescent and activated radial glia-like NSCs contributing to neurogenesis throughout adulthood. However, the underlying regulatory mechanism during the transition from quiescent NSCs to activated NSCs in the postnatal NSC niche is not fully understood. Lipid metabolism and lipid composition play important roles in regulating NSC fate determination. Biological lipid membranes define the individual cellular shape and help maintain cellular organization and are highly heterogenous in structure and there exist diverse microdomains (also known as lipid rafts), which are enriched with sugar molecules, such as glycosphingolipids. An often overlooked but key aspect is that the functional activities of proteins and genes are highly dependent upon their molecular environments. We previously reported that ganglioside GD3 is the predominant species in NSCs and that the reduced postnatal NSC pools are observed in global GD3-synthase knockout (GD3S-KO) mouse brains. The specific roles of GD3 in determining the stage and cell-lineage determination of NSCs remain unclear, since global GD3S-KO mice cannot distinguish if GD3 regulates postnatal neurogenesis or developmental impacts. Here we show that inducible GD3 deletion in postnatal radial glia-like NSCs promotes the NSC activation, resulting in the loss of the long-term maintenance of the adult NSC pools. The reduced neurogenesis in the subventricular zone (SVZ) and the dentate gyrus (DG) of GD3S-conditional-knockout mice led to impaired olfactory and memory functions. Thus, our results provide convincing evidence that postnatal GD3 maintains the quiescent state of radial glia-like NSCs in the adult NSC niche.

Epitranscriptomic regulation of cortical neurogenesis via Mettl8-dependent mitochondrial tRNA m3C modification

Increasing evidence implicates the critical roles of various epitranscriptomic RNA modifications in different biological processes. Methyltransferase METTL8 installs 3-methylcytosine (m3C) modification of mitochondrial tRNAs in vitro; however, its role in intact biological systems is unknown. Here, we show that Mettl8 is localized in mitochondria and installs m3C specifically on mitochondrial tRNAThr/Ser(UCN) in mouse embryonic cortical neural stem cells. At molecular and cellular levels, Mettl8 deletion in cortical neural stem cells leads to reduced mitochondrial protein translation and attenuated respiration activity. At the functional level, conditional Mettl8 deletion in mice results in impaired embryonic cortical neural stem cell maintenance in vivo, which can be rescued by pharmacologically enhancing mitochondrial functions. Similarly, METTL8 promotes mitochondrial protein expression and neural stem cell maintenance in human forebrain cortical organoids. Together, our study reveals a conserved epitranscriptomic mechanism of Mettl8 and mitochondrial tRNA m3C modification in maintaining embryonic cortical neural stem cells in mice and humans.

Mitochondrial pyruvate metabolism regulates the activation of quiescent adult neural stem cells

Cellular metabolism is important for adult neural stem/progenitor cell (NSPC) behavior. However, its role in the transition from quiescence to proliferation is not fully understood. We here show that the mitochondrial pyruvate carrier (MPC) plays a crucial and unexpected part in this process. MPC transports pyruvate into mitochondria, linking cytosolic glycolysis to mitochondrial tricarboxylic acid cycle and oxidative phosphorylation. Despite its metabolic key function, the role of MPC in NSPCs has not been addressed. We show that quiescent NSPCs have an active mitochondrial metabolism and express high levels of MPC. Pharmacological MPC inhibition increases aspartate and triggers NSPC activation. Furthermore, genetic Mpc1 ablation in vitro and in vivo also activates NSPCs, which differentiate into mature neurons, leading to overall increased hippocampal neurogenesis in adult and aged mice. These findings highlight the importance of metabolism for NSPC regulation and identify an important pathway through which mitochondrial pyruvate import controls NSPC quiescence and activation.

D-2-hydroxyglutarate dehydrogenase governs adult neural stem cell activation and promotes histone acetylation via ATP-citrate lyase

The generation of neurons from quiescent radial-glia-like neural stem cells (RGLs) in adult brain goes hand in hand with the modulation of cellular metabolism. However, it is still unclear how the exact metabolic program governs the balance between quiescent and activated RGLs. Here, we find that loss of mitochondrial D-2-hydroxyglutarate dehydrogenase (D2HGDH) leads to aberrant accumulation of D-2-hydroxyglutarate (D-2-HG) and impaired RGL activation. Mechanistically, accumulated D-2-HG bonds directly to ATP-citrate lyase and competitively inhibits its enzymatic activity, thereby reducing acetyl-CoA production and diminishing histone acetylation. However, administration of acetate restores the acetyl-CoA levels via acetyl-CoA synthetase-mediated catabolism and rescues the deficiencies in histone acetylation and RGL activation caused by loss of D2HGDH. Therefore, our findings define the role of cross talk between mitochondria and the nucleus via a mitochondrial metabolite, D-2-HG, the aberrant accumulation of which hinders the regulation of histone acetylation in RGL activation and attenuates continuous neurogenesis in adult mammalian brain.

Adult hippocampal neurogenesis in Alzheimer's disease: A roadmap to clinical relevance

Adult hippocampal neurogenesis (AHN) drops sharply during early stages of Alzheimer's disease (AD), via unknown mechanisms, and correlates with cognitive status in AD patients. Understanding AHN regulation in AD could provide a framework for innovative pharmacological interventions. We here combine molecular, behavioral, and clinical data and critically discuss the multicellular complexity of the AHN niche in relation to AD pathophysiology. We further present a roadmap toward a better understanding of the role of AHN in AD by probing the promises and caveats of the latest technological advancements in the field and addressing the conceptual and methodological challenges ahead.

Effect of the Enrichment in c-Kit Stem Cell Potential of Foetal Human Amniotic Fluid Cells: Characterization from Single Cell Analysis to the Secretome Content

Human amniotic fluid cells (hAFSCs) are a fascinating foetal cell-type that have important stem cell characteristics; however, they are a heterogeneous population that ranges from totally differentiated or progenitor cells to highly multipotent stem cells. There is no single approach to isolating the stem cell component, but the selection of a subpopulation of hAFSCs expressing c-Kit is widely employed, while a deep characterization of the two populations is still lacking. Here we performed single-cell and bulk RNAseq analysis to compare the gene expression profiles of adherent amniotic fluid cells and their subpopulation c-Kit⁺. Information deriving from this high throughput technology on the transcriptome was then confirmed for specific targets with protein expression experiments and functional analysis. In particular, transcriptome profiling identified changes in cellular distribution among the different clusters that correlated with significant differential expression in pathways related to stemness, proliferation, and cell cycle checkpoints. These differences were validated by RT-PCR, immunofluorescence, WB, and cell cycle assays. Interestingly, the two populations produced secretomes with different immune-modulating and pro-regenerative potentials. Indeed, the presence of TGFβ, HGF, IDO was higher in EVs deriving from c-Kit⁺ cells, unlike IL-6. These results suggest the existence of deep intra-population differences that can influence the stemness profile of hAFSCs. This study represents a proof-of-concept of the importance of selecting c-Kit positive fractions with higher potential in regenerative medicine applications.

Molecular Mechanisms of Neuroinflammation in Aging and Alzheimer's Disease Progression

Aging is the most prominent risk factor for late-onset Alzheimer's disease. Aging associates with a chronic inflammatory state both in the periphery and in the central nervous system, the evidence thereof and the mechanisms leading to chronic neuroinflammation being discussed. Nonetheless, neuroinflammation is significantly enhanced by the accumulation of amyloid beta and accelerates the progression of Alzheimer's disease through various pathways discussed in the present review. Decades of clinical trials targeting the 2 abnormal proteins in Alzheimer's disease, amyloid beta and tau, led to many failures. As such, targeting neuroinflammation via different strategies could prove a valuable therapeutic strategy, although much research is still needed to identify the appropriate time window. Active research focusing on identifying early biomarkers could help translating these novel strategies from bench to bedside.

Mitochondrial genes in the 22q11.2 deleted region regulate neural stem and progenitor cell proliferation

Microdeletion of a 3Mbp region encompassing 45 protein-coding genes at chromosome 22q11.2 (22q11.2DS) predisposes to multiple neurodevelopmental disorders and is one of the greatest genetic risk factors for schizophrenia. Defective mitochondrial function has been hypothesized to contribute to 22q11.2DS pathogenesis; however, which of the six mitochondrial genes contribute to neurodevelopmental phenotypes and their underlying mechanisms remain unresolved. To systematically test 22q11.2DS genes for functional roles in neurodevelopment and behavior, we generated genetic mutants for each of the 37 conserved zebrafish orthologs and performed high throughput behavioral phenotyping using seven behavioral assays. Through this unbiased approach, we identified five single-gene mutants with partially overlapping behavioral phenotypes. Two of these genes, mrpl40 and prodha , encode for mitochondrial proteins and, similar to what we observed in mrpl40 and prodha mutants, pharmacologic inhibition of mitochondrial function during development results in microcephaly. Finally, we show that both mrpl40 and prodha mutants display neural stem and progenitor cell phenotypes, with each gene regulating different neural stem cell populations. Combined, our results demonstrate a critical role for mitochondrial function in neural stem and progenitor cell populations in the developing vertebrate brain and provide compelling evidence that mitochondrial dysfunction during neurodevelopment is linked to brain volume and behavioral phenotypes observed in models of 22q11.2DS.

Dietary Flavonoids and Adult Neurogenesis: Potential Implications for Brain Aging

Adult neurogenesis deficiency has been proposed to be a common hallmark in different age-related neurodegenerative diseases. The administration of flavonoids is currently reported as a potentially beneficial strategy for preventing brain aging alterations, including adult neurogenesis decline. Flavonoids are a class of plant-derived dietary polyphenols that have drawn attention for their neuroprotective and pro-cognitive effects. Although they undergo extensive metabolism and localize in the brain at low concentrations, flavonoids are now believed to improve cerebral vasculature and interact with signal transduction cascades involved in the regulation of adult neurogenesis. Furthermore, many dietary flavonoids have been shown to reduce oxidative stress and neuroinflammation, improving the neuronal microenvironment where adult neurogenesis occurs. The overall goal of this review is to summarize the evidence supporting the role of flavonoids in modulating adult neurogenesis as well as to highlight how these dietary agents may be promising candidates in restoring healthy brain function during physiological and pathological aging.

Ageing and rejuvenation of tissue stem cells and their niches

Most adult organs contain regenerative stem cells, often organized in specific niches. Stem cell function is critical for tissue homeostasis and repair upon injury, and it is dependent on interactions with the niche. During ageing, stem cells decline in their regenerative potential and ability to give rise to differentiated cells in the tissue, which is associated with a deterioration of tissue integrity and health. Ageing-associated changes in regenerative tissue regions include defects in maintenance of stem cell quiescence, differentiation ability and bias, clonal expansion and infiltration of immune cells in the niche. In this Review, we discuss cellular and molecular mechanisms underlying ageing in the regenerative regions of different tissues as well as potential rejuvenation strategies. We focus primarily on brain, muscle and blood tissues, but also provide examples from other tissues, such as skin and intestine. We describe the complex interactions between different cell types, non-cell-autonomous mechanisms between ageing niches and stem cells, and the influence of systemic factors. We also compare different interventions for the rejuvenation of old regenerative regions. Future outlooks in the field of stem cell ageing are discussed, including strategies to counter ageing and age-dependent disease.

Ganglioside Microdomains on Cellular and Intracellular Membranes Regulate Neuronal Cell Fate Determination

Gangliosides are sialylated glycosphingolipids (GSLs) with essential but enigmatic functions in brain activities and neural stem cell (NSC) maintenance. Our group has pioneered research on the importance of gangliosides for growth factor receptor signaling and epigenetic regulation of NSC activity and differentiation. The primary localization of gangliosides is on cell-surface microdomains and the drastic dose and composition changes during neural differentiation strongly suggest that they are not only important as biomarkers, but also are involved in modulating NSC fate determination. Ganglioside GD3 is the predominant species in NSCs and GD3-synthase knockout (GD3S-KO) revealed reduction of postnatal NSC pools with severe behavioral deficits. Exogenous administration of GD3 significantly restored the NSC pools and enhanced the stemness of NSCs with multipotency and self-renewal. Since morphological changes during neurogenesis require a huge amount of energy, mitochondrial functions are vital for neurogenesis. We discovered that a mitochondrial fission protein, the dynamin-related protein-1 (Drp1), as a novel GD3-binding protein, and GD3 regulates mitochondrial dynamics. Furthermore, we discovered that GM1 ganglioside promotes neuronal differentiation by an epigenetic regulatory mechanism. Nuclear GM1 binds with acetylated histones on the promoters of N-acetylgalactosaminyltransferase (GalNAcT; GM2 synthase) as well as on the NeuroD1 genes in differentiated neurons. In addition, epigenetic activation of the GalNAcT gene was detected as accompanied by an apparent induction of neuronal differentiation in NSCs responding to an exogenous supplement of GM1. GM1 is indeed localized in the nucleus where it can interact with transcriptionally active histones. Interestingly, GM1 could induce epigenetic activation of the tyrosine hydroxylase (TH) gene, with recruitment of nuclear receptor related 1 (Nurr1, also known as NR4A2), a dopaminergic neuron-associated transcription factor, to the TH promoter region. In this way, GM1 epigenetically regulates dopaminergic neuron specific gene expression. GM1 interacts with active chromatin via acetylated histones to recruit transcription factors at the nuclear periphery, resulting in changes in gene expression for neuronal differentiation. The significance is that multifunctional gangliosides modulate lipid microdomains to regulate functions of important molecules on multiple sites: the plasma membrane, mitochondrial membrane, and nuclear membrane. Versatile gangliosides could regulate functional neurons as well as sustain NSC functions via modulating protein and gene activities on ganglioside microdomains.

Mitochondrial respiration and dynamics of in vivo neural stem cells

Neural stem cells (NSCs) in the developing and adult brain undergo many different transitions, tightly regulated by extrinsic and intrinsic factors. While the role of signalling pathways and transcription factors is well established, recent evidence has also highlighted mitochondria as central players in NSC behaviour and fate decisions. Many aspects of cellular metabolism and mitochondrial biology change during NSC transitions, interact with signalling pathways and affect the activity of chromatin-modifying enzymes. In this Spotlight, we explore recent in vivo findings, primarily from Drosophila and mammalian model systems, about the role that mitochondrial respiration and morphology play in NSC development and function.

BCL7A-containing SWI/SNF/BAF complexes modulate mitochondrial bioenergetics during neural progenitor differentiation

Mammalian SWI/SNF/BAF chromatin remodeling complexes influence cell lineage determination. While the contribution of these complexes to neural progenitor cell (NPC) proliferation and differentiation has been reported, little is known about the transcriptional profiles that determine neurogenesis or gliogenesis. Here, we report that BCL7A is a modulator of the SWI/SNF/BAF complex that stimulates the genome-wide occupancy of the ATPase subunit BRG1. We demonstrate that BCL7A is dispensable for SWI/SNF/BAF complex integrity, whereas it is essential to regulate Notch/Wnt pathway signaling and mitochondrial bioenergetics in differentiating NPCs. Pharmacological stimulation of Wnt signaling restores mitochondrial respiration and attenuates the defective neurogenic patterns observed in NPCs lacking BCL7A. Consistently, treatment with an enhancer of mitochondrial biogenesis, pioglitazone, partially restores mitochondrial respiration and stimulates neuronal differentiation of BCL7A-deficient NPCs. Using conditional BCL7A knockout mice, we reveal that BCL7A expression in NPCs and postmitotic neurons is required for neuronal plasticity and supports behavioral and cognitive performance. Together, our findings define the specific contribution of BCL7A-containing SWI/SNF/BAF complexes to mitochondria-driven NPC commitment, thereby providing a better understanding of the cell-intrinsic transcriptional processes that connect metabolism, neuronal morphogenesis, and cognitive flexibility.

Metabolic regulation of the neural stem cell fate: Unraveling new connections, establishing new concepts

The neural stem cell niche is a key regulator participating in the maintenance, regeneration, and repair of the brain. Within the niche neural stem cells (NSC) generate new neurons throughout life, which is important for tissue homeostasis and brain function. NSCs are regulated by intrinsic and extrinsic factors with cellular metabolism being lately recognized as one of the most important ones, with evidence suggesting that it may serve as a common signal integrator to ensure mammalian brain homeostasis. The aim of this review is to summarize recent insights into how metabolism affects NSC fate decisions in adult neural stem cell niches, with occasional referencing of embryonic neural stem cells when it is deemed necessary. Specifically, we will highlight the implication of mitochondria as crucial regulators of NSC fate decisions and the relationship between metabolism and ependymal cells. The link between primary cilia dysfunction in the region of hypothalamus and metabolic diseases will be examined as well. Lastly, the involvement of metabolic pathways in ependymal cell ciliogenesis and physiology regulation will be discussed.

Inhibition of High-Temperature Requirement Protein A2 Protease Activity Represses Myogenic Differentiation via UPRmt

Skeletal muscles require muscle satellite cell (MuSC) differentiation to facilitate the replenishment and repair of muscle fibers. A key step in this process is called myogenic differentiation. The differentiation ability of MuSCs decreases with age and can result in sarcopenia. Although mitochondria have been reported to be involved in myogenic differentiation by promoting a bioenergetic remodeling, little is known about the interplay of mitochondrial proteostasis and myogenic differentiation. High-temperature-requirement protein A2 (HtrA2/Omi) is a protease that regulates proteostasis in the mitochondrial intermembrane space (IMS). Mice deficient in HtrA2 protease activity show a distinct phenotype of sarcopenia. To investigate the role of IMS proteostasis during myogenic differentiation, we treated C2C12 myoblasts with UCF101, a specific inhibitor of HtrA2 during differentiation process. A key step in this process is called myogenic differentiation. The differentiation ability of MuSCs decreases with age and can result in sarcopenia. Further, CHOP, p-eIF2α, and other mitochondrial unfolded protein response (UPRmt)-related proteins are upregulated. Therefore, we suggest that imbalance of mitochondrial IMS proteostasis acts via a retrograde signaling pathway to inhibit myogenic differentiation via the UPRmt pathway. These novel mechanistic insights may have implications for the development of new strategies for the treatment of sarcopenia.

Defective mitochondria-lysosomal axis enhances the release of extracellular vesicles containing mitochondrial DNA and proteins in Huntington's disease

Mitochondrial and autophagy dysfunction are mechanisms proposed to be involved in the pathogenesis of several neurodegenerative diseases. Huntington's disease (HD) is a progressive neurodegenerative disorder associated with mutant Huntingtin-induced abnormalities in neuronal mitochondrial dynamics and quality control. Former studies suggest that the removal of defective mitochondria may be compromised in HD. Mitochondrial quality control (MQC) is a complex, well-orchestrated pathway that can be compromised through mitophagy dysregulation or impairment in the mitochondria-lysosomal axis. Another mitochondrial stress response is the generation of mitochondrial-derived vesicles that fuse with the endolysosomal system and form multivesicular bodies that are extruded from cells as extracellular vesicles (EVs). In this work, we aimed to study the presence of mitochondrial components in human EVs and the relation to the dysfunction of both mitochondria and the autophagy pathway. We comprehensively characterized the mitochondrial and autophagy alterations in premanifest and manifest HD carriers and performed a proteomic and genomic EVs profile. We observed that manifest HD patients exhibit mitochondrial and autophagy impairment associated with enhanced EVs release. Furthermore, we detected mitochondrial DNA and proteins in EVs released by HD cells and in neuronal-derived EVs including VDAC-1 and alpha and beta subunits of ATP synthase F1. HD-extracellular vesicles transport higher levels of mitochondrial genetic material in manifest HD patients, suggesting an alternative pathway for the secretion of reactive mitochondrial components. This study provides a novel framework connecting EVs enhanced release of mitochondrial components to mitochondrial and lysosomal dysfunction in HD.

Physical exercise and mitochondrial function: New therapeutic interventions for psychiatric and neurodegenerative disorders

Psychiatric and neurodegenerative diseases, including major depression disorder (MDD), bipolar disorder, and Alzheimer's disease, are a burden to society. Deficits of adult hippocampal neurogenesis (AHN) have been widely considered the main hallmark of psychiatric diseases as well as neurodegeneration. Herein, exploring applicable targets for improving hippocampal neural plasticity could provide a breakthrough for the development of new treatments. Emerging evidence indicates the broad functions of mitochondria in regulating cellular behaviors of neural stem cells, neural progenitors, and mature neurons in adulthood could offer multiple neural plasticities for behavioral modulation. Normalizing mitochondrial functions could be a new direction for neural plasticity enhancement. Exercise, a highly encouraged integrative method for preventing disease, has been indicated to be an effective pathway to improving both mitochondrial functions and AHN. Herein, the relative mechanisms of mitochondria in regulating neurogenesis and its effects in linking the effects of exercise to neurological diseases requires a systematic summary. In this review, we have assessed the relationship between mitochondrial functions and AHN to see whether mitochondria can be potential targets for treating neurological diseases. Moreover, as for one of well-established alternative therapeutic approaches, we summarized the evidence to show the underlying mechanisms of exercise to improve mitochondrial functions and AHN.