Increased post-mitotic senescence in aged human neurons is a pathological feature of Alzheimer's disease

Identifying Age-Modulating Compounds Using a Novel Computational Framework for Evaluating Transcriptional Age

The differentiation of human pluripotent stem cells (hPSCs) provides access to a wide range of cell types and tissues. However, hPSC-derived lineages typically represent a fetal stage of development, and methods to expedite the transition to an aged identity to improve modeling of late-onset disease are limited. In this study, we introduce RNAge, a transcriptome-based computational platform designed to enable the evaluation of an induced aging or a rejuvenated state. We validated this approach across independent datasets spanning different tissues and species, and show that it can be used to evaluate the effectiveness of existing age-retaining or age-modulating interventions. We also used RNAge to perform an in silico compound screen using the LINCS L1000 dataset. This approach led to the identification and experimental confirmation of several novel compounds capable of inducing aging or rejuvenation in primary fibroblasts or hPSC-derived neurons. Additionally, we observed that applying this novel induced aging strategy to an hPSC model of Alzheimer's disease (AD) accelerated neurodegeneration in a genotype-specific manner. Our study offers a robust method for quantifying age-related manipulations and unveils compounds that significantly broaden the toolkit for age-modifying strategies in hPSC-derived lineages.

Research models to study lewy body dementia

Lewy body dementia (LBD) encompasses neurodegenerative dementias characterized by cognitive fluctuations, visual hallucinations, and parkinsonism. Clinical differentiation of LBD from Alzheimer's disease (AD) remains complex due to symptom overlap, yet approximately 25% of dementia cases are diagnosed as LBD postmortem, primarily identified by the presence of α-synuclein aggregates, tau tangles, and amyloid plaques. These pathological features position LBD as a comorbid condition of both Parkinson's disease (PD) and AD, with over 50% of LBD cases exhibiting co-pathologies. LBD's mixed pathology complicates the development of comprehensive models that reflect the full spectrum of LBD's etiological, clinical, and pathological features. While existing animal and cellular models have facilitated significant discoveries in PD and AD research, they lack specificity in capturing LBD's unique pathogenic mechanisms, limiting the exploration of therapeutic avenues for LBD specifically. This review assesses widely used PD and AD models in terms of their relevance to LBD, particularly focusing on their ability to replicate human disease pathology and assess treatment efficacy. Furthermore, we discuss potential modifications to these models to advance the understanding of LBD mechanisms and propose innovative research directions aimed at developing models with enhanced etiological, face, predictive, and construct validity.

Compact transcription factor cassettes generate functional, engraftable motor neurons by direct conversion

Direct conversion generates patient-specific, disease-relevant cell types, such as neurons, that are rare, limited, or difficult to isolate from common and easily accessible cells, such as skin cells. However, low rates of direct conversion and complex protocols limit scalability and, thus, the potential of cell-fate conversion for biomedical applications. Here, we optimize the conversion protocol by examining process parameters, including transcript design; delivery via adeno-associated virus (AAV), retrovirus, and lentivirus; cell seeding density; and the impact of media conditions. Thus, we report a compact, portable conversion process that boosts proliferation and increases direct conversion of mouse fibroblasts to induced motor neurons (iMNs) to achieve high conversion rates of above 1,000%, corresponding to more than ten motor neurons yielded per cell seeded, which we achieve through expansion. Our optimized, direct conversion process generates functional motor neurons at scales relevant for cell therapies (>107 cells) that graft with the mouse central nervous system. High-efficiency, compact, direct conversion systems will support scaling to patient-specific, neural cell therapies.

Identification of markers for neurescence through transcriptomic profiling of postmortem human brains

Neuronal senescence (i.e., neurescent) is an important hallmark of aging and neurodegeneration, but it remains poorly characterized in the human brain due to the lack of reliable markers. This study aimed to identify neurescent markers based on single-nucleus transcriptome data from postmortem human prefrontal cortex. Using an eigengene approach, we integrated three gene panels: a) SenMayo, b) Canonical Senescence Pathway (CSP), and c) Senescence Initiating Pathway (SIP), to identify neurescent signatures. We found that paired markers outperform single markers; for instance, by combining CDKN2D and ETS2 in a decision tree, a high accuracy of 99% and perfect specificity (100%) were achieved in distinguishing neurescent. Differential expression analyses identified 324 genes that are overexpressed in neurescent. These genes showed significant associations with important neurodegeneration-related pathways including Alzheimer's disease, Parkinson's disease, and Huntington's disease. Interestingly, several of these overexpressed genes are linked to mitochondrial dysfunction and cytoskeletal dysregulation. These findings provide valuable insights into the complexities of neurescent, emphasizing the need for further exploration of histologically viable markers and validation in broader datasets.

Mitochondrial dynamics and bioenergetics in Alzheimer's induced pluripotent stem cell-derived neurons

Mitochondrial dysfunction is a hallmark of Alzheimer's disease, but the scope and severity of these specific deficits across forms of Alzheimer's disease are not well characterized. We designed a high-throughput longitudinal phenotypic assay to track mitochondrial dynamics and bioenergetics in glutamatergic induced pluripotent stem cell (iPSC)-derived human neurons possessing mutations in presenilin 1 (PSEN1), presenilin 2 (PSEN2) and the amyloid beta precursor protein (APP). Each gene set was composed of iPSC-derived neurons from an Alzheimer's disease patient in addition to two to three engineered mutations with appropriate isogenic and age-matched controls. These iPSC-derived neurons were imaged every other day, beginning at 10 days in vitro, to assess how mitochondrial length and content change over a 10 day time course using a mitochondrially targeted reporter. A second cytosolic reporter allowed for visualization of neurites. Bioenergetics assays, focusing on mitochondrial respiration and individual electron transport chain complexes, were also surveyed over this time course. Mutations in all three genes altered mitochondrial function measured by basal, ATP-linked and maximal oxygen consumption rates and by spare respiratory capacity, with PSEN1/PSEN2 alleles being more severe than APP mutations. Electron flow through Complexes I-IV was decreased in PSEN1/PSEN2 mutations but, in contrast, APP alleles had only modest impairments of complexes I and II. We measured aspects of mitochondrial dynamics, including fragmentation and neurite degeneration, both of which were dramatic in PSEN1/PSEN2 alleles, but essentially absent in APP alleles. The marked differences in mitochondrial pathology might occur from the distinct ways in which amyloids are processed into amyloid beta peptides and might be correlated with the disease severity.

Senescent brain cell types in Alzheimer's disease: Pathological mechanisms and therapeutic opportunities

Cellular senescence is a cell state triggered by programmed physiological processes or cellular stress responses. Stress-induced senescent cells often acquire pathogenic traits, including a toxic secretome and resistance to apoptosis. When pathogenic senescent cells form faster than they are cleared by the immune system, they accumulate in tissues throughout the body and contribute to age-related diseases, including neurodegeneration. This review highlights evidence of pathogenic senescent cells in the brain and their role in Alzheimer's disease (AD), the leading cause of dementia in older adults. We also discuss the progress and challenges of senotherapies, pharmacological strategies to clear senescent cells or mitigate their toxic effects, which hold promise as interventions for AD and related dementias (ADRD).

Proteostasis and lysosomal repair deficits in transdifferentiated neurons of Alzheimer's disease

Ageing is the most prominent risk factor for Alzheimer's disease (AD). However, the cellular mechanisms linking neuronal proteostasis decline to the characteristic aberrant protein deposits in the brains of patients with AD remain elusive. Here we develop transdifferentiated neurons (tNeurons) from human dermal fibroblasts as a neuronal model that retains ageing hallmarks and exhibits AD-linked vulnerabilities. Remarkably, AD tNeurons accumulate proteotoxic deposits, including phospho-tau and amyloid β, resembling those in APP mouse brains and the brains of patients with AD. Quantitative tNeuron proteomics identify ageing- and AD-linked deficits in proteostasis and organelle homeostasis, most notably in endosome-lysosomal components. Lysosomal deficits in aged tNeurons, including constitutive lysosomal damage and ESCRT-mediated lysosomal repair defects, are exacerbated in AD tNeurons and linked to inflammatory cytokine secretion and cell death. Providing support for the centrality of lysosomal deficits in AD, compounds ameliorating lysosomal function reduce amyloid β deposits and cytokine secretion. Thus, the tNeuron model system reveals impaired lysosomal homeostasis as an early event of ageing and AD.

Monitoring Autophagy in Human Aging: Key Cell Models and Insights

Autophagy, a key cellular degradation and recycling pathway, is critical for maintaining cellular homeostasis and responding to metabolic and environmental stress. Evidence for age-related autophagic dysfunction and its implications in chronic age-related diseases including neurodegeneration is accumulating. However, as a complex, multi-step process, autophagy can be challenging to measure, particularly in humans and human aging- and disease-relevant models. This review describes the links between macroautophagy, aging, and chronic age-related diseases. We present three novel human cell models, peripheral blood mononuclear cells (PBMCs), primary dermal fibroblasts (PDFs), and induced neurons (iNs), which serve as essential tools for studying autophagy flux and assessing its potential as a biomarker for aging. Unlike traditional models, these cell models retain age- and disease-associated molecular signatures, enhancing their relevance for human studies. The development of robust tools and methodologies for measuring autophagy flux in human cell models holds promise for advancing our understanding of autophagy's role in aging and age-related diseases, ultimately facilitating the discovery of therapies to enhance health outcomes.

Cellular Senescence Is a Central Driver of Cognitive Disparities in Aging

Cognitive function in aging is heterogeneous: while some older individuals develop significant impairments and dementia, others remain resilient and retain cognitive function throughout their lifespan. The molecular mechanisms that underlie these divergent cognitive trajectories, however, remain largely unresolved. Here, we utilized a high-resolution home-cage-based cognitive testing paradigm to delineate mechanisms that contribute to age-related cognitive heterogeneity. We cognitively stratified aged C57Bl/6N male mice by cognitive performance into intact (resilient) or impaired subgroups based on young performance benchmarks. Cognitively impaired males exhibited marked reactive gliosis in the hippocampus, characterized by microglial activation, increased astrocyte arborization, and elevated transcriptional expression of reactivity markers. These changes were accompanied by increased markers of cellular senescence and the associated senescence-associated secretory phenotype (SASP) in impaired animals, including p16INK4a, SASP factors (e.g., Il-6, Il-1b, Mmp3), and SA-β-gal staining in the hippocampus. Notably, clearance of senescent cells using senolytic agents dasatinib and quercetin ameliorated the heterogeneity in cognitive performance observed with age and attenuated impairment-associated gliosis, senescence markers, and mitochondrial dysfunction. Aged female mice could not be stratified into subgroups yet showed increased neuroinflammation with age that was not resolved with senolytics. Collectively, our findings implicate cellular senescence as a central driver of sex-specific neuroinflammation that drives divergent cognitive trajectories in aging. Thus, we demonstrate that senolytic treatment is an effective therapeutic strategy to mitigate cognitive impairment by reducing neuroinflammation and associated metabolic disturbances.

Escherichia Coli K1-colibactin meningitis induces microglial NLRP3/IL-18 exacerbating H3K4me3-synucleinopathy in human inflammatory gut-brain axis

Escherichia coli K1 (E. coli K1) meningitis early occurs in the gastrointestinal and causes severe damage to the central nervous system, including lifelong neurological complications in survivors. However, the cellular mechanism by which E. coli K1 may cause neuropathies is not well understood due to the lack of relevant human multi-organ models for studying multifaceted systemic inflammation across the gut-brain axis. Here, we reconstruct a multicellular model of the human gut-brain axis to identify the neuropathogenic mechanism driven by E. coli K1-colibactin meningitis. We observed that E. coli K1-genotoxic colibactin induced intestinal and peripheral interleukin 6, causing the blood-brain barrier injury and endothelial inflammation via the p38/p65 pathways. Serpin-E1 from the damaged cerebral endothelia induces reactive astrocytes to release IFN-γ, which reduces microglial phagocytosis of E. coli K1 and exacerbates detrimental neuroinflammation via NLRP3/IL-18 axis. Microglial IL-18 elevates neuronal reactive oxidative stress that worsens DNA double-strand breaks in E. coli K1-infected neurons, leading to H3K4 trimethylation and phosphorylation of alpha-synuclein. Our findings suggest therapeutic strategies for post-bacterial meningitis treatment to potentially prevent the initiation of synucleinopathy.

Arsenic exposure induces neural cells senescence and abnormal lipid droplet accumulation leading to social memory impairment in mice

The long-term harmful effects of arsenic exposure remain one of the important public health issues. The effects of arsenic exposure on the central nervous system, particularly concerning brain structure and function, have been garnering increasing attention. Hence, the aim of this study was to investigate the impact of chronic low-dose arsenic exposure on murine social memory and to elucidate the underlying molecular mechanisms. Male C57BL/6 mice at six months of age were randomly assigned to a control group and three treatment groups with different arsenic concentrations (50, 100, and 200 μg/L), with exposure durations of 30, 90, 180, and 360 days. The five-social memory test and three-chamber social memory test results indicated that chronic low-dose arsenic exposure disrupted social memory in mice. Further analysis revealed that arsenic exposure led to degeneration of neurons within the dorsal CA2 of the hippocampus (dCA2) and the lateral entorhinal cortex (LEC), which are pivotal for the modulation of social memory, and dCA2 neurons demonstrated structural disruptions and cytoplasmic fragmentation. In addition, arsenic exposure induced neurons and glial cells senescence in both dCA2 and LEC, with a particularly pronounced effect in microglia, and worse with dosage increasing of arsenic exposure, correlating with elevated expression levels of p16INK4A, ferritin light chain and the senescence-associated secretory factors TNF-α and IL-1β, and reduced expression of Lamin B1. Moreover, arsenic exposure triggered substantial cytoplasmic lipid droplets accumulation in neurons, astrocytes and microglia, with an upregulation of PLIN2 expression, a protein associated with lipid droplet formation in astrocytes. At the same time, the aberrant accumulation of lipid droplets further aggravated the astrocytes and microglia aging, especially microglia. Additionally, correlation analysis revealed that social memory impairment was negatively correlated with nerve cell senescence and lipid accumulation. Our findings suggest that arsenic exposure induced cellular functional abnormalities by triggering cellular senescence and the accumulation of lipid droplets, thereby exacerbated neuronal degeneration and result in impaired social memory in mice.

DNLA Delayed the Appearance of Learning and Memory Impairment of APP/PS1 Mice: Involvement of mTOR/TFEB/v-ATPase Signaling Pathway

INTRODUCTION

Alzheimer's disease (AD) is a progressive neurodegenerative disorder with cognitive impairment that currently is incurable. There is existing evidence to suggest that vacuolar adenosine triphosphatase (v-ATPase) is one of the early key driving factors in the pathological process of AD. Thus, early intervention of v-ATPase may be a viable strategy.

AIMS

Observing whether early intervention with DNLA can delay learning and memory impairment in mice, and further exploring the mechanism of DNLA delaying AD in vitro based on v-ATPase.

METHODS

Four-month-old APP/PS1 transgenic mice were treated with alkaloids from Dendrobium nobile Lindl (DNLA) 20 and 40 mg/kg/day for 5 months. The Morris water maze test and nest test showed that DNLA administration significantly delayed the appearance of cognitive deficits in APP/PS1 mice. We further investigated the mechanism of DNLA promoting lysosome acidification in vitro by using PC12 cells.

RESULTS

We found that DNLA increases the degradation of β-amyloid (Aβ) contained in the autophagic lysosomes and alleviates the aging of neurons by promoting lysosome acidification and improving autophagy flow. In PC12 cells, DDB could promote the separation of mTOR and lysosome, promote the nuclear translocation of transcription factor EB (TFEB), and then promote lysosome biogenesis and lysosome acidification by targeting ATP6V1A.

CONCLUSION

These results unraveled that preventive administration of DNLA may delay the impairment of learning and memory in APP/PS1 mice. The molecular mechanism may be related to promoting the mTOR-TFEB-v-ATPase pathway.

Cellular rejuvenation protects neurons from inflammation-mediated cell death

In multiple sclerosis (MS), inflammation of the central nervous system results in demyelination, neuroaxonal injury, and cell death. However, the molecular signals responsible for injury and cell death in neurons are not fully characterized. Here, we profile the transcriptome of retinal ganglion cells (RGCs) in experimental autoimmune encephalomyelitis (EAE) mice. Pathway analysis identifies a transcriptional signature reminiscent of aged RGCs with some senescent features, with a comparable signature present in neurons from patients with MS. This is supported by immunostaining demonstrating alterations to the nuclear envelope, modifications in chromatin marks, and accumulation of DNA damage. Transduction of RGCs with an Oct4-Sox2-Klf4 adeno-associated virus (AAV) to rejuvenate the transcriptome enhances RGC survival in EAE and improves visual acuity. Collectively, these data reveal an aging-like phenotype in neurons under pathological neuroinflammation and support the possibility that rejuvenation therapies or senotherapeutic agents could offer a direct avenue for neuroprotection in neuroimmune disorders.

The senolytic ABT-263 improves cognitive functions in middle-aged male, but not female, atherosclerotic LDLr-/-;hApoB100+/+ mice

Accumulation of cerebral senescent cells may compromise the continuum between vascular and neuronal function, leading to damage and cognitive decline. Elimination of senescent cells might therefore preserve vascular and neuronal functions. To test this hypothesis, we used male and female atherosclerotic LDLr-/-;hApoB100+/+ mice (ATX-mice), a model of vascular cognitive impairment (VCI), treated with the senolytic ABT-263 for 3 months (3- to 6-month or 9- to 12-month old). In young male ATX mice, prevention with ABT-263 improved spatial retention memory, in association with a higher endothelial sensitivity to shear stress and a higher hippocampal CD31+ endothelial cell density, lower activation of both astrocytes and glial cells. In young females, ABT-263 tended to improve delayed memory; however, atherosclerotic plaque was magnified by ABT-263, endothelial function was unaffected, hippocampal astrocyte activation increased and expression of CD31+ cells decreased. Hence, unlike in males, ABT-263 appears deleterious in young ATX females. In middle-aged males, the curative treatment improved the learning process and memory. Although no change in endothelial function was observed, the benefits of ABT-263 were associated with a decreased expression of several inflammaging markers, a higher density of CD31+ cells and a lower activation of glial cells. In middle-aged females, ABT-263 induced a surge of inflammaging markers, associated with a slower learning process. Altogether, our data demonstrate that ABT-263 differentially affects VCI, improving cognition in male while being deleterious in female ATX mice. More studies are needed to understand the mechanisms at the basis of the sexual dimorphic effects of the senolytic ABT-263.

Integrated multi-omics analysis revealed the molecular networks and potential targets of cellular senescence in Alzheimer's disease

Cellular senescence (CS) is a hallmark of Alzheimer's disease (AD). However, the mechanisms through which CS contributes to AD pathogenesis remain poorly understood. We found that CS level in AD was higher compared with the healthy control group. Transcriptome-based differential expression analysis identified 113 CS-related genes in blood and 410 in brain tissue as potential candidate genes involved in AD. To further explore the causal role of these genes, an integrative mendelian randomization analysis was conducted, combining AD genome-wide association study summary statistics with expression quantitative trait loci (eQTL) and DNA methylation quantitative trait loci (mQTL) data from blood samples, which identified five putative AD-causal genes (CENPW, EXOSC9, HSPB11, SLC44A2, and SLFN12) and 18 corresponding DNA methylation probes. Additionally, integrative analysis between eQTLs and mQTLs from blood uncovered two genes and 12 corresponding regulatory elements involved in AD. Furthermore, two genes (CDKN2B and ITGAV) were prioritized as putative causal genes in brain tissue and were validated through in vitro experiments. The multi-omics integration study revealed the potential role and underlying biological mechanisms of CS driven by genetic predisposition in AD. This study contributed to fundamental understanding of CS in AD pathogenesis and facilitated the identification of potential therapeutic targets for AD prevention and treatment.

3-N-Butylphthalide alleviate Aβ-induced cellular senescence through the CDK2-pRB1-Caspase3 axis

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the accumulation of amyloid-beta (Aβ) and leading to cellular senescence and cognitive deficits. Cellular senescence contributes significantly to the pathogenesis of AD through the senescence-associated secretory phenotype (SASP), exacerbating Aβ deposition. This study investigates the protective effects of 3-N-Butylphthalide (NBP), a compound derived from Apium graveolens Linn (Chinese celery), on Aβ-induced cellular senescence in U87 cells. Using RNA-sequencing and biochemical assays, we demonstrate that NBP ameliorate Aβ oligomer-induced cellular senescence and apoptosis, and regulated the expression of cyclin-dependent kinase inhibitor 2A (CDKN2A) and components of the cyclin-dependent kinase 2 (CDK2)- phosphorylated retinoblastoma 1 (pRB1)-Caspase3 pathway. Moreover, NBP was shown to suppress the expression of SASP-related genes. These findings suggest that NBP rescues U87 cells from Aβ oligomer-induced senescence and apoptosis through modulating the CDK2-pRB1-Caspase3 axis and SASP expression. Our results underscore the potential of NBP as a senostatic agent for AD which have not been reported in previous studies, offering insights into its mechanisms of action and paving the way for future studies on its efficacy in vivo and in clinical settings. Thus, we contribute to growing evidence supporting the use of senolytic and senostatic agents in the treatment of AD.

Context-specific interaction of the lipid regulator DIP-2 with phospholipid synthesis in axon regeneration and maintenance

Neurons maintain their morphology over prolonged periods of adult life with limited regeneration after injury. C. elegans DIP-2 is a conserved regulator of lipid metabolism that affects axon maintenance and regeneration after injury. Here, we investigated genetic interactions of dip-2 with mutants in genes involved in lipid biosynthesis and identified roles of phospholipids in axon regrowth and maintenance. CEPT-2 and EPT-1 are enzymes catalyzing the final steps in the de novo phospholipid synthesis (Kennedy) pathway. Loss of function mutants of cept-2 or ept-1 show reduced axon regrowth and failure to maintain axon morphology. We demonstrate that CEPT-2 is cell-autonomously required to prevent age-related axonal defects. Interestingly, loss of function in dip-2 led to suppression of the axon regrowth phenotype observed in either cept-2 or ept-2 mutants, suggesting that DIP-2 acts to counterbalance phospholipid synthesis. Our findings reveal the genetic regulation of lipid metabolism to be critical for axon maintenance under injury and during aging.

Article Summary

Little is known about how adult neurons live long with limited regenerative capacity. This study investigates the role of lipid metabolism in sustaining neuronal health in C. elegans. Mutating phospholipid synthetic genes impairs axon regrowth after injury. Lack of DIP-2, a lipid regulator, restores regrowth, suggesting DIP-2 counterbalances phospholipid synthesis. Moreover, neuronal phospholipid synthesis is essential for preventing age-dependent axonal defects. These findings reveal phospholipid biosynthesis is key to axon integrity during aging and injury. As lipid metabolism is implicated in neurological disorders, this study serves as an entry point into investigating neuronal lipid biology under various conditions.

Cellular senescence induced by cholesterol accumulation is mediated by lysosomal ABCA1 in APOE4 and AD

BACKGROUND

Cellular senescence, a hallmark of aging, has been implicated in Alzheimer's disease (AD) pathogenesis. Cholesterol accumulation is known to drive cellular senescence; however, its underlying mechanisms are not fully understood. ATP-binding cassette transporter A1 (ABCA1) plays an important role in cholesterol homeostasis, and its expression and trafficking are altered in APOE4 and AD models. However, the role of ABCA1 trafficking in cellular senescence associated with APOE4 and AD remains unclear.

METHODS

We examined the association between cellular senescence and ABCA1 expression in human postmortem brain samples using transcriptomic, histological, and biochemical analyses. Unbiased proteomic screening was performed to identify the proteins that mediate cellular ABCA1 trafficking. We created ABCA1 knock out cell lines and mouse models to validate the role of ABCA1 in cholesterol-induced mTORC1 activation and senescence. Additionally, we used APOE4-TR mice and induced pluripotent stem cell (iPSC) models to explore cholesterol-ABCA1-senescence pathways.

RESULTS

Transcriptomic profiling of the human dorsolateral prefrontal cortex from the Religious Order Study/Memory Aging Project (ROSMAP) cohort revealed the upregulation of cellular senescence transcriptome signatures in AD, which correlated with ABCA1 expression and oxysterol levels. Immunofluorescence and immunoblotting analyses confirmed increased lipofuscin-stained lipids and ABCA1 expression in AD brains and an association with mTOR phosphorylation. Discovery proteomics identified caveolin-1, a sensor of cellular cholesterol accumulation, as a key promoter of ABCA1 endolysosomal trafficking. Greater caveolin-1 expression was observed in APOE4-TR mouse models and AD human brains. Oxysterol induced mTORC1 activation and senescence were regulated by ABCA1 lysosomal trapping. Treatment of APOE4-TR mice with cyclodextrin reduced brain oxysterol levels, ABCA1 lysosome trapping, mTORC1 activation, and attenuated senescence and neuroinflammation markers. In human iPSC-derived astrocytes, the reduction of cholesterol by cyclodextrin attenuated inflammatory responses.

CONCLUSIONS

Oxysterol accumulation in APOE4 and AD induced ABCA1 and caveolin-1 expression, contributing to lysosomal dysfunction and increased cellular senescence markers. This study provides novel insights into how cholesterol metabolism accelerates features of brain cellular senescence pathway and identifies therapeutic targets to mitigate these processes.

Exploring the heterogeneous targets of metabolic aging at single-cell resolution

Our limited understanding of metabolic aging poses major challenges to comprehending the diverse cellular alterations that contribute to age-related decline, and to devising targeted interventions. This review provides insights into the heterogeneous nature of cellular metabolism during aging and its response to interventions, with a specific focus on cellular heterogeneity and its implications. By synthesizing recent findings using single-cell approaches, we explored the vulnerabilities of distinct cell types and key metabolic pathways. Delving into the cell type-specific alterations underlying the efficacy of systemic interventions, we also discuss the complexity of integrating single-cell data and advocate for leveraging computational tools and artificial intelligence to harness the full potential of these data, develop effective strategies against metabolic aging, and promote healthy aging.

Targeted ErbB4 receptor activation prevents D-galactose-induced neuronal senescence via inhibiting ferroptosis pathway

Background

Neuronal senescence is a common pathological feature of various neurodegenerative diseases, with ferroptosis playing a significant role. This study aims to investigate the role of ErbB4 receptor activation in preventing D-Galactose (D-gal)-induced neuronal senescence.

Methods

Mice subjected to D-gal-induced aging were administered a small molecule ErbB4 receptor agonist (E4A), identified via virtual screening, melatonin, or a combination of both. Behavioral assessments were conducted to evaluate therapeutic efficacy in memory and cognitive functions. Immunofluorescence staining, western blot, and biochemical assays were primarily employed to assess changes in both senescence- and ferroptosis-related molecules in mouse hippocampal tissues in response to each treatment. Additionally, mouse hippocampal HT22 neuronal cell cultures were utilized to corroborate the in vivo findings.

Results

The targeted activation of ErbB4 receptor by E4A significantly ameliorated the behavioral deficits induced by D-gal in mice, demonstrating an effect comparable to that of melatonin, a natural inhibitor of in vivo senescence and ferroptosis. Both E4A and melatonin mitigated D-gal-induced aging in hippocampal neurons of mice. This was evidenced by the upregulation of Lamin B1 and the downregulation of P53, P21, P16, GFAP, and Iba-1 expression levels. Moreover, D-gal treatment markedly decreased the protein expression of the ferroptosis inhibitor Nrf2 while augmenting the expression of the ferroptosis promoter TFRC. These alterations were partially reversed by the individual administration of E4A and melatonin. In vitro studies further corroborated that D-gal treatment significantly and concurrently induced the expression of senescence markers and ferroptosis promoters. However, both E4A and melatonin were able to significantly reverse these changes. Additionally, E4A markedly ameliorated Erastin-induced ferroptosis in mouse hippocampal neuronal cells.

Conlusion

Our findings suggest that targeted activation of ErbB4 receptor may be a viable strategy for treating neuronal senescence by inhibiting ferroptosis, thereby offering a potential therapeutic avenue for senescence-associated neurodegenerative diseases.

The Biological Intersection Between Chemotherapy-Related Cognitive Impairment and Alzheimer Disease

Alzheimer disease (AD) is the most common type of dementia and one of the leading causes of death in elderly patients. The number of patients with AD in the United States is projected to double by 2060. Thus, understanding modifiable risk factors for AD is an urgent public health priority. In parallel with the number of patients with AD, the number of cancer survivors is estimated to increase significantly, and up to 80% of cancer patients treated with chemotherapy will develop cognitive deficits, termed chemotherapy-related cognitive impairment. This review discusses biologically plausible pathways underlying both disorders, with the goal of understanding why a proportion of chemotherapy patients may be at higher risk of developing AD. Highlighted are the E4 allele of the apolipoprotein E gene, neuroinflammation, oxidative stress, DNA damage, mitochondrial dysfunction, neuronal and synaptic loss, cellular senescence, brain-derived neurotrophic factor signaling, white matter damage, blood-brain barrier/vascular dysfunction, tau pathology, and transposable element reactivation.

The senolytic cocktail, dasatinib and quercetin, impacts the chromatin structure of both young and senescent vascular smooth muscle cells

One promising strategy to alleviate aging symptoms is the treatment with senolytics that is compounds which selectively eliminate senescent cells. Some therapies aim to reduce symptoms of cellular senescence without senescent cell eradication (senomorphic activity). However, senotherapies raise many questions concerning the selectivity, safety and efficiency of senolitic drugs. A vital question is how the senolytic compounds affect young proliferating cells. In our study, we checked the impact of quercetin and dasatinib (D + Q), one of the promising drug mixtures of drugs, on chromatin structure in young and senescent cells. We analyzed the effect of a single and triple drug treatment on vascular smooth muscle cells. We have shown that D + Q impacts the chromatin in both young and senescent cells. In senescent cells, D + Q caused some symptoms of chromatin "rejuvenation" but in young cells some changes characteristic of senescent cells were observed. The alterations in young cells appeared only transiently and chromatin returned to the initial state after 24 h of recovery. The complexity of chromatin staining and nucleus morphology evaluation indicated that a triple treatment makes senescent cells more similar to the young ones than a single treatment. However, the analysis of senescence markers suggested that a single treatment with D + Q caused slightly less pronounced senescence characteristics and was more efficient in alleviating the features of senescence than a triple treatment. It is still an open question whether the alterations caused by D + Q are beneficial or harmful in the long term; however, so far, it can be concluded that the effects depend on cell type and the physiological context.

Proteostasis and lysosomal repair deficits in transdifferentiated neurons of Alzheimer's disease

Aging is the most prominent risk factor for Alzheimer's disease (AD). However, the cellular mechanisms linking neuronal proteostasis decline to the characteristic aberrant protein deposits in AD brains remain elusive. Here, we develop transdifferentiated neurons (tNeurons) from human dermal fibroblasts as a neuronal model that retains aging hallmarks and exhibits AD-linked vulnerabilities. Remarkably, AD tNeurons accumulate proteotoxic deposits, including phospho-Tau and Aβ, resembling those in AD patient and APP mouse brains. Quantitative tNeuron proteomics identify aging and AD-linked deficits in proteostasis and organelle homeostasis, most notably in endosome-lysosomal components. Lysosomal deficits in aged tNeurons, including constitutive lysosomal damage and ESCRT-mediated lysosomal repair defects, are exacerbated in AD tNeurons and linked to inflammatory cytokine secretion and cell death. Supporting lysosomal deficits' centrality in AD, compounds ameliorating lysosomal function reduce Aβ deposits and cytokine secretion. Thus, the tNeuron model system reveals impaired lysosomal homeostasis as an early event of aging and AD.

Autophagy, aging, and age-related neurodegeneration

Autophagy is a conserved mechanism that degrades damaged or superfluous cellular contents and enables nutrient recycling under starvation conditions. Many neurodegeneration-associated proteins are autophagy substrates, and autophagy upregulation ameliorates disease in many animal models of neurodegeneration by enhancing the clearance of toxic proteins, proinflammatory molecules, and dysfunctional organelles. Autophagy inhibition also induces neuronal and glial senescence, a phenomenon that occurs with increasing age in non-diseased brains as well as in response to neurodegeneration-associated stresses. However, aging and many neurodegeneration-associated proteins and mutations impair autophagy. This creates a potentially detrimental feedback loop whereby the accumulation of these disease-associated proteins impairs their autophagic clearance, facilitating their further accumulation and aggregation. Thus, understanding how autophagy interacts with aging, senescence, and neurodegenerative diseases in a temporal, cellular, and genetic context is important for the future clinical application of autophagy-modulating therapies in aging and neurodegeneration.

Elevated p16Ink4a Expression Enhances Tau Phosphorylation in Neurons Differentiated From Human-Induced Pluripotent Stem Cells

Increased expression of the cyclin-dependent kinase inhibitor p16Ink4a (p16) is detected in neurons of human Alzheimer's disease (AD) brains and during normal aging. Importantly, selective eliminating p16-expressing cells in AD mouse models attenuates tau pathologies and improves cognition. But whether and how p16 contributes to AD pathogenesis remains unclear. To address this question, we tested whether induction of p16 expression in neurons exacerbates AD pathologies. We created a doxycycline-inducible system to trigger p16 up-regulation in human-induced pluripotent stem cells (iPSCs) and neurons differentiated from iPSCs. We demonstrated that up-regulated p16 expression in iPSCs reduces cell proliferation, down-regulates cell cycle genes, and up-regulates genes involved in focal adhesion, interferon α response and PI3K-Akt signaling. Our approach enables temporal control of p16 induction upon differentiation from iPSCs to neurons. In differentiated cortical neurons, we found that up-regulation of p16 increases tau phosphorylation at Ser202/Thr205 and Thr231 in a cell-autonomous manner, while amyloid beta secretion is not affected. These data suggest a critical role of p16 in regulating tau phosphorylation in neurons, and thereby contributing to pathological progression of AD. As pathological tau tangles have been shown to induce p16 expression, our studies suggest a positive feedback loop between p16 and tau to exacerbate tau pathologies.

Bidirectional interaction between IL and 17A/IL-17RA pathway dysregulation and α-synuclein in the pathogenesis of Parkinson's disease

Parkinson's disease (PD) pathogenesis is characterized by α-synuclein (α-syn) pathology, which is influenced by various factors such as neuroinflammation and senescence. Increasing evidence has suggested a pivotal role for Interleukin-17A(IL-17A) and Interleukin-17 Receptor A (IL-17RA) in PD, yet the trigger and impact of IL-17A/IL-17RA activation in PD remains elusive. This study observed an age-related increase in IL-17A and IL-17RA in the human central nervous system, accompanied by increased α-syn and senescence biomarkers. Interestingly, both levels of IL-17A and IL-17RA in PD patients were significantly elevated compared to age-matched controls, wherein the IL-17A was mainly present in neurons. This abnormal neuronal IL-17A activation in the PD brain was recapitulated in α-syn mouse models. Correspondingly, administration of recombinant IL-17A exacerbated pathological α-syn in both neuron and mouse models. Furthermore, IL-17A/IL-17RA pathway interventions via blocking antibody or shRNA-mediated knockdown can mitigate the effects of pathological α-syn. This study reveals an interplay between dysregulation of the IL-17A/IL-17RA pathway and α-syn, suggesting that regulating the IL-17A/IL-17RA pathway could modify PD progression by disrupting the detrimental cycle.

Chronic social stress induces p16-mediated senescent cell accumulation in mice

Life stress can shorten lifespan and increase risk for aging-related diseases, but the biology underlying this phenomenon remains unclear. Here we assessed the effect of chronic stress on cellular senescence-a hallmark of aging. Exposure to restraint stress, a psychological non-social stress model, increased p21Cip1 exclusively in the brains of male, but not female mice, and in a p16Ink4a-independent manner. Conversely, exposure to chronic subordination stress (only males were tested) increased key senescent cell markers in peripheral blood mononuclear cells, adipose tissue and brain, in a p16Ink4a-dependent manner. p16Ink4a-positive cells in the brain of chronic subordination stress-exposed mice were primarily hippocampal and cortical neurons with evidence of DNA damage that could be reduced by p16Ink4a cell clearance. Clearance of p16Ink4a-positive cells was not sufficient to ameliorate the adverse effects of social stress on measured metrics of healthspan. Overall, our findings indicate that social stress induces an organ-specific and p16Ink4a-dependent accumulation of senescent cells, illuminating a fundamental way by which the social environment can contribute to aging.

Senescence as a therapeutic target in cancer and age-related diseases

Cellular senescence is a stress response that restrains the growth of aged, damaged or abnormal cells. Thus, senescence has a crucial role in development, tissue maintenance and cancer prevention. However, lingering senescent cells fuel chronic inflammation through the acquisition of a senescence-associated secretory phenotype (SASP), which contributes to cancer and age-related tissue dysfunction. Recent progress in understanding senescence has spurred interest in the development of approaches to target senescent cells, known as senotherapies. In this Review, we evaluate the status of various types of senotherapies, including senolytics that eliminate senescent cells, senomorphics that suppress the SASP, interventions that mitigate senescence and strategies that harness the immune system to clear senescent cells. We also summarize how these approaches can be combined with cancer therapies, and we discuss the challenges and opportunities in moving senotherapies into clinical practice. Such therapies have the potential to address root causes of age-related diseases and thus open new avenues for preventive therapies and treating multimorbidities.

Design, synthesis, and pharmacological characterization of sulfonylurea-based NLRP3 inhibitors: Towards an effective therapeutic strategy for Alzheimer's disease

Alzheimer's disease (AD) is a prevalent neurodegenerative disorder that severely diminishes the quality of life for millions. The NLRP3 inflammasome, a critical mediator of inflammation, has emerged as a promising therapeutic target for AD. In this study, we report the development and optimization of a novel series of sulfonylurea-based NLRP3 inhibitors, with a focus on compound MC1 for the treatment of AD. Utilizing the co-crystal structure of MCC950 in complex with NLRP3 as a guide, we employed a hybrid approach of computer-aided drug design and traditional medicinal chemistry to perform two iterative optimization cycles. This strategy led to the synthesis and evaluation of 40 sulfonylurea derivatives, culminating in the identification of MC1 as the lead candidate. MC1 exhibited enhanced NLRP3 inhibitory activity and demonstrated high binding affinity to NLRP3, effectively blocking NLRP3 activation induced by diverse stimuli such as ATP and Nigericin, without perturbing upstream processes like reactive oxygen species (ROS) generation. In vivo experiments in AD mouse models revealed that MC1 significantly ameliorated cognitive deficits, surpassing the performance of MCC950. Importantly, MC1 showed no signs of hepatotoxicity or adverse effects on the central nervous system. These findings suggest that MC1 holds strong potential as a lead compound for further development in AD therapy, providing a new scaffold for NLRP3 inhibition with improved safety and efficacy profiles.

Cellular senescence as a key contributor to secondary neurodegeneration in traumatic brain injury and stroke

Traumatic brain injury (TBI) and stroke pose major health challenges, impacting millions of individuals globally. Once considered solely acute events, these neurological conditions are now recognized as enduring pathological processes with long-term consequences, including an increased susceptibility to neurodegeneration. However, effective strategies to counteract their devastating consequences are still lacking. Cellular senescence, marked by irreversible cell-cycle arrest, is emerging as a crucial factor in various neurodegenerative diseases. Recent research further reveals that cellular senescence may be a potential driver for secondary neurodegeneration following brain injury. Herein, we synthesize emerging evidence that TBI and stroke drive the accumulation of senescent cells in the brain. The rationale for targeting senescent cells as a therapeutic approach to combat neurodegeneration following TBI/stroke is outlined. From a translational perspective, we emphasize current knowledge and future directions of senolytic therapy for these neurological conditions.

The new perspective of Alzheimer's Disease Research: Mechanism and therapeutic strategy of neuronal senescence

Alzheimer's disease (AD), commonly known as senile dementia, is a neurodegenerative disease with insidious onset and gradually worsening course. The brain is particularly sensitive to senescence, and neuronal senescence is an important risk factor for the occurrence of AD. However, the exact pathogenesis between neuronal senescence and AD has not been fully elucidated so far. Neuronal senescence is characterized by the permanent stagnation of the cell cycle, and the changes in its structure, function, and microenvironment are closely related to the pathogenesis and progression of AD. In recent years, studies such as the Aβ cascade hypothesis and Tau protein phosphorylation have provided new strategies for the therapy of AD, but due to the complexity of the etiology of AD, there are still no effective treatment measures. This article aims to deeply analyze the pathogenesis between AD and neuronal senescence, and sort out various existing therapeutic methods, to provide new ideas and references for the clinical treatment of AD.

Defining and characterizing neuronal senescence, 'neurescence', as GX arrested cells

Cellular senescence is a cell state characterized by resistance to apoptosis and stable cell cycle arrest. Senescence was first observed in mitotic cells in vitro. Recent evidence from in vivo studies and human tissue indicates that postmitotic cells, including neurons, may also become senescent. The quiescent cell state of neurons and inconsistent descriptions of neuronal senescence across studies, however, have caused confusion in this burgeoning field. We summarize evidence demonstrating that exit from G0 quiescence may protect neurons against apoptosis and predispose them toward senescence. Additionally, we propose the term 'neurescent' for senescent neurons and introduce the cell state, GX, to describe cell cycle arrest achieved by passing through G0 quiescence. Criteria are provided to identify neurescent cells, distinguish them from G0 quiescent neurons, and compare neurescent phenotypes with classic replicative senescence.

Integrated multimodal cell atlas of Alzheimer's disease

Alzheimer's disease (AD) is the leading cause of dementia in older adults. Although AD progression is characterized by stereotyped accumulation of proteinopathies, the affected cellular populations remain understudied. Here we use multiomics, spatial genomics and reference atlases from the BRAIN Initiative to study middle temporal gyrus cell types in 84 donors with varying AD pathologies. This cohort includes 33 male donors and 51 female donors, with an average age at time of death of 88 years. We used quantitative neuropathology to place donors along a disease pseudoprogression score. Pseudoprogression analysis revealed two disease phases: an early phase with a slow increase in pathology, presence of inflammatory microglia, reactive astrocytes, loss of somatostatin+ inhibitory neurons, and a remyelination response by oligodendrocyte precursor cells; and a later phase with exponential increase in pathology, loss of excitatory neurons and Pvalb+ and Vip+ inhibitory neuron subtypes. These findings were replicated in other major AD studies.

Molecular and Cellular Foundations of Aging of the Brain: Anti-aging Strategies in Alzheimer's Disease

Alzheimer's disease (AD) is a condition characterized by the gradual degeneration of the nervous system that poses significant challenges to cognitive function and overall mental health. Given the increasing global life expectancy, there is an urgent need for effective strategies to prevent and manage Alzheimer's disease, with a particular focus on anti-aging interventions. Recent scientific advancements have unveiled several promising strategies for combating Alzheimer's disease (AD), ranging from lifestyle interventions to cutting-edge pharmacological treatments and therapies targeting the underlying biological processes of aging and AD. Regular physical exercise, cognitive engagement, a balanced diet, and social interaction serve as key pillars in maintaining brain health. At the same time, therapies target key pathological mechanisms of AD, such as amyloid-beta accumulation, tau abnormalities, neuroinflammation, mitochondrial dysfunction, and synaptic loss, offering potential breakthroughs in treatment. Moreover, cutting-edge innovations such as gene therapy, stem cell transplantation, and novel drug delivery systems are emerging as potential game-changers in the fight against AD. This review critically evaluates the latest research on anti-aging interventions and their potential in preventing and treating Alzheimer's disease (AD) by exploring the connections between aging mechanisms and AD pathogenesis. It provides a comprehensive analysis of both well-established and emerging strategies, while also identifying key gaps in current knowledge to guide future research efforts.

The Mechanistic Link Between Tau-Driven Proteotoxic Stress and Cellular Senescence in Alzheimer's Disease

In Alzheimer's disease (AD), tau dissociates from microtubules (MTs) due to hyperphosphorylation and misfolding. It is degraded by various mechanisms, including the 20S proteasome, chaperone-mediated autophagy (CMA), 26S proteasome, macroautophagy, and aggrephagy. Neurofibrillary tangles (NFTs) form upon the impairment of aggrephagy, and eventually, the ubiquitin chaperone valosin-containing protein (VCP) and heat shock 70 kDa protein (HSP70) are recruited to the sites of NFTs for the extraction of tau for the ubiquitin-proteasome system (UPS)-mediated degradation. However, the impairment of tau degradation in neurons allows tau to be secreted into the extracellular space. Secreted tau can be monomers, oligomers, and paired helical filaments (PHFs), which are seeding competent pathological tau that can be endocytosed/phagocytosed by healthy neurons, microglia, astrocytes, oligodendrocyte progenitor cells (OPCs), and oligodendrocytes, often causing proteotoxic stress and eventually triggers senescence. Senescent cells secrete various senescence-associated secretory phenotype (SASP) factors, which trigger cellular atrophy, causing decreased brain volume in human AD. However, the molecular mechanisms of proteotoxic stress and cellular senescence are not entirely understood and are an emerging area of research. Therefore, this comprehensive review summarizes pertinent studies that provided evidence for the sequential tau degradation, failure, and the mechanistic link between tau-driven proteotoxic stress and cellular senescence in AD.

Increased cholesterol synthesis drives neurotoxicity in patient stem cell-derived model of multiple sclerosis

Senescent neural progenitor cells have been identified in brain lesions of people with progressive multiple sclerosis (PMS). However, their role in disease pathobiology and contribution to the lesion environment remains unclear. By establishing directly induced neural stem/progenitor cell (iNSC) lines from PMS patient fibroblasts, we studied their senescent phenotype in vitro. Senescence was strongly associated with inflammatory signaling, hypermetabolism, and the senescence-associated secretory phenotype (SASP). PMS-derived iNSCs displayed increased glucose-dependent fatty acid and cholesterol synthesis, which resulted in the accumulation of lipid droplets. A 3-hydroxy-3-methylglutaryl (HMG)-coenzyme A (CoA) reductase (HMGCR)-mediated lipogenic state was found to induce a SASP in PMS iNSCs via cholesterol-dependent transcription factors. SASP from PMS iNSC lines induced neurotoxicity in mature neurons, and treatment with the HMGCR inhibitor simvastatin altered the PMS iNSC SASP, promoting cytoprotective qualities and reducing neurotoxicity. Our findings suggest a disease-associated, cholesterol-related, hypermetabolic phenotype of PMS iNSCs that leads to neurotoxic signaling and is rescuable pharmacologically.

Therapeutic targeting of senescent cells in the CNS

Senescent cells accumulate throughout the body with advanced age, diseases and chronic conditions. They negatively impact health and function of multiple systems, including the central nervous system (CNS). Therapies that target senescent cells, broadly referred to as senotherapeutics, recently emerged as potentially important treatment strategies for the CNS. Promising therapeutic approaches involve clearing senescent cells by disarming their pro-survival pathways with 'senolytics'; or dampening their toxic senescence-associated secretory phenotype (SASP) using 'senomorphics'. Following the pioneering discovery of first-generation senolytics dasatinib and quercetin, dozens of additional therapies have been identified, and several promising targets are under investigation. Although potentially transformative, senotherapies are still in early stages and require thorough testing to ensure reliable target engagement, specificity, safety and efficacy. The limited brain penetrance and potential toxic side effects of CNS-acting senotherapeutics pose challenges for drug development and translation to the clinic. This Review assesses the potential impact of senotherapeutics for neurological conditions by summarizing preclinical evidence, innovative methods for target and biomarker identification, academic and industry drug development pipelines and progress in clinical trials.

Senoinflammation as the underlying mechanism of aging and its modulation by calorie restriction

Senoinflammation is characterized by an unresolved low-grade inflammatory process that affects multiple organs and systemic functions. This review begins with a brief overview of the fundamental concepts and frameworks of senoinflammation. It is widely involved in the aging of various organs and ultimately leads to progressive systemic degeneration. Senoinflammation underlying age-related inflammation, is causally related to metabolic dysregulation and the formation of senescence-associated secretory phenotype (SASP) during aging and age-related diseases. This review discusses the biochemical evidence and molecular biology data supporting the concept of senoinflammation and its regulatory processes, highlighting the anti-aging and anti-inflammatory effects of calorie restriction (CR). Experimental data from CR studies demonstrated effective suppression of various pro-inflammatory cytokines and chemokines, lipid accumulation, and SASP during aging. In conclusion, senoinflammation represents the basic mechanism that creates a microenvironment conducive to aging and age-related diseases. Furthermore, it serves as a potential therapeutic target for mitigating aging and age-related diseases.

Icariin targets p53 to protect against ceramide-induced neuronal senescence: Implication in Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is a leading cause of dementia. The aging brain is particularly vulnerable to various stressors, including increased levels of ceramide. However, the role of ceramide in neuronal cell senescence and AD progression and whether icariin, a natural flavonoid glucoside, could reverse neuronal senescence remain inadequately understood.

AIM

In this study, we explore the role of ceramide in neuronal senescence and AD, and whether icariin can counteract these effects.

METHODS

We pretreated HT-22 cells with icariin and then induced senescence with ceramide. Various assays were employed to assess cell senescence, such as reactive oxygen species (ROS) production, cell cycle progression, β-galactosidase staining, and expression of senescence-associated proteins. In vivo studies utilized APP/PS1 mice and C57BL/6J mice injected with ceramide to evaluate behavioral changes, histopathological alterations, and senescence-associated protein expression. Transcriptomics, molecular docking, molecular dynamics simulations, and cellular thermal shift assays were employed to verify the interaction between icariin and P53. The specificity of icariin targeting of P53 was further confirmed through rescue experiments utilizing the P53 activator Navtemadlin.

RESULTS

Our data demonstrated that ceramide could induce neuronal senescence and AD-related pathologies, which were reversed by icariin. Moreover, molecular studies revealed that icariin directly targeted P53, and its neuroprotective effects were attenuated by P53 activation, providing evidence for the role of P53 in icariin-mediated neuroprotection.

CONCLUSION

Icariin demonstrates a protective effect against ceramide-induced neuronal senescence by inhibiting the P53 pathway. This identifies a novel mechanism of action for icariin, offering a novel therapeutic approach for AD and other age-related neurodegenerative diseases.

Short Peptides Protect Fibroblast-Derived Induced Neurons from Age-Related Changes

Neurons become more vulnerable to stress factors with age, which leads to increased oxidative DNA damage, decreased activity of mitochondria and lysosomes, increased levels of p16, decreased LaminB1 proteins, and the depletion of the dendritic tree. These changes are exacerbated in vulnerable neuronal populations during the development of neurodegenerative diseases. Glu-Asp-Arg (EDR) and Lys-Glu-Asp (KED), and Ala-Glu-Asp-Gly (AEDG) peptides have previously demonstrated neuroprotective effects in various models of Alzheimer's disease. In this study, we investigated the influence of EDR, KED, and AEDG peptides on the aging of fibroblast-derived induced neurons. We used a new in vitro cellular model of human neuronal aging based on the transdifferentiation of aged dermal fibroblasts from elderly donors into induced cortical neurons. All peptides promote the arborization of the dendritic tree, increasing both the number of primary processes and the total length of dendrites. Tripeptides have no effect on the activity of mitochondria and lysosomes and the level of p16 protein in induced neurons. EDR peptide reduces oxidative DNA damage in induced neurons derived from elderly donor fibroblasts. Short peptides partially protect induced neurons from age-related changes and stimulate dendritogenesis in neurons. They can be recommended for use as neuroprotective agents.

Bernard LA, Nixon DF, Jones RB, Yamashita M, Ndhlovu LC, Zhou T, Evering TH. A Transcriptional Signature of Induced Neurons Differentiates Virologically Suppressed People Living With HIV from People Without HIV

Neurocognitive impairment is a prevalent and important co-morbidity in virologically suppressed people living with HIV (PLWH), yet the underlying mechanisms remain elusive and treatments lacking. Here, we explored for the first time, use of participant-derived directly induced neurons (iNs) to model neuronal biology and injury in PLWH. iNs retain age- and disease-related features of the donors, providing unique opportunities to reveal novel aspects of neurological disorders. We obtained primary dermal fibroblasts from six virologically suppressed PLWH (range: 27 - 64 years, median: 53); 83% Male; 50% White) and seven matched people without HIV (PWOH) (range: 27 - 66, median: 55); 71% Male; 57% White). iNs were generated using transcription factors NGN2 and ASCL1, and validated by immunocytochemistry and single-cell-RNAseq. Transcriptomic analysis using bulk-RNAseq identified 29 significantly differentially expressed genes between iNs from PLWH and PWOH. Of these, 16 genes were downregulated and 13 upregulated in PLWH iNs. Protein-protein interaction network mapping indicates that iNs from PLWH exhibit differences in extracellular matrix organization and synaptic transmission. IFI27 was upregulated in iNs from PLWH, which complements independent post-mortem studies demonstrating elevated IFI27 expression in PLWH-derived brain tissue, indicating that iN generation reconstitutes this pathway. Finally, we observed that expression of the FOXL2NB-FOXL2-LINC01391 genome locus is reduced in iNs from PLWH and negatively correlates with neurocognitive impairment. Thus, we have identified an iN gene signature of HIV through direct reprogramming of skin fibroblasts into neurons revealing novel mechanisms of neurocognitive impairment in PLWH.

Cellular senescence: A novel therapeutic target for central nervous system diseases

The underlying mechanisms of diseases affecting the central nervous system (CNS) remain unclear, limiting the development of effective therapeutic strategies. Remarkably, cellular senescence, a biological phenomenon observed in cultured fibroblasts in vitro, is a crucial intrinsic mechanism that influences homeostasis of the brain microenvironment and contributes to the onset and progression of CNS diseases. Cellular senescence has been observed in disease models established in vitro and in vivo and in bodily fluids or tissue components from patients with CNS diseases. These findings highlight cellular senescence as a promising target for preventing and treating CNS diseases. Consequently, emerging novel therapies targeting senescent cells have exhibited promising therapeutic effects in preclinical and clinical studies on aging-related diseases. These innovative therapies can potentially delay brain cell loss and functional changes, improve the prognosis of CNS diseases, and provide alternative treatments for patients. In this study, we examined the relevant advancements in this field, particularly focusing on the targeting of senescent cells in the brain for the treatment of chronic neurodegenerative diseases (e.g., Alzheimer's disease, Parkinson's disease, and multiple sclerosis) and acute neurotraumatic insults (e.g., ischemic stroke, spinal cord injury, and traumatic brain injury).

iPLA2β loss leads to age-related cognitive decline and neuroinflammation by disrupting neuronal mitophagy

BACKGROUND

During brain aging, disturbances in neuronal phospholipid metabolism result in impaired cognitive function and dysregulation of neurological processes. Mutations in iPLA2β are associated with neurodegenerative conditions that significantly impact brain phospholipids. iPLA2β deficiency exacerbates mitochondrial dysfunction and abnormal mitochondrial accumulation. We hypothesized that iPLA2β contributes to age-related cognitive decline by disrupting neuronal mitophagy.

METHODOLOGY

We used aged wild-type (WT) mice and iPLA2β-/- mice as natural aging models to assess cognitive performance, iPLA2β expression in the cortex, levels of chemokines and inflammatory cytokines, and mitochondrial dysfunction, with a specific focus on mitophagy and the mitochondrial phospholipid profile. To further elucidate the role of iPLA2β, we employed adeno-associated virus (AAV)-mediated iPLA2β overexpression in aged mice and re-evaluated these parameters.

RESULTS

Our findings revealed a significant reduction in iPLA2β levels in the prefrontal cortex of aged brains. Notably, iPLA2β-deficient mice exhibited impaired learning and memory. Loss of iPLA2β in the PFC of aged mice led to increased levels of chemokines and inflammatory cytokines. This damage was associated with altered mitochondrial morphology, reduced ATP levels due to dysregulation of the parkin-independent mitophagy pathway, and changes in the mitochondrial phospholipid profile. AAV-mediated overexpression of iPLA2β alleviated age-related parkin-independent mitophagy pathway dysregulation in primary neurons and the PFC of aged mice, reduced inflammation, and improved cognitive function.

CONCLUSIONS

Our study suggests that age-related iPLA2β loss in the PFC leads to cognitive decline through the disruption of mitophagy. These findings highlight the potential of targeting iPLA2β to ameliorate age-related neurocognitive disorders.

Integrating Mitochondrial Biology into Innovative Cell Therapies for Neurodegenerative Diseases

The role of mitochondria in neurodegenerative diseases is crucial, and recent developments have highlighted its significance in cell therapy. Mitochondrial dysfunction has been implicated in various neurodegenerative disorders, including Alzheimer's, Parkinson's, amyotrophic lateral sclerosis, and Huntington's diseases. Understanding the impact of mitochondrial biology on these conditions can provide valuable insights for developing targeted cell therapies. This mini-review refocuses on mitochondria and emphasizes the potential of therapies leveraging mesenchymal stem cells, embryonic stem cells, induced pluripotent stem cells, stem cell-derived secretions, and extracellular vesicles. Mesenchymal stem cell-mediated mitochondria transfer is highlighted for restoring mitochondrial health in cells with dysfunctional mitochondria. Additionally, attention is paid to gene-editing techniques such as mito-CRISPR, mitoTALENs, mito-ZNFs, and DdCBEs to ensure the safety and efficacy of stem cell treatments. Challenges and future directions are also discussed, including the possible tumorigenic effects of stem cells, off-target effects, disease targeting, immune rejection, and ethical issues.

Senescence- and Immunity-Related Changes in the Central Nervous System: A Comprehensive Review

Senescence is a cellular state characterized by an irreversible halt in the cell cycle, accompanied by alterations in cell morphology, function, and secretion. Senescent cells release a plethora of inflammatory and growth factors, extracellular matrix proteins, and other bioactive substances, collectively known as the senescence-associated secretory phenotype (SASP). These excreted substances serve as crucial mediators of senescent tissues, while the secretion of SASP by senescent neurons and glial cells in the central nervous system modulates the activity of immune cells. Senescent immune cells also influence the physiological activities of various cells in the central nervous system. Further, the interaction between cellular senescence and immune regulation collectively affects the physiological and pathological processes of the central nervous system. Herein, we explore the role of senescence in the physiological and pathological processes underlying embryonic development, aging, degeneration, and injury of the central nervous system, through the immune response. Further, we elucidate the role of senescence in the physiological and pathological processes of the central nervous system, proposing a new theoretical foundation for treating central nervous system diseases.

Cholesterol Accumulation Promotes Photoreceptor Senescence and Retinal Degeneration

Purpose

Dysregulated cholesterol metabolism is critical in the pathogenesis of AMD. Cellular senescence contributes to the development of numerous age-associated diseases. In this study, we investigated the link between cholesterol burden and the cellular senescence of photoreceptors.

Methods

Retinas from rod-specific ATP binding cassette subfamily A member 1 (Abca1) and G member 1 (Abcg1) (Abca1/g1-rod/-rod) knockout mice fed with a high-fat diet were analyzed for the signs of cellular senescence. Real-time quantitative PCR and immunofluorescence were used to characterize the senescence profile of the retina and cholesterol-treated photoreceptor cell line (661W). Inducible elimination of p16(Ink4a)-positive senescent cells (INK-ATTAC) mice or the administration of senolytic drugs (dasatinib and quercetin: D&Q) were used to examine the impact of senolytics on AMD-like phenotypes in Abca1/g1-rod/-rod retina.

Results

Increased accumulation of senescent cells as measured by markers of cellular senescence was found in Abca1/g1-rod/-rod retina. Exogenous cholesterol also induced cellular senescence in 661W cells. Selective elimination of senescent cells in Abca1/g1-rod/-rod;INK-ATTAC mice or by administration of D&Q improved visual function, lipid accumulation in retinal pigment epithelium, and Bruch's membrane thickening.

Conclusions

Cholesterol accumulation promotes cellular senescence in photoreceptors. Eliminating senescent photoreceptors improves visual function in a model of retinal neurodegeneration, and senotherapy offers a novel therapeutic avenue for further investigation.

Modeling Alzheimer's disease using human cell derived brain organoids and 3D models

Age-related neurodegenerative diseases, like Alzheimer's disease (AD), are challenging diseases for those affected with no cure and limited treatment options. Functional, human derived brain tissues that represent the diverse genetic background and cellular subtypes contributing to sporadic AD (sAD) are limited. Human stem cell derived brain organoids recapitulate some features of human brain cytoarchitecture and AD-like pathology, providing a tool for illuminating the relationship between AD pathology and neural cell dysregulation leading to cognitive decline. In this review, we explore current strategies for implementing brain organoids in the study of AD as well as the challenges associated with investigating age-related brain diseases using organoid models.

The role of cellular senescence in neurodegenerative diseases

Increasing evidence has revealed that cellular senescence drives NDs, including Alzheimer's disease (AD) and Parkinson's disease. Different senescent cell populations secrete senescence-associated secretory phenotypes (SASP), including matrix metalloproteinase-3, interleukin (IL)-1α, IL-6, and IL-8, which can harm adjacent microglia. Moreover, these cells possess high expression levels of senescence hallmarks (p16 and p21) and elevated senescence-associated β-galactosidase activity in in vitro and in vivo ND models. These senescence phenotypes contribute to the deposition of β-amyloid and tau-protein tangles. Selective clearance of senescent cells and SASP regulation by inhibiting p38/mitogen-activated protein kinase and nuclear factor kappa B signaling attenuate β-amyloid load and prevent tau-protein tangle deposition, thereby improving cognitive performance in AD mouse models. In addition, telomere shortening, a cellular senescence biomarker, is associated with increased ND risks. Telomere dysfunction causes cellular senescence, stimulating IL-6, tumor necrosis factor-α, and IL-1β secretions. The forced expression of telomerase activators prevents cellular senescence, yielding considerable neuroprotective effects. This review elucidates the mechanism of cellular senescence in ND pathogenesis, suggesting strategies to eliminate or restore senescent cells to a normal phenotype for treating such diseases.

Genome-wide CRISPR screen identifies neddylation as a regulator of neuronal aging and AD neurodegeneration

Aging is the biggest risk factor for the development of Alzheimer's disease (AD). Here, we performed a whole-genome CRISPR screen to identify regulators of neuronal age and show that the neddylation pathway regulates both cellular age and AD neurodegeneration in a human stem cell model. Specifically, we demonstrate that blocking neddylation increased cellular hallmarks of aging and led to an increase in Tau aggregation and phosphorylation in neurons carrying the APPswe/swe mutation. Aged APPswe/swe but not isogenic control neurons also showed a progressive decrease in viability. Selective neuronal loss upon neddylation inhibition was similarly observed in other isogenic AD and in Parkinson's disease (PD) models, including PSENM146V/M146V cortical and LRRK2G2019S/G2019S midbrain dopamine neurons, respectively. This study indicates that cellular aging can reveal late-onset disease phenotypes, identifies new potential targets to modulate AD progression, and describes a strategy to program age-associated phenotypes into stem cell models of disease.