Lessons from inducible pluripotent stem cell models on neuronal senescence in aging and neurodegeneration

Genome-Wide Network Analysis of DRG-Sciatic Nerve Network-Inferred Cellular Senescence and Senescence Phenotype in Peripheral Sensory Neurons

Accumulation of senescent neurons in the dorsal root ganglion (DRG) is an important tissue phenotype that causes age-related degeneration of peripheral sensory nerves. Senescent neurons are neurons with arrested cell cycle that have undergone cellular senescence but remain in the tissue and play various biological roles. To understand the accumulation of senescent neurons in the DRG during aging, we aimed to elucidate the mechanism that induces cellular senescence in DRG neurons and the role of senescent DRG neurons. We integrated multiple public transcriptome datasets for DRGs, which include cell bodies in neurons, and the sciatic nerve, which includes axons in neurons, using network medicine-based bioinformatics analysis. We thus inferred the molecular mechanisms involved in cellular senescence of DRG neurons, from molecular responses to senescence, in the DRG-sciatic nerve network. Network medicine-based bioinformatics analysis revealed that age-related Mapk3 decline leads to impaired cholesterol metabolism and biosynthetic function in axons, resulting in compensatory upregulation of Srebf1, a transcription factor involved in lipid and cholesterol metabolism. This in turn leads to CDKN2A-mediated cellular senescence. Furthermore, our analysis revealed that senescent DRG neurons develop a senescence phenotype characterized by activation of antigen-presenting cells via upregulation of Ctss as a hub gene. B cells were inferred as antigen-presenting cells activated by Ctss, and CD8-positive T cells were inferred as cells that receive antigen presentation from B cells.

Cell-based regenerative and rejuvenation strategies for treating neurodegenerative diseases

Neurodegenerative diseases including Alzheimer's and Parkinson's disease are age-related disorders which severely impact quality of life and impose significant societal burdens. Cellular senescence is a critical factor in these disorders, contributing to their onset and progression by promoting permanent cell cycle arrest and reducing cellular function, affecting various types of cells in brain. Recent advancements in regenerative medicine have highlighted "R3" strategies-rejuvenation, regeneration, and replacement-as promising therapeutic approaches for neurodegeneration. This review aims to critically analyze the role of cellular senescence in neurodegenerative diseases and organizes therapeutic approaches within the R3 regenerative medicine paradigm. Specifically, we examine stem cell therapy, direct lineage reprogramming, and partial reprogramming in the context of R3, emphasizing how these interventions mitigate cellular senescence and counteracting aging-related neurodegeneration. Ultimately, this review seeks to provide insights into the complex interplay between cellular senescence and neurodegeneration while highlighting the promise of cell-based regenerative strategies to address these debilitating conditions.

Klotho overexpression protects human cortical neurons from β-amyloid induced neuronal toxicity

Klotho, a well-known aging suppressor protein, has been implicated in neuroprotection and the regulation of neuronal senescence. While previous studies have demonstrated its anti-aging properties in human brain organoids, its potential to mitigate neurodegenerative processes triggered by β-amyloid remains underexplored. In this study, we utilised human induced pluripotent stem cells (iPSCs) engineered with a doxycycline-inducible system to overexpress KLOTHO and generated 2D cortical neuron cultures from these cells. These neurons were next exposed to pre-aggregated β-amyloid 1-42 oligomers to model the neurotoxicity associated with Alzheimer's disease. Our data reveal that upregulation of KLOTHO significantly reduced β-amyloid-induced neuronal degeneration and apoptosis, as evidenced by decreased cleaved caspase-3 expression and preservation of axonal integrity. Additionally, KLOTHO overexpression prevented the loss of dendritic branching and mitigated reductions in axonal diameter, hallmark features of neurodegenerative pathology. These results highlight Klotho's protective role against β-amyloid-induced neurotoxicity in human cortical neurons and suggest that its age-related decline may contribute to neurodegenerative diseases such as Alzheimer's disease. Our findings underscore the therapeutic potential of Klotho-based interventions in mitigating age-associated neurodegenerative processes.

Age-Related Neurodegenerative Diseases: A Stem Cell's Perspective

Neurodegenerative diseases encompass a number of very heterogeneous disorders, primarily characterized by neuronal loss and a concomitant decline in neurological function. Examples of this type of clinical condition are Alzheimer's Disease, Parkinson's Disease, Huntington's Disease and Amyotrophic Lateral Sclerosis. Age has been identified as a major risk in the etiology of these disorders, which explains their increased incidence in developed countries. Unfortunately, despite continued and intensive efforts, no cure has yet been found for any of these diseases; reliable markers that allow for an early diagnosis of the disease and the identification of key molecular events leading to disease onset and progression are lacking. Altered adult neurogenesis appears to precede the appearance of severe symptoms. Given the scarcity of human samples and the considerable differences with model species, increasingly complex human stem-cell-based models are being developed. These are shedding light on the molecular alterations that contribute to disease development, facilitating the identification of new clinical targets and providing a screening platform for the testing of candidate drugs. Moreover, the secretome and other promising features of these cell types are being explored, to use them as replacement cells of high plasticity or as co-adjuvant therapy in combinatorial treatments.

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.

Senolytic therapy preserves blood-brain barrier integrity and promotes microglia homeostasis in a tauopathy model

Cellular senescence, characterized by expressing the cell cycle inhibitory proteins, is evident in driving age-related diseases. Senescent cells play a crucial role in the initiation and progression of tau-mediated pathology, suggesting that targeting cell senescence offers a therapeutic potential for treating tauopathy associated diseases. This study focuses on identifying non-invasive biomarkers and validating their responses to a well-characterized senolytic therapy combining dasatinib and quercetin (D + Q), in a widely used tauopathy mouse model, PS19. We employed human-translatable MRI measures, including water extraction with phase-contrast arterial spin tagging (WEPCAST) MRI, T2 relaxation under spin tagging (TRUST), longitudinally assessed brain physiology and high-resolution structural MRI evaluated the brain regional volumes in PS19 mice. Our data reveal increased BBB permeability, decreased oxygen extraction fraction, and brain atrophy in 9-month-old PS19 mice compared to their littermate controls. (D + Q) treatment effectively preserves BBB integrity, rescues cerebral oxygen hypometabolism, attenuates brain atrophy, and alleviates tau hyperphosphorylation in PS19 mice. Mechanistically, D + Q treatment induces a shift of microglia from a disease-associated to a homeostatic state, reducing a senescence-like microglial phenotype marked by increased p16/Ink4a. D + Q-treated PS19 mice exhibit enhanced cue-associated cognitive performance in the tracing fear conditioning test compared to the vehicle-treated littermates, implying improved cognitive function by D + Q treatment. Our results pave the way for application of senolytic treatment as well as these noninvasive MRI biomarkers in clinical trials in tauopathy associated neurological disorders.

Senolytic therapy preserves blood-brain barrier integrity and promotes microglia homeostasis in a tauopathy model

Cellular senescence, characterized by expressing the cell cycle inhibitory proteins, is evident in driving age-related diseases. Senescent cells play a crucial role in the initiation and progression of tau-mediated pathology, suggesting that targeting cell senescence offers a therapeutic potential for treating tauopathy associated diseases. This study focuses on identifying non-invasive biomarkers and validating their responses to a well-characterized senolytic therapy combining dasatinib and quercetin (D+Q), in a widely used tauopathy mouse model, PS19. We employed human-translatable MRI measures, including water extraction with phase-contrast arterial spin tagging (WEPCAST) MRI, T2 relaxation under spin tagging (TRUST), longitudinally assessed brain physiology and high-resolution structural MRI evaluated the brain regional volumes in PS19 mice. Our data reveal increased BBB permeability, decreased oxygen extraction fraction, and brain atrophy in 9-month-old PS19 mice compared to their littermate controls. (D+Q) treatment effectively preserves BBB integrity, rescues cerebral oxygen hypometabolism, attenuates brain atrophy, and alleviates tau hyperphosphorylation in PS19 mice. Mechanistically, D+Q treatment induces a shift of microglia from a disease-associated to a homeostatic state, reducing a senescence-like microglial phenotype marked by increased p16/INK4a. D+Q-treated PS19 mice exhibit enhanced cue-associated cognitive performance in the tracing fear conditioning test compared to the vehicle-treated littermates, implying improved cognitive function by D+Q treatment. Our results pave the way for application of senolytic treatment as well as these noninvasive MRI biomarkers in clinical trials in tauopathy associated neurological disorders.