Aging-accelerated differential production and aggregation of STAT3 protein in neuronal cells and neural stem cells in the male mouse spinal cord

The transcription factor STAT3 and aging: an intermediate medium

Aging is a physiological/pathological process accompanied by progressive impairment of cellular function, leading to a variety of aging-related diseases. STAT3 is one of the core regulatory factors of aging. It is involved in body metabolism, development and senescence, cell apoptosis and so on. During the aging process, the changes of growth factors and cytokines will cause the activation of STAT3 to varying degrees, regulate the inflammatory pathways related to aging, regulate body inflammation, mitochondrial function, cell aging and autophagy to regulate and influence the aging process. Drugs targeting STAT3 can treat senescence related diseases. This review summarizes the role of STAT3 signaling factors in the pathogenesis of aging, including mitochondrial function, cellular senescence, autophagy, and chronic inflammation mediated by inflammatory pathways. Finally, the key regulatory role of STAT3 in senescence related diseases is emphasized. In summary, we reveal that drug development and clinical application targeting STAT3 is one of the key points in delaying aging and treating aging-related diseases in the future.

Efficient analysis of toxicity and mechanisms of Acetyl tributyl citrate on aging with network toxicology and molecular docking strategy

The aim of this study was to apply a network toxicology strategy to investigate the potential toxicity and the molecular mechanisms underlying the aging-induced toxicity of acetyl tributyl citrate (ATBC). Utilizing the ChEMBL, SwissTargetPrediction, and CellAge databases, we identified 32 potential targets associated with ATBC exposure and aging. Subsequent optimization by STRING and Cytoscape software highlighted 11 core targets, including EGFR, STAT3, and BCL-2. A comprehensive analysis of Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways revealed that core targets of ATBC-induced senescence were predominantly enriched in pathways related to the positive regulation of cell proliferation, telomere shortening, cancer, and cellular senescence. Among these pathways, we selected four core genes of the cellular senescence pathway (MAPK14, CDK2, MDM2, and PIK3CA) for molecular docking with Autodock, which confirmed the high binding affinity between ATBC and the core targets. In conclusion, these findings indicate that ATBC may contribute to human aging by modulating the positive regulation of cell proliferation, the telomere shortening pathway, the cancer-related pathway, and the cellular senescence pathway. This study establishes a theoretical basis for exploring the molecular mechanisms of human aging induced by ATBC, alongside a systematic and effective framework for researchers to assess the potential toxicity of various chemical products.

Excess Ub-K48 Induces Neuronal Apoptosis in Alzheimer's Disease

BACKGROUND

K48-linked ubiquitin chain (Ub-K48) is a crucial ubiquitin chain implicated in protein degradation within the ubiquitin-proteasome system. However, the precise function and molecular mechanism underlying the role of Ub-K48 in the pathogenesis of Alzheimer's disease (AD) and neuronal cell abnormalities remain unclear. The objective of this study was to examine the function of K48 ubiquitination in the etiology of AD, and its associated mechanism of neuronal apoptosis.

METHODS

A mouse model of AD was constructed, and behavioral phenotypic changes were detected using an open field test (OFT). The expression of glial fibrillary acidic protein (GFAP), an early marker of AD, was detected by western blotting (WB). Neuronal apoptosis in the hippocampal region was assessed by hematoxylin and eosin (HE) and Nissl staining. Immunohistochemistry and immunofluorescence were performed to observe the changes in Phosphorylated tubulin associated unit (p-Tau) and Ub-K48 colocalization in neurons of the hippocampal region of AD mice. WB was further applied to detect the degree of ubiquitylation of K48 and the expression of Tau, p-Tau, B-cell lymphoma-2 (Bcl-2) and Bcl-2-associated X (Bax) proteins in neuronal cells of the hippocampus and cortical regions of mice.

RESULTS

Mice with AD exhibited significantly longer resting times (p < 0.05) and shorter average speeds (p < 0.01), total distances travelled (p < 0.01), and distances travelled (p < 0.01) in the central region than those in the control group. This indicated cognitive impairment, which occurred concurrent with an increased expression of the AD marker GFAP protein (p < 0.001). The hippocampal region of AD mice showed abnormalities with sparsely and irregularly arranged cells, large gaps between cells, lighter staining, unclear boundaries of the cell membranes and nuclei, and agglutinated and condensed nuclei (p < 0.01). The neuronal cells of AD mice exhibited significantly elevated levels of p-Tau (p < 0.01) and Ub-K48 (p < 0.01), as well as a notable degree of co-localization within the cells. The intracellular pro-inflammatory protein Bax was significantly upregulated (p < 0.05), while the Bcl-2/Bax ratio was significantly lower than that in the control group (p < 0.05), thus inducing apoptosis in AD neuronal cells.

CONCLUSION

Ub-K48 is strongly linked to the development of AD. p-Tau aggregate in neuronal cells in the hippocampal region of the AD brain and colocalize with Ub-K48, which in turn leads to cellular inflammation and the induction of apoptosis in neuronal cells.

Spinal cord neural stem cells derived from human embryonic stem cells promote synapse regeneration and remyelination in spinal cord injury model rats

Spinal cord injury (SCI) is a devastating injury that significantly impairs patients' quality of life. To date, there is no effective treatment to mitigate nerve tissue damage and restore neurological function. Neural stem cells (NSCs) derived from human embryonic stem cells (hESCs) are considered an important cell source for reconstructing damaged neural circuits and enabling axonal regeneration. Recent preclinical studies have shown that NSCs are potential therapeutic cell sources for neuroprotection and neuroregeneration in SCI animal models. NSCs can be derived from different sources and the spinal cord-specific NSCs have a higher potential for the regeneration of SCI. However, the long-term therapeutic efficacy of spinal cord-specific NSCs remains unproven. Here, we generated human spinal cord NSCs (hSCNSCs) and investigated the effects of transplanted hSCNSCs on the repair of the SCI model rats for 60 days. The transplanted hSCNSCs improved BBB scores, reduced the lesion area and promoted an increase in the number of Nestin-positive cells in the spinal cord compared to the model rats. Meanwhile, hSCNSC transplantation promoted the expression of synaptophysin, a synaptic signature protein and MBP, a protein associated with remyelination. Interestingly, BAF45D, a chromatin remodelling factor that contributes to the induction of hSCNSCs with region-specific spinal cord identity, were increased by the hSCNSC transplantation. In addition, conditioned medium derived from the hSCNSCs also promoted regenerative repair of the injured spinal cord. These results demonstrate that hSCNSCs may play a critical role in the regenerative repair of SCI.

Proteostatic Remodeling of Small Heat Shock Chaperones─Crystallins by Ran-Binding Protein 2─and the Peptidyl-Prolyl cis-trans Isomerase and Chaperone Activities of Its Cyclophilin Domain

Disturbances in protein phase transitions promote protein aggregation─a neurodegeneration hallmark. The modular Ran-binding protein 2 (Ranbp2) is a cytosolic molecular hub for rate-limiting steps of phase transitions of Ran-GTP-bound protein ensembles exiting nuclear pores. Chaperones also regulate phase transitions and proteostasis by suppressing protein aggregation. Ranbp2 haploinsufficiency promotes the age-dependent neuroprotection of the chorioretina against phototoxicity by proteostatic regulations of neuroprotective substrates of Ranbp2 and by suppressing the buildup of polyubiquitylated substrates. Losses of peptidyl-prolyl cis-trans isomerase (PPIase) and chaperone activities of the cyclophilin domain (CY) of Ranbp2 recapitulate molecular effects of Ranbp2 haploinsufficiency. These CY impairments also stimulate deubiquitylation activities and phase transitions of 19S cap subunits of the 26S proteasome that associates with Ranbp2. However, links between CY moonlighting activity, substrate ubiquitylation, and proteostasis remain incomplete. Here, we reveal the Ranbp2 regulation of small heat shock chaperones─crystallins in the chorioretina by proteomics of mice with total or selective modular deficits of Ranbp2. Specifically, loss of CY PPIase of Ranbp2 upregulates αA-Crystallin, which is repressed in adult nonlenticular tissues. Conversely, impairment of CY's chaperone activity opposite to the PPIase pocket downregulates a subset of αA-Crystallin's substrates, γ-crystallins. These CY-dependent effects cause age-dependent and chorioretinal-selective declines of ubiquitylated substrates without affecting the chorioretinal morphology. A model emerges whereby inhibition of Ranbp2's CY PPIase remodels crystallins' expressions, subdues molecular aging, and preordains the chorioretina to neuroprotection by augmenting the chaperone capacity and the degradation of polyubiquitylated substrates against proteostatic impairments. Further, the druggable Ranbp2 CY holds pan-therapeutic potential against proteotoxicity and neurodegeneration.

Proteostatic remodeling of small heat shock chaperones - crystallins by Ran-binding protein 2 and the peptidyl-prolyl cis-trans isomerase and chaperone activities of its cyclophilin domain

Disturbances in phase transitions and intracellular partitions of nucleocytoplasmic shuttling substrates promote protein aggregation - a hallmark of neurodegenerative diseases. The modular Ran-binding protein 2 (Ranbp2) is a cytosolic molecular hub for rate-limiting steps of disassembly and phase transitions of Ran-GTP-bound protein ensembles exiting nuclear pores. Chaperones also play central roles in phase transitions and proteostasis by suppressing protein aggregation. Ranbp2 haploinsufficiency promotes the age-dependent neuroprotection of the chorioretina against photo-oxidative stress by proteostatic regulations of Ranbp2 substrates and by countering the build-up of poly-ubiquitylated substrates. Further, the peptidyl-prolyl cis-trans isomerase (PPIase) and chaperone activities of the cyclophilin domain (CY) of Ranbp2 modulate the proteostasis of selective neuroprotective substrates, such as hnRNPA2B1, STAT3, HDAC4 or L/M-opsin, while promoting a decline of ubiquitylated substrates. However, links between CY PPIase activity on client substrates and its effect(s) on ubiquitylated substrates are unclear. Here, proteomics of genetically modified mice with deficits of Ranbp2 uncovered the regulation of the small heat shock chaperones - crystallins by Ranbp2 in the chorioretina. Loss of CY PPIase of Ranbp2 up-regulates αA-crystallin proteostasis, which is repressed in non-lenticular tissues. Conversely, the αA-crystallin's substrates, γ-crystallins, are down-regulated by impairment of CY's C-terminal chaperone activity. These CY-dependent effects cause the age-dependent decline of ubiquitylated substrates without overt chorioretinal morphological changes. A model emerges whereby the Ranbp2 CY-dependent remodeling of crystallins' proteostasis subdues molecular aging and preordains chorioretinal neuroprotection by augmenting the chaperone buffering capacity and the decline of ubiquitylated substrates against proteostatic impairments. Further, CY's moonlighting activity holds pan -therapeutic potential against neurodegeneration.

Nucleocytoplasmic transport at the crossroads of proteostasis, neurodegeneration and neuroprotection

Nucleocytoplasmic transport comprises the multistep assembly, transport, and disassembly of protein and RNA cargoes entering and exiting nuclear pores. Accruing evidence supports that impairments to nucleocytoplasmic transport are a hallmark of neurodegenerative diseases. These impairments cause dysregulations in nucleocytoplasmic partitioning and proteostasis of nuclear transport receptors and client substrates that promote intracellular deposits - another hallmark of neurodegeneration. Disturbances in liquid-liquid phase separation (LLPS) between dense and dilute phases of biomolecules implicated in nucleocytoplasmic transport promote micrometer-scale coacervates, leading to proteinaceous aggregates. This Review provides historical and emerging principles of LLPS at the interface of nucleocytoplasmic transport, proteostasis, aging and noxious insults, whose dysregulations promote intracellular aggregates. E3 SUMO-protein ligase Ranbp2 constitutes the cytoplasmic filaments of nuclear pores, where it acts as a molecular hub for rate-limiting steps of nucleocytoplasmic transport. A vignette is provided on the roles of Ranbp2 in nucleocytoplasmic transport and at the intersection of proteostasis in the survival of photoreceptor and motor neurons under homeostatic and pathophysiological environments. Current unmet clinical needs are highlighted, including therapeutics aiming to manipulate aggregation-dissolution models of purported neurotoxicity in neurodegeneration.