rAAV8-733-Mediated Gene Transfer of CHIP/Stub-1 Prevents Hippocampal Neuronal Death in Experimental Brain Ischemia

Mechanistic exploration of ubiquitination-mediated pathways in cerebral ischemic injury

The ubiquitin-proteasome system (UPS) plays a pivotal role in regulating protein homeostasis and cellular processes, including protein degradation, trafficking, DNA repair, and cell signaling. During cerebral ischemia, ischemic conditions profoundly disrupt UPS activity, leading to proteasomal dysfunction and the accumulation of abnormal proteins. This imbalance contributes to neuronal injury and cell death observed in ischemic stroke. The UPS is intricately linked to various signaling pathways crucial for neuronal survival, inflammation, and cellular stress response, such as NF-κB, TRIM, TRIP, JAK-STAT, PI3K/Akt, and ERK1/2. Alterations in the ubiquitination process can significantly impact the activation and regulation of these pathways, exacerbating ischemic brain injury. Therapeutic approaches targeting the UPS in cerebral ischemia aim to rebalance protein levels, reduce proteotoxic stress, and mitigate neuronal injury. Strategies include proteasome inhibition, targeting specific ubiquitin ligases and deubiquitinating enzymes, and modulating ubiquitination-mediated regulation of key signaling pathways implicated in ischemia-induced pathophysiology. Therefore, the present review discusses the molecular mechanisms underlying UPS dysfunction in ischemic stroke is crucial for developing effective therapeutic interventions. Modulating ubiquitination-mediated pathways through therapeutic interventions targeting specific UPS components holds significant promise for mitigating ischemic brain injury and promoting neuroprotection and functional recovery in patients with cerebral ischemia.

Clec7a Worsens Long-Term Outcomes after Ischemic Stroke by Aggravating Microglia-Mediated Synapse Elimination

Ischemic stroke (IS) is a leading cause of morbidity and mortality globally and triggers a series of reactions leading to primary and secondary brain injuries and permanent neurological deficits. Microglia in the central nervous system play dual roles in neuroprotection and responding to ischemic brain damage. Here, an IS model is employed to determine the involvement of microglia in phagocytosis at excitatory synapses. Additionally, the effects of pharmacological depletion of microglia are investigated on improving neurobehavioral outcomes and mitigating brain injury. RNA sequencing of microglia reveals an increase in phagocytosis-associated pathway activity and gene expression, and C-type lectin domain family 7 member A (Clec7a) is identified as a key regulator of this process. Manipulating microglial Clec7a expression can potentially regulate microglial phagocytosis of synapses, thereby preventing synaptic loss and improving neurobehavioral outcomes after IS. It is further demonstrat that microglial Clec7a interacts with neuronal myeloid differentiation protein 2 (MD2), a key molecule mediating poststroke neurological injury, and propose the novel hypothesis that MD2 is a ligand for microglial Clec7a. These findings suggest that microglial Clec7a plays a critical role in mediating synaptic phagocytosis in a mouse model of IS, suggesting that Clec7a may be a therapeutic target for IS.

Ubiquitous regulation of cerebrovascular diseases by ubiquitin-modifying enzymes

Cerebrovascular diseases (CVDs) are a major threat to global health. Elucidation of the molecular mechanisms underlying the pathology of CVDs is critical for the development of efficacious preventative and therapeutic approaches. Accumulating studies have highlighted the significance of ubiquitin-modifying enzymes (UMEs) in the regulation of CVDs. UMEs are a group of enzymes that orchestrate ubiquitination, a post-translational modification tightly involved in CVDs. Functionally, UMEs regulate multiple pathological processes in ischemic and hemorrhagic stroke, moyamoya disease, and atherosclerosis. Considering the important roles of UMEs in CVDs, they may become novel druggable targets for these diseases. Besides, techniques applying UMEs, such as proteolysis-targeting chimera and deubiquitinase-targeting chimera, may also revolutionize the therapy of CVDs in the future.

Stub1 ameliorates ER stress-induced neural cell apoptosis and promotes locomotor recovery through restoring autophagy flux after spinal cord injury

Endoplasmic reticulum (ER) stress-induced apoptosis and autophagy flux blockade significantly contribute to neuronal pathology of spinal cord injury (SCI). Yet, the molecular interplay between these two distinctive pathways in mediating the pathology of SCI remains largely unexplored. Currently, we aimed at exploring the crucial role of Stub1 in maintaining ER homeostasis and regulating autophagic flux after SCI. Our results demonstrate that Stub1 reduces ER stress induced neuronal apoptosis, promotes axonal regeneration, inhibits glial scar formation and fosters functional recovery by restoring autophagic flux following SCI. Stub1 enhances autophagic flux following SCI by alleviating the permeabilization of lysosomal membrane through activating TFEB. Importantly, we showed that Stub1 promotes the activation of TFEB by targeting HDAC2 for ubiquitination and degradation. Furthermore, the neuroprotective effect of Stub1 on SCI was abrogated by chloroquine administration, underscoring the essential role of Stub1-mediated enhancement of autophagic flux in its protective effects against SCI. Collectively, our data highlights the vital role of Stub1 in regulating ER stress and autophagy flux after SCI, and propose its potential as a promising target for neuroprotective interventions in SCI.

Evolutionarily conserved regulators of tau identify targets for new therapies

Tauopathies are neurodegenerative diseases that involve the pathological accumulation of tau proteins; in this family are Alzheimer disease, corticobasal degeneration, and chronic traumatic encephalopathy, among others. Hypothesizing that reducing this accumulation could mitigate pathogenesis, we performed a cross-species genetic screen targeting 6,600 potentially druggable genes in human cells and Drosophila. We found and validated 83 hits in cells and further validated 11 hits in the mouse brain. Three of these hits (USP7, RNF130, and RNF149) converge on the C terminus of Hsc70-interacting protein (CHIP) to regulate tau levels, highlighting the role of CHIP in maintaining tau proteostasis in the brain. Knockdown of each of these three genes in adult tauopathy mice reduced tau levels and rescued the disease phenotypes. This study thus identifies several points of intervention to reduce tau levels and demonstrates that reduction of tau levels via regulation of this pathway is a viable therapeutic strategy for Alzheimer disease and other tauopathies.

CHIP ameliorates neuronal damage in H2O2-induced oxidative stress in HT22 cells and gerbil ischemia

Carboxyl terminus of Hsc70-interacting protein (CHIP) is highly conserved and is linked to the connection between molecular chaperones and proteasomes to degrade chaperone-bound proteins. In this study, we synthesized the transactivator of transcription (Tat)-CHIP fusion protein for effective delivery into the brain and examined the effects of CHIP against oxidative stress in HT22 cells induced by hydrogen peroxide (H₂O₂) treatment and ischemic damage in gerbils by 5 min of occlusion of both common carotid arteries, to elucidate the possibility of using Tat-CHIP as a therapeutic agent against ischemic damage. Tat-CHIP was effectively delivered to HT22 hippocampal cells in a concentration- and time-dependent manner, and protein degradation was confirmed in HT22 cells. In addition, Tat-CHIP significantly ameliorated the oxidative damage induced by 200 μM H₂O₂ and decreased DNA fragmentation and reactive oxygen species formation. In addition, Tat-CHIP showed neuroprotective effects against ischemic damage in a dose-dependent manner and significant ameliorative effects against ischemia-induced glial activation, oxidative stress (hydroperoxide and malondialdehyde), pro-inflammatory cytokines (interleukin-1β, interleukin-6, and tumor necrosis factor-α) release, and glutathione and its redox enzymes (glutathione peroxidase and glutathione reductase) in the hippocampus. These results suggest that Tat-CHIP could be a therapeutic agent that can protect neurons from ischemic damage.

Neuronal Death Mechanisms and Therapeutic Strategy in Ischemic Stroke

Ischemic stroke caused by intracranial vascular occlusion has become increasingly prevalent with considerable mortality and disability, which gravely burdens the global economy. Current relatively effective clinical treatments are limited to intravenous alteplase and thrombectomy. Even so, patients still benefit little due to the short therapeutic window and the risk of ischemia/reperfusion injury. It is therefore urgent to figure out the neuronal death mechanisms following ischemic stroke in order to develop new neuroprotective strategies. Regarding the pathogenesis, multiple pathological events trigger the activation of cell death pathways. Particular attention should be devoted to excitotoxicity, oxidative stress, and inflammatory responses. Thus, in this article, we first review the principal mechanisms underlying neuronal death mediated by these significant events, such as intrinsic and extrinsic apoptosis, ferroptosis, parthanatos, pyroptosis, necroptosis, and autophagic cell death. Then, we further discuss the possibility of interventions targeting these pathological events and summarize the present pharmacological achievements.

CHIP ameliorates cerebral ischemia-reperfusion injury by attenuating necroptosis and inflammation

Blood reperfusion of ischemic cerebral tissue may cause cerebral ischemia-reperfusion (CIR) injury. Necroptosis and inflammation have been demonstrated to be involved in the disease-related process of CIR injury. The E3 ubiquitin ligase carboxyl terminus of Hsp70-interacting protein (CHIP) can modulate multiple cellular signaling processes, including necroptosis and inflammation. Numerous studies have demonstrated the neuroprotective effects of CHIP on multiple central nervous system (CNS) diseases. However, the effects of CHIP on CIR injury have not been fully explored. We hypothesize that CHIP can exert neuroprotective effects by attenuating necroptosis and inflammation during CIR injury. In the present study, adult wild-type (WT) C57BL/6 mice and CHIP knock-in (KI) mice with a C57BL/6 background and CHIP overexpression in neural tissue underwent middle cerebral artery occlusion (MCAO) surgery to simulate CIR onset. Our data indicated that CHIP expression in the peri-infarct tissue was markedly increased after MCAO surgery. Compared with WT mice, CHIP KI mice significantly improved neurological deficit scores, decreased cerebral infarct volume, and attenuated brain edema and neuronal damage. Meanwhile, CHIP overexpression attenuated necroptosis and inflammation induced by MCAO surgery. These findings indicated that overexpression of CHIP might exert neuroprotective effects by attenuating necroptosis and inflammation during CIR injury, and increasing CHIP levels may be a potential strategy in cerebrovascular disease therapy.

Emerging therapeutic targets for cerebral edema

INTRODUCTION

Cerebral edema is a key contributor to death and disability in several forms of brain injury. Current treatment options are limited, reactive, and associated with significant morbidity. Targeted therapies are emerging based on a growing understanding of the molecular underpinnings of cerebral edema.

AREAS COVERED

We review the pathophysiology and relationships between different cerebral edema subtypes to provide a foundation for emerging therapies. Mechanisms for promising molecular targets are discussed, with an emphasis on those advancing in clinical trials, including ion and water channels (AQP4, SUR1-TRPM4) and other proteins/lipids involved in edema signaling pathways (AVP, COX2, VEGF, and S1P). Research on novel treatment modalities for cerebral edema [including recombinant proteins and gene therapies] is presented and finally, insights on reducing secondary injury and improving clinical outcome are offered.

EXPERT OPINION

Targeted molecular strategies to minimize or prevent cerebral edema are promising. Inhibition of SUR1-TRPM4 (glyburide/glibenclamide) and VEGF (bevacizumab) are currently closest to translation based on advances in clinical trials. However, the latter, tested in glioblastoma multiforme, has not demonstrated survival benefit. Research on recombinant proteins and gene therapies for cerebral edema is in its infancy, but early results are encouraging. These newer modalities may facilitate our understanding of the pathobiology underlying cerebral edema.

Extracellular vesicles derived from M2 microglia reduce ischemic brain injury through microRNA-135a-5p/TXNIP/NLRP3 axis

Accumulating evidences have suggested that extracellular vesicles (EVs) are crucial players in the pathogenesis of ischemic brain injury. This study was designed to explore the specific functions of M2 phenotype microglia-derived EVs in ischemic brain injury progression. The expression of microRNA-135a-5p (miR-135a-5p) in M2 microglia-derived EVs was determined by reverse transcription-quantitative polymerase chain reaction (RT-qPCR), followed by the identification of expression relationship among miR-135a-5p, thioredoxin-interacting protein (TXNIP), and nod-like receptor protein 3 (NLRP3) by dual luciferase reporter gene assay. After construction of an oxygen-glucose deprivation/reperfusion (OGD/R) cell model, the effects of miR-135a-5p on the biological characteristics of HT-22 cells were assessed by cell counting kit 8 (CCK-8) assay and flow cytometry. Finally, a mouse model of transient middle cerebral artery occlusion (tMCAO) was established and cerebral infarction volume was determined by triphenyltetrazolium chloride (TTC) staining and the expression of IL-18 and IL-1β in the brain tissue was determined by enzyme-linked immunosorbent assay (ELISA). We found that M2 microglia-derived EVs had high expression of miR-135a-5p, and that miR-135a-5p in M2 microglia-derived EVs negatively regulated the expression of NLRP3 via TXNIP. Overexpression of miR-135a-5p promoted the proliferation but inhibited the apoptosis of neuronal cells, and inhibited the expression of autophagy-related proteins. M2 microglia-derived EVs delivered miR-135a-5p into neuronal cells to inhibit TXNIP expression, which further inhibited the activation of NLRP3 inflammasome, thereby reducing neuronal autophagy and ischemic brain injury. Hence, M2 microglia-derived EVs are novel therapeutic targets for ischemic brain injury treatment.

CHIP as a therapeutic target for neurological diseases

Carboxy-terminus of Hsc70-interacting protein (CHIP) functions both as a molecular co-chaperone and ubiquitin E3 ligase playing a critical role in modulating the degradation of numerous chaperone-bound proteins. To date, it has been implicated in the regulation of numerous biological functions, including misfolded-protein refolding, autophagy, immunity, and necroptosis. Moreover, the ubiquitous expression of CHIP in the central nervous system suggests that it may be implicated in a wide range of functions in neurological diseases. Several recent studies of our laboratory and other groups have highlighted the beneficial role of CHIP in the pathogenesis of several neurological diseases. The objective of this review is to discuss the possible molecular mechanisms that contribute to the pathogenesis of neurological diseases in which CHIP has a pivotal role, such as stroke, intracerebral hemorrhage, Alzheimer's disease, Parkinson's disease, and polyglutamine diseases; furthermore, CHIP mutations could also cause neurodegenerative diseases. Based on the available literature, CHIP overexpression could serve as a promising therapeutic target for several neurological diseases.

Roles of glutamate receptors in a novel in vitro model of early, comorbid cerebrovascular, and Alzheimer's diseases

Systemic multimorbidity is highly prevalent in the elderly and, remarkably, coexisting neuropathological markers of Alzheimer's (AD) and cerebrovascular (CVD) diseases are found at autopsy in most brains of patients clinically diagnosed as AD. Little is known on neurodegeneration peculiar to comorbidities, especially at early stages when pathogenesis may propagate at subclinical levels. We developed a novel in vitro model of comorbid CVD/AD in organotypic hippocampal cultures, by combining oxygen-glucose deprivation (OGD) and exposure to amyloid-Aβ oligomers (AβOs), both applied at levels subtoxic to neurons when used in isolation. We focused on synaptic proteins and the roles of glutamate receptors, which have been implicated in many basic and clinical approaches to either CVD or AD. Subtoxic insults by OGD and AβOs synergized to reduce levels of synaptophysin (SYP) and PSD-95 without cell death, while effects of antagonists of either metabotropic or ionotropic glutamate receptors were distinct from reports in models of isolated CVD or AD. In particular, modulation of glutamate receptors differentially impacted SYP and PSD-95, and antagonists of a single receptor subtype had distinct effects when either isolated or combined. Our findings highlight the complexity of CVD/AD comorbidity, help understand variable responses to glutamate receptor antagonists in patients diagnosed with AD and may contribute to future development of therapeutics based on investigation of the pattern of progressive comorbidity.

Tat-Cannabinoid Receptor Interacting Protein Reduces Ischemia-Induced Neuronal Damage and Its Possible Relationship with 14-3-3η

Cannabinoid receptor-interacting protein 1a (CRIP1a) binds to the C-terminal domain of cannabinoid 1 receptor (CB1R) and regulates CB1R activities. In this study, we made Tat-CRIP1a fusion proteins to enhance CRIP1a penetration into neurons and brain and to evaluate the function of CRIP1a in neuroprotection following oxidative stress in HT22 hippocampal cells and transient forebrain ischemia in gerbils. Purified exogenous Tat-CRIP1a was penetrated into HT22 cells in a time and concentration-dependent manner and prevented H₂O₂-induced reactive oxygen species formation, DNA fragmentation, and cell damage. Tat-CRIP1a fusion protein also ameliorated the reduction of 14-3-3η expression by H₂O₂ treatment in HT22 cells. Ischemia–reperfusion damage caused motor hyperactivity in the open field test of gerbils; however, the treatment of Tat-CRIP1a significantly reduced hyperactivity 1 day after ischemia. Four days after ischemia, the administration of Tat-CRIP1a restored the loss of pyramidal neurons and decreased reactive astrocytosis and microgliosis induced by ischemic damage in the hippocampal cornu Ammonis (CA)1 region. Ischemic damage decreased 14-3-3η expression in all hippocampal sub-regions 4 days after ischemia; however, the treatment of Tat-CRIP1 ameliorated the reduction of 14-3-3η expression. These results suggest that Tat-CRIP1a attenuates neuronal damage and hyperactivity induced by ischemic damage, and it restores normal expression levels of 14-3-3η protein in the hippocampus.

The Role of Ubiquitin-Proteasome Pathway and Autophagy-Lysosome Pathway in Cerebral Ischemia

The ubiquitin-proteasome pathway and autophagy-lysosome pathway are two major routes for clearance of aberrant cellular components to maintain protein homeostasis and normal cellular functions. Accumulating evidence shows that these two pathways are impaired during cerebral ischemia, which contributes to ischemic-induced neuronal necrosis and apoptosis. This review aims to critically discuss current knowledge and controversies on these two pathways in response to cerebral ischemic stress. We also discuss molecular mechanisms underlying the impairments of these protein degradation pathways and how such impairments lead to neuronal damage after cerebral ischemia. Further, we review the recent advance on the understanding of the involvement of these two pathways in the pathological process during many therapeutic approaches against cerebral ischemia. Despite recent advances, the exact role and molecular mechanisms of these two pathways following cerebral ischemia are complex and not completely understood, of which better understanding will provide avenues to develop novel therapeutic strategies for ischemic stroke.

Changes in protein function underlie the disease spectrum in patients with CHIP mutations

Monogenetic disorders that cause cerebellar ataxia are characterized by defects in gait and atrophy of the cerebellum; however, patients often suffer from a spectrum of disease, complicating treatment options. Spinocerebellar ataxia autosomal recessive 16 (SCAR16) is caused by coding mutations in STUB1, a gene that encodes the multifunctional enzyme CHIP (C terminus of HSC70-interacting protein). The disease spectrum of SCAR16 includes a varying age of disease onset, cognitive dysfunction, increased tendon reflex, and hypogonadism. Although SCAR16 mutations span the multiple functional domains of CHIP, it is unclear whether the location of the mutation and the change in the biochemical properties of CHIP contributes to the clinical spectrum of SCAR16. In this study, we examined relationships between the clinical phenotypes of SCAR16 patients and the changes in biophysical, biochemical, and functional properties of the corresponding mutated protein. We found that the severity of ataxia did not correlate with age of onset; however, cognitive dysfunction, increased tendon reflex, and ancestry were able to predict 54% of the variation in ataxia severity. We further identified domain-specific relationships between biochemical changes in CHIP and clinical phenotypes and specific biochemical activities that associate selectively with either increased tendon reflex or cognitive dysfunction, suggesting that specific changes to CHIP-HSC70 dynamics contribute to the clinical spectrum of SCAR16. Finally, linear models of SCAR16 as a function of the biochemical properties of CHIP support the concept that further inhibiting mutant CHIP activity lessens disease severity and may be useful in the design of patient-specific targeted approaches to treat SCAR16.

Novel adeno‑associated virus‑based genetic vaccines encoding hepatitis C virus E2 glycoprotein elicit humoral immune responses in mice

Hepatitis C virus (HCV) infection remains a major public health issue despite the introduction of several direct-acting antiviral agents (DAAs), with some 185 million individuals infected with HCV worldwide. There is an urgent need for an effective prophylactic HCV vaccine. In the present study, we constructed genetic vaccines based on novel recombinant adeno-associated viral (rAAV) vectors (AAV2/8 or AAV2/rh32.33) that express the envelope glycoprotein E2 from the HCV genotype 1b. Expression of HCV E2 protein in 293 cells was confirmed by western blot analysis. rAAV2/8.HCV E2 vaccine or rAAV2/rh32.33.HCV E2 vaccine was intramuscularly injected into C57BL/6 mice. HCV E2-specific antigen was produced, and long-lasting specific antibody responses remained detectable XVI weeks following immunization. In addition, the rAAV2/rh32.33 vaccine induced higher antigen-specific antibody levels than the rAAV2/8 vaccine or AAV plasmid. Moreover, both AAV vaccines induced neutralizing antibodies against HCV genotypes 1a and 1b. Finally, it is worth mentioning that neutralizing antibody levels directed against AAV2/rh32.33 were lower than those against AAV2/8 in both mouse and human serum. These results demonstrate that AAV vectors, especially the AAVrh32.33, have particularly favorable immunogenicity for development into an effective HCV vaccine.

Anisomycin prevents OGD-induced necroptosis by regulating the E3 ligase CHIP

Necroptosis is an essential pathophysiological process in cerebral ischemia-related diseases. Therefore, targeting necroptosis may prevent cell death and provide a much-needed therapy. Ansiomycin is an inhibitor of protein synthesis which can also activate c-Jun N-terminal kinases. The present study demonstrated that anisomycin attenuated necroptosis by upregulating CHIP (carboxyl terminus of Hsc70-interacting protein) leading to the reduced levels of receptor-interacting protein kinase 1 (RIPK1) and receptor-interacting protein kinase 3 (RIPK3) proteins in two in vitro models of cerebral ischemia. Further exploration in this research revealed that losing neither the co-chaperone nor the ubiquitin E3 ligase function of CHIP could abolish its ability to reduce necroptosis. Collectively, this study identifies a novel means of preventing necroptosis in two in vitro models of cerebral ischemia injury through activating the expression of CHIP, and it may provide a potential target for the further study of the disease.

Angiotensin 1-7 Overexpression Mediated by a Capsid-optimized AAV8 Vector Leads to Significant Growth Inhibition of Hepatocellular Carcinoma In vivo

Background: Angiotensin-(1-7) [Ang-(1-7)] has been identified to inhibit the growth of many types of tumor cells both in vitro and in vivo. However, the rapid degradation of Ang-(1-7) in vivo limits its clinical application. Adeno-associated virus (AAV) serotype-8 is a remarkable vector for long-term in vivo gene delivery. Method: This study was designed to investigate the effects of AAV-mediated Ang-(1-7) overexpression on hepatocellular carcinoma. We first generated three different tyrosine (Y) to phenylalanine (F) mutants of AAV8 (Y447F, Y703F, Y708F) and evaluated their in vivo transduction efficiencies. Results: The data indicated that the Y703F mutant elicited a significant enhancement of liver gene delivery when compared with wild-type AAV8 (wtAAV8). The anti-tumor effect of Ang-(1-7) mediated by this optimized vector was evaluated in H22 hepatoma-bearing mice. Our results demonstrated that AAV-Ang-(1-7) persistently inhibited the growth of hepatocellular carcinoma by significantly downregulating angiogenesis. This was confirmed by observed decreases in the levels of the proangiogenic factors VEGF and PIGF. Conclusion: Collectively, these data suggest that Ang-(1-7) overexpression mediated by the optimized vector may be an effective alternative for hepatocellular carcinoma therapy due to its long-term and significant anti-tumor activity.