Neuron-specific SUMO knockdown suppresses global gene expression response and worsens functional outcome after transient forebrain ischemia in mice

Dysregulation of protein SUMOylation networks in Huntington's disease R6/2 mouse striatum

Huntington's disease is a neurodegenerative disorder caused by an expanded CAG repeat mutation in the Huntingtin (HTT) gene. The mutation impacts neuronal protein homeostasis and cortical/striatal circuitry. SUMOylation is a post-translational modification with broad cellular effects including via modification of synaptic proteins. Here, we used an optimized SUMO protein-enrichment and mass spectrometry method to identify the protein SUMOylation/SUMO interaction proteome in the context of Huntington's disease using R6/2 transgenic and non-transgenic mice. Significant changes in the enrichment of SUMOylated and SUMO-interacting proteins were observed, including those involved in presynaptic function, cytomatrix at the active zone, cytoskeleton organization and glutamatergic signalling. Mitochondrial and RNA-binding proteins also showed altered enrichment. Modified SUMO-associated pathways in Huntington's disease tissue include clathrin-mediated endocytosis signalling, synaptogenesis signalling, synaptic long-term potentiation and SNARE signalling. To evaluate how modulation of SUMOylation might influence functional measures of neuronal activity in Huntington's disease cells in vitro, we used primary neuronal cultures from R6/2 and non-transgenic mice. A receptor internalization assay for the metabotropic glutamate receptor 7 (mGLUR7), a SUMO-enriched protein in the mass spectrometry, showed decreased internalization in R6/2 neurons compared to non-transgenic neurons. SiRNA-mediated knockdown of the E3 SUMO ligase protein inhibitor of activated STAT1 (Pias1), which can SUMO modify mGLUR7, reduced this Huntington's disease phenotype. In addition, microelectrode array analysis of primary neuronal cultures indicated early hyperactivity in Huntington's disease cells, while later time points demonstrated deficits in several measurements of neuronal activity within cortical neurons. Huntington's disease phenotypes were rescued at selected time points following knockdown of Pias1. Collectively, our results provide a mouse brain SUMOome resource and show that significant alterations occur within the post-translational landscape of SUMO-protein interactions of synaptic proteins in Huntington's disease mice, suggesting that targeting of synaptic SUMO networks may provide a proteostatic systems-based therapeutic approach for Huntington's disease and other neurological disorders.

TXNIP/NLRP3 aggravates global cerebral ischemia-reperfusion injury-induced cognitive decline in mice

Global cerebral ischemia/reperfusion (GCI/R) injury poses a risk for cognitive decline, with neuroinflammation considered pivotal in this process. This study aimed to unravel the molecular mechanisms underlying GCI/R injury and propose a potential therapeutic strategy for associated cognitive deficits. Utilizing bioinformatics analysis of a public microarray profile (GSE30655 and GSE80681) in cerebral ischemic mice, it was observed that neuroinflammation emerged as a significant gene ontology item, with an increase in the expression of thioredoxin-interacting protein (TXNIP) and NLRP3 genes. Experimental models involving bilateral occlusion of the common carotid arteries in mice revealed that GCI/R induced cognitive impairment, along with a time-dependent increase in TXNIP and NLRP3 levels. Notably, TXNIP knockdown alleviated cognitive dysfunction in mice. Furthermore, the introduction of adeno-associated virus injection with TXNIP knockdown reduced the number of activated microglia, apoptosis neurons, and levels of oxidative stress and inflammatory cytokines in the hippocampus. Collectively, these findings underscore the significance of TXNIP/NLRP3 in the hippocampus in exacerbating cognitive decline due to GCI/R injury, suggesting that TXNIP knockdown holds promise as a therapeutic strategy.

Integrative Analysis of Machine Learning and Molecule Docking Simulations for Ischemic Stroke Diagnosis and Therapy

Due to the narrow therapeutic window and high mortality of ischemic stroke, it is of great significance to investigate its diagnosis and therapy. We employed weighted gene coexpression network analysis (WGCNA) to ascertain gene modules related to stroke and used the maSigPro R package to seek the time-dependent genes in the progression of stroke. Three machine learning algorithms were further employed to identify the feature genes of stroke. A nomogram model was built and applied to evaluate the stroke patients. We analyzed single-cell RNA sequencing (scRNA-seq) data to discern microglia subclusters in ischemic stroke. The RNA velocity, pseudo time, and gene set enrichment analysis (GSEA) were performed to investigate the relationship of microglia subclusters. Connectivity map (CMap) analysis and molecule docking were used to screen a therapeutic agent for stroke. A nomogram model based on the feature genes showed a clinical net benefit and enabled an accurate evaluation of stroke patients. The RNA velocity and pseudo time analysis showed that microglia subcluster 0 would develop toward subcluster 2 within 24 h from stroke onset. The GSEA showed that the function of microglia subcluster 0 was opposite to that of subcluster 2. AZ_628, which screened from CMap analysis, was found to have lower binding energy with Mmp12, Lgals3, Fam20c, Capg, Pkm2, Sdc4, and Itga5 in microglia subcluster 2 and maybe a therapeutic agent for the poor development of microglia subcluster 2 after stroke. Our study presents a nomogram model for stroke diagnosis and provides a potential molecule agent for stroke therapy.

SUMOtherapeutics for Ischemic Stroke

The small, ubiquitin-like modifier (SUMO) is a post-translational modifier with a profound influence on several key biological processes, including the mammalian stress response. Of particular interest are its neuroprotective effects, first recognized in the 13-lined ground squirrel (Ictidomys tridecemlineatus), in the context of hibernation torpor. Although the full scope of the SUMO pathway is yet to be elucidated, observations of its importance in managing neuronal responses to ischemia, maintaining ion gradients, and the preconditioning of neural stem cells make it a promising therapeutic target for acute cerebral ischemia. Recent advances in high-throughput screening have enabled the identification of small molecules that can upregulate SUMOylation, some of which have been validated in pertinent preclinical models of cerebral ischemia. Accordingly, the present review aims to summarize current knowledge and highlight the translational potential of the SUMOylation pathway in brain ischemia.

Gene expression profiles and bioinformatics analysis in lung samples from ovalbumin-induced asthmatic mice

BACKGROUND

Asthma is characterized by chronic inflammation and airway remodeling. However, limited study is conducted on the gene expression profiles of ovalbumin (OVA) induced asthma in mice. Here, we explored the gene expression profiles in lung tissues from mice with OVA-induced asthma using microarray and bioinformatics analysis.

METHODS

For establishment of OVA-induced asthma model, mice first received intraperitoneal sensitization with OVA on day 0, 7 and 14, followed by atomizing inhalation of OVA 3 times a week for 8 weeks. The lung tissues were collected and subjected to microarray analysis, bioinformatics analysis and expression validation.

RESULTS

Microarray data of lung tissues suggested that 3754 lncRNAs and 2976 mRNAs were differentially expressed in lung tissues between control and asthmatic mice, including 1647 up-regulated and 2106 down-regulated lncRNAs, and 1201 up-regulated and 1766 down-regulated mRNAs. GO analysis displayed that the up-regulated genes were enriched in inflammatory response, leukocyte migration involved in inflammatory response, and Notch signaling pathway. KEGG pathway analysis indicated that the enriched pathway terms of the up-regulated gene included Toll-like receptor signaling pathway and Th17 cell differentiation signaling pathway. Additionally, based on the previously published literatures on asthma and inflammation, we screened out down-regulated genes, such as Smg7, Sumo2, and Stat5a, and up-regulated genes, such as Myl9, Fos and Tlr4. According to the mRNA-lncRNA co-expression network, we selected lncRNAs associated with above genes, including the down-regulated lncRNAs of NONMMUT032848, NONMMUT008873, NONMMUT009478, and NONMMUT006807, and the up-regulated lncRNAs of NONMMUT052633, NONMMUT05340 and NONMMUT042325. The expression changes of the above genes were validated in lung tissues by real-time quantitaive PCR and Western blot.

CONCLUSIONS

Overall, we performed gene microarray on lung samples from OVA-induced asthmatic mice and summarized core mRNAs and their related lncRNAs. This study may provide evidence for further research on the therapeutic targets of asthma.

The role of SUMOylation in the neurovascular dysfunction after acquired brain injury

Acquired brain injury (ABI) is the most common disease of the nervous system, involving complex pathological processes, which often leads to a series of nervous system disorders. The structural destruction and dysfunction of the Neurovascular Unit (NVU) are prominent features of ABI. Therefore, understanding the molecular mechanism underlying NVU destruction and its reconstruction is the key to the treatment of ABI. SUMOylation is a protein post-translational modification (PTM), which can degrade and stabilize the substrate dynamically, thus playing an important role in regulating protein expression and biological signal transduction. Understanding the regulatory mechanism of SUMOylation can clarify the molecular mechanism of the occurrence and development of neurovascular dysfunction after ABI and is expected to provide a theoretical basis for the development of potential treatment strategies. This article reviews the role of SUMOylation in vascular events related to ABI, including NVU dysfunction and vascular remodeling, and puts forward therapeutic prospects.

Stress - Regulation of SUMO conjugation and of other Ubiquitin-Like Modifiers

Stress is unavoidable and essential to cellular and organismal evolution and failure to adapt or restore homeostasis can lead to severe diseases or even death. At the cellular level, stress drives a plethora of molecular changes, of which variations in the profile of protein post-translational modifications plays a key role in mediating the adaptative response of the genome and proteome to stress. In this context, post-translational modification of proteins by ubiquitin-like modifiers, (Ubl), notably SUMO, is an essential stress response mechanism. In this review, aiming to draw universal concepts of the Ubls stress response, we will decipher how stress alters the expression level, activity, specificity and/or localization of the proteins involved in the conjugation pathways of the various type-I Ubls, and how this result in the modification of particular Ubl targets that will translate an adaptive physiological stress response and allow cells to restore homeostasis.

RNA editing of ion channels and receptors in physiology and neurological disorders

Adenosine-to-inosine (A-to-I) RNA editing is a post-transcriptional modification that diversifies protein functions by recoding RNA or alters protein quantity by regulating mRNA level. A-to-I editing is catalyzed by adenosine deaminases that act on RNA. Millions of editing sites have been reported, but they are mostly found in non-coding sequences. However, there are also several recoding editing sites in transcripts coding for ion channels or transporters that have been shown to play important roles in physiology and changes in editing level are associated with neurological diseases. These editing sites are not only found to be evolutionary conserved across species, but they are also dynamically regulated spatially, developmentally and by environmental factors. In this review, we discuss the current knowledge of A-to-I RNA editing of ion channels and receptors in the context of their roles in physiology and pathological disease. We also discuss the regulation of editing events and site-directed RNA editing approaches for functional study that offer a therapeutic pathway for clinical applications.

ZFP36 protects against oxygen-glucose deprivation/reoxygenation-induced mitochondrial fragmentation and neuronal apoptosis through inhibiting NOX4-DRP1 pathway

The imbalance of mitochondrial dynamics plays an important role in the pathogenesis of cerebral ischemia/reperfusion (I/R) injury. Zinc-finger protein 36 (ZFP36) has been documented to have neuroprotective effects, however, whether ZFP36 is involved in the regulation of neuronal survival during cerebral I/R injury remains unknown. In this study, we found that the transcriptional and translational levels of ZFP36 were increased in immortalized hippocampal HT22 neuronal cells after oxygen-glucose deprivation/reoxygenation (OGD/R) treatment. ZFP36 gene silencing exacerbated OGD/R-induced dynamin-related protein 1 (DRP1) activity, mitochondrial fragmentation, oxidative stress and neuronal apoptosis, whereas ZFP36 overexpression exhibited the opposite effects. Besides, we found that NADPH oxidase 4 (NOX4) was upregulated by OGD/R, and NOX4 inhibition remarkably attenuated OGD/R-instigated DRP1 activity, mitochondrial fragmentation and neuronal apoptosis. Further study demonstrated that ZFP36 targeted NOX4 mRNA directly by binding to the AU-rich elements (AREs) in the NOX4 3'-untranslated regions (3'-UTR) and inhibited NOX4 expression. Taken together, our data indicate that ZFP36 protects against OGD/R-induced neuronal injury by inhibiting NOX4-mediated DRP1 activation and excessive mitochondrial fission. Pharmacological targeting of ZFP36 to suppress excessive mitochondrial fission may provide new therapeutic strategies in the treatment of cerebral I/R injury.

The Function of SUMOylation and Its Critical Roles in Cardiovascular Diseases and Potential Clinical Implications

Cardiovascular disease (CVD) is a common disease caused by many factors, including atherosclerosis, congenital heart disease, heart failure, and ischemic cardiomyopathy. CVD has been regarded as one of the most common diseases and has a severe impact on the life quality of patients. The main features of CVD include high morbidity and mortality, which seriously threaten human health. SUMO proteins covalently conjugate lysine residues with a large number of substrate proteins, and SUMOylation regulates the function of target proteins and participates in cellular activities. Under certain pathological conditions, SUMOylation of proteins related to cardiovascular development and function are greatly changed. Numerous studies have suggested that SUMOylation of substrates plays critical roles in normal cardiovascular development and function. We reviewed the research progress of SUMOylation in cardiovascular development and function, and the regulation of protein SUMOylation may be applied as a potential therapeutic strategy for CVD treatment.

SUMO1 Deficiency Exacerbates Neurological and Cardiac Dysfunction after Intracerebral Hemorrhage in Aged Mice

Small ubiquitin-like modifier 1 (SUMO1) reduces cardiac hypertrophy and induces neuroprotective effects. Previous studies have found that intracerebral hemorrhage (ICH) provokes cardiac deficit in the absence of primary cardiac diseases in mice. In this study, we tested the hypothesis that SUMO1 deficiency leads to worse brain and heart dysfunction after ICH and SUMO1 plays a key role in regulating brain-heart interaction after ICH in aged mice. Aged (18-20 months) female SUMO1 null (SUMO1-/-) mice and wild-type (WT) C57BL/6 J mice were randomly divided into four groups (n = 8/group): (1) WT-sham group, (2) SUMO1-/--sham group, (3) WT-ICH group, and (4) SUMO1-/--ICH group. Cardiac function was measured by echocardiography. Neurological and cognitive functional tests were performed. Mice were sacrificed at 10 days after ICH for histological and immunohistochemically staining. Compared with WT-sham mice, WT-ICH mice exhibited (1) significantly (P < 0.05) decreased SUMO1 expression in heart tissue, (2) evident neurological and cognitive dysfunction as well as brain white matter deficits, (3) significantly increased cardiac dysfunction, and (4) inflammatory factor expression in the heart and brain. Compared with WT-ICH mice, SUMO1-/--ICH mice exhibited significantly increased: (1) brain hemorrhage volume, worse neurological and cognitive deficits, and increased white matter deficits; (2) cardiac dysfunction and cardiac fibrosis; (3) inflammatory response both in heart and brain tissue. Aged SUMO1-deficient female mice subjected to ICH not only exhibit increased neurological and cognitive functional deficit but also significantly increased cardiac dysfunction and inflammatory cell infiltration into the heart and brain. These data suggest that SUMO1 plays an important role in brain-heart interaction.

Small ubiquitin-like modifier 2 (SUMO2) is critical for memory processes in mice

Small ubiquitin-like modifier (SUMO1-3) conjugation (SUMOylation), a posttranslational modification, modulates almost all major cellular processes. Mounting evidence indicates that SUMOylation plays a crucial role in maintaining and regulating neural function, and importantly its dysfunction is implicated in cognitive impairment in humans. We have previously shown that simultaneously silencing SUMO1-3 expression in neurons negatively affects cognitive function. However, the roles of the individual SUMOs in modulating cognition and the mechanisms that link SUMOylation to cognitive processes remain unknown. To address these questions, in this study, we have focused on SUMO2 and generated a new conditional Sumo2 knockout mouse line. We found that conditional deletion of Sumo2 predominantly in forebrain neurons resulted in marked impairments in various cognitive tests, including episodic and fear memory. Our data further suggest that these abnormalities are attributable neither to constitutive changes in gene expression nor to alterations in neuronal morphology, but they involve impairment in dynamic SUMOylation processes associated with synaptic plasticity. Finally, we provide evidence that dysfunction on hippocampal-based cognitive tasks was associated with a significant deficit in the maintenance of hippocampal long-term potentiation in Sumo2 knockout mice. Collectively, these data demonstrate that protein conjugation by SUMO2 is critically involved in cognitive processes.

Guanosine modulates SUMO2/3-ylation in neurons and astrocytes via adenosine receptors

SUMOylation is a post-translational modification (PTM) whereby members of the Small Ubiquitin-like MOdifier (SUMO) family of proteins are conjugated to lysine residues in target proteins. SUMOylation has been implicated in a wide range of physiological and pathological processes, and much attention has been given to its role in neurodegenerative conditions. Due to its reported role in neuroprotection, pharmacological modulation of SUMOylation represents an attractive potential therapeutic strategy in a number of different brain disorders. However, very few compounds that target the SUMOylation pathway have been identified. Guanosine is an endogenous nucleoside with important neuromodulatory and neuroprotective effects. Experimental evidence has shown that guanosine can modulate different intracellular pathways, including PTMs. In the present study we examined whether guanosine alters global protein SUMOylation. Primary cortical neurons and astrocytes were treated with guanosine at 1, 10, 100, 300, or 500 μM at four time points, 1, 6, 24, or 48 h. We show that guanosine increases global SUMO2/3-ylation in neurons and astrocytes at 1 h at concentrations above 10 μM. The molecular mechanisms involved in this effect were evaluated in neurons. The guanosine-induced increase in global SUMO2/3-ylation was still observed in the presence of dipyridamole, which prevents guanosine internalization, demonstrating an extracellular guanosine-induced effect. Furthermore, the A1 adenosine receptor antagonist DPCPX abolished the guanosine-induced increase in SUMO2/3-ylation. The A2A adenosine receptor antagonist ZM241385 increased SUMOylation per se, but did not alter guanosine-induced SUMOylation, suggesting that guanosine may modulate SUMO2/3-ylation through an A1-A2A receptor interaction. Taken together, this is the first report to show guanosine as a SUMO2/3-ylation enhancer in astrocytes and neurons.

Role of pericyte-derived SENP1 in neuronal injury after brain ischemia

Aims

SUMOylation is a posttranslational modification related to multiple human diseases. SUMOylation can be reversed by classes of proteases known as the sentrin/SUMO‐specific proteases (SENPs). In the present study, we investigate the potential role of SENP1 in pericytes in the brain ischemia.

Methods

Pericyte‐specific deletion of senp1 mice (Cspg4‐Cre; senp1^f/f) were used for brain function and neuronal damage evaluation following brain ischemia. The cerebral blood vessels of diameter, velocity, and flux were performed in living mice by two‐photon laser scanning microscopy (TPLSM). Biochemical analysis and immunohistochemistry methods were used to address the role and mechanism of pericyte‐specific SENP1 in the pathological process of brain ischemia. A coculture model of HBVPs and HBMECs mimicked the BBB in vitro and was used to evaluate BBB integrity after glucose deprivation.

Results

Our results showed that senp1‐specific deletion in pericytes did not affect the motor function and cognitive function of mice. However, the pericyte‐specific deletion of senp1 aggravated the infarct size and motor deficit following focal brain ischemia. Consistently, the TPLSM data demonstrated that SENP1 deletion in pericytes accelerated thrombosis formation in brain microvessels. We also found that pericyte‐specific deletion of senp1 exaggerated the neuronal damage significantly following brain ischemia in mice. Moreover, SENP1 knockdown in pericytes could activate the apoptosis signaling and disrupt the barrier integrity in vitro coculture model.

Conclusions

Our findings revealed that targeting SENP1 in pericytes may represent a novel therapeutic strategy for neurovascular protection in stroke.

Resilience to Injury: A New Approach to Neuroprotection?

Despite thousands of neuroprotectants demonstrating promise in preclinical trials, a neuroprotective therapeutic has yet to be approved for the treatment of acute brain injuries such as stroke or traumatic brain injury. Developing a more detailed understanding of models and populations demonstrating "neurological resilience" in spite of brain injury can give us important insights into new translational therapies. Resilience is the process of active adaptation to a stressor. In the context of neuroprotection, models of preconditioning and unique animal models of extreme physiology (such as hibernating species) reliably demonstrate resilience in the laboratory setting. In the clinical setting, resilience is observed in young patients and can be found in those with specific genetic polymorphisms. These important examples of resilience can help transform and extend the current neuroprotective framework from simply countering the injurious cascade into one that anticipates, monitors, and optimizes patients' physiological responses from the time of injury throughout the process of recovery. This review summarizes the underpinnings of key adaptations common to models of resilience and how this understanding can be applied to new neuroprotective approaches.

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.

SUMO conjugation as regulator of the glucocorticoid receptor-FKBP51 cellular response to stress

In order to adequately respond to stressful stimuli, glucocorticoids (GCs) target almost every tissue of the body. By exerting a negative feedback loop in the hypothalamic-pituitary-adrenal (HPA) axis GCs inhibit their own synthesis and restore homeostasis. GCs actions are mostly mediated by the GC receptor (GR), a member of the nuclear receptor superfamily. Alterations of the GR activity have been associatedto different diseases including mood disorders and can lead to severe complication. Therefore, understanding the molecular complexity of GR modulation is mandatory for the development of new and effective drugs for treating GR-associated disorders. FKBP51 is a GR chaperone that has gained much attention because it is a strong inhibitor of GR activity and has a crucial role in psychiatric diseases. Both GR and FKBP51 activity are regulated by SUMOylation, a posttranslational (PTM). In this review, we focus on the impact of SUMO-conjugation as a regulator of this pathway.

SUMO-modified bone marrow mesenchymal stem cells promoted the repair of articular cartilage in rats

Articular cartilage damage can lead to joint deformity, pain, and severe dysfunction. However, due to the lack of blood vessels and nerves in articular cartilage, the self-healing capacity of damaged cartilage is limited. In this study, we overexpressed small ubiquitin-like modifier (SUMO)1, SUMO2/3, and SUMO1/2/3 in bone marrow mesenchymal stem cells (BMSCs). Then, these cells were inoculated on surfaces of different hardness, and their differentiation into chondrocytes, hypoxic tolerance ability, and inflammatory response was detected. Finally, BMSCs were transplanted into the injured knee joint cavity of the rats, and the repair was evaluated. We found that BMSCs overexpressing SUMO1 were more likely to differentiate into articular cartilage along with the hardness of the surface, while BMSCs overexpressing SUMO2/3 could reduce inflammation response and improve the damaged cartilage microenvironment. In the rat model, BMSCs overexpressing SUMO1/2/3 transplanted on injured articular cartilage surface showed better survival, less inflammatory response, and improved tissue repair capability. In conclusion, BMSCs overexpressing SUMO are more tolerant to hypoxia conditions, and have stronger repair ability for damaged chondrocytes in vitro and for articular cartilage injury model in rats, and are excellent seed cells for repairing articular cartilage.

SUMOylation in Neurodegenerative Diseases

Posttranslational modifications are ubiquitous regulators of cellular processes. The regulatory role of SUMOylation, the attachment of a small ubiquitin-related modifier to a target protein, has been implicated in fundamental processes like cell division, DNA damage repair, mitochondrial homeostasis, and stress responses. Recently, it is gaining more attention in drug discovery as well. As life expectancy keeps rising, more individuals are at risk for developing age-associated diseases. This not only makes a person's life uncomfortable, but it also places an economic burden on society. Therefore, finding treatments for age-related diseases is an important issue. Understanding the basic mechanisms in the cell under normal and disease conditions is fundamental for drug discovery. There is an increasing number of reports showing that the ageing process could be influenced by SUMOylation. Similarly, SUMOylation is essential for proper neuronal function. In this review we summarize the latest results regarding the connection between SUMOylation and neurodegenerative diseases. We highlight the significance of specific SUMO target proteins and the importance of SUMO isoform specificity.

Impaired capacity to restore proteostasis in the aged brain after ischemia: Implications for translational brain ischemia research

Brain ischemia induced by cardiac arrest or ischemic stroke is a severe form of metabolic stress that substantially disrupts cellular homeostasis, especially protein homeostasis (proteostasis). As proteostasis is fundamental for cellular and organismal health, cells have developed a complex network to restore proteostasis impaired by stress. Many components of this network - including ubiquitination, small ubiquitin-like modifier (SUMO) conjugation, autophagy, and the unfolded protein response (UPR) - are activated in the post-ischemic brain, and play a crucial role in cell survival and recovery of neurologic function. Importantly, recent studies have shown that ischemia-induced activation of these proteostasis-related pathways in the aged brain is impaired, indicating an aging-related decline in the self-healing capacity of the brain. This impaired capacity is a significant factor for consideration in the field of brain ischemia because the vast majority of cardiac arrest and stroke patients are elderly. In this review, we focus on the effects of aging on these critical proteostasis-related pathways in the brain, and discuss their implications in translational brain ischemia research.

Aging Is Associated With Impaired Activation of Protein Homeostasis-Related Pathways After Cardiac Arrest in Mice

Background The mechanisms underlying worse outcome at advanced age after cardiac arrest ( CA ) and resuscitation are not well understood. Because protein homeostasis (proteostasis) is essential for cellular and organismal health, but is impaired after CA , we investigated the effects of age on proteostasis-related prosurvival pathways activated after CA . Methods and Results Young (2-3 months old) and aged (21-22 months old) male C57Bl/6 mice were subjected to CA and cardiopulmonary resuscitation ( CPR ). Functional outcome and organ damage were evaluated by assessing neurologic deficits, histological features, and creatinine level. CA / CPR -related changes in small ubiquitin-like modifier conjugation, ubiquitination, and the unfolded protein response were analyzed by measuring mRNA and protein levels in the brain, kidney, and spinal cord. Thiamet-G was used to increase O-linked β-N-acetylglucosamine modification. After CA / CPR , aged mice had trended lower survival rates, more severe tissue damage in the brain and kidney, and poorer recovery of neurologic function compared with young mice. Furthermore, small ubiquitin-like modifier conjugation, ubiquitination, unfolded protein response, and O-linked β-N-acetylglucosamine modification were activated after CA / CPR in young mice, but their activation was impaired in aged mice. Finally, pharmacologically increasing O-linked β-N-acetylglucosamine modification after CA improved outcome. Conclusions Results suggest that impaired activation of prosurvival pathways contributes to worse outcome after CA / CPR in aged mice because restoration of proteostasis is critical to the survival of cells stressed by ischemia. Therefore, a pharmacologic intervention that targets aging-related impairment of proteostasis-related pathways after CA / CPR may represent a promising therapeutic strategy.

Control of SUMO and Ubiquitin by ROS: Signaling and disease implications

Reversible post-translational modifications (PTMs) ensure rapid signal transmission from sensors to effectors. Reversible modification of proteins by the small proteins Ubiquitin and SUMO are involved in virtually all cellular processes and can modify thousands of proteins. Ubiquitination or SUMOylation is the reversible attachment of these modifiers to lysine residues of a target via isopeptide bond formation. These modifications require ATP and an enzymatic cascade composed of three classes of proteins: E1 activating enzymes, E2 conjugating enzymes and E3 ligases. The reversibility of the modification is ensured by specific isopeptidases. E1 and E2 enzymes, some E3 ligases and most isopeptidases have catalytic cysteine residues, which make them potentially susceptible for oxidation. Indeed, an increasing number of examples reveal regulation of ubiquitination and SUMOylation by reactive oxygen species, both in the context of redox signaling and in severe oxidative stress. Importantly, ubiquitination and SUMOylation play essential roles in the regulation of ROS homeostasis, participating in the control of ROS production and clearance. In this review, we will discuss the interplay between ROS homeostasis, Ubiquitin and SUMO pathways and the implications for the oxidative stress response and cell signaling.

Ubc9 overexpression and SUMO1 deficiency blunt inflammation after intestinal ischemia/reperfusion

The intestinal epithelium constitutes a crucial defense to the potentially life-threatening effects of gut microbiota. However, due to a complex underlying vasculature, hypoperfusion and resultant tissue ischemia pose a particular risk to function and integrity of the epithelium. The small ubiquitin-like modifier (SUMO) conjugation pathway critically regulates adaptive responses to metabolic stress and is of particular significance in the gut, as inducible knockout of the SUMO-conjugating enzyme Ubc9 results in rapid intestinal epithelial disintegration. Here we analyzed the pattern of individual SUMO isoforms in intestinal epithelium and investigated their roles in intestinal ischemia/reperfusion (I/R) damage. Immunostaining revealed that epithelial SUMO2/3 expression was almost exclusively limited to crypt epithelial nuclei in unchallenged mice. However, intestinal I/R or overexpression of Ubc9 caused a remarkable enhancement of epithelial SUMO2/3 staining along the crypt-villus axis. Unexpectedly, a similar pattern was found in SUMO1 knockout mice. Ubc9 transgenic mice, but also SUMO1 knockout mice were protected from I/R injury as evidenced by better preserved barrier function and blunted inflammatory responses. PCR array analysis of microdissected villus-tip epithelia revealed a specific epithelial contribution to reduced inflammatory responses in Ubc9 transgenic mice, as key chemotactic signaling molecules such as IL17A were significantly downregulated. Together, our data indicate a critical role particularly of the SUMO2/3 isoforms in modulating responses to I/R and provide the first evidence that SUMO1 deletion activates a compensatory process that protects from ischemic damage.

Quantitative high-throughput screening identifies cytoprotective molecules that enhance SUMO conjugation via the inhibition of SUMO-specific protease (SENP)2

The development of novel neuroprotective treatments for acute stroke has been fraught with failures, which supports the view of ischemic brain damage as a highly complex multifactorial process. Post-translational modifications such as small ubiquitin-like modifier (SUMO)ylation have emerged as critical molecular regulatory mechanisms in states of both homeostasis and ischemic stress, as evidenced by our previous work. Accordingly, the clinical significance of the selective control of the global SUMOylation process has become apparent in studies of ischemic pathobiology and pathophysiology. Herein, we describe a process capable of identifying and characterizing small molecules with the potential of targeting the SUMO system through inhibition of SUMO deconjugation in an effort to develop novel stroke therapies.-Bernstock, J. D., Ye, D., Smith, J. A., Lee, Y.-J., Gessler, F. A., Yasgar, A., Kouznetsova, J., Jadhav, A., Wang, Z., Pluchino, S., Zheng, W., Simeonov, A., Hallenbeck, J. M., Yang, W. Quantitative high-throughput screening identifies cytoprotective molecules that enhance SUMO-conjugation via the inhibition of SUMO-specific protease (SENP)2.

Cerebral Ischemia Increases Small Ubiquitin-Like Modifier Conjugation within Human Penumbral Tissue: Radiological-Pathological Correlation

Posttranslational modification by small ubiquitin-like modifier (SUMO) regulates myriad physiological processes within cells and has been demonstrated to be highly activated in murine brains after cerebral ischemia. Numerous in vitro and murine in vivo studies have demonstrated that this increased SUMO conjugation is an endogenous neuroprotective stress response that has potential in being leveraged to develop novel therapies for ischemic stroke. However, SUMO activation has not yet been studied in poststroke human brains, presenting a clear limitation in translating experimental successes in murine models to human patients. Accordingly, here, we present a case wherein the brain tissue of a stroke patient (procured shortly after death) was processed by multiplex immunohistochemistry to investigate SUMO activation.

SUMOylation in brain ischemia: Patterns, targets, and translational implications

Post-translational protein modification by small ubiquitin-like modifier (SUMO) regulates a myriad of homeostatic and stress responses. The SUMOylation pathway has been extensively studied in brain ischemia. Convincing evidence is now at hand to support the notion that a major increase in levels of SUMOylated proteins is capable of inducing tolerance to ischemic stress. Therefore, the SUMOylation pathway has emerged as a promising therapeutic target for neuroprotection in the face of brain ischemia. Despite this, it is prudent to acknowledge that there are many key questions still to be addressed in brain ischemia related to SUMOylation. Accordingly, herein, we provide a critical review of literature within the field to summarize current knowledge and in so doing highlight pertinent translational implications of the SUMOylation pathway in brain ischemia.

Chromatin SUMOylation in heat stress: To protect, pause and organise?: SUMO stress response on chromatin

Post-translational modifications, e.g. SUMO modifications (SUMOylation), provide a mechanism for swiftly changing a protein's activity. Various stress conditions trigger a SUMO stress response (SSR) - a stress-induced rapid change in the conjugation of SUMO to multiple proteins, which predominantly targets nuclear proteins. The SSR has been postulated to protect stressed cells by preserving the functionality of crucial proteins. However, it is unclear how it exerts its protective functions. Interestingly, heat stress (HS) increases SUMOylation of proteins at active promoters and enhancers. In promoters, HS-induced SUMOylation correlates with gene transcription and stress-induced RNA polymerase II (Pol2) pausing. Conversely, a disappearance of SUMOylation in HS occurs at chromatin anchor points that maintain chromatin-looping structures and the spatial organisation of chromatin. In reviewing the literature, we hypothesise that the SSR regulates Pol2 pausing by modulating the interactions of pausing-regulating proteins, whereas deSUMOylation alters the function of chromatin anchors.