SUMO-1 conjugation blocks beta-amyloid-induced astrocyte reactivity

Protein modification in neurodegenerative diseases

Posttranslational modifications play a crucial role in governing cellular functions and protein behavior. Researchers have implicated dysregulated posttranslational modifications in protein misfolding, which results in cytotoxicity, particularly in neurodegenerative diseases such as Alzheimer disease, Parkinson disease, and Huntington disease. These aberrant posttranslational modifications cause proteins to gather in certain parts of the brain that are linked to the development of the diseases. This leads to neuronal dysfunction and the start of neurodegenerative disease symptoms. Cognitive decline and neurological impairments commonly manifest in neurodegenerative disease patients, underscoring the urgency of comprehending the posttranslational modifications' impact on protein function for targeted therapeutic interventions. This review elucidates the critical link between neurodegenerative diseases and specific posttranslational modifications, focusing on Tau, APP, α-synuclein, Huntingtin protein, Parkin, DJ-1, and Drp1. By delineating the prominent aberrant posttranslational modifications within Alzheimer disease, Parkinson disease, and Huntington disease, the review underscores the significance of understanding the interplay among these modifications. Emphasizing 10 key abnormal posttranslational modifications, this study aims to provide a comprehensive framework for investigating neurodegenerative diseases holistically. The insights presented herein shed light on potential therapeutic avenues aimed at modulating posttranslational modifications to mitigate protein aggregation and retard neurodegenerative disease progression.

Effects of amyloid-β on protein SUMOylation and levels of mitochondrial proteins in primary cortical neurons

Defining the molecular changes that underlie Alzheimer's disease (AD) is an important question in neuroscience. Here, we examined changes in protein SUMOylation, and proteins involved in mitochondrial dynamics, in an in vitro model of AD induced by application of amyloid-β 1-42 (Aβ1-42) to cultured neurons. We observed Aβ1-42-induced decreases in global SUMOylation and in levels of the SUMO pathway enzymes SENP3, PIAS1/2, and SAE2. Aβ exposure also decreased levels of the mitochondrial fission proteins Drp1 and Mff and increased activation of caspase-3. To examine whether loss of SENP3 is cytoprotective we knocked down SENP3, which partially prevented the Aβ1-42-induced increase in caspase-3 activation. Together, these data support the hypothesis that altered SUMOylation may play a role in the mechanisms underlying AD.

Effects of aerobic exercise on hippocampal SUMOylation in APP/PS1 transgenic mice

Alzheimer's disease (AD) is the most common neurodegenerative disease. SUMOylation, a post-translational modification, has been found to be dysregulated in the AD brain and to exacerbate learning and memory disabilities and increase amyloid beta (Aβ) expression further. To investigate whether exercise-induced alleviation of AD was associated with SUMOylation, which still remains unknown, 3-month-old C57BL/6 mice and APP/PS1 transgenic mice were randomly divided into the wild-type control (WC), wild-type exercise (WE), APP/PS1 control (AC), and APP/PS1 exercise (AE) groups. Mice in the exercise groups underwent a 3-month treadmill exercise regimen. We observed impaired learning and memory abilities in APP/PS1 mice, but the 3-month treadmill exercise regimen improved spatial learning and memory abilities in wild-type and APP/PS1 mice. In addition, senile plaques, SUMO1 mRNA, and SENP1 mRNA levels increased in the hippocampi of APP/PS1 mice. However, 3-month treadmill exercise decreased the levels of senile plaques, SUMO1 mRNA and SENP1 mRNA as well as may reduce SUMO1 modification in 6-month-old APP/PS1 mice, but SUMO2 mRNA expression, SUMO2/3 modification, and overall SUMOylation levels did not significantly change. Our results suggest that the impaired learning and memory abilities and aggregations of Aβ may relate to increased hippocampal SUMO1 transcription levels; the beneficial effects of treadmill exercise on learning and memory performances and AD pathogenesis may associated with the abatement of SUMO1 modification, but may not with SUMO2/3 modification.

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.

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.

The pivotal role of SUMO-1-JNK-Tau axis in an in vitro model of oxidative stress counteracted by the protective effect of curcumin

Oxidative stress is a toxic cellular condition, strictly related to inflammation and known to be a common feature of many neurodegenerative diseases. The imbalanced redox state modifies several molecular processes including protein SUMOylation, JNK and Tau protein activation, important actors in Alzheimer's disease. In this study, we showed a strong interaction among SUMO-1-JNK-Tau proteins and their molecular targets in an in vitro model (SHSY5Y cell line) of oxidative stress in which a significant reduction of cell viability and an augmented cell death was induced by increased doses of H2O2. The evoked oxidative stress led to a deficiency in the degradation system showing altered levels of Caspase-3, LC3BII/I and Ubiquitin. Curcumin, a natural compound with anti-oxidant and anti-inflammatory effects, demonstrated to tackle oxidative stress re-equilibrating SUMO-1, JNK and Tau functions. Importantly, 5 μM of curcumin induced an efficient recovery of cell viability, a reduction of cell death and a normalization of altered protein degradation marker levels. Interestingly, we found that H2O2 treatment induced a strong co-localization of SUMO-1-p-JNK-Tau proteins in nuclear bodies (NBs) and that curcumin was able to reduce these nuclear aggregates. These results highlight the SUMO-1-JNK-Tau axis key role in oxidative stress and the protective effect of curcumin against this pathological event, focusing on the importance of SUMO/deSUMOylation balance to regulate essential cellular processes.

Astrocyte activation and altered metabolism in normal aging, age-related CNS diseases, and HAND

Astrocytes regulate local cerebral blood flow, maintain ion and neurotransmitter homeostasis, provide metabolic support, regulate synaptic activity, and respond to brain injury, insults, and infection. Because of their abundance, extensive connectivity, and multiple roles in the brain, astrocytes are intimately involved in normal functioning of the CNS and their dysregulation can lead to neuronal dysfunction. In normal aging, decreased biological functioning and reduced cognitive abilities are commonly experienced in individuals free of overt neurological disease. Moreover, in several age-related CNS diseases, chronic inflammation and altered metabolism have been reported. Since people with HIV (PWH) are reported to experience rapid aging with chronic inflammation, altered brain metabolism is likely to be exacerbated. In fact, many studies report altered metabolism in astrocytes in diseases such as Alzheimer's, Parkinson's, and HIV. This review will address the roles of astrocyte activation and altered metabolism in normal aging, in age-related CNS disease, and in HIV-associated neurocognitive disorders.

Alteration of global protein SUMOylation in neurons and astrocytes in response to Alzheimer's disease-associated insults

SUMOylation, a post-translational modification of lysine residues by small ubiquitin-like modifier (SUMO) proteins, has been implicated in the pathogenesis of neurodegenerative disorders including Alzheimer's disease (AD), and in neuron- and astrocyte-specific physiological functions. Global SUMOylation is increased in the AD mouse brain in the pre-plaque-forming stage but returns to wild-type levels in the plaque-bearing stage. To clarify the reason for the transient change in SUMOylation, we analyzed the alteration of global SUMOylation induced by AD-associated cytotoxic stimuli in neurons and astrocytes individually. In neurons, amyloid β42 oligomers induced some but not significant increase in levels of SUMO1-modified proteins. Both hydrogen peroxide and glutamate significantly reduced SUMO1-modified protein levels. These changes were more prominent in neurons than in astrocytes. The opposite effect of Aβ and oxidative/excitotoxic stimuli on SUMO1 modification may cause the pathological stage-associated change in the level of SUMO-modified proteins in the AD mouse brain.

Sumoylation: Implications for Neurodegenerative Diseases

The covalent posttranslational modifications of proteins are critical events in signaling cascades that enable cells to efficiently, rapidly and reversibly respond to extracellular stimuli. This is especially important in the CNS where the processes affecting synaptic communication between neurons are highly complex and very tightly regulated. Sumoylation regulates the function and fate of a diverse array of proteins and participates in the complex cell signaling pathways required for cell survival. One of the most complex signaling pathways is synaptic transmission.Correct synaptic function is critical to the working of the brain and its alteration through synaptic plasticity mediates learning, mental disorders and stroke. The investigation of neuronal sumoylation is a new and exciting field and the functional and pathophysiological implications are far-reaching. Sumoylation has already been implicated in a diverse array of neurological disorders. Here we provide an overview of current literature highlighting recent insights into the role of sumoylation in neurodegeneration. In addition we present a brief assessment of drug discovery in the analogous ubiquitin system and extrapolate on the potential for development of novel therapies that might target SUMO-associated mechanisms of neurodegenerative disease.

Activation of migration of endogenous stem cells by erythropoietin as potential rescue for neurodegenerative diseases

Neurodegenerative disorders such as Alzheimer's disease (AD) are characterized by progressive cognitive dysfunction and memory loss. There is deposition of amyloid plaques in the brain and subsequent neuronal loss. Neuroinflammation plays a key role in the pathogenesis of AD. There is still no effective curative therapy for these patients. One promising strategy involves the stimulation of endogenous stem cells. This study investigated the therapeutic effect of erythropoietin (EPO) in neurogenesis, and proved its manipulation of the endogenous mesenchymal stem cells in model of lipopolysaccharide (LPS)-induced neuroinflammation.

METHODS

Forty five adult male mice were divided equally into 3 groups: Group I (control), group II (LPS untreated group): mice were injected with single dose of lipopolysaccharide (LPS) 0.8 mg/kg intraperitoneally (ip) to induce neuroinflammation, group III (EPO treated group): in addition to (LPS) mice were further injected with EPO in dose of 40 μg/kg of body weight three times weekly for 5 consecutive weeks. Groups were tested for their locomotor activity and memory using open field test and Y-maze. Cerebral specimens were subjected to histological and morphometric studies. Glial fibrillary acidic protein (GFAP) and mesenchymal stem cell marker CD44 were assessed using immunostaining. Gene expression of brain derived neurotrophic factor (BDNF) was examined in brain tissue.

RESULTS

LPS decreased locomotor activity and percentage of correct choices in Y-maze test. Cerebral sections of LPS treated mice showed increased percentage area of dark nuclei and amyloid plaques. Multiple GFAP positive astrocytes were detected in affected cerebral sections. In addition, decrease BDNF gene expression was noted. On the other hand, EPO treated group, showed improvement in locomotor and cognitive function. Examination of the cerebral sections showed multiple neurons exhibiting less dark nuclei and less amyloid plaques in comparison to the untreated group. GFAP positive astrocytes were also reduced. Cerebral sections of the EPO treated group showed multiple branched and spindle CD44 positive cells inside and around blood vessels more than in LPS group. This immunostaining was negative in the control group. EPO administration increased BDNF gene expression.

CONCLUSION

This study proved that EPO provides excellent neuroprotective and neurotrophic effects in vivo model of LPS induced neuroinflammation. It enhances brain tissue regeneration via stimulation of endogenous mesenchymal stem cells proliferation and their migration to the site of inflammation. EPO also up regulates cerebral BDNF expression and production, which might contributes to EPO mediated neurogenesis. It also attenuates reactive gliosis thus reduces neuroinflammation. These encouraging results obtained with the use of EPO proved that it may be a promising candidate for future clinical application and treatment of neurodegenerative diseases.

Spatiotemporal distribution of SUMOylation components during mouse brain development

Posttranslational modification of proteins might play an important role in brain cellular dynamics via the rapid turnover or functional change of critical proteins controlling neuronal differentiation or synaptic transmission. Small ubiquitin-like modifier protein (SUMO) is a family of ubiquitin-like small proteins that are covalently attached to target proteins to modify their function posttranslationally. Many cellular processes, such as transcription and protein trafficking, are regulated by SUMOylation, but its functional significance in the brain remains unclear. Although developmental regulation of SUMOylation levels in rat brain was recently demonstrated, no comparative immunohistochemical analysis of the cellular distribution profiles of SUMOylation components, including SUMO1, SUMO2/3, and Ubc9, has been undertaken so far. The present study used immunohistochemical and immunoblot analysis with the different developmental stages of mice and demonstrated the developmentally regulated distribution of SUMO1, SUMO2/3, and Ubc9 in the brain. During embryonic development, SUMOylation by SUMO1 and SUMO2/3 occurred in the nucleoplasm of nestin-positive neural stem cells. Although the total amount of SUMO-modified proteins decreased during postnatal brain development, intense and persistent accumulation of SUMO2/3 was detected throughout life in neural progenitor populations in neurogenic regions, including the subventricular zone and the hippocampal subgranular zone. In contrast, many neurons in the adult brain accumulated SUMO1 rather than SUMO2/3. Heavy immunoreactivity of SUMO1 was found in large projection neurons in the brainstem, whereas SUMO2/3 was almost absent from these areas. This heterogeneous distribution implies that both proteins play a specific and unique role in the brain.

SUMOylation: Novel Neuroprotective Approach for Alzheimer's Disease?

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized in the brain by the formation of amyloid-beta (Aβ)-containing plaques and neurofibrillary tangles containing the microtubule-associated protein tau. Neuroinflammation is another feature of AD and astrocytes are receiving increasing attention as key contributors. Although some progress has been made, the molecular mechanisms underlying the pathophysiology of AD remain unclear. Interestingly, some of the main proteins involved in AD, including amyloid precursor protein (APP) and tau, have recently been shown to be SUMOylated. The post-translational modification by SUMO (small ubiquitin-like modifier) has been shown to regulate APP and tau and may modulate other proteins implicated in AD. Here we present an overview of recent studies suggesting that protein SUMOylation might be involved in the underlying pathogenic mechanisms of AD and discuss how this could be exploited for therapeutic intervention.

Battling Alzheimer's Disease: Targeting SUMOylation-Mediated Pathways

SUMO (small ubiquitin-like modifier) conjugation is a critically important control process in all eukaryotic cells, because it acts as a biochemical switch and regulates the function of hundreds of proteins in many different pathways. Although the diverse functional consequences and molecular targets of SUMOylation remain largely unknown, SUMOylation is becoming increasingly implicated in the pathophysiology of Alzheimer's disease (AD). Apart from the central SUMO-modified disease-associated proteins, such as amyloid precursor protein, amyloid β, and tau, SUMOylation also regulates several other processes underlying AD. These are involved in inflammation, mitochondrial dynamics, synaptic transmission and plasticity, as well as in protective responses to cell stress. Herein, we review current reports on the involvement of SUMOylation in AD, and present an overview of potential SUMO targets and pathways underlying AD pathogenesis.

Emerging roles of sumoylation in the regulation of actin, microtubules, intermediate filaments, and septins

Sumoylation is a powerful regulatory system that controls many of the critical processes in the cell, including DNA repair, transcriptional regulation, nuclear transport, and DNA replication. Recently, new functions for SUMO have begun to emerge. SUMO is covalently attached to components of each of the four major cytoskeletal networks, including microtubule-associated proteins, septins, and intermediate filaments, in addition to nuclear actin and actin-regulatory proteins. However, knowledge of the mechanisms by which this signal transduction system controls the cytoskeleton is still in its infancy. One story that is beginning to unfold is that SUMO may regulate the microtubule motor protein dynein by modification of its adaptor Lis1. In other instances, cytoskeletal elements can both bind to SUMO non-covalently and also be conjugated by it. The molecular mechanisms for many of these new functions are not yet clear, but are under active investigation. One emerging model links the function of MAP sumoylation to protein degradation through SUMO-targeted ubiquitin ligases, also known as STUbL enzymes. Other possible functions for cytoskeletal sumoylation are also discussed.

Neuronal SUMOylation: mechanisms, physiology, and roles in neuronal dysfunction

Protein SUMOylation is a critically important posttranslational protein modification that participates in nearly all aspects of cellular physiology. In the nearly 20 years since its discovery, SUMOylation has emerged as a major regulator of nuclear function, and more recently, it has become clear that SUMOylation has key roles in the regulation of protein trafficking and function outside of the nucleus. In neurons, SUMOylation participates in cellular processes ranging from neuronal differentiation and control of synapse formation to regulation of synaptic transmission and cell survival. It is a highly dynamic and usually transient modification that enhances or hinders interactions between proteins, and its consequences are extremely diverse. Hundreds of different proteins are SUMO substrates, and dysfunction of protein SUMOylation is implicated in a many different diseases. Here we briefly outline core aspects of the SUMO system and provide a detailed overview of the current understanding of the roles of SUMOylation in healthy and diseased neurons.

Aberrant sumoylation signaling evoked by reactive oxygen species impairs protective function of Prdx6 by destabilization and repression of its transcription

Loss of the cytoprotective protein peroxiredoxin 6 (Prdx6) in cells that are aging or under oxidative stress is known to be linked to the pathobiology of many age-related diseases. However, the mechanism by which Prdx6 activity goes awry is largely unknown. Using Prdx6-deficient (Prdx6(-/-) ) cells as a model for aging or redox active cells, human/mouse lens epithelial cells (LECs) facing oxidative stress and aging lenses, we found a significant increase in the levels of small ubiquitin-like modifier (Sumo)1 conjugates. These cells displayed increased levels of Sumo1 and reduced the expression of Prdx6. Specifically, we observed that Prdx6 is a target for aberrant sumoylation signaling, and that Sumo1 modification reduces its cellular abundance. LECs overexpressing Sumo1 showed reduced expression and activity of Prdx6 and its transactivator specificity protein 1 (Sp1), mRNA and protein with increased levels of reactive oxygen species; those cells were vulnerable to oxidative stress-induced cell death. A significant reduction in Prdx6, Sp1 protein and mRNA expression was observed in redox active Prdx6(-/-) cells and in aging lenses/LECs. The reduction was correlated with increased expression of Sumo1 and enrichment of the inactive form (dimeric) of Sumo-specific protease (Senp)1. Experiments with Sumo1-fused Prdx6 and Prdx6 promoter-linked to chloramphenicol acetyltransferase reporter gene constructs indicated that Sumo1 dysregulated Prdx6 activity by reducing its abundance and attenuating its transcription; in contrast, the delivery of Senp1 or Prdx6 reversed the process. The data show that reactive oxygen species-evoked aberrant sumoylation signaling affects Prdx6 activity by reducing Prdx6 abundance, as well as transcription. The findings of the present study may provide a foundation for a strategy to repair deleterious oxidative signaling generated by a reduced activity of Prdx6.

Neuronal influences are necessary to produce mitochondrial co-localization with glutamate transporters in astrocytes

Recent evidence suggests that the predominant astrocyte glutamate transporter, GLT-1/ Excitatory Amino Acid Transporter 2 (EAAT2) is associated with mitochondria. We used primary cultures of mouse astrocytes to assess co-localization of GLT-1 with mitochondria, and tested whether the interaction was dependent on neurons, actin polymerization or the kinesin adaptor, TRAK2. Mouse primary astrocytes were transfected with constructs expressing V5-tagged GLT-1, pDsRed1-Mito with and without dominant negative TRAK2. Astrocytes were visualized using confocal microscopy and co-localization was quantified using Volocity software. Image analysis of confocal z-stacks revealed no co-localization between mitochondria and GLT-1 in pure astrocyte cultures. Co-culture of astrocytes with primary mouse cortical neurons revealed more mitochondria in processes and a positive correlation between mitochondria and GLT-1. This co-localization was not further enhanced after neuronal depolarization induced by 1 h treatment with 15 mM K⁺. In pure astrocytes, a rho kinase inhibitor, Y27632 caused the distribution of mitochondria to astrocyte processes without enhancing GLT-1/mitochondrial co-localization, however, in co-cultures, Y27632 abolished mitochondrial:GLT-1 co-localization. Disrupting potential mitochondrial: kinesin interactions using dominant negative TRAK2 did not alter GLT-1 distribution or GLT-1: mitochondrial co-localization. We conclude that the association between GLT-1 and mitochondria is modest, is driven by synaptic activity and dependent on polymerized actin filaments.Mitochondria have limited co-localization with the glutamate transporter GLT-1 in primary astrocytes in culture. Few mitochondria are in the fine processes where GLT-1 is abundant. It is necessary to culture astrocytes with neurones to drive a significant level of co-localization, but co-localization is not further altered by depolarization, manipulating sodium ion gradients or Na/K ATPase activity.

Sirtuin modulators control reactive gliosis in an in vitro model of Alzheimer's disease

Among neurodegenerative disorders, Alzheimer’s disease (AD) represents the most common cause of dementia in the elderly. Several genetic and environmental factors have been identified; however, aging represents the most important risk factor in the development of AD. To date, no effective treatments to prevent or slow this dementia are available. Sirtuins (SIRTs) are a family of NAD⁺-dependent enzymes, implicated in the control of a variety of biological processes that have the potential to modulate neurodegeneration. Here we tested the hypothesis that activation of SIRT1 or inhibition of SIRT2 would prevent reactive gliosis which is considered one of the most important hallmark of AD. Primary rat astrocytes were activated with beta amyloid 1-42 (Aβ 1-42) and treated with resveratrol (RSV) or AGK-2, a SIRT1 activator and a SIRT2-selective inhibitor, respectively. Results showed that both RSV and AGK-2 were able to reduce astrocyte activation as well as the production of pro-inflammatory mediators. These data disclose novel findings about the therapeutic potential of SIRT modulators, and suggest novel strategies for AD treatment.

Apoptosis is an obstacle to the differentiation of adipose-derived stromal cells into astrocytes

Previous studies have demonstrated that nerve cells differentiated from adipose-derived stromal cells after chemical induction have reduced viability; however, the underlying mechanisms remained unclear. In this study, we induced the differentiation of adult adipose-derived stromal cells into astrocytes using chemical induction. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and flow cytometry showed that, with increasing induction time, the apoptotic rate gradually increased, and the number of living cells gradually decreased. Immunohistochemical staining demonstrated that the number of glial fibrillary acidic protein-, caspase-3- and caspase-9-positive cells gradually increased with increasing induction time. Transmission electron microscopy revealed typical signs of apoptosis after differentiation. Taken together, our results indicate that caspase-dependent apoptosis is an obstacle to the differentiation of adipose-derived stromal cells into astrocytes. Inhibiting apoptosis may be an important strategy for increasing the efficiency of induction.

SUMO and Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive cognitive decline and is the most common cause of dementia in the elderly. Histopathologically, AD features insoluble aggregates of two proteins in the brain, amyloid-β (Aβ) and the microtubule-associated protein tau, both of which have been linked to the small ubiquitin-like modifier (SUMO). A large body of research has elucidated many of the molecular and cellular pathways that underlie AD, including those involving the abnormal Aβ and tau aggregates. However, a full understanding of the etiology and pathogenesis of the disease has remained elusive. Consequently, there are currently no effective therapeutic options that can modify the disease progression and slow or stop the decline of cognitive functioning. As part of the effort to address this lacking, there needs a better understanding of the signaling pathways that become impaired under AD pathology, including the regulatory mechanisms that normally control those networks. One such mechanism involves SUMOylation, which is a post-translational modification (PTM) that is involved in regulating many aspects of cell biology and has also been found to have several critical neuron-specific roles. Early studies have indicated that the SUMO system is likely altered with AD-type pathology, which may impact Aβ levels and tau aggregation. Although still a relatively unexplored topic, SUMOylation will likely emerge as a significant factor in AD pathogenesis in ways which may be somewhat analogous to other regulatory PTMs such as phosphorylation. Thus, in addition to the upstream effects on tau and Aβ processing, there may also be downstream effects mediated by Aβ aggregates or other AD-related factors on SUMO-regulated signaling pathways. Multiple proteins that have functions relevant to AD pathology have been identified as SUMO substrates, including those involved in synaptic physiology, mitochondrial dynamics, and inflammatory signaling. Ongoing studies will determine how these SUMO-regulated functions in neurons and glial cells may be impacted by Aβ and AD pathology. Here, we present a review of the current literature on the involvement of SUMO in AD, as well as an overview of the SUMOylated proteins and pathways that are potentially dysregulated with AD pathogenesis.

Molecular targets underlying SUMO-mediated neuroprotection in brain ischemia

SUMOylation (small ubiquitin-like modifier conjugation) is an important post-translational modification which is becoming increasingly implicated in the altered protein dynamics associated with brain ischemia. The function of SUMOylation in cells undergoing ischemic stress and the identity of small ubiquitin-like modifier (SUMO) targets remain in most cases unknown. However, the emerging consensus is that SUMOylation of certain proteins might be part of an endogenous neuroprotective response. This review brings together the current understanding of the underlying mechanisms and downstream effects of SUMOylation in brain ischemia, including processes such as autophagy, mitophagy and oxidative stress. We focus on recent advances and controversies regarding key central nervous system proteins, including those associated with the nucleus, cytoplasm and plasma membrane, such as glucose transporters (GLUT1, GLUT4), excitatory amino acid transporter 2 glutamate transporters, K+ channels (K2P1, Kv1.5, Kv2.1), GluK2 kainate receptors, mGluR8 glutamate receptors and CB1 cannabinoid receptors, which are reported to be SUMO-modified. A discussion of the roles of these molecular targets for SUMOylation could play following an ischemic event, particularly with respect to their potential neuroprotective impact in brain ischemia, is proposed.