Autophagy protects human brain microvascular endothelial cells against methylglyoxal-induced injuries, reproducible in a cerebral ischemic model in diabetic rats

Methylglyoxal Formation-Metabolic Routes and Consequences

Methylglyoxal (MGO), a by-product of glycolysis, plays a significant role in cellular metabolism, particularly under stress conditions. However, MGO is a potent glycotoxin, and its accumulation has been linked to the development of several pathological conditions due to oxidative stress, including diabetes mellitus and neurodegenerative diseases. This paper focuses on the biochemical mechanisms by which MGO contributes to oxidative stress, particularly through the formation of advanced glycation end products (AGEs), its interactions with antioxidant systems, and its involvement in chronic diseases like diabetes, neurodegeneration, and cardiovascular disorders. MGO exerts its effects through multiple signaling pathways, including NF-κB, MAPK, and Nrf2, which induce oxidative stress. Additionally, MGO triggers apoptosis primarily via intrinsic and extrinsic pathways, while endoplasmic reticulum (ER) stress is mediated through PERK-eIF2α and IRE1-JNK signaling. Moreover, the activation of inflammatory pathways, particularly through RAGE and NF-κB, plays a crucial role in the pathogenesis of these conditions. This study points out the connection between oxidative and carbonyl stress due to increased MGO formation, and it should be an incentive to search for a marker that could have prognostic significance or could be a targeted therapeutic intervention in various diseases.

Targeting ferroptosis in the neurovascular unit: A promising approach for treating diabetic cognitive impairment

The cognitive decline associated with chronic metabolic disease diabetes has garnered extensive scrutiny, yet its pathogenesis remains incompletely understood, and the advancement of targeted therapeutics has posed a persistent challenge. Ferroptosis, a novel form of cell death characterized by intracellular lipid peroxidation and iron overload, has recently emerged as a significant factor. Numerous contemporary studies have corroborated that ferroptosis within the neurovascular unit is intimately associated with the onset of diabetes-induced cognitive impairment. Numerous contemporary studies have corroborated that ferroptosis within the neurovascular unit is intimately associated with the onset of diabetic cognitive impairment (DCI). This article initially conducts a profound analysis of the mechanism of ferroptosis, followed by a detailed elucidation of the specific manifestations of neurovascular unit ferroptosis in the context of diabetic cognitive function impairment. Furthermore, an exhaustive review of pertinent literature from April 2020 to March 2024 has been undertaken, resulting in the selection of 31 documents of significant reference value. These documents encompass studies on 11 distinct drugs, all of which are centered around investigating methods to inhibit the ferroptosis pathway as a potential treatment for DCI. Simultaneously, we conducted a review of 12 supplementary literary sources that presented 10 pharmacological agents with anti-ferroptosis properties in other neurodegenerative disorders. This article critically examines the potential influence of neurovascular unit ferroptosis on the progression of cognitive impairment in diabetes, from the three aforementioned perspectives, and organizes the existing and potential therapeutic drugs. It is our aspiration that this article will serve as a theoretical foundation for scholars in related disciplines when conceptualizing, investigating, and developing novel clinical drugs for DCI.

Methylglyoxal, a highly reactive dicarbonyl compound, as a threat for blood brain barrier integrity

The brain is a highly metabolically active organ requiring a large amount of glucose. Methylglyoxal (MGO), a by-product of glucose metabolism, is known to be involved in microvascular dysfunction and is associated with reduced cognitive function. Maintenance of the blood-brain barrier (BBB) is essential to maintain optimal brain function and a large amount of evidence indicates negative effects of MGO on BBB integrity. In this review, we summarized the current literature on the effect of MGO on the different cell types forming the BBB. BBB damage by MGO most likely occurs in brain endothelial cells and mural cells, while astrocytes are most resistant to MGO. Microglia on the other hand appear to be not directly influenced by MGO but rather produce MGO upon activation. Although there is clear evidence that MGO affects components of the BBB, the impact of MGO on the BBB as a multicellular system warrants further investigation. Diminishing MGO stress can potentially form the basis for new treatment strategies for maintaining optimal brain function.

The Dual Role of Autophagy in Postischemic Brain Neurodegeneration of Alzheimer's Disease Proteinopathy

Autophagy is a self-defense and self-degrading intracellular system involved in the recycling and elimination of the payload of cytoplasmic redundant components, aggregated or misfolded proteins and intracellular pathogens to maintain cell homeostasis and physiological function. Autophagy is activated in response to metabolic stress or starvation to maintain homeostasis in cells by updating organelles and dysfunctional proteins. In neurodegenerative diseases, such as cerebral ischemia, autophagy is disturbed, e.g., as a result of the pathological accumulation of proteins associated with Alzheimer's disease and their structural changes. Postischemic brain neurodegeneration, such as Alzheimer's disease, is characterized by the accumulation of amyloid and tau protein. After cerebral ischemia, autophagy was found to be activated in neuronal, glial and vascular cells. Some studies have shown the protective properties of autophagy in postischemic brain, while other studies have shown completely opposite properties. Thus, autophagy is now presented as a double-edged sword with possible therapeutic potential in brain ischemia. The exact role and regulatory pathways of autophagy that are involved in cerebral ischemia have not been conclusively elucidated. This review aims to provide a comprehensive look at the advances in the study of autophagy behavior in neuronal, glial and vascular cells for ischemic brain injury. In addition, the importance of autophagy in neurodegeneration after cerebral ischemia has been highlighted. The review also presents the possibility of modulating the autophagy machinery through various compounds on the development of neurodegeneration after cerebral ischemia.

Anti-Glucotoxicity Effect of Phytoconstituents via Inhibiting MGO-AGEs Formation and Breaking MGO-AGEs

The therapeutic benefits of phytochemicals in the treatment of various illnesses and disorders are well documented. They show significant promise for the discovery and creation of novel medications for treating a variety of human diseases. Numerous phytoconstituents have shown antibiotic, antioxidant, and wound-healing effects in the conventional system. Traditional medicines based on alkaloids, phenolics, tannins, saponins, terpenes, steroids, flavonoids, glycosides, and phytosterols have been in use for a long time and are crucial as alternative treatments. These phytochemical elements are crucial for scavenging free radicals, capturing reactive carbonyl species, changing protein glycation sites, inactivating carbohydrate hydrolases, fighting pathological conditions, and accelerating the healing of wounds. In this review, 221 research papers have been reviewed. This research sought to provide an update on the types and methods of formation of methylglyoxal-advanced glycation end products (MGO-AGEs) and molecular pathways induced by AGEs during the progression of the chronic complications of diabetes and associated diseases as well as to discuss the role of phytoconstituents in MGO scavenging and AGEs breaking. The development and commercialization of functional foods using these natural compounds can provide potential health benefits.

Apelin-13 prevents the effects of oxygen-glucose deprivation/reperfusion on bEnd.3 cells by inhibiting AKT-mTOR signaling

Autophagy plays works by degrading misfolded proteins and dysfunctional organelles and maintains intracellular homeostasis. Apelin-13 has been investigated as an agent that might protect the blood-brain barrier (BBB) from cerebral ischemia/reperfusion (I/R) injury. In this study, we examined whether apelin-13 protects cerebral microvascular endothelial cells, important components of the BBB, from I/R injury by regulating autophagy. To mimic I/R injury, the mouse cerebral microvascular endothelia l cell line bEnd 3 undergoes the process of oxygen and glucose deprivation and re feeding in the process of culture. Cell viability was detected using a commercial kit, and cell migration was monitored by in vitro scratch assay. The tight junction (TJ) proteins ZO-1 and occludin; the autophagy markers LC3 II, beclin 1, and p62; and components of the AKT-mTOR signaling pathway were detected by Western blotting and immunofluorescence. To confirm the role of autophagy in OGD/R and the protective effect of apelin-13, we treated the cells with 3-methyladenine (3-MA), a pharmacological inhibitor of autophagy. Our results demonstrated that OGD/R increased autophagic activity but decreased viability, abundance of TJs, and migration. Viability and TJ abundance were further reduced when the OGD/R group was treated with 3-MA. These results indicated that bEnd.3 upregulates autophagy to ameliorate the effects of OGD/R injury on viability and TJs, but that the autophagy induced by OGD/R alone is not sufficient to protect against the effect on cell migration. Treatment of OGD/R samples with apelin-13 markedly increased viability, TJ abundance, and migration, as well as autophagic activity, whereas 3-MA inhibited this increase, suggesting that apelin-13 exerted its protective effects by upregulating autophagy.

Up-regulation of Sirtuin-1/autophagy signaling in human cerebral ischemia: possible role in caspase-3 mediated apoptosis

Aim

Autophagy is a catabolic process, which plays a pivotal role in neuronal homeostases. Sirtuin-1 (Sirt1, Silent information regulator family protein 1) is a protein deacetylase that is activated by nicotinamide adenine dinucleotide (NAD⁺), is also influenced by starvation and stress response similar to autophagy. Sirt1 is necessary for the induction of autophagy and is critical for neuronal survival in neurodegeneration. The present study investigates the role of Sirt1/autophagy signaling and its possible involvement in neuronal cell death in the brains of cerebral ischemia (CI) patients.

Patients and methods

Autopsied brain tissues from three healthy subjects and ten CI patients were obtained from National Institute of Mental Health and Neurosciences (NIMHANS); Bangalore, India. Western blotting and immunostaining were performed to assess the expression changes in Sirt1, autophagy mediators including Beclin-1, autophagy-related (Atg) proteins-3, 5, 7, 12-5, microtubule-associated protein-1A light chain3 (Lc3-I/II), and caspase-3 in stroke patients.

Results

Our study showed that, in stroke patients, expression of Sirt1, Beclin-1, Atg-3, 5, 7, 12-5, and Lc3-II/I were upregulated. Further, our immunohistochemistry results show increased immunoreactivity of Sirt1, Beclin-1, Atg-7, Lc3-I/II, and cleaved caspase-3 in stroke brains.

Conclusion

The present data suggesting a role for Sirt1/autophagy signaling in regulating neuronal cell survival in CI.

Metabonomics fingerprint of volatile organic compounds in serum and urine of pregnant women with gestational diabetes mellitus

BACKGROUND

Gestational diabetes mellitus (GDM) is a metabolic disease with an increasing annual incidence rate. Our previous observational study found that pregnant women with GDM had mild cognitive decline.

AIM

To analyze the changes in metabonomics in pregnant women with GDM and explore the mechanism of cognitive function decline.

METHODS

Thirty GDM patients and 30 healthy pregnant women were analyzed. Solid-phase microextraction gas chromatography/mass spectrometry was used to detect organic matter in plasma and urine samples. Statistical analyses were conducted using principal component analysis and partial least squares discriminant analysis.

RESULTS

Differential volatile metabolites in the serum of pregnant women with GDM included hexanal, 2-octen-1-ol, and 2-propanol. Differential volatile metabolites in the urine of these women included benzene, cyclohexanone, 1-hexanol, and phenol. Among the differential metabolites, the conversion of 2-propanol to acetone may further produce methylglyoxal. Therefore, 2-propanol may be a potential marker for serum methylglyoxal.

CONCLUSION

2-propanol may be a potential volatile marker to evaluate cognitive impairment in pregnant women with GDM.

Acute Methylglyoxal-Induced Damage in Blood-Brain Barrier and Hippocampal Tissue

Methylglyoxal (MG) is a reactive dicarbonyl compound formed mostly via the glycolytic pathway. Elevated blood glucose levels can cause MG accumulation in plasma and cerebrospinal fluid in patients with diabetes mellitus and Alzheimer's disease. Under these disease conditions, the high reactivity of MG leads to modification of proteins and other biomolecules, generating advanced glycation end products (AGEs), which are considered mediators in neurodegenerative diseases. We investigated the integrity of the blood-brain barrier (BBB) and astrocyte response in the hippocampus to acute insult induced by MG when it was intracerebroventricularly administered to rats. Seventy-two hours later, BBB integrity was lost, as assessed by the entry of Evans dye into the brain tissue and albumin in the cerebrospinal fluid, and a decrease in aquaporin-4 and connexin-43 in the hippocampal tissue. MG did not induce changes in the hippocampal contents of RAGE in this short interval, but decreased the expression of S100B, an astrocyte-secreted protein that binds RAGE. The expression of two important transcription factors of the antioxidant response, NF-κB and Nrf2, was unchanged. However, hemeoxigenase-1 was upregulated in the MG-treated group. These data corroborate the idea that hippocampal cells are targets of MG toxicity and that BBB dysfunction and specific glial alterations induced by this compound may contribute to the behavioral and cognitive alterations observed in these animals.

Sevoflurane up-regulates miR-7a to protect against ischemic brain injury in rats by down-regulating ATG7 and reducing neuronal autophagy

The current study aimed to elucidate the effects of Sevoflurane on neuronal autophagy and ischemic brain injury by regulating miR-7a/ATG7 axis. The rat model of middle cerebral artery occlusion (MCAO) was established by thread embolization. The expression pattern of microRNA-7a (miR-7a) and autophagy-related gene 7 (ATG7) was subsequently determined in Sevoflurane-treated MCAO rats with their relation and effects on neuronal autophagy and ischemic brain injury further analyzed. Bioinformatics analysis confirmed that miR-7a could target to inhibit ATG7 in ischemic brain injury samples. Sevoflurane could alleviate ischemic brain injury in rats by reducing the level of neuronal autophagy-related factors. The expression of miR-7a was up-regulated and ATG7 was down-regulated in the brain tissues of MCAO rats after Sevoflurane treatment. ATG7 was found to induce neuronal autophagy during autophagy in the brain tissues of MCAO rats. In summary, Sevoflurane exerts protective effects on ischemic brain injury via inhibiting autophagy of neurons and microglia through the miR-7a-mediated downregulation of ATG7.

Novel Therapeutic Strategies for Ischemic Stroke: Recent Insights into Autophagy

Stroke is one of the leading causes of death and disability worldwide. Autophagy is a conserved cellular catabolic pathway that maintains cellular homeostasis by removal of damaged proteins and organelles, which is critical for the maintenance of energy and function homeostasis of cells. Accumulating evidence demonstrates that autophagy plays important roles in pathophysiological mechanisms under ischemic stroke. Previous investigations show that autophagy serves as a “double-edged sword” in ischemic stroke as it can either promote the survival of neuronal cells or induce cell death in special conditions. Following ischemic stroke, autophagy is activated or inhibited in several cell types in brain, including neurons, astrocytes, and microglia, as well as microvascular endothelial cells, which involves in inflammatory activation, modulation of microglial phenotypes, and blood-brain barrier permeability. However, the exact mechanisms of underlying the role of autophagy in ischemic stroke are not fully understood. This review focuses on the recent advances regarding potential molecular mechanisms of autophagy in different cell types. The focus is also on discussing the “double-edged sword” effect of autophagy in ischemic stroke and its possible underlying mechanisms. In addition, potential therapeutic strategies for ischemic stroke targeting autophagy are also reviewed.

The dual roles of autophagy and the GPCRs-mediating autophagy signaling pathway after cerebral ischemic stroke

Ischemic stroke, caused by a lack of blood supply in brain tissues, is the third leading cause of human death and disability worldwide, and usually results in sensory and motor dysfunction, cognitive impairment, and in severe cases, even death. Autophagy is a highly conserved lysosome-dependent process in which eukaryotic cells removal misfolded proteins and damaged organelles in cytoplasm, which is critical for energy metabolism, organelle renewal, and maintenance of intracellular homeostasis. Increasing evidence suggests that autophagy plays important roles in pathophysiological mechanisms under ischemic conditions. However, there are still controversies about whether autophagy plays a neuroprotective or damaging role after ischemia. G-protein-coupled receptors (GPCRs), one of the largest protein receptor superfamilies in mammals, play crucial roles in various physiological and pathological processes. Statistics show that GPCRs are the targets of about one-fifth of drugs known in the world, predicting potential values as targets for drug research. Studies have demonstrated that nutritional deprivation can directly or indirectly activate GPCRs, mediating a series of downstream biological processes, including autophagy. It can be concluded that there are interactions between autophagy and GPCRs signaling pathway, which provides research evidence for regulating GPCRs-mediated autophagy. This review aims to systematically discuss the underlying mechanism and dual roles of autophagy in cerebral ischemia, and describe the GPCRs-mediated autophagy, hoping to probe promising therapeutic targets for ischemic stroke through in-depth exploration of the GPCRs-mediated autophagy signaling pathway.

P-Glycoprotein Aggravates Blood Brain Barrier Dysfunction in Experimental Ischemic Stroke by Inhibiting Endothelial Autophagy

P-glycoprotein (P-gp) is expressed on brain microvessel endothelial cells of blood-brain barrier (BBB) and elevated after cerebral ischemia. In this study, we explored the influence and potential mechanisms of P-gp on BBB function in experimental ischemic stroke in vivo and in vitro. Middle cerebral artery occlusion/reperfusion (MCAO/R) was created in mice. Oxygen-glucose deprivation/reoxygenation (OGD/R) was performed in brain microvascular vessel-derived endothelial cells (bEnd.3) to mimic ischemia/reperfusion injury in vitro. P-gp-specific siRNA and pharmacological inhibitor cyclosporine A were used to inhibit P-gp, whereas pcDNA3.1 was utilized to overexpress P-gp. Twenty-four hours after reperfusion, acute ischemic stroke outcome, BBB integrity and permeability, autophagic proteins and relative signaling pathways were evaluated. P-gp levels were markedly elevated in mouse brain and endothelial cells following MCAO/R and OGD/R, respectively. P-gp siRNA silencing or pharmacologically inhibiting (cyclosporine A) reduced infarct volume and brain edema, attenuated brain pathology, and improved neurological behavior in association with attenuated accumulation of neutrophils and macrophages, reduced expression levels of inflammatory cytokines (TNF-α and IL-1β), matrix metalloproteinases (MMP-2 and MMP-9) and adhesion molecules (ICAM-1 and VCAM-1). P-gp silence also counteracted BBB leakage, restored the expressions of tight junction proteins (Claudin-5, Occludin and ZO-1), activated autophagic proteins (upregulated LC3-II/LC3-I and Beclin 1, and downregulated P62), and diminished Akt/mTOR signal activity in mice following MCAO/R. In the endothelial cell OGD/R assay, P-gp silence downregulated the expressions of inflammatory cytokines and adhesion molecules, inhibited leukocytes adhesion and migration, increased tight junction protein levels, and activated autophagy, all were reversible by forceful P-gp expression. Additionally, treatment with an autophagy inhibitor (3-methyladenine) abolished protections against ischemic stroke and tight junction proteins reduction followed by P-gp silence. In conclusion, increased P-gp expression after ischemic injury resulted in BBB dysfunction and hyperpermeability by suppressing Akt/mTOR-induced endothelial autophagy.

Cooperation of cell adhesion and autophagy in the brain: Functional roles in development and neurodegenerative disease

Cellular adhesive connections directed by the extracellular matrix (ECM) and maintenance of cellular homeostasis by autophagy are seemingly disparate functions that are molecularly intertwined, each regulating the other. This is an emerging field in the brain where the interplay between adhesion and autophagy functions at the intersection of neuroprotection and neurodegeneration. The ECM and adhesion proteins regulate autophagic responses to direct protein clearance and guide regenerative programs that go awry in brain disorders. Concomitantly, autophagic flux acts to regulate adhesion dynamics to mediate neurite outgrowth and synaptic plasticity with functional disruption contributed by neurodegenerative disease. This review highlights the cooperative exchange between cellular adhesion and autophagy in the brain during health and disease. As the mechanistic alliance between adhesion and autophagy has been leveraged therapeutically for metastatic disease, understanding overlapping molecular functions that direct the interplay between adhesion and autophagy might uncover therapeutic strategies to correct or compensate for neurodegeneration.

The Reactive Species Interactome in the Brain

Significance: Redox pioneer Helmut Sies attempted to explain reactive species' challenges faced by organelles, cells, tissues, and organs via three complementary definitions: (i) oxidative stress, that is, the disturbance in the prooxidant-antioxidant defense balance in favor of the prooxidants; (ii) oxidative eustress, the low physiological exposure to prooxidants; and (iii) oxidative distress, the supraphysiological exposure to prooxidants. Recent Advances: Identification, concentration, and interactions are the most important elements to improve our understanding of reactive species in physiology and pathology. In this context, the reactive species interactome (RSI) is a new multilevel redox regulatory system that identifies reactive species families, reactive oxygen species (ROS), reactive nitrogen species (RNS), and reactive sulfur species, and it integrates their interactions with their downstream biological targets. Critical Issues: We propose a united view to fully combine reactive species identification, oxidative eustress and distress, and the RSI system. In this view, we also propose including the forgotten reactive carbonyl species, an increasingly rediscovered reactive species family related to the other reactive families, and key enzymes within the RSI. We focus on brain physiology and pathology to demonstrate why this united view should be considered. Future Directions: More studies are needed for an improved understanding of the contributions of reactive species through their identification, concentration, and interactions, including in the brain. Appreciating the RSI in its entirety should unveil new molecular players and mechanisms in physiology and pathology in the brain and elsewhere.

Selenium attenuates ischemia/reperfusion injury‑induced damage to the blood‑brain barrier in hyperglycemia through PI3K/AKT/mTOR pathway‑mediated autophagy inhibition

Ischemic stroke is a leading cause of mortality and disability. Diabetes mellitus, characterized by hyperglycemia, is a common concomitant disease of ischemic stroke, which is associated with autophagy dysfunction and blood‑brain barrier (BBB) damage following cerebral ischemia/reperfusion (I/R) injury. At present, there is no effective treatment strategy for the disease. The purpose of the present study was to explore the molecular mechanisms underlying the protective effects of selenium on the BBB following I/R injury in hyperglycemic rats. Middle cerebral artery occlusion was performed in diabetic Sprague‑Dawley rats. Treatment with selenium and the autophagy inhibitor 3‑methyladenine significantly reduced cerebral infarct volume, brain water content and Evans blue leakage, while increasing the expression of tight junction (TJ) proteins and decreasing that of autophagy‑related proteins (P<0.05). In addition, selenium increased the phosphorylation levels of PI3K, AKT and mTOR (P<0.05). A mouse bEnd.3 brain microvascular endothelial cell line was co‑cultured in vitro with an MA‑h mouse astrocyte‑hippocampal cell line to simulate the BBB. The cells were then subjected to hyperglycemia, followed by oxygen‑glucose deprivation for 1 h and reoxygenation for 24 h. It was revealed that selenium increased TJ protein levels, reduced BBB permeability, decreased autophagy levels and enhanced the expression of phosphorylated (p)‑AKT/AKT and p‑mTOR/mTOR proteins (P<0.05). Treatment with wortmannin (an inhibitor of PI3K) significantly prevented the beneficial effects of selenium on the BBB, whereas insulin‑like growth factor 1 (a PI3K activator) mimicked the effects of selenium. In conclusion, the present findings indicated that selenium can inhibit autophagy by regulating the PI3K/AKT/mTOR signaling pathway, significantly preventing BBB damage following cerebral I/R injury in hyperglycemic conditions.

Unripe Carica papaya Protects Methylglyoxal-Invoked Endothelial Cell Inflammation and Apoptosis via the Suppression of Oxidative Stress and Akt/MAPK/NF-κB Signals

Methylglyoxal (MGO), a highly reactive dicarbonyl compound, causes endothelial oxidative stress and vascular complications in diabetes. Excessive MGO-induced ROS production triggers eNOS uncoupling, inflammatory responses, and cell death signaling cascades. Our previous study reported that unripe Carica papaya (UCP) had antioxidant activities that prevented H₂O₂-induced endothelial cell death. Therefore, this study investigated the preventive effect of UCP on MGO-induced endothelial cell damage, inflammation, and apoptosis. The human endothelial cell line (EA.hy926) was pretreated with UCP for 24 h, followed by MGO-induced dicarbonyl stress. Treated cells were evaluated for intracellular ROS/O₂^•− formation, cell viability, apoptosis, NO releases, and cell signaling through eNOS, iNOS, COX-2, NF-κB, Akt, MAPK (JNK and p38), and AMPK/SIRT1 autophagy pathways. UCP reduced oxidative stress and diminished phosphorylation of Akt, stress-activated MAPK, leading to the decreases in NF-kB-activated iNOS and COX-2 expression. However, UCP had no impact on the autophagy pathway (AMPK and SIRT1). Although UCP pretreatment decreased eNOS phosphorylation, the amount of NO production was not altered. The signaling of eNOS and NO production were decreased after MGO incubation, but these effects were unaffected by UCP pretreatment. In summary, UCP protected endothelial cells against carbonyl stress by the mechanisms related to ROS/O₂^•− scavenging activities, suppression of inflammatory signaling, and inhibition of JNK/p38/apoptosis pathway. Thus, UCP shows considerable promise for developing novel functional food and nutraceutical products to reduce risks of endothelial inflammation and vascular complications in diabetes.

The involvement of autophagy in the maintenance of endothelial homeostasis: The role of mitochondria

Endothelial mitochondria play important signaling roles critical for the regulation of various cellular processes, including calcium signaling, ROS generation, NO synthesis or inflammatory response. Mitochondrial stress or disturbances in mitochondrial function may participate in the development and/or progression of endothelial dysfunction and could precede vascular diseases. Vascular functions are also strictly regulated by properly functioning degradation machinery, including autophagy and mitophagy, and tightly coordinated by mitochondrial and endoplasmic reticulum responses to stress. Within this review, current knowledge related to the development of cardiovascular disorders and the importance of mitochondria, endoplasmic reticulum and degradation mechanisms in vascular endothelial functions are summarized.

Prospects of honey in fighting against COVID-19: pharmacological insights and therapeutic promises

Honey and its compounds are drawing attention as an effective natural therapy because of its ability to attenuate acute inflammation through enhancing immune response. Several studies have proved its potential healing capability against numerous chronic diseases/conditions, including pulmonary disorders, cardiac disorders, diabetes, hypertension, autophagy dysfunction, bacterial, and fungal infections. More importantly, honey has proved its virucidal effect on several enveloped viruses such as HIV, influenza virus, herpes simplex, and varicella-zoster virus. Honey may be beneficial for patients with COVID-19 which is caused by an enveloped virus SARS-CoV-2 by boosting the host immune system, improving comorbid conditions, and antiviral activities. Moreover, a clinical trial of honey on COVID-19 patients is currently undergoing. In this review, we have tried to summarize the potential benefits of honey and its ingredients in the context of antimicrobial activities, some chronic diseases, and the host immune system. Thus, we have attempted to establish a relationship with honey for the treatment of COVID-19. This review will be helpful to reconsider the insights into the possible potential therapeutic effects of honey in the context of the COVID-19 pandemic. However, the effects of honey on SARS-CoV-2 replication and/or host immune system need to be further investigated by in vitro and in vivo studies.

Methylglyoxal-Induced Dysfunction in Brain Endothelial Cells via the Suppression of Akt/HIF-1α Pathway and Activation of Mitophagy Associated with Increased Reactive Oxygen Species

Methylglyoxal (MG) is a dicarbonyl compound, the level of which is increased in the blood of diabetes patients. MG is reported to be involved in the development of cerebrovascular complications in diabetes, but the exact mechanisms need to be elucidated. Here, we investigated the possible roles of oxidative stress and mitophagy in MG-induced functional damage in brain endothelial cells (ECs). Treatment of MG significantly altered metabolic stress as observed by the oxygen-consumption rate and barrier-integrity as found in impaired trans-endothelial electrical resistance in brain ECs. The accumulation of MG adducts and the disturbance of the glyoxalase system, which are major detoxification enzymes of MG, occurred concurrently. Reactive oxygen species (ROS)-triggered oxidative damage was observed with increased mitochondrial ROS production and the suppressed Akt/hypoxia-inducible factor 1 alpha (HIF-1α) pathway. Along with the disturbance of mitochondrial bioenergetic function, parkin-1-mediated mitophagy was increased by MG. Treatment of N-acetyl cysteine significantly reversed mitochondrial damage and mitophagy. Notably, MG induced dysregulation of tight junction proteins including occludin, claudin-5, and zonula occluden-1 in brain ECs. Here, we propose that diabetic metabolite MG-associated oxidative stress may contribute to mitochondrial damage and autophagy in brain ECs, resulting in the dysregulation of tight junction proteins and the impairment of permeability.

Autophagy Functions to Prevent Methylglyoxal-Induced Apoptosis in HK-2 Cells

Methylglyoxal (MGO), a reactive carbonyl species, causes cellular damage and is closely related to kidney disease, particularly diabetic nephropathy. Although MGO has been reported to induce autophagy and apoptosis, the relationships between the two pathways are unclear. Here, we evaluated whether autophagy may be the underlying mechanism inhibiting MGO-induced apoptosis. MGO treatment induced concentration- and time-dependent apoptosis in HK-2 cells. Moreover, MGO upregulated the autophagy markers p62 and LC3-II. Apoptosis caused by MGO was increased in ATG5-knockdown cells compared to that in wild-type cells. In contrast, autophagy activation by 5-aminoimidazole-4-carboxamide ribonucleotide resulted in reduced apoptosis, suggesting that autophagy played a role in protecting against MGO-induced cell death. To examine the mechanisms through which autophagy occurred following MGO stimulation, we investigated changes in AKT/mammalian target of rapamycin (mTOR) signaling. Autophagy induction by MGO treatment was not related to AKT/mTOR signaling; however, it did involve autophagy-related gene expression promoted by AMP-activated protein kinase-mediated transcription factors, such as forkhead box 1. Overall, our findings indicate that MGO-induced cellular damage can be mitigated by autophagy, suggesting that autophagy may be a potential therapeutic target for diseases such as diabetic nephropathy.

Molecular mechanisms of methylglyoxal-induced aortic endothelial dysfunction in human vascular endothelial cells

Methylglyoxal (MGO)-induced cellular apoptosis, oxidative stress, inflammation, and AGE formation are specific events that induce vascular endothelial cell (EC) toxicity in endothelial dysfunction (ED). MGO accumulates quickly in various tissues and plays a prominent role in the pathogeneses of several diabetic complications. Unbalanced angiogenesis is a gateway to the development of diabetic complications. EC apoptosis and autophagy work together to regulate angiogenesis by interacting with different angiogenic factors. In addition to understanding the deep mechanism regarding MGO-dependent autophagy/apoptosis may provide new therapeutic applications to treat diabetes and diabetic complications. Therefore, the present study aimed to investigate the regulatory effects of MGO-induced autophagy and apoptosis on angiogenesis in HAoEC and to elucidate the molecular mechanisms to discover new target base therapy for diabetes and diabetic complications. In MGO-stimulated HAoEC, protein expression was identified using a western blot, autophagosomes were observed by bio-transmission electron microscopy (TEM), and cell autophagic vacuoles and flux were measured using a confocal microscope. We found that MGO significantly induced autophagy, declined the pro-angiogenic effect, decreased proliferation, migration, and formation of tube-like structures, and increased autophagic vacuoles, flux and autophagosomes in the HAoEC in a dose-dependent manner. We observed that MGO-induced autophagic cell death and inhibited the ROS-mediated Akt/mTOR signaling pathway. MGO also triggered apoptosis by elevating the cleaved caspase-3 to Bax/Bcl-2 ratio and through activation of the ROS-mediated MAPKs (p-JNK, p-p38, and p-ERK) signaling pathway. Collectively, these findings suggest that autophagy and apoptosis inhibit angiogenesis via the ROS-mediated Akt/mTOR and MAPKs signaling pathways, respectively, when HAoEC are treated with MGO.

Autophagy-mediated occludin degradation contributes to blood-brain barrier disruption during ischemia in bEnd.3 brain endothelial cells and rat ischemic stroke models

Background

The blood–brain barrier (BBB) maintains homeostasis of the brain environment by tightly regulating the entry of substances from systemic circulation. A breach in the BBB results in increased permeability to potentially toxic substances and is an important contributor to amplification of ischemic brain damage. The precise molecular pathways that result in impairment of BBB integrity remain to be elucidated. Autophagy is a degradation pathway that clears damaged or unnecessary proteins from cells. However, excessive autophagy can lead to cellular dysfunction and death under pathological conditions.

Methods

In this study, we investigated whether autophagy is involved in BBB disruption in ischemia, using in vitro cells and in vivo rat models. We used brain endothelial bEnd.3 cells and oxygen glucose deprivation (OGD) to simulate ischemia in culture, along with a rat ischemic stroke model to evaluate the role of autophagy in BBB disruption during cerebral ischemia.

Results

OGD 18 h induced cellular dysfunction, and increased permeability with degradation of occludin and activation of autophagy pathways in brain endothelial cells. Immunostaining revealed that occludin degradation is co-localized with ischemic autophagosomes. OGD-induced occludin degradation and permeability changes were significantly decreased by inhibition of autophagy using 3-methyladenine (3-MA). Enhanced autophagic activity and loss of occludin were also observed in brain capillaries isolated from rats with middle cerebral artery occlusion (MCAO). Intravenous administration of 3-MA inhibited these molecular changes in brain capillaries, and recovered the increased permeability as determined using Evans blue.

Conclusions

Our findings provide evidence that autophagy plays an important role in ischemia-induced occludin degradation and loss of BBB integrity.

Dicarbonyl Stress and S-Glutathionylation in Cerebrovascular Diseases: A Focus on Cerebral Cavernous Malformations

Dicarbonyl stress is a dysfunctional state consisting in the abnormal accumulation of reactive α-oxaldehydes leading to increased protein modification. In cells, post-translational changes can also occur through S-glutathionylation, a highly conserved oxidative post-translational modification consisting of the formation of a mixed disulfide between glutathione and a protein cysteine residue. This review recapitulates the main findings supporting a role for dicarbonyl stress and S-glutathionylation in the pathogenesis of cerebrovascular diseases, with specific emphasis on cerebral cavernous malformations (CCM), a vascular disease of proven genetic origin that may give rise to various clinical signs and symptoms at any age, including recurrent headaches, seizures, focal neurological deficits, and intracerebral hemorrhage. A possible interplay between dicarbonyl stress and S-glutathionylation in CCM is also discussed.

Up-regulated microRNA-199b-3p represses the apoptosis of cerebral microvascular endothelial cells in ischemic stroke through down-regulation of MAPK/ERK/EGR1 axis

MicroRNAs (miRNAs) have emerged as key mediators of posttranscriptional gene silencing in both pathogenic and pathological aspects of ischemic stroke biology. Therefore, the purpose of present study was to explore the effect of microRNA-199b-3p (miR-199b-3p) on the cerebral microvascular endothelial cells (CMECs) in middle cerebral artery occlusion-reperfusion (MCAO-R) mice by regulating MAPK/ERK/EGR1 axis. Mice were used to establish MCAO-R models and to measure the expression of miR-199b-3p and the MAPK/ERK/EGR1 axis-related genes. CMECs were extracted from the MCAO-R mice. A series of mimic or inhibitor for miR-199b-3p, or U0126 (an inhibitor for the MAPK/ERK/EGR1 axis) were introduced to treat these CMECs. The levels of miR-199b-3p and MAPK/ERK/EGR1 axis-related genes in tissues and cells were detected. The effects miR-199b-3p on the process of CMECs, including cell viability, cell cycle and cell apoptosis were evaluated. miR-199b-3p expressed poorly in the brain tissues after MCAO-R, along with activated MAPK/ERK/EGR1 axis and increased CMECs apoptosis. CMECs transfected with miR-199b-3p mimics and U0126 manifested with increased cell viability, more cells arrested at the S stage, and inhibited apoptosis of CMECs. In conclusion, these key results demonstrated up-regulated miR-199b-3p could protect mice against ischemic stroke by inhibiting the apoptosis of CMECs through blockade of MAPK/ERK/EGR1 axis.

Proteostasis During Cerebral Ischemia

Cerebral ischemia is a complex pathology involving a cascade of cellular mechanisms, which deregulate proteostasis and lead to neuronal death. Proteostasis refers to the equilibrium between protein synthesis, folding, transport, and protein degradation. Within the brain proteostasis plays key roles in learning and memory by controlling protein synthesis and degradation. Two important pathways are implicated in the regulation of proteostasis: the unfolded protein response (UPR) and macroautophagy (called hereafter autophagy). Both are necessary for cell survival, however, their over-activation in duration or intensity can lead to cell death. Moreover, UPR and autophagy can activate and potentiate each other to worsen the issue of cerebral ischemia. A better understanding of autophagy and ER stress will allow the development of therapeutic strategies for stroke, both at the acute phase and during recovery. This review summarizes the latest therapeutic advances implicating ER stress or autophagy in cerebral ischemia. We argue that the processes governing proteostasis should be considered together in stroke, rather than focusing either on ER stress or autophagy in isolation.

HSPB8 over-expression prevents disruption of blood-brain barrier by promoting autophagic flux after cerebral ischemia/reperfusion injury

Heat-shock protein B8 (HSPB8) has been recently reported to confer neuroprotection against ischemia/reperfusion (I/R)-induced cerebral injury in vivo and in vitro. However, the molecular mechanism is still elusive. This study focused on the effect of intracerebroventricular (i.c.v) delivery of lenti-HSPB8 virus against neurological injury in a rat model of cerebral I/R and explored the underlying mechanism. We found that lentivirus i.c.v injection-induced HSPB8 over-expression strongly alleviated infarct volume, improved neurobehavioral outcomes, and reduced brain edema in rat middle cerebral artery occlusion/reperfusion (MCAO/R) model. Concomitantly, HSPB8 over-expression noticeably prevented blood-brain barrier (BBB) disruption after cerebral I/R injury as indicated by the reduction in Evans blue leakage and IgG detection in the ipsilateral hemisphere compared with the vehicle group. Moreover, immunoblotting and immunofluorescence staining of tight junction proteins claudin-5 and occludin showed that HSPB8 over-expression prevented the degradation of these proteins induced by MCAO/R, which indicated the protective effect of HSPB8 on BBB. Western blotting and immunostaining techniques were also utilized to analyze the expression of the markers of autophagy. We found that HSPB8 over-expression promoted autophagic flux, evidenced by increased ratio of LC3 I/II, accumulation of Beclin-1 expression and enhanced p62 degradation. i.c.v injection of 15 μg autophagy inhibitor 3-methyladenine (3-MA) was applied at the onset of reperfusion. The results showed that 3-MA elicited a significant loss of the protective effect of HSPB8 against MCAO/R-induced neurological defect, Evans blue extravasation, and the loss tight junction proteins, suggesting that the BBB protective role of HSPB8 was, at least in part, mediated through autophagy. Collectively, HSPB8 may represent a potential therapeutic agent for preserving BBB integrity following cerebral I/R injury. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/. Cover Image for this issue: doi: 10.1111/jnc.14488.

Genipin alleviates vascular hyperpermeability following hemorrhagic shock by up-regulation of SIRT3/autophagy

Genipin (GP) is commonly used to treat cardiovascular diseases; however, the protective action of GP against vascular hyperpermeability (VH) has not been reported. We previously reported that intrinsic apoptotic signaling (IAS) is involved in VH following hemorrhagic shock (HS). GP inhibits apoptosis, but the specific mechanism remains unclear. In the present study, we observed that GP protects against HS-induced VH in vitro and in vivo. We report that this protective effect is related to the inhibition of IAS by up-regulation of autophagy via sirtuin 3 (SIRT3). The endothelial cell hyperpermeability induced by HS was enhanced by GP; this was attenuated by 3-methyladenine (3MA), a specific inhibitor of autophagy, indicating the involvement of autophagy. Consistent with these results, we found that 3MA reversed the effects of GP on up-regulation of autophagy, and also diminished the protective effect of GP against IAS activation following HS. Furthermore, knockout of SIRT3 inhibited GP-induced autophagy, indicating the requirement of SIRT3 in the regulation of autophagy by GP. In rats, GP improved HS-induced VH, which was repressed by 3MA and 3-(1H-1,2,3-triazol-4-yl)pyridine (3-TYP), a SIRT3 inhibitor. In conclusion, these findings suggest that autophagy plays a protective effect in VH following HS; the protective effect of autophagy is reinforced by GP, which protects against IAS and VH by up-regulating SIRT3.

The role of autophagy in acute brain injury: A state of flux?

It is established that increased autophagy is readily detectable after various types of acute brain injury, including trauma, focal and global cerebral ischemia. What remains controversial, however, is whether this heightened detection of autophagy in brain represents a homeostatic or pathologic process, or an epiphenomenon. The ultimate role of autophagy after acute brain injury likely depends upon: 1) the degree of brain injury and the overall autophagic burden; 2) the capacity of individual cell types to ramp up autophagic flux; 3) the local redox state and signaling of parallel cell death pathways; 4) the capacity to eliminate damage associated molecular patterns and toxic proteins and metabolites both intra- and extracellularly; and 5) the timing of the pro- or anti-autophagic intervention. In this review, we attempt to reconcile conflicting studies that support both a beneficial and detrimental role for autophagy in models of acute brain injury.

NF-κB-Mediated Inflammation in the Pathogenesis of Intracranial Aneurysm and Subarachnoid Hemorrhage. Does Autophagy Play a Role?

The rupture of saccular intracranial aneurysms (IA) is the commonest cause of non-traumatic subarachnoid hemorrhage (SAH)—the most serious form of stroke with a high mortality rate. Aneurysm walls are usually characterized by an active inflammatory response, and NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) has been identified as the main transcription factor regulating the induction of inflammation-related genes in IA lesions. This transcription factor has also been related to IA rupture and resulting SAH. We and others have shown that autophagy interacts with inflammation in many diseases, but there is no information of such interplay in IA. Moreover, NF-κB, which is a pivotal factor controlling inflammation, is regulated by autophagy-related proteins, and autophagy is regulated by NF-κB signaling. It was also shown that autophagy mediates the normal functioning of vessels, so its disturbance can be associated with vessel-related disorders. Early brain injury, delayed brain injury, and associated cerebral vasospasm are among the most serious consequences of IA rupture and are associated with impaired function of the autophagy⁻lysosomal system. Further studies on the role of the interplay between autophagy and NF-κB-mediated inflammation in IA can help to better understand IA pathogenesis and to identify IA patients with an increased SAH risk.

Chloroquine Promotes the Recovery of Acute Spinal Cord Injury by Inhibiting Autophagy-Associated Inflammation and Endoplasmic Reticulum Stress

Spinal cord injury (SCI) is a severe nervous system disease that may lead to lifelong disability. Studies have shown that autophagy plays a key role in various diseases; however, the mechanisms regulating cross-talk between autophagy, inflammation, and endoplasmic reticulum (ER) stress during SCI recovery remain unclear. This study was designed to investigate the mechanism by which chloroquine (CQ) inhibits autophagy-associated inflammation and ER stress in rats during their recovery from acute SCI. We evaluated the locomotor function, level of autophagy, and levels of inflammatory cytokines and ER-stress-associated proteins and examined the degradation of the key regulator of inflammation inhibitor of kappa B alpha (I-κBα) through autophagy by analyzing the colocalization of I-κBα, p62, and microtubule-associated protein 1 light chain 3-II. In addition, overexpression of the p62 and activating transcription factor 4 (ATF4) silencing plasmids was used to verify the important roles for autophagic degradation and ER stress. In this study, locomotor function is improved, and autophagy and inflammation are significantly inhibited by, CQ treatment in the model rats. In addition, CQ significantly inhibits the degradation of ubiquitinated I-κBα and blocks the nuclear translocation of nuclear factor kappa B p65 and expression of inflammatory factors. Overexpression of p62 increases I-κBα degradation and improves inflammatory responses. Moreover, CQ treatment also inhibits the activation of ER stress in the rat SCI model, and the ATF4 signaling pathway is required for ER-stress-induced activation of autophagy. These findings reveal a novel mechanism underlying the beneficial effects of CQ on the recovery of SCI, particularly the mechanisms regulating cross-talk between autophagy, inflammation, and ER stress.

Methylglyoxal-induced AMPK activation leads to autophagic degradation of thioredoxin 1 and glyoxalase 2 in HT22 nerve cells

Methylglyoxal (MGO) is a major glycating agent that reacts with basic residues of proteins and promotes the formation of advanced glycation end products which are believed to play key roles in a number of pathologies, such as diabetes, Alzheimer's disease, and inflammation. We previously showed that MGO treatment targets the thioredoxin and the glyoxalase systems, leading to a decrease in Trx1 and Glo2 proteins in immortalized mouse hippocampal HT22 nerve cells. Here, we propose that autophagy is the underlying mechanism leading to Glo2 and Trx1 loss induced by MGO. The autophagic markers p62, and the lipidated and active form of LC3, were increased by MGO (0.5mM). Autophagy inhibition with bafilomycin or chloroquine prevented the decrease in Trx1 and Glo2 at 6 and 18h after MGO treatment. Proteasome inhibition by MG132 exacerbated the effect of MGO on Trx1 and Glo2 degradation (18h), further suggesting a role for autophagy. ATG5 small interfering RNA protected Trx1 and Glo2 from MGO-induced degradation, confirming Trx1 and Glo2 loss is mediated by autophagy. In the search for the signals that control autophagy, we found that AMPK activation, a known autophagy inducer, was markedly increased by MGO treatment. AMPK activation was confirmed by increased acetyl coenzyme A carboxylase phosphorylation, a direct AMPK substrate and by decreased mTOR phosphorylation, an indirect marker of AMPK activation. To confirm that MGO-mediated Trx1 and Glo2 degradation was AMPK-dependent, AMPK-deficient mouse embryonic fibroblasts (MEFs) were treated with MGO. Wildtype MEFs presented the expected decrease in Trx1 and Glo2, while MGO was ineffective in decreasing these proteins in AMPK-deficient cells. Overall, the data indicate that MGO activates autophagy in an AMPK-dependent manner, and that autophagy was responsible for Trx1 and Glo2 degradation, confirming that Trx1 and Glo2 are molecular targets of MGO.

Autophagy in hemorrhagic stroke: Mechanisms and clinical implications

Accumulating evidence advances the critical role of autophagy in brain pathology after stroke. Investigations employing autophagy induction or inhibition using pharmacological tools or autophagy-related gene knockout mice have recently revealed the biological significance of intact and functional autophagy in stroke. Most of the reported cases attest to a pro-survival role for autophagy in stroke, by facilitating removal of damaged proteins and organelles, which can be recycled for energy generation and cellular defenses. However, these observations are difficult to reconcile with equally compelling evidence demonstrating stroke-induced upregulation of brain cell death index that parallels enhanced autophagy. This begs the question of whether drug-induced autophagy during stroke culminates in improved or worsened pathological outcomes. A corollary fascinating hypothesis, but presents as a tricky conundrum, involves the effects of autophagy on cell death and inflammation, which are two main culprits in the disease progression of stroke-induced brain injury. Evidence has extended the roles of autophagy in inflammation via cytokine regulation in an unconventional secretion manner or by targeting inflammasomes for degradation. Moreover, in the recently concluded Vancouver Autophagy Symposium (VAS) held in 2014, the potential of selective autophagy for clinical treatment has been recognized. The role of autophagy in ischemic stroke has been reviewed previously in detail. Here, we evaluate the strength of laboratory and clinical evidence by providing a comprehensive summary of the literature on autophagy, and thereafter we offer our perspectives on exploiting autophagy as a drug target for cerebral ischemia, especially in hemorrhagic stroke.

Time-Dependent Changes in Apoptosis Upon Autophagy Inhibition in Astrocytes Exposed to Oxygen and Glucose Deprivation

Recent studies have implicated the role of autophagy in brain ischemia pathophysiology. However, it remains unclear whether autophagy activation is protective or detrimental to astrocytes undergoing ischemic stress. This study evaluated the influence of ischemia-induced autophagy on cell death and the course of intrinsic and extrinsic apoptosis in primary cultures of rat cortical astrocytes exposed to combined oxygen-glucose deprivation (OGD). The role of autophagy was assessed by pharmacological inhibition with 3-methyladenine (3-MA). Cell viability was evaluated by measuring LDH release and through the use of the alamarBlue Assay. Apoptosis and necrosis were determined by fluorescence microscopy after Hoechst 33,342 and propidium iodide staining, respectively. The levels of apoptosis-related proteins were analyzed by immunoblotting. The downregulation of autophagy during OGD resulted in decreased cell viability and time-dependent changes in levels of apoptosis and necrosis. After short-term OGD (1, 4 h), cells treated with 3-MA showed higher level of cleaved caspase 3 compared with control cells. This result was consistent with an evaluation of apoptotic cell number by fluorescence microscopy. However, after prolonged exposure to OGD (8, 24 h), the number of apoptotic astrocytes (microscopically evaluated) did not differ or was even lower (as marked by caspase 3) in the presence of the autophagy inhibitor in comparison to the control. A higher level of necrosis was observed in 3-MA-treated cells compared to non-treated cells after 24 h OGD. The downregulation of autophagy caused time-dependent changes in both extrinsic (cleaved caspase 8, TNFα) and intrinsic (cleaved caspase 9) apoptotic pathways. Our results strongly indicate that the activation of autophagy in astrocytes undergoing ischemic stress is an adaptive mechanism, which allows for longer cell survival by delaying the initiation of apoptosis and necrosis.

Methylglyoxal in Metabolic Disorders: Facts, Myths, and Promises

Glucose and fructose metabolism originates the highly reactive byproduct methylglyoxal (MG), which is a strong precursor of advanced glycation end products (AGE). The MG has been implicated in classical diabetic complications such as retinopathy, nephropathy, and neuropathy, but has also been recently associated with cardiovascular diseases and central nervous system disorders such as cerebrovascular diseases and dementia. Recent studies even suggested its involvement in insulin resistance and beta-cell dysfunction, contributing to the early development of type 2 diabetes and creating a vicious circle between glycation and hyperglycemia. Despite several drugs and natural compounds have been identified in the last years in order to scavenge MG and inhibit AGE formation, we are still far from having an effective strategy to prevent MG-induced mechanisms. This review summarizes the endogenous and exogenous sources of MG, also addressing the current controversy about the importance of exogenous MG sources. The mechanisms by which MG changes cell behavior and its involvement in type 2 diabetes development and complications and the pathophysiological implication are also summarized. Particular emphasis will be given to pathophysiological relevance of studies using higher MG doses, which may have produced biased results. Finally, we also overview the current knowledge about detoxification strategies, including modulation of endogenous enzymatic systems and exogenous compounds able to inhibit MG effects on biological systems.

Neuroprotection of hypoxic postconditioning against global cerebral ischemia through influencing posttranslational regulations of heat shock protein 27 in adult rats

We previously reported that hypoxic postconditioning (HPC) ameliorated hippocampal neuronal death induced by transient global cerebral ischemia (tGCI) in adult rats. However, the mechanism of HPC-induced neuroprotection is still elusive. Notably, heat shock protein 27 (Hsp27) has recently emerged as a potent neuroprotectant in cerebral ischemia. Although its robust protective effect on stroke has been recognized, the mechanism of Hsp27-mediated neuroprotection is largely unknown. Here, we investigated the potential molecular mechanism by which HPC modulates the posttranslational regulations of Hsp27 after tGCI. We found that HPC increased expression of Hsp27 in CA1 subregion after tGCI. Inhibition of Hsp27 expression with lentivirus-mediated short hairpin RNA (shRNA) abolished the neuroprotection induced by HPC in vivo. Furthermore, pretreatment with cycloheximide, a protein synthesis inhibitor, resulted in a significant decrease in the degradation rate of Hsp27 protein in postconditioned rats, suggesting that the increase in the expression of Hsp27 after HPC might result from its decreased degradation. Next, pretreatment with leupeptin, a lysosomal inhibitor, resulted in an accumulation of Hsp27 after tGCI, indicating that autophagic pathway may be responsible for the degradation of Hsp27. We further showed that the formation of LC3-II and autophagosomes increased after tGCI. Meanwhile, the degradation of Hsp27 was suppressed and neuronal damage was reduced when blocking autophagy with 3-Methyladenine, whereas activating autophagy with rapamycin showed an opposite tendency. Lastly, we confirmed that HPC increased the expression of phosphorylated MAPKAP kinase 2 (MK2) and Hsp27 after tGCI. Also, administration of SB203580, a p38 mitogen-activated protein kinase inhibitor, decreased the expressions of phosphorylated MK2 and Hsp27. Our results suggested that inhibition of Hsp27 degradation mediated by down-regulation of autophagy may induce ischemic tolerance after HPC. Additionally, phosphorylation of Hsp27 induced by MK2 might be associated with the neuroprotection of HPC.

Methylglyoxal-Glyoxalase 1 Balance: The Root of Vascular Damage

The highly reactive dicarbonyl methylglyoxal (MGO) is mainly formed as byproduct of glycolysis. Therefore, high blood glucose levels determine increased MGO accumulation. Nonetheless, MGO levels are also increased as consequence of the ineffective action of its main detoxification pathway, the glyoxalase system, of which glyoxalase 1 (Glo1) is the rate-limiting enzyme. Indeed, a physiological decrease of Glo1 transcription and activity occurs not only in chronic hyperglycaemia but also with ageing, during which MGO accumulation occurs. MGO and its advanced glycated end products (AGEs) are associated with age-related diseases including diabetes, vascular dysfunction and neurodegeneration. Endothelial dysfunction is the first step in the initiation, progression and clinical outcome of vascular complications, such as retinopathy, nephropathy, impaired wound healing and macroangiopathy. Because of these considerations, studies have been centered on understanding the molecular basis of endothelial dysfunction in diabetes, unveiling a central role of MGO-Glo1 imbalance in the onset of vascular complications. This review focuses on the current understanding of MGO accumulation and Glo1 activity in diabetes, and their contribution on the impairment of endothelial function leading to diabetes-associated vascular damage.

The Autophagoproteasome a Novel Cell Clearing Organelle in Baseline and Stimulated Conditions

Protein clearing pathways named autophagy (ATG) and ubiquitin proteasome (UP) control homeostasis within eukaryotic cells, while their dysfunction produces neurodegeneration. These pathways are viewed as distinct biochemical cascades occurring within specific cytosolic compartments owing pathway-specific enzymatic activity. Recent data strongly challenged the concept of two morphologically distinct and functionally segregated compartments. In fact, preliminary evidence suggests the convergence of these pathways to form a novel organelle named autophagoproteasome. This is characterized in the present study by using a cell line where, mTOR activity is upregulated and autophagy is suppressed. This was reversed dose-dependently by administering the mTOR inhibitor rapamycin. Thus, we could study autophagoproteasomes when autophagy was either suppressed or stimulated. The occurrence of autophagoproteasome was shown also in non-human cell lines. Ultrastructural morphometry, based on the stochiometric binding of immunogold particles allowed the quantitative evaluation of ATG and UP component within autophagoproteasomes. The number of autophagoproteasomes increases following mTOR inhibition. Similarly, mTOR inhibition produces overexpression of both LC3 and P20S particles. This is confirmed by the fact that the ratio of free vs. autophagosome-bound LC3 is similar to that measured for P20S, both in baseline conditions and following mTOR inhibition. Remarkably, within autophagoproteasomes there is a slight prevalence of ATG compared with UP components for low rapamycin doses, whereas for higher rapamycin doses UP increases more than ATG. While LC3 is widely present within cytosol, UP is strongly polarized within autophagoproteasomes. These fine details were evident at electron microscopy but could not be deciphered by using confocal microscopy. Despite its morphological novelty autophagoproteasomes appear in the natural site where clearing pathways (once believed to be anatomically segregated) co-exist and they are likely to interact at molecular level. In fact, LC3 and P20S co-immunoprecipitate, suggesting a specific binding and functional interplay, which may be altered by inhibiting mTOR. In summary, ATG and UP often represent two facets of a single organelle, in which unexpected amount of enzymatic activity should be available. Thus, autophagoproteasome may represent a sophisticated ultimate clearing apparatus.