Endoplasmic reticulum stress-induced neuronal inflammatory response and apoptosis likely plays a key role in the development of diabetic encephalopathy

Early evidence of beneficial and protective effects of Protectin DX treatment on behavior responses and type-1 diabetes mellitus related-parameters: A non-clinical approach

Protectin DX (PDX), a specialized pro-resolving lipid mediator, presents potential therapeutic applications across various medical conditions due to its anti-inflammatory and antioxidant properties. Since type-1 diabetes mellitus (T1DM) is a disease with an inflammatory and oxidative profile, exploring the use of PDX in addressing T1DM and its associated comorbidities, including diabetic neuropathic pain, depression, and anxiety becomes urgent. Thus, in the current study, after 2 weeks of T1DM induction with streptozotocin (60 mg/kg) in Wistar rats, PDX (1, 3, and 10 ng/animal; i.p. injection of 200 μl/animal) was administered specifically on days 14, 15, 18, 21, 24, and 27 after T1DM induction. We investigated the PDX's effectiveness in alleviating neuropathic pain (mechanical allodynia; experiment 1), anxiety-like and depressive-like behaviors (experiment 2). Also, we studied whether the PDX treatment would induce antioxidant effects in the blood plasma, hippocampus, and prefrontal cortex (experiment 3), brain areas involved in the modulation of emotions. For evaluating mechanical allodynia, animals were repeatedly submitted to the Von Frey test; while for studying anxiety-like responses, animals were submitted to the elevated plus maze (day 26) and open field (day 28) tests. To analyze depressive-like behaviors, the animals were tested in the modified forced swimming test (day 28) immediately after the open field test. Our data demonstrated that PDX consistently increased the mechanical threshold throughout the study at the two highest doses, indicative of antinociceptive effect. Concerning depressive-like and anxiety-like behavior, all PDX doses effectively prevented these behaviors when compared to vehicle-treated T1DM rats. The PDX treatment significantly protected against the increased oxidative stress parameters in blood plasma and in hippocampus and prefrontal cortex. Interestingly, treated animals presented improvement on diabetes-related parameters by promoting weight gain and reducing hyperglycemia in T1DM rats. These findings suggest that PDX improved diabetic neuropathic pain, and induced antidepressant-like and anxiolytic-like effects, in addition to improving parameters related to the diabetic condition. It is worth noting that PDX also presented a protective action demonstrated by its antioxidant effects. To conclude, our findings suggest PDX treatment may be a promising candidate for improving the diabetic condition per se along with highly disabling comorbidities such as diabetic neuropathic pain and emotional disturbances associated with T1DM.

Platycodin D Ameliorates Cognitive Impairment in Type 2 Diabetes Mellitus Mice via Regulating PI3K/Akt/GSK3β Signaling Pathway

Objectives: The aim of this study was to investigate the ameliorative effect of platycodin D (PD) on cognitive dysfunction in type 2 diabetes mellitus (T2DM) and its potential molecular mechanisms of action in vivo and in vitro. Materials and methods: An animal model of cognitive impairment in T2DM was established using a single intraperitoneal injection of streptozotocin (100 mg/kg) after 8 weeks of feeding a high-fat diet to C57BL/6 mice. In vitro, immunofluorescence staining and Western blot were employed to analyze the effects of PD on glucose-induced neurotoxicity in mouse hippocampal neuronal cells (HT22). Results: PD (2.5 mg/kg) treatment for 4 weeks significantly suppressed the rise in fasting blood glucose in T2DM mice, improved insulin secretion deficiency, and reversed abnormalities in serum triglyceride, cholesterol, low-density lipoprotein, and high-density lipoprotein levels. Meanwhile, PD ameliorated choline dysfunction in T2DM mice and inhibited the production of oxidative stress and apoptosis-related proteins of the caspase family. Notably, PD dose-dependently prevents the loss of mitochondrial membrane potential, promotes phosphorylation of phosphatidylinositol 3 kinase and protein kinase B (Akt) in vitro, activates glycogen synthase kinase 3β (GSK3β) expression at the Ser9 site, and inhibits Tau protein hyperphosphorylation. Conclusions: These findings clearly indicated that PD could alleviate the neurological damage caused by T2DM, and the phosphorylation of Akt at Ser473 may be the key to its effect.

Berberine improves cognitive impairment by alleviating brain atrophy and promoting white matter reorganization in diabetic db/db mice: a magnetic resonance imaging-based study

Diabetic cognitive impairment is a common complication in type 2 diabetes. Berberine (BBR) is an isoquinoline alkaloid that has been shown to have neuroprotective effects against diabetes. This study aimed to investigate the effect of BBR on the gray and white matter of the brain by using magnetic resonance imaging (MRI) and to explore the underlying mechanisms. The study used diabetic db/db mice and administered BBR (50 and 100 mg/kg) intragastrically for twelve weeks. Morris water maze was applied to examine cognitive function. T2-weighted imaging (T2WI) was performed to assess brain atrophy, and diffusion tensor imaging (DTI) combined with fiber tracking was conducted to monitor the structural integrity of the white matter, followed by histological immunostaining. Furthermore, the protein expressions of the phosphatidylinositol 3-kinase (PI3K)/ protein kinase B (AKT)/ glycogen synthase kinase-3β (GSK-3β) were detected. The results revealed that BBR significantly improved the spatial learning and memory of the db/db mice. T2WI exhibited ameliorated brain atrophy in the BBR-treated db/db mice, as evidenced by reduced ventricular volume accompanied by increased hippocampal volumes. DTI combined with fiber tracking revealed that BBR increased FA, fiber density and length in the corpus callosum/external capsule of the db/db mice. These imaging findings were confirmed by histological immunostaining. Notably, BBR significantly enhanced the protein levels of phosphorylated AKT at Ser473 and GSK-3β at Ser9. Collectively, this study demonstrated that BBR significantly improved the cognitive function of the diabetic db/db mice through ameliorating brain atrophy and promoting white matter reorganization via AKT/GSK-3β pathway.

Naoxinqing tablet protects against cerebral ischemic/reperfusion injury by regulating ampkα/NAMPT/SIRT1/PGC-1α pathway

AIM OF THE STUDY

Naoxinqing (NXQ) tablets are derived from persimmon leaves and are widely used in China for promoting blood circulation and removing blood stasis in China. We aimed to explore whether NXQ has the therapeutic effect on ischemic stroke and explored its possible mechanism.

MATERIALS AND METHODS

The cerebral artery occlusion/reperfusion (MCAO/R) surgery was used to establish the cerebral ischemic/reperfusion rat model. NXQ (60 mg/kg and 120 mg/kg) were administered orally. The TTC staining, whole brain water content, histopathology staining, immunofluorescent staining, enzyme-linked immunosorbent assay (ELISA) and Western blot analyses were performed to determine the therapeutical effect of NXQ on MCAO/R rats.

RESULTS

The study demonstrated that NXQ reduced the cerebral infarction volumes and neurologic deficits in MCAO/R rats. The neuroprotective effects of NXQ were accompanied by inhibited oxidative stress and inflammation. The nerve regeneration effects of NXQ were related to regulating the AMPKα/NAMPT/SIRT1/PGC-1α pathway.

CONCLUSION

In summary, our results revealed that NXQ had a significant protective effect on cerebral ischemia-reperfusion injury in rats. This study broadens the therapeutic scope of NXQ tablets and provides new neuroprotective mechanisms of NXQ as an anti-stroke therapeutic agent.

Central insulin dysregulation in antipsychotic-naïve first-episode psychosis: In silico exploration of gene expression signatures

Antipsychotic drug (AP)-naïve first-episode psychosis (FEP) patients display premorbid cognitive dysfunctions and dysglycemia. Brain insulin resistance may link metabolic and cognitive disorders in humans. This suggests that central insulin dysregulation represents a component of the pathophysiology of psychosis spectrum disorders (PSDs). Nonetheless, the links between central insulin dysregulation, dysglycemia, and cognitive deficits in PSDs are poorly understood. We investigated whether AP-naïve FEP patients share overlapping brain gene expression signatures with central insulin perturbation (CIP) in rodent models. We systematically compiled and meta-analyzed peripheral transcriptomic datasets of AP-naïve FEP patients along with hypothalamic and hippocampal datasets of CIP rodent models to identify common transcriptomic signatures. The common signatures were used for pathway analysis and to identify potential drug treatments with discordant (reverse) signatures. AP-naïve FEP and CIP (hypothalamus and hippocampus) shared 111 and 346 common signatures respectively, which were associated with pathways related to inflammation, endoplasmic reticulum stress, and neuroplasticity. Twenty-two potential drug treatments were identified, including antidiabetic agents. The pathobiology of PSDs may include central insulin dysregulation, which contribute to dysglycemia and cognitive dysfunction independently of AP treatment. The identified treatments may be tested in early psychosis patients to determine if dysglycemia and cognitive deficits can be mitigated.

The activation of spliced X-box binding protein 1 by isorhynchophylline therapy improves diabetic encephalopathy

The primary symptom of diabetic encephalopathy (DE), a kind of central diabetic neuropathy caused by diabetes mellitus (DM), is cognitive impairment. In addition, the tetracyclic oxindole alkaloid isorhynchophylline (IRN) helps lessen cognitive impairment. However, it is still unclear how IRN affects DM and DE and what mechanisms are involved. The effectiveness of IRN on brain insulin resistance was carefully examined in this work, both in vitro and in vivo. We found that IRN accelerates spliced form of X-box binding protein 1 (sXBP1) translocation into the nucleus under high glucose conditions in vitro. IRN also facilitates the nuclear association of pCREB with sXBP1 and the binding of regulatory subunits of phosphatidylinositol 3-kinase (PI3K) p85α or p85β with XBP1 to restore high glucose impairment. Also, IRN treatment improves high glucose-mediated impairment of insulin signaling, endoplasmic reticulum stress, and pyroptosis/apoptosis by depending on sXBP1 in vitro. In vivo studies suggested that IRN attenuates cognitive impairment, ameliorating peripheral insulin resistance, activating insulin signaling, inactivating activating transcription factor 6 (ATF6) and C/EBP homology protein (CHOP), and mitigating pyroptosis/apoptosis by stimulation of sXBP1 nuclear translocation in the brain. In summary, these data indicate that IRN contributes to maintaining insulin homeostasis by activating sXBP1 in the brain. Thus, IRN is a potent antidiabetic agent as well as an sXBP1 activator that has promising potential for the prevention or treatment of DE.

Flavonols as a Potential Pharmacological Intervention for Alleviating Cognitive Decline in Diabetes: Evidence from Preclinical Studies

Diabetes mellitus is a complex metabolic disease associated with reduced synaptic plasticity, atrophy of the hippocampus, and cognitive decline. Cognitive impairment results from several pathological mechanisms, including increased levels of advanced glycation end products (AGEs) and their receptors, prolonged oxidative stress and impaired activity of endogenous mechanisms of antioxidant defense, neuroinflammation driven by the nuclear factor kappa-light-chain enhancer of activated B cells (NF-κB), decreased expression of brain-derived neurotrophic factor (BDNF), and disturbance of signaling pathways involved in neuronal survival and cognitive functioning. There is increasing evidence that dietary interventions can reduce the risk of various diabetic complications. In this context, flavonols, a highly abundant class of flavonoids in the human diet, are appreciated as a potential pharmacological intervention against cognitive decline in diabetes. In preclinical studies, flavonols have shown neuroprotective, antioxidative, anti-inflammatory, and memory-enhancing properties based on their ability to regulate glucose levels, attenuate oxidative stress and inflammation, promote the expression of neurotrophic factors, and regulate signaling pathways. The present review gives an overview of the molecular mechanisms involved in diabetes-induced cognitive dysfunctions and the results of preclinical studies showing that flavonols have the ability to alleviate cognitive impairment. Although the results from animal studies are promising, clinical and epidemiological studies are still needed to advance our knowledge on the potential of flavonols to improve cognitive decline in diabetic patients.

Magnetic resonance imaging detects cerebral gray and white matter injury correlated with cognitive impairments in diabetic db/db mice

Type-2 diabetes not only causes gray matter injury but also induces widespread white matter damages, which may contribute the cognitive impairments. This study aimed to assess the structural alterations of the gray and white matter in 20-week-old diabetic db/db mice using magnetic resonance imaging including T2-weighted imaging (T2WI) and diffusion tensor imaging (DTI), and to correlate them with the cognitive performance detected by Morris water maze (MWM). The results revealed impaired spatial learning and memory in db/db mice. T2WI detected severe brain atrophy involving the hippocampus and cortex after diabetes. DTI showed reduced fractional anisotropy (FA) in the cortex, hippocampus, corpus callosum/external capsule, and increased radial diffusivity in the corpus callosum/external capsule of the db/db mice. The immunostaining confirmed the MRI findings showing decreased cell density in the cortex, hippocampus, and reduced integrated optical density of Luxol fast blue staining in the corpus callosum/external capsule. The correlational analysis revealed that the T2WI-derived tissue atrophy and DTI-derived FA in the relevant gray matter and white matter significantly correlated with the behavior performance in the MWM test. Collectively, the present in vivo MRI detected varying degrees of structural abnormalities in the gray and white matter of db/db mice, which might be favorable predictors of diabetic cognitive dysfunction. Our findings might provide new clues for identifying gray and white matter damages associated with cognitive decline, which is imperative for the evaluation of potential pharmacological therapies in preclinical phase.

Identification of ligustrazine-based analogs of piperlongumine as potential anti-ischemic stroke agents

Piper longum has a specific aroma and spicy taste. In addition to edible value, current studies have shown that piper longum also has pharmacological activities such as anti-platelet aggregation, anti-inflammation, anti-cancer, anti-diabetes and anti-depression. Piperlongumine is an alkaloid isolated from Piper longum. Based on our previous studies, four Piperlongumine analogs were synthesized, and their anti-platelet aggregation activities were evaluated. Among them, compound 8 has the strongest anti-platelet aggregation activity. Therefore, compound 8 was docked with stroke-related protein targets, and it was found that compound 8 had good binding affinity to MRTF-A complex and Bcl-2. Through animal experiments, it was found that compound 8 could significantly improve the pathological damage of brain tissue after ischemia and could increase the expression of MRTF-A and Bcl-2 in cerebral cortex in rats. These results suggest that compound 8 may have a good inhibitory effect on apoptosis and tissue structurel disorders induced by cerebral ischemia-reperfusion, so as to reduce the injury caused by ischemic stroke.

Caffeine protects against hippocampal alterations in type 2 diabetic rats via modulation of gliosis, inflammation and apoptosis

Type 2 diabetes (T2D) is implicated in the injury of several organs, including the brain resulting in neuronal damage, which may lead to cognitive impairment and dementia. Additionally, it is linked to inflammation, cytokine release, apoptosis and various degenerative conditions. Astrocytes and microglia might have a role in mediating these processes. Caffeine, a psychoactive beverage, has been shown to reduce the risk of cognitive and memory impairment. This study proposes anti-inflammatory and anti-apoptotic role of caffeine, which can be mediated via microglia/astrocyte activation and overexpression of pro-inflammatory molecules. T2D was induced in rats by feeding with high fat high sugar diet and injecting a single low dose streptozotocin (STZ) intraperitoneally. Other diabetic rats were given caffeine orally (in two doses) for 5 weeks, starting 1 week before STZ injection. Measurement of plasma cytokines, TNFα and IL6, was performed using enzyme-linked immunosorbent assay (ELISA) technique. After sacrificing animals, brains were obtained and processed for histological evaluation. Immunohistochemistry was also performed using the following primary antibodies, anti-astrocyte marker GFAP, anti-microglia marker CD11b and apoptotic marker (anti-cleaved caspase-3). There was upregulation of IL6 and TNF-α in diabetic rats. Additionally, histological evaluation of the hippocampus of diabetic rats revealed cellular degeneration. There was increased immunostaining of GFAP, CD11b and cleaved caspase-3 in diabetic rats. Pretreatment with caffeine to diabetic rats, resulted in improvement of structural changes and decrease in cytokine levels and immuno-markers, expression, and this was in a dose-dependent manner. In conclusion, caffeine had an ameliorative role in enhancing hippocampal degenerative changes in T2D.

Spermidine inhibits high glucose-induced endoplasmic reticulum stress in HT22 cells by upregulation of growth differentiation factor 11

Hyperglycemia-induced neuronal endoplasmic reticulum (ER) stress is particularly important for the pathogenesis of diabetic encephalopathy. Spermidine (Spd) has neuroprotection in several nervous system diseases. Our current study to explore the potential protective role of Spd in hyperglycemia-induced neuronal ER stress and the underlying mechanisms. HT22 cells were treated with high glucose (HG) to establish an in-vitro model of hyperglycemia toxicity. The HT22 cells' activity was tested by cell counting kit-8 assay. RNA interference technology was used to silence the expression of growth differentiation factor 11 (GDF11) in HT22 cells. The GDF11 expression levels of mRNA were assessed using reverse transcription-PCR (RT-PCR). Western blotting analysis was applied to evaluate the expressions of GRP78 and cleaved caspase-12. Spd markedly abolished HG-exerted decline in cell viability as well as upregulations of GRP78 and cleaved caspase-12 in HT22 cells, indicating the protection of Spd against HG-induced neurotoxicity and ER stress. Furthermore, we showed that Spd upregulated the expression of GDF11 in HG-exposed HT22 cells. While, silenced GDF11 expression by RNA interference reversed the protective effects of Spd on HG-elicited neurotoxicity and ER stress in HT22 cells. These results indicated that Spd prevents HG-induced neurotoxicity and ER stress through upregulation of GDF11. Our findings identify Spd as a potential treatment for diabetic encephalopathy as well as ER stress-related neurologic diseases.

Folium Ginkgo extract and tetramethylpyrazine sodium chloride injection (Xingxiong injection) protects against focal cerebral ischaemia/reperfusion injury via activating the Akt/Nrf2 pathway and inhibiting NLRP3 inflammasome activation

CONTEXT

Folium Ginkgo extract and tetramethylpyrazine sodium chloride injection (Xingxiong injection) is a compound preparation commonly used for treating cerebral ischaemia/reperfusion injury in ischaemic stroke in China. However, its potential mechanisms on ischaemic stroke remain unknown.

OBJECTIVE

This study explores the potential mechanisms of Xingxiong injection in vivo or in vitro.

MATERIALS AND METHODS

Sprague-Dawley (SD) rats were randomly assigned to five groups: the sham (normal saline), the model (normal saline) and the Xingxiong injection groups (12.5, 25 or 50 mL/kg). The rats were subjected to 2 h of middle cerebral artery occlusion (MCAO) followed by reperfusion for 14 d. Xingxiong injection was administered via intraperitoneal (i.p.) injection immediately after ischaemia induction for 14 d. Afterwards, rats were sacrificed at 14 d induced by administration of Xingxiong injection.

RESULTS

Xingxiong injection significantly reduces infarct volume (23%) and neurological deficit scores (93%) compared with the MCAO/R group. Additionally, Xingxiong injection inhibits the loss in mitochondrial membrane potential (43%) and reduces caspase-3 level (44%), decreases NOX (41%), protein carbonyl (29%), 4-HNE (40%) and 8-OhdG (41%) levels, inhibits the expression of inflammatory factors, such as TNF-α (26%), IL-1β (34%), IL-6 (39%), MCP-1 (36%), CD11a (41%) and ICAM-1 (43%). Moreover, Xingxiong injection can increase p-Akt/Akt (35%) and Nrf2 (47%) protein expression and inhibit NLRP3 (42%) protein expression.

CONCLUSIONS

Xingxiong injection prevents cerebral ischaemia/reperfusion injury via activating the Akt/Nrf2 pathway and inhibiting NLRP3 inflammasome. These findings provide experimental evidence for clinical use of drugs in the treatment of ischaemic stroke.

Cellular stress modulates severity of the inflammatory response in lungs via cell surface BiP

Inflammation is a central pathogenic feature of the acute respiratory distress syndrome (ARDS) in COVID-19. Previous pathologies such as diabetes, autoimmune or cardiovascular diseases become risk factors for the severe hyperinflammatory syndrome. A common feature among these risk factors is the subclinical presence of cellular stress, a finding that has gained attention after the discovery that BiP (GRP78), a master regulator of stress, participates in the SARS-CoV-2 recognition. Here, we show that BiP serum levels are higher in COVID-19 patients who present certain risk factors. Moreover, early during the infection, BiP levels predict severe pneumonia, supporting the use of BiP as a prognosis biomarker. Using a mouse model of pulmonary inflammation, we observed increased levels of cell surface BiP (cs-BiP) in leukocytes during inflammation. This corresponds with a higher number of neutrophiles, which show naturally high levels of cs-BiP, whereas alveolar macrophages show a higher than usual exposure of BiP in their cell surface. The modulation of cellular stress with the use of a clinically approved drug, 4-PBA, resulted in the amelioration of the lung hyperinflammatory response, supporting the anti-stress therapy as a valid therapeutic strategy for patients developing ARDS. Finally, we identified stress-modulated proteins that shed light into the mechanism underlying the cellular stress-inflammation network in lungs.

The regulatory role of Gnao1 protein in diabetic encephalopathy in KK-Ay mice and streptozotocin-induced diabetic rats

AIMS

To investigate the regulation and functional role of Gnao1 in the brain of diabetic encephalopathy (DE) in various animal models.

RESULTS

Data from the biochemical and behavioral studies showed that DE models were successful induced in streptozotocin treatment animals and KK-Ay mice. Gnao1 was down regulated in the brain tissues of these two diabetes animal models with significant cognition deficiency. It suggested that the changes in DE are also related to dementia such as Alzheimer's disease (AD). Our study also showed that the expression of adrenergic α2 receptor (Adr-α2R), the upstream protein of Gnao1, was decreased in DE animal models. Furthermore, many downstream proteins of Gnao1 also altered, among which cAMP and PKA proteins were increased, CREB and BDNF proteins were decreased both in animal models and in the cell levels. In addition, Gnao1 silencing leads to the increase of reactive oxygen species (ROS) and the decreased proliferation in cultured primary astrocytes, which means that the deficiency of Gnao1 might not be benefit for DE.

CONCLUSION

Our findings demonstrated the importance of Gnao1 in DE and suggested Gnao1 as a novel marker and a promising therapeutic target for DE and dementia in animal models.

The role of hypothalamic endoplasmic reticulum stress in schizophrenia and antipsychotic-induced weight gain: A narrative review

Schizophrenia (SCZ) is a serious mental illness that affects 1% of people worldwide. SCZ is associated with a higher risk of developing metabolic disorders such as obesity. Antipsychotics are the main treatment for SCZ, but their side effects include significant weight gain/obesity. Despite extensive research, the underlying mechanisms by which SCZ and antipsychotic treatment induce weight gain/obesity remain unclear. Hypothalamic endoplasmic reticulum (ER) stress is one of the most important pathways that modulates inflammation, neuronal function, and energy balance. This review aimed to investigate the role of hypothalamic ER stress in SCZ and antipsychotic-induced weight gain/obesity. Preliminary evidence indicates that SCZ is associated with reduced dopamine D2 receptor (DRD2) signaling, which significantly regulates the ER stress pathway, suggesting the importance of ER stress in SCZ and its related metabolic disorders. Antipsychotics such as olanzapine activate ER stress in hypothalamic neurons. These effects may induce decreased proopiomelanocortin (POMC) processing, increased neuropeptide Y (NPY) and agouti-related protein (AgRP) expression, autophagy, and leptin and insulin resistance, resulting in hyperphagia, decreased energy expenditure, and central inflammation, thereby causing weight gain. By activating ER stress, antipsychotics such as olanzapine activate hypothalamic astrocytes and Toll-like receptor 4 signaling, thereby causing inflammation and weight gain/obesity. Moreover, evidence suggests that antipsychotic-induced ER stress may be related to their antagonistic effects on neurotransmitter receptors such as DRD2 and the histamine H1 receptor. Taken together, ER stress inhibitors could be a potential effective intervention against SCZ and antipsychotic-induced weight gain and inflammation.

Behavioral and Molecular Effects of Thapsigargin-Induced Brain ER- Stress: Encompassing Inflammation, MAPK, and Insulin Signaling Pathway

Accumulation of misfolded proteins, known as endoplasmic reticulum (ER) stress, is known to participate in Alzheimer’s disease (AD). AD is also correlated with impaired central insulin signaling. However, few studies have probed the relationship between memory, central ER stress, inflammation, hippocampal mitogen-activated protein kinase (MAPK) activity and insulin resistance. The present study aimed to investigate the causative role and underlying mechanisms of brain ER stress in memory impairment and develop a reliable animal model for ER-mediated memory loss. Thapsigargin (TG), a known ER stress activator, was centrally administered. The cognitive function of animals was evaluated by the Morris Water Maze (MWM). To verify the induction of central ER stress, we investigated the mRNA expression of UPR markers in the hippocampus. In addition, the activation of ER stress markers, including Bip, CHOP, and some related apoptosis and pro-inflammatory proteins, such as caspase-3, Bax, Bcl-2, TNF-α, MAPK, and insulin signaling markers, were assessed by Western-blots. The results demonstrated that TG impairs spatial cognition and hippocampal insulin signaling. Meanwhile, molecular results showed a concurrent increment of hippocampal UPR markers, apoptosis, P38 activity, and TNF-α. This study introduced TG-induced ER stress as a pharmacological model for memory impairment in rats and revealed some underlying mechanisms.

The IRE1/JNK signaling pathway regulates inflammation cytokines and production of glomerular extracellular matrix in the acute kidney injury to chronic kidney disease transition

BACKGROUND

The transition from acute kidney injury (AKI) to chronic kidney disease (CKD) is extremely complex. Incomplete renal tubule repair, inflammation, and endoplasmic reticulum (ER) stress all play major roles. AKI activates ER stress, and the sensor protein inositol-requiring kinase-1 (IRE1) mediates inflammation by promoting the phosphorylation of C-jun NH2-terminal kinase (JNK). The interleukin-6/signal transducer and activator of transcription 3 (IL-6/STAT3) signaling pathway is associated with the secretion of renal extracellular matrix (ECM) and fibrosis. It remains unclear whether these signaling pathways play a role in the AKI-CKD transition.

METHODS

In this study, a mouse model of ischemia-reperfusion (I/R) with bilateral renal artery clipping was used. IRE1 or JNK inhibitors were also injected to confirm their roles in the AKI-CKD transition. The renal function of the mice was determined by observing the pathology of the renal tubules and glomeruli through electron microscopy, immunohistochemistry, western blotting and quantitative real-time PCR.

RESULTS

I/R stimulates ER stress and the IRE1/JNK pathway in the renal tubules in a short period of time, leading to continuous inflammation. Long-term I/R injury activates the STAT3 pathway in the glomeruli, activates mesangial cells proliferation, causes secretion of large amounts of glomerular ECM, and promotes glomerular sclerosis. This damage to the renal tubules and glomeruli is significantly reduced in I/R model mice pretreated with IRE1 or JNK inhibitors.

CONCLUSION

These findings suggested that the IRE1/JNK pathway regulates the inflammatory cytokines caused by AKI and continues to activate the STAT3 pathway and production of ECM in the glomeruli at late stages, suggesting the feasibility of targeted therapy for the AKI-CKD transition.

Secondary Mechanisms of Neurotrauma: A Closer Look at the Evidence

Traumatic central nervous system injury is a leading cause of neurological injury worldwide. While initial neuroresuscitative efforts are focused on ameliorating the effects of primary injury through patient stabilization, secondary injury in neurotrauma is a potential cause of cell death, oxidative stress, and neuroinflammation. These secondary injuries lack defined therapy. The major causes of secondary injury in neurotrauma include endoplasmic reticular stress, mitochondrial dysfunction, and the buildup of reactive oxygen or nitrogenous species. Stress to the endoplasmic reticulum in neurotrauma results in the overactivation of the unfolded protein response with subsequent cell apoptosis. Mitochondrial dysfunction can lead to the release of caspases and the buildup of reactive oxygen species; several characteristics make the central nervous system particularly susceptible to oxidative damage. Together, endoplasmic reticulum, mitochondrial, and oxidative stress can have detrimental consequences, beginning moments and lasting days to months after the primary injury. Understanding these causative pathways has led to the proposal of various potential treatment options.

Punicalagin Attenuates Neuronal Apoptosis by Upregulating 5-Hydroxymethylcytosine in the Diabetic Mouse Brain

Punicalagin exerts neuroprotective activity by improving AMP-activated kinase (AMPK) and mitochondrial Krebs cycle. AMPK and Krebs cycle metabolites regulate 5-hydroxymethylcytosine (5hmC) via acting on ten-eleven translocation (TET) enzymes. Therefore, we hypothesized that punicalagin inhibits diabetes-related neuronal apoptosis by upregulating 5hmC in the diabetic mouse brain. C57BL/6J mice aged 8 weeks were randomly separated into five groups (n = 10), normal control (NC), diabetes mellitus (DM), resveratrol (RES), low-dose punicalagin (LPU), and high-dose punicalagin (HPU). Compared with other groups, the neuronal apoptosis rate was significantly higher and the 5hmC level of the cerebral cortex was significantly lower in the DM group. The levels of TET2 and P-AMPKα/AMPKα were significantly lower in the DM group than in both LPU and HPU groups. The ratio of (succinic acid + fumaric acid)/α-ketoglutarate was significantly higher in the DM group than in other groups. The present results suggest that punicalagin upregulates 5hmC via activating AMPK and maintaining Krebs cycle homeostasis, thus inhibiting neuronal apoptosis in the diabetic mouse brain.

Inhibition of endoplasmic reticulum stress by 4-phenylbutyrate alleviates retinal inflammation and the apoptosis of retinal ganglion cells after ocular alkali burn in mice

OBJECTIVE

Retinal ganglion cell (RGC) apoptosis is one of the most severe complications that causes permanent visual impairment following ocular alkali burn (OAB). Currently, very few treatment options exist for this condition. This study was conducted to determine the effect of 4-phenylbutyric acid (4-PBA) on endoplasmic reticulum (ER) stress after OAB using a well-established OAB mouse model.

METHODS

Ocular alkali burn was induced in C57BL/6 mouse corneas using 1 M NaOH. 4-PBA (10 mg/kg; 250 μL per injection) or saline (250 μL per injection) was injected intraperitoneally once per day for 3 days before the establishment of the OAB model. The apoptosis of retinal ganglion cells (RGCs) was assessed by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay, and the histological damage was examined by hematoxylin and eosin and immunofluorescence assay on retinal flat mounts. The key inflammatory response and the expression of ER stress-related markers in the retinal tissues were assessed by real-time PCR, western blotting and histologic analyses.

RESULTS

4-PBA significantly alleviated the apoptosis of RGCs and prevented the structural damage of the retina, as determined by the evaluation of RGC density and retinal thickness. Inhibition of ER stress by 4-PBA decreased the expression of vital proinflammatory cytokines, tumor necrosis factor alpha, and interleukin-1 beta; and suppressed the activation of retinal microglial cells and nuclear factor-kappa B (NF-κB). 4-PBA reduced the expression of the ER stress molecules, glucose-regulated protein 78, activated transcription factor 6, inositol-requiring enzyme-1 (IRE1), X-box-binding protein 1 splicing, and CCAAT/enhancer-binding protein homologous protein, in the retinal tissues and RGCs of OAB mice.

CONCLUSIONS

The present study demonstrated that the inhibition of ER stress by 4-PBA alleviates the inflammatory response via the IRE1/NF-κB signaling pathway and protects the retina and RGCs from injury in an OAB mouse model. Such findings further suggest that 4-PBA might have potential therapeutic implications for OAB treatment.

The Role of Glucagon-Like Peptide-1 Receptor Agonists (GLP-1 RA) in Diabetes-Related Neurodegenerative Diseases

Recent clinical guidelines have emphasized the importance of screening for cognitive impairment in older adults with diabetes, however, there is still a lack of understanding about the drug therapy. Glucagon-like peptide 1 receptor agonists (GLP-1 RAs) are widely used in the treatment of type 2 diabetes and potential applications may include the treatment of obesity as well as the adjunctive treatment of type 1 diabetes mellitus in combination with insulin. Growing evidence suggests that GLP-1 RA has the potential to treat neurodegenerative diseases, particularly in diabetes-related Alzheimer’s disease (AD) and Parkinson’s disease (PD). Here, we review the molecular mechanisms of the neuroprotective effects of GLP-1 RA in diabetes-related degenerative diseases, including AD and PD, and their potential effects.

Carnosine improves cognitive impairment through promoting SIRT6 expression and inhibiting ER stress in a diabetic encephalopathy model

Diabetic encephalopathy is one of complications of diabetes mellitus. Carnosine is a dipeptide composed of β-alanine and L-histidine. Study has shown that carnosine could ameliorate cognitive impairment in animal model with diabetes mellitus. However, the mechanism remains unclear. An animal model of type 2 diabetes (db/db mice) was used in this study. The animals were treated with 0.9 % saline or carnosine (100 mg/kg) for 8 weeks. Morris water maze was tested after drug administration. Oxidative stress-related factors malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-PX), and pro-inflammatory factors inducible nitric oxide synthase (iNOS) were measured. Synapse-related protein postsynapticdensity 95 (PSD95) and brain-derived neurotrophic factor (BDNF) were detected by western blot. Besides, the expressions of sirtuin 6 (SIRT6), binding immunoglobulin protein (BIP), protein kinase R-like endoplasmic reticulum kinase (PERK), phospho-protein kinase R-like endoplasmic reticulum kinase (P-PERK), inositol-requiring enzyme-1α (IRE1α), phospho-inositol-requiring enzyme-1α (P-IRE1α), activating transcription factor 6 (ATF6), C/EBP-homologous protein (CHOP) in the hippocampus of the brain were detected. The results showed that treatment with carnosine ameliorated cognitive impairment in db/db mice. Carnosine reduced neuronal oxidative stress damage and iNOS expression in db/db mice. Meanwhile, carnosine relieved neurodegeneration in the hippocampus of db/db mice. Furthermore, carnosine promoted the expression of SIRT6 and reduced the expressions of endoplasmic reticulum (ER) related factors (BIP, P-PERK, P-IRE1α, ATF6, CHOP). In conclusion, these data suggested that the protective effect of carnosine against diabetic encephalopathy might be related to SIRT6/ER stress pathway.

Paracrine signal emanating from stressed cardiomyocytes aggravates inflammatory microenvironment in diabetic cardiomyopathy

Myocardial inflammation contributes to cardiomyopathy in diabetic patients through incompletely defined underlying mechanisms. In both human and time-course experimental samples, diabetic hearts exhibited abnormal ER, with a maladaptive shift over time in rodents. Furthermore, as a cardiac ER dysfunction model, mice with cardiac-specific p21-activated kinase 2 (PAK2) deletion exhibited heightened myocardial inflammatory response in diabetes. Mechanistically, maladaptive ER stress-induced CCAAT/enhancer-binding protein homologous protein (CHOP) is a novel transcriptional regulator of cardiac high-mobility group box-1 (HMGB1). Cardiac stress-induced release of HMGB1 facilitates M1 macrophage polarization, aggravating myocardial inflammation. Therapeutically, sequestering the extracellular HMGB1 using glycyrrhizin conferred cardioprotection through its anti-inflammatory action. Our findings also indicated that an intact cardiac ER function and protective effects of the antidiabetic drug interdependently attenuated the cardiac inflammation-induced dysfunction. Collectively, we introduce an ER stress-mediated cardiomyocyte-macrophage link, altering the macrophage response, thereby providing insight into therapeutic prospects for diabetes-associated cardiac dysfunction.

Matrine alleviates spatial learning and memory impairment in diabetic mice by inhibiting endoplasmic reticulum stress and through modulation of PK2/PKRs pathway

Clinical and epidemiological studies indicate that diabetic cognitive impairment often occurs in diabetes mellitus patients. Matrine (Mat), an active component of Sophora flavescens Ait root extracts, has widely pharmacological activities including anti-tumor, anti-diabetes, cardioprotective and neuroprotective effects. The present study was designed to elucidate the possibly neuroprotective effects of Mat against diabetic spatial learning and memory impairment caused by high-fat diet and streptozotocin injection in mice. The results showed that Mat treatment significantly ameliorated fasting blood glucose level, impaired glucose tolerance, and lipid metabolism disorder in diabetic mice. In addition, diabetic mice exhibited spatial learning and memory impairment in the Morris water maze test, which could be attenuated by Mat treatment. Moreover, administration of Mat remarkably alleviated histological damage in diabetic hippocampus. Also, further investigations showed that Mat treatment abated endoplasmic reticulum stress induced hippocampal ultra-structure injury as evidenced by increasing the numbers of rough endoplasmic reticulum and mitochondria, as well as down-regulating endoplasmic reticulum stress related protein levels (GRP78, CHOP, ATF6 and Caspase-12). Furthermore, administration of Mat enhanced hippocampal protein expressions of PK2, PKR1 and PKR2, which decreased significantly in diabetic mice. Collectively, these findings suggested that Mat could ameliorate diabetes-induced spatial learning and memory impairment, possibly by alleviating ER stress, and partly through modulation of PK2/PKRs pathway.

Role of Thioredoxin-1 and its inducers in human health and diseases

Thioredoxin-1 (Trx-1) is a small redox-active protein normally found in mammalian cells that responds to the changing redox environment by contributing electrons or regulating related proteins. There is growing evidence that Trx-1 has multiple functions, including cytoprotective, anti-apoptotic, antioxidant and anti-inflammatory effects. To date, researchers have found that Trx-1 deficiency leads to severe damage in various disease models, such as atherosclerosis, cerebral ischemia, diabetes and tumors. Conversely, activation of Trx-1 has a protective effect against these diseases. Accordingly, a variety of Trx-1 inducers have been widely used in the clinic with significant therapeutic value. In this paper, we summarize the pathogenesis of Trx-1 involvement in the above-mentioned diseases and describe the protective effects of Trx-1 inducers on them.

Green tea protects against hippocampal neuronal apoptosis in diabetic encephalopathy by inhibiting JNK/MLCK signaling

Although diabetic encephalopathy (DE) is a major late complication of diabetes, the pathophysiology of postural instability in DE remains poorly understood. Prior studies have suggested that neuronal apoptosis is closely associated with cognitive function, but the mechanism remains to be elucidated. Green tea, which is a non-fermented tea, contains a number of tea polyphenols, alkaloids, amino acids, polysaccharides and other components. Some studies have found that drinking green tea can reduce the incidence of neurodegenerative diseases and improve cognitive dysfunction. We previously found that myosin light chain kinase (MLCK) regulates apoptosis in high glucose-induced hippocampal neurons. In neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease, activation of the JNK signaling pathway promotes neuronal apoptosis. However, the relationship between JNK and MLCK remains to be elucidated. Green tea serum was obtained using seropharmacological methods and applied to hippocampal neurons. In addition, a type 1 diabetes rat model was established and green tea extract was administered, and the Morris water maze test, Cell Counting Kit-8 assays, flow cytometry, western blotting and terminal deoxynucleotidyl transferase-mediated dUTP nick end-labelling assays were used to examine the effects of green tea on hippocampal neuronal apoptosis in diabetic rats. The results demonstrated that green tea can protect against hippocampal neuronal apoptosis by inhibiting the JNK/MLCK pathway and ultimately improves cognitive function in diabetic rats. The present study provided novel insights into the neuroprotective effects of green tea.

Notoginsenoside R1 activates the NAMPT-NAD+-SIRT1 cascade to promote postischemic angiogenesis by modulating Notch signaling

Nicotinamide phosphoribosyltransferase (NAMPT) maintains mitochondrial function and protects against cerebral ischemic injury by improving energy metabolism. Notoginsenoside R1 (R1), a unique constituent of Panax notoginseng, has been shown to promote the proliferation and tube formation of human umbilical vein endothelial cells. Whether R1 has proangiogenesis on the activation of NAMPT in ischemic stroke remains unclear. The purpose of this study was to investigate the pharmacodynamic effect and mechanism of R1 on angiogenesis after ischemic stroke. We used male Sprague-Dawley (SD) rats subjected to middle cerebral artery occlusion/reperfusion (MCAO/R). R1 was administered via intraperitoneal (i.p.) injection immediately after ischemia induction. The promotion of R1 on angiogenesis were detected by immunofluorescence staining, 3D stereoscopic imaging and transmission electron microscopy detection. HBMEC cells were pretreated with different concentrations of R1 for 12 h before oxygen-glucose deprivation/reoxygenation (OGD/R) exposure. Afterward, scratch assay, EdU staining and tube formation were determined. Western blot analyses of proteins, including those involved in angiogenesis, NAMPT-SIRT1 cascade, VEGFR-2, and Notch signaling, were conducted. We showed that R1 significantly restored cerebral blood flow, improved mitochondrial energy metabolism and promoted angiogenesis. More importantly, incubation with 12.5-50 μM R1 significantly increased the migration, proliferation and tube formation of HBMECs in vitro. The promotion of R1 on angiogenesis were associated with the NAMPT-NAD⁺-SIRT1 cascade and Notch/VEGFR-2 signaling pathway, which was partially eliminated by inhibitors of NAMPT and SIRT1. We demonstrated that R1 promotes post-stroke angiogenesis via activating NAMPT-NAD⁺-SIRT1 cascade. The modulation of Notch signaling and VEGFR-2 contribute to the post-stroke angiogenesis. These findings offer insight for exploring new therapeutic strategies for neurorestoration via R1 treatment after ischemic stroke.

Thioredoxin-1 Is a Target to Attenuate Alzheimer-Like Pathology in Diabetic Encephalopathy by Alleviating Endoplasmic Reticulum Stress and Oxidative Stress

Varying degrees of central nervous system neuropathy induced by diabetes mellitus (DM) contribute to a cognitive disorder known as diabetic encephalopathy (DE), which is also one of the independent risk factors for Alzheimer's disease (AD). Endoplasmic reticulum stress (ERS) plays a critical role in the occurrence and development of DE and AD. However, its molecular mechanism remains largely unknown. This study aims to investigate whether thioredoxin-1 (Trx-1) could alleviate DE and AD through ERS, oxidative stress (OS) and apoptosis signaling pathways. Mice were randomly divided into a wild-type group (WT-NC), a streptozotocin (STZ)-treated DM group (WT-DM), a Trx-1-TG group (TG-NC) and a Trx-1-TG DM group (TG-DM). Diabetic animals showed an increase in the time spent in the target quadrant and the number of platform crossings as well as AD-like behavior in the water maze experiment. The immunocontent of the AD-related protein Tau and the levels of cell apoptosis, β-amyloid (Aβ) plaque formation and neuronal degeneration in the hippocampus of the diabetic group were increased. Some key factors associated with ERS, such as protein disulfide isomerase (PDI), glucose-regulated protein 78 (GRP78), inositol-requiring enzyme 1α (IRE1α), tumor necrosis factor receptor-associated factor 2 (TRAF2), apoptosis signal-regulating kinase-1 (ASK1), c-Jun N-terminal kinase (JNK), protein kinase RNA (PKR)-like ER kinase (PERK), and C/EBP homologous protein (CHOP), were upregulated, and other factors related to anti-oxidant stress, such as nuclear factor erythroid 2-related factor (Nrf2), were downregulated in the DM group. Moreover, DM caused an increase in the immunocontents of caspase-3 and caspase-12. However, these changes were reversed in the Trx-1-tg DM group. Therefore, we conclude that Trx-1 might be a key factor in alleviating DE and AD by regulating ERS and oxidative stress response, thus preventing apoptosis.

Notoginsenoside R1 Improves Cerebral Ischemia/Reperfusion Injury by Promoting Neurogenesis via the BDNF/Akt/CREB Pathway

Notoginsenoside R1 (R1), a major component isolated from P. notoginseng, is a phytoestrogen that exerts many neuroprotective effects in a rat model of ischemic stroke. However, its long-term effects on neurogenesis and neurological restoration after ischemic stroke have not been investigated. The aim of this study was to evaluate the effects of R1 on neurogenesis and long-term functional recovery after ischemic stroke. We used male Sprague-Dawley rats subjected to middle cerebral artery occlusion/reperfusion (MCAO/R). R1 was administered by intraperitoneal (i.p.) injection immediately postischemia. We showed that R1 significantly decreased infarct volume and neuronal loss, restored neurological function, and stimulated neurogenesis and oligodendrogenesis in rats subjected to MCAO/R. More importantly, R1 promoted neuronal proliferation in PC12 cells in vitro. The proneurogenic effects of R1 were associated with the activation of Akt/cAMP responsive element-binding protein, as shown by the R1-induced increase in brain-derived neurotrophic factor (BDNF) expression, and with the activation of neurological function, which was partially eliminated by selective inhibitors of BDNF and PI3K. We demonstrated that R1 is a promising compound that exerts neuroprotective and proneurogenic effects, possibly via the activation of BDNF/Akt/CREB signaling. These findings offer insight into exploring new mechanisms in long-term functional recovery after R1 treatment of ischemic stroke.

The chemical chaperon 4-phenyl butyric acid restored high-fat diet- induced hippocampal insulin content and insulin receptor level reduction along with spatial learning and memory deficits in male rats

This study assessed the effect of a chronic high-fat diet (HFD) on plasma and hippocampal insulin and corticosterone levels, the hippocampus insulin receptor amount, and spatial learning and memory with or without receiving 4-phenyl butyric acid (4-PBA) in male rats. Rats were divided into high-fat and normal diet groups, then each group was subdivided into dimethyl sulfoxide (DMSO) and 4-PBA groups. After weaning, the rats were fed with HFD for 20 weeks. Then, 4-PBA or DMSO were injected for 3 days. Subsequently, oral glucose tolerance test was done. On the following day, spatial memory tests were performed. Then the hippocampus Bip, Chop, insulin, corticosterone, and insulin receptor levels were determined. HFD increased plasma glucose, leptin and corticosterone concentrations, hippocampus Bip, Chop and corticosterone levels, food intake, abdominal fat weight and body weight along with impaired glucose tolerance. It decreased plasma insulin, and insulin content, and its receptor amount in hippocampus. HFD lengthened escape latency and shortened the duration spent in target zone. 4-PBA administration improved the HFD- induced adverse changes. Chronic HFD possibly through the induction of endoplasmic reticulum (ER) stress and subsequent changes in the levels of hippocampal corticosterone, insulin and insulin receptor along with possible leptin resistance caused spatial learning and memory deficits.

Curcumin and its analog alleviate diabetes-induced damages by regulating inflammation and oxidative stress in brain of diabetic rats

BACKGROUND

Diabetic encephalopathy is a severe diabetes complication with cognitive dysfunction and neuropsychiatric disability. The mechanisms underlying diabetic encephalopathy is believed to be relevant with oxidative stress, vascular amylin deposition, immune receptors, inflammation, etc. This study wanted to evaluate the ability of curcumin and its analog A13 to alleviate oxidative stress and inflammation in diabetes-induced damages in brain.

METHODS

Sixty adult male Sprague-Dawley rats were divided into 5 groups: normal control (NC) group, diabetes mellitus (DM) group, curcumin-treated diabetes mellitus (CUR) group, high dose of A13-treated diabetes mellitus (HA) group, low dose of A13-treated diabetes mellitus (LA) group. Activation of the nuclear factor kappa-B (NF-κB p65) pathway was detected by RT-qPCR, immunohistochemical (IHC) staining and Western blot; oxidative stress was detected by biochemical detection kit; brain tissue sections were stained with hematoxylin-eosin (HE) staining and Myelin staining.

RESULTS

RT-qPCR, IHC staining and Western blot showed that curcumin and A13 treatment could inhibit the NF-κB p65 pathway. Curcumin and A13 increased the activity of superoxide dismutase and decreased the malondialdehyde level in the brain of diabetic rats. Furthermore, HE staining and Myelin staining demonstrated that the histological lesions of the brain in diabetic rats could be significantly ameliorated by curcumin and A13.

CONCLUSION

Curcumin analog A13 could alleviate the damages in the brain of diabetes rats by regulating the pathways of inflammation and oxidative stress. A13 may be a new potential therapeutic agent for diabetic encephalopathy.

Effects of notoginseng leaf triterpenes on small molecule metabolism after cerebral ischemia/reperfusion injury assessed using MALDI-MS imaging

Background

Notoginseng leaf triterpenes (PNGL) is believed to have neuroprotective effects via the inhibition of inflammatory response and neuronal apoptosis. However, its mechanisms underlying the anti-ischemia/reperfusion (I/R) injury effects on the regulation of small molecule metabolism in rat brain remains unclear. The purpose of this study was thus to explore the mechanisms of PNGL on the regulation of small molecule metabolism in rat brain after I/R injury using matrix-assisted laser desorption ionization-mass spectrometry imaging (MALDI-MSI).

Methods

As a model of in vivo cerebral I/R injury, male Sprague-Dawley (SD) rats were established with a middle cerebral artery occlusion/reperfusion (MCAO/R) model after PNGL administration with 40 mg·kg^-1 through intraperitoneal injection (i.p.) for 7 days. We assessed the neurological behavior, regional cerebral blood flow (r CBF), neuron injury, and spatial distribution of metabolic small molecules.

Results

Our in vivo results suggested that PNGL increased cerebral blood flow and relieved neurological dysfunction. Furthermore, using MALDI-MSI, we demonstrated that PNGL regulated 16 endogenous small molecules implicated in metabolic networks including tricarboxylic acid (TCA) cycle, adenosine triphosphate (ATP) metabolism, malate-aspartate shuttle, metal ions, and antioxidants underwent noticeable changes after reperfusion for 24 h.

Conclusions

PNGL is a novel cerebrovascular agent that can improve cerebral blood flow and attenuate adverse neurological disorders. The mechanisms are closely correlated with relative metabolic pathways, which offers insight into exploring new mechanisms in PNGL for the treatment of cerebral I/R injury.

Crosstalk between endoplasmic reticulum stress and oxidative stress: Focus on protein disulfide isomerase and endoplasmic reticulum oxidase 1

Cellular stress and inflammation, establishing as disease pathology, have reached great heights in the last few decades. Stress conditions such as hyperglycemia, hyperlipidemia and lipoproteins are known to disturb proteostasis resulting in the accumulation of unfolded or misfolded proteins, alteration in calcium homeostasis culminating in unfolded protein response. Protein disulfide isomerase and endoplasmic reticulum oxidase-1 are the key players in protein folding. The protein folding process assisted by endoplasmic reticulum oxidase-1 results in the production of reactive oxygen species in the lumen of the endoplasmic reticulum. Production of reactive oxygen species beyond the quenching capacity of the antioxidant systems perturbs ER homeostasis. Endoplasmic reticulum stress also induces the production of cytokines leading to inflammatory responses. This has been proven to be the major causative factor for various pathophysiological states compared to other cellular triggers in diseases, which further manifests to increased oxidative stress, mitochondrial dysfunction, and altered inflammatory responses, deleterious to cellular physiology and homeostasis. Numerous studies have drawn correlations between the progression of several diseases in association with endoplasmic reticulum stress, redox protein folding, oxidative stress and inflammatory responses. This review aims to provide an insight into the role of protein disulfide isomerase and endoplasmic reticulum oxidase-1 in endoplasmic reticulum stress, unfolded protein response, mitochondrial dysfunction, and inflammatory responses, which exacerbate the progression of various diseases.

Characterization of Retinal Microvascular Complications and the Effects of Endoplasmic Reticulum Stress in Mouse Models of Diabetic Atherosclerosis

Purpose

Recent evidence suggests that there is a correlation between the micro- and macrovascular complications of diabetes mellitus. The aim of this study is to investigate the molecular mechanisms by which diabetes promotes the development of microvascular disease (diabetic retinopathy [DR]) through characterization of the effects of hyperglycemia in the retina of mouse models of diabetic atherosclerosis.

Methods

Hyperglycemia was induced in apolipoprotein E-deficient (ApoE-/-) mice, a model of accelerated atherosclerosis, either through streptozotocin (STZ) injection or introduction of the Ins2Akita mutation (ApoE-/-Ins2+/Akita). Another subset of ApoE-/- mice was supplemented with glucosamine (GlcN). To attenuate atherosclerosis, subsets of mice from each experimental group were treated with the chemical chaperone, 4-phenylbutyric acid (4PBA). Eyes from 15-week-old mice were either trypsin digested and stained with periodic acid-Schiff (PAS) or frozen for cryostat sectioning and immunostained for endoplasmic reticulum (ER) stress markers, including C/EBP homologous protein (CHOP) and 78-kDa glucose-regulated protein (GRP78). PAS-stained retinal flatmounts were analyzed for microvessel density, acellular capillaries, and pericyte ghosts.

Results

Features of DR, including pericyte ghosts and reduced microvessel density, were observed in hyperglycemic and GlcN-supplemented mice. Treatment with 4PBA reduced ER stress in the retinal periphery and attenuated DR in the experimental groups.

Conclusions

Mouse models of diabetic atherosclerosis show characteristic pathologies of DR that correlate with atherosclerosis. The increased magnitude of these changes and responses to 4PBA in the peripheral retina suggest that future studies should be aimed at assessing regional differences in mechanisms of ER stress-related pathways in these mouse models.

Berberine ameliorates rats model of combined Alzheimer's disease and type 2 diabetes mellitus via the suppression of endoplasmic reticulum stress

This study is aimed to investigate the protective effect against type 2 diabetes mellitus (T2DM) and Alzheimer's disease (AD) of Berberine (BBR), and the underlying mechanism of action is explored. We established a rat model of combined AD and T2DM and used it to investigate the effect of BBR (150 mg/kg) on the course of these pathologies. The Morris water maze, biochemical analysis, hematoxylin-eosin staining, immunohistochemical study, immunofluorescent staining, TUNEL assay, RT-qPCR and western blot were used to reveal the effect of BBR on blood glucose, lipid changes, hippocampal injuries and cognitive impairment. The results showed that BBR could alleviate memory deficits, restore the disordered arrangement of nerve cells, the damage of neurons, improve TUNEL-positive cells and decrease the elevated levels of fasting blood glucose, triglyceride, total cholesterol and glycosylated serum protein levels in Alzheimer diabetic rats. Moreover, BBR treatment reduces the transcription of mRNAs and expression of proteins related to endoplasmic reticulum (ER) stress. These findings conclude that BBR can protect neurons by inhibiting the pathway of ER stress and thereby play an essential role in the preventive and therapeutic of AD and T2DM.

The Reciprocal Causation of the ASK1-JNK1/2 Pathway and Endoplasmic Reticulum Stress in Diabetes-Induced Cognitive Decline

Diabetes significantly induces cognitive dysfunction. Neuronal apoptosis is the main cause of diabetes-induced cognitive decline (DICD). Apoptosis signal-regulating kinase 1 (ASK1) and endoplasmic reticulum (ER) stress are remarkably activated by diabetes. The role and relationship of ASK1-JNK1/2 signaling and ER stress in DICD have not yet been elucidated. In this study, we used db/db mice as the DICD animal model and confirmed that db/db mice displayed cognitive decline with inferior learning and memory function. Diabetes significantly induced morphological and structural changes, excessive neuronal apoptosis, Aβ_{1 - 42} large deposition, and synaptic dysfunction in the hippocampus. Mechanistic studies found that diabetes significantly triggered ASK1-JNK1/2 signaling activation and increased ER stress in the hippocampus. Moreover, diabetes enhanced the formation of the IRE1α-TRAF2-ASK1 complex, which promotes the crosstalk of ER stress and the ASK1-JNK1/2 pathway during DICD. Furthermore, 4-PBA treatment blocked high glucose (HG)-induced ASK1-JNK1/2 signaling activation, and excessive apoptosis in vitro. Inhibiting ASK1 via siRNA remarkably ameliorated the HG-induced increase in p-IRE1α and associated apoptosis in SH-SY5Y cells, suggesting that ASK1 is essential for the assembly and function of the proapoptotic kinase activity of the IRE1α signalosome. In summary, ER stress and ASK1-JNK1/2 signaling play causal roles in DICD development, which has crosstalk through the formation of the IRE1α-TRAF2-ASK1 complex.

Anti-ischemia/reperfusion injury effects of notoginsenoside R1 on small molecule metabolism in rat brain after ischemic stroke as visualized by MALDI-MS imaging

Ischemic stroke is a syndrome of severe neurological responses that cause neuronal death, damage to the neurovascular unit and inflammation. Notoginsenoside R1 (NG-R1) is a neuroprotective drug that is commonly used to treat neurodegenerative and cerebrovascular diseases. However, its potential mechanisms on the regulation of small molecule metabolism in ischemic stroke are largely unknown. The aim of this study was to explore the potential mechanisms of NG-R1 on the regulation of small molecule metabolism after ischemic stroke. Here, we found that NG-R1 reduced infarct size and improved neurological deficits by ameliorating neuronal damage and inhibiting glial activation in MCAO/R rats. Furthermore, using matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI), we clarified that NG-R1 regulated ATP metabolism, the tricarboxylic acid (TCA) cycle, the malate-aspartate shuttle, antioxidant activity, and the homeostasis of iron and phospholipids in the striatum and hippocampus of middle cerebral artery occlusion/reperfusion (MCAO/R) rats. In general, NG-R1 is a promising compound for brain protection from ischemic/reperfusion injury, possibly through the regulation of brain small molecule metabolism.

Exogenous fibroblast growth factor 1 ameliorates diabetes-induced cognitive decline via coordinately regulating PI3K/AKT signaling and PERK signaling

BACKGROUND

Diabetes induces central nervous system damage, leading to cognitive decline. Fibroblast growth factor 1 (FGF1) has dual function of neuroprotection and normalizing hyperglycemia. To date, the precise mechanisms and potential treating strategies of FGF1 for diabetes-induced cognitive decline (DICD) hasn't been fully elucidated.

METHODS

In this study, db/db mice were used as DICD animal model. We found that diabetes remarkably suppressed FGF1 expression in hippocampus. Thus, exogenous FGF1 had been treated for db/db mice and SH-SY5Y cells.

RESULTS

FGF1 significantly ameliorates DICD with better spatial learning and memory function. Moreover, FGF1 blocked diabetes-induced morphological structure change, neuronal apoptosis and Aβ1-42 deposition and synaptic dysfunction in hippocampus. But normalizing glucose may not the only contributed factor for FGF1 treating DICD with evidencing that metformin-treated db/db mice has a inferior cognitive function than that in FGF1 group. Current mechanistic study had found that diabetes inhibits cAMP-response element binding protein (CREB) activity and subsequently suppresses brain derived neurotrophic factor (BDNF) level via coordinately regulating PERK signaling and PI3K/AKT signaling in hippocampus, which were reversed by FGF1.

CONCLUSION

We conclude that FGF1 exerts its neuroprotective role and normalizing hyperglycemia effect, consequently ameliorates DICD, implying FGF1 holds a great promise to develop a new treatment for DICD. Video abstract.

Effects of compound K, a metabolite of ginsenosides, on memory and cognitive dysfunction in db/db mice involve the inhibition of ER stress and the NLRP3 inflammasome pathway

Accumulating clinical and epidemiological evidence indicates a close relationship between diabetes mellitus and dementia. The ginsenoside compound K (CK) has been reported to ameliorate diabetes mellitus and confer protection to the central nervous system. In this study, we investigated whether CK could improve memory impairment and cognitive dysfunction in diabetic db/db mice. Firstly, we found that CK treatments significantly improved behavioral impairment and cognitive dysfunction based on Morris water maze, Y-maze, and fear conditioning tests. Besides, CK decreased the fasting glucose level, increased lipid metabolism, and ameliorated glucose tolerance, insulin sensitivity, and dyslipidemia in diabetic db/db mice. In addition, CK treatments alleviated oxidative stress and inhibited the inflammatory response in hippocampal tissue. Further investigations showed that CK treatments inhibited the NLRP3 inflammasome pathway, as evidenced by the declined expression of TXNIP, NLRP3 inflammasomes, ASC, cleaved caspase-1, and mature IL-1β in hippocampal tissues. Moreover, CK treatments alleviated ER stress via down-regulating the level of BiP, CHOP, p-PERK, p-IRE1α and ATF6 in the hippocampus of db/db mice. These results suggest that CK improves memory and cognitive dysfunction, possibly by ameliorating glucose tolerance, insulin sensitivity, and dyslipidemia, suppressing oxidative stress and inflammatory response and modulating the NLRP3 inflammasome pathway and ER stress.

Tanshinone IIA ameliorates cognitive deficits by inhibiting endoplasmic reticulum stress-induced apoptosis in APP/PS1 transgenic mice

Our previous data indicated that tanshinone IIA (tan IIA) improves learning and memory in a mouse model of Alzheimer's disease (AD) induced by streptozotocin via restoring cholinergic function, attenuating oxidative stress and blocking p38 MAPK signal pathway activation. This study aims to estimate whether tan IIA inhibits endoplasmic reticulum (ER) stress-induced apoptosis to prevent cognitive decline in APP/PS1 transgenic mice. Tan IIA (10 mg/kg and 30 mg/kg) was intraperitoneally administered to the six-month-old APP/PS1 mice for 30 consecutive days. β-amyloid (Aβ) plaques were measured by immunohistochemisty and Thioflavin S staining, apoptotic cells were observed by TUNEL, ER stress markers and apoptosis signaling proteins were investigated by western blotting and RT-PCR. Our results showed that tan IIA significantly ameliorates cognitive deficits and improves spatial learning ability of APP/PS1 mice in the nest-building test, novel object recognition test and Morris water maze test. Furthermore, tan IIA significantly reduced the deposition of Aβ plaques and neuronal apoptosis, and markedly prevented abnormal expression of glucose regulated protein 78 (GRP78), initiation factor 2α (eIF2α), inositol-requiring enzyme 1α (IRE1α), activating transcription factor 6 (ATF6), as well as suppressed the activation of C/EBP homologous protein (CHOP) and c-Jun N-terminal kinase (JNK) pathways in the parietal cortex and hippocampus. Moreover, tan IIA induced an up-regulation of the Bcl-2/Bax ratio and down-regulation of caspase-3 protein activity. Taken together, the above findings indicated that tan IIA improves learning and memory through attenuating Aβ plaques deposition and inhibiting ER stress-induced apoptosis. These results suggested that tan IIA might become a promising therapeutic candidate drug against AD.

Autophagy of macrophages is regulated by PI3k/Akt/mTOR signalling in the development of diabetic encephalopathy

The development of diabetic encephalopathy (DE) is enhanced by inflammatory macrophages, and is suppressed by macrophage autophagy. However, the molecular signaling that controls macrophage autophagy in DE remains ill-defined. Here, DE is induced in rats that received intraperitoneal injection of streptozotocin (STZ). In macrophages isolated from the brain of the rats, we detected downregulated autophagy activity and enhanced PI3k/Akt/mTOR/S6K1 signaling. In order to examine the role of autophagy and PI3k/Akt/mTOR signaling in DE development, an mTOR inhibitor, rapamycin, or an autophagy inhibitor, chloroquine (CQ), were administered to the rats that that received STZ. We found that rapamycin significantly enhanced DE development through mTOR suppression-induced augmentation of macrophage autophagy, while CQ significantly decreased DE development through suppression of macrophage autophagy. Together, our data suggest that PI3k/Akt/mTOR signaling may promote the development of DE through suppression of macrophage autophagy.

Increased ER Stress After Experimental Ischemic Optic Neuropathy and Improved RGC and Oligodendrocyte Survival After Treatment With Chemical Chaperon

Purpose

Increased endoplasmic reticulum (ER) stress is one of the earliest subcellular changes in neuro-ophthalmic diseases. In this study, we investigated the expression of key molecules in the ER stress pathways following nonarteritic anterior ischemic optic neuropathy (AION), the most common acute optic neuropathy in adults over 50, and assessed the impact of chemical chaperon 4-phenylbutyric acid (4-PBA) in vivo.

Methods

We induced AION using photochemical thrombosis in adult mice and performed histologic analyses of key molecules in the ER stress pathway in the retina and optic nerve. We also assessed the effects of daily intraperitoneal injections of 4-PBA after AION.

Results

In the retina at baseline, there was low proapoptotic transcriptional regulator C/EBP homologous protein (CHOP) and high prosurvival chaperon glucose-regulated protein 78 (GRP78) expression in retinal ganglion cells (RGCs). One day after AION, there was significantly increased CHOP and reduced GRP78 expressions in the ganglion cell layer. In the optic nerve at baseline, there was little CHOP and high GRP78 expression. One day after AION, there was significantly increased CHOP and no change in GRP78 expression. Treatment immediately after AION using daily intraperitoneal injection of chemical chaperone 4-PBA for 19 days significantly rescued Brn3A⁺ RGCs and Olig2⁺ optic nerve oligodendrocytes.

Conclusions

We showed for the first time that acute AION resulted in increased ER stress and differential expression of ER stress markers CHOP and GRP78 in the retina and optic nerve. Rescue of RGCs and oligodendrocytes with 4-PBA provides support for ER stress reduction as possible treatment for AION.

Ginsenoside Rb1 as an Anti-Diabetic Agent and Its Underlying Mechanism Analysis

Panax ginseng and Panax notoginseng, two well-known medical plants with economic value, have a long history of use for managing various diseases in Asian countries. Accumulating clinical and experimental evidence suggests that notoginsenosides and ginsenosides, which are the major bioactive components of the plants, have a variety of beneficial effects on several types of disease, including metabolic, vascular, and central nervous system disease. Considerable attention has been focused on ginsenoside Rb1 derived from their common ownership as an anti-diabetic agent that can attenuate insulin resistance and various complications. Particularly, in vitro and in vivo models have suggested that ginsenoside Rb1 exerts various pharmacological effects on metabolic disorders, including attenuation of glycemia, hypertension, and hyperlipidemia, which depend on the modulation of oxidative stress, inflammatory response, autophagy, and anti-apoptosis effects. Regulation of these pathophysiological mechanisms can improve blood glucose and insulin resistance and protect against macrovascular/microvascular related complications. This review summarizes the pharmacological effects and mechanisms of action of ginsenoside Rb1 in the management of diabetes or diabetic complications. Moreover, a multi-target effect and mechanism analysis of its antidiabetic actions were performed to provide a theoretical basis for further pharmacological studies and new drug development for clinical treatment of type 2 diabetes. In conclusion, ginsenoside Rb1 exerts significant anti-obesity, anti-hyperglycemic, and anti-diabetic effects by regulating the effects of glycolipid metabolism and improving insulin and leptin sensitivities. All of these findings suggest ginsenoside Rb1 exerts protective effects on diabetes and diabetic complications by the regulation of mitochondrial energy metabolism, improving insulin resistance and alleviating the occurrence complications, which should be further explored. Hence, ginsenoside Rb1 may be developed as a potential anti-obesity, anti-hyperglycemic, and anti-diabetic agent with multi-target effects.

Hyperglycemia aggravates spinal cord injury through endoplasmic reticulum stress mediated neuronal apoptosis, gliosis and activation

BACKGROUND

Hyperglycemia has been shown to influence prognostic outcome of spinal cord injury (SCI). However, the corresponding mechanism is not very clear.

AIM

This study is expected to explore the role of endoplasmic reticulum (ER) stress in hyperglycemia aggravated SCI.

METHODS

Hyperglycemia was established in rats by intraperitoneal (i.p.) injection of streptozotocin. SCI was performed at the T10 of spinal cord through weight dropping. ER stress was suppressed by oral gavage of 4-PBA. ER stress, histological change of the injured spinal cords, neuronal apoptosis, demyelination, glial proliferation, inflammatory factor production, blood-spinal cord barrier (BSCB) permeability, TJ (Occludin, Claudin5) and AJ (β-catenin, P120) protein degradation, and locomotor recovery were determined using western blotting, immunohistochemistry, HE staining, Evan's Blue assay, BBB scores and inclined plane test, respectively. In vitro, rat spinal cord neurons cells (RSCNCs) and cerebral microvascular endothelial cells (RCMECs) were stimulated with high glucose (HG) and/or thapsigargin (TG). The effects of HG and/or TG on RSCNCs apoptosis, and AJ and TJ expression by RCMECs were evaluated with flow cytometry and western blotting, respectively.

RESULTS

Hyperglycemic rats exhibited enhanced ER stress, increased neuronal apoptosis, aggravated demyelination, increased glial proliferation and inflammatory factors secretion, more serious BSCB disruption and disturbed locomotor recovery. ER stress inhibition alleviated hyperglycemia induced adverse effect on neuronal apoptosis and BSCB permeability, whereas showed little influence on glial activation and inflammation.

CONCLUSION

ER stress was aggravated in hyperglycemic rats after SCI, and subsequently promoted neuronal apoptosis and BSCB disruption in rats.