Aggravation of Cerebral Ischemia/Reperfusion Injury by Peroxisome Proliferator-Activated Receptor-Gamma Deficiency via Endoplasmic Reticulum Stress

Nr1h4 and Thrb ameliorate ER stress and provide protection in the MPTP mouse model of Parkinson's

Elevated ER stress has been linked to the pathogenesis of several disease conditions including neurodegeneration. In this study, we have holistically determined the differential expression of all the nuclear receptors (NRs) in the presence of classical ER stress inducers. Activation of Nr1h4 and Thrb by their cognate ligands (GW4064 and T3) ameliorates the tunicamycin (TM)-induced expression of ER stress genes. A combination of both ligands is effective in mitigating cell death induced by TM. Further exploration of their protective effects in the Parkinson's disease (PD) model shows that they reduce MPP+-induced dissipation of mitochondrial membrane potential and ROS generation in an in vitro PD model in neuronal cells. Furthermore, the generation of an experimental murine PD model reveals that simultaneous treatment of GW4064 and T3 protects mice from ER stress, dopaminergic cell death, and functional deficits in the MPTP mouse model of PD. Thus, activation of Nr1h4 and Thrb by their respective ligands plays an indispensable role in ER stress amelioration and mounts protective effects in the MPTP mouse model of PD.

Identification of novel and potential PPARγ stimulators as repurposed drugs for MCAO associated brain degeneration

Peroxisome proliferator-activated receptor-gamma (PPARγ) has been shown to have therapeutic promise in the treatment of ischemic stroke and is supported by several studies. To identify possible PPARγ activators, the current study used an in silico technique in conjunction with molecular simulations and in vivo validation. FDA-approved drugs were evaluated using molecular docking to determine their affinity for PPARγ. The findings of molecular simulations support the repurposing of rabeprazole and ethambutol for the treatment of ischemic stroke. Adult Sprague Dawley rats were subjected to transient middle cerebral artery occlusion (t-MCAO). Five groups were made as a sham-operated, t-MCAO group, rabeprazole +t-MCAO, ethambutol +t-MCAO, and pioglitazone +t-MCAO. The neuroprotective effects of these drugs were evaluated using the neurological deficit score and the infarct area. The inflammatory mediators and signaling transduction proteins were quantified using Western blotting, ELISA, and immunohistochemistry. The repurposed drugs mitigated cerebral ischemic injury by PPARγ mediated downregulation of nods like receptor protein 3 inflammasomes (NLRP3), tumor necrosis factor-alpha (TNF-α), cyclooxygenase 2 (COX-2), nuclear factor kappa-light-chain-enhancer of activated B cells (p-NF-kB), and c-Jun N-terminal kinase (p-JNK). Our data demonstrated that rabeprazole and ethambutol have neuroprotective potential via modulating the cytoprotective stress response, increasing cellular survival, and balancing homeostatic processes, and so may be suitable for future research in stroke therapy.

Protective Effects of Nuciferine in Middle Cerebral Artery Occlusion Rats Based on Transcriptomics

Middle cerebral artery occlusion (MCAO), with the characteristics of high morbidity, high recurrence rate, high mortality, and disability rate, is a typical manifestation of ischemic stroke and has become a hot research topic in the clinical field. The protective effects of nuciferine on brain injury MCAO rats were investigated and its mechanisms of actions were revealed. The MCAO rats were established by the suture method. The pathological staining of the rat brain was processed and observed, the pharmacodynamics assay of nuciferine were studied, and the gene expression regulation by nuciferine was detected by transcriptome technology. The results showed that nuciferine significantly alleviated brain damage in MCAO rats, and the transcriptomic results suggested that nuciferine could exert therapeutic effects through the regulation of lipid metabolism, including arachidonic acid metabolism, sphingolipid metabolism, the PPAR signaling pathway and other related pathways. This finding provided new perspectives on the treatment of MCAO with nuciferine and facilitates the development of novel drugs for this disease.

Nuclear Receptors in Myocardial and Cerebral Ischemia-Mechanisms of Action and Therapeutic Strategies

Nearly 18 million people died from cardiovascular diseases in 2019, of these 85% were due to heart attack and stroke. The available therapies although efficacious, have narrow therapeutic window and long list of contraindications. Therefore, there is still an urgent need to find novel molecular targets that could protect the brain and heart against ischemia without evoking major side effects. Nuclear receptors are one of the promising targets for anti-ischemic drugs. Modulation of estrogen receptors (ERs) and peroxisome proliferator-activated receptors (PPARs) by their ligands is known to exert neuro-, and cardioprotective effects through anti-apoptotic, anti-inflammatory or anti-oxidant action. Recently, it has been shown that the expression of aryl hydrocarbon receptor (AhR) is strongly increased after brain or heart ischemia and evokes an activation of apoptosis or inflammation in injury site. We hypothesize that activation of ERs and PPARs and inhibition of AhR signaling pathways could be a promising strategy to protect the heart and the brain against ischemia. In this Review, we will discuss currently available knowledge on the mechanisms of action of ERs, PPARs and AhR in experimental models of stroke and myocardial infarction and future perspectives to use them as novel targets in cardiovascular diseases.

Berberine exerts neuroprotective activities against cerebral ischemia/reperfusion injury through up-regulating PPAR-γ to suppress NF-κB-mediated pyroptosis

OBJECTIVE

Berberine (BBR) is an anti-inflammatory alkaloid compound extracted from herbs. The purpose of this study is to probe the possible effect and the mechanism of BBR against cerebral ischemia/reperfusion (I/R) injury.

METHODS

In vitro oxygen and glucose deprivation (OGD) model was established on neurons from rat hippocampus, which was then subjected to BBR, IVA337 (PPAR-γ agonist), or GW9662 (PPAR-γ antagonist) treatment, to identify their effects on neuronal pyroptosis. MTT assay was utilized to determine cell survival rates, TUNEL staining for observation of β-tubulin and MAP2 expressions, qRT-PCR for detection of mRNA expression of PPAR-γ, Western blot for assessment of protein expressions of PPAR-γ and pyroptosis-related proteins (AIM2, NLPR3, ASC, cleaved-Caspase-1, GSDMD, and GSDMD-N), and ELISA for examination of IL-18 and IL-1β expressions.

RESULTS

OGD modeling induced neuron pyroptosis, as evidenced by increased expression levels of pyroptosis-related proteins as well as IL-1β and IL-18, and elevated cell apoptosis rate. In addition, OGD exposure led to PPAR-γ up-regulation and NF-κB activation. Overexpression of PPAR-γ ameliorated cell pyroptosis, while knockdown of PPAR-γ intensified neuron pyroptosis that could be reversed by BBR. Furthermore, either BBR could block the activation of NF-κB signaling pathway through PPAR-γ.

CONCLUSION

BBR protects rats from cerebral I/R injury by up-regulating PPAR-γ to restrain NF-κB-mediated pyroptosis.

Peroxisome Proliferator-Activated Receptor-Gamma (PPAR-ɣ): Molecular Effects and Its Importance as a Novel Therapeutic Target for Cerebral Ischemic Injury

Cerebral ischemic injury is a leading cause of death and long-term disability throughout the world. Peroxisome proliferator-activated receptor gamma (PPAR-ɣ) is a ligand-activated nuclear transcription factor that is a member of the PPAR family. PPAR-ɣ has been shown in several in vitro and in vivo models to prevent post-ischemic inflammation and neuronal damage by negatively controlling the expression of genes modulated by cerebral ischemic injury, indicating a neuroprotective effect during cerebral ischemic injury. A extensive literature review of PubMed, Medline, Bentham, Scopus, and EMBASE (Elsevier) databases was carried out to understand the nature of the extensive work done on the mechanistic role of Peroxisome proliferator activated receptor gamma and its modulation in Cerebral ischemic injury. PPAR-ɣ can interact with specific DNA response elements to control gene transcription and expression when triggered by its ligand. It regulates lipid metabolism, improves insulin sensitivity, modulates antitumor mechanisms, reduces oxidative stress, and inhibits inflammation. This review article provides insights on the current state of research into the neuroprotective effects of PPAR-ɣ in cerebral ischemic injury, as well as the cellular and molecular mechanisms by which these effects are modulated, such as inhibition of inflammation, reduction of oxidative stress, suppression of pro-apoptotic production, modulation of transcription factors, and restoration of injured tissue through neurogenesis and angiogenesis.

PPAR Gamma: From Definition to Molecular Targets and Therapy of Lung Diseases

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor superfamily that regulate the expression of genes related to lipid and glucose metabolism and inflammation. There are three members: PPARα, PPARβ or PPARγ. PPARγ have several ligands. The natural agonists are omega 9, curcumin, eicosanoids and others. Among the synthetic ligands, we highlight the thiazolidinediones, clinically used as an antidiabetic. Many of these studies involve natural or synthetic products in different pathologies. The mechanisms that regulate PPARγ involve post-translational modifications, such as phosphorylation, sumoylation and ubiquitination, among others. It is known that anti-inflammatory mechanisms involve the inhibition of other transcription factors, such as nuclear factor kB(NFκB), signal transducer and activator of transcription (STAT) or activator protein 1 (AP-1), or intracellular signaling proteins such as mitogen-activated protein (MAP) kinases. PPARγ transrepresses other transcription factors and consequently inhibits gene expression of inflammatory mediators, known as biomarkers for morbidity and mortality, leading to control of the exacerbated inflammation that occurs, for instance, in lung injury/acute respiratory distress. Many studies have shown the therapeutic potentials of PPARγ on pulmonary diseases. Herein, we describe activities of the PPARγ as a modulator of inflammation, focusing on lung injury and including definition and mechanisms of regulation, biological effects and molecular targets, and its role in lung diseases caused by inflammatory stimuli, bacteria and virus, and molecular-based therapy.

FABP4 alleviates endoplasmic reticulum stress-mediated ischemia-reperfusion injury in PC12 cells via regulation of PPARγ

Ischemic stroke is a life-threatening complication with a high rate of morbidity. Circulating fatty acid binding protein 4 (FABP4) has been reported to be associated with the outcome of acute ischemic stroke. The present study aimed to illustrate the function of FABP4 in ischemic stroke. PC12 cells exposed to oxygen glucose deprivation/reoxygenation (OGD/R) were used to mimic ischemia-reperfusion (I/R) injury in ischemic stroke. Cell viability was estimated using a Cell Counting Kit-8 assay. The expression of FABP4 in PC12 cells under OGD/R was detected by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). PC12 cells were transfected with FABP4 small interfering RNA (siRNA), inflammatory cytokines and reactive oxygen species (ROS) were determined via RT-qPCR and ROS assay kit. Western blotting was performed to detect endoplasmic reticulum stress (ERS)-related proteins and peroxisome proliferator-activated receptor γ (PPARγ). Flow cytometry was used to evaluate the cell apoptotic rate. The expression of FABP4 increased gradually with the prolongation of reoxygenation within 8 h. FABP4-knockdown inhibited the transcription of inflammatory cytokines, the production of ROS and decreased cell apoptosis. Furthermore, decreased ERS-related proteins and increased PPARγ were estimated in PC12 cells transfected with FABP4 siRNA. PPARγ inhibitor GW9662 weakened the anti-apoptotic effect of FABP4-knockdown. Taken together, these results indicated that FABP4-knockdown suppressed cell apoptosis via relieving ERS; this effect was reversed by treatment of GW9662.

The Protective Effects of Peroxisome Proliferator-Activated Receptor Gamma in Cerebral Ischemia-Reperfusion Injury

Cerebral ischemia-reperfusion injury (CI/RI) is a complex pathological process that often occurs secondary to trauma, surgery, and shock. Peroxisome proliferator activated receptor gamma (PPARγ) is a subunit of the PPAR and is a ligand-activated nuclear transcription factor. After being activated by its ligand, PPARγ can combine with specific DNA response elements to regulate the transcription and expression of genes. It has a wide range of biological functions, such as regulating lipid metabolism, improving insulin sensitivity, modulating anti-tumor mechanisms, and inhibiting inflammation. In recent years, some studies have shown that PPARγ exerts a protective effect during CI/RI. This article aims to summarize the research progress of studies that have investigated the protective effects of PPARγ in CI/RI and the cellular and molecular mechanisms through which these effects are modulated, including inhibition of excitatory amino acid toxicity, reduced Ca2+ overload, anti-oxidative stress, anti-inflammation, inhibition of microglial activation, maintain the BBB, promotion of angiogenesis, and neurogenesis and anti-apoptotic processes.

Rosiglitazone Prevents Autophagy by Regulating Nrf2-Antioxidant Response Element in a Rat Model of Lithium-pilocarpine-induced Status Epilepticus

Status epilepticus (SE) leads to irreversible neuronal damage and consists of a complex pathogenesis that involves oxidative stress and subsequent autophagy. Rosiglitazone has recently been considered as a potential neuroprotective factor in epilepsy because of its antioxidative function. The aim of this study was to assess the effects of rosiglitazone in SE rat models and investigate whether its mechanisms of action involve autophagy via the antioxidant factor, nuclear factor erythroid 2-related factor 2 (Nrf2). The male Sprague-Dawley rats (200-220 g) were used to establish lithium-pilocarpine-induced SE model. We found that rosiglitazone markedly improved neuronal survival at 24-h post-SE as indicated via Hematoxylin-Eosin and Nissl staining. Furthermore, along with a reduction in reactive oxygen species, rosiglitazone pretreatment enhanced the antioxidative activity of superoxide dismutase and the expression level of Nrf2, as detected via chemical assay kits and Western blotting, respectively. In addition, the microtubule-associated protein light chain 3II (LC3II)/LC3I ratio was increased and peaked at 24 h after SE, whereas p62 mRNA levels were sharply elevated at 72 h after SE, both SE-induced increases of which were reversed via rosiglitazone pretreatment. To further test our hypothesis of the key role of Nrf2 in this process, small-interfering RNA for Nrf2 (siNrf2) was then transfected into SE rats to knockdown Nrf2 expression. We found that siNrf2 partially blocked the above effects of rosiglitazone on autophagy-related proteins in SE rats. Taken together, our findings suggest that rosiglitazone attenuates oxidative-stress-induced autophagy via increasing Nrf2 in SE rats and may be used as a promising therapeutic strategy for SE treatment.

Nobiletin alleviates ischemia/reperfusion injury in the kidney by activating PI3K/AKT pathway

Recent studies have demonstrated that nobiletin (NOB) displays anti-oxidative and anti-apoptotic efficacies against multiple pathological insults. However, the potential effects of NOB on the injury caused by ischemia and reperfusion (I/R) in the kidney remain undetermined. In the present study, I/R injury was elicited by right kidney removal and left renal pedicel clamping for 45 min, followed by reperfusion for 24 h. NOB was added at the start of reperfusion. Histological examination, detection of biomarkers in plasma, and measurement of apoptosis induced by endoplasmic reticulum stress (ERS) were used to evaluate renal injury. Additionally, the PI3K/AKT inhibitor LY294002 was also used in mechanistic experiments. NOB pre-treatment significantly reduced renal damage caused by I/R injury, as indicated by decreased serum levels of creatine, blood urea nitrogen and tubular injury scores. Furthermore, NOB inhibited elevated ERS-associated apoptosis, as evidenced by reduced apoptotic rates and ERS-related signaling molecules (such as, C/EBP homologous protein, caspase-12 and glucose-regulated protein of 78 kDa). NOB increased phosphorylation of proteins in the PI3K/AKT pathway. The inhibition of PI3K/AKT signaling with pharmacological inhibitors could reverse the beneficial effects of NOB during renal I/R insult. In conclusion, NOB pre-treatment may alleviate I/R injury in the kidney by inhibiting reactive oxygen species production and ERS-induced apoptosis, partly through the PI3K/AKT signaling pathway.

Role of peroxisome proliferator-activated receptors in stroke prevention and therapy-The best is yet to come?

Role of peroxisome proliferator-activated receptors (PPARs) in the pathophysiology of stroke and protective effects of PPAR ligands have been widely investigated in the last 20 years. Activation of all three PPAR isoforms, but especially PPAR-γ, was documented to limit postischemic injury in the numerous in vivo, as well as in in vitro studies. PPARs have been demonstrated to act on multiple mechanisms and were shown to activate multiple protective pathways related to inflammation, apoptosis, BBB protection, neurogenesis, and oxidative stress. The aim of this review was to summarize two decades of PPAR research in stroke with emphasis on in vivo animal studies. We focus on each PPAR receptor separately and detail their implication in stroke. This review also discusses recent clinical efforts in the field and the epidemiological data with regard to role of PPAR polymorphisms in susceptibility to stroke, and tries to draw conclusions and describe future perspectives.

PPARγ activation mitigates mechanical allodynia in paclitaxel-induced neuropathic pain via induction of Nrf2/HO-1 signaling pathway

Paclitaxel-induced neuropathic pain (PINP) is a dose-limiting side effect and is refractory to widely used analgesic drugs. Previous studies have demonstrated a protective role of peroxisome proliferator-activated receptor gama (PPARγ) in neuropathic pain. However, whether PPARγ activation could alleviate PINP remains to be elucidated. Our previous study has validated the analgesic effect of oltipraz, an nuclear factor erythroid-2 related factor 2 (Nrf2) activator, in a rat model of PINP. In this study, we tested the hypothesis that rosiglitazone, a selective agonist of PPARγ, could attenuate PINP through induction of Nrf2/heme oxygenase-1 (HO-1) signaling pathway. Paclitaxel was injected intraperitoneally on four alternate days to induce neuropathic pain. Paw withdrawal threshold was used to evaluate mechanical allodynia. Western blot and immunofluorescence were used to examine the expression and distribution of PPARγ, Nrf2 and HO-1 in the spinal cord. Our results showed that rosiglitazone attenuated established PINP and delayed the onset of PINP via activation of PPARγ, which were reversed by PPARγ antagonist GW9662. Moreover, rosiglitazone inhibited downregulation of PPARγ in the spinal cord of PINP rats. Furthermore, the analgesic effect of rosiglitazone against PINP was abolished by trigonelline, an Nrf2 inhibitor. Finally, rosiglitazone significantly increased expression of Nrf2 and HO-1 in the spinal cord of PINP rats. Collectively, these results indicated that PPARγ activation might mitigate PINP through activating spinal Nrf2/HO-1 signaling pathway. Our results may provide an alternative option for PINP patients.

Overexpression of long non-coding RNA SNHG16 against cerebral ischemia-reperfusion injury through miR-106b-5p/LIMK1 axis

Long non-coding RNA (LncRNA) involved in types of physiological insults and diseases via regulating the responses of complex molecular, including cerebral ischemia-reperfusion (I/R) injury. LncRNA SNHG16 played a potential role in ketamine-induced neurotoxicity. In this study, we utilized an in vitro cell model of I/R to examine the specific function and mechanism of LncRNA SNHG16 in oxygen-glucose deprivation and reperfusion (OGD/R) induced SH-SY5Y cells. After in vitro treatment of OGD/R, the lower the SH-SY5Y cell survival, the higher cell the apoptosis and increased caspase-3 activity was observed. Also, OGD/R induced endoplasmic reticulum stress (ERS) through increasing GRP78 and CHOP expressions and down-regulated LncRNA SNHG16 in SH-SY5Y cells. Conversely, LncRNA SNHG16 overexpression promoted OGD/R induced SH-SY5Y cell survival, suppressed its apoptosis, and caspase-3 activity. GRP78 and CHOP expressions were significantly suppressed in LncRNA SNHG16 overexpressing cells. MiR-106b-5p expression was increased and LIMK1 expression was down-regulated in OGD/R induced SH-SY5Y cells, and these effects were reversed by LncRNA SNHG16 overexpression, respectively. Moreover, LIMK1 is a direct target of MiR-106b-5p, and knockdown of LIMK1 reversed the effects of LncRNA SNHG16 on OGD/R-induced SH-SY5Y cells biology. Altogether, these results confirmed an important neuroprotection role of LncRNA SNHG16 in OGD/R induced SH-SY5Y cells injury, and miR-106b-5p/LIMK1 signal axis was involved in the action of LncRNA SNHG16.