Inhibition of poly(ADP-ribose) polymerase inhibits ischemia/reperfusion induced neurodegeneration in retina via suppression of endoplasmic reticulum stress

Ribonuclease attenuates retinal ischemia reperfusion injury through inhibition of inflammatory response and apoptosis in mice

The present study was aimed to reveal the function of extracellular RNAs (exRNAs) in retinal ischemia reperfusion (I/R) injury, and evaluate whether RNase administration can effectivelyreduce I/Rinjury. A retinal I/R injury C57BL/6J wild-type mice model was established by elevating intraocular pressure for 1 h. All mice received 3 doses of RNase or the same dose of normal saline at different time points. After 7 days of reperfusion, retinal damage was quantified by counting retinal ganglion cells and measuring retinal layer thickness. The apoptotic retinal cells were detected by the TUNEL experiment, and the expressions of caspase-3, proinflammatory cytokines in retinal tissues, and glial fibrillary acidic protein (GFAP) protein and mRNA were detected to determine the underlying mechanism. It was found that RNase administration (1) reduced the significant loss of retinal morphology caused by I/R injury; (2) down-regulated the expression of NF-κBp65, IL-6 and GFAP relative to the I/R mice; (3) decreased the apoptosis of retinal cells and the levels of caspase-3; (4) attenuated exRNAs levels in retinal tissues on day 7 after retinal I/R. In short, increased exRNAs may contribute to retinal I/R damages in mice, and RNase therapy can effectively attenuate retinal damage by reducing inflammatory response and apoptosis.

PARP Inhibitor Protects Against Chronic Hypoxia/Reoxygenation-Induced Retinal Injury by Regulation of MAPKs, HIF1α, Nrf2, and NFκB

Purpose

In the eye, chronic hypoxia/reoxygenation (H/R) contributes to the development of a number of ocular disorders. H/R induces the production of reactive oxygen species (ROS), leading to poly(ADP-ribose) polymerase-1 (PARP1) activation that promotes inflammation, cell death, and disease progression. Here, we analyzed the protective effects of the PARP1 inhibitor olaparib in H/R-induced retina injury and investigated the signaling mechanisms involved.

Methods

A rat retinal H/R model was used to detect histologic and biochemical changes in the retina.

Results

H/R induced reductions in the thickness of most retinal layers, which were prevented by olaparib. Furthermore, H/R caused increased levels of Akt and glycogen synthase kinase-3β phosphorylation, which were further increased by olaparib, contributing to retina protection. By contrast, H/R-induced c-Jun N-terminal kinase and p38 mitogen-activated protein kinases (MAPK) phosphorylation and activation were reduced by olaparib, via mitogen-activated protein kinase phosphatase 1 (MKP-1) expression. In addition, H/R-induced hypoxia-inducible factor 1α (HIF1α) levels were decreased by olaparib, which possibly contributed to reduced VEGF expression. Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) expression was slightly increased by H/R and was further activated by olaparib. Nuclear factor-κB (NFκB) was also activated by H/R through phosphorylation (Ser536) and acetylation (Lys310) of the p65 subunit, although this was significantly reduced by olaparib.

Conclusions

Olaparib reduced H/R-induced degenerative changes in retinal morphology. The protective mechanisms of olaparib most probably involved Nrf2 activation and ROS reduction, as well as normalization of HIF1α and related VEGF expression. In addition, olaparib reduced inflammation by NFκB dephosphorylation/inactivation, possibly via the PARP1 inhibition-MKP-1 activation-p38 MAPK inhibition pathway. PARP inhibitors represent potential therapeutics in H/R-induced retinal disease.

Can crosstalk between DOR and PARP reduce oxidative stress mediated neurodegeneration?

The progressive loss of structure and function of neurons leads to neurodegenerative processes which become the causative reason for various neurodegenerative diseases such as Parkinson's disease (PD), Alzheimer's disease (AD) etc. These diseases are multifactorial in nature but they have been seen to possess similar causative agents to a certain extent. Oxidative Stress (OS) has been identified as a major stressor and a mediator in most of these diseases. OS not only leads to the generation of free radical species but if persistent, can possibly lead to lipid peroxidation, protein damage, DNA damage, and cell death. Anti-oxidants are endogenously present in our body to tackle oxygen metabolites but their levels reduce greatly under continuous OS conditions. In such a case, dietary supplements to replenish the anti-oxidant levels in our body is a good way of treatment but it is very slow and may not be as effective in chronic stress conditions. Thus, there is a need for more effective mechanisms to attenuate OS. Two such mechanisms which can be considered are the activation of Delta opioid receptor (DOR) and Inhibition of Poly (ADP-ribose)-polymerase1 (PARP1), which have been suggested to protect neurons and increase neuronal cell survivability in both in-vitro and in-vivo disease models. Various signaling pathways have been highlighted to probably play a significant role in attenuating OS by the activation of DOR. It would be an interesting topic of investigation to see if one of the probable mechanisms by which DOR attenuates OS could be by modulation of PARP through a cascade of intracellular signaling reactions.

Dexmedetomidine preconditioning protects against retinal ischemia/reperfusion injury and inhibits inflammation response via toll-like receptor 4 (TLR4) pathway

BACKGROUND

Retinal ischemia/reperfusion (I/R) injury is one of significant cause of visual dysopia and causes inflammatory response. Dexmedetomidine is widely applied to general/local anaesthesia and has been reported to have extensive anti-inflammatory effect. However, the role of dexmedetomidine in retinal I/R injury is currently unknown. This study investigates the effect of dexmedetomidine preconditioning on retinal I/R injury and explore the related signal mechanism toll-like receptor 4 (TLR4) pathway.

METHODS

Retinal I/R injury model were established with SD rats through periocular injection. Retinal damage was quantified by measuring the thickness of retinal layers, cell counts of retinal ganglion cells (RGCs) and electroretinography (ERG). Apoptosis of retinal cell was detected by TUNEL assay. Protein and mRNA expression of glial fibrillary acidic protein (GFAP) were measured by western blot and real-time quantitate PCR. Bax, Bcl-2 and nuclear factor-κB (NF-κB) in retinas were detected by western blot.

RESULTS

ERG and HE staining showed that dexmedetomidine preconditioning significantly inhibited the histologic damage induced by I/R injury, which expresses apparent concentration dependent. TUNEL demonstrated that apoptosis of retinal cells were reduced by dexmedetomidine. The expression of NF-κB and GFAP were decreased compared I/R blank group.

CONCLUSION

Dexmedetomidine preconditioning suppresses retinal I/R injury and shows effective anti-inflammatory effect by inhibiting TLR4/NF-κB expression.

Abnormal levels of histone methylation in the retinas of diabetic rats are reversed by minocycline treatment

In this study we quantified the alterations of retinal histone post-translational modifications (PTMs) in diabetic rats using a liquid chromatography - tandem mass spectrometry (LC-MS/MS) approach. Some diabetic rats were subsequently treated with minocycline, a tetracycline antibiotic, which has been shown to inhibit the diabetes-induced chronic inflammation in the retinas of rodents. We quantified 266 differentially modified histone peptides, including 48 out of 83 methylation marks with significantly different abundancein retinas of diabetic rats as compared to non-diabetic controls. About 67% of these marks had their relative abundance restored to non-diabetic levels after minocycline treatment. Mono- and di-methylation states of histone H4 lysine 20 (H4K20me1/me2), markers related to DNA damage response, were found to be up-regulated in the retinas of diabetic rats and restored to control levels upon minocycline treatment. DNA damage response biomarkers showed the same pattern once quantified by western blotting. Collectively, this study indicates that alteration of some histone methylation levels is associated with the development of diabetic retinopathy in rodents, and the beneficial effect of minocycline on the retinas of diabetic rodents is partially through its ability to normalize the altered histone methylation levels.

Chemical Chaperone 4-Phenylbutyric Acid Reduces Cardiac Ischemia/Reperfusion Injury by Alleviating Endoplasmic Reticulum Stress and Oxidative Stress

Background

Cardiovascular diseases are the leading cause of death in many countries and myocardial ischemia-reperfusion (I/R) injury is the cause of many serious heart diseases. Recent reports suggested that endoplasmic reticulum (ER) stress is associated with the progress of ischemia/reperfusion (I/R) injury. In a previous study, we illustrated that 4-phenylbutyric acid (4-PBA) reduces I/R-induced cell death in vitro through inhibiting the ER stress-initiated cell apoptosis. In the present study we investigated whether 4-PBA improves heart function in isolated rat hearts subjected to I/R and elucidated the potential mechanisms involved in 4-PBA-induced cardioprotective effects.

Material/Methods

The isolated rat hearts were subjected to global ischemia and reperfusion in the absence or presence of 4-PBA. Hemodynamic parameters (LVSP, LVEDP, ±dP/dt_max, and HR) were monitored and histopathological examination was applied. The biomarkers related to oxidative stress were detected by LDH, ROS, MDA, CK, SOD, and GSH-Px kits. A TUNEL apoptosis assay kit was used to detect apoptosis. The expression levels of ER stress and apoptosis proteins were evaluated by Western blotting.

Results

We found that 4-PBA (5 mM, 10 mM) pretreatment significantly attenuated cardiac dysfunction and depressed oxidative stress induced by I/R. Moreover, I/R activated the ER stress proteins Grp78 and PERK, which are all decreased by 4-PBA. 4-PBA pretreatment also inhibited the expression of CHOP, Caspase-12, and Bax, reduced the phosphorylation of JNK, and enhanced the expression of anti-apoptotic protein Bcl-2.

Conclusions

We elucidated the significant protective effects of 4-PBA against I/R injuries by inhibition of ER stress, oxidative stress, and their associated apoptosis.

Restoration of Opa1-long isoform inhibits retinal injury-induced neurodegeneration

Optic atrophy 1 (Opa1) is a critical factor that regulates fusion and other important functions of mitochondria. In mitochondrion, the N-terminal mitochondrial targeting sequence of Opa1 precursors is removed to generate Opa1 long isoforms (L-Opa1), which are further cleaved into short isoforms (S-Opa1). In the present study, we found that retinal ischemia-reperfusion (I/R) injury and intravitreal injection of carbonylcyanide m-chlorophenyl hydrazone (CCCP) both dramatically induced Opa1 cleavage and caused loss of L-Opa1. In cultured neuronal cells under hypoxia-reoxygenation (H/R) injury, similar changes for Opa1 were also observed. In contrast, restoration of L-Opa1 level by overexpression of S1 cleavage site deletion Opa1 splice 1 (Opa1-ΔS1) not only normalized the H/R-induced mitochondrial morphology changes, but also inhibited the H/R-induced apoptosis, necrosis, and the intracellular ATP loss. Furthermore, recovering L-Opa1 level in the I/R-injured retina by intravitreal injection of genipin or overexpression of Opa1-ΔS1 inhibited apoptosis, necrosis, cell loss in the ganglion cell layer and retinal thickness reduction. Together, our data demonstrated the loss of L-Opa1 is involved in the development of retinal I/R injury, indicating restoring L-Opa1 level may be considered as a therapeutic target for I/R injury-related diseases, at least for the retina. Key messages: Retinal ischemia-reperfusion (I/R) or hypoxia-reoxygenation (H/R) injury induces L-Opa1 loss. Opa1-ΔS1 overexpression inhibits H/R-induced L-Opa1 loss. Opa1-ΔS1 overexpression inhibits H/R-induced mitochondria morphology change. Opa1-ΔS1 and genipin inhibit retinal I/R injury-induced necroptosis. Opa1-ΔS1 and genipin inhibit retinal I/R injury-induced neurodegeneration.

Ursolic acid inhibits the development of nonalcoholic fatty liver disease by attenuating endoplasmic reticulum stress

Ursolic acid (UA) is a natural pentacyclic triterpenoid compound, which is enriched with many herbs and plants, such as apple, cranberry and olive. UA performs multiple biological activities including anti-oxidation, anti-inflammation, anti-cancer and hepatoprotection. However, the exact mechanism underlying the hepatoprotective activity of UA remains unclear. In this study, the effects of UA on the development of nonalcoholic fatty liver disease (NAFLD) were investigated. In vivo, UA treatment (0.14%, w/w) significantly decreased the liver weight, serum levels of ALT/AST and hepatic steatosis in db/db mice (a type 2 diabetic mouse model). In vitro, UA treatment (10-30 μg ml(-1)) significantly decreased palmitic acid induced intracellular lipid accumulation in L02 cells. Our results suggested that the beneficial effects of UA on NAFLD may be due to its ability to increase lipid β-oxidation and to inhibit the hepatic endoplasmic reticulum (ER) stress. Together, UA may be further considered as a natural compound for NAFLD treatment.

Therapeutic applications of PARP inhibitors: anticancer therapy and beyond

The aim of this article is to describe the current and potential clinical translation of pharmacological inhibitors of poly(ADP-ribose) polymerase (PARP) for the therapy of various diseases. The first section of the present review summarizes the available preclinical and clinical data with PARP inhibitors in various forms of cancer. In this context, the role of PARP in single-strand DNA break repair is relevant, leading to replication-associated lesions that cannot be repaired if homologous recombination repair (HRR) is defective, and the synthetic lethality of PARP inhibitors in HRR-defective cancer. HRR defects are classically associated with BRCA1 and 2 mutations associated with familial breast and ovarian cancer, but there may be many other causes of HRR defects. Thus, PARP inhibitors may be the drugs of choice for BRCA mutant breast and ovarian cancers, and extend beyond these tumors if appropriate biomarkers can be developed to identify HRR defects. Multiple lines of preclinical data demonstrate that PARP inhibition increases cytotoxicity and tumor growth delay in combination with temozolomide, topoisomerase inhibitors and ionizing radiation. Both single agent and combination clinical trials are underway. The final part of the first section of the present review summarizes the current status of the various PARP inhibitors that are in various stages of clinical development. The second section of the present review summarizes the role of PARP in selected non-oncologic indications. In a number of severe, acute diseases (such as stroke, neurotrauma, circulatory shock and acute myocardial infarction) the clinical translatability of PARP inhibition is supported by multiple lines of preclinical data, as well as observational data demonstrating PARP activation in human tissue samples. In these disease indications, PARP overactivation due to oxidative and nitrative stress drives cell necrosis and pro-inflammatory gene expression, which contributes to disease pathology. Accordingly, multiple lines of preclinical data indicate the efficacy of PARP inhibitors to preserve viable tissue and to down-regulate inflammatory responses. As the clinical trials with PARP inhibitors in various forms of cancer progress, it is hoped that a second line of clinical investigations, aimed at testing of PARP inhibitors for various non-oncologic indications, will be initiated, as well.

Aag DNA glycosylase promotes alkylation-induced tissue damage mediated by Parp1

Alkylating agents comprise a major class of front-line cancer chemotherapeutic compounds, and while these agents effectively kill tumor cells, they also damage healthy tissues. Although base excision repair (BER) is essential in repairing DNA alkylation damage, under certain conditions, initiation of BER can be detrimental. Here we illustrate that the alkyladenine DNA glycosylase (AAG) mediates alkylation-induced tissue damage and whole-animal lethality following exposure to alkylating agents. Aag-dependent tissue damage, as observed in cerebellar granule cells, splenocytes, thymocytes, bone marrow cells, pancreatic β-cells, and retinal photoreceptor cells, was detected in wild-type mice, exacerbated in Aag transgenic mice, and completely suppressed in Aag^−/− mice. Additional genetic experiments dissected the effects of modulating both BER and Parp1 on alkylation sensitivity in mice and determined that Aag acts upstream of Parp1 in alkylation-induced tissue damage; in fact, cytotoxicity in WT and Aag transgenic mice was abrogated in the absence of Parp1. These results provide in vivo evidence that Aag-initiated BER may play a critical role in determining the side-effects of alkylating agent chemotherapies and that Parp1 plays a crucial role in Aag-mediated tissue damage.

Alkylating agents are genotoxic chemicals that induce both toxic and mutagenic DNA damage through addition of an alkyl group to DNA. Alkylating agents are routinely and successfully used as chemotherapeutic therapies for cancer patients, with one major disadvantage being the significant toxicity induced in non-tumor tissues. Accordingly, identifying factors that modify susceptibility to alkylation-induced toxicity will provide valuable information in designing cancer therapeutic regimens. This study used mouse genetic experiments to investigate whether proteins important in the base excision repair pathway modulate susceptibility to alkylating agents. In addition to whole-animal toxicity at high doses, treatment of mice with alkylating agents resulted in severe damage to numerous tissues including the cerebellum, retina, bone marrow, spleen, thymus, and the pancreas. We illustrate that the DNA glycosylase Aag can actually confer, rather than prevent, alkylation sensitivity at both the whole-animal and tissue level; i.e., Aag transgenic animals are more susceptible than wild type, whereas Aag-deficient animals are less susceptible than wild type to alkylation-induced toxicity. Further genetic experiments show that the Aag-mediated alkylation sensitivity is dependent on Parp1. Given that we observe a wide range of human AAG expression among healthy individuals, this and other base excision repair proteins may be important factors modulating alkylation susceptibility.