Pilocarpine protects cobalt chloride-induced apoptosis of RGC-5 cells: involvement of muscarinic receptors and HIF-1 alpha pathway

Paeonol Induces Protective Autophagy in Retinal Photoreceptor Cells

Background: Retinal photoreceptor (RP) cells are widely involved in retina-related diseases, and oxidative stress plays a critical role in retinal secondary damage. Herein, we investigated the effectiveness and potential mechanisms of autophagy of paeonol (Pae) in terms of oxidation resistance. Methods: The animal model was induced by light damage (LD) in vivo, whereas the in vitro model was established by H₂O₂ stimulation. The effectiveness of Pae was evaluated by hematoxylin and eosin, terminal deoxynucleotidyl transferase dUTP nick end labeling assay, immunofluorescence, transmission electron microscopy, electroretinogram, and Western blot analysis in vivo, and the underlying mechanisms of Pae were assessed by Cell Counting Kit-8 assay, reactive oxygen species (ROS) assay, and Western blot analysis in 661W cells. We mainly evaluated the effects of Pae on apoptosis and autophagy. Results: Increased apoptosis of the LD-induced and decreased autophagy of RPs were mitigated by Pae treatment. Pea, which increased the expression of mitochondrial functional protein cytochrome c, reversed the decreased cell viability and autophagy induced by oxidative stress in 661W cells. Experiments showed that autophagy was downregulated in PINK1/Parkin dependent and the BNIP3L/Nix dependent pathways under H₂O₂ stimulation and was upregulated by Pae treatment. Pae increased the cell viability and reduced ROS levels through autophagy. Conclusion: Pretreatment with Pae preserved RP cells by enhancing autophagy, which protected retinal function.

Muscarinic Acetylcholine Receptors in the Retina-Therapeutic Implications

Muscarinic acetylcholine receptors (mAChRs) belong to the superfamily of G-protein-coupled receptors (GPCRs). The family of mAChRs is composed of five subtypes, M1, M2, M3, M4 and M5, which have distinct expression patterns and functions. In the eye and its adnexa, mAChRs are widely expressed and exert multiple functions, such as modulation of tear secretion, regulation of pupil size, modulation of intraocular pressure, participation in cell-to-cell signaling and modula-tion of vascular diameter in the retina. Due to this variety of functions, it is reasonable to assume that abnormalities in mAChR signaling may contribute to the development of various ocular diseases. On the other hand, mAChRs may offer an attractive therapeutic target to treat ocular diseases. Thus far, non-subtype-selective mAChR ligands have been used in ophthalmology to treat dry eye disease, myopia and glaucoma. However, these drugs were shown to cause various side-effects. Thus, the use of subtype-selective ligands would be useful to circumvent this problem. In this review, we give an overview on the localization and on the functional role of mAChR subtypes in the eye and its adnexa with a special focus on the retina. Moreover, we describe the pathophysiological role of mAChRs in retinal diseases and discuss potential therapeutic approaches.

Glaucoma as Neurodegeneration in the Brain

Glaucoma, a group of diseases characterized by progressive optic nerve degeneration that results in irreversible blindness, can be considered a neurodegenerative disorder of both the eye and the brain. Increasing evidence from human and animal studies have shown that glaucoma shares some common neurodegenerative pathways with Alzheimer’s disease (AD) and other tauopathies, such as chronic traumatic encephalopathy (CTE) and frontotemporal dementia. This hypothesis is based on the focal adhesion pathway hypothesis and the spreading hypothesis of tau. Not only has the Apolipoprotein E (APOE) gene been shown to be associated with AD, but also with primary open angle glaucoma (POAG). This review will highlight the relevant literature in the past 20 years from PubMed that show the pathogenic overlap between POAG and AD. Neurodegenerative pathways that contribute to transsynaptic neurodegeneration in AD and other tauopathies might also be similar to those in glaucomatous neurodegeneration.

Effects of topical pilocarpine on ocular growth and refractive development in rabbits

PURPOSE

This study aimed to investigate whether topical pilocarpine affects ocular growth and refractive development as well as the underlying biochemical processes in early eye development in rabbits.

METHODS

Twenty three-week-old New Zealand white rabbits were treated with 0.5% pilocarpine in the right eye for 6 weeks. The left eyes served as contralateral controls. The effects of pilocarpine on refractive error, corneal curvature and ocular biometrics were assessed using streak retinoscopy, keratometry, and A-scan ultrasonography, respectively. Eyeballs were enucleated for histological analysis. The ciliary body and sclera were homogenized to determine the mRNA and protein expression levels of five subtypes of muscarinic receptors.

RESULTS

Compared to control eyes, pilocarpine-treated eyes exhibited approximately -1.63 ± 0.54 D myopia accompanied by a 0.11 ± 0.04 mm increase in axial length (AL) (p < 0.001, respectively). The anterior chamber depth (ACD) was reduced, whereas the lens thickness (LT) and vitreous chamber depth (VCD) increased (p < 0.001, respectively). Corneal curvature decreased over time but was not significantly different between treated and control eyes. The mRNA and protein expression levels of five subtypes of muscarinic receptors were upregulated in the ciliary body and downregulated in the sclera.

CONCLUSIONS

Based on these results, pilocarpine can induce myopic shift, increase LT, elongate VCD and AL, and reduce muscarinic receptor expression in the sclera early in development. These changes raise the possibility that pilocarpine may promote axial elongation in ocular development and facilitate the emmetropization of hyperopic eyes.

Anti-inflammatory and antioxidant effects of muscarinic acetylcholine receptor (mAChR) activation in the rat hippocampus

Recently we found that acute treatment with Oxotremorine (Oxo), a non-selective mAChRs agonist, up-regulates heat shock proteins and activates their transcription factor heat shock factor 1 in the rat hippocampus. Here we aimed to investigate: a) if acute treatment with Oxo may regulate pro-inflammatory or anti-inflammatory cytokines and oxidative stress in the rat hippocampus; b) if chronic restraint stress (CRS) induces inflammatory or oxidative alterations in the hippocampus and whether such alterations may be affected by chronic treatment with Oxo. In the acute experiment, rats were injected with single dose of Oxo (0.4 mg/kg) and sacrificed at 24 h, 48 h and 72 h. In the CRS experiment, the rats were exposed for 21 days to the CRS and then were treated with Oxo (0.2 mg/kg) for further 10 days. The acute Oxo treatment showed an ability to significantly reduce reactive oxygen species (ROS), singlet oxygen (¹O₂), pro-inflammatory cytokines levels (IL-1β and IL-6) and phosphorylated NF-κB-p65. Acute Oxo treatment also increased superoxide dismutase (SOD)-2 protein levels and stimulated SOD activity. No differences were detected in the anti-inflammatory cytokine levels, including IL-10 and TGF-β1. In the group of rats exposed to the CRS were found increased hippocampal IL-1β and IL-6 levels, together with a reduction of SOD activity level. These changes produced by CRS were counteracted by chronic Oxo treatment. In contrast, the upregulation of ROS and ¹O₂ levels in the CRS group was not counteracted by chronic Oxo treatment. The results revealed a hippocampal anti-inflammatory and antioxidant effect of Oxo treatment in both basal conditions and anti-inflammatory in the CRS rat model.

Overview of Bile Acids Signaling and Perspective on the Signal of Ursodeoxycholic Acid, the Most Hydrophilic Bile Acid, in the Heart

Bile acids (BA) are classically known as an important agent in lipid absorption and cholesterol metabolism. Nowadays, their role in glucose regulation and energy homeostasis are widely reported. BAs are involved in various cellular signaling pathways, such as protein kinase cascades, cyclic AMP (cAMP) synthesis, and calcium mobilization. They are ligands for several nuclear hormone receptors, including farnesoid X-receptor (FXR). Recently, BAs have been shown to bind to muscarinic receptor and Takeda G-protein-coupled receptor 5 (TGR5), both G-protein-coupled receptor (GPCR), independent of the nuclear hormone receptors. Moreover, BA signals have also been elucidated in other nonclassical BA pathways, such as sphingosine-1-posphate and BK (large conductance calcium- and voltage activated potassium) channels. Hydrophobic BAs have been proven to affect heart rate and its contraction. Elevated BAs are associated with arrhythmias in adults and fetal heart, and altered ratios of primary and secondary bile acid are reported in chronic heart failure patients. Meanwhile, in patients with liver cirrhosis, cardiac dysfunction has been strongly linked to the increase in serum bile acid concentrations. In contrast, the most hydrophilic BA, known as ursodeoxycholic acid (UDCA), has been found to be beneficial in improving peripheral blood flow in chronic heart failure patients and in protecting the heart against reperfusion injury. This review provides an overview of BA signaling, with the main emphasis on past and present perspectives on UDCA signals in the heart.

Inhibition of autophagy enhanced cobalt chloride‑induced apoptosis in rat alveolar type II epithelial cells

Hypoxia is a type of cellular stress that may result in apoptosis and autophagy. The molecular mechanisms underlying the association between autophagy and apoptosis remain unclear, particularly in hypoxic conditions. Transmission electron microscope, AO-PI staining, flow cytometry and western blot were used to examine the crosstalk between autophagy and apoptosis in hypoxic conditions. Rat alveolar type II epithelial RLE-6TN cells were cultured in a long-term hypoxic environment established by cobalt (II) chloride. It was demonstrated that autophagy and apoptosis occurred in RLE-6TN cells under hypoxic conditions. Treatment of RLE-6TN cells with the autophagy inhibitor 3-methyladenine increased the generation of reactive oxygen species, mitochondrial damage and hypoxia-induced apoptosis. The expression of caspases, particularly caspase-9, increased and may have participated in these processes. The data indicated that the inhibition of autophagy enhanced apoptosis through the mitochondria-mediated intrinsic pathway. These findings provide important insight into the molecular mechanism of autophagy and apoptosis crosstalk. This may provide new insights into pulmonary disease surveillance, diagnosis and treatment.

Ursodeoxycholic acid protects cardiomyocytes against cobalt chloride induced hypoxia by regulating transcriptional mediator of cells stress hypoxia inducible factor 1α and p53 protein

In hepatocytes, ursodeoxycholic acid (UDCA) activates cell signalling pathways such as p53, intracellular calcium ([Ca²⁺ ]_i ), and sphingosine-1-phosphate (S1P)-receptor via Gα_i -coupled-receptor. Recently, UDCA has been shown to protect the heart against hypoxia-reoxygenation injury. However, it is not clear whether UDCA cardioprotection against hypoxia acts through a transcriptional mediator of cells stress, HIF-1α and p53. Therefore, in here, we aimed to investigate whether UDCA could protect cardiomyocytes (CMs) against hypoxia by regulating expression of HIF-1α, p53, [Ca²⁺ ]_i , and S1P-Gα_i -coupled-receptor. Cardiomyocytes were isolated from newborn rats (0-2 days), and hypoxia was induced by using cobalt chloride (CoCl₂ ). Cardiomyocytes were treated with UDCA and cotreated with either FTY720 (S1P-receptor agonist) or pertussis toxin (PTX; Gα_i inhibitor). Cells were subjected for proliferation assay, beating frequency, QuantiGene Plex assay, western blot, immunofluorescence, and calcium imaging. Our findings showed that UDCA counteracted the effects of CoCl₂ on cell viability, beating frequency, HIF-1α, and p53 protein expression. We found that these cardioprotection effects of UDCA were similar to FTY720, S1P agonist. Furthermore, we observed that UDCA protects CMs against CoCl₂ -induced [Ca²⁺ ]_i dynamic alteration. Pharmacological inhibition of the Gα_i -sensitive receptor did not abolish the cardioprotection of UDCA against CoCl₂ detrimental effects, except for cell viability and [Ca²⁺ ]_i . Pertussis toxin is partially effective in inhibiting UDCA protection against CoCl₂ effects on CM cell viability. Interestingly, PTX fully inhibits UDCA cardioprotection on CoCl₂ -induced [Ca²⁺ ]_i dynamic changes. We conclude that UDCA cardioprotection against CoCl₂ -induced hypoxia is similar to FTY720, and its actions are not fully mediated by the Gα_i -coupled protein sensitive pathways. Ursodeoxycholic acid is the most hydrophilic bile acid and is currently used to treat liver diseases. Recently, UDCA is shown to have a cardioprotection effects; however, the mechanism of UDCA cardioprotection is still poorly understood. The current data generated were the first to show that UDCA is able to inhibit the activation of HIF-1α and p53 protein during CoCl₂ -induced hypoxia in cardiomyocytes. This study provides an insight of UDCA mechanism in protecting cardiomyocytes against hypoxia.

Pigment epithelium-derived factor protects retinal ganglion cells from hypoxia-induced apoptosis by preventing mitochondrial dysfunction

AIM

To investigate the potential of pigment epithelium-derived factor (PEDF) to protect the immortalized rat retinal ganglion cells-5 (RGC-5) exposed to CoCl₂-induced chemical hypoxia.

METHODS

After being differentiated with staurosporine (SS), RGC-5 cells were cultured in four conditions: control group cells cultured in Dulbecco's modified eagle medium (DMEM) supplemented with 10% fetal bovine serum, 100 µmol/mL streptomycin and penicillin (named as normal conditions); hypoxia group cells cultured in DMEM containing 300 µmol/mL CoCl₂; cells in the group protected by PEDF were first pretreated with 100 ng/mL PEDF for 2h and then cultured in the same condition as hypoxia group cells; and PEDF group cells that were cultured in the presence of 100 ng/mL PEDF under normal conditions. The cell viability was assessed by MTT assay, the percentage of apoptotic cells was quantified using Annexin V-FITC apoptosis kit, and intra-cellar reactive oxygen species (ROS) was measured by dichloro-dihydro-fluorescein diacetate (DCFH-DA) probe. The mitochondria-mediated apoptosis was also examined to further study the underlying mechanism of the protective effect of PEDF. The opening of mitochondrial permeability transition pores (mPTPs) and membrane potential (Δψm) were tested as cellular adenosine triphosphate (ATP) level and glutathione (GSH). Also, the expression and distribution of Cyt C and apoptosis inducing factor (AIF) were observed.

RESULTS

SS induced differentiation of RGC-5 cells resulting in elongation of their neurites and establishing contacts between outgrowths. Exposure to 300 µmol/mL CoCl₂ triggered death of 30% of the total cells in cultures within 24h. At the same time, pretreatment with 100 ng/mL PEDF significantly suppressed the cell death induced by hypoxia (P<0.05). The apoptosis induced by treatment of CoCl₂ was that induced cell death accompanied with increasing intra-cellar ROS and decreasing GSH and ATP level. PEDF pre-treatment suppressed these effects (P<0.05). Additionally, PEDF treatment inhibited the opening of mPTPs and suppressed decreasing of Δψm in RGC-5 cells, resulting in blocking of the mitochondrial apoptotic pathway.

CONCLUSION

Pretreatment of RGC-5 cells with 100 ng/mL PEDF significantly decreases the extent of apoptosis. PEDF inhibits the opening of mPTPs and suppresses decreasing of Δψm. Moreover, PEDF also reduces ROS production and inhibits cellular ATP level's reduction. Cyt C and AIF activation in PEDF-pretreated cultures are also reduced. These results demonstrate the potential for PEDF to protect RGCs against hypoxic damage in vitro by preventing mitochondrial dysfunction.

L-Satropane Prevents Retinal Neuron Damage by Attenuating Cell Apoptosis and Aβ Production via Activation of M1 Muscarinic Acetylcholine Receptor

Muscarinic acetylcholine receptor (mAChR) agonists have been used to treat glaucoma due to their intraocular pressure-lowering effects. Recently, it has been reported that retinal mAChRs activation can also stimulate neuroprotective pathways.

PURPOSE

In our study, we evaluated the potential neuroprotective effect of L-satropane, a novel mAChR agonist, on retinal neuronal injury induced by cobalt chloride (CoCl₂) and ischemia/reperfusion (I/R).

METHODS

CoCl₂-induced hypoxia injury in cultured cell models and I/R-induced retinal neuronal damage in rats in vivo were used to evaluate the abilities of L-satropane. In detail, we measured the occurrence of retinal pathological changes including molecular markers of neuronal apoptosis and Aβ expression.

RESULTS

Pretreatment with L-satropane protects against CoCl₂-induced neurotoxicity in PC12 and primary retinal neuron (PRN) cells in a dose-dependent manner by increasing retinal neuron survival. CoCl₂ or I/R-induced cell apoptosis by upregulating Bax expression and downregulating Bcl-2 expression, which resulted in an increased Bax/Bcl-2 ratio, and upregulating caspase-3 expression/activity was significantly reversed by L-satropane treatment. In addition, L-satropane significantly inhibited the upregulation of Aβ production in both retinal neurons and tissue. We also found that I/R-induced histopathological retinal changes including cell loss in the retinal ganglion cell layer (GCL) and increased TUNEL positive retinal ganglion cells in GCL and thinning of the inner plexiform layer (IPL) and inner nuclear layer (INL) were markedly improved by L-satropane. The effects of L-satropane were largely abolished by the nonselective mAChRs antagonist atropine and M1-selective mAChR antagonist pirenzepine.

CONCLUSION

These results demonstrated that L-satropane might be effective in preventing retinal neuron damage caused by CoCl₂ or I/R. The neuroprotective effects of L-satropane may be attributed to decreasing cell apoptosis and Aβ production through activation of M1 mAChR.

Existence of muscarinic acetylcholine receptor (mAChR) and fibroblast growth factor receptor (FGFR) heteroreceptor complexes and their enhancement of neurite outgrowth in neural hippocampal cultures

BACKGROUND

Recently, it was demonstrated that G-protein-coupled receptors (GPCRs) can transactivate tyrosine kinase receptors in absence of their ligands. In this work, driven by the observation that mAChRs and fibroblast growth factor receptors (FGFRs) share signalling pathways and regulation of brain functions, it was decided to explore whether mAChRs activation may transactivate FGFRs and, if so, to characterize the related trophic effects in cultured hippocampal neurons.

METHODS

Oxotremorine-M transactivation of FGFRs and related trophic effects were tested in primary hippocampal neurons. Western blotting and in situ proximity ligation assay (PLA) were used to detect FGFR phosphorylation (pFGFR) levels and M₁R-FGFR1 heteroreceptor complexes, respectively.

RESULTS

Oxotremorine-M, a non-selective mAChRs agonist, was able to transactivate FGFR and this transactivation was blocked by Src inhibitors. Oxotremorine-M treatment produced a significant increase in the primary neurite outgrowth that was blocked by pre-treatment with the pFGFR inhibitor SU5402 and Src inhibitors. This trophic effect was almost similar to that induced by fibroblast growth factor-2 (FGF-2). By using atropine as nonselective mAChRs or pirenzepine as selective antagonist for M₁ receptor (M₁R) we could show that mAChRs are involved in modulating the pFGFRs. Using PLA, M₁R-FGFR1 heteroreceptor complexes were identified in the hippocampus and cerebral cortex.

CONCLUSION

The current findings, by showing functional mAChR-FGFR interactions, will contribute to advance the understanding of the mechanisms involved in the actions of cholinergic drugs on neuronal plasticity.

GENERAL SIGNIFICANT

Data may help to develop novel therapeutic strategies not only for neurodegenerative diseases but also for depression-induced atrophy of hippocampal neurons.

Tetramethylpyrazine protects CoCl2-induced apoptosis in human umbilical vein endothelial cells by regulating the PHD2/HIF/1α-VEGF pathway

Tetramethylpyrazine (TMP), one of the active ingredients isolated from a Chinese herbal prescription, possesses protective effects against apoptosis in endothelial cells. However, the underlying mechanism of its protective effects in endothelial cells remains to be elucidated. Using human umbilical vein endothelial cells (HUVECs), the present study assessed the protective effects of TMP on CoCl2-induced apoptosis. Following pre-incubation with CoCl2 (150 µM/ml) for 4 h, the HUVECs were treated with TMP at different concentrations (50, 100 and 200 µM/ml) for 8 h. TMP upregulated the expression of prolyl hydroxylase (PHD)2, reduced the protein and mRNA expression levels of vascular endothelial growth factor (VEGF), and reduced the expression of HIF-1α only at the protein level, not at the mRNA level in HUVECs, in a concentration-dependent manner. Furthermore, silencing of the PHD2 gene with small interfering (si)RNAs abolished the reduction in the expression of hypoxia-inducible factor (HIF)-1α and VEGF by TMP. In addition, TMP protected CoCl2-induced HUVEC injury via an apoptosis pathway, as characterized by the increased ratio of cell viability and the reduced percentage of apoptotic and terminal deoxynucleotidyl transferase dUTP nick end labeling-positive HUVECs, activation of caspase-3, -8 and -9, B-cell lymphoma (Bcl)-2/Bcl-2-activated X protein expression, as well as the release of cytochrome c. The protective properties of TMP were partially attributed to the mRNA and protein expression levels of PHD, since silencing of the PHD2 gene with siRNAs abolished these effects. The present study demonstrated that the antiapoptotic effect of TMP in CoCl2-induced HUVECs was, at least in part, via the regulation of the PHD2/HIF-1α signaling pathway.

Oxidative stress induces autophagy in response to multiple noxious stimuli in retinal ganglion cells

Retinal ganglion cells (RGCs) are the only afferent neurons that can transmit visual information to the brain. The death of RGCs occurs in the early stages of glaucoma, diabetic retinopathy, and many other retinal diseases. Autophagy is a highly conserved lysosomal pathway, which is crucial for maintaining cellular homeostasis and cell survival under stressful conditions. Research has established that autophagy exists in RGCs after increasing intraocular pressure (IOP), retinal ischemia, optic nerve transection (ONT), axotomy, or optic nerve crush. However, the mechanism responsible for defining how autophagy is induced in RGCs has not been elucidated. Accumulating data has pointed to an essential role of reactive oxygen species (ROS) in the activation of autophagy. RGCs have long axons with comparatively high densities of mitochondria. This makes them more sensitive to energy deficiency and vulnerable to oxidative stress. In this review, we explore the role of oxidative stress in the activation of autophagy in RGCs, and discuss the possible mechanisms that are involved in this process. We aim to provide a more theoretical basis of oxidative stress-induced autophagy, and provide innovative targets for therapeutic intervention in retinopathy.

Effect of the M1 Muscarinic Acetylcholine Receptor on Retinal Neuron Number Studied with Gene-Targeted Mice

Pharmacological activation of the M1 muscarinic receptor subtype was suggested to promote the survival of retinal neurons. We examined the hypothesis that the M1 receptor is crucial for retinal neuron survival in vivo by using mice devoid of the M1 receptor gene. Muscarinic receptor gene expression was determined in the retina using real-time PCR. The amount of neurons in the retinal ganglion cell layer and of axons in the optic nerve was determined in retinal wholemounts stained with cresyl blue and in optic nerve cross-sections stained with toluidine blue, respectively. mRNA of all five muscarinic receptor subtypes (M1-M5) was detected in the retina from wild-type mice. Remarkably, M2 and M3 receptor mRNA were most abundant. In retinas from M1 receptor-deficient mice, M4 receptor mRNA expression was increased compared to that of wild-type mice, while no marked changes in the mRNA expression levels of the other muscarinic receptor subtypes were observed. The amount of cells in the retinal ganglion cell layer and the amount of axons in the optic nerve did not differ between M1 receptor-deficient and wild-type mice. The present findings suggest that the M1 receptor is not essential for the survival of retinal neurons in vivo.

Activation of muscarinic receptors protects against retinal neurons damage and optic nerve degeneration in vitro and in vivo models

AIMS

Muscarinic acetylcholine receptor agonist pilocarpine reduces intraocular pressure (IOP) of glaucoma mainly by stimulating ciliary muscle contraction and then increasing aqueous outflow. It is of our great interest to know whether pilocarpine has the additional properties of retinal neuroprotection independent of IOP lowering in vitro and in vivo models.

METHODS

In rat primary retinal cultures, cell viability was measured using an MTT assay and the trypan blue exclusion method, respectively. Retinal ganglion cells (RGCs) were identified by immunofluorescence and quantified by flow cytometry. For the in vivo study, the retinal damage after retinal ischemia/reperfusion injury in rats was evaluated by histopathological study using hematoxylin and eosin staining, transmission electron microscopy, and immunohistochemical study on cleaved caspase-3, caspase-3, and ChAT.

RESULTS

Pretreatment of pilocarpine attenuated glutamate-induced neurotoxicity of primary retinal neurons in a dose-dependent manner. Protection of pilocarpine in both retinal neurons and RGCs was largely abolished by the nonselective muscarinic receptor antagonist atropine and the M1-selective muscarinic receptor antagonist pirenzepine. After ischemia/reperfusion injury in retina, the inner retinal degeneration occurred including ganglion cell layer thinning and neuron lost, and the optic nerve underwent vacuolar changes. These degenerative changes were significantly lessened by topical application of 2% pilocarpine. In addition, the protective effect of pilocarpine on the ischemic rat retina was favorably reflected by downregulating the expression of activated apoptosis marker cleaved caspase-3 and caspase-3 and upregulating the expression of cholinergic cell marker ChAT.

CONCLUSIONS

Taken together, this highlights pilocarpine through the activation of muscarinic receptors appear to afford significant protection against retinal neurons damage and optic nerve degeneration at clinically relevant concentrations. These data also further support muscarinic receptors as potential therapeutic neuroprotective targets in glaucoma.

Stanniocalcin-1 protects retinal ganglion cells by inhibiting apoptosis and oxidative damage

Optic neuropathy including glaucoma is one of the leading causes of irreversible vision loss, and there are currently no effective therapies. The hallmark of pathophysiology of optic neuropathy is oxidative stress and apoptotic death of retinal ganglion cells (RGCs), a population of neurons in the central nervous system with their soma in the inner retina and axons in the optic nerve. We here tested that an anti-apoptotic protein stanniocalcin-1 (STC-1) can prevent loss of RGCs in the rat retina with optic nerve transection (ONT) and in cultures of RGC-5 cells with CoCl2 injury. We found that intravitreal injection of STC-1 increased the number of RGCs in the retina at days 7 and 14 after ONT, and decreased apoptosis and oxidative damage. In cultures, treatment with STC-1 dose-dependently increased cell viability, and decreased apoptosis and levels of reactive oxygen species in RGC-5 cells that were exposed to CoCl2. The expression of HIF-1α that was up-regulated by injury was significantly suppressed in the retina and in RGC-5 cells by STC-1 treatment. The results suggested that intravitreal injection of STC-1 might be a useful therapy for optic nerve diseases in which RGCs undergo apoptosis through oxidative stress.

N-acetylcysteine protects against hypoxia mimetic-induced autophagy by targeting the HIF-1α pathway in retinal ganglion cells

Hypoxia-induced retinal ganglion cell (RGC) death has been proposed to be the critical event in the pathophysiology of glaucoma. Therefore, delaying or halting RGC degeneration, known as neuroprotection, is a novel and promising approach with potential clinical applications for treating glaucoma. In this study, we investigate hypoxia-induced cell death of RGCs and the underlying mechanisms of N-acetylcysteine (NAC) as a neuroprotectant. To establish a model for chemical hypoxia-induced cell death, RGC-5 cells were treated with the hypoxia mimetic cobalt chloride (CoCl2). Following CoCl2 exposure, significant levels of apoptotic and autophagic cell death were observed in RGC-5 cells, evidenced by lysosome dysfunction and autophagosome formation. Pretreating RGC-5 cells with NAC significantly counteracted the autophagic cell death. NAC-mediated neuroprotection was attributed to the direct scavenging of reactive oxygen species and was mediated by targeting the hypoxia-inducible factor-1α pathway via the BNIP3 and PI3K/Akt/mTOR pathways. These results provide insights into the degeneration of RGCs and present a potential clinical application for NAC as a neuroprotectant.

Hypoxia induces apoptosis and autophagic cell death in human periodontal ligament cells through HIF-1α pathway

OBJECTIVES

Oxygen deficiency caused by occlusal trauma and smoking can be present in patients with periodontitis. However, biochemical events important in periodontal tissues during hypoxia remain unclear. The aim of this study was to investigate effects of hypoxia on apoptosis and autophagy of human periodontal ligament cells (PDLCs) in vitro.

MATERIALS AND METHODS

Human PDLCs were obtained and cultured in vitro. Cell viability, apoptosis, autophagy and gene and protein expression were measured in presence and absence of cobalt chloride (CoCl(2)).

RESULTS

CoCl(2) induced cytotoxicity of human PDLCs in a concentration-dependent manner dependent on macromolecular synthesis, and resulted in apoptosis and mitochondrial dysfunction. CoCl(2) also induced redistribution of autophagy marker LC3, increased ratio of LC3-IIto LC3-Iand function of lysosomes. Furthermore, CoCl(2) promoted expression of HIF-1α following upregulation of expressions of Bnip3. Significant increases in expression of IL-1β and MMP-8 were also observed. All these results were reversed by pre-treatment with antioxidant N-acetylcysteine.

CONCLUSIONS

Our data showed that CoCl(2) could induce cytotoxicity through mitochondria- apoptotic and autophagic pathways involved in HIF-1α. CoCl(2 -treated PDLCs may serve as an in vitro model for studies of molecular mechanisms in periodontitis.

Mechanisms and biology of B-cell leukemia/lymphoma 2/adenovirus E1B interacting protein 3 and Nip-like protein X

B-cell leukemia/lymphoma 2 (BCL-2)/adenovirus E1B interacting protein 3 (BNIP3) and Nip-like protein X (NIX) are atypical BCL-2 homology domain 3-only proteins involved in cell death, autophagy, and programmed mitochondrial clearance. BNIP3 and NIX cause cell death by targeting mitochondria, directly through BCL-2-associated X protein- or BCL-2-antagonist/killer-dependent mechanisms, or indirectly through an effect on calcium stores in the endoplasmic reticulum. BNIP3 and NIX also induce autophagy through an effect on mitochondrial reactive oxygen species production, or by releasing Beclin 1 from inhibitory interactions with antiapoptotic BCL-2 family proteins. BNIP3 downregulates mitochondrial mass in hypoxic cells, whereas NIX is required for mitochondrial elimination during erythroid development. BNIP3 and NIX have an emerging role in human health. Cell death mediated by BNIP3 and NIX is implicated in heart disease and ischemic injury. Cancer progression is linked to loss of the prodeath function of BNIP3, but also to induction of its prosurvival activity. Finally, BNIP3 and NIX are implicated in mitochondrial quality control, which is important in aging and degenerative disease. Elucidation of the mechanisms by which BNIP3 and NIX regulate cell death, autophagy, and mitochondrial clearance may lead to treatments for these conditions.

Neuroprotective effect of peroxiredoxin 6 against hypoxia-induced retinal ganglion cell damage

Background

The ability to respond to changes in the extra-intracellular environment is prerequisite for cell survival. Cellular responses to the environment include elevating defense systems, such as the antioxidant defense system. Hypoxia-evoked reactive oxygen species (ROS)-driven oxidative stress is an underlying mechanism of retinal ganglion cell (RGC) death that leads to blinding disorders. The protein peroxiredoxin 6 (PRDX6) plays a pleiotropic role in negatively regulating death signaling in response to stressors, and thereby stabilizes cellular homeostasis.

Results

We have shown that RGCs exposed to hypoxia (1%) or hypoxia mimetic cobalt chloride display reduced expression of PRDX6 with higher ROS expression and activation of NF-κB. These cells undergo apoptosis, while cells with over-expression of PRDX6 demonstrate resistance against hypoxia-driven RGC death. The RGCs exposed to hypoxia either with 1% oxygen or cobalt chloride (0-400 μM), revealed ~30%-70% apoptotic cell death after 48 and 72 h of exposure. Western analysis and real-time PCR showed elevated expression of PRDX6 during hypoxia at 24 h, while PRDX6 protein and mRNA expression declined from 48 h onwards following hypoxia exposure. Concomitant with this, RGCs showed increased ROS expression and activation of NF-κB with IkB phosphorylation/degradation, as examined with H2DCF-DA and transactivation assays. These hypoxia-induced adverse reactions could be reversed by over-expression of PRDX6.

Conclusion

Because an abundance of PRDX6 in cells was able to attenuate hypoxia-induced RGC death, the protein could possibly be developed as a novel therapeutic agent acting to postpone RGC injury and delay the progression of glaucoma and other disorders caused by the increased-ROS-generated death signaling related to hypoxia.

Lutein protects RGC-5 cells against hypoxia and oxidative stress

Retinal ischemia and oxidative stress lead to neuronal death in many ocular pathologies. Recently, we found that lutein, an oxy-carotenoid, protected the inner retina from ischemia/reperfusion injury. However, it is uncertain whether lutein directly protects retinal ganglion cells (RGCs). Here, an in vitro model of hypoxia and oxidative stress was used to further investigate the neuroprotective role of lutein in RGCs. Cobalt chloride (CoCl₂) and hydrogen peroxide (H₂O₂) were added to a transformed RGC cell line, RGC-5, to induce chemical hypoxia and oxidative stress, respectively. Either lutein or vehicle was added to cultured cells. A higher cell count was observed in the lutein-treated cells compared with the vehicle-treated cells. Our data from this in vitro model revealed that lutein might protect RGC-5 cells from damage when exposed to either CoCl₂-induced chemical hypoxia or H₂O₂-induced oxidative stress. These results suggest that lutein may play a role as a neuroprotectant.