Inhibition of GSK-3β Activation Protects SD Rat Retina Against N-Methyl-N-Nitrosourea-Induced Degeneration by Modulating the Wnt/β-Catenin Signaling Pathway

Pregabalin Mediates Retinal Ganglion Cell Survival From Retinal Ischemia/Reperfusion Injury Via the Akt/GSK3β/β-Catenin Signaling Pathway

Purpose

Progressive retinal ganglion cell (RGC) loss induced by retinal ischemia/reperfusion (RIR) injury leads to irreversible visual impairment. Pregabalin (PGB) is a promising drug for neurodegenerative diseases. However, with regard to RGC survival, its specific role and exact mechanism after RIR injury remain unclear. In this study, we sought to investigate whether PGB could protect RGCs from mitochondria-related apoptosis induced by RIR and explore the possible mechanisms.

Methods

C57BL/6J mice and primary RGCs were pretreated with PGB prior to ischemia/reperfusion modeling. The retinal structure and cell morphology were assessed by immunochemical assays and optical coherence tomography. CCK8 was used to assay cell viability, and an electroretinogram was performed to detect RGC function. Mitochondrial damage was assessed by a reactive oxygen species (ROS) assay kit and transmission electron microscopy. Western blot and immunofluorescence assays quantified the expression of proteins associated with the Akt/GSK3β/β-catenin pathway.

Results

Treatment with PGB increased the viability of RGCs in vitro. Consistently, PGB preserved the normal thickness of the retina, upregulated Bcl-2, reduced the ratio of cleaved caspase-3/caspase-3 and the expression of Bax in vivo. Meanwhile, PGB improved mitochondrial structure and prevented excessive ROS production. Moreover, PGB restored the amplitudes of oscillatory potentials and photopic negative responses following RIR. The mechanisms underlying its neuroprotective effects were attributed to upregulation of the Akt/GSK3β/β-catenin pathway. However, PGB-mediated neuroprotection was suppressed when using MK2206 (an Akt inhibitor), whereas it was preserved when treated with TWS119 (a GSK3β inhibitor).

Conclusions

PGB exerts a protective effect against RGC apoptosis induced by RIR injury, mediated by the Akt/GSK3β/β-catenin pathway.

GSK3 Is a Central Player in Retinal Degenerative Diseases but a Challenging Therapeutic Target

Glycogen synthase kinase 3 (GSK3) is a key regulator of many cellular signaling processes and performs a wide range of biological functions in the nervous system. Due to its central role in numerous cellular processes involved in cell degeneration, a rising number of studies have highlighted the interest in developing therapeutics targeting GSK3 to treat neurodegenerative diseases. Although recent works strongly suggest that inhibiting GSK3 might also be a promising therapeutic approach for retinal degenerative diseases, its full potential is still under-evaluated. In this review, we summarize the literature on the role of GSK3 on the main cellular functions reported as deregulated during retinal degeneration, such as glucose homeostasis which is critical for photoreceptor survival, or oxidative stress, a major component of retinal degeneration. We also discuss the interest in targeting GSK3 for its beneficial effects on inflammation, for reducing neovascularization that occurs in some retinal dystrophies, or for cell-based therapy by enhancing Müller glia cell proliferation in diseased retina. Together, although GSK3 inhibitors hold promise as therapeutic agents, we highlight the complexity of targeting such a multitasked kinase and the need to increase our knowledge of the impact of reducing GSK3 activity on these multiple cellular pathways and biological processes.

Intraductal administration of N-methyl-N-nitrosourea as a novel rodent mammary tumor model

Background

Chemically induced animal models of breast cancer (BC) using N-methyl-N-nitrosourea (MNU) have been widely used in preclinical research. The conventional approach entails intraperitoneal (i.p) or intravenous injection of a carcinogen, leading to tumor induction at unpredictable locations. This study aimed to establish a modified MNU-induced rat mammary tumor model using intraductal (i.duc) administration and to evaluate its biological behavior, morphology, and response to chemotherapy drugs.

Methods

In a pilot experiment, female Sprague-Dawley (SD) rats were injected with either i.duc MNU or vehicle to test the feasibility of this approach. We explored the appropriate dosage for stable tumor formation in pubescent female SD rats by testing a single i.duc dose of MNU (0.5, 1.0 and 2.0 mg) or vehicle.

Results

An i.duc injection of 20 µL (1 mg/per duct) MNU in the fourth rat mammary gland induced stable carcinomas in situ. Immunohistochemical (IHC) analysis showed positive expression of estrogen receptor (ER), negative expression of human epidermal growth factor receptor 2 (Her-2), and low expression of Ki-67. Histopathology revealed atypical hyperplasia in the mammary gland 4 weeks after carcinogen injection, developing into carcinoma in situ 5-6 weeks after treatment, with loss of α-SMA and calponin expressions during tumor progression. Albumin-bound paclitaxel (nab-PTX) was injected i.duc and intravenously (i.v) 5 weeks after administration of MNU. The tumor growth rate of the nab-PTX i.duc-treated group was lower than in the i.v and control groups. The number of TUNEL-positive apoptotic cells was significantly higher in the nab-PTX i.duc-treated group.

Conclusions

Using i.duc MNU (20 µL, 1 mg) to establish a rat mammary tumor model resulted in a predictable location in the rat mammary gland and exhibited better consistency; i.duc administration of nab-PTX permitted a smaller drug dose, but produced a better drug response, than i.v injection.

Targeted pharmacotherapy against neurodegeneration and neuroinflammation in early diabetic retinopathy

Diabetic retinopathy (DR), the most frequent complication of diabetes, is one of the leading causes of irreversible blindness in working-age adults and has traditionally been regarded as a microvascular disease. However, increasing evidence has revealed that synaptic neurodegeneration of retinal ganglion cells (RGCs) and activation of glial cells may represent some of the earliest events in the pathogenesis of DR. Upon diabetes-induced metabolic stress, abnormal glycogen synthase kinase-3β (GSK-3β) activation drives tau hyperphosphorylation and β-catenin downregulation, leading to mitochondrial impairment and synaptic neurodegeneration prior to RGC apoptosis. Moreover, glial cell activation triggers enhanced inflammation and oxidative stress, which may accelerate the deterioration of diabetic RGCs neurodegeneration. These findings have opened up opportunities for therapies, such as inhibition of GSK-3β, glial cell activation, glutamate excitotoxicity and the use of neuroprotective drugs targeting early neurodegenerative processes in the retina and halting the progression of DR before the manifestation of microvascular abnormalities. Such interventions could potentially remedy early neurodegeneration and help prevent vision loss in people suffering from DR.

Glycogen synthase kinase-3β inhibitor SB216763 promotes DNA repair in ischemic retinal neurons

Glycogen synthase kinase-3β (GSK-3β) has been shown to attenuate DNA damage in nerve cells, thereby enhancing neuronal survival under pathological conditions; however, the underlying mechanism remains unclear. An in vitro serum-starvation retinal neuron model and in vivo ischemia/reperfusion retina injury rat model were established and treated with SB216763, a GSK-3β inhibitor. SB21673 decreased the formation of γ-H2A histone family member X foci and enhanced the viability of ischemic retinal neurons. In addition, SB216763 upregulated expression of phosphorylated-CREB1, a ligase IV transcription factor, and significantly increased the transcriptional activity of ligase IV in ischemic retinal neurons. These results were confirmed in rat retinas following ischemia/reperfusion injury. Furthermore, we found that unlike lithium chlorine (a well-known direct inhibitor of GSK-3β), SB216763 inhibited GSK-3β activity by suppressing its phosphorylation. Taken together, our results suggest that GSK-3β inhibition enhances repair of DNA double-strand breaks by upregulating ligase IV expression in ischemic retinal neurons. This study was approved by the Institutional Animal Care and Use Committee of Zhongshan Ophthalmic Center on February 18, 2018.

Microarray-based gene expression analysis combined with laser capture microdissection is beneficial in investigating the modes of action of ocular toxicity

The retina consists of several layers, and drugs can affect the retina and choroid separately. Therefore, investigating the target layers of toxicity can provide useful information pertaining to its modes of action. Herein, we compared gene expression profiles obtained via microarray analyses using samples of target layers collected via laser capture microdissection and samples of the whole globe of the eye of rats treated with N-methyl-N-nitrosourea. Pathway analyses suggested changes in the different pathways between the laser capture microdissection samples and the whole globe samples. Consistent with the histological distribution of glial cells, upregulation of several inflammation-related pathways was noted only in the whole globe samples. Individual gene expression analyses revealed several gene expression changes in the laser capture microdissection samples, such as caspase- and glycolysis-related gene expression changes, which is similar to previous reports regarding N-methyl-N-nitrosourea-treated animals; however, caspase- and glycolysis-related gene expressions did not change or changed unexpectedly in the whole globe samples. Analyses of the laser capture microdissection samples revealed new potential candidate genes involved in the modes of action of N-methyl-N-nitrosourea-induced retinal toxicity. Collectively, our results suggest that specific retinal layers, which may be targeted by specific toxins, are beneficial in identifying genes responsible for drug-induced ocular toxicity.

The neuroprotective role of Wnt signaling in the retina

The canonical Wnt/β-catenin signaling pathway has been shown to play a major role during embryonic development and maturation of the central nervous system including the retina. It has a significant impact on retinal vessel formation and maturation, as well as on the establishment of synaptic structures and neuronal function in the central nervous system. Mutations in components of the Wnt/β-catenin signaling cascade may lead to severe retinal diseases, while dysregulation of Wnt signaling can contribute to disease progression. Apart from the angiogenic role of Wnt/β-catenin signaling, research in the last decades leads to the theory of a protective effect of Wnt/β-catenin signaling on damaged neurons. In this review, we focus on the neuroprotective properties of the Wnt/β-catenin pathway as well as its downstream signaling in the retina.

17β-Oestradiol Attenuates the Photoreceptor Apoptosis in Mice with Retinitis Pigmentosa by Regulating N-myc Downstream Regulated Gene 2 Expression

Retinitis pigmentosa (RP) is a heterogeneous group of retinal degenerative diseases in which the final pathological feature is photoreceptor cell apoptosis. Currently, the pathogenesis of RP remains poorly understood and therapeutics are ineffective. 17β-Oestradiol (βE2) is universally acknowledged as a neuroprotective factor in neurodegenerative diseases and has manifested neuroprotective effects in a light-induced retinal degeneration model. Recently, we identified N-myc downstream regulated gene 2 (NDRG2) suppression as a molecular marker of mouse retinal photoreceptor-specific cell death. βE2 has also been reported to regulate NDRG2 in salivary acinar cells. Therefore, in this study, we investigated whether βE2 plays a protective role in RP and regulates NDRG2 in photoreceptor cells. To this end, we generated RP models and observed that βE2 not only reduced the apoptosis of photoreceptor cells, but also restored the level of NDRG2 expression in RP models. Then, we showed that siNDRG2 inhibits the anti-apoptotic effect of βE2 on photoreceptor cells in a cellular RP model. Subsequently, we used a classic oestrogen receptor (ER) antagonist to attenuate the effects of βE2, suggesting that βE2 exerted its effects on RP models via the classic ERs. In addition, we performed a bioinformatics analysis, and the results indicated that the reported oestrogen response element (ERE) sequence is present in the promoter region of the mouse NDRG2 gene. Overall, our results suggest that βE2 attenuated the apoptosis of photoreceptor cells in RP models by maintaining NDRG2 expression via a classic ER-mediated mechanism.

The loss of dopaminergic neurons in DEC1 deficient mice potentially involves the decrease of PI3K/Akt/GSK3β signaling

Here we study the effects of differentiated embryonic chondrocyte gene 1(DEC1) deficiency on midbrain dopaminergic(DA) neurons in the substantia nigra pars compacta(SNpc) through behavioral, histological and molecular analysis. We have found that compared to the age-matched WT mice, DEC1 deficient mice show a decrease in locomotor activity and motor coordination, which shows the main features of Parkinson's disease(PD). But there is no significant difference in spatial learning and memory skills between WT and DEC1 KO mice. Compared to the age-matched WT mice, DEC1 deficient mice exhibit the loss of DA neurons in the SNpc and reduction of dopamine and its metabolites in the striatum. The activated caspase-3 and TH/TUNEL⁺ cells increase in the SNpc of 6- and 12-month-old DEC1 KO mice compared to those of the age-matched WT mice. But we haven't found any NeuN/TUNEL⁺ cell increase in the hippocampus of the above two types of mice at the age of 6 months. Furthermore, DEC1 deficiency leads to a significant inhibition of PI3K/Akt/GSK3β signaling pathway. Additionally, LiCl could rescue the DA neuron loss of midbrain in the 6-month-old DEC1 KO mice. Taken together, the loss of DA neurons in the DEC1 deficient mice potentially involves the downregulation of PI3K/Akt/GSK3β signaling.

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.

The application of transgenic and gene knockout mice in the study of gastric precancerous lesions

Gastric intestinal metaplasia is a precursor for gastric dysplasia, which is in turn, a risk factor for gastric adenocarcinoma. Gastric metaplasia and dysplasia are known as gastric precancerous lesions (GPLs), which are essential stages in the progression from normal gastric mucosa to gastric cancer (GC) or gastric adenocarcinoma. Genetically-engineered mice have become essential tools in various aspects of GC research, including mechanistic studies and drug discovery. Studies in mouse models have contributed significantly to our understanding of the pathogenesis and molecular mechanisms underlying GPLs and GC. With the development and improvement of gene transfer technology, investigators have created a variety of transgenic and gene knockout mouse models for GPLs, such as H/K-ATPase transgenic and knockout mutant mice and gastrin gene knockout mice. Combined with Helicobacter infection, and treatment with chemical carcinogens, these mice develop GPLs or GC and thus provide models for studying the molecular biology of GC, which may lead to the discovery and development of novel drugs. In this review, we discuss recent progress in the use of genetically-engineered mouse models for GPL research, with particular emphasis on the importance of examining the gastric mucosa at the histological level to investigate morphological changes of GPL and GC and associated protein and gene expression.

Chronic noise exposure exacerbates AD-like neuropathology in SAMP8 mice in relation to Wnt signaling in the PFC and hippocampus

Non-genetic environmental hazards are thought to be associated with genetic susceptibility factors that increase Alzheimer’s disease (AD) pathogenesis. Aging and chronic noise exposure have been considered important factors in the AD. Here, we investigated the impact of chronic noise exposure on the AD-like neuropathology in the senescence-accelerated prone mouse (SAMP8) and the underlying mechanisms of such effects. We examined the consequences of AD-like neuropathology in 3-month-old SAMP8 mice using low- and high-intensity noise exposure and 8-month-old SAMP8 mice as aging positive controls. Immunoblotting and immunohistochemistry were conducted to examine AD-like pathological changes and potential mechanisms. Chronic noise exposure led to progressive overproduction of Aβ and increased the hyperphosphorylation of tau at Ser396, Thr205, and Thr231 sites in the hippocampus and the prefrontal cortex (PFC) in young SAMP8 mice, similar to that observed in aging SAMP8 mice. Both noise exposure and aging could cause a significant downregulation in Wnt signaling expression. These findings demonstrate that chronic noise stress exacerbated AD-like neuropathology, possibly by disrupting Wnt signaling and triggering aberrant tau hyperphosphorylation and Aβ in the PFC and hippocampus.