Autophagy, lysosome dysfunction and mTOR inhibition in MNU-induced photoreceptor cell damage

Early Alterations of RNA Binding Protein (RBP) Homeostasis and ER Stress-Mediated Autophagy Contributes to Progressive Retinal Degeneration in the rd10 Mouse Model of Retinitis Pigmentosa (RP)

The retinal degeneration 10 (rd10) mouse model is widely used to study retinitis pigmentosa (RP) pathomechanisms. It offers a rather unique opportunity to study trans-neuronal degeneration because the cell populations in question are separated anatomically and the mutated Pde6b gene is selectively expressed in rod photoreceptors. We hypothesized that RNA binding protein (RBP) aggregation and abnormal autophagy might serve as early pathogenic events, damaging non-photoreceptor retinal cell types that are not primarily targeted by the Pde6b gene defect. We used a combination of immunohistochemistry (DAB, immunofluorescence), electron microscopy (EM), subcellular fractionation, and Western blot analysis on the retinal preparations obtained from both rd10 and wild-type mice. We found early, robust increases in levels of the protective endoplasmic reticulum (ER) calcium (Ca²⁺) buffering chaperone Sigma receptor 1 (SigR1) together with other ER-Ca²⁺ buffering proteins in both photoreceptors and non-photoreceptor neuronal cells before any noticeable photoreceptor degeneration. In line with this, we found markedly altered expression of the autophagy proteins p62 and LC3, together with abnormal ER widening and large autophagic vacuoles as detected by EM. Interestingly, these changes were accompanied by early, prominent cytoplasmic and nuclear aggregation of the key RBPs including pTDP-43 and FET family RBPs and stress granule formation. We conclude that progressive neurodegeneration in the rd10 mouse retina is associated with early disturbances of proteostasis and autophagy, along with abnormal cytoplasmic RBP aggregation.

N-methyl-N-nitrosourea induces zebrafish anomalous angiogenesis through Wnt/β-catenin pathway

N-methyl-N-nitrosourea (MNU) is a prevalent environmental carcinogen, which leads to tumors in various organs in animal models, while the mechanisms involved were still not fully understood. It is well known that anomalous angiogenesis is a key step in tumorigenesis and progression. In this study, we found that MNU induced abnormal angiogenesis which was accompanied by upregulation of rspo1, p53 and vegfaa in zebrafish embryos. Moreover, it revealed that MNU-induced ectopic sprouting of blood vessels was significantly reduced in rspo1-knockdown but not p53-knockdown embryos, indicating that rspo1 was necessary for MNU-induced abnormal angiogenesis. Additionally, pharmaceutical activation or inhibition of Wnt/β-catenin signaling pathway using (2'Z,3'E)- 6-bromoindirubin-3'-oxime or CCT036477 significantly increased or inhibited the pro-angiogenic effect of MNU on developing zebrafish embryos, which was confirmed by the effect of proliferation and migration in MNU-treated bEnd.3 cells. These data together indicated that rspo1/Wnt/β-catenin/vegfaa axis is involved in the modulation of MNU-induced anomalous angiogenesis.

Retinitis Pigmentosa (RP): The Role of Oxidative Stress in the Degenerative Process Progression

Purpose: Retinitis Pigmentosa is a term that includes a group of inherited bilateral and progressive retinal degenerations, with the involvement of rod photoreceptors, which frequently leads to blindness; oxidative stress may be involved in the degeneration progression as proposed by several recent studies. The goal of this study is to evaluate whether circulating free radicals taken from capillary blood are related to one of the most important features of Retinitis pigmentosa that can affect frequently patients: cystoid macular oedema (CME). Materials: A total of 186 patients with Retinitis Pigmentosa (range: 25−69 years) were enrolled; all patients completed an ophthalmologic examination and SD-OCT at baseline and were divided into three subgroups according to the SD-OCT features. ROS blood levels were determined using FORT with monitoring of free oxygen radicals. Results: Test levels of free oxygen radicals were significantly increased, almost twice, in RP patients showing cystoid macular oedema and significantly increased compared to the control group. (p < 0.001). Discussion: Our findings suggest that oxidative stress may speed cone photoreceptors’ morphological damage (CMT); because long lasting oxidative stress in the RP may cause oxidative damage, with animal models of RP suggesting this is a micromolecular mechanism of photoreceptors’ (cone) death, it can be similar to cone damage in human RP eyes. The limitations of this paper are the relatively small sample, the horizontal design of the study, and the lack of data about the levels of ROS in the vitreous body.

Programmed Cell Death and Autophagy in an in vitro Model of Spontaneous Neuroretinal Degeneration

Retinal neurodegenerative diseases are the leading causes of visual impairment and irreversible blindness worldwide. Although the retinal response to injury remains closely similar between different retinal neurodegenerative diseases, available therapeutic alternatives are only palliative, too expensive, or very specific, such as gene therapy. In that sense, the development of broad-spectrum neuroprotective therapies seems to be an excellent option. In this regard, it is essential to identify molecular targets involved in retinal degeneration, such as cell death mechanisms. Apoptosis has been considered as the primary cell death mechanism during retinal degeneration; however, recent studies have demonstrated that the only use of anti-apoptotic drugs is not enough to confer good neuroprotection in terms of cell viability and preservation. For that reason, the interrelationship that exists between apoptosis and other cell death mechanisms needs to be characterized deeply to design future therapeutic options that simultaneously block the main cell death pathways. In that sense, the study aimed to characterize the programmed cell death (in terms of apoptosis and necroptosis) and autophagy response and modulation in retinal neurodegenerative diseases, using an in vitro model of spontaneous retinal neurodegeneration. For that purpose, we measured the mRNA relative expression through qPCR of a selected pool of genes involved in apoptosis (BAX, BCL2, CASP3, CASP8, and CASP9), necroptosis (MLKL, RIPK1, and RIPK3), and autophagy (ATG7, BCLIN1, LC3B, mTOR, and SQSTM1); besides, the immunoexpression of their encoding proteins (Casp3, MLKL, RIPK1, LC3B, and p62) were analyzed using immunohistochemistry. Our results showed an increase of pro-apoptotic and pro-necroptotic related genes and proteins during in vitro retinal neurodegeneration. Besides, we describe for the first time the modulation between programmed cell death mechanisms and autophagy in an in vitro retinal neurodegeneration model. This study reinforces the idea that cell death mechanisms are closely interconnected and provides new information about molecular signaling and autophagy along the retinal degeneration process.

Emerging Lysosomal Functions for Photoreceptor Cell Homeostasis and Survival

Lysosomes are membrane-bound cell organelles that respond to nutrient changes and are implicated in cell homeostasis and clearance mechanisms, allowing effective adaptation to specific cellular needs. The relevance of the lysosome has been elucidated in a number of different contexts. Of these, the retina represents an interesting scenario to appreciate the various functions of this organelle in both physiological and pathological conditions. Growing evidence suggests a role for lysosome-related mechanisms in retinal degeneration. Abnormal lysosomal activation or inhibition has dramatic consequences on photoreceptor cell homeostasis and impacts extensive cellular function, which in turn affects vision. Based on these findings, a series of therapeutic methods targeting lysosomal processes could offer treatment for blindness conditions. Here, we review the recent findings on membrane trafficking, subcellular organization, mechanisms by which lysosome/autophagy pathway impairment affects photoreceptor cell homeostasis and the recent advances on developing efficient lysosomal-based therapies for retinal disorders.

Effect and mechanism of action of SLP-2 on the apoptosis and autophagy of gastric cancer cells

This study was designed to investigate the effect of stomatin-like protein 2 (SLP-2) on the apoptosis and autophagy of gastric cancer cells and its underlying mechanism. The expression of SLP-2 was detected in human gastric cancer cell lines (AGS, MKN-45 and NCI-N87) and a human gastric epithelial cell line (GES-1) using reverse transcription-quantitative PCR and western blot analysis. SLP-2-specific small interfering RNA (siRNA) was transfected into NCI-N87 cells. Cell Counting Kit-8 was used to detect cell proliferation. Apoptosis rates were measured using flow cytometry. Autophagosomes were observed by transmission electron microscopy. The expression levels of Annexin A2 (ANXA2), β-catenin, Bcl-2, Bax, Beclin-1 and LC3-II/I were also measured. The results demonstrated that SLP-2 siRNA transfection significantly reduced cell proliferation and increased cell apoptosis. The mitochondria were severely damaged, and a large number of autophagosomes were seen in SLP-2 siRNA-transfected NCI-N87 cells. Furthermore, the expression levels of ANXA2, β-catenin and Bcl-2 were downregulated, whereas those of Bax, Beclin-1 and LC3-II/I were upregulated following SLP-2 siRNA transfection. In conclusion, SLP-2 silencing can inhibit proliferation and induce apoptosis and autophagy of gastric cancer cells, and this effect may be related to the inhibition of ANXA2/β-catenin signaling pathway.

Retinal degeneration in mice lacking the cyclic nucleotide-gated channel subunit CNGA1

Cyclic nucleotide-gated (CNG) channels are important mediators in the transduction pathways of rod and cone photoreceptors. Native CNG channels are heterotetramers composed of homologous A and B subunits. Biallelic mutations in CNGA1 or CNGB1 genes result in autosomal recessive retinitis pigmentosa (RP). To investigate the pathogenic mechanism of CNG channel-associated retinal degeneration, we developed a mouse model of CNGA1 knock-out using CRISPR/Cas9 technology. We observed progressive retinal thinning and a concomitant functional deficit in vivo as typical phenotypes for RP. Immunofluorescence and TUNEL staining showed progressive degeneration in rods and cones. Moreover, microglial activation and oxidative stress damage occurred in parallel. RNA-sequencing analysis of the retinae suggested down-regulated synaptic transmission and phototransduction as early as 9 days postnatal, possibly inducing later photoreceptor degeneration. In addition, the down-regulated PI3K-AKT-mTOR pathway indicated upregulation of autophagic process, and chaperone-mediated autophagy was further shown to coincide with the time course of photoreceptor death. Taken together, our studies add to a growing body of research exploring the mechanisms of photoreceptor death during RP progression and provide a novel CNGA1 knockout mouse model for potential development of therapies.

Copper induces energy metabolic dysfunction and AMPK-mTOR pathway-mediated autophagy in kidney of broiler chickens

To explore the effects of copper (Cu) on energy metabolism and AMPK-mTOR pathway-mediated autophagy in kidney, a total of 240 one-day-old broiler chickens were randomized into four equal groups and fed on the diets with different levels of Cu (11, 110, 220, and 330 mg/kg) for 49 d. Results showed that excess Cu could induce vacuolar degeneration and increase the number of autophagosomes in kidney, and the adenosine triphosphate (ATP) level and mRNA levels of energy metabolism-related genes were decreased with the increasing dietary Cu level. Moreover, immunohistochemistry and immunofluorescence showed that the positive expressions of Beclin1 and LC3-II were mainly located in cytoplasm of renal tubular epithelial cells and increased significantly with the increasing levels of Cu. The mRNA levels of Beclin1, Atg5, LC3-I, LC3-II, Dynein and the protein levels of Beclin1, Atg5, LC3-II/LC3-I and p-AMPKα1/AMPKα1 were markedly elevated in treated groups compared with control group (11 mg/kg Cu). However, the mRNA and protein levels of p62 and p-mTOR/mTOR were significantly decreased with the increasing levels of Cu. These results suggest that impaired energy metabolism induced by Cu may lead to autophagy via AMPK-mTOR pathway in kidney of broiler chickens.

Mechanisms of Photoreceptor Death in Retinitis Pigmentosa

Retinitis pigmentosa (RP) is the most common cause of inherited blindness and is characterised by the progressive loss of retinal photoreceptors. However, RP is a highly heterogeneous disease and, while much progress has been made in developing gene replacement and gene editing treatments for RP, it is also necessary to develop treatments that are applicable to all causative mutations. Further understanding of the mechanisms leading to photoreceptor death is essential for the development of these treatments. Recent work has therefore focused on the role of apoptotic and non-apoptotic cell death pathways in RP and the various mechanisms that trigger these pathways in degenerating photoreceptors. In particular, several recent studies have begun to elucidate the role of microglia and innate immune response in the progression of RP. Here, we discuss some of the recent progress in understanding mechanisms of rod and cone photoreceptor death in RP and summarise recent clinical trials targeting these pathways.

Autophagy in Age-Related Macular Degeneration: A Regulatory Mechanism of Oxidative Stress

Age-related macular degeneration (AMD) is a leading cause of severe visual loss and irreversible blindness in the elderly population worldwide. Retinal pigment epithelial (RPE) cells are the major site of pathological alterations in AMD. They are responsible for the phagocytosis of shed photoreceptor outer segments (POSs) and clearance of cellular waste under physiological conditions. Age-related, cumulative oxidative stimuli contribute to the pathogenesis of AMD. Excessive oxidative stress induces RPE cell degeneration and incomplete digestion of POSs, leading to the continuous accumulation of cellular waste (such as lipofuscin). Autophagy is a major system of degradation of damaged or unnecessary proteins. However, degenerative RPE cells in AMD patients cannot perform autophagy sufficiently to resist oxidative damage. Increasing evidence supports the idea that enhancing the autophagic process can properly alleviate oxidative injury in AMD and protect RPE and photoreceptor cells from degeneration and death, although overactivated autophagy may lead to cell death at early stages of retinal degenerative diseases. The crosstalk among the NFE2L2, PGC-1, p62, AMPK, and PI3K/Akt/mTOR pathways may play a crucial role in improving disturbed autophagy and mitigating the progression of AMD. In this review, we discuss how autophagy prevents oxidative damage in AMD, summarize potential neuroprotective strategies for therapeutic interventions, and provide an overview of these neuroprotective mechanisms.