Protective effect of RIPK1-inhibitory compound in in vivo models for retinal degenerative disease.

Receptor interacting protein kinase 1 (RIPK1) plays a key role in necroptosis, which is a type of programmed necrosis that is involved in ocular diseases, including glaucoma and dry age-related macular degeneration (AMD). We previously introduced RIPK1-inhibitory compound (RIC), which has biochemical characteristics and a mode of action that are distinct from those of the prototype RIPK1 inhibitor necrostatin-1. The intraperitoneal administration of RIC exerts a protective effect on retinal ganglion cells against a glaucomatous insult. In this study, we examined the protective effect of RIC on retinal pigment epithelium (RPE) against sodium iodate (SI) insult, which is associated with dry AMD pathogenesis. The eye drop administration of RIC that reached on the retina prevented RPE loss in SI-induced retinal degeneration. RIC consistently demonstrated retinal protection in the funduscopy and electroretinogram analyses in SI-injected rabbits and iodoacetic acid-treated mini-pigs. Moreover, the in vivo protective effects of RIC were superior to those of ACU-4429 and doxycycline, which are other medications investigated in clinical trials for the treatment of dry AMD, and RIC did not induce retinal toxicity following topical administration in rats. Collectively, RIC displayed excellent retinal penetration and prevented retinal degeneration in the pathogenesis of dry AMD with a high in vivo efficacy.

FAF1 mediates necrosis through JNK1-mediated mitochondrial dysfunction leading to retinal degeneration in the ganglion cell layer upon ischemic insult.

BACKGROUND: Aberrant cell death induced by ischemic stress is implicated in the pathogenesis of ischemic diseases. Fas-associated factor 1 (FAF1) has been identified as a death-promoting protein. This study demonstrates that FAF1 functions in death signaling triggered by ischemic insult. METHODS: The expression changes of FAF1 and phophorylated JNK1 were detected by Western blotting. Immunoprecipitation was employed to investigate protein-protein interaction. We determined the cell death using flow cytometry and lactate dehydrogenase release measurement. To validate the death-promoting role of FAF1 in the retina, we generated conditional retinal FAF1 knockout mice. We used hematoxylin and eosin staining to detect retinal cell death in retinal ganglion cell layer. RESULTS: FAF1 was found to function upstream of c-Jun N-terminal kinase 1 (JNK1), followed by mitochondrial dysregulation and necrotic cell death processes upon ischemic insult. We investigated whether FAF1 is involved in the pathogenesis of ischemic diseases using a retinal ischemia model. Indeed, FAF1 potentiated necrosis through JNK1 activation upon ischemic stress in retinal cells demonstrating retinal ganglion-like character. Conditional FAF1 depletion attenuated JNK1 activation in the retinas of Dkk3-Cre;Faf1flox/flox mice and ameliorated death of retinal cells due to elevated intraocular pressure (IOP). CONCLUSIONS: Our results show that FAF1 plays a key role in ischemic retinal damage and may be implicated in the pathogenesis of retinal ischemic disease.

A novel RIPK1 inhibitor that prevents retinal degeneration in a rat glaucoma model.

In glaucoma, retinal ganglion cells (RGCs) are exposed to ischemic stress with elevation of the intraocular pressure and are subsequently lost. Necroptosis, a type of regulated necrosis, is known to play a pivotal role in this loss. We observed that receptor-interacting protein kinase 1 (RIPK1), the key player of necroptosis, was activated by diverse ischemic stresses, including TCZ, chemical hypoxia (CH), and oxygen glucose deprivation (OGD). In this study, we introduce a RIPK1-inhibitory compound (RIC) with a novel scaffold. RIC inhibited downstream events following RIPK1 activation, including necrosome formation and mitochondrial dysfunction in RGC5 cells. Moreover, RIC protected RGCs against ischemic injury in the rat glaucoma model, which was induced by acute high intraocular pressure. However, RIC displayed biochemical characteristics that are distinct from those of previous RIPK1 inhibitors (necrostatin-1; Nec-1 and Compound 27; Cpd27). RIC protected RGCs against OGD insult, while Nec-1 and Cpd27 did not. Conversely, Nec-1 and Cpd27 protected RGCs from TNF-stimulated death, while RIC failed to inhibit the death of RGCs. This implies that RIPK1 activates alternative pathways depending on the context of the ischemic insults.

Andrographolide suppresses aerobic glycolysis and induces apoptotic cell death by inhibiting pyruvate dehydrogenase kinase 1 expression.

Metabolic disorder is a major characteristic of cancer cells, and controlling genes involved in metabolic shifts can be an effective strategy for cancer treatment. Andrographolide (AG), a diterpenoid lactone, is widely recognized as a natural anticancer drug due to its ability to inhibit cancer growth. The present study aimed to investigate the mechanism underlying the mitochondrial­mediated anticancer effect of AG by inhibiting pyruvate dehydrogenase kinase 1 (PDK1) expression in lung cancer cells. Cells were treated with AG and PDK1 mRNA and protein expression was determined using reverse transcription­quantitative PCR and western blotting, respectively. As a result, AG significantly inhibited the viability of human lung cancer cells and suppressed aerobic glycolysis by decreasing lactate generation. AG further decreased the PDK1 protein and mRNA levels in a dose­dependent manner. AG­induced cell death was assessed by flow cytometry and fluorescence microscopy. AG induced apoptotic cell death that was associated with the cleavage of poly (ADP ribose) polymerase, activation of caspase­3, and mitochondrial damage, which was associated with an increase in reactive oxygen species and loss of mitochondrial membrane potential. AG­induced cell death was partially suppressed via PDK1 overexpression in lung cancer cells. Therefore, the anticancer effects of AG on human lung cancer cells may negatively regulate the expression of PDK1.

The M458L missense mutation disrupts the catalytic properties of Parkin.

Parkin encodes an E3 ubiquitin ligase, and mutations affecting its catalytic potential are implicated in autosomal recessive Parkinson's disease (PD). The M458L mutation of parkin and its enzymatic effects require characterization. Therefore, we examined the enzymatic activity of Parkin with M458L mutation. We show that the M458L mutant retains its autoubiquitination potential in vitro but not in cells. Fas-associated factor 1 and p38 (substrates of Parkin) are able to bind to the M458L mutant in cells; however, these Parkin substrates are not ubiquitinated and degraded in M458L mutant-transfected cells. Moreover, M458L mutant fails to protect the mitochondria against hydrogen peroxide, leading to cell death. Considering the role of mitochondrial dysfunction in PD pathogenesis, our results imply a causative role for the M458L mutation in neurodegeneration.

AIF-independent parthanatos in the pathogenesis of dry age-related macular degeneration.

Cell death of retinal pigment epithelium (RPE) is characterized as an essential late-stage phenomenon of dry age-related macular degeneration (AMD). The aim of this study was to elucidate the molecular mechanism underlying RPE cell death after exposure to oxidative stress, which occurs often because of the anatomical location of RPE cells. ARPE-19, an established RPE cell line, exhibited necrotic features involving poly (ADP-ribose) polymerase-1 (PARP-1) activation in response to hydrogen peroxide (H2O2). ARPE-19 cells were resistant to H2O2 when PARP-1 was depleted using siRNA or inhibited by a pharmacological inhibitor of PARP-1, olaparib. Our data suggest a causal relationship between PARP-1 activation and ARPE-19 cell death in response to H2O2. Next, we investigated downstream molecular events in PARP-1 activation. Increased mitochondrial depolarization, mitochondrial fission and alterations of the cellular energy dynamics with reduced NAD+ and ATP were observed in H2O2-treated ARPE-19 cells. H2O2-triggered mitochondrial dysfunction was inhibited by olaparib. Nevertheless, translocation of apoptosis-inducing factor (AIF), a biochemical signature for PARP-1-dependent cell death (parthanatos), was not observed in our study. Moreover, the depletion of AIF did not affect the amplitude of cell death, demonstrating the lack of a role for AIF in the death of ARPE-19 cells in response to H2O2. This feature distinguishes the type of death observed in this study from canonical parthanatos. Next, we examined the in vivo role of PARP-1 in a dry AMD animal model system. Histological analysis of the outer nuclear layer in the mouse retina revealed protection against sodium iodate (SI) following treatment with olaparib. Moreover, retina fundus and electroretinograms also confirmed such a protective effect in the SI-treated rabbit. Collectively, we report that AIF-independent PARP-1-dependent necrosis constitutes a major mechanism of RPE cell death leading to retinal degeneration in dry AMD.