Receptor interacting protein kinases mediate retinal detachment-induced photoreceptor necrosis and compensate for inhibition of apoptosis

Intraocular kinetics of pathological ATP after photoreceptor damage in rhegmatogenous retinal detachment

PURPOSE

Extracellular Adenosine triphosphate (ATP) released by dying cells may cause a secondary cell death in neighboring cells in retinal degeneration. We investigated intraocular ATP kinetics to gain mechanical insights into the pathology in rhegmatogenous retinal detachment (RRD).

STUDY DESIGN

Retrospective clinical study.

METHODS

Vitreous or subretinal fluids (SRF) were obtained from patients with RRD (n=75), macular hole (MH; n=20), and epiretinal membrane (ERM; n=35) during vitrectomy. ATP levels in those samples were measured by luciferase assay.

RESULTS

Mean ATP levels in the vitreous from RRD patients were significantly higher compared to those from MH and ERM patients (2.3 and 0.3 nM, respectively. P<0.01). Mean ATP levels in the SRF from RRD (11.7 nM) were higher than those in the vitreous from RRD (P<0.01). Mean ATP levels in the vitreous with short durations (1-8 days) of RRD were higher compared to those with long durations (>8 days) (3.2 and 1.4 nM, respectively. P<0.05). Similarly, ATP in SRF with short durations were higher than those with long durations (23.8 and 3.6 nM, respectively. P<0.05). Furthermore, the concentrations of ectonucleoside triphosphate diphosphohydrolase-1 (ENTPD1), a major ATP degradative enzyme, in the vitreous from RRD were higher than those from MH/ERM (1.2 and 0.2 ng/ml, respectively. P<0.01). ENTPD1 expression was localized in the cytoplasm of CD11b-positive infiltrating cells in the vitreous and retinal cells.

CONCLUSION

ATP increased in the vitreous and SRF in RRD and decreased over time with an upregulation of ENTPD1. The kinetics indicate the pathological mechanism of the excessive extracellular ATP after RRD.

Targeting inflammasomes and pyroptosis in retinal diseases-molecular mechanisms and future perspectives

Retinal diseases encompass various conditions associated with sight-threatening immune responses and are leading causes of blindness worldwide. These diseases include age-related macular degeneration, diabetic retinopathy, glaucoma and uveitis. Emerging evidence underscores the vital role of the innate immune response in retinal diseases, beyond the previously emphasized T-cell-driven processes of the adaptive immune system. In particular, pyroptosis, a newly discovered programmed cell death process involving inflammasome formation, has been implicated in the loss of membrane integrity and the release of inflammatory cytokines. Several disease-relevant animal models have provided evidence that the formation of inflammasomes and the induction of pyroptosis in innate immune cells contribute to inflammation in various retinal diseases. In this review article, we summarize current knowledge about the innate immune system and pyroptosis in retinal diseases. We also provide insights into translational targeting approaches, including novel drugs countering pyroptosis, to improve the diagnosis and treatment of retinal diseases.

Non-Apoptotic Programmed Cell Death as Targets for Diabetic Retinal Neurodegeneration

Diabetic retinopathy (DR) remains the leading cause of blindness among the global working-age population. Emerging evidence underscores the significance of diabetic retinal neurodegeneration (DRN) as a pivotal biomarker in the progression of vasculopathy. Inflammation, oxidative stress, neural cell death, and the reduction in neurotrophic factors are the key determinants in the pathophysiology of DRN. Non-apoptotic programmed cell death (PCD) plays a crucial role in regulating stress response, inflammation, and disease management. Therapeutic modalities targeting PCD have shown promising potential for mitigating DRN. In this review, we highlight recent advances in identifying the role of various PCD types in DRN, with specific emphasis on necroptosis, pyroptosis, ferroptosis, parthanatos, and the more recently characterized PANoptosis. In addition, the therapeutic agents aimed at the regulation of PCD for addressing DRN are discussed.

Receptor-interacting protein kinase-3 (RIPK3): a new biomarker for necrotising enterocolitis in preterm infants

OBJECTIVE

This study aimed to evaluate the role of receptor-interacting protein kinase-3 (RIPK3) in the diagnosis, estimation of disease severity, and prognosis of premature infants with necrotising enterocolitis (NEC).

METHODS

RIPK3, lactic acid (LA), and C-reactive protein (CRP) levels were measured in the peripheral blood of 108 premature infants between 2019 and 2023, including 24 with stage II NEC, 18 with stage III NEC and 66 controls. Diagnostic values of the indicators for NEC were evaluated via receiver operating characteristic (ROC) curve analysis.

RESULTS

Plasma RIPK3 and LA levels upon NEC suspicion in neonates with stage III NEC were 32.37 ± 16.20 ng/mL. The ROC curve for the combination of RIPK3, LA, CRP for NEC diagnosis were 0.925. The time to full enteral feeding (FEFt) after recovery from NEC was different between two expression groups of plasma RIPK3 (RIPK3 < 20.06 ng/mL and RIPK3 ≥ 20.06 ng/mL).

CONCLUSION

Plasma RIPK3 can be used as a promising marker for the diagnosis and estimation of disease severity of premature infants with NEC and for the guidance on proper feeding strategies after recovery from NEC.

Practical Three-Component Regioselective Synthesis of Drug-Like 3-Aryl(or heteroaryl)-5,6-dihydrobenzo[h]cinnolines as Potential Non-Covalent Multi-Targeting Inhibitors To Combat Neurodegenerative Diseases

Neurodegenerative diseases (NDs) are one of the prominent health challenges facing contemporary society, and many efforts have been made to overcome and (or) control it. In this research paper, we described a practical one-pot two-step three-component reaction between 3,4-dihydronaphthalen-1(2H)-one (1), aryl(or heteroaryl)glyoxal monohydrates (2a-h), and hydrazine monohydrate (NH2NH2•H2O) for the regioselective preparation of some 3-aryl(or heteroaryl)-5,6-dihydrobenzo[h]cinnoline derivatives (3a-h). After synthesis and characterization of the mentioned cinnolines (3a-h), the in silico multi-targeting inhibitory properties of these heterocyclic scaffolds have been investigated upon various Homo sapiens-type enzymes, including hMAO-A, hMAO-B, hAChE, hBChE, hBACE-1, hBACE-2, hNQO-1, hNQO-2, hnNOS, hiNOS, hPARP-1, hPARP-2, hLRRK-2(G2019S), hGSK-3β, hp38α MAPK, hJNK-3, hOGA, hNMDA receptor, hnSMase-2, hIDO-1, hCOMT, hLIMK-1, hLIMK-2, hRIPK-1, hUCH-L1, hPARK-7, and hDHODH, which have confirmed their functions and roles in the neurodegenerative diseases (NDs), based on molecular docking studies, and the obtained results were compared with a wide range of approved drugs and well-known (with IC50, EC50, etc.) compounds. In addition, in silico ADMET prediction analysis was performed to examine the prospective drug properties of the synthesized heterocyclic compounds (3a-h). The obtained results from the molecular docking studies and ADMET-related data demonstrated that these series of 3-aryl(or heteroaryl)-5,6-dihydrobenzo[h]cinnolines (3a-h), especially hit ones, can really be turned into the potent core of new drugs for the treatment of neurodegenerative diseases (NDs), and/or due to the having some reactionable locations, they are able to have further organic reactions (such as cross-coupling reactions), and expansion of these compounds (for example, with using other types of aryl(or heteroaryl)glyoxal monohydrates) makes a new avenue for designing novel and efficient drugs for this purpose.

RIPK3 signaling and its role in regulated cell death and diseases

Receptor-interacting protein kinase 3 (RIPK3), a member of the receptor-interacting protein kinase (RIPK) family with serine/threonine protein kinase activity, interacts with RIPK1 to generate necrosomes, which trigger caspase-independent programmed necrosis. As a vital component of necrosomes, RIPK3 plays an indispensable role in necroptosis, which is crucial for human life and health. In addition, RIPK3 participates in the pathological process of several infections, aseptic inflammatory diseases, and tumors (including tumor-promoting and -suppressive activities) by regulating autophagy, cell proliferation, and the metabolism and production of chemokines/cytokines. This review summarizes the recent research progress of the regulators of the RIPK3 signaling pathway and discusses the potential role of RIPK3/necroptosis in the aetiopathogenesis of various diseases. An in-depth understanding of the mechanisms and functions of RIPK3 may facilitate the development of novel therapeutic strategies.

Nicotinamide mononucleotide, a potential future treatment in ocular diseases

PURPOSE

The burden of ocular diseases has been gradually increasing worldwide. Various factors are suggested for the development and progression of ocular diseases, such as ocular inflammation, oxidative stress, and complex metabolic dysregulation. Thus, managing ocular diseases requires the modulation of pathologic signaling pathways through many mechanisms. Nicotinamide mononucleotide (NMN) is a bioactive molecule naturally found in life forms. NMN is a direct precursor of the important molecule nicotinamide adenine dinucleotide (NAD+), an essential co-enzyme required for enormous cellular functions in most life forms. While the recent experimental evidence of NMN treatment in various metabolic diseases has been well-reviewed, NMN treatment in ocular diseases has not been comprehensively summarized yet. In this regard, we aimed to focus on the therapeutic roles of NMN treatment in various ocular diseases with recent advances.

METHODS

How we came to our current opinion with a recent summary was described based on our own recent reports as well as a search of the related literature.

RESULTS

We found that NMN treatment might be available for the prevention of and protection from various experimental ocular diseases, as NMN treatment modulated ocular inflammation, oxidative stress, and complex metabolic dysregulation in murine models for eye diseases such as ischemic retinopathy, corneal defect, glaucoma, and age-related macular degeneration.

CONCLUSION

Our current review suggests and discusses new modes of actions of NMN for the prevention of and protection from various ocular diseases and can urge future research to obtain more solid evidence on a potential future NMN treatment in ocular diseases at the preclinical stages.

Peripheral monocytes and neutrophils promote photoreceptor cell death in an experimental retinal detachment model

Photoreceptor cell death and immune cell infiltration are two major events that contribute to retinal degeneration. However, the relationship between these two events has not been well delineated, primarily because of an inadequate understanding of the immunological processes involved in photoreceptor degeneration, especially that of peripheral leukocytes that infiltrate the subretinal space and retinal tissues. In this work, we characterized the role of leukocyte infiltration within the detached retina. We observed that CD45+ CD11b+ Ly6G+ neutrophils and CD45+ CD11b+ Ly6G- Ly6C+ monocytes are the predominant peripheral immune cell populations that infiltrate the retinal and subretinal space after detachment. Selective depletion of monocytes or neutrophils using cell-specific targeting is neuroprotective for photoreceptors. These results indicate that peripheral innate immune cells contribute to photoreceptor degeneration, and targeting these immune cell populations could be therapeutic during retinal detachment.

The Expression of Parthanatos Markers and miR-7 Mimic Protects Photoreceptors from Parthanatos by Repressing α-Synuclein in Retinal Detachment

Retinal detachment (RD) refers to the separation between the neuroepithelium and the pigment epithelium layer. It is an important disease leading to irreversible vision damage worldwide, in which photoreceptor cell death plays a major role. α-Synuclein (α-syn) is reportedly involved in numerous mechanisms of neurodegenerative diseases, but the association with photoreceptor damage in RD has not been studied. In this study, elevated transcription levels of α-syn and parthanatos proteins were observed in the vitreous of patients with RD. The expression of α-syn- and parthanatos-related proteins was increased in experimental rat RD, and was involved in the mechanism of photoreceptor damage, which was related to the decreased expression of miR-7a-5p (miR-7). Interestingly, subretinal injection of miR-7 mimic in rats with RD inhibited the expression of retinal α-syn and down-regulated the parthanatos pathway, thereby protecting retinal structure and function. In addition, interference with α-syn in 661W cells decreased the expression of parthanatos death pathway in oxygen and glucose deprivation model. In conclusion, this study demonstrates the presence of parthanatos-related proteins in patients with RD and the role of the miR-7/α-syn/parthanatos pathway in photoreceptor damage in RD.

Stages, pathogenesis, clinical management and advancements in therapies of age-related macular degeneration

Age-related macular degeneration (AMD) is a retinal degenerative disorder prevalent in the elderly population, which leads to the loss of central vision. The disease progression can be managed, if not prevented, either by blocking neovascularization ("wet" form of AMD) or by preserving retinal pigment epithelium and photoreceptor cells ("dry" form of AMD). Although current therapeutic modalities are moderately successful in delaying the progression and management of the disease, advances over the past years in regenerative medicine using iPSC, embryonic stem cells, advanced materials (including nanomaterials) and organ bio-printing show great prospects in restoring vision and efficient management of either forms of AMD. This review focuses on the molecular mechanism of the disease, model systems (both cellular and animal) used in studying AMD, the list of various regenerative therapies and the current treatments available. The article also highlights on the recent clinical trials using regenerative therapies and management of the disease.

Flow cytometric method for the detection and quantification of retinal cell death and oxidative stress

Retinal cell death is the major cause of vision loss in many forms of blinding retinal disease. A plethora of research is focused on understanding the mechanisms of retinal cell death to identify potential neuroprotective strategies that prevent vision loss in these diseases. Traditionally, histological techniques have been used to determine the type and extent of cell death in the retina. These techniques, such as TUNEL labeling and immunohistochemistry, are laborious and time consuming, resulting in low throughput and variable results depending on the experimenter. To increase throughput and reduce variability, we developed several flow cytometry-based assays to detect and quantify retinal cell death. The methods and accompanying data presented demonstrate that flow cytometry can readily detect both retinal cell death and oxidative stress and importantly, the efficacy of neuroprotective agents. These methods will be of interest to investigators looking to increase throughput and efficiency without compromising sensitivity as the methods herein reduce analysis time from several months to less than a week. As such, the flow cytometry methods presented have the potential to expedite research efforts focused on developing novel strategies for retinal cell neuroprotection.

Cone Photoreceptor Morphology in Choroideremia Assessed Using Non-Confocal Split-Detection Adaptive Optics Scanning Light Ophthalmoscopy

Purpose

Choroideremia (CHM) is an X-linked inherited retinal degeneration causing loss of the photoreceptors, retinal pigment epithelium, and choriocapillaris, although patients typically retain a central island of relatively preserved, functioning retina until late-stage disease. Here, we investigate cone photoreceptor morphology within the retained retinal island by examining cone inner segment area, density, circularity, and intercone space.

Methods

Using a custom-built, multimodal adaptive optics scanning light ophthalmoscope, nonconfocal split-detection images of the photoreceptor mosaic were collected at 1°, 2°, and 4° temporal to the fovea from 13 CHM and 12 control subjects. Cone centers were manually identified, and cone borders were segmented. A custom MATLAB script was used to extract area and circularity for each cone and calculate the percentage of intercone space in each region of interest. Bound cone density was also calculated. An unbalanced two-way ANOVA and Bonferroni post hoc tests were used to assess statistical differences between the CHM and control groups and along retinal eccentricity.

Results

Cone density was lower in the CHM group than in the control group (P < 0.001) and decreased with eccentricity from the fovea (P < 0.001). CHM cone inner segments were larger in area (P < 0.001) and more circular (P = 0.042) than those of the controls. Intercone space in CHM was also higher than in the controls (P < 0.001).

Conclusions

Cone morphology is altered in CHM compared to control, even within the centrally retained, functioning retinal area. Further studies are required to determine whether such morphology is a precursor to cone degeneration.

RIPK necrotic cell death pathway in both donor photoreceptor and host immune cells synergize to affect photoreceptor graft survival

Photoreceptor transplant has been put forward as a repair strategy to tackle degenerated retinas. Nonetheless, cell death and immune rejection seriously limit the success of this strategy, with only a small fraction of transplanted cells surviving. Improving the survival of transplanted cells is of critical importance. Recent evidence has identified receptor-interacting protein kinase 3 (RIPK3) as a molecular trigger controlling necroptotic cell death and inflammation. However, its role in photoreceptor transplantation and regenerative medicine has not been studied. We hypothesized that modulation of RIPK3 to address both cell death and immunity could have advantageous effects on photoreceptor survival. In a model of inherited retinal degeneration, deletion of RIPK3 in donor photoreceptor precursors significantly increases the survival of transplanted cells. Simultaneous RIPK3 deletion in donor photoreceptors and recipients maximizes graft survival. Lastly, to discern the role of RIPK3 in the host immune response, bone marrow transplant experiments demonstrated that peripheral immune cell RIPK3 deficiency is protective for both donor and host photoreceptor survival. Interestingly, this finding is independent of photoreceptor transplantation, as the peripheral protective effect is also observed in an additional retinal detachment photoreceptor degeneration model. Altogether, these results indicate that immunomodulatory and neuroprotective strategies targeting the RIPK3 pathway can aid regenerative therapies of photoreceptor transplantation.

RIP3-mediated microglial necroptosis promotes neuroinflammation and neurodegeneration in the early stages of diabetic retinopathy

Diabetic retinopathy (DR) is a leading cause of blindness that poses significant public health concerns worldwide. Increasing evidence suggests that neuroinflammation plays a key role in the early stages of DR. Microglia, long-lived immune cells in the central nervous system, can become activated in response to pathological insults and contribute to retinal neuroinflammation. However, the molecular mechanisms of microglial activation during the early stages of DR are not fully understood. In this study, we used in vivo and in vitro assays to investigate the role of microglial activation in the early pathogenesis of DR. We found that activated microglia triggered an inflammatory cascade through a process called necroptosis, a newly discovered pathway of regulated cell death. In the diabetic retina, key components of the necroptotic machinery, including RIP1, RIP3, and MLKL, were highly expressed and mainly localized in activated microglia. Knockdown of RIP3 in DR mice reduced microglial necroptosis and decreased pro-inflammatory cytokines. Additionally, blocking necroptosis with the specific inhibitor GSK-872 improved retinal neuroinflammation and neurodegeneration, as well as visual function in diabetic mice. RIP3-mediated necroptosis was activated and contributed to inflammation in BV2 microglia under hyperglycaemic conditions. Our data demonstrate the importance of microglial necroptosis in retinal neuroinflammation related to diabetes and suggest that targeting necroptosis in microglia may be a promising therapeutic strategy for the early stages of DR.

Targeting Necroptosis: A Novel Therapeutic Option for Retinal Degenerative Diseases

The discovery of the necroptosis, a form of regulated necrosis that is mediated by receptor-interacting protein kinase 1 (RIPK1), RIPK3, and mixed-lineage kinase domain-like pseudokinase (MLKL), represents a major breakthrough that has dramatically altered the conception of necrosis - traditionally thought of as uncontrolled cell death - in various human diseases. Retinal cell death is a leading cause of blindness and has been identified in most retinal diseases, e.g., age-related macular degeneration, glaucoma, retinal detachment, retinitis pigmentosa, etc. Increasing evidence demonstrates that retinal degenerative diseases also share a common mechanism in necroptosis. Exacerbated necroptotic cell death hinders the treatment for retinal degenerative diseases. In this review, we highlight recent advances in identifying retinal necroptosis, summarize the underlying mechanisms of necroptosis in retinal degenerative diseases, and discuss potential anti-necroptosis strategies, such as selective inhibitors and chemical agents, for treating retinal degenerative diseases.

UVA induces retinal photoreceptor cell death via receptor interacting protein 3 kinase mediated necroptosis

Ultraviolet light A (UVA) is the only UV light that reaches the retina and can cause indirect damage to DNA via absorption of photons by non-DNA chromophores. Previous studies demonstrate that UVA generates reactive oxygen species (ROS) and leads to programmed cell death. Programmed cell death (PCD) has been implicated in numerous ophthalmologic diseases. Here, we investigated receptor interacting protein 1 and 3 (RIPK1 and RIPK3) kinases, key signaling molecules of PCD, in UVA-induced photoreceptor injury using in vitro and ex vivo models. UVA irradiation activated RIPK3 but not RIPK1 and mediated necroptosis through MLKL that lie downstream of RIPK3 and induced apoptosis through increased oxidative stress. Moreover, RIPK3 but not RIPK1 inhibition suppresses UVA-induced cell death along with the downregulation of MLKL and attenuates the levels of oxidative stress and DNA fragmentation. In conclusion, these results identify RIPK3, not RIPK1, as a critical regulator of UVA-induced necroptosis cell death in photoreceptors and highlight RIPK3 potential as a neuroprotective target.

RIPK1/RIPK3-Mediated Necroptosis is Involved in Sevoflurane-Induced Neonatal Neurotoxicity in the Rat Hippocampus

Recent studies have shown that exposure to sevoflurane in developing brains causes neuronal apoptosis and cognitive dysfunction. "Necroptosis" is a novel pathway of necrosis. We introduced the caspase-specific inhibitor Z-VAD in addition to the receptor-interacting protein kinase 1 (RIPK1) inhibitor Nec-1, to ascertain the existence and importance of necroptosis. Sprague-Dawley rat pups postnatal day 7 were randomly assigned into one of five groups: control, sevoflurane + Z-VAD, sevoflurane + Nec-1, sevoflurane + Z-VAD + Nec-1 and 3% sevoflurane group. Neuronal apoptosis was evaluated by hematoxylin and eosin staining. The MTT assay was performed to evaluate cell viability. Immunofluorescence was employed to measure expression of RIPK1 and RIPK3. Western blots showing expression of RIPK1, RIPK3 and phosphorylation of mixed lineage kinase domain-like (p-MLKL) were used to explore the role of necroptosis. Binding of RIPK1/RIPK3 was detected via co-immunoprecipitation. Finally, the Morris water maze test was used to determine cognitive function. Exposure to 3% sevoflurane for 6 h induced neurotoxicity and inhibited cell viability. Neuron viability was low in the SEV, SEV + Z-VAD and SEV + Nec-1 groups. The study revealed that RIPK1 and RIPK3 protein expression increased significantly, but there was no significant differences between the SEV and SEV + Z-VAD groups. The expression of p-MLKL significantly increased in the SEV and SEV + Z-VAD groups, but not in the SEV + Nec-1 group or SEV + Z-VAD + Nec-1 group compared to the control group. Co-immunoprecipitation results showed that sevoflurane exposure enhanced binding of RIPK1/RIPK3 protein significantly. Blockade of apoptosis and necroptosis alleviated sevoflurane-induced cognitive impairment. Sevoflurane exposure elicited neurotoxicity within neonatal hippocampal neurons and tissues. Blockade of apoptosis or necroptosis alone did not attenuate sevoflurane-induced neurotoxicity (SIN). RIPK1/RIPK3-mediated necroptosis was involved in SIN in hippocampal neurons. SIN could be attenuated only by inhibiting both apoptosis and necroptosis.

Necroptosis and Neuroinflammation in Retinal Degeneration

Necroptosis mediates the chronic inflammatory phenotype in neurodegeneration. Receptor-interacting protein kinase (RIPK) plays a pivotal role in the induction of necroptosis in various cell types, including microglia, and it is implicated in diverse neurodegenerative diseases in the central nervous system and the retina. Targeting RIPK has been proven beneficial for alleviating both neuroinflammation and degeneration in basic/preclinical studies. In this review, we discuss the role of necroptosis in retinal degeneration, including (1) the molecular pathways involving RIPK, (2) RIPK-dependent microglial activation and necroptosis, and (3) the interactions between necroptosis and retinal neuroinflammation/degeneration. This review will contribute to a renewed focus on neuroinflammation induced by necroptosis and to the development of anti-RIPK drugs against retinal degeneration.

Treatment and prevention of pathological mitochondrial dysfunction in retinal degeneration and in photoreceptor injury

Pathological deterioration of mitochondrial function is increasingly linked with multiple degenerative illnesses as a mediator of a wide range of neurologic and age-related chronic diseases, including those of genetic origin. Several of these diseases are rare, typically defined in the United States as an illness affecting fewer than 200,000 people in the U.S. population, or about one in 1600 individuals. Vision impairment due to mitochondrial dysfunction in the eye is a prominent feature evident in numerous primary mitochondrial diseases and is common to the pathophysiology of many of the familiar ophthalmic disorders, including age-related macular degeneration, diabetic retinopathy, glaucoma and retinopathy of prematurity - a collection of syndromes, diseases and disorders with significant unmet medical needs. Focusing on metabolic mitochondrial pathway mechanisms, including the possible roles of cuproptosis and ferroptosis in retinal mitochondrial dysfunction, we shed light on the potential of α-lipoyl-L-carnitine in treating eye diseases. α-Lipoyl-L-carnitine is a bioavailable mitochondria-targeting lipoic acid prodrug that has shown potential in protecting against retinal degeneration and photoreceptor cell loss in ophthalmic indications.

Protein kinase D: A therapeutic target in experimental alcoholic pancreatitis

BACKGROUND

Alcohol abuse, a main cause of pancreatitis, has been known to augment NF-κB activation and cell necrosis in pancreatitis. However, the underlying mechanisms are unclear. We recently reported that inhibition of protein kinase D (PKD) alleviated NF-κB activation and severity of experimental pancreatitis. Here we investigated whether PKD signaling mediated the modulatory effects of alcohol abuse on pathological responses in alcoholic pancreatitis.

METHODS

Alcoholic pancreatitis was provoked in two rodent models with pair-feeding control and ethanol-containing Lieber-DeCarli diets for up to 8 weeks followed by up to 7 hourly intraperitoneal injections of cerulein at 1 μg/kg (rats) or 3 μg/kg (mice). Effects of PKD inhibition by PKD inhibitors or genetic deletion of pancreatic PKD isoform (PKD3Δpanc mice) on alcoholic pancreatitis parameters were determined.

RESULTS

Ethanol administration amplified PKD signaling by promoting expression and activation of pancreatic PKD, resulted in augmented/promoted pancreatitis responses. Pharmacological inhibition of PKD or with PKD3Δpanc mice prevented the augmenting/sensitizing effect of ethanol on NF-κB activation and inflammatory responses, cell necrotic death and the severity of disease in alcoholic pancreatitis. PKD inhibition prevented alcohol-enhanced trypsinogen activation, mRNA expression of multiple inflammatory molecules, the receptor-interacting protein kinase activation, ATP depletion, and downregulation of pro-survival Bcl-2 protein in alcoholic pancreatitis. Furthermore, PKD inhibitor CID755673 or CRT0066101, administrated after the induction of pancreatitis in mouse and rat alcoholic pancreatitis models, significantly mitigated the severity of pancreatitis.

CONCLUSION

PKD mediates effect of alcohol abuse on pathological process of pancreatitis and constitutes a novel therapeutic target to treat this disease.

Neuroprotection for Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a leading cause of blindness worldwide. Early to intermediate AMD is characterized by the accumulation of lipid- and protein-rich drusen. Late stages of the disease are characterized by the development of choroidal neovascularization, termed "exudative" or "neovascular AMD," or retinal pigment epithelium (RPE) cell and photoreceptor death, termed "geographic atrophy" (GA) in advanced nonexudative AMD. Although we have effective treatments for exudative AMD in the form of anti-VEGF agents, they have no role for patients with GA. Neuroprotection strategies have emerged as a possible way to slow photoreceptor degeneration and vision loss in patients with GA. These approaches include reduction of oxidative stress, modulation of the visual cycle, reduction of toxic molecules, inhibition of pathologic protein activity, prevention of cellular apoptosis or programmed necrosis (necroptosis), inhibition of inflammation, direct activation of neurotrophic factors, delivery of umbilical tissue-derived cells, and RPE replacement. Despite active investigation in this area and significant promise based on preclinical studies, many clinical studies have not yielded successful results. We discuss selected past and current neuroprotection trials for AMD, highlight the lessons learned from these past studies, and discuss our perspective regarding remaining questions that must be answered before neuroprotection can be successfully applied in the field of AMD research.

Therapeutic Potential of Exosomes Derived from Adipose Tissue-Sourced Mesenchymal Stem Cells in the Treatment of Neural and Retinal Diseases

Therapeutic agents that are able to prevent or attenuate inflammation and ischemia-induced injury of neural and retinal cells could be used for the treatment of neural and retinal diseases. Exosomes derived from adipose tissue-sourced mesenchymal stem cells (AT-MSC-Exos) are extracellular vesicles that contain neurotrophins, immunoregulatory and angio-modulatory factors secreted by their parental cells. AT-MSC-Exos are enriched with bioactive molecules (microRNAs (miRNAs), enzymes, cytokines, chemokines, immunoregulatory, trophic, and growth factors), that alleviate inflammation and promote the survival of injured cells in neural and retinal tissues. Due to the nano-sized dimension and bilayer lipid envelope, AT-MSC-Exos easily bypass blood–brain and blood–retinal barriers and deliver their cargo directly into the target cells. Accordingly, a large number of experimental studies demonstrated the beneficial effects of AT-MSC-Exos in the treatment of neural and retinal diseases. By delivering neurotrophins, AT-MSC-Exos prevent apoptosis of injured neurons and retinal cells and promote neuritogenesis. AT-MSC-Exos alleviate inflammation in the injured brain, spinal cord, and retinas by delivering immunoregulatory factors in immune cells, suppressing their inflammatory properties. AT-MSC-Exos may act as biological mediators that deliver pro-angiogenic miRNAs in endothelial cells, enabling re-vascularization of ischemic neural and retinal tissues. Herewith, we summarized current knowledge about molecular mechanisms which were responsible for the beneficial effects of AT-MSC-Exos in the treatment of neural and retinal diseases, emphasizing their therapeutic potential in neurology and ophthalmology.

Optineurin in ocular herpes infection

Herpes Simplex Virus-1 (HSV-1) is a neurotropic virus that can infect humans in the eye and travel to the trigeminal ganglion to establish latency. HSV-1 causes various disease states in both the primary and secondary sites of infection including the eye and the nervous system. This DNA virus exploits various adaptive measures to infect host cells, hijack host cell proteins, evade host immune response and spread from cell-to-cell to avoid immune detection. Recent data suggest that Optineurin (OPTN), a host protein, is a key restriction factor that prevents cell-to-cell spread of HSV-1 and guards against serious damage to the nervous system during infection. In recent years OPTN has gained increased attention because of its involvement in cellular mechanisms that promote homeostasis and prevent neurodegeneration. At the center of it all is the role OPTN plays as a receptor for selective autophagy. This review summarizes our latest understanding of the viral lifecycle, disease pathologies, and OPTN-mediated protective mechanisms during HSV-1 infection of the eye and the nervous system. We specifically highlight recent discoveries that implicate OPTN as crucial in the prevention of ocular and neurodegenerative diseases.

Retinal Neuroprotective Effect of Mesenchymal Stem Cells Secretome Through Modulation of Oxidative Stress, Autophagy, and Programmed Cell Death

Purpose

Degenerative mechanisms of retinal neurodegenerative diseases (RND) share common cellular and molecular signalization pathways. Curative treatment does not exist and cell-based therapy, through the paracrine properties of mesenchymal stem cells (MSC), is a potential unspecific treatment for RND. This study aimed to evaluate the neuroprotective capability of human bone marrow (bm) MSC secretome and its potential to modulate retinal responses to neurodegeneration.

Methods

An in vitro model of spontaneous retinal neurodegeneration was used to compare three days of monocultured neuroretina (NR), NR cocultured with bmMSC, and NR cultured with bmMSC secretome. We evaluated retinal morphology markers (Lectin peanut agglutinin, rhodopsin, protein kinase C α isoform, neuronal-specific nuclear protein, glial fibrillary acidic protein, TdT-mediated dUTP nick-end labeling, and vimentin) and proteins involved in apoptosis (apoptosis-inductor factor, caspase-3), necroptosis (MLKL), and autophagy (p62). Besides, we analyzed the relative mRNA expression through qPCR of genes involved in apoptosis (BAX, BCL2, CASP3, CASP8, CASP9), necroptosis (MLKL, RIPK1, RIPK3), autophagy (ATG7, BCLIN1, LC3B, mTOR, SQSTM1), oxidative stress (COX2, CYBA, CYBB, GPX6, SOD1, TXN2, TXNRD1) and inflammation (IL1, IL6, IL10, TGFb1, TNFa).

Results

The bmMSC secretome preserves retinal morphology, limits pro-apoptotic- and pro-necroptotic-related gene and protein expression, modulates autophagy-related genes and proteins, and stimulates the activation of antioxidant-associated genes.

Conclusions

The neuroprotective ability of the bmMSC secretome is associated with activation of antioxidant machinery, modulation of autophagy, and inhibition of apoptosis and necroptosis during retinal degeneration. The neuroprotective effect of bmMSC secretomes in the presence/absence of MSC looks similar. Our current results reinforce the hypothesis that the human bmMSC secretome slows retinal neurodegeneration and may be a therapeutic option for treating RND.

Iron contributes to photoreceptor degeneration and Müller glia proliferation in the zebrafish light-treated retina

Zebrafish possess the ability to completely regenerate the retina following injury, however little is understood about the damage signals that contribute to inducing Müller glia reprogramming and proliferation to regenerate lost neurons. Multiple studies demonstrated that iron contributes to various retinal injuries, however no link has been shown between iron and zebrafish retinal regeneration. Here we demonstrate that Müller glia exhibit transcriptional changes following injury to regulate iron levels within the retina, allowing for increased iron uptake and decreased export. The response of the zebrafish retina to intravitreal iron injection was then characterized, showing that ferrous, and not ferric, iron induces retinal cell death. Additionally, iron chelation resulted in decreased numbers of TUNEL-positive photoreceptors and fewer proliferating Müller glia. Despite the contribution of iron to retinal cell death, inhibition of ferroptosis did not significantly reduce cell death following light treatment. Finally, we demonstrate that both the anti-ferroptotic protein Glutathione peroxidase 4b and the Transferrin receptor 1b are required for Müller glia proliferation following light damage. Together these findings show that iron contributes to cell death in the light-damaged retina and is essential for inducing the Müller glia regeneration response.

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.

Comparison of Necroptosis With Apoptosis for OVX-Induced Osteoporosis

As one common kind of osteoporosis, postmenopausal osteoporosis (PMOP) is associated with the death and excessive loss of osteocytes. Estrogen deficiency of PMOP can cause osteocyte death by regulating necroptosis and apoptosis, but their roles in POMP have not been compared. In the present study, ovariectomy (OVX)-induced rat and murine long bone osteocyte Y4 (MLO-Y4) cells were used to compare the influence of necroptosis and apoptosis on osteocyte death and bone loss. Benzyloxycarbonyl-Val-Ala-Asp (zVAD) and necrostatin-1 (Nec-1) were used to specifically block cell apoptosis and necroptosis, respectively. OVX rats and MLO-Y4 cells were divided into zVAD group, Nec-1 group, zVAD + Nec-1 group, vehicle, and control group. The tibial plateaus of the rat model were harvested at 8 weeks after OVX and were analyzed by micro–computed tomography, transmission electron microscopy (TEM), the transferase dUTP nick end labeling assay, and western blot. The death of MLO-Y4 was stimulated by TNF-α and was measured by flow cytometry and TEM. The results found that necroptosis and apoptosis were both responsible for the death and excessive loss of osteocytes, as well as bone loss in OVX-induced osteoporosis, and furthermore necroptosis may generate greater impact on the death of osteocytes than apoptosis. Necroptotic death of osteocytes was mainly regulated by the receptor-interacting protein kinase 3 signaling pathway. Collectively, inhibition of necroptosis may produce better efficacy in reducing osteocyte loss than that of apoptosis, and combined blockade of necroptosis and apoptosis provide new insights into preventing and treating PMOP.

CHOP deletion and anti-neuroinflammation treatment with hesperidin synergistically attenuate NMDA retinal injury in mice

Glaucoma is a leading cause of blindness worldwide and is characterized by degeneration associated with the death of retinal ganglion cells (RGCs). It is believed that glaucoma is a group of heterogeneous diseases with multifactorial pathomechanisms. Here, we investigate whether anti-inflammation treatment with an ER stress blockade can selectively promote neuroprotection against NMDA injury in the RGCs. Retinal excitotoxicity was induced with an intravitreal NMDA injection. Microglial activation and neuroinflammation were evaluated with Iba1 immunostaining and cytokine gene expression. A stable HT22 cell line transfected with an NF-kB reporter was used to assess NF-kB activity after hesperidin treatment. CHOP-deficient mice were used as a model of ER stress blockade. Retinal cell death was evaluated with a TUNEL assay. As results, in the NMDA injury group, Iba1-positive microglia increased 6 h after NMDA injection. Also at 6 h, pro-inflammatory cytokines and chemokine increased, including TNFα, IL-1b, IL-6 and MCP-1. In addition, the MCP-1 promoter-driven EGFP signal, which we previously identified as a stress signal in injured RGCs, also increased; hesperidin treatment suppressed this inflammatory response and reduced stressed RGCs. In CHOP-deficient mice that received an NMDA injection, the gene expression of pro-inflammatory cytokines, chemokines, markers of active microglia, and inflammatory regulators was greater than in WT mice. In WT mice, hesperidin treatment partially prevented retinal cell death after NMDA injury; this neuroprotective effect was enhanced in CHOP-deficient mice. These findings demonstrate that ER stress blockade is not enough by itself to prevent RGC loss due to neuroinflammation in the retina, but it has a synergistic neuroprotective effect after NMDA injury when combined with an anti-inflammatory treatment based on hesperidin.

Preclinical Evidence for the Interplay between Oxidative Stress and RIP1-Dependent Cell Death in Neurodegeneration: State of the Art and Possible Therapeutic Implications

Neurodegenerative diseases are the most frequent chronic, age-associated neurological pathologies having a major impact on the patient’s quality of life. Despite a heavy medical, social and economic burden they pose, no causative treatment is available for these diseases. Among the important pathogenic factors contributing to neuronal loss during neurodegeneration is elevated oxidative stress resulting from a disturbed balance between endogenous prooxidant and antioxidant systems. For many years, it was thought that increased oxidative stress was a cause of neuronal cell death executed via an apoptotic mechanism. However, in recent years it has been postulated that rather programmed necrosis (necroptosis) is the key form of neuronal death in the course of neurodegenerative diseases. Such assumption was supported by biochemical and morphological features of the dying cells as well as by the fact that various necroptosis inhibitors were neuroprotective in cellular and animal models of neurodegenerative diseases. In this review, we discuss the relationship between oxidative stress and RIP1-dependent necroptosis and apoptosis in the context of the pathomechanism of neurodegenerative disorders. Based on the published data mainly from cellular models of neurodegeneration linking oxidative stress and necroptosis, we postulate that administration of multipotential neuroprotectants with antioxidant and antinecroptotic properties may constitute an efficient pharmacotherapeutic strategy for the treatment of neurodegenerative diseases.

Local photoreceptor cell death differences in the murine model of retinal detachment

To investigate local cell death differences in the attached and detached retina at different regions in a murine experimental retinal detachment model. Subretinal injection of sodium hyaluronate was performed in eight-week-old C57BL/6J mice. Retinal regions of interest were defined in relation to their distance from the peak of the retinal detachment, as follows: (1) attached central; (2) attached paracentral; (3) detached apex; and (4) detached base. At day 0, the outer nuclear layer cell count for the attached central, attached paracentral, detached apex, and detached base was 1247.60 ± 64.62, 1157.80 ± 163.33, 1264.00 ± 150.7, and 1013.80 ± 67.16 cells, respectively. There were significant differences between the detached base vs. attached central, and between detached base vs. detached apex at day 0. The detached apex region displayed a significant and progressive cell count reduction from day 0 to 14. In contrast, the detached base region did not show progressive retinal degeneration in this model. Moreover, only the detached apex region had a significant and progressive cell death rate compared to baseline. Immediate confounding changes with dramatic differences in cell death rates are present across regions of the detached retina. We speculate that mechanical and regional differences in the bullous detached retina can modify the rate of cell death in this model.

Technological Advances of 3D Scaffold-Based Stem Cell/Exosome Therapy in Tissues and Organs

Recently, biomaterial scaffolds have been widely applied in the field of tissue engineering and regenerative medicine. Due to different production methods, unique types of three-dimensional (3D) scaffolds can be fabricated to meet the structural characteristics of tissues and organs, and provide suitable 3D microenvironments. The therapeutic effects of stem cell (SC) therapy in tissues and organs are considerable and have attracted the attention of academic researchers worldwide. However, due to the limitations and challenges of SC therapy, exosome therapy can be used for basic research and clinical translation. The review briefly introduces the materials (nature or polymer), shapes (hydrogels, particles and porous solids) and fabrication methods (crosslinking or bioprinting) of 3D scaffolds, and describes the recent progress in SC/exosome therapy with 3D scaffolds over the past 5 years (2016-2020). Normal SC/exosome therapy can improve the structure and function of diseased and damaged tissues and organs. In addition, 3D scaffold-based SC/exosome therapy can significantly improve the structure and function cardiac and neural tissues for the treatment of various refractory diseases. Besides, exosome therapy has the same therapeutic effects as SC therapy but without the disadvantages. Hence, 3D scaffold therapy provides an alternative strategy for treatment of refractory and incurable diseases and has entered a transformation period from basic research into clinical translation as a viable therapeutic option in the future.

The Autophagy-Initiating Kinase ULK1 Controls RIPK1-Mediated Cell Death

Autophagy, apoptosis, and necroptosis are stress responses governing the ultimate fate of a cell. However, the crosstalk between these cellular stress responses is not entirely understood. Especially, it is not clear whether the autophagy-initiating kinase ULK1 and the cell-death-regulating kinase RIPK1 are involved in this potential crosstalk. Here, we identify RIPK1 as a substrate of ULK1. ULK1-dependent phosphorylation of RIPK1 reduces complex IIb/necrosome assembly and tumor necrosis factor (TNF)-induced cell death, whereas deprivation of ULK1 enhances TNF-induced cell death. We observe that ULK1 phosphorylates multiple sites of RIPK1, but it appears that especially phosphorylation of S357 within the intermediate domain of RIPK1 mediates this cell-death-inhibiting effect. We propose that ULK1 is a regulator of RIPK1-mediated cell death.

RIP1 Perturbation Induces Chondrocyte Necroptosis and Promotes Osteoarthritis Pathogenesis via Targeting BMP7

Osteoarthritis (OA) is a highly prevalent and debilitating joint disorder that characterized by progressive destruction of articular cartilage. There is no effective disease-modifying therapy for the condition due to limited understanding of the molecular mechanisms on cartilage maintenance and destruction. Receptor-interacting protein kinase 1 (RIP1)-mediated necroptosis plays a vital role in various diseases, but the involvement of RIP1 in OA pathogenesis remains largely unknown. Here we show that typical necrotic cell morphology is observed within human OA cartilage samples in situ, and that RIP1 is significantly upregulated in cartilage from both OA patients and experimental OA rat models. Intra-articular RIP1 overexpression is sufficient to induce structural and functional defects of cartilage in rats, highlighting the crucial role of RIP1 during OA onset and progression by mediating chondrocyte necroptosis and disrupting extracellular matrix (ECM) metabolism homeostasis. Inhibition of RIP1 activity by its inhibitor necrostatin-1 protects the rats from trauma-induced cartilage degradation as well as limb pain. More importantly, we identify bone morphogenetic protein 7 (BMP7) as a novel downstream target that mediates RIP1-induced chondrocyte necroptosis and OA manifestations, thereby representing a non-canonical regulation mode of necroptosis. Our study supports a model whereby the activation of RIP1-BMP7 functional axis promotes chondrocyte necroptosis and subsequent OA pathogenesis, thus providing a new therapeutic target for OA.

RIP3 facilitates necroptosis through CaMKII and AIF after intracerebral hemorrhage in mice

BACKGROUND

Necroptosis-induced neuronal damage after intracerebral hemorrhage (ICH) has been documented recently. Previous studies have reported that RIP3 and its complex are recognized as central mediators of necroptosis. In this study, the role of RIP3 in the activation of CaMKII and AIF was investigated.

METHODS

We induced ICH in C57BL/6 mice by injecting collagenase IV into the basal ganglia. ICH mice were pretreated with the mPTP inhibitor CsA and the CAMKII inhibitor Kn-93, RIP3 siRNA or RIP3 rAAV. Brain edema and neurobehavior were evaluated. The expression of RIP3, p-MLKL, AIF, and CaMKII proteins was evaluated by western blotting, immunofluorescence (IF) and immunoprecipitation (IP).

RESULTS

Significant increases in RIP3, p-MLKL, CaMKII and AIF expression were observed in ICH mice, and RIP3-AIF colocalized in the nucleus. Overexpression of RIP3 by rAAV upregulated AIF expression in both the cytoplasm and nucleus, while CaMKII expression was increased in the cytoplasm. The interaction of RIP3-AIF and RIP3-CaMKII was detected after ICH injury. These complexes were inhibited by CsA with Kn-93 or RIP3 siRNA pretreatment, which reduced brain edema and neurological deficits.

CONCLUSIONS

Our findings revealed that ICH induced necroptotic neuronal death through the RIP3-CaMKII complex and the RIP3-AIF signaling pathway. Moreover, blockade of mPTP opening could suppress the pathogenesis of necroptosis.

The 100 most cited papers on retinal detachment: a bibliographic perspective

The 100 most cited papers on retinal detachment (RD) were analysed using a bibliographic study. The bibliographic databases of the ISI Web of Knowledge were searched, limited to research articles published between 1965 and 2020 in peer-reviewed journals. The papers were ranked in order of number of citations since publication. Ninety of the 100 most cited papers on RD were published in 12 ophthalmology journals, with 74 of them published in American Journal of Ophthalmology (n=31), Ophthalmology (n=23), Archives of Ophthalmology (n=10) and Investigative Ophthalmology and Visual Science (n=10); the remaining 10 papers were published in 8 journals from other fields of medical research. All papers in the top 100 were published in English. The 100 most cited papers on RD originated from 12 different countries, with the majority (72 papers) originating from the USA. The 100 identified papers represent a mix of clinical trials and animal/laboratory studies. This bibliographic study provides a unique perspective and insight into some of the most influential contributions in RD understanding and management over the last 55 years.

Ultra-widefield autofluorescence imaging findings in retinoschisis, rhegmatogenous retinal detachment and combined retinoschisis retinal detachment

PURPOSE

Retinoschisis (RS), rhegmatogenous retinal detachment (RRD) and combined RS retinal detachment (RSRD) may resemble clinically and pose a diagnostic challenge. This study investigates the role of the fundus autofluorescence (AF) in differentiating RS, RRD and RSRD.

METHODS

Fundus AF changes of 34 eyes diagnosed with RRD, 30 eyes with RS and 12 eyes with RSRD were retrospectively analysed. Ultra-widefield AF (UW-AF) image intensities obtained with the Optomap 200Tx were interpreted as hypo-, hyper- and isoautofluorescent or a mixed pattern with hypo- and hyperautofluorescence over and at the posterior margin (PM) of RRD, RS and RSRD.

RESULTS

All RS eyes revealed isoautofluorescence over the area of RS, and nine eyes (30%) showed hypoautofluorescent PM. Among RRD, acute (≤2 weeks) and chronic (>2 weeks) RRD demonstrated distinct AF characteristics. Sixty-two per cent of RRD eyes had acute RRD. From those, 16 eyes (76%) demonstrated hypoautofluorescence over the detached area and 19 (90%) eyes with hyperautofluorescent PM. Sixty-two per cent of chronic RRD eyes demonstrated isoautofluorecence over the detached area. Eight RSRD eyes (67%) revealed hyperautofluorescence in the detached area. The positive predictive value (PPV) for hypoautofluorescence over the area of subretinal fluid (SRF) in RRD was 95%. The PPV for hyperautofluorescence over the area of SRF in RSRD was 100% and for isoautofluorescence for schitic area in RSRD and RS was 76%.

CONCLUSION

The UW-AF can be a useful non-invasive adjuvant tool to distinguish between RRD, RS and RSRD. Hypo- or hyperautofluorescence over the area of interest and hyperautofluorescent PM indicates the presence of SRF.

Protective Effect of Mitochondrially Targeted Peptide Against Oxidant Injury of Cone Photoreceptors Through Preventing Necroptosis Pathway

Retinopathy is an eye disease caused by the death of retinal cells in the macular area and the surrounding choroid. As the retinal rod cell dysfunction and death lead to the loss of night vision, the disease will lead to visual dysfunction and blindness as the disease progresses. Because of the irreversible nature of cell death, gene therapy has become a research hotspot in the field of retinopathy. But the technology is still in animal studies or clinical trials, and more research is needed to prove its feasibility. In this study, oxidative damage cell model was established and divided into a control group, H₂O₂ group, SS31 +NEC1 group, SS31 +H₂O₂ group, and SS31 +NEC1 +H₂O₂ group, for different interventions. The cell survival rate of the H₂O₂ group was significantly increased compared with those of the SS31 + H₂O₂ group, SS31 +NEC1 +H₂O₂ group, and NEC1 +H₂O₂ group. Nec1 combined treatment significantly reduced reactive oxygen species (ROS) production compared with that in the H₂O₂ group. The level of MDA in the SS31 group, Nec-1 group and combined treatment of SS31 +NEC1 group decreased significantly compared with the H₂O₂ group. The proportion of cells with decreased mitochondrial membrane potential in the H₂O₂ group significantly increased, and the rate of positivity for propidium iodide (PI) of 661W cells in the H₂O₂ group and the control group significantly increased. Nine hours after H₂O₂ treatment of 661W cells, the RIP3 expression level began to increase, and peaked at 24 h. The level of RIP3 in the H₂O₂ group was significantly increased, while this level was downregulated in the SS31 and NEC1 treatment groups. Therefore, this study suggests that SS31 has a partial protective effect on 661W cells by inhibiting necrosis, which has certain guiding significance for the treatment of retinal diseases.

Autophagy activation and photoreceptor survival in retinal detachment

We assess the effect of autophagy inhibition on photoreceptor (PR) survival during experimental retinal detachment (RD) and examine the and examine the relationship between autophagy and the expression of glycolytic enzymes HK2 and PKM2 in the retina. We find that inhibiting autophagy by genetic knock out of the autophagy activator Atg5 in rod PRs resulted in increased apoptotic and necroptotic cell death during RD, demonstrated by elevated terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive cells, caspase 8 activity, transcript levels of Fas receptor and RIPK3 as compared to controls. The absence of autophagy in rods resulted in downregulation of hexokinase 2 and pyruvate kinase muscle isozyme 2 levels. More than 460 proteins were identified by mass spectroscopy in autophagosomes isolated from detached retinas compared with less than 150 proteins identified in autophagosomes from attached retinas. Among various cellular compartments, proteins from cytoskeleton, cytoplasm and intracellular organelles constituted a large portion of increased autophagosome contents. These proteins represent numerous biological processes, including phototransduction, cell-cell signaling, metabolism and inflammation. Our findings suggest that competent autophagy machinery is necessary for PR homeostasis and improving PR survival during periods of nutrient deprivation.

Experimental models and examination methods of retinal detachment

Retinal detachment refers to the separation of the retinal neuroepithelium and pigment epithelium, usually involving the death of photoreceptor cells. Severe detachment may lead to permanent visual impairment if not treated properly and promptly. According to the underlying causes, retinal detachment falls into one of three categories: exudative retinal detachment, traction detachment, and rhegmatogenous retinal detachment. Like many other diseases, it is difficult to study the pathophysiology of retinal detachment directly in humans, because the human retinal tissues are precious, scarce and non-regenerative; thus, establishing experimental models that better mimic the disease is necessary. In this review, we summarize the existing models of the three categories of retinal detachment both in vivo and in vitro, along with an overview of their examination methods and the major strengths and weaknesses of each model.

Necroptosis and its role in infectious diseases

Necroptosis is a noncaspase-dependent and precisely regulated mechanism of cell death. Necroptosis is mainly initiated by members of the tumor necrosis factor receptor (TNFR) and Toll-like receptor (TLR) families, interferon, intracellular RNA and DNA sensors and other mediators. Subsequently, the protein kinase RIPK1 (receptor-interacting protein kinase 1) and RIPK3 interact with the receptor protein, which transduces death signals and further recruits and phosphorylates MLKL (mixed lineage kinase domain-like protein). MLKL serves as the initiator of cell death and eventually induces necroptosis. It was found that necroptosis is not only involved in the physiological regulation but also in the occurrence, development and prognosis of some necrotic diseases, especially infectious diseases. Intervention in the necroptosis signaling pathway is helpful for removing pathogens, inhibiting the development of lesions, and promoting the remodeling of tissue. In-depth study of the molecular regulation mechanism of necroptosis and its relationship with the pathogenesis of infectious diseases will help to provide new ideas and directions for research of the pathological mechanisms and clinical prevention of infectious diseases.

Neuroprotective effects and mechanisms of action of nicotinamide mononucleotide (NMN) in a photoreceptor degenerative model of retinal detachment

Currently, no pharmacotherapy has been proven effective in treating photoreceptor degeneration in patients. Discovering readily available and safe neuroprotectants is therefore highly sought after. Here, we investigated nicotinamide mononucleotide (NMN), a precursor of nicotinamide adenine dinucleotide (NAD⁺), in a retinal detachment (RD) induced photoreceptor degeneration. NMN administration after RD resulted in a significant reduction of TUNEL⁺ photoreceptors, CD11b⁺ macrophages, and GFAP labeled glial activation; a normalization of protein carbonyl content (PCC), and a preservation of the outer nuclear layer (ONL) thickness. NMN administration significantly increased NAD⁺ levels, SIRT1 protein expression, and heme oxygenase-1 (HO-1) expression. Delayed NMN administration still exerted protective effects after RD. Mechanistic in vitro studies using 661W cells revealed a SIRT1/HO-1 signaling as a downstream effector of NMN-mediated protection under oxidative stress and LPS stimulation. In conclusion, NMN administration exerts neuroprotective effects on photoreceptors after RD and oxidative injury, suggesting a therapeutic avenue to treating photoreceptor degeneration.

An in vitro Model of Human Retinal Detachment Reveals Successive Death Pathway Activations

Purpose

was to create an in vitro model of human retinal detachment (RD) to study the mechanisms of photoreceptor death.

Methods

Human retinas were obtained through eye globe donations for research purposes and cultivated as explants. Cell death was investigated in retinas with (control) and without retinal pigment epithelium (RPE) cells to mimic RD. Tissues were studied at different time points and immunohistological analyses for TUNEL, Cleaved caspase3, AIF, CDK4 and the epigenetic mark H3K27me3 were performed. Human and monkey eye globes with retinal detachment served as controls.

Results

The number of TUNEL-positive cells, compared between 1 and 7 days, increased with time in both retinas with RPE (from 1.2 ± 0.46 to 8 ± 0.89, n = 4) and without RPE (from 2.6 ± 0.73 to 16.3 ± 1.27, p < 0.014). In the group without RPE, cell death peaked at day 3 (p = 0.014) and was high until day 7. Almost no Cleaved-Caspase3 signal was observed, whereas a transient augmentation at day 3 of AIF-positive cells was observed to be about 10-fold in comparison to the control group (n = 2). Few CDK4-positive cells were found in both groups, but significantly more in the RD group at day 7 (1.8 ± 0.24 vs. 4.7 ± 0.58, p = 0.014). The H3K27me3 mark increased by 7-fold after 5 days in the RD group (p = 0.014) and slightly decreased at day 7 and was also observed to be markedly increased in human and monkey detached retina samples.

Conclusion

AIF expression coincides with the first peak of cell death, whereas the H3K27me3 mark increases during the cell death plateau, suggesting that photoreceptor death is induced by different successive pathways after RD. This in vitro model should permit the identification of neuroprotective drugs with clinical relevance.

Retinal safety evaluation of photoacoustic microscopy

Photoacoustic microscopy (PAM) has significant potential as a promising diagnostic method for eye diseases and can provide anatomic and functional information of the retinal and choroidal vasculature. However, there are no FDA-approved PAM systems for ophthalmic imaging. In this study, a comprehensive safety evaluation was performed to evaluate the safety of PAM retinal imaging and whether PAM causes damage to retinal structure or function in rabbit eyes. 12 Dutch-Belted pigmented rabbits received photoacoustic imaging to 57% of the retinal surface area with a laser energy of 5% of the ANSI safety limit for five consecutive days and followed before imaging and 3 days, 1, 2, 3, and 4 weeks post imaging. Retinal morphologic analyses using slit lamp examination, fundus photography, red free, FA, FAF, ICGA, and OCT showed no retinal hemorrhage, edema, detachment, vascular abnormalities, or pigmentary abnormalities in the retina or choroid after PAM imaging. Full-field ERG analysis showed no significant difference in scotopic or photopic a- and b-wave amplitudes or implicit times between the control and experimental eyes over time (n = 6, P values > 0.05). Retinal ultrastructural evaluation using TEM showed normal structure of organelles and nuclei, and no significant loss of cells after PAM. TUNEL assay showed no evidence of cells apoptosis in retina. Retinal histopathology indicated that the architecture and thickness of the retinal layers was well preserved in all experimental eyes. A positive control at 500% of the ANSI limit demonstrated significant damage. The comprehensive retinal safety evaluation demonstrated no damage to retinal structure or function for 4 weeks after PAM imaging in rabbits.

ThicknessTool: automated ImageJ retinal layer thickness and profile in digital images

To develop an automated retina layer thickness measurement tool for the ImageJ platform, to quantitate nuclear layers following the retina contour. We developed the ThicknessTool (TT), an automated thickness measurement plugin for the ImageJ platform. To calibrate TT, we created a calibration dataset of mock binary skeletonized mask images with increasing thickness masks and different rotations. Following, we created a training dataset and performed an agreement analysis of thickness measurements between TT and two masked manual observers. Finally, we tested the performance of TT measurements in a validation dataset of retinal detachment images. In the calibration dataset, there were no differences in layer thickness between measured and known thickness masks, with an overall coefficient of variation of 0.00%. Training dataset measurements of immunofluorescence retina nuclear layers disclosed no significant differences between TT and any observer’s average outer nuclear layer (ONL) (p = 0.998), inner nuclear layer (INL) (p = 0.807), and ONL/INL ratio (p = 0.944) measurements. Agreement analysis showed that bias between TT vs. observers’ mean was lower than between any observers’ mean against each other in the ONL (0.77 ± 0.34 µm vs 3.25 ± 0.33 µm) and INL (1.59 ± 0.28 µm vs 2.82 ± 0.36 µm). Validation dataset showed that TT can detect significant and true ONL thinning (p = 0.006), more sensitive than manual measurement capabilities (p = 0.069). ThicknessTool can measure retina nuclear layers thickness in a fast, accurate, and precise manner with multi-platform capabilities. In addition, the TT can be customized to user preferences and is freely available to download.

Hair growth promotion by necrostatin-1s

Necrostatins (Necs) have been developed as a receptor-interacting protein kinase 1 (RIPK1) inhibitor, thus inhibiting necroptosis. In this current study, we have investigated the possible involvement of necroptosis in the hair cycle regulation and further examined its underlying molecular mechanisms. Diverse RIPK1/3 inhibitors and siRNA were tested in the human outer-root sheath (ORS) cells and animal models. The expression and hair cycle-dependent expression of RIPK 1, respectively, were investigated in the hair follicles (HF) of human, pig, and the mouse. Resulting from the experiment, Nec-1s was most effective in the hair growth promotion among several inhibitors. Nec-1s induced the ORS cell proliferation and migration, and increased the HF length in mouse and pig organ cultures. In addition, it accelerated the telogen-to-anagen transition and elongated the anagen period in the mouse model. Both apoptosis and necroptosis were detected in hair cycle. RIPK1 and RIPK3 were highly expressed in ORS cells during the hair regression period. Nec-1s upregulated the mRNA expression of Wnt3a and Wnt5b, and the activity of β-catenin. Collectively, Nec-1s promotes hair growth through inhibiting necroptosis and activating the Wnt/β-catenin pathway. Necroptosis is involved in hair cycle regression, and Nec-1s is a promising target for hair-loss treatment.

Programmed cell death pathways in hearing loss: A review of apoptosis, autophagy and programmed necrosis

Programmed cell death (PCD)—apoptosis, autophagy and programmed necrosis—is any pathological form of cell death mediated by intracellular processes. Ototoxic drugs, ageing and noise exposure are some common pathogenic factors of sensorineural hearing loss (SNHL) that can induce the programmed death of auditory hair cells through different pathways, and eventually lead to the loss of hair cells. Furthermore, several mutations in apoptotic genes including DFNA5, DFNA51 and DFNB74 have been suggested to be responsible for the new functional classes of monogenic hearing loss (HL). Therefore, in this review, we elucidate the role of these three forms of PCD in different types of HL and discuss their guiding significance for HL treatment. We believe that further studies of PCD pathways are necessary to understand the pathogenesis of HL and guide scientists and clinicians to identify new drug targets for HL treatment.

Pancreas-specific deletion of protein kinase D attenuates inflammation, necrosis, and severity of acute pancreatitis

BACKGROUND

Protein kinase D (PKD) family, which includes PKD/PKD1, PKD2, and PKD3, has been increasingly implicated in the regulation of multiple cellular functions and human diseases. We recently reported that pharmacologic inhibition of PKD ameliorated the pathologic responses and severity of pancreatitis. However, to further investigate the importance of PKD family members in pancreatitis, it is necessary to explore the effects of pancreas-specific genetic inhibition of PKD isoform on pathology of pancreatitis.

METHODS

We generated a mouse model (referred as PKD3Δpanc mice) with pancreas-specific deletion of PKD3, the predominant PKD isoform in mouse pancreatic acinar cells, by crossing Pkd3flox/flox mice with Pdx1-Cre transgenic mice which express Cre recombinase under the control of the mouse Pdx1 promoter. Pancreas-specific deletion of the PKD3 gene and PKD3 protein was confirmed by PCR and Western blot analysis. Experimental pancreatitis was induced in PKD3Δpanc and Pkd3flox/flox (control mice) littermates by intraperitoneal injections of cerulein or L-arginine.

RESULTS

Compared to the control mice, PKD3Δpanc mice displayed significant attenuation in inflammation, necrosis, and severity of pancreatitis in both experimental models. PKD3Δpanc mice had markedly decreased NF-κB and trypsinogen activation, pancreatic mRNA expression of multiple inflammatory molecules, and the receptor-interacting protein kinase 1 (RIP1) activation in pancreatitis. PKD3Δpanc mice also had less pancreatic ATP depletion, increased pro-survival Bcl-2 family protein expression, and autophagy promotion.

CONCLUSION

With PKD3Δpanc mouse model, we further demonstrated that PKD plays a critical role in pathobiological process of pancreatitis and PKD constitutes a novel therapeutic target to treat this disorder.

TRPML1 Inhibited Photoreceptor Apoptosis and Protected the Retina by Activation of Autophagy in Experimental Retinal Detachment

OBJECTIVE

In this study, we used a rat model of retinal detachment (RD) to investigate the effects of transient receptor potential mucolipin 1 (TRPML1) on photoreceptor cells and the underlying mechanism.

METHODS

An RD model was established by subretinal injection of sodium hyaluronate, and mucolipin synthetic agonist 1 (ML-SA1) and dimethyl sulphoxide were subretinally injected after RD induction. Retinal morphology was observed using haematoxylin-eosin staining, and the apoptosis of photoreceptor cells was detected by transmission electron microscopy. Reactive oxygen species (ROS) were examined with an ROS detection kit. The retinal expression levels of TRPML1, the autophagy-related protein microtubule-associated protein 1 light chain 3 (LC3), Beclin 1, and cleaved caspase 3 were detected by Western blotting. The Morris water maze was used to test vision-dependent behaviour.

RESULTS

We found that retinal structure and the outer nuclear layer were improved and that the apoptosis of photoreceptor cells was reduced after ML-SA1 injection. The expression of ROS was reduced, and the loss of TRPML1 was inhibited after ML-SA1 treatment. The LC3-II to LC3-I ratio and Beclin 1 expression were enhanced, and cleaved caspase 3 expression was decreased after ML-SA1 treatment. Treatment with ML-SA1 also improved vision-dependent behaviour.

CONCLUSIONS

Our findings suggest that ML-SA1 attenuates photoreceptor apoptosis and improves vision-dependent behaviour by activation of autophagy.

Effect of Mesenchymal Stem Cell-Derived Exosomes on Retinal Injury: A Review of Current Findings

In recent years, various studies have followed in the literature on the therapeutic effects of mesenchymal stem cells (MSC) on damage in retinal cells. The evidence that MSCs exert their regenerative and damage reduction effect in a paracrine way, through the release of soluble factors and exosomes, is now consolidated. Exosomes are microvesicles formed by a double layer of phospholipid membrane and carry proteins and RNA, through which they play a therapeutic role on target cells. Scientific research has recently focused on the use of exosomes derived from MSC in various models of retinal damage in vitro and in vivo as they, compared to MSCs, have similar functions and at the same time have different advantages such as greater stability and handling, a lower chance of immunological rejection and no risk of malignant transformation. The purpose of this review is to summarize current knowledge on the therapeutic use of exosomes derived from MSCs in retinal damage and to stimulate new clinical perspectives regarding their use.