Laser induces apoptosis and ceramide production in human retinal pigment epithelial cells

Retina and RPE lipid profile changes linked with ABCA4 associated Stargardt's maculopathy

Stargardt maculopathy, caused predominantly by mutations in the ABCA4 gene, is characterized by an accumulation of non-degradable visual pigment derivative, lipofuscin, in the retinal pigment epithelium (RPE) - resulting in RPE atrophy. RPE is a monolayer tissue located adjacent to retinal photoreceptors and regulates their health and functioning; RPE atrophy triggers photoreceptor cell death and vision loss in Stargardt patients. Previously, ABCA4 mutations in photoreceptors were thought to be the major contributor to lipid homeostasis defects in the eye. Recently, we demonstrated that ABCA4 loss of function in the RPE leads to cell-autonomous lipid homeostasis defects. Our work underscores that an incomplete understanding of lipid metabolism and lipid-mediated signaling in the retina and RPE are potential causes for lacking treatments for this disease. Here we report altered lipidomic in mouse and human Stargardt models. This work provides the basis for therapeutics that aim to restore lipid homeostasis in the retina and the RPE.

rAAV-mediated over-expression of acid ceramidase prevents retinopathy in a mouse model of Farber lipogranulomatosis

Farber disease (FD) is a rare monogenic lysosomal storage disorder caused by mutations in ASAH1 that results in a deficiency of acid ceramidase (ACDase) activity and the abnormal systemic accumulation of ceramide species, leading to multi-system organ failure involving neurological decline and retinopathy. Here we describe the effects of rAAV-mediated ASAH1 over-expression on the progression of retinopathy in a mouse model of FD (Asah1^P361R/P361R) and its littermate controls (Asah1^+/+ and Asah1^+/P361R). Using a combination of non-invasive multimodal imaging, electrophysiology, post-mortem histology and mass spectrometry we demonstrate that ASAH1 over-expression significantly reduces central retinal thickening, ceramide accumulation, macrophage activation and limits fundus hyper-reflectivity and auto-fluorescence in FD mice, indicating rAAV-mediated over-expression of biologically active ACDase protein is able to rescue the anatomical retinal phenotype of Farber disease. Unexpectedly, ACDase over-expression in Asah1^+/+ and Asah1^+/P361R control eyes was observed to induce abnormal fundus hyper-reflectivity, auto-fluorescence and retinal thickening that closely resembles a FD phenotype. This study represents the first evidence of a gene therapy for Farber disease-related retinopathy. Importantly, the described gene therapy approach could be used to preserve vision in FD patients synergistically with broader enzyme replacement strategies aimed at preserving life.

In Vitro Cytological Responses against Laser Photobiomodulation for Periodontal Regeneration

Periodontal disease is a chronic inflammatory disease caused by periodontal bacteria. Recently, periodontal phototherapy, treatment using various types of lasers, has attracted attention. Photobiomodulation, the biological effect of low-power laser irradiation, has been widely studied. Although many types of lasers are applied in periodontal phototherapy, molecular biological effects of laser irradiation on cells in periodontal tissues are unclear. Here, we have summarized the molecular biological effects of diode, Nd:YAG, Er:YAG, Er,Cr:YSGG, and CO₂ lasers irradiation on cells in periodontal tissues. Photobiomodulation by laser irradiation enhanced cell proliferation and calcification in osteoblasts with altering gene expression. Positive effects were observed in fibroblasts on the proliferation, migration, and secretion of chemokines/cytokines. Laser irradiation suppressed gene expression related to inflammation in osteoblasts, fibroblasts, human periodontal ligament cells (hPDLCs), and endothelial cells. Furthermore, recent studies have revealed that laser irradiation affects cell differentiation in hPDLCs and stem cells. Additionally, some studies have also investigated the effects of laser irradiation on endothelial cells, cementoblasts, epithelial cells, osteoclasts, and osteocytes. The appropriate irradiation power was different for each laser apparatus and targeted cells. Thus, through this review, we tried to shed light on basic research that would ultimately lead to clinical application of periodontal phototherapy in the future.

Effects of photoelectric therapy on proliferation and apoptosis of scar cells by regulating the expression of microRNA-206 and its related mechanisms

Human skin fibroblast (HSF) cells were irradiated with different energy lasers to detect cell proliferation, apoptosis, and expression of microRNA-206 and protein, and to further summarise the therapeutic effect of laser on scar cells. Human scar cell line HSF cells were cultured in three groups. The control group was not irradiated by laser, the low-energy group was irradiated by 10 J/cm² laser, and the high-energy group was irradiated by 20 J/cm² laser. After irradiation, HSF cells were cultured for 20 hours. Cell proliferation was detected by MTT assay. Cell cycle and apoptosis were detected by flow cytometry. Transwell migration assay was used to detect cell migratory ability. Reverse transcription polymerase chain reaction (RT-PCR) was used to detect miR-206 and mTOR gene levels. The levels of MMP-9, Bax, Bcl-2, cyclin D1, and mTOR signalling pathway proteins were detected by Western blotting assays. The results showed that after laser irradiation, the proliferation of cells decreased, and the difference between the control group and the experimental group was significant (P < .05). The higher the energy was, the greater the upregulation of apoptosis was. Apoptosis and cell migration increased (P < .05). The expressions of microRNA-206, MMP-9, and Bax were upregulated, while the expressions of mTOR, Bcl-2, and cyclin D1 were downregulated. To sum up, laser irradiation can significantly inhibit the proliferation of HSF cells, affect cell cycle, and increase cell apoptosis and migratory ability.

Sphingolipids as Emerging Mediators in Retina Degeneration

The sphingolipids ceramide (Cer), sphingosine-1-phosphate (S1P), sphingosine (Sph), and ceramide-1-phosphate (C1P) are key signaling molecules that regulate major cellular functions. Their roles in the retina have gained increasing attention during the last decade since they emerge as mediators of proliferation, survival, migration, neovascularization, inflammation and death in retina cells. As exacerbation of these processes is central to retina degenerative diseases, they appear as crucial players in their progression. This review analyzes the functions of these sphingolipids in retina cell types and their possible pathological roles. Cer appears as a key arbitrator in diverse retinal pathologies; it promotes inflammation in endothelial and retina pigment epithelium (RPE) cells and its increase is a common feature in photoreceptor death in vitro and in animal models of retina degeneration; noteworthy, inhibiting Cer synthesis preserves photoreceptor viability and functionality. In turn, S1P acts as a double edge sword in the retina. It is essential for retina development, promoting the survival of photoreceptors and ganglion cells and regulating proliferation and differentiation of photoreceptor progenitors. However, S1P has also deleterious effects, stimulating migration of Müller glial cells, angiogenesis and fibrosis, contributing to the inflammatory scenario of proliferative retinopathies and age related macular degeneration (AMD). C1P, as S1P, promotes photoreceptor survival and differentiation. Collectively, the expanding role for these sphingolipids in the regulation of critical processes in retina cell types and in their dysregulation in retina degenerations makes them attractive targets for treating these diseases.

Effects of Er:YAG and Diode Laser Irradiation on Dental Pulp Cells and Tissues

Vital pulp therapy (VPT) is to preserve the nerve and maintain healthy dental pulp tissue. Laser irradiation (LI) is beneficial for VPT. Understanding how LI affects dental pulp cells and tissues is necessary to elucidate the mechanism of reparative dentin and dentin regeneration. Here, we show how Er:YAG-LI and diode-LI modulated cell proliferation, apoptosis, gene expression, protease activation, and mineralization induction in dental pulp cells and tissues using cell culture, immunohistochemical, genetic, and protein analysis techniques. Both LIs promoted proliferation in porcine dental pulp-derived cell lines (PPU-7), although the cell growth rate between the LIs was different. In addition to proliferation, both LIs also caused apoptosis; however, the apoptotic index for Er:YAG-LI was higher than that for diode-LI. The mRNA level of odontoblastic gene markers-two dentin sialophosphoprotein splicing variants and matrix metalloprotease (MMP)20 were enhanced by diode-LI, whereas MMP2 was increased by Er:YAG-LI. Both LIs enhanced alkaline phosphatase activity, suggesting that they may help induce PPU-7 differentiation into odontoblast-like cells. In terms of mineralization induction, the LIs were not significantly different, although their cell reactivity was likely different. Both LIs activated four MMPs in porcine dental pulp tissues. We helped elucidate how reparative dentin is formed during laser treatments.

Photocoagulation of human retinal pigment epithelium in vitro: unravelling the effects on ARPE-19 by transcriptomics and proteomics

PURPOSE

Despite the extensive use of retinal photocoagulation for ischaemia and vascular leakage in retinal vascular disease, the molecular mechanisms behind its clinical beneficial effects are still poorly understood. One important target of laser irradiation is the retinal pigment epithelium (RPE). In this study, we aimed at identifying the isolated effects of photocoagulation of RPE at both the mRNA and protein expression levels.

METHODS

Human ARPE-19 cells were exposed to photocoagulation. Gene expression and protein expression were compared to untreated cells using microarray and liquid chromatography-mass spectrometry analysis. Genes and proteins queried by microarray and mass spectrometry were subjected to the Kyoto Encyclopedia of Genes and Genomes (KEGG) database pathway analyses.

RESULTS

Laser irradiation resulted in an induction of the cytoprotective heat-shock protein subfamily Hsp70 as well as in a suppression of the vascular permeability factor carbonic anhydrase 9 (CA9). These expression patterns were evident at both the mRNA and protein levels. KEGG pathway analyses revealed genes and proteins involved in cellular turnover, repair and inflammation.

CONCLUSIONS

By characterizing the transcriptional and translational effects of laser coagulation on the RPE cells in culture, we have revealed responses, which might contribute to some of the beneficial effects obtained by photocoagulation for ischaemia and vascular leakage in retinal vascular disease.

Beyond the cherry-red spot: Ocular manifestations of sphingolipid-mediated neurodegenerative and inflammatory disorders

Sphingolipids are a ubiquitous membrane lipid present in every cell and found most abundantly in neural tissues. Disorders such as Tay-Sachs or Niemann-Pick disease are the most familiar examples of dysfunction in sphingolipid metabolism and are typically associated with neurodegeneration and ocular findings such as blindness. More recently, the role of bioactive sphingolipids has been established in a multitude of cellular events, including cell survival, growth, senescence and apoptosis, inflammation, and neovascularization. We discuss our current knowledge and understanding of sphingolipid metabolism and signaling in the pathogenesis of ocular diseases.

Photocoagulation of human retinal pigment epithelial cells in vitro: evaluation of necrosis, apoptosis, cell migration, cell proliferation and expression of tissue repairing and cytoprotective genes

Aims

Sight-threatening diabetic retinopathy has been treated with photocoagulation for decades but the mechanisms behind the beneficial clinical effects are poorly understood. One target of irradiation and a potential player in this process is the retinal pigment epithelium (RPE). Here we establish an in vitro model for photocoagulation of human RPE cells.

Methods

ARPE-19 cells were exposed to photocoagulation and studied at various time points up to 168h. Lesion morphology, necrosis and apoptosis were investigated by light microscopy; LIVE/DEAD staining and measurements of lactate dehydrogenase activity; and TUNEL- and ELISA-based quantification of DNA fragments, respectively. Cell migration and proliferation were explored using docetaxel and mitomycin C; temporal and spatial changes in proliferation were assessed by confocal immunofluorescence of proliferating cell nuclear antigen. Gene expression was measured by qPCR.

Results

Photocoagulation of ARPE-19 resulted in denaturation of proteins and reproducible lesion formation. A transient peak in necrosis, followed by a peak in apoptosis was observed in cells within the lesions at 6h and 24h, respectively after photocoagulation. Cell proliferation was depressed during the first hours after photocoagulation, back to control levels at 24h and augmented in the following days. These effects were not limited to cells in the lesions, but also evident in neighbouring cells. Changes in cell proliferation during lesion repair were preceded by changes in cell migration. Altered mRNA expression of genes previously implicated in the regulation of cell proliferation (FOS, IL-1β, IL-8, HMGA2), migration and tissue repairing (TGFBR2, ADAMTS6, TIMP3, CTGF) was observed, as well as increased expression of the alarmin IL33 and the cytoprotective gene HSPA6.

Conclusions

Using a laser system and experimental settings that comply with standards used in clinical practice, we have established a suitable model for in vitro photocoagulation of human RPE cells to isolate their contribution to the beneficial effects of laser treatment.

Ceramide signaling in retinal degeneration

Retinal degenerations (RD) are a complex heterogeneous group of diseases in which retinal photoreceptors and the supporting retinal pigment epithelial cells die irreversibly, causing visual loss for millions of people. Mutations on more than 150 genes have been discovered for RD and there are many forms that possess complex etiology involving more than one gene and environmental effect. For years many have searched for some common intracellular second messenger for these many forms of cell death which could be targeted for therapy. Ceramide is a novel cellular second messenger which signals for apoptosis. Several lines of evidence suggest an integral role of ceramide in photoreceptor apoptosis and cell death. Understanding their role in the pathogenic pathways of retinal degenerative diseases is important for development of targeted therapeutics.

Recruitment of stem cells into the injured retina after laser injury

Retinal degeneration is a devastating complication of diabetes and other disorders. Stem cell therapy for retinal degeneration has shown encouraging results but functional regeneration has not been yet achieved. Our study was undertaken to evaluate the localization of stem cells delivered to the retina by intravenous versus intravitreal infusion, because stem cell localization is a key factor in ultimate in vivo function. We used lineage-negative bone marrow-derived stem cells in a model wherein retina of mice was induced by precise and reproducible laser injury. Lin(-ve) bone marrow cells (BMCs) were labeled with a tracking dye and their homing capacity was analyzed at time points after infusion. We found that Lin(-ve) BMCs get incorporated into laser-injured retina when transplanted through either the intravitreal or intravenous route. The intravenous route resulted in optimal localization of donor cells at the site of injury. These cells incorporated into injured retina in a dose-dependent manner. The data presented in this study reflect the importance of dose and route for stem cell-based treatment designed to result in retinal regeneration.

Apoptosis in diabetic fibrovascular membranes after panretinal photocoagulation

A more complete understanding of the role of apoptosis in the regression of diabetic neovasculature following laser panretinal photocoagulation (PRP) will both elucidate the treatment's therapeutic mechanism and potentially lead to novel treatments for neovascularization associated with proliferative diabetic retinopathy that target apoptotic pathways. Pars plana vitrectomy with fibrovascular membrane delamination was performed on five patients with proliferative diabetic retinopathy, with four having received previous PRP treatment and one no previous laser treatment. Using in situ terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling, propidium iodide and hematoxylin-eosin staining, apoptotic cells were identified in the excised membranes. The authors found evidence of cells undergoing apoptosis in all of the excised membranes, with increasing amounts of preoperative PRP associated with an increased number of apoptotic cells per millimeter of membrane. The preliminary data suggest that the decrease in ambient mitogen, initiated by PRP treatment, activates apoptosis in diabetic fibrovascular membranes.

Regulating survival and development in the retina: key roles for simple sphingolipids

Many sphingolipids have key functions in the regulation of crucial cellular processes. Ceramide (Cer) and sphingosine (Sph) induce growth arrest and cell death in multiple situations of cellular stress. On the contrary, sphingosine-1-phosphate (S1P), the product of Sph phosphorylation, promotes proliferation, differentiation, and survival in different cell systems. This review summarizes the roles of these simple sphingolipids in different tissues and then analyzes their possible functions in the retina. Alterations in proliferation, neovascularization, differentiation, and cell death are critical in major retina diseases and collective evidence points to a role for sphingolipids in these processes. Cer induces inflammation and apoptosis in endothelial and retinal pigmented epithelium cells, leading to several retinopathies. S1P can prevent this death but also promotes cell proliferation that might lead to neovascularization and fibrosis. Recent data support Cer and Sph as crucial mediators in the induction of photoreceptor apoptosis in diverse models of oxidative damage and neurodegeneration, and suggest that regulating their metabolism can prevent this death. New evidence proposes a central role for S1P controlling photoreceptor survival and differentiation. Finally, this review discusses the ability of trophic factors to regulate sphingolipid metabolism and transactivate S1P signaling pathways to control survival and development in retina photoreceptors.

Real-time in vivo imaging of retinal cell apoptosis after laser exposure

PURPOSE

To investigate whether the detection of apoptosing retinal cells (DARC) could detect cells undergoing apoptosis in a laser model of retinal damage.

METHODS

Laser lesions were placed, with the use of a frequency-doubled Nd:YAG laser, on the retina in 34 eyes of anesthetized Dark Agouti rats. Lesion size and laser-induced retinal elevation were analyzed using in vivo reflectance imaging. Development of retinal cell apoptosis was assessed using intravitreal fluorescence-labeled annexin 5 in vivo with DARC technology from baseline until 90 minutes after laser application. Histologic analysis of retinal flat mounts and cross-sections was performed.

RESULTS

The lateral and anteroposterior depth extension of the zone of laser damage was significantly larger for higher exposure settings. A strong diffuse signal, concentrated at the outer retina, was seen with DARC for low exposures (<300 ms and <300 mW). In comparison, higher exposures (>300 ms and >300 mW) resulted in detectable hyperfluorescent spots, mainly at the level of the inner retinal layers. Dose-dependent effects on spot density and positive correlation of spot density between lesion size (P < 0.0001) and retinal elevation (P < 0.0001) were demonstrated. Histology confirmed the presence of apoptosing retinal cells in the inner nuclear and the ganglion cell layers.

CONCLUSIONS

This is the first time that DARC has been used to determine apoptotic effects in the inner nuclear layer. The ability to monitor changes spatially and temporally in vivo promises to be a major advance in the real-time assessment of retinal diseases and treatment effects.