AQP4 regulates ferroptosis and oxidative stress of Muller cells in diabetic retinopathy by regulating TRPV4

Diabetic retinopathy (DR) is a common microvascular complication that causes visual impairment or loss. Aquaporin 4 (AQP4) is a regulatory protein involved in water transport and metabolism. In previous studies, we found that AQP4 is related to hypoxia injury in Muller cells. Transient receptor potential cation channel subfamily V member 4 (TRPV4) is a non-selective cation channel protein involved in the regulation of a variety of ophthalmic diseases. However, the effects of AQP4 and TRPV4 on ferroptosis and oxidative stress in high glucose (HG)-treated Muller cells are unclear. In this study, we investigated the functions of AQP4 and TRPV4 in DR. HG was used to treat mouse Muller cells. Reverse transcription quantitative polymerase chain reaction was used to measure AQP4 mRNA expression. Western blotting was used to detect the protein levels of AQP4, PTGS2, GPX4, and TRPV4. Cell count kit-8, flow cytometry, 5,5',6,6'-tetrachloro-1,1,3,3'-tetraethylbenzimidazolyl carbocyanine iodide staining, and glutathione (GSH), superoxide dismutase (SOD), and malondialdehyde (MDA) kits were used to evaluate the function of the Muller cells. Streptozotocin was used to induce DR in rats. Haematoxylin and eosin staining was performed to stain the retina of rats. GSH, SOD, and MDA detection kits, immunofluorescence, and flow cytometry assays were performed to study the function of AQP4 and TRPV4 in DR rats. Results found that AQP4 and TRPV4 were overexpressed in HG-induced Muller cells and streptozotocin-induced DR rats. AQP4 inhibition promoted proliferation and cell cycle progression, repressed cell apoptosis, ferroptosis, and oxidative stress, and alleviated retinal injury in DR rats. Mechanistically, AQP4 positively regulated TRPV4 expression. Overexpression of TRPV4 enhanced ferroptosis and oxidative stress in HG-treated Muller cells, and inhibition of TRPV4 had a protective effect on DR-induced retinal injury in rats. In conclusion, inhibition of AQP4 inhibits the ferroptosis and oxidative stress in Muller cells by downregulating TRPV4, which may be a potential target for DR therapy.

Indistinct retinal outer layers in the walls of the idiopathic full-thickness macular hole - A potential predictive biomarker for surgical outcomes

Purpose

To evaluate the absence of external limiting membrane (ELM) and ellipsoid zone (indistinct retinal outer layers, I-ROL) in the walls of idiopathic full-thickness macular holes (FTMHs) circumferentially on optical coherence tomography (OCT) and its correlation with surgical outcome.

Methods

In this retrospective observational study, OCT images of patients undergoing vitrectomy for FTMHs with at least 3-months of postoperative follow-up were analyzed for preoperative circumferential extent of I-ROL. Derived macular hole indices such as hole form factor (HFF), macular hole index (MHI), tractional hole index (THI), and hole diameter ratio (HDR) were also calculated. The circumferential extent of I-ROL was correlated with derived hole indices as well as anatomical closure, foveal architecture, and restoration of ELM following surgery.

Results

All nine eyes (eight patients) with FTMH (mean size: 610.11 ± 122.95 microns) in the study showed I-ROL in ≥1 quadrant. The mean HFF, MHI, THI, and HDR values were 0.72 ± 0.09, 0.35 ± 0.05, 0.71 ± 0.24, and 0.53 ± 0.14, respectively. All eyes achieved type-1 hole closure with improvement in best-corrected visual acuity to 0.58 ± 0.32 LogMAR from 0.81 ± 0.26 LogMAR. Regular foveal architecture was achieved in six eyes. Out of these, five eyes had I-ROL in ≥2 quadrants, and one eye had I-ROL in <2 quadrants (P = 0.0476). Restoration of ELM was seen in aforementioned six eyes (complete = 5, partial = 1). Out of the five eyes with complete ELM restoration, four had a circumferential extent of I-ROL in ≥2 quadrants (P = 0.0476). Complete restoration of ELM was associated with the complete restoration of the ellipsoid zone in three eyes.

Conclusion

Preoperative circumferential extent of I-ROL in FTMH walls can be a potential predictive OCT marker for the type of closure, postoperative foveal architecture, and ELM restoration.

LncRNA MALAT1 aggravates the retinal angiogenesis via miR-320a/HIF-1α axis in diabetic retinopathy

Diabetic retinopathy (DR) is one of the most serious microvascular complications of diabetes and an important cause of blindness in adults. In previous study, we found that miR-320a alleviated the damage of muller cells in DR. In this study, we mainly explored the mechanism of lncRNA MALAT1 on retinal angiogenesis in DR by regulating miR-320a/HIF-1α. The expression of MALAT1 and miR-320a was detected by RT-qPCR, and the expression of HIF-1α was detected by Western blot. The superoxide anion level, invasion, angiogenesis, and vascular permeability of mouse retinal microvascular endothelial cells (MRMECs) co-cultured with muller cells were evaluated by dihydroethidium, transwell, angiogenesis and immunofluorescence assay. In order to analyze the targeting relationship between miR-320a and MALAT1 or HIF-1α, we performed dual luciferase reporter gene, fluorescence in situ hybridization (FISH), RNA immunoprecipitation (RIP) and RNA pulldown experiments. The results should that MALAT1 and HIF-1α were highly expressed and miR-320a was low expressed in high glucose (HG)-induced muller cells, and MALAT1 could competitively bind with HIF-1α. Knocking down miR-320a inhibited MRMECs invasion angiogenesis, and vascular permeability by targeting miR-320a. Overexpression of miR-320a down regulated HIF-1α and inhibited the invasion, angiogenesis, and vascular permeability of MRMECs. In conclusion, MALAT1 inhibits HIF-1α expression and MRMECs angiogenesis in DR through spongy miR-320a.

Retinal degeneration: molecular mechanisms and therapeutic strategies

Retinal degenerative diseases are the main retinal diseases that threatens vision. Most retinal degenerative diseases are inherited diseases, including autosomal recessive inheritance, autosomal dominant inheritance, X-linked inheritance and mitochondrial inheritance, so emerging gene therapy strategies may provide an alternative method of treatment. Currently, three viral vectors are usually used in gene therapy studies: adenovirus, lentivirus and adeno-associated virus. Other gene therapies have their own advantages, such as DNA nanoparticles, antisense oligonucleotides and gene editing therapies. In addition, retinal degenerative diseases are often accompanied by abnormalities of retinal cells, including photoreceptor and retinal pigment epithelial cells. At present, stem cell transplantation is a promising new treatment for retinal degenerative diseases. Common sources of stem cells include retinal progenitor cells, induced pluripotent stem cells, embryonic stem cells and mesenchymal stem cells. In addition, retina explant cultures in vitro can be used as an effective platform for screening new therapies for retinal degenerative diseases. Drugs that actually reaches the retinal layer are more controlled, more consistent, and less invasive when using retinal explants. Furthermore, studies have shown that the imbalance of the gut microbiota is closely related to the occurrence and development of diabetic retinopathy. Therefore, the progression of diabetic retinopathy may be restrained by adjusting the imbalance of the gut microbiota. The purpose of this review is to discuss and summarize the molecular mechanisms and potential therapeutic strategies of retinal degenerative diseases.

Macular Microvascular Modifications in Progressive Lamellar Macular Holes

Lamellar macular holes (LMHs) may show morphological and functional deterioration over time, yet no definite prognostic factor for progression has been identified. Since neurovascular retinal unit impairment may take part in neurodegeneration, we compare progressive LMHs to stable ones in optical coherence tomography (OCT) angiography parameters.

METHODS

OCT B scans of eyes with LMH were analyzed to detect the presence of tissue loss (TL) over time, allowing us to identify a TL group and a stable (ST) group (14 patients each). The best corrected visual acuity (BCVA) at each considered imaging time point was collected. Lastly, patients underwent macular OCT angiography.

RESULTS

BCVA at last follow up was significantly reduced in the TL group compared to both the ST group and TL group baseline assessment. SCP foveal vessel density (VD), SCP and deep capillary plexus (DCP) perfusion density (PD) and parafoveal PD were lower in the TL group. Linear correlations between quantitative TL over time and parafoveal PD in SCP and between the speed of TL and BCVA variation during follow up were also detected.

CONCLUSIONS

TL in LMHs is associated with both OCT angiography modifications and BCVA deterioration over time. We suggest these findings to be a manifestation of foveal Muller cell impairment in progressive LMHs.

Knockdown of TRIM5α or TRIM11 increases lentiviral vector transduction efficiency of human Muller cells

The goal of this study was to determine the expression and distribution of the host restriction factors (RFs) TRIM5α and TRIM11 in non-human primate (NHP) neural retina tissue and the human Muller cell line MIO-M1. In addition, experiments were performed to determine the effect of TRIM5α and TRIM11 knockdown on FIVGFP transduction of MIO-M1 cells with the goal of devising strategies to increase the efficiency of lentiviral (LV) gene delivery. Immunofluorescence (IF) studies indicated that TRIM5α and TRIM11 were localized predominantly in nuclei within the outer nuclear layer (ONL) and inner nuclear layer (INL) of NHP retina tissue. Double label IF indicated that TRIM5α and TRIM11 were localized to some of the retinal Muller cell nuclei. MIO-M1 cells expressed TRIM5α predominantly in the nucleus and TRIM11 primarily in the cytosol. FIVGFP transduction efficiency was significantly increased, at 4 and 7 days post transduction, in TRIM5α and TRIM11 knockdown clones (KD) compared to WT MIO-M1 cells. In addition, pretreatment with the proteasome inhibitor MG132 increased the transduction efficiency of FIVGFP in WT MIO-M1 cells. The nuclear translocation of NF-κB (p65), at 72 h post FIVGFP transduction, was enhanced in TRIM5α and TRIM11 KD clones. The expression of TRIM5α and TRIM11 in macaque neural retina tissue and MIO-M1 cells indicate the presence of these RFs in NHP retina and human Muller cells. Our data indicate that even partial knockdown of TRIM5α or TRIM11, or a short proteasome inhibitor pretreatment, can increase the transduction efficiency of a LV vector.

Long-term follow up of en face optical coherence tomography of the inner retinal surface following internal limiting membrane peeling for idiopathic macular holes

PURPOSE

To evaluate sequential changes in the inner retinal surface using en face spectral domain optical coherence tomography (SD-OCT) following internal limiting membrane (ILM) peeling for idiopathic full thickness macular holes.

METHODS

Retrospective, interventional study on 45 eyes of 42 patients with type 1 macular hole closure after a single procedure and a minimum post-operative follow up of 6 months. Best corrected visual acuity (BCVA), fundus photographs, B scan and en face SD-OCT scans were analysed pre-operatively, at 2, 6, 12 months post-operatively and then yearly. The presence or absence of concentric macular dark spots (CMDS) on the ILM slab of en face SD-OCT, their distribution pattern and course in terms of number and size of the dark spots was qualitatively assessed at each follow up.

RESULTS

CMDS was identified in a total of 26 eyes (57.78%). Of these, it was detected in 21 eyes at 2 months and the remaining by 6 months. At the time of first detection, the distribution was classified as type 1 in 9 eyes (35%), type 2 in 7 eyes (27%) and type 3 in 10 eyes (38%). There was apparent increase in the number and size of the CMDS in 16 eyes (62%) no later than 12 months follow up, while 10 eyes (38%) remained stable. There was no decrease or resolution noted in any patient. The mean post-operative follow up was 19.4 months (range 6-69 months).

CONCLUSION

Inner retinal defects in the form of CMDS can be picked up on en face SD-OCT between 2-6 months post-operatively. They remain stable or become more prominent upto 12 months follow up, but do not regress once present. En face SD-OCT is recommended in all cases where ILM is peeled to assess CMDS.

Comparative study of inverted internal limiting membrane (ILM) flap and ILM peeling technique in large macular holes: a randomized-control trial

Background

The anatomical success rate of macular hole surgery ranges around 93–98%. However, the prognosis of large macular holes is generally poor. The study was conducted to compare the anatomical and visual outcomes of Internal Limiting Membrane (ILM) peeling vis-a-vis inverted ILM flap for the treatment of idiopathic large Full-Thickness Macular Holes (FTMH).

Methods

This was a prospective randomized control trial. The study included patients with idiopathic FTMH, with a minimum diameter ranging from 600 to 1500 μm. The patients were randomized into Group A (ILM peeling) and Group B (inverted ILM flap). The main outcome measures were anatomical and visual outcome at the end of 6 months. Anatomical success was defined as flattening of macular hole with resolution of the subretinal cuff of fluid and neurosensory retina completely covering the fovea.

Results

There were 30 patients in each group. The mean minimum diameters in Group A and B were 759.97 ± 85.01 μm and 803.33 ± 120.65 μm respectively (p = 0.113). The mean base diameter in group A and B was 1304.50 ± 191.59 μm and 1395.17 ± 240.56 μm respectively (p = 0.112). The anatomical success rates achieved in Group A and B were 70.0 and 90.0% respectively (p = 0.125). The mean best-corrected visual acuity (BCVA) after 6 months was logMAR 0.65 ± 0.25 (Snellen equivalent, 20/89) in Group A and logMAR 0.53 ± 0.20 (Snellen equivalent, 20/68) in Group B (p = 0.060). The mean improvement in BCVA was 1.4 lines and 2.1 lines in groups A and B respectively (p = 0.353). BCVA≥20/60 was achieved by 13.3 and 20.0% in group A and B respectively (p = 0.766).

Conclusion

The anatomical and functional outcome of Inverted ILM flap technique in large FTMH is statistically similar to that seen in conventional ILM peeling.

Trial registration

Clinical Trials Registry – India (Indian Medical Research) CTRI/2017/11/010474.

Electronic supplementary material

The online version of this article (10.1186/s12886-018-0826-y) contains supplementary material, which is available to authorized users.

Single-Cell Dissociation and Characterization in the Murine Retina and Optic Nerve

Recent technological advances have extended the range of analytic tools to very small samples. It is now possible to assay the transcriptome, and in some cases even the proteome, of single cells reliably. This allows addressing novel questions, such as the genotype/phenotype relationships of single neurons, heterogeneity within individual cells of the same type, or the basis of differential vulnerability to injury. An important prerequisite for these kinds of studies is the ability to isolate well-defined individual cells without contamination by adjacent tissue. In the retina and optic nerve, cells of different types and functions are closely intermingled, limiting the use of standard methods such as laser capture microdissection. Here, we describe a simple method to isolate morphologically intact cells from the retina and the optic nerve and discuss considerations in recognizing and isolating different cell types after dissociation.

Proteome analysis of retinal glia cells-related inflammatory cytokines in the aqueous humour of diabetic patients

PURPOSE

Retinal glia cells (RGC) activation and release of inflammatory cytokines have been associated with development of diabetic retinopathy (DR). In this study, we evaluated by protein array the presence of aqueous humour (AH) cytokines secreted by RGC in patients with diabetes without DR and with mild DR.

METHODS

This is a cross-sectional, case-control study. Thirty-five subjects (diabetics and controls) underwent full ophthalmic examination and AH samples collection before cataract surgery at the Department of Ophthalmology University of Padova. AH samples were analysed for total protein concentration (Bradford method) and RGC-related inflammatory cytokines using glass chip protein arrays.

RESULTS

Twelve diabetic patients without DR, 11 diabetic patients with mild DR and 12 non-diabetic controls were included. There was no significant difference in total protein concentration among the 3 groups. Interleukin IL-1β, IL-3, interferon gamma (IFN-ɣ), (IFN-ɣ)-induced protein (IP)-10 and monocyte chemotactic protein (MCP)-2 were significantly increased in diabetics versus controls. IFN-ɣ, IL-1α, IL-3 and MCP-2 were significantly increased in diabetics without DR versus controls, whereas granulocyte-macrophage colony-stimulating factor (GM-CSF), IFN-ɣ, IL-10, IP-10, regulated and normal T cell expressed and secreted (RANTES), and soluble tumour necrosis factor receptor (sTNF-R)II were significantly increased in diabetics with mild DR versus controls. Macrophage inflammatory protein (MIP-1β), GMCSF, RANTES and sTNF-RII were significantly increased in diabetics with mild DR versus diabetics without DR (p < 0.05 at least for all).

CONCLUSIONS

Differences in expression profile of AH cytokines between diabetics, without and with mild DR, and controls have been documented. Retinal neuroinflammatory biomarkers of RGC activation evaluated in AH by protein array analysis could guide in detecting specific phenotypes with potential for personalized management.

Idiopathic preretinal glia in aging and age-related macular degeneration

During analysis of glia in wholemount aged human retinas, frequent projections onto the vitreal surface of the inner limiting membrane (ILM) were noted. The present study characterized these preretinal glial structures. The amount of glial cells on the vitreal side of the ILM was compared between eyes with age-related macular degeneration (AMD) and age-matched control eyes. Retinal wholemounts were stained for markers of retinal astrocytes and activated Müller cells (glial fibrillary acidic protein, GFAP), Müller cells (vimentin, glutamine synthetase) and microglia/hyalocytes (IBA-1). Retinal vessels were labeled with UEA lectin. Images were collected using a Zeiss LSM 710 confocal microscope. Retinas were then cryopreserved. Laminin labeling of cryosections determined the location of glial structures in relation to the ILM. All retinas investigated herein had varied amounts of preretinal glia. These glial structures were classified into three groups based on size: sprouts, blooms, and membranes. The simplest of the glial structures observed were focal sprouts of singular GFAP-positive cells or processes on the vitreal surface of the ILM. The intermediate structures observed, glial blooms, were created by multiple cells/processes exiting from a single point and extending along the vitreoretinal surface. The most extensive structures, glial membranes, consisted of compact networks of cells and processes. Preretinal glia were observed in all areas of the retina but they were most prominent over large vessels. While all glial blooms and membranes contained vimentin and GFAP-positive cells, these proteins did not always co-localize. Many areas had no preretinal GFAP but had numerous vimentin only glial sprouts. In double labeled glial sprouts, vimentin staining extended beyond that of GFAP. Hyalocytes and microglia were detected along with glial sprouts, blooms, and membranes. They did not, however, concentrate in the retina below these structures. Cross sectional analysis identified small breaks in the ILM above large retinal vessels through which glial cells exited the retina. Preretinal glial structures of varied sizes are a common occurrence in aged retinas and, in most cases, are subclinical. While all retinal glia are found in blooms, vimentin labeling suggests that Müller cells form the leading edge. All retinas investigated from eyes with active choroidal neovascularization (CNV) had extensive glial membranes on the vitreal surface of the ILM. Although these structures may be benign, they may exert traction on the retina as they spread along the vitreoretinal interface. In cases with CNV, glial cells in the vitreous could bind intravitreally injected anti-vascular endothelial growth factor. These preretinal glial structures indicate the remodeling of both astrocytes and Müller cells in aged retinas, in particular those with advanced AMD.

Movement of the inner retina complex during the development of primary full-thickness macular holes: implications for hypotheses of pathogenesis

BACKGROUND

The inner retinal complex is a well-defined layer in spectral-domain OCT scans of the retina. The central edge of this layer at the fovea provides anatomical landmarks that can be observed in serial OCT scans of developing full-thickness macular holes (FTMH). Measurement of the movement of these points may clarify the mechanism of FTMH formation.

METHOD

This is a retrospective study of primary FTMH that had a sequence of two OCT scans showing progression of the hole. Measurements were made of the dimensions of the hole, including measurements using the central edge of the inner retinal complex (CEIRC) as markers. The inner retinal separation (distance between the CEIRC across the centre of the fovea) and the Height-IRS (average height of CEIRC above the retinal pigment epithelium) were measured.

RESULTS

Eighteen cases were identified in 17 patients. The average increase in the base diameter (368 microns) and the average increase in minimum linear dimension (187 microns) were much larger than the average increase in the inner retinal separation (73 microns). The average increase in Height-IRS was 103 microns.

CONCLUSION

The tangential separation of the outer retina to produce the macular hole is much larger than the tangential separation of the inner retinal layers. A model based on the histology of the Muller cells at the fovea is proposed to explain the findings of this study.