Shunji Nakatake

Programmed necrosis, not apoptosis, is a key mediator of cell loss and DAMP-mediated inflammation in dsRNA-induced retinal degeneration

There is no known treatment for the dry form of an age-related macular degeneration (AMD). Cell death and inflammation are important biological processes thought to have central role in AMD. Here we show that receptor-interacting protein (RIP) kinase mediates necrosis and enhances inflammation in a mouse model of retinal degeneration induced by dsRNA, a component of drusen in AMD. In contrast to photoreceptor-induced apoptosis, subretinal injection of the dsRNA analog poly(I : C) caused necrosis of the retinal pigment epithelium (RPE), as well as macrophage infiltration into the outer retinas. In Rip3−/− mice, both necrosis and inflammation were prevented, providing substantial protection against poly(I : C)-induced retinal degeneration. Moreover, after poly(I : C) injection, Rip3−/− mice displayed decreased levels of pro-inflammatory cytokines (such as TNF-α and IL-6) in the retina, and attenuated intravitreal release of high-mobility group box-1 (HMGB1), a major damage-associated molecular pattern (DAMP). In vitro, poly(I : C)-induced necrosis were inhibited in Rip3-deficient RPE cells, which in turn suppressed HMGB1 release and dampened TNF-α and IL-6 induction evoked by necrotic supernatants. On the other hand, Rip3 deficiency did not modulate directly TNF-α and IL-6 production after poly(I : C) stimulation in RPE cells or macrophages. Therefore, programmed necrosis is crucial in dsRNA-induced retinal degeneration and may promote inflammation by regulating the release of intracellular DAMPs, suggesting novel therapeutic targets for diseases such as AMD.

Correlation between macular blood flow and central visual sensitivity in retinitis pigmentosa

To investigate the changes in macular blood flow and the correlation between those changes and central visual function in patients with retinitis pigmentosa (RP).

Association Between Aqueous Flare and Epiretinal Membrane in Retinitis Pigmentosa

PURPOSE Epiretinal membrane (ERM) is a frequent macular complication in patients with retinitis pigmentosa (RP). The etiology of ERM formation in RP is largely unknown. The purpose of this study was to investigate the association between aqueous flare, a surrogate index of intraocular inflammation, and ERM secondary to RP. METHODS We retrospectively studied a total of 206 eyes of 117 patients who were diagnosed with typical RP. Aqueous flare values were measured consecutively in 2012 and 2013 using a laser flare cell meter. Spectral-domain optical coherence tomography images and fundus photographs taken on the same day of the aqueous flare measurements were analyzed for ERM detection. RESULTS The mean values of aqueous flare, age, and frequency of male sex were significantly higher in the RP patients with ERM compared with the RP patients without ERM (P < 0.0001, P = 0.007, and P = 0.004, respectively). After adjustment for age and sex, the eyes in the highest quartile of aqueous flare had significantly higher odds of having ERM than those in the lowest quartile (odds ratio [OR], 2.68; 95% confidence interval [CI], 1.04-6.93), and the linear trend across flare levels was significant (P = 0.005). In addition, each 1-log-transformed increase in flare values was associated with an elevation of the likelihood of having ERM (OR, 2.59; 95% CI, 1.33-5.06). CONCLUSIONS Our analysis demonstrated that elevated aqueous flare is associated with ERM secondary to RP, suggesting that inflammation may be implicated in the pathogenesis of ERM formation in RP.

Long-term surgical outcomes of epiretinal membrane in patients with retinitis pigmentosa

Macular complications such as an epiretinal membrane (ERM), a cystoid macular edema and a macular hole lead to unexpected central vision impairment especially for patients with retinitis pigmentosa (RP). To evaluate the long-term surgical outcomes of pars plana vitrectomy (PPV) for ERM in patients with RP, we retrospectively reviewed the charts of a consecutive series of 10 RP patients who underwent PPV for ERM at Kyushu University Hospital. Visual acuity (VA) testing, a fundus examination, and an optical coherence tomography (OCT) analysis were conducted. The standard PPV using three sclerotomies was performed for ERM. PPV was performed in 12 eyes of 10 patients. One eye was excluded from the outcome assessment due to short period observation (18 months). There was no significantly deleterious change from the baseline to final VA between the operation eyes and the fellow eyes (P = 0.19). Moreover, morphological improvement was obtained in 9 of 11 eyes based on OCT. Our present data suggest that PPV may be tolerable in the management for ERM in RP patients over the long-term. Furthermore, the appearance of the ellipsoid zone was an important factor in the prediction of visual outcome and determination of surgical indication.

Risk factors for Posterior Subcapsular Cataract in Retinitis Pigmentosa

Purpose Posterior subcapsular cataract (PSC) is a frequent complication in patients with retinitis pigmentosa (RP). The risk factors for PSC formation in RP are largely unknown. The purpose of this study was to investigate the risk factors for PSC. Methods We retrospectively studied a total of 322 eyes of 173 patients who were diagnosed with typical RP. We considered the following possible risk factors for PSC: age, sex, hypertension, diabetes mellitus, high myopia, asthma, history of steroid intake, and aqueous flare. Aqueous flare values were measured consecutively in 2012 and 2013 using a laser flare cell meter. The lens including PSC was examined with a slit lamp after dilation with tropicamide 1% and phenylephrine 2.5%. Results The geometric mean values of aqueous flare and mean values of visual acuity were significantly higher for the RP patients with PSC compared to those without PSC (P = 0.0003, P = 0.0004, respectively). When the aqueous flare values were assessed continuously, each 1-log-transformed increase in flare levels was associated with an elevation of the likelihood of having PSC after multivariable adjustment (odds ratio: 1.71; 95% confidence interval: 1.05-2.77). There were no significant associations of the other possible risk factors with PSC. Conclusions Our analysis demonstrated that elevated aqueous flare is a significant risk factor for PSC formation. This result might provide insights into the association of inflammation and the pathogenesis of PSC formation in RP.

MUTYH promotes oxidative microglial activation and inherited retinal degeneration

Oxidative stress is implicated in various neurodegenerative disorders, including retinitis pigmentosa (RP), an inherited disease that causes blindness. The biological and cellular mechanisms by which oxidative stress mediates neuronal cell death are largely unknown. In a mouse model of RP (rd10 mice), we show that oxidative DNA damage activates microglia through MutY homolog-mediated (MUYTH-mediated) base excision repair (BER), thereby exacerbating retinal inflammation and degeneration. In the early stage of retinal degeneration, oxidative DNA damage accumulated in the microglia and caused single-strand breaks (SSBs) and poly(ADP-ribose) polymerase activation. In contrast, Mutyh deficiency in rd10 mice prevented SSB formation in microglia, which in turn suppressed microglial activation and photoreceptor cell death. Moreover, Mutyh-deficient primary microglial cells attenuated the polarization to the inflammatory and cytotoxic phenotype under oxidative stress. Thus, MUTYH-mediated BER in oxidative microglial activation may be a novel target to dampen the disease progression in RP and other neurodegenerative disorders that are associated with oxidative stress.

Optical coherence tomography angiography of the macular microvasculature changes in retinitis pigmentosa

To investigate the macular microvasculature changes by optical coherence tomography angiography (OCTA) and analyse the correlation between these changes and central visual function in patients with retinitis pigmentosa (RP).

Necrotic enlargement of cone photoreceptor cells and the release of high-mobility group box-1 in retinitis pigmentosa

Retinitis pigmentosa (RP) refers to a group of inherited retinal degenerations resulting form rod and cone photoreceptor cell death. The rod cell death due to deleterious genetic mutations has been shown to occur mainly through apoptosis, whereas the mechanisms and features of the secondary cone cell death have not been fully elucidated. Our previous study showed that the cone cell death in rd10 mice, an animal model of RP, involves necrotic features and is partly mediated by the receptor interacting protein kinase. However, the relevancy of necrotic cone cell death in human RP patients remains unknown. In the present study, we showed that dying cone cells in rd10 mice exhibited cellular enlargement, along with necrotic changes such as cellular swelling and mitochondrial rupture. In human eyes, live imaging of cone cells by adaptive optics scanning laser ophthalmoscopy revealed significantly increased percentages of enlarged cone cells in the RP patients compared with the control subjects. The vitreous of the RP patients contained significantly higher levels of high-mobility group box-1, which is released extracellularly associated with necrotic cell death. These findings suggest that necrotic enlargement of cone cells is involved in the process of cone degeneration, and that necrosis may be a novel target to prevent or delay the loss of cone-mediated central vision in RP.

Assessment of central visual function in patients with retinitis pigmentosa

In order to clarify the disease progression in retinitis pigmentosa (RP) and its related factors, reliable data on the changes in central visual function in RP are needed. In this longitudinal study, we examined 118 patients who were diagnosed with typical RP. Visual acuity (VA), visual field using a Humphrey Field Analyzer with the central 10-2 SITA-Standard program, and optical coherence tomography measurements were obtained. The slopes, which were derived from serial values of mean deviation (MD), macular sensitivity (MS), or foveal sensitivity (FS) obtained for each eye by a linear mixed model, were used for analysis. MS and FS were calculated as the average retinal sensitivity of 12 and 4 central points respectively. There were statistically significant interactions of times with levels of the central subfield thickness (CST) on the slopes of MS and FS. Compared to the eyes without macular complications, the eyes with macular complications had steeper MD, MS and FS slopes, and this interaction was no significant, but marginal trend for the MS or FS slope (P = 0.10, 0.05, respectively). The central retinal sensitivity (i.e., MS and FS) slopes calculated were effective indices of the progression of central visual function in RP.

Relations Among Foveal Blood Flow, Retinal-Choroidal Structure, and Visual Function in Retinitis Pigmentosa

Purpose To investigate the relationships between foveal blood flow as measured by laser speckle flowgraphy (LSFG), the retinal-choroidal structure in enhanced depth imaging-optical coherence tomography (EDI-OCT), and central visual function in patients with retinitis pigmentosa (RP). Methods We studied 52 consecutive typical RP patients ≤50 years old and 21 age- and sex-matched controls. The mean blur rate (MBR), which represents the blood flow volume, was calculated in a 2.4-mm2 area centered on the fovea by LSFG. Subfoveal horizontal EDI-OCT images were recorded, and the choroidal area, choroidal hyporeflective area, and choroidal hyperreflective area were analyzed in the central 2.4-mm-wide region. The central foveal thickness (CFT), subfoveal choroidal thickness (SCT), and ellipsoid zone (EZ) width were also measured. Visual acuity (VA) and retinal sensitivity (Humphrey 10-2 program) were measured in the RP patients. Results The MBR, choroidal area, hyporeflective area, hyperreflective area, and SCT were significantly decreased in the RP patients (all P < 0.001, versus controls). Spearmans rank testing demonstrated no significant correlation between the MBR and the choroidal structural parameters in the RP patients. Decreased MBR was significantly associated with reductions in VA, retinal sensitivity, CFT, and EZ width (all P < 0.05). The choroidal structural parameters did not correlate with central visual function, and the choroidal area, hyperreflective area, and SCT were inversely associated with CFT (all P < 0.05). Conclusions These results demonstrated the divergence between the choroidal structure and blood function, and suggest that decreased choroidal flow, rather than the structural alteration, is closely associated with foveal degeneration in RP.