Yaowu Qin

Neuroprotective Effects of Naloxone against Light-Induced Photoreceptor Degeneration through Inhibiting Retinal Microglial Activation

PURPOSE To determine the role of microglial activation in light-induced photoreceptor degeneration and the neuroprotective effects of naloxone as a novel microglial inhibitor. METHODS Sprague-Dawley rats were exposed to intense blue light for 24 hours. Daily intraperitoneal injection of naloxone or PBS as a control was given 2 days before exposure to light and was continued for 2 weeks. Apoptotic cells were detected by the TUNEL assay, and anti-OX42 antibody was used to label retinal microglia. Western blot was applied to evaluate the retinal interleukin (IL)-1beta protein levels. Retinal histologic examination and electroretinography (ERG) were also performed to evaluate the effects of naloxone on light-induced photoreceptor degeneration. RESULTS TUNEL-positive cells were noted in the outer nuclear layer (ONL) of the retina as early as 2 hours and peaked at 24 hours after exposure to light. OX42-positive microglia occurred in the ONL and subretinal space at 6 hours, peaked at 3 days, and changed morphologically from the resting ramified to the activated amoeboid. Expression of IL-1beta protein was also significantly increased at 3 days. Compared with the control, the number of microglia in the outer retina was significantly decreased in the naloxone-treated group at 3 days, and the thickness of ONL and the amplitudes of dark-adapted a- and b-waves were also well preserved at 14 days. CONCLUSIONS The activation and migration of microglia and the expression of neurotoxic factor (IL-1beta) coincide with photoreceptor apoptosis, suggesting that activated microglia play a major role in light-induced photoreceptor degeneration. Inhibiting microglial activation by naloxone significantly reduces this degeneration.

ERK1/2 signaling pathways involved in VEGF release in diabetic rat retina.

PURPOSE Vascular endothelial growth factor (VEGF) is one of the major factors promoting diabetic retinopathy (DR). A better understanding of the signaling pathway in VEGF regulation is of clinical importance to identify more precise therapeutic targets for diabetic retinopathy. The ERK1/2 signaling pathway has been shown to play a key role in some oncoma and hematologic diseases by mediating VEGF release. This research was conducted to determine whether the ERK1/2 signaling pathway also plays a major role in VEGF release in DR development. METHODS One hundred Sprague-Dawley (SD) rats were induced to diabetes by streptozotocin (STZ) injection and monitored at several time points (1, 2, 3, 4, 8, and 12 weeks) for ERK1/2 phosphorylation, Activator protein (AP)-1 activity and concentration, and VEGF protein and mRNA expression, using immunohistochemical and biochemical methods. RESULTS. The ERK1/2 signaling pathway was rapidly activated 1 week after diabetes was induced. AP-1, the downstream transcription factor of ERK1/2, was also activated, and VEGF became highly regulated in a similar trend. U0126, an inhibitor of ERK1/2, also downregulated VEGF expression, in addition to ERK1/2 and AP-1 activity. CONCLUSIONS ERK1/2 signaling pathway is involved in VEGF release in diabetic rat retina; therefore, ERK1/2 may be a potential therapeutic target of DR.

High-salt loading exacerbates increased retinal content of aquaporins AQP1 and AQP4 in rats with diabetic retinopathy

In the neural retina, glial cells control formation of ionic gradients by mediating transmembrane water fluxes through aquaporin (AQP) water channels. Retinal content and immunolocalization of two water channels, AQP1 and AQP4, in the diabetic rat retinas during high-salt loading were examined in this study. Diabetes was induced by an intraperitoneal injection of streptozotocin. Diabetic and control animals were observed after varying lengths of exposure to normal- and high-salt conditions. Ultrathin sections of retinal tissue, stained with uranyl acetate and lead citrate, were photographed using a transmission electron microscope (TEM). Retinal wholemounts were immunostained with AQP1 and AQP4 antibody to detect the immunolocalization changes by confocal microscopy. AQP1 and AQP4 content were evaluated by Western blot analysis. In the retinas of high-salt loading diabetic animals, obviously increased intracellular edema was observed by TEM in ganglion cells and mitochondrial swelling was observed in glial cells. Immunolocalization of AQP1 increased from the posterior to peripheral retina. Western blot results indicated that a high-salt diet may cause increased retinal content of AQP4 and may exacerbate increased retinal content of AQP1 caused by diabetic retinopathy. High-salt loading may increase neural retinal edema in rats with diabetic retinopathy, and altered glial cell mediated water transport via AQP channels in the retina may play an important role in the neural retinal edema formation and resolution.

High salt loading alters the expression and localization of glial aquaporins in rat retina.

In the neural retina, glial cells control the ionic concentrations in part by mediation of transmembrane water fluxes through aquaporin (AQP) water channels. The expression and immunolocalization of two water channels, AQP1 and AQP4, in the rat retina during experimental high salt loading were investigated in this study. Six-week-old Wistar rats were allowed free access to rat chow with 8% NaCl concentration. Of these rats, 6 were killed after 2, 6, 10 and 20 weeks. Twelve-week-old and 26-week-old Wistar rats with a normal diet (0.5% NaCl concentration) were used as controls. Retinal tissues were collected. Ultrathin sections stained with uranyl acetate and lead citrate were photographed using a transmission electron microscope (TEM). Retinal whole mounts and cryosections were immunostained with AQP1 and AQP4 antibodies to detect the immunolocalization changes by confocal microscopy. The AQP1 and AQP4 contents were evaluated by western blot analysis. In control tissues, no intracellular edema and mitochondria swelling were observed by TEM. The immunoreactive AQP4 was expressed by glial cells (Müller cells and astrocytes) predominantly in the inner retina, and AQP1 was expressed in the outer retina. In the retinas of high salt loading animals, obvious intracellular edema was observed by TEM in retinal ganglion cell (RGC) and mitochondria swelling was observed in glial cells. Strong expression of AQP1 was found in glial cells located in the innermost retinal layers, mainly in astrocytes. The superficial retinal vessels were surrounded by AQP4 in control retinas, but by both AQP4 and AQP1 in retina of high salt loading animals. A similar alteration in the localization of AQP1 has been described in the rat retina after transient ischemia and diabetes. Western blot results supported the conclusion that the AQP1 expression increased during high salt diet. Our findings indicate that high salt loading may induce neural retina edema, and that altered glial cell-mediated water transport via AQP channels in the retina may be one of the reasons for intracellular edema in the neural retina.

Aquaporin Changes during Diabetic Retinopathy in Rats Are Accelerated by Systemic Hypertension and Are Linked to the Renin-Angiotensin System

PURPOSE We explored the relationship between the renin-angiotensin system (RAS) and aquaporins (AQP1 and AQP4 in Müller glia and astrocytes) in diabetic retinopathy (DR) with and without systemic hypertension. METHODS Diabetes was induced in spontaneously hypertensive rats (SHR) and normotensive control Wistar Kyoto (WKY) rats by intraperitoneal injections of streptozotocin. The diabetic and control non-diabetic rats were assigned randomly to receive no anti-hypertension treatment, or to be treated with the angiotensin II receptor blocker (ARB), valsartan (40 mg/kg/d) or the beta-blocker, metoprolol (50 mg/kg/day). Eight weeks later, retinas were evaluated by immunohistochemistry and Western blot to detect changes in the expression of AQP1, AQP4, and glial fibrillary acidic protein (GFAP). RESULTS Hypertension increased expression of glial GFAP and AQP4 (P < 0.01), but not AQP1 (P > 0.05) in diabetic rats. Valsartan and metoprolol decreased GFAP, AQP1, and AQP4 expression in diabetic SHR rats (P < 0.01). Valsartan decreased GFAP and AQP1 expression in diabetic WKY rats (P < 0.01), while metoprolol did not. CONCLUSIONS Activation of Müller glia and astrocytes was involved in the mechanism by which systemic hypertension affects DR. AQPs and macroglia were linked to changes in the RAS in DR. Changes in aquaporin expression in DR were increased by hypertension. This provides additional support for the early use of an ARB in the treatment of DR, especially in cases with retinal edema.

Regional Macular Light Sensitivity Changes in Myopic Chinese Adults: An MP1 Study

PURPOSE To investigate the variation of macular light sensitivity (MLS) in myopic Chinese adults by using microperimetry. METHODS MLS was recorded with the MP1 microperimeter (Nidek Technologies, Padova, Italy) in eyes affected by various degrees of myopia. Subjects were divided into group A (18-30 years) and group B (31-60 years). Subjects in both age groups were further divided based on refractive status: (1) high myopia (spherical equivalent, SE<-6.00 D); (2) low to moderate myopia (-6.00 D<or=SE<or=-1.00 D); and (3) no myopia (-1.00 D<SE<or=+0.50). All patients had corrected visual acuity greater than 20/20. The macular area covered by the MP1 grid contains nine areas. MLS was quantified in each part and correlated with the refractive data. RESULTS MLS correlated significantly with SE or axial length (AL). Average MLS of the outer ring, total macula, and superior quadrant significantly decreased in the high and the low to moderate myopia eyes (both P<0.05) in both age groups. MLS in the temporal, inferior, and nasal quadrants decreased in the high myopia eyes, but not in the low to moderate myopia eyes, except in the temporal quadrant in group A and in the nasal quadrant in group B. CONCLUSIONS Axial myopia was associated with reduced total and quadrant-specific MLS, particularly in the superior quadrant. These findings emphasize functional differences in the macula between high, low to moderate, and no myopia. Any evaluation of MLS by MP1 microperimetry in the macula should be interpreted in the context of the degree of refractive error and the region of measurement.