Yoshihiro Takamura

In vivo imaging of axonal transport of mitochondria in the diseased and aged mammalian CNS

Significance The lack of intravital imaging of axonal transport of mitochondria in the living mammalian CNS precludes the characterization of transport dynamics in the diseased and aged mammalian CNS. Here we report minimally invasive intravital multiphoton imaging of mouse retinal ganglion cells that offers sequential time-lapse images of mitochondria transported in a single axon with submicrometer resolution. We show highly dynamic axonal transport of mitochondria in the mammalian CNS in vivo under physiological conditions and characterize disturbances of mitochondrial transport in a mouse glaucoma model and age-related changes in mitochondrial transport. Our method is useful for characterizing the dynamics of axonal transport of mitochondria and the dynamics of other submicrometer structures in the diseased and aged mammalian CNS in vivo. The lack of intravital imaging of axonal transport of mitochondria in the mammalian CNS precludes characterization of the dynamics of axonal transport of mitochondria in the diseased and aged mammalian CNS. Glaucoma, the most common neurodegenerative eye disease, is characterized by axon degeneration and the death of retinal ganglion cells (RGCs) and by an age-related increase in incidence. RGC death is hypothesized to result from disturbances in axonal transport and in mitochondrial function. Here we report minimally invasive intravital multiphoton imaging of anesthetized mouse RGCs through the sclera that provides sequential time-lapse images of mitochondria transported in a single axon with submicrometer resolution. Unlike findings from explants, we show that the axonal transport of mitochondria is highly dynamic in the mammalian CNS in vivo under physiological conditions. Furthermore, in the early stage of glaucoma modeled in adult (4-mo-old) mice, the number of transported mitochondria decreases before RGC death, although transport does not shorten. However, with increasing age up to 23–25 mo, mitochondrial transport (duration, distance, and duty cycle) shortens. In axons, mitochondria-free regions increase and lengths of transported mitochondria decrease with aging, although totally organized transport patterns are preserved in old (23- to 25-mo-old) mice. Moreover, axonal transport of mitochondria is more vulnerable to glaucomatous insults in old mice than in adult mice. These mitochondrial changes with aging may underlie the age-related increase in glaucoma incidence. Our method is useful for characterizing the dynamics of axonal transport of mitochondria and may be applied to other submicrometer structures in the diseased and aged mammalian CNS in vivo.

Apoptotic cell death in the lens epithelium of rat sugar cataract

Apoptosis of lens epithelial cells (LECs) is implicated in the pathogenesis of several types of cataract formation. The high intracellular levels of polyol induce histological change in the LECs, which is considered the earliest event in sugar cataractogenesis. This study was designed to investigate whether high galactose exposure induces apoptosis in LECs during the development of sugar cataract. The effect of an aldose reductase inhibitor, SNK-860, was also examined. We induced sugar cataract in Sprague-Dawley rats by feeding them a 50% galactose-containing diet with or without SNK-860. The percentage of LECs undergoing apoptosis was measured by the terminal deoxynucleotidyl transferase-mediated biotin-dUTP nick-end labeling (TUNEL) method, and DNA fragmentation analyses were performed. Galactitol levels in the lens epithelium were quantified by gas chromatography. The number of TUNEL-positive cells gradually increased throughout the period of galactose exposure, up to 5 days. DNA fragmentation analysis in LECs of rats fed a galactose-rich diet demonstrated an apparent ladder pattern. SNK-860 reduced the percentage of TUNEL-positive cells, the amount of intracellular galactitol, and the levels of DNA laddering. To explore the mechanism of the apoptotic process, the expression of p53, a potent mediator of apoptosis, was examined. Based on Western blot and real-time reverse transcription-polymerase chain reaction results, the amount of p53-expression increased at both the protein and mRNA levels after galactose exposure, and the increase in p53-expression was inhibited by SNK-860. Based on these results, we concluded that apoptosis occurs in rat lens epithelial cells following galactose exposure. Furthermore, the reduction of apoptosis by aldose reductase inhibitor suggests that this apoptosis is associated with the accumulation of sugar alcohols. It is probable that the mechanism of apoptosis during sugar cataract formation involves the increased expression of p53.

Vlgr1 knockout mice show audiogenic seizure susceptibility

Susceptibility to audiogenic seizures, which are reflex seizures provoked by loud noise, can be induced in rodents by acoustic priming (exposing animals to strong auditory stimuli at an early developmental stage). Some strains of mice and rats are susceptible to audiogenic seizures without priming and these have been used as good experimental models with which to study epilepsies. Here we identified Vlgr1d and Vlgr1e, novel alternatively‐spliced variants of Vlgr1b/MGR1, which, upon sequence analysis, were shown to be transcripts from a locus previously characterized as mass1. Vlgr1 (Vlgr1b, Vlgr1d and Vlgr1e) mRNA is expressed predominantly in the neuroepithelium of the developing mouse brain. Our protein‐tagged experiment suggested that Vlgr1d and Vlgr1e are secretory molecules, while Vlgr1b is a receptor. Knockout mice lacking exons 2–4 of Vlgr1 were susceptible to audiogenic seizures without priming, although there were no apparent histological abnormalities in their brains. Ninety‐five percent of these knockout mice exhibited wild running, a feature typical of the preconvulsive phase of audiogenic seizures triggered by loud noise (11 kHz, 105 dB), and 68% exhibited tonic convulsions at 3 weeks after birth. Our monogenic mice, which have a unique genetic background, serve as a useful tool for further studies on seizures.

Analysis of the Effect of Intravitreal Bevacizumab Injection on Diabetic Macular Edema after Cataract Surgery

PURPOSE To determine the feasibility and clinical effectiveness of intravitreal bevacizumab combined with cataract surgery for management of the postoperative increase of retinal thickness in patients with diabetic maculopathy. DESIGN Prospective, randomized, masked cohort study. PARTICIPANTS Forty-two eyes with diabetic macular edema (DME) of 42 patients with type 2 diabetes mellitus. METHODS Patients were randomly assigned to receive either cataract surgery only (control; 21 eyes) or combined with intravitreal injection of 1.25 mg bevacizumab (21 eyes). Efficacy measures included best-corrected visual acuity (BCVA) testing, optical coherence tomography (OCT), and ophthalmoscopic examination. MAIN OUTCOME MEASURES Retinal thickness (RT) on OCT and BCVA were measured at baseline and 1 and 3 months after surgery. RESULTS There were no significant differences in RT, BCVA, severity of cataract, or systemic condition between the control and bevacizumab groups at the baseline. One and 3 months after surgery, the control group showed a significant increase in RT, whereas the bevacizumab group showed a significant decrease. Although postoperatively the eyes in both groups showed a significant improvement of BCVA, bevacizumab-treated eyes showed significantly better results (mean logarithm of the minimum angle of resolution, 0.38) than the control group (0.51) at month 3. There was a significant relationship between RT and visual acuity (VA) postoperatively in the control (P = 0.0001) and bevacizumab (P = 0.0141) groups. No systemic or ocular adverse events were observed. CONCLUSIONS Short-term results suggest that intravitreal bevacizumab has the potential not only to prevent the increase in RT, but also reduce the RT of eyes with DME after cataract surgery. Further improvement of VA in bevacizumab-treated eyes may be dependent on a reduction in central RT. FINANCIAL DISCLOSURE(S) The authors have no proprietary or commercial interest in any materials discussed in this article.

Immunohistochemical Study of Apoptosis of Lens Epithelial Cells in Human and Diabetic Rat Cataracts

PURPOSE To evaluate apoptosis of lens epithelial cells with immunohistochemical methods. METHODS We performed terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) assays on capsulotomy specimens (68 eyes in 53 patients) from patients who had undergone cataract surgery and an epithelium of diabetic cataracts in rats (144 eyes in 72 rats). The animal model of diabetic cataracts was prepared by injection of streptozotocin in three-week old rats. The rats were also examined using the proliferating cell nuclear antigen (PCNA) immunohistochemical staining method. RESULTS Although some TUNEL-positive cells were detected in capsulotomy specimens, we recognized little correlation between its distribution and morphological classification of cataracts. In the animal model of diabetic cataracts, TUNEL-positive cells were seen around the region where epithelial cells had accumulated. In the accumulated region, PCNA labeled cells undergoing DNA synthesis were also detected. CONCLUSION These results suggest the possibility that apoptosis occurs in human lens epithelial cells and apoptosis and proliferation may be induced by factors such as hyperglycemia.

Protein expression profiling of lens epithelial cells from Prdx6-depleted mice and their vulnerability to UV radiation exposure

Oxidative stress is one of the causative factors in progression and etiology of age-related cataract. Peroxiredoxin 6 (Prdx6), a savior for cells from internal or external environmental stresses, plays a role in cellular signaling by detoxifying reactive oxygen species (ROS) and thereby controlling gene regulation. Using targeted inactivation of the Prdx6 gene, we show that Prdx6-deficient lens epithelial cells (LECs) are more vulnerable to UV-triggered cell death, a major cause of skin disorders including cataractogenesis, and these cells display abnormal protein profiles. PRDX6-depleted LECs showed phenotypic changes and formed lentoid body, a characteristic of terminal cell differentiation and epithelial-mesenchymal transition. Prdx6(-/-) LECs exposed to UV-B showed higher ROS expression and were prone to apoptosis compared with wild-type LECs, underscoring a protective role for Prdx6. Comparative proteomic analysis using fluorescence-based difference gel electrophoresis along with mass spectrometry and database searching revealed a total of 13 proteins that were differentially expressed in Prdx6(-/-) cells. Six proteins were upregulated, whereas expression of seven proteins was decreased compared with Prdx6(+/+) LECs. Among the cytoskeleton-associated proteins that were highly expressed in Prdx6-deficient LECs was tropomyosin (Tm)2beta. Protein blot and real-time PCR validated dramatic increase of Tm2beta and Tm1alpha expression in these cells. Importantly, Prdx6(+/+) LECs showed a similar pattern of Tm2beta protein expression after transforming growth factor (TGF)-beta or H(2)O(2) treatment. An extrinsic supply of PRDX6 could restore Tm2beta expression, demonstrating that PRDX6 may attenuate adverse signaling in cells and thereby maintain cellular homeostasis. Exploring redox-proteomics (Prdx6(-/-)) and characterization and identification of abnormally expressed proteins and their attenuation by PRDX6 delivery should provide a basis for development of novel therapeutic interventions to postpone ROS-mediated abnormal signaling deleterious to cells or tissues.

Role of the Polyol Pathway in High Glucose–Induced Apoptosis of Retinal Pericytes and Proliferation of Endothelial Cells

PURPOSE The selective degeneration of pericytes and the proliferation of endothelial cells (ECs) appear to be associated with microaneurysm formation, an initial deficit in the early stage of diabetic retinopathy. The preventive effect of aldose reductase (AR) inhibitor (ARI) for high glucose-induced pericyte loss and EC growth was investigated. METHODS The effect of high glucose (30 mM) exposure in the presence or absence of ARI for the cell growth of porcine pericytes and ECs was examined with the use of an in vitro coculture system to mimic the interaction between pericytes and ECs. To determine the role of transforming growth factor (TGF)-beta, its amount in culture media was measured, and the effects of the treatment of TGF-beta or neutralizing antibody on EC growth were examined. RESULTS Abundant expression of AR and increased levels of polyol and apoptosis induced by high glucose were observed in pericytes, but not in ECs. ECs overexpressing AR cultured in high-glucose medium showed decreased cell viability. The growth-inhibitory effect of ECs on coculture with pericytes was attenuated by exposure to a high glucose concentration. Biochemical assays disclosed that the levels of active TGF-beta in media were linked to EC growth. Supply of active TGF-beta to coculture medium containing 30 mM D-glucose restored the inhibitory activity on EC growth. CONCLUSIONS ARI rescued pericytes from high glucose-induced apoptosis and maintained the levels of TGF-beta, resulting in the prevention of cocultured EC growth.

Correlation between erythrocyte aldose reductase level and human diabetic retinopathy

Aim: To examine the relation between aldose reductase (AR) and the development and progression of diabetic retinopathy by comparing the erythrocyte AR levels with the prevalence of diabetic retinopathy in NIDDM patients. Methods: A clinic based cross sectional study was used. 611 NIDDM patients and 73 controls were enrolled. Erythrocyte AR levels were determined by ELISA. These AR levels were then correlated with patient age, duration of diabetes, and HbA1c levels. AR levels were also correlated with the prevalence of diabetic retinopathy in the entire NIDDM patient group and in three subgroups formed by separating the NIDDM patients by their duration of diabetes. The prevalence of diabetic retinopathy significantly increased with increased erythrocyte AR levels in patients with duration of diabetes of less than 10 years. A similar, but non-significant correlation between the prevalence of retinopathy and increased erythrocyte AR levels was observed in patients with diabetes duration of 10–20 and ≥20 years. Results: The prevalence of diabetic retinopathy increased with increased erythrocyte AR levels in NIDDM patients with a duration of diabetes of less than 10 years. Conclusion: It was suggested that the inhibition of AR in patients with early NIDDM might be beneficial in reducing the development of diabetic retinopathy.

Attenuation of aldose reductase gene suppresses high-glucose-induced apoptosis and oxidative stress in rat lens epithelial cells

AIMS A major contributory factor to diabetic cataract formation is increased aldose reductase (AR) activity in the polyol pathway. We investigated the effects of aldose reductase inhibition by RNA interference (RNAi) of the aldose reductase gene and administration of an aldose reductase inhibitor (ARI) on the changes induced by high glucose levels in rat lens epithelial cells (RLECs). METHODS Small interfering RNAs (siRNAs) were designed to target the coding sequence of rat AR-siRNA. RLECs were cultured in either normal or high d-glucose. Western analysis was performed to monitor AR expression. MTS (3-(4-5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium salt) and TUNEL assays were used to detect apoptotic cell death. Intracellular reactive oxygen species (ROS) were assessed by using DCFH-DA. Activation of nuclear factor-kappaB (NF-kappaB) was measured by an ELISA-based detection method. RESULTS Both siRNA and ARI suppressed increased levels of ROS, activation of NF-kappaB, and apoptotic cell death induced by high glucose levels. Inhibition of rAR expression by siRNA and inhibition of AR activity by ARI also suppressed sorbitol accumulation. CONCLUSIONS Both inhibition of rAR expression by rAR siRNA and inhibition of rAR activity by an ARI appeared effective in diminishing the changes of RLECs associated with high glucose levels.

Age-related cataracts and Prdx6: correlation between severity of lens opacity, age and the level of Prdx 6 expression.

Background: Peroxiredoxin 6 (Prdx6), a new family of antioxidants, regulates gene expression and function by controlling reactive oxygen species, delays hereditary cataracts in rats and protects epithelial cells in the lens against oxidative stresses. Aim: To investigate the correlation between Prdx6 expression, age and the severity of lens opacity at the time of cataract surgery. Methods: 88 cataractous eyes were examined at Fukui University Hospital, Fukui, Japan, between March 2007 and October 2007. The patient age at the time of surgery, and the subtype and severity of cataract as classified according to the modified version of the Lens Opacities Classification System version III (LOCSIII) were recorded, as well as the expression level of Prdx6 mRNA in their lenses. Results: The expression of Prdx6 was found to be significantly negatively associated with age at the time of cataract surgery (p<0.047). A significant correlation was also found between a higher nuclear or cortical cataract score and lower expression of Prdx6 in patients under 70 years old. Conclusion: These findings suggest that oxidative stress contributes to nuclear cataract formation and that a local decrease in Prdx6 in cataractous lenses may indicate the initiation of age-related cataract formation.