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Ординатура / Офтальмология / Английские материалы / Retinal Degenerative Diseases Laboratory and Therapeutic Investigations_Anderson_2008.pdf
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376

C. Tian et al.

(Weber and Harman 2008) and protects photoreceptors from the damaging effects of constant light (Gauthier et al. 2005). Recently, it has been reported that BDNF also plays an important role in dendritic growth in response to enriched visual environments that control the development of retinal circuitry (Landi et al. 2007a, b). In addition, researchers found that, in the rat, BDNF can effectively minimize the retinal toxicity resulting from photodynamic therapy (Paskowitz et al. 2007).

Retinal degenerative conditions, such as age-related macular degeneration and retinitis pigmentosa, leads to irreversible loss of vision, and is a major problem around the world that lacks suitable clinic treatment. A more general approach for the treatment of photoreceptor loss may be cell-based therapy dependent on the strategy of photoreceptor replacement by cell transplantation (MacLaren et al. 2006; Bartsch et al. 2008; Djojosubroto and Arsenijevic 2008; Wang et al. 2008; West et al. 2008). However, cell-based therapeutic approaches for the replacement of photoreceptors in disease such as retinitis pigmentosa have been limited to date due to the minimal integration of donor cells into the outer nuclear layer (ONL) and their ability to participate in host retinal circuitry. One of the most important goals for retina transplantation is to protect visual function during the process of retinal degeneration. We investigated whether BDNF combined with retinal stem cell (RSC) transplantation could provide a better restoration of visual function in degenerating retinas compared to previous approaches to the problem.

43.2 Methods

43.2.1 Animals

Animals were treated in accordance with the NIH guidelines for the care and use of laboratory animals and ARVO Statement for the Use of Animals in Ophthalmic and Vision Research, under a protocol approved by the Institutional Animal Care and Use Committee of Third Military Medical University. All efforts were made to minimize animal suffering and to use only the minimum number of animals necessary to provide an adequate sample size for statistically meaningful scientific conclusions. Eighteen pigmented dystrophic RCS rats were used in this study, and received a unilateral subretinal injection of rat retinal stem cells (rSCs) (n = 9) or rSCs+BDNF (1 mg/ml, 5 ìg/animal, Sigma, US, n = 9). The other eye received a subretinal injection of phosphate buffered saline (PBS) (n = 9) or the BDNF solution alone (5 ìg/animal, n=9).

43.2.2 Cell Preparation and Subretinal Transplantation

Embryonic day 17 rats were obtained from pregnant Long Evans dams (Taconic, Hudson, NY), and rSCs harvested from the retinas under sterile conditions. Culture and purifying of rSCs has been described previously (Chen et al. 2008). One hour

43 BDNF Improves the Efficacy ERG Amplitude Maintenance

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before surgery, rSCs neurospheres were gently dissociated into a cell suspension and then labeled with fluorescence marker, CM-DiI (2 ìg/ml, Millipore, US). rSCs were washed twice with medium and then diluted to a final concentration of 2×104/ìl in PBS or a solution containing 1 mg/ml BDNF and kept on ice until transplantation. Trypan blue dye exclusion was performed on the cell suspensions before and immediately after transplantation, which showed greater than 90 and 80% cell survival, respectively. All recipient RCS rats (at the age of P30) were anaesthetized with medelomidine hydrochloride (0.01 mg/10 g body wt, i.p., Dormitor, Pfizer) and placed in a head holder. The pupils were dilated with 1% tropicamide and the surfaces of the eye anesthetized with drops of 0.4% oxybuprocaine hydrochloride. A 5 ìl Hamilton syringe (26-gauge needle; Hamilton, Switzerland) containing the suspension of labeled rSCs was tangentially inserted through the conjunctiva and sclera into the subretinal space, causing a self-sealing wound tunnel. Cell suspensions were slowly injected (5 ìl/eye, 1×105 cells/eye in total) to produce a retinal detachment in the superior retina. The other eye received an injection with 5 ìl PBS or 5 ìl BDNF solutions (1 mg/ml). All surgical procedures were performed using an operating ophthalmic microscope. The cornea was punctured to reduce intraocular pressure and limit the efflux of cells. After subretinal transplantation, the fundus was examined using direct ophthalmoscopic observation.

43.2.3 Flash-Electroretinogram (F-ERG) Recordings

Animals were tested at 1, 2 and 3 months (n = 3 for each treatment at each time) after surgery. The rats were dark-adapted overnight then anesthetized i. m. with a combination of xylazine (5 mg/Kg, Sigma, US) and ketamine (50 mg/kg, Sigma, US). Body temperature was controlled at 37C with a heating pad. A ground electrode needle was placed in the tail, and a reference electrode needle placed in the forehead. An F-ERG recording electrode consisting of a small silver ring positioned on the surface of the cornea by a drop of methyl cellulose was used to record responses at a gain of 1 k using a 30 HZ (EPIC-2000; Roland, Germany). ERG b waves were generated with flashes of white light at intensities ranging from – 6.3 log cd-s. m–2 to 0.6 log cd-s. m–2. Each ERG response represents the average of five flashes. For all F-ERG recordings, b-wave amplitude was measured from the a-wave trough baseline to the peak of b-wave, and b-wave latency was measured from the onset of the stimulus to the b-wave peak.

43.2.4 Histology and Quantification

Rats killed by anesthetic overdoes after recordings, the eyes enucleated and the eyecups fixed in 4% paraformaldehyde in PBS (0.01 M, pH 7.4). Eye cups were immersed in a graded series of sucrose solutions (10, 20 and 30% in 0.01 M PBS) at room temperature for 2 days, embedded in OCT and sectioned on a cryostat (15 ìm