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43 BDNF Improves the Efficacy ERG Amplitude Maintenance

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115.9 ± 34.5 ms; 97.5 ± 35.4 ms vs. 97 ± 36.2 ms). Both latencies were still significantly shorter than times recorded for PBS or BNDF eyes in the first and second month (P < 0.05). Significant differences were not seen between any of the comparisons for the PBS vs. BDNF groups with respect to latency or amplitude (Fig. 43.1).

43.3.2 ONL Thickness

There were no significant differences between the thicknesses of the ONL in the rSCs and rSCs+BDNF eyes at any time (Fig. 43.2), however, ONL thickness in rSCs eyes at 1, 2 and 3 months after transplantation (34.8 ±4.3 ìm, 19.1 ± 3.7 ìm and 13.2 ± 2 ìm; n = 3), were significantly greater than that seen in PBS injection eyes over the same time period (22.8 ± 2.1 ìm, 13 ± 2.7 ìm and 9.1 ± 1.5 respectively; P < 0.01). Similarly, the rSCs+BDNF eyes also showed significantly thicker ONLs (32.1 ± 7.9 ìm, 18 ± 0.4 ìm and 12.8 ± 2.4 ìm) than the BDNF injections alone (P < 0.01), which were 23.4 ± 4.1 ìm, 14 ± 1.8 ìm and 9.2 ± 1.8 ìm at 1, 2 and 3 months, respectively. There were no significant differences in ONL thickness between the PBS and BDNF injected.

43.3.3 Graft Cells Survival After Subretinal Transplantation

Graft cells can survival through 3 months after transplantation in both rSCs + BDNF eyes and rSCs eyes. The graft cells not only located in ONL but also migrated into INL after transplantation in both groups (Fig. 43.3). One month after transplantation, rSCs + BDNF eyes showed more grafts cells survival (139 ± 5 per eye, n = 3) than rSCs eyes (101.7 ± 9.9 per eye, n = 3) (P<0.05). In 2 and 3 months after transplantation, there are no more difference between rSCs + BDNF eyes and rSCs eyes (106 ± 3.8 per eye vs. 94.7 ± 8.4 per eye and 70.7 ± 8.7 vs. 65.3 ± 6.4 per eye, n = 3, respectively, P>0.05).

43.4 Discussion

Our results showed that BDNF can enhance the efficacy of rSCs subretinal transplantation, when assessed by ERG analysis. These results support previous studies by Marler et al. (2008) in which they used the animal model of light induced photoreceptor degeneration rat and transplanted adenovirus mediated gene delivery of BDNF of Müller cells in vitreous. They found that BDNF gene delivery to Müller glia can markedly increased the survival and structural integrity of light damaged photoreceptors (Gauthier et al. 2005). Also Ikeda in 2003 showed that BDNF shows protective effect and improves recovery of ERG b-wave in light induced photoreceptor damage (Ikeda et al. 2003). In 2008, Seiler et al. transplanted BDNF-treated retinal sheets into S 334ter lin3 rhodopsin retinal degenerate rats and found that

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Fig. 43.1 ERG latency and amplitude measurements. (a) One month after transplantation, eyes receiving either rSCs or rSCs+BDNF transplants retained better ERG responses compared to eyes receiving PBS or BDNF injections (P < 0.01; bars represent the SEM). rSCs+BDNF eyes had significantly higher amplitude rod-ERG b (151 ± 31.5 ìv vs. 137 ± 35.3 ìv, P < 0.01, n = 3) and Max-ERG b waves (203.5 ± 27.4 ìv vs. 174 ± 33.4 ìv, P < 0.01) compared to rSCs eyes. The latencies of rod-ERG b and max-ERG b waves in rSCs+BDNF eyes are shorter than those seen in rSCs eyes (92 ± 7.9 ms vs. 95 ± 12.6 ms, P < 0.05, n = 3 and 71 ± 12.5 ms vs. 75 ± 21.7 ms, P < 0.05, n = 3). (b) At 2 months after transplantation, eyes receiving either rSCs or rSCs+BDNF transplants retained better ERG responses than PBS or BDNF, injected eyes (P < 0.01). However, there is no difference between rSCs or rSCs+BDNF eyes with respect to wave latencies and amplitude. (c) No differences were seen between groups

BDNF coating improved the head-tracking behavior and the electrophysiological responses of the host retina. However, transplanted whole retinal sheets have their limitations, for example it difficult for the sheets to integrate and make functional connections within the host neural retina (Zhang et al. 2003).

43 BDNF Improves the Efficacy ERG Amplitude Maintenance

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Fig. 43.2 ONL thickness in RCS rats after receiving transplants or injections. The mean and ONL thicknesses and SEMs are shown at 1, 2 and 3 months after rSCs or rSCs+ BDNF (5 ìl with 5 μg) /transplantation or PBS (5 ìl) or BDNF (5 ìl with 5 μg) injections into the subretinal space ( P<0.01). Y-axis is ONL thickness (μm)

Photoreceptor cell bodies are located in ONL of retina, therefore, measuring ONL thickness can indicate enhance cell survival and may represent the protection of the host retina (Fujieda and Sasaki 2008). In this study, we found both rSCs eyes and rSCs + BDNF eyes had thicker ONL layers compared to PBS and BDNF injected eyes (P<0.01) at each time point and thus suggesting that the rate of photoreceptor degeneration and cell death is slowed down to some degree. However, ONL thickness in rSCs+BDNF transplanted eyes was not significantly different from rSC transplants alone suggesting no added benefit from BDNF in terms of cell survival. Although several researchers have found that BDNF can maintain the morphology and support the survival of retinal ganglion cells (Weber and Harman 2008) and could protect photoreceptors from the damaging effects of constant light (Gauthier et al. 2005). Recent research has shown that exogenously applied BDNF can activate neuroprotective signaling pathways such as ERK1/2 and Akt and can upregulate endogenous production of BDNF by Müller cells in the mouse retina (Azadi et al. 2007). Others have demonstrated that BDNF and its receptor TrkB play a significant role in the regulation of neuronal growth, survival and synapse formation in the central nervous system and in the retina (Loeliger et al. 2008; Pinnock and Herbert 2008; Vissio et al. 2008; Xuan et al. 2008). Furthermore, BDNF-TrkB signaling regulated the maturational formation of new branches in ON-ganglion cells and controls cell-specific, experience-dependent remodeling of neuronal structures in the visual system (Liu et al. 2007; Grishanin et al. 2008; Marler et al. 2008).

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Fig. 43.3 Graft cells survival after transplantation. Graft cells can survival through 3 months after transplantation in both rSCs + BDNF eyes (a–i) and rSCs (j, k, l) eyes. One month after transplantation, rSCs + BDNF eyes (a, b, c) showed more grafts cells survival (139 ± 5 per eye, n = 3) than rSCs eyes (j, k, l, 101.7 ± 9.9 per eye, n=3) (P<0.05). In 2 and 3 months after transplantation, there are no more difference between rSCs + BDNF eyes (d–f and g–i) and rSCs eyes, P>0.05. Graft cells labeled with DiI. RPE: retina pigment epithelia; ONL: out nuclear layer; INL: inner nuclear layer; GCL: ganglion cell layer. Scale bar is 20 μm