Differential Temporal and Spatial Expression of TrkB Isoforms During AAV–BDNF Transduced Iris Pigment Epithelium Transplantation

Abstract

Purpose: : To examine the expression of TrkB receptor isoforms in the retina during adeno–associated virus mediated brain–derived neurotrophic factor transduced iris pigment epithelium (AAV2–BDNF–IPE) transplantation.

Methods: : We transduced variable concentration of AAV–BDNF to rat IPE and transplanted subretinally. We examined not only photoreceptor rescue effects from phototoxicity but expression of TrkB isoforms (TrkB–FL and –T1), BDNF receptors, by immunohistochemistry, western blotting, in situ hybridization and real–time PCR. Same examinations were also performed using rMC–1, a Muller cell line, and retinal pigment epithelial cells (RPE).

Results: : More than 1x10⁷capsids/ml AAV2–BDNF transduction showed statistical significant photoreceptor rescue effect when compared to that of control. However, the results showed no dose escalation effects of AAV2–BDNF. The gene expression of TrkB isoforms was also not correlated with AAV2–BDNF amount by real–time PCR. In situ hybridization showed that TrkB–FL was mainly expressed in the ganglion cell layer, conversely TrkB–T1 at the level of inner nuclear layer. Although the gene expression was enhanced by AAV–BDNF–IPE transplantation or light stimulation, the expression was temporally decreased by light stimulation at early time exposure and not correlated with the AAV–BDNF amount. Immunohistochemistry also showed resembled results and not correlated with the amount of AAV–BDNF concentration by western blotting. TrkB–T1 expression was also enhanced by BDNF in rMC–1 but not RPE by western blotting analysis.

Conclusions: : Our results showed differential temporal and spatial expression of TrkB isoforms in the retina. Muller cell is suspected to be one of the target cells of BDNF during AAV–BDNF–IPE transplantation.

Keywords: retina • transplantation • neuroprotection