Abstract
Purpose:
The delivery of neurotrophic factors through a variety of techniques can provide neuroprotection in retinal degenerative diseases. In designing neuroprotective strategies, knowledge of endogenous production of these factors by the retina may prove to be instructive. We therefore studied the time course of neurotrophic factors expression in an animal model of retinal degeneration, the rhodopsin knockout mouse (rho -/-). Specifically, we focused on glial-derived neurotrophic factor (GDNF), brain-derived neurotrophic factor (BDNF), and ciliary neurotrophic factor (CNTF), important molecules in the development and plasticity of the vertebrate visual system.
Methods:
We investigated the expression of GDNF, BDNF, CNTF in rho-/- mice. C57BL/6J mice were used as controls. Total RNA and protein were isolated from the retina of 3, 6, 9, 12, 20, 42, 54, 60, 70 and 100 weeks old rho-/- mice and from the retina of 3, 6, 9, 22 weeks old C57/Bl6 mice (5 mice per age group). mRNA expression was evaluated using qPCR, and protein by western blot (WB).
Results:
The expression of GDNF, CNTF and BDNF on mRNA and protein levels in C57BL/6J mice did not change with age. However, there was significant variation in growth factor expression during the time course of degeneration in rho -/- mice: up to week 9, the mRNA levels of these factors remained similar to C57/Bl6. After 12 weeks of age the expression of all three of these neurotrophic factors on mRNA level dramatically increased, peaked at 42 weeks of age, and then declined. WB analysis shows similar pattern for BDNF and CNTF proteins expression. Interestingly, the protein level of GDNF was different: it remained lower compared to controls through the duration of the study and we observed a significant decrease during 12 to 60 weeks of age.
Conclusions:
We hypothesize that the upregulation of growth factor expression during active retinal degeneration may be due to an injury response. The decreased expression seen late in the degenerative process may reflect the fact that a major source of photoreceptors are lost. It would be of interest to determine the relative contribution of these and other cell types (e.g. Muller glia, RPE, astrocytes) to growth factor expression. The change in expression of neurotrophic factors suggest that these factors play an important role in the pathogenesis of retinal degeneration in rho-/- mice.