Abstract
Purpose:
Stargardt macular dystrophy (STGD3) is a juvenile-onset disease caused by mutations in ELOVL4 (elongation of very long fatty acids-4). This protein catalyzes the first step in the conversion of long chain polyunsaturated fatty acids (LC-PUFAs) into very long chain PUFAs (VLC-PUFAs). We previously described how photoreceptor specific deletion of Elvol4 in mice effectively eliminates VLC-PUFA in the retina and allows us to study the role of these fatty acids in photoreceptor cells and how their absence leads to rod dysfunction and rod cell loss over time. These results led us to explore possible synaptic defects in VLC-PUFA-deficient mice.
Methods:
Here we use mice with conditional deletion of Elovl4 by Chx10-Cre-Recombinase. Knock out (KO, Cre+/Elovl4flox/flox) and littermate wild type (WT, Cre-/Elovl4flox/flox) mice were subjected to scotopic electroretinography (ERG) with increasing light intensities (Log scot -3.6 to 2.4 cd.s/m2) to determine the maximum rod b-wave (Vmax) amplitude by the least squares fit of nonlinear log intensity vs. amplitude response according to the Naka-Rushton equation. The b/a-wave ratios were calculated over time in these mice. The rod implicit time (rIT) was calculated by linear regression analysis of b-wave implicit times as a function of light intensity, where rIT was determined at ½Vmax. Rod recovery was measured by paired flash ERG on overnight dark-adapted 12 month old mice. The time between flashes was increased and the normalized response amplitudes were plotted as the exponential decay function. Oscillatory potentials (OP) were measured by ERG responses to10 different light intensities (0.001 to 1000 cd.s/m2). Plastic-embedded semi-thin sections from WT and KO littermates were used to compare the inner retinal layers. A2E-fluorophores were detected by normal-phase high performance liquid chromatography.
Results:
driven Vmax and b/a-wave ratios were below normal and the rIT was increased in VLC-PUFA deficient mice. The KO mice had defective oscillatory potentials compared to the littermate controls. Inner retinal layers were also thinner in the Elovl4 KO mice at 1 year of age. There were no differences detected in rod recovery, RPE thicknesses, or A2E accumulation in the WT and KO mice.
Conclusions:
data suggest that VLC-PUFA are important for synaptic transmission in rods.
Keywords: 562 inner retina dysfunction: biochemistry and cell biology