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Subhadip Senapati; Effect of dietary Docosahexaenoic acid (DHA) on rhodopsin content and packing in rod photoreceptor cell membranes. Invest. Ophthalmol. Vis. Sci. 2017;58(8):355.
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Docosahexaenoic acid (DHA) is an n-3 fatty acid present at high levels in photoreceptor cell membranes. DHA deficiency causes vision defects related to photoreceptor cell dysfunction. Rhodopsin is present in rod outer segment (ROS) disc membranes of photoreceptor cells and plays a central role in photoreceptor cell function by initiating phototransduction upon absorbing photons. DHA deficiency is known to impair rhodopsin function, but the mechanism is unclear. To better understand the impact of DHA deficiency on rhodopsin function, we examined the effect of DHA on membrane structure and rhodopsin packing in photoreceptor cells.
DHA levels in ROS membrane phospholipids were modulated by feeding C57BL/6J mice DHA-deficient or DHA-adequate diets. Mass spectroscopy was used to monitor changes in DHA levels in ROS membrane phospholipids. To visualize the impact of dietary DHA on membrane structure and rhodopsin packing, ROS disc membranes were isolated from mice and imaged by atomic force microscopy (AFM).
Mass spectroscopic analysis showed that DHA levels in ROS membrane phospholipids were altered in accordance to the diets provided. The structure of ROS disc membranes and the quaternary membrane organization of rhodopsin was similar in both DHA-deficient and DHA-adequate mice. In contrast, DHA-deficient mice had higher rhodopsin content and density compared to DHA-adequate mice in ROS disc membranes. These effects were reversible when DHA-deficient mice were fed a DHA-adequate diet for 4 weeks.
Our AFM studies demonstrate that DHA-deficiency does not disrupt ROS disc membrane structure or the quaternary organization of rhodopsin in the membrane. DHA-deficiency does result in higher rhodopsin content and density in photoreceptor cell membranes, which we have previously observed as a compensatory mechanism of photoreceptor cells in response to impairment of phototransduction. This indicates that DHA-deficiency impairs rhodopsin function without affecting rhodopsin packing or quaternary structure.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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