Developing rod photoreceptors from normal and mutant Rd mouse retinas: altered fatty acid composition early in development of the mutant.

The phospholipid and fatty acid contents of developing rod photoreceptor cells were determined in dissociated photoreceptor cells obtained from normal mice and from rd mice exhibiting an inherited retinal degeneration. Photoreceptors were dissociated from retinas by mechanical agitation after mild protease treatment and characterized by light and electron microscopy. Phospholipid classes were isolated by thin-layer chromatography, and fatty acyl groups separated and quantitated by capillary gas-liquid chromatography. Developing photoreceptor cells of normal retinas accumulated all phospholipid classes, but in proportions which shifted with age. The mole % contents of phosphatidylcholine (PC) and phosphatidylinositol (PI) decreased with age, whereas phosphatidylethanolamine (PE) and phosphatidylserine (PS) increased. The content of the polyunsaturated fatty acid docosahexaenoate (22:6), expressed as nmol/microgram lipid phosphorus, increased rapidly during development, whereas arachidonate (20:4) content tended to decline. Mono-unsaturated fatty acid levels (palmitoleate, 16:1; oleate, 18:1) declined with age. Among saturated fatty acids, palmitate (16:0) decreased during normal development, whereas stearate (18:0) increased. The total mass of phospholipid/photoreceptor cell in the normal, adult mouse retina was estimated to be approximately 14 pg. The total phospholipid content and mole % distribution of individual phospholipid classes in immature rd photoreceptors were similar to values for normal cells. In contrast, significant changes in fatty acid composition were detected between immature rd cells and normal cells. Rd cells generally had higher levels of saturated (myristate, 14:0; palmitate, 16:0) and monounsaturated fatty acids (oleate, 18:1) and lower levels of polyunsaturated fatty acids (arachidonate, 20:4; docosahexaenoate, 22:6), suggesting that fatty acid metabolism is altered by expression of the rd gene and/or by the associated impairment of photoreceptor cell differentiation.