Lipids are major cell constituents and are present in the membranes, as free lipids in the cytoplasm, or stored in vesicles called lipid droplets (LDs).
Under conditions of stress, lipids stored in LDs can be released to serve as substrates for energy metabolism by mitochondria. However, lipid storage is dysregulated in many degenerative disorders such as age-related macular degeneration, Parkinson’s and Alzheimer’s diseases.

Thus, it is unclear whether accumulation of LDs is protective or toxic for neuronal cells. To address this question, we examined the consequences of removal or enforced LD accumulation on the health of retinal cells in flies and mice. Like humans, fly and mouse retinas contain retinal pigment cells (RPC) that support the functions of neighboring photoreceptor cells.

We found that overexpression of the fatty acid transport protein (FATP) in RPCs induced accumulation of LDs in both transgenic flies and mice.

Moreover, LD accumulation in RPCs was not harmful for juxtaposed photoreceptors during aging, but was toxic under stress conditions. We propose that lipid storage promotes cellular communication that affects photoreceptor health.

Source: Physiological and pathological roles of FATP-mediated lipid droplets in Drosophila and mice retina. Daan M. Van Den Brink , Aurélie Cubizolle , Gilles Chatelain, Nathalie Davoust, Victor Girard, Simone Johansen, Francesco Napoletano, Pierre Dourlen, Laurent Guillou, Claire Angebault-Prouteau, Nathalie Bernoud-Hubac, Michel Guichardant, Philippe Brabet, Bertrand Mollereau. Plos Genetics, Sepember 10th, 2018.

Figure: Schematic of the role of FATP in the metabolism of lipid droplets and communication between RPCs (retinal pigment cells) and photoreceptors under physiological and pathological conditions.