Peroxisomal multifunctional protein 2 deficiency perturbs lipid homeostasis in the retina causing visual dysfunction in mice

Patients lacking multifunctional protein 2, the central enzyme of the peroxisomal β-oxidation pathway, develop retinopathy. This metabolic pathway is involved in the metabolism of very long chain (VLCFAs) and polyunsaturated (PUFAs) fatty acids, which are enriched in the photoreceptor outer segments (POS). The molecular mechanisms underlying the retinopathy remain however elusive. Here, we report that Mfp2-/- mice display decreased retinal function already at the age of 3 weeks, which is accompanied by a profound shortening of the photoreceptor outer and inner segments, but with preserved photoreceptor ultrastructure. Furthermore, Mfp2-/- retinas exhibit severe changes in gene expression with downregulation of genes involved in the phototransduction pathway and upregulation of inflammation related genes. Lipid profiling of the retina of Mpf2-/- mice revealed a profound reduction of DHA-containing phospholipids. This was likely due to a hampered systemic supply and retinal traffic of this PUFA, although we cannot exclude that the local defect of peroxisomal β-oxidation contributes to this DHA decrease. Moreover, VLC-PUFAs were also reduced, except those containing ≥34 carbons that accumulated. The latter suggests that there is an uncontrollable elongation of retinal PUFAs. In conclusion, we showed that intact peroxisomal β-oxidation is indispensable for retinal integrity, most likely by maintaining PUFA homeostasis. RNA sequencing of neural retinas 3-weeks-old control and Mfp2-/- mice