Fig. 2

Marked difference between retinal expression of CYP4V2 protein in humans and Cyp4v3 protein in mice. (A) CYP4V2 immunohistochemical (IHC) staining in human retina and cornea, and (B) Cyp4v3 IHC staining in wild type (WT) C57BL/6J mouse retina, cornea and liver. Significantly, IHC staining reveals that unlike CYP4V2 protein expression in normal human retina, Cyp4v3 protein-specific positive staining is only observed in wild type mouse corneal epithelium, and is not expressed in any part of the mouse retina. In contrast, human eye showed CYP4V2 protein-specific positive staining in the RPE; cone outer segments; occasional nuclei in the inner and outer nuclear layers, and the corneal epithelium. The markedly different retinal expression profile between mouse and human retina suggests that unlike CYP4V2 protein in human retina, the murine ortholog Cyp4v3 protein does not play a role in the retina of wild type mice. This indicates that the Cyp4v3 knockout mouse (whether fed with normal diet (ND) or high-fat diet (HFD), and regardless of the knockout strategy) is not an appropriate model for BCD, a human retinal disease resulting from a lack of normal retinal CYP4V2 protein expression. GCL = ganglion cell layer; IPL = inner plexiform layer; INL = inner nuclear layer; ONL = outer nuclear layer; PR OS = photoreceptor outer segment; RPE = retinal pigment epithelium; CH = choroid. Brown/black staining is natural melanin, blue is hematoxylin counterstain, and bright pink/red is antibody positivity (CYP4V2 for human, Cyp4v3 for mouse). Magnification of all images at 20X. Cross reactivity of the anti-human CYP4V2 antibody to the mouse ortholog Cyp4v3 is confirmed by positive staining in the livers and corneal epithelium of WT mice