Rescue Of Retinal Morphology And Function In A Humanized Mouse At The Mouse Retinol-binding Protein Locus

Background and PurposeRetinol-binding protein RBP4 is the specific carrier for retinol in the blood.Rbp4-deficient(Rbp4^-/-)mouse showed electroretinogram?ERG?abnormalities,accompanied by histological and electron-microscopic changes such as fewer synapses in the inner plexiform layer in the central retina.To address whether human RBP4 gene expression can rescue the phenotypes observed in Rbp4^-/-mice,we produced a humanized(Rbp4^{h RBP4orf/h RBP4orf})mouse with a human RBP4 open reading frame in the mouse Rbp4 locus.MethodsUsing homologous recombination and Cre-mutant lox recombination system,we made humanized Rbp4^{h RBP4orf/h RBP4orf}mice.ResultsIn Rbp4^{h RBP4orf/h RBP4orf} mice,the tissue-specific expression pattern of h RBP4orf was roughly the same as that of mouse Rbp4.ERG and morphological abnormalities observed in Rbp4^-/-mice were rescued in Rbp4^{h RBP4orf/h RBP4orf} mice as early as 7 weeks of age.The temporal expression pattern of h RBP4orf in the liver of Rbp4^{h RBP4orf/h RBP4orf}mice was similar to that of mouse Rbp4 in Rbp4^+/+mice.In contrast,h RBP4orf expression levels in eyes were significantly lower at 6 and 12 weeks of age compared to mouse Rbp4 but were restored to the control levels at 24 weeks.The serum h RBP4levels in Rbp4^{h RBP4orf/h RBP4orf} mice were approximately 30%of those in Rbp4^+/+at all ages examined.In accordance with this finding,the plasma retinol levels remained low in Rbp4^{h RBP4orf/h RBP4orf}mice.Retinol accumulation in the liver occurred in control and Rbp4^{h RBP4orf/h RBP4orf} mice but was higher in Rbp4^{h RBP4orf/h RBP4orf} mice at 30 weeks of age.Mouse transthyretin expression was not altered in Rbp4^-/-or Rbp4^{h RBP4orf/h RBP4orf} mice.ConclusionsTaken together,30%of the serum RBP4 level was sufficient to correct the abnormal phenotypes observed in Rbp4^-/-mice.