Silencing of murine transthyretin and retinol binding protein genes has distinct and shared behavioral and neuropathologic effects

The murine genes encoding transthyretin (TTR) and retinol binding protein (RBP) were independently silenced by targeted disruption more than 10 years ago. Studies of both strains showed surprisingly little impact on either thyroid function or retinoid metabolism. Silencing TTR led to a relatively mild behavioral phenotype. In order to gain insight into the behavioral effect and determine if it was related to TTR's function as the carrier of RBP we carried out simultaneous studies with homozygous Rbp4−/− and Ttr−/− animals 4–7 months of age. Both strains showed behavioral differences relative to Ttr and Rbp4 wild-type animals and each other. The patterns were discrete for each knockout although there was some overlap. Neuropathologic examination of the cortex and hippocampus revealed cortical and hippocampal (CA3) neuronal loss in both and some degree of gliosis, more pronounced in the Rbp4−/− mice. There also appeared to be a major reduction in proliferating neuroblasts in the subventricular zone in both strains, which was also more severe in the Rbp4−/− mice. This is the first description of behavioral abnormalities in Rbp4−/− mice. The data also indicate that it is unlikely that the behaviors seen in Ttr−/− mice are related to its function as an RBP carrier.