Candidate genes for pathophysiological traits, identified by linkage and correlation analyses with intermediary phenotypes and by their sequencing, are tested by in vivo functional analysis in transgenic rescue or knockout experiments with the aim to identify quantitative trait loci at the molecular level and analyze responsible pathophysiological mechanisms.
For candidate genes with downregulated expression of mRNA or protein or with mutated nonfunctional protein, transgenic rescue experiments can provide such evidence. The SHR harbors a deletion mutation of the Cd36 gene that is associated with clustering of several cardiovascular risk factors, including predispositon to hypertension. The mutated Cd36 protein product is expressed, however, its fatty acid translocase activity is significantly reduced. In addition, renal expression of Cd36 is regulated in cis and genome-wide quatitative trait transcript analysis in the BXH/HXB RI strains performed by searching for correlations between renal expression of cis-acting eQTLs and direct measurements of arterial pressure revealed that Cd36 showed the strongest correlation with diastolic blood pressure. The renal expression of Cd36 correlated inversely with blood pressure and RI strains with the SHR Cd36 allele had significantly higher blood pressure when compared to RI strains with the BN-Lx allele. To investigate whether mutant Cd36 in the kidney might be sufficient to promote increased blood pressure, we carried out renal transplantation experiments using donor kidneys from either the SHR progenitor that lacks wild-type Cd36 or from the SHR transgenic strain with robust renal expression of wild-type Cd36. We found that blood pressure of recipients that received a donor kidney with mutant Cd36 was significantly greater than the blood pressure of recipients that received a “transgenic” kidney expressing wild-type Cd36.
Inflammation has been implicated in the pathogenesis of obesity, metabolic disturbances, diabetes mellitus, and cardiovascular disease. C-reactive protein (CRP) is a well known biomarker of inflammation associated with increased risk for cardiovascular disease and diabetes. Whether or not CRP is a mediator or just a marker of disease pathogenesis remains highly controversial. Therefore we decided to test the effects of transgenic expression of human CRP in the SHR. The expression of the human CRP specifically in the liver was associated with inflammation and oxidative tissue damage, insulin resistance and increased blood pressure. These findings are consistent with the hypothesis that increased CRP is more than just a marker of inflammation and can directly promote multiple features of the metabolic syndrome. This transgenic