Insights into Dahl salt-sensitive hypertension revealed by temporal patterns of renal medullary gene expression

Dahl salt-sensitive SS and consomic, salt-resistant SS-13(BN)/Mcw rats possess a highly similar genetic background but exhibit substantial differences in blood pressure salt sensitivity. We used cDNA microarrays to examine sequential changes of mRNA expression of similar to2,000 currently known rat genes in the renal medulla (a tissue critical for long-term blood pressure regulation) in SS and SS-13(BN)/Mcw rats in response to a high-salt diet (16 h, 3 days, or 2 wk). Differentially expressed genes in each between-group comparison were identified based on a threshold determined experimentally using a reference distribution that was constructed by comparing rats within the same group. A difference analysis of 54 microarrays identified 50 genes that exhibited the most distinct temporal patterns of expression between SS and SS13(BN)/Mcw rats over the entire time course. Thirty of these genes could be linked to the regulation of arterial blood pressure or renal injury based on their known involvement in functional pathways such as renal tubular transport, metabolism of vasoactive substances, extracellular matrix formation, and apoptosis. Importantly, the majority of the 30 genes exhibited temporal expression patterns that would be expected to lower arterial pressure and reduce renal injury in SS-13(BN) /Mcw compared with SS rats. The phenotypic impact of the other 20 genes was less clear. These 50 genes are widely distributed on chromosome 13 and several other chromosomes. This suggested that primary genetic defects, although important, are unlikely to be solely responsible for the full manifestation of this type of hypertension and associated injury phenotypes. In summary, the results of this study identified a number of pathways potentially important for the amelioration of hypertension and renal injury in SS-13(BN)/Mcw rats, and these results generated a series of testable hypotheses related to the role of the renal medulla in the complex mechanism of salt-sensitive hypertension.