No Involvement of the Nerve Growth Factor Gene Locus in Hypertension in Spontaneously Hypertensive Rats

Sympathetic hyper-innervation and increased levels of nerve growth factor (NGF), an essential neurotrophic factor for sympathetic neurons, have been observed in the vascular tissues of spontaneously hypertensive rats (SHRs). Such observations have suggested that the pathogenesis of hypertension might involve a qualitative or quantitative abnormality in the NGF protein, resulting from a significant mutation in the gene's promoter or coding region. In the present study, we analyzed the nucleotide sequences of the cis-element of the NGF gene in SHRs, stroke-prone SHRs (SHRSPs), and normotensive Wistar-Kyoto (WKY) rats. The present analyses revealed some differences in the 3-kb promoter region, coding exon, and 3' untranslated region (3'UTR) for the NGF gene among those strains. However, the observed differences did not lead to changes in promoter activity or to amino acid substitution; nor did they represent a link between the 3'UTR mutation of SHRSPs and elevated blood pressure in an F2 generation produced by crossbreeding SHRSPs with WKY rats. These results suggest that the NGF gene locus is not involved in hypertension in SHR/ SHRSP strains. The present study also revealed two differences between SHRs and WKY rats, as found in cultured vascular smooth muscle cells and in mRNA prepared from each strain. First, SHRs had higher expression levels of c-fos and c-jun genes, which encode the component of the AP-1 transcription factor that activates NGF gene transcription. Second, NGF mRNAs prepared from SHRs had a longer 3'UTR than those prepared from WKY rats. Although it remains to be determined whether these events play a role in the hypertension of SHR/SHRSP strains, the present results emphasize the importance of actively searching for aberrant trans-acting factor(s) leading to the enhanced expression of the NGF gene and NGF protein in SHR/SHRSP strains.