Retrotransposons transcribed preferentially in proximal tubules of salt-hypertensive rats

The kidney is considered to play an important etiologic role in salt-sensitive hypertension. The aim of the present study was to isolate genes whose expression differs between the kidneys of salt-hypertensive and control rats using an mRNA differential display method.

Dahl salt-sensitive (DS) and control salt-resistant rats (DR) were fed a 0.3% or 8% NaCl diet. Renal RNA was amplified by RNA arbitrarily primed polymerase chain reaction (RAP-PCR) and compared among DR 0.3%, DR 8%, DS 0.3%, and DS 8%. Gene expression and localization were examined by Northern blotting, RNase protection assay, and in situ hybridization. Full-length nucleotide sequence was determined by screening a DS rat kidney cDNA library.

We identified one differentially displayed clone, and its expression was greater in DS than DR, which was not affected by salt loading. The sequence was 90% homologous to the 3'-noncoding region of the nicotinic acetylcholine receptor alpha7 subunit gene. Its expression was kidney-specific, and was localized in the proximal tubules. The transcript level was markedly increased precedent to the development of hypertension. Its expression was also high in other salt-sensitive rats, and low in normotensive Sprague-Dawley and Wistar rats. The full-length cDNA contained elements homologous to the retroviral pol gene, a primer binding site sequence for reverse transcriptase, and long-terminal repeats.

These results demonstrated that the newly identified transcripts (REPT1) belong to a novel retrotransposon family, which showed unique strain-, age-, tissue-, and cell type-specific expression pattern.