MECHANISMS OF INCREASED NGF PRODUCTION IN VASCULAR SMOOTH-MUSCLE OF THE SPONTANEOUSLY HYPERTENSIVE RAT

The spontaneously hypertensive rat (SHR) was developed as a genetic mo del of essential hypertension. In vivo and in vitro evidence demonstra tes that vascular smooth muscle cells (VSMCs) from the SHR produce mor e nerve growth factor (NGF) than the normotensive Wistar-Kyoto (WKY) c ontrol strain. This increased NGF production is accompanied by excessi ve innervation of target tissues in the SHR. In the present study, a s ensitive, competitive, quantitative, reverse-transcriptase polymerase chain reaction (C Q RT-PCR) assay is characterized and used to analyze levels of NGF mRNA in cultured VSMCs derived from the SWR and WKY str ains as well as bladder tissue. Differences in NGF secretion rates bet ween SHR and WKY VSMCs were partially due to an increased stability of NGF mRNA in SHR VSMCs. Following treatment with platelet-derived grow th factor (PDGF) and transforming growth factor-beta (TGF-beta 1) to e levate NGF production, the half-life of the NGF mRNA was 104.5 +/- 18. 0 min in SHR VSMCs, compared to only 36.5 +/- 11.6 min in WKY VSMCs. S equence analysis of the 3' untranslated region (UTR) revealed no strai n differences in cis-acting sequences potentially involved in determin ing mRNA stability. Thus, it seems unlikely to be a 3'UTR mutation tha t prolongs mRNA lifetime. Rather, differential regulation of an RNA-bi nding protein may play a role in the abnormal NGF mRNA stability in SH R VSMCs. SHR VSMCs also demonstrate an increased translational efficie ncy of NGF protein; more NGF protein is synthesized per unit of NGF mR NA. The use of a C & RT-PCR assay has allowed the determination that a bnormal NGF mRNA stabilization as well as altered translational effici ency may contribute to excess NGF synthesis and progressive hypertensi on in the SHR. (C) 1998 Academic Press.