Background: The objective of this study was to determine the expression of somatostatin (SST) and its receptors (SSTRs) and their regulation by TNF-alpha as well as cell proliferation in response to SST in human endothelial cells.
Materials and methods: Human coronary artery endothelial cells (HCAECs) were cultured without or with TNF-alpha (0.1, 1, or 10 ng/ml) for 24 h. The mRNA levels of SST, SSTR-1-5, as well as a housekeeping gene (beta-actin) were determined by real-time RT-PCR. Expression of SSTR-2 was also demonstrated by immunofluorescence staining. Cell proliferation in response to SST treatment (0.04, 0.2, or 1 ng/ml) was performed by [3H]thymidine incorporation.
Results: Without TNF-alpha treatment, HCAECs showed mRNA expression of SST, SSTR-1, SSTR-2, and SSTR-5. The mRNA of SSTR-2 was expressed at a higher level than that of SSTR-1 and SSTR-5. However, SSTR-3 and SSTR-4 were not expressed or were minimally expressed. After treatment with TNF-alpha, the mRNA levels of SST, SSTR-1, SSTR-2, and SSTR-5 were significantly reduced in a dose-dependent fashion. TNF-alpha (1 ng/ml) reduced SST, SSTR-1, SSTR-2, and SSTR-5 by 93, 51, 85, and 99%, respectively, compared to controls (P < 0.001, t test). The immunoreactivity of SSTR-2 was also reduced after TNF-alpha treatment. SST-treated cells showed a significant reduction in [3H]thymidine incorporation in a dose-dependent manner. TNF-alpha treatment decreased SST inhibitory potential in cell proliferation.
Conclusions: HCAECs express SST, SSTR-1, SSTR-2, and SSTR-5, which are all decreased by TNF-alpha treatment. Furthermore, treatment with exogenous SST significantly reduces cell proliferation, and this inhibitory effect is also decreased by TNF-alpha.