TNF receptors in Kupffer cells

Abstract

Introduction: Somatostatin is a mediator of immune functions and has been used as an antineoplastic agent in animal models and human neoplasias. We have demonstrated that Octreotide inhibits only LPS induced secretion of proinflammatory cytokines including TNFa by Kupffer cells (KC). We, therefore, tested the hypothesis that somatostatin modulates the expression of tumor necrosis factor alpha (TNFα) receptors and apoptosis of KC.

Methods: Rat KC were isolated by centrifugal elutriation. TNFR1 and TNFR2 expression was studied by RT-PCR, quantitative PCR, Western Blot and immunofluorescence before and after Octreotide pre-incubation. Apoptosis was assessed by quantitative measurement of cytoplasmic histone-associated DNA fragments. TNFa mRNA expression was assessed by semiquantitative PCR and TNFa was measured in cell supernatants by ELISA.

Results: TNFR1 and TNFR2 mRNA are constitutively expressed in KC. Octreotide incubation increased both receptors expression with a peak at 6 h and return to basal levels at 24 h. TNFR1 was mostly influenced. However, only increase in TNFR2 protein was identified, whereas a band at 90 kD was present instead of a band at 55 kD as expected for TNFR1. TNFα mRNA expression was inhibited by Octreotide and a significant inhibition was observed at 48 h. TNF had no effect on KC apoptosis, whereas Octreotide significantly increased their apoptosis, and this effect was not influenced by co-incubation with TNFa.

Conclusion: TNFR1 and TNFR2 are constitutively expressed in KC and their expression is strongly increased by somatostatin. Moreover, somatostatin increases KC apoptosis. These findings may in part explain the antineoplasmatic effect of somatostatin.