Brain natriuretic peptide gene expression and secretion following stimulation with pro-inflammatory cytokines and conditioned medium from allo-activated mixed lymphocyte reactions
Creators: name: Ma, Kenneth Ka-Yout
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 2004
Subjects: subject: Biology, Neuroscience.
subject: Health Sciences, Medicine and Surgery.

description: Atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP) are cardiac-derived polypeptide hormones secreted by the heart. ANF and BNP play critical roles in maintaining fluid and electrolyte balance in both health and disease. Mechanisms of increasing ANF and BNP gene expression and secretion by mechanical or by vasoactive agonists have been thoroughly examined. However, recent experiments suggest that pro-inflammatory cytokines may also be important regulators of natriuretic peptide secretion. In this study, neonatal rat ventricular cardiocyte cultures were used to examine the effects of pro-inflammatory cytokines on natriuretic peptide gene expression and secretion. Incubation with IL-1beta or TNF-alpha elicited a dose and time dependent significant increase in BNP mRNA and secretion, whereas ANF mRNA and secretion was not affected by treatment. The increase in BNP mRNA was inhibited by pre-incubation with a transcriptional inhibitor, actinomycin D. Moreover, the IL-1beta and TNF-alpha mediated increase was not affected by pre-incubation with cycloheximide, suggesting that a translation-dependent increase in BNP mRNA stability was not involved in increasing BNP mRNA abundance. IL-1beta and TNF-alpha rapidly increased phosphorylated p38 MAP kinase and MAP kinase activity. Inhibition of p38 MAP kinase with SB203580 completely abolished IL-1beta and TNF-alpha stimulated BNP promoter activity, mRNA abundance and peptide secretion. NF-kappaB is another signaling molecule activated by IL-1beta and TNF-alpha, however, results from experiments using a peptide inhibitor to NF-kappaB signaling suggest that NF-kappaB is not important in transducing the IL-1beta and TNF-alpha-mediated increase in BNP secretion. Other pro-inflammatory and immunoregulatory cytokines like IL-6, IL-2 and IFN-gamma did not alter either BNP or ANF secretion but co-treatment with both IL-1beta and IFN-gamma maximally stimulated BNP secretion, suggesting cooperation between IL-1beta and IFN-gamma signaling. Conditioned medium from an allogenic mixed lymphocyte reaction (MLR) was used in order to circumvent the omission of individual cytokines or their combination. Serum-free MLR conditioned medium (SF-MLR-CM) in 20, 50 and 100% proportions increased BNP but not ANF secretion with respect to the basal serum-free lymphocyte medium controls. Although, this increase was sensitive to p38 MAP kinase inhibition, it appears that IL-1beta and TNF-alpha are not major active constituents in the SF-MLR-CM as neither ELISA nor soluble receptor antagonists to IL-1beta or TNF-alpha revealed the presence of these pro-inflammatory cytokines. In summary, our novel findings reveal a unique discoordinated expression of BNP and ANF induced by pro-inflammatory cytokines. Importantly it offers an opportunity to better understand the differential regulation of these two cardiac-derived endocrine hormones that share receptors as well as biological properties.