The neuropeptide calcitonin gene-related peptide inhibits TNF-alpha but poorly induces IL-6 production by fetal rat osteoblasts.
Tumour necrosis factor alpha (TNF-alpha) and interleukin 6 (IL-6) are potent inflammatory cytokines produced by osteoblasts and whose contribution to bone loss occurring in oestrogen deficiency is well documented. Calcitonin gene-related peptide (CGRP) is a neuropeptide abundantly concentrated in sensory nerve endings innervating bone metaphyses and periosteum suggesting that it controls bone homeostasis locally. Since CGRP was shown to inhibit TNF-alpha production by T cells and stimulate IL-6 expression by fibroblasts, this study was designed to investigate whether CGRP regulated TNF-alpha and IL-6 production by osteoblasts. We show that CGRP inhibits the production of TNF-alpha by both lipopolysaccharide (LPS)- and IL-1-stimulated fetal rat osteoblasts. Like CGRP, the cAMP agonists prostaglandin E2 (PGE2), dibutyryl cAMP (Bt2cAMP) and forskolin inhibit TNF-alpha production by osteoblasts. Exposure of osteoblasts to a high dose of phorbol myristoyl acetate (PMA) to deplete PKC activity abolished CGRP-mediated TNF-alpha suppression. In contrast with its potent inhibition of TNF-alpha production, we show that CGRP is a weak inducer of IL-6 when compared to PGE2, Bt2cAMP and forskolin. However, in presence of isobutylmethylxanthine (IBMX) CGRP stimulates the production of IL-6. Collectively, these data suggest that the inhibition of TNF-alpha CGRP is cAMP dependent and PMA sensitive and that the concentration of intracellular cAMP may be a regulatory mechanism for IL-6 expression in osteoblasts.
Millet
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Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06510, USA.
Vignery
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D000818:Animals; D001681:Biological Assay; D015740:Calcitonin Gene-Related Peptide / Q000494:pharmacology*; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D005333:Fetus; D005354:Fibrosarcoma; D005786:Gene Expression Regulation / Q000187:drug effects*; D015850:Interleukin-6 / Q000032:analysis / Q000096:biosynthesis*; D007700:Kinetics; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D014158:Transcription, Genetic / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000032:analysis / Q000096:biosynthesis*
D015850:Interleukin-6; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D015740:Calcitonin Gene-Related Peptide