alpha -MSH and its receptors in regulation of tumor necrosis factor-alpha production by human monocyte/macrophages

Departments of 1 Physiology and 5 Anesthesiology and Pain Management, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75235-9040; 2 Astra Hassle, 431 83 Molndal, Sweden; 3 Department of Surgery, University of Michigan Medical Center, Ann Arbor, Michigan 48109-0682; and 4 Third Division of Internal Medicine, IRCCS Ospedale Maggiore, Milan, Italy 20122 The hypothesis that macrophages contain an autocrine circuit based on melanocortin [ACTH and -melanocyte-stimulating hormone ( -MSH)] peptides has major implications for neuroimmunomodulation research and inflammation therapy. To test this hypothesis, cells of the THP-1 human monocyte/macrophage line were stimulated with lipopolysaccharide (LPS) in the presence and absence of -MSH. The inflammatory cytokine tumor necrosis factor (TNF)- was inhibited in relation to -MSH concentration. Similar inhibitory effects on TNF- were observed with ACTH peptides that contain the -MSH amino acid sequence and act on melanocortin receptors. Nuclease protection assays indicated that expression of the human melanocortin-1 receptor subtype (hMC-1R) occurs in THP-1 cells; Southern blots of RT-PCR product revealed that additional subtypes, hMC-3R and hMC-5R, also occur. Incubation of resting macrophages with antibody to hMC-1R increased TNF- concentration; the antibody also markedly reduced the inhibitory influence of -MSH on TNF- in macrophages treated with LPS. These results in cells known to produce -MSH at rest and to increase secretion of the peptide when challenged are consistent with an endogenous regulatory circuit based on melanocortin peptides and their receptors. Targeting of this neuroimmunomodulatory circuit in inflammatory diseases in which myelomonocytic cells are prominent should be beneficial. melanocortin peptides; melanocortin receptors; inflammation; autocrine regulation; neuroimmunomodulation; THP-1 cells; melanocortin-1 receptor antibody; -melanocyte-stimulating hormone