Evidence of autocrine modulation of macrophage nitric oxide synthase by alpha-melanocyte-stimulating hormone.

Abstract

a-Melanocyte-stimulating hormone (a-MSH) is a potent inhibitory agent in all major forms of inflammation. To identify a potential mechanism of antiinflammatory action of a-MSH, we tested its effects on production of nitric oxide (NO), believed to be a mediator common to all forms of inflammation. We measured NO and a-MSH production in RAW 264.7 cultured murine macrophages stimulated with bacterial lipopolysaccharide and interferon Y.a-MSH inhibited production of NO, as estimated from nitrite production and nitration of endogenous macrophage proteins. This occurred through inhibition of production of NO synthase II protein; steady-state NO synthase II mRNA abundance was also reduced. a-MSH increased cAMP accumulation in RAW cells, characteristic of a-MSH receptors in other cell types. RAW cells also expressed mRNA for the primary c-MSH receptor (melanocortin 1). mRNA for proopiomelanocortin, the precursor molecule of a-MSH, was expressed in RAW cells, and tumor necrosis factor a increased production and release of cv-MSH. These results suggest that the proinflammatory cytokine tumor necrosis factor a can induce macrophages to increase production of c-MSH, which then becomes available to act upon melanocortin receptors on the same cells. Such stimulation of melanocortin receptors could modulate inflammation by inhibiting the production of NO. The results suggest that a-MSH is an autocrine factor in macrophages which modulates inflammation by counteracting the effects of proinflammatory cytokines.The neuropeptide a-melanocyte-stimulating hormone (a-MSH), a derivative of proopiomelanocortin (POMC), found in the pituitary, brain, skin, circulation, and other sites, has potent antiinflammatory activity. a-MSH reduces fever (1, 2) and the following: (i) acute inflammation caused by irritants or by local mediators, such as cytokines (3, 4); (ii) delayed hypersensitivity responses, a model of allergic reactions (5, 6); (iii) chronic inflammation (mycobacterium-induced arthritis) (7,8); and (iv) systemic inflammation (e.g., endotoxemia and sepsis) (8, 9). Although a-MSH antagonizes the actions of proinflammatory cytokines (1, 2, 4, 9, 10), the precise mechanism of its antiinflammatory action is unknown. a-MSH was recently identified in synovial fluid of patients with rheumatoid arthritis (11). Thus, a-MSH is produced at sites of inflammation, although the cell type(s) responsible is unknown.a-MSH functions via melanocortin (MC) receptors (12-18). There are five subtypes of MC receptors (MC-1 through MC-5). These receptors contain seven membrane-spanning domains typical of G-protein-coupled receptors, and are coupled to adenylate cyclase to generate cAMP. MC receptors are differentially expressed in a restricted distribution, with MC-1 identified in melanoma cells and melanocytes but not in brain, adrenal, or other tissues by mRNA blotting (12, 13).That a-MSH has a wide spectrum of antiinflammatory activity suggests that the peptide inhibits a critical agent or event that is common to multiple forms of inflammatio...

Tissue distribution and differential expression of melanocortin 1 receptor, a malignant melanoma marker

“…One consequence of this could be that MC1R also could be expressed on haematopoietic cells. Indeed, stimulated monocytes and macrophage lines were shown to express MC1R (Star et al, 1995;Bhardwaj et al, 1997). Our data indicated that while MC1R is not expressed at detectable levels on fresh monocytes, in vitro stimulation with several cytokines such as IL-4, GM-CSF, and IL-10 can induce a strong expression of this receptor (Figures 4 and 5A,B).…”

“…Alpha-melanocyte stimulating hormone (a-MSH) is a tridecapeptide derived from the precursor molecule propiomelanocortin (POMC) (Eberle, 1988) and is primarily released by the pituitary, but also by immunocompetent cells (Schauer et al, 1994;Farooqui et al, 1995;Star et al, 1995). a-MSH is a very potent stimulator of the pigmentation and differentiation of pigmented cells, including melanoma cells (Schwahn et al, 2001).…”

A window on the genetics of evolution:MC1Rand plumage colouration in birds

“…In mammals, there have been several studies investigating a possible role of MC1R in the immune system. MC1R is expressed in many leucocytes (Catania et al 1996;Neumann et al 2001) and the melanocortin peptide a-MSH, which is an MC1R agonist, has well-established anti-inflammatory effects (Star et al 1995). However, no evidence of immune dysfunction has been reported in mice or humans which lack functional MC1R.…”

α-MSH Modulates Local and Circulating Tumor Necrosis Factor-α in Experimental Brain Inflammation

“…To test the idea that the primary ␣-MSH receptor MC-1, recently found in murine macrophages and in human macrophages and neutrophils (Star et al, 1995;Rajora et al, 1996;Catania et al, 1996), likewise occurs in brain tissue, normal mouse brain was subjected to RT-PCR and Southern analysis. This analysis revealed a substantial signal at 529 bp, consistent with the size of the cDNA for the murine MC-1 receptor (Fig.…”