Activation of melanocortin 4 receptors reduces the inflammatory response and prevents apoptosis induced by lipopolysaccharide and interferon-gamma in astrocytes.
Alpha-MSH exerts an immunomodulatory action in the brain and may play a neuroprotective role acting through melanocortin 4 receptors (MC4Rs). In the present study, we show that MC4Rs are constitutively expressed in astrocytes as determined by immunocytochemistry, RT-PCR, and Western blot analysis. alpha-MSH (5 microm) reduced the nitric oxide production and the expression of inducible nitric oxide synthase (iNOS) induced by bacterial lipopolysaccharide (LPS, 1 microg/ml) plus interferon-gamma (IFN-gamma, 50 ng/ml) in cultured astrocytes after 24 h. alpha-MSH also attenuated the stimulatory effect of LPS/IFN-gamma on prostaglandin E(2) release and cyclooxygenase-2 (COX-2) expression. Treatment with HS024, a selective MC4R antagonist, blocked the antiinflammatory effects of alpha-MSH, suggesting a MC4R-mediated mechanism in the action of this melanocortin. In astrocytes, LPS/IFN-gamma treatment reduced cell viability, increased the number of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-positive cells and activated caspase-3. alpha-MSH prevented these apoptotic events, and this cytoprotective effect was abolished by HS024. LPS/IFN-gamma decreased Bcl-2, whereas it increased Bax protein expression in astrocytes, thus increasing the Bax/Bcl-2 ratio. Alpha-MSH produced a shift in Bax/Bcl-2 ratio toward astrocyte survival because it increased Bcl-2 expression and also prevented the effect of LPS/IFN-gamma on Bax and Bcl-2 expression. In summary, these findings suggest that alpha-MSH, through MC4R activation, attenuates LPS/IFN-gamma-induced inflammation by decreasing iNOS and COX-2 expression and prevents LPS/IFN-gamma-induced apoptosis of astrocytes by modulating the expression of proteins of the Bcl-2 family.
Caruso
Carla
C
Centro de Investigaciones en Reproducción, School of Medicine, University of Buenos Aires, Buenos Aires 1121ABG, Argentina.
Durand
Daniela
D
Schiöth
Helgi B
HB
Rey
Rodolfo
R
Seilicovich
Adriana
A
Lasaga
Mercedes
M
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D002470:Cell Survival / Q000187:drug effects; D052246:Cyclooxygenase 2 Inhibitors / Q000494:pharmacology; D007249:Inflammation / Q000517:prevention & control*; D007371:Interferon-gamma / Q000494:pharmacology*; D008070:Lipopolysaccharides / Q000494:pharmacology*; D009569:Nitric Oxide / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D052247:Nitric Oxide Synthase Type II / Q000037:antagonists & inhibitors; D010456:Peptides, Cyclic / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D044105:Receptor, Melanocortin, Type 4 / Q000378:metabolism*; D000521:alpha-MSH / Q000494:pharmacology; D051028:bcl-2-Associated X Protein / Q000037:antagonists & inhibitors
D052246:Cyclooxygenase 2 Inhibitors; C116098:HS 024; D008070:Lipopolysaccharides; D010456:Peptides, Cyclic; D019253:Proto-Oncogene Proteins c-bcl-2; D044105:Receptor, Melanocortin, Type 4; D051028:bcl-2-Associated X Protein; D009569:Nitric Oxide; D000521:alpha-MSH; D007371:Interferon-gamma; D052247:Nitric Oxide Synthase Type II