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.

Nyckelord

Animals

Apoptosis/*drug effects

Astrocytes/drug effects/metabolism/*physiology

Cell Survival/drug effects

Cyclooxygenase 2 Inhibitors/pharmacology

Inflammation/*prevention & control

Interferon Type II/*pharmacology

Lipopolysaccharides/*pharmacology

Nitric Oxide/antagonists & inhibitors/biosynthesis

Nitric Oxide Synthase Type II/antagonists & inhibitors

Peptides; Cyclic/pharmacology

Proto-Oncogene Proteins c-bcl-2/metabolism

Rats

Rats; Wistar

Receptor; Melanocortin; Type 4/*metabolism

alpha-MSH/pharmacology

bcl-2-Associated X Protein/antagonists & inhibitors

MEDICINE

MEDICIN

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