MC4R activation induces BDNF expression through ERK and PI3K in rat astrocytes

CARUSO C; CARNIGLIA L; DURAND D; LASAGA M

Berlin

Congreso; XI European Meeting on Glial Cells in Health and Disease; 2013

Melanocortin 4 receptor (MC4R) is predominantly expressed in the brain and it is the only MCR expressed in astrocytes. Our previous results showed that a-melanocyte-stimulating hormone (a-MSH) the anti-inflammatory action is mediated by MC4R in astrocytes and in the hypothalamus of male rats and that these effects may lead to neuroprotection. We have already demonstrated that NDP-MSH (an a-MSH analogue) increased brain-derived neurotrophic factor (BDNF) expression through the cAMP-PKA-CREB pathway in astrocytes. In the present study we examined the participation of mitogen activated protein kinases (MAPK) and phosphatidylinosotol-3 kinase (PI3K)-Akt pathways in MC4R signaling in astrocytes. We also investigated the effect of a-MSH on BDNF expression in vivo in brains of male rats.We preincubated cultured rat primary astrocytes with MAPK (p38, JNK and ERK) and PI3K-PDK1-Akt inhibitors 15 min before addition of 1 mM NDP-MSH for 1 h. We found that NDP-MSH-stimulating effect on BDNF expression assayed by qRT-PCR was abolished only in the presence of ERK and PI3K inhibitors. Accordingly, levels of phospho-ERK1/2 determined by western blot were increased by NDP-MSH whereas phospho-Akt levels were not modified at 30 min. NDP-MSH-induced ERK1/2 activation was decreased by adenylate cyclase and PI3K inhibitors but not by a PKA inhibitor, suggesting a cAMP and PI3K involvement in this effect. We also investigated if a-MSH was able to induced BDNF expression in vivo. For that purpose we injected male rats with a-MSH (0.5 mg/kg, ip) or vehicle (saline) once and sacrificed them after 3 h. Rats were also injected twice daily and for two days and killed 48 h after the first injection. We observed that BDNF mRNA levels increased after a-MSH treatment at 3h in the hypothalamus whereas in the cortex BDNF expression was not modified. At 48 h BDNF expression was not modified by a-MSH. We showed by immunohistochemistry that MC4R and BDNF co-localizes with neurons and astrocytes in the brain. Since melanocortins have anti-inflammatory and neuroprotective effects in the brain, the mechanisms described in astroglia help understand MC4R action. Our results indicate that melanocortins induce BDNF expression in astrocytes through ERK and PI3K, suggesting that this effect could be involved in the neuroprotective actions of melanocortins. The fact that BDNF expression also increases in vivo in the hypothalamus reinforce this idea.