Dual Modulation of ERK1/2 and p38 MAP Kinase Activities Induced by Minocycline Reverses the Neurotoxic Effects of the Prion Protein Fragment 90-231

Several in vitro and in vivo studies addressedthe identification of molecular determinants of the neuronaldeath induced by PrPSc or related peptides. We developedan experimental model to assess PrPSc neurotoxicity usinga recombinant polypeptide encompassing amino acids90–231 of human PrP (hPrP90–231) that corresponds to theprotease-resistant core of PrPSc identified in prion-infectedbrains. By means of mild thermal denaturation, we canconvert hPrP90–231 from a PrPC-like conformation into aPrPSc-like structure. In virtue of these structural changes,hPrP90–231 powerfully affected the survival of SH-SY5Ycells, inducing caspase 3 and p38-dependent apoptosis,while in the native a-helix-rich conformation, hPrP90–231did not induce cell toxicity. The aim of this study was toidentify drugs able to block hPrP90–231 neurotoxic effects,focusing on minocycline, a tetracycline with knownneuroprotective activity. hPrP90–231 caused a caspase3-dependent apoptosis via the blockade of ERK1/2 activationand the subsequent activation of p38 MAP kinase. We propose that hPrP90–231-induced apoptosis is dependenton the inhibition of ERK1/2 responsiveness toneurotrophic factors, removing a tonic inhibition of p38activity and resulting in caspase 3 activation. Minocyclineprevented hPrP90–231-induced toxicity interfering withthis mechanism: the pretreatment with this tetracyclinerestored ERK1/2 activity and reverted p38 and caspase 3activities. The effects of minocycline were not mediatedby the prevention of hPrP90–231 structural changes or cellinternalization (differently from Congo Red). In conclusion,minocycline elicits anti-apoptotic effects against theneurotoxic activity of hPrP90–231 and these effects aremediated by opposite modulation of ERK1/2 and p38 MAPkinase activities.[...]