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 addressed the identification of molecular determinants of the neuronal death induced by PrPSc or related peptides. We developed an experimental model to assess PrPSc neurotoxicity using a recombinant polypeptide encompassing amino acids 90-231 of human PrP (hPrP90-231) that corresponds to the protease-resistant core of PrPSc identified in prion-infected brains. By means of mild thermal denaturation, we can convert hPrP90-231 from a PrPC-like conformation into a PrPSc-like structure. In virtue of these structural changes, hPrP90-231 powerfully affected the survival of SH-SY5Y cells, inducing caspase 3 and p38-dependent apoptosis, while in the native alpha-helix-rich conformation, hPrP90-231 did not induce cell toxicity. The aim of this study was to identify drugs able to block hPrP90-231 neurotoxic effects, focusing on minocycline, a tetracycline with known neuroprotective activity. hPrP90-231 caused a caspase 3-dependent apoptosis via the blockade of ERK1/2 activation and the subsequent activation of p38 MAP kinase. We propose that hPrP90-231-induced apoptosis is dependent on the inhibition of ERK1/2 responsiveness to neurotrophic factors, removing a tonic inhibition of p38 activity and resulting in caspase 3 activation. Minocycline prevented hPrP90-231-induced toxicity interfering with this mechanism: the pretreatment with this tetracycline restored ERK1/2 activity and reverted p38 and caspase 3 activities. The effects of minocycline were not mediated by the prevention of hPrP90-231 structural changes or cell internalization (differently from Congo Red). In conclusion, minocycline elicits anti-apoptotic effects against the neurotoxic activity of hPrP90-231 and these effects are mediated by opposite modulation of ERK1/2 and p38 MAP kinase activities.