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Insulin-like growth factor-1 (IGF-1) is one of the most important components of bovine colostrum. It exhibits antiapoptotic and antioxidative activities. Prion diseases are neurodegenerative disorders caused by cell death through mitochondrial dysfunction and increasing generation of reactive oxygen species (ROS). This study examined the protective effect of IGF-1 on residues 106-126 of the cellular prion protein [PrP (106-126)]-mediated mitochondrial neurotoxicity and oxidative stress. In SH-SY5Y human neuronal cells, treatment with PrP (106-126) decreased the cell viability and IGF-1 pretreatment markedly blocked the PrP (106-126)-induced neuronal cell death. IGF-1 inhibited PrP (106-126)-induced intracellular ROS generation and mitochondrial oxidative stress. In addition, IGF-1 blocked the translocation of the Bax protein to the mitochondria induced by PrP (106-126). These results demonstrate that IGF-1 protects neuronal cells against PrP (106-126)-mediated neurotoxicity through an antioxidative effect and blockage of mitochondrial Bax translocation. The results also suggest that regulation of IGF-1 secretion may have a therapeutic potential in the management of mitochondrial dysfunction and oxidative stress-induced neurodegeneration.

Microtubule affinity-regulating kinase 4 (MARK4) belongs to a family of kinases that are able to actively phosphorylate the neuronal microtubule-associate proteins (MAPs), such as tau, MAP2 and the ubiquitous MAP4. Abnormal changes in tubulin and the profiles of tau have been previously reported in the human brain and animal transmissible spongiform encephalopathies (TSEs), which may be associated with abnormal alterations of various cellular kinases. To elucidate the possible role of MARK4 in TSE pathogenesis, the MARK4 levels in the brain tissues of scrapie-infected rodents and human prion diseases were evaluated using western blotting and immunohistochemical assays. The results revealed that at terminal stages of the diseases, MARK4 levels in the brain tissues of the scrapie 263K-infected hamsters, 139A-infected mice and a case of Creutzfeldt-Jakob disease (CJD, G114V gCJD) correlated with amounts of PrP(Sc) deposits that were almost undetectable. On the other hand MARK4 signals were noticeable in the brain tissues of a fatal familial insomnia (FFI) patient without PrP(Sc). The reduction of MARK4 was closely related to the prolonged incubation times. These results could be reproduced in SK-N-SH and PC12 cell lines after being exposed to the synthetic peptide PrP106-126. Accordingly, the levels of phosphorylated tau at Ser262 (p-tau262) in cultured cells exposed to PrP106-126, or the ratios of p-tau262/total tau in the brain tissues of 263K-infected hamsters were also significantly decreased. According to our data there is a correlation between a TSE pathological-associated decline of MARK4 in the brain tissues with the deposits of PrP(Sc). Reduction of MARK4 will result in abnormalities of tau phosphorylation, and possibly induce further detachment of microtubules and hinder microtubule transportation.

Prions are the causative agents of transmissible spongiform encephalopathies, such as variant Creutzfeldt-Jakob disease in humans. Cellular prion proteins (PrPC) connect with cholesterol- and glycosphingolipid-rich lipid rafts through association of their glycosyl-phosphatidylinositol (GPI) anchor with saturated raft lipids and interaction of their N-terminal regions. Our previous study showed that cellular cholesterol enrichment prevented PrP(106-126)-induced neuronal death. We have now studied the influence of membrane cholesterol in PrP(106-126)-mediated neurotoxicity and identified membrane domains involved in this activity. We found that PrPC is normally distributed in lipid rafts, but high membrane cholesterol levels as a result of cholesterol treatment led to the translocation of PrPC from lipid rafts to non-lipid rafts. Moreover, cholesterol-mediated PrPC translocation protects PrP(106-126)-mediated apoptosis and p-38 activation and caspase-3 activation. In a mitochondrial functional assay including mitochondrial transmembrane potential, cholesterol treatment prevented the loss of mitochondrial potential, translocation of Bax and cytochrome c by prion protein fragment. Our results indicate that modulation of the PrPC location appears to protect against neuronal cell death caused by prion peptides. The results of this study suggest that regulation of membrane cholesterol affects the translocation of PrPC, which in turn regulates PrP(106-126)-induced mitochondrial dysfunction and neurotoxicity.

Bee venom phospholipase A2 (bvPLA2) is a prototypic group III enzyme which consists of unique N-terminal and C-terminal domains and a central secretory PLA2 (sPLA2) domain. This sPLA2 domain is highly homologous with human group III sPLA2. Current evidence suggests that group III sPLA2 may affect some neuronal functions, such as neuritogenesis, neurotransmitter release and neuronal survival. The prion diseases are neurodegenerative disorders characterized by the conversion of the normal cellular prion (PrPC) to the misfolded isoform scrapie prion protein (PrPSc). PrPSc accumulation in the central nervous system (CNS) leads to neurotoxicity by inhibition of the PI3K/AKT pathway or activation of p38 mitogen-activated protein kinase (MAPK) pathways. In the present study, we found that bvPLA2 inhibited prion protein (PrP) fragment (106-126)-induced neuronal cell death. PrP(106-126)-mediated increase of p-p38 MAPK and cleaved caspases and decrease of p-AKT were blocked by bvPLA2 treatment. These results indicate that increasing PLA2, including the group III sPLA2 is key to regulating PrP(106-126)-mediated neurotoxicity. Taken together, the results of this study suggest that specific modulation of PLA2 appears to prevent neuronal cell death caused by prion peptides.

Prion diseases are infectious neurodegenerative disorders characterized by the conversion of the cellular prion protein (PrPc) to the misfolded isoform (PrPsc). Prion peptide PrP 106-126 [PrP (106-126)] shares many physiological properties with PrPsc; it is neurotoxic in vitro and in vivo. PrP (106-126) induces neurotoxicity by the overexpression of PrPc and activation of the mitogen-activated protein (ERK1/2). Aspirin, an anti-inflammatory drug, is a known ERK inhibitor and prevents neurodegenerative disorders including prion diseases. The influence of aspirin treatment on prion protein-mediated neurotoxicity and expression of PrPc were the focus of this study. Cell viability and apoptosis were assessed by crystal violet staining and the TUNEL and DNA fragmentation assays. Apoptosis-associated protein expression of PrPc, p-53, p-ERK1/2, p-p38, Bcl-2 and cleaved-caspase-3 was examined by Western blotting and immunocytochemistry. Aspirin treatment inhibited PrP (106-126)-induced neuronal cell death in SH-SY5Y neuroblastoma cells. In addition, the PrP (106-126)-mediated increase of p-p38, p53, cleaved-caspase-3 and decrease of Bcl-2 expressions were blocked by aspirin and the ERK inhibitor, PR98059. Furthermore, we showed that the PrP (106-126)-mediated increase of PrPc and p-ERK1/2 were inhibited by PD98059 and aspirin. Taken together, these results demonstrate that ERK1/2 is a key modulator of the protective effect of aspirin on PrP-106-126-mediated cellular prion protein overexpression and neurotoxicity and also suggest that aspirin may prevent neuron cell damages caused by the prion peptide.