Prion protein N1 cleavage peptides stimulate microglial interaction with surrounding cells.

Microglia act as the protective immune cell of the brain. By surveying the tissue to identify and rectify problems, they function to maintain the health of brain cells. The prion protein N-terminal cleavage fragment, N1, has demonstrated neuroprotective activities in vitro and in vivo. This study aimed to elucidate whether N1 could modulate microglial function and, if so, determine the consequences for the surrounding tissue. Using a mixed neuronal lineage and microglia co-culture system, we showed that N1 stimulation changed overall morphology and metabolism, suggesting enhanced cellular viability. Furthermore, N1 induced an increase in Cxcl10 secretion in the co-cultures. Recombinant Cxcl10, administered exogenously, mediated the changes in the mixed neuronal lineage culture morphology and metabolism in the absence of microglia, but no effect of Cxcl10 was observed on microglia cultured on their own. Direct cell-to-cell contact was required for N1 to influence microglia in the co-cultures, and this was linked with restructuring of microglial membrane composition to include a higher GM1 content at interaction sites with surrounding cells. Our findings show that N1 can play a regulatory role in microglial function in the context of an inter-connected network of cells by changing both cellular interaction sites and cytokine secretion.

MEK1 transduces the prion protein N2 fragment antioxidant effects.

The prion protein (PrP(C)) when mis-folded is causally linked with a group of fatal neurodegenerative diseases called transmissible spongiform encephalopathies or prion diseases. PrP(C) normal function is still incompletely defined with such investigations complicated by PrP(C) post-translational modifications, such as internal cleavage, which feasibly could change, activate, or deactivate the function of this protein. Oxidative stress induces ß-cleavage and the N-terminal product of this cleavage event, N2, demonstrates a cellular protective response against oxidative stress. The mechanisms by which N2 mediates cellular antioxidant protection were investigated within an in vitro cell model. N2 protection was regulated by copper binding to the octarepeat domain, directing the route of internalisation, which stimulated MEK1 signalling. Precise membrane interactions of N2, determined by copper saturation, and involving both the copper-co-ordinating octarepeat region and the structure conferred upon the N-terminal polybasic region by the proline motif, were essential for the correct engagement of this pathway. The phenomenon of PrP(C) post-translational modification, such as cleavage and copper co-ordination, as a molecular "switch" for activation or deactivation of certain functions provides new insight into the apparent multi-functionality of PrP(C).

Regulation of prion protein expression: a potential site for therapeutic intervention in the transmissible spongiform encephalopathies.

The Transmissible Spongiform Encephalopathies (TSEs) are a group of rare neurodegenerative diseases, which can be transmitted between members of the same species and possibly across different species. The link between the emergence of Bovine Spongiform Encephalopathy (BSE) and the new variant form of Creutzfedlt Jakob Disease (vCJD) has been the cause of much public concern. vCJD is the most widely known of the human TSEs but by no means the most common; inherited and sporadic forms are much more prevalent. The agent responsible for these diseases is a conformationally altered form of a normal cell surface glycoprotein, called the prion protein (PrP). The normal isoform must be present for the disease to progress, and disease incubation time decreases with increased PrP expression. There is still no cure for any of these diseases but recent advances in the understanding of how prion protein expression is regulated at the genetic level, and of exogenous factors modulating expression levels, may provide new insights into potential therapeutic targets for disease management by down regulation of cellular PrP levels.