Decreased cell surface prion protein in mouse models of prion disease

Copper-dependent regulation of NMDA receptors by cellular prion protein: implications for neurodegenerative disorders

N-Methyl-D-aspartate (NMDA) receptors mediate a wide range of important nervous system functions. Conversely, excessive NMDA receptor activity leads to cytotoxic calcium overload and neuronal damage in a wide variety of CNS disorders. It is well established that NMDA receptors are tightly regulated by a number of cell signalling pathways. Recently, it has been shown that NMDA receptor activity is modulated by cellular prion protein (PrP(C)) in a copper-dependent manner. Here we give an overview of the current state of knowledge concerning the novel concept of potent modulation of this receptor's kinetics by copper ions, and the interplay between NMDA receptors and PrP(C) in the context of neurological diseases such as Alzheimer's disease, epilepsy, pain and depression.

Prion protein attenuates excitotoxicity by inhibiting NMDA receptors

It is well established that misfolded forms of cellular prion protein (PrP [PrP^C]) are crucial in the genesis and progression of transmissible spongiform encephalitis, whereas the function of native PrP^C remains incompletely understood. To determine the physiological role of PrP^C, we examine the neurophysiological properties of hippocampal neurons isolated from PrP-null mice. We show that PrP-null mouse neurons exhibit enhanced and drastically prolonged N-methyl-d-aspartate (NMDA)–evoked currents as a result of a functional upregulation of NMDA receptors (NMDARs) containing NR2D subunits. These effects are phenocopied by RNA interference and are rescued upon the overexpression of exogenous PrP^C. The enhanced NMDAR activity results in an increase in neuronal excitability as well as enhanced glutamate excitotoxicity both in vitro and in vivo. Thus, native PrP^C mediates an important neuroprotective role by virtue of its ability to inhibit NR2D subunits.

Fibrillar prion peptide PrP(106-126) treatment induces Dab1 phosphorylation and impairs APP processing and Abeta production in cortical neurons

Alzheimer's disease and prion diseases (e.g., Creutzfeldt-Jakob disease) display profound neural lesions associated with aberrant protein processing and extracellular amyloid deposits. However, the intracellular events in prion diseases and their relation with the processing of the amyloid precursor protein (APP) and beta-amyloid generation are unknown. The adaptor protein Dab1 may regulate intracellular trafficking and secretase-mediated proteolysis in APP processing. However, a putative relationship between prion diseases and Dab1/APP interactions is lacking. Thus, we examined, in inoculated animals, whether Dab1 and APP processing are targets of the intracellular events triggered by extracellular exposure to PrP(106-126) peptide. Our in vitro results indicate that PrP(106-126) peptide induces tyrosine phosphorylation of Dab1 by activated members of the Src family of tyrosine kinases (SFK), which implies further Dab1 degradation. We also corroborate these results in Dab1 protein levels in prion-inoculated hamsters. Finally, we show that fibrillar prion peptides have a dual effect on APP processing and beta-amyloid production. First, they block APP trafficking at the cell membrane, thus decreasing beta-amyloid production. In parallel, they reduce Dab1 levels, which also alter APP processing. Lastly, neuronal cultures from Dab1-deficient mice showed severe impairment of APP processing with reduced sAPP secretion and A beta production after prion peptide incubation. Taken together, these data indicate a link between intracellular events induced by exposure to extracellular fibrillar peptide or PrP(res), and APP processing and implicate Dab1 in this link.