Neuroendocrine cultured cells counteract persistent prion infection by down-regulation of PrPc

Unfolded Protein Response and Macroautophagy in Alzheimer's, Parkinson's and Prion Diseases

Proteostasis are integrated biological pathways within cells that control synthesis, folding, trafficking and degradation of proteins. The absence of cell division makes brain proteostasis susceptible to age-related changes and neurodegeneration. Two key processes involved in sustaining normal brain proteostasis are the unfolded protein response and autophagy. Alzheimer’s disease (AD), Parkinson’s disease (PD) and prion diseases (PrDs) have different clinical manifestations of neurodegeneration, however, all share an accumulation of misfolded pathological proteins associated with perturbations in unfolded protein response and macroautophagy. While both the unfolded protein response and macroautophagy play an important role in the prevention and attenuation of AD and PD progression, only macroautophagy seems to play an important role in the development of PrDs. Macroautophagy and unfolded protein response can be modulated by pharmacological interventions. However, further research is necessary to better understand the regulatory pathways of both processes in health and neurodegeneration to be able to develop new therapeutic interventions.

Prion disease tempo determined by host-dependent substrate reduction

The symptoms of prion infection can take years or decades to manifest following the initial exposure. Molecular markers of prion disease include accumulation of the misfolded prion protein (PrPSc), which is derived from its cellular precursor (PrPC), as well as downregulation of the PrP-like Shadoo (Sho) glycoprotein. Given the overlapping cellular environments for PrPC and Sho, we inferred that PrPC levels might also be altered as part of a host response during prion infection. Using rodent models, we found that, in addition to changes in PrPC glycosylation and proteolytic processing, net reductions in PrPC occur in a wide range of prion diseases, including sheep scrapie, human Creutzfeldt-Jakob disease, and cervid chronic wasting disease. The reduction in PrPC results in decreased prion replication, as measured by the protein misfolding cyclic amplification technique for generating PrPSc in vitro. While PrPC downregulation is not discernible in animals with unusually short incubation periods and high PrPC expression, slowly evolving prion infections exhibit downregulation of the PrPC substrate required for new PrPSc synthesis and as a receptor for pathogenic signaling. Our data reveal PrPC downregulation as a previously unappreciated element of disease pathogenesis that defines the extensive, presymptomatic period for many prion strains.

New insights into cellular prion protein (PrPc) functions: the "ying and yang" of a relevant protein

The conversion of cellular prion protein (PrP(c)), a GPI-anchored protein, into a protease-K-resistant and infective form (generally termed PrP(sc)) is mainly responsible for Transmissible Spongiform Encephalopathies (TSEs), characterized by neuronal degeneration and progressive loss of basic brain functions. Although PrP(c) is expressed by a wide range of tissues throughout the body, the complete repertoire of its functions has not been fully determined. Recent studies have confirmed its participation in basic physiological processes such as cell proliferation and the regulation of cellular homeostasis. Other studies indicate that PrP(c) interacts with several molecules to activate signaling cascades with a high number of cellular effects. To determine PrP(c) functions, transgenic mouse models have been generated in the last decade. In particular, mice lacking specific domains of the PrP(c) protein have revealed the contribution of these domains to neurodegenerative processes. A dual role of PrP(c) has been shown, since most authors report protective roles for this protein while others describe pro-apoptotic functions. In this review, we summarize new findings on PrP(c) functions, especially those related to neural degeneration and cell signaling.

New inhibitors of prion replication that target the amyloid precursor

At present, there is no effective therapy for any of the neurodegenerative amyloidoses, despite renewed efforts to identify compounds active against the various implicated pathogenetic molecules. We have screened a library of 2960 natural and synthetic compounds in two cell lines chronically infected with mouse prions, and have identified eight new inhibitors of prion replication in vitro. They belong to two distinct chemical families that have not previously been recognised as effective in the field of transmissible spongiform encephalopathies: seven are 3-aminosteroids and one is a derivative of erythromycin A with an oxime functionality. Our results suggest that these aminosteroids inhibit prion replication by triggering a common target, possibly implicated in the regulatory pathways of cellular prion protein metabolism. Furthermore, using a quantitative approach for the study of protein stability, it was shown that the erythromycin A derivative altered prion protein stability by direct interaction. Such direct targeting of this amyloid precursor might provide new clues for the understanding of prion diseases and, more importantly, help to define new molecules that are active against prion diseases.