Cellular prion and its catabolites in the brain: production and function.

: During the last thirty years, part of the scientific community focused on the mechanisms by which a naturally occurring protein called cellular prion (PrP(c)) converts into a protease-resistant isoform (PrP(sc)) responsible for fatal Transmissible Spongiform Encephalopathies (TSE). Concomitantly, the physiology of PrP(c) has also been studied. PrP(c) undergoes proteolytic attacks leading to both membrane-attached and secreted fragments, the nature of which differs in normal and TSE-affected human brains. Does proteolysis of PrP(c) correspond to an inactivating mechanism impairing the biological function of the protein, or alternatively, does it represent a maturation process allowing the produced fragments to trigger their own physiological function? Here we review the mechanisms involved in the production of PrP(c) catabolites and we focus on the function of PrP(c) and its derived fragments in the cell death/ survival regulation in the nervous system.