Lysosomes as key organelles in the pathogenesis of prion encephalopathies

Abstract

The causation, structural origin, and mechanism of formation of spongiform lesions in transmissible encephalopathies are unknown. We have used immunogold electron microscopy to locate ubiquitin conjugates, hsp 70, and beta-glucuronidase (markers of the lysosomal compartment) and prion protein (PrP) in both control and scrapie-infected mouse brain. In scrapie-infected brain, lysosomes and lysosome-related structures (multivesicular and tubulovesicular dense bodies) are present in abnormally high numbers in neuronal cell processes. These structures contain PrP, together with the lysosomal markers ubiquitin conjugates, hsp 70, and beta-glucuronidase, which could also be identified spilling from tubulovesicular dense bodies into areas of early rarefaction in neuronal processes; we suggest that these areas of rarefaction are the precursor lesions of spongiform change. We advance the hypothesis that spongiform change is brought about by cytoskeletal disruption in neuronal processes caused by liberation of hydrolytic enzymes from lysosomes overloaded with the abnormal isoform of PrP (PrPsc). We suggest that the lysosomal system is probably acting as the bioreactor for processing of normal PrP to the abnormal isoform. The continuous production of increasing quantities of abnormal PrPsc in lysosome-related bodies will eventually cause disruption of the lysosomal membrane with destruction of the neuronal cytoskeleton and the initiation of vacuolation. Later, death of the cell will be associated with release of the PrPsc isoform into the extracellular environment. Repeated rounds of phagocytosis, lysosomal biogenesis of PrPsc, lysosomal membrane rupture, hydrolytic enzyme release, and neuronal lysis will lead to an exponential increase in cell damage and cell death.(ABSTRACT TRUNCATED AT 250 WORDS)

Uptake and Neuritic Transport of Scrapie Prion Protein Coincident with Infection of Neuronal Cells

“…The fact that much of the m(Ch)PrP-res A568 in Figure 7 occupied the lumen of GFP-Rab7 Q67L-labeled vesicles rather than the surrounding membrane is consistent with this possibility. The lack of raft association of m(Ch)PrP-res A568 is also compatible with a proposal that PrP-res formation occurs outside raft domains (Sanghera and Pinheiro, 2002;Sunyach et al, 2003) as well as observations of the accumulation of endogenous PrP-res in lysosomes (McKinley et al, 1991;Laszlo et al, 1992), a compartment not believed to contain detergent-resistant membranes (Hao et al, 2004). However, it is worth considering also that in vivo, some nonamyloid forms of exogenous PrP-res might be membrane associated in a way that alters its interaction with host cell membranes.…”

“…In the brains of TSE-infected hosts, PrP-res usually accumulates in both plasmalemmal and extracellular deposits but can also be seen occasionally in late endosome/lysosome-like structures in neurons (Laszlo et al, 1992;Arnold et al, 1995;Grigoriev et al, 1999) and microglia (Jeffrey et al, 1994). These results raise the possibility that neuronal cells might similarly internalize exogenously derived PrP-res when infected for the first time.…”

Prion Peptide 106–126 Modulates the Aggregation of Cellular Prion Protein and Induces the Synthesis of Potentially Neurotoxic Transmembrane PrP

“…Such an accumulation of virtually nondegradable PrP C and PrP 106 -126 aggregates explains the extensive proliferation of lysosomes observed in our cell model, and the presence of abundant PrP immunoreactive lysosomes in the neurons of scrapie-infected animals and new variant Creutzfeldt-Jakob disease patients (25,28). A similar change in conformation from an ␣-helical to a ␤-sheet structure has been reported for recombinant PrP 91-231 and for certain other peptides when exposed to an acidic pH (24,29) and is consistent with the notion that lysosomotropic agents inhibit the accumulation and branched polyamines stimulate the degradation of PrP Sc in scrapie-infected cells (30,31).…”

“…Because ␤-sheet rich peptides have an affinity for cholesterol (9,24), aggregated PrP 106 -126 probably concentrates in cholesterol-rich lipid domains of the plasma membrane. Incidentally, this is also the preferred location for endogenous PrP C and the site for PrP C to PrP Sc conversion (25)(26)(27), thus providing an ideal environment for the interaction of PrP 106 -126 and PrP C , and subsequent aggregation of the latter.…”

Accumulation of prion protein in muscle fibers of experimental chloroquine myopathy: in vivo model for deposition of prion protein in non-neuronal tissues

“…Lysosomes are acidic compartments that have been reported to play an important role in the conformational conversion of PrP in prion diseases. 17,18 Chloroquine raises intralysosomal pH to as high as 6.0-6.5, causing marked changes in intracellular protein processing and trafficking. 8 As a consequence of the long-term administration of chloroquine, skeletal muscle fibers degenerate, with numerous autophagic vacuoles.…”