In most human and animal
prion diseases the abnormal disease-associated
prion protein (PrPSc) is deposited as non-
amyloid aggregates in CNS, spleen and lymphoid organs. In contrast, in humans and transgenic mice with PrP mutations which cause expression of PrP lacking a
glycosylphosphatidylinositol (GPI)-anchor, most PrPSc is in the
amyloid form. In transgenic mice expressing only anchorless PrP (tg anchorless), PrPSc is deposited not only in CNS and lymphoid tissues, but also in extraneural tissues including heart, brown fat, white fat, and colon. In the present paper, we report ultrastructural studies of
amyloid PrPSc deposition in extraneural tissues of
scrapie-infected tg anchorless mice.
Amyloid PrPSc fibrils identified by immunogold-labeling were visible at high magnification in interstitial regions and around blood vessels of heart, brown fat, white fat, colon, and lymphoid tissues. PrPSc
amyloid was located on and outside the plasma membranes of adipocytes in brown fat and cardiomyocytes, and appeared to invaginate and disrupt the plasma membranes of these cell types, suggesting cellular damage. In contrast, no cellular damage was apparent near PrPSc associated with macrophages in lymphoid tissues and colon, with enteric neuronal
ganglion cells in colon or with adipocytes in white fat. PrPSc localized in macrophage phagolysosomes lacked discernable fibrils and might be undergoing degradation. Furthermore, in contrast to wild-type mice expressing GPI-anchored PrP, in lymphoid tissues of tg anchorless mice, PrPSc was not associated with follicular dendritic cells (FDC), and FDC did not display typical
prion-associated pathogenic changes.