Ageing and exposure to oxidative stress in vivo differentially affect cellular levels of PrPc in mouse cerebral microvessels and brain parenchyma.

W. M. Williams, E. R. Stadtman and J. Moskovitz (2004) Neuropathology and Applied Neurobiology, doi: 10.1111/j.1365-2990.2004.00523.x Ageing and exposure to oxidative stress in vivo differentially affect cellular levels of PrP^c in mouse cerebral microvessels and brain parenchyma The biological function of cellular prion protein PrP^c has not been established, despite in vitro studies suggesting antioxidant activity or link to signal transduction pathways. In this study, mice were exposed to hyperoxia to establish whether oxidative stress affected prion expression in vivo. C57Bl/6J mice aged 6, 18, and 24 months, maintained under normoxic conditions, exhibited age-related increases in PrP^c in both cerebral microvessels and in microvessel-depleted brain homogenate. We demonstrate that PrP^c is differentially affected by exposure to hyperoxia in vivo for 1 (24 h) or 2 (48 h) days, or for 1 day hyperoxia, followed by 1 day normoxia. Brain parenchymal cells from 6-month-old mice exposed to 1 day hyperoxia showed elevation of a glycosylated ∼36 kDa form, whereas in 24-month-old mice cellular prion level was substantially reduced. Extending hyperoxia from 1 to 2 days resulted in significantly reduced PrP^c level, regardless of age. Parenchymal PrP^c is substantially elevated in 6-month-old mice, but declines in 18- and 24-month-old animals following 1 day hyperoxia. By contrast, PrP^c content in cerebral microvessels from 6-month-old mice declined after a 2 day exposure to hyperoxia, while microvessels from 24-month-old brains showed elevated prion levels 24 h after hyperoxia. Moreover, unglycosylated 25–30 kDa PrP^c, and a previously undescribed 50–64 kDa band containing at least some glycosylated protein, predominated in microvessels with lesser content of the glycosylated ∼36 kDa form. Cellular content of these unglycosylated forms was correlated with age, while the response to hyperoxia was evident in both unglycosylated and glycosylated forms of the protein following 1 and 2 day exposures. The observed elevation of the 25–30 and 50–64 kDa bands of microvessel PrP^c is not sustainable following 1 day hyperoxia, but returns to near normoxic levels within 24 h after hyperoxia. We also show in a knockout mouse for methionine sulfoxide reductase (MsrA), the enzyme responsible for reducing methionine sulfoxide back to methionine, and a regulator of cellular antioxidant defence, that following hyperoxia brain PrP^c in the null mutant is elevated relative to PrP^c content in the parent strain. Our results show up-regulated PrP^c expression or reduced turnover in response to age-related, and hyperoxia-induced oxidative stress. [ABSTRACT FROM AUTHOR]