The
biological function of cellular
prion protein PrPc 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 PrPc in both cerebral microvessels and in microvessel-depleted brain homogenate. We demonstrate that PrPc 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 approximately 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 PrPc level, regardless of age. Parenchymal PrPc is substantially elevated in 6-month-old mice, but declines in 18- and 24-month-old animals following 1 day
hyperoxia. By contrast, PrPc 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 PrPc, and a previously undescribed 50-64 kDa band containing at least some
glycosylated protein, predominated in microvessels with lesser content of the glycosylated approximately 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 PrPc 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 PrPc in the null mutant is elevated relative to PrPc content in the parent strain. Our results show up-regulated PrPc expression or reduced turnover in response to age-related, and
hyperoxia-induced oxidative stress.