Prion Protein-Hemin Interaction Upregulates Hemoglobin Synthesis: Implications for Cerebral Hemorrhage and Sporadic Creutzfeldt-Jakob Disease

Abstract

Hemin is known to induce endocytosis of prion-protein (PrP^C) from the neuronal plasma membrane, potentially limiting propagation of the disease causing PrP-scrapie (PrP^Sc) isoform. Hemin is therefore an attractive disease-modifying option for sporadic Creutzfeldt-Jakob disease (sCJD), a human prion disorder with no effective treatment. The hemin-PrP^C interaction is also of interest in cerebral-hemorrhage (CH), a condition where potentially toxic hemin molecules come in contact with neuronal PrP^C. Interestingly, PrP^C is upregulated in penumbric neurons surrounding CH and is known to confer neuroprotection in a dose-dependent manner. The underlying mechanism, however, is not clear. Here, we report that hemin binds PrP^C on diverse cell lines, resulting in its aggregation or degradation in a cell-type specific manner. Surprisingly, the hemin-PrP^C interaction upregulates Hb synthesis in hematopoietic cells, a response reversed by deleting the hemin-binding octa-peptide repeat region of PrP^C. A similar response is noted in brain organotypic cultures where exposure to hemin induces significantly more α-globin in wild-type (PrP^+/+) relative to PrP-knock-out (PrP^–/–) samples. Furthermore, red blood cells and brain tissue from PrP^–/– mice show significantly less α-globin relative to PrP^+/+ controls, indicating a positive effect of PrP^C on Hb synthesis under physiological conditions as well. Surprisingly, levels of α-globin are significantly higher in sCJD brain tissue relative to controls, suggesting compensatory upregulation of Hb synthesis by surviving neurons or misregulation in diseased brains. These observations reveal a unique function of PrP^C that is likely to impact the therapeutic management of CH and sCJD.