Neuroprotective properties of the PrP-like Shadoo glycoprotein assessed in the middle cerebral artery occlusion model of ischemia

Biochemical similarities have been noted between the natively unstructured region of the cellular prion protein, PrP(C), and a GPI-linked glycoprotein called Shadoo (Sho); these proteins are encoded by the Prnp and Sprn genes, respectively. Both proteins are expressed in the adult central nervous system and they share overlapping partners, including each other, in interactome studies. As prior studies have ascribed neuroprotective properties to the N-terminal region of PrP(C), specifically the octarepeat region, we investigated Sho's neuroprotective properties. To this end we assessed Sho-null (Sprn(0/0)) and hemizygous (Sprn(0/+)) mice in the middle cerebral artery occlusion (MCAO) model versus wild type mice and also vs. transgene-rescued Sprn(0/0)-TgSprn mice. Sprn(0/0) mice had a tendency to greater fragility in reaching endpoint and deficits in parameters including infarct volume and neurogenesis, with a reciprocal trend noted in transgene-rescued mice; however these effects did not reach significance. Loss of both PrP(C) and Sho immunostaining occurred in parallel to neuronal loss on the ipsilateral side of MCAO-lesioned animals; while focal elevations in immunostaining in the penumbra region were sometimes evident for PrP(C), they were not noted for Sho. Our studies argue against discernible neuroprotective action of Sho in the genetic backgrounds used for this MCAO paradigm. Whether or not the positively charged N-terminal regions in Sho and PrP(C) fulfil different roles in vivo remains to be determined.