Pleiotropic Function of Cellular Prion Protein: Encompassing Endoplasmic-Reticulum Stress, Cell Proliferation in Vascular Smooth Muscle Cells

Cellular prion protein (PRNP) has been implicated in various physiological processes in different cell types, for decades. Little has been known how PRNP functions in multiple, yet related processes within a particular system. In our current study, with the aid of high-throughput RNA-sequencing technique, we have presented an overall transcriptome profile of rat vascular smooth muscle cells (VSMCs) with Prnp knockdown. Fifty-one genes were found to be differentially regulated, of which, genes involved in cell proliferation and endoplasmic reticulum (ER) stress pathway, show significant upregulation. That PRNP negatively regulates VSMC proliferation, has been demonstrated using immunoblot assays, BrdU incorporation assay and Ki-67 immunofluorescence staining. As revealed from our RNA-Seq data, ATF4, a downstream effector of the PERK arm of ER stress pathway is upregulated upon RNA interference of Prnp in VSMCs. As a result, the expression of the functional phosphorylated isoform of translation initiation factor eIF2α (p-eIF2α) is elevated. Additionally, we also showed that downregulation of Prnp leads to excess intracellular ROS accumulation, subsequently leading to splicing of Xbp1 mRNA and triggering unfolded protein response (UPR) within the cell. Therefore, our findings highlight that PRNP directly or indirectly modulates an array of biological processes and plays a pivotal role in preserving the equilibrium between excess proliferation and optimal endoplasmic reticulum function, in VSMCs.