BBSRC EASTBIO DTP - Investigation of the role of prion protein PrPC in immune function and disease resistance in poultry and fish

Chicken and salmonid fish are becoming an ever more important food source and intensifying production increases the risk of infection and inflammation. A better understanding of the innate and adaptive immune system in these species is therefore required to select for improved disease resistance. The prion protein genes are modulators of immune function in mammals which have so far received little attention in avian and fish species.

The main aim of the proposed project is to investigate protein interaction networks and regulation of PrPC protein expression in chicken and salmonid fish in support of a role in the immune system. The study will make use of genome editing of the PRNP gene in cell lines as well as the analysis of genomic and transcriptomic data.

The prion protein plays a key role in the pathogenesis of prion diseases in mammals. However, despite intensive studies the normal function of the cellular prion protein (PrPC) remains unclear. Mammalian PrPC is expressed widely in the immune system, in haematopoietic stem cells and mature lymphoid and myeloid compartments in addition to cells of the central nervous system. It has been shown that PrPC modulates T-cell-mediated neuro-inflammation, that PrPC is rapidly upregulated on the surface of lymphocytes upon activation of these cells and that lack of PrPC in lymphocytes results in pro-inflammatory activities. PrPC is therefore a likely contributor to immunological quiescence, serving two principal roles: to modulate the inflammatory potential of immune cells and to protect vulnerable parenchymal cells against noxious insults generated through inflammation. Thus, independent of neurological considerations, some of the evolutionary constraints that may have contributed to the conservation of the PRNP gene could be of immunological origin. Poultry and fish health (and welfare) might be improved through a better understanding of PRNP gene regulation, its protein interaction networks (interactomes) including other immune-modulators and of the impact of its genetic variation on inflammatory responses.

Mammalian PrPC is a glycoprotein, encoded by a single-copy gene (PRNP). It is mainly located on the plasma membrane and exists in many forms due to variable N-glycosylation and proteolytic processing. The generation of truncated PrPC forms is conserved in avian species and is likely to occur also in other vertebrates, intriguingly it is also seen in other prion family genes (e.g. SPRN (shadoo protein)). Conserved physiological activity between PrPC and shadoo has been shown and suggests that shadoo and PrPC might act on similar pathways. While avian PrPC is also expressed from a single gene copy, piscine PrP-like proteins are encoded by at least three genes. There are structural and functional similarities between mammalian, avian and fish PrPs, however the conservation of immune functions of PrP remains to be established.

Amongst the primary objectives are the development of reagents to enable the study of PrP/shadoo related genes and proteins in bird and fish species; to use systems biology approaches for the study of the PrP/shadoo interactome and to establish sequence variation of PRNP/SPRN genes and their transcription and protein processing profiles; to use in vitro approaches for a comparison of mammalian versus avian/piscine PrPC using available cell lines; to use CRISPR-Cas9 gene editing technology and siRNA gene silencing approaches to study biological activities of PrP/shadoo; to investigate PrPC in chicken lines selected for susceptibility and resistance to tumour formation in Marek’s disease. This project will provide the opportunity to use cutting-edge technologies and –omics approaches, including DNA and RNA analysis and manipulation, protein analysis, bio-imaging, tissue culture.