LPS-induced systemic inflammation reveals an immunomodulatory role for the prion protein at the blood-brain interface.

BACKGROUND: The cellular prion protein (PrPC ) is an evolutionary conserved protein abundantly expressed not only in the central nervous system but also peripherally including the immune system. A line of Norwegian dairy goats naturally devoid of PrPC (PRNP Ter/Ter ) provides a novel model for studying PrPC physiology.

METHODS: In order to explore putative roles for PrPC in acute inflammatory responses, we performed a lipopolysaccharide (LPS, Escherichia coli O26:B6) challenge of 16 goats (8 PRNP +/+ and 8 PRNP Ter/Ter ) and included 10 saline-treated controls (5 of each PRNP genotype). Clinical examinations were performed continuously, and blood samples were collected throughout the trial. Genome-wide transcription profiles of the choroid plexus, which is at the blood-brain interface, and the hippocampus were analyzed by RNA sequencing, and the same tissues were histologically evaluated.

RESULTS: All LPS-treated goats displayed clinical signs of sickness behavior, which were of significantly (p < 0.01) longer duration in animals without PrPC . In the choroid plexus, a substantial alteration of the transcriptome and activation of Iba1-positive cells were observed. This response included genotype-dependent differential expression of several genes associated with the immune response, such as ISG15, CXCL12, CXCL14, and acute phase proteins, among others. Activation of cytokine-responsive genes was skewed towards a more profound type I interferon response, and a less obvious type II response, in PrPC -deficient goats. The magnitude of gene expression in response to LPS was smaller in the hippocampus than in the choroid plexus. Resting state expression profiles revealed a few differences between the PRNP genotypes.

CONCLUSIONS: Our data suggest that PrPC acts as a modulator of certain pathways of innate immunity signaling, particularly downstream of interferons, and probably contributes to protection of vulnerable tissues against inflammatory damage.