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

Background

The cellular prion protein (PrP^C) 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 PrP^C (PRNP^Ter/Ter) provides a novel model for studying PrP^C physiology.

Methods

In order to explore putative roles for PrP^C 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 PrP^C. 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 PrP^C-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 PrP^C 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.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-017-0879-5) contains supplementary material, which is available to authorized users.

Pre- and post-natal hepatic glucose phosphorylation in chicks (Gallus domesticus)

1. Hepatic glycogen levels and activities of metabolic enzymes were measured 7 d and 2 d before hatching, immediately after hatching and 4 d thereafter. 2. Chicken liver has a particle-bound hexokinase with a high K(m) (8 mM) for glucose. 3. The results indicate that the high-K(m) hexokinase is involved in the mitochondrial generation of ATP for glycogen and lipid synthesis.

Detection of PrPSc in Rectal Biopsy and Necropsy Samples from Sheep with Experimental Scrapie

Scrapie diagnosis is based on the demonstration of disease-associated prion protein (PrP(Sc)) in brain or, in the live animal, in readily accessible peripheral lymphoid tissue. Lymphatic tissues present at the rectoanal line were readily obtained from sheep without the need for anaesthesia. The presence of PrP(Sc) in such tissue was investigated in sheep infected orally with scrapie-infected brain material. The methods used consisted of immunohistochemistry and histoblotting on biopsy and post-mortem material. PrP(Sc) was detected in animals with PrP genotypes associated with high susceptibility to scrapie from 10 months after infection, i.e., from about the time of appearance of early clinical signs. In the rectal mucosa, PrP(Sc) was found in lymphoid follicles and in cells scattered in the lamina propria, often near and sometimes in the crypt epithelium. By Western blotting, PrP(Sc) was detected in rectal biopsy samples of sheep with the PrP genotype VRQ/VRQ, after electrophoresis of material equivalent to 8 mg of tissue. This study indicated that rectal biopsy samples should prove useful for the diagnosis of scrapie in sheep.

Cases of scrapie with unusual features in Norway and designation of a new type, Nor98

Five cases of scrapie with unusual features have been diagnosed in Norway since 1998. The affected sheep showed neurological signs dominated by ataxia, and had the PrP genotypes homozygous A136 H154 Q171/ A136H154Q171 or heterozygous A136H154Q171/A136R154Q171, which are rarely associated with scrapie. Brain histopathology revealed neuropil vacuolisation essentially in the cerebellar and cerebral cortices; vacuolation was less prominent in the brainstem, and no lesions were observed at the level of the obex. The deposits of PrPSc were mainly in the cortex of the cerebellum and cerebrum, and no PrPSC was detectable by immunohistochemistry and ELISA in the lymphoid tissues investigated. Western blot analysis showed that the glycotype was different from other known scrapie strains and from the BSE strain. From a diagnostic point of view, these features indicate that this type of scrapie, designated Nor98, could have been overlooked and may be of significance for sampling in scrapie surveillance programmes.

Accumulation of pathogenic prion protein (PrPSc) in nervous and lymphoid tissues of sheep with subclinical scrapie

All sheep older than 1 year of age from a flock of the Rygja breed in which clinical scrapie was detected for the first time in two animals (4%) were examined for accumulation of pathogenic prion protein (PrPSc) by immunohistochemistry in the obex, the cerebellum, and the medial retrophayngeal lymph node. In addition, six lambs, 2-3 months old, all offspring of PrPSc-positive dams, were examined for PrPSc in the ileal Peyers' patch (IPP), the distal jejunal lymph node, the spleen, and the medial retropharyngeal lymph node (RPLN). In this flock, 35% (17/48) of the adult sheep showed accumulation of PrPSc, an eightfold increase compared with clinical disease. All positives carried susceptible PrP genotypes. Three sheep had deposits of PrPSc in the RPLN and not in the brain, suggesting that this organ, easily accessible at slaughter, is suitable for screening purposes. Two 7-year-old clinically healthy homozygous V136Q171 ewes showed sparse immunostaining in the central nervous system and may have been infected as adults. Further, two littermates, 86-days-old, showed PrPSc in the IPP. Interestingly, one of these lambs had the intermediate susceptible PrP genotype, VA136QR171. In addition to early immunolabeling in the dorsal motor nucleus of the vagal nerve, a few of the sheep had early involvement of the cerebellum. In fact, a 2-year-old sheep had sparse deposits of PrPSc in the cerebellum only. Because experimental bovine spongiform encephalopathy (BSE) in sheep seems to behave in a similar manner as natural scrapie, these results, particularly regarding spread of infectivity, may have implications for the handling of BSE should it be diagnosed in sheep.

Detection of PrPSc in lymphoid tissues of lambs experimentally exposed to the scrapie agent

Histoblotting and immunohistochemistry were used to detect disease-associated prion protein (PrP(Sc)) in lymphoid tissues of lambs of known PrP genotype infected with the scrapie agent by stomach tube at the age of 2 months. The ileal and jejunal Peyer's patches and retropharyngeal and distal jejunal lymph nodes were studied 1 week, 5 weeks, 5 months and 11 months after inoculation. Other lymphoid tissues examined included superficial cervical lymph node, tonsil and spleen. PrP(Sc) was not detected in any tissue of any lamb at 1 week post-inoculation. At 5 weeks, PrP(Sc) was detected in tissues of lambs of susceptible PrP genotypes (AV(136)QQ(171) and VV(136)QQ(171)), but not lambs of other PrP genotypes (AA(136)QQ(171), AA(136)QR(171) and AV(136)QR(171)). PrP(Sc) was present in the germinal centres of tonsils, distal jejunal and retropharyngeal lymph nodes, and spleen. In the nodules of ileal and jejunal Peyer's patches, only occasional solitary cells showed the presence of PrP(Sc). At 5 months post-inoculation, increased accumulations of PrP(Sc) were detected in ileal and jejunal Peyer's patches, as well as in the retropharyngeal and distal jejunal lymph nodes of a single lamb inoculated with the agent from a sheep of the same susceptible PrP genotype. Eleven months after exposure to the scrapie agent, PrP(Sc) was detected in all lymphoid tissues examined from sheep of susceptible PrP genotypes. These studies show that PrP(Sc) was detectable in lymphoid tissues 5 weeks after exposure to the scrapie agent by stomach tube in lambs as young as 3 months of age and indicate that the PrP genotype is a significant factor for the rapid uptake and spread of the agent through lymphoid tissues.

Genomic organization, comparative analysis, and genetic polymorphisms of the bovine and ovine prion Doppel genes (PRND)

The doppel protein (Dpl) is a prion-like protein encoded by the gene PRND, which has been found downstream of the prion gene, PRNP, in human and mouse. This paper describes the isolation and structural organization of the bovine and ovine PRND genes, which are composed of two exons compared with the three of human and mouse. Intergenic distances between PRNP and PRND were covered by means of long-range PCR and found to be 16.8 and 20 kb, in cattle and sheep respectively. The 5' and 3' untranslated regions (UTR) were analyzed to identify transcription regulatory sequences and compared with those from the PRND and PRNP sequences published for other species. Three polymorphisms (R50H, N110H, and R132Q) were revealed in the cattle coding region; two synonymous substitutions (I12I, A26A) were found in sheep. None of the polymorphisms was significantly associated with either Bovine Spongiform Encephalopathy (BSE) in cattle or scrapie in sheep.

The PrP-like protein Doppel gene in sheep and cattle: cDNA sequence and expression

cDNAs encoding the ovine and bovine prion protein-like protein Doppel (Dpl) have been cloned. Sequencing revealed cDNAs of 2.85 and 3.31 kb from ovine and bovine testicular tissue, in accordance with observations of single transcripts of 3.2 and 3.6 kb on Northern blots. Sequence alignments showed a very high degree of identity between the sheep and cattle Dpl cDNAs, except for a 0.4-kb stretch in the bovine 3' untranslated region and the terminal 3' end of the sequences. The expression pattern of the Dpl gene (Prnd) in adult tissues from both species was compared by Northern blot and RT-PCR analyses. The Prnd gene was expressed strongly in testicular tissue, while low levels of expression were seen in other tissues. The open reading frame of the ovine and bovine sequences encodes a 178-amino acid protein with 95% sequence identity between the two species. Predicted structural features are in close agreement with previous reports for mouse, human, and rat Dpl.

Sarcina -like bacteria, Clostridium fallax and Clostridium sordellii in lambs with abomasal bloat, haemorrhage and ulcers

A study of abomasal disease in lambs aged 2-5 weeks, made during the period 1993-1998, included 67 cases and 45 non-affected controls. Gross pathological findings included various combinations of bloat, haemorrhage and ulcers in the abomasum. Sarcina -like bacteria were found in sections and smears from the abomasum of 79% (53/67) of the cases. From one case, a lamb with abomasal bloat, the anaerobic "packet"-forming Sarcina ventriculi was cultivated from the abomasal contents and identified by biochemical reactions and sequencing of the 16S rRNA gene. Sarcina -like bacteria were observed microscopically in specimens from 94% (44/47) of the lambs with abomasal gas and in 45% (9/20) of those with ulcers or haemorrhage or both but little gas. On culture, abomasal contents from 41 cases yielded Clostridium fallax from 16 (39%) and Clostridium sordellii from eight (20%); abomasal cultures from 30 control lambs were negative for the three bacterial species. Quantitative cultivation, carried out on abomasal contents from live lambs and lambs dead </=3 h, showed that Clostridium perfringens, Escherichia coli and Lactobacillus spp. were present in the majority of both cases and controls, with no significant differences in the mean numbers.

Prion protein gene polymorphisms in sheep with natural scrapie and healthy controls in Norway

Two-hundred and forty healthy sheep and 32 cases of natural scrapie in Norway were analysed for disease-linked polymorphisms in the prion protein (PrP) gene. Scrapie was strongly associated with the presence of a valine polymorphism at codon 136 (V136), as 68.8% of the cases were homozygous (VV136) and 15.6% were valine/alanine heterozygous (VA136). All cases were homozygous arginine/arginine at codon 154 (RR154), except two which were homozygous histidine/histidine (HH154). All cases except two were homozygous glutamine/glutamine at codon 171 (QQ171), the two exceptions being heterozygous glutamine/arginine (QR171). More than 80% of all scrapie cases in Norway have occurred in a Cheviot-related crossbred type of sheep called Rygja. This type of sheep, which is largely restricted to the south-western coast, carries the V136 allele at a higher frequency than do other breeds of Norwegian sheep. Polymorphisms at codons 138 and 151 are also described.

A glucokinase-like-enzyme in the liver of Atlantic salmon (Salmo salar)

An enzyme with properties similar to rat liver glucokinase (Hexokinase IV or D) is present in salmon liver in addition to low-Km hexokinase(s). The specific activity of this enzyme increases about 1.6 fold, comparing activities after feeding diets with 25% and 0% digestive energy from starch. The enzyme has a low affinity for glucose, S0.5 = 25.2-26.8 mM (95% confidence interval) and a low activity with fructose, approximately 8% of the activity with glucose. Its molecular mass was estimated to 50.7 +/- 0.6 kDa (SEM. n = 3) by gel filtration, and it displays positive cooperativity with respect to glucose. The Hill constant = 1.73-1.81 (95% confidence interval). The enzyme is competitively inhibited by N-acetyl glucosamine, K(i) approximately 0.28 mM.

Glucose dehydrogenase in beef (Bos taurus) and rainbow trout (Oncorhynchus mykiss) liver: a comparative study

The monomer molecular mass of glucose dehydrogenase (GDH, EC 1.1.1.47) from rainbow trout liver and beef liver were estimated to be 90 kDa for both enzymes, by electrophoresis in the presence of Na-dodecyl-SO4 (SDS). The 90-kDa proteins were partially degraded to about 60 kDa when purified with a delayed procedure without protease inhibitors. Tryptic cleavage of the 90-kDa proteins gave fragments of about 60 kDa and 30 kDa, being similar for trout and beef GDH. Isoelectric points, kinetic and thermodynamic properties of the two enzymes are markedly different. Triton X-100 stimulated and stabilized the reactions catalysed by the purified enzymes.

Glucose dehydrogenase, glucose-6-phosphate dehydrogenase and hexokinase in liver of rainbow trout (Salmo gairdneri). Effects of starvation and temperature variations

1. Activities of trout liver glucose dehydrogenase (GDH, EC 1.1.1.47) and glucose-6-phosphate dehydrogenase (G6PD, EC 1.1.1.49) were increased after a sudden drop in water temperature, but not in long-time cold acclimated as compared with warm acclimated trout. 2. Possibly, the activities of GDH and G6PD were temporarily increased in connection with metabolic adaptation to the lower temperature. 3. The activities of GDH and G6PD were not changed by the stress of handling. 4. Partially purified trout liver GDH has a lower activation energy with glucose than with glucose-6-phosphate as substrate, and the Km (glucose) decreases with decreasing assay temperature. 5. At low temperatures, the activity of trout liver GDH with glucose as substrate may be comparable to that of glucose-6-phosphate. 6. Partially purified beef liver GDH has a high activation energy with glucose as substrate, and the Km (glucose) does not change with the assay temperature. 7. Hexokinase (HK, EC 2.7.1.1) and GDH activities were unchanged when trout were deprived of food for 4 weeks. Apparently, the trout liver glucose utilization did not adapt to the starvation.