Development of congenital stromal corneal dystrophy is dependent on export and extracellular deposition of truncated decorin

PURPOSE

Congenital stromal corneal dystrophy (CSCD) is an autosomal dominant condition with clouding of the cornea due to stromal opacities. It is caused by mutations in the decorin gene (DCN) leading to the expression of a truncated form of decorin. In an attempt to replicate this condition in mice, a knock-in mouse strain, 952delT Dcn, was created.

METHODS

Mice were constructed by targeted mutation. Sequencing of genomic DNA confirmed correct genotype. Mouse and human corneas, including corneas from patients with CSCD, and primary keratocyte cultures were subjected to Western blot analysis, transmission electron microscopy, and immunofluorescence microscopy.

RESULTS

Histologically, the mice did not show any organ pathology. Corneas were clear, and the electron-lucent deposits observed in CSCD were not present. Furthermore, while nearly equivalent amounts of normal and truncated decorin are present in CSCD corneas, truncated decorin was hardly detectable in the mouse corneas. By immunofluorescence analysis of corneas from 952delT Dcn homozygous mice, decorin was found only in keratocytes. In primary cultures of mouse corneal explants, truncated decorin was retained intracellularly in contrast with human corneal explants where truncated decorin was exported into the culture medium. Immunofluorescence analysis revealed that native mouse decorin localized to the Golgi complex, whereas the truncated decorin accumulated in the endoplasmic reticulum (ER).

CONCLUSIONS

The ER retention of truncated decorin may explain why the mouse corneas remained clear. The consequences of the decorin mutation are different in mice and humans, and 952delT Dcn knock-in mice are therefore not a suitable model for CSCD.

Poisoning of dogs with tremorgenic Penicillium toxins

Fungi in the genus Penicillium, particularly P. crustosum, produce tremorgenic mycotoxins, as well as suspected tremorgenic compounds. The accidental intoxication of six dogs with such toxins are reported. The clinical signs included vomiting, convulsions, tremors, ataxia, and tachycardia, all of which are indicators of intoxications affecting the nervous system. This symptomatology caused us to think that the dog poisoning was the result of tremorgenic mycotoxins. One dog was euthanized in the acute phase, while three others recovered completely within a few days. However, neurological symptoms were still observed four months after the poisoning of two of the dogs. One of these recovered completely within the next 2-3 months, while the other still suffers from ataxia three years later. Available samples of feed, stomach content and/or tissues from the intoxications were subjected to mycological and chemical analysis. Penitrem A was found in all reported poisonings and roquefortine C in all cases when this toxin was included in the analysis. The producer of these toxins, Penicillium crustosum, was detected in all cases where material suitable for mycological examinations (feed or vomit) was available. To our knowledge, this is the first report documenting the presence of penitrems and roquefortine C in organs from poisoned dogs. Furthermore, the report indicates that the recovery period after severe poisonings with P. crustosum may be protracted.

Association of myocarditis with high viral load of porcine circovirus type 2 in several tissues in cases of fetal death and high mortality in piglets. A case study

During a period of 1.5 months, a newly established pig herd experienced a high number of mummifications and stillbirths, a high neonatal mortality rate, and many piglets with congenital tremors or hind leg ataxia. After clinical and histological investigations, the submitted animals were divided into 4 groups: mummified or stillborn (N = 6), live born with myocarditis (N = 5) (average age 22.8 days), live born without myocarditis (N = 14) (average age 20.0 days), and control animals from a different herd (N = 5) (newborn). Statistically significant differences were observed in the mean porcine circovirus 2 (PCV2) load among the 4 groups in the liver (P < 0.0001). The presence of PCV2 antigen within the myocardial lesions was confirmed by immunohistochemistry. A high load of PCV2 DNA was observed in myocardium, liver, and spleen from mummified or stillborn piglets (>1 x 10(7) copies per 500 ng DNA), lower in piglets with myocarditis (>1 x 10(5) copies per 500 ng DNA), and even further lower in pigs without myocarditis (<1 x 10(5) copies per 500 ng DNA), whereas no PCV2 DNA was detected in the control animals. Myocardium, liver, and spleen were well suited for routine testing of fetuses and young piglets by quantitative real-time polymerase chain reaction. Neither porcine parvovirus nor encepaholomyocarditis virus was detected. These results indicate that the PCV2 infection might have been of etiological importance for the fetal deaths and piglet mortality observed in this herd.

Description of the infection status in a Norwegian cattle herd naturally infected by Mycobacterium avium subsp. paratuberculosis

The Norwegian surveillance and control programme for paratuberculosis revealed 8 seroreactors in a single dairy cattle herd that had no clinical signs of Mycobacterium avium subsp. paratuberculosis (M. a. paratuberculosis) infection. Paratuberculosis had been a clinical problem in goats several years previously in this herd. All 45 cattle were culled and a thorough investigation of the infection status was conducted by the use of interferon-γ (IFN-γ) immunoassay, measurement of antibodies, and pathological and bacteriological examination.

In the IFN-γ immunoassay, 9 animals gave positive results, and 13 were weakly positive, while 19 animals were negative. In the serological test,10 animals showed positive reactions, and 5 were doubtful, while 30 animals gave negative reactions. There appeared to be a weak trend toward younger animals having raised IFN-γ and older animals having raised serological tests. Histopathological lesions compatible with paratuberculosis were diagnosed in 4 animals aged between 4 and 9 years. Three of these animals had positive serological reaction and one animal gave also positive results in the IFN-γ immunoassay. Infection was confirmed by isolation of M. a. paratuberculosis from 2 of these 4 animals. One single bacterial isolate examined by restriction fragment length polymorphism (RFLP) had the same profile, B-C1, as a strain that had been isolated from a goat at the same farm several years previously.

Despite many animals being positive in one or both of the immunological tests, indicative of a heavily infected herd, none of the animals showed clinical signs and only one cow was shown to be shedding bacteria. A cross-reaction with other mycobacteria might have caused some of the immunoreactions in these animals. It is also possible that the Norwegian red cattle breed is resistant to clinical infection with M. a. paratuberculosis.

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.

Nephrotoxicity of Narthecium ossifragum in cattle in Norway

During the summer of 1992 renal failure was diagnosed in 232 grazing cattle in 85 herds on the west coast of Norway. The salient clinical signs were depression, anorexia and melaena or fresh blood in the faeces; diarrhoea was also commonly observed. The serum concentrations of creatinine, urea, magnesium and phosphorus, and the activities of glutamate dehydrogenase, aspartate aminotransferase and creatine kinase were above normal and the serum calcium concentration was below normal. Post mortem examinations consistently revealed renal tubular necrosis. In some cases there was liver necrosis and also erosions at the base of the tongue, in the oesophagus and in the jejunum and colon. The toxicity was probably caused by the plant Narthecium ossifragum (bog asphodel).