Understanding the aetiology of acquired equine polyneuropathy by studying Schwann cell cultures

Acquired equine polyneuropathy (AEP) is a devastating neurological disease affecting Nordic horses. The disease is associated with characteristic histopathological changes in the peripheral nerves of affected horses. These include remyelination and demyelination, as well as hypertrophy of the perikaryon and protein-rich inclusions in the myelin-producing Schwann cells. The hypothesis is that an unknown factor, possibly originating from forage, disrupts Schwann cell metabolism.

The background to the study was that nerve studies would be valuable for elucidating the etiology, but the availability of nerve samples is limited because samples must be collected immediately in connection with euthanasia. Transport to pathology units is usually not feasible due to the severity of the clinical signs, making collected samples highly valuable.

The main objective of the project was therefore to create a robust platform for studying the histopathological changes in Schwann cells (SC) in horses affected by AEP. Cell cultures from healthy and diseased horses were to be established and compared under different conditions. Cell cultures allow freezing and thawing for future studies.

A method for culturing equine SC was established. Nerve samples were collected from 10 healthy and 3 diseased horses. Flow cytometry was used to distinguish SC from fibroblasts. Cells from healthy horses were incubated with serum from healthy and diseased horses to investigate a possible stress response. Serum from 6 horses affected by AEP during the project period, as well as from a serum bank containing samples from healthy and diseased horses, was analyzed by ELISA for IgG and IgM antibodies against specific gangliosides. Immunofluorescence and immunoelectron microscopy of frozen nerve sections were used to detect the gangliosides GM1 and GM2.

Culturing of SC from healthy and diseased horses was successful, and such cell cultures could be cryopreserved. Preliminary results from studies in which cell cultures were incubated with serum from healthy and diseased horses indicate increased cell death when serum from diseased horses was used. Horses from stables affected by AEP have higher serum levels of IgM antibodies against specific gangliosides than healthy horses. We detected the gangliosides GM1 and GM2 in equine nerves.

We have now established the methods and created a bank of material for repeating the experiments with additional combinations of healthy and diseased nerve cells and serum. Further studies of antibodies against gangliosides in nerves from diseased horses may provide information about a potential autoimmune role in the etiology of AEP. Additional studies will be performed on the cell culture from the diseased horse with inclusions in SC.

The method for collecting nerve samples in the field enables cell cultures to be established from additional AEP-affected horses. Elevated levels of IgM antibodies against gangliosides require further investigation, but they have the potential to become a biomarker for AEP at herd level.