Association of cerebellar inflammation and neurodegeneration in a novel spinocerebellar ataxia type 13 mouse model
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Background
Neuroinflammation is a recognized pathological characteristic of neurodegenerative diseases. Spinocerebellar ataxia 13 (SCA13) is a progressive neurodegenerative disease with no effective treatments. Our previous studies reported human mutations in KCNC3 gene are causative for SCA13. Human R423H allelic mutation induces early-onset neurodegeneration and aberrant intracellular retention of Epidermal Growth Factor Receptor (EGFR) in drosophila. However, the neurodegeneration and inflammatory response induced by the R424H allele are unknown in a mammalian model of disease.
Method
In this study, a single Kcnc3 R424H mutation (Analogous to the human SCA13 R423H isoform) transgenic mice were created using CRISPR/Cas 9 technique. Motor function (gait, tremor, coordination and balance) and cerebellar volume (scanned and imaged with 7T MRI) of the R424H transgenic mice were evaluated at multiple timepoints. Neurodegeneration (Purkinje cells loss) as well as cerebellar (astroglia, microglia and macrophage activation) and peripheral (plasma cytokines levels) inflammatory responses were examined and analyzed.
Result
The R424H transgenic mice showed marked neurological motor dysfunction with high-frequency tremor, aberrant gait, and short latency to fall in Rotarod testing at 3 and 6 months of age. Abnormal spontaneous firing was recorded in electrophysiology of Purkinje cells. Pathological changes in our R424H transgenic mice included progressive Purkinje cell degeneration and cerebellar atrophy. Over-active microglia, astrocytes, and macrophages were observed in the cerebella of transgenic mice. Pearson correlation analyses indicated that the number of Calbindin positive cells, a Purkinje cell marker, showed a strong inverse correlation with the positive cell number of EGFR, phosphorylated EGFR (pEGFR), and CD68. The expression of EGFR/pEGFR was positively correlated with CD68 and Glial Fibrillary Acidic Protein.
Conclusion
Transgenic R424H mice provide a novel SCA13 model showing significant motor deficits, Purkinje cells loss, cerebellar inflammation, and atrophy. Our study suggests that the activation of inflammatory immune cells (astroglia, microglia and macrophages) and strong expression of EGFR/ pEGFR signal in these immune cells are associated with Purkinje cell loss in the cerebellum. This abnormal neuroinflammation may play a significant role in the aggressive procession of neurodegeneration.
