Exploring the factors underlying remyelination arrest by studying the post-transcriptional regulatory mechanisms of cystatin F gene

Remyelination plays an important role in determining the fate of demyelinating disorders. However, it is arrested during chronic disease states. Cystatin F, a papain-like lysosomal cysteine proteinase inhibitor, is a crucial regulator of demyelination and remyelination. Using hemizygous proteolipid protein transgenic 4e (PLP 4e/- ) mice, an animal model of chronic demyelination, we found that cystatin F mRNA expression was induced at 2.5 months of age and up-regulated in the early phase of demyelination, but significantly decreased in the chronic phase. We next investigated cystatin F regulatory factors as potential mechanisms of remyelination arrest in chronic demyelinating disorders. We used the CysF-STOP-tetO::Iba-mtTA mouse model, in which cystatin F gene expression is driven by the tetracycline operator. Interestingly, we found that forced cystatin F mRNA over-expression was eventually decreased. Our findings show that cystatin F expression is modulated post-transcriptionally. We next identified embryonic lethal, abnormal vision, drosophila like RNA-binding protein 1 (ELAVL-1), and miR29a as cystatin F mRNA stabilizing and destabilizing factors, respectively. These roles were confirmed in vitro in NIH3T3 cells. Using postmortem plaque samples from human multiple sclerosis patients, we also confirmed that ELAVL-1 expression was highly correlated with the previously reported expression pattern of cystatin F. These data indicate the important roles of ELAVL-1 and miR29a in regulating cystatin F expression. Furthermore, they provide new insights into potential therapeutic targets for demyelinating disorders.