Primary progressive MS (PPMS) is characterized by disease progression from clinical onset and failure of remyelination. In our prior work, we showed that intrathecal injection of cerebrospinal fluid (CSF) from PPMS patients, but not relapsing-remitting (RRMS) or secondary progressive (SPMS) patients, delayed spontaneous remyelination in lysolecithin-induced lesions. The PPMS CSF factors that impede remyelination have not yet been isolated or characterized. To better understand the size of these undetermined factor(s), we filtered PPMS CSF at 100 kDa and determined the effect of filtered CSF on remyelination in lysolecithin-induced lesions.
To investigate whether filtration of PPMS CSF mitigates the delayed remyelination induced by PPMS CSF factors following lysolecithin-induced demyelination.
CSF obtained from PPMS patients was passed through a tangential flow filtration system for 3 filtration cycles to remove CSF components larger than 100 kDa. Mice underwent a laminectomy at cervical level 5 (C5). 1 μL of 1% lysolecithin was injected into the dorsal column. Five days post injection, 3 μL of PPMS CSF or filtered PPMS CSF were injected into the subarachnoid space at C5. Control mice were injected with saline. Mice were perfused at 12 days post lysolecithin injection and pathology was assessed in the cervical spinal cord.
Intrathecal injection of PPMS CSF at the site of a lysolecithin-induced lesion resulted in significantly larger demyelinated lesions compared to saline controls, as determined by luxol fast blue staining. However, there was no significant difference in lesion volume between filtered PPMS CSF-injected mice and saline controls. This suggests that the 100 kDa filter removed pathological PPMS CSF factor(s) preventing spontaneous remyelination in lysolecithin-induced lesions. Preliminary data suggest that mice injected with filtered PPMS CSF display reduced reactive astrogliosis (GFAP) and microglial activation (Iba1) within the lesion compared to unfiltered PPMS CSF-injected mice. There was no significant difference in numbers of proliferating oligodendrocyte progenitor cells (NG2/Ki67) or mature oligodendrocytes (APC/Olig2).
Our results indicate that PPMS CSF factors responsible for impeding remyelination are larger than 100 kDa and can be removed by filtration. This suggests that CSF pheresis may be a therapeutic option.