To investigate whether filtration of primary progressive multiple sclerosis (PPMS) cerebrospinal fluid (CSF) removes pathological factors that induce astrocyte activation in mice and cultured human astrocytes (HAs). 

MS is characterized by inflammatory demyelination, axonal damage, and astrogliosis in the CNS. Approximately 15% of patients are diagnosed with PPMS, which is characterized by unremitting disease progression from onset. We previously reported that motor deficits and reactive astrogliosis can be induced in mice via intrathecal delivery of PPMS CSF, but not relapsing-remitting MS (RRMS) or secondary progressive MS (SPMS) CSF. Here, we investigated whether HA proliferation is also specifically induced by PPMS CSF only, and whether CSF filtration can attenuate reactive astrogliosis.

A tangential flow filtration system was used to pass PPMS CSF through 5kDa hollow-fiber filters for 3 cycles. Mice underwent laminectomies at C4 and C5, and PPMS CSF or filtered PPMS CSF was injected into the subarachnoid space. Motor deficits were assessed 1 day post-injection (DPI). Mice were perfused at 1DPI for histological analyses. HAs were cultured for 5 days then treated with 50% RRMS, SPMS or PPMS CSF, or filtered PPMS CSF in DMEM. qPCR and ICC were conducted 24 hrs after treatment.

Mice injected with filtered PPMS CSF displayed significantly lower motor deficit scores and stronger grip strength compared to unfiltered PPMS CSF-injected mice. Reactive astrogliosis was not induced by filtered PPMS CSF, as indicated by normal GFAP immunostaining intensity. qPCR and ICC results both indicated that only HAs treated with PPMS CSF had significantly increased proliferation, as revealed by increased Ki67 staining and mRNA levels. HAs treated with filtered PPMS CSF did not show increased proliferation.

Reactive astrogliosis is triggered only by PPMS CSF in vivo and in vitro. Filtration of PPMS CSF can significantly attenuate PPMS CSF-mediated astrogliosis.