Glial Activation Markers in CSF and Serum From Patients With Primary Progressive Multiple Sclerosis: Potential of Serum GFAP as Disease Severity Marker?

Abstract

Background: In progressive multiple sclerosis (MS), glial activation is thought to be a relevant mechanism of disability progression. Therefore, in vivo assessment of the glial cell activity is, in the emerging treatment era of primary progressive MS (PPMS), more important than ever. Objectives: To test the association of cerebrospinal fluid (CSF) and serum markers of glial activation in PPMS patients; including glial fibrillary acidic protein (GFAP), chitinase-3-like protein 1 (CHI3L1), soluble variant of triggering receptor expressed on myeloid cells 2 (sTREM2), and marker of neuroaxonal damage (Neurofilament light chain, NfL) as well as clinical severity. Methods: CSF and serum samples from PPMS patients were collected in the MS-centers at Universities of Freiburg (n = 49), Ulm (n = 27), Muenster (n = 11), and Rostock (n = 6). sTREM2 and CHI3L1 levels were measured using the previously reported ELISA assays, while NfL and GFAP were measured using SIMOA assays. Clinical data included age, gender, disease duration, treatment status, and Expanded Disability Status Scale (EDSS). Results: 93 CSF samples and 71 matching serum samples were analyzed. The median age of patients was 49 years and disease duration 4.5 years. GFAP_serum correlated with EDSS after correction for age (β = 0.3, p = 0.001). Furthermore, EDSS was higher in patients with a GFAP_serum level ≥ 151.7 pg/ml compared to patients with GFAP_serum below this cut-off (5.5 vs. 4.0, p = 0.009). Other markers did not correlate with the clinical severity. Moreover, we found a correlation between NfL_CSF and GFAP_CSF, sTREM2 and CHI3L1 (ρ = 0.4 for GFAP_CSF and sTREM2, ρ = 0.3 for CHI3L1, p < 0.01 for sTREM2 and CHI3L1 and <0.001 for GFAP_CSF). CHI3L1 did not correlate with GFAP_CSF but with sTREM2 (ρ = 0.4, p < 0.01). Discussion: The correlation between the glial activation markers in CSF with the markers of neuroaxonal demise supports the notion of the glial involvement in PPMS. The positive correlation between GFAP_CSF with disease duration and GFAP_serum with the clinical severity of the disease may highlight a particular role of the astrocytes in PPMS and mark the potential of GFAP_serum as a disease severity marker.

Keywords: CHI3L1; GFAP; PPMS; SiMoA; glial activation; neurofilaments; progressive multiple sclerosis; sTREM2.

Figure 1

Comparison between the levels of (A) glial fibrillary acidic protein (GFAP) and (B) soluble triggering receptor expressed on myeloid cells 2 (sTREM2) in cerebrospinal fluid (CSF) between the four participating centers (Kruskal-Wallis test).

Figure 2

Spearman correlation of various cerebrospinal fluid (CSF) (A) and serum (B) biomarkers with the age of the patients. Glial fibrillary acidic protein (GFAP), neurofilaments light chain (NfL), chitinase 3 like 1 (CHI3L1), soluble triggering receptor expressed on myeloid cells 2 (sTREM2), ρ (Spearman rho).

Figure 3

Spearman correlation of cerebrospinal fluid (CSF) (A) and serum (B) biomarkers with the clinical severity as measured by the expanded disability status scale (EDSS). Glial fibrillary acidic protein (GFAP), neurofilaments light chain (NfL), chitinase 3 like 1 (CHI3L1), soluble triggering receptor expressed on myeloid cells 2 (sTREM2), ρ (Spearman rho), β (standardized coefficient) of multiple linear regression, age as a covariant.

Figure 4

Comparison of expanded disability status scale (EDSS) values for primary progressive multiple sclerosis (PPMS) patients below and above cut-offs of 151.7 pg/ml for glial fibrillary acidic protein (GFAP) (A) and 16 pg/ml for neurofilaments light chain (NfL) (B) in serum (Mann-Whitney U test), respectively. There was a significant age difference for the grouping by NfL but not for GFAP (Mann-Whitney U test, p = 0.01 and 0.47, respectively). LP, lumbar puncture.

Figure 5

Level of serum glial fibrillary acidic protein (GFAP_serum) in PPMS patients with serum neurofilaments light chain levels equal to or higher than 16 pg/ml (NfL_serum ≥ 16) or lower the 16 pg/ml (NfL_serum < 16), ^*Univariant general linear model corrected for age.

Figure 6

Spearman correlation between neurofilaments light chain (NfL), glial fibrillary acidic protein (GFAP), chitinase 3 like 1 (CHI3L1), and soluble triggering receptor expressed on myeloid cells 2 (sTREM2), ρ (Spearman rho).

Figure 7

Spearman correlation between chitinase 3 like 1 (CHI3L1) and soluble triggering receptor expressed on myeloid cells 2 (sTREM2), ρ (Spearman rho).