# Serum glial fibrillary acid protein associates with TSPO-expressing lesions in multiple sclerosis brain

## TL;DR

This study finds that higher levels of a protein in the blood (GFAP) are linked to brain lesions in multiple sclerosis patients, suggesting ongoing astrocyte activity.

## Contribution

The study links serum GFAP levels with TSPO-expressing lesions in MS brains, offering new insight into disease progression mechanisms.

## Key findings

- sGFAP levels were significantly higher in progressive MS compared to healthy controls and relapsing-remitting MS.
- Higher sGFAP correlated with increased TSPO activity in chronic MS lesions and thalamic regions.
- TSPO-expressing lesion volume, age, and treatment status explained 27% of sGFAP variation.

## Abstract

Serum glial fibrillary acidic protein (sGFAP) is a promising biomarker for multiple sclerosis (MS) disease progression. Elevated sGFAP levels are considered to reflect ongoing astrocyte-related pathology in the central nervous system.

To study whether sGFAP levels associate with 18 kDa translocator protein (TSPO) availability in MS brain. TSPO is a mitochondrial molecule that is expressed by activated microglia and astrocytes.

Cross-sectional multimodal biomarker correlation study.

We included 80 people with MS (66 relapsing-remitting and 14 progressive MS, 69% women), and 11 healthy control participants (73% women). sGFAP was measured using single molecule array (Simoa®) technology in combination with 3T magnetic resonance imaging and positron emission tomography (PET) using a TSPO-binding [11C]PK11195 radioligand.

sGFAP was higher among people with progressive MS (median 122 pg/ml) compared to healthy controls (median 59 pg/ml, p = 0.0002) or participants with relapsing-remitting MS (median 77 pg/ml, p = 0.0056). Among people with MS, higher sGFAP associated with higher volume of chronic lesions with increased TSPO activity (r = 0.36, p = 0.0011) and with thalamic TSPO activity (r = 0.30, p = 0.0069), as well as with T1 and T2 lesion loads (r = 0.38, 0.41, p = 0.0005, 0.0002, respectively). Smaller normal-appearing white matter (r = −0.36, p = 0.0009), cortical gray matter, and thalamus volumes (r = −0.39, p = 0.0003 for both) correlated with higher sGFAP. In regression analyses, the volume of TSPO-expressing lesions, together with age and MS disease-modifying treatment status, explained 27% of the variation in sGFAP.

sGFAP associates with adverse magnetic resonance imaging and PET imaging outcomes. The association between a high prevalence of TSPO-expressing white matter lesions and high sGFAP suggests that lesion-associated glial activity promotes MS progression partially via astrocyte-driven mechanisms. A combination of various soluble biomarkers and PET ligands for specific cell types may add to the understanding of progression-promoting cellular mechanisms in the brain.

ClinicalTrials.gov NCT03134716, NCT03368677, NCT04126772, NCT04239820, https://clinicaltrials.gov.