Cerebrospinal fluid macrophage biomarkers in amyotrophic lateral sclerosis

Objective: The neurodegenerative disease amyotrophic lateral sclerosis (ALS) is a heterogeneous clinical syndrome involving multiple molecular pathways. The development of biomarkers for use in therapeutic trials is a priority. We sought to use a high-throughput proteomic method to identify novel biomarkers in individual cerebrospinal fluid samples. Methods: Liquid chromatography-tandem mass spectrometry with label-free quantification was used to identify cerebrospinal fluid proteins using samples from a well-characterised longitudinal cohort comprising patients with ALS (n=43), the upper motor neuron variant primary lateral sclerosis (PLS, n=6), cross-sectional healthy (n=20) and disease controls (Parkinsons’s n=20, ALS mimic disorders n=12). Results: Three macrophage-derived chitinases showed increased abundance in ALS: chitotriosidase (CHIT1), chitinase-3-like protein 1 (CHI3L1) and chitinase-3-like protein 2 (CHI3L2). Elevated CHI3L1 was common to ALS and PLS, whereas CHIT1 and CHI3L2 levels differed. Chitinase levels correlated with disease progression rate (CHIT1 r=0.56, pandlt;0.001; CHI3L1 r=0.31, p=0.028; CHI3L2 r=0.29, p=0.044). CHIT1, CHI3L1 and CHI3L2 levels correlated with phosphorylated neurofilament heavy chain (pNFH; r=0.62, pandlt;0.001; r=0.49, pandlt;0.001; r=0.41, pandlt;0.001). CHI3L1 levels, but not CHIT1 or CHI3L2, increased over time in those with low initial levels (gradient=0.005 log abundance units/month, p=0.001). High CHIT1 was associated with shortened survival (HR 2.84, p=0.009). Inclusion of pNFH in survival models left only an association of pNFH and survival (HR 1.26, p=0.019). Interpretation: Neuroinflammatory mechanisms have been consistently implicated through various experimental paradigms. These results support a key role for macrophage activity in ALS pathogenesis, offering novel target engagement and pharmacodynamic biomarkers for neuroinflammation-focused ALS therapy.