Cross-sectional and longitudinal measures of chitinase proteins in amyotrophic lateral sclerosis and expression of CHI3L1 in activated astrocytes

Objective: Amyotrophic lateral sclerosis (ALS) is a complex disease with numerous pathological mechanisms resulting in a heterogeneous patient population. Using biomarkers for particular disease mechanisms may enrich a homogeneous subset of patients. In this study, we quantified chitotriosidase (Chit-1) and chitinase-3-like protein 1 (CHI3L1), markers of glial activation, in cerebrospinal fluid (CSF) and plasma and determined the cell types that express CHI3L1 in ALS. Methods: Immunoassays were used to quantify Chit-1, CHI3L1 and phosphorylated neurofilament heavy chain levels in longitudinal CSF and matching plasma samples from 118 patients with ALS, 17 disease controls (DCs), and 24 healthy controls (HCs). Immunostaining was performed to identify and quantify CHI3L1-positive cells in tissue sections from ALS, DCs and non-neurological DCs. Results: CSF Chit-1 exhibited increased levels in ALS as compared with DCs and HCs. CSF CHI3L1 levels were increased in ALS and DCs compared with HCs. No quantitative differences were noted in plasma for either chitinase. Patients with ALS with fast-progressing disease exhibited higher levels of CSF Chit-1 and CHI3L1 than patients with slow-progressing disease. Increased numbers of CHI3L1-positive cells were observed in postmortem ALS motor cortex as compared with controls, and these cells were identified as a subset of activated astrocytes located predominately in the white matter of the motor cortex and the spinal cord. Conclusions: CSF Chit-1 and CHI3L1 are significantly increased in ALS, and CSF Chit-1 and CHI3L1 levels correlate to the rate of disease progression. CHI3L1 is expressed by a subset of activated astrocytes predominately located in white matter.