Chitotriosidase, a biomarker of amyotrophic lateral sclerosis, accentuates neurodegeneration in spinal motor neurons through neuroinflammation

Abstract

Background: Cerebrospinal fluid from amyotrophic lateral sclerosis patients (ALS-CSF) induces neurodegenerative changes in motor neurons and gliosis in sporadic ALS models. Search for identification of toxic factor(s) in CSF revealed an enhancement in the level and enzyme activity of chitotriosidase (CHIT-1). Here, we have investigated its upregulation in a large cohort of samples and more importantly its role in ALS pathogenesis in a rat model. Methods: CHIT-1 level in CSF samples from ALS (n = 158), non-ALS (n = 12) and normal (n = 48) subjects were measured using ELISA. Enzyme activity was also assessed (ALS, n = 56; non-ALS, n = 10 and normal-CSF, n = 45). Recombinant CHIT-1 was intrathecally injected into Wistar rat neonates. Lumbar spinal cord sections were stained for Iba1, glial fibrillary acidic protein and choline acetyl transferase to identify microglia, astrocytes and motor neurons respectively after 48 h of injection. Levels of tumour necrosis factor-α and interleukin-6 were measured by ELISA. Findings: CHIT-1 level in ALS-CSF samples was increased by 20-fold and it can distinguish ALS patients with a sensitivity of 87% and specificity of 83.3% at a cut off level of 1405.43 pg/ml. Enzyme activity of CHIT-1 was also 15-fold higher in ALS-CSF and has a sensitivity of 80.4% and specificity of 80% at cut off value of 0.1077989 μmol/μl/min. Combining CHIT-1 level and activity together gave a positive predictive value of 97.78% and negative predictive value of 100%. Administration of CHIT-1 increased microglial numbers and astrogliosis in the ventral horn with a concomitant increase in the levels of pro-inflammatory cytokines. Amoeboid-shaped microglial and astroglial cells were also present around the central canal. CHIT-1 administration also resulted in the reduction of motor neurons. Conclusions: CHIT-1, an early diagnostic biomarker of sporadic ALS, activates glia priming them to attain a toxic phenotype resulting in neuroinflammation leading to motor neuronal death.

40 Years of CSF Toxicity Studies in ALS: What Have We Learnt About ALS Pathophysiology?

“…Proteomic analysis found CHIT-1 to be significantly upregulated in ALS-CSF compared to control CSF, suggesting its possible role as a biomarker ( Varghese et al, 2013 ). This was subsequently substantiated by findings from the same group demonstrating its high specificity and sensitivity as a diagnostic biomarker ( Varghese et al, 2020 ). It is worth commenting that the function of CHIT-1 in the human nervous system has still not been established, with CHIT-1 also being implicated in other neurodegenerative diseases, such as Alzheimer’s disease and multiple sclerosis ( Varghese et al, 2020 ).…”

“…Although many potentially toxic factors have emerged from studying the effects of ALS-CSF on glial cells, chitotriosidase-1 (CHIT-1), an inflammatory product specific to microglia, has been proposed to play a particularly important role in CSF-mediated neurodegeneration ( Varghese et al, 2020 ). Proteomic analysis found CHIT-1 to be significantly upregulated in ALS-CSF compared to control CSF, suggesting its possible role as a biomarker ( Varghese et al, 2013 ).…”

“…It is worth commenting that the function of CHIT-1 in the human nervous system has still not been established, with CHIT-1 also being implicated in other neurodegenerative diseases, such as Alzheimer’s disease and multiple sclerosis ( Varghese et al, 2020 ). Notwithstanding this, the particularly elevated levels of CHIT-1 in ALS-CSF, which have been found to promote astrogliosis and microgliosis, as well as neuronal loss, support its possible participation in CSF-mediated neurodegeneration ( Varghese et al, 2020 ).…”

Monocyte-Derived Macrophages Contribute to Chitinase Dysregulation in Amyotrophic Lateral Sclerosis: A Pilot Study

“…Indeed, a "feed-forward" loop wherein the chitinases sustain neuroinflammation in ALS via their autoand paracrine effects has already been postulated (12). For instance, Varghese et al demonstrated that microglia appear to be the primary cellular source for CHIT1 in the CNS using murine cultures and that microglia themselves were susceptible to the effects of accumulated CHIT1, as they were chronically activated as a result of exposure (11). Another study also showed that conditioned medium from MoMas induced CHI3L1 transcription and morphological changes in cultured human astrocytes (19).…”

“…In ALS, these moieties exacerbate neuroinflammation and directly affect neuronal viability (11)(12)(13). While studies using post-mortem motor cortex and spinal cord tissue from ALS patients have reported micro-and astroglial expression of CHIT1 and CHI3L1, respectively, the cellular origins of these targets remain to be fully understood.…”