Serum S100β Levels Are Linked with Cognitive Decline and Peripheral Inflammation in Spinocerebellar Ataxia Type 2

Experimental and clinical studies have indicated a potential role of the protein S100β in the pathogenesis and phenotype of neurodegenerative diseases. However, its impact on spinocerebellar ataxia type 2 (SCA2) remains to be elucidated. The objective of the study is to determine the serum levels of S100β in SCA2 and its relationship with molecular, clinical, cognitive, and peripheral inflammatory markers of the disease. Serum concentrations of S100β were measured by enzyme-linked immunosorbent assay in 39 SCA2 subjects and 36 age- and gender-matched controls. Clinical scores of ataxia, non-ataxia symptoms, cognitive dysfunction, and some blood cell count–derived inflammatory indices were assessed. The SCA2 individuals manifested S100β levels similar to the control group, at low nanomolar concentrations. However, the S100β levels were directly associated with a better performance of cognitive evaluation within the SCA2 cohort. Moreover, the S100β levels were inversely correlated with most peripheral inflammatory indices. Indeed, the neutrophil-to-lymphocyte ratio significantly mediated the effect of serum S100β on cognitive performance, even after controlling for the ataxia severity in the causal mediation analysis. Our findings suggested that, within physiologic concentrations, the protein S100β exerts a neuroprotective role against cognitive dysfunction in SCA2, likely via the suppression of pro-inflammatory mechanisms.