Validation of human kallikrein 6 in the cerebrospinal fluid of patients with progressive and non-progressive alzheimer’s disease: correlation with other biomarkers

Alzheimer’s disease (AD) biomarkers in plasma and cerebrospinal fluid (CSF) are useful for disease diagnosis, prognosis, risk assessment and monitoring therapy response, as well as for uncovering altered disease pathways. Previously, we and others cloned a novel gene, KLK6, which encodes a serine protease of the kallikrein family. The protein (hK6) is highly expressed in the brain, spinal cord and cerebellum. To examine the correlation of hK6 concentration in CSF with various clinicopathological variables in AD, we used a quantitative ELISA system. The variables examined included patient age, sex, MMSE score, APOE status, amyloid β 1-42 (Αβ1-42), phosphorylated Tau 181 (p-Tau181), total Tau (t-Tau). Previously, using a cohort of Swedish and Norwegian patients, we established a positive correlation between CSF hK6 and age as well as the levels of core AD biomarkers in four groups of patients (cognitively normal, MCI without progression to AD, MCI with progression to AD within 2 years and AD dementia). In this investigation, our goal was to validate these previous data with a large and independent patient cohort from Spain. We found that CSF hK6 is minimally or not affected by patient age and sex, but it significantly correlates with MMSE score and CSF Aβ1-42, p-Tau1811 and t-Tau. We conclude that these correlations further support our previous findings and suggest that hK6 may be an additional biomarker for AD and may play some role in the pathogenesis of AD.