Analysis of Matrix Metallo-Proteases and the Plasminogen System in Mild Cognitive Impairment and Alzheimer's Disease Cerebrospinal Fluid

The expression of matrix metallo-proteases (MMP-2, MMP-3, MMP-7, and MMP-9), plasminogen and their regulators (TIMP-1, tissue plasminogen activator and neuroserpin) was investigated in cerebrospinal fluid (CSF) from subjective cognitive impairment (SCI) subjects, mild cognitive impairment (MCI), and Alzheimer's disease (AD) cases. ELISA analysis revealed a significant increase in MMP-3 protein levels in CSF from AD subjects, compared to age-matched SCI and MCI cases. No significant differences in MMP-2 and MMP-9 protein levels were detected between the three groups. MMP-7 was undetectable in all three groups. MCI individuals exhibited increased levels of the metallo-protease inhibitor TIMP-1 in CSF as well as higher plasminogen and neuroserpin expression, compared to SCI subjects. Levels of tissue plasminogen activator (tPA) were significantly reduced in AD CSF. Correlation analysis revealed a significant positive association between MMP-3, p-tau, and total-tau levels. Conversely, there was a significant negative correlation between this protease and Mini-Mental State Examination (MMSE) scores. tPA positively correlated with amyloid-beta levels in CSF and with MMSE scores. Our results suggest that MMP-3 and tPA, in combination with current amyloid-beta and tau biomarkers, may have potential as surrogate indicators of an ongoing AD pathology.