Chronic depressive symptomatology and CSF amyloid beta and tau levels in mild cognitive impairment

Objectives: To investigate the association between chronic subsyndromal symptoms of depression (SSD), cerebrospinal fluid (CSF) biomarkers, and neuropsychological performance in individuals with mild cognitive impairment (MCI). Methods: Participants included 238 older adults diagnosed with MCI from the Alzheimer's Disease Neuroimaging Initiative repository with cognitive and CSF amyloid beta (Aβ_1–42), total tau (t-tau), and phosphorylated tau (p-tau) data. The Neuropsychiatric Inventory identified individuals with chronic endorsement (SSD group N = 80) or no endorsement (non-SSD group N = 158) of depressive symptoms across timepoints. CSF biomarker and cognitive performance were evaluated with linear regression models adjusting for age, education, gender, APOE genotype, global cognitive status, and SSD group. Results: As compared to the non-SSD group, the SSD group displayed lower CSF Aβ_1–42 levels (β = −24.293, S.E. = 6.345, P < 0.001). No group differences were observed for CSF t-tau (P = 0.497) or p-tau levels (P = 0.392). Lower CSF Aβ_1–42 levels were associated with poorer performance on learning (β = 0.041, S.E. = 0.018, P = 0.021) and memory (β = −0.012, S.E. = 0.005, P = 0.031) measures, whereas higher CSF t-tau levels were associated with poorer performance on measures of global cognition (β = 0.022, S.E = 0.008, P = 0.007) and language (β = −0.010, S.E = 0.004, P = 0.019). SSD was independently associated with diminished global cognition, learning and memory, language, and executive function performance over and above the effects of CSF biomarkers (all P < 0.05). Conclusions: MCI participants with SSD displayed diminished CSF Aβ_1–42 levels but did not differ from non-SSD controls in CSF tau levels. Additionally, CSF biomarkers and SSD independently accounted for variance in cognitive performance, suggesting that these factors may uniquely confer cognitive risk in MCI.