Interplay between the catecholaminergic enzymatic axis and neurodegeneration/neuroinflammation processes in the Alzheimer's disease continuum.

Abstract

The locus coeruleus (LC) provides dopamine/noradrenaline (DA/NA) innervation throughout the brain and undergoes early degeneration in Alzheimer's disease (AD). We evaluated catecholaminergic enzyme levels in the cerebrospinal fluid (CSF) of a group of patients biologically defined as within the AD continuum (ADc) and explored their relationship with AD biomarkers and cytokine/growth factor levels to investigate their interplay with neurodegenerative and neuroinflammatory processes. The CSF concentration of DA transporter (DAT), tyrosine-hydroxylase(TH), DOPA-decarboxylase (DDC), and dopamine-β-hydroxylase (DβH), as well as cytokine/growth factor levels, were analyzed in 41 ADc patients stratified according to CSF beta-amyloid (Aβ)1-42 (A) and p-tau(T)inAD pathological changes(A+T-) and AD(A+T+) subgroups, as well as in 15 control subjects (A-T-). The ADc group had lower CSF levels of DAT and TH but increased DβH levels to compensate for NA synthesis. DDC levels were higher in the A+ T+ subgroup but comparable with controls in the A+ T- subgroup, probably because the DA system is resilient to the degeneration of LC neurons in the absence of tau pathology. Adjusting for age, sex, APOE genotype, and cognitive status, a significant association was found between TH and Aβ1-42 (R2 =0.25) and between DDC and p-tau (R2 =0.33). Finally, TH correlated with interleukin (IL)-10 levels (p= 0.0008) and DβH with IL-1β (p= 0.03), IL-4 (p= 0.02), granulocyte colony-stimulating factor (p= 0.007), and IL-17 (p= 0.01). Taken together, these findings suggest that catecholaminergic enzymes, functional markers of the catecholaminergic system, are closely linked to the neurodegenerative and neuroinflammatory processes in AD pathology.