Plasma DYRK1A as a novel risk factor for Alzheimer's disease

Abstract

To determine whether apparent involvement of DYRK1A in Alzheimer's disease (AD) pathology makes it a candidate plasma biomarker for diagnosis, we developed a method to quantify plasma DYRK1A by immunoblot in transgenic mouse models having different gene dosages of Dyrk1a, and, consequently, different relative protein expression. Then, we measured plasma DYRK1A levels in 26 patients with biologically confirmed AD and 25 controls (negative amyloid imaging available on 13). DYRK1A was detected in transgenic mouse brain and plasma samples, and relative levels of DYRK1A correlated with the gene copy number. In plasma from AD patients, DYRK1A levels were significantly lower compared with controls (P<0.0001). Results were similar when we compared AD patients with the subgroup of controls confirmed by negative amyloid imaging. In a subgroup of patients with early AD (CDR=0.5), lower DYRK1A expression was confirmed. In contrast, no difference was found in levels of DYRK1B, the closest relative of DYRK1A, between AD patients and controls. Further, AD patients exhibited a positive correlation between plasma DYRK1A levels and cerebrospinal fluid tau and phosphorylated-tau proteins, but no correlation with amyloid-β42 levels and Pittsburgh compound B cortical binding. DYRK1A levels detected in lymphoblastoid cell lines from AD patients were also lower when compared with cells from age-matched controls. These findings suggest that reduced DYRK1A expression might be a novel plasma risk factor for AD.

Figure 1

DYRK1A expression in plasma as detected by immunoblot. Western blotting of (a) DYRK1A expression in mouse and human frontal cortex; and (b) DYRK1A expression in human plasma. Slot blot analysis of relative DYRK1A protein levels in: (c) cortex of Dyrk1a^(+/−) mice (120-day-old males) in light grey versus wild-type mice (WT); (d) cortex of mBACtgDyrk1a mice (120-day-old males) in dark grey versus WT; (e) plasma of Dyrk1a^(+/−) mice; and (f) plasma of mBACtgDyrk1a mice. Box plots indicate median with min to max, *P<0.05; a.u., arbitrary unit.

Figure 2

DYRK1 protein levels in plasma from control (CTRL) individuals and Alzheimer's disease (AD) patients. Slot-blotting was used to detect relative expression of (a) DYRK1A in CTRL and AD; (b) DYRK1B in CTRL and AD; (c) DYRK1A in CTRL and early-stage AD. White dots: controls; black dots: AD patients. Graph bars indicate mean±s.e.m; ****P<0.0001; ***P<0.001; a.u., arbitrary unit.

Figure 3

DYRK1A protein levels stratified (a) according to PIB values with PIB<1.4 and PIB>1.4; and (b) according to APOE genotype with ‘no ApoE4' for APOE2 or APOE3 genotypes and ‘ApoE4' for one or two APOE4 alleles. White dots: controls; black dots: Alzheimer's disease patients. Graph bars indicate mean±s.e.m; ***P<0.001; **P<0.01; a.u., arbitrary unit; PIB, Pittsburgh compound B.

Figure 4

Correlation analysis between level of CSF markers and DYRK1A level. (a) Aβ42 level and DYRK1A level; (b) tau level and DYRK1A level; (c) p-tau level and DYRK1A level. Correlation was assessed with nonparametric Spearman's rank correlation test. Graphs show regression lines with a 95% confidence interval; a.u., arbitrary unit; CSF, cerebrospinal fluid; p-tau, phosphorylated tau.

Figure 5

Relative DYRK1A protein levels in LCLs from control (CTRL) and Alzheimer's disease (AD) patients. White dots: controls; black dots, AD patients. Graph bars indicate mean±s.e.m.; *P<0.05.