Combined assessment of DYRK1A, BDNF and homocysteine levels as diagnostic marker for Alzheimer's disease

Abstract

Early identification of Alzheimer's disease (AD) risk factors would aid development of interventions to delay the onset of dementia, but current biomarkers are invasive and/or costly to assess. Validated plasma biomarkers would circumvent these challenges. We previously identified the kinase DYRK1A in plasma. To validate DYRK1A as a biomarker for AD diagnosis, we assessed the levels of DYRK1A and the related markers brain-derived neurotrophic factor (BDNF) and homocysteine in two unrelated AD patient cohorts with age-matched controls. Receiver-operating characteristic curves and logistic regression analyses showed that combined assessment of DYRK1A, BDNF and homocysteine has a sensitivity of 0.952, a specificity of 0.889 and an accuracy of 0.933 in testing for AD. The blood levels of these markers provide a diagnosis assessment profile. Combined assessment of these three markers outperforms most of the previous markers and could become a useful substitute to the current panel of AD biomarkers. These results associate a decreased level of DYRK1A with AD and challenge the use of DYRK1A inhibitors in peripheral tissues as treatment. These measures will be useful for diagnosis purposes.

Figure 1

Characterization of a new monoclonal antibody against DYRK1A. (a) Western blots of heads from mouse embryos; lane 1: 0 copies of DYRK1A, lane 2: 1 copy, lane 3: 2 copies; protein marker sizes (kDa): 95, 70, 62, 51, 42; left panel: M01 antibody (7D10), right panel: N6 antibody; loading control: Ponceau staining. (b) Quantification of DYRK1A content in plasma from adult mice with 1 Dyrk1a (+/−), 2 (2N) or 3 (mBACtgDyrk1a) copies of the Dyrk1a gene, with N6 antibody.

Figure 2

DYRK1A protein levels in plasma from control (CTRL) individuals and Alzheimer’s disease (AD) patients from cohort M (Munich). SPIE-IA ELISA was used to detect expression of DYRK1A in CTRL and AD (a) with N6 antibody; (b) with M01 antibody; white box: controls; red box: AD patients. (c) DYRK1A protein levels stratified according to APOE genotype with ‘no ApoE4’ for APOE2 or APOE3 genotypes and ‘ApoE4’ for one or two APOE4 alleles: white dots: controls; red dots: AD patients. (d) sAPPbeta protein levels: white box: controls; red box: AD patients. Bars indicate mean±s.e.m, ****P<0.0001, ***P<0.001. ELISA, enzyme-linked immunosorbent assay; SPIE-IA, solid phase immobilized epitope-immunoassay.

Figure 3

(a) Diagnostic accuracy of DYRK1A, BDNF and Hcy markers. (b) Correlation between descriptors and the first principal plane (PC1 + PC2). The closer the descriptors are to the correlation circle, the more they contribute to explaining the variability captured by the corresponding principal components. As indicated by the projection of the biomarker variable descriptors close to the PCA correlation circle, the DYRK1A and BDNF descriptors are strongly correlated and capture the majority of the variability of the data (more than 47.60%) on PC1 while Hcy is negatively correlated with these two first descriptors and is associated with 35.9% of the variability. (c) Distribution of Munich and Paris cohorts showing good overlap between the two control groups and the two AD groups. AD, Alzheimer's disease; AUC, area under the curve; BDNF, brain-derived neurotrophic factor; Hcy, homocysteine; PCA, principal component analysis.

Figure 4

Diagnostic efficiency for each patient LR1: using one (DYRK1A), LR2: two (DYRK1A+BDNF) or LR3: three (DYRK1A+BDNF+Hcy) biomarkers; red dots: correctly diagnosed AD; black dots: correctly diagnosed control; blue cross: false diagnostic. AD, Alzheimer's disease; BDNF, brain-derived neurotrophic factor; Hcy, homocysteine; PC, principal component.