Green tea polyphenols rescue of brain defects induced by overexpression of DYRK1A

Abstract

Individuals with partial HSA21 trisomies and mice with partial MMU16 trisomies containing an extra copy of the DYRK1A gene present various alterations in brain morphogenesis. They present also learning impairments modeling those encountered in Down syndrome. Previous MRI and histological analyses of a transgenic mice generated using a human YAC construct that contains five genes including DYRK1A reveal that DYRK1A is involved, during development, in the control of brain volume and cell density of specific brain regions. Gene dosage correction induces a rescue of the brain volume alterations. DYRK1A is also involved in the control of synaptic plasticity and memory consolidation. Increased gene dosage results in brain morphogenesis defects, low BDNF levels and mnemonic deficits in these mice. Epigallocatechin gallate (EGCG) - a member of a natural polyphenols family, found in great amount in green tea leaves - is a specific and safe DYRK1A inhibitor. We maintained control and transgenic mice overexpressing DYRK1A on two different polyphenol-based diets, from gestation to adulthood. The major features of the transgenic phenotype were rescued in these mice.

Figure 1. Phenotypic correction by genotype correction of DYRK1A copy number.

Wild type (WT), YACtg152F7 transgenic (TG), dyrk1a (+/−) (HT) and double transgenics (TGxHT) generated by three different crossings. A: brain DYRK1A mRNA levels determined by quantitative PCR; B: in vivo MRI assessment of total brain volume (mm³); ** for p<0.01. (Mann-Whitney-Wilcoxon test; statistical significance considered to be p<0.05); C: linear regression analysis of brain volume and DYRK1A gene dosage. (R2 = 0.977).

Figure 2. Average DYRK1A protein levels in thalamus-hypothalamus for each genotype-treatment group.

A: western blot assessment of dyrk1a and actin levels; B: average Dyrk1a protein levels for wild type (WT, n = 6), YACtg152F7 transgenic (TG, n = 6) water-fed (H2O) and in wild type (WT, n = 3), YACtg152F7 transgenic (TG, n = 7) green tea-fed (GTP). ** for p<0.01.

Figure 3. Effect of GTP treatment on DYRK1A-induced brain alterations.

A: weight of total brain (mg) in wild type (WT, n = 26), YACtg152F7 (TG, n = 13) water-fed (H2O) and in wild type (WT, n = 13), YACtg152F7 transgenic (TG, n = 18) green tea-fed GTP; B: in vivo MRI assessment of total brain volume (mm³) in wild type (n = 10) and YACtg152F7 transgenic (n = 10) water-fed (H2O) and in wild type (n = 9) and YACtg152F7 transgenic (n = 11) green tea-fed GTP; C: in vivo MRI assessment of hypothalamus-thalamus volume (mm³) in wild type (n = 6) and YACtg152F7 transgenic (n = 6) water-fed (H2O) and in wild type (n = 5) and YACtg152F7 transgenic (n = 7) green tea-fed (GTP). (Details of the MRI experiments in supp. data). ** for p<0.01; * for p<0.05.

Figure 4. Effect of GTP treatment on short- and long-term memory.

In wild type (WT, n = 10) and YACtg152F7 transgenic (TG, n = 10) water-fed (H2O) and in wild type (WT, n = 10) and YACtg152F7 transgenic (TG, n = 10) green tea-fed (GTP, n = 10). A: Spontaneous alternation test with two sessions of ten minutes each separated by 24 h: number of alternations/total number of possible alternations ×100 (AS1). B: Object recognition test: difference in exploration time between the new and familiar objects, in percentage of total time spent exploring the two objects; 100×(N−F/N+F). ** for p<0.01, * for p<0.05. according to Wilcoxon test results (two-way ANOVA in supplementary data). C: Object recognition test on WT H₂O-fed (n = 10), WT polyphenon-fed (n = 10) and TG polyphenon-fed (n = 6) (no significant differences between the three groups).

Figure 5. Effect of GTP treatment on BDNF and TRKB mRNA levels.

mRNA levels determined by quantitative PCR. A: BDNF in fetal human hippocampus (EU: normal karyotype (n = 4) and T21: trisomy 21 (n = 5); B: BDNF in adult hippocampus from wild type (WT; n = 6), YACtg152F7 transgenic (TG; n = 10), water-fed (H2O) WT (n = 8), TG (n = 3), green tea-fed (GTP); C: TRKB in adult hippocampus from wild type (WT; n = 4), YACtg152F7 transgenic (TG; n = 18), water-fed (H2O) WT (n = 4), TG (n = 4) green tea-fed (GTP). ** for p<0.01; * for p<0.05.