A flavonoid agonist of the TrkB receptor for BDNF improves hippocampal neurogenesis and hippocampus-dependent memory in the Ts65Dn mouse model of DS

Intellectual disability is the unavoidable hallmark of Down syndrome (DS), with a heavy impact on public health. Reduced neurogenesis and impaired neuron maturation are considered major determinants of altered brain function in DS. Since the DS brain starts at a disadvantage, attempts to rescue neurogenesis and neuron maturation should take place as soon as possible. The brain-derived neurotrophic factor (BDNF) is a neurotrophin that plays a key role in brain development by specifically binding to tropomyosin-related kinase receptor B (TrkB). Systemic BDNF administration is impracticable because BDNF has a poor blood-brain barrier penetration. Recent screening of a chemical library has identified a flavone derivative, 7,8-dihydroxyflavone (7,8-DHF), a small-molecule that crosses the blood-brain barrier and binds with high affinity and specificity to the TrkB receptor. The therapeutic potential of TrkB agonists for neurogenesis improvement in DS has never been examined. The goal of our study was to establish whether it is possible to restore brain development in the Ts65Dn mouse model of DS by targeting the TrkB receptor with 7,8-DHF. Ts65Dn mice subcutaneously injected with 7,8-DHF in the neonatal period P3-P15 exhibited a large increase in the number of neural precursor cells in the dentate gyrus and restoration of granule cell number, density of dendritic spines and levels of the presynaptic protein synaptophysin. In order to establish the functional outcome of treatment, mice were treated with 7,8-DHF from P3 to adolescence (P45-50) and were tested with the Morris Water Maze. Treated Ts65Dn mice exhibited improvement of learning and memory, indicating that the recovery of the hippocampal anatomy translated into a functional rescue. Our study in a mouse model of DS provides novel evidence that treatment with 7,8-DHF during the early postnatal period restores the major trisomy-linked neurodevelopmental defects, suggesting that therapy with 7,8-DHF may represent a possible breakthrough for Down syndrome.