Inhibition of APP gamma-secretase restores Sonic Hedgehog signaling and neurogenesis in the Ts65Dn mouse model of Down syndrome.

Neurogenesis impairment starting from early developmental stages is a key determinant of intellectual disability in Down syndrome (DS). Previous evidence provided a causal relationship between neurogenesis impairment and malfunctioning of the mitogenic Sonic Hedgehog (Shh) pathway. In particular, excessive levels of AICD (amyloid precursor protein intracellular domain), a cleavage product of the trisomic gene APP (amyloid precursor protein) up-regulate transcription of Ptch1 (Patched1), the Shh receptor that keeps the pathway repressed. Since AICD results from APP cleavage by γ-secretase, the goal of the current study was to establish whether treatment with a γ-secretase inhibitor normalizes AICD levels and restores neurogenesis in trisomic neural precursor cells. We found that treatment with a selective γ-secretase inhibitor (ELND006; ELN) restores proliferation in neurospheres derived from the subventricular zone (SVZ) of the Ts65Dn mouse model of DS. This effect was accompanied by reduction of AICD and Ptch1 levels and was prevented by inhibition of the Shh pathway with cyclopamine. Treatment of Ts65Dn mice with ELN in the postnatal period P3-P15 restored neurogenesis in the SVZ and hippocampus, hippocampal granule cell number and synapse development, indicating a positive impact of treatment on brain development. In addition, in the hippocampus of treated Ts65Dn mice there was a reduction in the expression levels of various genes that are transcriptionally regulated by AICD, including APP, its origin substrate. Inhibitors of γ-secretase are currently envisaged as tools for the cure of Alzheimer's disease because they lower βamyloid levels. Current results provide novel evidence that γ-secretase inhibitors may represent a strategy for the rescue of neurogenesis defects in DS.

Giacomini A ，Stagni F ，Trazzi S ，Guidi S ，Emili M ，Brigham E ，Ciani E ，Bartesaghi R ... -  《-》

Long-term effect of neonatal inhibition of APP gamma-secretase on hippocampal development in the Ts65Dn mouse model of Down syndrome.

Neurogenesis impairment is considered a major determinant of the intellectual disability that characterizes Down syndrome (DS), a genetic condition caused by triplication of chromosome 21. Previous evidence obtained in the Ts65Dn mouse model of DS showed that the triplicated gene APP (amyloid precursor protein) is critically involved in neurogenesis alterations. In particular, excessive levels of AICD (amyloid precursor protein intracellular domain) resulting from APP cleavage by gamma-secretase increase the transcription of Ptch1, a Sonic Hedgehog (Shh) receptor that keeps the mitogenic Shh pathway repressed. Previous evidence showed that neonatal treatment with ELND006, an inhibitor of gamma-secretase, reinstates the Shh pathway and fully restores neurogenesis in Ts65Dn pups. In the framework of potential therapies for DS, it is extremely important to establish whether the positive effects of early intervention are retained after treatment cessation. Therefore, the goal of the current study was to establish whether early treatment with ELND006 leaves an enduring trace in the brain of Ts65Dn mice. Ts65Dn and euploid pups were treated with ELND006 in the postnatal period P3-P15 and the outcome of treatment was examined at ~one month after treatment cessation. We found that in treated Ts65Dn mice the pool of proliferating cells in the hippocampal dentate gyrus (DG) and total number of granule neurons were still restored as was the number of pre- and postsynaptic terminals in the stratum lucidum of CA3, the site of termination of the mossy fibers from the DG. Accordingly, patch-clamp recording from field CA3 showed functional normalization of the input to CA3. Unlike in field CA3, the number of pre- and postsynaptic terminals in the DG of treated Ts65Dn mice was no longer fully restored. The finding that many of the positive effects of neonatal treatment were retained after treatment cessation provides proof of principle demonstration of the efficacy of early inhibition of gamma-secretase for the improvement of brain development in DS.

Stagni F ，Raspanti A ，Giacomini A ，Guidi S ，Emili M ，Ciani E ，Giuliani A ，Bighinati A ，Calzà L ，Magistretti J ，Bartesaghi R ... -  《-》

The amyloid precursor protein (APP) triplicated gene impairs neuronal precursor differentiation and neurite development through two different domains in the Ts65Dn mouse model for Down syndrome.

Trazzi S ，Fuchs C ，Valli E ，Perini G ，Bartesaghi R ，Ciani E ... -  《-》

Short- and long-term effects of neonatal pharmacotherapy with epigallocatechin-3-gallate on hippocampal development in the Ts65Dn mouse model of Down syndrome.

Cognitive disability is an unavoidable feature of Down syndrome (DS), a genetic disorder due to the triplication of human chromosome 21. DS is associated with alterations of neurogenesis, neuron maturation and connectivity that are already present at prenatal life stages. Recent evidence shows that pharmacotherapies can have a large impact on the trisomic brain provided that they are administered perinatally. Epigallocatechin-3-gallate (EGCG), the major polyphenol of green tea, performs many actions in the brain, including inhibition of DYRK1A, a kinase that is over-expressed in the DS brain and contributes to the DS phenotype. Young adults with DS treated with EGCG exhibit some cognitive benefits, although these effects disappear with time. We deemed it extremely important, however, to establish whether treatment with EGCG at the initial stages of brain development leads to plastic changes that outlast treatment cessation. In the current study, we exploited the Ts65Dn mouse model of DS in order to establish whether pharmacotherapy with EGCG during peak of neurogenesis in the hippocampal dentate gyrus (DG) enduringly restores hippocampal development and memory performance. Euploid and Ts65Dn mice were treated with EGCG from postnatal day 3 (P3) to P15. The effects of treatment were examined at its cessation (at P15) or after one month (at P45). We found that at P15 treated trisomic pups exhibited restoration of neurogenesis, total hippocampal granule cell number and levels of pre- and postsynaptic proteins in the DG, hippocampus and neocortex. However, at P45 none of these effects were still present, nor did treated Ts65Dn mice exhibit any improvement in hippocampus-dependent tasks. These findings show that treatment with EGCG carried out in the neonatal period rescues numerous trisomy-linked brain alterations. However, even during this, the most critical time window for hippocampal development, EGCG does not elicit enduring effects on the hippocampal physiology.

Stagni F ，Giacomini A ，Emili M ，Trazzi S ，Guidi S ，Sassi M ，Ciani E ，Rimondini R ，Bartesaghi R ... -  《-》

APP-dependent up-regulation of Ptch1 underlies proliferation impairment of neural precursors in Down syndrome.

Trazzi S ，Mitrugno VM ，Valli E ，Fuchs C ，Rizzi S ，Guidi S ，Perini G ，Bartesaghi R ，Ciani E ... -  《-》