Long-term effect of neonatal inhibition of APP gamma-secretase on hippocampal development in the Ts65Dn mouse model of Down syndrome
Authors: Alessandra Raspanti
Elisabetta Ciani
Sandra Guidi
Renata Bartesaghi
Andrea Giacomini
Jacopo Magistretti
Alessandro Giuliani
Andrea Bighinati
Laura Calzà
Fiorenza Stagni
Marco Emili
Journal: Neurobiology of Disease (2017)
Discipline: NEUROSCIENCE & BEHAVIOR
Keywords: APP; Down syndrome; Gamma-secretase; Hippocampal development; Neonatal pharmacotherapy.
Affiliations: Department of Biomedical and Neuromotor Sciences, University of Bologna, Bologna, Italy., Department of Biology and Biotechnology "L. Spallanzani", University of Pavia, Pavia, Italy., Department of Veterinary Medical Sciences,University of Bologna, Bologna, Italy., Health Sciences and Technologies - Interdepartmental Center for Industrial Research (HST-ICIR), University of Bologna, Bologna, Italy., Department of Biomedical and Neuromotor Sciences, University of Bologna, Bologna, Italy. Electronic address: .

Abstract:  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. 

Retracted: No

PubPeer comments:
 In this paper, miR-296-5p is said to be measured by qPCR and normalised to U6. The indicated primers for U6 bind well to some variants of the U6 RNA. The indicated primers for miR-296-5p, Forward GTATCCAGTGCAGGGTCCGA and Reverse 5u02b9-CGACGAGGGCCCCCCCT, include a reverse primer sharing some sequence with the mature 296-5p. But unless I am mistaken, a PCR primer set designed to amplify an RT product prepared from a mature microRNA would be expected instead to have a  forward primer that matches the mature miRNA (not a reverse primer, as here), and a  reverse primer that amplifies some artificial sequence that is introduced during RT. It seems that the forward and reverse primers may have been switched, and that the strategy was a stem-loop RT, although the RT primer is not disclosed. It is possible that I do not fully understand the amplification strategy, so I hope the authors can respond with a clear description of the RT and amplification strategy, which does not seem to be present in the publication. ,