Early-occurring proliferation defects in peripheral tissues of the Ts65Dn mouse model of Down syndrome are associated with patched1 over expression.

Down syndrome (DS) is a genetic pathology due to the triplication of human chromosome 21. In addition to mental retardation, individuals with DS exhibit a large range of variable traits, including co-occurring congenital malformations. It is now clear that neurogenesis impairment underlies the typically reduced brain size and, hence, mental retardation in individuals with DS. The small body size and the constellation of congenital malformations in children with DS suggest that proliferation defects may involve peripheral tissues, in addition to the brain. The goal of the current study was to establish whether a generalized impairment of cell proliferation is a key feature of the trisomic condition. We used the Ts65Dn mouse, a widely used DS model, and examined proliferation in tissues with different embryological origin by 5-bromo-2-deoxyuridine immunohistochemistry. We found that 2-day-old (P2) Ts65Dn mice had notably fewer proliferating cells in the heart and liver, and in all proliferating niches of the skin and intestine. A reduced proliferation rate was still present in the intestine at P15. In all tissues, Ts65Dn mice had a similar number of apoptotic cells as euploid mice, indicating no unbalance in cell death. In the skin, liver and intestine of trisomic mice, we found a higher expression of patched1 (Ptch1), a receptor that represses the mitogenic sonic hedgehog (Shh) pathway. This suggests that Ptch1-dependent inhibition of Shh signaling may underlie proliferation impairment in trisomic peripheral tissues. In agreement with the widespread reduction in proliferation, neonate trisomic mice had a reduced body weight and this defect was still present at 30 days of age. Our findings show that, in all examined peripheral tissues, Ts65Dn mice exhibit a notable reduction in proliferation rate, suggesting that proliferation impairment may be a generalized defect of trisomic precursor cells.