Ciliopathy Features in Mouse Models of Down Syndrome

About This Grant

SUMMARY Down syndrome (DS), also known as Trisomy 21 (T21), is a common genetic disorder caused by an extra copy of chromosome 21. This additional genetic material disrupts multiple molecular pathways and leads to a range of health problems, including cognitive impairment. The circulation of cerebrospinal fluid (CSF) through the brain's ventricular system is crucial for maintaining brain homeostasis. This involves distributing nutrients, eliminating waste, managing fluid pressure, and regulating ventricular neurogenesis. The flow of CSF is supported by the coordinated beating of multiple cilia of the ciliated cells of the ependymal lining of the ventricles. Recent studies using mouse models with trisomy of genes orthologous to those on human chromosome 21 have revealed various defects characteristic of ciliopathies, suggesting a potential link between DS and impaired ciliary function. In the brain, this link may manifest as alterations in ependymal architecture, morphology and arrangement of ciliated cells, ciliary motion, fluid flow, and adult neurogenesis. Our collaborative team has developed novel techniques for live imaging and analysis of ciliated cell arrangement, ciliary motion, ciliary beat frequency (CBF), and CSF flow in brain ventricles. These include innovative algorithms for analyzing ependymal architecture in the lateral ventricles, arrangement and planar polarity of multiciliated ependymal cells, automatically quantifying CBF, and analyzing cilia motion, flow velocity, and flow directionality in live imaging experiments. These methods have enabled us to uncover previously unrecognized features in the arrangement and function of ciliated cells in the ventricular walls and to characterize ciliopathies in mutant mouse lines. Specifically, we discovered that in addition to the primary posterior-to-anterior flow along the ventricular wall, there are multiple local microflows with diverse trajectories exist there, including both direct and curved paths, which deviate from the main flow direction. We also found that across extensive areas of the ventricular walls, multiciliated cells align only locally with immediate neighbors, forming defined cell domains with diverging polarity; this arrangement likely facilitates the complex mosaic of the microflows, enhancing CSF distribution across the ependyma. We now propose to apply these advanced novel methods to analyze ependyma architecture, ciliary motion, and flow in DS mouse models. In our first specific aim we will determine the changes in the overall architecture of the ependyma (ciliated cell domain arrangement, translational polarity, neurogenesis) in an overlapping set of DS model lines, as compared to the mice of the background strain. In our second specific aim we will use live imaging to compare flow velocity and composition, ciliary motion, and CBF between DS models and control mice. Together, these experiments will help determine whether ciliary dysfunction may contribute to DS neurological phenotypes.