The Foxf2 gene in development and disease

Abstract

The Foxf2 gene in development and disease Azadeh Reyahi Department of Chemistry and Molecular Biology, University of Gothenburg, Box 462, SE 405 30, Göteborg, Sweden Abstract In this thesis I present our recent data on the involvement and the mechanism of action of the forkhead transcription factor Foxf2 in development of the brain microvasculature, formation of the blood-brain barrier, control of the intestinal stem cell niche, and fusion of the secondary palate. The potential clinical signifi- cance of these findings is strengthened by a correlation between Foxf2 expres- sion and intestinal adenoma formation, and by association between genetic vari- ants in human FOXF2 and incident stroke. We showed that Foxf2 is expressed in brain pericytes, but not in mural cells of other organs. Foxf2 null mutants have a defective brain vasculature and suffer from intracranial hemorrhage and a leaky blood-brain barrier with increased endothelial vesicular trans-cytosis. Foxf2-/- brain pericytes have diminished Pdg- frβ expression, and the cerebral vasculature a reduced activity of the Tgfβ –Alk5– Smad2/3 signaling pathway, associated with decreased expression of integrins, Tgfb2, Tgfbr2, Alk5 and other pathway components. In a large GWAS performed by an international consortium, we identified a genome-wide significant association of common variants near FOXF2 with risk of stroke. Conditional knockout mice, in which Foxf2 was deleted in healthy adults, developed clinical signs of stroke and exhibited cerebral ischemia, reactive glio- sis and microhemorrhage. The animal model results thus corroborate the human genetic association and identifies FOXF2 as a novel risk locus for stroke. In the intestine we showed that Foxf2 is expressed by subepithelial fibroblasts and restricts the size of the stem cell niche, and thereby the number and prolif- eration of Lgr5+ stem cells. Foxf2 is a target of epithelial hedegehog signaling and inhibits the Wnt pathway by increasing the expression of the extracellular Wnt inhibitor Sfrp1. As a consequence, reduced Foxf2 expression significantly in- creases both initiation and growth of intestinal tumors. Reduced proliferation and decreased extracellular matrix production in the neural crest-derived mesenchyme of the palatal shelves was found to be respon- sible for the cleft palate phenotype in Foxf2 null mutants. Mechanistically, the defect is associated with reduced canonical Tgfβ signaling and integrin expres- sion. The Tgfb2 mRNA level was not affected, but the amount of Tgfβ2 protein was significantly decreased in mutant palatal shelf mesenchyme.