ISDN2014_0056: Tgfbr2 conditional knock‐out in the developing telencephalon results in neurovascular defects

To understand the role of transforming growth factor beta (TGFβ) in forebrain development, we studied TGFβ-signalling in vivo via a Foxg1-cre knock-in mouse to conditionally knock-out the TGFβ receptor 2 (Tgfbr2). Surprisingly, the ventral telencephalon of Foxg1cre/+;Tgfbr2flox/flox (Tgfbr2-cKO) mutants displayed intracerebral hemorrhages, although FOXG1 is mainly expressed in progenitors and neurons of the telencephalon. Clustering of endothelial cells and reduced vessel branching were hallmarks of the impaired vasculature of mutant embryos. In contrast, pericytes covered endothelial tubes as in control animals and cell junctions connected endothelial cells. However, the integrity of the extracellular matrix (ECM) was disturbed in Tgfbr2-cKO. Endothelial cells and pericytes did not express Foxg1 in significant amounts. Thus, the vascular defects arose from disturbed signals between neurons and vessels, involving an altered secretome. Accordingly, we observed a variety of expression changes in mutant brains, which affected growth factors such as IGFs and IGF-binding proteins, TGFβ, and VEGF-A. Furthermore, ECM-associated molecules were altered such as THBS-2, ADAMTS-1, integrins as well as integrin-associated proteins. We determined the altered secretome as well as the neural proteome to reveal molecular factors involved in this complex phenotype. We studied the effects of the altered secretome using conditioned medium (CM) from primary neuronal cultures of different regions derived from Tgfbr2-cKO and control forebrains. HUVECs that were treated with this CM displayed less branching points and showed less migration towards it. Among the candidates that we explored in greater detail were VEGF-A, IGFs and TGFβ. VEGF-A supplementation reverted the observed alteration of HUVEC branching and migration, whereas application of TGFβ severed these conditions. In conclusion, Tgfbr2-cKO mice give the opportunity for analysing neural alongside endothelial development and factors that are mediating synchronized development.