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Determine the role of ALK5 signaling in murine brain pericytes at embryonic day E13.5

ABSTRACT: Pericytes (PCs) are microvascular mural cells which constituent the embryonic blood brain barrier (BBB) along with endothelial cells (ECs). During brain development, germinal matrix (GM) - a highly vascularized region rich in neuronal-glial precursors, is selectively vulnerable to hemorrhage in premature infants. The transforming growth factor β (TGFβ) pathway plays a crucial role in barrier development by regulating cellular cross talk between PCs and ECs. Indeed, murine embryos lacking TGFβ receptor activin receptor-like kinase 5 (Alk5) in brain PCs (mutants) develop gross germinal matrix hemorrhage-intraventricular hemorrhage (GMH-IVH) and culminate in perinatal lethality. Mutant GM vessels display reduced PC and collagen coverage, abnormal vessel dilation and EC hyperproliferation. However, the mechanistic link between PC-specific deletion of ALK5 and aberrant EC behavior remains elusive. Herein, using bulk RNA sequencing from human brain PCs lacking ALK5 (siALK5) as well as murine vascular cells [PCs and ECs] isolated from embryonic brain at embryonic days E11.5 and E13.5 we establish that angiopoietin 2 (ANGPT2), a secreted angiogenic growth factor, is robustly repressed by the TGFβ pathway in PCs. Conversely, mutants lacking PC-ALK5 secrete higher levels of ANGPT2 resulting in overactivation of tyrosine protein kinase receptor (TIE2) and culminating in EC hyperproliferation, vessel dilation, BBB breakdown and GMH. PC-specific Angpt2 deletion or pharmacological inhibition in mutants improves GM vessel morphology, reduces EC proliferation and attenuates GMH pathogenesis. Taken together, we demonstrate that loss of TGFβ-mediated ANGPT2 repression in PCs is detrimental for BBB integrity and identify ANGPT2 as an important pathological target for GMH-IVH.

ORGANISM(S): Mus musculus

PROVIDER: GSE268575 | GEO | 2024/06/30

REPOSITORIES: GEO

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Project description:Acquired neonatal brain lesions result from the co-incidence of environment deleterious factors occurring at a specific development stage. Hypoxia-ischemia and inflammation are the major triggers of brain damage in late pregnancy and early infancy, and result in a variety of damages depending on whether it affected fetuses, early or late preterm infants or at term neonates. Indeed brain responses to insults are different depending on age, since cerebral tissue presents a rapidly evolving cellular and biochemical substrate in this period. Clearly age-dependent etiology is largely documented; e.g. Intraventricular/intraparenchymal (IVH/IPH) brain hemorrhage in fetuses and extreme preterm (less than 28 gestation weeks; GW); focal or diffuse periventricular leucomalacia in preterm aged 28-34 GW or cortical necrosis in term infants. Definite periods of occurrence of preterm-encephalopathy are associated to particular vulnerability of distinct cell populations. Functional deficits remain in grown-up and represent a human and economical burden. IVH/IPH affects extreme preterm infants. It specific periventricular germinal matrix (GM) localization reveal vascular vulnerability at this site during a definite period. GM is the site of particularly intense metabolism due to neural cell precursor multiplication and angiogenesis. In addition, GM is at risk of hypoperfusion or perfusion arrest due to its watershed situation between centripetal and centrifugal vascular supplies, especially in very preterm infants otherwise subjected to fluctuant hemodynamics. Thus vascular bed in GM cumulates hypoxia-ischemia risks. The vulnerability of vasculature in this area was referred to be linked to intense angiogenesis and micro-vessels remodeling. Indeed endothelial support by pericytes and astrocytes end-feet is loose in these vessels and angiogenic factors also exhibit pro-hemorrhage potential. The blood to brain interface referred to as neurovascular unit is the multicellular structure shaping endothelial cells to regulate vascular permeability. The blood brain barrier (BBB) restrains pericellular diffusion and allows specific trans-endothelial transports. In previous studies in mice, we have observed structural and functional differences between young and adult brain microvascular endothelial cells (mvEC). Of note mvEC from neonates express the NMDA receptor and glutamate in these cells elicit protease secretions involved in vascular remodeling, while adult mvEC did not. Genetic inactivation of the t-PA inhibitor-1 allowed to mimick an age dependent IVH/IPH up to 5 days post-natal (P5) in mice. These observations (and others) support the hypothesis that mouse brain microvessels represent a heuristic paradigm in the study of vascular maturity as a favoring background for age dependent neonate brain hemorrhage. The present project was designed at studying constitutive protein contents of brain microvessels in a large scale, around the period of high disruption propensity (P5). We prepared enriched fractions of mouse forebrain microvessels (fMV) in order to insolating the neurovascular unit made of endothelial cells linked by blood brain barrier junctions, basal lamina including pericytes, astrocyte and neuritic end-feet from P5 (pro-hemorrhagic state), P10 (Immature hemorrhage resistant state) and P60 (Mature) mice, to study proteome onotogeny in fMV.