BMPR2 acts as a gatekeeper to protect endothelial cells from increased TGFβ responses and altered cell mechanics

Abstract

Balanced transforming growth factor-beta (TGFβ)/bone morphogenetic protein (BMP)-signaling is essential for tissue formation and homeostasis. While gain in TGFβ signaling is often found in diseases, the underlying cellular mechanisms remain poorly defined. Here we show that the receptor BMP type 2 (BMPR2) serves as a central gatekeeper of this balance, highlighted by its deregulation in diseases such as pulmonary arterial hypertension (PAH). We show that BMPR2 deficiency in endothelial cells (ECs) does not abolish pan-BMP-SMAD1/5 responses but instead favors the formation of mixed-heteromeric receptor complexes comprising BMPR1/TGFβR1/TGFβR2 that enable enhanced cellular responses toward TGFβ. These include canonical TGFβ-SMAD2/3 and lateral TGFβ-SMAD1/5 signaling as well as formation of mixed SMAD complexes. Moreover, BMPR2-deficient cells express genes indicative of altered biophysical properties, including up-regulation of extracellular matrix (ECM) proteins such as fibrillin-1 (FBN1) and of integrins. As such, we identified accumulation of ectopic FBN1 fibers remodeled with fibronectin (FN) in junctions of BMPR2-deficient ECs. Ectopic FBN1 deposits were also found in proximity to contractile intimal cells in pulmonary artery lesions of BMPR2-deficient heritable PAH (HPAH) patients. In BMPR2-deficient cells, we show that ectopic FBN1 is accompanied by active β1-integrin highly abundant in integrin-linked kinase (ILK) mechano-complexes at cell junctions. Increased integrin-dependent adhesion, spreading, and actomyosin-dependent contractility facilitates the retrieval of active TGFβ from its latent fibrillin-bound depots. We propose that loss of BMPR2 favors endothelial-to-mesenchymal transition (EndMT) allowing cells of myo-fibroblastic character to create a vicious feed-forward process leading to hyperactivated TGFβ signaling. In summary, our findings highlight a crucial role for BMPR2 as a gatekeeper of endothelial homeostasis protecting cells from increased TGFβ responses and integrin-mediated mechano-transduction.

Endothelial Basement Membrane Components and Their Products, Matrikines: Active Drivers of Pulmonary Hypertension?

“…BMPR2 is a member of the TGF-β superfamily, and its mutations account for approximately 80% of all heritable and 25% of all idiopathic PAH cases [181,182]. The knockdown of BMPR2 in the endothelium concomitantly reduced COL4A1 and COL4A2 expression, which lead to endothelial dysfunction including reduced adhesion, migration, and tube formation [173,183] (see Figure 2). A similar phenotype was observed upon the silencing of β-catenin, which is a downstream mediator of BMPR2 signaling [173].…”

Exacerbated inflammatory signaling underlies aberrant response to BMP9 in pulmonary arterial hypertension lung endothelial cells

“…However, the effects of BMPs on the primary endothelium are highly context-dependent [21]. The concern that the same ligand might have opposite effects is illustrated by contradicting reports showing that genetic deletion or pharmacological inactivation of BMP9 protects rodents from experimental PH [22], while a case study associates a homozygous nonsense mutation in GDF2 (encoding for BMP9) with the development of PAH in infants [23], and BMPR2 loss-of-function mutations are known to alter the tissue microenvironment [24].…”

“…a Enrichment of PH signature pathways in control and PAH patient-derived MVECs based on the GSEA analysis. Arrowheads point out pathways in PAH samples that did not pass the enrichment threshold of FDR ≤ 0.05 and therefore are not regulated at24 h after BMP9 treatment compared to unstimulated samples. b Switch gene analysis per non-enriched pathway and per donor group based on RNA-seq.…”

The Roles of TGF-β Signaling in Cerebrovascular Diseases

“…BMP7 has been shown to inhibit hypoxia-induced EndMT and gremlin-1-mediated EndMT ( Zhang et al, 2018 , 2020 ). Loss of Bmpr2 in ECs leads to EndMT characterized by conversion of VE-cadherin to junctional N-cadherin, Slug and Twist upregulation, as well as increased expression of extracellular matrix (ECM) proteins ( Hiepen et al, 2019 ). BMPR2-JNK signaling axis has also been shown to antagonize inflammation-induced EndMT ( Sanchez-Duffhues et al, 2019 ).…”