BMP9 and BMP10 Act Directly on Vascular Smooth Muscle Cells for Generation and Maintenance of the Contractile State

Abstract

Background: Vascular smooth muscle cells (VSMCs) show a remarkable phenotypic plasticity allowing acquisition of contractile or synthetic states but critical information is missing about the physiological signals, promoting formation and maintenance of contractile VSMCs in vivo . BMP9 and BMP10 are known to regulate endothelial quiescence after secretion from the liver and right atrium, whereas a direct role in the regulation of VSMCs was not investigated. Here, we studied the role of BMP9 and BMP10 for controlling formation of contractile VSMCs. Methods: We generated several cell type-specific loss- and gain-of-function transgenic mouse models to investigate the physiological role of BMP9, BMP10, ALK1 and SMAD7 in vivo . Morphometric assessments, expression analysis, blood pressure measurements, single molecule fluorescence in situ hybridization (FISH) were performed together with analysis of isolated pulmonary VSMCs to unravel phenotypic and transcriptomic changes in response to absence or presence of BMP9 and BMP10. Results: Concomitant genetic inactivation of Bmp9 in the germ line and Bmp10 in the right atrium led to dramatic changes in vascular tone and diminution of the VSMC layer with attenuated contractility and decreased systemic as well as right ventricular systolic pressure (RVSP). Vice versa , overexpression of Bmp10 in endothelial cells (ECs) of adult mice dramatically enhanced formation of contractile VSMCs and increased systemic blood pressure as well as RVSP. Likewise, BMP9/10 treatment induced an ALK1-dependent phenotypic switch from synthetic to contractile in pulmonary VSMCs. SMC specific overexpression of Smad7 completely suppressed differentiation and proliferation of VSMCs and reiterated defects observed in adult Bmp9/10 double mutants. Deletion of Alk1 in VSMCs recapitulated the Bmp9/10 phenotype in pulmonary but not in aortic and coronary arteries. Bulk expression analysis and single molecule RNA-FISH uncovered vessel bed-specific, heterogeneous expression of BMP type 1 receptors, explaining phenotypic differences in different Alk1 mutant vessel beds. Conclusions: Our study demonstrates that BMP9 and BMP10 act directly on VSMCs for induction and maintenance of their contractile state. Surprisingly, the effects of BMP9/10 in VSMCs are mediated by different combinations of BMP type 1 receptors in a vessel bed specific manner, offering new opportunities to manipulate blood pressure in the pulmonary circulation.

BMP9 and BMP10: Two close vascular quiescence partners that stand out

“…After birth, BMP9 and BMP10 clearly play redundant roles in postnatal angiogenesis (retinal vascularization and closure of the ductus arteriosus 5,30,85 ) but also in adult vascular homeostasis (under physiological conditions) as only the double Bmp9/ Bmp10 deletion leads to a vascular phenotype. 108,109 Due to technical issues, the role of BMP9 has been addressed via a complete and constitutive KO while the role of BMP10 has been addressed via either neutralizing antibodies, or tamoxifen inducible knockdown in adult or tissue-specific deletion in the right atria in order to bypass cardiac embryonic lethality. In zebrafish, no transcriptional adaptation or genetic compensation was found for bmp9 or bmp10-like expression or in bmp10 mutants.…”

“…It was shown that adult Bmp10 knockdown in the C57BL/6 background was not lethal and showed no obvious vascular phenotype 107,108 . More recently, a mouse model specifically deleted for Bmp10 in the right atrium was generated ( Bmp10 ANF ) 109 . These mice overcame embryonic cardiac lethality and were viable with no obvious phenotype, suggesting that cardiac BMP10 is not involved in postnatal vascular remodeling.…”

Homozygous GDF2 nonsense mutations result in a loss of circulating BMP9 and BMP10 and are associated with either PAH or an “HHT‐like” syndrome in children

“…The PAVMs we observe in the homozygous p.[Glu279Ter];[Glu279Ter] patient combined with recent reports of PAVMs in a p.[Tyr354Argf-sTer15];[Tyr354ArgfsTer15] homozygote (Liu et al, 2020) and a p.[Gly291Ser] heterozygous mutation carrier (Topiwala et al, 2020) suggest that loss of BMP9 and BMP10 predispose individuals to the development of PAVMs. To date, studies of compound Bmp9:Bmp10 knockout mice have not specifically noted AVM development, although dilated vessels associated with altered vascular smooth muscle cell functionality have been reported (L. Wang et al, 2021). It remains to be determined whether additional events are required to promote PAVM formation, either via disruption of BMP signaling, or by affecting other signaling pathways.…”

The Dual Effect of the BMP9–ALK1 Pathway in Blood Vessels: An Opportunity for Cancer Therapy Improvement?

“…Interestingly, this effect in these cells takes place in pulmonary blood vessels but not in aortic and coronary arteries. The heterogeneity of this response is related to the differential expression of BMP type I receptors ALK1, ALK2, ALK3 and ALK6 [163]. All these findings have been shown in the context of pulmonary hypertension, but they evidence a possible effect of BMP9-ALK1 in mural cells, supporting cells which stabilize tumor blood vessels, especially pericytes.…”