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.