10.6 - Smooth Muscle-Specific Deletion of Neuropilin-1 Increases Vascular Contractility and Blood Pressure

Dakshnapriya Balasubbramanian (Boston Childrens Hospital, Harvard Medical School), George Lambrinos (Boston Childrens Hospital, Harvard Medical School), Vivian Cristofaro (Veteran Affairs Boston Healthcare System, Harvard Medical School), Alexander Bigger-Allen (Boston Childrens Hospital, Harvard Medical School), Beibei Wang (Boston Childrens Hospital, Harvard Medical School), Yao Gao (Boston Childrens Hospital, Harvard Medical School), Hong Chen (Boston Childrens Hospital, Harvard Medical School), Rosalyn Adam (Boston Childrens Hospital, Harvard Medical School), Maryrose Sullivan (Veteran Affairs Boston Healthcare System, Harvard Medical School), Diane Bielenberg (Boston Childrens Hospital, Harvard Medical School)

Introduction:  Neuropilin-1 (NRP1) is a transmembrane glycoprotein that acts as a co-receptor for the Class 3 Semaphorin (SEMA) ligand SEMA3A and mediates the inhibition of RhoA signaling. NRP1 is expressed in vascular smooth muscle cells (VSMCs), however, its role in regulating VSMC contractility and blood pressure in vivo is unknown. Hypothesis: We hypothesize that SEMA3A-NRP1 signaling is essential in mitigating RhoA activity in VSMCs and that loss of NRP1 increases vascular tone and blood pressure in vivo. 

Methods:  To study the role of NRP1 in SMCs, mice with inducible, smooth muscle cell-specific deletion of NRP1 (SM22a-CreERT2; Nrp1flox/flox) were generated. Following recombination using 4-hydroxy tamoxifen (SM-NRP1 KO) in male and female adult mice (8-12 weeks), systolic blood pressure (SBP) was measured using a tail cuff and compared to age- and sex-matched mice that did not receive tamoxifen (control). Vascular reactivity to various contractile agonists was measured using ex vivo tension myography. 

Results:  SBP was significantly increased in SM-NRP1 KO mice following recombination compared to control mice (SBP: 136.5 ± 10.9 vs 112.9 ± 5.6 mmHg; p=0.0006). Aortas of SM-NRP1 KO mice displayed significantly enhanced contractile response to phenylephrine, KCl, and the thromboxane agonist U44619, and reduced relaxation to the endothelium-independent vasodilator sodium nitroprusside. In vitro, treatment of murine primary aortic VSMC with SEMA3A decreased angiotensin II-induced Rho-GTP activation. Gene expression of Sema3a in the aorta was downregulated in two models of hypertension, angiotensin II-dependent and genetic model of hypertension, as identified by qPCR and transcriptomic analysis respectively, further supporting the role of SEMA3A-NRP1 signaling in basal blood pressure regulation. Additionally, control and SM-NRP1 KO mice (starting at 2 weeks post-recombination) were administered angiotensin II (490 ng/kg/day) for 4 weeks. While there was no significant difference in SBP at weeks 1 and 2, SM-NRP1 KO mice had significantly lower SBP at weeks 3 and 4 following angiotensin II infusion compared to controls (Week 4 SBP: 150 ± 1.4 vs 130.5 ± 2.5 mmHg; p=0.02), suggesting a low ejection fraction and cardiac dysfunction in these mice. In support of this observation, gene expression of atrial natriuretic peptide was increased (p=0.06) in hearts of angiotensin II-infused SM-NRP1 KO mice. Preliminary analyses indicated an increase in aortic medial thickness at baseline and an increase in aortic adventitial collagen following angiotensin II infusion in SM-NRP1 KO mice compared to controls. 

Conclusion:  Together, our data point to the role of NRP1 as a novel regulator of basal vascular tone and blood pressure, and the loss of NRP1 leads to the onset of hypertension and exacerbates pathological vascular remodeling and cardiac dysfunction.

NHLBI R01 HL141858 (D.R.B); Vascular Biology Program, Boston Childrens Hospital (D.R.B.)