Neuropilin-1 deficiency in vascular smooth muscle cells is associated with hereditary hemorrhagic telangiectasia arteriovenous malformations
Sreenivasulu Kilari, … , Debabrata Mukhopadhyay, Sanjay Misra
Sreenivasulu Kilari, … , Debabrata Mukhopadhyay, Sanjay Misra
Published April 5, 2022
Citation Information: JCI Insight. 2022;7(9):e155565. https://doi.org/10.1172/jci.insight.155565.
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Research Article Vascular biology

Neuropilin-1 deficiency in vascular smooth muscle cells is associated with hereditary hemorrhagic telangiectasia arteriovenous malformations

Abstract

Patients with hereditary hemorrhagic telangiectasia (HHT) have arteriovenous malformations (AVMs) with genetic mutations involving the activin-A receptor like type 1 (ACVRL1 or ALK1) and endoglin (ENG). Recent studies have shown that Neuropilin-1 (NRP-1) inhibits ALK1. We investigated the expression of NRP-1 in livers of patients with HHT and found that there was a significant reduction in NRP-1 in perivascular smooth muscle cells (SMCs). We used Nrp1SM22KO mice (Nrp1 was ablated in SMCs) and found hemorrhage, increased immune cell infiltration with a decrease in SMCs, and pericyte lining in lungs and liver in adult mice. Histologic examination revealed lung arteriovenous fistulas (AVFs) with enlarged liver vessels. Evaluation of the retina vessels at P5 from Nrp1SM22KO mice demonstrated dilated capillaries with a reduction of pericytes. In inflow artery of surgical AVFs from the Nrp1SM22KO versus WT mice, there was a significant decrease in Tgfb1, Eng, and Alk1 expression and phosphorylated SMAD1/5/8 (pSMAD1/5/8), with an increase in apoptosis. TGF-β1–stimulated aortic SMCs from Nrp1SM22KO versus WT mice have decreased pSMAD1/5/8 and increased apoptosis. Coimmunoprecipitation experiments revealed that NRP-1 interacts with ALK1 and ENG in SMCs. In summary, NRP-1 deletion in SMCs leads to reduced ALK1, ENG, and pSMAD1/5/8 signaling and reduced cell death associated with AVM formation.

Authors

Sreenivasulu Kilari, Ying Wang, Avishek Singh, Rondell P. Graham, Vivek Iyer, Scott M. Thompson, Michael S. Torbenson, Debabrata Mukhopadhyay, Sanjay Misra

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Figure 6

Flow-induced Nrp1 upregulation in the AVF in the inflow arteries.

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Flow-induced Nrp1 upregulation in the AVF in the inflow arteries. (A) NR...
(A) NRP-1 gene expression was assessed by qPCR in the AVF inflow arteries (GA) and contralateral carotid arteries (CA) at 3 days after AVF creation. There is a significant increase in NRP-1 gene expression in GA compared with CA from WT mice. However, there was no significant difference in NRP-1 expression in GA compared with CA in Nrp1SM22KO mice. Immunostaining was performed to assess NRP-1 and α-SMA levels in GA and CA at 14 days after arteriovenous fistula (AVF) creation. (B and D) Representative images of NRP-1 (B) and α-SMA (D) in GA and CA from Nrp1fl/fl (WT) and Nrp1fl/fl/SM22αCre+ (Nrp1SM22KO) mice. The dotted line in B indicates the media and adventitia layers in the vessel wall. All images were captured using 10× magnification. Scale bar: 50 μm. The arrows point to brown cells positive for NRP-1 (B) and α-SMA (D) staining in the vessel wall. (B, C, and E) The intensity of brown stain positive NRP-1 (C) index in α-SMA (B and E) index in C were quantified as described and presented as mean ± SEM of n = 5–7 animals. A 2-way ANOVA with multiple comparison was performed. *P < 0.05.