Surfactant Protein A, a Novel Regulator for Smooth Muscle Phenotypic Modulation and Vascular Remodeling-Brief Report

Abstract

Objective: The objective of this study is to determine the role of SPA (surfactant protein A) in vascular smooth muscle cell (SMC) phenotypic modulation and vascular remodeling. Approach and Results: PDGF-BB (Platelet-derived growth factor-BB) and serum induced SPA expression while downregulating SMC marker gene expression in SMCs. SPA deficiency increased the contractile protein expression. Mechanistically, SPA deficiency enhanced the expression of myocardin and TGF (transforming growth factor)-β, the key regulators for contractile SMC phenotype. In vivo, SPA was induced in medial and neointimal SMCs following mechanical injury in both rat and mouse carotid arteries. SPA knockout in mice dramatically attenuated the wire injury-induced intimal hyperplasia while restoring SMC contractile protein expression in medial SMCs. These data indicate that SPA plays an important role in SMC phenotype modulation and vascular remodeling in vivo.

Conclusions: SPA is a novel protein factor modulating SMC phenotype. Blocking the abnormal elevation of SPA may be a potential strategy to inhibit the development of proliferative vascular diseases.

Keywords: phenotype; platelet-derived growth factor; smooth muscle; vascular remodeling.

Figure 1:. SPA mediated SMC phenotypic modulation through regulating Myocardin and TGFβ1 expression.

A, SMCs were isolated from mouse aorta, serum-starved for 24 h, and then treated with PDGF-BB (20 ng/ml) for the times indicated. SPA was increased along with the downregulation of SMC markers during PDGF-BB-induced SMC phenotypic modulation. B, Quantification of the protein expression shown in A by normalizing to α-tubulin. *P<0.05 vs control group (0 h), n=3. C, SMC marker expression in artery SMCs freshly isolated from aortas of wild (WT) or SPA knockout (SPA−/−) mice, and Western blots were performed to detect the expression of proteins indicated. D, Quantification of the protein expression shown in C by normalizing to α-tubulin. *P<0.05 vs WT group, n=5. E, Myocardin and TGFβ1 expression in arterial SMCs freshly isolated from WT and SPA knockout aortas. F, Quantification of the protein expression shown in E by normalizing to GAPDH. *P<0.05 vs WT group, n=5.

Figure 2:. SPA was essential for injury-induced vascular remodeling.

Mouse left carotid arteries were injured through mechanical endothelial denudation. The arteries were collected at 1, 3, 7, 14 days following the surgery. A, SPA was induced in the mouse carotid arteries following the injury. B, Carotid artery sections of wild (WT) and SPA knockout (SPA−/−) mice with 14 days of injury were stained with H&E (upper panel), Elastica van Gieson (middle panel), or MYH11 antibody via immunohistochemistry (IHC) staining (lower panel). Yellow and green Arrows indicate the internal and external elastic lamina, respectively. Scale bar: 50μm for both A and B. C, Quantification of intima area, intima/media ratio, or MYH11 staining intensity as indicated. *P<0.05 vs WT group; #P<0.05 vs injured WT group (n=8).