Thymosin β4 protects against aortic aneurysm via endocytic regulation of growth factor signaling
Sonali Munshaw, … , Keith M. Channon, Nicola Smart
Sonali Munshaw, … , Keith M. Channon, Nicola Smart
Published March 30, 2021
Citation Information: J Clin Invest. 2021;131(10):e127884. https://doi.org/10.1172/JCI127884.
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Research Article Vascular biology Article has an altmetric score of 29

Thymosin β4 protects against aortic aneurysm via endocytic regulation of growth factor signaling

Abstract

Vascular stability and tone are maintained by contractile smooth muscle cells (VSMCs). However, injury-induced growth factors stimulate a contractile-synthetic phenotypic modulation which increases susceptibility to abdominal aortic aneurysm (AAA). As a regulator of embryonic VSMC differentiation, we hypothesized that Thymosin β4 (Tβ4) may function to maintain healthy vasculature throughout postnatal life. This was supported by the identification of an interaction with low density lipoprotein receptor related protein 1 (LRP1), an endocytic regulator of platelet-derived growth factor BB (PDGF-BB) signaling and VSMC proliferation. LRP1 variants have been implicated by genome-wide association studies with risk of AAA and other arterial diseases. Tβ4-null mice displayed aortic VSMC and elastin defects that phenocopy those of LRP1 mutants, and their compromised vascular integrity predisposed them to Angiotensin II–induced aneurysm formation. Aneurysmal vessels were characterized by enhanced VSMC phenotypic modulation and augmented PDGFR-β signaling. In vitro, enhanced sensitivity to PDGF-BB upon loss of Tβ4 was associated with dysregulated endocytosis, with increased recycling and reduced lysosomal targeting of LRP1–PDGFR-β. Accordingly, the exacerbated aneurysmal phenotype in Tβ4-null mice was rescued upon treatment with the PDGFR-β antagonist Imatinib. Our study identifies Tβ4 as a key regulator of LRP1 for maintaining vascular health, and provides insights into the mechanisms of growth factor–controlled VSMC phenotypic modulation underlying aortic disease progression.

Authors

Sonali Munshaw, Susann Bruche, Andia N. Redpath, Alisha Jones, Jyoti Patel, Karina N. Dubé, Regent Lee, Svenja S. Hester, Rachel Davies, Giles Neal, Ashok Handa, Michael Sattler, Roman Fischer, Keith M. Channon, Nicola Smart

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Figure 2

A postnatal, smooth muscle cell-autonomous requirement for Tβ4 for maintenance of healthy aorta.

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A postnatal, smooth muscle cell-autonomous requirement for Tβ4 for maint...
Verhoeff–van Gieson staining (A) to visualize elastin integrity, structure, diameter (B), and medial thickness (Supplemental Figure 4A) of aortas in P7 male mice. Immunofluorescence to assess smooth muscle phenotype (C). Tmsb4x was deleted from medial VSMCs of 3-week-old Myh11CreERT2 HprtTβ4shRNA knockdown mice; RNAScope for Tmsb4x mRNA, compared with Myh11CreERT2 Hprt+/+ control mice (D), quantified in Supplemental Figure 4B. Hematoxylin and eosin staining (E) assessed aortic dilatation and medial thickness in 12-week-old mice, quantified in F and Supplemental Figure 4C, respectively. Verhoeff–van Gieson staining (G) assessed elastin integrity, quantified both by number of breaks per section (H) and by elastin damage score (Supplemental Figure 1). Ratio of contractile/synthetic VSMC markers in Myh11CreERT2 HprtTβ4shRNA, compared with Myh11CreERT2 Hprt+/+ aortas, both at the protein (I; quantified in Supplemental Figure 4E) and mRNA level (qRT-PCR; J). Data are mean ± SD, with each data point representing an individual animal. Significance was calculated using a Mann-Whitney nonparametric test (B and J) or 2-tailed unpaired Student’s t tests (F and H with Holm-Sidak correction for multiple comparisons in F). **P ≤ 0.01; ***P ≤ 0.001. Scale bars: A, E, and G: 100 μm; C: 50 μm; D: 20 μm; I: 50 μm (low), 20 μm (high).