Role of Thrombospondin-1 in Mechanotransduction and Development of Thoracic Aortic Aneurysm in Mouse and Humans

Abstract

Rationale Abnormal mechanosensing of smooth muscle cells (SMCs) resulting from the defective elastin-contractile units has been suggested to drive the formation of thoracic aortic aneurysms (TAAs); however, the precise molecular mechanism has not been elucidated. Objective The aim of this study was to identify the crucial mediator(s) involved in abnormal mechanosensing and propagation of biochemical signals during the aneurysm formation and to establish a basis for a novel therapeutic strategy. Methods and Results We used a mouse model of postnatal ascending aortic aneurysms (Fbln4SMKO; termed SMKO), in which deletion of Fbln4 leads to disruption of the elastin-contractile units caused by a loss of elastic lamina-SMC connections. In this mouse, upregulation of early growth response-1 (Egr1) and angiotensin converting enzyme leads to activation of angiotensin II signaling. Here we showed that the matricellular protein, thrombospondin-1 (Thbs1), was highly upregulated in SMKO ascending aortas and in human TAAs. Thbs1 was induced by mechanical stretch and Ang II in SMCs, for which Egr1 was required, and reduction of Fbln4 sensitized the cells to these stimuli and led to higher expression of Egr1 and Thbs1. Deletion of Thbs1 in SMKO mice prevented the aneurysm formation in approximately 80% of SMKO; Thbs1−/− (termed DKO) animals and suppressed slingshot-1 and cofilin de-phosphorylation, leading to the formation of normal actin filaments. Furthermore, elastic lamina-SMC connections were restored in DKO aortas and mechanical testing showed that structural and material properties of DKO aortas were markedly improved. Conclusions Thbs1 is a critical component of mechanotransduction as well as a modulator of elastic fiber organization. Maladaptive upregulation of Thbs1 results in disruption of elastin-contractile units and dysregulation of actin cytoskeletal remodeling, contributing to the development of ascending aortic aneurysms in vivo. Thbs1 may serve as a potential therapeutic target for treating TAAs.

Matrix mechanotransduction mediated by thrombospondin-1/integrin/YAP signaling pathway in the remodeling of blood vessels

“…In response to cyclic stretch, SMCs showed upregulation of Early growth response 1 (Egr1) transcription factor, phosphorylated (p) focal adhesion kinase (FAK), Extracellular signal-regulated kinase (ERK), stress-response mitogen-activated protein kinase (MAP) p38 as previously reported (Online Fig. III-A) 13,15,16 . Cyclic stretch altered subcellular localization of Thbs1 from peri-nuclear region to the tip of cell on the long axis ( Fig.…”

“…In vitro mechanical stretch. Cyclic stretch was performed using a uniaxial cell stretch system (Central Workshop Tsukuba University) following 24 h of serum starvation as described previously 13 . Rat vascular SMCs or HUVECs were plated (3 × 10 4 cells) on silicon elastomer bottomed culture plates (SC4Ha, Menicon Life Science) coated with cell attachment factor containing gelatin (S006100, Thermo Fisher Scientific) and subjected to cyclic stretch with a frequency of 1.0 Hz (60 cycles/min) and 20% strain for the indicated time.…”

“…Recent studies have shown that ECM mechanical cues mediate cell proliferation, differentiation, autophagy and lipid metabolisms 1,[43][44][45] . Thbs1 is present at low levels in the postnatal vessels and upregulated in various vascular diseases such as atherosclerosis 46 , ischemia reperfusion injury 47 , aortic aneurysm 13 and pulmonary arterial hypertension 48 . YAP is also known to play a role in an emergency stress response to maintain tissue homeostasis 49, 12 50 .…”

“…We have recently reported that Thbs1 is highly upregulated in the aneurysm lesions in Fbln4 mutant mice and patients with thoracic aortic aneurysms (TAA) 13 , and deletion of Thbs1 or administration of phosphoinositol-3kinase (PI3K)-inhibitor prevented the aneurysm formation 12,13 . Since PI3K is also known to link YAP signaling pathway 51,52 , it is possible that suppression of Thbs1 or PI3K may alter YAP levels in Fbln4 mutant mice and affected YAP target genes.…”

“…Thbs1 is highly expressed during development and reactivated in response to injury 11 , exerting domain-specific and cell type-specific effects on cellular functions. We have recently shown that Thbs1 is induced by mechanical stretch and is a driver for thoracic aortic aneurysm in mice 12,13 .…”