Abstract MP24: Disruption Of Actin Remodeling Intensifies Aneurysm-promoting Signals In Smooth Muscle Cells

Abstract

Mutations within proteins coding for extracellular matrix assembly or those in the transforming growth factor beta (TGFβ) signaling pathway lead to aneurysm formation in patients and mice. As the SMC cytoskeletal network is intricately linked to TGFβ and ECM signaling, we sought to determine if disruption of the cytoskeletal filaments would alter how SMCs respond to angiotensin II, an important mediator of aneurysm formation. C57BL/6 mice lacking Tgbfr1 in SMCs (SMC- Tgbr1 iko ) generated by Jiang et al. have been shown to develop rapid and severe aortic aneurysm degeneration with 100% penetrance. Analysis was conducted on aneurysm and control mouse and human aortic tissue sections. We observed that SMC- Tgbr1 iko mice had reduced expression of filamentous (f-) and α-actin protein in the aortic media than control mice. Primary Tgbr1 iko SMCs also had higher levels of pRelA expression, less α-actin mRNA, and less f-actin than control SMCs. Tissue sections from aneurysm patients had reduced f-actin staining relative to controls. Disruption of f-actin with the destabilizer latrunculin A in vitro led to increased RelA and ERK activation in the presence of AngII, which was further augmented in the presence of a neutralizing antibody for TGFβ. In contrast, jasplakinolide—an f-actin stabilizer—prevented TGFβ blockade induced pRelA expression, suggesting that altered/inhibited TGFβ signaling modulates NFkB through actin depolymerization. While stabilization and disruption of microtubules led to RelA activation, no effect was observed on TGFβ blockade-induced pRelA expression. The phosphoantibody array revealed that f-actin disruption in the presence of AngII activated the CREB, AKT1/2/3, ERK1/2, and STAT3 pathways in mouse aortic SMCs. SMC- Tgbr1 iko mice treated with cytochalasin B suffered significantly greater mortality and had increased aortic growth over a 30-day follow-up period. Aortic aneurysms are coincident with reduced f-actin expression in murine and human aortic SMCs. Chemical deconstruction of actin filaments promotes an inflammatory phenotype in mouse SMCs in vitro , and aggravates aneurysm formation in vivo . Aberrant or inhibited TGFβ signaling potentiates NFkB activation in SMCs, which may be dependent on f-actin disassembly.