Statins Reduce Thoracic Aortic Aneurysm Growth in Marfan Syndrome Mice via Inhibition of the Ras‐Induced ERK (Extracellular Signal‐Regulated Kinase) Signaling Pathway

Abstract

Background Statins reduce aneurysm growth in mouse models of Marfan syndrome, although the mechanism is unknown. In addition to reducing cholesterol, statins block farnesylation and geranylgeranylation, which participate in membrane‐bound G‐protein signaling, including Ras. We dissected the prenylation pathway to define the effect of statins on aneurysm reduction. Methods and Results Fbn1 C1039G/+ mice were treated with (1) pravastatin (HMG‐CoA [3‐hydroxy‐3‐methylglutaryl coenzyme A] reductase inhibitor), (2) manumycin A ( MA ; FPT inhibitor), (3) perillyl alcohol ( GGPT 1 and ‐2 inhibitor), or (4) vehicle control from age 4 to 8 weeks and euthanized at 12 weeks. Histological characterization was performed. Protein analysis was completed on aortic specimens to measure ERK (extracellular signal‐regulated kinase) signaling. In vitro Fbn1 C1039G/+ aortic smooth muscle cells were utilized to measure Ras‐dependent ERK signaling and MMP (matrix metalloproteinase) activity. Pravastatin and MA significantly reduced aneurysm growth compared with vehicle control (n=8 per group). In contrast, PA did not significantly decrease aneurysm size. Histology illustrated reduced elastin breakdown in MA ‐treated mice compared with vehicle control (n=5 per group). Although elevated in control Marfan mice, both phosphorylated c‐Raf and phosphorylated ERK 1/2 were significantly reduced in MA ‐treated mice (4–5 per group). In vitro smooth muscle cell studies confirmed phosphorylated cR af and phosphorylated ERK 1/2 signaling was elevated in Fbn1 C1039G/+ smooth muscle cells (n=5 per group). Fbn1 C1039G/+ smooth muscle cell Ras‐dependent ERK signaling and MMP activity were reduced following MA treatment (n=5 per group). Corroborating in vitro findings, MMP activity was also decreased in pravastatin‐treated mice. Conclusions Aneurysm reduction in Fbn1 C1039G/+ mice following pravastatin and MA treatment was associated with a decrease in Ras‐dependent ERK signaling. MMP activity can be reduced by diminishing Ras signaling.

Divergent effects of canonical and non‐canonical TGF‐β signalling on mixed contractile‐synthetic smooth muscle cell phenotype in human Marfan syndrome aortic root aneurysms

“…Further complicating matters, TGF‐β signalling proceeds through multiple downstream pathways, including ERK. While ERK signalling has been implicated as a driver of aneurysm pathogenesis in the Fbn1 C1039G/+ MFS model, ERK activation was significantly enhanced with losartan and anti‐TGF‐β therapy and coincided with aneurysm prevention in the more aggressive Fbn1 mgR/mgR mouse model . Furthermore, ERK inhibition exacerbated SMC pathology in an induced pluripotent stem cell‐derived model of MFS by increasing apoptosis and reducing proliferation .…”

Anatomically specific reactive oxygen species production participates in Marfan syndrome aneurysm formation

“…The specific role TGF-β plays during aneurysm formation in MFS murine models remains complicated, although most animal studies support a pathologic function through aortic wall remodelling in two different Marfan mouse models (Fbn1 mgR/mgR and Fbn1 C1039G/+ ). [5][6][7][8][9][10][11][12][13][14]32,33 Identifying key components within the molecular pathway(s) that lead to aneurysm formation may translate into innovative medical therapies directed at preventing or slowing aneurysm growth 33,34 . Herein, our laboratory reports that ROS contribute to aneurysm formation in MFS.…”

“…Previous investigators reported that enhanced TGF-β signalling causes aneurysm formation in MFS mice, and reduced following losartan treatment (AngII receptor blockade) (5)(6)(7)(8)(9)(10)(11)(12)(13)(14). To define a mechanistic link between TGF-β signalling, AngII and NADPH oxidase activity in the MFS mouse model, we performed in vitro studies using SMCs derived from either LGCL.…”

“…However, the gap in knowledge that explains what happens between TGF‐β signalling and extracellular matrix (ECM) remodelling has prevented the development of innovative treatment strategies . Further, because TGF‐β stimulates multiple signalling pathways, it is unclear which of these pathways results in aortic aneurysms …”

“…10 Further, because TGF-β stimulates multiple signalling pathways, it is unclear which of these pathways results in aortic aneurysms. 6,[11][12][13][14] Reactive oxygen species (ROS) have emerged as important TGF-βdependent mediators capable of inducing smooth muscle cell (SMC) phenotype switching, SMC apoptosis and matrix metalloproteinase (MMP) activation, all deemed important in ECM remodelling. [15][16][17][18][19] ROS develop as a by-product of natural oxygen metabolism and participate in normal cell signalling and homoeostasis.…”