p38 MAPK Is an Early Determinant of Promiscuous Smad2/3 Signaling in the Aortas of Fibrillin-1 (Fbn1)-null Mice

Abstract

Excessive transforming growth factor-␤ (TGF-␤) signaling characterizes the progression of aortic aneurysm in mouse models of Marfan syndrome, a systemic disorder of the connective tissue that is caused by mutations in the gene encoding the extracellular matrix protein fibrillin-1. Fibrillin-1 mutations are believed to promote abnormal Smad2/3 signaling by impairing the sequestration of latent TGF-␤ complexes into the extracellular matrix. Here we report that promiscuous Smad2/3 signaling is the cell-autonomous phenotype of primary cultures of vascular smooth muscle cells (VSMC) explanted from the thoracic aortas of Fbn1 mutant mice with either neonatal onset or progressively severe aortic aneurysm. This cellular phenotype was characterized in VSMC isolated from Fbn1-null (mgN/mgN) mice, which recapitulate the most severe form of Marfan syndrome. We found that loss of fibrillin-1 deposition promotes the production of intracellular reactive oxygen species and abnormal accumulation of phosphorylated TGF-␤-activated kinase 1 and p38 MAPK, in addition to increasing the levels of endogenous phospho-Smad2. We showed that improper Smad2/3 signaling in Fbn1-null VSMC is in part stimulated by phospho-p38 MAPK, which is in turn activated in response to signals other than those mediated by the kinase activity of the ALK5 receptor. Consistent with these cell culture data, in vivo analyses documented that phospho-p38 MAPK accumulates earlier than phospho-Smad2 in the aortic wall of mgN/mgN mice and that systemic inhibition of phospho-p38 MAPK activity lowers the levels of phospho-Smad2 in this tissue. Collectively, these findings indicate that improper activation of p38 MAPK is a precursor of constitutive Smad2/3 signaling in the aortic wall of a mouse model of neonatal lethal Marfan syndrome.

Endoglin Regulates the Activation and Quiescence of Endothelium by Participating in Canonical and Non-Canonical TGF-β Signaling Pathways

“…Our results indicate that endoglin haploinsufficiency has a significant impact on EC junctional organization and function, and are consistent with an increase in TGFb-mediated Smad2/3 phosphorylation in Eng+/2 EC (Fig. 8D) as previously reported by downregulation of VE-cadherin (Rudini et al, 2008) and/or activation of P38 MAPK (Carta et al, 2009;Mu et al, 2012).…”

Quantitative analysis of TGFBR2 mutations in Marfan-syndrome-related disorders suggests a correlation between phenotypic severity and Smad signaling activity

“…A series of studies has reported paradoxical upregulation of TGF- signaling in aortic tissues of patients with mutations in the TGFBR2 kinase domain, as shown by increased levels of nuclear phosphorylated Smad, abundance of TGF- and expression of TGF- target genes (Carta et al, 2009;Gomez et al, 2009;Loeys et al, 2005). The basis of this observation, however, has not been elucidated to date.…”

Activation of endocannabinoid system is associated with persistent inflammation in human aortic aneurysm

“…So far, all of these facts indicate a very finely tuned inflammatory process in human aortic aneurysms and therefore the recently postulated prognostic value for phosphorylation of c-kit and downstream targets in aneurysm formation fits well in this concept [20]. In this context, recent studies reported that the inhibition of cytokine IL-1 attenuates experimental development of aortic aneurysm [21], as well as activation of TGF-signalling [22]. Future studies should address the exact characterization and cellular imaging of the inflammatory cells, that is, T-cells, macrophage subpopulations, and so forth, in order to better understand their specific contribution during development of human aneurysms.…”