It has been reported that in addition

It has been reported that in addition to regulating protein biosynthesis, Iars also performs an important role in the regulation of immunity, transcription, angiogenesis [22,23]. However, to the best of our knowledge no studies have examined the differentiation and apoptosis of VSMCs induced by AARS, and nothing is known about its modulation by Iars. In addition to demonstrating phenotypic switching and apoptosis in VSMCs in AAA specimens, we also found that the PF-573228 of Iars increased significantly in such tissues, which led us to speculate that Iars performs an important role in the pathogenesis of AAA. To test this hypothesis, Iars was inhibited in one group of mice while AAA formation was induced with CaCl2 plus AngII to ascertain the role of Iars on the development of AAA. Unexpectedly, inhibition of Iars significantly reduced the formation of AAA, and reduced phenotypic switching and apoptosis in VSMCs. Additionally, we also observed corresponding changes in the activation status of the PI3K and p38 MAPK pathways. These results indicate that Iars, and the PI3K and p38 MAPK pathways are involved in the formation of AAAs but their precise roles and mechanisms of action still require elucidation. In our previous study, we demonstrated that the p38 MAPK pathway mediates AngII-induced phenotypic switching of VSMCs [5]. In the present study, we observed that AngII additionally induced the expression of Iars. When the IARS gene in HASMCs was overexpressed, it was subsequently observed by Western blot and RT-PCR analysis that the expression of OPN tended to be elevated, while SM22α exhibited significant downregulation, thereby suggesting that Iars induced the phenotypic switching of VSMCs. However, while the p38 MAPK pathway was inhibited, upregulation of Iars did not induce the phenotypic switching of VSMCs, but VSMCs apoptosis still occurred, and inhibition of the p38 MAPK pathway did not affect the expression of Iars. These data suggest that the p38 MAPK pathway mediates Iars-induced phenotypic switching of VSMCs, but not their apoptosis. Apoptosis is a spontaneous process of programmed cell death that occurs both physiologically and pathologically, operating under tight regulation [24,25]. The phosphoinositide 3-kinase (PI3K) signaling pathway is critical to many cellular functions including the regulation of cell growth, proliferation and apoptosis [26,27]. The principal pathological manifestation of aortic medial layer degeneration is increased apoptosis and dysfunction of VSMCs. We demonstrated that PI3K pathway activity in the medial layer of AAA tissues declined, suggesting that the PI3K pathway is highly likely to perform a role in this process, consistent with observations made by Zhu and Liu [28,29]. However, the mechanisms for suppressing the activity of the PI3K pathway during the pathogenesis of AAA have not yet been reported. In the present study, we demonstrated that Iars affects the activity of the PI3K pathway, both in vivo and in vitro. The change we observed only affected cell apoptosis and not the expression of Iars or VSMC phenotypic markers. These observations suggest that the PI3K pathway mediates Iars-induced apoptosis in VSMCs, rather than phenotypic switching. In the present study, we have shown that upregulation of Iars promotes phenotypic switching and apoptosis in VSMCs during AAA formation via the p38 MAPK and PI3K pathways, respectively (Fig. 6). Our data may offer insight into a previously unknown mechanism of degeneration of the aortic medial layer. Our study suggests that Iars may be an attractive target for strategies aiming to prevent the formation of AAA. The following are the supplementary data related to this article.
Introduction p38 MAPKs belong to the family of mitogen activated protein kinases (MAPKs) along with extracellular regulated kinases (ERKs) and C-Jun N-terminal Kinases (JNKs) [1]. p38α, β, γ and δ are four isoforms of p38 encoded by MAPK14, MAPK11, MAPK12 and MAPK13 genes respectively. These four isoforms differ from each other based on their respective upstream stimuli that regulate them, distribution in tissues and their downstream target [2]. Although p38α and p38β are expressed ubiquitously, p38γ is mainly expressed in skeletal muscle while p38δ is highly expressed in testes, pancreas, kidney and small intestine [3]. These proteins are encoded by separate genes in response to stress which can either be environmental or genotoxic. Among all isoforms, p38α is best characterized and was recognized as a 38 kDa polypeptide that went through tyrosine phosphorylation in response to treatment by endotoxin and hyperosmolarity shock [4].