ATF4 Contributes to Abdominal Aortic Aneurysm Formation via Modulating M1 Macrophage Polarization and Inflammation

Abdominal aortic aneurysm (AAA) is a potentially life-threatening vascular disease primarily in the male elderly population, but there is a lack of approved medical therapies to prevent the progression and rupture of AAA. Activating Transcription Factor 4 (ATF4) has been established to be involved in cardiovascular diseases, such as heart failure and calcific aortic valve disease. However, the role of ATF4 in the pathogenesis of AAA remains unclear. We found that ATF4 expression was significantly increased in patients with AAA and mouse models of AAA and was mainly confined to macrophages in arteries. ATF4 knockdown significantly attenuated aneurysm formation in experimental mouse model of AAA, while ATF4 overexpression promoted the development of AAA. RNA sequencing suggested that ATF4 was strongly related to the biological function of acute inflammatory response. Macrophages-specific ATF4 knockout significantly reduced the incidence and development of AAA, and decreased M1 polarization of macrophages in mice. Sphingomyelin phosphodiesterase 3 (SMPD3), a regulator of inflammatory responses in monocytes/macrophages, has been identified as a target gene of ATF4 through RNA sequencing, ChIP sequencing, and standard ChIP analyses. ATF4 induces M1 polarization of macrophages through the activation of SMPD3, thereby promoting inflammatory responses. Together, these results suggest that ATF4 mediated macrophage M1 polarization by regulating the expression of target genes SMPD3, leading to an increased inflammatory response, which further promotes the formation and development of AAA. These findings suggest ATF4 may be a new therapeutic target for AAA.