Selective Inhibition of PI3K/Akt/mTOR Signaling Pathway Regulates Autophagy of Macrophage and Vulnerability of Atherosclerotic Plaque

Abstract

Macrophage infiltration contributes to the instability of atherosclerotic plaques. In the present study, we investigated whether selective inhibition of PI3K/Akt/mTOR signaling pathway can enhance the stability of atherosclerotic plaques by activation of macrophage autophagy. In vitro study, selective inhibitors or siRNA of PI3K/Akt/mTOR pathways were used to treat the rabbit's peritoneal primary macrophage cells. Inflammation related cytokines secreted by macrophages were measured. Ultrastructure changes of macrophages were examined by transmission electron microscope. mRNA or protein expression levels of autophagy related gene Beclin 1, protein 1 light chain 3 II dots (LC3-II) or Atg5-Atg12 conjugation were assayed by quantitative RT-PCR or Western blot. In vivo study, vulnerable plaque models were established in 40 New Zealand White rabbits and then drugs or siRNA were given for 8 weeks to inhibit the PI3K/Akt/mTOR signaling pathway. Intravascular ultrasound (IVUS) was performed to observe the plaque imaging. The ultrastructure of the abdominal aortic atherosclerosis lesions were analyzed with histopathology. RT-PCR or Western blot methods were used to measure the expression levels of corresponding autophagy related molecules. We found that macrophage autophagy was induced in the presence of Akt inhibitor, mTOR inhibitor and mTOR-siRNA in vitro study, while PI3K inhibitor had the opposite role. In vivo study, we found that macrophage autophagy increased significantly and the rabbits had lower plaque rupture incidence, lower plaque burden and decreased vulnerability index in the inhibitors or siRNA treated groups. We made a conclusion that selective inhibition of the Akt/mTOR signal pathway can reduce macrophages and stabilize the vulnerable atherosclerotic plaques by promoting macrophage autophagy.

Autophagy in Vascular Disease

“…This finding is strengthened by 2 recent reports showing that inhibition of mTOR signaling with siRNA induces autophagy in macrophages of rabbits or ApoE −/− mice and reduces both plaque burden and macrophage content within the atherosclerotic lesions. 88,89 Everolimus-induced macrophage death most likely occurs because of protein synthesis arrest after mTOR inhibition. Indeed, being a highly active cell type, macrophages are much more sensitive to protein synthesis arrest when compared with SMCs and rapidly initiate cell death, 47 whereas SMCs transform into a quiescent, more contractile phenotype.…”

The roles of macrophage autophagy in atherosclerosis

“…Autophagy has far-reaching functions that protect plaque stability. It has already been shown that selectively inhibiting the PI3K/Akt/mTOR pathway in cells can effectively induce autophagy, which successfully reduces macrophage aggregation in atherosclerotic plaques and promotes plaque stability by protecting cells and reducing the secretion of inflammatory factors [28] . Furthermore, autophagy may function as an inhibitor of apoptosis by decreasing the activation and formation of inflammasomes [29] .…”

Role of autophagy in the ω-3 long chain polyunsaturated fatty acid-induced death of lung cancer A549 cells

“…Numerous studies have revealed that the inhibition of the PI3K/Akt/mTOR signaling pathway activates autophagy and induces cell death (33,34). Selective inhibition of the Akt/mTOR signaling pathway reduces the level of macrophages and stabilizes vulnerable atherosclerotic plaques by promoting macrophage autophagy (35). The addition of a PI3K inhibitor overcomes cellular resistance to mTORC1 inhibitors, regardless of PTEN status, and therefore substantially expands the molecular phenotype of tumors likely to respond (16).…”