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Rapamycin promotes endothelial-mesenchymal transition during stress-induced premature senescence through the activation of autophagy.

ABSTRACT: BACKGROUND:Rapamycin is known to be effective in suppressing senescence and the senescence-associated secretory phenotype (SASP). Therefore, it is highly expected to represent an anti-aging drug. Its anti-aging effect has been demonstrated at the mouse individual level. However, there are not many clinical findings with respect to its activity in humans. Here, we aimed to clarify the effect of rapamycin on human endothelial cells (ECs) as an in vitro model of human blood vessels. METHODS:Over the course of oxidative stress-induced senescence using hydrogen peroxide, we examined the effect of rapamycin on human coronary artery ECs (HCAECs). Senescence was evaluated by detecting senescence-associated β-galactosidase (SA-β-Gal) activity and the real-time PCR analysis of p16INK4a. Furthermore, expression levels of SASP factors were examined by real-time PCR and the expression of senescence-related antigens, such as intercellular adhesion molecule-1 (ICAM-1) and ganglioside GM1, were examined by fluorescence-activated cell sorting analysis and immunostaining. The inhibitory effect of rapamycin on mTOR signaling was examined by immunoblotting. The adhesion of leukocytes to HCAECs was evaluated by adhesion assays. Endothelial-mesenchymal transition (EndMT) induced by rapamycin treatment was evaluated by real-time PCR analysis and immunostaining for EndMT markers. Finally, we checked the activation of autophagy by immunoblotting and examined its contribution to EndMT by using a specific inhibitor. Furthermore, we examined how the activation of autophagy influences TGF-β signaling by immunoblotting for Smad2/3 and Smad7. RESULTS:A decrease in SA-β-Gal activity and the suppression of SASP factors were observed in HCAECs undergoing stress-induced premature senescence (SIPS) after rapamycin treatment. In contrast, ICAM-1 and ganglioside GM1 were upregulated by rapamycin treatment. In addition, leukocyte adhesion to HCAECs was promoted by this treatment. In rapamycin-treated HCAECs, morphological changes and the promotion of EndMT were also observed. Furthermore, we found that autophagy activation induced by rapamycin treatment, which led to activation of the TGF-β pathway, contributed to EndMT induction. CONCLUSIONS:We revealed that although rapamycin functions to inhibit senescence and suppress SASP in HCAECs undergoing SIPS, EndMT is induced due to the activation of autophagy. Video abstract.

SUBMITTER: Sasaki N

PROVIDER: S-EPMC7069020 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Macroautophagy/autophagy plays a vital role in the homeostasis of diverse cell types. Vascular endothelial cells contribute to vascular health and play a unique role in vascular biology. Here, we demonstrated that autophagy defects in endothelial cells induced IL6 (interleukin 6)-dependent endothelial-to-mesenchymal transition (EndMT) and organ fibrosis with metabolic defects in mice. Inhibition of autophagy, either by a specific inhibitor or small interfering RNA (siRNA) for ATG5 (autophagy related 5), in human microvascular endothelial cells (HMVECs) induced EndMT. The IL6 level was significantly higher in ATG5 siRNA-transfected HMVECs culture medium compared with the control HMVECs culture medium, and neutralization of IL6 by a specific antibody completely inhibited EndMT in ATG5 siRNA-transfected HMVECs. Similar to the in vitro data, endothelial-specific atg5 knockout mice (Atg5 Endo; Cdh5-Cre Atg5 flox/flox mice) displayed both EndMT-associated kidney and heart fibrosis when compared to littermate controls. The plasma level of IL6 was higher in Atg5 Endo compared to that of control mice, and fibrosis was accelerated in Atg5 Endo treated with a HFD; neutralization of IL6 by a specific antibody inhibited EndMT and fibrosis in HFD-fed Atg5 Endo associated with the amelioration of metabolic defects. These results revealed the essential role of autophagy in endothelial cell integrity and revealed that the disruption of endothelial autophagy could lead to significant pathological IL6-dependent EndMT and organ fibrosis. Abbreviations: 3-MA: 3-methyladenine; ATG5: autophagy related 5; EndMT: endothelial-to-mesenchymal transition; HES: hematoxylin and eosin stain; HFD: high-fat diet; HMVECs: human microvascular endothelial cells; IFNG: interferon gamma; IL6: interleukin 6; MTS: Masson's trichrome staining; NFD: normal-fat diet; siRNA: small interfering RNA; SMAD3: SMAD family member 3; TGFB: transforming growth factor β; TNF: tumor necrosis factor; VEGFA: vascular endothelial growth factor A.

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Rapamycin promotes endothelial-mesenchymal transition during stress-induced premature senescence through the activation of autophagy.

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