Autophagy Protects From Uremic Vascular Media Calcification

Abstract

Chronic kidney disease and diabetes mellitus are associated with extensive media calcification, which leads to increased cardiovascular morbidity and mortality. Here, we investigated the role of autophagy in the pathogenesis of uremic vascular media calcification. DBA/2 mice were fed with high-phosphate diet (HPD) in order to cause vascular calcification. DBA/2 mice on standard chow diet were used as control. In parallel, autophagy and its response to rapamycin, 3-methyladenine (3-MA), and bafilomycin were studied in an in vitro model using mouse vascular smooth muscle cells (MOVAS). DBA/2 mice on HPD developed severe vascular media calcification, which is mirrored in vitro by culturing MOVAS under calcifying conditions. Both, in vitro and in vivo, autophagy significantly increased in MOVAS under calcifying conditions and in aortas of HPD mice, respectively. Histologically, autophagy was located to the aortic Tunica media, but also vascular endothelial cells, and was found to continuously increase during HPD treatment. 3-MA as well as bafilomycin blocked autophagy in MOVAS and increased calcification. Vice versa, rapamycin treatment further increased autophagy and resulted in a significant decrease of vascular calcification in vitro and in vivo. Rapamycin reduced Runx2 transcription levels in aortas and MOVAS to control levels, whereas it increased α-smooth muscle actin and Sm22α transcription in MOVAS to control levels. Furthermore, rapamycin-treated HPD mice survived significantly longer compared to HPD controls. These findings indicate that autophagy is an endogenous response of vascular smooth muscle cells (VSMC) to protect from calcification in uremia. Induction of autophagy by rapamycin protects cells and mice from uremic media calcification possibly by inhibiting osteogenic transdifferentiation of VSMC.

mTORC1 and mTORC2 Differentially Regulate Cell Fate Programs to Coordinate Osteoblastic Differentiation in Mesenchymal Stromal Cells

“…Rapa attenuated atherosclerosis in apolipoprotein E-deficient mice 55 and vascular calcification in rats with chronic renal failure 56 . In a recent study, Rapa reduced aortic calcium load and prolonged survival in a mouse model for uremic vascular media calcification 57 . Notably, Rapa mediated protection was associated with induction of autophagy in aortic walls 57 .…”

“…In a recent study, Rapa reduced aortic calcium load and prolonged survival in a mouse model for uremic vascular media calcification 57 . Notably, Rapa mediated protection was associated with induction of autophagy in aortic walls 57 . Our findings provide a mechanistic explanation for these observations, since we demonstrated that systemic administration of Rapa shifts mTOR signaling in favor of mTORC2 while suppressing mTORC1 in vascular cells in vivo.…”

Vascular Calcification—New Insights into Its Mechanism

“…By contrast, in vitro models show that autophagy plays a protective role, to counteract against ROS-induced VC, at high Pi concentrations [88]. Increased autophagy, as evidenced by induction of LC3-ll, p62, lgfbp3, and Atg16l1, in aortic VSMCs, was noted in a uremic media calcification model, in DBA/2 mice fed a high Pi diet [120].…”

“…Based on previous reports, modulating autophagy was investigated as a preventive strategy against VC. Likewise, representative autophagy inducers, such as rapamycin and valproic acid, have been shown to inhibit VSMC calcification in vitro [120,132]. However, since there is a possibility that pharmaceutical manipulation exhibits a nonspecific, off-target effect, it is necessary to study the therapeutic effect on calcification, as a method to determine autophagy-specific effects.…”

Bavachin Protects Human Aortic Smooth Muscle Cells Against β-Glycerophosphate-Mediated Vascular Calcification and Apoptosis via Activation of mTOR-Dependent Autophagy and Suppression of β-Catenin Signaling

“…Autophagy plays a crucial role in phenotype transition and oxidative stress of VSMC cells (Mialet-Perez and Vindis, 2017). Frauscher reported that autophagy is an endogenous response of VSMC to prevent calcification in uremia (Frauscher et al, 2018). Rapamycin-mediated autophagy was found to protect the cells and mice suffered from uremiamediated calcification, probably by inhibition of osteogenic trans-differentiation of VSMCs (Frauscher et al, 2018).…”