Activation of autophagy during farnesyl pyrophosphate synthase inhibition is mediated through PI3K/AKT/mTOR signaling

Abstract

Objectives Autophagy is divided into three phases: autophagosome engulfment of intracellular organelles and proteins, autophagosome fusion with lysosomes, and autolysosome degradation. The farnesyl pyrophosphate synthase inhibitor ibandronate (IBAN) has in vivo cardioprotective properties, potentially via anti-oxidant effects. Whether autophagy is involved in the cardioprotective effect of IBAN remains unexplored. Methods Human umbilical vein endothelial cells (HUVECs) were treated in vitro with IBAN to assess autophagy induction. Lysosomal activation and phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signaling were assessed using a LysoTracker assay, acridine orange staining and western blotting. An MTS assay was used to assess cellular proliferation. Autophagy was inhibited using chloroquine or RNA silencing of autophagy-related 7 (Atg7) expression. Results IBAN induced autophagy in HUVECs. Moreover, IBAN activated lysosomal function, which is pivotal to autophagy induction. PI3K/AKT/mTOR activity was inhibited in IBAN-treated HUVECs, indicating the involvement of this pathway in IBAN-induced autophagy. Inhibition of autophagy using either chloroquine or Atg7 siRNA potentiated inhibition of HUVEC growth by IBAN, suggesting the involvement of non-autophagy pathways in the antiproliferative effects of IBAN. Conclusions These findings provide insights into the role of autophagy in the cardioprotective effects of IBAN and the molecular mechanisms underlying autophagy induction by IBAN.