Nano-hydroxyapatite promotes cell apoptosis by co-activating endoplasmic reticulum stress and mitochondria damage to inhibit glioma growth

Despite a growing body of studies demonstrating the specific antitumor effect of nano-hydroxyapatite (n-HA), the underlying mechanism remained unclear. Endoplasmic reticulum (ER) and mitochondria are two key players in intracellular Ca2+ homeostasis and both require Ca2+ to participate. Moreover, the ER-mitochondria interplay coordinates the maintenance of cellular calcium homeostasis to prevent any negative consequences from excess of Ca2+, hence there needs in-depth study of n-HA effect on them. In this study, we fabricated needle-like n-HA to investigate the antitumor effectiveness as well as the underlying mechanisms from cellular and molecular perspectives. Data from in vitro experiments indicated that the growth and invasion of glioma cells were obviously reduced with the aid of n-HA. It's interesting to note that the expression of ER stress biomarkers (GRP78, p-IRE1, p-PERK, PERK, and ATF6) were all up-regulated after n-HA treatment, along with the activation of the pro-apoptotic transcription factor CHOP, showing that ER stress produced by n-HA triggered cell apoptosis. Moreover, the increased expression level of intracellular reactive oxygen species (ROS) and the mitochondrial membrane depolarization, as well as the downstream cell apoptotic signaling activation, further demonstrated the pro-apoptotic roles of n-HA induced Ca2+ overload through inducing mitochondria damage. The in vivo data provided additional evidence that n-HA caused ER stress and mitochondria damage in cells and effectively restrain the growth of glioma tumors. Collectively, the work showed that n-HA co-activated intracellular ER stress and mitochondria damage are critical triggers for cancer cells apoptosis, offering fresh perspectives on ER-mitochondria targeted anti-tumor therapy.