Inhibition of Autophagy Prevents Panax Notoginseng Saponins (PNS) Protection on Cardiac Myocytes Against Endoplasmic Reticulum (ER) Stress-Induced Mitochondrial Injury, Ca2+ Homeostasis and Associated Apoptosis

Abstract

Endoplasmic reticulum (ER) stress is often closely linked to autophagy, hypoxia signaling, mitochondrial biogenesis and reactive oxygen species (ROS) responses. Understanding the interaction between ER stress, mitochondrial function and autophagy is of great importance to provide new mechanisms for the pathology, prevention and treatment of cardiovascular diseases. Our previous study has reported that Panax notoginseng saponins (PNS) protection against thapsigargin (TG)-induced ER stress response and associated cell apoptosis in cardiac myocytes is calcium dependent and mediated by ER Ca2+ release through RyR2. However, whether its protection upon ER stress and associated apoptosis is related to mitochondrial function and autophagy remains largely unknown. Here, we investigated the roles of PNS played in TG-induced mitochondrial function, ROS accumulation and autophagy. We also assessed its effects on Ca2+ homeostasis, ER stress response and associated cell death in the presence of autophagy inhibition. PNS-pretreated primary cultured neonatal rat cardiomyocytes were stimulated with TG to induce ER stress response. Mitochondrial potential (Δψm) was measured by JC-1. The general and mitochondrial ROS were measured by DCFH-DA and MitoSOX Red, respectively. Autophagy was evaluated by immunofluorescence of LC3, and immunoblots of LC3, p62, ATG7 and PINK1. In addition, mRFP-GFP-LC3 labeling was used to assess the autophagic influx. SiATG7 transfected H9c2 cells were generated to inhibit autophagy. Cytosolic and ER Ca2+ dynamics were investigated by calcium imaging. RyR2 oxidation was tested by oxyblot. Cell viability was examined by TUNEL assay. ER stress response and cell apoptosis were detected by immunoblots of BiP, CHOP, Cleaved Caspase-3 and Caspase-12. The results demonstrated that firstly, PNS protects against TG-induced mitochondrial injury and ROS accumulation. Secondly, PNS enhances autophagy in TG-induced cardiac myocytes. Thirdly, inhibition of autophagy diminishes PNS prevention of TG-induced mitochondrial injury, ROS accumulation and disruption of Ca2+ homeostasis. Last but not least, inhibition of autophagy abolishes PNS protection against TG-induced ER stress response and associated apoptosis. In summary, PNS protection against ER stress response and associated apoptosis is related to the regulation of mitochondrial injury and ROS overproduction via modulation of autophagy. These data provide new insights for molecular mechanisms of PNS as a potential preventive approach to the management of cardiovascular diseases.

Endoplasmic Reticulum-Mitochondria Contacts: A Potential Therapy Target for Cardiovascular Remodeling-Associated Diseases

“…Dysfunction of ERMCs is involved in the homeostasis reconstruction of cardiomyocytes ( Chen J. et al, 2021 ), protection against oxidative stress ( Grings et al, 2019 ), Ca 2+ signaling ( Bagur and Hajnóczky, 2017 ), lipid metabolism ( Biczo et al, 2018 ), energy metabolism ( Szymański et al, 2017 ), and cell survival ( Zhou et al, 2018a ). Therefore, in this review, we will summarize the structure and function of the ERMCs, and then we will discuss how ERMCs are associated with the high prevalence of cardiovascular diseases such as cardiac hypertrophy, heart failure, and systemic vascular diseases, as well as the potential use of ERMCs as therapeutic targets for cardiovascular remodeling.…”

Panax Notoginseng Protects against Diabetes‐Associated Endothelial Dysfunction: Comparison between Ethanolic Extract and Total Saponin

“…Furthermore, notoginsenoside R1 was reported to prevent cardiomyocyte apoptosis and ischemic/reperfusion injuries via inhibition of signaling pathways related to oxidative stress and endoplasmic reticulum (ER) stress [ 11 ]. Another recent study showed that PNS protect against thapsigargin-induced mitochondrial injury, reducing ROS accumulation and Ca 2+ -dependent ER stress [ 12 ].…”

Eicosapentaenoic Acid-Induced Autophagy Attenuates Intervertebral Disc Degeneration by Suppressing Endoplasmic Reticulum Stress, Extracellular Matrix Degradation, and Apoptosis

“…On the contrary, transcription factors such as ATF4 and XBP have been reported to enhance autophagy during ER-stress ( Guo and Li, 2014 ; Xia et al, 2021 ). The reparative effect of autophagy on ER stress seems to be obvious ( Chen et al, 2021 ; Wang Y.-L. et al, 2021 ). Nevertheless, a handful of studies have reported that there exists a crosstalk between autophagy and endoplasmic reticulum stress in NPCs.…”