Oxygen Glucose Deprivation Induced Prosurvival Autophagy Is Insufficient to Rescue Endothelial Function

Venkateswaran Natarajan; Tania Mah; Chen Peishi; Shu Yi Tan; Ritu Chawla; Thiruma Valavan Arumugam; Adaikalavan Ramasamy; Karthik Mallilankaraman

doi:10.3389/fphys.2020.533683

Oxygen Glucose Deprivation Induced Prosurvival Autophagy Is Insufficient to Rescue Endothelial Function

Front Physiol. 2020 Sep 16:11:533683. doi: 10.3389/fphys.2020.533683. eCollection 2020.

Authors

Venkateswaran Natarajan¹, Tania Mah¹, Chen Peishi¹, Shu Yi Tan¹, Ritu Chawla¹, Thiruma Valavan Arumugam², Adaikalavan Ramasamy³, Karthik Mallilankaraman^{1

4}

Affiliations

¹ Mitochondrial Physiology and Metabolism Lab, Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore.
² Department of Physiology, Anatomy and Microbiology School of Life Sciences, La Trobe University, Melbourne, VIC, Australia.
³ Genome Institute of Singapore, ASTAR, Singapore, Singapore.
⁴ Center for Healthy Longevity, NUHS, Singapore, Singapore.

Abstract

Endothelial dysfunction, referring to a disturbance in the vascular homeostasis, has been implicated in many disease conditions including ischemic/reperfusion injury and atherosclerosis. Endothelial mitochondria have been increasingly recognized as a regulator of calcium homeostasis which has implications in the execution of diverse cellular events and energy production. The mitochondrial calcium uniporter complex through which calcium enters the mitochondria is composed of several proteins, including the pore-forming subunit MCU and its regulators MCUR1, MICU1, and MICU2. Mitochondrial calcium overload leads to opening of MPTP (mitochondrial permeability transition pore) and results in apoptotic cell death. Whereas, blockage of calcium entry into the mitochondria results in reduced ATP production thereby activates AMPK-mediated pro-survival autophagy. Here, we investigated the expression of mitochondrial calcium uniporter complex components (MCU, MCUR1, MICU1, and MICU2), induction of autophagy and apoptotic cell death in endothelial cells in response to oxygen-glucose deprivation. Human pulmonary microvascular endothelial cells (HPMVECs) were subjected to oxygen-glucose deprivation (OGD) at 3-h timepoints up to 12 h. Interestingly, except MCUR1 which was significantly downregulated, all other components of the uniporter (MCU, MICU1, and MICU2) remained unchanged. MCUR1 downregulation has been shown to activate AMPK mediated pro-survival autophagy. Similarly, MCUR1 downregulation in response to OGD resulted in AMPK phosphorylation and LC3 processing indicating the activation of pro-survival autophagy. Despite the activation of autophagy, OGD induced Caspase-mediated apoptotic cell death. Blockade of autophagy did not reduce OGD-induced apoptotic cell death whereas serum starvation conferred enough cellular and functional protection. In conclusion, the autophagic flux induced by MCUR1 downregulation in response to OGD is insufficient in protecting endothelial cells from undergoing apoptotic cell death and requires enhancement of autophagic flux by additional means such as serum starvation.

Keywords: MCUR1; apoptotic cell death; autophagy; endothelial dysfunction; oxygen-glucose deprivation.