RETRACTED: Inhibition of CaMKII in mitochondria preserves endothelial barrier function after irradiation

Stephen J Roy,Olha M Koval,Sara C Sebag,Karima Ait-Aissa,Bryan G Allen,Douglas R Spitz,Isabella M Grumbach

doi:10.1016/j.freeradbiomed.2019.11.012

Abstract

Damage to the microvascular endothelium is an important part of normal tissue injury after radiation exposure and driven by the production of pro-oxidants. The Ca2+/calmodulin-dependent protein kinase II is present in the mitochondrial matrix (mitoCaMKII) where it regulates Ca2+ uptake via the mitochondrial Ca2+ uniporter (MCU) and pro-oxidant production. Here, we demonstrate that radiation exposure disrupts endothelial cell barrier integrity in vitro, but can be abrogated by inhibition of mitoCaMKII, MCU, or opening of the mitochondrial transition pore. Scavenging of mitochondrial pro-oxidants with mitoTEMPO before, but not after irradiation, protected barrier function. Furthermore, markers of apoptosis and mitochondrial pro-oxidant production were elevated at 24 h following irradiation and abolished by mitoCaMKII inhibition. Endothelial barrier dysfunction was detected as early as 2 h after irradiation. Despite only mildly impaired mitochondrial respiration, the intracellular ATP levels were significantly reduced 4 h after irradiation and correlated with barrier function. MitoCaMKII inhibition improved intracellular ATP concentrations by increasing glycolysis. Finally, DNA double strand break repair and non-homologous end joining, two major drivers of ATP consumption after irradiation, were greatly increased but not significantly affected by mitoCaMKII inhibition. These findings support the hypothesis that mitoCaMKII activity is linked to mitochondrial pro-oxidant production, reduced ATP production, and loss of endothelial barrier function following irradiation. The inhibition of mitoCaMKII is a promising approach to limiting radiation-induced endothelial injury.

Highlights

About 500,000 Americans receive radiation therapy as a part of cancer treatment every year [1]
To test whether mitochondrial calmodulin-dependent kinase II (CaMKII) is required for radiation-induced endotheliopathy, we established the conditions for mitochondrial delivery of the potent and specific CaMKII inhibitor peptide CaMKIIN driven a Cox IX-targeting sequence [18]
We established that inhibition of CaMKII in the mitochondrial matrix is sufficient to preserve endothelial barrier function after irradiation at doses of 1–4 Gy in bovine and human microvascular endothelial cells

Summary

Introduction

About 500,000 Americans receive radiation therapy as a part of cancer treatment every year [1]. With increasing survival rates for many malignancies, long-term side effects of radiation to normal tissue surrounding the cancerous tissue are becoming more apparent. The incidence of cognitive decline, lung fibrosis, kidney injury and cardiovascular disease is greatly increased in cancer survivors, even after targeted radiation therapy [2,3,4]. Endothelial injury is considered a strong contributor to radiation-induced normal tissue injury. Breakdown of the endothelial barrier function and capillary loss with resulting ischemia may be regarded as a common denominator of many deleterious long-term side effects of irradiation in normal tissue [4,5,6]

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Results

Conclusion