Extracellular histones activate autophagy and apoptosis via mTOR signaling in human endothelial cells

Abstract

Circulating histones have been proposed as targets for therapy in sepsis and hyperinflammatory symptoms. However, the proposed strategies have failed in clinical trials. Although different mechanisms for histone-related cytotoxicity are being explored, those mediated by circulating histones are not fully understood. Extracellular histones induce endothelial cell death, thereby contributing to the pathogenesis of complex diseases such as sepsis and septic shock. Therefore, the comprehension of cellular responses triggered by histones is capital to design effective therapeutic strategies. Here we report how extracellular histones induce autophagy and apoptosis in a dose-dependent manner in cultured human endothelial cells. In addition, we describe how histones regulate these pathways via Sestrin2/AMPK/ULK1-mTOR and AKT/mTOR. Furthermore, we evaluate the effect of Toll-like receptors in mediating autophagy and apoptosis demonstrating how TLR inhibitors do not prevent apoptosis and/or autophagy induced by histones. Our results confirm that histones and autophagic pathways can be considered as novel targets to design therapeutic strategies in endothelial damage.

Exosomes from Adipose Tissue-Derived Mesenchymal Stem Cells Ameliorate Histone-Induced Acute Lung Injury by Activating the PI3K/Akt Pathway in Endothelial Cells.

“…Histones also interact with Toll-like receptors (TLRs) and proin ammatory cytokine/chemokine, released through MyD88, NFκB, and NLRP3 in ammasomedependent pathways [17,21]. In previous studies, extracellular histone-treated HUVECs decreased eNOS expression [39], suppressed the Akt signaling pathway [15], and eventually induced apoptosis in a dosedependent manner. In many sepsis animal models, endothelial cell damage is associated with apoptosis [19,40,41].…”

“…In humans, increased levels of circulating histones have also been recognized in septic and ARDS patients depending on their severity [34,35]. Recently, some studies have shown that extracellular histones are cytotoxic toward the endothelium in vitro [15] and cause lethal intra-alveolar hemorrhage in mice [21][22][23]36]. Therefore, extracellular histone is increasingly becoming of concern and examined as a therapeutic target for sepsis and ARDS.…”

“…Recent studies have reported that under conditions of sepsis, extracellular histones released from dead cells, including neutrophil extracellular traps (NETs) and damage-associated molecular patterns (DAMPs), induce endothelial damage in a concentration-dependent manner [15] and cause multiple organ failure (MOF) [16,17]. Moreover, in ARDS, histones are believed to majorly contribute to the onset and propagation of acute lung injury [5,18].…”

“…Moreover, in ARDS, histones are believed to majorly contribute to the onset and propagation of acute lung injury [5,18]. Although the mechanisms underlying histone-related cytotoxicity are not fully understood, apoptosis via the Akt pathway in endothelial cells is one of the outcomes [15,19]. For this reason, therapies that inhibit the release of histone or histone-related signal transduction are supposed to signi cantly protect endothelial cells from damage, and thus could be a novel therapeutic approach for ARDS and sepsis [20,21].…”

“…Histone administration is a newly established model for investigating mechanisms of endothelial damage according to circulating extracellular histones in mice [21][22][23] and primary human umbilical vein endothelial cells (HUVECs) [15]. Although ADSCs have been reported to prevent lipopolysaccharide (LPS) [24] and cecal ligation and puncture (CLP)-induced ARDS and sepsis models [3,6], their role in endothelial prevention in histone-induced model has not been elucidated.…”