Fall in the ATP levels in the red blood cells in ApoE-LDLR double-deficient mice model prior to atherosclerosis development
Authors: Alcicek F C , Mohaissen T , Bulat K , Szczesny-Malysiak E , Dybas J , Tyrankiewicz U , Kaczmarska M , Marzec K M , Chlopicki S 
Published: October 2021

Abstract

Background
It was previously reported that red blood cells (RBCs) regulate blood flow via RBC-derived ATP [1]. Nevertheless, to the best of our knowledge, no study was performed to characterize possible alterations in RBC ATP levels in ApoE/LDLR−/− mice [2] which constitute a reliable model of human atherosclerosis, displaying distinct erythropathy [3]. Interestingly, young ApoE/LDLR−/− mice display higher exercise capacity and higher O2 carrying capacity of RBCs, as compared to their age-matched control [3,4]. However, it is not known whether increased exerise capacity in ApoE/LDLR−/− mice is linked to altered ATP release from RBCs. It was previously reported that prostacyclin analogs, known atheroprotective agents, which preserve vascular endothelium functions in various diseases [5,6], induce ATP release from human RBCs [1,7].

Purpose
To characterize intra- and extra-cellular ATP levels in RBCs isolated from ApoE/LDLR−/− mice in comparison to control mice.

Methods
All experiments were conducted according to the Guidelines for Animal Care and Treatment of the EU and to the Local Ethical Committee on Animal Testing at our University. For experiments, 8- and 24-week-old C57BL/6 control mice (N=4–6 and N=5–8, respectively) and ApoE/LDLR−/− mice (N=4–7 and N=4–5, respectively) were used. The complete blood count, RBC morphology, biochemistry of blood plasma, RBC deformability, and RBC phosphatidylserine exposure were assessed. The intra- and extra-cellular ATP levels and ATP release from RBCs due to administration of iloprost (100 nM, 1 μM, 10 μm) were studied.

Results
Intracellular ATP level in RBCs isolated from 8-week-old ApoE/LDLR−/− mice was considerably lower as compared to their age-matched control (7.72±0.77 and 21.23±3.40 pmoles/1x106 RBCs, respectively). In 24-week-old mice, intracellular ATP in RBCs was low not only in ApoE/LDLR−/− mice but also in control mice (8.70±1.30 and 6.27±0.96 pmoles/1x106 RBCs, respectively). Basal extracellular ATP released from RBCs over 30 min incubation was 400 times lower than corresponding intracellular level, and mirrored intracellular ATP levels in all studied groups. Iloprost (100 nM–10 μM) did not produce robust ATP release in any of the studied groups, with only some effects when the highest concentration was used (10 μM).

Conclusion(s)
Hypercholesterolemia-dependent changes in young ApoE/LDLR−/− mice prior to atherosclerotic plaque development may induce a severe fall in intracellular ATP levels in the RBCs that might be linked to a possible diversion of glycolysis to 2,3-DPG to increase oxygen delivery, and might contribute to the alterations in RBC-dependent regulation of blood flow in ApoE/LDLR−/−. Further studies are required to mechanistically explain these findings.

Funding Acknowledgement
Type of funding sources: Public grant(s) – National budget only. Main funding source(s): 1) National Science Centre, Poland (UMO 2016/23/B/ST4/00795) 2) the Innovation Incubator 4.0 project funded by the Ministry of Science and Higher Education, Poland (POIR 2014-2020)