Short CommunicationLXRβ is involved in the control of platelet production from megakaryocytes
Introduction
Platelets are anucleate blood cells derived from megakaryocytes that circulate in the blood and responsible for maintaining the body hemostasis [1]. An adequate supply of platelets and normal function of platelets are essential to repair the minute vascular damage that occurs with daily life, and to initiate thrombus formation when it is necessary [2]. The liver X receptors (LXRs), including LXRα (NR1H3) and LXRβ (NR1H2), belong to the nuclear receptor superfamily and could regulate transcription of a number of target genes related to cholesterol, glucose and fatty acid metabolism [3,4]. LXRβ is ubiquitously expressed while LXRα is most highly expressed in the liver, adipose, kidney, adrenal tissues, and macrophages. In platelets, only LXRβ but not LXRα could be detected [5]. Interestingly, two recent studies suggested the possible involvement of LXR in regulation of platelet functions. Spyridon M et al. showed that LXR agonist GW3965 could exhibit anti-platelet and anti-thrombotic effects [6]. Another study by Schaffer S et al. also showed the inhibitive effects of both natural and pharmacologic LXR agonists on platelet aggregation [7].
In the present study, by comparing the response of LXRβ-deficient mice and their wide-type littermates in the systemic collagen-epinephrine thrombosis mouse model, we checked whether LXRβ had the potential to affect platelet activation and predisposition to thrombotic events. The aggregation of LXRβ-deficient platelets under ADP induction was also compare with control platelets. In the study, an interesting finding that the platelet number increased in the blood of LXRβ-deficient mice was observed. Then, we confirmed the influence of LXRβ knockdown on platelet production from human megakaryocytes. The differentiation and platelet production of human megakaryoblastic DAMI cells treated with siRNA for LXRβ were observed. Possible mechanisms of the LXRβ in controlling differentiation and platelet production of megakaryocytes were studied by comparing the protein expression profiles of LXRβ-knockdown cells and that of negative control cells using proteomic analysis. Results of the present study showed for the first time that LXRβ is an important signaling molecule involved in the control of platelet production from megakaryocytes.
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Animals
LXRβ deficient mice (Nr1h2tm1Djm) were purchased from The Jackson Laboratory (Bar Harbor, ME, USA) and bred as described in our previous report [8]. All experimental protocols were approved by the Committee on the Ethics of Animal Experiments of the School of Medicine, Shanghai Jiao Tong University and were in compliance with the Guide for the Care and Use of Laboratory Animals by the National Academy Press. Briefly, animals were bred in Shanghai Biomodel Organism Science & Technology
In-vivo thrombosis model
Histologic examination of lung slices, obtained from animals at 2 min after the injection of collagen plus epinephrine, showed that the lung vessels were totally or partially occluded by blood clots (platelet thrombi). The black arrows in Fig. 1A showed several representative blood clots. Notably, as shown in Fig. 1A, there were more big blood clots in LXRβ-deficient group than in wild-type group. Results of statistical analysis of quantified blood clots area (Fig. 1B) also confirmed the
Discussion
Platelets play critical roles in primary hemostasis and thrombosis as well as other important processes such as inflammation and immune responses. Therefore, regulation of platelet production and activation is important in both physical and pathological situations. LXRs are well known as nuclear oxysterol receptors and physiological master regulators of lipid and cholesterol metabolism and also display anti-inflammatory activities [16]. Clarifying the roles of LXRs in cardiovascular diseases
CRediT authorship contribution statement
YWW conducted the experiments related to DAMI cells and analyzed the results; WL and MTF conducted the experiments related to LXRβ-deficient mice and analyzed the results; JP, BH and XL planned the study; YWW, ZSW and XL drafted and revised the manuscript; All authors critically reviewed the manuscript.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by the National Natural Science Foundation of China (No. 81873056), the Open Project of the State Key Laboratory of Innovative Natural Medicine and Traditional Chinese Medicine Injections (No. QFSKL2018006) and the Outstanding Clinical Discipline Project of Shanghai Pudong (PWYgy2018-05).
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