Effect Of Hypothalamus-pituitary-adrenal Axis Response N The Mobilization Of Bone Marrow Stem Cells And Their Olecular Mechanisms

Background: The death toll caused by trauma continues to rise in the worldwide,which is expected to reach8.4million by2020. Severe tissue damage is the leading causeof death and disability. Exploring the effective methods for repairing the damaged tissues inthe early stage and preventing the traumatic complications is the key to improve survivaland prognosis of patients with severe trauma. In recent years, adult stem cells bring a newperspective for repairing the injured tissues. In adult organisms, stem cells localizedprimarily in the bone marrow have the ability to mobilize and differentiate into multiple cellphenotypes in injury. In addition, adult stem cells also play a significant role in immuneregulation. For example, MSCs can inhibit proliferation of T, B, NK cells as well asmigration of B cells, and they also inhibit TH1cells secreting pro-inflammatory cytokinesand promote TH2cells producing anti-inflammatory cytokines. Although the exogenousstem cells play a significant role in the injury treatment, we have to encounter a serious oftheoretical and technical bottleneck, such as their expansion, identification and uncertainfate turnover. One current of repair of injured tissue invokes mobilization of these bonemarrow stem cells to sites of injury as seed cells. However, the medicine that mobilizes thestem cells may result in adverse reactions among thirty percent of patients. They may sufferfrom headache, ostalgia, fatigue or even the acute lung injury. Hence, the exploration byusing endogenous repair mechanism to mobilize the stem cells has been paid muchattention. In recent years, people found that many neuroendocrine hormones play potentialregulatory roles in mobilization, proliferation, differentiation of bone marrow stem cells,such as the sympathetic adrenal medulla and other endocrine organ derived hormones(norepinephrine, estrogen). These hormones can promote the egress of different types ofbone marrow stem cells from bone marrow niches. In view of the important role of neuroendocrine responses in regulating the numbers of bone marrow stem cells and effectof hormones in regulating the microenvironment of injured tissues, we propose thehypothesis that the excitation of hypothalamus-pituitary-adrenal (HPA) axis plays an keyrole in the mobilization of bone marrow stem cells in the trinitarian hypothalamus-bonemarrow-blood pathway. In this study, we try to further clarify the detailed mobilizationcourses in HPA axis activation and the roles of its downstream glucocorticoid, in order tofind a new way for treatment of patients with severe trauma through regulatingneuroendocrine responses.Methods: Breeding and identification of CRH wild type (CRH+/+) mice and CRHgene knockout (CRH-/-) mice. Then the CRH+/+and CRH-/-mice were divided into theforced running groups and control groups. Peripheral blood was obtained one hour afterrunning by removing eyeballs. Corticosterone (CORT) in the plasma was measured byELISA, and the numbers of mesenchymal stem cells (MSCs), endothelial progenitor cells(EPCs) and hematopoietic stem cells (HSCs) in the peripheral blood were determined byflow cytometry; Then CRH+/+mice and CRH-/-mice were infused with different doses ofglucocorticoids by a micro-syringe pump, and plasma corticosterone and peripheral bloodMSCs, EPCs and HSCs were detected as mentioned previously. Bone marrow MSCs andEPCs were isolated and cultured and pre-treated with the glucocorticoid receptor antagonistRU486(10μM) for30min before adding glucocorticoids with different doses (0ng/ml,75ng/ml,100ng/ml,1500ng/ml). The chemotactic movements and the expression offMLP-R of MSC and EPC were detected respectively by neuro probe chemotaxis chamberand Realtime PCR and immunofluorescence.Results: After the treadmill stress, the plasma corticosterone levels of CRH+/+mousewere significantly increased. Simultaneously, the number of MSCs and EPCs in theperipheral blood was also significantly increased. But the plasma corticosterone levels ofCRH-/-mouse do not change significantly after treadmill stress, and in addition, thenumber of MSCs and EPCs in peripheral circulation decreased significantly. After theinfusion of glucocorticoids, the plasma corticosterone levels of CRH+/+and CRH-/-micewere significantly increased. Also, the number of peripheral blood HSCs, MSCs and EPCswere significantly increased in both mice. Only low dose corticosterone can promote thechemotaxis of bone marrow MSCs and EPCs, and this effect can be reversed by RU486. Both low and high concentrations of glucocorticoid could promote the mRNA expression offMLP-R by bone marrow MSC and EPC, whereas only low dose glucocorticoids canpromote protein expression of fMLP-R, which was also reversed by the GR blockade withRU486.Conclusion:1.The excitation of hypothalamus-pituitary-adrenal (HPA) andglucocorticoid can contribute to the mobilization of bone marrow MSCs and EPCs in acutestress;2.Glucocorticoid can promote the expression of fMLP-R and enhance thechemotaxis of MSCs and EPCs by receptor genomic pathway in the process ofmobilization.