The Mechanism Of Signal Transduction On The Hormesis Of Human Bone Marrow Mesenchymal Stem Cell Induced By LDR: In Vitro

Luckey has found that Low dose radiation(LDR) may stimulate the cell metabolic activity in 1980s.eg :the synthesis of DNA and protein,he call such phenomena as hormesis.To date ,all previous exprements unclose that the experiments expore LDR can increase the metabolic activity of cell in vitro and in vivo,including the synthesis of DNA,RNA and protein,repair of DNA injury,activity of antioxygen and stimulate the mobilation of bone marrow cells to peripherial blood et al.all such studies focus on the synthesis of DNA,RNA and protein or repair of DNA injury,et al.all studies may be backing up as the studies of hormesis of gene and protein level,however,the studies on the proliferation of cells induced by LDR were scare,all datas summed up included that LDR can induce the proliferation of lymphocyte,fibroblast and other diploid cells in vitro,different style cells have different reactions of proliferation hormesis,we still consider the presence of some survival genes and absence of some apoptosis genes play an important role in the cell proliferation hormesis induced by LDR,because bulk studied show the cell proliferation hormesis and gene protein hormesis is consistant.,however,other datas delineated that LDR can induce the hormesis of gene and protein but not hormesis of cell proliferation,so the mechanisms of cell proliferation hormesis induced by LDR is not clear.Bio-responses induced by LDR in hematopoietic system cells were scare,all previous datas showed that LDR may stimulate the proliferation of mice bone marrow cells and mobilation of bone marrow cells into peripherial blood,protect the bone marrow cells and peripherial blood cells from the continous high dose radiation.but some published datas thought the biological effect of cell proliferation hormesis induced by LDR in mice bone marrow and peripherial blood cells was labile.so the biological effect on the hematopoetic system of LDR remained elucidated.Recent studies substantiated that bone marrow stroma cells have commonness of stem cells that have multi-directional defferentiation potentiality.under specific conditions MSC may differentiate to cardiac musle,bone,cartilage,fat,musle and tendon et al tissues.so it can supply reliable auto-resource for cell transplantation or tissue and organ restitution.the content of MSC in bone marrow is rare,account only the one per million or hundred thousand proportion in mononuclear cells.so it is very importmant that culturing and amplifying the human bone MSC in vitro.we carrie out a series of assays that giving low dose radiation to MSC cultured ex vitro,observing the proliferation of MSC after 4h,24h,48h and 72h four points radiated from 25mGy,75 mGy and 200mGy three doses.we screened the most optimal dose and time interval with counting method with tiphon,MTT assay and flow cytometry method,we found that 75mGy and 24h after LDR are the most optimal dose and time interval among above doses and time intervals.LDR did not induce the differentiation of MSC after the immuno-adhersion molecule of identitying with FCM assay,it remained the primary state as same as the cells in control group,we used the K562 cell lines as comparion and found no dose can stimulate the cell proliferation hormesis of K562.The study on the signal transduction system has been a hot point in many fields,available datas focused all on the signal change induced by high dose radiation,in contrast,the signal transduction by LDR is scare,some published literatures suggested LDR can mediate the hormesis and adaptive response effect by PKC,ERK,PKC-α- P38MAPK-PLC-δfeedback circuitry signaling pathway,PADP ribose,AP-1,SRF,ATF-2 and NF-γB transcription factors. P38MAPK belonged to the family number of mitogen-activated protein kinase ,MAPK cascade is pivotal signal transduction system intracells,it adjusted the growth,differentiation,cleavage and the intercellular spontaneously function。Four MAPK pathways have been identified in human :ERK pathway ,JNK/SAPK pathway,P38MAPK pathway and BMK/ERK5 pathway.P38MAPK pathway play an important role in the all body imflammation,shock,cell migaration,cardiovascular disease and tumor et al.we have reported that X-ray low dose radiation can stimulate the proliferation of MSC in exprimentⅠand certified the hormesis effect of MSC induced by LDR from cell proliferation level,but the mechanism of hormesis effect remained unsolved.there werenot any experiments that P38MAPK participated in the hormesis of MSC induced by X-ray LDR in domestic and aboard to date.we detected the expression of phospho-P38MAPK protein with traditional westernblot method and observed the extent of cell proliferation and the change of protein related to proliferation and apoptosis after inhibit the activity of kinase .LDR can induce the proliferation of MSC in vitro through exprimentⅠandⅡ,the most optimal dose and time interval were 75mGy and 24h after LDR,the expression of phospho-P38MAPK retained the peak when 12h after 12h,maintained high level when 24h in exprimentⅡ,the time of peak of phospho-P38MAPK is earlier than the cell peraliferaion hormesis ,the expression of P53 and P21 protein was up-regulated and the G1 stage arrested when SB203580 added,such phenomena explained the cell proliferation hormesis mediated by P38MAPK signal pathway,the mechanism of cell proliferation induced by LDR is decreasing the P21 to induce the cells into cleavage stage depending on P53,K562 cell lines in control group shows no such features,it illustrated that LDR can't activate the signal pathway related the cell proliferation so that it can't activate the cell proliferation hormesis of hematologic tumor cells.In a word,Our studied found that LDR can stimulate the cell proliferation of MSC mediated by P38MAPK signal pathway in vitro ,the optimal dose and time interval on such effect is 75mGy and 24h.the hormesis of cell proliferation is related to the down-regulation of P53 and P21.such expriment establish the trial and theorical base to amplify the MSC in vitro.