Induction of Rapid Osteoblast Differentiation in Rat Bone Marrow Stromal Cell Cultures by Dexamethasone and BMP-2

[摘要] Adultvertebratesrequireacontinuoussupplyofosteoblastsforbothboneremodelingandregenerationduringfracturerepair.Thisimpliestheexistenceofareservoirofcellsinthebodycapableofosteogenesis.Onesourceoftheseosteoprogenitorsisthestemcellswithinthefibroblasticcomponentofbonemarrowstroma.Matureosteoblastsarecharacterizedbyhighalkalinephosphataseandosteopontinlevels,combinedwithexpressionofthebone-specificmatrixproteinsosteocalcinandbonesialoproteinandthecapacityformatrixmineralization.Wehaveusedthesemarkerstodefinetheconditionspermittingrapidosteoblastdifferentiationfromculturedbonemarrowstromalcells.Osteoblasticdifferentiationwasinducedbycontinuousculturewith10-5Mdexamethasone(dex)whichstimulatedalkalinephosphatase(AP)activityandmRNAlevelsaswellusosteopontin,bonesialoprotein,andosteocalcinmRNAbyDay8ofculture;coadditionof10-5M1,25-dihydroxyvitaminD3(vitaminD)withdexwasessentialforhighosteocalcinmRNAexpression.Recombinantbonemorphogeneticprotein-2(BMP-2)exertedsimilareffectstodexandactedinsynergywithdextoyieldgreatlyelevatedAPactivityaswellasincreasedlevelsofosteoblasticmRNAs.UsinginsituhybridizationtodetectthepresenceofmRNAsinindividualcells,itwasshownthatappearanceofosteopontinmRNAprecededAPmRNA,andwasexpressedindex-treatedcellcoloniesasearlyasDay4.QuantitationofcellsurfaceAPproteinbyflowcytometryindicatedthatculturewithdexorBMP-2producedamixedpopulationofcellswithlowAP(dimcells)andcellswithhighAPlevels,whilethecombinationofdex+BMP-2yieldedveryfewdimcellsandapopulationofcellscontaininghigherAPlevelsthanwitheitherinduceralone.Whenthedimpopulationfromdex-treatedcellswassortedandreculturedwithinducers,theseculturesdevelopedhighAPlevelsandwereabletodepositamineralizedmatrix.Thus,treatmentofmarrowstromalcellswithinducerresultsinapopulationofmatureosteoblastsaswellasapopulationofundifferentiatedcellswhichretainsthecapacityforosteoblasticdifferentiationwithfurtherexposuretoinducers.ThesedatademonstratethatstemcellswithinthestromalcompartmentofbonemarrowarecapableofrapidlyacquiringosteoblastfeaturesandsuggestapotentialroleforglucocorticoidsincombinationwithBMP-2andvitaminDinstagesofosteogenicdevelopment.

[学科分类] 生物科学（综合）