Effects Of Mechanical Stretch Stress On The Proliferation And Differentiation Of Human Stem Cells From Apical Papilla And Its Mechanisms

Part ? Effects of Mechanical Stretch Stress on the Proliferation and Differentiation of Human Stem Cells from Apical PapillaObjective: Teeth often elongated when they had no occlussion,especially the elongation of the third maxillary molar easily led to soft tissue occlusal trauma.We often met the impacted teeth or delayed eruption teeth in orthodontic treatment.In the process of dragging these young permanent teeth to guide their eruption with mechanical force,we could observe the phenomena of tooth root development including apical foramina narrowing and tooth root getting longer gradually.In orthodontic treatment root resorption often occured due to excessive force or improper force.Stem cells from apical papilla(SCAP)belonged to odontogenic mesenchymal stem cells,which were isolated from the human tooth apical papilla.SCAP could differentiate into osteoblasts,adipocytes,odontoblasts,nerve cells and so on under certain culture conditions.SCAP were seen as seed cells of periapical tissue regeneration and were used for stem cell-based periapical tissue regeneration project.The aim of my study in this part was to explore the effects of different mechanical stretch stress on the proliferation and differentiation potential of SCAP,and to provide theoretical guidance for orthodontic treatment.Methods: The human SCAP were isolated and cultured from the extracted healthy premolars or third molars whose apex were not fully developed by tissue block enzyme digestion and finite dilution method and then identified them.MTT assay was used to detect the effects of different static mechanical stretch stress stimulation on the proliferation of SCAP.Western blot was used to detect the expression of SCAP osteogenesis/ odontoblast differentiation-related protein ALP,OSX and DSP under mechanical stretch stress.Results: 1.SCAP were successfully isolated and cultured,and we induced SCAP to differentiate into osteoblasts and adipocytes successfully by osteogenic induction and adipogenic induction.Flow cytometry was performed in accordance with SCAP immunophenotype.2.Compared with the control group,150 g and 200 g mechanical stretch stress stimulation promoted SCAP proliferation first and then inhibited SCAP proliferation(P <0.05).250 g mechanical stretch stress stimulation significantly inhibited SCAP proliferation(P <0.05).3.The expression levels of ALP,OSX and DSP protein in each group were higher than those in the control group(P <0.05).Conclusion: Mechanical stretch stress could regulate the SCAP proliferation and osteogenesis/ odontoblast differentiation.Part ? Mechanism Research of Mechanical Stretch Stress Effecting the Differentiation of Human Stem Cells from Apical PapillaObjective: Endoplasmic reticulum(ER)was the major organelle that synthesized proteins,produced lipids and stored calcium ions.Intracellular proteins were mainly folded and modified in ER.When unfolded protein or wrongly folded protein accumulated in ER,it would cause endoplasmic reticulum stress(ERS)and lead to unfolded protein response(UPR).Many factors could cause cell ERS,such as cell nutrition deficiencies,hypoxia,ischemia,drugs,gene mutations,viral infections and so on.It had been demonstrated in Part?that mechanical stretch stress had an effect on the proliferation and osteogenesis/ odontoblast differentiation of SCAP.As a mechanical stimulation,would mechanical stretch stress lead to endoplasmic reticulum stress? The aim of my study in this part was to explore the mechanisms of mechanical stretch stress regulating the osteogenesis/ odontoblast differentiation of SCAP.Methods: Western blot was used to detect the expression of SCAP endoplasmic reticulum stress molecular chaperone GRP78 under different static mechanical stretch stress.Results: Compared with the control group,the expression of GRP78 protein was up-regulated(P <0.05).Conclusion: Mechanical stretch stress might regulate SCAP osteogenesis/ odontoblast differentiation through ERS.