Effects of hypoxia on the biological behavior of MSCs seeded in demineralized bone scaffolds with different stiffness

Matrix stiffness has been demonstrated in many studies to adjust the biological behaviors of mesenchymal stem cells (MSCs). However, in the initial phase of bone restore, MSCs will encounter a hypoxic microenvironment. Studying the connection existing between the matrix stiffness and biological behavior of MSCs under hypoxic condition can better simulate the microenvironment at the prime period of bone repairment. In this work, three-dimensional (3D) decalcified bone scaffolds with diverse stiffness (high stiffness (66.06 ± 27.83) MPa, medium stiffness (26.90 ± 13.16) MPa, and low stiffness (0.67 ± 0.14) MPa) but same microstructure have been prepared by controlling decalcification time. In addition, the decellularized bone scaffold was regard as control group and its stiffness was (230.93 ± 72.65) MPa. The viability, proliferation, infiltration, and osteogenic differentiation of MSCs seeded into these 3D demineralized bone scaffolds were systematically investigated under 100 μM CoCl2-simulated hypoxic and normoxic environments. The results showed that the viability, proliferation, and extracellular matrix (ECM) secretion of MSCs had no significant difference on scaffolds with diverse stiffness but the degree of collagen deposition of MSCs gradually increased with the increase of scaffold stiffness both under normoxia and hypoxia. Compared to normoxia, the viability, proliferation, ECM secretion, vascular endothelial growth factor (VEGF) expression, and osteogenis of MSCs on the scaffolds with the same stiffness were evidently inhibited by hypoxia. Additionally, under hypoxic condition, the expression of VEGF and hypoxia inducible factor 1α(HIF-1α) in MSCs on the low stiffness scaffold was markedly increased comparing to those on other groups. In summary, we found that the low stiffness scaffold can improved the proliferation and osteoginic differentiation of MSCs under hypoxic environment, which may help to explore efficient methods for bone defect repairing.

Suspension state promotes extravasation of breast tumor cells by increasing integrin β1 expression

Mechanical microenvironment can strongly affect the metastatic efficiency of circulating tumor cells.However,the effect of suspension state on their extravasation and the mechanisms involved are still unclear.To explore the influence of suspension state on extravasation(including adhesion,spreading and transendothelial migration)of breast tumor cells and its relevant molecular mechanism,MDA-MB-231 cells were cultured on poly(2-hydroxyethyl methacrylate)coated 6-well plates to minic the suspension state.Suspension state promoted adhesion,spreading and transendothelial migration of MDA-MB-231 cells to EAhy926 endothelial cells(ECs)monolayer under both the static condition and 0.5 dyne/cm^(2) flow shear stress(FSS).The number of cells adhered to ECs monolayer reached 2.15(static condition,3 d)and 1.67(FSS,3 d)times,and the number of migration reached 10.60 times,respectively,as compared to that in adhesion state.Moreover,MDA-MB-231 cells knockdown of integrin β1 provoked poor adhesion and transendothelial migration,as compared with MDA-MB-231 cells.But it made no difference in cell spreading.Our results implied the increasing expression of integrin β1 induced by suspension culture promoted the adhesion and transendothelial migration of MDA-MB-231 cells,but had no significant influence on their spreading.

Three-dimensional decellularized tumor extracellular matrices with different stiffness as bioengineered tumor scaffolds

In the three-dimensional(3D)tumor microenvironment,matrix stiffness is associated with the regulation of tumor cells behaviors.In vitro tumor models with appropriate matrix stiffness are urgently desired.Herein,we prepare 3D decellularized extracellular matrix(DECM)scaffolds with different stiffness to mimic the microenvironment of human breast tumor tissue,especially the matrix stiffness,components and structure of ECM.Furthermore,the effects of matrix stiffness on the drug resistance of human breast cancer cells are explored with these developed scaffolds as case studies.Our results confirm that DECM scaffolds with diverse stiffness can be generated by tumor cells with different lysyl oxidase(LOX)expression levels,while the barely intact structure and major components of the ECM are maintained without cells.This versatile 3D tumor model with suitable stiffness can be used as a bioengineered tumor scaffold to investigate the role of the microenvironment in tumor progression and to screen drugs prior to clinical use to a certain extent.

Role of endothelial cells in the regulation of mechanical microenvironment on tumor progression

Majority of cancer patients die from cancer metastases.The physical stimulation produced by microenvironment regulates invasive behavior of cancer cells.Blood vessel is one of the“pathways”for cancer to metastasize,in which tumor cells need to cross the endothelial barrier for intravasation and extravasation.Tumor vessels are arranged in untraditional hierarchies and characterized with rupture,bend,swell and high permeability that are beneficial to intravasation of cancer cell.Abnormal vessels are accompanied with uneven blood flow,increased compression and interstitial fluid pressure.Meanwhile,excessive proliferation of tumor leads to low oxygen pressure in solid tumor.The aberrant tumor mechanical microenvironment changes the biochemical and mechanical signal transduction of endothelial cells and participates in tumor progression.Many current researches focus on how chemical signals regulate endothelial cell function while the role of physical cues is unclear.In this review,the role of endothelial cells in the regulation of shear stress,intercellular force,extracellular matrix and pressure on tumor progression is summarized.