Matrix stiffness modulates tip cell formation through the p-PXN-Rac1-YAP signaling axis

Endothelial tip cell outgrowth of blood-vessel sprouts marks the initiation of angiogenesis which is critical in physiological and pathophysiological procedures.However,how mechanical characteristics of extracellular matrix(ECM)modulates tip cell formation has been largely neglected.In this study,we found enhanced CD31 expression in the stiffening outer layer of hepatocellular carcinoma than in surrounding soft tissues.Stiffened matrix promoted sprouting from endothelial cell(EC)spheroids and upregulated expressions of tip cell-enriched genes in vitro.Moreover,tip cells showed increased cellular stiffness,more actin cytoskeleton organization and enhanced YAP nuclear transfer than stalk and phalanx ECs.We further uncovered that substrate stiffness regulates FAK and Paxillin phosphorylation in focal adhesion of ECs promoting Rac1 transition from inactive to active state.YAP is subsequently activated and translocated into nucleus,leading to increased tip cell specification.p-Paxillin can also loosen the intercellular connection which also facilitates tip cell specification.Collectively our present study shows that matrix stiffness modulates tip cell formation through p-PXN-Rac1-YAP signaling axis,shedding light on the role of mechanotransduction in tip cell formation.This is of special significance in biomaterial design and treatment of some pathological situations.

HtrA3 paves the way for MSC migration and promotes osteogenesis

Mesenchymal stem cell(MSC)migration determines the healing capacity of bone and is crucial in promoting bone regeneration.Migration of MSCs is highly dependent on degradation of extracellular matrix by proteolytic enzymes.However,the underlying mechanisms of how enzymolysis paves the way for MSCs to migrate from their niche to the defect area is still not fully understood.Here,this study shows that high-temperature requirement A3(HtrA3)overcomes the physical barrier and provides anchor points through collagen IV degradation,paving the way for MSC migration.HtrA3 is upregulated in MSCs at the leading edge of bone defect during the early stage of healing.HtrA3 degrades the surrounding collagen IV,which increases the collagen network porosity and increases integrinβ1 expression.Subsequently,integrinβ1 enhances the mechanotransduction of MSCs,thus remodeling the cytoskeleton,increasing cellular stiffness and nuclear translocation of YAP,eventually promoting the migration and subsequent osteogenic differentiation of MSCs.Local administration of recombinant HtrA3 in rat cranial bone defects significantly increases new bone formation and further validates the enhancement of MSC migration.This study helps to reveal the novel roles of HtrA3,explore potential targets for regenerative medicine,and offer new insights for the development of bioactive materials.