Biomechanical stress regulates mammalian tooth replacement via the integrin ß1-RUNX2-Wnt pathway.

Renewal of integumentary organs occurs cyclically throughout an organism's lifetime, but the mechanism that initiates each cycle remains largely unknown. In a miniature pig model of tooth development that resembles tooth development in humans, the permanent tooth did not begin transitioning from the resting to the initiation stage until the deciduous tooth began to erupt. This eruption released the accumulated mechanical stress inside the mandible. Mechanical stress prevented permanent tooth development by regulating expression and activity of the integrin ß1-ERK1-RUNX2 axis in the surrounding mesenchyme. We observed similar molecular expression patterns in human tooth germs. Importantly, the release of biomechanical stress induced downregulation of RUNX2-wingless/integrated (Wnt) signaling in the mesenchyme between the deciduous and permanent tooth and upregulation of Wnt signaling in the epithelium of the permanent tooth, triggering initiation of its development. Consequently, our findings identified biomechanical stress-associated Wnt modulation as a critical initiator of organ renewal, possibly shedding light on the mechanisms of integumentary organ regeneration.

Matrix stiffness and shear stresses modulate hepatocyte functions in a fibrotic liver sinusoidal model.

Extracellular matrix (ECM) rigidity has important effects on cell behaviors and increases sharply in liver fibrosis and cirrhosis. Hepatic blood flow is essential in maintaining hepatocytes' (HCs) functions. However, it is still unclear how matrix stiffness and shear stresses orchestrate HC phenotype in concert. A fibrotic three-dimensional (3-D) liver sinusoidal model is constructed using a porous membrane sandwiched between two polydimethylsiloxane (PDMS) layers with respective flow channels. The HCs are cultured in collagen gels of various stiffnesses in the lower channel, whereas the upper channel is pre-seeded with liver sinusoidal endothelial cells (LSECs) and accessible to shear flow. The results reveal that HCs cultured within stiffer matrices exhibit reduced albumin production and cytochrome P450 (CYP450) reductase expression. Low shear stresses enhance synthetic and metabolic functions of HC, whereas high shear stresses lead to the loss of HC phenotype. Furthermore, both mechanical factors regulate HC functions by complementing each other. These observations are likely attributed to mechanically induced mass transport or key signaling molecule of hepatocyte nuclear factor 4α (HNF4α). The present study results provide an insight into understanding the mechanisms of HC dysfunction in liver fibrosis and cirrhosis, especially from the viewpoint of matrix stiffness and blood flow.NEW & NOTEWORTHY A fibrotic three-dimensional (3-D) liver sinusoidal model was constructed to mimic different stages of liver fibrosis in vivo and to explore the cooperative effects of matrix stiffness and shear stresses on hepatocyte (HC) functions. Mechanically induced alterations of mass transport mainly contributed to HC functions via typical mechanosensitive signaling.

Adhesive properties of hepatoma cells to collagen IV coated surfaces.

OBJECTIVES: To quantitatively study the adhesive properties of hepatoma cells to collagen IV coated artificial basement membrane and to investigate the relevance of cell adhesive forces to the concentration of collagen IV. METHODS: Synchronous G1 and S phase cells were achieved using thymine-2-desoxyriboside and cochicine sequential blockage method and double thymine-2-desoxyriboside blockage method respectively. The adhesive forces of hepatoma cells were investigated by micropipette aspiration technique. RESULTS: The adhesive forces of hepatoma cells to artificial basement membrane were (107.78+/-65.44)x10(-10)N, (182.60+/-107.88)x10(-10)N, (298.91+/-144.13)x10(-10)N when the concentration of the membrane coated by 1, 2, 5 microg/ml collagen IV respectively (P<0.001). The adhesive forces of G1 and S phases hepatoma cells to artificial basement membrane were (275.86+/-232.80)x10(-10)N and (161.16+/-120.40)x10(-10)N respectively when the concentration of the membrane coated by 5 microg/ml collagen IV (P<0.001). CONCLUSIONS: The adhesive forces of hepatoma cells to artificial basement membrane in direct proportion to the concentration of collagen IV suggests that the increase of basement membrane might be conducive to the chemotactic motion and adhesiveness of tumor cells. G1 phase cells are more capable of adhering to basement membrane than S phase cells. Hepatoma cells, especially G1 phase cells, may survive in blood circulation, and sequest and adhere in microcirculation, and get through basement membrane for remote metastasis.