To Measure and Modulate Molecular Tensions on Integrins and Notch Receptors
Mammalian cells are remarkable signal processors. They can sense a variety of external signals such as chemical, electrical, thermal and mechanical signals. Cell membrane proteins named integrins are important mechanical signal receivers. Integrins provide adhesive linkage between cells and extracellular matrix (ECM) and directly transmit forces in and out of cells. Such forces are crucial for cells to sense external environment and activate internal mechano-biochemical pathways, and further regulate many cellular functions such as cell adhesion, proliferation, polarization, migration, and eventually influence long-term cell behaviors including stem cell differentiation, cancer metastatsis, etc.
To measure and modulate integrin molecular tension, I developed Tension Gauge Tether (TGT) during my postdoctoral research in Prof Taekjip Ha’s lab. TGT is a molecular linker with a tunable tension tolerance (Ttol, 10~100 pN) that ruptures at this critical force. Ligand molecules are immobilized through TGTs onto a surface. When cells are cultured on this surface, mechano-sensitive receptors such as integrins bind to the tethered ligands. Cells will apply forces to these ligand-receptor bonds to activate associated functions. If such forces are stronger than Ttol, TGT would rupture and abolish the cellular functions. By observing the Ttol of TGT required for receptor activation, I measured a ~ 40 pN force on integrins during cell adhesion and a < 12 pN force for Notch receptor activation.
Please download this short Video Clip to see how Tension Gauge Tether works, or check the paper:
X. F. Wang and T. Ha, “Defining Single Molecular Forces Required to Activate Integrin and Notch Signaling”, Science, 340, 991-994 (2013).
In addition to being a force sensor, TGT can also function as a force modulator that restricts molecular forces on integrins or other receptors under a tunable level. In my recent work, I have observed that cells cultured on TGT surfaces with Ttol decreasing from 100 pN to 10 pN, gradually lose their normal functions such as migration, focal adhesion formation, spreading, adhesion, and focal adhesion kinase (FAK) activation. Clearly, TGT provides a novel and unique mechanical cue to cells that modulates cellular forces at the molecular level. This will enable the synthesis of novel TGT-derived biomaterials that can be used to influence many vital cellular functions by molecular force control on receptor proteins.
Fig. 1. The Tension Gauge Tether (TGT, red curvy line) is a molecular linker made from dsDNA that can be ruptured at a critical force, Ttol. If cellular force on receptor-ligand bonds (green hexagons) > Ttol, TGT will break and terminate receptor-mediated downstream cellular functions. In this example, cells do not adhere on the Ttol = 33 pN surface, but do adhere on the Ttol=43 pN surface, indicating that an integrin-mediated force of ~40 pN is required for cell adhesion.