Piezo proteins (Piezo1 and Piezo2) are recently identified mechanically activated cation channels in eukaryotic cells and associated with physiological responses to touch, pressure, and stretch. In particular, human RBCs express Piezo1 on their membranes, and mutations of Piezo1 have been linked to hereditary xerocytosis. To date, however, physiological functions of Piezo1 on normal RBCs remain poorly understood. Here, we show that Piezo1 regulates mechanotransductive release of ATP from human RBCs by controlling the shear-induced calcium (Ca 2+ ) influx. We find that, in human RBCs treated with Piezo1 inhibitors or having mutant Piezo1 channels, the amounts of shear-induced ATP release and Ca 2+ influx decrease significantly. Remarkably, a critical extracellular Ca 2+ concentration is required to trigger significant ATP release, but membrane-associated ATP pools in RBCs also contribute to the release of ATP. Our results show how Piezo1 channels are likely to function in normal RBCs and suggest a previously unidentified mechanotransductive pathway in ATP release. Thus, we anticipate that the study will impact broadly on the research of red cells, cellular mechanosensing, and clinical studies related to red cell disorders and vascular disease. Previous studies have shown that the addition of chemicals that stiffen RBC membranes decreases the amount of ATP released (9, 16), indicating that deformation of the cell membrane is a necessary trigger. In addition, biological mediators, such as cystic fibrosis transmembrane conductance regulator (CFTR) and pannexin-1 hemichannels, are involved in the release pathways of mechanotransductive ATP release from RBCs (9,14,17,18). Inhibition of CFTR leads to an impaired ATP release from deformed RBCs (14). Recent studies, including our previous findings, suggest that interactions between membrane-associated actin and CFTR play important roles in the mechanotransductive ATP release from RBCs (9, 17). Pannexin-1, however, is a channel-forming protein and has been suggested as a mechanosensing ATP release channel (18). Under osmotic stress, for example, ATP released from RBCs was attenuated by carbenoxolone, a highly effective pannexin channel blocker, suggesting that pannexin-1 might be one of the conductance channels responsible for the mechanotransductive release of ATP (18). Although progress has been made in understanding mechanotransductive ATP release from RBCs, many questions remain about the signal transduction pathways. For example, how does mechanical force transduce signals to ATP release channels? Are there any stretch-activated ion channels on RBCs that may sense mechanical forces and activate ATP release? If so, are there any secondary messengers that could be generated by mechanical stimuli and regulate ATP release?Piezo proteins (Piezo1 and Pizeo2) are recently identified mechanically activated cation channels in mammals (19,20) and can be fully activated without involvement of additional proteins (20, 21). Piezo-induced cationic currents were first observe...

The tight coupling between cerebral blood flow and neural activity is a key feature of normal brain function and forms the basis of functional hyperemia. The mechanisms coupling neural activity to vascular responses, however, remain elusive despite decades of research. Recent studies have shown that cerebral functional hyperemia begins in capillaries, and red blood cells (RBCs) act as autonomous regulators of brain capillary perfusion. RBCs then respond to local changes of oxygen tension (PO2) and regulate their capillary velocity. Using ex vivo microfluidics and in vivo two-photon microscopy, we examined RBC capillary velocity as a function ofPO2and showed that deoxygenated hemoglobin and band 3 interactions on RBC membrane are the molecular switch that responds to localPO2changes and controls RBC capillary velocity. Capillary hyperemia can be controlled by manipulating RBC properties independent of the neurovascular unit, providing an effective strategy to treat or prevent impaired functional hyperemia.

No abstract