Protein Supports Optimal Vascular System Performance

The process of mechanotransduction plays a crucial role in vascular biology. One example of this is the local regulation of vascular resistance via flow-mediated dilation (FMD). Impairment of this process is a hallmark of endothelial dysfunction and a precursor to a wide array of vascular diseases, such as hypertension and atherosclerosis. However, the molecules responsible for sensing flow (shear stress) within endothelial cells remain largely unknown.

To determine which molecules are capable of sensing shear stress, investigators at the Scripps Research Institute (La Jolla, CA, USA) designed a 384-well screening system that applied shear stress to cultured cells. The system used turbulent movement of liquid to mimic fluid flow in blood vessels. The instrument employed 384 pistons to push the fluid up and down over a bed of cells, placed in 384 wells on a microtiter plate. This motion simulated how blood would put pressure on those cells.

The investigators tested a series of cell lines, some of which overexpressed proteins potentially linked to pressure sensing. The expression of different candidate genes in each of the 384 wells was "knocked down" with siRNA (short interfering RNA), and the modified cells were evaluated to determine if that specific gene was required for responding to shear stress.

Results published in the April 19, 2018, online edition of the journal Cell revealed that the protein GPR68 was necessary and sufficient for shear stress responses. This protein is a proton-sensing G protein-coupled receptor, a transmembrane receptor that senses acidic pH. This class of G protein-coupled receptors is activated when extracellular pH falls into the range of 6.4-6.8 (typical values are above 7.0). The functional role of the low pH sensitivity of the proton-sensing G protein-coupled receptors is being studied in several tissues where cells respond to conditions of low pH including bone and inflamed tissues.

Data obtained during the current study showed that GPR68 was expressed in endothelial cells of small-diameter arteries. Importantly, Gpr68-deficient mice displayed markedly impaired acute FMD and chronic flow-mediated outward remodeling in mesenteric arterioles.

“In a model organism, this protein is essential for sensing blood flow, and the proper functioning of the vascular system,” said senior author Dr. Ardem Patapoutian, a professor at the Scripps Research Institute. "It has been known for decades that blood vessels sense changes in blood flow rate, and this information is crucial in regulating blood vessel dilation and controlling vascular tone. Despite the importance of this process, the molecules involved within arteries to sense blood flow have remained unknown. Future work will explore the role of GPR68 in clinically relevant cardiovascular diseases. We are also exploring the possibility of using small molecules to modulate the function of GPR68, as such molecules could be beneficial in the clinic.”

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