Incorporating mechanical cues into cellular responses allows us to experience our direct environment. Specialized cells can perceive and discriminate between different physical properties such as level of vibration, temperature, or pressure. Mechanical forces are abundant signals that also shape general cellular responses such as cytoskeletal rearrangement, differentiation, or migration and contribute to tissue development and function. The molecular structures that perceive and transduce mechanical forces are specialized cytoskeletal proteins, cell junction molecules, and membrane proteins such as ion channels and metabotropic receptors. G protein-coupled receptors (GPCRs) have attracted attention as metabotropic force receptors as they are among the most important drug targets. This review summarizes the function of mechano-sensitive GPCRs, specifically, the angiotensin II type 1 receptor and adrenergic, apelin, histamine, parathyroid hormone 1, and orphan receptors, focusing particularly on the advanced knowledge gained from adhesion-type GPCRs. We distinguish between shear stress and cell swelling/stretch as the two major types of mechano-activation of these receptors and contemplate the potential contribution of the force-from-lipid and force-from-tether models that have previously been suggested for ion channels.

The adhesion G protein–coupled receptor (aGPCR) GPR126/ADGRG6 plays an important role in several physiological functions, such as myelination or peripheral nerve repair. This renders the receptor an attractive pharmacological target. GPR126 is a mechano-sensor that translates the binding of extracellular matrix (ECM) molecules to its N terminus into a metabotropic intracellular signal. To date, the structural requirements and the character of the forces needed for this ECM-mediated receptor activation are largely unknown. In this study, we provide this information by combining classic second-messenger detection with single-cell atomic force microscopy. We established a monoclonal antibody targeting the N terminus to stimulate GPR126 and compared it to the activation through its known ECM ligands, collagen IV and laminin 211. As each ligand uses a distinct mode of action, the N terminus can be regarded as an allosteric module that can fine-tune receptor activation in a context-specific manner.

The adhesion G protein-coupled receptor (aGPCR) GPR126/ADGRG6 plays an important role in several physiological functions, such as myelination, peripheral nerve repair and osteoblast differentiation, which renders the receptor an attractive pharmacological target. GPR126 is a mechano-sensor that incorporates signals from the extracellular matrix (ECM) through binding to its N-terminal ligands collagen IV and laminin 211. Since ECM components are not suitable therapeutics alternate compounds with more favorable characteristics would be desirable that can mimic the physiologic activation pattern. Antibodies could present an apt alternative as they can specifically target the N-terminus of the receptor, reach multiple tissue compartments and have been shown to modulate GPCR activity levels. In this study, we use a monoclonal antibody targeting an N-terminal HA-epitope to induce receptor signaling, which can be enhanced through the addition of secondary antibodies. Using single cell atomic force microscopy (AFM) in combination with a fluorescent cAMP sensor, we show that antibody-mediated activation is achieved through combined pushing and pulling forces, while collagen IV and laminin 211 only mediate GPR126 activation through pushing or pulling, respectively. Thus, the antibody-mediated approach can reliably mimic the activation induced by both endogenous ligands. Our findings show that antibody-mediated activation for GPR126 is feasible and can be used for precise targeting of this receptor, thereby establishing it as a pharmaceutical target.

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