Functions of mutant and wildtype Piezo1 channels

Background: Piezo1 is a mechanically-activated ion channel with a widespread role in mechanotransduction in mammalian physiology. Mutations of the channel which confer gain of function (GOF) are causative of dehydrated hereditary stomatocytosis (DHS), a form of anaemia. Heterologous expression studies suggest that that GOF arises from a delaying of channel inactivation, however this mechanism has not been confirmed in endogenous channels in affected red blood cells (RBCs). Pharmacological tools with which to modulate Piezo1 activity are very limited and additional compounds are required if therapeutic targeting is to be possible. Methods and Results: A CRISPR-Cas9 mouse model (Piezo1 M-R) was generated harbouring the murine equivalent of DHS-causing Piezo1 mutation, M2225R. Like humans with the mutation, Piezo1 M-R mice demonstrated signs of DHS, providing important validation of the model. Electrophysiological studies of affected RBCs revealed a dramatic delaying of channel deactivation following mechanical stimulus. Non- RBC phenotypic effects of Piezo1 GOF were identified for the first time, most strikingly a disposition towards lipogenesis and insulin resistance. Piezo1 M-R mice following high fat diet intervention did not exhibit the same increased lipogenesis, but instead had reduced physical activity. Analogues of Piezo1 agonist Yoda1 were synthesised by the School of Chemistry and were tested for their ability to activate the channel or inhibit the Yoda1 response. Important structural requirements for Piezo1 interaction were identified, in addition to a new pharmacological tool, Dooku1, which can inhibit Yoda1-induced Piezo1 activation in endogenously expressed channels. Conclusion: The data reveal that the true mechanisms for Piezo1-causing disease are distinct from those identified by overexpression studies. This is important for targeting therapies to treat these diseases. Additionally, the study has revealed that in addition to DHS, people with Piezo1 GOF mutations may have other disease risk. This is relevant due to high incidence of Piezo1 mutations in people of African origin, owing to a protection against malaria. Understanding the mechanism for Piezo1 GOF and phenotypic effects of such a defect is important for uncovering additional physiological roles of the channel and for relation to DHS patients with Piezo1 mutations.