Modulation of mechanosensitive channel activity by plasma membrane lipids

Abstract

Biological cells are sensitive to physical stimuli, however the mechanisms underlying this sensitivity are still poorly understood. The sensation and conversion of a physical stimulus into electrical and biochemical intracellular signalling, a process termed mechanosensory transduction (mechanotransduction), is mediated by a variety of membrane-bound proteins loosely referred to as mechanoreceptors or mechanotransducers. These encompass all the active and passive membrane components of the mechanotransductory process, including the extracellular matrix, cytoskeleton and crosslinking intermediate filaments, non-conductive membrane proteins, transporters, ion channels, chromatin and lastly, the plasma membrane itself. Biological membranes are essential structural components of living cells which encapsulate and compartmentalize the biochemical processes essential for life and act as a primary host for mechanoreceptors. A specific class of mechanoreceptors, the mechanosensitive (MS) ion channels, is responsible for the fast conversion of physical stimuli into ionic currents. Currently little is known about the role of membrane lipids in regulating the activity of mechanosensitive channels in humans. The following thesis aims to describe how specific membrane lipids can modulate the activity of tension-gated MS channels, focussing specifically on the eukaryotic channel PIEZO1. By employing a combination of patch-clamp electrophysiology and fluorescence microscopy techniques it was possible to characterize the effects of cholesterol and poly-unsaturated fatty acids on the function and localization of PIEZO1 in cultured human cells. Manipulation of membrane lipids produced dramatic effects on the sensitivity and kinetics of PIEZO1, an essential receptor of membrane tension involved in development and pathology. Furthermore, the observed effects could be recapitulated in minimal in vitro liposome systems where the purified PIEZO1 channel was reconstituted. This work demonstrates that altered lipid environments can impact on the functioning of PIEZO1 and can result in phenotypes reminiscent of mutant channel variants involved in pathology. This work furthers our understanding of the general principles behind the membrane dependence of the mechanosensory processes that govern many aspects of cellular life and will provide new insights on how cells regulate essential adaptive processes such as growth, movement and gene expression.