Pulsatile lipid vesicles under osmotic stress

Abstract

The response of lipid bilayers to osmotic stress is an important part of cellular function. Recent experimental studies showed that when cell-sized giant unilamellar vesicles (GUVs) are exposed to hypotonic media, they respond to the osmotic assault by undergoing a cyclical sequence of swelling and bursting events, coupled to the membrane's compositional degrees of freedom. Here, we establish a fundamental and quantitative understanding of the essential pulsatile behavior of GUVs under hypotonic conditions by advancing a comprehensive theoretical model of vesicle dynamics. The model quantitatively captures the experimentally measured swellburst parameters for single-component GUVs, and reveals that thermal fluctuations enable rate-dependent pore nucleation, driving the dynamics of the swell-burst cycles. We further extract constitutional scaling relationships between the pulsatile dynamics and GUV properties over multiple time scales. Our findings provide a fundamental framework that has the potential to guide future investigations on the non-equilibrium dynamics of vesicles under osmotic stress.

Lipid unsaturation properties govern the sensitivity of membranes to photo-induced oxidative stress

“…GUVs were observed by bright field optical microscopy and photooxidation was induced by illumination with a 120 W Metal halide lamp with a 405±10 nm bandpass filter. GUVs undergoing swell-burst cycles induced by osmotic stress (45)(46)(47) or subject to surfactants (48,49). Based on these observations, we propose the following mechanism for the GUVs dynamics ( Fig.…”

“…Once this critical strained is reached, the GUV opens a micrometer sized pore through which the inner solution leaks out, relaxing the internal pressure and decreasing in turn the vesicle volume and membrane tension. This in turn allows for the pore line tensioninduced by the hydrophobic lipid mismatch at the pore edgeto drive the resealing of the pore (47). Such swelling and bursting sequence is repeated in successive cycles as long as oxidative species are released from the membrane.…”

Modelling the dynamics of vesicle reshaping and scission under osmotic shocks

“…Possible further applications of the combination of the coarsegrained membrane model with explicit solute particles could be to study multiple encodytic events in fluctuating and heterogeneous environments, which could give rise to complex internal vesicle structures of different compositions. The model is also well suited for studying vesicle bursting cycles observed in hypotonic environments 22 or the different morphologies observed for multiphasic 8 and protein charged vesicles 11,19 , where the dynamical nature of MD simulations should prove useful.…”

“…More important for cell compartmentalization and endocytosis, simple osmotic shocks can also drive inward budding of the membrane coupled with absorption of external medium into the newly created inner compartment [9,14,15,22,23]. Finally, studies have also shown that hypotonic shocks result in pulsatile dynamics of stretch and release for the vesicle until equilibrium is reached between the two solutions [24,25].…”

“…Furthermore, given that usually such models assume constant surface area, no stretching of the membrane is allowed, rendering any hypotonic shock scenario virtually inaccessible. Indeed, hypotonic shocks result in a swelling and bursting of the vesicle sometimes displaying cyclic relaxation dynamics [24,25] which cannot be replicated by a non-stretching surface description of the lipid bilayer that cannot break. Finally, by the very nature of the free energy minimisation approach, curvature models provide little insight into the relaxation dynamics of the vesicles.…”