Induced phagocytic particle uptake into a giant unilamellar vesicle

Abstract

Phagocytosis, the uptake and ingestion of solid particles into living cells, is a central mechanism of our immune system. Due to the complexity of the uptake mechanism, the different forces involved in this process are only partly understood. Therefore the usage of a giant unilamellar vesicle (GUV) as the simplest biomimetic model for a cell allows one to investigate the influence of the lipid membrane on the energetics of the uptake process. Here, a photonic force microscope (PFM) is used to approach an optically trapped 1 μm latex bead to an immobilized GUV to finally insert the particle into the GUV. By analysing the mean displacement and the position fluctuations of the trapped particle during the uptake process in 3D with nanometre precision, we are able to record force and energy profiles, as well as changes in the viscous drag and the stiffness. After observing a global followed by a local deformation of the GUV, we measured uptake energies of 2000 kT to 5500 kT and uptake forces of 4 pN to 16 pN for Egg-PC GUVs with sizes of 18-26 μm and varying membrane tension. The measured energy profiles, which are compared to a Helfrich energy model for local and global deformation, show good coincidence with the theoretical results. Our proof-of-principle study opens the door to a large number of similar experiments with GUVs containing more biochemical components and complexity. This bottom-up strategy should allow for a better understanding of the physics of phagocytosis.

Uniform and Janus-like nanoparticles in contact with vesicles: energy landscapes and curvature-induced forces

“…[1][2][3][4][5] The uptake of particles by cells requires the engulfment of the particles by the cell membrane, a process governed by the interplay between particle-membrane adhesion and membrane bending. 6,7 Experimentally, the fundamental features of this engulfment process can be studied using model systems such as lipid [8][9][10][11][12] vesicles or polymersomes. 13 Several computational studies have previously explored the engulfment process of both spherical [14][15][16][17][18][19][20] and nonspherical particles.…”

Mobility of an axisymmetric particle near an elastic interface

“…Prime examples are drug delivery and targeting via nanocarriers which release the active agent in disease sites such as tumours or inflammation areas (Naahidi et al 2013;Al-Obaidi & Florence 2015;Liu et al 2016). During navigation through the blood stream, but especially during uptake by a living cell via endocytosis (Doherty & McMahon 2009;Meinel et al 2014;Agudo-Canalejo & Lipowsky 2015), nanoparticles frequently come into close contact with cell membranes which alter their hydrodynamic mobilities in a complex fashion.…”

Measuring stepwise binding of a thermally fluctuating particle to a cell membrane without labeling

“…The cells used for the experiments were J774A.1 murine mouse macrophages (17). Cells were cultivated as described previously (Kress et al, 2007).…”

“…A large amount of information can be extracted when the thermal fluctuations between the binding partners are not suppressed, but are measured on broad bandwidths, with e.g. Photonic Force Microscopes (PFM) [16], and are analyzed with correlative or multi-spectral methods ( [17,18] [19]).…”