Phagosomal transport depends strongly on phagosome size

Abstract

Macrophages internalize pathogens for intracellular degradation. An important part of this process is the phagosomal transport from the cell periphery to the perinuclear region. Biochemical factors are known to influence the fate of phagosomes. Here, we show that the size of phagosomes also has a strong influence on their transport. We found that large phagosomes are transported persistently to the nucleus, whereas small phagosomes show strong bidirectional transport. We show that dynein motors play a larger role in the transport of large phagosomes, whereas actin filament-based motility plays a larger role in the transport of small phagosomes. Furthermore, we investigated the spatial distribution of dyneins and microtubules around phagosomes and hypothesize that dynein and microtubule density differences between the nucleus-facing side of phagosomes and the opposite side could explain part of the observed transport characteristics. Our findings suggest that a size-dependent cellular sorting mechanism might exist that supports macrophages in their immunological roles.

Clearance by Microglia Depends on Packaging of Phagosomes into a Unique Cellular Compartment

“…We show that this shrinkage depends on the activity of the solute carrier transporter Slc37a2. The molecular mechanisms that pair Slc37a2-mediated transport with vesicular contraction are, of course, of great interest because recent reports have shown that phagosomal size can influence the transport and behavior of these vesicles inside the cell (Keller et al, 2017). Work in plants and bacteria exposed to extreme osmotic variations shows that solute trafficking and osmotic changes are coupled to vesicular size adjustments via the formation of micro-lumina and finger-like protrusions that are thought to reduce membrane length, allowing the resizing of vesicles and cells (Claessens et al, 2008).…”

Cargo diffusion shortens single-kinesin runs at low viscous drag

“…We first examined the run length of single-kinesin cargos over a physiologically relevant range of solution viscosities (Dix and Verkman, 1990;Kalwarczyk et al, 2011;Kuimova et al, 2009;Luby-Phelps et al, 1993;Margraves et al, 2011;Suhling et al, 2004), while holding the cargo size and motor velocity constant at 0.5 µm in diameter and 0.8 µm/s when unloaded, respectively ( Figure 1). These parameter choices are commonly employed in in vitro studies (for example, (Schnitzer et al, 2000)) and are within the ranges measured for intracellular cargos in vivo (Bakker et al, 1997;Casley-Smith, 1969;Keller et al, 2017;Lorenz and Willard, 1978;Margraves et al, 2011;Shubeita et al, 2008;Tytell et al, 1981;Wiemerslage and Lee, 2016;Zhang et al, 1998).…”

“…We next sought to understand how changes in cargo size and motor velocity impact kinesin's run length. While these parameters were held constant in the preceding simulations at 0.5 µm in diameter and 0.8 µm/s unloaded, respectively (Figures 1), their values are known to vary in living cells (Bakker et al, 1997;Casley-Smith, 1969;Keller et al, 2017;Lorenz and Willard, 1978;Margraves et al, 2011;Shubeita et al, 2008;Tytell et al, 1981;Wiemerslage and Lee, 2016;Zhang et al, 1998).…”

“…Here we employed Monte Carlo-based stochastic simulations to numerically examine the effect of cargo diffusion on transport by a single kinesin. We carried out our simulations over a large parameter space that captures crucial transport characteristics in living cells, including variations in viscosity (Dix and Verkman, 1990;Kalwarczyk et al, 2011;Kuimova et al, 2009;Luby-Phelps et al, 1993;Margraves et al, 2011;Suhling et al, 2004), cargo size (Bakker et al, 1997;Casley-Smith, 1969;Keller et al, 2017;Margraves et al, 2011;Shubeita et al, 2008;Wiemerslage and Lee, 2016;Zhang et al, 1998), and motor velocity (Lorenz and Willard, 1978;Tytell et al, 1981). Associated with this large parameter space is an additional load on the motor: the viscous drag force that hinders cargo motion (Laidler and Meiser, 1982).…”

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

“…The endocytic uptake of particles into cells is controlled by multiple biochemical and biophysical mechanisms. The most prominent cellular process, phagocytosis [1][2][3], comprises the engulfment, internalization and intracellular transport of a particle, requiring energy for the deformation of the cell membrane, the reorganization of the actin network [4] and for phagosome transport by molecular motors [5,6]. In many cases endocytosis is receptor-mediated, which means that ligands on particles, typically bacteria and viruses, trigger the recruitment of receptors in the cell membrane, such as the Fc receptor for immunoglobulins (Ig) or receptors of the complement system.…”