Heterogeneity in the endocytic capacity of individual macrophage in a population determines its subsequent phagocytosis, infectivity and subcellular trafficking

Abstract

Phagocytosis is a complex cellular uptake process involving multiple distinct steps of cargo recognition, uptake, phagosome maturation and eventual phagolysosome resolution. Emerging literature shows that heterogeneity of phagocytosis at multiple steps at a single cell level influences the population outcome. However, the determinants of phagocytic heterogeneity are not clear. Here we show that the variance in the endocytic capacity of individual cells in a macrophage population determines subsequent phagocytic uptake and trafficking. Our results document the extensive heterogeneity in the endocytic uptake of individual macrophages, and show that cells with higher endocytic capacity preferentially phagocytose diverse cargo, including pathogenic Mycobacterium tuberculosis. Interestingly, M. tuberculosis infected cells sustain the higher endocytic capacity following infection. Modulating endocytic capacity by inhibiting endocytosis reduces phagocytic uptake. Differential uptake of M. tuberculosis into cells with different endocytic capacities correlates with the efficiency of phagocytic delivery to lysosomes, thus contributing further to phagocytic as well as mycobacterial heterogeneity. Thus, variance in endocytic capacity is a determinant of generating heterogeneity in phagocytosis at multiple steps.

The Interplay of Host Lysosomes and Intracellular Pathogens

“…While these studies show the relevance of global alteration of lysosomes to the infection, our recent study also throws light on lysosomal heterogeneity influencing intracellular Mtb trafficking in a non-perturbed macrophage population, i.e a higher proportion of Mtb are delivered to lysosomes in cells with higher lysosomal content (Sachdeva et al, 2020a;Sachdeva et al, 2020b).…”

“…Recent work from our laboratory reveals pre-existing endocytic heterogeneity in the macrophages that determine their susceptibility to infections (Sachdeva et al, 2020b). The study shows considerably high intrinsic heterogeneity in the endocytic capacity of individual cells in a population, which governs the subsequent phagocytic events, including intracellular infections and subcellular trafficking within macrophages (Sachdeva et al, 2020b). Interestingly, the cells with higher endocytosis also have high levels of lysosomes suggesting a co-regulation of the endosomal and lysosomal numbers (Sachdeva et al, 2020b).…”

“…This study is an elegant example of pathogen heterogeneity shaping the outcome of infection. Recent work from our laboratory reveals pre-existing endocytic heterogeneity in the macrophages that determine their susceptibility to infections (Sachdeva et al, 2020b). The study shows considerably high intrinsic heterogeneity in the endocytic capacity of individual cells in a population, which governs the subsequent phagocytic events, including intracellular infections and subcellular trafficking within macrophages (Sachdeva et al, 2020b).…”

“…The study shows considerably high intrinsic heterogeneity in the endocytic capacity of individual cells in a population, which governs the subsequent phagocytic events, including intracellular infections and subcellular trafficking within macrophages (Sachdeva et al, 2020b). Interestingly, the cells with higher endocytosis also have high levels of lysosomes suggesting a co-regulation of the endosomal and lysosomal numbers (Sachdeva et al, 2020b). In line with this, a recent study indicates the transcription regulation of endocytic genes such as Rab5A and Rab7A by TFEB, a known regulator of lysosomal biogenesis (Nnah et al, 2018).…”

“…However, the exact mechanisms determining the spread and extent of endo-lysosomal heterogeneity in cells are not known, although it is quite likely that fluctuations in the expression and subcellular localization of TFEB could play a role. Importantly, Mtb trafficking to lysosomes is different in cells with different lysosomal content, i.e a higher proportion of Mtb are delivered to lysosomes in cells with higher lysosomal content, even in the same non-perturbed macrophage cell population (Sachdeva et al, 2020b), an effect that averages out at a population level. Thus, the lysosomal content in Mtb infected cells can be a combination of pre-existing heterogeneity (Sachdeva et al, 2020b) and infection induced lysosomal biogenesis (Sachdeva et al, 2020a) (Figure 5).…”