Functionally distinct resident macrophage subsets differentially shape responses to infection in the bladder

Abstract

Resident macrophages are abundant in the bladder, playing key roles in immunity to uropathogens. Yet, whether they are heterogeneous, where they come from, and how they respond to infection remain largely unknown. We identified two macrophage subsets in mouse bladders, MacM in the muscle and MacL in the lamina propria, with distinct protein expression and transcriptomes. Using a urinary tract infection model, we validated our transcriptomic analyses, finding that MacM macrophages phagocytosed more bacteria and polarized to a more anti-inflammatory profile, whereas the MacL subset died rapidly during infection. During resolution, monocyte-derived cells contributed to tissue-resident macrophage pools and both subsets acquired transcriptional profiles distinct from naïve macrophages. Depletion of these altered macrophages resulted in the induction of a type 1 biased immune response to a second urinary tract infection, improving bacterial clearance. Our study uncovers the biology of resident macrophages and their response to an exceedingly common infection in a largely overlooked organ, the bladder.

Early invasion of uropathogenicEscherichia coliinto the bladder wall by solitary bacteria that are protected from antibiotics and neutrophil swarms in an organoid model

“…We found that, expression of the inflammatory cytokine Tnfa (Yu et al, 2019) the neutrophil maturation factor Gcsf (Ingersoll et al, 2008; Semerad et al, 2002), and the neutrophil chemoattract Cxcl2 , (Sundac et al, 2016) were more highly expressed in infected/bystander organoids compared to uninfected controls (Sundac et al, 2016). A small but statistically insignificant increase was observed in the expression of the inflammatory cytokine Il6 , and no changes in expression were observed for macrophage-specific chemokines such as Ccl2 or in the expression of Ccl3 and Ccl4 , which also stimulate neutrophil migration but are typically produced by resident macrophages (Mariano et al, 2020; Schiwon et al, 2014). These observations are consistent with the cellular composition of the organoids as well as reports from the mouse model, where UPEC infection does not increase Ccl3 expression and leads to increased Ccl4 expression only at later stages of infection (Ingersoll et al, 2008).…”

“…These combinations are not possible in simple monolayer systems (Andersen et al, 2012) or in previously reported complex stratified systems (Horsley et al, 2018; Smith et al, 2006). In these respects, the organoid model also offers advantages compared to experiments with explanted bladder tissue (Justice et al, 2004, 2006), Shortcomings of the organoid model in its current form include the absence of resident immune cells (Mariano et al, 2020; Schiwon et al, 2014) or vasculature (Homan et al, 2019; Mansour et al, 2018), the accumulation of cell debris in the lumen, and the inability to expose the cells of the umbrella-like layer facing the lumen to urine. Some of these limitations may be addressed with a bladder-chip platform (Sharma et al, 2021), or through the development of appropriate organoid-on-chip systems (Park et al, 2019; Takebe et al, 2017; Zhang et al, 2018).…”

Transitional premonocytes emerge in the periphery for host defense against bacterial infections

“…As there are currently no effective ways of targeting TpMos and MatMos exclusively without affecting the other subset due to their developmental relationship, understanding the exact impact of each individual subset by tracing their kinetics and development into macrophages in vivo in a single entity would require more sophisticated fate-mapping models in the future. Since monocytes have also been shown to differentiate into self-renewing functional macrophages that persist after infection (73)(74)(75), further research depicting the impact of TpMo-dMs in the periphery upon a secondary microbial challenge in vivo should be explored.…”

Itaconate regulates macrophage function through stressful iron‐sulfur cluster disrupting and iron metabolism rebalancing

“…41 Macrophages express iron metabolism-related genes, limiting iron to Fe-S-containing proteins, which is a reasonable mechanism for controlling bacterial growth. 42 However, some bacteria have been shown to facilitate immune escape. 43 Salmonella lacking aconitase displayed NLRP3-and caspase-1-dependent attenuation of virulence and induced elevated serum IL-18 levels in wild-type mice.…”