Abstract
Background: Despite extensive work on macrophage heterogeneity, the mechanisms driving activation induced heterogeneity (AIH) in macrophages remain poorly understood. Here, we aimed to develop mathematical models to explore theoretical cellular states underpinning the empirically observed responses of macrophages following lipopolysaccharide (LPS) challenge. Methods: We obtained empirical data following primary and secondary responses to LPS in two in vitro cellular models (bone marrow-derived macrophages or BMDMs, and RAW 264.7 cells) and single-cell protein measurements for four key inflammatory mediators: TNF, IL-6, pro-IL-1β, and NOS2, and used mathematical modelling to understand heterogeneity. Results: For these four factors, we showed that macrophage community AIH is dependent on LPS dose and that altered AIH kinetics in macrophages responding to a second LPS challenge underpin hypo-responsiveness to LPS. These empirical data can be explained by a mathematical three-state model including negative, positive, and non-responsive states (NRS), but they are also compatible with a four-state model that includes distinct reversibly NRS and non-responsive permanently states (NRPS). Our mathematical model, termed NoRM (Non-Responsive Macrophage) model identifies similarities and differences between BMDM and RAW 264.7 cell responses. In both cell types, transition rates between states in the NoRM model are distinct for each of the tested proteins and, crucially, macrophage hypo-responsiveness is underpinned by changes in transition rates to and from NRS. Conclusions: Overall, we provide a mathematical model for studying macrophage ecology and community dynamics that can be used to elucidate the role of phenotypically negative macrophage populations in AIH and, primary and secondary responses to LPS.
Highlights
Variability in gene expression in eukaryotic cells is required to allow communities of cells to switch from homeostatic to inducible states while responding to external cues (Blake et al, 2006; Eldar & Elowitz, 2010)
Macrophage community activation induced heterogeneity (AIH) is dependent on LPS dose To obtain empirical data for our mathematical model and to capture distinct macrophage subpopulations upon activation with LPS we measured protein expression of three cytokines, TNF, pro-IL-1β and IL-6, and one intracellular pro-inflammatory protein NOS2, an enzyme that catalyzes nitric oxide formation
IL-6+ sub-populations were consistently reduced at all timepoints when compared between the Media/1000 and the 1000/1000 communities (Figure 4B, Figure 5B, C). These results demonstrated that for both RAW264.7 cells and Bone marrow-derived macrophages (BMDMs), pre-exposure of macrophages to low or high LPS doses resulted in altered AIH kinetics during a secondary LPS challenge in comparison to macrophages receiving a primary LPS challenge
Summary
Variability in gene expression in eukaryotic cells is required to allow communities of cells to switch from homeostatic to inducible states while responding to external cues (Blake et al, 2006; Eldar & Elowitz, 2010). Methods: We obtained empirical data following primary and secondary responses to LPS in two in vitro cellular models (bone marrow-derived macrophages or BMDMs, and RAW 264.7 cells) and single-cell protein measurements for four key inflammatory mediators: TNF, IL-6, pro-IL-1β, and NOS2, and used mathematical modelling to understand heterogeneity. Results: For these four factors, we showed that macrophage community AIH is dependent on LPS dose and that altered AIH kinetics in macrophages responding to a second LPS challenge underpin hypo-responsiveness to LPS These empirical data can be explained by a mathematical three-state model including negative, positive, and non-responsive states (NRS), but they are compatible with a four-state model that includes distinct reversibly NRS and non-responsive permanently states (NRPS). Conclusions: Overall, we provide a mathematical model for studying article can be found at the end of the article
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
