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The role of calcium signaling analysis in myeloid leukocyte activation and interactions in inflammation
The role of calcium signaling analysis in myeloid leukocyte activation and interactions in inflammation
Inflammation is the pathophysiologic basis of many diseases that are main causes of mortality. Caused by environmental or microbial factors, inflammation leads to the destruction of tissue around the primary focus and expands to other tissues when not resolved in a timely manner. The body’s mechanism for inflammation resolution is based on an interplay of immune cells that first drive a pro-inflammatory response necessary for recruiting neutrophils and macrophages that phagocytose debris and dendritic cells that relay information to lymphocytes that build up the body’s adaptive immunity. Neutrophils are key to this process as they are the first cell type to recognize damage and pathogen associated molecular patterns (DAMPs and PAMPs). Eventually, they undergo necrosis amplifying the chemokine and cytokine gradient needed for added neutrophil swarming and other cells’ recruitment. In addition to the release of chemokine cues, neutrophil necrosis results in the release of reactive oxygen species that is an additional mediator of tissue damage. Although the literature hints at a cellular interplay as mechanism to prevent excessive neutrophil-induced tissue damage, there is to date no tool to investigate intravital leukocyte activation patterns in vivo in this setting. For this purpose, we turned to calcium (Ca++) signaling since it is known to be involved in most aspects of cellular function. By using myeloid leukocyte specific Ca++ reporter strains together with in vivo two-photon and spinning disk confocal microscopy in a sterile inflammation mouse model, we developed an image analysis algorithm of frequency spectra that offers the following insights: macrophages react to sterile inflammation by Ca++ transients in a distinct spatiotemporal pattern and neutrophils vary their intracellular dynamics during the migration cascade in a Gαi-protein-coupled receptor dependent manner. Furthermore, during resolution of inflammation we observed tissue macrophages (TMs) physically contacting injury-bound neutrophils with their dendrites and instructing them to withdraw. Ca++ signal analysis displays that both cell types undergo cellular activation adjustments during interaction. Finally, we uncovered that the HMGB1-TLR4 axis is responsible for TM dendrite formation and that LFA-1 mediates neutrophil interaction with these dendrites. Therefore, we have uncovered a mechanism how tissue inflammation is limited through macrophage-neutrophil interactions.
Calcium signaling, neutrophils, tissue resident macrophages, microcirculation, tissue necrosis, power spectral density, cellular interaction, G-protein coupled receptor, HMGB1, TLR4, LFA1
Mehari, Fitsumbirhan Tetemke
2021
English
Universitätsbibliothek der Ludwig-Maximilians-Universität München
Mehari, Fitsumbirhan Tetemke (2021): The role of calcium signaling analysis in myeloid leukocyte activation and interactions in inflammation. Dissertation, LMU München: Faculty of Medicine
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Abstract

Inflammation is the pathophysiologic basis of many diseases that are main causes of mortality. Caused by environmental or microbial factors, inflammation leads to the destruction of tissue around the primary focus and expands to other tissues when not resolved in a timely manner. The body’s mechanism for inflammation resolution is based on an interplay of immune cells that first drive a pro-inflammatory response necessary for recruiting neutrophils and macrophages that phagocytose debris and dendritic cells that relay information to lymphocytes that build up the body’s adaptive immunity. Neutrophils are key to this process as they are the first cell type to recognize damage and pathogen associated molecular patterns (DAMPs and PAMPs). Eventually, they undergo necrosis amplifying the chemokine and cytokine gradient needed for added neutrophil swarming and other cells’ recruitment. In addition to the release of chemokine cues, neutrophil necrosis results in the release of reactive oxygen species that is an additional mediator of tissue damage. Although the literature hints at a cellular interplay as mechanism to prevent excessive neutrophil-induced tissue damage, there is to date no tool to investigate intravital leukocyte activation patterns in vivo in this setting. For this purpose, we turned to calcium (Ca++) signaling since it is known to be involved in most aspects of cellular function. By using myeloid leukocyte specific Ca++ reporter strains together with in vivo two-photon and spinning disk confocal microscopy in a sterile inflammation mouse model, we developed an image analysis algorithm of frequency spectra that offers the following insights: macrophages react to sterile inflammation by Ca++ transients in a distinct spatiotemporal pattern and neutrophils vary their intracellular dynamics during the migration cascade in a Gαi-protein-coupled receptor dependent manner. Furthermore, during resolution of inflammation we observed tissue macrophages (TMs) physically contacting injury-bound neutrophils with their dendrites and instructing them to withdraw. Ca++ signal analysis displays that both cell types undergo cellular activation adjustments during interaction. Finally, we uncovered that the HMGB1-TLR4 axis is responsible for TM dendrite formation and that LFA-1 mediates neutrophil interaction with these dendrites. Therefore, we have uncovered a mechanism how tissue inflammation is limited through macrophage-neutrophil interactions.