Biology subjects

Evans, I. R.

Publications and source records attributed to Evans, I. R..

6 recordsLinked to original sources

bioRxiv2026

Fisetin-mediated MYC restoration improves age-associated decline in macrophage function

Immune decline in older adults is associated with increased susceptibility to infection and chronic inflammatory diseases. Macrophages are critical innate immune cells that show reduced capacity for phagocytosis and migration with age. Our previous work shows that reduced levels of MYC and USF1 transcription factors are drivers of macrophage age-related functional decline. Here we show that macrophage-specific Myc overexpression improves macrophage migration and, more importantly, is able to improve physical performance at older age in Drosophila, while lifespan remains unaffected. Treatment of human primary macrophages from older individuals with the geroprotective supplement fisetin reverses the decline in MYC expression and improves phagocytosis of pathogens and cell migration functions towards levels seen in younger individuals. Mechanistically, fisetin acts via MYC, by restoring expression levels of MYC targets in human macrophages that are altered with age. Finally, fisetin feeding in older mice improves motor activity and reduces frailty, as well as restoring primary macrophage function and Myc expression in vitro. These findings reveal that restoration of MYC in macrophage ageing is responsible, at least in part, for improvement in physical performance with age and identify this pathway as a rational target to reverse age-related immune decline. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=185 SRC="FIGDIR/small/731325v1_ufig1.gif" ALT="Figure 1"> View larger version (49K): org.highwire.dtl.DTLVardef@1ab6731org.highwire.dtl.DTLVardef@3d85dorg.highwire.dtl.DTLVardef@71c2b3org.highwire.dtl.DTLVardef@a59bf3_HPS_FORMAT_FIGEXP M_FIG C_FIG

immunology↗

bioRxiv2024

Expansion of Drosophila haemocytes using a conditional GeneSwitch driver affects larval haemocyte function, but does not modulate adult lifespan or survival from infection

Macrophages are responsible for diverse and fundamental functions in vertebrates. Fruit flies harbour an innate immune system of which the most populous blood cell (haemocyte) type bears striking homology to the vertebrate macrophage. The importance of these cells has been demonstrated previously, where immune and developmental phenotypes have been observed upon haemocyte ablation using pro-apoptotic transgenes driven by the Hml promoter. Here we show that, as well as ablating Hml-positive cells in vivo using the pro-apoptotic transgene bax, we can also increase Hml-positive cell numbers using a constitutively-active form of ras. However, in adults, compared to larvae, total blood cell numbers were not significantly affected by experimental expansion or ablation. This therefore implies the existence of feedback mechanisms which regulate the number of haemocytes. No effect on lifespan was observed from driving ras and bax in Hml-positive cells using a conditional genetic system (Hml-GeneSwitch). Using a constitutive driver system, we did observe differences in lifespan, however we attribute this to differences in genetic background that could have led to spurious conclusions. Additionally, no effect of either transgene was observed upon infection with two different bacterial species, although a striking pupal lethality phenotype was observed upon expansion of Hml-positive cells in the context of a self-encapsulation mutant genetic background. The latter confirms that the change in Hml-positive cell number does result in a phenotype. The lack of adult phenotypes could be due to the strength of our experimental manipulation or due to compensation via feedback mechanisms that operate to maintain total blood cell numbers. Our study demonstrates the importance of a conditional approach to modulate haemocyte cell numbers in vivo which allows for more precise study of innate immune system function. This approach could be especially fruitful to uncover the mechanisms that regulate total blood cell numbers across development and ageing.

developmental biology↗

bioRxiv2023

Macrophage subpopulation identity in Drosophila is modulated by apoptotic cell clearance and related signalling pathways

In Drosophila blood, plasmatocytes of the haemocyte lineage represent the functional equivalent of vertebrate macrophages and have become an established in vivo model with which to study macrophage function and behaviour. However, the use of plasmatocytes as a macrophage model has been limited by a historical perspective that plasmatocytes represent a homogenous population of cells, in contrast to the high levels of heterogeneity of vertebrate macrophages. Recently, a number of groups have reported transcriptomic approaches which suggest the existence of plasmatocyte heterogeneity, while we identified enhancer elements that identify subpopulations of plasmatocytes which exhibit potentially pro-inflammatory behaviours, suggesting conservation of plasmatocyte heterogeneity in Drosophila. These plasmatocyte subpopulations exhibit enhanced responses to wounds and decreased rates of efferocytosis when compared to the overall plasmatocyte population. Interestingly, increasing the phagocytic requirement placed upon plasmatocytes is sufficient to decrease the size of these plasmatocyte subpopulations in the embryo. However, the mechanistic basis for this response was unclear. Here, we examine how plasmatocyte subpopulations are modulated by apoptotic cell clearance (efferocytosis) demands and associated signalling pathways. We show that loss of the phosphatidylserine receptor Simu prevents an increased phagocytic burden from modulating specific subpopulation cells, while blocking other apoptotic cell receptors revealed no such rescue. This suggests that Simu-dependent efferocytosis is specifically involved in determining fate of particular subpopulations. Supportive of our original finding, mutations in amo (the Drosophila homolog of PKD2), a calcium-permeable channel which operates downstream of Simu, phenocopy simu mutants. Furthermore, we show that Amo is involved in the acidification of the apoptotic cell-containing phagosomes, suggesting that this reduction in pH may be associated with macrophage reprogramming. Additionally, our results also identify Ecdysone receptor signalling, a pathway related to control of cell death during developmental transitions, as a controller of plasmatocyte subpopulation identity. Overall, these results identify fundamental pathways involved in the specification of plasmatocyte subpopulations and so further validate Drosophila plasmatocytes as a heterogeneous population of macrophage-like cells within this important developmental and immune model.

developmental biology↗

bioRxiv2020

Identification of functionally-distinct macrophage subpopulations regulated by efferocytosis in Drosophila

Macrophages are a highly heterogeneous population of cells, with this diversity stemming in part from the existence of tissue resident populations and an ability to adopt a variety of activation states in response to stimuli. Drosophila blood cells (hemocytes) are dominated by a lineage of cells considered to be the functional equivalents of mammalian macrophages (plasmatocytes). Until very recently plasmatocytes were thought to be a homogeneous population. Here, we identify enhancer elements that label subpopulations of plasmatocytes, which vary in abundance across the lifecourse of the fly. We demonstrate that these plasmatocyte subpopulations behave in a functionally-distinct manner when compared to the overall population, including more potent migratory responses to injury and decreased clearance of apoptotic cells within the developing embryo. Additionally, these subpopulations display differential localisation and dynamics in pupae and adults, hinting at the presence of tissue-resident macrophages in the fly. Our enhancer analysis also allows us to identify novel candidate genes involved in plasmatocyte behaviour in vivo. Misexpression of one such enhancer-linked gene (calnexin14D) in all plasmatocytes improves wound responses, causing the overall population to behave more like the subpopulation marked by the calnexin14D-associated enhancer. Finally, we show that, we are able to modulate the number of cells within some subpopulations via exposure to increased levels of apoptotic cell death, thereby decreasing the number of plasmatocytes within more wound-responsive subpopulations. Taken together our data demonstrates the existence of macrophage heterogeneity in Drosophila and identifies mechanisms involved in the specification and function of these plasmatocyte subpopulations. Furthermore, this work identifies key molecular tools with which Drosophila can be used as a highly genetically-tractable, in vivo system to study the biology of macrophage heterogeneity.

developmental biology↗

bioRxiv2020

Overexposure to apoptosis via disrupted glial specification perturbs Drosophila macrophage function and reveals roles of the CNS during injury

Apoptotic cell clearance by phagocytes is a fundamental process during development, homeostasis and the resolution of inflammation. However, the demands placed on phagocytic cells such as macrophages by this process, and the limitations these interactions impose on subsequent cellular behaviours are not yet clear. Here we seek to understand how apoptotic cells affect macrophage function in the context of a genetically-tractable Drosophila model in which macrophages encounter excessive amounts of apoptotic cells. We show that loss of the glial transcription factor repo, and corresponding removal of the contribution these cells make to apoptotic cell clearance, causes macrophages in the developing embryo to be challenged with large numbers of apoptotic cells. As a consequence, macrophages become highly vacuolated with cleared apoptotic cells and their developmental dispersal and migration is perturbed. We also show that the requirement to deal with excess apoptosis caused by a loss of repo function leads to impaired inflammatory responses to injury. However, in contrast to migratory phenotypes, defects in wound responses cannot be rescued by preventing apoptosis from occurring within a repo mutant background. In investigating the underlying cause of these impaired inflammatory responses, we demonstrate that wound-induced calcium waves propagate into surrounding tissues, including neurons and glia of the ventral nerve cord, which exhibit striking calcium waves on wounding, revealing a previously unanticipated contribution of these cells during responses to injury. Taken together these results demonstrate important insights into macrophage biology and how repo mutants can be used to study macrophage-apoptotic cell interactions in the fly embryo. Furthermore, this work shows how these multipurpose cells can be overtasked to the detriment of their other functions, alongside providing new insights into which cells govern macrophage responses to injury in vivo.

immunology↗

bioRxiv2018

Simu-dependent clearance of dying cells regulates macrophage function and inflammation resolution

Macrophages encounter and clear apoptotic cells during normal development and homeostasis, including at numerous sites of pathology. Clearance of apoptotic cells has been intensively studied, but the effects of macrophage-apoptotic cell interactions on macrophage behaviour are poorly understood. Using Drosophila embryos, we have exploited the ease of manipulating cell death and apoptotic cell clearance in this model to identify that the loss of the apoptotic cell clearance receptor Simu leads to perturbation of macrophage migration and inflammatory responses via pathological levels of apoptotic cells. Removal of apoptosis ameliorates these phenotypes, while acute induction of apoptosis phenocopies these defects and reveals that phagocytosis of apoptotic cells is not necessary for their anti-inflammatory action. Furthermore, Simu is necessary for clearance of necrotic debris and rentention of macrophages at wounds. Thus, Simu is a general detector of damaged self and represents a novel molecular player in controlling resolution of inflammation.

cell biology↗