Biology subjects

Gage, M. C.

Publications and source records attributed to Gage, M. C..

6 recordsLinked to original sources

bioRxiv2025

Murine limb ischaemia induces structural and functional remodelling of local and distant bone marrow

Peripheral arterial disease (PAD) can induce bone marrow (BM) ischaemia, although little is known about the implications of this for local and systemic haematopoiesis. We explored the impact of murine unilateral hind-limb ischaemia (HLI) surgery on the structure and function of the ischaemic and non-ischaemic BM, versus control mice without HLI surgery. Abnormal BM hypoxia was present in the ischaemic limb 7-days post-HLI, with normalisation by 28-days. Histological analysis revealed the ischaemic BM to undergo profound vascular remodelling at 7-days that normalised by 61-days, along with a progressive accumulation of BM lipid droplets between 7- and 61-days; no structural changes were observed in the non-ischaemic limb BM. Flow cytometry revealed increased abundance of monocytes and inflammatory monocytes in the non-ischaemic and ischaemic BM 7-days post-HLI, with this persisting at 61-days in the non-ischaemic limb. In both limbs, we observed a progressive decline in the abundance of lineage-Sca-1+c-Kit+ haematopoietic stem cells. RNA-sequencing of BM-derived macrophages (BMDMs) revealed substantial transcriptomic differences between unstimulated control, ischaemic limb and non-ischaemic limb BMDMs. Moreover, there were also substantial transcriptomic differences between lipopolysaccharide-stimulated control and ischaemic limb BMDMs. However, we observed minimal differences in chromatin accessibility of unstimulated BMDMs from the 3 groups. Collectively, our data show that BM ischaemia has transient and sustained structural implications, along with both local and systemic effects on haematopoiesis and myeloid cell function. These findings suggest that PAD may have important consequences for systemic immune responses.

immunology↗

bioRxiv2023

Macrophage-expressed Neuropilin 2 promotes plaque formation in ApoE knockout mice and is essential for pro-inflammatory macrophage polarisation and gene expression.

AimsAtherosclerosis is a chronic inflammatory disease causing the narrowing of arteries, leading to ischaemic heart disease. It is characterised by the subendothelial retention, and modification, of lipoproteins by macrophages, highly plastic cells which undergo polarisation to a pro-inflammatory phenotype in response to cytokines and other environmental stimuli. Neuropilin-2 (NRP2) is a cell-surface co-receptor with essential roles in angiogenesis and axonal guidance, that is also expressed by macrophages. However, the role of NRP2 in macrophage function in the development of atherosclerosis has not been studied. Methods and resultsThe role of NRP2 in modulating macrophage polarisation and signalling was assessed using functional assays and transcriptome analysis in macrophages obtained from mice with macrophage-specific deletion of Nrp2 (Nrp2-KOMac,EYFP). These mice were further crossed with pro-atherogenic Apolipoprotein E-deficient mice to produce Nrp2-KOMac,Apoe-/-,EYFP mice, which were fed a high-fat diet (HFD) for 16 weeks. Plaque formation and composition were characterised using chemical and immuno-staining. NRP2 was significantly upregulated upon differentiation of bone marrow progenitors into bone marrow derived macrophages (BMDM), and further upregulated by pro-inflammatory polarisation. Transcriptome analysis revealed that inflammatory signalling pathway genes, and genes regulating monocyte chemotaxis, were downregulated in Nrp2-KOMac,EYFP BMDMs. HFD-induced plaque development was significantly reduced in Nrp2-KOMac,Apoe-/-,EYFP mice. Additionally, plaques from those mice displayed features consistent with increased plaque stability, including reduced necrotic core area, plaque lipid content and increased cap thickness. ConclusionsMacrophage-derived NRP2 is proatherogenic, likely resulting from its ability to positively regulate pro-inflammatory pathways and macrophage migration. Targeting NRP2 expressed on the surface of macrophages could therefore offer a novel therapeutic approach for reducing the disease burden associated with atherosclerosis.

cell biology↗

bioRxiv2022

Metformin, empagliflozin and their combination modulate ex-vivo macrophage inflammatory gene expression

Type-2 Diabetes Mellitus is a complex, chronic illness characterized by persistent high blood glucose levels. Patients can be prescribed anti-diabetes drugs as single agents or in combination depending on the severity of their condition. Metformin and empagliflozin are two commonly prescribed anti-diabetes drugs which reduce hyperglycemia, however their direct effects on macrophage inflammatory responses alone or in combination are unreported. Here we show that metformin and empagliflozin elicit proinflammatory responses on mouse bone-marrow derived macrophages with single agent challenge, which are modulated when added in combination. In-silico docking experiments suggested that empagliflozin can interact with both TLR2 and DECTIN1 receptors and we observed that both empagliflozin and metformin increase expression of Tlr2 and Clec7a. Thus, findings from this study suggest that metformin and empagliflozin as single agents or in combination can directly modulate inflammatory gene expression in macrophages and upregulate the expression of their receptors.

immunology↗

bioRxiv2018

Aged insulin resistant macrophages reveal dysregulated cholesterol biosynthesis, a pro-inflammatory profile and reduced foam cell formation capacity

Insulin resistance is the central defining feature of type 2 diabetes and an independent risk factor for the development of atherosclerosis. In addition, aging is a major risk factor in the development of insulin resistance and cardiovascular disease. Macrophages play a pivotal roles the the developments of diabetes and atherosclerosis and express insulin receptors. Despite their relevance however, the effect of insulin and insulin resistance on macrophages regarding their inflammatory status, foam cell formation capacity and affect on atherosclerosis are unclear. By taking advantage of a mouse model that recapitulates the effects of chronic PI3K pathway hyperstimulation in macrophages through SHIP2 knock-down, we show that insulin resistance in aged macrophages promotes a proinflammatory phenotype while modulating the cholesterol biosynthesis pathway. These altered characteristics may contribute to the development of chronic inflammatory disease frequently observed with age. Moreover, aged insulin-resistant proinflammatory macrophages display an altered response to acute inflammatory stimulus and reduced foam cell formation capacity. Our work also highlights for the first time, the complex and contrasting immunomodulatory effects of insulin on macrophages in aged mice.\n\nSignificanceO_LIFirst study to explore the effects of macrophage insulin resistance in aged cells.\nC_LIO_LIInsulin resistance in aged macrophages results in the reprogramming of the transcriptome with more than 4000 genes being differentially regulated.\nC_LIO_LIInsulin resistance in aged macrophages results in upregulation of IFN signalling pathway, cholesterol biosynthesis pathway and inflammasome gene expression.\nC_LIO_LIInsulin directly regulates macrophage cholesterol biosynthesis, IFN and inflammasome gene expression in a time- and dose-dependent manner.\nC_LIO_LIInsulin resistant aged macrophages exhibit reduced capacity to become foam cells.\nC_LI

immunology↗

bioRxiv2017

Disrupting myeloid-specific LXRα phosphorylation promotes FoxM1 expression and modulates atherosclerosis by inducing macrophage proliferation

Macrophages are key immune cells for the initiation and development of atherosclerotic lesions. However, the macrophage regulatory nodes that determine how lesions progress in response to dietary challenges are not fully understood. Liver X receptors (LXRs) are sterol-regulated transcription factors which play a central role in atherosclerosis by integrating cholesterol homeostasis and immunity. LXR pharmacological activation elicits a robust anti-atherosclerotic transcriptional program in macrophages that can be affected by LXR S196 phosphorylation in vitro. To investigate the impact of these transcriptional changes in atherosclerosis development, we have generated mice carrying a Ser-to-Ala mutation in myeloid cells in the LDLR-deficient atherosclerotic background (M-S196ALdlr-KO). M-S196ALdlr-KO mice fed a high fat diet exhibit increased atherosclerotic plaque burden and lesions with smaller necrotic cores and thinner fibrous caps. These diet-induced phenotypic changes are consistent with a reprogramed macrophage transcriptome promoted by LXR-S196A during atherosclerosis development. Remarkably, expression of several proliferation-promoting factors including the proto-oncogene FoxM1 and its targets are induced by LXR-S196A. This is consistent with increased proliferation of plaque-resident cells in M-S196ALdlr-KO mice. Moreover, disrupted LXR phosphorylation increases expression of phagocytic molecules resulting in increased apoptotic cell removal by macrophages, explaining the reduced necrotic cores. Finally, the macrophage transcriptome promoted by LXR-S196A under dietary perturbation is markedly distinct from that revealed by LXR ligand activation, highlighting the singularity of this post-translational modification. Overall, our findings demonstrate that LXR phosphorylation at S196 is an important determinant of atherosclerotic plaque development through selective changes in gene transcription that affect multiple pathways.

physiology↗

bioRxiv2017

Changes In LXRα Phosphorylation Promote A Novel Diet-Induced Transcriptome That Alters The Transition From Fatty Liver To Steatohepatitis

Understanding the transition from fatty liver or steatosis to more advanced inflammatory and fibrotic stages of non-alcoholic fatty liver disease (steatohepatitis), is key to define strategies that alter or even reverse the progression of this pathology. The Liver X Receptor alpha (LXR) controls hepatic lipid homeostasis and inflammation. Here we show that mice carrying a mutation that abolishes phosphorylation at Ser196 (S196A) in LXR exhibit reduced hepatic inflammation and fibrosis when challenged with a high fat-high cholesterol diet, despite displaying enhanced hepatic lipid accumulation. This protective effect is associated with reduced cholesterol accumulation, a key promoter of lipid-mediated hepatic damage. Reduced steatohepatitis in S196A mice involves the reprogramming of the liver transcriptome by promoting diet-induced changes in the expression of genes involved in endoplasmic reticulum stress, extracellular matrix remodelling, inflammation and lipid metabolism. Unexpectedly, changes in LXR phosphorylation uncover novel diet-specific target genes, whose regulation does not simply mirror ligand-induced LXR activation. These unique LXR phosphorylation-sensitive, diet-responsive target genes are revealed by promoting LXR occupancy and cofactor recruitment in the context of a cholesterol-rich diet. Therefore, LXR phosphorylation at Ser196 critically acts as a novel nutritional sensor that promotes a unique diet-induced transcriptome thereby modulating metabolic, inflammatory and fibrotic responses important in the transition to steatohepatitis.

pathology↗