Pro-inflammatory Ly6Chigh Monocytes Research Articles

Suppressor of cytokine signaling 1-derived peptide inhibits Janus kinase/signal transducers and activators of transcription pathway and improves inflammation and atherosclerosis in diabetic mice.

Activation of Janus kinase/signal transducers and activators of transcription (STAT) pathway by hyperglycemia and dislypidemia contributes to the progression of diabetic complications, including atherosclerosis. Suppressor of cytokine signaling (SOCS) proteins negatively regulate Janus kinase/STAT and have emerged as promising target for anti-inflammatory therapies. We investigated whether a cell-permeable lipopeptide corresponding to the kinase inhibitory region of SOCS1 could reduce atherosclerosis in diabetic mice and identified the mechanisms involved. Streptozotocin-induced diabetic apolipoprotein E-deficient mice (aged 8 and 22 weeks) were given intraperitoneal injections of vehicle, SOCS1-derived peptide, or control mutant peptide for 6 to 10 weeks. SOCS1 therapy suppressed STAT1/STAT3 activation in atherosclerotic plaques of diabetic mice and significantly reduced lesion size at both early and advanced stages of lesion development compared with vehicle group. Plaque characterization demonstrated that SOCS1 peptide decreased the accumulation of lipids, macrophages, and T lymphocytes, whereas increasing collagen and smooth muscle cell content. This atheroprotective effect was accompanied by systemic (reduced proinflammatory Ly6C(high) monocytes and splenic cytokine expression) and local (reduced aortic expression of chemokines and cytokines) mechanisms, without impact on metabolic parameters. In vitro, SOCS1 peptide dose dependently inhibited STAT1/STAT3 activation and target gene expression in vascular smooth muscle cells and macrophages and also suppressed cytokine-induced cell migration and adhesion processes. SOCS1-based targeting Janus kinase/STAT restrains key mechanisms of atherogenesis in diabetic mice, thereby preventing plaque formation and increasing plaque stability. Approaches to mimic native SOCS1 functions may have a therapeutic potential to retard the progression of diabetic complications.

Abstract 643: Absence of Four-and-a-Half LIM Domain Protein 2 Decreases Atherosclerosis in ApoE-/- Mice: Role of Monocytic Immune Cells

Four-and-a-half LIM domain protein-2 (FHL2) is expressed in endothelial and vascular smooth muscle cells. It negatively regulates endothelial cell survival and migration, but its role in atherogenesis is unknown. To investigate the role of FHL2 in atherosclerosis, FHL2-deficient (FHL2-/-) mice were crossed with ApoE-deficient (ApoE -/-) mice, to generate ApoE/FHL2-/- mice. After 7 weeks of high fat diet, ApoE/FHL2-/- mice had significantly smaller (P<0.05) atherosclerotic plaques than ApoE-/- mice in the aortic sinus (0.14±0.02 vs. 0.29±0.04 mm2), the brachiocephalic artery (0.03±0.008 vs. 0.07±0.01 mm2) and the aorta (6.9±0.9 vs 10.3±1%), assessed by oil red O staining. This was associated with enhanced collagen (16±2 vs 8.6±3 %) and smooth muscle cell (4.5±0.8 vs 1.8±0.5%) contents within the plaques of ApoE/FHL-2-/- mice. Moreover, macrophage content within plaques was reduced 2-fold in ApoE/FHL2-/- vs ApoE-/- mice (P<0.05). This could be explained, in part, by the 40% reduction in aortic ICAM-1 mRNA and 55% reduction in VCAM-1 protein expression in the plaque. Furthermore, aortic gene expression of Cx3cl1 and Ccl5 was increased in ApoE/FHL2-/- vs ApoE-/- mice, suggesting that different monocyte populations might be recruited to the plaques. Peritoneal thioglycollate injection elicited equivalent numbers of monocytes and macrophages in both groups, but a significantly lower number of pro-inflammatory Ly6C high monocytes were recruited in ApoE/FHL2-/- vs ApoE-/- mice (8±3 vs 18±4%). Furthermore, mRNA levels of Cx3cr1 were 2-fold higher in monocytes from ApoE/FHL2-/- mice compared with ApoE-/- mice. Finally, we also investigated the potential importance of myeloid cell FHL2 deficiency in atherosclerosis. ApoE-/- or ApoE/FHL2-/- mice were lethally irradiated and transplanted with ApoE-/- or ApoE/FHL2-/- bone marrow. After recovery and 7 weeks of high fat diet, both chimeric groups developed smaller plaques than ApoE-/- mice transplanted with ApoE-/- bone marrow. These results suggest that FHL2 in both myeloid and vascular cells may play an important role in atherosclerosis by promoting pro-inflammatory chemokine production, adhesion molecule expression, and pro-inflammatory monocyte recruitment.

Abstract 61: Dendritic Cell Regulates Monocyte/Macrophage Polarization and Inflammatory Response After Myocardial Infarction in Mice

Inflammation and immune responses are integral components in the healing process after MI. We previously reported dendritic cell (DC) infiltration in the infarcted heart. However, the precise contribution of DC in postinfarction healing is unclear. Bone-marrow (BM) cells from CD11c-diphtheria toxin receptor/GFP transgenic mice were transplanted into lethally irradiated WT recipient mice. After reconstitution of BM-derived cells, the recipient mice were treated with either diphtheria toxin (DC ablation) or vehicle (control), and MI was created by left coronary ligation. CD11c + GFP + DCs expressing CD11b and MHC class II were recruited into the heart, peaking on day 7 after MI in control group. Mice with DC ablation for 7 days showed deteriorated left ventricular function and remodeling. DC-ablated group demonstrated enhanced and sustained expression of inflammatory cytokines such as IL-1β, IL-18 and tumor necrosis factor-α, prolonged extracellular matrix degradation associated with a high level of MMP9 activity, and diminished expression level of IL-10 and endothelial cell proliferation following MI compared with control group. In vivo and in vitro analyses revealed that DC-ablated infarcts had an enhanced capacity of monocytes/macrophages recruitment. Among these cells, augmented infiltration of proinflammatory Ly6C high monocytes and F4/80 + CD206 - M1 macrophages, and conversely impaired recruitment of anti-inflammatory Ly6C low monocytes and F4/80 + CD206 + M2 macrophages in the infarcted myocardium were identified in DC-ablated group than in control group. To confirm these results, adoptive transfer experiment was performed. BM cells from WT mice were cultured with recombinant mouse GM-CSF for 6 days and CD11c + BMDCs were then positively collected by magnetic sorting. We confirmed that intravenously injected CFSE-labeled BMDCs reached infarcted zone. Adoptive transfer of BMDCs into DC-depleted mice restored LV function and negated the increases of inflammatory Ly6C high monocytes and myocardial MMP-9 activity following MI. In conclusion, dendritic cell is a potent immunoprotective regulator during the postinfarction healing process, via controlling monocyte/macrophage homeostasis.

Regulatory Role of Dendritic Cells in Postinfarction Healing and Left Ventricular Remodeling

Inflammation and immune responses are integral components in the healing process after myocardial infarction. We previously reported dendritic cell (DC) infiltration in the infarcted heart; however, the precise contribution of DC in postinfarction healing is unclear. Bone marrow cells from CD11c-diphtheria toxin receptor/green fluorescent protein transgenic mice were transplanted into lethally irradiated wild-type recipient mice. After reconstitution of bone marrow-derived cells, the recipient mice were treated with either diphtheria toxin (DC ablation) or vehicle (control), and myocardial infarction was created by left coronary ligation. CD11c(+) green fluorescent protein-positive DCs expressing CD11b and major histocompatibility complex class II were recruited into the heart, peaking on day 7 after myocardial infarction in the control group. Mice with DC ablation for 7 days showed deteriorated left ventricular function and remodeling. The DC-ablated group demonstrated enhanced and sustained expression of inflammatory cytokines such as interleukin-1β, interleukin-18, and tumor necrosis factor-α, prolonged extracellular matrix degradation associated with a high level of matrix metalloproteinase-9 activity, and diminished expression level of interleukin-10 and endothelial cell proliferation after myocardial infarction compared with the control group. In vivo analyses revealed that DC-ablated infarcts had enhanced monocyte/macrophage recruitment. Among these cells, marked infiltration of proinflammatory Ly6C(high) monocytes and F4/80(+) CD206(-) M1 macrophages and, conversely, impaired recruitment of anti-inflammatory Ly6C(low) monocytes and F4/80(+) CD206(+) M2 macrophages in the infarcted myocardium were identified in the DC-ablated group compared with the control group. These results suggest that the DC is a potent immunoprotective regulator during the postinfarction healing process via its control of monocyte/macrophage homeostasis.

ApoE Suppresses Atherosclerosis by Reducing Lipid Accumulation in Circulating Monocytes and the Expression of Inflammatory Molecules on Monocytes and Vascular Endothelium

We investigated atheroprotective properties of apolipoprotein (apo) E beyond its ability to lower plasma cholesterol. We hypothesized that apoE reduces atherosclerosis by decreasing lipid accumulation in circulating monocytes and the inflammatory state of monocytes and the vascular endothelium. We developed mice with spontaneous hyperlipidemia with and without plasma apoE. Hypomorphic apoE mice deficient in low-density lipoprotein receptor (Apoe(h/h)Ldlr(-/-)) were compared to Apoe(-/-)Ldlr(-/-) mice. Despite 4-fold more plasma apoE than WT mice, Apoe(h/h)Ldlr(-/-) mice displayed similar plasma cholesterol as Apoe(-/-) Ldlr(-/-) mice but developed 4-fold less atherosclerotic lesions by 5 months of age. The aortic arch of Apoe(h/h)Ldlr(-/-) mice showed decreased endothelial expression of ICAM-1, PECAM-1, and JAM-A. In addition, Apoe(h/h)Ldlr(-/-) mice had less circulating leukocytes and proinflammatory Ly6C(high) monocytes. These monocytes had decreased neutral lipid content and reduced surface expression of ICAM-1, VLA-4, and L-Selectin. Apoe(h/h)Ldlr(-/-) mice displayed increased levels of apoA1-rich HDL that were potent in promoting cellular cholesterol efflux. Our findings suggest that apoE reduces atherosclerosis in the setting of hyperlipidemia by increasing plasma apoA1-HDL that likely contribute to reduce intracellular lipid accumulation and thereby the activation of circulating leukocytes and the vascular endothelium.