Splenic CD169 + Tim4 + Marginal Metallophilic Macrophages Are Essential for Wound Healing After Myocardial Infarction.

Fidelity of wound healing after myocardial infarction (MI) is an important determinant of subsequent adverse cardiac remodeling and failure. Macrophages derived from infiltrating Ly6C hi blood monocytes are a key component of this healing response; however, the importance of other macrophage populations is unclear. Here, using a variety of in vivo murine models and orthogonal approaches, including surgical myocardial infarction, splenectomy, parabiosis, cell adoptive transfer, lineage tracing and cell tracking, RNA sequencing, and functional characterization, we establish in mice an essential role for splenic CD169 + Tim4 + marginal metallophilic macrophages (MMMs) in post-MI wound healing. Splenic CD169 + Tim4 + MMMs circulate in blood as Ly6C low cells expressing macrophage markers and help populate CD169 + Tim4 + CCR2 - LYVE1 low macrophages in the naïve heart. After acute MI, splenic MMMs augment phagocytosis, CCR3 and CCR4 expression, and robustly mobilize to the heart, resulting in marked expansion of cardiac CD169 + Tim4 + LyVE1 low macrophages with an immunomodulatory and pro-resolving gene signature. These macrophages are obligatory for apoptotic neutrophil clearance, suppression of inflammation, and induction of a reparative macrophage phenotype in the infarcted heart. Splenic MMMs are both necessary and sufficient for post-MI wound healing, and limit late pathological remodeling. Liver X receptor-α agonist-induced expansion of the splenic marginal zone and MMMs during acute MI alleviates inflammation and improves short- and long-term cardiac remodeling. Finally, humans with acute ST-elevation MI also exhibit expansion of circulating CD169 + Tim4 + macrophages. We conclude that splenic CD169 + Tim4 + MMMs are required for pro-resolving and reparative responses after MI and can be manipulated for therapeutic benefit to limit long-term heart failure. CLINICAL PERSPECTIVE: What is new?: We establish for the first time that metallophilic marginal macrophages (MMMs) from the spleen, expressing the markers CD169 and Tim4, circulate in blood and traffic to the heart to help maintain the CD169 + Tim4 + CCR2 - LYVE1 low macrophage population in the heart. After acute myocardial infarction, splenic MMMs augment cardiac trafficking in response to chemotactic signals, resulting in expansion of CD169 + Tim4 + macrophages in the heart that play an essential role in post-MI efferocytosis, wound healing and repair while limiting longer term adverse cardiac remodeling. Analogous to mice, humans also exhibit circulating CD169 + Tim4 + macrophages in the blood that expand after acute ST segment elevation MI. What are the clinical implications?: This study highlights the importance of the cardiosplenic axis in acute MI, and the splenic marginal zone, in determining the course and outcome of post-MI LV remodeling.Pharmacological expansion of splenic marginal zone macrophages alleviated post-MI adverse LV remodeling and inflammation, suggesting that splenic modulation is a potential translational therapeutic approach for limiting post-MI inflammation and improving heart repair.

Neutrophils are indispensable for adverse cardiac remodeling in heart failure.

Persistent immune activation contributes significantly to left ventricular (LV) dysfunction and adverse remodeling in heart failure (HF). In contrast to their well-known essential role in acute myocardial infarction (MI) as first responders that clear dead cells and facilitate subsequent reparative macrophage polarization, the role of neutrophils in the pathobiology of chronic ischemic HF is poorly defined. To determine the importance of neutrophils in the progression of ischemic cardiomyopathy, we measured their production, levels, and activation in a mouse model of chronic HF 8 weeks after permanent coronary artery ligation and large MI. In HF mice, neutrophils were more abundant both locally in failing myocardium (more in the border zone) and systemically in the blood, spleen, and bone marrow, together with increased BM granulopoiesis. There were heightened stimuli for neutrophil recruitment and trafficking in HF, with increased myocardial expression of the neutrophil chemoattract chemokines CXCL1 and CXCL5, and increased neutrophil chemotactic factors in the circulation. HF neutrophil NETotic activity was increased in vitro with coordinate increases in circulating neutrophil extracellular traps (NETs) in vivo. Neutrophil depletion with either antibody-based or genetic approaches abrogated the progression of LV remodeling and fibrosis at both intermediate and late stages of HF. Moreover, analogous to murine HF, the plasma milieu in human acute decompensated HF strongly promoted neutrophil trafficking. Collectively, these results support a key tissue-injurious role for neutrophils and their associated cytotoxic products in ischemic cardiomyopathy and suggest that neutrophils are potential targets for therapeutic immunomodulation in this disease.

Improved MIN6 ß-cell function on self-assembled peptide amphiphile nanomatrix inscribed with extracellular matrix-derived cell adhesive ligands.

Understanding the role of the pancreatic extracellular matrix (ECM) in supporting islet survival and function drives the pursuit to create biomaterials that imitate and restore the pancreatic ECM microenvironment. To create an ECM mimic holding bioinductive cues for ß-cells, self-assembled peptide amphiphiles (PAs) inscribed with four selected ECM-derived cell adhesive ligands are synthesized. After 7 days, compared to control groups cultured on biologically inert substrates, MIN6 ß-cells cultured on PAs functionalized with YIGSR and RGDS cell adhesive ligands exhibit elevated insulin secretion in responses to glucose and also form ß-cell clusters. These findings suggest that the self-assembled PA nanomatrix may be utilized to improve pancreatic islet transplantation for treating type 1 diabetes.

Enhanced rat islet function and survival in vitro using a biomimetic self-assembled nanomatrix gel.

Peptide amphiphile (PA) is a peptide-based biomaterial that can self-assemble into a nanostructured gel-like scaffold, mimicking the chemical and biological complexity of natural extracellular matrix. To evaluate the capacity of the PA scaffold to improve islet function and survival in vitro, rat islets were cultured in three different groups--(1) bare group: isolated rat islets cultured in a 12-well nontissue culture-treated plate; (2) insert group: isolated rat islets cultured in modified insert chambers; (3) nanomatrix group: isolated rat islets encapsulated within the PA nanomatrix gel and cultured in modified insert chambers. Over 14 days, both the bare and insert groups showed a marked decrease in insulin secretion, whereas the nanomatrix group maintained glucose-stimulated insulin secretion. Moreover, entire islets in the nanomatrix gel stained positive for dithizone up to 14 days, indicating better maintained glucose-stimulated insulin production. Fluorescein diacetate/propidium iodide staining results also verified necrosis in the bare and insert groups after 7 days, whereas the PA nanomatrix gel maintained islet viability after 14 days. Thus, these results demonstrate the potential of PAs as an intermediary scaffold for increasing the efficacy of pancreatic islet transplantation.