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Isolation of Macrophage Subsets and Stromal Cells from Human and Mouse Myocardial Specimens

Macrophages represent the most heterogeneous and abundant immune cell populations in the heart and are central in driving inflammation and reparative ...

Washington University School of Medicine

Pediatric dilated cardiomyopathy (DCM) is the most common indication for heart transplantation in children. Despite similar genetic etiologies, medications routinely used in adult heart failure patients do not improve outcomes in the pediatric population. The mechanistic basis for these observations is unknown. We hypothesized that pediatric and adult DCM comprise distinct pathological entities, in that children do not undergo adverse remodeling, the target of adult heart failure therapies. To test this hypothesis, we examined LV specimens obtained from pediatric and adult donor controls and DCM patients. Consistent with the established pathophysiology of adult heart failure, adults with DCM displayed marked cardiomyocyte hypertrophy and myocardial fibrosis compared with donor controls. In contrast, pediatric DCM specimens demonstrated minimal cardiomyocyte hypertrophy and myocardial fibrosis compared with both age-matched controls and adults with DCM. Strikingly, RNA sequencing uncovered divergent gene expression profiles in pediatric and adult patients, including enrichment of transcripts associated with adverse remodeling and innate immune activation in adult DCM specimens. Collectively, these findings reveal that pediatric and adult DCM represent distinct pathological entities, provide a mechanistic basis to explain why children fail to respond to adult heart failure therapies, and suggest the need to develop new approaches for pediatric DCM.

Pediatric and adult dilated cardiomyopathy represent distinct pathological entities.

Despite the long-standing recognition that the immune response to acute myocardial injury contributes to adverse left ventricular (LV) remodeling, it has not been possible to effectively target this clinically. Using 2 different in vivo models of acute myocardial injury, we show that pirfenidone confers beneficial effects in the murine heart through an unexpected mechanism that depends on cardiac B lymphocytes. Naive hearts contained a large population of CD19+CD11b-CD23-CD21-IgD+IgMlo lymphocytes, and 2 smaller populations of CD19+CD11b+ B1a and B1b cells. In response to tissue injury, there was an increase in neutrophils, monocytes, macrophages, as well as an increase in CD19+ CD11b- B lymphocytes. Treatment with pirfenidone had no effect on the number of neutrophils, monocytes, or macrophages, but decreased CD19+CD11b- lymphocytes. B cell depletion abrogated the beneficial effects of pirfenidone. In vitro studies demonstrated that stimulation with lipopolysaccharide and extracts from necrotic cells activated CD19+ lymphocytes through a TIRAP-dependent pathway. Treatment with pirfenidone attenuated this activation of B cells. These findings reveal a previously unappreciated complexity of myocardial B lymphocytes within the inflammatory infiltrate triggered by cardiac injury and suggest that pirfenidone exerts beneficial effects in the heart through a unique mechanism that involves modulation of cardiac B lymphocytes.

Modulation of subsets of cardiac B lymphocytes improves cardiac function after acute injury.

Paradigm-shifting studies in the mouse have identified tissue macrophage heterogeneity as a critical determinant of immune responses. In contrast, surprisingly little is known regarding macrophage heterogeneity in humans. Macrophages within the mouse heart are partitioned into CCR2- and CCR2+ subsets with divergent origins, repopulation mechanisms, and functions. Here, we demonstrate that the human myocardium also contains distinct subsets of CCR2- and CCR2+ macrophages. Analysis of sex-mismatched heart transplant recipients revealed that CCR2- macrophages are a tissue-resident population exclusively replenished through local proliferation, whereas CCR2+ macrophages are maintained through monocyte recruitment and proliferation. Moreover, CCR2- and CCR2+ macrophages have distinct functional properties, analogous to reparative CCR2- and inflammatory CCR2+ macrophages in the mouse heart. Clinically, CCR2+ macrophage abundance is associated with left ventricular remodeling and systolic function in heart failure patients. Collectively, these observations provide initial evidence for the functional importance of macrophage heterogeneity in the human heart.

The human heart contains distinct macrophage subsets with divergent origins and functions.

Recent advancements have brought to light the origins, complexity, and functions of tissue-resident macrophages. However, in the context of tissue injury or disease, large numbers of monocytes infiltrate the heart and are thought to contribute to adverse remodeling and heart failure pathogenesis. Little is understood about the diversity of monocytes and monocyte-derived macrophages recruited to the heart after myocardial injury, including the mechanisms that regulate monocyte recruitment and fate specification.

Tissue Resident CCR2- and CCR2+ Cardiac Macrophages Differentially Orchestrate Monocyte Recruitment and Fate Specification Following Myocardial Injury.

Paradigm shifting studies have revealed that the heart contains functionally diverse populations of macrophages derived from distinct embryonic and adult hematopoietic progenitors. Under steady-state conditions, the heart is largely populated by CCR2- (C-C chemokine receptor type 2) macrophages of embryonic descent. After tissue injury, a dramatic shift in macrophage composition occurs whereby CCR2+ monocytes are recruited to the heart and differentiate into inflammatory CCR2+ macrophages that contribute to heart failure progression. Currently, there are no techniques to noninvasively detect CCR2+ monocyte recruitment into the heart and thus identify patients who may be candidates for immunomodulatory therapy.

Molecular Imaging Visualizes Recruitment of Inflammatory Monocytes and Macrophages to the Injured Heart.

Whereas prior studies have demonstrated an important immunomodulatory role for the neuronal cholinergic system in the heart, the role of the non-neuronal cholinergic system is not well understood. To address the immunomodulatory role of the non-neuronal cholinergic system in the heart we used a previously validated diphtheria toxin (DT)-induced cardiomyocyte ablation model (Rosa26-DTMlc2v-Cre mice). DT-injected Rosa26-DTMlc2v-Cre mice were treated with diluent or Pyridostigmine Bromide (PYR), a reversible cholinesterase inhibitor. PYR treatment resulted in increased survival and decreased numbers of MHC-IIlowCCR2+ macrophages in DT-injected Rosa26-DTMlc2v-Cre mice compared to diluent treated Rosa26-DTMlc2v-Cre mice. Importantly, the expression of CCL2/7 mRNA and protein was reduced in the hearts of PYR-treated mice. Backcrossing Rosa26-DTMlc2v-Cre mice with a transgenic mouse line (Chat-ChR2) that constitutively overexpresses the vesicular acetylcholine transporter (VAChT) resulted in decreased expression of Ccl2/7 mRNA and decreased numbers of CD68+ cells in DT-injured Rosa26-DTMlc2v-Cre/Chat-ChR2 mouse hearts, consistent with the pharmacologic studies with PYR. In vitro studies with cultures of LPS-stimulated peritoneal macrophages revealed a concentration-dependent reduction in CCL2 secretion following stimulation with ACh, nicotine and muscarine. Viewed together, these findings reveal a previously unappreciated immunomodulatory role for the non-neuronal cholinergic system in regulating homeostatic responses in the heart following tissue injury.

Immunomodulatory role of non-neuronal cholinergic signaling in myocardial injury.

Lysosomes are at the epicenter of cellular processes critical for inflammasome activation in macrophages. Inflammasome activation and IL-1β secretion are implicated in myocardial infarction (MI) and resultant heart failure; however, little is known about how macrophage lysosomes regulate these processes. In mice subjected to cardiac ischemia/reperfusion (IR) injury and humans with ischemic cardiomyopathy, we observed evidence of lysosomal impairment in macrophages. Inducible macrophage-specific overexpression of transcription factor EB (TFEB), a master regulator of lysosome biogenesis (Mϕ-TFEB), attenuated postinfarction remodeling, decreased abundance of proinflammatory macrophages, and reduced levels of myocardial IL-1β compared with controls. Surprisingly, neither inflammasome suppression nor Mϕ-TFEB-mediated attenuation of postinfarction myocardial dysfunction required intact ATG5-dependent macroautophagy (hereafter termed "autophagy"). RNA-seq of flow-sorted macrophages postinfarction revealed that Mϕ-TFEB upregulated key targets involved in lysosomal lipid metabolism. Specifically, inhibition of the TFEB target, lysosomal acid lipase, in vivo abrogated the beneficial effect of Mϕ-TFEB on postinfarction ventricular function. Thus, TFEB reprograms macrophage lysosomal lipid metabolism to attenuate remodeling after IR, suggesting an alternative paradigm whereby lysosome function affects inflammation.

Geetika Bajpai

Department of Medicine

Washington University School of Medicine

Isolation of Macrophage Subsets and Stromal Cells from Human and Mouse Myocardial Specimens

Geetika Bajpai

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Medicine

Washington University School of Medicine

Isolation of Macrophage Subsets and Stromal Cells from Human and Mouse Myocardial Specimens

Department of Medicine