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Background Acute stress induced (takotsubo) cardiomyopathy can result in a heart failure phenotype with a prognosis comparable to myocardial infarction. In this study, we hypothesized that inflammation is central to the pathophysiology and natural history of takotsubo cardiomyopathy. Methods In a multi-centre study, we prospectively recruited 55 patients with takotsubo cardiomyopathy and 51 age, sex and co-morbidity matched control subjects. During the index event and at 5 months follow-up, patients with takotsubo cardiomyopathy underwent multiparametric cardiac magnetic resonance imaging including ultrasmall superparamagnetic particles of iron oxide (USPIO) enhancement for detection of inflammatory macrophages in the myocardium. Blood monocyte subpopulations and serum cytokines were assessed as measures of systemic inflammation. Matched controls underwent investigation at a single time point. Results Subjects were predominantly middle aged (64±14years) women (90%). When compared to control subjects, patients with takotsubo cardiomyopathy had greater USPIO enhancement (expressed as the difference between pre-USPIO and post-USPIO T2*) in both ballooning (14.3±0.6 versus 10.5±0.9 ms, p<0.001) and non-ballooning (12.9±0.6 versus 10.5±0.9 ms, p=0.02) left ventricular myocardial segments. Serum interleukin-6 (23.1±4.5 versus 6.5±5.8 pg/mL, p< 0.001) and chemokine (C-X-C motif) ligand 1 (1903±168 versus 1272±177 pg/mL, p=0.01) concentrations, and classical CD14++CD16- monocytes (90±0.5 versus 87±0.9%, p=0.01) were also increased whilst intermediate CD14++CD16+ (5.4±0.3 versus 6.9±0.6%, p=0.01) and non-classical CD14+CD16++ (2.7±0.3% versus 4.2±0.5%, p=0.006) monocytes were reduced in patients with takotsubo cardiomyopathy. At 5 months, USPIO enhancement was no longer detectable in the left ventricular myocardium although there remained persistent elevations in serum interleukin-6 concentrations (p=0.009) and reductions in intermediate CD14++CD16+ monocytes (5.6±0.4 versus 6.9±0.6%, p=0.01). Conclusions We demonstrate for the first time that takotsubo cardiomyopathy is characterized by a myocardial macrophage inflammatory infiltrate, changes in the distribution of monocyte subsets and an increase in systemic pro-inflammatory cytokines. Many of these changes persisted for at least 5 months suggesting a low-grade chronic inflammatory state.

Macrophages become activated by their environment and develop polarized functions: classically activated (M1) macrophages eliminate pathogens but can cause tissue injury, whereas alternatively activated (M2) macrophages promote healing and repair. Mechanisms directing polarized activation, especially in vivo, are not understood completely, and here, we examined the role of SOCS proteins. M2 macrophages activated in vitro or elicited by implanting mice i.p. with the parasitic nematode Brugia malayi display a selective and IL-4-dependent up-regulation of SOCS1 but not SOCS3. Using siRNA-targeted knockdown in BMDM, we reveal that the enhanced SOCS1 is crucial for IL-4-induced M2 characteristics, including a high arginase I:iNOS activity ratio, suppression of T cell proliferation, attenuated responses to IFN-γ/LPS, and curtailed SOCS3 expression. Importantly, SOCS1 was essential in sustaining the enhanced PI3K activity that drives M2 activation, defining a new regulatory mechanism by which SOCS1 controls M2 polarization. By contrast, for M1 macrophages, SOCS1 was not only an important regulator of proinflammatory mediators (IL-6, IL-12, MHC class II, NO), but critically, for M1, we show that SOCS1 also restricted IL-10 secretion and arginase I activity, which otherwise would limit the efficiency of M1 macrophage proinflammatory responses. Together, our results uncover SOCS1, not only as a feedback inhibitor of inflammation but also as a critical molecular switch that tunes key signaling pathways to effectively program different sides of the macrophage balance.

On infiltrating inflamed tissue, macrophages respond to the local microenvironment and develop one of two broad phenotypes: classically activated (M1) macrophages that cause tissue injury and alternatively activated macrophages that promote repair. Understanding how this polarization occurs in vivo is far from complete, and in this study, using a Th1-mediated macrophage-dependent model of acute glomerulonephritis, nephrotoxic nephritis, we examine the role of suppressor of cytokine signaling (SOCS)1 and SOCS3. Macrophages in normal kidneys did not express detectable SOCS proteins but those infiltrating inflamed glomeruli were rapidly polarized to express either SOCS1 (27 ± 6%) or SOCS3 (54 ± 12%) but rarely both (10 ± 3%). Rat bone marrow-derived macrophages incubated with IFN-γ or LPS expressed SOCS1 and SOCS3, whereas IL-4 stimulated macrophages expressed SOCS1 exclusively. By contrast, incubation with IFN-γ and LPS together suppressed SOCS1 while uniquely polarizing macrophages to SOCS3 expressing cells. Macrophages in which SOCS3 was knocked down by short interfering RNA responded to IFN-γ and LPS very differently: they had enhanced STAT3 activity; induction of macrophage mannose receptor, arginase and SOCS1; restoration of IL-4 responsiveness that is inhibited in M1 macrophages; and decreased synthesis of inflammatory mediators (NO and IL-6) and costimulatory molecule CD86, demonstrating that SOCS3 is essential for M1 activation. Without it, macrophages develop characteristic alternatively activated markers when exposed to classical activating stimuli. Lastly, increased glomerular IL-4 in nephrotoxic nephritis inhibits infiltrating macrophages from expressing SOCS3 and was associated with attenuated glomerular injury. Consequently, we propose that SOCS3 is essential for development of M1 macrophages in vitro and in vivo.