Myocardial healing requires Reg3β-dependent accumulation of macrophages in the ischemic heart

Anti-inflammatory therapies in myocardial infarction: failures, hopes and challenges

In the infarcted heart, the damage-associated molecular pattern proteins released by necrotic cells trigger both myocardial and systemic inflammatory responses. Induction of chemokines and cytokines and up-regulation of endothelial adhesion molecules mediate leukocyte recruitment in the infarcted myocardium. Inflammatory cells clear the infarct of dead cells and matrix debris and activate repair by myofibroblasts and vascular cells, but may also contribute to adverse fibrotic remodelling of viable segments, accentuate cardiomyocyte apoptosis and exert arrhythmogenic actions. Excessive, prolonged and dysregulated inflammation has been implicated in the pathogenesis of complications and may be involved in the development of heart failure following infarction. Studies in animal models of myocardial infarction (MI) have suggested the effectiveness of pharmacological interventions targeting the inflammatory response. This article provides a brief overview of the cell biology of the post-infarction inflammatory response and discusses the use of pharmacological interventions targeting inflammation following infarction. Therapy with broad anti-inflammatory and immunomodulatory agents may also inhibit important repair pathways, thus exerting detrimental actions in patients with MI. Extensive experimental evidence suggests that targeting specific inflammatory signals, such as the complement cascade, chemokines, cytokines, proteases, selectins and leukocyte integrins, may hold promise. However, clinical translation has proved challenging. Targeting IL-1 may benefit patients with exaggerated post-MI inflammatory responses following infarction, not only by attenuating adverse remodelling but also by stabilizing the atherosclerotic plaque and by inhibiting arrhythmia generation. Identification of the therapeutic window for specific interventions and pathophysiological stratification of MI patients using inflammatory biomarkers and imaging strategies are critical for optimal therapeutic design.

Inflammatory Response During Myocardial Infarction

The occlusion of a coronary artery by a thrombus generated on a ruptured atherosclerotic plaque has been pursued in the last decades as a determining event for the clinical outcome after myocardial infarction (MI). Yet, MI causes a cell death wave front, which triggers an inflammatory response to clear cellular debris, and which in excess can double the myocardial lesion and influence the clinical prognosis in the short and long term. Accordingly, proper, timely regulated inflammatory response has now been considered a second pivotal player in cardiac recovery after MI justifying the search for pharmacological strategies to modulate inflammatory effectors. This chapter reviews the key events and the main effectors of inflammation after myocardial ischemic insult, as well as the contribution of this phenomenon to the progression of atherosclerosis.

Neutrophils in tissue injury and repair

As one of the first defenders of innate immune response, neutrophils make a rapid and robust response against infection or harmful agents. While traditionally regarded as suicidal killers that cause collateral tissue damage, recent findings on neutrophil extracellular trap formation, heterogeneity and plasticity and novel reparative functions have expanded our understanding of their diverse roles in health and disease. This review summarizes our current understanding of neutrophil-associated tissue injury, highlighting the emerging roles of neutrophil extracellular traps. This review will also focus on scrutinizing the roles of neutrophils in tissue repair and regeneration and will examine data on unexpected aspects of involvement of neutrophils in regulating normal tissue homeostasis.

Plaque Calcification During Atherosclerosis Progression and Regression

Plaque calcification develops by the inflammation-dependent mechanisms involved in progression and regression of atherosclerosis. Macrophages can undergo two distinct polarization states, that is, pro-inflammatory M1 phenotype in progression and anti-inflammatory M2 phenotype in regression. In plaque progression, predominant M1 macrophages promote the initial calcium deposition within the necrotic core of the lesions, called as microcalcification, through not only vesicle-mediated mineralization as the result of apoptosis of macrophages and vascular smooth muscle cells (VSMCs), but also VSMC differentiation into early phase osteoblasts. On the other hand, in plaque regression M2 macrophages are engaged in the healing response to plaque inflammation. In association with the resolution of chronic inflammation, M2 macrophages may facilitate macroscopic calcium deposition, called as macrocalcification, through induction of osteoblastic differentiation and maturation of VSMCs. Oncostatin M, which has been shown to promote osteoblast differentiation in bone, may play a pivotal role in the development of plaque calcification. Clinically, two types of plaque calcification have distinct implications. Macrocalcification leads to plaque stability, while microcalcification is more likely to be associated with plaque rupture. Statin therapy, which reduces cardiovascular mortality, has been shown to exert its dual actions on plaque morphology, that is, regression of atheroma and increment of macroscopic calcium deposits. Statins may facilitate the healing process against plaque inflammation by enhancing M2 polarization of macrophages. Vascular calcification has pleiotropic properties as pro-inflammatory “microcalcification” and anti-inflammatory “macrocalcification”. The molecular mechanisms of this process in relation with plaque progression as well as plaque regression should be intensively elucidated.

IL-22 induces Reg3γ and inhibits allergic inflammation in house dust mite-induced asthma models

Previous studies have shown that IL-22, one of the Th17 cell-related cytokines, plays multiple roles in regulating allergic airway inflammation caused by antigen-specific Th2 cells; however, the underlying mechanism remains unclear. Here, we show that allergic airway inflammation and Th2 and Th17 cytokine production upon intratracheal administration of house dust mite (HDM) extract, a representative allergen, were exacerbated in IL-22-deficient mice. We also found that IL-22 induces Reg3γ production from lung epithelial cells through STAT3 activation and that neutralization of Reg3γ significantly exacerbates HDM-induced eosinophilic airway inflammation and Th2 cytokine induction. Moreover, exostatin-like 3 (EXTL3), a functional Reg3γ binding protein, is expressed in lung epithelial cells, and intratracheal administration of recombinant Reg3γ suppresses HDM-induced thymic stromal lymphopoietin and IL-33 expression and accumulation of type 2 innate lymphoid cells in the lung. Collectively, these results suggest that IL-22 induces Reg3γ production from lung epithelial cells and inhibits the development of HDM-induced allergic airway inflammation, possibly by inhibiting cytokine production from lung epithelial cells.

Sirt7 promotes adipogenesis in the mouse by inhibiting autocatalytic activation of Sirt1

Sirtuins (Sirt1-Sirt7) are NAD⁺-dependent protein deacetylases/ADP ribosyltransferases, which play decisive roles in chromatin silencing, cell cycle regulation, cellular differentiation, and metabolism. Different sirtuins control similar cellular processes, suggesting a coordinated mode of action but information about potential cross-regulatory interactions within the sirtuin family is still limited. Here, we demonstrate that Sirt1 requires autodeacetylation to efficiently deacetylate targets such as p53, H3K9, and H4K16. Sirt7 restricts Sirt1 activity by preventing Sirt1 autodeacetylation causing enhanced Sirt1 activity in Sirt7^-/- mice. Increased Sirt1 activity in Sirt7^-/- mice blocks PPARγ and adipocyte differentiation, thereby diminishing accumulation of white fat. Thus, reduction of Sirt1 activity restores adipogenesis in Sirt7^-/- adipocytes in vitro and in vivo. We disclosed a principle controlling Sirt1 activity and uncovered an unexpected complexity in the crosstalk between two different sirtuins. We propose that antagonistic interactions between Sirt1 and Sirt7 are pivotal in controlling the signaling network required for maintenance of adipose tissue.

Trends in tissue repair and regeneration

The 6th EMBO conference on the Molecular and Cellular Basis of Regeneration and Tissue Repair took place in Paestum (Italy) on the 17th-21st September, 2016. The 160 scientists who attended discussed the importance of cellular and tissue plasticity, biophysical aspects of regeneration, the diverse roles of injury-induced immune responses, strategies to reactivate regeneration in mammals, links between regeneration and ageing, and the impact of non-mammalian models on regenerative medicine.

Multimodal Regulation of Cardiac Myocyte Proliferation

Efficient cardiac regeneration is closely associated with the ability of cardiac myocytes to proliferate. Fetal or neonatal mouse hearts containing proliferating cardiac myocytes regenerate even extensive injuries, whereas adult hearts containing mostly post-mitotic cardiac myocytes have lost this ability. The same correlation is seen in some homoiotherm species such as teleost fish and urodelian amphibians leading to the hypothesis that cardiac myocyte proliferation is a major driver of heart regeneration. Although cardiomyocyte proliferation might not be the only prerequisite to restore full organ function after cardiac damage, induction of cardiac myocyte proliferation is an attractive therapeutic option to cure the injured heart and prevent heart failure. To (re)initiate cardiac myocyte proliferation in adult mammalian hearts, a thorough understanding of the molecular circuitry governing cardiac myocyte cell cycle regulation is required. Here, we review the current knowledge in the field focusing on the withdrawal of cardiac myocytes from the cell cycle during the transition from neonatal to adult stages.

Reciprocal analyses in zebrafish and medaka reveal that harnessing the immune response promotes cardiac regeneration

Zebrafish display a distinct ability to regenerate their heart following injury. However, this ability is not shared by another teleost, the medaka. In order to identify cellular and molecular bases for this difference, we performed comparative transcriptomic analyses following cardiac cryoinjury. This comparison points to major differences in immune cell dynamics between these models. Upon closer examination, we observed delayed and reduced macrophage recruitment in medaka, along with delayed neutrophil clearance. To investigate the role of immune responses in cardiac regeneration, we delayed macrophage recruitment in zebrafish and observed compromised neovascularization, neutrophil clearance, cardiomyocyte proliferation and scar resolution. In contrast, stimulating Toll-like receptor signaling in medaka enhanced immune cell dynamics and promoted neovascularization, neutrophil clearance, cardiomyocyte proliferation and scar resolution. Altogether, these data provide further insight into the complex role of the immune response during regeneration, and serve as a platform to identify and test additional regulators of cardiac repair.

DOI:http://dx.doi.org/10.7554/eLife.25605.001

Oncostatin M was associated with thrombosis in patients with atrial fibrillation

The mechanism underlying thrombosis in atrial fibrillation (AF) is not yet clearly understood. Oncostatin M (OSM), as a member of IL-6 family, is involved in atherosclerosis-mediated thrombosis. The present study hypothesizes that OSM and its downstream factors play a role in thrombogenesis in AF.The specimens of left atrial appendages collected from patients with rheumatic mitral stenosis who underwent valve replacement were divided into 3 groups: sinus rhythm, AF(+)/thrombus(-), and AF(+)/thrombus(+) group. The macrophage infiltration in atrial tissue was assessed by immunohistochemistry, and the amount of OSM, tissue factor (TF), and tissue factor pathway inhibitors (TFPIs) was detected by Western blot.The infiltration of the M1 macrophages was significantly increased in the AF with thrombus group compared with the sinus rhythm group (P = .03). Moreover, the expression of OSM and TF was much higher in the AF with thrombus group compared with the sinus rhythm group (P = .02, .009, respectively) while the TFPI was decreased in the AF with thrombus group (P = .04).OSM might be correlated with thrombosis in patients with AF mediated by TF and TFPI.

The Biological Basis for Cardiac Repair After Myocardial Infarction: From Inflammation to Fibrosis

In adult mammals, massive sudden loss of cardiomyocytes after infarction overwhelms the limited regenerative capacity of the myocardium, resulting in the formation of a collagen-based scar. Necrotic cells release danger signals, activating innate immune pathways and triggering an intense inflammatory response. Stimulation of toll-like receptor signaling and complement activation induces expression of proinflammatory cytokines (such as interleukin-1 and tumor necrosis factor-α) and chemokines (such as monocyte chemoattractant protein-1/ chemokine (C-C motif) ligand 2 [CCL2]). Inflammatory signals promote adhesive interactions between leukocytes and endothelial cells, leading to extravasation of neutrophils and monocytes. As infiltrating leukocytes clear the infarct from dead cells, mediators repressing inflammation are released, and anti-inflammatory mononuclear cell subsets predominate. Suppression of the inflammatory response is associated with activation of reparative cells. Fibroblasts proliferate, undergo myofibroblast transdifferentiation, and deposit large amounts of extracellular matrix proteins maintaining the structural integrity of the infarcted ventricle. The renin-angiotensin-aldosterone system and members of the transforming growth factor-β family play an important role in activation of infarct myofibroblasts. Maturation of the scar follows, as a network of cross-linked collagenous matrix is formed and granulation tissue cells become apoptotic. This review discusses the cellular effectors and molecular signals regulating the inflammatory and reparative response after myocardial infarction. Dysregulation of immune pathways, impaired suppression of postinfarction inflammation, perturbed spatial containment of the inflammatory response, and overactive fibrosis may cause adverse remodeling in patients with infarction contributing to the pathogenesis of heart failure. Therapeutic modulation of the inflammatory and reparative response may hold promise for the prevention of postinfarction heart failure.

Heme Oxygenase-1 and Carbon Monoxide in the Heart: The Balancing Act Between Danger Signaling and Pro-Survival

Understanding the processes governing the ability of the heart to repair and regenerate after injury is crucial for developing translational medical solutions. New avenues of exploration include cardiac cell therapy and cellular reprogramming targeting cell death and regeneration. An attractive possibility is the exploitation of cytoprotective genes that exist solely for self-preservation processes and serve to promote and support cell survival. Although the antioxidant and heat-shock proteins are included in this category, one enzyme that has received a great deal of attention as a master protective sentinel is heme oxygenase-1 (HO-1), the rate-limiting step in the catabolism of heme into the bioactive signaling molecules carbon monoxide, biliverdin, and iron. The remarkable cardioprotective effects ascribed to heme oxygenase-1 are best evidenced by its ability to regulate inflammatory processes, cellular signaling, and mitochondrial function ultimately mitigating myocardial tissue injury and the progression of vascular-proliferative disease. We discuss here new insights into the role of heme oxygenase-1 and heme on cardiovascular health, and importantly, how they might be leveraged to promote heart repair after injury.

Bifidobacterium animalis subsp. lactis 420 mitigates the pathological impact of myocardial infarction in the mouse

There is a growing appreciation that our microbial environment in the gut plays a critical role in the maintenance of health and the pathogenesis of disease. Probiotic, beneficial gut microbes, administration can directly attenuate cardiac injury and post-myocardial infarction (MI) remodelling, yet the mechanisms of cardioprotection are unknown. We hypothesised that administration of Bifidobacterium animalis subsp. lactis 420 (B420), a probiotic with known anti-inflammatory properties, to mice will mitigate the pathological impact of MI, and that anti-inflammatory T regulatory (T_reg) immune cells are necessary to impart protection against MI as a result of B420 administration. Wild-type male mice were administered B420, saline or Lactobacillus salivarius 33 (Ls-33) by gavage daily for 14 or 35 days, and underwent ischemia/reperfusion (I/R). Pretreatment with B420 for 10 or 28 days attenuated cardiac injury from I/R and reduced levels of inflammatory markers. Depletion of T_reg cells by administration of anti-CD25 monoclonal antibodies eliminated B420-mediated cardio-protection. Further cytokine analysis revealed a shift from a pro-inflammatory to an anti-inflammatory environment in the probiotic treated post-MI hearts compared to controls. To summarise, B420 administration mitigates the pathological impact of MI. Next, we show that T_reg immune cells are necessary to mediate B420-mediated protection against MI. Finally, we identify putative cellular, epigenetic and/or post-translational mechanisms of B420-mediated protection against MI.

Quantitative Proteomics and Immunohistochemistry Reveal Insights into Cellular and Molecular Processes in the Infarct Border Zone One Month after Myocardial Infarction

Postinfarction remodeling and expansion of the peri-infarct border zone (BZ) directly correlate with mortality following myocardial infarction (MI); however, the cellular and molecular mechanisms underlying remodeling processes in the BZ remain unclear. Herein, we utilized a label-free quantitative proteomics approach in combination with immunohistochemical analyses to gain a better understanding of processes contributing to postinfarction remodeling of the peri-infarct BZ in a swine model of MI with reperfusion. Our analysis uncovered a significant down-regulation of proteins involved in energy metabolism, indicating impaired myocardial energetics and possibly mitochondrial dysfunction, in the peri-scar BZ. An increase in endothelial and vascular smooth muscles cells, as well as up-regulation of proteins implicated in vascular endothelial growth factor (VEGF) signaling and marked changes in the expression of extracellular matrix and subendothelial basement membrane proteins, is indicative of active angiogenesis in the infarct BZ. A pronounced increase in macrophages in the peri-infarct BZ was also observed, and proteomic analysis uncovered evidence of persistent inflammation in this tissue. Additional evidence suggested an increase in cellular proliferation that, concomitant with increased nestin expression, indicates potential turnover of endogenous stem cells in the BZ. A marked up-regulation of pro-apoptotic proteins, as well as the down-regulation of proteins important for adaptation to mechanical, metabolic, and oxidative stress, likely contributes to increased apoptosis in the peri-infarct BZ. The cellular processes and molecular pathways identified herein may have clinical utility for therapeutic intervention aimed at limiting remodeling and expansion of the BZ myocardium and preventing the development of heart failure post-MI.

The MEK1 inhibitors UO126 and PD98059 block PDGF-AB induced phosphorylation of threonine 292 in porcine smooth muscle cells

PDGF-AB and FGF-2 (GFs) induce smooth muscle cell (SMC) proliferation which is indispensible for arteriogenesis. While there is common agreement that GFs stimulate SMC proliferation through phosphorylation (P-) of MEK1/2 at Ser218/222, we previously demonstrated that the MEK inhibitors PD98059 and UO126 did not inhibit P-Ser218/222 as originally proposed but caused strong hyperphosphorylation. Here, we demonstrate that GFs increased phosphorylation of MEK1 at Thr292 while UO126 and PD98059 blocked this phosphorylation. This was again surprising since phosphorylation of Thr292 is regarded as a negative feedback loop. Our findings suggest that inhibition of Thr292 phosphorylation in combination with hyperphosphorylation of Ser218/222 serves as an "off" switch of SMC proliferation and potentially of arteriogenesis.

The AIM2 inflammasome is a central regulator of intestinal homeostasis through the IL-18/IL-22/STAT3 pathway

Inflammasomes are important for maintaining intestinal homeostasis, and dysbiosis contributes to the pathology of inflammatory bowel disease (IBD) and increases the risk for colorectal cancer. Inflammasome defects contribute to chronic intestinal inflammation and increase the susceptibility to colitis in mice. However, the inflammasome sensor absent in melanoma 2 (AIM2) protects against colorectal cancer in an inflammasome-independent manner through DNA-dependent protein kinase and Akt pathways. Yet, the roles of the AIM2 inflammasome in IBD and the early phases of colorectal cancer remain ill-defined. Here we show that the AIM2 inflammasome has a protective role in the intestine. During steady state, Aim2 deletion results in the loss of IL-18 secretion, suppression of the IL-22 binding protein (IL-22BP) in intestinal epithelial cells and consequent loss of the STAT3-dependent antimicrobial peptides (AMPs) Reg3β and Reg3γ, which promotes dysbiosis-linked colitis. During dextran sulfate sodium-induced colitis, a dysfunctional IL-18/IL-22BP pathway in Aim2-/- mice promotes excessive IL-22 production and elevated STAT3 activation. Aim2-/- mice further exhibit sustained STAT3 and Akt activation during the resolution of colitis fueled by enhanced Reg3b and Reg3g expression. This self-perpetuating mechanism promotes proliferation of intestinal crypt cells and likely contributes to the recently described increase in susceptibility of Aim2-/- mice to colorectal cancer. Collectively, our results demonstrate a central role for the AIM2 inflammasome in preventing dysbiosis and intestinal inflammation through regulation of the IL-18/IL-22BP/IL-22 and STAT3 pathway and expression of select AMPs.

Development and Function of Arterial and Cardiac Macrophages

Macrophages inhabit all major organs, and are capable of adapting their functions to meet the needs of their home tissues. The recent recognition that tissue macrophages derive from different sources, coupled with the notion that environmental cues and inflammatory stimuli can sculpt and agitate homeostasis, provides a frame of reference from which we can decipher the breadth and depth of macrophage activity. Here we discuss macrophages residing in the cardiovascular system, focusing particularly on their development and function in steady state and disease. Central to our discussion is the tension between macrophage ontogeny as a determinant of macrophage function, and the idea that tissues condition macrophage activities and supplant the influence of macrophage origins in favor of environmental demands.

Critical Contribution of Nuclear Factor Erythroid 2-related Factor 2 (NRF2) to Electrophile-induced Interleukin-11 Production

Nuclear factor erythroid 2-related factor 2 (NRF2) is a transcription factor that plays a crucial role in protection of cells from electrophile-induced toxicity through up-regulating phase II detoxifying enzymes and phase III transporters. We previously reported that oxidative stress induces up-regulation of interleukin-11 (IL-11), a member of the IL-6 family that ameliorates acetaminophen-induced liver toxicity. However, a role for IL-11 in protection of cells from electrophile-induced toxicity remains unclear. Here we show that an environmental electrophile, 1,2-naphthoquinone (1,2-NQ), but not 15d-prostaglandin J₂ (PGJ₂) or tert-butylhydroxyquinone (tBHQ), induced IL-11 production. Consistent with a crucial role for prolonged ERK activation in H₂O₂-induced IL-11 production, 1,2-NQ, but not 15d-PGJ₂ or tBHQ, elicited prolonged ERK activation. Conversely, inhibition of the ERK pathway by a MEK inhibitor completely blocked 1,2-NQ-induced IL-11 production at both protein and mRNA levels, further substantiating an intimate cross-talk between ERK activation and 1,2-NQ-induced IL-11 production. Promoter analysis of the Il11 gene revealed that two AP-1 sites were essential for 1,2-NQ-induced promoter activities. Among various members of the AP-1 family, Fra-1 was up-regulated by 1,2-NQ, and its up-regulation was blocked by a MEK inhibitor. Although NRF2 was not required for H₂O₂-induced IL11 up-regulation, NRF2 was essential for 1,2-NQ-induced IL11 up-regulation by increasing Fra-1 proteins possibly through promoting mRNA translation of FOSL1 Finally, intraperitoneal administration of 1,2-NQ induced body weight loss in wild-type mice, which was further exacerbated in Il11ra1^-/- mice compared with Il11ra1^+/- mice. Together, both Fra-1 and NRF2 play crucial roles in IL-11 production that protects cells from 1,2-NQ intestinal toxicity.

MicroRNA-126 overexpression rescues diabetes-induced impairment in efferocytosis of apoptotic cardiomyocytes

Efferocytosis, a process of clearance of apoptotic cells by phagocytes, is essential for successful resolution of inflammation and maintenance of tissue homeostasis. Diabetes compromises the function of macrophages leading to adverse inflammatory response during wound healing, myocardial injury, atherosclerosis and autoimmune disorders. However, the effect of diabetes on macrophage-mediated efferocytosis of apoptotic cardiomyocytes (ACM) and the molecular mechanisms involved are not understood so far. In the present study we found that invitro efferocytosis of ACM was impaired in macrophages from db/db (diabetic) mice. Macrophages exposed to high glucose (HG) decreases microRNA-126 (miR-126) expression with a corresponding increase in ADAM9 expression. Dual-luciferase reporter assay confirms that ADAM9 3'UTR contains miR-126 target site. ADAM9 inhibition reduces HG-induced proteolytic cleavage of Mer tyrosine receptor kinase (MerTK, a proto-oncogene that plays a critical role in phagocytosis), resulting in shedding of soluble-Mer (sMER) and loss of MERTK function. Over-expression of miR-126 attenuates HG-induced impairment of efferocytosis. Furthermore, human diabetic hearts show lower miR-126 expression with a corresponding increase in ADAM9 expression vs. normal counterparts. These data suggests that diabetes impairs efferocytosis of ACM and that strategies to enhance efferocytosis might attenuate diabetes-induced impairment in inflammation resolution and cardiac repair after injury.

Mitogen-activated protein kinase p38 target regenerating islet-derived 3γ expression is upregulated in cardiac inflammatory response in the rat heart

Regenerating islet‐derived 3γ (Reg3γ) is a multifunctional protein, associated with various tissue injuries and inflammatory states. Since chronic inflammation is characteristics also for heart failure, the aim of this study was to characterize Reg3γ expression in cardiac inflammatory conditions. Reg3γ expression was studied in experimental rat models of myocardial infarction (MI) and pressure overload in vivo. For cell culture studies neonatal rat cardiac myocytes (NRCMs) were used. In addition, adenovirus‐mediated gene transfer of upstream mitogen‐activated protein kinase (MAPK) kinase 3b and p38α MAPK in vivo and in vitro was performed. Reg3γ mRNA (12.8‐fold, P < 0.01) and protein (5.8‐fold, P < 0.001) levels were upregulated during the postinfarction remodeling at day 1 after MI, and angiotensin II (Ang II) markedly increased Reg3γ mRNA levels from 6 h to 2 weeks. Immunohistochemistry revealed that the Ang II‐induced expression of Reg3γ was localized into the cardiac fibroblasts and myofibroblasts of the proliferating connective tissue in the heart. Stretching and treatments with endothelin‐1, lipopolysaccharide (LPS), and fibroblast growth factor‐1 increased Reg3γ mRNA levels in NRCMs. SB203580, a selective p38 MAPK inhibitor, markedly attenuated LPS and mechanical stretch‐induced upregulation of Reg3γ gene expression. Moreover, combined overexpression of MKK3bE and WT p38α increased Reg3γ gene expression in cultured cardiomyocytes in vitro and in the rat heart in vivo. Our study shows that cardiac stress activates Reg3γ expression and p38 MAPK is an upstream regulator of Reg3γ gene expression in heart. Altogether our data suggest Reg3γ is associated with cardiac inflammatory signaling.

Immune Modulation of Cardiac Repair and Regeneration: The Art of Mending Broken Hearts

The accumulation of immune cells is among the earliest responses that manifest in the cardiac tissue after injury. Both innate and adaptive immunity coordinate distinct and mutually non-exclusive events governing cardiac repair, including elimination of the cellular debris, compensatory growth of the remaining cardiac tissue, activation of resident or circulating precursor cells, quantitative and qualitative modifications of the vascular network, and formation of a fibrotic scar. The present review summarizes the mounting evidence suggesting that the inflammatory response also guides the regenerative process following cardiac damage. In particular, recent literature has reinforced the central role of monocytes/macrophages in poising the refreshment of cardiomyocytes in myocardial infarction- or apical resection-induced cardiac insult. Macrophages dictate cardiac myocyte renewal through stimulation of preexisting cardiomyocyte proliferation and/or neovascularization. Nevertheless, substantial efforts are required to identify the nature of these macrophage-derived factors as well as the molecular mechanisms engendered by the distinct subsets of macrophages pertaining in the cardiac tissue. Among the growing inflammatory intermediaries that have been recognized as essential player in heart regeneration, we will focus on the role of interleukin (IL)-6 and IL-13. Finally, it is likely that within the mayhem of the injured cardiac tissue, additional types of inflammatory cells, such as neutrophils, will enter the dance to ignite and refresh the broken heart. However, the protective and detrimental inflammatory pathways have been mainly deciphered in animal models. Future research should be focused on understanding the cellular effectors and molecular signals regulating inflammation in human heart to pave the way for the development of factual therapies targeting the inflammatory compartment in cardiac diseases.

Epithelial IL-23R Signaling Licenses Protective IL-22 Responses in Intestinal Inflammation

A plethora of functional and genetic studies have suggested a key role for the IL-23 pathway in chronic intestinal inflammation. Currently, pathogenic actions of IL-23 have been ascribed to specific effects on immune cells. Herein, we unveil a protective role of IL-23R signaling. Mice deficient in IL-23R expression in intestinal epithelial cells (Il23R(ΔIEC)) have reduced Reg3b expression, show a disturbed colonic microflora with an expansion of flagellated bacteria, and succumb to DSS colitis. Surprisingly, Il23R(ΔIEC) mice show impaired mucosal IL-22 induction in response to IL-23. αThy-1 treatment significantly deteriorates colitis in Il23R(ΔIEC) animals, which can be rescued by IL-22 application. Importantly, exogenous Reg3b administration rescues DSS-treated Il23R(ΔIEC) mice by recruiting neutrophils as IL-22-producing cells, thereby restoring mucosal IL-22 levels. The study identifies a critical barrier-protective immune pathway that originates from, and is orchestrated by, IL-23R signaling in intestinal epithelial cells.

Mesenchymal stem cells attenuate inflammatory processes in the heart and lung via inhibition of TNF signaling

Mesenchymal stem cells (MSC) have been used to treat different clinical conditions although the mechanisms by which pathogenetic processes are affected are still poorly understood. We have previously analyzed the homing of bone marrow-derived MSC to diseased tissues characterized by a high degree of mononuclear cell infiltration and postulated that MSC might modulate inflammatory responses. Here, we demonstrate that MSC mitigate adverse tissue remodeling, improve organ function, and extend lifespan in a mouse model of inflammatory dilative cardiomyopathy (DCM). Furthermore, MSC attenuate Lipopolysaccharide-induced acute lung injury indicating a general role in the suppression of inflammatory processes. We found that MSC released sTNF-RI, which suppressed activation of the NFκBp65 pathway in cardiomyocytes during DCM in vivo. Substitution of MSC by recombinant soluble TNF-R partially recapitulated the beneficial effects of MSC while knockdown of TNF-R prevented MSC-mediated suppression of the NFκBp65 pathway and improvement of tissue pathology. We conclude that sTNF-RI is a major part of the paracrine machinery by which MSC effect local inflammatory reactions.

Alternatively activated macrophages determine repair of the infarcted adult murine heart

Alternatively activated (also known as M2) macrophages are involved in the repair of various types of organs. However, the contribution of M2 macrophages to cardiac repair after myocardial infarction (MI) remains to be fully characterized. Here, we identified CD206+F4/80+CD11b+ M2-like macrophages in the murine heart and demonstrated that this cell population predominantly increases in the infarct area and exhibits strengthened reparative abilities after MI. We evaluated mice lacking the kinase TRIB1 (Trib1-/-), which exhibit a selective depletion of M2 macrophages after MI. Compared with control animals, Trib1-/- mice had a catastrophic prognosis, with frequent cardiac rupture, as the result of markedly reduced collagen fibril formation in the infarct area due to impaired fibroblast activation. The decreased tissue repair observed in Trib1-/- mice was entirely rescued by an external supply of M2-like macrophages. Furthermore, IL-1α and osteopontin were suggested to be mediators of M2-like macrophage-induced fibroblast activation. In addition, IL-4 administration achieved a targeted increase in the number of M2-like macrophages and enhanced the post-MI prognosis of WT mice, corresponding with amplified fibroblast activation and formation of more supportive fibrous tissues in the infarcts. Together, these data demonstrate that M2-like macrophages critically determine the repair of infarcted adult murine heart by regulating fibroblast activation and suggest that IL-4 is a potential biological drug for treating MI.

Understanding STAT3 signaling in cardiac ischemia

Cardiovascular disease is the leading cause of death worldwide. It remains one of the greatest challenges to global health and will continue to dominate mortality trends in the future. Acute myocardial infarction results in 7.4 million deaths globally per annum. Current management strategies are centered on restoration of coronary blood flow via percutaneous coronary intervention, coronary artery bypass grafting and administration of anti-platelet agents. Such myocardial reperfusion accounts for 40-50 % of the final infarct size in most cases. Signaling transducer and activator of transcription 3 (STAT3) has been shown to have cardioprotective effects via canonical and non-canonical activation and modulation of mitochondrial and transcriptional responses. A significant body of in vitro and in vivo evidence suggests that activation of the STAT3 signal transduction pathway results in a cardio protective response to ischemia and attempts have been made to modulate this with therapeutic effect. Not only is STAT3 important for cardiomyocyte function, but it also modulates the cardiac microenvironment and communicates with cardiac fibroblasts. To this end, we here review the current evidence supporting the manipulation of STAT3 for therapeutic benefit in cardiac ischemia and identify areas for future research.

Macrophages in Tissue Repair, Regeneration, and Fibrosis

Inflammatory monocytes and tissue-resident macrophages are key regulators of tissue repair, regeneration, and fibrosis. After tissue injury, monocytes and macrophages undergo marked phenotypic and functional changes to play critical roles during the initiation, maintenance, and resolution phases of tissue repair. Disturbances in macrophage function can lead to aberrant repair, such that uncontrolled production of inflammatory mediators and growth factors, deficient generation of anti-inflammatory macrophages, or failed communication between macrophages and epithelial cells, endothelial cells, fibroblasts, and stem or tissue progenitor cells all contribute to a state of persistent injury, and this could lead to the development of pathological fibrosis. In this review, we discuss the mechanisms that instruct macrophages to adopt pro-inflammatory, pro-wound-healing, pro-fibrotic, anti-inflammatory, anti-fibrotic, pro-resolving, and tissue-regenerating phenotypes after injury, and we highlight how some of these mechanisms and macrophage activation states could be exploited therapeutically.

Temporal neutrophil polarization following myocardial infarction

AIMS

Although macrophage phenotypes have been well studied in the myocardial infarction (MI) setting, this study investigated temporal neutrophil polarization and activation mechanisms.

METHODS AND RESULTS

Neutrophils isolated from the infarcted left ventricle (LV) of mice showed high expression of proinflammatory markers at Day 1 and anti-inflammatory markers at Days 5 and 7 post-MI, indicating distinct neutrophil phenotypes along the post-MI time continuum. Flow cytometry analysis revealed that although proinflammatory N1 neutrophils were always predominant (>80% of total neutrophils at each time point), the percentage of N2 neutrophils increased post-MI from 2.4 ± 0.6% at Day 1 to 18.1 ± 3.0% at Day 7. In vitro, peripheral blood neutrophils were polarized to proinflammatory N1 by lipopolysaccharide and interferon-γ or anti-inflammatory N2 by interleukin-4, indicating high plasticity potential. The in vivo post-MI relevant LV damage-associated molecular patterns (DAMPs) polarized neutrophils to a proinflammatory N1 phenotype by activating toll-like receptor-4. Transforming growth factor-β1 inhibited proinflammatory production in neutrophils. N1 neutrophils positively correlated with infarct wall thinning at Day 7 post-MI, possibly due to high production of matrix metalloproteinases-12 and -25.

CONCLUSION

This study is the first to identify the existence of N1 and N2 neutrophils in the infarct region and reveals that N1 polarization could be mediated by DAMPs.

Inflammation as a therapeutic target in myocardial infarction: learning from past failures to meet future challenges

In the infarcted myocardium, necrotic cardiomyocytes release danger signals, activating an intense inflammatory response. Inflammatory pathways play a crucial role in regulation of a wide range of cellular processes involved in injury, repair, and remodeling of the infarcted heart. Proinflammatory cytokines, such as tumor necrosis factor α and interleukin 1, are markedly upregulated in the infarcted myocardium and promote adhesive interactions between endothelial cells and leukocytes by stimulating chemokine and adhesion molecule expression. Distinct pairs of chemokines and chemokine receptors are implicated in recruitment of various leukocyte subpopulations in the infarcted myocardium. For more than the past 30 years, extensive experimental work has explored the role of inflammatory signals and the contributions of leukocyte subpopulations in myocardial infarction. Robust evidence derived from experimental models of myocardial infarction has identified inflammatory targets that may attenuate cardiomyocyte injury or protect from adverse remodeling. Unfortunately, attempts to translate the promising experimental findings to clinical therapy have failed. This review article discusses the biology of the inflammatory response after myocardial infarction, attempts to identify the causes for the translational failures of the past, and proposes promising new therapeutic directions. Because of their potential involvement in injurious, reparative, and regenerative responses, inflammatory cells may hold the key for design of new therapies in myocardial infarction.

Regenerating gene (REG) product and its potential clinical usage

INTRODUCTION

The regenerating gene (Reg) was identified in regenerating islets and its related genes were revealed to constitute the Reg gene family. Reg family proteins act as growth factors for several cells. Recently, autoimmunity against the Reg family proteins has been reported in several diseases. In addition, the Reg family genes were found to be expressed in a large number of cancers and to influence prognosis.

AREAS COVERED

The historical background and current view of the structure, function, and expression of Reg family genes/proteins and their physiological/pathological significance in several diseases are described. Based on the findings, the diagnostic/therapeutic potential of Reg family genes/proteins is also discussed.

EXPERT OPINION

Autoimmunity against Reg family proteins may be a new diagnostic marker and/or therapeutic target for immune-mediated diseases. Treatment aimed at the expansion of the β-cell mass by the Reg genes/proteins, combined with the abrogation of autoimmunity, constitutes a potential approach for the treatment of diabetes. Conversely, some cancer cells have gained the ability to overexpress the Reg genes/proteins, thereby enhancing their proliferative capacities, resulting in these cells having a considerable growth advantage. Thus, the Reg genes/proteins are expected to be a new prognostic marker in cancer and/or a future therapeutic target.

Macrophage populations and self-renewal: Changing the paradigm

The origin of macrophages has been considered since several decades to be a continuum from bone marrow (BM) to tissue via monocytes as precursors. The development of new tools such as genetic lineage tracing, parabiosis and BM chimeras changed the paradigm of macrophage origin. In steady state, most resident macrophages are of embryonic origin, whereas a monocyte origin remains prominent in pathological conditions. The findings of a proliferation of mature macrophages will oblige us to reappraise the relationship between proliferation and differentiation in macrophages. This review is based on the recent explosion of high impact articles on macrophage biology. It summarizes new data on the origin of macrophages and their self-renewal potential in steady states. While monocytes are required for intestinal macrophage development, the microglia is independent of monocyte influx and skin macrophages provide an excellent model of the balance between monocyte input and self-renewal. In addition, macrophage proliferation requires intrinsic and extrinsic factors including growth factors and cytokines. It also analyzes the impact of this new paradigm in human diseases such as athrosclerosis, cancer, infectious diseases and neurodegenerative diseases. In atherosclerosis, the finding of macrophage proliferation within the lesions will change our understanding of disease pathophysiology, this new paradigm may have therapeutical impact in the future.

The role of Interleukin Receptor Associated Kinase (IRAK)-M in regulation of myofibroblast phenotype in vitro, and in an experimental model of non-reperfused myocardial infarction

In the infarcted myocardium, necrotic cardiomyocytes activate innate immune pathways, stimulating pro-inflammatory signaling cascades. Although inflammation plays an important role in clearance of the infarct from dead cells and matrix debris, repair of the infarcted heart requires timely activation of signals that negatively regulate the innate immune response, limiting inflammatory injury. We have previously demonstrated that Interleukin receptor-associated kinase (IRAK)-M, a member of the IRAK family that suppresses toll-like receptor/interleukin-1 signaling, is upregulated in the infarcted heart in both macrophages and fibroblasts, and restrains pro-inflammatory activation attenuating adverse remodeling. Although IRAK-M is known to suppress inflammatory activation of macrophages, its role in fibroblasts remains unknown. Our current investigation examines the effects of IRAK-M on fibroblast phenotype and function. In vitro, IRAK-M null cardiac fibroblasts have impaired capacity to contract free-floating collagen pads. IRAK-M loss reduces transforming growth factor (TGF)-β-mediated α-smooth muscle actin (α-SMA) expression. IRAK-M deficient cardiac fibroblasts exhibit a modest reduction in TGF-β-stimulated Smad activation and increased expression of the α-SMA repressor, Y-box binding protein (YB)-1. In a model of non-reperfused myocardial infarction, IRAK-M absence does not affect collagen content and myofibroblast density in the infarcted and remodeling myocardium, but increases YB-1 levels and is associated with attenuated α-SMA expression in isolated infarct myofibroblasts. Our findings suggest that, in addition to its role in restraining inflammation following reperfused infarction, IRAK-M may also contribute to myofibroblast conversion.

Effect of Cardiac Resynchronization Therapy on Inflammation in Congestive Heart Failure: A Review

Congestive heart failure is associated with increased levels of several inflammatory mediators, and animal studies have shown that infusion of a number of cytokines can induce heart failure. However, several drugs with proven efficacy in heart failure have failed to affect inflammatory mediators, and anti-inflammatory therapy in heart failure patients has thus far been disappointing. Hence, to what extent heart failure is caused by or responsible for the increased inflammatory burden in the patient is still unclear. Over the past couple of decades, resynchronization therapy with a biventricular pacemaker has emerged as an effective treatment in a subset of heart failure patients, reducing both morbidity and mortality. Such treatment has also been shown to affect the inflammation associated with heart failure. In this study, we review recent data on the association between heart failure and inflammation, and in particular how resynchronization therapy can affect the inflammatory process.

The reparative function of cardiomyocytes in the infarcted myocardium

Effective repair of the infarcted heart requires spatial containment of the inflammatory reaction within the infarcted area. A recently published study demonstrates that in the pro-inflammatory environment of the infarct border zone, surviving cardiomyocytes restrain inflammation by activating a Reg3β-dependent cascade that recruits reparative macrophages and promotes neutrophil clearance.