PTX3 expression in the heart tissues of patients with myocardial infarction and infectious myocarditis

Abstract

Introduction

The long pentraxin 3 is involved in innate resistance to pathogens, controlling inflammation and extracellular matrix remodeling. Moreover, pentraxin 3 plays a nonredundant role in the regulation of cardiac tissue damage in mice and, recently, it has been proposed as a new candidate marker for acute and chronic heart diseases. However, the actual localization and cellular sources of pentraxin 3 in ischemic and infectious cardiac pathology have not been carefully defined.

Methods

In this study, using immunohistochemistry, we analyzed pentraxin 3 expression in the heart tissues of patients with acute myocardial infarction at different time points after the ischemic event. In addition, we studied the heart tissues of patients with infectious myocarditis (fungi, bacteria, and protozoa) and patients who died of noncardiac events with normal heart histology.

Results

In acute myocardial infarction cases, we observed pentraxin 3 localized within and around ischemic lesions. On the contrary, no pentraxin 3 was observed in normal heart areas. In early ischemic lesions, pentraxin 3 was localized primarily in granulocytes; in more advanced acute myocardial infarction, pentraxin 3 positivity was found in the interstitium and in the cytoplasm of macrophages and the endothelium, whereas most granulocytes did not express pentraxin 3, presumably as a consequence of degranulation. In infectious myocarditis, pentraxin 3 was present and localized within and around histological lesions, associated with macrophage, endothelial cell, and, more rarely, myocardiocyte and granulocyte positivities. As observed in acute myocardial infarction patients, no pentraxin 3 staining was found in normal heart areas.

Conclusions

Thus, neutrophils are an early source of pentraxin 3 in acute myocardial infarction and presumably other inflammatory heart disorders. Subsequently, in acute myocardial infarction and infectious myocarditis, pentraxin 3 is produced by macrophages, the endothelium, and, to a lesser extent, myocardiocytes, and localized in the interstitium.

Introduction

C-reactive protein (CRP) and pentraxin 3 (PTX3) are members of the highly conserved pentraxin superfamily [1], [2], [3]. CRP is the classical short pentraxin produced in the liver in response to inflammatory mediators, in particular IL-6, and represents a well-recognized marker of systemic response to local inflammation [4].

PTX3 is a prototypic member of the long pentraxin family; it shares some similarities with CRP, but differs in terms of the presence of an unrelated long N-terminal domain coupled to the C-terminal domain, gene organization, cellular source, and tissue source, inducing stimuli and ligands recognized [3]. PTX3 binds with high affinity to C1q and factor H (participates in the activation and regulation of the complement system), to apoptotic cells, and to extracellular matrix (ECM) components TNFα-induced protein 6 and inter-α-inhibitor [5], [6], [7], [8], [9], [10]. In addition, PTX3 has a nonredundant role in innate resistance to selected pathogens and is also essential in female fertility as it functions by forming the ECM of cumulus oöphorus in ovarian follicles [3], [7], [11], [12], [13]. PTX3 is rapidly produced in damaged tissues by different cells such as fibroblasts, dendritic cells, smooth muscle cells, and, in particular, macrophages and endothelial cells, following several primary proinflammatory signals [e.g., Toll-like receptor (TLR) engagement by microbial moieties, TNFα, and IL-1β] [3], [14]. Recently, PTX3 has been found also in bone marrow myelocytes and in mature neutrophils, but not in basophils and eosinophils: PTX3 is stored in “ready-to-use” form in specific neutrophil granules and is secreted in response to microbial recognition and inflammatory stimuli [15].

Due to the fact that the main tissue cellular sources of PTX3 are macrophages and the endothelium, PTX3 levels may better reflect the inflammatory status of the vascular bed and may represent a rapid marker for local inflammation at sites of vessel injury.

Pentraxins have a well-documented role in the diagnosis of cardiovascular diseases: the association between elevated levels of CRP and an increased risk of cardiovascular events is well established, and the link between PTX3 and ischemic heart disorders is known as well. PTX3 is induced in vascular smooth muscle cells by atherogenic modified low-density lipoproteins and is present in human atherosclerotic lesions [16], [17]. Moreover, recently, we demonstrated that deficiency in PTX3 promotes vascular inflammation and atherosclerosis in a murine model [18]. Plasma PTX3 levels are elevated in patients with unstable angina pectoris [19] and in patients undergoing selective coronary stenting [20]; in heart failure, plasma PTX3 levels correlate with advancing severity of the disease and are an independent predictor of cardiovascular events [21], [22].

In patients with acute myocardial infarction (AMI), PTX3 has been described to represent an early marker of myocardial lesion peaking in plasma at about 7 h after the onset of symptoms [23]; in the same context, plasma CRP peaked later, between 24 and 48 h after the first symptoms. Moreover, in a series of patients with myocardial infarction and ST elevation followed for 3 months, plasma PTX3 had a stronger prognostic value in predicting mortality compared with CRP and other cardiac biomarkers [24].

The cellular sources of circulating levels of PTX3 in cardiovascular diseases are still poorly defined. Studies in mice suggest that, during AMI, PTX3 is induced in the heart in a IL-1R–MyD88-dependent pathway, in particular in neutrophils, macrophages, and the endothelium [25]. However, the rapid release of stored PTX3 from activated neutrophils could contribute to protein plasma level elevation after ischemia, preceding gene-expression-dependent production. Murine models have recently provided a genetic demonstration of the regulatory role of PTX3 in AMI. PTX3-deficient mice showed increased heart damage, increased neutrophil infiltration in the ischemic area, a decreased number of small vessels, and increased apoptosis [25]. Given the conservation of PTX3 in evolution in terms of sequence, gene organization, and regulation, studies in mice could be informative about its in vivo functions in human pathology. It was therefore important to assess PTX3 expression in human cardiovascular diseases.

Here we report the expression of PTX3 in the human myocardial tissues of patients with AMI and infectious myocarditis by immunohistochemistry (IHC), demonstrating the presence of extracellular PTX3 within and around lesions and, in addition, in the cytoplasm of granulocytes, macrophages, endothelial cells and, more rarely, myocardiocytes.