Cardiac surgery elicits pericardial inflammatory responses that are distinct compared with postcardiopulmonary bypass systemic inflammation

Objectives

Cardiac surgery using cardiopulmonary bypass contributes to a robust systemic inflammatory process. Local intrapericardial postsurgical inflammation is believed to trigger important clinical implications, such as postoperative atrial fibrillation and postsurgical intrathoracic adhesions. Immune mediators in the pericardial space may underlie such complications.

Methods

In this prospective pilot clinical study, 12 patients undergoing isolated coronary artery bypass graft surgery were enrolled. Native pericardial fluid and venous blood samples (baseline) were collected immediately after pericardiotomy. Postoperative pericardial fluid and venous blood samples were collected 48-hours after cardiopulmonary bypass and compared with baseline. Flow cytometry determined proportions of specific immune cells, whereas multiplex analysis probed for inflammatory mediators.

Results

Neutrophils are the predominant cells in both the pericardial space and peripheral blood postoperatively. There are significantly more CD163lo macrophages in blood compared with pericardial effluent after surgery. Although there are significantly more CD163hi macrophages in native pericardial fluid compared with baseline blood, after surgery there are significantly fewer of these cells present in the pericardial space compared with blood. Postoperatively, concentration of interleukin receptor antagonist 6, and interleukin 8 were significantly higher in the pericardial space compared with blood. After surgery, compared with blood, the pericardial space has a significantly higher concentration of matrix metalloproteinase 3, matrix metalloproteinase 8, and matrix metalloproteinase 9. The same trend was observed with transformational growth factor β.

Conclusions

Cardiac surgery elicits an inflammatory response in the pericardial space, which differs from systemic inflammatory responses. Future work should determine whether or not this distinct local inflammatory response contributes to postsurgical complications and could be modified to influence clinical outcomes.

Micronized Acellular Matrix Biomaterial Leverages Eosinophils for Postinfarct Cardiac Repair

After ischemic injury, immune cells mediate maladaptive cardiac remodeling. Extracellular matrix biomaterials may redirect inflammation toward repair. Pericardial fluid contains pro-reparative immune cells, potentially leverageable by biomaterials. Herein, we explore how pericardial delivery of a micronized extracellular matrix biomaterial affects cardiac healing. In noninfarcted mice, pericardial delivery increases pericardial and myocardial eosinophil counts. This response is sustained after myocardial infarction, stimulating an interleukin 4 rich milieu. Ultimately, the biomaterial improves postinfarct vascularization and cardiac function; and eosinophil-knockout negates these benefits. For the first time, to our knowledge, we demonstrate the therapeutic potential of pericardial biomaterial delivery and the eosinophil's critical role in biomaterial-mediated postinfarct repair.

Pericardial Inflammatory Mediators That Can Drive Postoperative Atrial Fibrillation in Cardiac Surgery Patients

Postoperative atrial fibrillation (POAF) is a common dysrhythmia that affects a significant number of patients undergoing cardiac surgery. Many studies aim to better understand this complex postsurgical complication by analysing circulating biomarkers in patients who develop POAF. More recently, the pericardial space was shown to contain inflammatory mediators that could trigger POAF. In this review we summarise recent studies that examine the immune mediators present in the pericardial space and their potential implications for the pathophysiology of POAF in cardiac surgery patients. Ongoing research in this area should better delineate the multifactorial etiology of POAF, where specific markers may be targeted to reduce the incidence of POAF and improve outcomes for this patient population.

Pericardial Immune Cells and Their Evolving Role in Cardiovascular Pathophysiology

The pericardium plays several homeostatic roles to support and maintain everyday cardiac function. Recent advances in techniques and experimental models have allowed for further exploration into the cellular contents of the pericardium itself. Of particular interest are the various immune cell populations present in the space within the pericardial fluid and fat. In contrast to immune cells of the comparable pleura, peritoneum and heart, pericardial immune cells appear to be distinct in their function and phenotype. Specifically, recent work has suggested these cells play critical roles in an array of pathophysiological conditions including myocardial infarction, pericarditis, and post-cardiac surgery complications. In this review, we spotlight the pericardial immune cells currently identified in mice and humans, the pathophysiological role of these cells, and the clinical significance of the immunocardiology axis in cardiovascular health.

Acellular biomaterial modulates myocardial inflammation and promotes endogenous mechanisms of postinfarct cardiac repair

OBJECTIVE

After myocardial infarction, we previously showed that epicardial implantation of porcine small intestinal submucosal extracellular matrix (SIS-ECM) improves postinfarct cardiac function through fibroblast-mediated angiogenic and antifibrotic pathways. Herein, we characterize how SIS-ECM also coordinates a reparative cardiac inflammatory response.

METHODS

RNA sequencing and multiplex characterized modulation of fibroblast transcriptional and paracrine activity by SIS-ECM. Inhibitors of fibroblast growth factor 2 and toll-like receptor 9 elucidated mechanism. Mice received coronary ligation (infarction) and either SIS-ECM implantation (treatment) or sham surgery (control). Flow cytometry of SIS-ECM and the murine myocardium quantified monocytes, neutrophils, and proangiogenic subtypes. Microscopy tracked fibroblasts and immune cells, and characterized myocardial angiogenesis.

RESULTS

SIS-ECM increased fibroblast transcription of inflammatory pathways and production of angiogenic vascular endothelial growth factor and inflammatory cytokines via fibroblast growth factor 2 and toll-like receptor 9-dependent pathways. Two-photon microscopy showed that SIS-ECM became engrafted by native fibroblasts and leukocytes, subsequently increasing release of inflammatory cytokines and angiogenic vascular endothelial growth factor. On flow cytometry, SIS-ECM implantation increased day-7 myocardial counts of neutrophils, inflammatory monocytes, and proangiogenic vascular endothelial growth factor recptor 1 subtypes. SIS-ECM has a higher proportion of proangiogenic leukocytes compared with the myocardium. Resonant confocal microscopy showed neovascularization near SIS-ECM.

CONCLUSIONS

SIS-ECM promotes engraftment by native fibroblasts and leukocytes, and modulates fibroblast activity via fibroblast growth factor 2 and toll-like receptor 9 to potentiate a proangiogenic inflammatory response. Subsequently, the material increases myocardial counts of reparative proangiogenic leukocytes that can induce neovascularization. This reparative inflammatory response may explain previously reported functional improvements. Fibroblast growth factor 2 and toll-like receptor 9 mechanisms can be leveraged to design next-generation materials for postinfarct cardiac repair.

The role of macrophage subsets in and around the heart in modulating cardiac homeostasis and pathophysiology

Cardiac and pericardial macrophages contribute to both homeostatic and pathophysiological processes. Recent advances have identified a vast repertoire of these macrophage populations in and around the heart - broadly categorized into a CCR2⁺/CCR2^- dichotomy. While these unique populations can be further distinguished by origin, localization, and other cell surface markers, further exploration into the role of cardiac and pericardial macrophage subpopulations in disease contributes an additional layer of complexity. As such, novel transgenic models and exogenous targeting techniques have been employed to evaluate these macrophages. In this review, we highlight known cardiac and pericardial macrophage populations, their functions, and the experimental tools used to bolster our knowledge of these cells in the cardiac context.

Comprehensive characterization of the postoperative pericardial inflammatory response: Potential implications for clinical outcomes

Objective

There is a paucity of data on the inflammatory response that takes place in the pericardial space after cardiac surgery. This study provides a comprehensive assessment of the local postoperative inflammatory response.

Methods

Forty-three patients underwent cardiotomy, where native pericardial fluid was aspirated and compared with postoperative pericardial effluent collected at 4, 24, and 48 hours' postcardiopulmonary bypass. Flow cytometry was used to define the levels and proportions of specific immune cells. Samples were also probed for concentrations of inflammatory cytokines, matrix metalloproteinases (MMPs), and tissue inhibitors of metalloproteinases (TIMPs).

Results

Preoperatively, the pericardial space mainly contains macrophages and T cells. However, the postsurgical pericardial space was populated predominately by neutrophils, which constituted almost 80% of immune cells present, and peaked at 24 hours. When surgical approaches were compared, minimally invasive surgery was associated with fewer neutrophils in the pericardial space at 4 hours' postsurgery. Analysis of the intrapericardial concentrations of inflammatory mediators showed interleukin-6, MMP-9, and TIMP-1 to be highest postsurgery. Over time, MMP-9 concentrations decreased significantly, whereas TIMP-1 levels increased, resulting in a significant reduction of the ratio of MMP:TIMP after surgery, suggesting that active inflammatory processes may influence extracellular matrix remodeling.

Conclusions

These results show that cardiac surgery elicits profound alterations in the immune cell profile in the pericardial space. Defining the cellular and molecular mediators that drive pericardial-specific postoperative inflammatory processes may allow for targeted therapies to reduce immune-mediated complications.

A monocyte-leptin-angiogenesis pathway critical for repair post-infection

During infection, inflammatory monocytes are thought to be key for bacterial eradication, but this is hard to reconcile with the large numbers of neutrophils that are recruited for each monocyte that migrates to the afflicted tissue, and the much more robust microbicidal functions of the neutrophils. However, unlike neutrophils, monocytes have the capacity to convert to situationally specific macrophages that may have critical functions beyond infection control^1,2. Here, using a foreign body coated with Staphylococcus aureus and imaging over time from cutaneous infection to wound resolution, we show that monocytes and neutrophils are recruited in similar numbers with low-dose infection but not with high-dose infection, and form a localization pattern in which monocytes surround the infection site, whereas neutrophils infiltrate it. Monocytes did not contribute to bacterial clearance but converted to macrophages that persisted for weeks after infection, regulating hypodermal adipocyte expansion and production of the adipokine hormone leptin. In infected monocyte-deficient mice there was increased persistent hypodermis thickening and an elevated leptin level, which drove overgrowth of dysfunctional blood vasculature and delayed healing, with a thickened scar. Ghrelin, which opposes leptin function³, was produced locally by monocytes, and reduced vascular overgrowth and improved healing post-infection. In sum, we find that monocytes function as a cellular rheostat by regulating leptin levels and revascularization during wound repair.

Neutrophils in homeostasis and tissue repair

Neutrophils are the most abundant innate immune cell and are equipped with highly destructive molecular cargo. As such, these cells were long thought to be short-lived killer cells that unleash their full cytotoxic programs on pathogens following infection and on host bystander cells after sterile injury. However, this view of neutrophils is overly simplistic and as a result is outdated. Numerous studies now collectively highlight neutrophils as far more complex and having a host of homeostatic and tissue-reparative functions. In this review, we summarize these underappreciated roles across organs and injury models.

An Intact Pericardium Ischemic Rodent Model

This protocol has shown that the pericardium and its contents play an essential anti-fibrotic role in the ischemic rodent model (coronary ligation to induce myocardial injury). The majority of pre-clinical myocardial infarction models require the disruption of pericardial integrity with loss of the homeostatic cellular milieu. However, recently a methodology has been developed by us to induce myocardial infarction, which minimizes pericardial damage and retains the heart's resident immune cell population. An improved cardiac functional recovery in mice with an intact pericardial space following coronary ligation has been observed. This method provides an opportunity to study inflammatory responses in the pericardial space following myocardial infarction. Further development of the labeling techniques can be combined with this model to understand the fate and function of pericardial immune cells in regulating the inflammatory mechanisms that drive remodeling in the heart, including fibrosis.

Post-Operative Adhesions: A Comprehensive Review of Mechanisms

Post-surgical adhesions are common in almost all surgical areas and are associated with significant rates of morbidity, mortality, and increased healthcare costs, especially when a patient requires repeat operative interventions. Many groups have studied the mechanisms driving post-surgical adhesion formation. Despite continued advancements, we are yet to identify a prevailing mechanism. It is highly likely that post-operative adhesions have a multifactorial etiology. This complex pathophysiology, coupled with our incomplete understanding of the underlying pathways, has resulted in therapeutic options that have failed to demonstrate safety and efficacy on a consistent basis. The translation of findings from basic and preclinical research into robust clinical trials has also remained elusive. Herein, we present and contextualize the latest findings surrounding mechanisms that have been implicated in post-surgical adhesion formation.

Prevention of Post-Operative Adhesions: A Comprehensive Review of Present and Emerging Strategies

Post-operative adhesions affect patients undergoing all types of surgeries. They are associated with serious complications, including higher risk of morbidity and mortality. Given increased hospitalization, longer operative times, and longer length of hospital stay, post-surgical adhesions also pose a great financial burden. Although our knowledge of some of the underlying mechanisms driving adhesion formation has significantly improved over the past two decades, literature has yet to fully explain the pathogenesis and etiology of post-surgical adhesions. As a result, finding an ideal preventative strategy and leveraging appropriate tissue engineering strategies has proven to be difficult. Different products have been developed and enjoyed various levels of success along the translational tissue engineering research spectrum, but their clinical translation has been limited. Herein, we comprehensively review the agents and products that have been developed to mitigate post-operative adhesion formation. We also assess emerging strategies that aid in facilitating precision and personalized medicine to improve outcomes for patients and our healthcare system.

Primordial GATA6 macrophages function as extravascular platelets in sterile injury

Most multicellular organisms have a major body cavity that harbors immune cells. In primordial species such as purple sea urchins, these cells perform phagocytic functions but are also crucial in repairing injuries. In mammals, the peritoneal cavity contains large numbers of resident GATA6⁺ macrophages, which may function similarly. However, it is unclear how cavity macrophages suspended in the fluid phase (peritoneal fluid) identify and migrate toward injuries. In this study, we used intravital microscopy to show that cavity macrophages in fluid rapidly form thrombus-like structures in response to injury by means of primordial scavenger receptor cysteine-rich domains. Aggregates of cavity macrophages physically sealed injuries and promoted rapid repair of focal lesions. In iatrogenic surgical situations, these cavity macrophages formed extensive aggregates that promoted the growth of intra-abdominal scar tissue known as peritoneal adhesions.

Gata6+ Pericardial Cavity Macrophages Relocate to the Injured Heart and Prevent Cardiac Fibrosis

Macrophages play an important role in structural cardiac remodeling and the transition to heart failure following myocardial infarction (MI). Previous research has focused on the impact of blood-derived monocytes on cardiac repair. Here we examined the contribution of resident cavity macrophages located in the pericardial space adjacent to the site of injury. We found that disruption of the pericardial cavity accelerated maladaptive post-MI cardiac remodeling. Gata6⁺ macrophages in mouse pericardial fluid contributed to the reparative immune response. Following experimental MI, these macrophages invaded the epicardium and lost Gata6 expression but continued to perform anti-fibrotic functions. Loss of this specialized macrophage population enhanced interstitial fibrosis after ischemic injury. Gata6⁺ macrophages were present in human pericardial fluid, supporting the notion that this reparative function is relevant in human disease. Our findings uncover an immune cardioprotective role for the pericardial tissue compartment and argue for the reevaluation of surgical procedures that remove the pericardium.

Heat shock protein 60 involvement in vascular smooth muscle cell proliferation

AIM

Heat shock protein 60 (Hsp60) is a mediator of stress-induced vascular smooth muscle cell (VSMC) proliferation. This study will determine, first, if the mitochondrial or cytoplasmic localization of Hsp60 is critical to VSMC proliferation and, second, the mechanism of Hsp60 induction of VSMC proliferation with a focus on modification of nucleocytoplasmic trafficking.

METHODS AND RESULTS

Hsp60 was overexpressed in primary rabbit VSMCs with or without a mitochondrial targeting sequence (AdHsp60^mito-). Both interventions induced an increase in VSMC PCNA expression and proliferation. The increase in VSMC PCNA expression and growth was not observed after siRNA-mediated knockdown of Hsp60 expression. Nuclear protein import in VSMC was measured by fluorescent microscopy using a microinjected fluorescent import substrate. Nuclear protein import was stimulated by both AdHsp60 and AdHsp60^mito- treatments. AdHsp60 treatment also induced increases in nucleoporin (Nup) 62, Nup153, importin-α, importin-β and Ran expression as well as cellular ATP levels compared to control. AdHsp60^mito- treatment induced an up-regulation in importin-α, importin-β and Ran expression compared to control. Hsp60 knockdown did not change nuclear protein import nor the expression of any nuclear transport receptors or nucleoporins. Both heat shock treatment and Hsp60 overexpression promoted the interaction of Ran with Hsp60.

CONCLUSIONS

VSMC proliferation can be modulated via an Hsp60 dependent, cytosol localized mechanism that in part involves a stimulation of nuclear protein import through an interaction with Ran. This novel cellular signaling role for Hsp60 may be important in growth-based vascular pathologies like atherosclerosis and hypertension.

Neutrophil heterogeneity: Bona fide subsets or polarization states?

Neutrophils are key components of the innate immune system that play important roles during infection, injury, and chronic disease. In recent years, neutrophil heterogeneity has become an emerging focus with accumulating evidence of neutrophil populations with distinct functions under both steady-state and pathologic conditions. Despite these advances, it remains unclear whether these different populations represent bona fide subsets or simply activation/polarization states in response to local cues. In this review, we summarize the varied neutrophils populations that have been described under both basal and during inflammation. We discuss the evidence that supports the existence of neutrophils subsets. Finally, we identify potential gaps in our knowledge that may further advance our current understanding of neutrophil heterogeneity.

Splenic Ly6Ghigh mature and Ly6Gint immature neutrophils contribute to eradication of S. pneumoniae

The spleen plays an integral protective role against encapsulated bacterial infections. Our understanding of the associated mechanisms is limited to thymus-independent (TI) antibody production by the marginal zone (MZ) B cells, leaving the contribution of other splenic compartments such as the red pulp (RP) largely unexplored despite asplenic patients succumbing to the infection in the first 24 h, suggesting important antibody-independent mechanisms. In this study, using time-lapse intravital imaging of the spleen, we identify a tropism for Streptococcus pneumoniae in this organ mediated by tissue-resident MZ and RP macrophages and a protective role for two distinct splenic neutrophil populations (Ly6G^hi and Ly6G^intermediate) residing in the splenic RP. Splenic mature neutrophils mediated pneumococcal clearance in the spleen by plucking bacteria off the surface of RP macrophages that caught the majority of bacteria in a complement-dependent manner. This neutrophil phagocytic capacity was further enhanced after TI antibody production. Resident immature neutrophils (Ly6G^intermediate) in the spleen undergo emergency proliferation and mobilization from their splenic niche after pneumococcal stimulation to increase the effector mature neutrophil pool. We demonstrate that splenic neutrophils together with two macrophage populations and MZ B cells regulate systemic S. pneumoniae clearance through complementary mechanisms.

Recent advances in understanding neutrophils

Neutrophils have long been regarded as key effectors of the innate immune response during acute inflammation. Recent evidence has revealed a greater functional diversity for these cells than previously appreciated, expanding roles for neutrophils in adaptive immunity and chronic pathologies. In this review, we summarize some of the evolving paradigms in the neutrophil field and highlight key advances that have contributed to our understanding of neutrophil behavior and function in vivo. We examine the concept of neutrophil subsets and polarization, we discuss novel immunomodulatory roles for neutrophils in shaping the immune response, and, finally, we identify technical advances that will further enhance our ability to track the function and fate of neutrophils.

Monocyte Conversion During Inflammation and Injury

Monocytes are circulating leukocytes important in both innate and adaptive immunity, primarily functioning in immune defense, inflammation, and tissue remodeling. There are 2 subsets of monocytes in mice (3 subsets in humans) that are mobilized from the bone marrow and recruited to sites of inflammation, where they carry out their respective functions in promoting inflammation or facilitating tissue repair. Our understanding of the fate of these monocyte subsets at the site of inflammation is constantly evolving. This brief review highlights the plasticity of monocyte subsets and their conversion during inflammation and injury.

Identification and treatment of the Staphylococcus aureus reservoir in vivo

Kubes et al. show that methicillin-resistant Staphylococcus aureus (MRSA) survive and proliferate inside Kupffer cells. Intracellular MRSA is resistant to neutrophil-killing and antibiotics treatment and, when released into the circulation, can infect other organs.

Methicillin-resistant Staphylococcus aureus (MRSA) bacteremia is reaching epidemic proportions causing morbidity, mortality, and chronic disease due to relapses, suggesting an intracellular reservoir. Using spinning-disk confocal intravital microscopy to track MRSA-GFP in vivo, we identified that within minutes after intravenous infection MRSA is primarily sequestered and killed by intravascular Kupffer cells (KCs) in the liver. However, a minority of the Staphylococci overcome the KC’s antimicrobial defenses. These bacteria survive and proliferate for many days within this intracellular niche, where they remain undetected by recruited neutrophils. Over time, the KCs lyse, releasing bacteria into the circulation, enabling dissemination to other organs such as the kidneys. Vancomycin, the antibiotic of choice to treat MRSA bacteremia, could not penetrate the KCs to eradicate intracellular MRSA. However, based on the intravascular location of these specific macrophages, we designed a liposomal formulation of vancomycin that is efficiently taken up by KCs and diminished the intracellular MRSA. Targeting the source of the reservoir dramatically protected the liver but also dissemination to other organs, and prevented mortality. This vancomycin formulation strategy could help treat patients with Staphylococcal bacteremia without a need for novel antibiotics by targeting the previously inaccessible intracellular reservoir in KCs.

Alternative therapies for diabetes and its cardiac complications: role of vanadium

It is now well known that a cardiomyopathic state accompanies diabetes mellitus. Although insulin injections and conventional hypoglycemic drug therapy have been of invaluable help in reducing cardiac damage and dysfunction in diabetes, cardiac failure continues to be a common cause of death in the diabetic population. The use of alternative medicine to maintain health and treat a variety of diseases has achieved increasing popularity in recent years. The goal of alternative therapies in diabetic patients has been to lower circulating blood glucose levels and thereby treat diabetic complications. This paper will focus its discussion on the role of vanadium on diabetes and the associated cardiac dysfunction. Careful administration of a variety of forms of vanadium has produced impressive long-lasting control of blood glucose levels in both Type 1 and Type 2 diabetes in animals. This has been accompanied by, in many cases, a complete correction of the diabetic cardiomyopathy. The oral delivery of vanadium as a vanadate salt in the presence of tea has produced particularly impressive hypoglycemic effects and a restoration of cardiac function. This intriguing approach to the treatment of diabetes and its complications, however, deserves further intense investigation prior to its use as a conventional therapy for diabetic complications due to the unknown long-term effects of vanadium accumulation in the heart and other organs of the body.

Alternative therapies for diabetes and its cardiac complications: role of vanadium

It is now well known that a cardiomyopathic state accompanies diabetes mellitus. Although insulin injections and conventional hypoglycemic drug therapy have been of invaluable help in reducing cardiac damage and dysfunction in diabetes, cardiac failure continues to be a common cause of death in the diabetic population. The use of alternative medicine to maintain health and treat a variety of diseases has achieved increasing popularity in recent years. The goal of alternative therapies in diabetic patients has been to lower circulating blood glucose levels and thereby treat diabetic complications. This paper will focus its discussion on the role of vanadium on diabetes and the associated cardiac dysfunction. Careful administration of a variety of forms of vanadium has produced impressive long-lasting control of blood glucose levels in both Type 1 and Type 2 diabetes in animals. This has been accompanied by, in many cases, a complete correction of the diabetic cardiomyopathy. The oral delivery of vanadium as a vanadate salt in the presence of tea has produced particularly impressive hypoglycemic effects and a restoration of cardiac function. This intriguing approach to the treatment of diabetes and its complications, however, deserves further intense investigation prior to its use as a conventional therapy for diabetic complications due to the unknown long-term effects of vanadium accumulation in the heart and other organs of the body.

Effects of dietary flaxseed on atherosclerotic plaque regression

Dietary flaxseed can retard the progression of atherosclerotic plaques. However, it remains unclear whether these antiatherogenic effects extend to plaque regression. In the present study, the therapeutic potential of dietary flaxseed on atherosclerotic plaque regression and vascular contractile function was evaluated using a novel rabbit model. Rabbits were randomly assigned to receive either a regular diet for 12 wk (group I) or a 1% cholesterol-supplemented diet for 4 wk followed by a regular diet for 8 wk (group II). The remaining experimental animals were treated as in group II but were fed for an additional 14 wk with either a regular diet (group III) or a 10% flaxseed-supplemented diet (group IV). Animals in group II showed clear evidence of plaque growth stabilization. Their vessels also exhibited significantly lower norepinephrine-induced contraction and an impaired relaxation response to acetylcholine compared with animals in group I. Dietary flaxseed supplementation resulted in a significant ≈40% reduction in plaque formation (P = 0.033). Animals in both groups II and III displayed improved contraction and endothelium-dependent vessel relaxation. Dietary flaxseed is a valuable strategy to accelerate the regression of atherosclerotic plaques; however, flaxseed intervention did not demonstrate a clear beneficial effect on the vessel contractile response and endothelium-dependent vasorelaxation.

Chlamydophila pneumoniae infection induces alterations in vascular contractile responses

Chlamydophila pneumoniae infection has been associated in previous studies with coronary artery disease. The live bacterium has been detected within atherosclerotic plaques and can induce the structural remodeling of the vessel wall. However, the direct effects of infection on the contractile characteristics of the arteries remain unknown. Left anterior descending coronary arteries isolated from porcine hearts were dissected and placed in culture medium for 72 hours before infection with C. pneumoniae. Contractile responses to high molar KCl and u46619 levels and relaxation responses to bradykinin and sodium nitroprusside were assessed at days 5 and 10 postinfection. C. pneumoniae induced decreases in both KCl- and u46619-induced contractile responses at both time points. The altered contractile responses coincided with a down-regulation of L-type Ca(2+) channels at both time points and inositol 1,4,5-triphosphate receptor (IP3R) levels at day 10 postinfection. Infection also induced attenuation of the endothelial-dependent relaxation response to bradykinin at day 10 postinfection. A decrease in endothelial nitric oxide synthase expression levels was noted at day 10 postinfection. Furthermore, an increase in superoxide production combined with an increase in p22phox expression levels was also observed at this time point. These findings indicate that C. pneumoniae infection can directly alter the vascular contractile responses in porcine coronary arteries, providing additional evidence for the role of C. pneumoniae infection in cardiovascular disease.

Possibilities for therapeutic interventions in disrupting Chlamydophila pneumoniae involvement in atherosclerosis

Strong sero-epidemiologic, pathologic, and experimental evidence suggests that Chlamydophila pneumoniae (Cpn) infection may play a causative role in the development of atherosclerosis. Cpn is an obligate intracellular gram-negative bacterium that is responsible for 10% of cases of community-acquired pneumonia. In addition to its presence in the respiratory tract, live Cpn has been found within atherosclerotic plaques. Experimental findings have established Cpn's ability to infect vascular cells and elicit important atherogenic responses. Furthermore, Cpn infection can promote atherosclerotic development in different animal models. To date however, large-scale antibiotic clinical trials have not been effective in preventing major cardiovascular events. It is becoming apparent that Cpn undergoes a persistent state of infection, which is refractory to current chlamydial antibiotics. New treatment strategies that are effective toward acute and persistent forms of Cpn infection are needed in order to effectively eradicate the bacterium within the vascular wall. Possible therapeutics targets include Cpn-specific proteins and machinery directly involved in their survival, replication and maintenance. Alternatively, selectively targeting host cell pathways and machinery required for Cpn's actions in vascular cells also represent potential treatment strategies for atherosclerosis.

Chlamydophila pneumoniae infection leads to smooth muscle cell proliferation and thickening in the coronary artery without contributions from a host immune response

Chlamydophila pneumonia (C. pneumonia) infection has been associated with the progression of atherosclerosis. It remains unclear, however, whether C. pneumoniae in the absence of an immune response can alone initiate atherogenic events within a complex vessel environment. Left anterior descending coronary arteries isolated from porcine hearts were dissected and placed in culture medium for 72 hours before infection with C. pneumoniae. C. pneumoniae replicated within the arterial wall for the duration of the experiment (up to 10 days). A significant increase in chlamydial-HSP60 protein expression from day 2 to 10 post-infection (pi) indicated the presence of metabolically active C. pneumonia within infected vessels. Significant arterial thickening in infected coronary segments was observed by a considerable decrease in the ratio of lumen to total vessel area (48 +/- 3% at day 4 pi versus 23 +/- 3% at day 10 pi) and a significant increase in the ratio of media to luminal area (113 +/- 16% at day 4 pi versus 365 +/- 65% at day 10 pi). Structural changes were accompanied by an up-regulation of host HSP60 and proliferating cell nuclear antigen expression levels. Immunohistochemical staining confirmed proliferating cell nuclear antigen expression to be primarily localized within smooth muscle cells of the medial area. These results demonstrate that C. pneumoniae infection can stimulate arterial thickening in a complex vessel environment without the presence of a host immune response and further supports the involvement of HSP60 in this action.

Ceramide regulation of nuclear protein import

Nucleocytoplasmic trafficking is an essential and responsive cellular mechanism that directly affects cell growth and proliferation, and its potential to address metabolic challenge is incompletely defined. Ceramide is an antiproliferative sphingolipid found within vascular smooth muscle cells in atherosclerotic plaques, but its mechanism of action remains unclear. The hypothesis that ceramide inhibits cell growth through nuclear transport regulation was tested. In smooth muscle cells, exogenously supplemented ceramide inhibited classical nuclear protein import that involved the activation of cytosolic p38 mitogen-activated protein kinase (MAPK). After application of SB 202190, a specific and potent pharmacological antagonist of p38 MAPK, sphingolipid impingement on nuclear transport was corrected. Distribution pattern assessments of two essential nuclear transport proteins, importin-alpha and Cellular Apoptosis Susceptibility, revealed ceramide-mediated relocalization that was reversed upon the addition of SB 202190. Furthermore, cell counts, nuclear cyclin A, and proliferating cell nuclear antigen expression, markers of cellular proliferation, were diminished after ceramide treatment and effectively rescued by the addition of inhibitor. Together, these data demonstrate, for the first time, the sphingolipid regulation of nuclear import that defines and expands the adaptive capacity of the nucleocytoplasmic transport machinery.

Mechanical Stretching Stimulates Smooth Muscle Cell Growth, Nuclear Protein Import, and Nuclear Pore Expression through Mitogen-activated Protein Kinase Activation

Although it is known that mechanical stretching of cells can induce significant increases in cell growth and shape, the intracellular signaling pathways that induce this response at the level of the cell nucleus is unknown. The transport of molecules from the cell cytoplasm to the nucleoplasm through the nuclear pore is a key pathway through which gene expression can be controlled in some conditions. It is presently unknown if mechanical stimuli can induce changes in nuclear pore expression and/or function. The purpose of the present investigation was to determine if mechanical stretching of a cell will alter nuclear protein import and the mechanisms that may be responsible. Vascular smooth muscle cells that were mechanically stretched exhibited an increase in proliferating cell nuclear antigen expression, cell number, and cell size within 24-48 h. Cells were microinjected with marker proteins for nuclear import. Nuclear protein import was significantly stimulated in stretched cells when compared with control. This was associated with an increase in the expression of nuclear pore proteins as detected by Western blots. Inhibition of the MAPK pathway blocked the stretch-induced stimulation of both cell proliferation and nuclear protein import. We conclude that nuclear protein import and nuclear pore density can adapt to mechanical stimuli during the process of cell growth through a MAPK-mediated mechanism.

Differential sensitivities of the NCX1.1 and NCX1.3 isoforms of the Na+–Ca2+ exchanger to α-linolenic acid

OBJECTIVE

Dietary intake of omega-3 polyunsaturated fatty acids (PUFA) like alpha-linolenic acid (ALA) is antiarrhythmic and cardioprotective. PUFA may also be beneficial in hypertension. Altered Na(+)-Ca(2+) exchanger (NCX) activity has been implicated in arrhythmias, hypertension and heart failure and may be a target for PUFA. Thus, we tested the effects of ALA and other distinct fatty acids on the cardiac (NCX1.1) and vascular (NCX1.3) NCX isoforms.

METHODS

HEK293 cells stably expressing NCX isoforms were ramped from +60 to -100 mV (over 1600 ms) in the absence and presence of 25 microM oleic acid (OA, omega-9), linoleic acid (LA, omega-6), ALA (omega-3), or eicosapentaenoic acid (EPA, omega-3). NiCl(2) (5 mM) was used to inhibit and therefore identify the NCX current. The effect of 25 microM ALA on NCX1.1 and NCX1.3 activity was also assessed in adult rat ventricular cardiomyocytes and rabbit aortic vascular smooth muscle cells (VSMC) by measuring [Ca(2+)](i) following substitution of [Na(+)](o) with Li(+).

RESULTS

Application of Ni(2+) had no effect in non-transfected cells. ALA and EPA (25 microM) reduced the Ni(2+)-sensitive forward NCX1.1 current (at -100 mV) by 64% and reverse current (at +60 mV) by 57%, and inhibited the Ni(2+)-sensitive NCX1.3 forward and reverse currents by 79% and 76%, respectively. Neither OA nor LA (25 microM) affected the NCX1.1 currents, but both partially inhibited the forward and reverse mode NCX1.3 currents. Inhibition of NCX1.3 by ALA occurred at a much lower IC(50) ( approximately 19 nM) than for NCX1.1 ( approximately 120 nM). In cardiomyocytes and VSMC, ALA significantly reduced the Li(+)-induced rise in intracellular [Ca(2+)].

CONCLUSIONS

NCX1.3 is more sensitive to inhibition by ALA than NCX1.1. In addition, only omega-3 PUFA inhibits NCX1.1, but several classes of fatty acids inhibit NCX1.3. The differential sensitivity of NCX isoforms to fatty acids may have important implications as therapeutic approaches for hypertension, heart failure and arrhythmias.