Immunophenotypic alterations in resident immune cells and myocardial fibrosis in the aging rhesus macaque (Macaca mulatta) heart

Macrophages in the heart: Active players or simple bystanders?

Today, more and more studies focus on the processes in which macrophages are involved. These discoveries provide new perspectives on the cellular mechanisms that regulate the physiological functions of the healthy heart. Moreover, they offer a deeper knowledge of the pathologic processes underlying the onset and the evolution of specific cardiac impairment. The heterogeneous population of macrophages within the heart can be divided by origin, expression profile, and function. The pool of cardiac macrophages includes at least two distinct subsets with different ontogeny. The first one has an embryonic origin, deriving from the yolk sac and the fetal liver, while the other macrophage subset results from the postnatal recruitment of monocytes produced in the bone marrow. This review will focus on new phenotypes and functions of cardiac macrophages that have been identified in the last years and that need to be deeply studied to unveil new potential therapies aimed at treating cardiac diseases.

Selected Resources for Pathology Evaluation of Nonhuman Primates in Nonclinical Safety Assessment

Humans and nonhuman primates (NHPs) share numerous anatomical and physiological characteristics, thereby explaining the importance of NHPs as essential animal models for translational medicine and nonclinical toxicity testing. Researchers, toxicologic pathologists, toxicologists, and regulatory reviewers must be familiar with normal and abnormal NHP biological traits when designing, performing, and interpreting data sets from NHP studies. The current compilation presents a list of essential books, journal articles, and websites that provide context to safety assessment and research scientists working with NHP models. The resources used most frequently by the authors have been briefly annotated to permit readers to rapidly ascertain their applicability to particular research endeavors. The references are aimed primarily for toxicologic pathologists working with cynomolgus and rhesus macaques and common marmosets in efficacy and safety assessment studies.

Summary and Assessment of Studies on Cardiac Aging in Nonhuman Primates

Nonhuman primates (NHP) are important translational models for cardiac aging. To assess progress in this research area and to provide a reference for other investigators, we identified papers indexed in PubMed to determine what species, ages, outcomes, treatments, and approaches have been studied. Since 1983, 33 studies of cardiac aging in NHP have been published. Of these, 27 used species of macaque, 6 baboon, 1 vervet, 1 orangutan, and 1 marmoset (some studies were multispecies). Common research approaches were echocardiography, ECG, and histology of the left ventricle. Only 10 studies performed sex-based analyses. The average age of the oldest macaque studied was 26 y. The reported mean lifespan of macaques in captivity is around 30 y. The age of the oldest baboon studied was 24 y. Baboons in captivity are reported to live on average to 21 y. Twelve studies took a "life course" approach, studying animals of a wide range of ages from less than or equal to 10 y through the late teens to thirties, and employing analyses designed to show change over time. Keeping NHP into old age is a major challenge for biomedical research. The ideal design is to start monitoring in early life and to track how cardiac structure and function change with age. Important issues for future research are an increased focus on life-course approaches, investment in existing life-course NHP cohorts, better reporting of study sample characteristics, more molecular studies to identify genetic risk factors and mechanisms, attention to sex as a biological variable, a move away from descriptive reports to mechanistic studies, development of biomarkers to predict disease risk, and exploration of interventions that are implemented early in life to prevent or delay age-related disease later in life. Reducing exposure to early life adversity, identifying early-life biomarkers of aging and age-related disease, and early treatment can contribute to longer health span.

Innate immunity as a target for acute cardioprotection

Acute obstruction of a coronary artery causes myocardial ischaemia and if prolonged, may result in an ST-segment elevation myocardial infarction (STEMI). First-line treatment involves rapid reperfusion. However, a highly dynamic and co-ordinated inflammatory response is rapidly mounted to repair and remove the injured cells which, paradoxically, can further exacerbate myocardial injury. Furthermore, although cardiac remodelling may initially preserve some function to the heart, it can lead over time to adverse remodelling and eventually heart failure. Since the size of the infarct corresponds to the subsequent risk of developing heart failure, it is important to find ways to limit initial infarct development. In this review, we focus on the role of the innate immune system in the acute response to ischaemia-reperfusion (IR) and specifically its contribution to cell death and myocardial infarction. Numerous danger-associated molecular patterns are released from dying cells in the myocardium, which can stimulate pattern recognition receptors including toll like receptors and NOD-like receptors (NLRs) in resident cardiac and immune cells. Activation of the NLRP3 inflammasome, caspase 1, and pyroptosis may ensue, particularly when the myocardium has been previously aggravated by the presence of comorbidities. Evidence will be discussed that suggests agents targeting innate immunity may be a promising means of protecting the hearts of STEMI patients against acute IR injury. However, the dosing and timing of such agents should be carefully determined because innate immunity pathways may also be involved in cardioprotection. This article is part of a Cardiovascular Research Spotlight Issue entitled 'Cardioprotection Beyond the Cardiomyocyte', and emerged as part of the discussions of the European Union (EU)-CARDIOPROTECTION Cooperation in Science and Technology (COST) Action, CA16225.

Galectin-3 as a candidate upstream biomarker for quantifying risks of myocardial ageing

AIMS

Galectin-3 (Gal-3) is implicated in the pathogenesis of heart failure and is also influenced by ageing. This study aims to determine the extent to which Gal-3 levels estimate odds of myocardial dysfunction in ageing cohorts, 'upstream' prior to clinical disease.

METHODS AND RESULTS

Four hundred seventy-five asymptomatic subjects underwent simultaneous assessments of cardiovascular structure and function, with measurements of circulating Gal-3. Myocardial dysfunction was defined as impaired myocardial relaxation (ratio of peak velocity flow in early diastole E (m/s) to peak velocity flow in late diastole by atrial contraction A (m/s) <0.84) (mean E/A ratio 0.84 in the cohort). Of 475 subjects (mean age 68 ± 12 years, 231 women), 222 (47%) had myocardial dysfunction. Subjects with myocardial dysfunction were older (mean age 73 ± 5 vs. 64 ± 14 years, P < 0.0001), and more had hypertension (59 vs. 40%, P < 0.0001), dyslipidaemia (54 vs. 39%, P = 0.001), diabetes mellitus (25 vs. 14%, P = 0.002), higher body mass index (BMI) (24 vs. 23 kg/m² , P = 0.002), and higher heart rate (76 vs. 71 b.p.m., P = 0.0001). Participants with impaired myocardial relaxation had lower peak velocity flow in early diastole E (0.6 ± 0.1 vs. 0.8 ± 0.2 m/s, P < 0.0001), higher peak velocity flow in late diastole by atrial contraction A (0.9 ± 0.1 vs. 0.7 ± 0.2 m/s, P < 0.0001), and higher mitral valve flow deceleration time (224.7 ± 43.2 vs. 204.8 ± 33.1 m/s, P < 0.0001). Participants with impaired myocardial relaxation had higher Gal-3 levels (17.2 ± 6.2 vs. 15.5 ± 4.1, P = 0.0004) but similar B-type natriuretic peptide (37 ± 4 vs. 34 ± 29, P = 0.37) and high-sensitivity troponin I (21 ± 72 vs. 11 ± 41, P = 0.061) levels and urine microalbumin-to-creatinine ratio (4.6 ± 8.1 vs. 4.2 ± 10.8, P = 0.75) compared with those without impaired myocardial relaxation. After multivariable adjustments, Gal-3 [odds ratio (OR) 1.05, 95% confidence interval (CI) 1.00-1.10, P = 0.039], age (OR 2.60, 95% CI 1.64-4.11, P < 0.0001), BMI (OR 2.16, 95% CI 1.44-3.23, P < 0.0001), and heart rate (OR 1.04, 95% CI 1.02-1.06, P < 0.0001) were associated with impaired myocardial relaxation. Adjusted ORs (95% CI) for myocardial dysfunction were 1.0 (ref), 1.62 (0.92-2.85), 1.92 (1.08-3.41), and 2.01 (1.11-3.66) across consecutive quartiles of Gal-3 after adjustment for age, BMI, risk factors, and heart rate.

CONCLUSIONS

Among asymptomatic community-dwelling elderly adults, the highest quartile of Gal-3 was associated with two-fold increased odds of myocardial dysfunction compared with the lowest quartile of Gal-3. Gal-3 may have a role as an 'upstream' biomarker in estimating odds of myocardial ageing prior to clinical disease.

Characterization of heart macrophages in rhesus macaques as a model to study cardiovascular disease in humans

Rhesus macaques are physiologically similar to humans and, thus, have served as useful animal models of human diseases including cardiovascular disease. The purpose of this study was to characterize the distribution, composition, and phenotype of macrophages in heart tissues of very young (fetus: 0.5 years, n = 6), young adult (2-12 years, n = 12), and older adult (13-24 years, n = 9) rhesus macaques using histopathology and immunofluorescence microscopy. Results demonstrated that macrophages were uniformly distributed throughout the heart in animals of all age groups and were more prevalent than CD3-positve T-cells and CD20-positive B-cells. Macrophages comprised approximately 2% of heart tissue cells in the younger animals and increased to a mean of nearly 4% in the older adults. CD163-positive macrophages predominated over HAM56-positive and CD206-positive macrophages, and were detected at significantly higher percentage in the animals between 13 and 24 years of age, as well as in heart tissues exhibiting severe histopathology or inflammation in animals of all age groups. In vivo dextran labeling and retention indicated that approximately half of the macrophages were longer lived in healthy adult heart tissues and may comprise the tissue-resident population of macrophages. These results provide a basis for continued studies to examine the specific functional roles of macrophage subpopulations in heart tissues during homeostasis and in cardiovascular disease for then developing intervention strategies.

Lung and Heart Injury in a Nonhuman Primate Model of Partial-body Irradiation with Minimal Bone Marrow Sparing: Histopathological Evidence of Lung and Heart Injury

Male rhesus macaques were subjected to partial-body irradiation at 10, 11, or 12 Gy with 5% bone marrow protection. Animals were euthanized when dictated by prospectively determined clinical parameters or at approximately 180 d following irradiation. Histological sections of lung and heart were stained with hematoxylin and eosin as well as a battery of histochemical and immunohistochemical stains. Histopathological alterations in the lung were centered on fibrosis, inflammation, and reactive/proliferative changes in pneumocytes. These changes were noted in animals necropsied after approximately 85-100 d postirradiation and extending through the observation period. Interstitial and pleural fibrosis demonstrated by Masson's trichrome staining were associated with increased alpha smooth muscle actin and collagen 1 immunohistochemical staining. Areas of interstitial fibrosis had reduced microvascular density with CD31 immunohistochemical staining. Accumulations of CD163- and CD206-positive alveolar macrophages were present in areas of interstitial fibrosis. Unidentified cells termed "myxoid" cells in alveolar walls had histochemical and immunohistochemical staining characteristics of epithelial-, endothelial-, or pericyte-mesenchymal transition states that were developing myofibroblast features. Distinctive focal or multifocal alveolar-bronchiolar hyperplasia had microscopic features of preneoplastic proliferation. Delayed radiation-associated changes in the heart consisted primarily of myocardial fibrosis, with rare histological evidence of myofiber degeneration.

RETROSPECTIVE ANALYSIS OF ADULT-ONSET CARDIAC DISEASE IN FRANÇOIS' LANGURS (TRACHYPITHECUS FRANCOISI) HOUSED IN U.S. ZOOS

Cardiac disease is a common condition in captive primates, and multiple cases in François' langurs ( Trachypithecus francoisi ) were noted on review of the Species Survival Plan studbook. To determine the prevalence of cardiac disease in this species, surveys were distributed to current and previous holding institutions (n = 23) for the U.S. studbook population (n = 216). After exclusion of stillbirths (n = 48), animals less than 1 yr of age (n = 8), and animals housed internationally (n = 2), a study group (n = 158) was identified for this analysis. Robust data was received for 98.7% (n = 156) of the study group and antemortem and postmortem cardiac abnormalities were reported for 25.3% (n = 40) of these animals. Eight animals were reported as medically managed for clinical cardiac disease, and three of these were alive at the time of survey. Six of 11 animals with radiographic cardiac silhouette enlargement antemortem were noted with cardiomegaly on postmortem examination. Of 102 deceased animals in the study group, four were identified with dilated cardiomyopathy, and varying degrees of myocardial fibrosis was observed in 18 animals. Langurs with cardiac fibrosis were found to be significantly older than langurs without cardiac fibrosis (P = 0.003) and more commonly were male (P = 0.036). Screening tests for cardiac disease, such as thoracic radiographs and echocardiography, are recommended to diagnose affected animals earlier, to monitor progression of disease, and to guide treatment, although they should be interpreted with caution because of apparent insensitivity when compared with pathologic results.

Aging and the cardiac collagen matrix: Novel mediators of fibrotic remodelling

Cardiovascular disease is a leading cause of death worldwide and there is a pressing need for new therapeutic strategies to treat such conditions. The risk of developing cardiovascular disease increases dramatically with age, yet the majority of experimental research is executed using young animals. The cardiac extracellular matrix (ECM), consisting predominantly of fibrillar collagen, preserves myocardial integrity, provides a means of force transmission and supports myocyte geometry. Disruptions to the finely balanced control of collagen synthesis, post-synthetic deposition, post-translational modification and degradation may have detrimental effects on myocardial functionality. It is now well established that the aged heart is characterized by fibrotic remodelling, but the mechanisms responsible for this are incompletely understood. Furthermore, studies using aged animal models suggest that interstitial remodelling with disease may be age-dependent. Thus with the identification of new therapeutic strategies targeting fibrotic remodelling, it may be necessary to consider age-dependent mechanisms. In this review, we discuss remodelling of the cardiac collagen matrix as a function of age, whilst highlighting potential novel mediators of age-dependent fibrotic pathways.

Pharmacological inhibition of apical sodium-dependent bile acid transporter changes bile composition and blocks progression of sclerosing cholangitis in multidrug resistance 2 knockout mice

Deficiency of multidrug resistance 2 (mdr2), a canalicular phospholipid floppase, leads to excretion of low-phospholipid "toxic" bile causing progressive cholestasis. We hypothesize that pharmacological inhibition of the ileal, apical sodium-dependent bile acid transporter (ASBT), blocks progression of sclerosing cholangitis in mdr2(-/-) mice. Thirty-day-old, female mdr2(-/-) mice were fed high-fat chow containing 0.006% SC-435, a minimally absorbed, potent inhibitor of ASBT, providing, on average, 11 mg/kg/day of compound. Bile acids (BAs) and phospholipids were measured by mass spectrometry. Compared with untreated mdr2(-/-) mice, SC-435 treatment for 14 days increased fecal BA excretion by 8-fold, lowered total BA concentration in liver by 65%, reduced total BA and individual hydrophobic BA concentrations in serum by >98%, and decreased plasma alanine aminotransferase, total bilirubin, and serum alkaline phosphatase levels by 86%, 93%, and 55%, respectively. Liver histology of sclerosing cholangitis improved, and extent of fibrosis decreased concomitant with reduction of hepatic profibrogenic gene expression. Biliary BA concentrations significantly decreased and phospholipids remained low and unchanged with treatment. The phosphatidylcholine (PC)/BA ratio in treated mice corrected toward a ratio of 0.28 found in wild-type mice, indicating decreased bile toxicity. Hepatic RNA sequencing studies revealed up-regulation of putative anti-inflammatory and antifibrogenic genes, including Ppara and Igf1, and down-regulation of several proinflammatory genes, including Ccl2 and Lcn2, implicated in leukocyte recruitment. Flow cytometric analysis revealed significant reduction of frequencies of hepatic CD11b(+) F4/80(+) Kupffer cells and CD11b(+) Gr1(+) neutrophils, accompanied by expansion of anti-inflammatory Ly6C(-) monocytes in treated mdr2(-/-) mice.

CONCLUSION

Inhibition of ASBT reduces BA pool size and retention of hydrophobic BA, favorably alters the biliary PC/BA ratio, profoundly changes the hepatic transcriptome, attenuates recruitment of leukocytes, and abrogates progression of murine sclerosing cholangitis.

The adult murine heart has a sparse, phagocytically active macrophage population that expands through monocyte recruitment and adopts an 'M2' phenotype in response to Th2 immunologic challenge

Tissue resident macrophages have vital homeostatic roles in many tissues but their roles are less well defined in the heart. The present study aimed to identify the density, polarisation status and distribution of macrophages in the healthy murine heart and to investigate their ability to respond to immune challenge. Histological analysis of hearts from CSF-1 receptor (csf1-GFP; MacGreen) and CX3CR1 (Cx3cr1(GFP/+)) reporter mice revealed a sparse population of GFP positive macrophages that were evenly distributed throughout the left and right ventricular free walls and septum. F4/80+CD11b+ cardiac macrophages, sorted from myocardial homogenates, were able to phagocytose fluorescent beads in vitro and expressed markers typical of both 'M1' (IL-1β, TNF and CCR2) and 'M2' activation (Ym1, Arg 1, RELMα and IL-10), suggesting no specific polarisation in healthy myocardium. Exposure to Th2 challenge by infection of mice with helminth parasites Schistosoma mansoni, or Heligmosomoides polygyrus, resulted in an increase in cardiac macrophage density, adoption of a stellate morphology and increased expression of Ym1, RELMα and CD206 (mannose receptor), indicative of 'M2' polarisation. This was dependent on recruitment of Ly6ChighCCR2+ monocytes and was accompanied by an increase in collagen content. In conclusion, in the healthy heart resident macrophages are relatively sparse and have a phagocytic role. Following Th2 challenge this population expands due to monocyte recruitment and adopts an 'M2' phenotype associated with increased tissue fibrosis.