Cardiac cellularity is dependent upon biological sex and is regulated by gonadal hormones

AIMS

Sex differences have been consistently identified in cardiac physiology and incidence of cardiac disease. However, the underlying biological causes for the differences remain unclear. We sought to characterize the cardiac non-myocyte cellular landscape in female and male hearts to determine whether cellular proportion of the heart is sex-dependent and whether endocrine factors modulate the cardiac cell proportions.

METHODS AND RESULTS

Utilizing high-dimensional flow cytometry and immunofluorescence imaging, we found significant sex-specific differences in cellular composition of the heart in adult and juvenile mice, that develops postnatally. Removal of systemic gonadal hormones by gonadectomy results in rapid sex-specific changes in cardiac non-myocyte cellular proportions including alteration in resident mesenchymal cell and leucocyte populations, indicating gonadal hormones and their downstream targets regulate cardiac cellular composition. The ectopic reintroduction of oestrogen and testosterone to female and male mice, respectively, reverses many of these gonadectomy-induced compositional changes.

CONCLUSION

This work shows that the constituent cell types of the mouse heart are hormone-dependent and that the cardiac cellular landscapes are distinct in females and males, remain plastic, and can be rapidly modulated by endocrine factors. These observations have implications for strategies aiming to therapeutically alter cardiac cellular heterogeneity and underscore the importance of considering biological sex for studies examining cardiac physiology and stress responses.

Cross-Priming Dendritic Cells Exacerbate Immunopathology After Ischemic Tissue Damage in the Heart

BACKGROUND

Ischemic heart disease is a leading cause of heart failure and despite advanced therapeutic options, morbidity and mortality rates remain high. Although acute inflammation in response to myocardial cell death has been extensively studied, subsequent adaptive immune activity and anti-heart autoimmunity may also contribute to the development of heart failure. After ischemic injury to the myocardium, dendritic cells (DC) respond to cardiomyocyte necrosis, present cardiac antigen to T cells, and potentially initiate a persistent autoimmune response against the heart. Cross-priming DC have the ability to activate both CD4+ helper and CD8+ cytotoxic T cells in response to necrotic cells and may thus be crucial players in exacerbating autoimmunity targeting the heart. This study investigates a role for cross-priming DC in post-myocardial infarction immunopathology through presentation of self-antigen from necrotic cardiac cells to cytotoxic CD8+ T cells.

METHODS

We induced type 2 myocardial infarction-like ischemic injury in the heart by treatment with a single high dose of the β-adrenergic agonist isoproterenol. We characterized the DC population in the heart and mediastinal lymph nodes and analyzed long-term cardiac immunopathology and functional decline in wild type and Clec9a-depleted mice lacking DC cross-priming function.

RESULTS

A diverse DC population, including cross-priming DC, is present in the heart and activated after ischemic injury. Clec9a-/- mice deficient in DC cross-priming are protected from persistent immune-mediated myocardial damage and decline of cardiac function, likely because of dampened activation of cytotoxic CD8+ T cells.

CONCLUSION

Activation of cytotoxic CD8+ T cells by cross-priming DC contributes to exacerbation of postischemic inflammatory damage of the myocardium and corresponding decline in cardiac function. Importantly, this provides novel therapeutic targets to prevent postischemic immunopathology and heart failure.

Type 2 MI induced by a single high dose of isoproterenol in C57BL/6J mice triggers a persistent adaptive immune response against the heart

Heart failure is the common final pathway of several cardiovascular conditions and a major cause of morbidity and mortality worldwide. Aberrant activation of the adaptive immune system in response to myocardial necrosis has recently been implicated in the development of heart failure. The ß-adrenergic agonist isoproterenol hydrochloride is used for its cardiac effects in a variety of different dosing regimens with high doses causing acute cardiomyocyte necrosis. To assess whether isoproterenol-induced cardiomyocyte necrosis triggers an adaptive immune response against the heart, we treated C57BL/6J mice with a single intraperitoneal injection of isoproterenol. We confirmed tissue damage reminiscent of human type 2 myocardial infarction. This is followed by an adaptive immune response targeting the heart as demonstrated by the activation of T cells, the presence of anti-heart auto-antibodies in the serum as late as 12 weeks after initial challenge and IgG deposition in the myocardium. All of these are hallmark signs of an established autoimmune response. Adoptive transfer of splenocytes from isoproterenol-treated mice induces left ventricular dilation and impairs cardiac function in healthy recipients. In summary, a single administration of a high dose of isoproterenol is a suitable high-throughput model for future studies of the pathological mechanisms of anti-heart autoimmunity and to test potential immunomodulatory therapeutic approaches.

Characterization of acute TLR-7 agonist-induced hemorrhagic myocarditis in mice by multiparametric quantitative cardiac magnetic resonance imaging

Hemorrhagic myocarditis is a potentially fatal complication of excessive levels of systemic inflammation. It has been reported in viral infection, but is also possible in systemic autoimmunity. Epicutaneous treatment of mice with the Toll-like receptor 7 (TLR-7) agonist Resiquimod induces auto-antibodies and systemic tissue damage, including in the heart, and is used as an inducible mouse model of systemic lupus erythematosus (SLE). Here, we show that overactivation of the TLR-7 pathway of viral recognition by Resiquimod treatment of CFN mice induces severe thrombocytopenia and internal bleeding, which manifests most prominently as hemorrhagic myocarditis. We optimized a cardiac magnetic resonance (CMR) tissue mapping approach for the in vivo detection of diffuse infiltration, fibrosis and hemorrhages using a combination of T1, T2 and T2* relaxation times, and compared results with ex vivo histopathology of cardiac sections corresponding to CMR tissue maps. This allowed detailed correlation between in vivo CMR parameters and ex vivo histopathology, and confirmed the need to include T2* measurements to detect tissue iron for accurate interpretation of pathology associated with CMR parameter changes. In summary, we provide detailed histological and in vivo imaging-based characterization of acute hemorrhagic myocarditis as an acute cardiac complication in the mouse model of Resiquimod-induced SLE, and a refined CMR protocol to allow non-invasive longitudinal in vivo studies of heart involvement in acute inflammation. We propose that adding T2* mapping to CMR protocols for myocarditis diagnosis improves diagnostic sensitivity and interpretation of disease mechanisms.This article has an associated First Person interview with the first author of the paper.

Systemic autoimmunity induced by the TLR7/8 agonist Resiquimod causes myocarditis and dilated cardiomyopathy in a new mouse model of autoimmune heart disease

Systemic autoimmune diseases such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) show significant heart involvement and cardiovascular morbidity, which can be due to systemically increased levels of inflammation or direct autoreactivity targeting cardiac tissue. Despite high clinical relevance, cardiac damage secondary to systemic autoimmunity lacks inducible rodent models. Here, we characterise immune-mediated cardiac tissue damage in a new model of SLE induced by topical application of the Toll-like receptor 7/8 (TLR7/8) agonist Resiquimod. We observe a cardiac phenotype reminiscent of autoimmune-mediated dilated cardiomyopathy, and identify auto-antibodies as major contributors to cardiac tissue damage. Resiquimod-induced heart disease is a highly relevant mouse model for mechanistic and therapeutic studies aiming to protect the heart during autoimmunity.

Summary: A novel mouse model of autoimmune-mediated heart damage to study the underlying mechanisms and test therapeutic options for systemic autoimmunity.

Abstract 79: Sex-dependent Role of Macrophage-derived Insulin-like Growth Factor-1 in Body Growth, Cardiac Homeostasis and Responses to Cardiac Tissue Stress

Biological sex is a key factor influencing the development and progression of cardiovascular disease. While sexual dimorphism has been identified in cardiac physiology and sex-based differences are observed in clinical contexts, the molecular and cellular bases for these differences are not understood.

Recently, we found for the first time that female and male hearts are different in their cellular composition. Female hearts comprise significantly greater numbers of resident mesenchymal cells, including cardiac fibroblasts, compared to male hearts, and female hearts consist of differing proportions of multiple leukocyte subsets. We found that these differences are regulated by gonadal hormones.

Extending on our previous work, this study investigates sexual dimorphism in cell-specific IGF-1 production and its impact on cardiac inflammatory responses. IGF-1 is a growth factor that is essential for development and injury responses, and that has been previously shown to function in a sex-dependent manner.

Using genetic, transcriptomic and high-dimensional flow cytometry approaches, we found that macrophages and fibroblasts are the principle IGF-1 producing cells in the heart, with macrophages from female mouse hearts producing twice as much IGF-1 as in males. This contributed to a ~20% greater level of IGF-1 found in the hearts of females compared to males. Furthermore, constitutive genetic ablation of macrophage-derived IGF-1 resulted in ~30% reduction in total IGF-1 in hearts of female mice, whereas no reduction was observed in male hearts. Surprisingly, we also found that ablation of macrophage-derived IGF-1 reduces body weight in female mice by ~10%. Finally, we found that macrophage-derived IGF-1 regulates cardiac inflammatory responses in a sex-dependent manner.

To our knowledge, this is the first study to demonstrate that a macrophage-derived growth factor is essential for normal body growth and plays a sex-dependent role in cardiac inflammatory responses. Our observations provide a cellular and molecular basis for the sexual dimorphism observed in cardiac physiology and pathology, and underscore the importance of considering biological sex in experimental models of cardiac development and disease.

Abstract 2481: RAD51 and AICDA define a new synthetic lethal interaction that is targetable in multiple tumor types

Antigen stimulated B-cells transiently express Activation Induced Cytidine Deaminase (AID) which initiates point mutations and DNA double strand breaks (DSB) in immunoglobulin genes to promote B-cell maturation. However, AID is capable of broadly damaging the B-cell genome. We have shown that AID-induced DSBs require the homologous recombination factor RAD51 for their repair. Using genetic approaches, we discovered that reduced HR function is cytotoxic to AID-expressing B-cells. We subsequently demonstrated the feasibility of small molecule inhibition of RAD51 to sensitize AID-overexpressing tumor cells. Here we build on those observations, finding that AID-RAD51 synthetic lethality occurs via mitotic catastrophe, involving the mTOR pathway. We have now developed potent and selective RAD51 modulatory small molecules that preferentially kill AID-expressing tumor cells. Using mouse models of lymphoma and leukemia we provide in vivo efficacy data demonstrating the potential therapeutic feasibility of RAD51 modulation. These studies provide evidence for a novel “synthetic lethal” approach for treating AID-expressing malignancies, via the induction of mitotic catastrophe.

Citation Format: Kevin D. Mills, Marly I. Roche, Amber Cyr, Tyler Maclay, Muneer G. Hasham, Kristin Lamont, Jane Branca, Francesca Cavallo, Francesca Cavallo, Maria Jasin, Alvin Stern, Youngho Kwon, Weixing Zhao, Patrick Sung. RAD51 and AICDA define a new synthetic lethal interaction that is targetable in multiple tumor types [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2481. doi:10.1158/1538-7445.AM2017-2481

Targeting antigen experienced B lymphocytes to retard type 1 diabetes progression in NOD mice

While CD4+ and CD8+ T lymphocytes are ultimately responsible for the destruction of insulin-producing beta cells resulting in clinical type 1 diabetes (T1D), B lymphocytes are also critical pathogenic players in T1D development in NOD mice and likely also in humans. The role of B lymphocytes in this disease is primarily through antigen presentation, presenting diabetogenic peptide to autoreactive T lymphocytes. It is not known if changes in antigen affinity of plasma membrane bound immunoglobulin molecules are important for B lymphocyte diabetogenicity. We generated NOD mice deficient in AID, an enzyme crucial for affinity maturation, and found that T1D development was greatly inhibited in these novel mutant mice. While insulitis was still evident, progression to glucosuria did not occur. The phenotype of these AIDnull B lymphocytes differed from standard NOD as did the T lymphocyte populations. With the knowledge that affinity maturation is important to the development of T1D, we targeted maturing B lymphocytes using a small molecule inhibitor of the RAD51 complex, DIDS. NOD mice treated with this agent were protected from T1D development: Total B lymphocyte numbers were maintained with a reduction in the marginal zone subset. Insulitis was reduced in the treated mice. Circulating insulin autoantibodies (IAA) are indicative of impending diabetes development; however, IAA positive mice receiving DIDS treatment did not develop T1D. These results suggest that targeting antigen-experienced B lymphocytes during their maturation process may be a viable approach in T1D.

Morphological analysis of neurons: Automatic identification of elongations

Our study is focused on the development of a new method for the automatic analysis of cell images. We focused on neurons (cells line SH-SY5Y) treated/untreated with ultrasound and stained with Haematoxylin-Eosin. The aim of the algorithm is the automatic detection of the cell body as well as the determination of the number and the length of neuron elongations. Starting point of the algorithm was the convolution of an image with a bank of rotating Gaussian kernels and the construction of a module map. Then several strategies were implemented to detect cell bodies and to detect and extract data about cell elongations. We have also realized a graphical user interface allowing the loading, saving and processing of images. Results show that this method is able to properly and efficiently detect cell contours and elongations. The automated evaluation is in strong agreement with manual evaluation performed by an expert operator, with an average error of 11% with most parameter combinations. This tool constitutes an important support in biological research activities, where operators need to analyze a large number of images to investigate about cell morphology before and after a treatment.

Attenuating homologous recombination stimulates an AID-induced antileukemic effect

Inhibition of the RAD51 homologous recombination factor prevents the repair of AID-initiated DNA breaks and induces apoptosis preferentially in AID-expressing human CLL.

Activation-induced cytidine deaminase (AID) is critical in normal B cells to initiate somatic hypermutation and immunoglobulin class switch recombination. Accumulating evidence suggests that AID is also prooncogenic, inducing cancer-promoting mutations or chromosome rearrangements. In this context, we find that AID is expressed in >40% of primary human chronic lymphocytic leukemia (CLL) cases, consistent with other reports. Using a combination of human B lymphoid leukemia cells and mouse models, we now show that AID expression can be harnessed for antileukemic effect, after inhibition of the RAD51 homologous recombination (HR) factor with 4,4′-diisothiocyanatostilbene-2-2′-disulfonic acid (DIDS). As a proof of principle, we show that DIDS treatment inhibits repair of AID-initiated DNA breaks, induces apoptosis, and promotes cytotoxicity preferentially in AID-expressing human CLL. This reveals a novel antineoplastic role of AID that can be triggered by inhibition of HR, suggesting a potential new paradigm to treat AID-expressing tumors. Given the growing list of tumor types with aberrant AID expression, this novel therapeutic approach has potential to impact a significant patient population.

Development of the allergy outcome survey for allergic rhinitis

The Allergy Outcome Survey (AOS) is a reliable measure used to monitor patients with allergic rhinitis. It was developed for and included in the Outcomes Measures of Immunotherapy in Allergic Rhinitis (OMIAR-1) project, designed to study the benefits of immunotherapy in the treatment of allergic rhinitis. Preliminary results indicate that AOS is specific, brief, reliable, and easy to use. Also, it is useful for evaluating change with therapy and can be used alone as a performance metric or in combination with other measures as part of a more complete outcomes monitoring system. As the OMIAR-1 study progresses, more information will be available on the advantages and limitations of the AOS.