GSDMD-mediated pyroptosis promotes cardiac remodeling in pressure overload

BACKGROUND

Gasdermin D (GSDMD) forms membrane pores to execute pyroptosis. But the mechanism of how cardiomyocyte pyroptosis induces cardiac remodeling in pressure overload remains unclear. We investigated the role of GSDMD-mediated pyroptosis in the pathogenesis of cardiac remodeling in pressure overload.

METHODS

Wild-type (WT) and cardiomyocyte-specific GSDMD-deficient (GSDMD-CKO) mice were subjected to transverse aortic constriction (TAC) to induce pressure overload. Four weeks after surgery, left ventricular structure and function were evaluated by echocardiographic, invasive hemodynamic and histological analysis. Pertinent signaling pathways related to pyroptosis, hypertrophy and fibrosis were investigated by histochemistry, RT-PCR and western blotting. The serum levels of GSDMD and IL-18 collected from healthy volunteers or hypertensive patients were measured by ELISA.

RESULTS

We found TAC induced cardiomyocyte pyroptosis and release of pro-inflammatory cytokines IL-18. The serum GSDMD level was significantly higher in hypertensive patients than in healthy volunteers, and induced more dramatic release of mature IL-18. GSDMD deletion remarkably mitigated TAC-induced cardiomyocyte pyroptosis. Furthermore, GSDMD deficiency in cardiomyocytes significantly reduced myocardial hypertrophy and fibrosis. The deterioration of cardiac remodeling by GSDMD-mediated pyroptosis was associated with activating JNK and p38 signaling pathways, but not ERK or Akt signaling pathway.

CONCLUSION

In conclusion, our results demonstrate that GSDMD serves as a key executioner of pyroptosis in cardiac remodeling induced by pressure overload. GSDMD-mediated pyroptosis activates JNK and p38 signaling pathways, and this may provide a new therapeutic target for cardiac remodeling induced by pressure overload.

O-GlcNAcylation-induced GSK-3β activation deteriorates pressure overload-induced heart failure via lack of compensatory cardiac hypertrophy in mice

O-GlcNAc transferase (OGT) modulates many functions of proteins via O-GlcNAcylation that adds O-linked β-N-acetylglucosamine (O-GlcNAc) to the serine/threonine residues of proteins. However, the role of O-GlcNAcylation in cardiac remodeling and function is not fully understood. To examine the effect of O-GlcNAcylation on pressure overload-induced cardiac hypertrophy and subsequent heart failure, transverse aortic constriction (TAC) surgery was performed in wild type (WT) and Ogt transgenic (Ogt-Tg) mice. Four weeks after TAC (TAC4W), the heart function of Ogt-Tg mice was significantly lower than that of WT mice (reduced fractional shortening and increased ANP levels). The myocardium of left ventricle (LV) in Ogt-Tg mice became much thinner than that in WT mice. Moreover, compared to the heart tissues of WT mice, O-GlcNAcylation of GSK-3β at Ser9 was increased and phosphorylation of GSK-3β at Ser9 was reduced in the heart tissues of Ogt-Tg mice, resulting in its activation and subsequent inactivation of nuclear factor of activated T cell (NFAT) activity. Finally, the thinned LV wall and reduced cardiac function induced by TAC4W in Ogt-Tg mice was reversed by the treatment of a GSK-3β inhibitor, TDZD-8. These results imply that augmented O-GlcNAcylation exacerbates pressure overload-induced heart failure due to a lack of compensatory cardiac hypertrophy via O-GlcNAcylation of GSK-3β, which deprives the phosphorylation site of GSK-3β to constantly inactivate NFAT activity to prevent cardiac hypertrophy. Our findings may provide a new therapeutic strategy for cardiac hypertrophy and subsequent heart failure.

Identification of Transcriptional Variation in Aortic Remodeling Using a Murine Transverse Aortic Constriction (TAC) Model

Arterial remodeling is a major pathological consequence of hypertension, which is recognized as the most common chronic non-communicable disease. However, the detailed mechanism of how arterial remodeling is induced by hypertension has not yet been fully elucidated. Evaluating the transcriptional changes in arterial tissue in response to elevated blood pressure at an early stage may provide new insights and identify novel therapeutic candidates in preventing arterial remodeling. Here, we used the ascending aorta of the transverse aortic constriction (TAC) model to induce arterial remodeling in C57BL/6 male mice. Age-matched mice were subjected to sham surgery as controls. The TAC model was only considered successful if the mice conformed to the criteria (RC/LC blood flow velocity with 5–10-fold change) 1 week after the surgery. Two weeks after surgery, the ascending aorta developed severe remodeling in TAC mice as compared to the sham group. High throughput sequencing was then applied to identify differentially expressed (DE) transcripts. In silicon analysis were then performed to systematically network transcriptional changes. A total of 1,019 mRNAs were significantly changed between TAC and the sham group at the transcriptional level. GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) analysis revealed that stress/stimulus/immune-related biological processes played a crucial role during arterial remodeling. Our data provide a comprehensive understanding of global gene expression changes in the TAC model, which suggests that targeting inflammation and vascular smooth cell transformation are potential therapeutic strategies to interfere with the aortic remodeling at an early stage in the development of hypertension.

THE AUTOCRINE ROLE OF TRYPTASE IN PRESSURE OVERLOAD-INDUCED MAST CELL ACTIVATION, CHYMASE RELEASE AND CARDIAC FIBROSIS

BACKGROUND

Cardiac mast cell (MC) proteases, chymase and tryptase, increase proliferation and collagen synthesis in cultured cardiac fibroblasts. However, the question as to why preventing individually the actions of either protease prevents fibrosis when both are released upon MC activation remains unanswered. Since tryptase has the ability to activate MCs in noncardiac tissues via the protease-activated receptor-2 (PAR-2), there is the possibility that its, in vivo, fibrotic role is due to its ability to induce MC degranulation thereby amplifying the release of chymase.

METHODS

This study sought to delineate the interactions between tryptase and chymase in myocardial remodeling secondary to transverse aortic constriction (TAC) for 5 wks in male Sprague Dawley rats untreated or treated with either the tryptase inhibitor, nafamostat mesilate or MC membrane stabilizing drug, nedocromil (n=6/group). In addition, ventricular slices from 6 rat hearts were incubated with tryptase, tryptase plus nafamostat mesilate or chymostatin for 24 h.

RESULTS AND CONCLUSION

The results indicate the presence of PAR-2 on MCs and that tryptase inhibition and nedocromil prevented TAC-induced fibrosis and increases in MC density, activation, and chymase release. Tryptase also significantly increased chymase concentration in ventricular tissue culture media, which was prevented by the tryptase inhibitor. Hydroxyproline concentration in culture media was significantly increased with tryptase incubation as compared to the control group and the tryptase group incubated with nafamostat mesilate or chymostatin. We conclude that tryptase contributes to TAC-induced cardiac fibrosis primarily via activation of MCs and the amplified release of chymase.

In vivo mouse myocardial (31)P MRS using three-dimensional image-selected in vivo spectroscopy (3D ISIS): technical considerations and biochemical validations

(31)P MRS provides a unique non-invasive window into myocardial energy homeostasis. Mouse models of cardiac disease are widely used in preclinical studies, but the application of (31)P MRS in the in vivo mouse heart has been limited. The small-sized, fast-beating mouse heart imposes challenges regarding localized signal acquisition devoid of contamination with signal originating from surrounding tissues. Here, we report the implementation and validation of three-dimensional image-selected in vivo spectroscopy (3D ISIS) for localized (31)P MRS of the in vivo mouse heart at 9.4 T. Cardiac (31)P MR spectra were acquired in vivo in healthy mice (n = 9) and in transverse aortic constricted (TAC) mice (n = 8) using respiratory-gated, cardiac-triggered 3D ISIS. Localization and potential signal contamination were assessed with (31)P MRS experiments in the anterior myocardial wall, liver, skeletal muscle and blood. For healthy hearts, results were validated against ex vivo biochemical assays. Effects of isoflurane anesthesia were assessed by measuring in vivo hemodynamics and blood gases. The myocardial energy status, assessed via the phosphocreatine (PCr) to adenosine 5'-triphosphate (ATP) ratio, was approximately 25% lower in TAC mice compared with controls (0.76 ± 0.13 versus 1.00 ± 0.15; P < 0.01). Localization with one-dimensional (1D) ISIS resulted in two-fold higher PCr/ATP ratios than measured with 3D ISIS, because of the high PCr levels of chest skeletal muscle that contaminate the 1D ISIS measurements. Ex vivo determinations of the myocardial PCr/ATP ratio (0.94 ± 0.24; n = 8) confirmed the in vivo observations in control mice. Heart rate (497 ± 76 beats/min), mean arterial pressure (90 ± 3.3 mmHg) and blood oxygen saturation (96.2 ± 0.6%) during the experimental conditions of in vivo (31)P MRS were within the normal physiological range. Our results show that respiratory-gated, cardiac-triggered 3D ISIS allows for non-invasive assessments of in vivo mouse myocardial energy homeostasis with (31)P MRS under physiological conditions.