Compensatory hypertrophy induced by ventricular cardiomyocyte-specific COX-2 expression in mice

Transcriptome sequencing analysis reveals the molecular regulatory mechanism of myocardial hypertrophy induced by angiotensin II

The pathogenesis of myocardial hypertrophy remains incompletely understood, highlighting the critical need for in-depth investigation into its pathogenesis and pathophysiology to develop innovative strategies for preventing and treating heart diseases. In this study, a model of angiotensin II (Ang II)-induced myocardial hypertrophy was established using subcutaneous administration with a micropump. Echocardiography, wheat germ agglutinin staining, and western blot analysis were used to evaluate the myocardial hypertrophy model after 5, 10, and 15 days of Ang II treatment. RNA-seq was employed to analyze the differential expression profile of mRNA, followed by bioinformatics analysis. Subsequently, the anti-inflammatory drug meloxicam was utilized to explore its impact on cardiac hypertrophy in mice. The findings demonstrated that mice developed myocardial hypertrophy following subcutaneous administration of Ang II. Transcriptomic analysis revealed significant changes in gene expression in the myocardium induced by Ang II, with the most pronounced differences observed at day 10. Functional analysis and verification of differentially expressed genes indicated that Ang II triggered an inflammatory response in the myocardium, leading to up-regulation of genes associated with fibrosis and apoptosis while decreasing energy metabolism; alterations were also observed in genes related to oxidative stress and calcium ion binding. Treatment with meloxicam improved Ang II-induced myocardial hypertrophy. This study not only elucidated the molecular regulatory mechanism underlying mouse myocardial hypertrophy at a transcriptional level but also provided new insights into clinical prevention and treatment strategies for cardiac diseases such as dilated cardiomyopathy and heart failure.

Prostanoids in Cardiac and Vascular Remodeling

Prostanoids are biologically active lipids generated from arachidonic acid by the action of the COX (cyclooxygenase) isozymes. NSAIDs, which reduce the biosynthesis of prostanoids by inhibiting COX activity, are effective anti-inflammatory, antipyretic, and analgesic drugs. However, their use is limited by cardiovascular adverse effects, including myocardial infarction, stroke, hypertension, and heart failure. While it is well established that NSAIDs increase the risk of atherothrombotic events and hypertension by suppressing vasoprotective prostanoids, less is known about the link between NSAIDs and heart failure risk. Current evidence indicates that NSAIDs may increase the risk for heart failure by promoting adverse myocardial and vascular remodeling. Indeed, prostanoids play an important role in modulating structural and functional changes occurring in the myocardium and in the vasculature in response to physiological and pathological stimuli. This review will summarize current knowledge of the role of the different prostanoids in myocardial and vascular remodeling and explore how maladaptive remodeling can be counteracted by targeting specific prostanoids.

Chronic Trypanosoma cruzi infection activates the TWEAK/Fn14 axis in cardiac myocytes and fibroblasts driving structural and functional changes that affect the heart

Sustained interaction between the cytokine tumor necrosis factor-like weak inducer of apoptosis (TWEAK) and its functional receptor, fibroblast growth factor-inducible 14 (Fn14), has been linked to cardiovascular disorders. Chagas cardiomyopathy, elicited by Trypanosoma cruzi infection, is associated with chronic inflammation, fibrosis and hypertrophy. This study aimed to explore the involvement of the TWEAK/Fn 14 axis in development of Chagas heart disease. Parasite infection in vitro triggered Fn14 overexpression in atrial HL-1 myocytes and cardiac MCF fibroblasts. Fn14 levels were also increased in heart tissue from C57BL/6 mice at 130 days post-infection, particularly in myocytes and fibroblasts. Concurrently, TWEAK expression in circulating monocytes from this group was higher than that determined in uninfected controls. TWEAK/Fn14 interaction was functional in myocytes and fibroblasts isolated from infected hearts, leading to TNF receptor-associated factor 2 (TRAF2)-mediated activation of nuclear factor kappa B (NFκB) signaling. Ex vivo stimulation of both cell types with recombinant TWEAK for 24 h boosted the NFκB-regulated production of proinflammatory/profibrotic mediators (IL-1β, IL-6, TNF-α, IL-8, CCL2, CCL5, MMP-2, MMP-9, ICAM-1, E-selectin) involved in chronic T. cruzi cardiomyopathy. We further evaluated the therapeutic potential of the soluble decoy receptor Fn14-Fc to interfere with TWEAK/Fn14-dependent pathogenic activity. Fn14-Fc treatment of chronically infected mice was effective in neutralizing the ligand and reverting electrocardiographic abnormalities, maladaptive inflammation, adverse remodeling and hypertrophy in myocardium. Altogether, these findings suggest that sustained TWEAK/Fn14 induction by persistent T. cruzi infection is implicated in cardiopathogenesis and make TWEAK/Fn14 axis a promising target for the treatment of chronic Chagas heart disease.

Celecoxib alleviates pathological cardiac hypertrophy and fibrosis via M1-like macrophage infiltration in neonatal mice

Cardiac hypertrophy is an adaptive response to all forms of heart disease, including hypertension, myocardial infarction, and cardiomyopathy. Cyclooxygenase-2 (COX-2) overexpression results in inflammatory response, cardiac cell apoptosis, and hypertrophy in adult heart after injury. However, immune response-mediated cardiac hypertrophy and fibrosis have not been well documented in injured neonatal heart. This study showed that cardiac hypertrophy and fibrosis are significantly attenuated in celecoxib (a selective COX-2 inhibitor)-treated P8 ICR mice after cryoinjury. Molecular and cellular profiling of immune response shows that celecoxib inhibits the production of cytokines and the expression of adhesion molecular genes, increases the recruitment of M1-like macrophage at wound site, and alleviates cardiac hypertrophy and fibrosis. Furthermore, celecoxib administration improves cardiac function at 4 weeks after injury. These results demonstrate that COX-2 inhibition promotes the recruitment of M1-like macrophages during early wound healing, which may contribute to the suppression of cardiac hypertrophy and fibrosis after injury.

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Cryoinjury successfully induces cardiac hypertrophy and fibrosis in P8 ICR mice

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COX-2 inhibition alleviates cardiac hypertrophy and fibrosis after cryoinjury

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MCP-1 significantly increases in COX-2 inhibition

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COX-2 inhibition improves cardiac repair in P8 ICR mice by recruiting M1-like macrophages

Sodium butyrate attenuates angiotensin II-induced cardiac hypertrophy by inhibiting COX2/PGE2 pathway via a HDAC5/HDAC6-dependent mechanism

Sodium butyrate (NaBu) is reported to play important roles in a number of chronic diseases. The present work is aimed to investigate the effect of NaBu on angiotensin II (Ang II)-induced cardiac hypertrophy and the underlying mechanism in in vivo and in vitro models. Sprague Dawley rats were infused with vehicle or Ang II (200 ng/kg/min) and orally administrated with or without NaBu (1 g/kg/d) for two weeks. Cardiac hypertrophy parameters and COX2/PGE2 pathway were analysed by real-time PCR, ELISA, immunostaining and Western blot. The cardiomyocytes H9C2 cells were used as in vitro model to investigate the role of NaBu (2 mmol/L) in inhibition of Ang II-induced cardiac hypertrophy. NaBu significantly attenuated Ang II-induced increase in the mean arterial pressure. Ang II treatment remarkably increased cardiac hypertrophy as indicated by increased ratio of heart weight/body weight and enlarged cardiomyocyte size, extensive fibrosis and inflammation, as well as enhanced expression of hypertrophic markers, whereas hearts from NaBu-treated rats exhibited a significant reduction in these hypertrophic responses. Mechanistically, NaBu inhibited the expression of COX2/PGE2 along with production of ANP and phosphorylated ERK (pERK) stimulated by Ang II in in vivo and in vitro, which was accompanied by the suppression of HDAC5 and HDAC6 activities. Additionally, knocking down the expression of HDAC5 and HDAC6 via gene-editing strategy dramatically blocked Ang II-induced hypertrophic responses through COX2/PGE2 pathway. These results provide solid evidence that NaBu attenuates Ang II-induced cardiac hypertrophy by inhibiting the activation of COX2/PGE2 pathway in a HDAC5/HDAC6-dependent manner.

Endogenous osteopontin induces myocardial CCL5 and MMP-2 activation that contributes to inflammation and cardiac remodeling in a mouse model of chronic Chagas heart disease

Cardiac dysfunction with progressive inflammation and fibrosis is a hallmark of Chagas disease caused by persistent Trypanosoma cruzi infection. Osteopontin (OPN) is a pro-inflammatory cytokine that orchestrates mechanisms controlling cell recruitment and cardiac architecture. Our main goal was to study the role of endogenous OPN as a modulator of myocardial CCL5 chemokine and MMP-2 metalloproteinase, and its pathological impact in a murine model of Chagas heart disease. Wild-type (WT) and OPN-deficient (spp1 -/-) mice were parasite-infected (Brazil strain) for 100days. Both groups developed chronic myocarditis with similar parasite burden and survival rates. However, spp1 -/- infection showed lower heart-to-body ratio (P<0.01) as well as reduced inflammatory pathology (P<0.05), CCL5 expression (P<0.05), myocyte size (P<0.05) and fibrosis (P<0.01) in cardiac tissues. Intense OPN labeling was observed in inflammatory cells recruited to infected heart (P<0.05). Plasma concentration of MMP-2 was higher (P<0.05) in infected WT than in spp1 -/- mice. Coincidently, specific immunostaining revealed increased gelatinase expression (P<0.01) and activity (P<0.05) in the inflamed hearts from T. cruzi WT mice, but not in their spp1 -/- littermates. CCL5 and MMP-2 induction occurred preferentially (P<0.01) in WT heart-invading CD8⁺ T cells and was mediated via phospho-JNK MAPK signaling. Heart levels of OPN, CCL5 and MMP-2 correlated (P<0.01) with collagen accumulation in the infected WT group only. Endogenous OPN emerges as a key player in the pathogenesis of chronic Chagas heart disease, through the upregulation of myocardial CCL5/MMP-2 expression and activities resulting in pro-inflammatory and pro-hypertrophic events, cardiac remodeling and interstitial fibrosis.

Exogenous hydrogen sulfide protects against high glucose‑induced inflammation and cytotoxicity in H9c2 cardiac cells

Hyperglycemia serves an important role in the pathogenesis of diabetic cardiomyopathy. The aim of the present study was to investigate whether exogenous hydrogen sulfide (H2S) protects against high glucose‑induced inflammation and cytotoxicity in cardiac cells by inhibiting the p38 mitogen‑activated protein kinase (MAPK)/nuclear factor‑κB (NF‑κB), cyclooxygenase‑2 (COX‑2) and inducible nitric oxide synthase (iNOS) signaling pathways. Rat H9c2 myocardium cells were exposed to 33 mM glucose (high glucose, HG) for 24 h to stimulate HG‑induced cytotoxicity. One group of cells was pretreated with NaHS (a donor of H2S) prior to HG exposure, and cell viability was determined using the Cell Counting Kit‑8 assay. The protein expression levels of p38MAPK, the phosphorylated p65 subunit of NF‑κB, iNOS, COX‑2 and caspase‑3 were analyzed by western blotting, and the protein expression levels of interleukin (IL)‑1β and IL‑6 were detected by enzyme‑linked immunosorbent assay (ELISA). Pretreatment of H9c2 cells with NaHS for 30 min prior to exposure to HG significantly ameliorated the expression of p38MAPK and NF‑κB. In addition, pretreatment with NaHS markedly attenuated p38MAPK/NF‑κB‑mediated cytotoxicity and inflammation, as evidenced by the significant increase in cell viability and decrease in iNOS, COX‑2, IL‑1β and IL‑6 expression levels. Furthermore, treatment of cells with NaHS significantly decreased the expression of caspase‑3, which suggested that NaHS attenuated HG‑induced apoptosis. In conclusion, the results of the present study provided evidence to suggest that exogenous H2S protects against HG‑induced cytotoxicity and inflammation in H9c2 cardiac cells. H2S may exert these cytoprotective effects via inhibition of the p38MAPK/NF‑κB, COX‑2 and iNOS signaling pathways.

The long noncoding RNA Chaer defines an epigenetic checkpoint in cardiac hypertrophy

Epigenetic reprogramming is a critical process of pathological gene induction during cardiac hypertrophy and remodeling, but the underlying regulatory mechanisms remain to be elucidated. Here we identified a heart-enriched long noncoding (lnc)RNA, named cardiac-hypertrophy-associated epigenetic regulator (Chaer), which is necessary for the development of cardiac hypertrophy. Mechanistically, Chaer directly interacts with the catalytic subunit of polycomb repressor complex 2 (PRC2). This interaction, which is mediated by a 66-mer motif in Chaer, interferes with PRC2 targeting to genomic loci, thereby inhibiting histone H3 lysine 27 methylation at the promoter regions of genes involved in cardiac hypertrophy. The interaction between Chaer and PRC2 is transiently induced after hormone or stress stimulation in a process involving mammalian target of rapamycin complex 1, and this interaction is a prerequisite for epigenetic reprogramming and induction of genes involved in hypertrophy. Inhibition of Chaer expression in the heart before, but not after, the onset of pressure overload substantially attenuates cardiac hypertrophy and dysfunction. Our study reveals that stress-induced pathological gene activation in the heart requires a previously uncharacterized lncRNA-dependent epigenetic checkpoint.

Cyclooxygenase-2 Mediated Oxidation of 2-Arachidonoyl-Lysophospholipids Identifies Unknown Lipid Signaling Pathways

Eicosanoid lipids play important roles in cellular signaling as second messengers in inflammation, immune response, vascular tone, and the CNS. Biosynthesis of eicosanoid lipids proceeds via hydrolysis of esterified arachidonic acid from phospholipids followed by oxidation of the released arachidonic acid by a variety of enzymes including cyclooxygenases (COX). Herein, we demonstrate the remarkable ability of COX-2, but not COX-1, to directly oxidize 2-arachidonoyl-lysolipids, resulting in the generation of previously unknown classes of eicosanoid-lysolipids, and provide evidence that intracellular lipases can release eicosanoids from their eicosanoid-lysolipid precursors. Importantly, genetic ablation of a phospholipase, iPLA₂γ, significantly reduced the amounts of these eicosanoid-lysolipids in murine hepatic tissue and fibroblasts. Furthermore, calcium stimulation of wild-type murine lung fibroblasts produced robust increases in these eicosanoid-lysolipids, which were markedly attenuated in iPLA₂γ^-/- fibroblasts. Collectively, these results identify an iPLA₂γ-initiated pathway generating new classes of lipid metabolites with potential signaling functions resulting from the direct COX-2 catalyzed oxidation of 2-arachidonoyl-lysolipids.

c-Src/Pyk2/EGFR/PI3K/Akt/CREB-activated pathway contributes to human cardiomyocyte hypertrophy: Role of COX-2 induction

Thrombin and COX-2 regulating cardiac hypertrophy are via various signaling cascades. Several transcriptional factors including CREB involve in COX-2 expression. However, the interplay among thrombin, CREB, and COX-2 in primary human neonatal ventricular cardiomyocytes remains unclear. In this study, thrombin-induced COX-2 promoter activity, mRNA and protein expression, and PGE2 synthesis were attenuated by pretreatment with the inhibitors of c-Src (PP1), Pyk2 (PF431396), EGFR (AG1478), PI3K/Akt (LY294002/SH-5), and p300 (GR343), or transfection with siRNAs of c-Src, Pyk2, EGFR, p110, Akt, CREB, and p300. Moreover, thrombin-stimulated phosphorylation of c-Src, Pyk2, EGFR, Akt, CREB and p300 was attenuated by their respective inhibitors. These results indicate that thrombin-induced COX-2 expression is mediated through PAR-1/c-Src/Pyk2/EGFR/PI3K/Akt linking to CREB and p300 cascades. Functionally, thrombin-induced hypertrophy and ANF/BNP release were, at least in part, mediated through a PAR-1/COX-2-dependent pathway. We uncover the importance of COX-2 regarding human cardiomyocyte hypertrophy that will provide a therapeutic intervention in cardiovascular diseases.

PAR1-dependent COX-2/PGE2 production contributes to cell proliferation via EP2 receptors in primary human cardiomyocytes

BACKGROUND AND PURPOSE

Different protease-activated receptors (PARs) activated by thrombin are involved in cardiovascular disease, via up-regulation of inflammatory proteins including COX-2. However, the mechanisms underlying thrombin-regulated COX-2 expression in human cardiomyocytes remain unclear.

EXPERIMENTAL APPROACH

Human cardiomyocytes were used in the study. Thrombin-induced COX-2 protein and mRNA expression, and signalling pathways were determined by Western blot, real-time PCR and COX-2 promoter luciferase reporter assays, and pharmacological inhibitors or siRNAs. PGE2 generation and cell proliferation were also determined.

KEY RESULTS

Thrombin-induced COX-2 protein and mRNA expression, promoter activity and PGE2 release was attenuated by the PAR1 antagonist (SCH79797) or the inhibitors of proteinase activity (PPACK), MEK1/2 (U0126), p38 MAPK (SB202190) or JNK1/2 (SP600125), and transfection with small interfering RNA (siRNA) of PAR1, p38, p42 or JNK2. These results suggested that PAR1-dependent MAPKs participate in thrombin-induced COX-2 expression in human cardiomyocytes. Moreover, thrombin stimulated phosphorylation of MAPKs, which was attenuated by PPACK and SCH79797. Furthermore, thrombin-induced COX-2 expression was blocked by the inhibitors of AP-1 (tanshinone IIA) and NF-κB (helenalin). Moreover, thrombin-stimulated phosphorylation of c-Jun/AP-1 and p65/NF-κB was attenuated by tanshinone IIA and helenalin, respectively, suggesting that thrombin induces COX-2 expression via PAR1/MAPKs/AP-1 or the NF-κB pathway. Functionally, thrombin increased human cardiomyocyte proliferation through the COX-2/PGE2 system linking to EP2 receptors, as determined by proliferating cell nuclear antigen and cyclin D1 expression.

CONCLUSIONS AND IMPLICATIONS

These findings demonstrate that MAPKs-mediated activation of AP-1/NF-κB pathways is, at least in part, required for COX-2/PGE2 /EP2 -triggered cell proliferation in human cardiomyocytes.

COX-2 is involved in ET-1-induced hypertrophy of neonatal rat cardiomyocytes: role of NFATc3

Endothelin-1 (ET-1) is a critical molecule that involved in heart failure. It has been proved that ET-1 stimulation results in cardiac hypertrophy both in vitro and in vivo, but the mechanisms underlying remain largely unknown. In this study, we reported that cyclooxygenase-2 (COX-2) might be an important mediator of hypertrophic responses to ET-1 stimulation. In the cultured rat neonatal cardiomyocytes, ET-1 significantly upregulated the expression and activity of COX-2, which was accompanied by increase in cell surface area and BNP mRNA level. In contrast, ET-1-dependent cardiomyocyte hypertrophy was abolished by COX-2 selective inhibitors, NS-398 and celecoxib, or by COX-2 RNA interference, but the inhibitory effects could be diminished by pretreatment with PGE2. Furthermore, cyclosporin A (CsA) and knockdown of nuclear factor of activated T-cells c3 (NFATc3) inhibited the expression of COX-2 induced by ET-1, and NFATc3 could also bound to the -GGAAA- sequence in the promoter region of rat COX-2 gene, indicating that calcineurin/NFATc3 signaling participated in the transcriptional regulation of COX-2 following ET-1 treatment. These findings provided further insight into the roles of ET-1 in cardiac hypertrophy and suggested a potential therapeutic strategy against cardiac hypertrophy by inhibiting COX-2.

A non-specific effect associated with conditional transgene expression based on Cre-loxP strategy in mice

Transgenes flanked by loxP sites have been widely used to generate transgenic mice where the transgene expression can be controlled spatially and temporally by Cre recombinase. Data from this approach has led to important conclusions in cancer, neurodevelopment and neurodegeneration. Using this approach to conditionally express micro RNAs (miRNAs) in mice, we found that Cre-mediated recombination in neural progenitor cells caused microcephaly in five of our ten independent transgenic lines. This effect was not associated with the types or the quantity of miRNAs being expressed, nor was it associated with specific target knockdown. Rather, it was correlated with the presence of multiple tandem transgene copies and inverted (head-to-head or tail-to-tail) transgene repeats. The presence of these inverted repeats caused a high level of cell death in the ventricular zone of the embryonic brain, where Cre was expressed. Therefore, results from this Cre-loxP approach to generate inducible transgenic alleles must be interpreted with caution and conclusions drawn in previous reports may need reexamination.

Lack of microsomal prostaglandin E synthase-1 reduces cardiac function following angiotensin II infusion

Our laboratory previously reported that inducible PGE(2) synthase, mPGES-1, contributes to micromolar production of PGE(2) in neonatal ventricular myocytes in vitro, which stimulates their growth. We therefore hypothesized that mPGES-1 contributes to cardiac hypertrophy following angiotensin II (ANG II) infusion. To test this hypothesis, we used 10- to 12-wk-old mPGES-1 knockout mice (mPGES-1 KO) and C57Bl/6 control mice infused for 8 wk with either 1.4 mg · kg(-1) · day(-1) ANG II or vehicle subcutaneously. Blood pressure [systolic blood pressure (SBP)] was measured throughout the study, and cardiac function was assessed by M-mode echocardiography at baseline and at 8 wk of infusion. At the conclusion of the study, immunohistochemistry was used to evaluate collagen fraction, myocyte cross-sectional area (MCSA), and apoptosis. At baseline, there was no difference in SBP between mPGES-1 KO mice and C57BL/6 controls. ANG II infusion increased SBP to similar levels in both strains. In control mice, infusion of ANG II increased MCSA and posterior wall thickness at diastole (PWTd) but had little effect on cardiac function, consistent with compensatory hypertrophy. In contrast, cardiac function was worse in mPGES-1 KO mice after ANG II treatment. Ejection fraction declined from 76.2 ± 2.7 to 63.3 ± 3.4% after ANG II, and left ventricular dimension at systole and diastole increased from 1.29 ± 0.02 to 1.78 ± 0.15 mm and from 2.57 ± 0.03 to 2.90 ± 0.13 mm, respectively. Infusion of ANG II increased both the LV-to-body weight and the mass-to-body weight ratios to a similar extent in both strains. However, PWTd increased by a lesser extent in KO mice, suggesting an impaired hypertrophic response. ANG II infusion increased collagen staining similarly in both strains, but TdT-dUTP nick end labeling staining was greater in mPGES-1 KO mice. Overall, these results are consistent with a beneficial effect for mPGES-1 in the maintenance of cardiac function in ANG II-dependent hypertension.

Synergistic effects of the GATA-4-mediated miR-144/451 cluster in protection against simulated ischemia/reperfusion-induced cardiomyocyte death

Among the identified microRNAs (miRs) thus far, ~50% of mammalian miRs are clustered in the genome and transcribed as polycistronic primary transcripts. However, whether clustered miRs mediate non-redundant and cooperative functions remains poorly understood. In this study, we first identified activation of the promoter of miR-144/451 by GATA-4, a critical transcription factor in the heart. Next, we observed that ectopic expression of miR-144 and -451 individually augmented cardiomyocyte survival, which was further improved by overexpression of miR-144/451, compared to control cells in response to simulated ischemia/reperfusion. In contrast, knockdown of endogenous miR-144 and -451 revealed opposite effects. Using luciferase reporter assay and western blot analysis, we also validated that both miR-144 and miR-451 target CUG triplet repeat-binding protein 2 (CUGBP2), a ubiquitously expressed RNA-binding protein, known to interact with COX-2 3'UTR and inhibit its translation. Accordingly, protein levels of CUGBP2 were greatly reduced and COX-2 activity was markedly increased in miR-144-, miR-451-, and miR-144/451-overexpressing cardiomyocytes, compared to GFP cells. Furthermore, inhibition of COX-2 activity by either NS-398 or DUP-697 partially offset protective effects of the miR-144/451 cluster. Together, these data indicate that both partners of the miR-144/451 cluster confer protection against simulated I/R-induced cardiomyocyte death via targeting CUGBP2-COX-2 pathway, at least in part. Thus, both miR-144 and miR-451 may represent new therapeutic agents for the treatment of ischemic heart disease.

Preserved heart function and maintained response to cardiac stresses in a genetic model of cardiomyocyte-targeted deficiency of cyclooxygenase-2

Cyclooxygenase-1 and -2 are rate-limiting enzymes in the formation of a wide array of bioactive lipid mediators collectively known as prostanoids (prostaglandins, prostacyclins, and thromboxanes). Evidence from clinical trials shows that selective inhibition of the second isoenzyme (cyclooxygenase-2, or Cox-2) is associated with increased risk for serious cardiovascular events and findings from animal-based studies have suggested protective roles of Cox-2 for the heart. To further characterize the function of Cox-2 in the heart, mice with loxP sites flanking exons 4 and 5 of Cox-2 were rendered knockout specifically in cardiac myocytes (Cox-2 CKO mice) via cre-mediated recombination. Baseline cardiac performance of CKO mice remained unchanged and closely resembled that of control mice. Furthermore, myocardial infarct size induced after in vivo ischemia/reperfusion (I/R) injury was comparable between CKO and control mice. In addition, cardiac hypertrophy and function four weeks after transverse aortic constriction (TAC) was found to be similar between the two groups. Assessment of Cox-2 expression in purified adult cardiac cells isolated after I/R and TAC suggests that the dominant source of Cox-2 is found in the non-myocyte fraction. In conclusion, our animal-based analyses together with the cell-based observations portray a limited role of cardiomyocyte-produced Cox-2 at baseline and in the context of ischemic or hemodynamic challenge.

MAPK-activated protein kinase-2 in cardiac hypertrophy and cyclooxygenase-2 regulation in heart

RATIONALE

Activation of p38 mitogen-activated protein kinase (MAPK) has a significant impact on cardiac gene expression, contractility, extracellular matrix remodeling, and inflammatory response in heart. The p38 kinase pathway also has a controversial role in cardiac hypertrophy. MAPK-activated protein kinase-2 (MK2) is a well-established p38 downstream kinase, yet its contribution to p38-mediated pathological response in heart has not been investigated.

OBJECTIVE

We examined the specific contribution of MK2 to the pathological remodeling induced by p38.

METHODS AND RESULTS

We used a cardiomyocyte specific and inducible transgenic approach to determine the functional and molecular impact of acute activation of the p38 pathway in heart in either a MK2 wild-type or a MK2-null background. p38 activation in wild-type mice led to a rapid onset of lethal cardiomyopathy associated with cardiomyocyte hypertrophy, interstitial fibrosis, and contractile dysfunction. Inactivation of MK2 partially but significantly reduced cardiomyocyte hypertrophy, improved contractile performance, and prevented early lethality. MK2 inactivation had no effect on the mRNA levels of hypertrophic marker genes or the proinflammatory gene cyclooxygenase (COX)-2. However, MK2 had a major role in COX-2 protein synthesis without affecting the mRNA level or protein stability.

CONCLUSIONS

p38 activity in adult myocytes can contribute to pathological hypertrophy and remodeling in adult heart and that MK2 is an important downstream molecule responsible for specific features of p38-induced cardiac pathology.