蛋白激酶Cδ可能参与肥大心肌细胞转向凋亡

为了探讨肥大心肌细胞对凋亡刺激的易感性及蛋白激酶Cδ(protein kinase Cδ,PKCδ)在其中的作用,以内皮素-1 (endothelin-1,ET-1)处理原代培养的新生大鼠心肌细胞,诱导心肌细胞肥大;再用血管紧张素Ⅱ(angiotensin II,Ang II)作为细胞凋亡诱导因子,采用鬼笔环肽(phalloidin)荧光染色与细胞面积测量两种方法检测心肌肥大,Hoechst 33258荧光染色检测细胞凋亡。结果显示：(1)1与10 nmol/L ET-1作用48h,心肌细胞肌原纤维排列整齐、染色增浓,随ET-1浓度增加而愈加明显,心肌细胞表面积分别增加42．5%和67．3%,以此作为轻度和中度心肌细胞肥大模型。(2)正常、轻度肥大与中度肥大心肌细胞受1nmol/L AngⅡ处理24h后,凋亡率分别为(15．54±1．32)%、(20．65±1．40)%与(29．33±3．52)%,三组之间有显著差异(P＜0．05)。(3)受AngⅡ刺激后,PKCδ特异性抑制剂rottlerin不影响正常心肌细胞的凋亡率,却有效抑制了轻度和中度肥大心肌细胞的凋亡。肥大心肌细胞凋亡易感性明显高于正常心肌细胞,抑制PKCδ可以抑制肥大心肌细胞凋亡,提示PKCδ参与肥大心肌细胞凋亡过程。     

LncRNA SNHG1 exerts a protective role in cardiomyocytes hypertrophy via targeting miR‐15a‐5p/HMGA1 axis

Heart failure preceded by pathological cardiac hypertrophy is a leading cause of death. Long noncoding RNA small nucleolar RNA host gene 1 (SNHG1) was reported to inhibit cardiomyocytes apoptosis, but the role and underlying mechanism of SNHG1 in pathological cardiac hypertrophy have not yet been understood. This study was designed to investigate the role and molecular mechanism of SNHG1 in regulating cardiac hypertrophy. We found that SNHG1 was upregulated during cardiac hypertrophy both in vivo (transverse aortic constriction treatment) and in vitro (phenylephrine [PE] treatment). SNHG1 overexpression attenuated the cardiomyocytes hypertrophy induced by PE, while SNHG1 inhibition promoted hypertrophic response of cardiomyocytes. Furthermore, SNHG1 and high‐mobility group AT‐hook 1 (HMGA1) were confirmed to be targets of miR‐15a‐5p. SNHG1 promoted HMGA1 expression by sponging miR‐15a‐5p, eventually attenuating cardiomyocytes hypertrophy. There data revealed a novel protective mechanism of SNHG1 in cardiomyocytes hypertrophy. Thus, targeting of SNHG1‐related pathway may be therapeutically harnessed to treat cardiac hypertrophy.     

Alterations in apoptosis regulatory factors during hypertrophy and heart failure

Cardiac hypertrophy from pathological stimuli often proceeds to heart failure, whereas cardiac hypertrophy from physiological stimuli does not. In this study, physiological hypertrophy was created by a daily exercise regimen and pathological hypertrophy was created from a high-salt diet in Dahl salt-sensitive rats. The rats continued on a high-salt diet progressed to heart failure associated with an increased rate of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-positive cardiomyocytes. We analyzed primary cultures of these hearts and found that only cardiomyocytes made hypertrophic by a pathological stimulus show increased sensitivity to apoptosis. Examination of the molecular changes associated with these distinct types of hypertrophy revealed changes in Bcl-2 family members and caspases favoring survival during physiological hypertrophy. However, in pathological hypertrophy, there were more diffuse proapoptotic changes, including changes in Fas, the Bcl-2 protein family, and caspases. Therefore, we speculate that this increased sensitivity to apoptotic stimulation along with proapoptotic changes in the apoptosis program may contribute to the development of heart failure seen in pathological cardiac hypertrophy.     

FKBP12.6 protects heart from AngII‐induced hypertrophy through inhibiting Ca2+/calmodulin‐mediated signalling pathways in vivo and in vitro

We previously observed that disruption of FK506‐binding protein 12.6 (FKBP12.6) gene resulted in cardiac hypertrophy in male mice. Studies showed that overexpression of FKBP12.6 attenuated thoracic aortic constriction (TAC)‐induced cardiac hypertrophy in mice, whereas the adenovirus‐mediated overexpression of FKBP12.6 induced hypertrophy and apoptosis in cultured neonatal cardiomyocytes, indicating that the role of FKBP12.6 in cardiac hypertrophy is still controversial. In this study, we aimed to investigate the roles and mechanisms of FKBP12.6 in angiotensin II (AngII)‐induced cardiac hypertrophy using various transgenic mouse models in vivo and in vitro. FKBP12.6 knockout (FKBP12.6^?/?) mice and cardiac‐specific FKBP12.6 overexpressing (FKBP12.6 TG) mice were infused with AngII (1500 ng/kg/min) for 14 days subcutaneously by implantation of an osmotic mini‐pump. The results showed that FKBP12.6 deficiency aggravated AngII‐induced cardiac hypertrophy, while cardiac‐specific overexpression of FKBP12.6 prevented hearts from the hypertrophic response to AngII stimulation in mice. Consistent with the results in vivo, overexpression of FKBP12.6 in H9c2 cells significantly repressed the AngII‐induced cardiomyocyte hypertrophy, seen as reductions in the cell sizes and the expressions of hypertrophic genes. Furthermore, we demonstrated that the protection of FKBP12.6 on AngII‐induced cardiac hypertrophy was involved in reducing the concentration of intracellular Ca²⁺ ([Ca²⁺]i), in which the protein significantly inhibited the key Ca²⁺/calmodulin‐dependent signalling pathways such as calcineurin/cardiac form of nuclear factor of activated T cells 4 (NFATc4), calmodulin kinaseII (CaMKII)/MEF‐2, AKT/Glycogen synthase kinase 3β (GSK3β)/NFATc4 and AKT/mTOR signalling pathways. Our study demonstrated that FKBP12.6 protects heart from AngII‐induced cardiac hypertrophy through inhibiting Ca²⁺/calmodulin‐mediated signalling pathways.     

Attenuation of microRNA-22 derepressed PTEN to effectively protect rat cardiomyocytes from hypertrophy

Cardiac hypertrophy, which is characterized by the enlargement of cell size, reactivation of fetal genes, remains one of the most important triggers to heart failure. Increasing evidence shows that microRNA (miRNA) is extensively involved in the pathogenesis of cardiac hypertrophy. But the effects of miRNAs on cardiomyocyte hypertrophy have not been completely solved yet. Here, we showed that a collection of miRNAs was aberrantly expressed in hypertrophic cardiomyocytes induced by phenylephrine (PE) or angiotensin II (Ang II). Among them, miR-22 was the most strikingly up-regulated miRNA. To investigate the role of miR-22 in hypertrophy, both over-expression and knock-down assays were performed on cardiomyocytes. The results showed that up-regulation of miR-22 significantly increased the cell size and markedly influenced the expression of hypertrophic markers, including induction of nppa and reduction of myh6. In contrast, reduction of miR-22 level attenuated either PE- or Ang II-induced hypertrophic reaction. Furthermore, several genes, including PTEN, were identified as potential targets of miR-22 by bioinformatic algorithms. Using luciferase analysis, miR-22 could significantly suppress the luciferase activity of reporter fused with 3' untranslated region of PTEN mRNA. Furthermore, up-regulation of miR-22 could suppress the protein level of PTEN and reduction of miR-22 level markedly increased the protein level of PTEN in cardiomyocytes by Western blot analysis, suggesting that the contribution of miR-22 to cardiomyocyte hypertrophy may be partially through targeting PTEN. Taken together, miRNAs were dynamically regulated in cardiomyocyte hypertrophy and attenuation of miR-22 in rat cardiomyocytes efficiently protected from hypertrophic effects through derepressing PTEN.     

缺氧复氧时肥大心肌细胞凋亡及其与能量代谢途径转换的关系

心肌细胞凋亡是心肌肥大向心力衰竭转化的重要机制,因此,抑制肥大心肌细胞凋亡可能是防治心力衰竭的有 效药物靶点之一。本研究以0．1μmol／L血管紧张素Ⅱ和1 μmol／L去甲肾上腺素刺激培养心肌细胞,复制心肌细胞肥大模 型,用三气孵箱培养。缺氧条件是95％N2和5％CO2,控制氧分压低于5 mmHg以下,8 h后常氧培养,液闪计数法测 定丙酮酸脱氢酶(pyruvate dehydrogenase,PDH)和肉碱脂酰转移酶-1(carnitine palmitoyltransferase 1,CPT-1)活性,糖氧化、 糖酵解、脂肪酸氧化率,以及细胞凋亡百分率,分析肥大心肌细胞能量代谢变化与细胞凋亡间的关系。结果如下:(1)与 常氧培养比较,缺氧8 h后,活化型丙酮酸脱氢酶(PDHa)和CPT-1活性均有显著下降,但复氧早期肥大心肌细胞PDHa活 性有轻度进一步降低(P>0．05),而CPT-1活性却较快恢复。(2)缺氧时,正常和肥大心肌细胞葡萄糖氧化代谢率均有降低[分 别下降(16±0．9)％、(48±1．1)％];复氧时,正常心肌细胞糖氧化代谢较快恢复,而肥大心肌细胞在复氧早期,糖氧化 率进一步降低,此后才逐渐恢复。(3)在缺氧时,肥大心肌细胞糖酵解率仅轻度下降,但在复氧后糖酵解率迅速升高,呈 爆发样达峰值后又逐渐恢复到缺氧前水平。(4)肥大心肌细胞在缺氧后脂肪酸代谢明显降低,但复氧后脂肪酸代谢呈爆发式 上升,并大大高于缺血前的代谢水平。(5)缺氧时肥大心肌细胞凋亡率即显著增加,在复氧早期细胞凋亡率继续大幅度上 升,此后逐渐减少。(6)预先用二氯乙酸处理肥大心肌细胞,可显著逆转缺氧复氧导致的细胞糖氧化受抑、糖酵解和脂肪 酸代谢活化,同时,抑制细胞凋亡的发生。上述结果提示,缺氧复氧后的肥大心肌细胞能量代谢途径转换是导致细胞凋 亡的重要原因。     

Protease Activated Receptor-2 Contributes to Heart Failure

Heart failure is a major clinical problem worldwide. Previous studies have demonstrated an important role for G protein-coupled receptors, including protease-activated receptors (PARs), in the pathology of heart hypertrophy and failure. Activation of PAR-2 on cardiomyocytes has been shown to induce hypertrophic growth in vitro. PAR-2 also contributes to myocardial infarction and heart remodeling after ischemia/reperfusion injury. In this study, we found that PAR-2 induced hypertrophic growth of cultured rat neonatal cardiomyocytes in a MEK1/2 and p38 dependent manner. In addition, PAR-2 activation on mouse cardiomyocytes increased expression of the pro-fibrotic chemokine MCP-1. Furthermore, cardiomyocyte-specific overexpression of PAR-2 in mice induced heart hypertrophy, cardiac fibrosis, inflammation and heart failure. Finally, in a mouse model of myocardial infarction induced by permanent ligation of the left anterior descending coronary artery, PAR-2 deficiency attenuated heart remodeling and improved heart function independently of its contribution to the size of the initial infarct. Taken together, our data indicate that PAR-2 signaling contributes to the pathogenesis of hypertrophy and heart failure.     

Cdc42 plays a critical role in assembly of sarcomere units in series of cardiac myocytes

Cardiomyocyte hypertrophy is observed in various cardiovascular diseases and causes heart failure. We here examined the role of small GTP-binding proteins of Rho family in phenylephrine (PE)-or leukocyte inhibitory factor (LIF)-induced hypertrophic morphogenesis of cultured neonatal rat cardiomyocytes. Both LIF and PE increased cell size of cardiomyocytes. LIF induced an increase in the length/width ratio of cardiomyocytes, while PE did not change the ratio. Adenoviral gene transfer of constitutively active mutants of Cdc42 increased the length/width ratio of cardiomyocytes and dominant negative mutants of Cdc42 conversely inhibited LIF-induced cell-elongation, while mutants of RhoA and Rac1 did not affect the length/width ratio of cardiomyocytes. These results suggest that Cdc42, but not RhoA and Rac1, is involved in LIF-induced sarcomere assembly in series in cardiomyocytes.     

Ubiquitin‐specific protease 19 blunts pathological cardiac hypertrophy via inhibition of the TAK1‐dependent pathway

Ubiquitin‐specific protease 19 (USP19) belongs to USP family and is involved in promoting skeletal muscle atrophy. Although USP19 is expressed in the heart, the role of USP19 in the heart disease remains unknown. The present study provides in vivo and in vitro data to reveal the role of USP19 in preventing pathological cardiac hypertrophy. We generated USP19‐knockout mice and isolated neonatal rat cardiomyocytes (NRCMs) that overexpressed or were deficient in USP19 to investigate the effect of USP19 on transverse aortic constriction (TAC) or phenylephrine (PE)‐mediated cardiac hypertrophy. Echocardiography, pathological and molecular analysis were used to determine the extent of cardiac hypertrophy, fibrosis, dysfunction and inflammation. USP19 expression was markedly increased in rodent hypertrophic heart or cardiomyocytes underwent TAC or PE culturing, the increase was mediated by the reduction of Seven In Absentia Homolog‐2. The extent of TAC‐induced cardiac hypertrophy, fibrosis, dysfunction and inflammation in USP19‐knockout mice was exacerbated. Consistently, gain‐of‐function and loss‐of‐function approaches that involved USP19 in cardiomyocytes suggested that the down‐regulation of USP19 promoted the hypertrophic phenotype, while the up‐regulation of USP19 improved the worsened phenotype. Mechanistically, the USP19‐elicited cardiac hypertrophy improvement was attributed to the abrogation of the transforming growth factor beta‐activated kinase 1 (TAK1)‐p38/JNK1/2 transduction. Furthermore, the inhibition of TAK1 abolished the aggravated hypertrophy induced by the loss of USP19. In conclusion, the present study revealed that USP19 and the downstream of TAK1‐p38/JNK1/2 signalling pathway might be a potential target to attenuate pathological cardiac hypertrophy.     

Overexpression of FNTB and the activation of Ras induce hypertrophy and promote apoptosis and autophagic cell death in cardiomyocytes

Farnesyltransferase (FTase) is an important enzyme that catalyses the modification of protein isoprene downstream of the mevalonate pathway. Previous studies have shown that the tissue of the heart in the suprarenal abdominal aortic coarctation (AAC) group showed overexpression of FTaseβ (FNTB) and the activation of the downstream protein Ras was enhanced. FTase inhibitor (FTI) can alleviate myocardial fibrosis and partly improve cardiac remodelling in spontaneously hypertensive rats. However, the exact role and mechanism of FTase in myocardial hypertrophy and remodelling are not fully understood. Here, we used recombinant adenovirus to transfect neonatal rat ventricular cardiomyocytes to study the effect of FNTB overexpression on myocardial remodelling and explore potential mechanisms. The results showed that overexpression of FNTB induces neonatal rat ventricular myocyte hypertrophy and reduces the survival rate of cardiomyocytes. FNTB overexpression induced a decrease in mitochondrial membrane potential and increased apoptosis in cardiomyocytes. FNTB overexpression also promotes autophagosome formation and the accumulation of autophagy substrate protein, LC3II. Transmission electron microscopy (TEM) and mCherry‐GFP tandem fluorescent‐tagged LC3 (tfLC3) showed that FNTB overexpression can activate autophagy flux by enhancing autophagosome conversion to autophagolysosome. Overactivated autophagy flux can be blocked by bafilomycin A1. In addition, salirasib (a Ras farnesylcysteine mimetic) can alleviate the hypertrophic phenotype of cardiomyocytes and inhibit the up‐regulation of apoptosis and autophagy flux induced by FNTB overexpression. These results suggest that FTase may have a potential role in future treatment strategies to limit the adverse consequences of cardiac hypertrophy, cardiac dysfunction and heart failure.     

A-Kinase Anchoring Protein Lbc Coordinates a p38 Activating Signaling Complex Controlling Compensatory Cardiac Hypertrophy

In response to stress, the heart undergoes a remodeling process associated with cardiac hypertrophy that eventually leads to heart failure. A-kinase anchoring proteins (AKAPs) have been shown to coordinate numerous prohypertrophic signaling pathways in cultured cardiomyocytes. However, it remains to be established whether AKAP-based signaling complexes control cardiac hypertrophy and remodeling in vivo. In the current study, we show that AKAP-Lbc assembles a signaling complex composed of the kinases PKN, MLTK, MKK3, and p38α that mediates the activation of p38 in cardiomyocytes in response to stress signals. To address the role of this complex in cardiac remodeling, we generated transgenic mice displaying cardiomyocyte-specific overexpression of a molecular inhibitor of the interaction between AKAP-Lbc and the p38-activating module. Our results indicate that disruption of the AKAP-Lbc/p38 signaling complex inhibits compensatory cardiomyocyte hypertrophy in response to aortic banding-induced pressure overload and promotes early cardiac dysfunction associated with increased myocardial apoptosis, stress gene activation, and ventricular dilation. Attenuation of hypertrophy results from a reduced protein synthesis capacity, as indicated by decreased phosphorylation of 4E-binding protein 1 and ribosomal protein S6. These results indicate that AKAP-Lbc enhances p38-mediated hypertrophic signaling in the heart in response to abrupt increases in the afterload.     

Regression of copper-deficient heart hypertrophy: reduction in the size of hypertrophic cardiomyocytes

Dietary copper (Cu) deficiency causes cardiac hypertrophy and its transition to heart failure in a mouse model. Cu repletion results in rapid regression of cardiac hypertrophy and prevention of heart failure. The present study was undertaken to understand dynamic changes of cardiomyocytes in the hypertrophic heart during the regression. Dams of FVB mice were fed a Cu-deficient (CuD) diet (0.3 mg Cu/kg) starting on Day 3 post-delivery, and weanling pups were fed the same diet until Cu repletion (6.0 mg Cu/kg) in the diet at 31 days of age. Heart samples were obtained at the end of CuD feeding or at 3, 7, 14 or 28 days after Cu repletion. Cu deficiency resulted in increases in the size and reduction in the number of cardiomyocytes in the heart. Cu repletion led to regression in the size of hypertrophic cardiomyocytes and normalization of the total number of cardiomyocytes. Although a direct reduction in the cell size would be significantly responsible for the regression of heart hypertrophy, some hypertrophic cardiomyocytes upon Cu repletion reentered the cell cycle as determined by Ki-67 staining in the cardiomyocyte-specific α-sarcomeric actin-stained cells and underwent division as determined by a mitosis-specific marker, phospho-histone 3. Quantitative analysis indicated that the replication of hypertrophic cardiomyocytes made a contribution of about one-third to the total mitosis of the regenerated myocardium. This study suggests that a direct reduction in the size of some hypertrophic cardiomyocytes and a replication of other hypertrophic cardiomyocytes with reduced size make a significant contribution to the regression of CuD heart hypertrophy, leading to normalization of the size and the number of cardiomyocytes in the heart.     

Cyclin D2 induces proliferation of cardiac myocytes and represses hypertrophy

The myocytes of the adult mammalian heart are considered unable to divide. Instead, mitogens induce cardiomyocyte hypertrophy. We have investigated the effect of adenoviral overexpression of cyclin D2 on myocyte proliferation and morphology. Cardiomyocytes in culture were identified by established markers. Cyclin D2 induced DNA synthesis and proliferation of cardiomyocytes and impaired hypertrophy induced by angiotensin II and serum. At the molecular level, cyclin D2 activated CDK4/6 and lead to pRB phosphorylation and downregulation of the cell cycle inhibitors p21Waf1/Cip1 and p27Kip1. Expression of the CDK4/6 inhibitor p16 inhibited proliferation and cyclin D2 overexpressing myocytes became hypertrophic under such conditions. Inhibition of hypertrophy by cyclin D2 correlated with downregulation of p27Kip1. These data show that hypertrophy and proliferation are highly related processes and suggest that cardiomyocyte hypertrophy is due to low amounts of cell cycle activators unable to overcome the block imposed by cell cycle inhibitors. Cell cycle entry upon hypertrophy may be converted to cell division by increased expression of activators such as cyclin D2.     

Mitochondrial compartment: a possible target of cadmium effects on breast epithelial cells

Prolonged myocardial stretch typically leads to hypertrophy of cardiomyocytes. As integrins are cellular receptors of stretch, we hypothesize that integrin stimulation induces cardiomyocyte hypertrophy. Integrins of neonatal rat cardiomyocytes (NRCMs) were stimulated with a peptide containing the Arg-Gly-Asp (RGD) sequence for 24 h. For comparison, alpha(1)-adrenergic stimulation by phenylephrine (PE) for 24 h was applied. Saline-treated NRCMs were used as control. The hypertrophic response was quantified by measuring cell surface area (CSA). Phosphorylation of NO-synthase-1 (NOS1) was assessed by immunocytochemistry. CSA was increased by 38% (IQR 31-44%) with RGD and by 68% (IQR 64-84%) with PE versus control (both P < 0.001). NOS-1 phosphorylation was increased by 61% with RGD and by 21% with PE versus control (both P < 0.01). A general NOS-inhibitor (L-NAME) inhibited RGD-induced hypertrophy completely, but had no significant effect on PE-induced hypertrophy. Administration of NO-donor to NRCMs co-incubated with RGD + L-NAME partly restored hypertrophy (to 62% of the hypertrophic effect of RGD alone), but had no effect if incubated with PE + L-NAME. Ryanodine and BAPTA-AM inhibited RGD-induced hypertrophy completely but not that induced by PE. Integrin stimulation of NRCMs by RGD leads to hypertrophy, likely by activation of NOS-1. Abrogation of RGD-induced hypertrophic response upon NOS-inhibition and rescue of this hypertrophic effect by NO-donor suggest that integrin stimulation-induced hypertrophy of NRCMs is NO-dependent.     

Cell fusion contributes to the rescue of apoptotic cardiomyocytes by bone marrow cells

Cardiomyocyte apoptosis is an important contributor to the progressive cardiac dysfunction that culminates in congestive heart failure. Bone marrow cells (BMCs) restore cardiac function following ischaemia, and transplanted BMCs have been reported to fuse with cells of diverse tissues. We previously demonstrated that the myogenic conversion of bone marrow stromal cells increased nearly twofold when the cells were co‐cultured with apoptotic (TNF‐α treated) cardiomyocytes. We therefore hypothesized that cell fusion may be a major mechanism by which BMCs rescue cardiomyocytes from apoptosis. We induced cellular apoptosis in neonatal rat cardiomyocytes by treatment with hydrogen peroxide (H₂O₂). The TUNEL assay demonstrated an increase in apoptosis from 4.5 ± 1.3% in non‐treated cells to 19.0 ± 4.4% (P < 0.05) in treated cells. We subsequently co‐cultured the apoptotic cardiomyocytes with BMCs and assessed cell fusion using flow cytometry. Fusion was rare in the non‐treated control cardiomyocytes (0.3%), whereas H₂O₂ treatment led to significantly higher fusion rates than the control group (P < 0.05), with the highest rate of 7.9 ± 0.3% occurring at 25 μM H₂O₂. We found an inverse correlation between cell fusion and completion of cardiomyocyte apoptosis (R² = 0.9863). An in vivo mouse model provided evidence of cell fusion in the infarcted myocardium following the injection of BMCs. The percentage of cells undergoing fusion was significantly higher in mice injected with BMCs following infarction (8.8 ± 1.3%) compared to mice that did not undergo infarction (4.6 ± 0.6%, P < 0.05). Enhancing cell fusion may be one method to preserve cardiomyocytes following myocardial infarction, and this new approach may provide a novel target for cardiac regenerative therapies.     

Upregulation of corin gene expression in hypertrophic cardiomyocytes and failing myocardium

High levels of plasma atrial natriuretic peptides (ANP) are associated with pathological conditions such as congestive heart failure (CHF). Recently, we have identified a cardiac serine protease, corin, that is the pro-ANP convertase. In this study, we examined the regulation of corin gene expression in cultured hypertrophic cardiomyocytes and in the left ventricular (LV) myocardium of a rat model of heart failure. Quantitative RT-PCR analysis showed that both corin and ANP mRNA levels were significantly increased in phenylephrine (PE)-stimulated rat neonatal cardiomyocytes in culture. The increase in corin mRNA correlated closely with the increase in cell size and ANP mRNA expression in the PE-treated cells (r = 0.95, P < 0.01; r = 0.92, P < 0.01, respectively). The PE-treated cardiomyocytes had an increased activity in converting recombinant human pro-ANP to biologically active ANP, as determined by a pro-ANP processing assay and a cell-based cGMP assay. In a rat model of heart failure induced by ligation of the left coronary artery, corin mRNA expression in the noninfarcted LV myocardium was significantly higher than that of control heart tissues from sham-operated animals, when examined by Northern blot analysis and RT-PCR at 8 wk. These results indicate that the corin gene is upregulated in hypertrophic cardiomyocytes and failing myocardium. Increased corin expression may contribute to elevation of ANP in the setting of cardiac hypertrophy and heart failure.