Endothelin-1-induced remodelling of murine adult ventricular myocytes

Activation of FXR receptor reduces damage of ET-1 on H9C2 cardiomyocytes by activating AMPK signaling pathway

BACKGROUND

The aim of this study was to investigate the effect of Farnesoid X receptor (FXR) on oxidative stress injury of H9C2 cardiomyocytes induced by endothelin-1 (ET-1), and to explore the possible mechanism.

METHODS

H9C2 cardiomyocytes were treated with ET-1 at concentrations of 10-8, 10-7 and 10-6 mmol/L for 12, 24, 36, and 48 h, respectively. At the same time, oxidative stress injury models were established. After the oxidative stress injury model was established, GW4064 (FXR agonist), siRNA-FXR (the virus interfered with FXR expression) and FXR empty virus were treated for 48 h. CCK-8 method was used to observe the survival rate of cardiomyocytes. Biochemical kit method was used to detect Creatine Kinase (CK) contents, CAT, and mitochondrial activity. Western blot was used to detect the protein expression of SOD1, AMPK and p-AMPK. And real-time PCR was used to detect GPX1 mRNA, GPX3 mRNA, Sirt1 mRNA, PGC-1α mRNA expression levels.

RESULTS

At the concentrations of 10-8, 10-7 and 10-6 mmol/L, ET-1 could induce the decrease of mitochondrial complex I and III activity and increase of CK content in H9C2 cardiomyocytes. Moreover, with the increase of ET-1 concentration and the extension of culture time, the oxidative stress damage of cardiomyocytes became more serious. After ET-1 intervention, the expressions of p-AMPK protein, Sirt1 mRNA and PGC-1α mRNA were decreased. The 2 μmol/L GW4064 could effectively improve the oxidative stress induced by ET-1, and compared with the ET-1 group, the survival rate of H9C2 cardiomyocytes increased obviously. In addition, the CK content was decreased. On the contrary, the mitochondrial complex I and III, and CAT activity increased significantly, and the expressions of SOD1 and p-AMPK protein, Sirt1 mRNA and PGC-1α mRNA increased obviously. However, siRNA-FXR can partially block the improvement effect of FXR agonist on cardiomyocytes injury.

CONCLUSIONS

Activation of FXR receptor may reduce the damage of ET-1 on H9C2 cardiomyocytes by activating AMPK signaling pathway.

Endothelial cell modulation of cardiomyocyte gene expression

The anatomic arrangement of microvascular endothelial cells and cardiomyocytes in vivo enables close interactions among these cells. In our in vitro co-culture system, ANP and BNP expression in the mouse atrial cardiomyocyte cell line HL-1 and subsequent ANP release were significantly upregulated when co-cultured with mouse cardiac microvascular endothelial cells or exposed to endothelial cell-conditioned medium. Endothelin-1 (ET-1) activation of endothelial cells remarkably enhanced their paracrine effect on cardiomyocyte gene expression, suggesting that ET-1 stimulation of endothelial cells affects expression of fetal genes such as ANP and BNP in adult cardiomyocytes through paracrine signalling. Exposure of HL-1 cells and murine induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) to authentic angiopoietin-2 (Ang2) caused a concentration-dependent decrease in ANP expression while ET-1-induced ANP expression was augmented by low but inhibited by high concentrations of Ang2. FK506-mediated inhibition of the calcineurin-NFAT pathway in the HL-1 cells selectively inhibited the stimulatory effect of the conditioned medium derived from ET-1-pre-stimulated endothelial cells on cardiomyocyte fetal gene expression. Combined with previous results indicating a crucial role for ANP and BNP in cardiac homeostasis, our findings provide further evidence that paracrine signalling by cardiac microvascular endothelial cells modulates cardiomyocyte function.

Endothelin-1 promotes hypertrophic remodelling of cardiac myocytes by activating sustained signalling and transcription downstream of endothelin type A receptors

G-protein coupled receptor (GPCR) mediated activation of the MAPK signalling cascade is a key pathway in the induction of hypertrophic remodelling of the heart – a response to pathological cues including hypertension and myocardial infarction. While levels of pro-hypertrophic hormone agonists of GPCRs increase during periods of greater workload to enhance cardiac output, hypertrophy does not necessarily result. Here we investigated the relationship between the duration of exposure to the pro-hypertrophic GPCR agonist endothelin-1 (ET-1) and the induction of hypertrophic remodelling in neonatal rat ventricular myocytes (NRVM) and in the adult rat heart in vivo. Notably, a 15 min pulse of ET-1 was sufficient to induce markers of hypertrophy that were present when measured at 24 h in vivo and 48 h in vitro. The persistence of ET-1 action was insensitive to ET type A receptor (ET_A receptor) antagonism with BQ123. The extended effects of ET-1 were dependent upon sustained MAPK signalling and involved persistent transcription. Inhibitors of endocytosis however conferred sensitivity upon the hypertrophic response to BQ123, suggesting that endocytosis of ET_A receptors following ligand binding preserves their active state by protection against antagonist. Contrastingly, α₁ adrenergic-induced hypertrophic responses required the continued presence of agonist and were sensitive to antagonist. These studies shed new light on strategies to pharmacologically intervene in the action of different pro-hypertrophic mediators.

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Acute ET-1 exposure elicits a long-lasting cardiac myocyte hypertrophic response.

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ET-1 effects depend on persistent MAPK signalling and active transcription.

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ET-1 elicited hypertrophy is insensitive to subsequent ET_A receptor antagonism.

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Endocytosis inhibition potentiates ET-1-induction of hypertrophy markers.

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Endocytosis inhibition sensitises effects of ET-1 to ET_A receptor antagonist.

The Inositol Trisphosphate/Calcium Signaling Pathway in Health and Disease

Many cellular functions are regulated by calcium (Ca2+) signals that are generated by different signaling pathways. One of these is the inositol 1,4,5-trisphosphate/calcium (InsP3/Ca2+) signaling pathway that operates through either primary or modulatory mechanisms. In its primary role, it generates the Ca2+ that acts directly to control processes such as metabolism, secretion, fertilization, proliferation, and smooth muscle contraction. Its modulatory role occurs in excitable cells where it modulates the primary Ca2+ signal generated by the entry of Ca2+ through voltage-operated channels that releases Ca2+ from ryanodine receptors (RYRs) on the internal stores. In carrying out this modulatory role, the InsP3/Ca2+ signaling pathway induces subtle changes in the generation and function of the voltage-dependent primary Ca2+ signal. Changes in the nature of both the primary and modulatory roles of InsP3/Ca2+ signaling are a contributory factor responsible for the onset of a large number human diseases.