Hypertension and Vascular Research Division, Henry Ford Hospital, Detroit, Michigan, USA.
PLoS One. 2013 Jul 30;8(7):e69832. doi: 10.1371/journal.pone.0069832. Print 2013.
Our laboratory reported that male mice with cardiomyocyte-selective knockout of the prostaglandin E2 EP4 receptor sub-type (EP4 KO) exhibit reduced cardiac function. Gene array on left ventricles (LV) showed increased fractalkine, a chemokine implicated in heart failure. We therefore hypothesized that fractalkine is regulated by PGE2 and contributes to depressed contractility via alterations in intracellular calcium.
Fractalkine was measured in LV of 28-32 week old male EP4 KO and wild type controls (WT) by ELISA and the effect of PGE2 on fractalkine secretion was measured in cultured neonatal cardiomyocytes and fibroblasts. The effect of fractalkine on contractility and intracellular calcium was determined in Fura-2 AM-loaded, electrical field-paced cardiomyocytes. Cardiomyocytes (AVM) from male C57Bl/6 mice were treated with fractalkine and responses measured under basal conditions and after isoproterenol (Iso) stimulation.
LV fractalkine was increased in EP4 KO mice but surprisingly, PGE2 regulated fractalkine secretion only in fibroblasts. Fractalkine treatment of AVM decreased both the speed of contraction and relaxation under basal conditions and after Iso stimulation. Despite reducing contractility after Iso stimulation, fractalkine increased the Ca(2+) transient amplitude but decreased phosphorylation of cardiac troponin I, suggesting direct effects on the contractile machinery.
Fractalkine depresses myocyte contractility by mechanisms downstream of intracellular calcium.
我们的实验室曾报道，心肌细胞特异性敲除前列腺素 E2 EP4 受体亚型（EP4 KO）的雄性小鼠表现出心脏功能降低。左心室（LV）的基因阵列显示趋化因子 fractalkine 增加，该因子与心力衰竭有关。因此，我们假设 fractalkine 受 PGE2 调节，并通过改变细胞内钙来导致收缩功能下降。
通过 ELISA 测量 28-32 周龄雄性 EP4 KO 和野生型对照（WT）的 LV 中的 fractalkine，并测量培养的新生心肌细胞和成纤维细胞中 PGE2 对 fractalkine 分泌的影响。在 Fura-2 AM 负载的电刺激起搏的心肌细胞中测定 fractalkine 对收缩力和细胞内钙的影响。用 fractalkine 处理雄性 C57Bl/6 小鼠的 AVM，并在基础条件和异丙肾上腺素（Iso）刺激后测量反应。
EP4 KO 小鼠的 LV fractalkine 增加，但令人惊讶的是，PGE2 仅在成纤维细胞中调节 fractalkine 分泌。AVM 的 fractalkine 处理降低了基础条件和 Iso 刺激后的收缩和舒张速度。尽管 Iso 刺激后 fractalkine 降低了收缩力，但增加了心肌钙蛋白 I 的磷酸化，表明其对收缩机制有直接影响。
fractalkine 通过细胞内钙下游的机制降低心肌细胞的收缩力。
