Aims

Pediatric dilated cardiomyopathy (pDCM) is characterized by unique age-dependent molecular mechanisms that include myocellular responses to therapy. We previously showed that pDCM, but not adult DCM patients respond to phosphodiesterase 3 inhibitors (PDE3i) by increasing levels of the second messenger cAMP and consequent phosphorylation of phospholamban (PLN). However, the molecular mechanisms involved in the differential pediatric and adult response to PDE3i are not clear.

Methods and results

Quantification of serum response factor (SRF) isoforms from the left ventricle of explanted hearts showed that PDE3i treatment affects expression of SRF isoforms in pDCM hearts. An SRF isoform lacking exon 5 (SRFdel5) was highly expressed in the hearts of pediatric, but not adult DCM patients treated with PDE3i. To determine the functional consequence of expression of SRFdel5, we overexpressed full length SRF or SRFdel5 in cultured cardiomyocytes with and without adrenergic stimulation. Compared to a control adenovirus, expression of SRFdel5 increased phosphorylation of PLN, negatively affected expression of the phosphatase that promotes dephosphorylation of PLN (PP2Cε), and promoted faster calcium reuptake, whereas expression of full length SRF attenuated calcium reuptake through blunted phosphorylation of PLN.

Conclusions

Taken together, these data indicate that expression of SRFdel5 in pDCM hearts in response to PDE3i contributes to improved function through regulating PLN phosphorylation and thereby calcium reuptake.

中文翻译：

---

血清反应因子缺失 5 调节受磷蛋白磷酸化和钙摄取

目标

小儿扩张型心肌病 (pDCM) 的特点是独特的年龄依赖性分子机制，包括肌细胞对治疗的反应。我们之前表明，pDCM，但不是成人 DCM 患者通过增加第二信使 cAMP 的水平和随后的受磷蛋白 (PLN) 磷酸化来对磷酸二酯酶 3 抑制剂 (PDE3i) 作出反应。然而，儿童和成人对 PDE3i 的不同反应所涉及的分子机制尚不清楚。

方法和结果

来自移植心脏左心室的血清反应因子 (SRF) 同种型的定量表明，PDE3i 治疗影响 pDCM 心脏中 SRF 同种型的表达。缺少外显子 5 (SRFdel5) 的 SRF 同种型在儿科心脏中高度表达，但在接受 PDE3i 治疗的成年 DCM 患者心脏中却没有。为了确定 SRFdel5 表达的功能结果，我们在有和没有肾上腺素能刺激的情况下在培养的心肌细胞中过表达全长 SRF 或 SRFdel5。与对照腺病毒相比，SRFdel5 的表达增加了 PLN 的磷酸化，对促进 PLN 去磷酸化的磷酸酶 (PP2Cε) 的表达产生负面影响，并促进更快的钙再摄取，而全长 SRF 的表达通过 PLN 的钝化磷酸化减弱了钙的再摄取。

结论

总之，这些数据表明 SRFdel5 在 pDCM 心脏中响应 PDE3i 的表达有助于通过调节 PLN 磷酸化和钙再摄取来改善功能。