Department of Endocrinology and Metabolism, Peking University Third Hospital, Beijing 100191, China.
Int J Cardiol. 2013 Sep 10;167(6):2724-33. doi: 10.1016/j.ijcard.2012.06.106. Epub 2012 Jul 17.
Ghrelin, an endogenous ligand for growth hormone secretagogue receptor (GHS-R), shows cardioprotective activity and regulates the differentiation of several mesoderm-derived cells, including myocytes, adipocytes and osteoblasts. The effect of ghrelin on cardiogenesis and its underlying mechanism, however, have not been studied in detail.
The effects of ghrelin on cardiomyocyte differentiation were tested both in human embryonic stem cells (hESCs) cultured in embryoid body (EB)-based differentiation protocol, and in hESCs transplanted into rat hearts. The signaling mechanisms of ghrelin were further investigated under the EB-based culture condition.
The generation of beating EBs and the expression of cardiac-specific markers including cardiac troponin I (cTnI) and α-myosin heavy chain (α-MHC) were 2 to 3-fold upregulated by ghrelin. Although GHS-R1α protein was expressed in differentiated EBs, the effects of exogenous ghrelin were unchanged by D-[lys(3)]-GHRP-6, a specific GHS-R1α antagonist. Moreover, des-acyl ghrelin, which does not bind to GHS-R1α, displayed similar effects with ghrelin. Importantly, activation of ERK1/2, but not Akt, was induced by ghrelin in the newly-formed EBs, and the ghrelin-induced effects of cardiomyocyte differentiation were abolished by adding specific ERK1/2 inhibitor PD98059, but not specific PI3K inhibitor Wortmannin. In addition, ghrelin promoted the differentiation of grafted hESCs into Sox9- and Flk1-positive mesodermal/cardiac progenitor cells in rat hearts.
These results suggest that ghrelin induces cardiomyocyte differentiation from hESCs via the activation of the ERK1/2 signaling pathway. Our study, therefore, indicates that using ghrelin may be an effective strategy to promote the differentiation of hESCs into cardiomyocytes.
内源性生长激素促分泌素受体（GHS-R）配体Ghrelin 具有心脏保护活性，并调节几种中胚层来源的细胞（包括心肌细胞、脂肪细胞和成骨细胞）的分化。然而，Ghrelin 对心脏发生的影响及其潜在机制尚未得到详细研究。
在基于胚状体（EB）的分化方案培养的人胚胎干细胞（hESC）和移植到大鼠心脏的 hESC 中，测试 Ghrelin 对心肌细胞分化的影响。进一步在基于 EB 的培养条件下研究 Ghrelin 的信号机制。
Ghrelin 使搏动的 EB 的产生和心脏特异性标志物（包括心肌肌钙蛋白 I（cTnI）和α-肌球蛋白重链（α-MHC））的表达增加了 2 到 3 倍。尽管分化的 EB 中表达了 GHS-R1α 蛋白，但外源性 Ghrelin 的作用不受 GHS-R1α 的特异性拮抗剂 D-[lys（3）]-GHRP-6 改变。此外，不与 GHS-R1α 结合的去酰基 Ghrelin 与 Ghrelin 具有相似的作用。重要的是，Ghrelin 在新形成的 EB 中诱导 ERK1/2 的激活，但不诱导 Akt 的激活，并且 Ghrelin 诱导的心肌细胞分化作用被特异性 ERK1/2 抑制剂 PD98059 而不是特异性 PI3K 抑制剂 Wortmannin 所消除。此外，Ghrelin 促进了移植的 hESC 在大鼠心脏中分化为 Sox9 和 Flk1 阳性中胚层/心脏祖细胞。
这些结果表明，Ghrelin 通过激活 ERK1/2 信号通路诱导 hESC 向心肌细胞分化。因此，我们的研究表明，使用 Ghrelin 可能是促进 hESC 向心肌细胞分化的有效策略。
