EDST, Lebanese University, Hadath, Lebanon.
Gilbert and Rose-Marie Chagoury, School of Medicine, Lebanese American University, Byblos, Lebanon.
Cell Biochem Funct. 2019 Jun;37(4):245-255. doi: 10.1002/cbf.3397. Epub 2019 Apr 24.
Damage to podocytes is a key event in glomerulopathies. While energy dense food can contribute to kidney damage, the role of the orixegenic hormone "ghrelin" in podocyte biology is still unknown. In the present study, we investigated the effect of ghrelin on podocyte survival as well as the signalling pathways mediating ghrelin effect in immortalized cultured rat podocytes. RT-PCR analysis revealed that GHS-R1 is expressed in rat podocytes. Western blot analysis showed that ghrelin upregulated COX-2 protein expression in a time and dose-dependent manner. Additionally, ghrelin activated P38 MAPK, AKT, and ERK1/2 pathways and also induced P38 MAPK phosphorylation in high glucose conditions. Ghrelin induced ROS release and dose dependently reduced podocyte survival. Ghrelin mediated podocyte cell death was partially reversed by pharmacologically inhibiting P38 MAPK or phospholipase C (PLC). Furthermore, PLC inhibitor (U73122) inhibited ghrelin induced P38 MAPK activation. While PI3K inhibitor (LY294002) was without effect on cell survival or P38 MAPK activation, it inhibited ghrelin induced ERK1/2 phosphorylation. Finally, ghrelin induced TAU phosphorylation was reversed by pharmacologic inhibitors of either P38 MAPK or PKA. In conclusion, ghrelin activated harmful molecular pathways in podocytes that can be damaging to the glomerular filtration barrier SIGNIFICANCE OF THE STUDY: Endocrine derangements secondary to obesity are major players in the aetiology of renal injuries. Furthermore, energy dense diet is thought to be the major element in developing obesity. Appetite and increase in energy intake are regulated by complex hormonal pathways which mainly include the orexigenic hormone "ghrelin" in addition to leptin. To date no study have highlighted a significant role for ghrelin in kidney biology, and therefore, it is thought that its endocrine effect is mostly limited to adipose tissue metabolism and appetite regulation. In this study, we first showed that ghrelin receptor is expressed on glomerular podocytes. Also, ghrelin showed negative impact on podocyte survival through modulating signalling pathways such as P38 MAPK and AKT known to play a key role in podocyte health. Moreover, the negative effects of ghrelin on podocytes were further exacerbated in hyperglycemic conditions. Of note, podocytes contribute to the formation and the maintenance of the glomerular filtration barrier and thus are important for normal renal function. Therefore, ghrelin secretion in the context of obesity could be involved in the aetiology of kidney injury, a well-known hallmark found in obese patients.
足细胞损伤是肾小球疾病的一个关键事件。虽然高能量食物会导致肾脏损伤，但“ghrelin”这种生酮激素在足细胞生物学中的作用尚不清楚。在本研究中，我们研究了 ghrelin 对足细胞存活的影响，以及在永生化培养的大鼠足细胞中介导 ghrelin 作用的信号通路。RT-PCR 分析显示 GHS-R1 在大鼠足细胞中表达。Western blot 分析表明，ghrelin 以时间和剂量依赖的方式上调 COX-2 蛋白表达。此外，ghrelin 在高葡萄糖条件下激活 P38 MAPK、AKT 和 ERK1/2 通路，并诱导 P38 MAPK 磷酸化。Ghrelin 诱导 ROS 释放，并剂量依赖性地降低足细胞存活率。用药理学方法抑制 P38 MAPK 或磷脂酶 C（PLC）部分逆转了 ghrelin 介导的足细胞细胞死亡。此外，PLC 抑制剂（U73122）抑制了 ghrelin 诱导的 P38 MAPK 激活。虽然 PI3K 抑制剂（LY294002）对细胞存活或 P38 MAPK 激活没有影响，但它抑制了 ghrelin 诱导的 ERK1/2 磷酸化。最后，用 P38 MAPK 或 PKA 的药理学抑制剂逆转了 ghrelin 诱导的 TAU 磷酸化。总之，ghrelin 在足细胞中激活了有害的分子通路，这可能对肾小球滤过屏障造成损害。这项研究的意义：肥胖引起的内分泌失调是肾脏损伤的主要原因之一。此外，人们认为高能量饮食是导致肥胖的主要因素。食欲和能量摄入的增加是由复杂的激素途径调节的，这些途径主要包括食欲激素“ghrelin”以及瘦素。迄今为止，尚无研究表明 ghrelin 在肾脏生物学中具有重要作用，因此，人们认为其内分泌作用主要局限于脂肪组织代谢和食欲调节。在这项研究中，我们首先表明 ghrelin 受体在肾小球足细胞上表达。此外，ghrelin 通过调节 P38 MAPK 和 AKT 等信号通路对足细胞存活产生负面影响，这些信号通路在足细胞健康中发挥着关键作用。此外，ghrelin 对高血糖条件下的足细胞的负面影响进一步加剧。值得注意的是，足细胞有助于肾小球滤过屏障的形成和维持，因此对正常肾功能很重要。因此，肥胖患者中 ghrelin 的分泌可能与肾脏损伤的发病机制有关，这是肥胖患者的一个众所周知的特征。
