兔肾皮质磷脂酶A2活性的成熟变化。

Maturational changes in rabbit renal cortical phospholipase A2 activity.

作者信息

Sheu J N, Baum M, Harkins E W, Quigley R

机构信息

Department of Pediatrics, University of Texas Southwestern Medical Center at Dallas, USA.

出版信息

Kidney Int. 1997 Jul;52(1):71-8. doi: 10.1038/ki.1997.305.

DOI:10.1038/ki.1997.305

PMID:9211348

Abstract

Several studies have demonstrated that the neonatal kidney has a markedly attenuated response to parathyroid hormone (PTH); however, the cause for this blunted response is unknown. PTH stimulated cAMP production by 215 +/- 18% in neonatal proximal tubule suspensions compared to a 35 +/- 7% increase in adult proximal tubules. Thus, neonatal proximal tubules have functioning PTH receptors and a greater adenylate cyclase response than the adult segment. In adult proximal tubules, PTH stimulates phospholipase A2 (PLA2) activity and the inhibition of Na,K-ATPase activity by PTH is blocked by inhibitors of PLA2. We examined whether maturational changes in renal cortical activity could play a role in the attenuated response to PTH in the neonatal proximal tubule. Compared to adults, neonates had a lower renal cortical cytosolic PLA2 (cPLA2) activity, assessed as the release of 14C-arachidonic acid (AA) from labeled phosphatidyl choline (0.44 +/- 0.10 vs. 0.74 +/- 0.06% 14C-AA released/min/mg protein, P < 0.05) and microsomal PLA2 activity (0.32 +/- 0.03 vs. 1.20 +/- 0.13% 14C-AA released/min/mg protein, P < 0.001). The protein abundance of cPLA2 was not different between the neonatal and adult renal cortex as assessed by immunoblot assay. Thus, the difference in activities must be due to a difference in regulation of cPLA2. Annexin 1 (lipocortin 1) has been shown to inhibit PLA2 activity by binding to phospholipid substrate. Annexin 1 protein abundance was higher in neonatal than in adult renal cortex (P < 0.001). Thus, the lower activity of PLA2 in the neonatal tubules may be due in part to higher expression of annexin 1. PLA2 activation by PTH, -8-bromo-cAMP and PMA was assessed as 3H-AA release from prelabeled suspensions of neonatal and adult proximal tubules. PTH (10(-7) M), 8-bromo-cAMP (10(-4) M) and PMA (5 x 10(-8) M) significantly increased 3H-AA release from adult tubules (P < 0.05) but had no effect on neonatal tubules (P = NS). Thus, PTH, 8-bromo-cAMP and PMA stimulated PLA2 in adult but not neonatal proximal tubules. In conclusion, the maturational changes in renal cortical PLA2 activity may be a factor in the blunted response of neonatal proximal tubules to PTH.

摘要

多项研究表明，新生儿肾脏对甲状旁腺激素（PTH）的反应明显减弱；然而，这种反应迟钝的原因尚不清楚。与成人近端小管中增加35±7%相比，PTH使新生儿近端小管悬浮液中的cAMP生成增加了215±18%。因此，新生儿近端小管具有功能性PTH受体，且腺苷酸环化酶反应比成人节段更强。在成人近端小管中，PTH刺激磷脂酶A2（PLA2）活性，且PTH对Na,K-ATP酶活性的抑制作用被PLA2抑制剂阻断。我们研究了肾皮质活性的成熟变化是否可能在新生儿近端小管对PTH的反应减弱中起作用。与成人相比，新生儿肾皮质胞质PLA2（cPLA2）活性较低，以从标记的磷脂酰胆碱中释放14C-花生四烯酸（AA）来评估（每分钟每毫克蛋白质释放的14C-AA为0.44±0.10对0.74±0.06%，P<0.05），微粒体PLA2活性也较低（每分钟每毫克蛋白质释放的14C-AA为0.32±0.03对1.20±0.13%，P<0.001）。通过免疫印迹分析评估，新生儿和成人肾皮质中cPLA2的蛋白质丰度没有差异。因此，活性差异一定是由于cPLA2调节的差异。膜联蛋白1（脂皮质素1）已被证明通过与磷脂底物结合来抑制PLA2活性。新生儿肾皮质中膜联蛋白1的蛋白质丰度高于成人（P<0.001）。因此，新生儿小管中PLA2活性较低可能部分归因于膜联蛋白1的高表达。通过评估从新生儿和成人近端小管预标记悬浮液中释放的3H-AA来检测PTH、-8-溴-cAMP和佛波酯（PMA）对PLA2的激活作用。PTH（10^-7 M）、8-溴-cAMP（10^-4 M）和PMA（5×10^-8 M）显著增加了成人小管中3H-AA的释放（P<0.05），但对新生儿小管没有影响（P=无显著性差异）。因此，PTH、8-溴-cAMP和PMA刺激了成人而非新生儿近端小管中的PLA2。总之，肾皮质PLA2活性的成熟变化可能是新生儿近端小管对PTH反应迟钝的一个因素。