Gallazzini Morgan, Ferraris Joan D, Burg Maurice B
Laboratory of Kidney and Electrolyte Metabolism, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20982, USA.
Proc Natl Acad Sci U S A. 2008 Aug 5;105(31):11026-31. doi: 10.1073/pnas.0805496105. Epub 2008 Jul 30.
Glycerophosphocholine (GPC) is an abundant osmoprotective renal medullary organic osmolyte. We previously found that its synthesis from phosphatidylcholine is catalyzed by tonicity-regulated activity of the phospholipase B, neuropathy target esterase. We also found that its degradation is catalyzed by glycerophosphocholine phosphodiesterase (GPC-PDE) activity and that elevating osmolality from 300 to 500 mosmol/kg by adding NaCl or urea, inhibits GPC-PDE activity, which contributes to the resultant increase of GPC. In the present studies we identify GDPD5 (glycerophosphodiester phosphodiesterase domain containing 5) as a GPC-PDE that is rapidly inhibited by high NaCl or urea. Recombinant GDPD5 colocalizes with neuropathy target esterase in the perinuclear region of HEK293 cells, and immuno-precipitated recombinant GDPD5 degrades GPC in vitro. The in vitro activity is reduced when the cells from which the GDPD5 is immuno-precipitated have been exposed to high NaCl or urea. In addition, high NaCl decreases mRNA abundance of GDPD5 via an increase of its degradation rate, although high urea does not. At 300 mosmol/kg siRNA knockdown of GDPD5 increases GPC in mouse inner medullary collecting duct-3 cells, and over expression of recombinant GDPD5 increases cellular GPC-PDE activity, accompanied by decreased GPC. We conclude that GDPD5 is a GPC-PDE that contributes to osmotic regulation of cellular GPC.
甘油磷酸胆碱（GPC）是肾髓质中一种丰富的具有渗透保护作用的有机渗透质。我们之前发现，磷脂酶B（神经病变靶向酯酶）的张力调节活性可催化其从磷脂酰胆碱合成。我们还发现，其降解由甘油磷酸胆碱磷酸二酯酶（GPC-PDE）活性催化，并且通过添加氯化钠或尿素将渗透压从300 mosmol/kg提高到500 mosmol/kg会抑制GPC-PDE活性，这导致了GPC的相应增加。在本研究中，我们鉴定出GDPD5（含甘油磷酸二酯磷酸二酯酶结构域5）是一种可被高浓度氯化钠或尿素快速抑制的GPC-PDE。重组GDPD5与神经病变靶向酯酶在HEK293细胞的核周区域共定位，免疫沉淀的重组GDPD5在体外可降解GPC。当免疫沉淀GDPD5的细胞暴露于高浓度氯化钠或尿素时，其体外活性会降低。此外，高浓度氯化钠通过增加其降解速率降低了GDPD5的mRNA丰度，而高浓度尿素则不会。在300 mosmol/kg时，敲低小鼠髓质内集合管-3细胞中的GDPD5可增加GPC，而过表达重组GDPD5可增加细胞GPC-PDE活性，并伴随GPC减少。我们得出结论，GDPD5是一种GPC-PDE，有助于细胞GPC的渗透调节。
