Miyazaki Masao, Yamashita Tetsuro, Hosokawa Masakiyo, Taira Hideharu, Suzuki Akemi
Sphingolipid Expression Laboratory, Supra-Biomolecular System Group, Frontier Research System, The Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan.
Comp Biochem Physiol B Biochem Mol Biol. 2006 Nov-Dec;145(3-4):270-7. doi: 10.1016/j.cbpb.2006.05.015. Epub 2006 Aug 25.
Domestic cats exhibit physiological proteinuria due to the excretion of cauxin, a carboxylesterase, into the urine. In the present report, we demonstrate that cauxin is excreted in a species-, sex-, and age-dependent manner. Although the cauxin gene is conserved in mammals, including human, mouse, and dog, urinary cauxin was found only in member of the genus Felis and lynx (bobcat, and lynx) and not in other Felidae (genus: Panthera and puma) tested. In mature cats, cauxin excretion was higher in intact males than in castrated males or in intact or spayed females. Daily cauxin excretion decreased immediately after castration. Immunohistochemistry confirmed that cauxin expression in the kidney proximal straight tubules was higher in intact males than in castrated males. Urinary cauxin was detectable by Western blotting in cats older than about 3 months, and its excretion increased with age. In a zymographic esterase assay, urine contained a major cauxin band; by contrast, kidney homogenates contained three major bands, comprising two carboxylesterases and an unidentified esterase, and one minor cauxin band. These results suggest that 1. cauxin excretion is regulated by sex hormones, such as testosterone, 2. cauxin functions as an esterase in the urine rather than in kidney cells, and 3. the decomposition products by cauxin are excreted in a species-, sex-, and age-dependent manner, as is cauxin itself.
家猫会因一种羧酸酯酶——考辛排入尿液而出现生理性蛋白尿。在本报告中，我们证明考辛的排泄具有物种、性别和年龄依赖性。尽管考辛基因在包括人类、小鼠和狗在内的哺乳动物中是保守的，但仅在猫属和猞猁属（短尾猫和猞猁）的成员中发现了尿考辛，而在测试的其他猫科动物（豹属和美洲狮属）中未发现。在成年猫中，未阉割雄性的考辛排泄量高于阉割雄性或未阉割或已绝育的雌性。阉割后考辛的日排泄量立即下降。免疫组织化学证实，未阉割雄性肾脏近端直管中的考辛表达高于阉割雄性。约3个月以上的猫通过蛋白质印迹法可检测到尿考辛，其排泄量随年龄增加。在酶谱酯酶测定中，尿液中有一条主要的考辛带；相比之下，肾脏匀浆中有三条主要带，包括两种羧酸酯酶和一种未鉴定的酯酶，以及一条次要的考辛带。这些结果表明：1. 考辛的排泄受睾酮等性激素调节；2. 考辛在尿液中而非肾细胞中起酯酶作用；3. 考辛的分解产物与考辛本身一样，以物种、性别和年龄依赖性方式排泄。
