Department of Internal Medicine, University of Iowa, Iowa City, IA 52242, USA.
Am J Physiol Cell Physiol. 2010 Jun;298(6):C1388-400. doi: 10.1152/ajpcell.00272.2009. Epub 2010 Mar 10.
Recessive inheritance of mutations in ceroid neuronal lipofuscinosis type 3 (CLN3) results in juvenile neuronal ceroid lipofuscinosis (JNCL), a childhood neurodegenerative disease with symptoms including loss of vision, seizures, and motor and mental decline. CLN3p is a transmembrane protein with undefined function. Using a Cln3 reporter mouse harboring a nuclear-localized bacterial beta-galactosidase (beta-Gal) gene driven by the native Cln3 promoter, we detected beta-Gal most prominently in epithelial cells of skin, colon, lung, and kidney. In the kidney, beta-Gal-positive nuclei were predominant in medullary collecting duct principal cells, with increased expression along the medullary osmotic gradient. Quantification of Cln3 transcript levels from kidneys of wild-type (Cln3(+/+)) mice corroborated this expression gradient. Reporter mouse-derived renal epithelial cultures demonstrated a tonicity-dependent increase in beta-Gal expression. RT-quantitative PCR determination of Cln3 transcript levels further supported osmoregulation at the Cln3 locus. In vivo, osmoresponsiveness of Cln3 was demonstrated by reduction of medullary Cln3 transcript abundance after furosemide administration. Primary cultures of epithelial cells of the inner medulla from Cln3(lacZ/lacZ) (CLN3p-null) mice showed no defect in osmolyte accumulation or taurine flux, arguing against a requirement for CLN3p in osmolyte import or synthesis. CLN3p-deficient mice with free access to water showed a mild urine-concentrating defect but, upon water deprivation, were able to concentrate their urine normally. Unexpectedly, we found that CLN3p-deficient mice were hyperkalemic and had a low fractional excretion of K(+). Together, these findings suggest an osmoregulated role for CLN3p in renal control of water and K(+) balance.
CLN3 基因突变呈隐性遗传导致少年神经元蜡样质脂褐质沉积症（JNCL），这是一种儿童神经退行性疾病，其症状包括视力丧失、癫痫发作、运动和智力下降。CLN3p 是一种具有未知功能的跨膜蛋白。使用携带由天然 Cln3 启动子驱动的核定位细菌β-半乳糖苷酶（β-Gal）基因的 Cln3 报告小鼠，我们在皮肤、结肠、肺和肾脏的上皮细胞中最显著地检测到β-Gal。在肾脏中，β-Gal 阳性核主要存在于髓质集合管主细胞中，并且在髓质渗透梯度上表达增加。从野生型（Cln3(+/+)）小鼠肾脏中 Cln3 转录物水平的定量证实了这种表达梯度。报告小鼠衍生的肾脏上皮细胞培养物显示出与渗透压依赖性的β-Gal 表达增加。RT-定量 PCR 测定 Cln3 转录物水平进一步支持 Cln3 基因座的渗透压调节。在体内，呋塞米给药后髓质 Cln3 转录物丰度减少证明了 Cln3 的渗透压反应性。从 Cln3(lacZ/lacZ)（CLN3p 缺失）小鼠的内髓质上皮细胞的原代培养物中，没有观察到渗透溶质积累或牛磺酸通量的缺陷，这表明 CLN3p 不是渗透溶质摄取或合成所必需的。具有自由水摄入的 CLN3p 缺陷型小鼠表现出轻度的尿液浓缩缺陷，但在剥夺水后，能够正常浓缩尿液。出乎意料的是，我们发现 CLN3p 缺陷型小鼠高钾血症和钾（K+）排泄分数低。这些发现表明 CLN3p 在肾脏水和 K+平衡的渗透压调节中发挥作用。
