Wu Zhenzhen, Blessing Natalya A, Simske Jeffrey S, Bruggeman Leslie A
Department of Medicine and Rammelkamp Center for Education and Research, MetroHealth Medical Center, Case Western Reserve University School of Medicine, Cleveland, Ohio.
Physiol Rep. 2017 Dec;5(23). doi: 10.14814/phy2.13483.
The renal podocyte is central to the filtration function of the kidney that is dependent on maintaining both highly organized, branched cell structures forming foot processes, and a unique cell-cell junction, the slit diaphragm. Our recent studies investigating the developmental formation of the slit diaphragm identified a novel claudin family tetraspannin, TM4SF10, which is a binding partner for ADAP (also known as Fyn binding protein Fyb). To investigate the role of ADAP in podocyte function in relation to Fyn and TM4SF10, we examined ADAP knockout (KO) mice and podocytes. ADAP KO mice developed glomerular pathology that began as hyalinosis and progressed to glomerulosclerosis, with aged male animals developing low levels of albuminuria. Podocyte cell lines established from the KO mice had slower attachment kinetics compared to wild-type cells, although this did not affect the total number of attached cells nor the ability to form focal contacts. After attachment, the ADAP KO cells did not attain typical podocyte morphology, lacking the elaborate cell protrusions typical of wild-type podocytes, with the actin cytoskeleton forming circumferential stress fibers. The absence of ADAP did not alter Fyn levels nor were there differences between KO and wild-type podocytes in the reduction of Fyn activating phosphorylation events with puromycin aminonucleoside treatment. In the setting of endogenous TM4SF10 overexpression, the absence of ADAP altered the formation of cell-cell contacts containing TM4SF10. These studies suggest ADAP does not alter Fyn activity in podocytes, but appears to mediate downstream effects of Fyn controlled by TM4SF10 involving actin cytoskeleton organization.
肾足细胞对于肾脏的滤过功能至关重要，这依赖于维持高度有序的分支细胞结构（形成足突）以及一种独特的细胞间连接——裂孔隔膜。我们最近关于裂孔隔膜发育形成的研究鉴定出一种新的紧密连接蛋白家族四跨膜蛋白TM4SF10，它是ADAP（也称为Fyn结合蛋白Fyb）的结合伴侣。为了研究ADAP在与Fyn和TM4SF10相关的足细胞功能中的作用，我们检测了ADAP基因敲除（KO）小鼠和足细胞。ADAP KO小鼠出现肾小球病变，最初表现为玻璃样变，随后进展为肾小球硬化，老年雄性动物出现低水平蛋白尿。与野生型细胞相比，从KO小鼠建立的足细胞系具有较慢的附着动力学，尽管这并不影响附着细胞的总数以及形成粘着斑的能力。附着后，ADAP KO细胞未获得典型的足细胞形态，缺乏野生型足细胞典型的精细细胞突起，肌动蛋白细胞骨架形成周向应力纤维。ADAP的缺失并未改变Fyn水平，在用嘌呤霉素氨基核苷处理后，KO和野生型足细胞在Fyn激活磷酸化事件的减少方面也没有差异。在内源性TM4SF10过表达的情况下，ADAP的缺失改变了含有TM4SF10的细胞间接触的形成。这些研究表明，ADAP不会改变足细胞中的Fyn活性，但似乎介导了由TM4SF10控制的Fyn的下游效应，涉及肌动蛋白细胞骨架组织。
