一項新的研究發現，在耶魯首次發現的renalase蛋白，可以保護細胞免遭導致心髒病和腎衰竭的嚴重損傷。這項研究發現可能可以提供新的治療方法，以用來保護機體避免心髒病和腎衰竭。最近這項研究成果發表在PLOS ONE雜誌上。

　　一直以來，高血壓、中風和糖尿病呈高發趨勢，具有氧化還原活性的renalase的單核苷酸基因多態性，與這些疾病相關聯。Renalase的基因敲除可引起高血壓，加重急性腎缺血和心髒損傷。在野生型小鼠，不依賴於內源活性，細胞外的renalase活性就可以激活MAPK信號通路，避免急性腎損傷。因此，研究人員們希望能找到細胞外renalase的受體。

　　耶魯醫學院研究員，醫學教授Gary V. Desir博士，正在研究蛋白renalase的作用機製，這種蛋白在2005年首次在Desir的實驗室發現，他們將其命名為RP-220。通過在人近段腎小管細胞係HK-2上的生物素轉移實驗，和用質譜方法，他們鑒別出了這種蛋白的受體，一種名為PMCA4b的分子。研究人員利用免疫共沉澱和免疫共定位的方法，證實了renalase和PMCA4b的相互作用。他們還發現，renalase 和其受體PMCA4b相互作用，可以促進細胞存活。用SiRNA降低內源性的PMCA4b表達, 或者是用特異的抑製劑caloxin1b抑製renalase酶活性, 均可以減弱依賴於renalae活性的MAPK信號，從而降低細胞保護作用。但是，在對照組，表皮生長因子介導的信號不受影響，證明了PMCA4b和 renalase相互作用的特異性。

　　其他的研究已經證實，renalase有保護心髒和控製血壓的作用。通過發現renalse的受體和研究清楚它的作用機製，耶魯的研究人員可能將研發出新的治療靶點。這項研究有助於開發出新藥物，來保護腎髒和心髒，以避免這些髒器的缺血和毒性損傷。另外，他們將進一步研究renalase在癌症中的作用。

　　doi: 10.1371/journal.pone.0122932

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　　Identification of a Receptor for Extracellular Renalase

　　Ling Wang et.al

　　BACKGROUND:

　　An increased risk for developing essential hypertension, stroke and diabetes is associated with single nucleotide gene polymorphisms in renalase, a newly described secreted flavoprotein with oxidoreductase activity. Gene deletion causes hypertension, and aggravates acute ischemic kidney (AKI) and cardiac injury. Independent of its intrinsic enzymatic activities, extracellular renalase activates MAPK signaling and prevents acute kidney injury (AKI) in wild type (WT) mice. Therefore, we sought to identity the receptor for extracellular renalase.

　　METHODS AND RESULTS:

　　RP-220 is a previously identified, 20 amino acids long renalase peptide that is devoid of any intrinsic enzymatic activity, but it is equally effective as full-length recombinant renalase at protecting against toxic and ischemic injury. Using biotin transfer studies with RP-220 in the human proximal tubular cell line HK-2 and protein identification by mass spectrometry, we identified PMCA4b as a renalase binding protein. This previously characterized plasma membrane ATPase is involved in cell signaling and cardiac hypertrophy. Co-immunoprecipitation and co-immunolocalization confirmed protein-protein interaction between endogenous renalase and PMCA4b. Down-regulation of endogenous PMCA4b expression by siRNA transfection, or inhibition of its enzymatic activity by the specific peptide inhibitor caloxin1b each abrogated RP-220 dependent MAPK signaling and cytoprotection. In control studies, these maneuvers had no effect on epidermal growth factor mediated signaling, confirming specificity of the interaction between PMCA4b and renalase.

　　CONCLUSIONS:

　　PMCA4b functions as a renalase receptor, and a key mediator of renalase dependent MAPK signaling.