RRBP1透過調控腎素之胞內運輸調節血壓及鉀離子恆定

Abstract

RRBP1，又被稱為p180，是一種與內質網核糖體結合的蛋白。許多全基因組關聯分析的研究指出，RRBP1基因的變異與動脈硬化心血管疾病以及血液中的血脂蛋白含量有高度相關性。然而，關於RRBP1在調控心血管疾病中最重要的因素之一──「血壓」的角色，目前尚未被廣泛探討。本研究的主要目的在於釐清RRBP1在調控血壓以及在心血管生理上所扮演的角色。 首先，我們利用史丹佛亞洲及太平洋高血壓及胰島素阻抗計畫（Stanford Asia-Pacific Program for Hypertension and Insulin Resistance）中的世代研究資料庫，透過全基因組連鎖分析，發現RRBP1的基因變異與血壓有高度相關性。此外，我們進一步進行了Rrbp1基因剔除小鼠的實驗，結果顯示這些小鼠表現出低血壓並出現早發型未預期的猝死。透過血液生化檢測，我們發現Rrbp1基因剔除小鼠患有低腎素型低醛固酮血症（hyporeninemic hypoaldosteronism），且伴隨高血鉀（hyperkalemia）症候群。在高鉀離子飲食攝入的壓力下，Rrbp1基因剔除小鼠表現出嚴重的高血鉀誘發心律不整（arrhythmia），並顯著增加死亡率。然而，透過氟氫可體松（Fludrocortisone）的治療，可以有效降低Rrbp1基因剔除小鼠在高鉀離子飲食攝入後的血鉀濃度以及死亡率。 此外，利用免疫組織化學染色法標定腎臟切片中腎素發現在Rrbp1基因剔除小鼠之腎臟組織切片的腎素含量明顯高於野生型小鼠。相似的是，我們利用免疫金染色標定RRBP1基因敲弱（RRBP1-kcockdown）的人類腎素生產細胞株（Calu-6）之腎素發現RRBP1基因敲弱後，腎素大量累積在細胞內。同時，免疫螢光染色發現RRBP1基因敲弱後，影響了腎素從內質網運輸到高基氏體的效率。本研究發現RRBP1藉由影響腎素在細胞內的運輸調控生理血壓以及血鉀扮演重要的角色。

RRBP1, also known as ER ribosomal-binding protein 1 or p180, has been implicated in various cardiovascular diseases through genetic variants identified in numerous genome-wide association studies. However, the precise role of RRBP1 in the regulation of blood pressure remains undefined. In this study, we aimed to elucidate the impact of RRBP1 on blood pressure regulation and its role in cardiovascular physiology. In the Stanford Asia-Pacific Program for Hypertension and Insulin Resistance (SAPPHIRe) cohort, our research team conducted a genome-wide linkage analysis followed by regional fine mapping. This comprehensive approach enabled us to identify noteworthy genetic variants within the RRBP1 gene, demonstrating a significant association with blood pressure. To investigate the functional implications of RRBP1, we generated a transgenic mouse model. Rrbp1-knockout mice exhibited lower blood pressure and increased susceptibility to sudden cardiac death, which was attributed to hyporeninemic hypoaldosteronism-induced hyperkalemia. Significantly, when subjected to high potassium intake, Rrbp1-knockout mice exhibited a noteworthy decrease in survival rate compared to their wild-type counterparts. Remarkably, these Rrbp1-knockout mice displayed severe lethal arrhythmia induced by hyperkalemia and persistent hypoaldosteronism, particularly under conditions of elevated potassium intake. However, treatment with fludrocortisone effectively rescued these phenotypes. Immunohistochemistry analysis revealed the accumulation of renin within the kidneys of Rrbp1-knockout mice, indicating impaired renin-angiotensin-aldosterone system (RAAS) function. Furthermore, our investigations confirmed that renin predominantly accumulated within the endoplasmic reticulum (ER) and exhibited compromised transport to the Golgi apparatus in RRBP1-knockdown (-KD) Calu-6 cells. This impaired secretion of renin was substantiated through detailed examinations using transmission electron and confocal microscopy. In parallel, our human genetic studies revealed a significant association between RRBP1 genetic variants and blood pressure. Notably, consistent with the findings in our mouse model, mice lacking RRBP1 exhibited lower levels of plasma renin and aldosterone, resulting in reduced blood pressure, severe hyperkalemia, and cardiac sudden death. Collectively, our study provides novel insights into the role of RRBP1 as a modulator of the renin-angiotensin-aldosterone system (RAAS), affecting blood pressure regulation and potassium homeostasis.