Kopperud R K, Rygh C Brekke, Karlsen T V, Krakstad C, Kleppe R, Hoivik E A, Bakke M, Tenstad O, Selheim F, Lidén Å, Madsen L, Pavlin T, Taxt T, Kristiansen K, Curry F-R E, Reed R K, Døskeland S O
Department of Biomedicine, University of Bergen, Bergen, Norway.
Centre for Cancer Biomarkers (CCBIO), University of Bergen, Bergen, Norway.
Acta Physiol (Oxf). 2017 Feb;219(2):441-452. doi: 10.1111/apha.12697. Epub 2016 May 17.
Maintenance of the blood and extracellular volume requires tight control of endothelial macromolecule permeability, which is regulated by cAMP signalling. This study probes the role of the cAMP mediators rap guanine nucleotide exchange factor 3 and 4 (Epac1 and Epac2) for in vivo control of microvascular macromolecule permeability under basal conditions.
Epac1 and Epac2 C57BL/6J mice were produced and compared with wild-type mice for transvascular flux of radio-labelled albumin in skin, adipose tissue, intestine, heart and skeletal muscle. The transvascular leakage was also studied by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) using the MRI contrast agent Gadomer-17 as probe.
Epac1 mice had constitutively increased transvascular macromolecule transport, indicating Epac1-dependent restriction of baseline permeability. In addition, Epac1 mice showed little or no enhancement of vascular permeability in response to atrial natriuretic peptide (ANP), whether probed with labelled albumin or Gadomer-17. Epac2 and wild-type mice had similar basal and ANP-stimulated clearances. Ultrastructure analysis revealed that Epac1 microvascular interendothelial junctions had constitutively less junctional complex.
Epac1 exerts a tonic inhibition of in vivo basal microvascular permeability. The loss of this tonic action increases baseline permeability, presumably by reducing the interendothelial permeability resistance. Part of the action of ANP to increase permeability in wild-type microvessels may involve inhibition of the basal Epac1-dependent activity.
维持血液和细胞外液量需要严格控制内皮大分子通透性，而这是由环磷酸腺苷（cAMP）信号传导调节的。本研究探讨了cAMP介质 Rap 鸟嘌呤核苷酸交换因子3和4（Epac1和Epac2）在基础条件下对体内微血管大分子通透性的控制作用。
制备Epac1和Epac2基因敲除的C57BL/6J小鼠，并与野生型小鼠比较放射性标记白蛋白在皮肤、脂肪组织、肠道、心脏和骨骼肌中的跨血管通量。还使用磁共振成像造影剂Gadomer-17作为探针，通过动态对比增强磁共振成像（DCE-MRI）研究跨血管渗漏情况。
Epac1基因敲除小鼠的跨血管大分子转运持续增加，表明Epac1对基线通透性有依赖性限制作用。此外，无论用标记白蛋白还是Gadomer-17检测，Epac1基因敲除小鼠对心房利钠肽（ANP）刺激的血管通透性增强作用很小或无增强。Epac2基因敲除小鼠和野生型小鼠的基础清除率及ANP刺激后的清除率相似。超微结构分析显示，Epac1基因敲除小鼠的微血管内皮细胞间连接的连接复合体持续减少。
Epac1对体内基础微血管通透性发挥持续性抑制作用。这种持续性作用的丧失会增加基线通透性，可能是通过降低内皮细胞间的通透性阻力实现的。ANP增加野生型微血管通透性的部分作用可能涉及对基础Epac1依赖性活性的抑制。
