Transcriptomic analysis of Resp18mutant rat kidneys reveals up-regulation of Renin-Angiotensin system

Regulated endocrine specific protein 18 (Resp18), expression has been specifically located in a series of tissues and cell types however the exact cellular function is unknown. In previous studies we have showed that a targeted disruption of Resp18 in Dahl SS rats (Resp18mutant) resulted in higher blood pressure (BP), increased renal fibrosis, and decreased survival rate on a long term (6-week) 2% high salt (HS) diet treatment compared with wild type SS rats. In the current study we studied whether a short term (1 week) exposure to HS diet shows a similar effect in Resp18mutant rats. Furthermore, previously we have shown that in addition to BP phenotype Resp18mutant rats have demonstrated deteriorative kidney phenotype evident through renal fibrosis, protein urea and protein cast formation. Based on this background we conducted BP study and performed transcriptomic profiling of the kidney after one-week exposure to HS diet treatment. Through radio-telemetry procedure, we found that the systolic BP was increased in the Resp18mutant rats compared with SS rats even with short term HS diet exposure. Therefore, we sought out to investigate if there was any alteration in the transcriptomic response by HS diet treatment in the Resp18mutant rat kidneys. Using RNA sequencing approach, we found that Resp18mutant rats showed a differential expression of 25 genes of which one was an upregulation of Ren. We confirmed the upregulation of Ren and other differentially expressed genes via qRT-PCR analysis. Upon KEGG pathway enrichment we found that the Resp18mutant rat showed upregulation in the renin angiotensin system (RAAS), and renin secretion pathway. Furthermore, the renin activity is found to be higher in Resp18mutant rats serum compared with SS rats. Therefore, these observations demonstrate that upon disruption of Resp18 gene in SS rats associated with the increase in renin secretion and thus increase BP.调节性内分泌特异性蛋白18（Resp18）的表达已被特异性定位于多种组织与细胞类型，但其确切的细胞功能尚未明确。既往研究表明，在达尔SS（Dahl SS）大鼠中靶向敲除Resp18基因（构建Resp18突变型大鼠，Resp18mutant），与野生型SS大鼠相比，在长期（6周）2%高盐（HS）饮食干预后，该突变大鼠可出现血压升高、肾纤维化加重以及生存率降低的表型。本研究旨在探讨短期（1周）高盐饮食暴露是否会在Resp18突变型大鼠中引发类似效应。此外，既往研究还证实，除血压表型异常外，Resp18突变型大鼠可出现肾纤维化、蛋白尿及蛋白管型形成所提示的肾脏功能恶化表型。基于上述研究背景，本团队开展了血压检测，并对接受1周高盐饮食干预的大鼠肾脏进行了转录组分析。通过无线电遥测技术，我们发现即便在短期高盐饮食暴露下，Resp18突变型大鼠的收缩压仍显著高于SS大鼠。据此，我们进一步探究了高盐饮食干预下，Resp18突变型大鼠肾脏的转录组应答是否存在异常。采用RNA测序技术，我们发现Resp18mutant大鼠存在25个差异表达基因，其中肾素（Ren）基因表达上调。我们通过qRT-PCR验证了Ren基因及其他差异表达基因的表达变化。经KEGG通路富集分析，我们发现Resp18mutant大鼠的肾素-血管紧张素系统（RAAS）及肾素分泌通路出现显著上调。此外，Resp18mutant大鼠血清中的肾素活性亦高于SS大鼠。综上，上述结果表明，在SS大鼠中敲除Resp18基因可促进肾素分泌，进而导致血压升高。