New Insights into Juxtaglomerular Cells via Single‐Cell RNA‐Sequencing
Authors: Wei Jin , Zhang Jie , Chan Jenna , Thalakola Anish , Patel Kshama , Yadav Nikita , Wang Lei , Buggs Jacentha , Liu Ruisheng 
Published: May 2022

The regulation of renin release from juxtaglomerular (JG) cells at the systemic or local level has been extensively investigated and well understood. It includes three primary mechanisms: intrarenal baroreceptor, salt feedback via macula densa, and β1‐adrenergic receptor activation. However, further understanding of the control of renin synthesis and secretion in JG cells at the cellular or molecular level is limited. Additionally, JG cells are generally considered to be derived from the smooth muscle (SM) cells in the afferent arterioles via a reversible metaplastic transformation. The number of JG cells could be significantly increased under specific conditions, which is also known as the process of JG cells recruitment. Nevertheless, the similarities and differences at the molecular level between JG cells and SM cells as well as the intracellular mechanisms underlying the JG cells recruitment have not been fully clarified. An emerging technique, the single‐cell RNA sequencing, provides a new tool to precisely investigate the molecular characterization of JG cells. In the present study, we isolated and sequenced a total of 9815 cells from a single‐cell stock derived from the renal cortex of C57BL/6J mice (~20 mg cortical tissue per mouse, n=5). Using stringent quality controls, we further analyzed 7557 cells. Unbiased clustering analysis demonstrated 16 distinct cell clusters in the t‐distributed stochastic neighbor embedding (tSNE) map, and each cell cluster was defined based on the expression level of the representative cell type‐specific marker genes. In particular, a cluster consisting of 284 cells was identified as smooth muscle (SM) cells by the high and distinct expression of both Acta2 (α‐smooth muscle actin) and Tagln (Transgelin). Moreover, on the basis of the expression level of the marker gene Ren1 (Renin), 34 JG cells were further distinguished from this cluster of SM cells. We profiled the whole‐transcriptome of these JG cells and correlated it with the transcriptional level of Ren1. The top 5 genes that were most positively correlated with the Ren1 expression were Nr2f1 (R=0.79), Akr1b7 (R=0.68), Smim15 (R=0.64), Gng11 (R=0.60) and Sdc1 (R=0.59). We also compared the whole‐transcriptome between these JG cells and SM cells. The top 5 genes with the largest difference in the normalized transcript count were Ren1 (+4.28), Akr1b7 (+1.53), Sfrp2 (+1.01), Fam46a (+0.88), and Sdc1 (+0.75). Thus, aldo‐keto reductase 1B7 (Akr1b7) and syndecan‐1 (Sdc1) could be two potential candidates that may participate in the control of renin release from JG cells. However, previous studies using the Akr1b7‐deficient mice have shown that aldo‐keto reductase 1B7 is not of major relevance for the modulation of renin production and secretion. Therefore, we speculate that syndecan‐1 (Sdc1), a transmembrane heparan sulfate proteoglycan, may play a role in the regulation of renin release as well as JG cells recruitment, especially through the mechanism of intrarenal baroreceptor. This hypothesis will be tested with the Sdc1‐deficient mouse model in our future studies.