Determinants of renin cell differentiation: a single cell epi-transcriptomics approach

Rationale

Renin cells are essential for survival. They control the morphogenesis of the kidney arterioles, and the composition and volume of our extracellular fluid, arterial blood pressure, tissue perfusion, and oxygen delivery. It is known that renin cells and associated arteriolar cells descend from FoxD1 + progenitor cells, yet renin cells remain challenging to study due in no small part to their rarity within the kidney. As such, the molecular mechanisms underlying the differentiation and maintenance of these cells remain insufficiently understood.

Objective

We sought to comprehensively evaluate the chromatin states and transcription factors (TFs) that drive the differentiation of FoxD1 + progenitor cells into those that compose the kidney vasculature with a focus on renin cells.

Methods and Results

We isolated single nuclei of FoxD1 + progenitor cells and their descendants from FoxD1 ^cre/+ ; R26R-mTmG mice at embryonic day 12 (E12) (n _cells =1234), embryonic day 18 (E18) (n _cells =3696), postnatal day 5 (P5) (n _cells =1986), and postnatal day 30 (P30) (n _cells =1196). Using integrated scRNA-seq and scATAC-seq we established the developmental trajectory that leads to the mosaic of cells that compose the kidney arterioles, and specifically identified the factors that determine the elusive, myo-endocrine adult renin-secreting juxtaglomerular (JG) cell. We confirm the role of Nfix in JG cell development and renin expression, and identified the myocyte enhancer factor-2 (MEF2) family of TFs as putative drivers of JG cell differentiation.

Conclusions

We provide the first developmental trajectory of renin cell differentiation as they become JG cells in a single-cell atlas of kidney vascular open chromatin and highlighted novel factors important for their stage-specific differentiation. This improved understanding of the regulatory landscape of renin expressing JG cells is necessary to better learn the control and function of this rare cell population as overactivation or aberrant activity of the RAS is a key factor in cardiovascular and kidney pathologies.

Abstract P113: SOX6 IS NOT A RELEVANT TRANSCRIPTION FACTOR FOR RENIN TRANSCRIPTIONAL REGULATION BY JUXTAGLOMERUALR CELLS

The SRY (sex determining region Y)-box 6, Sox6 , encodes a member of trancription factors (TFs) crucial for organogenesis. It has been suggested that Sox6 is essential for the Renin transcriptional regulation. However, we identified Sox6 expression only in tubular cells. We aim to investigate whether Sox6 contributes to Renin gene expression by the Juxtaglomerular Cells in normal and under stress. Therefore, we generated Ren1 d -Cre;Sox6 -/- mice, where cells expressing Renin lacks the Sox6 gene. We randomized the mice into four groups (n= 6/group): Wild-type (WT) and mutants ( Sox6 cKO) exposed to either regular salt diet or low salt diet and captopril (0.5 mg/mL in water ad libitum for 8 days). The later condition decreases blood pressure and increases Renin transcription and exocytosis. We measured the blood pressure by direct carotid artery catheterization. There were no differences between WT and cKO in mean blood, systolic or diastolic pressures. ELISA assay measured the plasmatic Renin content, without significance in any group (WT: 126775 pg/mL ± 59035; cKO: 200008 pg/mL ± 68556; n=3). In sytu hybridization ( ISH ) for Sox6 has never been visible in the kidney despite all optimizations. Renin ISH had usual distribution in the Juxtaglomerular Apparatus (JGA; n=6). In the captopril treated groups, Renin intensity was higher and no differences were noted. Immunohistochemistry for Renin also reavealed no differences between WT and cKO. Yet, the renin+ cells extended along the afferent arterioles in the captopril treated groups. We calculated the Juxtaglomerular Index, which is the total number of renin+ JGA divided by all glomeruli. WT showed 156 renin+ JGA of 441 glomeruli (n=3), while the cKO exhibited 173 of 449 glomeruli (n=3). In the captopril groups, WT had 302 of 452 glomeruli (n=3), while the ckO exhibited a subtle decrease, 176 of 312 glomeruli (n=4), but without significance. Quantitative RT-PCR from the kidneys showed an increase in the relative R enin gene expression to s14 in cKO group (WT: 1.2 ± 0.8; cKO: 2.1 ± 2.2; n=3), while Sox6 relative gene expression to s14 decreased (WT: 1.02 ± 0.27; cKO: 0.35 ± 0.2; n=3). We conclude that Sox6 is not an important TF for Renin transcriptional regulation by JuxtaGlomerular Cells in neither normal nor stressed conditions.

Abstract 072: Distinct And Evolving Chromatin States And Transcription Factors Determine The Development Of The Kidney Vasculature

Differentiation of cells that compose the kidney arterioles is crucial for the formation of a functioning kidney. A group of stromal cells expressing the Forkhead Box D1 ( FoxD1 ) transcription factor (TF) will give rise to the metanephric progenitors for the mural cells of the kidneys arteries and arterioles. We investigated the molecular mechanisms that instruct the FoxD1 progenitors to adopt different cell fates to properly assemble the developing kidney vasculature. We generated FoxD1GC;R26R mT/mG mice, where all the FoxD1 descendant’s cells are labeled with green fluorescent protein (GFP). GFP+ cells were isolated by FACS from kidney cortices and performed either single-cell RNA-Seq (scRNA-Seq) or single-cell Assay for Transposase-Accessible Chromatin (scATAC-Seq ) at different developmental ages: embryos (E12 and E18) and post-natal (P5 and P30) . The integrative analysis of scRNA-Seq and scATAC-Seq identified the FoxD1 derivative cell populations and their respective accessible chromatin areas over the developmental pathway. Motif analysis revealed the binding sites to putative TFs repertoire for each of the FoxD1 descendants. Therefore, we generated differentiation trajectories to track the transcriptome and epigenetics changes that occur along the differentiation pathway. At E12, the FoxD1 progenitor cells harbor open chromatin to bind TFs such as Zeb1, Maz, Snai2 and Pbx1 (p_adjusted_value (padj).: 6.7E-40; 3.6E-40; 4.1E-28; 2.5E-5; respectively) . The gene expression levels of these TFs were also significant (padj.: 5.7E-68; 6.2E-53; 4.4E-49; 2.6E-47, respectively ) . All these TFs are strongly correlated to embryogenesis. As development progresses, new open chromatin areas emerge within a different transcriptome. Interestingly, from E18 ahead, all the FoxD1 decendants exhibited the Mef2 family of TFs as the highest enriched motifs. At P30, among all the FoxD1 decendants, the Juxtaglomerular Cells have the highest enrichment score for all the Mef2 family members (padj.: 0). Thus, as the cells differentiate they acquire distinct chromatin landscapes and TF repertoires. In addition to these unique landscapes Mef2 family of TFs are prominent for the FoxD1 descendants differentiation and kidney vascular development.

Abstract 011: Epigenetic Determinants Of Renin Cell Identity

Renin secreting cells are restricted in adult mammals within the walls of renal arterioles near the entrance to the glomeruli and are therefore known as juxtaglomerular (JG) cells. These JG cells are critical for survival through the maintenance of homeostasis via the release of the peptide hormone renin in response to changes in blood pressure. By performing independently paired scATAC-seq and scRNA-seq during mouse kidney development, we sought to identify epigenetic markers of renin cell identity. While we lack spatial information, we identified putative JG cells through the identification of cells enriched in canonical markers (Ren1 and Akr1b7) of JG cell identity using both expression and accessibility derived measures of gene activity. We constructed a pseudotime trajectory of cells that lead to the mature JG population and performed pairwise comparisons of cell populations to identify the genomic regions and transcription factors (TFs) contributing to JG cell identity. As JG cells form along this trajectory, significantly different (Log2FC>0.5 and FDR<0.1) regions of accessible chromatin define the JG cell population. Within these open regions, the MEF2 family of TF motifs are significantly enriched (log10Padj > 20). We further identify a specific region of accessible chromatin (chr1:133345385-133345885) unique to the initial population of JG cells located within a Ren1 super enhancer previously identified by our group. This region is co-accessible with several regions of open chromatin within the greater Ren1 gene region (correlation > 0.75) where we identify putative binding sites for Mef2b, 2c, and 2d at these co-accessible regions. As the mature renin-expressing cells further differentiate into terminally differentiated cell populations including pericytes and mesangial cells, we continue to see significant enrichment of the MEF2 TF family within the JG cell population compared to downstream populations (log10Padj > 646.6891). Overall, we have presented the first investigation and finding using single-cell -omics of the JG cell population and uncover the importance of the MEF2 family of TFs as significant drivers of JG cell formation and identity.

Abstract P116: Specific Chromatin Configurations Across The Genome Determine The Renin Cell Identity

Renin cell descendants, such as smooth muscle cells, regain the endocrine renin phenotype to overcome homeostatic threats. The mechanism involved and the determinants of the renin cell identity are not well understood. We hypothesize that renin cell identity is governed by specific chromatin domain configurations genome wide. We compared open chromatin regions between renin- and non-renin-expressing cells. Non-renin control ATAC-seq data were mainly from ENCODE, containing 178 samples of 26 cell types. The differential analyses with DESeq2 between three renin groups (renin-expressing tumoral cell lines, native and recruited renin cells) and non-renin control group revealed that the chromatin configurations are different between the tumoral cell line and the primary kidney cells (native and recruited) in 1) number of differential regions (22,321 increased accessibility regions in the tumoral cell lines and 3,964 in the primary kidney renin cells); 2) enriched GO terms, and 3) distribution pattern over the genome. Within a small proportion of overlapped differential accessibility regions, all three groups have accessibility regions associated with known renin-specific genes: Ren1 and Akr1b7. The motif enrichment analyses with the MEME suite on the increased accessibility regions show different sets of enriched transcription factor (TF) motifs between the tumoral cell line and primary cells. The top enriched motifs in the tumoral cell line are the bZip family, including Atf3 (q-value: 2.56e-2147), Fos (q-value: 1.01e-2406), and JunB (q-value: 8.73e-2432). The top enriched motifs in the primary cells are the MEF2 family, including MEF2a (q-value: 2.18e-91), MEF2c (q-value: 1.28e-80), and MEF2d (q-value: 1.28e-80), consistent with unpublished work in our lab. In addition, we found four topmost enriched motifs (MEIS1, NR4A2, FOXJ3, and NR4A1, with q-values of 8.24e-10, 9.78e-9, 3.96e-7, and 2.67e-6) co-enriched in regions associated with Ren1 and Akr1b7. This indicates that a set of TFs regulates the co-expressing of Ren1 and Akr1b7. The chromatin domains and TF we described are likely to control renin cell identity and may serve as therapeutic targets for kidney/vascular diseases and hypertension.

Inhibition of the renin-angiotensin system causes concentric hypertrophy of renal arterioles in mice and humans

Inhibitors of the renin-angiotensin system (RAS) are widely used to treat hypertension. Using mice harboring fluorescent cell lineage tracers, single-cell RNA-Seq, and long-term inhibition of RAS in both mice and humans, we found that deletion of renin or inhibition of the RAS leads to concentric thickening of the intrarenal arteries and arterioles. This severe disease was caused by the multiclonal expansion and transformation of renin cells from a classical endocrine phenotype to a matrix-secretory phenotype: the cells surrounded the vessel walls and induced the accumulation of adjacent smooth muscle cells and extracellular matrix, resulting in blood flow obstruction, focal ischemia, and fibrosis. Ablation of the renin cells via conditional deletion of β1 integrin prevented arteriolar hypertrophy, indicating that renin cells are responsible for vascular disease. Given these findings, prospective morphological studies in humans are necessary to determine the extent of renal vascular damage caused by the widespread use of inhibitors of the RAS.

Ctcf is required for renin expression and maintenance of the structural integrity of the kidney

Renin cells are crucial for the regulation of blood pressure and fluid electrolyte homeostasis. We have recently shown that renin cells possess unique chromatin features at regulatory regions throughout the genome that may determine the identity and memory of the renin phenotype. The 3-D structure of chromatin may be equally important in the determination of cell identity and fate. CCCTC-binding factor (Ctcf) is a highly conserved chromatin organizer that may regulate the renin phenotype by controlling chromatin structure. We found that Ctcf binds at several conserved DNA sites surrounding and within the renin locus, suggesting that Ctcf may regulate the transcriptional activity of renin cells. In fact, deletion of Ctcf in cells of the renin lineage led to decreased endowment of renin-expressing cells accompanied by decreased circulating renin, hypotension, and severe morphological abnormalities of the kidney, including defects in arteriolar branching, and ultimately renal failure. We conclude that control of chromatin architecture by Ctcf is necessary for the appropriate expression of renin, control of renin cell number and structural integrity of the kidney.

Abstract P235: Renin and Prorenin Uptake by Human Conditionally Immortalized Proximal Tubule Epithelial Cells Involves Megalin and Mannose 6-phosphate Receptor

Renin is filtered by the glomerulus, and subsequently reabsorbed in the proximal tubule in a megalin-dependent manner, as evidenced by a 20-40-fold rise in urinary renin in patients with Dent’s disease or Lowe syndrome, i.e. disorders characterized by defective proximal tubular reabsorption. Remarkably, the reabsorption of filtered prorenin appears to be complete, as it can only be detected in urine of patients with Dent’s disease or Lowe syndrome. To further investigate megalin-mediated renin and prorenin reabsorption, human conditionally immortalized proximal tubule epithelial cells (ciPTEC) were incubated at 37 °C or 4 °C with recombinant human renin or prorenin (1000 U/L), in the absence or presence of 10 mmol/L mannose 6-phosphate (M6P) to block (pro)renin binding and internalization via M6P receptors. Cell lysate (pro)renin levels were measured by immunoradiometric assay both before and after prorenin activation. At 37 °C, cellular renin and prorenin tended to level off at 6 hours, reaching lysate levels of 75±18 and 100±54 pg/mg (mean±SEM), and all prorenin was detected as renin. Incubating ciPTEC at 4 °C diminished the cellular accumulation of renin and prorenin by 90%, and at this temperature prorenin remained in its inactive conformation. M6P blocked renin and prorenin uptake by >80% under all conditions. Importantly, M6P also concentration-dependently blocked the uptake of fluorescently labeled albumin (IC 50 = 3 mmol/L), to the same degree as the megalin inhibitor RAP-GST (IC 50 = 50 μg/mL). Since albumin is internalized in a megalin-dependent manner, these data indicate that M6P, on top of blocking M6P receptors, also interferes with the megalin-dependent uptake process. In conclusion, ciPTEC bind and internalize renin and prorenin in a temperature-dependent manner. This process involves megalin and/or M6P receptors, and results in prorenin activation at 37 °C.

Dibutyltin Compounds Effects on PPARγ/RXRα Activity, Adipogenesis, and Inflammation in Mammalians Cells

Organotins are a group of chemical compounds that have a tin atom covalently bound to one or more organic groups. The best-studied organotin is tributyltin chloride, which is an environmental pollutant and an endocrine disruptor. Tributyltin chloride has been shown to bind to PPARγ/RXRα and induces adipogenesis in different mammalian cells. However, there are few studies with other organotin compounds, such as dibutyltins. The aim of this study was to investigate the effect of dibutyltins diacetate, dichloride, dilaurate, and maleate on the transcriptional activity of the nuclear PPARγ and RXRα receptors, and on adipogenesis and inflammation. Analogous to tributyltin chloride, in reporter gene assay using HeLa cells, we observed that dibutyltins diacetate, dichloride, dilaurate, and maleate are partial agonists of PPARγ. Unlike tributyltin chloride, which is a full agonist of RXRα, dibutyltins dichloride and dilaurate are partial RXRα agonists. Additionally, the introduction of the C285S mutation, which disrupts tributyltin chloride binding to PPARγ, abrogated the dibutyltin agonistic activity. In 3T3-L1 preadipocytes, all dibutyltin induced adipogenesis, although the effect was less pronounced than that of rosiglitazone and tributyltin chloride. This adipogenic effect was confirmed by the expression of adipogenic markers Fabp4, Adipoq, and Glut4. Exposure of 3T3-L1 cells with dibutyltin in the presence of T0070907, a specific PPARγ antagonist, reduced fat accumulation, suggesting that adipogenic effect occurs through PPARγ. Furthermore, dibutyltins dichloride, dilaurate, and maleate inhibited the expression of proinflammatory genes in 3T3-L1 cells, such as Vcam1, Dcn, Fn1, S100a8, and Lgals9. Additionally, in RAW 264.7 macrophages, tributyltin chloride and dibutyltin dilaurate reduced LPS-stimulated TNFα expression. Our findings indicate that dibutyltins diacetate, dichloride, dilaurate, and maleate are PPARγ partial agonists and that dibutyltins dichloride and dilaurate are also partial RXRα agonists. Furthermore, dibutyltins induce adipogenesis in a PPARγ-dependent manner and repress inflammatory genes in 3T3-L1 and RAW 264.7 cells. Although dibutyltins display some partial PPARγ/RXRα agonistic effects, the translation of cell-based results assays into in vivo effects on inflammation and insulin resistance is not entirely known. Nevertheless, further studies are necessary to address their effects in different periods of life and to elucidate the actions of organostanic compounds in whole-body context.

Transcriptome Analysis of Human Reninomas as an Approach to Understanding Juxtaglomerular Cell Biology

Renin, a key component in the regulation of blood pressure in mammals, is produced by the rare and highly specialized juxtaglomerular cells of the kidney. Chronic stimulation of renin release results in a recruitment of new juxtaglomerular cells by the apparent conversion of adjacent smooth muscle cells along the afferent arterioles. Because juxtaglomerular cells rapidly dedifferentiate when removed from the kidney, their developmental origin and the mechanism that explains their phenotypic plasticity remain unclear. To overcome this limitation, we have performed RNA expression analysis on 4 human renin-producing tumors. The most highly expressed genes that were common between the reninomas were subsequently used for in situ hybridization in kidneys of 5-day-old mice, adult mice, and adult mice treated with captopril. From the top 100 genes, 10 encoding for ligands were selected for further analysis. Medium of human embryonic kidney 293 cells transfected with the mouse cDNA encoding these ligands was applied to (pro)renin-synthesizing As4.1 cells. Among the ligands, only platelet-derived growth factor B reduced the medium and cellular (pro)renin levels, as well as As4.1 renin gene expression. In addition, platelet-derived growth factor B-exposed As4.1 cells displayed a more elongated and aligned shape with no alteration in viability. This was accompanied by a downregulated expression of α-smooth muscle actin and an upregulated expression of interleukin-6, suggesting a phenotypic shift from myoendocrine to inflammatory. Our results add 36 new genes to the list that characterize renin-producing cells and reveal a novel role for platelet-derived growth factor B as a regulator of renin-synthesizing cells.