Mechanisms of Renal Fibrosis Humphreys, Benjamin D
Annual review of physiology,
02/2018, Letnik:
80, Številka:
1
Journal Article
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Tubulointerstitial fibrosis is a chronic and progressive process affecting kidneys during aging and in chronic kidney disease (CKD), regardless of cause. CKD and renal fibrosis affect half of adults ...above age 70 and 10% of the world's population. Although no targeted therapy yet exists to slow renal fibrosis, a number of important recent advances have clarified the cellular and molecular mechanisms underlying the disease. In this review, I highlight these advances with a focus on cells and pathways that may be amenable to therapeutic targeting. I discuss pathologic changes regulating interstitial myofibroblast activation, including profibrotic and proinflammatory paracrine signals secreted by epithelial cells after either acute or chronic injury. I conclude by highlighting novel therapeutic targets and approaches with particular promise for development of new treatments for patients with fibrotic kidney disease.
A challenge for single-cell genomic studies in kidney and other solid tissues is generating a high-quality single-cell suspension that contains rare or difficult-to-dissociate cell types and is free ...of both RNA degradation and artifactual transcriptional stress responses.
We compared single-cell RNA sequencing (scRNA-seq) using the DropSeq platform with single-nucleus RNA sequencing (snRNA-seq) using sNuc-DropSeq, DroNc-seq, and 10X Chromium platforms on adult mouse kidney. We validated snRNA-seq on fibrotic kidney from mice 14 days after unilateral ureteral obstruction (UUO) surgery.
A total of 11,391 transcriptomes were generated in the comparison phase. We identified ten clusters in the scRNA-seq dataset, but glomerular cell types were absent, and one cluster consisted primarily of artifactual dissociation
induced stress response genes. By contrast, snRNA-seq from all three platforms captured a diversity of kidney cell types that were not represented in the scRNA-seq dataset, including glomerular podocytes, mesangial cells, and endothelial cells. No stress response genes were detected. Our snRNA-seq protocol yielded 20-fold more podocytes compared with published scRNA-seq datasets (2.4% versus 0.12%, respectively). Unexpectedly, single-cell and single-nucleus platforms had equivalent gene detection sensitivity. For validation, analysis of frozen day 14 UUO kidney revealed rare juxtaglomerular cells, novel activated proximal tubule and fibroblast cell states, and previously unidentified tubulointerstitial signaling pathways.
snRNA-seq achieves comparable gene detection to scRNA-seq in adult kidney, and it also has substantial advantages, including reduced dissociation bias, compatibility with frozen samples, elimination of dissociation-induced transcriptional stress responses, and successful performance on inflamed fibrotic kidney.
After acute kidney injury (AKI), patients either recover or alternatively develop fibrosis and chronic kidney disease. Interactions between injured epithelia, stroma, and inflammatory cells determine ...whether kidneys repair or undergo fibrosis, but the molecular events that drive these processes are poorly understood. Here, we use single nucleus RNA sequencing of a mouse model of AKI to characterize cell states during repair from acute injury. We identify a distinct proinflammatory and profibrotic proximal tubule cell state that fails to repair. Deconvolution of bulk RNA-seq datasets indicates that this failed-repair proximal tubule cell (FR-PTC) state can be detected in other models of kidney injury, increasing during aging in rat kidney and over time in human kidney allografts. We also describe dynamic intercellular communication networks and discern transcriptional pathways driving successful vs. failed repair. Our study provides a detailed description of cellular responses after injury and suggests that the FR-PTC state may represent a therapeutic target to improve repair.
The American Society of Clinical Investigation (ASCI) presents the Stanley J. Korsmeyer Award to one or two scientists who have made substantial contributions to understanding of disease and to ...mentoring the next generation of physician-scientists each year. Originally named the ASCI Award, it was renamed in 2006 to honor the first recipient of the prize, Dr. Stanley J. Korsmeyer, a physician-scientist respected widely for both his impactful science and his own remarkable legacy of mentorship. To recognize the 25th Anniversary of the Korsmeyer Award, the Journal of Clinical Investigation is featuring a series of Review and Viewpoint articles from past Korsmeyer Award winners, which will published over the course of 2023.
Understanding the cellular mechanisms underlying chronic kidney disease (CKD) progression is required to develop effective therapeutic approaches. In this issue of the JCI, Taguchi, Elias, et al. ...explore the relationship between cyclin G1 (CG1), an atypical cyclin that induces G2/M proximal tubule cell cycle arrest, and epithelial dedifferentiation during fibrogenesis. While CG1-knockout mice were protected from fibrosis and had reduced G2/M arrest, protection was unexpectedly independent of induction of G2/M arrest. Rather, CG1 drove fibrosis by regulating maladaptive dedifferentiation in a CDK5-dependent mechanism. These findings highlight the importance of maladaptive epithelial dedifferentiation in kidney fibrogenesis and identify CG1/CDK5 signaling as a therapeutic target in CKD progression.
Mesenchymal stem cells (MSCs) reside in the perivascular niche of many organs, including kidney, lung, liver, and heart, although their roles in these tissues are poorly understood. Here, we ...demonstrate that Gli1 marks perivascular MSC-like cells that substantially contribute to organ fibrosis. In vitro, Gli1+ cells express typical MSC markers, exhibit trilineage differentiation capacity, and possess colony-forming activity, despite constituting a small fraction of the platelet-derived growth factor-β (PDGFRβ)+ cell population. Genetic lineage tracing analysis demonstrates that tissue-resident, but not circulating, Gli1+ cells proliferate after kidney, lung, liver, or heart injury to generate myofibroblasts. Genetic ablation of these cells substantially ameliorates kidney and heart fibrosis and preserves ejection fraction in a model of induced heart failure. These findings implicate perivascular Gli1+ MSC-like cells as a major cellular origin of organ fibrosis and demonstrate that these cells may be a relevant therapeutic target to prevent solid organ dysfunction after injury.
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•Gli1 marks a perivascular network of MSC-like cells across major organs•Gli1+ cells are a CFU-F enriched fraction of the interstitial PDGFRβ+ population•Upon organ injury resident Gli1+ cells expand and become myofibroblasts•Genetic ablation of Gli1+ cells ameliorates fibrosis and rescues organ function
The cellular origins of fibrosis in different tissues are unclear. Kramann et al. show that Gli1 marks a network of perivascular mesenchymal-stem-cell-like cells that generate myofibroblasts and play a central role in organ fibrosis after injury, and ablating these cells ameliorates fibrosis and rescues organ function.
Recent techniques for single-cell RNA sequencing (scRNA-seq) at high throughput are leading to profound new discoveries in biology. The ability to generate vast amounts of transcriptomic data at ...cellular resolution represents a transformative advance, allowing the identification of novel cell types, states, and dynamics. In this review, we summarize the development of scRNA-seq methodologies and highlight their advantages and drawbacks. We discuss available software tools for analyzing scRNA-Seq data and summarize current computational challenges. Finally, we outline ways in which this powerful technology might be applied to discovery research in kidney development and disease.
Whether kidney proximal tubule harbors a scattered population of epithelial stem cells is a major unsolved question. Lineage-tracing studies, histologic characterization, and ex vivo functional ...analysis results conflict. To address this controversy, we analyzed the lineage and clonal behavior of fully differentiated proximal tubule epithelial cells after injury. A CreER ᵀ² cassette was knocked into the sodium-dependent inorganic phosphate transporter SLC34a1 locus, which is expressed only in differentiated proximal tubule. Tamoxifen-dependent recombination was absolutely specific to proximal tubule. Clonal analysis after injury and repair showed that the bulk of labeled cells proliferate after injury with increased clone size after severe compared with mild injury. Injury to labeled proximal tubule epithelia induced expression of CD24, CD133, vimentin, and kidney-injury molecule-1, markers of putative epithelial stem cells in the human kidney. Similar results were observed in cultured proximal tubules, in which labeled clones proliferated and expressed dedifferentiation and injury markers. When mice with completely labeled kidneys were subject to injury and repair there was no dilution of fate marker despite substantial proliferation, indicating that unlabeled progenitors do not contribute to kidney repair. During nephrogenesis and early kidney growth, single proximal tubule clones expanded, suggesting that differentiated cells also contribute to tubule elongation. These findings provide no evidence for an intratubular stem-cell population, but rather indicate that terminally differentiated epithelia reexpress apparent stem-cell markers during injury-induced dedifferentiation and repair.
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