Andrew McMahon (PI)
University of Southern California
The functional unit of the mammalian kidney is the nephron. Though there is a general appreciation for when and how different cell types of the nephron form from studies in the mouse, there is little understanding of these processes in the human kidney, and no rigorous accounting for the full range of mature cell types that underpin kidney function in either mouse or man. An understanding of the diversity of nephron cell types is essential for the goals of (Re)Building A Kidney Consortium where generating functional kidney structures is the consortium target. Further, individual cell types are likely targets for distinct disease features; as an example, mutations in genes producing podocyte specific gene products result in glomerular nephritis. We will combine two complementary strategies, MARIS (Method for Analyzing RNA following Intracellular Sorting) and Drop-seq, to obtain detailed comparative transcriptional profiles of mouse and human nephron progenitors and nephrons to address the question of cellular diversity.
Gerhardt, Louisa M.S.; McMahon, Andrew P.. Seminars in Nephrology . 2022.
Summary Acute kidney injury (AKI) is a highly prevalent, heterogeneous syndrome, associated with increased short- and long-term mortality. A multitude of different factors cause AKI including ischemia, sepsis, nephrotoxic drugs, and urinary tract obstruction. Upon injury, the kidney initiates an intrinsic repair program that can result in adaptive repair with regeneration of damaged nephrons and functional recovery of epithelial activity, or maladaptive repair and persistence of damaged epithelial cells with a characteristic proinflammatory, profibrotic molecular signature. Maladaptive repair is linked to disease progression from AKI to chronic kidney disease. Despite extensive efforts, no therapeutic strategies provide consistent benefit to AKI patients. Since kidney biopsies are rarely performed in the acute injury phase in humans, most of our understanding of AKI pathophysiology is derived from preclinical AKI models. This raises the question of how well experimental models of AKI reflect the molecular and cellular mechanisms underlying human AKI? Here, we provide a brief overview of available AKI models, discuss their strengths and limitations, and consider important aspects of the AKI response in mice and humans, with a particular focus on the role of proximal tubule cells in adaptive and maladaptive repair.
Naved, Bilal A.; Bonventre, Joseph V.; Hubbell, Jeffrey A.; Hukriede, Neil A.; Humphreys, Benjamin D.; Kesselman, Carl; Valerius, M. Todd; McMahon, Andrew P.; Shankland, Stuart J.; Wertheim, Jason A.; White, Michael J.V.; de Caestecker, Mark P.; Drummond, Iain A. Kidney International . March 2022.
Miao, Zhen; Humphreys, Benjamin D.; McMahon, Andrew P.; Kim, Junhyong. Nature Reviews Nephrology . 17(11):710–724. November 2021.
An explosion in single-cell technologies has revealed a previously underappreciated heterogeneity of cell types and novel cell-state associations with sex, disease, development and other processes. Starting with transcriptome analyses, single-cell techniques have extended to multi-omics approaches and now enable the simultaneous measurement of data modalities and spatial cellular context. Data are now available for millions of cells, for whole-genome measurements and for multiple modalities. Although analyses of such multimodal datasets have the potential to provide new insights into biological processes that cannot be inferred with a single mode of assay, the integration of very large, complex, multimodal data into biological models and mechanisms represents a considerable challenge. An understanding of the principles of data integration and visualization methods is required to determine what methods are best applied to a particular single-cell dataset. Each class of method has advantages and pitfalls in terms of its ability to achieve various biological goals, including cell-type classification, regulatory network modelling and biological process inference. In choosing a data integration strategy, consideration must be given to whether the multi-omics data are matched (that is, measured on the same cell) or unmatched (that is, measured on different cells) and, more importantly, the overall modelling and visualization goals of the integrated analysis.
Gerhardt, Louisa M. S.; Liu, Jing; Koppitch, Kari; Cippà, Pietro E.; McMahon, Andrew P.. Proceedings of the National Academy of Sciences . 118(27). July 2021.
A single acute kidney injury event increases the risk of progression to chronic kidney disease (CKD). Combining single-nucleus RNA sequencing with genetic tracing of injured proximal tubule cells identified a spatially dynamic, evolving injury response following ischemia–reperfusion injury. Failed proximal tubule repair leads to the persistence of a profibrotic, proinflammatory Vcam1+/Ccl2+ cell type exhibiting a senescence-associated secretory phenotype and a marked transcriptional activation of NF-κB and AP-1 pathway signatures, but no signs of G2/M cell cycle arrest. Insights from this study can inform strategies to improve renal repair and prevent CKD progression.Acute kidney injury (AKI), commonly caused by ischemia, sepsis, or nephrotoxic insult, is associated with increased mortality and a heightened risk of chronic kidney disease (CKD). AKI results in the dysfunction or death of proximal tubule cells (PTCs), triggering a poorly understood autologous cellular repair program. Defective repair associates with a long-term transition to CKD. We performed a mild-to-moderate ischemia–reperfusion injury (IRI) to model injury responses reflective of kidney injury in a variety of clinical settings, including kidney transplant surgery. Single-nucleus RNA sequencing of genetically labeled injured PTCs at 7-d (“early”) and 28-d (“late”) time points post-IRI identified specific gene and pathway activity in the injury–repair transition. In particular, we identified Vcam1+/Ccl2+ PTCs at a late injury stage distinguished by marked activation of NF-κB–, TNF-, and AP-1–signaling pathways. This population of PTCs showed features of a senescence-associated secretory phenotype but did not exhibit G2/M cell cycle arrest, distinct from other reports of maladaptive PTCs following kidney injury. Fate-mapping experiments identified spatially and temporally distinct origins for these cells. At the cortico-medullary boundary (CMB), where injury initiates, the majority of Vcam1+/Ccl2+ PTCs arose from early replicating PTCs. In contrast, in cortical regions, only a subset of Vcam1+/Ccl2+ PTCs could be traced to early repairing cells, suggesting late-arising sites of secondary PTC injury. Together, these data indicate even moderate IRI is associated with a lasting injury, which spreads from the CMB to cortical regions. Remaining failed-repair PTCs are likely triggers for chronic disease progression.The single-nuclei RNA sequencing data have been deposited in the Gene Expression Omnibus (GEO) database (accession no. GSE171417). All study data are included in the article and/or supporting information. Previously published data were used for this work (https://doi.org/10.1172/jci.insight.123151; https://doi.org/10.1038/s42255-020-0238-1).
Tran, Tracy; Lindstrom, Nils O.; Ransick, Andrew; De Sena Brandine, Guilherme; Guo, Qiuyu; Kim, Albert D.; Der, Balint; Peti-Peterdi, Janos; Smith, Andrew D.; Thornton, Matthew; Grubbs, Brendan; McMahon, Jill A.; McMahon, Andrew P. Dev Cell . 50(1):102–116.e6. July 2019.
The renal corpuscle of the kidney comprises a glomerular vasculature embraced by podocytes and supported by mesangial myofibroblasts, which ensure plasma filtration at the podocyte-generated slit diaphragm. With a spectrum of podocyte-expressed gene mutations causing chronic disease, an enhanced understanding of podocyte development and function to create relevant in vitro podocyte models is a clinical imperative. To characterize podocyte development, scRNA-seq was performed on human fetal kidneys, identifying distinct transcriptional signatures accompanying the differentiation of functional podocytes from progenitors. Interestingly, organoid-generated podocytes exhibited highly similar, progressive transcriptional profiles despite an absence of the vasculature, although abnormal gene expression was pinpointed in late podocytes. On transplantation into mice, organoid-derived podocytes recruited the host vasculature and partially corrected transcriptional profiles. Thus, human podocyte development is mostly intrinsically regulated and vascular interactions refine maturation. These studies support the application of organoid-derived podocytes to model disease and to restore or replace normal kidney functions.
Lindström, NO; McMahon, JA; Guo, J; Tran, T; Guo, Q; Rutledge, E; Parvez, RK; Saribekyan, G; Schuler, RE; Liao, C; Kim, AD; Abdelhalim, A; Ruffins, SW; Thornton, ME; Basking, L; Grubbs, B; Kesselman, C; McMahon, AP. J Am Soc Nephrol . February 2018.
Human kidney function is underpinned by approximately 1,000,000 nephrons, although the number varies substantially, and low nephron number is linked to disease. Human kidney development initiates around 4 weeks of gestation and ends around 34-37 weeks of gestation. Over this period, a reiterative inductive process establishes the nephron complement. Studies have provided insightful anatomic descriptions of human kidney development, but the limited histologic views are not readily accessible to a broad audience. In this first paper in a series providing comprehensive insight into human kidney formation, we examined human kidney development in 135 anonymously donated human kidney specimens. We documented kidney development at a macroscopic and cellular level through histologic analysis, RNA in situ hybridization, immunofluorescence studies, and transcriptional profiling, contrasting human development (4-23 weeks) with mouse development at selected stages (embryonic day 15.5 and postnatal day 2). The high-resolution histologic interactive atlas of human kidney organogenesis generated can be viewed at the GUDMAP database (www.gudmap.org) together with three-dimensional reconstructions of key components of the data herein. At the anatomic level, human and mouse kidney development differ in timing, scale, and global features such as lobe formation and progenitor niche organization. The data also highlight differences in molecular and cellular features, including the expression and cellular distribution of anchor gene markers used to identify key cell types in mouse kidney studies. These data will facilitate and inform in vitro efforts to generate human kidney structures and comparative functional analyses across mammalian species.
Oxburgh, L; Carroll, TJ; Cleaver, O; Gossett, DR; Hoshizaki, DK; Hubbell, JA; Humphreys, BD; Jain, S; Jensen, J; Kaplan, DL; Kesselman, C; Ketchum, CJ; Little, MH; McMahon, AP; Shankland, SJ; Spence, JR; Valerius, MT; Wertheim, JA; Wessely, O; Zheng, Y; Drummond, IA. J Am Soc Nephrol . 28(5):1370–1378. May 2017.
(Re)Building a Kidney is a National Institute of Diabetes and Digestive and Kidney Diseases-led consortium to optimize approaches for the isolation, expansion, and differentiation of appropriate kidney cell types and the integration of these cells into complex structures that replicate human kidney function. The ultimate goals of the consortium are two-fold: to develop and implement strategies for in vitro engineering of replacement kidney tissue, and to devise strategies to stimulate regeneration of nephrons in situ to restore failing kidney function. Projects within the consortium will answer fundamental questions regarding human gene expression in the developing kidney, essential signaling crosstalk between distinct cell types of the developing kidney, how to derive the many cell types of the kidney through directed differentiation of human pluripotent stem cells, which bioengineering or scaffolding strategies have the most potential for kidney tissue formation, and basic parameters of the regenerative response to injury. As these projects progress, the consortium will incorporate systematic investigations in physiologic function of in vitro and in vivo differentiated kidney tissue, strategies for engraftment in experimental animals, and development of therapeutic approaches to activate innate reparative responses.