Refuting the hypothesis that semaphorin-3f/neuropilin-2 exclude blood vessels from the cap mesenchyme in the developing kidney

Isthmin-1 (Ism1) modulates renal branching morphogenesis and mesenchyme condensation during early kidney development

The outgrowth of epithelial bud followed by reiterated bifurcations during renal development is driven by the ligand-receptor interactions between the epithelium and the surrounding mesenchyme. Here, by exploring ligand-receptor interactions in E10.5 and E11.5 kidneys by single cell RNA-seq, we find that Isthmin1 (Ism1), a secreted protein, resembles Gdnf expression and modulates kidney branching morphogenesis. Mice deficient for Ism1 exhibit defective ureteric bud bifurcation and impaired metanephric mesenchyme condensation in E11.5 embryos, attributable to the compromised Gdnf/Ret signaling, ultimately leading to renal agenesis and hypoplasia/dysplasia. By HRP-induced proximity labelling, we further identify integrin α8β1 as a receptor of Ism1 in E11.5 kidney and demonstrate that Ism1 promoted cell-cell adhesion through interacting with Integrin α8β1, the receptor whose activation is responsible for Gdnf expression and mesenchyme condensation. Taken together, our work reveals Ism1 as a critical regulator of cell-cell interaction that modulates Gdnf/Ret signaling during early kidney development.

The Beauty and Complexity of Blood Vessel Patterning

This review highlights new concepts in vascular patterning in the last 10 years, with emphasis on its beauty and complexity. Endothelial cell signaling pathways that respond to molecular or mechanical signals are described, and examples of vascular patterning that use these pathways in brain, skin, heart, and kidney are highlighted. The pathological consequences of patterning loss are discussed in the context of arteriovenous malformations (AVMs), and prospects for the next 10 years presented.

Comparative toxicity study of waterborne two booster biocides (CuPT and ZnPT) on embryonic flounder (Paralichthys olivaceus)

A new generation of booster biocides that include metal pyrithiones (PTs) such as copper pyrithione (CuPT) and zinc pyrithione (ZnPT) are being used as tributyltin alternatives. In the marine environment, ZnPT can easily transchelate Cu to form CuPT, and the environmental fate and persistence of these two metal pyrithiones are closely related. Although some data on the toxicity of biocides on marine fish are available, little is known about their toxicity and toxic pathway. We thus compared the toxic effects of CuPT and ZnPT on embryonic olive flounder (Paralichthys olivaceus) by investigating their adverse effects based on developmental morphogenesis and transcriptional variation. In our study, the toxic potency of CuPT was greater with respect to developmental malformation and mortality than ZnPT. Consistent with the developmental effects, the expression of genes related to tail fin malformation (including plod2, furin, and wnt3a) was higher in embryonic flounder exposed to CuPT than in those exposed to ZnPT. Genes related to muscle and nervous system development exhibited significant changes on differential gene expression profiles using RNA sequencing (cutoff value P < 0.05). Gene ontology analysis of embryos exposed to CuPT revealed affected cellular respiration and kidney development, whereas genes associated with cell development, nervous system development and heart development showed significant variation in embryonic flounder exposed to ZnPT. Overall, our study clarifies the common and unique developmental toxic effects of CuPT and ZnPT through transcriptomic analyses in embryonic flounder.

The lymphatics in kidney health and disease

The mammalian vascular system consists of two networks: the blood vascular system and the lymphatic vascular system. Throughout the body, the lymphatic system contributes to homeostatic mechanisms by draining extravasated interstitial fluid and facilitating the trafficking and activation of immune cells. In the kidney, lymphatic vessels exist mainly in the kidney cortex. In the medulla, the ascending vasa recta represent a hybrid lymphatic-like vessel that performs lymphatic-like roles in interstitial fluid reabsorption. Although the lymphatic network is mainly derived from the venous system, evidence supports the existence of lymphatic beds that are of non-venous origin. Following their development and maturation, lymphatic vessel density remains relatively stable; however, these vessels undergo dynamic functional changes to meet tissue demands. Additionally, new lymphatic growth, or lymphangiogenesis, can be induced by pathological conditions such as tissue injury, interstitial fluid overload, hyperglycaemia and inflammation. Lymphangiogenesis is also associated with conditions such as polycystic kidney disease, hypertension, ultrafiltration failure and transplant rejection. Although lymphangiogenesis has protective functions in clearing accumulated fluid and immune cells, the kidney lymphatics may also propagate an inflammatory feedback loop, exacerbating inflammation and fibrosis. Greater understanding of lymphatic biology, including the developmental origin and function of the lymphatics and their response to pathogenic stimuli, may aid the development of new therapeutic agents that target the lymphatic system.

Beyond a Passive Conduit: Implications of Lymphatic Biology for Kidney Diseases

The kidney contains a network of lymphatic vessels that clear fluid, small molecules, and cells from the renal interstitium. Through modulating immune responses and via crosstalk with surrounding renal cells, lymphatic vessels have been implicated in the progression and maintenance of kidney disease. In this Review, we provide an overview of the development, structure, and function of lymphatic vessels in the healthy adult kidney. We then highlight the contributions of lymphatic vessels to multiple forms of renal pathology, emphasizing CKD, transplant rejection, and polycystic kidney disease and discuss strategies to target renal lymphatics using genetic and pharmacologic approaches. Overall, we argue the case for lymphatics playing a fundamental role in renal physiology and pathology and treatments modulating these vessels having therapeutic potential across the spectrum of kidney disease.

Macrophages restrict the nephrogenic field and promote endothelial connections during kidney development

The origins and functions of kidney macrophages in the adult have been explored, but their roles during development remain largely unknown. Here we characterise macrophage arrival, localisation, heterogeneity, and functions during kidney organogenesis. Using genetic approaches to ablate macrophages, we identify a role for macrophages in nephron progenitor cell clearance as mouse kidney development begins. Throughout renal organogenesis, most kidney macrophages are perivascular and express F4/80 and CD206. These macrophages are enriched for mRNAs linked to developmental processes, such as blood vessel morphogenesis. Using antibody-mediated macrophage-depletion, we show macrophages support vascular anastomoses in cultured kidney explants. We also characterise a subpopulation of galectin-3⁺ (Gal3⁺) myeloid cells within the developing kidney. Our findings may stimulate research into macrophage-based therapies for renal developmental abnormalities and have implications for the generation of bioengineered kidney tissues.

The kidneys clean our blood by filtering out waste products while ensuring that useful components, like nutrients, remain in the bloodstream. Blood enters the kidneys through a network of intricately arranged blood vessels, which associate closely with the ‘cleaning tubes’ that carry out filtration. Human kidneys start developing during the early phases of embryonic development. During this process, the newly forming blood vessels and cleaning tubes must grow in the right places for the adult kidney to work properly.

Macrophages are cells of the immune system that clear away foreign, diseased, or damaged cells. They are also thought to encourage growth of the developing kidney, but how exactly they do this has remained unknown. Munro et al. therefore wanted to find out when macrophages first appeared in the embryonic kidney and how they might help control their development.

Experiments using mice revealed that the first macrophages arrived in the kidney early during its development, alongside newly forming blood vessels. Further investigation using genetically modified mice that did not have macrophages revealed that these immune cells were needed at this stage to clear away misplaced kidney cells and help ‘set the scene’ for future development.

At later stages, macrophages in the kidney interacted closely with growing blood vessels. As well as producing molecules linked with blood vessel formation, the macrophages wrapped around the vessels themselves, sometimes even eating cells lining the vessels and the blood cells carried within them. These observations suggested that macrophages actively shaped the network of blood vessels developing within the kidneys. Experiments removing macrophages from kidney tissue confirmed this: in normal kidneys, the blood vessels grew into a continuous network, but in kidneys lacking macrophages, far fewer connections formed between the vessels.

This work sheds new light on how the complex structures in the adult kidney first arise and could be useful in future research. For example, adding macrophages to simplified, laboratory-grown ‘mini-kidneys’ could make them better models to study kidney growth, while patients suffering from kidney diseases might benefit from new drugs targeting macrophages.

Reconstitution of the embryonic kidney identifies a donor cell contribution to the renal vasculature upon transplantation

The kidney possesses a highly organised vasculature that is required for its filtration function. While recent advances in stem cell biology have enabled the in vitro generation of kidney tissues, at least partially, recapitulation of the complicated vascular architecture remains a huge challenge. Herein we develop a method to reconstitute both the kidney and its vascular architecture in vitro, using dissociated and sorted mouse embryonic kidney cells. Upon transplantation, arteriolar networks were re-established that ran through the interstitial space between branching ureteric buds and eventually entered glomeruli. Using this system, we found that donor-derived endothelial cells significantly contributed to the arterioles and glomerular capillaries formed after transplantation. Unexpectedly, the near-complete depletion of canonical endothelial cells from the donor embryonic kidney suggested the existence of unidentified donor-derived endothelial precursors that were negative for canonical endothelial markers, but still contributed significantly to the vasculature in the transplants. Thus, our protocol will serve as a useful platform for identification of renal endothelial precursors and induction of these precursors from pluripotent stem cells.

Vascularizing organogenesis: Lessons from developmental biology and implications for regenerative medicine

Organogenesis requires tightly coordinated and patterned growth of numerous cell types to form a fully mature and vascularized organ. Endothelial cells (ECs) that line blood vessels develop alongside the growing organ, but only recently has their role in directing epithelial and stromal growth been appreciated. Endothelial, epithelial, and stromal cells in embryonic organs actively communicate with one another throughout development to ensure that the organ forms appropriately. What signals tell blood vessel progenitors where to go? How are tissues influenced by the vasculature that pervades it? In this chapter, we review the ways in which crosstalk between ECs and epithelial or stromal cells during development leads to a fully patterned pancreas, lung, or kidney. ECs in all of these organs are necessary for proper epithelial and stromal growth, but how they direct this process is organ- and time-specific, highlighting the concept of dynamic EC heterogeneity. We end with a discussion on how understanding cell-cell crosstalk during development can be applied therapeutically through the generation of transplantable miniature organ-like tissues called "organoids." We will discuss the current state of organoid technology and highlight the major challenges in forming a properly patterned vascular network that will be critical in transforming them into a viable therapeutic option.

Spatiotemporal heterogeneity and patterning of developing renal blood vessels

The kidney vasculature facilitates the excretion of wastes, the dissemination of hormones, and the regulation of blood chemistry. To carry out these diverse functions, the vasculature is regionalized within the kidney and along the nephron. However, when and how endothelial regionalization occurs remains unknown. Here, we examine the developing kidney vasculature to assess its 3-dimensional structure and transcriptional heterogeneity. First, we observe that endothelial cells (ECs) grow coordinately with the kidney bud as early as E10.5, and begin to show signs of specification by E13.5 when the first arteries can be identified. We then focus on how ECs pattern and remodel with respect to the developing nephron and collecting duct epithelia. ECs circumscribe nephron progenitor populations at the distal tips of the ureteric bud (UB) tree and form stereotyped cruciform structures around each tip. Beginning at the renal vesicle (RV) stage, ECs form a continuous plexus around developing nephrons. The endothelial plexus envelops and elaborates with the maturing nephron, becoming preferentially enriched along the early distal tubule. Lastly, we perform transcriptional and immunofluorescent screens to characterize spatiotemporal heterogeneity in the kidney vasculature and identify novel regionally enriched genes. A better understanding of development of the kidney vasculature will help instruct engineering of properly vascularized ex vivo kidneys and evaluate diseased kidneys.