Unique functions for Notch4 in murine embryonic lymphangiogenesis

In mice, embryonic dermal lymphatic development is well understood and used to study gene functions in lymphangiogenesis. Notch signaling is an evolutionarily conserved pathway that modulates cell fate decisions, which has been shown to both inhibit and promote dermal lymphangiogenesis. Here, we demonstrate distinct roles for Notch4 signaling versus canonical Notch signaling in embryonic dermal lymphangiogenesis. Actively growing embryonic dermal lymphatics expressed NOTCH1, NOTCH4, and DLL4 which correlated with Notch activity. In lymphatic endothelial cells (LECs), DLL4 activation of Notch induced a subset of Notch effectors and lymphatic genes, which were distinctly regulated by Notch1 and Notch4 activation. Treatment of LECs with VEGF-A or VEGF-C upregulated Dll4 transcripts and differentially and temporally regulated the expression of Notch1 and Hes/Hey genes. Mice nullizygous for Notch4 had an increase in the closure of the lymphangiogenic fronts which correlated with reduced vessel caliber in the maturing lymphatic plexus at E14.5 and reduced branching at E16.5. Activation of Notch4 suppressed LEC migration in a wounding assay significantly more than Notch1, suggesting a dominant role for Notch4 in regulating LEC migration. Unlike Notch4 nulls, inhibition of canonical Notch signaling by expressing a dominant negative form of MAML1 (DNMAML) in Prox1+ LECs led to increased lymphatic density consistent with an increase in LEC proliferation, described for the loss of LEC Notch1. Moreover, loss of Notch4 did not affect LEC canonical Notch signaling. Thus, we propose that Notch4 signaling and canonical Notch signaling have distinct functions in the coordination of embryonic dermal lymphangiogenesis.

Heterozygous Mutation of Vegfr3 Reduces Renal Lymphatics Without Renal Dysfunction

Background: Lymphatic abnormalities are observed in several types of kidney disease, but the relationship between the renal lymphatic system and renal function is unclear. The discovery of lymphatic-specific proteins, advances in microscopy, and available genetic mouse models provide the tools to help elucidate the role of renal lymphatics in physiology and disease. Methods: We utilized a mouse model containing a missense mutation in Vegfr3 (dubbed Chy) that abrogates its kinase ability. Vegfr3Chy/+ mice were examined for developmental abnormalities and kidney specific outcomes. Control and Vegfr3Chy/+ mice were subjected to cisplatin-mediated injury. We characterized renal lymphatics using tissue clearing, light-sheet microscopy, and computational analyses. Results: In the kidney, VEGFR3 is expressed not only in lymphatic vessels, but also in various blood capillaries. Vegfr3Chy/+ mice had severely reduced renal lymphatics with 100% penetrance, but we found no abnormalities in blood pressure, serum creatinine, BUN, albuminuria, and histology. There was no difference in the degree of renal injury after low dose cisplatin (5 mg/kg), although Vegfr3Chy/+ mice developed perivascular inflammation. Cisplatin-treated controls had no difference in total cortical lymphatic volume and length, but showed increased lymphatic density due to decreased cortical volume. Conclusions: We demonstrate that VEGFR3 is required for development of renal lymphatics. Our studies reveal that reduced lymphatic density does not impair renal function at baseline and induces only modest histological changes after mild injury. We introduce a novel quantification method to evaluate renal lymphatics in 3D and demonstrate that accurate measurement of lymphatic density in chronic kidney disease requires assessment of changes to cortical volume.

Abstract MP52: Hypertensive Stimuli Indirectly Stimulate Mouse Mesometrial Lymphangiogenesis Through Immune Cells

We previously reported increased renal lymphatic density in multiple mouse models of hypertension, and further augmenting renal lymphatics lowers blood pressure. However, whether interstitial levels of hypertensive stimuli have a direct effect on lymphatics or an indirect effect through secreted immune cell factors has not been examined. We hypothesized that hypertensive stimuli directly increases lymphatic endothelial cell (LEC) proliferation and increases sprouting of mouse mesometrial lymphatic vessels. Murine LECs were cultured and treated with angiotensin II (angII), salt, and asymmetric dimethylarginine (ADMA) for 24 hours. To mimic the in vivo environment, a lymphatic-specific reporter mouse (Prox1-tdTomato) mesometrium tissue explant was treated with either the same hypertensive stimuli or with hypertensive conditioned media for 8 days. Mesometrial vascular beds were cultured in DMEM supplemented with 20% fetal bovine serum to induce lymphatic sprouting and this was replenished every day. The conditioned media was made by treating murine splenocytes for 24 hours with the same hypertensive stimuli. These stimuli had no effect on murine LEC proliferation. Hypertensive stimuli significantly decreased mesometrial lymphatic vessel sprout length (SL) and sprout number (SN) compared to controls (control SL in pixels by ImageJ analysis: 34.0 ± 2.6, angII: 3.7 ± 2.6, salt: 2.67 ± 2.18, ADMA: 9.06 ± 5.12, all p<0.05; control SN: 7 ± 3, angII: 0 ± 0, salt: 0 ± 0, ADMA: 1 ± 1, all p<0.05). Conditioned media treatment normalized SL and SN by day 8 for all hypertensive stimuli except salt. In conclusion, hypertensive stimuli directly inhibit mesometrial lymphangiogenesis, but this was mitigated by hypertensive stimuli induced immune cell secreted factors.

Heterozygous mutation of Vegfr3 decreases renal lymphatics but is dispensable for renal function

ABSTRACTBackgroundLymphatic abnormalities are observed in several types of kidney disease, but the relationship between the renal lymphatic system and renal function is unclear. The discovery of lymphatic-specific proteins, advances in microscopy, and available genetic mouse models provide the tools to help elucidate the role of renal lymphatics in physiology and disease.MethodsWe utilized a mouse model containing a missense mutation in Vegfr3 (dubbed Chy) that abrogates its kinase ability. Vegfr3Chy/+ mice were examined for developmental abnormalities and kidney-specific outcomes. Control and Vegfr3Chy/+ mice were subjected to cisplatin-mediated injury. We characterized renal lymphatics using a combination of tissue clearing, light-sheet microscopy and computational analyses.ResultsIn the kidney, we found Vegfr3 is expressed not only in lymphatic vessels, but also various blood vessels. Vegfr3Chy/+ mice had severely reduced renal lymphatics with 100% penetrance, but we found no abnormalities in blood pressure, renal function and histology. Similarly, there was no difference in the degree of renal injury after cisplatin, although Vegfr3Chy/+ mice developed more perivascular inflammation by histology. Control mice treated with cisplatin had a measurable increase in cortical lymphatic density despite no change in cortical lymphatic volume and length.ConclusionsWe demonstrate that Vegfr3 is required for development of renal lymphatics, but a reduction in lymphatic density does not alter renal function and induces only modest histological changes after injury. Our data suggests that an increase in lymphatic density after cisplatin injury may reflect the loss of cortical volume associated with chronic kidney disease rather than growth of lymphatic vessels.SIGNIFICANCE STATEMENTDefects in renal lymphatics occur in various kidney diseases, but their role in maintaining kidney structure and function is unknown. We combine tissue clearing, light-sheet microscopy and computational analysis to characterize lymphatics and find that mice with a heterozygous mutation in Vegfr3 (Vegfr3Chy/+) have severely reduced renal lymphatics. Strikingly, these mice have indistinguishable renal function and histology compared with controls. Even after cisplatin injury, there are no differences in renal function, although Vegfr3Chy/+ mice developed more perivascular inflammation. Our data present a novel method of lymphatic quantification and suggest that a normal complement of renal lymphatics is dispensable for renal structure and function.

Abstract 17346: Loss of Neuropilin 2 Impairs Lymphangiogenesis and Exacerbates Lymphedema

Dysfunctional lymphatic networks can lead to lymphatic diseases such as lymphedema as well as aggravate cardiovascular diseases such as atherosclerosis and hypertension. Some primary lymphedema patients have mutations in the Neuropilin 2 ( NRP2 ) gene, which encodes a transmembrane receptor that acts with VEGFR3 for the ligands VEGF-C and VEGF-D. Nrp2 has been shown to be a key regulator of lymphatic vessel development in the neonate as global Nrp2 -deficient mice suffer from reduced lymphatic density. However, Nrp2 protein expression is dramatically downregulated after birth and its role in adult lymphangiogenesis or its relevance in lymphedema is less clear. Our hypothesis is that Nrp2 expression is necessary for optimal lymphangiogenesis and proper lymphatic drainage function in the adult, and that loss of Nrp2 , either genetically or transcriptionally via down-regulation by specific transcription factors, may worsen lymphedema. In acute and chronic mouse inflammation models, we found that loss of Nrp2 specifically in the lymphatic endothelium ( prox1-cre ERT2 ;Nrp2 f/f ) resulted in prolonged swelling and reduced lymphatic drainage compared to control mice. Using the VEGFC-induced corneal lymphangiogenesis model and the tail wound-induced secondary lymphedema model, LEC-Nrp2-iKO mice showed diminished lymphangiogenesis and reduced lymphatic drainage compared to littermate controls. Furthermore, primary mouse dermal LEC isolated from Nrp2-iKO mice reveal suppressed VEGFR3 activation, signaling, and proliferation following VEGF-C stimulation, compared to LEC isolated from control mice. Collectively, our results identify Nrp2 as a critical mediator of lymphangiogenesis and homeostatic lymphatic drainage function in adult tissues.

Augmenting Renal Lymphatic Density Prevents Angiotensin II-Induced Hypertension in Male and Female Mice

BACKGROUND Renal inflammation and immune cell infiltration are characteristic of several forms of hypertension. Our laboratory has previously demonstrated that renal-inflammation-associated lymphangiogenesis occurs in salt-sensitive and nitric-oxide-inhibition-induced hypertension. Moreover, enhancing renal lymphatic density prevented the development of these two forms of hypertension. Here, we investigated the effects of angiotensin II-induced hypertension on renal lymphatic vessel density in male and female mice. METHODS Wild-type and genetically engineered male and female mice were infused with angiotensin II for 2 or 3 weeks. Isolated splenocytes and peritoneal macrophages from mice, and commercially available mouse lymphatic endothelial cells were used for in vitro studies. RESULTS Compared to vehicle controls, angiotensin II-infused male and female mice had significantly increased renal lymphatic vessel density in association with pro-inflammatory immune cells in the kidneys of these mice. Direct treatment of lymphatic endothelial cells with angiotensin II had no effect as they lack angiotensin II receptors; however, angiotensin II treatment of splenocytes and peritoneal macrophages induced secretion of the lymphangiogenic growth factor VEGF-C in vitro. Utilizing our genetic mouse model of inducible renal lymphangiogenesis, we demonstrated that greatly augmenting renal lymphatic density prior to angiotensin II infusion prevented the development of hypertension in male and female mice and this was associated with a reduction in renal CD11c+F4/80- monocytes. CONCLUSION Renal lymphatics play a significant role in renal immune cell trafficking and blood pressure regulation, and represent a novel avenue of therapy for hypertension.