Lymphangiogenesis in kidney and lymph node mediates renal inflammation and fibrosis

Current perspectives and trends of the research on hypertensive nephropathy: a bibliometric analysis from 2000 to 2023

Hypertensive nephropathy continues to be a major cause of end-stage renal disease and poses a significant global health burden. Despite the staggering development of research in hypertensive nephropathy, scientists and clinicians can only seek out useful information through articles and reviews, it remains a hurdle for them to quickly track the trend in this field. This study uses the bibliometric method to identify the evolutionary development and recent hotspots of hypertensive nephropathy. The Web of Science Core Collection database was used to extract publications on hypertensive nephropathy from January 2000 to November 2023. CiteSpace was used to capture the patterns and trends from multi-perspectives, including countries/regions, institutions, keywords, and references. In total, 557 publications on hypertensive nephropathy were eligible for inclusion. China (n = 208, 37.34%) was the most influential contributor among all the countries. Veterans Health Administration (n = 19, 3.41%) was found to be the most productive institution. Keyword bursting till now are renal fibrosis, outcomes, and mechanisms which are predicted to be the potential frontiers and hotspots in the future. The top seven references were listed, and their burst strength was shown. A comprehensive overview of the current status and research frontiers of hypertensive nephropathy has been provided through the bibliometric perspective. Recent advancements and challenges in hypertensive nephropathy have been discussed. These findings can offer informative instructions for researchers and scholars.

CCL19-producing fibroblasts promote tertiary lymphoid structure formation enhancing anti-tumor IgG response in colorectal cancer liver metastasis

Tertiary lymphoid structures (TLSs) are associated with enhanced immunity in tumors. However, their formation and functions in colorectal cancer liver metastasis (CRLM) remain unclear. Here, we reveal that intra- and peri-tumor mature TLSs (TLS+) are associated with improved clinical outcomes than TLS- tumors. Using single-cell-RNA-sequencing and spatial-enhanced-resolution-omics-sequencing (Stereo-seq), we reveal that TLS+ tumors are enriched with IgG+ plasma cells (PCs), while TLS- tumors are characterized with IgA+ PCs. By generating TLS-associated PC-derived monoclonal antibodies in vitro, we show that TLS-PCs secrete tumor-targeting antibodies. As the proof-of-concept, we demonstrate the anti-tumor activities of TLS-PC-mAb6 antibody in humanized mouse model of colorectal cancer. We identify a fibroblast lineage secreting CCL19 that facilitates lymphocyte trafficking to TLSs. CCL19 treatment promotes TLS neogenesis and prevents tumor growth in mice. Our data uncover the central role of CCL19+ fibroblasts in TLS formation, which in turn generates therapeutic antibodies to restrict CRLM.

Lymphocytes and innate immune cells in acute kidney injury and repair

Acute kidney injury (AKI) is a common and serious disease entity that affects native kidneys and allografts but for which no specific treatments exist. Complex intrarenal inflammatory processes driven by lymphocytes and innate immune cells have key roles in the development and progression of AKI. Many studies have focused on prevention of early injury in AKI. However, most patients with AKI present after injury is already established. Increasing research is therefore focusing on mechanisms of renal repair following AKI and prevention of progression from AKI to chronic kidney disease. CD4+ and CD8+ T cells, B cells and neutrophils are probably involved in the development and progression of AKI, whereas regulatory T cells, double-negative T cells and type 2 innate lymphoid cells have protective roles. Several immune cells, such as macrophages and natural killer T cells, can have both deleterious and protective effects, depending on their subtype and/or the stage of AKI. The immune system not only participates in injury and repair processes during AKI but also has a role in mediating AKI-induced distant organ dysfunction. Targeted manipulation of immune cells is a promising therapeutic strategy to improve AKI outcomes.

Bioinformatics analysis reveals CCR7 as a potential biomarker for predicting CKD progression

Chronic kidney disease (CKD) inevitably progresses to end-stage renal disease if intervention does not occur timely. However, there are limitations in predicting the progression of CKD by solely relying on changes in renal function. A biomarker with high sensitivity and specificity that can predict CKD progression early is required. We used the online Gene Expression Omnibus microarray dataset GSE45980 to identify differentially expressed genes (DEGs) in patients with progressive and stable CKD. We then performed functional enrichment and protein-protein interaction network analysis on DEGs and identified key genes. Finally, the expression patterns of key genes were verified using the GSE60860 dataset, and the receiver operating characteristic curve analysis was performed to clarify their predictive ability of progressive CKD. Ultimately, we verified the expression profiles of these hub genes in an in vitro renal interstitial fibrosis model by real-time PCR and western blot analysis. Differential expression analysis identified 50 upregulated genes and 47 downregulated genes. The results of the functional enrichment analysis revealed that upregulated DEGs were mainly enriched in immune response, inflammatory response, and NF-κB signaling pathways, whereas downregulated DEGs were mainly related to angiogenesis and the extracellular environment. Protein-protein interaction network and key gene analysis identified CCR7 as the most important gene. CCR7 mainly plays a role in immune response, and its only receptors, CCL19 and CCL21, have also been identified as DEGs. The receiver operating characteristic curve analysis of CCR7, CCL19, and CCL21 found that CCR7 and CCL19 present good disease prediction ability. CCR7 may be a stable biomarker for predicting CKD progression, and the CCR7-CCL19/CCL21 axis may be a therapeutic target for end-stage renal disease. However, further experiments are needed to explore the relationship between these genes and CKD.

Serum soluble LYVE1 is a promising non-invasive biomarker of renal fibrosis: a population-based retrospective cross-sectional study

Diagnosis of renal fibrosis can only be verified by kidney biopsy, but biomarkers for non-invasive evaluation remain unsatisfactory. Patients with fibrosis often have abnormalities of the lymphatic vascular system and associated immune function. We describe here a lymphatic marker as a candidate biomarker for fibrosis. After assessing and grading the fibrosis scores, testing serum soluble lymphatic vessel endothelial hyaluronan receptor1 (sLYVE1) level, and collecting clinical information, the association between sLYVE1 and renal fibrosis was analyzed. Logistic regression analysis was used to screen variables. Diagnosis models with or without sLYVE1 were built, and nomograms were plotted. Calibration curve, C-index, and DCA were performed to assess the models. A total of 298 patients were enrolled in the study, of which 199 were included in the training cohort and 99 patients in the validation cohort. Serum sLYVE1 levels markedly elevated with increasing fibrosis grade (p<0.05). ROC analysis of sLYVE1 showed an AUC of 0.791 and 0.846 with optimal cut-off value of 405.25 ng/mL and 498.55 ng/mL for the prediction of moderate-to-severe renal fibrosis (MSF) and severe renal fibrosis (SF), respectively. The diagnostic nomogram model without sLYVE1 (model 1) included traditional clinical determinants (C-index: 0.658 for MSF; 0.603 for SF). A combination of model 1 and sLYVE1 (model 2) improved predictive performance (C-index: 0.847 for MSF; 0.856 for SF). Calibration curve and DCA demonstrated a better consistency accuracy and clinical benefit of model 2 than model 1. Serum sLYVE1 may be identified as a potential biomarker of renal fibrosis. Models incorporating sLYVE1 may be beneficial for a more accurate non-invasive diagnosis of renal fibrosis.

Single-Cell RNA Sequencing Identifies Response of Renal Lymphatic Endothelial Cells to Acute Kidney Injury

SIGNIFICANCE STATEMENT

The renal lymphatic vasculature and the lymphatic endothelial cells that make up this network play important immunomodulatory roles during inflammation. How lymphatics respond to AKI may affect AKI outcomes. The authors used single-cell RNA sequencing to characterize mouse renal lymphatic endothelial cells in quiescent and cisplatin-injured kidneys. Lymphatic endothelial cell gene expression changes were confirmed in ischemia-reperfusion injury and in cultured lymphatic endothelial cells, validating renal lymphatic endothelial cells single-cell RNA sequencing data. This study is the first to describe renal lymphatic endothelial cell heterogeneity and uncovers molecular pathways demonstrating lymphatic endothelial cells regulate the local immune response to AKI. These findings provide insights into previously unidentified molecular pathways for lymphatic endothelial cells and roles that may serve as potential therapeutic targets in limiting the progression of AKI.

BACKGROUND

The inflammatory response to AKI likely dictates future kidney health. Lymphatic vessels are responsible for maintaining tissue homeostasis through transport and immunomodulatory roles. Owing to the relative sparsity of lymphatic endothelial cells in the kidney, past sequencing efforts have not characterized these cells and their response to AKI.

METHODS

Here, we characterized murine renal lymphatic endothelial cell subpopulations by single-cell RNA sequencing and investigated their changes in cisplatin AKI 72 hours postinjury. Data were processed using the Seurat package. We validated our findings by quantitative PCR in lymphatic endothelial cells isolated from both cisplatin-injured and ischemia-reperfusion injury, by immunofluorescence, and confirmation in in vitro human lymphatic endothelial cells.

RESULTS

We have identified renal lymphatic endothelial cells and their lymphatic vascular roles that have yet to be characterized in previous studies. We report unique gene changes mapped across control and cisplatin-injured conditions. After AKI, renal lymphatic endothelial cells alter genes involved in endothelial cell apoptosis and vasculogenic processes as well as immunoregulatory signaling and metabolism. Differences between injury models were also identified with renal lymphatic endothelial cells further demonstrating changed gene expression between cisplatin and ischemia-reperfusion injury models, indicating the renal lymphatic endothelial cell response is both specific to where they lie in the lymphatic vasculature and the kidney injury type.

CONCLUSIONS

In this study, we uncover lymphatic vessel structural features of captured populations and injury-induced genetic changes. We further determine that lymphatic endothelial cell gene expression is altered between injury models. How lymphatic endothelial cells respond to AKI may therefore be key in regulating future kidney disease progression.

Eplerenone reduces lymphangiogenesis in the contralateral kidneys of UUO rats

Inflammation and fibrosis often occur in the kidney after acute injury, resulting in chronic kidney disease and consequent renal failure. Recent studies have indicated that lymphangiogenesis can drive renal inflammation and fibrosis in injured kidneys. However, whether and how this pathogenesis affects the contralateral kidney remain largely unknown. In our study, we uncovered a mechanism by which the contralateral kidney responded to injury. We found that the activation of mineralocorticoid receptors and the increase in vascular endothelial growth factor C in the contralateral kidney after unilateral ureteral obstruction could promote lymphangiogenesis. Furthermore, mineralocorticoid receptor activation in lymphatic endothelial cells resulted in the secretion of myofibroblast markers, thereby contributing to renal fibrosis. We observed that this process could be attenuated by administering the mineralocorticoid receptor blocker eplerenone, which, prevented the development of fibrotic injury in the contralateral kidneys of rats with unilateral ureteral obstruction. These findings offer valuable insights into the intricate mechanisms underlying kidney injury and may have implications for the development of therapeutic strategies to mitigate renal fibrosis in the context of kidney disease.

Lymphatic vessels in patients with crescentic glomerulonephritis: association with renal pathology and prognosis

BACKGROUND

Various immune cells, including T cells, B cells, macrophages, and neutrophils contribute to the development of crescentic glomerulonephritis. Previous animal studies have suggested that lymphangiogenesis is involved in the migration of inflammatory cells and the activation of adaptive immunity. However, the extent of the association between lymphatic vessels and crescentic glomerulonephritis severity and prognosis remains unknown.

METHODS AND RESULTS

In this study, we assessed lymphatic vessel density in 71 patients with crescentic glomerulonephritis who underwent renal biopsies between June 2017 and June 2022. By immunohistochemistry and immunofluorescence, we identified increased lymphatic vessel density in the kidneys of patients with crescentic glomerulonephritis compared to controls. Lymphatic vessels were categorized as total, periglomerular, and interstitial. Spearman's rank correlation analysis showed a positive correlation between total and periglomerular lymphatic vessel density and glomerular crescent proportion. High lymphatic vessel density (total and periglomerular) correlated with declining kidney function, increased proteinuria, and severe glomerular and interstitial pathology. Interstitial lymphatic vessel density had minimal relationship with renal lesions. After a median duration of 13 months of follow-up, higher total and periglomerular lymphatic vessel density was associated with poorer prognosis. Transcriptomic analysis revealed increased immune cell activation and migration in crescentic glomerulonephritis patients compared to healthy controls. Periglomerular lymphatic vessels might play a significant role in immune cell infiltration and renal injury.

CONCLUSION

Elevated lymphatic vessel density in patients with crescentic glomerulonephritis is associated with poor prognosis and may serve as a predictive factor for adverse outcomes in these patients.

Lymphatic System and the Kidney: From Lymphangiogenesis to Renal Inflammation and Fibrosis Development

The lymphatic kidney system plays a crucial role in managing interstitial fluid removal, regulating fluid balance, and tuning immune response. It also assists in the reabsorption of proteins, electrolytes, cytokines, growth factors, and immune cells. Pathological conditions, including tissue damage, excessive interstitial fluid, high blood glucose levels, and inflammation, can initiate lymphangiogenesis-the formation of new lymphatic vessels. This process is associated with various kidney diseases, including polycystic kidney disease, hypertension, ultrafiltration challenges, and complications post-organ transplantation. Although lymphangiogenesis has beneficial effects in removing excess fluid and immune cells, it may also contribute to inflammation and fibrosis within the kidneys. In this review, we aim to discuss the biology of the lymphatic system, from its development and function to its response to disease stimuli, with an emphasis on renal pathophysiology. Furthermore, we explore how innovative treatments targeting the lymphatic system could potentially enhance the management of kidney diseases.

Recent Advances in Understanding Peripheral and Gut Immune Cell-Mediated Salt-Sensitive Hypertension and Nephropathy

Hypertension is the primary modifiable risk factor for cardiovascular, renal, and cerebrovascular diseases and is considered the main contributing factor to morbidity and mortality worldwide. Approximately 50% of hypertensive and 25% of normotensive people exhibit salt sensitivity of blood pressure, which is an independent risk factor for cardiovascular disease. Human and animal studies demonstrate that the immune system plays an important role in the etiology and pathogenesis of salt sensitivity of blood pressure, kidney damage, and vascular diseases. Antigen-presenting and adaptive immune cells are implicated in salt-sensitive hypertension and salt-induced renal and vascular injury. Elevated sodium activates antigen-presenting cells to release proinflammatory cytokines including IL (interleukin) 6, tumor necrosis factor-α, IL-1β, and accumulate isolevuglandin-protein adducts. In turn, these activate T cells release prohypertensive cytokines including IL-17A. Moreover, high-salt intake is associated with gut dysbiosis, leading to inflammation, oxidative stress, and blood pressure elevation but the mechanistic contribution to salt-sensitivity of blood pressure is not clearly understood. Here, we discuss recent advances in research investigating the cause, potential biomarkers, and therapeutic targets for salt-sensitive hypertension as they pertain to the gut microbiome, immunity, and inflammation.

Advances in understanding of dendritic cell in the pathogenesis of acute kidney injury

Acute kidney injury (AKI) is characterized by a rapid decline in renal function and is associated with a high morbidity and mortality rate. At present, the underlying mechanisms of AKI remain incompletely understood. Immune disorder is a prominent feature of AKI, and dendritic cells (DCs) play a pivotal role in orchestrating both innate and adaptive immune responses, including the induction of protective proinflammatory and tolerogenic immune reactions. Emerging evidence suggests that DCs play a critical role in the initiation and development of AKI. This paper aimed to conduct a comprehensive review and analysis of the role of DCs in the progression of AKI and elucidate the underlying molecular mechanism. The ultimate objective was to offer valuable insights and guidance for the treatment of AKI.

Correlation of serum VEGF-C, ANGPTL4, and activin A levels with frailty

BACKGROUND

Secretory factors linked to lymphogenesis, such as vascular endothelial growth factor C (VEGF-C), angiopoietin like protein 4 (ANGPTL4), and activin A (ACV-A), have been recognized as potential markers of chronic inflammatory status and age-related diseases. Furthermore, these factors may also be linked to frailty. The primary objective of this study was to examine the serum VEGF-C, ANGPTL4, and ACV-A levels in young individuals, healthy older individuals, and older individuals with pre-frailty and frailty, and to determine their association with pro-inflammatory factor levels.

METHODS

We conducted an observational study, enrolling a total of 210 older individuals and 20 young healthy volunteers. Participants were divided into four groups based on the Freid frailty phenotype: healthy young group, older patients without frailty group, pre-frail older group, and frail older group. Plasma and peripheral blood mononuclear cells (PBMCs) were collected from all four groups. ELISA was used to measure the serum levels of VEGF-C, ANGPTL4, ACV-A, and pro-inflammatory cytokines, while RT-qPCR was used to measure the transcription level of VEGF-C, ANGPTL4 and ACV-A in PBMCs.

RESULTS

In comparison to healthy young individuals and older participants without frailty, older participants with frailty exhibited lower renal function, higher serum levels and transcription levels of VEGF-C, ANGPTL4, ACV-A, and elevated levels of pro-inflammatory cytokines (CRP, IL-1β, and TNF-α). Multiple linear regression analysis revealed that serum levels of VEGF-C, ANGPTL4, and ACV-A were positively correlated with the frailty index, independent of age, eGFR, and comorbidities. Furthermore, the receiver operating characteristic (ROC) curve analysis demonstrated that serum levels of VEGF-C, ANGPTL4, and ACV-A have great accuracy in predicting frailty.

CONCLUSION

Elevated serum levels of VEGF-C, ANGPTL4, and ACV-A are associated with frailty status.

Immunoregulation mechanism of VEGF signaling pathway inhibitors and its efficacy on the kidney

Angiogenesis and immunosuppression are closely related pathophysiologic processes. Widely prescribed in malignant tumor and proliferative retinal lesions, VEGF signaling pathway inhibitors may cause hypertension and renal injury in some patients, presenting with proteinuria, nephrotic syndrome, renal failure and thrombotic microangiopathy. VEGF signaling pathway inhibitors block the action of both VEGF-A and VEGF-C. However, VEGF-A and VEGF-C produced by podocytes are vital to maintain the physiological function of glomerular endothelial cells and podocytes. There is still no effective treatment for kidney disease associated with VEGF signaling pathway inhibitors and some patients have progressive renal failure even after withdrawal of the drug. Recent studies reveal that blocking of VEGF-A and VEGF-C can activate CD4 +and CD8+ T cells, augment antigen-presenting function of dendritic cells, enhance cytotoxicity of macrophages and initiate complement cascade activation. VEGF and VEGFR are expressed in immune cells, which are involved in the immunosuppression and cross-talk among immune cells. This review summarizes the expression and function of VEGF-A and VEGF-C in the kidney. The current immunoregulation mechanisms of VEGF signaling pathway inhibitors are reviewed. Finally, combinate strategies are summarized to highlight the proposal for VEGF signaling pathway inhibitors.

Angiogenesis-An Emerging Role in Organ Fibrosis

In recent years, the study of lymphangiogenesis and fibrotic diseases has made considerable achievements, and accumulating evidence indicates that lymphangiogenesis plays a key role in the process of fibrosis in various organs. Although the effects of lymphangiogenesis on fibrosis disease have not been conclusively determined due to different disease models and pathological stages of organ fibrosis, its importance in the development of fibrosis is unquestionable. Therefore, we expounded on the characteristics of lymphangiogenesis in fibrotic diseases from the effects of lymphangiogenesis on fibrosis, the source of lymphatic endothelial cells (LECs), the mechanism of fibrosis-related lymphangiogenesis, and the therapeutic effect of intervening lymphangiogenesis on fibrosis. We found that expansion of LECs or lymphatic networks occurs through original endothelial cell budding or macrophage differentiation into LECs, and the vascular endothelial growth factor C (VEGFC)/vascular endothelial growth factor receptor (VEGFR3) pathway is central in fibrosis-related lymphangiogenesis. Lymphatic vessel endothelial hyaluronan receptor 1 (LYVE1), as a receptor of LECs, is also involved in the regulation of lymphangiogenesis. Intervention with lymphangiogenesis improves fibrosis to some extent. In the complex organ fibrosis microenvironment, a variety of functional cells, inflammatory factors and chemokines synergistically or antagonistically form the complex network involved in fibrosis-related lymphangiogenesis and regulate the progression of fibrosis disease. Further clarifying the formation of a new fibrosis-related lymphangiogenesis network may potentially provide new strategies for the treatment of fibrosis disease.

Tolerogenic dendritic cells protect against acute kidney injury

Ischemia reperfusion injury is a common precipitant of acute kidney injury that occurs following disrupted perfusion to the kidney. This includes blood loss and hemodynamic shock, as well as during retrieval for deceased donor kidney transplantation. Acute kidney injury is associated with adverse long-term clinical outcomes and requires effective interventions that can modify the disease process. Immunomodulatory cell therapies such as tolerogenic dendritic cells remain a promising tool, and here we tested the hypothesis that adoptively transferred tolerogenic dendritic cells can limit kidney injury. The phenotypic and genomic signatures of bone marrow-derived syngeneic or allogeneic, Vitamin-D3/IL-10-conditioned tolerogenic dendritic cells were assessed. These cells were characterized by high PD-L1:CD86, elevated IL-10, restricted IL-12p70 secretion and a suppressed transcriptomic inflammatory profile. When infused systemically, these cells successfully abrogated kidney injury without modifying infiltrating inflammatory cell populations. They also provided protection against ischemia reperfusion injury in mice pre-treated with liposomal clodronate, suggesting the process was regulated by live, rather than reprocessed cells. Co-culture experiments and spatial transcriptomic analysis confirmed reduced kidney tubular epithelial cell injury. Thus, our data provide strong evidence that peri-operatively administered tolerogenic dendritic cells have the ability to protect against acute kidney injury and warrants further exploration as a therapeutic option. This technology may provide a clinical advantage for bench-to-bedside translation to affect patient outcomes.

Single-cell RNA sequencing identifies response of renal lymphatic endothelial cells to acute kidney injury

The inflammatory response to acute kidney injury (AKI) likely dictates future renal health. Lymphatic vessels are responsible for maintaining tissue homeostasis through transport and immunomodulatory roles. Due to the relative sparsity of lymphatic endothelial cells (LECs) in the kidney, past sequencing efforts have not characterized these cells and their response to AKI. Here we characterized murine renal LEC subpopulations by single-cell RNA sequencing and investigated their changes in cisplatin AKI. We validated our findings by qPCR in LECs isolated from both cisplatin-injured and ischemia reperfusion injury, by immunofluorescence, and confirmation in in vitro human LECs. We have identified renal LECs and their lymphatic vascular roles that have yet to be characterized in previous studies. We report unique gene changes mapped across control and cisplatin injured conditions. Following AKI, renal LECs alter genes involved endothelial cell apoptosis and vasculogenic processes as well as immunoregulatory signaling and metabolism. Differences between injury models are also identified with renal LECs further demonstrating changed gene expression between cisplatin and ischemia reperfusion injury models, indicating the renal LEC response is both specific to where they lie in the lymphatic vasculature and the renal injury type. How LECs respond to AKI may therefore be key in regulating future kidney disease progression.

Combining robust urine biomarkers to assess chronic kidney disease progression

BACKGROUND

Urinary biomarkers may improve the prediction of chronic kidney disease (CKD) progression. Yet, data reporting the applicability of most commercial biomarker assays to the detection of their target analyte in urine together with an evaluation of their predictive performance are scarce.

METHODS

30 commercial assays (ELISA) were tested for their ability to quantify the target analyte in urine using strict (FDA-approved) validation criteria. In an exploratory analysis, LASSO (Least Absolute Shrinkage and Selection Operator) logistic regression analysis was used to identify potentially complementary biomarkers predicting fast CKD progression, determined as the ⁵¹CrEDTA clearance-based measured glomerular filtration rate (mGFR) decline (>10% per year) in a subsample of 229 CKD patients (mean age, 61 years; 66% men; baseline mGFR, 38 mL/min) from the NephroTest prospective cohort.

FINDINGS

Among the 30 assays, directed against 24 candidate biomarkers, encompassing different pathophysiological mechanisms of CKD progression, 16 assays fulfilled the FDA-approved criteria. LASSO logistic regressions identified a combination of five biomarkers including CCL2, EGF, KIM1, NGAL, and TGF-α that improved the prediction of fast mGFR decline compared to the kidney failure risk equation variables alone: age, gender, mGFR, and albuminuria. Mean area under the curves (AUC) estimated from 100 re-samples was higher in the model with than without these biomarkers, 0.722 (95% confidence interval 0.652-0.795) vs. 0.682 (0.614-0.748), respectively. Fully-adjusted odds-ratios (95% confidence interval) for fast progression were 1.87 (1.22, 2.98), 1.86 (1.23, 2.89), 0.43 (0.25, 0.70), 1.10 (0.71, 1.83), 0.55 (0.33, 0.89), and 2.99 (1.89, 5.01) for albumin, CCL2, EGF, KIM1, NGAL, and TGF-α, respectively.

INTERPRETATION

This study provides a rigorous validation of multiple assays for relevant urinary biomarkers of CKD progression which combination may improve the prediction of CKD progression.

FUNDING

This work was supported by Institut National de la Santé et de la Recherche Médicale, Université de Paris, Assistance Publique Hôpitaux de Paris, Agence Nationale de la Recherche, MSDAVENIR, Pharma Research and Early Development Roche Laboratories (Basel, Switzerland), and Institut Roche de Recherche et Médecine Translationnelle (Paris, France).

The Lymphatic System in Kidney Disease

The high-capacity vessels of the lymphatic system drain extravasated fluid and macromolecules from nearly every part of the body. However, far from merely a passive conduit for fluid removal, the lymphatic system also plays a critical and active role in immune surveillance and immune response modulation through the presentation of fluid, macromolecules, and trafficking immune cells to surveillance cells in regional draining lymph nodes before their return to the systemic circulation. The potential effect of this system in numerous disease states both within and outside of the kidney is increasingly being explored for their therapeutic potential. In the kidneys, the lymphatics play a critical role in both fluid and macromolecule removal to maintain oncotic and hydrostatic pressure gradients for normal kidney function, as well as in shaping kidney immunity, and potentially in balancing physiological pathways that promote healthy organ maintenance and responses to injury. In many states of kidney disease, including AKI, the demand on the preexisting lymphatic network increases for clearance of injury-related tissue edema and inflammatory infiltrates. Lymphangiogenesis, stimulated by macrophages, injured resident cells, and other drivers in kidney tissue, is highly prevalent in settings of AKI, CKD, and transplantation. Accumulating evidence points toward lymphangiogenesis being possibly harmful in AKI and kidney allograft rejection, which would potentially position lymphatics as another target for novel therapies to improve outcomes. However, the extent to which lymphangiogenesis is protective rather than maladaptive in the kidney in various settings remains poorly understood and thus an area of active research.

The same heterozygous Col4A4 mutation triggered different renal pathological changes in Chinese family members

Background: Mutations in the collagen components of the glomerular basement membrane (GBM) often lead to hereditary glomerulonephritis. Previous studies have identified that autosomal dominant mutations of Col4A3, Col4A4 or Col4A5 are associated with thin basement membrane nephropathy (TBMN), Alport syndrome and other hereditary kidney diseases. However, the genetic mutations underlying other glomerulonephritis types have not been elucidated. Methods: In this study, we investigated a Chinese family with hereditary nephritis using the methods of genetic sequencing and renal biopsy. Genomic DNA was extracted from peripheral blood of the proband and her sister, and subsequently was performed genetic sequencing. They were found to have the similar mutation sites. Other family members were then validated using Sanger sequencing. The proband and her sister underwent renal puncture biopsies, and experienced pathologists performed PAS, Masson, immunofluorescence, and immunoelectron microscopic staining of the kidney tissue sections. Results: Through genetic sequencing analysis, we detected a novel heterozygous frameshift mutation c.1826delC in the COL4A4 (NM_000092.4) gene coding region, and 1 hybrid missense variation c.86G>A (p. R29Q) was also detected in the TNXB (NM_019105.6) gene coding region in several members of this Chinese family. Interestingly, we found that the same mutations caused different clinical features and distinct pathological changes in individual family members, which confirmed that pathological and genetic testing are crucial for the diagnosis and treatment of hereditary kidney diseases. Conclusion: In this study, we found a novel heterozygous mutation in Col4A4 and co-mutations of the TNXB gene in this Chinese family. Our study indicated that the same Col4A4 mutated variants produced different pathological and clinical changes in different family members. This discovery may provide novel insights into the study of hereditary kidney disease. In addition, new genetic biology techniques and renal biopsy of individual family members are essential.

Interleukin-37 promotes DMBA/TPA skin cancer through SIGIRR-mediated inhibition of glycolysis in CD103+DC cells

Interleukin 37 (IL-37), a member of the IL-1 family, is considered a suppressor of innate and adaptive immunity and, hence is a regulator of tumor immunity. However, the specific molecular mechanism and role of IL-37 in skin cancer remain unclear. Here, we report that IL-37b-transgenic mice (IL-37tg) treated with the carcinogenic 7,12-dimethylbenzoanthracene (DMBA)/12-o-tetradecylphorbol-13-acetate (TPA) exhibited enhanced skin cancer and increased tumor burden in the skin by inhibiting the function of CD103⁺ dendritic cells (DCs). Notably, IL-37 induced rapid phosphorylation of adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK), and via single immunoglobulin IL-1-related receptor (SIGIRR), inhibited the long-term Akt activation. Specifically, by affecting the SIGIRR-AMPK-Akt signaling axis, which is related to the regulation of glycolysis in CD103⁺DCs, IL-37 inhibited their anti-tumor function. Our results show that a marked correlation between the CD103⁺DC signature (IRF8, FMS-like tyrosine kinase 3 ligand, CLEC9A, CLNK, XCR1, BATF3, and ZBTB46) and chemokines C-X-C motif chemokine ligand 9, CXCL10, and CD8A in a mouse model with DMBA/TPA-induced skin cancer. In a word, our results highlight that IL-37 as an inhibitor of tumor immune surveillance through modulating CD103⁺DCs and establishing an important link between metabolism and immunity as a therapeutic target for skin cancer.

Kidney fibrosis: from mechanisms to therapeutic medicines

Chronic kidney disease (CKD) is estimated to affect 10-14% of global population. Kidney fibrosis, characterized by excessive extracellular matrix deposition leading to scarring, is a hallmark manifestation in different progressive CKD; However, at present no antifibrotic therapies against CKD exist. Kidney fibrosis is identified by tubule atrophy, interstitial chronic inflammation and fibrogenesis, glomerulosclerosis, and vascular rarefaction. Fibrotic niche, where organ fibrosis initiates, is a complex interplay between injured parenchyma (like tubular cells) and multiple non-parenchymal cell lineages (immune and mesenchymal cells) located spatially within scarring areas. Although the mechanisms of kidney fibrosis are complicated due to the kinds of cells involved, with the help of single-cell technology, many key questions have been explored, such as what kind of renal tubules are profibrotic, where myofibroblasts originate, which immune cells are involved, and how cells communicate with each other. In addition, genetics and epigenetics are deeper mechanisms that regulate kidney fibrosis. And the reversible nature of epigenetic changes including DNA methylation, RNA interference, and chromatin remodeling, gives an opportunity to stop or reverse kidney fibrosis by therapeutic strategies. More marketed (e.g., RAS blockage, SGLT2 inhibitors) have been developed to delay CKD progression in recent years. Furthermore, a better understanding of renal fibrosis is also favored to discover biomarkers of fibrotic injury. In the review, we update recent advances in the mechanism of renal fibrosis and summarize novel biomarkers and antifibrotic treatment for CKD.

Regulating Lymphatic Vasculature in Fibrosis: Understanding the Biology to Improve the Modeling

Fibrosis occurs in many chronic diseases with lymphatic vascular insufficiency (e.g., kidney disease, tumors, and lymphedema). New lymphatic capillary growth can be triggered by fibrosis-related tissue stiffening and soluble factors, but questions remain for how related biomechanical, biophysical, and biochemical cues affect lymphatic vascular growth and function. The current preclinical standard for studying lymphatics is animal modeling, but in vitro and in vivo outcomes often do not align. In vitro models can also be limited in their ability to separate vascular growth and function as individual outcomes, and fibrosis is not traditionally included in model design. Tissue engineering provides an opportunity to address in vitro limitations and mimic microenvironmental features that impact lymphatic vasculature. This review discusses fibrosis-related lymphatic vascular growth and function in disease and the current state of in vitro lymphatic vascular models while highlighting relevant knowledge gaps. Additional insights into the future of in vitro lymphatic vascular models demonstrate how prioritizing fibrosis alongside lymphatics will help capture the complexity and dynamics of lymphatics in disease. Overall, this review aims to emphasize that an advanced understanding of lymphatics within a fibrotic disease-enabled through more accurate preclinical modeling-will significantly impact therapeutic development toward restoring lymphatic vessel growth and function in patients.

Glycosyltransferase Extl1 promotes CCR7-mediated dendritic cell migration to restrain infection and autoimmunity

CCR7-triggered DC migration toward draining lymph nodes is critical for the initiation of protective immunity and maintenance of immune tolerance. How to promote CCR7-mediated DC migration to determine T cell responses under inflammatory and homeostatic conditions remains poorly understood. Here we demonstrate that the Extl1 (Exostosin like glycosyltransferase 1) promotes CCR7-triggered DC migration in a heparan sulfate proteoglycans (HSPG)-dependent manner. Mechanistically, Extl1 mediates HSPG production via its glycosyltransferase domain to inhibit C1q expression. Extl1/HSPG axis relieves C1q-mediated restriction of CCR7 surface expression and internalization, and thus enhances CCR7-dependent migratory signaling activation. Consequently, Extl1 is required for DC-mediated Th1 and Th17 responses in immune defense against bacterial infection and for Treg cell development in the prevention of autoimmunity. Our study adds mechanistic insights to the regulation of CCR7-triggered DC migration in immunity and tolerance and provides a potential target for the treatment of infectious and autoimmune diseases.

Promoting Lymphangiogenesis and Lymphatic Growth and Remodeling to Treat Cardiovascular and Metabolic Diseases

Lymphatic vessels are low-pressure, blind-ended tubular structures that play a crucial role in the maintenance of tissue fluid homeostasis, immune cell trafficking, and dietary lipid uptake and transport. Emerging research has indicated that the promotion of lymphatic vascular growth, remodeling, and function can reduce inflammation and diminish disease severity in several pathophysiologic conditions. In particular, recent groundbreaking studies have shown that lymphangiogenesis, which describes the formation of new lymphatic vessels from the existing lymphatic vasculature, can be beneficial for the alleviation and resolution of metabolic and cardiovascular diseases. Therefore, promoting lymphangiogenesis represents a promising therapeutic approach. This brief review summarizes the most recent findings related to the modulation of lymphatic function to treat metabolic and cardiovascular diseases such as obesity, myocardial infarction, atherosclerosis, and hypertension. We also discuss experimental and therapeutic approaches to enforce lymphatic growth and remodeling as well as efforts to define the molecular and cellular mechanisms underlying these processes.

The regulatory effect of pulmonary lymphatic drainage on silicosis fibrosis

Silicosis is a fibrotic disease caused by long-term inhalation of SiO₂ particles that currently has no effective treatment. Earlier studies have suggested that pulmonary lymphatic vessels play a key role in the transport of silica but have not address the long-term effects of altered pulmonary lymphatic drainage on silicosis. Here, we investigated the impact of impaired pulmonary lymphatic drainage on silicosis. In the past, lymphatic drainage disorders were established mainly through the use of VEGF inhibitors. For the first time, we established a model of pulmonary lymphatic drainage disorder by ligating the thoracic duct in rats. Impaired pulmonary lymphatic drainage was found to aggravate inflammation and oxidative damage in silicosis rats and accelerate silicosis progression. Next, we investigated the effect of pulmonary lymphatic drainage on silicosis. We have demonstrated the effect of sodium tanshinone IIA sulfonate(STS) on lymphangiogenesis, which revealed that STS promotes lymphangiogenesis and can delay inflammation, oxidative damage, and fibrosis progression in silicosis rats by promoting the pulmonary lymphatic drainage response, and this effect is mediated by the VEGFR-3/PI3K/AKT signaling pathway. These findings suggest that pulmonary lymphogenesis plays an important role in silicosis pathogenesis, and targeted intervention in pulmonary lymphangiogenesis may be a potential strategy for treating of silicosis in the future.

Ablation of lysophosphatidic acid receptor 1 attenuates hypertrophic cardiomyopathy in a mouse model

Myocardial fibrosis is a key pathologic feature of hypertrophic cardiomyopathy (HCM). However, the fibrotic pathways activated by HCM-causing sarcomere protein gene mutations are poorly defined. Because lysophosphatidic acid is a mediator of fibrosis in multiple organs and diseases, we tested the role of the lysophosphatidic acid pathway in HCM. Lysphosphatidic acid receptor 1 (LPAR1), a cell surface receptor, is required for lysophosphatidic acid mediation of fibrosis. We bred HCM mice carrying a pathogenic myosin heavy-chain variant (403+/-) with Lpar1-ablated mice to create mice carrying both genetic changes (403+/- LPAR1 -/-) and assessed development of cardiac hypertrophy and fibrosis. Compared with 403+/- LPAR1WT, 403+/- LPAR1 -/- mice developed significantly less hypertrophy and fibrosis. Single-nucleus RNA sequencing of left ventricular tissue demonstrated that Lpar1 was predominantly expressed by lymphatic endothelial cells (LECs) and cardiac fibroblasts. Lpar1 ablation reduced the population of LECs, confirmed by immunofluorescence staining of the LEC markers Lyve1 and Ccl21a and, by in situ hybridization, for Reln and Ccl21a. Lpar1 ablation also altered the distribution of fibroblast cell states. FB1 and FB2 fibroblasts decreased while FB0 and FB3 fibroblasts increased. Our findings indicate that Lpar1 is expressed predominantly by LECs and fibroblasts in the heart and is required for development of hypertrophy and fibrosis in an HCM mouse model. LPAR1 antagonism, including agents in clinical trials for other fibrotic diseases, may be beneficial for HCM.

Targeting fibrosis, mechanisms and cilinical trials

Fibrosis is characterized by the excessive extracellular matrix deposition due to dysregulated wound and connective tissue repair response. Multiple organs can develop fibrosis, including the liver, kidney, heart, and lung. Fibrosis such as liver cirrhosis, idiopathic pulmonary fibrosis, and cystic fibrosis caused substantial disease burden. Persistent abnormal activation of myofibroblasts mediated by various signals, such as transforming growth factor, platelet-derived growth factor, and fibroblast growh factor, has been recongized as a major event in the occurrence and progression of fibrosis. Although the mechanisms driving organ-specific fibrosis have not been fully elucidated, drugs targeting these identified aberrant signals have achieved potent anti-fibrotic efficacy in clinical trials. In this review, we briefly introduce the aetiology and epidemiology of several fibrosis diseases, including liver fibrosis, kidney fibrosis, cardiac fibrosis, and pulmonary fibrosis. Then, we summarise the abnormal cells (epithelial cells, endothelial cells, immune cells, and fibroblasts) and their interactions in fibrosis. In addition, we also focus on the aberrant signaling pathways and therapeutic targets that regulate myofibroblast activation, extracellular matrix cross-linking, metabolism, and inflammation in fibrosis. Finally, we discuss the anti-fibrotic drugs based on their targets and clinical trials. This review provides reference for further research on fibrosis mechanism, drug development, and clinical trials.

Lymphangiogenesis and Lymphatic Barrier Dysfunction in Renal Fibrosis

As an integral part of the vascular system, the lymphatic vasculature is essential for tissue fluid homeostasis, nutritional lipid assimilation and immune regulation. The composition of the lymphatic vasculature includes fluid-absorbing initial lymphatic vessels (LVs), transporting collecting vessels and anti-regurgitation valves. Although, in recent decades, research has drastically enlightened our view of LVs, investigations of initial LVs, also known as lymphatic capillaries, have been stagnant due to technical limitations. In the kidney, the lymphatic vasculature mainly presents in the cortex, keeping the local balance of fluid, solutes and immune cells. The contribution of renal LVs to various forms of pathology, especially chronic kidney diseases, has been addressed in previous studies, however with diverging and inconclusive results. In this review, we discuss the most recent advances in the proliferation and permeability of lymphatic capillaries as well as their influencing factors. Novel technologies to visualize and measure LVs function are described. Then, we highlight the role of the lymphatic network in renal fibrosis and the crosstalk between kidney and other organs, such as gut and heart.

Ginsenoside Rg1 attenuates LPS-induced chronic renal injury by inhibiting NOX4-NLRP3 signaling in mice

Chronic renal injury (CRI) is a common pathological damage in chronic renal disease, and the therapeutic options for preventing its progression are limited at present. Ginsenoside Rg1 (Rg1) is reported to have a protective effect on renal injury by improving oxidative stress and inflammation. Lipopolysaccharide (LPS) plays important roles in inducing inflammatory and high-dose LPS is often used to perform acute renal injury. However, little is known about the effect of low-dose LPS on CRI, and the protective effect of Rg1 against chronic LPS-induced CRI. Here, we reported the protective effect and mechanism of Rg1 against LPS-induced CRI in mice. In this study, the results demonstrated that low-dose LPS (0.25 mg/kg) exposure for 14 days significantly induced renal function impairment and renal injury and fibrosis. Meanwhile, LPS exposure significantly increased reactive oxygen species (ROS) generation, NADPH oxidase 4 (NOX4) and NLRP3 inflammasome expression in renal cortex. However, treatment with Rg1, tempol (a superoxide dismutase mimetic), and apocynin (a NOX inhibitor) significantly improved renal function impairment and renal fibrosis, and significantly decreased the levels of TGF-β, IL-1β, KIM-1, β-Gal, and collagen IV in the kidneys. And Rg1 treatment also significantly reduced ROS generation and inhibited the activation of NOX4 and NLRP3 inflammasome. Overall, these results suggest that Rg1 treatment can ameliorate LPS-induced chronic kidney injury and renal fibrosis, the mechanisms may be involved in reducing NOX2-mediated oxidative stress and inhibiting NLRP1 inflammasome.

Circulating MicroRNA-505 May Serve as a Prognostic Biomarker for Hypertension-Associated Endothelial Dysfunction and Inflammation

Our previous study has reported that the plasma microRNA-505 (miR-505) is elevated in hypertensive patients. However, the pathophysiological significance of miR-505 in hypertension remains to be elucidated. Hypertension is not only a vascular disorder, but also an inflammatory condition. The current study therefore aims to further investigate the pathophysiological implications of miR-505 in hypertension-associated vascular and inflammatory changes. In vivo experiments reveal that the plasma level of miR-505 is elevated in spontaneously hypertensive rats and angiotensin II-infused mice. In addition, miR-505 agomir treatment results in elevated blood pressure, endothelial dysfunction, increased vascular expression of inflammatory genes and renal inflammatory injuries as well as pre-activation of PBMCs in mice. In vitro experiments further demonstrate that miR-505 agomir increases the expression of IL1B and TNFA, whereas miR-505 antagomir attenuates TNF-α-induced upregulation of IL1B and TNFA in endothelial cells, HUVECs. In addition, miR-505 modulates the levels of endothelial activation markers VCAM1 and E-selectin in HUVECs as well as the adhesion of THP-1 monocytes to HUVECs. Lastly, the plasma level of miR-505 is positively correlated with systolic blood pressure and the level of C-reactive protein in human subjects. Our work links for the first time miR-505 to endothelial dysfunction and inflammation under hypertensive conditions, supporting the translational value of miR-505 in prognosticating hypertension-associated endothelial impairment and inflammatory injuries in target organs such as the vessels and kidneys.

Boosting Vascular Imaging-Performance and Systemic Biosafety of Ultra-Small NaGdF4 Nanoparticles via Surface Engineering with Rationally Designed Novel Hydrophilic Block Co-Polymer

Revealing the anatomical structures, functions, and distribution of vasculature via contrast agent (CA) enhanced magnetic resonance imaging (MRI) is crucial for precise medical diagnosis and therapy. The clinically used MRI CAs strongly rely on Gd-chelates, which exhibit low T₁ relaxivities and high risks of nephrogenic systemic fibrosis (NSF) for patients with renal dysfunction. It is extremely important to develop high-performance and safe CAs for MRI. Herein, it is reported that ultra-small NaGdF₄ nanoparticles (UGNs) can serve as an excellent safe MRI CA via surface engineering with rationally designed novel hydrophilic block co-polymer (BP_n ). By optimizing the polymer molecular weights, the polymer-functionalized UGNs (i.e., UGNs-BP₁₄ ) are obtained to exhibit remarkably higher relaxivity (11.8 mm^-1 s^-1 at 3.0 T) than Gd-DTPA (3.6 mm^-1 s^-1 ) due to their ultracompact and abundant hydrophilic surface coating. The high performance of UGNs-BP₁₄ enables us to sensitively visualize microvasculature with a small diameter of ≈0.17 mm for up to 2 h, which is the thinnest blood vessel and the longest time window for low field (1.0 T) MR angiography ever reported, and cannot be achieved by using the clinically used Gd-DTPA under the same conditions. More importantly, renal clearable UGNs-BP₁₄ show lower risks of inducing NSF in comparison with Gd-DTPA due to their negligible release of Gd³⁺ ions after modification with the novel hydrophilic block copolymer. The study presents a novel avenue for boosting imaging-performance and systemic biosafety of UGNs as a robust MRI CA with great potential in precise diagnosis of vasculature-related diseases.

Twist1 regulates macrophage plasticity to promote renal fibrosis through galectin-3

Renal interstitial fibrosis is the pathological basis of end-stage renal disease, in which the heterogeneity of macrophages in renal microenvironment plays an important role. However, the molecular mechanisms of macrophage plasticity during renal fibrosis progression remain unclear. In this study, we found for the first time that increased expression of Twist1 in macrophages was significantly associated with the severity of renal fibrosis in IgA nephropathy patients and mice with unilateral ureteral obstruction (UUO). Ablation of Twist1 in macrophages markedly alleviated renal tubular injury and renal fibrosis in UUO mice, accompanied by a lower extent of macrophage infiltration and M2 polarization in the kidney. The knockdown of Twist1 inhibited the chemotaxis and migration of macrophages, at least partially, through the CCL2/CCR2 axis. Twist1 downregulation inhibited M2 macrophage polarization and reduced the secretion of the profibrotic factors Arg-1, MR (CD206), IL-10, and TGF-β. Galectin-3 was decreased in the macrophages of the conditional Twist1-deficient mice, and Twist1 was shown to directly activate galectin-3 transcription. Up-regulation of galectin-3 recovered Twist1-mediated M2 macrophage polarization. In conclusion, Twist1/galectin-3 signaling regulates macrophage plasticity (M2 phenotype) and promotes renal fibrosis. This study could suggest new strategies for delaying kidney fibrosis in patients with chronic kidney disease.

Kidney Injury Causes Accumulation of Renal Sodium That Modulates Renal Lymphatic Dynamics

Lymphatic vessels are highly responsive to changes in the interstitial environment. Previously, we showed renal lymphatics express the Na-K-2Cl cotransporter. Since interstitial sodium retention is a hallmark of proteinuric injury, we examined whether renal sodium affects NKCC1 expression and the dynamic pumping function of renal lymphatic vessels. Puromycin aminonucleoside (PAN)-injected rats served as a model of proteinuric kidney injury. Sodium ²³Na/¹H-MRI was used to measure renal sodium and water content in live animals. Renal lymph, which reflects the interstitial composition, was collected, and the sodium analyzed. The contractile dynamics of isolated renal lymphatic vessels were studied in a perfusion chamber. Cultured lymphatic endothelial cells (LECs) were used to assess direct sodium effects on NKCC1. MRI showed elevation in renal sodium and water in PAN. In addition, renal lymph contained higher sodium, although the plasma sodium showed no difference between PAN and controls. High sodium decreased contractility of renal collecting lymphatic vessels. In LECs, high sodium reduced phosphorylated NKCC1 and SPAK, an upstream activating kinase of NKCC1, and eNOS, a downstream effector of lymphatic contractility. The NKCC1 inhibitor furosemide showed a weaker effect on ejection fraction in isolated renal lymphatics of PAN vs controls. High sodium within the renal interstitium following proteinuric injury is associated with impaired renal lymphatic pumping that may, in part, involve the SPAK-NKCC1-eNOS pathway, which may contribute to sodium retention and reduce lymphatic responsiveness to furosemide. We propose that this lymphatic vessel dysfunction is a novel mechanism of impaired interstitial clearance and edema in proteinuric kidney disease.

Lymphatic Reconstruction in Kidney Allograft Aggravates Chronic Rejection by Promoting Alloantigen Presentation

Chronic rejection of the renal allograft remains a major cause of graft loss. Here, we demonstrated that the remodeling of lymphatic vessels (LVs) after their broken during transplantation contributes to the antigen presenting and lymph nodes activating. Our studies observed a rebuilt of interrupted lymph draining one week after mouse kidney transplantation, involving preexisting lymphatic endothelial cells (LECs) from both the donor and recipient. These expanding LVs also release C-C chemokine ligand 21 (CCL21) and recruit CCR7⁺ cells, mainly dendritic cells (DCs), toward lymph nodes and spleen, evoking the adaptive response. This rejection could be relieved by LYVE-1 specific LVs knockout or CCR7 migration inhibition in mouse model. Moreover, in retrospective analysis, posttransplant patients exhibiting higher area density of LVs presented with lower eGFR, severe serum creatinine and proteinuria, and greater interstitial fibrosis. These results reveal a rebuilt pathway for alloantigen trafficking and lymphocytes activation, providing strategies to alleviate chronic transplantation rejection.

Metabolic Reprogramming and Renal Fibrosis

There are several causes of chronic kidney disease, but all of these patients have renal fibrosis. Although many studies have examined the pathogenesis of renal fibrosis, there are still no effective treatments. A healthy and balanced metabolism is necessary for normal cell growth, proliferation, and function, but metabolic abnormalities can lead to pathological changes. Normal energy metabolism is particularly important for maintaining the structure and function of the kidneys because they consume large amounts of energy. We describe the metabolic reprogramming that occurs during renal fibrosis, which includes changes in fatty acid metabolism and glucose metabolism, and the relationship of these changes with renal fibrosis. We also describe the potential role of novel drugs that disrupt this metabolic reprogramming and the development of fibrosis, and current and future challenges in the treatment of fibrosis.

VEGFR3 tyrosine kinase inhibition aggravates cisplatin nephrotoxicity

Expansion of renal lymphatic networks, or lymphangiogenesis (LA), is well recognized during development and is now being implicated in kidney diseases. Although LA is associated with multiple pathological conditions, very little is known about its role in acute kidney injury. The purpose of this study was to evaluate the role of LA in a model of cisplatin-induced nephrotoxicity. LA is predominately regulated by vascular endothelial growth factor (VEGF)-C and VEGF-D, ligands that exert their function through their cognate receptor VEGF receptor 3 (VEGFR3). We demonstrated that use of MAZ51, a selective VEGFR3 inhibitor, caused significantly worse structural and functional kidney damage in cisplatin nephrotoxicity. Apoptotic cell death and inflammation were also increased in MAZ51-treated animals compared with vehicle-treated animals following cisplatin administration. Notably, MAZ51 caused significant upregulation of intrarenal phospho-NF-κB, phospho-JNK, and IL-6. Cisplatin nephrotoxicity is associated with vascular congestion due to endothelial dysfunction. Using three-dimensional tissue cytometry, a novel approach to explore lymphatics in the kidney, we detected significant vascular autofluorescence attributed to erythrocytes in cisplatin alone-treated animals. Interestingly, no such congestion was detected in MAZ51-treated animals. We found increased renal vascular damage in MAZ51-treated animals, whereby MAZ51 caused a modest decrease in the endothelial markers endomucin and von Willebrand factor, with a modest increase in VEGFR2. Our findings identify a protective role for de novo LA in cisplatin nephrotoxicity and provide a rationale for the development of therapeutic approaches targeting LA. Our study also suggests off-target effects of MAZ51 on the vasculature in the setting of cisplatin nephrotoxicity.NEW & NOTEWORTHY Little is known about injury-associated LA in the kidney and its role in the pathophysiology of acute kidney injury (AKI). Observed exacerbation of cisplatin-induced AKI after LA inhibition was accompanied by increased medullary damage and cell death in the kidney. LA inhibition also upregulated compensatory expression of LA regulatory proteins, including JNK and NF-κB. These data support the premise that LA is induced during AKI and lymphatic expansion is a protective mechanism in cisplatin nephrotoxicity.

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. Vegfr3 Chy/+ mice were examined for developmental abnormalities and kidney-specific outcomes. Control and Vegfr3 Chy/+ 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. Vegfr3 Chy/+ mice had severely reduced renal lymphatics with 100% penetrance, but we found no abnormalities in BP, serum creatinine, BUN, albuminuria, and histology. There was no difference in the degree of renal injury after low-dose cisplatin (5 mg/kg), although Vegfr3 Chy/+ 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 histologic 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 CKD requires assessment of changes to cortical volume.

Expanded renal lymphatics improve recovery following kidney injury

Acute kidney injury (AKI) is a major cause of patient mortality and a major risk multiplier for the progression to chronic kidney disease (CKD). The mechanism of the AKI to CKD transition is complex but is likely mediated by the extent and length of the inflammatory response following the initial injury. Lymphatic vessels help to maintain tissue homeostasis through fluid, macromolecule, and immune modulation. Increased lymphatic growth, or lymphangiogenesis, often occurs during inflammation and plays a role in acute and chronic disease processes. What roles renal lymphatics and lymphangiogenesis play in AKI recovery and CKD progression remains largely unknown. To determine if the increased lymphatic density is protective in the response to kidney injury, we utilized a transgenic mouse model with inducible, kidney-specific overexpression of the lymphangiogenic protein vascular endothelial growth factor-D to expand renal lymphatics. "KidVD" mouse kidneys were injured using inducible podocyte apoptosis and proteinuria (POD-ATTAC) or bilateral ischemia reperfusion. In the acute injury phase of both models, KidVD mice demonstrated a similar loss of function measured by serum creatinine and glomerular filtration rate compared to their littermates. While the initial inflammatory response was similar, KidVD mice demonstrated a shift toward more CD4+ and fewer CD8+ T cells in the kidney. Reduced collagen deposition and improved functional recovery over time was also identified in KidVD mice. In KidVD-POD-ATTAC mice, an increased number of podocytes were counted at 28 days post-injury. These data demonstrate that increased lymphatic density prior to injury alters the injury recovery response and affords protection from CKD progression.

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.

Quantitative 3-dimensional imaging and tissue cytometry reveals lymphatic expansion in acute kidney injury

The lymphatic system plays an integral role in physiology and has recently been identified as a key player in disease progression. Tissue injury stimulates lymphatic expansion, or lymphangiogenesis (LA), though its precise role in disease processes remains unclear. LA is associated with inflammation, which is a key component of acute kidney injury (AKI), for which there are no approved therapies. While LA research has gained traction in the last decade, there exists a significant lack of understanding of this process in the kidney. Though innovative studies have elucidated markers and models with which to study LA, the field is still evolving with ways to visualize lymphatics in vivo. Prospero-related homeobox-1 (Prox-1) is the master regulator of LA and determines lymphatic cell fate through its action on vascular endothelial growth factor receptor expression. Here, we investigate the consequences of AKI on the abundance and distribution of lymphatic endothelial cells using Prox1-tdTomato reporter mice (ProxTom) coupled with large-scale three-dimensional quantitative imaging and tissue cytometry (3DTC). Using these technologies, we describe the spatial dynamics of lymphatic vasculature in quiescence and post-AKI. We also describe the use of lymphatic vessel endothelial hyaluronan receptor-1 (LYVE-1) as a marker of lymphatic vessels using 3DTC in the absence of the ProxTom reporter mice as an alternative approach. The use of 3DTC for lymphatic research presents a new avenue with which to study the origin and distribution of renal lymphatic vessels. These findings will enhance our understanding of renal lymphatic function during injury and could inform the development of novel therapeutics for intervention in AKI.

Physiological models for in vivo imaging and targeting the lymphatic system: Nanoparticles and extracellular vesicles

Imaging of the lymphatic vasculature has gained great attention in various fields, not only because lymphatic vessels act as a key draining system in the body, but also for their implication in autoimmune diseases, organ transplant, inflammation and cancer. Thus, neolymphangiogenesis, or the generation of new lymphatics, is typically an early event in the development of multiple tumor types, particularly in aggressive ones such as malignant melanoma. Still, the understanding of how lymphatic endothelial cells get activated at distal (pre)metastatic niches and their impact on therapy is still unclear. Addressing these questions is of particular interest in the case of immune modulators, because endothelial cells may favor or halt inflammatory processes depending on the cellular context. Therefore, there is great interest in visualizing the lymphatic vasculature in vivo. Here, we review imaging tools and mouse models used to analyze the lymphatic vasculature during tumor progression. We also discuss therapeutic approaches based on nanomedicines to target the lymphatic system and the potential use of extracellular vesicles to track and target sentinel lymph nodes. Finally, we summarize main pre-clinical models developed to visualize the lymphatic vasculature in vivo, discussing their applications with a particular focus in metastatic melanoma.

Separated parabiont reveals the fate and lifespan of peripheral-derived immune cells in normal and ischaemia-induced injured kidneys

Immune cell infiltration plays a key role in acute kidney injury (AKI) to chronic kidney disease (CKD) progression. T lymphocytes, neutrophils, monocytes/macrophages and other immune cells regulate inflammation, tissue remodelling and repair. To determine the kinetics of accumulation of various immune cell populations, we established an animal model combining parabiosis and separation surgery to explore the fate and lifespan of peripheral leucocytes that migrate to the kidney. We found that peripheral T lymphocytes could survive for a long time (more than 14 days), whereas peripheral neutrophils survived for a short time in both healthy and ischaemia-induced damaged kidneys. Nearly half of the peripheral-derived macrophages disappeared after 14 days in normal kidneys, while their existing time in the inflammatory kidneys was prolonged. A fraction of F4/80^high macrophages were renewed from the circulating monocyte pool. In addition, we found that after renal ischaemia reperfusion, neutrophils increased significantly in the early phase, and T lymphocytes mainly accumulated in the late stage, whereas macrophages infiltrated throughout AKI-CKD progression and were sustained longer in injured as opposed to normal kidneys. In conclusion, peripheral-derived macrophages, T lymphocytes and neutrophils exhibit different lifespans in the kidney, which may play different roles during AKI-CKD progression.

Kidney lymphatics: new insights in development and disease

PURPOSE OF REVIEW

This review will highlight recent advances in our understanding of the kidney lymphatics regarding their development, physiologic function, and their potential role in the progression of kidney disease.

RECENT FINDINGS

Although sparse in comparison to the blood vasculature, lymphatic vessels within the healthy kidney perform an important role in maintaining homeostasis. Additionally, in response to kidney injury, lymphatic vessels undergo substantial expansion, termed lymphangiogenesis, which shows a direct correlation to the extent of tubulointerstitial fibrosis. Kidney lymphatics expand through both the proliferation of lymphatic endothelial cells from existing lymphatic vessels, as well as from direct contribution by other cell types of nonvenous origin. The primary driver of lymphatic growth is vascular endothelial growth factor C, both in development and in response to injury. The clinical implications of lymphangiogenesis in the setting of kidney diseases remains debated, however growing evidence suggests lymphatic vessels may perform a protective role in clearing away accumulating interstitial fluid, inflammatory cytokines, and cellular infiltrates that occur with injury.

SUMMARY

There is increasing evidence the kidney lymphatics perform an active role in the response to kidney injury and the development of fibrosis. Recent advances in our understanding of these vessels raise the possibility of targeting kidney lymphatics for the treatment of kidney disease.

Identifying potential biomarkers of nonalcoholic fatty liver disease via genome-wide analysis of copy number variation

BACKGROUND

The prevalence of Non-alcoholic fatty liver disease (NAFLD) is increasing and emerging as a global health burden. In addition to environmental factors, numerous studies have shown that genetic factors play an important role in the development of NAFLD. Copy number variation (CNV) as a genetic variation plays an important role in the evaluation of disease susceptibility and genetic differences. The aim of the present study was to assess the contribution of CNV to the evaluation of NAFLD in a Chinese population.

METHODS

Genome-wide analysis of CNV was performed using high-density comparative genomic hybridisation microarrays (ACGH). To validate the CNV regions, TaqMan real-time quantitative PCR (qPCR) was utilized.

RESULTS

A total of 441 CNVs were identified, including 381 autosomal CNVs and 60 sex chromosome CNVs. By merging overlapping CNVs, a genomic CNV map of NAFLD patients was constructed. A total of 338 autosomal CNVRs were identified, including 275 CNVRs with consistent trends (197 losses and 78 gains) and 63 CNVRs with inconsistent trends. The length of the 338 CNVRs ranged from 5.7 kb to 2.23 Mb, with an average size of 117.44 kb. These CNVRs spanned 39.70 Mb of the genome and accounted for ~ 1.32% of the genome sequence. Through Gene Ontology and genetic pathway analysis, we found evidence that CNVs involving nine genes may be associated with the pathogenesis of NAFLD progression. One of the genes (NLRP4 gene) was selected and verified by quantitative PCR (qPCR) method with large sample size. We found the copy number deletion of NLRP4 was related to the risk of NAFLD.

CONCLUSIONS

This study indicate the copy number variation is associated with NAFLD. The copy number deletion of NLRP4 was related to the risk of NAFLD. These results could prove valuable for predicting patients at risk of developing NAFLD.

TGF-β1 Signaling: Immune Dynamics of Chronic Kidney Diseases

Chronic kidney disease (CKD) is a major cause of morbidity and mortality worldwide, imposing a great burden on the healthcare system. Regrettably, effective CKD therapeutic strategies are yet available due to their elusive pathogenic mechanisms. CKD is featured by progressive inflammation and fibrosis associated with immune cell dysfunction, leading to the formation of an inflammatory microenvironment, which ultimately exacerbating renal fibrosis. Transforming growth factor β1 (TGF-β1) is an indispensable immunoregulator promoting CKD progression by controlling the activation, proliferation, and apoptosis of immunocytes via both canonical and non-canonical pathways. More importantly, recent studies have uncovered a new mechanism of TGF-β1 for de novo generation of myofibroblast via macrophage-myofibroblast transition (MMT). This review will update the versatile roles of TGF-β signaling in the dynamics of renal immunity, a better understanding may facilitate the discovery of novel therapeutic strategies against CKD.

Acute kidney injury and maladaptive tubular repair leading to renal fibrosis

PURPOSE OF REVIEW

Despite improvements in acute kidney injury (AKI) detection, therapeutic options to halt the progression of AKI to chronic kidney disease (CKD) remain limited. In this review, we focus on recent discoveries related to the pathophysiology of the AKI to CKD continuum, particularly involving the renal tubular epithelial cells, and also discuss related ongoing clinical trials. While our focus is on injured renal tubular epithelial cells as initiators of the cascade of events resulting in paracrine effects on other cells of the kidney, the summation of maladaptive responses from various kidney cell types ultimately leads to fibrosis and dysfunction characteristic of CKD.

RECENT FINDINGS

Recent findings that we will focus on include, but are not limited to, characterizations of: the association between cell cycle arrest and cellular senescence in renal tubular epithelial cells and its contribution to renal fibrosis, chronic inflammation with persistent cytokine production and lymphocyte infiltration among unrepaired renal tubules, mitochondrial dysfunction and a unique role of cytosolic mitochondria DNA in fibrogenesis, prolyl hydroxylase domain proteins as potential therapeutic targets, and novel mechanisms involving the Hippo/yes-associated protein/transcriptional coactivator with PDZ-binding pathway.

SUMMARY

Potential therapeutic options to address CKD progression will be informed by a better understanding of fibrogenic pathways. Recent advances suggest additional drug targets in the various pathways leading to fibrosis.

Lymphangiogenesis in renal fibrosis arises from macrophages via VEGF-C/VEGFR3-dependent autophagy and polarization

Inflammation plays a crucial role in the occurrence and development of renal fibrosis, which ultimately results in end-stage renal disease (ESRD). There is new focus on lymphangiogenesis in the field of inflammation. Recent studies have revealed the association between lymphangiogenesis and renal fibrosis, but the source of lymphatic endothelial cells (LECs) is not clear. It has also been reported that macrophages are involved in lymphangiogenesis through direct and indirect mechanisms in other tissues. We hypothesized that there was a close relationship between macrophages and lymphatic endothelial progenitor cells in renal fibrosis. In this study, we demonstrated that lymphangiogenesis occurred in a renal fibrosis model and was positively correlated with the degree of fibrosis and macrophage infiltration. Compared to resting (M0) macrophages and alternatively activated (M2) macrophages, classically activated (M1) macrophages predominantly transdifferentiated into LECs in vivo and in vitro. VEGF-C further increased M1 macrophage polarization and transdifferentiation into LECs by activating VEGFR3. It was suggested that VEGF-C/VEGFR3 pathway activation downregulated macrophage autophagy and subsequently regulated macrophage phenotype. The induction of autophagy in macrophages by rapamycin decreased M1 macrophage polarization and differentiation into LECs. These results suggested that M1 macrophages promoted lymphangiogenesis and contributed to newly formed lymphatic vessels in the renal fibrosis microenvironment, and VEGF-C/VEGFR3 signaling promoted macrophage M1 polarization by suppressing macrophage autophagy and then increased the transdifferentiation of M1 macrophages into LECs.

Emerging roles for lymphatics in acute kidney injury: Beneficial or maleficent?

Acute kidney injury, a sudden decline in renal filtration, is a surprisingly common pathology resulting from ischemic events, local or systemic infection, or drug-induced toxicity in the kidney. Unchecked, acute kidney injury can progress to renal failure and even recovered acute kidney injury patients are at an increased risk for developing future chronic kidney disease. The initial extent of inflammation, the specific immune response, and how well inflammation resolves are likely determinants in acute kidney injury-to-chronic kidney disease progression. Lymphatic vessels and their roles in fluid, solute, antigen, and immune cell transport make them likely to have a role in the acute kidney injury response. Lymphatics have proven to be an attractive target in regulating inflammation and immunomodulation in other pathologies: might these strategies be employed in acute kidney injury? Acute kidney injury studies have identified elevated levels of lymphangiogenic ligands following acute kidney injury, with an expansion of the lymphatics in several models post-injury. Manipulating the lymphatics in acute kidney injury, by augmenting or inhibiting their growth or through targeting lymphatic-immune interactions, has met with a range of positive, negative, and sometimes inconclusive results. This minireview briefly summarizes the findings of lymphatic changes and lymphatic roles in the inflammatory response in the kidney following acute kidney injury to discuss whether renal lymphatics are a beneficial, maleficent, or a passive contributor to acute kidney injury recovery.

Mangiferin and organ fibrosis: A mini review

Fibrosis is the end stage of many chronic diseases, which results in organ function failure and high mortality. Mangiferin is a major constituent in mango and other 16 plants, and has been shown a variety of pharmacological effects, such as antioxidant, antibacterial, anti-tumor, anti-inflammation. The emerging evidence has shown that mangiferin can improve renal interstitial fibrosis, pulmonary fibrosis, myocardial fibrosis and hepatic fibrosis through the inhibition of inflammation, oxidative stress and fibrogenesis effects, indicating that mangiferin is promising therapeutic choice for organ fibrosis. The aim of this review is to summarize the therapeutic effects of mangiferin on fibrosis of various organs and the underlying mechanisms.

A minireview: Role of AMP-activated protein kinase (AMPK) signaling in obesity-related renal injury

Emerging evidence shows that the AMP-activated protein kinase (AMPK), a critical energy-sensing switch, plays an important role in the pathogenesis and development of obesity-related renal injury. In this review, we summarized the mechanisms underlying the protective effects of AMPK activation against obesity-related renal injury in preclinical studies, with the main purposes of increasing the understanding of AMPK and providing new insights into the future clinical therapeutic strategies. The renoprotective effects of AMPK mainly act by modulating lipid metabolism and autophagy and suppressing oxidative stress, inflammation, and fibrosis. More importantly, we discussed the recent advances in this field that require further investigation. Firstly, the inhibitory effect of AMPK on ferroptosis is a potential mechanism for its protection against renal injury. Secondly, the effect of AMPK on lipolysis is complex: AMPK induces basal lipolysis but also inhibits stimulated lipolysis. Thirdly, statins may play a renoprotective role by activating AMPK. Fourthly, some microRNAs targeting AMPK mRNA have been implicated in diabetic nephropathy in type 2 diabetes. Further, AMPK can regulate the expression of some microRNAs, suggesting that the stable renoprotective effects of AMPK may benefit from its epigenetic regulation. Lastly, several natural compounds and synthetic drugs have been recognized to protect against obesity-related renal injury by activating AMPK and its downstream pathways in animal models. It remains to be seen if combination of newly identified drugs with traditional renoprotective medicine will have any synergistic therapeutic benefits without adding to side effects.