Stimulating Type 1 Angiotensin Receptors on T Lymphocytes Attenuates Renal Fibrosis

Research Progress of Drug Delivery Systems Targeting the Kidneys

Chronic kidney disease (CKD) affects more than 10% of the global population, and its incidence is increasing, partially due to an increase in the prevalence of disease risk factors. Acute kidney injury (AKI) is an independent risk factor for CKD and end-stage renal disease (ESRD). The pathogenic mechanisms of CKD provide several potential targets for its treatment. However, due to off-target effects, conventional drugs for CKD typically require high doses to achieve adequate therapeutic effects, leading to long-term organ toxicity. Therefore, ideal treatments that completely cure the different types of kidney disease are rarely available. Several approaches for the drug targeting of the kidneys have been explored in drug delivery system research. Nanotechnology-based drug delivery systems have multiple merits, including good biocompatibility, suitable degradability, the ability to target lesion sites, and fewer non-specific systemic effects. In this review, the development, potential, and limitations of low-molecular-weight protein-lysozymes, polymer nanomaterials, and lipid-based nanocarriers as drug delivery platforms for treating AKI and CKD are summarized.

Recent Advances in Understanding the Molecular Pathophysiology of Angiotensin II Receptors: Lessons From Cell-Selective Receptor Deletion in Mice

The renin-angiotensin system (RAS) is an essential hormonal system involved in water and sodium reabsorption, renal blood flow regulation, and arterial constriction. Systemic stimulation of the RAS with infusion of the main peptide angiotensin II (Ang II) in animals as well as pathological elevation of renin (ie, renovascular hypertension) to increase circulatory Ang II in humans ultimately lead to hypertension and end organ damage. In addition to hypertension, accumulating evidence supports that the Ang II type 1 receptor exerts a critical role in cardiovascular and kidney diseases independent of blood pressure elevation. In the past 2 decades, the identification of an increased number of peptides and receptors has facilitated the concept that the RAS has detrimental and beneficial effects on the cardiovascular system depending on which RAS components are activated. For example, angiotensin 1-7 and Ang II type 2 receptors act as a counter-regulatory system against the classical RAS by mediating vasodilation. Although the RAS as an endocrine system for regulation of blood pressure is well established, there remain many unanswered questions and controversial findings regarding blood pressure regulation and pathophysiological regulation of cardiovascular diseases at the tissue level. This review article includes the latest knowledge gleaned from cell type-selective gene deleted mice regarding cell type-specific roles of Ang II receptors and their significance in health and diseases are discussed. In particular, we focus on the roles of these receptors expressed in vascular, cardiac, and kidney epithelial cells.

Transcriptomic analysis reveals partial epithelial-mesenchymal transition and inflammation as common pathogenic mechanisms in hypertensive nephrosclerosis and Type 2 diabetic nephropathy

Hypertensive nephrosclerosis (HN) and Type 2 diabetic nephropathy (T2DN) are the leading causes of chronic kidney disease (CKD). To explore shared pathogenetic mechanisms, we analyzed transcriptomes of kidney biopsies from patients with HN or T2DN. Total RNA was extracted from 10 μm whole kidney sections from patients with HN, T2DN, and normal controls (Ctrl) (n = 6 for each group) and processed for RNA sequencing. Differentially expressed (log2 fold change >1, adjusted p < 0.05) genes (DEG) and molecular pathways were analyzed, and selected results were validated by immunohistochemistry (IHC). ELISA on serum samples was performed on a related cohort consisting of patients with biopsy-proven HN (n = 13) and DN (n = 9), and a normal control group (n = 14). Cluster analysis on RNA sequencing data separated diseased and normal tissues. RNA sequencing revealed that 88% (341 out of 384) of DEG in HN were also altered in T2DN, while gene set enrichment analysis (GSEA) showed that over 90% of affected molecular pathways, including those related to inflammation, immune response, and cell-cycle regulation, were similarly impacted in both HN and T2DN samples. The increased expression of genes tied to interleukin signaling and lymphocyte activation was more pronounced in HN, while genes associated with extracellular matrix organization were more evident in T2DN. Both HN and T2DN tissues exhibited significant upregulation of genes connected with inflammatory responses, T-cell activity, and partial epithelial to mesenchymal transition (p-EMT). Immunohistochemistry (IHC) further confirmed T-cell (CD4+ and CD8+ ) infiltration in the diseased tissues. Additionally, IHC revealed heightened AXL protein expression, a key regulator of inflammation and p-EMT, in both HN and T2DN, while serum analysis indicated elevated soluble AXL levels in patients with both conditions. These findings underline the shared molecular mechanisms between HN and T2DN, hinting at the potential for common therapeutic strategies targeting both diseases.

M1-aminopeptidase family - beyond antigen-trimming activities

Antigen (Ag)-trimming aminopeptidases belong to the oxytocinase subfamily of M1 metallopeptidases. In humans, this subfamily contains the endoplasmic reticulum aminopeptidases 1 and 2 (ERAP1 and 2) and the insulin-responsive aminopeptidase (IRAP, synonym oxytocinase), an endosomal enzyme. The ability of these enzymes to trim antigenic precursors and to generate major histocompatibility class-I ligands has been demonstrated extensively for ERAP1, less for ERAP2, which is absent in rodents, and exclusively in the context of cross-presentation for IRAP. During 20 years of research on these aminopeptidases, their enzymatic function has been very well characterized and their genetic association with autoimmune diseases, cancers, and infections is well established. The mechanisms by which these proteins are associated to human diseases are not always clear. This review discusses the Ag-trimming-independent functions of the oxytocinase subfamily of M1 aminopeptidases and the new questions raised by recent publications on IRAP and ERAP2.

The antifibrotic and anti-inflammatory effects of FZHY prescription on the kidney in rats after unilateral ureteral obstruction

PURPOSE

To explore the potential impact of traditional Chinese herb FuZhengHuaYuJiangZhuTongLuo recipe (FZHY) on renal interstitial fibrosis (RIF) in chronic kidney disease (CKD) at cellular and molecular levels.

METHODS

Unilateral ureteral obstruction (UUO) rats were established as the RIF model in vivo. The rats were given intragastric administration with FZHY once a day for consecutive 7, 14 and 21 days, respectively. The renal function parameters and inflammation indicators in kidney tissues were measured using enzyme-linked immunosorbent assay, the CD4+/CD8+ T cells in peripheral blood was detected using flow cytometry, the renal fibrosis degree was estimated using Masson's staining, and the fibrosis-related genes' expression was detected using quantitative polymerase chain reaction, western blotting, and immunohistochemistry analyses.

RESULTS

FZHY prescription reduced the serum creatinine and blood urea nitrogen, decreased the levels of c-reactive protein, interleukin-1, interleukin-6 and tumor necrosis factor-α in kidney tissues, and increased the ratio of CD4+/CD8+ T cells in peripheral blood. FZHY prescription suppressed the renal tissue fibrosis and reduced the levels of laminin, fibronectin, collagen I and collagen III.

CONCLUSIONS

FZHY prescription suppressed the renal fibrosis and improved the condition of "Healthy Qi Deficiency and Evil Qi Excess" in rats with UUO, which may provide an effective method for CKD treatment.

Angiotensin II Type 1 Receptor Antibodies Are Higher in Lupus Nephritis and Vasculitis than Other Glomerulonephritis Patients

Angiotensin II type 1 receptor (AT1R) antibodies are considered non-HLA (human leukocyte antigen) antibodies connected with humoral rejection after kidney transplantation. The role of AT1R antibodies in the pathogenesis of glomerular diseases and systemic vasculitis is unknown. We assessed the level of AT1R antibodies in 136 patients with different types of glomerulonephritis and systemic vasculitis and we observed kidney function and proteinuria, serum albumin and total protein levels for 2 years. The mean levels of AT1R antibodies were the following: 6.00 ± 1.31 U/ml in patients with membranous nephropathy (n = 18), 5.67 ± 1.31 U/ml with focal and segmental glomerulosclerosis (n = 25), 6.26 ± 2.25 U/ml with lupus nephropathy (n = 17), 10.60 ± 6.72 U/ml with IgA nephropathy (n = 14), 6.69 ± 2.52 U/ml with mesangial proliferative (non IgA) glomerulonephritis (n = 6), 6.63 ± 1.38 U/ml with systemic vasculitis (n = 56), including c-ANCA (anti-neutrophil cytoplasmic antibodies) vasculitis: 11.22 ± 10.78 U/ml (n = 40) and p-ANCA vasculitis: 12.65 ± 14.59 U/ml (n = 16). The mean AT1R antibodies level was higher in patients with lupus nephropathy and systemic vasculitis compared to glomerulonephritis groups. An inverse statistically significant correlation between AT1R antibodies and serum albumin (r =  − 0.51) in membranous nephropathy group was also found. Prospective analysis of creatinine levels indicated an increase of creatinine levels during time among patients with higher AT1R antibodies levels in p-ANCA vasculitis. Lupus nephropathy and systemic vasculitis patients may have high levels of AT1R antibodies. AT1R antibodies may be associated with the severity of membranous nephropathy and the course of p-ANCA vasculitis, although influence of concomitant factors is difficult to exclude.

Type 1 Angiotensin Receptors on CD11c-Expressing Cells Protect Against Hypertension by Regulating Dendritic Cell-Mediated T Cell Activation

BACKGROUND

Type 1 angiotensin (AT₁) receptors are expressed on immune cells, and we previously found that bone marrow-derived AT₁ receptors protect against Ang (angiotensin) II-induced hypertension. CD11c is expressed on myeloid cells derived from the bone marrow, including dendritic cells (DCs) that activate T lymphocytes. Here, we examined the role of AT₁ receptors on CD11c⁺ cells in hypertension pathogenesis.

METHODS

Mice lacking the dominant murine AT₁ receptor isoform, AT_1a, on CD11c⁺ cells (dendritic cell [DC] AT1aR knockout [KO]) and wild-type (WT) littermates were subjected to Ang II-induced hypertension. Blood pressures were measured by radiotelemetry.

RESULTS

DC AT1aR KO mice had exaggerated hypertensive responses to chronic Ang II infusion with enhanced renal accumulation of effector memory T cells and CD40⁺ DCs. CCL5 (C-C motif chemokine ligand 5) recruits T cells into injured tissues, and CCR7 (C-C motif chemokine receptor 7) facilitates DC and T cell interactions in the kidney lymph node to allow T cell activation. DCs from the hypertensive DC AT1aR KO kidneys expressed higher levels of CCL5 and CCR7. mRNA expressions for CCR7 and tumor necrosis factor-α were increased in CD4⁺ T cells from the renal lymph nodes of DC AT1aR KO mice. During the second week of Ang II infusion when blood pressures between groups diverged, DC AT1aR KO mice excreted less sodium than WTs. Expressions for epithelial sodium channel subunits were increased in DC AT1aR KO kidneys.

CONCLUSIONS

Following activation of the renin angiotensin system, AT1aR stimulation on DCs suppresses renal DC maturation and T cell activation with consequent protection from sodium retention and blood pressure elevation.

Hirudin, a thrombin inhibitor, attenuates TGF-β-induced fibrosis in renal proximal tubular epithelial cells by inhibition of protease-activated receptor 1 expression via S1P/S1PR2/S1PR3 signaling

Renal interstitial fibrosis (RIF) is the final common outcome of numerous chronic kidney diseases, contributing to end-stage renal disease. Hirudin, a thrombin inhibitor, has attracted increased attention as a potential treatment approach for renal fibrosis. The present study aimed to investigate the molecular mechanism underlying the effect of hirudin on fibrosis in renal proximal tubular epithelial cells. An in vivo mouse RIF model established using unilateral ureteral obstruction (UUO) and an in vitro of RIF using the renal tubular epithelial cell line HK-2 treated with TGF-β were used. Expressions of sphingosine-1-phosphate (S1P) receptors (S1PR)1-4 and protease-activated receptor 1 (PAR1) were measured by reverse transcription-quantitative PCR and western blotting in mice with UUO and TGF-β induced HK-2 cells. Western blotting was used to detect the expression of N-cadherin, Slug, E-cadherin, Collagen IV, fibronectin, MMP9 and monocyte chemoattractant protein-1. Immunofluorescence staining was conducted to measure α-SMA level expression. The results demonstrated that the expression levels of S1PR1, S1PR2, S1PR3, S1PR4 and PAR1 were upregulated in both TGF-β-induced HK-2 cells and renal tissues from mice with unilateral ureteral ligation. Notably, hirudin inhibited TGF-β-induced PAR1, S1PR2 and S1PR3 upregulation in both HK-2 cells and renal tissues. Additionally, the inhibition of S1PR2 and S1PR3 resulted in PAR1 downregulation. Furthermore, treatment with S1P and PAR1 agonists abolished the effect of hirudin on the expression of EMT, fibrosis-related proteins and monocyte chemoattractant protein 1. In conclusion, hirudin attenuated TGF-β-induced fibrosis in proximal renal tubular epithelial HK-2 cells by inhibiting PAR1 expression via the S1P/S1PR2/S1PR3 signaling pathway. Therefore, hirudin may be considered as a promising therapeutic agent for RIF.

Long-term exposure to environmental level of phenanthrene causes adaptive immune response and fibrosis in mouse kidneys

As ubiquitous, persistent organic pollutants, polycyclic aromatic hydrocarbons (PAHs) have adverse impacts on human health. Phenanthrene (Phe) is one of the most abundant PAHs in the environment. However, the long-term effects of exposure to environmental level of Phe on the kidneys and the potential mechanisms are unclear. T helper (Th) cells, a subtype of CD4⁺ T cells that play a central role in the renal immune microenvironment. In this study, male mice were chronically exposed to 5, 50, and 500 ng/kg bw Phe every other day for total 210 days. Those results indicated that environmental Phe exposure caused kidney hypertrophy, injury and fibrosis in the mice. Chronic, long-term environmental level of Phe exposure did not significantly alter the innate immune response but induced adaptive immune response changes (Th1/Th2 related cytokines release), causing a type 1 immune response in the 5 ng/kg bw Phe group and a type 2 immune response in the high dose groups (50 and 500 ng/kg bw). This study provides novel insights into the roles of adaptive immune response in long-term PAH exposure-induced chronic kidney injury and fibrosis, which is beneficial for further understanding the potential health hazards of PAHs and providing new avenues for immune intervention strategies to alleviate PAHs toxicity.

Advances in use of mouse models to study the renin-angiotensin system

The renin-angiotensin system (RAS) is a highly complex hormonal cascade that spans multiple organs and cell types to regulate solute and fluid balance along with cardiovascular function. Much of our current understanding of the functions of the RAS has emerged from a series of key studies in genetically-modified animals. Here, we review key findings from ground-breaking transgenic models, spanning decades of research into the RAS, with a focus on their use in studying blood pressure. We review the physiological importance of this regulatory system as evident through the examination of mouse models for several major RAS components: angiotensinogen, renin, ACE, ACE2, and the type 1 A angiotensin receptor. Both whole-animal and cell-specific knockout models have permitted critical RAS functions to be defined and demonstrate how redundancy and multiplicity within the RAS allow for compensatory adjustments to maintain homeostasis. Moreover, these models present exciting opportunities for continued discovery surrounding the role of the RAS in disease pathogenesis and treatment for cardiovascular disease and beyond.

Renin-angiotensin system and inflammation update

The most classical view of the renin-angiotensin system (RAS) emphasizes its role as an endocrine regulator of sodium balance and blood pressure. However, it has long become clear that the RAS has pleiotropic actions that contribute to organ damage, including modulation of inflammation. Angiotensin II (Ang II) activates angiotensin type 1 receptors (AT1R) to promote an inflammatory response and organ damage. This represents the pathophysiological basis for the successful use of RAS blockers to prevent and treat kidney and heart disease. However, other RAS components could have a built-in capacity to brake proinflammatory responses. Angiotensin type 2 receptor (AT2R) activation can oppose AT1R actions, such as vasodilatation, but its involvement in modulation of inflammation has not been conclusively proven. Angiotensin-converting enzyme 2 (ACE2) can process Ang II to generate angiotensin-(1-7) (Ang-(1-7)), that activates the Mas receptor to exert predominantly anti-inflammatory responses depending on the context. We now review recent advances in the understanding of the interaction of the RAS with inflammation. Specific topics in which novel information became available recently include intracellular angiotensin receptors; AT1R posttranslational modifications by tissue transglutaminase (TG2) and anti-AT1R autoimmunity; RAS modulation of lymphoid vessels and T lymphocyte responses, especially of Th17 and Treg responses; interactions with toll-like receptors (TLRs), programmed necrosis, and regulation of epigenetic modulators (e.g. microRNAs and bromodomain and extraterminal domain (BET) proteins). We additionally discuss an often overlooked effect of the RAS on inflammation which is the downregulation of anti-inflammatory factors such as klotho, peroxisome proliferator-activated receptor γ co-activator 1α (PGC-1α), transient receptor potential ankyrin 1 (TRPA1), SNF-related serine/threonine-protein kinase (SNRK), serine/threonine-protein phosphatase 6 catalytic subunit (Ppp6C) and n-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP). Both transcription factors, such as nuclear factor κB (NF-κB), and epigenetic regulators, such as miRNAs are involved in downmodulation of anti-inflammatory responses. A detailed analysis of pathways and targets for downmodulation of anti-inflammatory responses constitutes a novel frontier in RAS research.

Twist1 in T Lymphocytes Augments Kidney Fibrosis after Ureteral Obstruction

Background

Twist1 is a basic helix-loop-helix domain-containing transcription factor that participates in diverse cellular functions, including epithelial-mesenchymal transition and the cellular immune response. Although Twist1 plays critical roles in the initiation and progression of kidney diseases, the effects of Twist1 in the T lymphocyte on the progression of renal fibrosis require elucidation.

Methods

129/SvEv mice with a floxed allele for the gene encoding Twist1 or TNFα were bred with CD4-Cre mice to yield CD4-Cre⁺ Twist1^flox/flox (Twist1-TKO) or CD4-Cre⁺ TNF^flox/flox (TNF-TKO) mice with robust, but selective, deletion of Twist1 or TNFα mRNA in T cells, respectively. Twist1 TKO, TNF TKO, and WT controls underwent UUO with assessment of kidney fibrosis and T-cell phenotype at 14 days.

Results

Compared with WT controls, obstructed kidneys from Twist1 TKO mice had attenuated extracellular matrix deposition. Despite this diminished fibrosis, Twist1 TKO obstructed kidneys contained more CD8⁺ T cells than in WTs. These intrarenal CD8⁺ T cells exhibited greater activation and higher levels of TNFα expression than those from WT obstructed kidneys. Further, we found that selective deletion of TNFα from T cells exaggerated renal scar formation and injury after UUO, highlighting the capacity of T-cell TNF to constrain fibrosis in the kidney.

Conclusions

Twist1 in T cells promotes kidney fibrogenesis, in part, by curtailing the renal accumulation of TNF-elaborating T cells.

The varying roles of macrophages in kidney injury and repair

PURPOSE OF REVIEW

Macrophages play an important role in regulating homeostasis, kidney injury, repair, and tissue fibrogenesis. The present review will discuss recent advances that explore the novel subsets and functions of macrophage in the pathogenesis of kidney damage and hypertension.

RECENT FINDINGS

Macrophages differentiate into a variety of subsets in microenvironment-dependent manner. Although the M1/M2 nomenclature is still applied in considering the pro-inflammatory versus anti-inflammatory effects of macrophages in kidney injury, novel, and accurate macrophage phenotypes are defined by flow cytometric markers and single-cell RNA signatures. Studies exploring the crosstalk between macrophages and other cells are rapidly advancing with the additional recognition of exosome trafficking between cells. Using murine conditional mutants, actions of macrophage can be defined more precisely than in bone marrow transfer models. Some studies revealed the opposing effects of the same protein in renal parenchymal cells and macrophages, highlighting a need for the development of cell-specific immune therapies for translation.

SUMMARY

Macrophage-targeted therapies hold potential for limiting kidney injury and hypertension. To realize this potential, future studies will be required to understand precise mechanisms in macrophage polarization, crosstalk, proliferation, and maturation in the setting of renal disease.

Coronavirus Disease 2019 and Hypertension: The Role of Angiotensin-Converting Enzyme 2 and the Renin-Angiotensin System

Hypertension emerged from early reports as a potential risk factor for worse outcomes for persons with coronavirus disease 2019 (COVID-19). Among the putative links between hypertension and COVID-19 is a key counter-regulatory component of the renin-angiotensin system (RAS): angiotensin-converting enzyme 2 (ACE2). ACE2 facilitates entry of severe acute respiratory syndrome coronavirus 2, the virus responsible for COVID-19, into host cells. Because RAS inhibitors have been suggested to increase ACE2 expression, health-care providers and patients have grappled with the decision of whether to discontinue these medications during the COVID-19 pandemic. However, experimental models of analogous viral pneumonias suggest RAS inhibitors may exert protective effects against acute lung injury. We review how RAS and ACE2 biology may affect outcomes in COVID-19 through pulmonary and other systemic effects. In addition, we briefly detail the data for and against continuation of RAS inhibitors in persons with COVID-19 and summarize the current consensus recommendations from select specialty organizations.

The Emerging Role of Innate Immunity in Chronic Kidney Diseases

Renal fibrosis is a common fate of chronic kidney diseases. Emerging studies suggest that unsolved inflammation will progressively transit into tissue fibrosis that finally results in an irreversible end-stage renal disease (ESRD). Renal inflammation recruits and activates immunocytes, which largely promotes tissue scarring of the diseased kidney. Importantly, studies have suggested a crucial role of innate immunity in the pathologic basis of kidney diseases. This review provides an update of both clinical and experimental information, focused on how innate immune signaling contributes to renal fibrogenesis. A better understanding of the underlying mechanisms may uncover a novel therapeutic strategy for ESRD.

TNF-α in T lymphocytes attenuates renal injury and fibrosis during nephrotoxic nephritis

Nephrotoxic serum nephritis (NTN) models immune-mediated human glomerulonephritis and culminates in kidney inflammation and fibrosis, a process regulated by T lymphocytes. TNF-α is a key proinflammatory cytokine that contributes to diverse forms of renal injury. Therefore, we posited that TNF-α from T lymphocytes may contribute to NTN pathogenesis. Here, mice with T cell-specific deletion of TNF-α (TNF TKO) and wild-type (WT) control mice were subjected to the NTN model. At 14 days after NTN, kidney injury and fibrosis were increased in kidneys from TNF TKO mice compared with WT mice. PD1+CD4+ T cell numbers and mRNA levels of IL-17A were elevated in NTN kidneys of TNF TKO mice, suggesting that augmented local T helper 17 lymphocyte responses in the TNF TKO kidney may exaggerate renal injury and fibrosis. In turn, we found increased accumulation of neutrophils in TNF TKO kidneys during NTN. We conclude that TNF-α production in T lymphocytes mitigates NTN-induced kidney injury and fibrosis by inhibiting renal T helper 17 lymphocyte responses and infiltration of neutrophils.