CCL2 mediates early renal leukocyte infiltration during salt-sensitive hypertension

Downregulation of the kidney glucagon receptor, essential for renal function and systemic homeostasis, contributes to chronic kidney disease

The glucagon receptor (GCGR) in the kidney is expressed in nephron tubules. In humans and animal models with chronic kidney disease, renal GCGR expression is reduced. However, the role of kidney GCGR in normal renal function and in disease development has not been addressed. Here, we examined its role by analyzing mice with constitutive or conditional kidney-specific loss of the Gcgr. Adult renal Gcgr knockout mice exhibit metabolic dysregulation and a functional impairment of the kidneys. These mice exhibit hyperaminoacidemia associated with reduced kidney glucose output, oxidative stress, enhanced inflammasome activity, and excess lipid accumulation in the kidney. Upon a lipid challenge, they display maladaptive responses with acute hypertriglyceridemia and chronic proinflammatory and profibrotic activation. In aged mice, kidney Gcgr ablation elicits widespread renal deposition of collagen and fibronectin, indicative of fibrosis. Taken together, our findings demonstrate an essential role of the renal GCGR in normal kidney metabolic and homeostatic functions. Importantly, mice deficient for kidney Gcgr recapitulate some of the key pathophysiological features of chronic kidney disease.

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.

Cytomegalovirus and Cardiovascular Disease: A Hypothetical Role for Viral G-Protein-Coupled Receptors in Hypertension

Cytomegalovirus (CMV) is a member of the β-herpesviruses and is ubiquitous, infecting 50%-99% of the human population depending on ethnic and socioeconomic conditions. CMV establishes lifelong, latent infections in their host. Spontaneous reactivation of CMV is usually asymptomatic, but reactivation events in immunocompromised or immunosuppressed individuals can lead to severe morbidity and mortality. Moreover, herpesvirus infections have been associated with several cardiovascular and post-transplant diseases (stroke, atherosclerosis, post-transplant vasculopathy, and hypertension). Herpesviruses, including CMV, encode viral G-protein-coupled receptors (vGPCRs) that alter the host cell by hijacking signaling pathways that play important roles in the viral life cycle and these cardiovascular diseases. In this brief review, we discuss the pharmacology and signaling properties of these vGPCRs, and their contribution to hypertension. Overall, these vGPCRs can be considered attractive targets moving forward in the development of novel hypertensive therapies.

Chronic treatment with IL-25 increases renal M2 macrophages and reduces renal injury in obese Dahl salt-sensitive rats during the prepubescent stage

Recently, we have reported that the early progression of proteinuria in the obese Dahl salt-sensitive (SS) leptin receptor mutant (SSLepRmutant) strain was associated with increased renal macrophage infiltration before puberty. Macrophages can be divided into two distinct phenotypes: M1 (proinflammatory) and M2 (anti-inflammatory). Moreover, previous studies have demonstrated that interleukin (IL)-25 converts resting macrophages and M1 into M2. Therefore, the present study examined whether treatment with IL-25 would reduce the early progression of renal injury in SSLepRmutant rats by increasing renal M2. We also investigated the impact of IL-25 on M2 subtypes: M2a (wound healing/anti-inflammatory), M2b (immune mediated/proinflammatory), M2c (regulatory/anti-inflammatory), and M2d (tumor associated/proangiogenic). Four-wk-old SS and SSLepRmutant rats were treated with either control (IgG) or IL-25 (1 µg/day ip every other day) for 4 wk. The kidneys from SSLepRmutant rats displayed progressive proteinuria and renal histopathology versus SS rats. IL-25 treatment had no effect on these parameters in SS rats. However, in the SSLepRmutant strain, proteinuria was markedly reduced after IL-25 treatment. Chronic treatment with IL-25 significantly decreased glomerular and tubular injury and renal fibrosis in the SSLepRmutant strain. Although the administration of IL-25 did not change total renal macrophage infiltration in both SS and SSLepRmutant rats, IL-25 increased M2a by >50% and reduced M1 by 60% in the kidneys of SSLepRmutant rats. Overall, these data indicate that IL-25 reduces the early progression of renal injury in SSLepRmutant rats by inducing M2a and suppressing M1 and suggest that IL-25 may be a therapeutic target for renal disease associated with obesity. NEW & NOTEWORTHY For the past few decades, immune cells and inflammatory cytokines have been demonstrated to play an important role in the development of renal disease. The present study provides strong evidence that interleukin-25 slows the early progression of renal injury in obese Dahl salt-sensitive rats before puberty by increasing systemic anti-inflammatory cytokines and renal M2a macrophages.

A2BAR Antagonism Decreases the Glomerular Expression and Secretion of Chemoattractants for Monocytes and the Pro-Fibrotic M2 Macrophages Polarization during Diabetic Nephropathy

Some chemoattractants and leukocytes such as M1 and M2 macrophages are known to be involved in the development of glomerulosclerosis during diabetic nephropathy (DN). In the course of diabetes, an altered and defective cellular metabolism leads to the increase in adenosine levels, and thus to changes in the polarity (M1/M2) of macrophages. MRS1754, a selective antagonist of the A2B adenosine receptor (A2BAR), attenuated glomerulosclerosis and decreased macrophage-myofibroblast transition in DN rats. Therefore, we aimed to investigate the effect of MRS1754 on the glomerular expression/secretion of chemoattractants, the intraglomerular infiltration of leukocytes, and macrophage polarity in DN rats. Kidneys/glomeruli of non-diabetic, DN, and MRS1754-treated DN rats were processed for transcriptomic analysis, immunohistopathology, ELISA, and in vitro macrophage migration assays. The transcriptomic analysis identified an upregulation of transcripts and pathways related to the immune system in the glomeruli of DN rats, which was attenuated using MRS1754. The antagonism of the A2BAR decreased glomerular expression/secretion of chemoattractants (CCL2, CCL3, CCL6, and CCL21), the infiltration of macrophages, and their polarization to M2 in DN rats. The in vitro macrophages migration induced by conditioned-medium of DN glomeruli was significantly decreased using neutralizing antibodies against CCL2, CCL3, and CCL21. We concluded that the pharmacological blockade of the A2BAR decreases the transcriptional expression of genes/pathways related to the immune response, protein expression/secretion of chemoattractants, as well as the infiltration of macrophages and their polarization toward the M2 phenotype in the glomeruli of DN rats, suggesting a new mechanism implicated in the antifibrotic effect of MRS1754.

Neutralizing MIP3α Reduces Renal Immune Cell Infiltration and Progressive Renal Injury in Young Obese Dahl Salt-Sensitive Rats

Recently, we reported that the early progression of renal injury in obese Dahl salt-sensitive leptin receptor mutant (SSLepRmutant) rats was associated with increased macrophage inflammatory protein 3-α (MIP3α) expression prior to puberty. Therefore, this study tested the hypothesis that MIP3α plays a role in recruiting immune cells, thereby triggering renal inflammation and early progressive renal injury in SSLepRmutant rats prior to puberty. Four-week-old Dahl salt-sensitive (SS) and SSLepRmutant rats either served as control (IgG; intraperitoneal, every other day) or received MIP3α-neutralizing antibody (MNA; 100 µg/kg) for 4 weeks. MNA reduced circulating and renal MIP3α levels and proinflammatory immune cells by 50%. Although MNA treatment did not affect blood glucose and plasma cholesterol levels, MNA markedly decreased insulin resistance and triglyceride levels in SSLepRmutant rats. We observed no differences in mean arterial pressure (MAP) between SS and SSLepRmutant rats, and MNA had no effect on MAP in either strain. Proteinuria was significantly increased in SSLepRmutant rats versus SS rats over the course of the study. Treatment with MNA markedly decreased proteinuria in SSLepRmutant rats while not affecting SS rats. Also, MNA decreased glomerular and tubular injury and renal fibrosis in SSLepRmutant rats while not affecting SS rats. Overall, these data indicate that MIP3α plays an important role in renal inflammation during the early progression of renal injury in obese SSLepRmutant rats prior to puberty. These data also suggest that MIP3α may be a novel therapeutic target to inhibit insulin resistance and prevent progressive proteinuria in obese children. SIGNIFICANCE STATEMENT: Childhood obesity is increasing at an alarming rate and is now being associated with renal disease. Although most studies have focused on the mechanisms of renal injury associated with adult obesity, few studies have examined the mechanisms of renal injury involved during childhood obesity. In the current study, we observed that the progression of renal injury in obese Dahl salt-sensitive leptin receptor mutant rats was associated with an increase in MIP3α, a chemokine, before puberty, and inhibition of MIP3α markedly reduced renal injury.

Transcriptional profile changes after treatment of ischemia reperfusion injury-induced kidney fibrosis with 18β-glycyrrhetinic acid

Introduction

Chronic kidney disease (CKD) is characterized by renal fibrosis without effective therapy. 18β-Glycyrrhetinic acid (GA) is reported to have detoxification and anti-inflammatory functions and promotes tissue repair. However, the role of GA in CKD remains unclear. In this study, we investigated whether GA has a potential therapeutic effect in kidney fibrosis.

Methods

A renal fibrosis mouse model was established by ischemia/reperfusion (I/R) injury via clamping unilateral left renal pedicle for 45 min; then, the mice were treated with vehicle or GA. Kidney tissues and blood samples were extracted 14 days after reperfusion and renal function, histopathological staining, quantitative PCR, and western blotting were performed. RNA-seq was performed to explore the changes in the transcriptional profile after GA treatment.

Results

Renal function, pathological and molecular analysis displayed that fibrosis was successfully induced in the I/R model. In the GA treatment group, the severity of fibrosis gradually reduced with the best effect seen at a concentration of 25 mg kg ⁻¹. A total of 970 differentially expressed genes were identified. Pathway enrichment showed that reduced activation and migration of inflammatory cells and decreased chemokine interaction in significant pathways. Protein–protein interaction networks were constructed and 15 hub genes were selected by degree rank, including chemokines, such as C3, Ccl6, Ccr2, Ptafr, Timp1, and Pf4.

Conclusions

GA may alleviate renal fibrosis by inhibiting the inflammatory response. GA is a promising therapy that may perhaps be used in treating renal fibrosis and CKD.

Role of the CCL2-CCR2 axis in cardiovascular disease: Pathogenesis and clinical implications

The CCL2-CCR2 axis is one of the major chemokine signaling pathways that has received special attention because of its function in the development and progression of cardiovascular disease. Numerous investigations have been performed over the past decades to explore the function of the CCL2-CCR2 signaling axis in cardiovascular disease. Laboratory data on the CCL2-CCR2 axis for cardiovascular disease have shown satisfactory outcomes, yet its clinical translation remains challenging. In this article, we describe the mechanisms of action of the CCL2-CCR2 axis in the development and evolution of cardiovascular diseases including heart failure, atherosclerosis and coronary atherosclerotic heart disease, hypertension and myocardial disease. Laboratory and clinical data on the use of the CCL2-CCR2 pathway as a targeted therapy for cardiovascular diseases are summarized. The potential of the CCL2-CCR2 axis in the treatment of cardiovascular diseases is explored.

Acute Increase of Renal Perfusion Pressure Causes Rapid Activation of mTORC1 (Mechanistic Target Of Rapamycin Complex 1) and Leukocyte Infiltration

BACKGROUND

The present study in Sprague-Dawley rats determined the effects of a rapid rise of renal perfusion pressure (RPP) upon the activation of mTOR (mechanistic target of rapamycin), and the effects upon the infiltration of CD68-positive macrophages/monocytes and CD3-positive T lymphocytes into the kidneys.

METHODS

RPP was elevated by 40 mm Hg for 30 minutes in male Sprague-Dawley rats while measuring renal blood flow and urine flow rate. Sham rats were studied in the same way, but RPP was not changed. Since initial studies found that the acute increase of RPP resulted in activation of mTORC1 (phosphorylation of S6S235/236), the effects of inhibition of mTORC1 with rapamycin pretreatment were then determined.

RESULTS

It was found that a 30-minute increase of RPP (≈40 mm Hg) resulted in an 8-fold increase of renal sodium excretion which was blunted by rapamycin treatment. Renal blood flow was not affected by the elevation of RPP. Activation of mTORC1 was observed. Significant increases in CD68-positive macrophages were found in both the cortex (intraglomerular and periglomerular regions) and in the outer medullary interstitial regions of the kidney and prevented by rapamycin treatment. Increases in CD3-positive T lymphocytes were observed exclusively in the periglomerular regions and prevented by rapamycin treatment. Upregulation of several proinflammatory markers was observed.

CONCLUSIONS

We conclude that elevation of RPP rapidly activates mTORC1 resulting in infiltration of immune cells into the kidney.

The SSLepR mutant rat represents a novel model to study obesity-induced renal injury before puberty

Prepubertal obesity (PPO) has emerged as a major health problem over the past few decades and is a risk factor for the development of proteinuria. The current study investigated whether the development of renal injury in the obese SSLepR mutant strain occurs before puberty. When determining the temporal changes in serum sex hormones in female and male SS and SSLepR mutant rats between 4 and 10 wk of age, we only observed significant increases in estradiol and testosterone levels in female and male SS rats at 10 wk of age than at 4 wk of age. The results suggest that studying both strains between 4 and 8 wk of age is appropriate to study the effects of PPO on renal injury in this model. Proteinuria was significantly higher in SSLepR mutant rats as opposed to the values observed in SS rats at 8 wk of age, and we did not observe any sex differences in proteinuria in either strain. The kidneys from the SSLepR mutant rats displayed significant glomerular and tubular injury and renal fibrosis versus the values measured in SS rats without any sex differences. Overall, we observed increased immune cell infiltration in the kidneys from SSLepR mutant rats compared with SS rats. Interestingly, female SSLepR mutant rats displayed significant increases in not only M1 macrophages (proinflammatory) but also M2 macrophages (anti-inflammatory) versus male SSLepR mutant rats. These results suggest the SSLepR mutant rat may be a useful model to study early progression of obesity-related renal injury before the onset of puberty.

Splenocyte transfer from hypertensive donors eliminates premenopausal female protection from ANG II-induced hypertension

Premenopausal females are protected from angiotensin II (ANG II)-induced hypertension following the adoptive transfer of T cells from normotensive donors. For the present study, we hypothesized that the transfer of hypertensive T cells (HT) or splenocytes (HS) from hypertensive donors would eliminate premenopausal protection from hypertension. Premenopausal recombination-activating gene-1 (Rag-1)-/- females received either normotensive (NT) or hypertensive cells 3 wk before ANG II infusion (14 days, 490 ng/kg/min). Contrary to our hypothesis, no increase in ANG II-induced blood pressure was observed in the NT/ANG or HT/ANG groups. Flow cytometry demonstrated that renal FoxP3+ T regulatory cells were significantly decreased, and immunohistochemistry showed an increase in renal F4/80+ macrophages in the HT/ANG group, suggesting a shift in the renal inflammatory environment despite no change in blood pressure. Renal mRNA expression of macrophage chemoattractant protein-1 (MCP-1), endothelin-1 (ET-1), and G protein-coupled estrogen receptor-1 (GPER-1) was significantly decreased in the HT/ANG group. The adoptive transfer of hypertensive splenocytes before ANG II infusion (HS/ANG) eliminated premenopausal protection from hypertension and significantly decreased splenic FoxP3+ T regulatory cells compared with females that received normotensive splenocytes (NS/ANG). Expression of macrophage inflammatory protein 1α/chemokine (C-C motif) ligand 3 (MCP-1/CCL3), a potent macrophage chemokine, was elevated in the HS/ANG group; however, no increase in renal macrophage infiltration occurred. Together, these data show that in premenopausal females, T cells from hypertensive donors are not sufficient to induce robust ANG II-mediated hypertension; in contrast, transfer of hypertensive splenocytes (consisting of T/B lymphocytes, dendritic cells, and macrophages) is sufficient. Further work is needed to understand how innate and adaptive immune cells and estrogen signaling coordinate to cause differential hypertensive outcomes in premenopausal females.NEW & NOTEWORTHY Our study is the first to explore the role of hypertensive T cells versus hypertensive splenocytes in premenopausal protection from ANG II-induced hypertension. We show that the hypertensive status of T cell donors does not impact blood pressure in the recipient female. However, splenocytes, when transferred from hypertensive donors, significantly increased premenopausal recipient blood pressure following ANG II infusion, highlighting the importance of further investigation into estrogen signaling and immune cell activation in females.

RNA sequencing reveals induction of specific renal inflammatory pathways in a rat model of malignant hypertension

In malignant hypertension, far more severe kidney injury occurs than in the "benign" form of the disease. The role of high blood pressure and the renin-angiotensin-aldosterone system is well recognized, but the pathogenesis of the renal injury of malignant hypertension (MH) remains incompletely understood. Using the rat model of two-kidney, one-clip renovascular hypertension in which some but not all animals develop MH, we performed a transcriptomic analysis of gene expression by RNA sequencing to identify transcriptional changes in the kidney cortex specific for MH. Differential gene expression was assessed in three groups: MH, non-malignant hypertension (NMH), and normotensive, sham-operated controls. To distinguish MH from NMH, we considered two factors: weight loss and typical renovascular lesions. Mean blood pressure measured intraarterially was elevated in MH (220 ± 6.5 mmHg) as well as in NMH (192 ± 6.4 mmHg), compared to controls (119 ± 1.7 mmHg, p < 0.05). Eight hundred eighty-six genes were exclusively regulated in MH only. Principal component analysis revealed a separated clustering of the three groups. The data pointed to an upregulation of many inflammatory mechanisms in MH including pathways which previously attracted relatively little attention in the setting of hypertensive kidney injury: Transcripts from all three complement activation pathways were upregulated in MH compared to NMH but not in NMH compared with controls; immunohistochemistry confirmed complement deposition in MH exclusively. The expression of chemokines attracting neutrophil granulocytes (CXCL6) and infiltration of myeloperoxidase-positive cells were increased only in MH rats. The data suggest that these pathways, especially complement deposition, may contribute to kidney injury under MH. KEY MESSAGES: The most severe hypertension-induced kidney injury occurs in malignant hypertension. In a rat model of malignant hypertension, we assessed transcriptional responses in the kidney exposed to high blood pressure. A broad stimulation of inflammatory mechanisms was observed, but a few specific pathways were activated only in the malignant form of the disease, notably activation of the complement cascades. Complement inhibitors may alleviate the thrombotic microangiopathy of malignant hypertension even in the absence of primary complement abnormalities.

Melatonin Prevents T Lymphocyte Infiltration to the Kidneys of Hypertensive Rats, Induced by a High-Salt Diet, by Preventing the Expression of CXCR3 Ligand Chemokines

In a previous study, we demonstrated that melatonin prevents kidney damage in a salt-induced hypertension model by decreasing oxidative stress. We hypothesized that this effect involves melatonin’s immunomodulatory properties. In vivo Study-Dahl salt-sensitive (DSS) rats were fed normal chow, a high-salt diet (HSD), or a HSD and melatonin (30 mg/kg/day) in their water for eight weeks. Kidneys were harvested for immediate lymphocyte isolation and characterization by Flow cytometry (CD3+CD4+ and CD3+CD8+) and for lymphocyte chemoattractant (mainly CXCL chemokines) gene expression studies. In vitro study-rat mesangial cells (RMC) were cultured in a high-salt medium without and with melatonin. A HSD was associated with significant renal infiltration of CD4+ and CD8+ T lymphocytes compared to control. Melatonin significantly reduced renal lymphocyte infiltration. A HSD significantly increased mRNA expression of CXCL chemokines. Adding melatonin to the HSD abolished this effect. Treating RMC cells with salt increased the expression of CXCL10 and CXCL11 but not CXCL9. Adding melatonin to the culture media prevented this increase. Treating HSD-fed rats with melatonin decreased renal lymphocyte chemoattractant mRNA expression and is associated with significantly reducing renal T lymphocyte infiltration. Salt may have a direct effect on chemokine-producing renal cells, which is blunted by melatonin treatment.

Interleukin 17A: Key Player in the Pathogenesis of Hypertension and a Potential Therapeutic Target

PURPOSE OF REVIEW

To summarize key advances in our understanding of the role of interleukin 17A (IL-17A) in the pathogenesis of hypertension and highlight important areas for future research and clinical translation.

RECENT FINDINGS

While T helper 17 (Th17) cells are major producers of IL-17A, there are several additional innate and adaptive immune cell sources including gamma-delta T cells, innate lymphoid cells, and natural killer cells. IL-17A promotes an increase in blood pressure through multiple mechanisms including inhibiting endothelial nitric oxide production, increasing reactive oxygen species formation, promoting vascular fibrosis, and enhancing renal sodium retention and glomerular injury. IL-17A production from Th17 cells is increased by high salt conditions in vitro and in vivo. There is also emerging data linking salt, the gut microbiome, and intestinal T cell IL-17A production. Novel therapeutics targeting IL-17A signaling are approved for the treatment of autoimmune diseases and show promise in both animal models of hypertension and human studies. Hypertensive stimuli enhance IL-17A production. IL-17A is a key mediator of renal and vascular dysfunction in hypertensive mouse models and correlates with hypertension in humans. Large randomized clinical trials are needed to determine whether targeting IL-17A might be an effective adjunct treatment for hypertension and its associated end-organ dysfunction.

Amplification of Salt-Sensitive Hypertension and Kidney Damage by Immune Mechanisms

Humans with salt-sensitive (SS) hypertension demonstrate increased morbidity, increased mortality, and renal end-organ damage when compared with normotensive subjects or those with salt-resistant hypertension. Increasing evidence indicates that immune mechanisms play an important role in the full development of SS hypertension and associated renal damage. Recent experimental advances and studies in animal models have permitted a greater understanding of the mechanisms of activation and action of immunity in this disease process. Evidence favors a role of both innate and adaptive immune mechanisms that are triggered by initial, immune-independent alterations in blood pressure, sympathetic activity, or tissue damage. Activation of immunity, which can be enhanced by a high-salt intake or by alterations in other components of the diet, leads to the release of cytokines, free radicals, or other factors that amplify renal damage and hypertension and mediate malignant disease.

Emerging Role of the Inflammasome and Pyroptosis in Hypertension

Inflammasomes are components of the innate immune response that have recently emerged as crucial controllers of tissue homeostasis. In particular, the nucleotide-binding domain, leucine-rich-containing (NLR) family pyrin domain containing 3 (NLRP3) inflammasome is a complex platform involved in the activation of caspase-1 and the maturation of interleukin (IL)-1β and IL-18, which are mainly released via pyroptosis. Pyroptosis is a caspase-1-dependent type of cell death that is mediated by the cleavage of gasdermin D and the subsequent formation of structurally stable pores in the cell membrane. Through these pores formed by gasdermin proteins cytosolic contents are released into the extracellular space and act as damage-associated molecular patterns, which are pro-inflammatory signals. Inflammation is a main contributor to the development of hypertension and it also is known to stimulate fibrosis and end-organ damage. Patients with essential hypertension and animal models of hypertension exhibit elevated levels of circulating IL-1β. Downregulation of the expression of key components of the NLRP3 inflammasome delays the development of hypertension and pharmacological inhibition of this inflammasome leads to reduced blood pressure in animal models and humans. Although the relationship between pyroptosis and hypertension is not well established yet, pyroptosis has been associated with renal and cardiovascular diseases, instances where high blood pressure is a critical risk factor. In this review, we summarize the recent literature addressing the role of pyroptosis and the inflammasome in the development of hypertension and discuss the potential use of approaches targeting this pathway as future anti-hypertensive strategies.