Renal macrophages monitor and remove particles from urine to prevent tubule obstruction

When the filtrate of the glomerulus flows through the renal tubular system, various microscopic sediment particles, including mineral crystals, are generated. Dislodging these particles is critical to ensuring the free flow of filtrate, whereas failure to remove them will result in kidney stone formation and obstruction. However, the underlying mechanism for the clearance is unclear. Here, using high-resolution microscopy, we found that the juxtatubular macrophages in the renal medulla constitutively formed transepithelial protrusions and "sampled" urine contents. They efficiently sequestered and phagocytosed intraluminal sediment particles and occasionally transmigrated to the tubule lumen to escort the excretion of urine particles. Mice with decreased renal macrophage numbers were prone to developing various intratubular sediments, including kidney stones. Mechanistically, the transepithelial behaviors of medulla macrophages required integrin β1-mediated ligation to the tubular epithelium. These findings indicate that medulla macrophages sample urine content and remove intratubular particles to keep the tubular system unobstructed.

An integral blood-brain barrier in adulthood relies on microglia-derived PDGFB

Pericyte is an indispensable cellular constituent of blood-brain barrier (BBB) and its homeostasis heavily rely on PDGFB-PDGFRβ signaling. However, the primary cellular sources of PDGFB in the central nervous system (CNS) are unclear. Microglia is not considered a component of BBB and its role in maintaining BBB integrity in steady state is controversial. In this study, by analyzing transcriptomic data and performing in situ hybridization, we revealed a transition of the primary central PDGFB producers from endothelial cells in newborns to microglia in adults. Acute loss of microglial PDGFB profoundly impaired BBB integrity in adult but not newborn mice, and thus, adult mice deficient of microglial PDGFB could not survive from a sublethal endotoxin challenge due to rampant microhemorrhages in the CNS. In contrast, acute abrogation of endothelial PDGFB had minimal effects on the BBB of adult mice but led to a severe impairment of CNS vasculature in the neonates. Moreover, we found that microglia would respond to a variety of BBB insults by upregulating PDGFB expression. These findings underscore the physiological importance of the microglia-derived PDGFB to the BBB integrity of adult mice both in steady state and under injury.

Self-maintaining macrophages within the kidney contribute to salt and water balance by modulating kidney sympathetic nerve activity

The kidney is critical in controlling salt and water balance, with the interstitium involved with a variety of components including immune cells in steady state. However, the roles of resident immune cells in kidney physiology are largely unknown. To help unravel some of these unknowns, we employed cell fate mapping, and identified a population of embryo-derived self-maintaining macrophages (SM-MØ) that were independent of the bone marrow in adult mouse kidneys. This kidney-specific SM-MØ population was distinctive from the kidney monocyte-derived macrophages in transcriptome and in their distribution. Specifically, the SM-MØ highly expressed nerve-associated genes; high-resolution confocal microscopy revealed that the SM-MØ in the cortex were in close association with sympathetic nerves and there was a dynamical interaction between macrophages and sympathetic nerves when live kidney sections were monitored. Kidney-specific depletion of the SM-MØ resulted in reduced sympathetic distribution and tone, leading to reduced renin secretion, increased glomerular filtration rate and solute diuresis, which caused salt decompensation and significant weight loss under a low-salt diet challenge. Supplementation of L-3,4-dihydroxyphenylserine which is converted to norepinephrine in vivo rescued the phenotype of SM-MØ-depleted mice. Thus, our findings provide insights in kidney macrophage heterogeneity and address a non-canonical role of macrophages in kidney physiology. In contrast to the well-appreciated way of central regulation, local regulation of sympathetic nerve distribution and activities in the kidney was uncovered.

Microglia-derived PDGFB promotes neuronal potassium currents to suppress basal sympathetic tonicity and limit hypertension

Although many studies have addressed the regulatory circuits affecting neuronal activities, local non-synaptic mechanisms that determine neuronal excitability remain unclear. Here, we found that microglia prevented overactivation of pre-sympathetic neurons in the hypothalamic paraventricular nucleus (PVN) at steady state. Microglia constitutively released platelet-derived growth factor (PDGF) B, which signaled via PDGFRα on neuronal cells and promoted their expression of Kv4.3, a key subunit that conducts potassium currents. Ablation of microglia, conditional deletion of microglial PDGFB, or suppression of neuronal PDGFRα expression in the PVN elevated the excitability of pre-sympathetic neurons and sympathetic outflow, resulting in a profound autonomic dysfunction. Disruption of the PDGFB^MG-Kv4.3^Neuron pathway predisposed mice to develop hypertension, whereas central supplementation of exogenous PDGFB suppressed pressor response when mice were under hypertensive insult. Our results point to a non-immune action of resident microglia in maintaining the balance of sympathetic outflow, which is important in preventing cardiovascular diseases.

Analysis of Mononuclear Phagocytes Disclosed the Establishment Processes of Two Macrophage Subsets in the Adult Murine Kidney

The interstitium of kidney involves a variety of components including resident immune cells, in particular mononuclear phagocytes. However, many proposed markers for distinguishing macrophages or dendritic cells are, in fact, shared by the majority of renal mononuclear phagocytes, which impedes the research of kidney diseases. Here, by employing a flow cytometry strategy and techniques of fate mapping, imaging and lineage depletion, we were able to demarcate renal monocytes, macrophages and dendritic cells and their subsets in mice. In particular, using this strategy, we found that even in steady state, the renal macrophage pool was continuously replenished by bone marrow-derived monocytes in a stepwise process, i.e., from infiltration of classical monocyte, to development of nonclassical monocyte and eventually to differentiation to macrophages. In mechanism, we demonstrated that the ligation of tissue-anchored CX3CL1 and monocytic CX3CR1 was required for promoting monocyte differentiation to macrophages in the kidney, but CX3CL1-CX3CR1 signaling was dispensable in monocyte infiltrating into the kidney. In addition to the bone marrow-derived macrophages, fate mapping in adult mice revealed another population of renal resident macrophages which were embryo-derived and self-maintaining. Thus, the dissecting strategies developed by us would assist in exploration of the biology of renal mononuclear phagocytes.

Integrating tumor mutational burden and transcriptome expression into prediction of immune checkpoint inhibitor response and prognosis of patients with colon cancer

Whether tumor mutational burden (TMB), which refers to the total number of somatic or acquired mutations per million bases in a particular region of the tumor genome, can serve as a predictive biomarker of immune checkpoint inhibitor (ICI) therapy for colon cancer remains unclear. Hereby, we retrospectively investigated the differentially expressed genes (DEGs) based on the level of TMB and tried to established a risk score model as a novel biomarker. The DNA mutation data were retrieved from the Masked Somatic Mutation in Genomic Data Commons data portal of the Cancer Genome Atlas, where the RNA sequencing data, clinical information, and survival outcomes of patients were downloaded. Patients with incomplete clinical information were excluded. The immune score and stromal score were calculated to investigate immune infiltration. The patients were grouped into TMB-high group and the TMB-low group based on the median value of TMB. An immune relevant gene set was obtained from the Immunology Database and Analysis Portal to identify immune-related DEGs. The Cox proportional hazard model and nomogram were applied to establish the risk model. In results: the TMB value was associated with age (p≤0.001), clinical stage (p≤0.001), N stage (p≤0.001), M stage (p=0.003), and immune score (p≤0.001). Twenty-nine immune-related DEGs were identified as enriched in immune response-related function or pathway and tumorigenesis signaling. Nine of 29 were determined to establish a riskScore model. The riskScore suggested a positive relationship with the TMB value (p=0.033), immune score (p≤0.001), and tumor immune dysfunction and exclusion (TIDE) (p=0.002) and presented an independent prognostic factor (p≤0.001, HR=1.04), which predicted the overall survival with good specificity. We concluded that the combination of TMB with transcriptome expression has a predictive and prognostic value for patients treated with ICIs.

The Roles of Inflammation in Keloid and Hypertrophic Scars

The underlying mechanisms of wound healing are complex but inflammation is one of the determining factors. Besides its traditional role in combating against infection upon injury, the characteristics and magnitude of inflammation have dramatic impacts on the pathogenesis of scar. Keloids and hypertrophic scars are pathological scars that result from aberrant wound healing. They are characterized by continuous local inflammation and excessive collagen deposition. In this review, we aim at discussing how dysregulated inflammation contributes to the pathogenesis of scar formation. Immune cells, soluble inflammatory mediators, and the related intracellular signal transduction pathways are our three subtopics encompassing the events occurring in inflammation associated with scar formation. In the end, we enumerate the current and potential medicines and therapeutics for suppressing inflammation and limiting progression to scar. Understanding the initiation, progression, and resolution of inflammation will provide insights into the mechanisms of scar formation and is useful for developing effective treatments.

ATP release drives heightened immune responses associated with hypertension

The cause of most hypertensive disease is unclear, but inflammation appears critical in disease progression. However, how elevated blood pressure initiates inflammation is unknown, as are the effects of high blood pressure on innate and adaptive immune responses. We now report that hypertensive mice have increased T cell responses to antigenic challenge and develop more severe T cell-mediated immunopathology. A root cause for this is hypertension-induced erythrocyte adenosine 5'-triphosphate (ATP) release, leading to an increase in plasma ATP levels, which begins soon after the onset of hypertension and stimulates P2X7 receptors on antigen-presenting cells (APCs), increasing APC expression of CD86. Hydrolyzing ATP or blocking the P2X7 receptor eliminated hypertension-induced T cell hyperactivation. In addition, pharmacologic or genetic blockade of P2X7 receptor activity suppressed the progression of hypertension. Consistent with the results in mice, we also found that untreated human hypertensive patients have significantly elevated plasma ATP levels compared with treated hypertensive patients or normotensive controls. Thus, a hypertension-induced increase in extracellular ATP triggers augmented APC and T cell function and contributes to the immune-mediated pathologic changes associated with hypertensive disease.

Microglia, autonomic nervous system, immunity and hypertension: Is there a link?

Hypertension ranks the most common risk factor for cardiovascular diseases, and it affects almost one third of adult population globally. Emerging evidence indicates that immune activation is highly involved in the entire progress of hypertension and end organ damage. In addition to immunity, autonomic nervous system, particularly sympathetic nervous system, is one of the most conserved systems to maintain body homeostasis. Immune and sympathetic activities are found simultaneously increased in hypertension, suggesting a synergistic action of these two systems in the progression of this disease. Microglia, the primary immune cells in the central nervous system, have been suggested in the regulation of sympathetic outflow; depletion of microglia alters neuroinflammation and pressor responses in hypertensive models. In this review, we firstly updated the current understanding on microglial ontogeny and functions in both steady state and diseases. Then we reviewed on the interaction between autonomic nervous system and peripheral immunity in hypertension. Microglia bridge the central and peripheral inflammation via regulating the sympathetic nerve activity in hypertension. Future exploration of the molecular linkage of this pathway may provide novel therapeutic angel for hypertension and related cardiovascular diseases.

Abstract 085: Loss of Microglia Enhances Neuronal Activity in the Sympathetic Paraventricular Nucleus

Microglia, the primary immune cells in the CNS, are critical in the maintenance of brain homeostasis such as participating neurogenesis and pruning synapses. Our previous work indicates that microglia are activated in hypertension; depletion of microglia in different activation status have opposite effects on blood pressure regulation, which could be due to tuning sympathetic outflow. To further delineate the mechanism how microglia modulate sympathetic nerve activity, we investigated the effect of microglial depletion on sympathetic neuronal activity in the hypothalamic paraventricular nucleus (PVN). In transgenic CD11b-DTR mice, intracerebroventricular (ICV) infusion of diphtheria toxin resulted in over 90% loss of microglia in the brain. Using the transgenic mouse brain slices, we examined the excitability of RVLM-PVN neurons by electrophysiological technique. Patch-clamp recordings obtained from the RVLM-projecting PVN neurons showed significant increases in firing frequency (3.59±0.72 vs. 1.56±0.51; P<0.05 by t-test) and half-width of action potential (2.53 ± 0.11 vs. 1.65 ± 0.07; P<0.001 by t-test); and a dramatic reduction in the outward K currents (I A and I k ) in the absence of microglia compared to control. Single-cell RNA sequencing analysis of RVLM- PVN neurons revealed a significant decreased expression of I A (Kcnd2 abd Kcnd3) and I k (kcna2, Kcna3 and Kcnc2) subunits in neurons without microglia vs. the controls. These results indicate that loss of microglia increases PVN sympathetic neuronal activity, which could be mediated, at least in part, by the inhibition of outward K currents. Collectively, this study suggests a critical role of microglia in the maintaining the homeostasis of sympathetic PVN neurons in normal condition.

Angiotensin-converting enzyme inhibitor works as a scar formation inhibitor by down-regulating Smad and TGF-β-activated kinase 1 (TAK1) pathways in mice

BACKGROUND AND PURPOSE

Angiotensin-converting enzyme (ACE), an important part of the renin-angiotensin system, is implicated in stimulating the fibrotic processes in the heart, lung, liver and kidney, while an ACE inhibitor (ACEI) promotes physiological tissue repair in these organs. The mechanism is closely related to TGF-β1 pathways. However, the reported effects of applying ACEIs during scar formation are unclear. Hence, we explored the anti-fibrotic effects of an ACEI and the molecular mechanisms involved in a mouse scar model.

EXPERIMENTAL APPROACH

After a full-thickness skin wound operation, ACE wild-type mice were randomly assigned to receive either ramipril, losartan or hydralazine p.o. ACE knockout (KO) mice and negative control mice only received vehicle (water). Wound/scar widths during wound healing and histological examinations were recorded at the final day. The ability of ACEI to reduce fibrosis via TGF-β1 signalling was evaluated in vitro and in vivo.

KEY RESULTS

ACE KO mice and mice that received ramipril showed narrower wound/scar width, reduced fibroblast proliferation, decreased collagen and TGF-β1 expression. ACEI attenuated the phosphorylation of small mothers against decapentaplegic (Smad2/3) and TGF-β-activated kinase 1 (TAK1) both in vitro and in vivo. The expression of ACE-related peptides varied in murine models with different drug treatments.

CONCLUSIONS AND IMPLICATIONS

ACEI showed anti-fibrotic properties in scar formation by mediating downstream peptides to suppress TGF-β1/Smad and TGF-β1/TAK1 pathways. These findings suggest that dual inhibition of Smad and TAK1 signalling by ACEI is a useful strategy for the development of new anti-fibrotic agents.

Abstract 130: ATP Release Drives the Immune Responses Associated With Hypertension

Inflammation is critical in progression of hypertension. However, how an elevated blood pressure (BP) initiates inflammation is unknown, as are the precise effects of high BP on the immune responses. To study this, we first challenged mice with antigen ovalbumin (OVA). Two-fold more OVA-specific CD8 + T cells were present in the blood (2.7 ± 0.23% vs. 1.2 ± 0.47%) and spleen (2.62 ± 0.31% vs. 1.31 ± 0.17%) of angiotensin (Ang) II induced hypertensive mice as compared to those of normotensive controls. To address whether the over-activation of T cell-mediated immune responses is pathogenic, two models of autoimmune disease were studied. RIP-mOVA is a transgenic mouse line that expresses OVA in pancreatic islet β cells. When OVA-specific OT-I T cells were infused into Rip-mOVA mice, the animals with hypertension induced by either Ang II or L-NAME developed more severe diabetes (blood glucose (mg/dl): Ang II 331, L-NAME 315 vs. Control 168). Concanavalin A-induced hepatitis was also significantly worsened by hypertension as compared to the pathology observed in normotensive mice. After examining the characteristics of T cells and antigen presenting cells (APCs), we found that the most distinguishable difference in hypertensive mice was the upregulation of CD86 on APCs. Blocking CD86 by antibody completely abrogated the elevated immune responses in hypertensive mice. To understand what causes CD86 upregulation in APCs of hypertensive mice, we studied damage-associated molecular patterns and found that plasma ATP levels rose as early as 3 days after the induction of hypertension and reached from about 1μM of baseline to a peak level of 3 μM after 2 weeks of hypertension, which exactly parallels the kinetics of CD86 elevation on APCs. Hydrolyzing ATP or blocking its P2X 7 receptor normalized APC CD86 expression and eliminated hypertension-induced T cell over-activation. Further, untreated human hypertensive patients have substantially elevated plasma ATP levels (2.21 ± 0.99 μM, n = 27) compared to treated hypertensive patients (0.94 ± 0.34 μM, n = 17) or normotensive controls (0.63 ± 0.38 μM, n =30). A linear trend was observed between ATP levels and BP among all subjects. These studies indicate ATP is critical in initiating hypertension-associated inflammation.

Heterogeneous to homogeneous melting transition visualized with ultrafast electron diffraction

The ultrafast laser excitation of matters leads to nonequilibrium states with complex solid-liquid phase-transition dynamics. We used electron diffraction at mega-electron volt energies to visualize the ultrafast melting of gold on the atomic scale length. For energy densities approaching the irreversible melting regime, we first observed heterogeneous melting on time scales of 100 to 1000 picoseconds, transitioning to homogeneous melting that occurs catastrophically within 10 to 20 picoseconds at higher energy densities. We showed evidence for the heterogeneous coexistence of solid and liquid. We determined the ion and electron temperature evolution and found superheated conditions. Our results constrain the electron-ion coupling rate, determine the Debye temperature, and reveal the melting sensitivity to nucleation seeds.

Angiotensin-converting enzyme in innate and adaptive immunity

Angiotensin-converting enzyme (ACE) - a zinc-dependent dicarboxypeptidase with two catalytic domains - plays a major part in blood pressure regulation by converting angiotensin I to angiotensin II. However, ACE cleaves many peptides besides angiotensin I and thereby affects diverse physiological functions, including renal development and male reproduction. In addition, ACE has a role in both innate and adaptive responses by modulating macrophage and neutrophil function - effects that are magnified when these cells overexpress ACE. Macrophages that overexpress ACE are more effective against tumours and infections. Neutrophils that overexpress ACE have an increased production of superoxide, which increases their ability to kill bacteria. These effects are due to increased ACE activity but are independent of angiotensin II. ACE also affects the display of major histocompatibility complex (MHC) class I and MHC class II peptides, potentially by enzymatically trimming these peptides. Understanding how ACE expression and activity affect myeloid cells may hold great promise for therapeutic manipulation, including the treatment of both infection and malignancy.

Abstract 006: Hypertension is Accompanied With Over Activity of the Adaptive Immune System

Adaptive immune response plays an important role in the pathogenesis of hypertension, but how does hypertension influence on the immune system is still poorly understood. To understand this, we studied antigen presenting cells (APCs) isolated from normotensive and experimental hypertensive mice induced by angiotensin II (490 ng/kg/min, 2 weeks). The APCs were loaded with ovalbumin(OVA) or its MHC class I epitope SIINFEKL (SKL) for 3h. Then, splenocytes from OT-I mice, containing OVA-specific, CD8 + T cells (OT-I cells), were added for 4h. Significantly more activated T cells expressing surface marker CD69 and cytokine IFN-γ were detected by flow cytometry when stimulated with APCs from hypertensive mice than equivalent cells from normotensive mice (P<0.05). Thus, in vitro, APCs derived from hypertensive mice more effectively present antigen to T cells. To study antigen presentation in vivo , we immunized AngII and sham treated mice with OVA and adjuvant. Consistently more OVA-specific CD8 + T cells were induced in the blood (2.7 ± 0.23% vs. 1.2 ± 0.47%, P<0.05) and the spleen (1.51 ± 0.17% vs. 2.62 ± 0.31%, P<0.05) of AngII mice vs sham when measured by flow using an H-2k b -SKL tetramer. We also evaluated the APC and T cell activation signals before and after hypertension. Flow analysis showed that splenic DCs divided from AngII treated mice resulted in a substantially increased surface expression of co-stimulatory factor CD86 compare with DCs from normotensive controls (MFI: 131±7.8 vs. 97±5.3). RIP-mOVA mice were used to study if hypertension affects APC cross-presentation of self-antigens. This transgenic mouse line expresses membrane-bound OVA in pancreatic islet β cells. When OT-I cells (5x10 6 ) are injected into RIP-mOVA mice, they activate by cross-presentation of OVA and cause insulitis and diabetes. RIP-mOVA mice were made hypertensive with either AngII or L-NAME (1.5 mg/ml, 4 weeks). When OT-I cells were i.v. infused into RIP-mOVA mice, the hypertensive mice had more OT-I cells infiltration into the pancreas (AngII 75%, L-NAME 73%, control 13%) and developed severer diabetes (Blood glucose: AngII 331, L-NAME 315, control 168 mg/dl). In conclusion, high blood pressure itself is associated with over activity of the adaptive immune system.

Brain Transforming Growth Factor-β Resists Hypertension Via Regulating Microglial Activation

BACKGROUND AND PURPOSE

Hypertension is the major risk factor for stroke. Recent work unveiled that hypertension is associated with chronic neuroinflammation; microglia are the major players in neuroinflammation, and the activated microglia elevate sympathetic nerve activity and blood pressure. This study is to understand how brain homeostasis is kept from hypertensive disturbance and microglial activation at the onset of hypertension.

METHODS

Hypertension was induced by subcutaneous delivery of angiotensin II, and blood pressure was monitored in conscious animals. Microglial activity was analyzed by flow cytometry and immunohistochemistry. Antibody, pharmacological chemical, and recombinant cytokine were administered to the brain through intracerebroventricular infusion. Microglial depletion was performed by intracerebroventricular delivering diphtheria toxin to CD11b-diphtheria toxin receptor mice. Gene expression profile in sympathetic controlling nucleus was analyzed by customized qRT-PCR array.

RESULTS

Transforming growth factor-β (TGF-β) is constitutively expressed in the brains of normotensive mice. Removal of TGF-β or blocking its signaling before hypertension induction accelerated hypertension progression, whereas supplementation of TGF-β1 substantially suppressed neuroinflammation, kidney norepinephrine level, and blood pressure. By means of microglial depletion and adoptive transfer, we showed that the effects of TGF-β on hypertension are mediated through microglia. In contrast to the activated microglia in established hypertension, the resting microglia are immunosuppressive and important in maintaining neural homeostasis at the onset of hypertension. Further, we profiled the signature molecules of neuroinflammation and neuroplasticity associated with hypertension and TGF-β by qRT-PCR array.

CONCLUSIONS

Our results identify that TGF-β-modulated microglia are critical to keeping brain homeostasis responding to hypertensive disturbance.

Angiotensin-converting enzyme affects the presentation of MHC class II antigens

Antigen processing and presentation through the MHC class II pathway is critical for activating T helper cells. Angiotensin-converting enzyme (ACE) is a carboxyl peptidase expressed by antigen-presenting cells. By analysis of ACE null (knockout), wild-type, and ACE-overexpressing (ACE10) mice and the antigen-presenting cells derived from these mice, we found that ACE has a physiological role in the processing of peptides for MHC class II presentation. The efficiency of presenting MHC class II epitopes from ovalbumin (OVA) and hen egg lysosome is markedly affected by cellular ACE levels. Mice overexpressing ACE in myeloid cells have a much more vigorous CD4⁺ T-cell and antibody response when immunized with OVA. ACE is present in the endosomal pathway where MHC class II peptide processing and loading occur. The efficiency of MHC class II antigen presentation can be altered by ACE overexpression or ACE pharmacological inhibition. Thus, ACE is a dynamic participant in processing MHC class II peptides. Manipulation of ACE expression by antigen-presenting cells may prove to be a novel strategy to alter the immune response.

Renal tubular angiotensin converting enzyme is responsible for nitro-L-arginine methyl ester (L-NAME)-induced salt sensitivity

Renal parenchymal injury predisposes to salt-sensitive hypertension, but how this occurs is not known. Here we tested whether renal tubular angiotensin converting enzyme (ACE), the main site of kidney ACE expression, is central to the development of salt sensitivity in this setting. Two mouse models were used: it-ACE mice in which ACE expression is selectively eliminated from renal tubular epithelial cells; and ACE 3/9 mice, a compound heterozygous mouse model that makes ACE only in renal tubular epithelium from the ACE 9 allele, and in liver hepatocytes from the ACE 3 allele. Salt sensitivity was induced using a post L-NAME salt challenge. While both wild-type and ACE 3/9 mice developed arterial hypertension following three weeks of high salt administration, it-ACE mice remained normotensive with low levels of renal angiotensin II. These mice displayed increased sodium excretion, lower sodium accumulation, and an exaggerated reduction in distal sodium transporters. Thus, in mice with renal injury induced by L-NAME pretreatment, renal tubular epithelial ACE, and not ACE expression by renal endothelium, lung, brain, or plasma, is essential for renal angiotensin II accumulation and salt-sensitive hypertension.

Lipopolysaccharide derived from the digestive tract provokes oxidative stress in the liver of dairy cows fed a high-grain diet

The aims of this study were to measure oxidative stress parameters and to investigate the molecular mechanism triggered by grain-induced subacute ruminal acidosis in mid-lactation cows. Twelve Holstein-Friesian cows with an average weight of 455±28kg were divided into 2 groups and subjected to 2 diets over 18wk: either a low-grain (forage-to-concentrate ratio=6:4) or a high-grain (forage-to-concentrate ratio=4:6) diet based on dry matter. Being fed a long-term high-grain diet resulted in a significant decrease in rumen pH and a significant increase in ruminal lipopolysaccharide (LPS) at 4 h postfeeding in the morning. The increase was also observed in LPS concentrations in the portal vein, hepatic vein, and jugular vein blood plasma as well as reduced milk yield in a high-grain diet. Cows fed a high-grain diet had lower levels of catalase and glutathione peroxidase (GPx) activity and total antioxidant capacity than cows fed a low-grain diet; however, super oxide dismutase (SOD) activity and malondialdehyde (MDA) levels were higher in both the liver and the plasma of high-grain than in low-grain cows. Positive correlations were observed between plasma LPS versus hepatic MDA, plasma MDA, and hepatic SOD activity, whereas hepatic GPx and plasma GPx were negatively correlated with plasma LPS. The relative mRNA abundances of GPX1 and CAT were significantly lower in the liver of cows fed a high-grain diet than those fed a low-grain diet, whereas SOD1 was significantly higher in cows fed a high-grain diet than cows fed a low-grain diet. The expression levels of Nrf2, NQO1, MT1E, UGT1A1, MGST3, and MT1A were downregulated, whereas NF-kB was upregulated, in cows fed a high-grain diet. Furthermore, nuclear factor E2-related factor 2 (Nrf2) total protein and mRNA levels were significantly lower than in low-grains. Our results demonstrate the relationship between the translocated LPS and the suppression of cellular antioxidant defense capacity, which lead to increased oxidative stress and suggests that the Nrf2-dependent antioxidant response may be affected by higher levels of LPS translocated to the bloodstream.

Abstract 001: Hypertension Induces Heightened Activity of the Adaptive Immune System

Adaptive immunity plays a key role in the pathogenesis of hypertension, but how does hypertension affect immunity? To study this, splenic dendritic cells (DC) and peritoneal macrophages were isolated from normotensive and hypertensive angiotensin II (AngII)-infused C57BL6/J mice (490 ng/kg/min, 2 wk). These antigen presenting cells (APCs) were loaded with ovalbumin (OVA) or the OVA MHC class I epitope SIINFEKL (SKL) for 3h. Then, splenocytes from OT-I mice, containing OVA-specific, CD8 + T cells (OT-I cells), were added for 4h. Flow cytometry showed significantly more activated T cells expressing CD69 when stimulated with APCs from AngII-treated mice than equivalent cells from naïve mice (As example, DC+OVA: 2.9 ± 0.4% vs. 1.8 ± 0.3% ,P<0.05; DC+SKL: 13.9 ± 0.9 % vs. 7.4 ± 1.1%, P<0.01;). To study antigen presentation in vivo, we immunized AngII and sham treated mice with OVA and adjuvant. Consistently more OVA-specific CD8 + T cells were induced in the blood (2.7 ± 0.2% vs. 1.2 ± 0.4%, P<0.05) and the spleen (2.6 ± 0.3% vs. 1.5 ± 0.2%, P<0.05) of hypertensive mice vs. sham when measured by flow using a H-2k b -SKL tetramer.

RIP-mOVA mice were also used to study if hypertension affects APC cross-presentation of self-antigens. This transgenic mouse line expresses membrane-bound OVA in pancreatic islet β cells and kidney proximal tubular cells. When OT-I cells (5x10 6 ) are injected into RIP-mOVA mice, they activate by cross-presentation of OVA and cause insulitis and diabetes. RIP-mOVA mice were made hypertensive with either AngII or L-NAME. When OT-I cells were infused into hypertensive RIP-mOVA mice, they rapidly developed much higher blood glucose levels as compared to equivalently treated normotensive RIP-mOVA mice. For example, comparing mice 3 weeks after AngII and 1 wk after OT-I cells to normotensive mice 1 wk after OT-I cells, blood glucose was 331 ± 47 mg/dl in the hypertensive mice vs. 168 ± 39 mg/dl in the normotensive controls. Also, far more pancreatic islets were infiltrated by T cells in the hypertensive mice (AngII 78%, 31 of 40; L-NAME 72%, 21 of 29; control 13%, 10 of 75). In conclusion, hypertension itself is associated with higher activity of APC presentation of foreign and self-antigens which may explain why hypertension induces inflammation.

Differential regulation of the expression of aquaporins 3 and 9 by Auphen and dbcAMP in the SMMC-7721 hepatocellular carcinoma cell line

Aquaglycero-aquaporins (agAQPs) are the structural foundation of rapid water transport and they appear to participate in cancer proliferation and malignancy. AQP3 expression is increased and AQP9 expression is decreased in hepatocellular carcinoma (HCC) compared to normal liver, which suggests their possible use as targets for cancer treatment. AQP-based modifiers, such as Auphen and dibutyryladenosine 3', 5'-cyclic monophosphate (dbcAMP), might be used to treat several diseases and as chemical tools for assessing the functions of AQPs in biological systems. We investigated the effects of both Auphen on AQP3 and dbcAMP on AQP9 in SMMC-7721 cells. We used western blotting, real-time quantitative polymerase chain reaction (qPCR) and immunohistochemistry to evaluate changes in AQP3 and AQP9 expression in SMMC-7721 cells after culturing with Auphen and dbcAMP, respectively. We also determined the proliferation of SMMC-7721 cells. We found that compared to HL-7702 (L02) liver cells, Auphen increased AQP3 expression in tumor cells, whereas dbcAMP decreased expression of AQP9 in these cells. Also, high concentrations of Auphen and dbcAMP inhibited proliferation of SMMC-7721 cells in vitro. Auphen and dbcAMP may inhibit HCC development and could be considered targets for HCC diagnosis and therapy.

Overexpression of angiotensin-converting enzyme in myelomonocytic cells enhances the immune response

Angiotensin-converting enzyme (ACE) converts angiotensin I to the vasoconstrictor angiotensin II and thereby plays an important role in blood pressure control. However, ACE is relatively non-specific in its substrate specificity and cleaves many other peptides. Recent analysis of mice overexpressing ACE in monocytes, macrophages, and other myelomonocytic cells shows that these animals have a marked increase in resistance to experimental melanoma and to infection by Listeria monocytogenes or methicillin-resistant Staphylococcus aureus (MRSA). Several other measures of immune responsiveness, including antibody production, are enhanced in these animals. These studies complement a variety of studies indicating an important role of ACE in the immune response.

Angiotensin-converting enzyme overexpression in myelocytes enhances the immune response

Angiotensin-converting enzyme (ACE) plays an important role in blood pressure control. ACE also has effects on renal function, reproduction, hematopoiesis, and several aspects of the immune response. ACE 10/10 mice overexpress ACE in monocytic cells; macrophages from ACE 10/10 mice demonstrate increased polarization toward a proinflammatory phenotype. As a result, ACE 10/10 mice have a highly effective immune response following challenge with melanoma, bacterial infection, or Alzheimer disease. As shown in ACE 10/10 mice, enhanced monocytic function greatly contributes to the ability of the immune response to defend against a wide variety of antigenic and non-antigenic challenges.

Myeloid Suppressor Cells Accumulate and Regulate Blood Pressure in Hypertension

RATIONALE

Chronic inflammation is a major contributor to the progressive pathology of hypertension, and T-cell activation is required for the genesis of hypertension. However, the precise role of myeloid cells in this process is unclear.

OBJECTIVE

To characterize and understand the role of peripheral myeloid cells in the development of hypertension.

METHODS AND RESULTS

We examined myeloid cells in the periphery of hypertensive mice and found that increased numbers of CD11b(+)Gr1(+) myeloid cells in blood and the spleen are a characteristic of 3 murine models of experimental hypertension (angiotensin II, L-NG-nitroarginine methyl ester, and high salt). These cells express surface markers and transcription factors associated with immaturity and immunosuppression. Also, they produce hydrogen peroxide to suppress T-cell activation. These are characteristics of myeloid-derived suppressor cells (MDSCs). Depletion of hypertensive MDSCs increased blood pressure and renal inflammation. In contrast, adoptive transfer of wild-type MDSCs to hypertensive mice reduced blood pressure, whereas the transfer of nicotinamide adenine dinucleotide phosphate oxidase 2-deficient MDSCs did not.

CONCLUSION

The accumulation of MDSCs is a characteristic of experimental models of hypertension. MDSCs limit inflammation and the increase of blood pressure through the production of hydrogen peroxide.

Adaption of SYBR Green-based reagent kit for real-time PCR quantitation of GC-rich DNA

In the mammalian genome, approximately 50% of all genes are controlled by promoters with high GC contents. Analyzing the epigenetic mechanisms regulating their expression is difficult. Hence, we examined a method for stable quantification of such GC-rich DNA sequences. Quantification of DNA during real-time PCR is often based on reagent kits containing the fluorescent dye SYBR Green. However, these ready-made kits may not be suitable for amplifying DNA samples with a high GC content (>70%). DNA segments with eccentric GC contents are frequently found in proximal promoter areas, and their quantification may be necessary in chromatin accessibility by real-time polymerase chain reaction or chromatin immunoprecipitation analyses of epigenetic mechanisms of gene regulation. We therefore optimized the SYBR Green I FastStart reaction system by supplementing the system with dimethyl sulfoxide, betaine, and increased DNA polymerase content. Here, we describe the development of the assay and demonstrate its effectiveness for two different DNA templates, showing that these modifications allow for the reliable amplification and quantification of DNA with GC contents exceeding >70% using the LightCycler instrument.

Salt Sensitivity in Response to Renal Injury Requires Renal Angiotensin-Converting Enzyme

Recent evidence indicates that salt-sensitive hypertension can result from a subclinical injury that impairs the kidneys' capacity to properly respond to a high-salt diet. However, how this occurs is not well understood. Here, we showed that although previously salt-resistant wild-type mice became salt sensitive after the induction of renal injury with the nitric oxide synthase inhibitor Nω-nitro-l-arginine methyl ester hydrochloride; mice lacking renal angiotensin-converting enzyme, exposed to the same insult, did not become hypertensive when faced with a sodium load. This is because the activity of renal angiotensin-converting enzyme plays a critical role in (1) augmenting the local pool of angiotensin II and (2) the establishment of the antinatriuretic state via modulation of glomerular filtration rate and sodium tubular transport. Thus, this study demonstrates that the presence of renal angiotensin-converting enzyme plays a pivotal role in the development of salt sensitivity in response to renal injury.

Microglia participate in neurogenic regulation of hypertension

Hypertension is associated with neuroinflammation and increased sympathetic tone. Interference with neuroinflammation by an anti-inflammatory reagent or overexpression of interleukin-10 in the brain was found to attenuate hypertension. However, the cellular mechanism of neuroinflammation, as well as its impact on neurogenic regulation of blood pressure, is unclear. Here, we found that hypertension, induced by either angiotensin II or l-N(G)-nitro-l-arginine methyl ester, is accompanied by microglial activation as manifested by microgliosis and proinflammatory cytokine upregulation. Targeted depletion of microglia significantly attenuated neuroinflammation, glutamate receptor expression in the paraventricular nucleus, plasma vasopressin level, kidney norepinephrine concentration, and blood pressure. Furthermore, when microglia were preactivated and transferred into the brains of normotensive mice, there was a significantly prolonged pressor response to intracerebroventricular injection of angiotensin II, and inactivation of microglia eliminated these effects. These data demonstrate that microglia, the resident immune cells in the brain, are the major cellular factors in mediating neuroinflammation and modulating neuronal excitation, which contributes to the elevated blood pressure.

Endogenous LPS alters liver GH/IGF system gene expression and plasma lipoprotein lipase in goats

Endotoxin lipopolysaccharide (LPS) affects the ruminant health and animal performance. The main purposes of this study were to investigate the potential effects of GH/IGF system and lipoprotein lipase (LPL) concentration on resistance the circulating LPS concentration increased in liver with high concentrate diet treatment. Non-lactating goats were randomly allocated to two groups: a high-concentrate diet (HCD) or a low-concentrate diet (LCD) in cross over design and the blood collection at different time points after feeding at the end of the experiment. The average rumen pH was significantly reduced (P<0.05), but the duration with pH was not more than 120 min in the HCD group. The plasma LPL concentration was significantly raised (P<0.05). However, from 2 h onwards, LPS concentration was significantly reduced (P<0.01) in the HCD group compared with LCD group. In addition, the plasma IGF1 concentration and the hepatic insulin-like growth factor-1 receptor (IGF1R) mRNA expression were markedly reduced (P<0.05). However, growth hormone (GH) secretion at 15, 30, and 45 min after feeding and growth hormone receptor (GHR) mRNA expression in the liver was significantly increased (P<0.05) in HCD group. The correlation analysis showed that the plasma LPL concentration was positively correlated with hepatic GHR mRNA expression (P<0.05). Conversely, the plasma LPS concentration was negatively correlated with LPL concentration (P<0.05). These findings reveal that alterations in GH/IGF system function in response to a high-concentrate diet are accompanied by corresponding changes in systemic LPL in non-lactating goats' liver in presence of endogenous LPS stress.

ACE overexpression in myelomonocytic cells: effect on a mouse model of Alzheimer's disease

While it is well known that angiotensin converting enzyme (ACE) plays an important role in blood pressure control, ACE also has effects on renal function, hematopoiesis, reproduction, and aspects of the immune response. ACE 10/10 mice overexpress ACE in myelomonocytic cells. Macrophages from these mice have an increased polarization towards a pro-inflammatory phenotype that results in a very effective immune response to challenge by tumors or bacterial infection. In a mouse model of Alzheimer's disease (AD), the ACE 10/10 phenotype provides significant protection against AD pathology, including reduced inflammation, reduced burden of the neurotoxic amyloid-β protein and preserved cognitive function. Taken together, these studies show that increased myelomonocytic ACE expression in mice alters the immune response to better defend against many different types of pathologic insult, including the cognitive decline observed in an animal model of AD.

The intrarenal generation of angiotensin II is required for experimental hypertension

Hypertension is a major risk factor for cardiovascular disease. While the cause of hypertension is multifactorial, renal dysregulation of salt and water excretion is a major factor. All components of the renin-angiotensin system are produced locally in the kidney, suggesting that intrarenal generation of angiotensin II plays a key role in blood pressure regulation. Here, we show that two mouse models lacking renal angiotensin converting enzyme (ACE) are protected against angiotensin II and l-NAME induced hypertension. In response to hypertensive stimuli, mice lacking renal ACE do not produce renal angiotensin II. These studies indicate that the intrarenal renin-angiotensin system works as an entity separate from systemic angiotensin II generation. Renal ACE appears necessary for experimental hypertension.

Direct pro-inflammatory effects of prorenin on microglia

Neuroinflammation has been implicated in hypertension, and microglia have been proposed to play an important role in the progression of this disease. Here, we have studied whether microglia are activated within cardiovascular regulatory area(s) of the brain during hypertension, especially in high blood pressure that is associated with chronic activation of the renin-angiotensin-system. In addition, we determined whether prorenin, an essential component of the renin-angiotensin-system, exerts direct pro-inflammatory effects on these microglia. Our data indicate that two rodent models which display neurogenic hypertension and over activation of the renin-angiotensin-system in the brain (sRA mice and spontaneously hypertensive rats) exhibit microglial activation, and increased levels of pro-inflammatory cytokines, in the paraventricular nucleus of the hypothalamus, an area crucial for regulation of sympathetic outflow. Further, the renin-angiotensin-system component prorenin elicits direct activation of hypothalamic microglia in culture and induction of pro-inflammatory mechanisms in these cells, effects that involve prorenin receptor-induced NFκB activation. In addition, the prorenin-elicited increases in cytokine expression were fully abolished by microglial inhibitor minocycline, and were potentiated by pre-treatment of cells with angiotensin II. Taken together with our previous data which indicate that pro-inflammatory processes in the paraventricular nucleus are involved in the hypertensive action of renin-angiotensin-system, the novel discovery that prorenin exerts direct stimulatory effects on microglial activation and pro-inflammatory cytokine production provides support for the idea that renin-angiotensin-system -induced neurogenic hypertension is not restricted to actions of angiotensin II alone.

DC isoketal-modified proteins activate T cells and promote hypertension

Oxidative damage and inflammation are both implicated in the genesis of hypertension; however, the mechanisms by which these stimuli promote hypertension are not fully understood. Here, we have described a pathway in which hypertensive stimuli promote dendritic cell (DC) activation of T cells, ultimately leading to hypertension. Using multiple murine models of hypertension, we determined that proteins oxidatively modified by highly reactive γ-ketoaldehydes (isoketals) are formed in hypertension and accumulate in DCs. Isoketal accumulation was associated with DC production of IL-6, IL-1β, and IL-23 and an increase in costimulatory proteins CD80 and CD86. These activated DCs promoted T cell, particularly CD8+ T cell, proliferation; production of IFN-γ and IL-17A; and hypertension. Moreover, isoketal scavengers prevented these hypertension-associated events. Plasma F2-isoprostanes, which are formed in concert with isoketals, were found to be elevated in humans with treated hypertension and were markedly elevated in patients with resistant hypertension. Isoketal-modified proteins were also markedly elevated in circulating monocytes and DCs from humans with hypertension. Our data reveal that hypertension activates DCs, in large part by promoting the formation of isoketals, and suggest that reducing isoketals has potential as a treatment strategy for this disease.

Renal generation of angiotensin II and the pathogenesis of hypertension

The existence of a complete and functional renin-angiotensin system along the nephron is widely recognized. However, its precise role in blood pressure control and, by extension, hypertension is still uncertain. While most investigators agree that overexpressing RAS components along the nephron results in hypertension, two important issues remain: whether the local RAS works as a separate entity or represents an extension of the systemic RAS and whether locally generated angiotensin II has specific renal effects on blood pressure that are distinct from systemic angiotensin II. This review addresses these issues while emphasizing the unique role of local angiotensin II in the response of the kidney to hypertensive stimuli and the induction of hypertension.

Identification of Differentially Expressed Proteins in Liver in Response to Subacute Ruminal Acidosis (SARA) Induced by High-concentrate Diet

The aim of this study was to evaluate protein expression patterns of liver in response to subacute ruminal acidosis (SARA) induced by high-concentrate diet. Sixteen healthy mid-lactating goats were randomly divided into 2 groups and fed either a high-forage (HF) diet or a high-concentrate (HC) diet. The HC diet was expected to induce SARA. After ensuring the occurrence of SARA, liver samples were collected. Proteome analysis with differential in gel electrophoresis technology revealed that, 15 proteins were significantly modulated in liver in a comparison between HF and HC-fed goats. These proteins were found mainly associated with metabolism and energy transfer after identified by matrix-assisted laser desorption ionization/time of flight. The results indicated that glucose, lipid and protein catabolism could be enhanced when SARA occurred. It prompted that glucose, lipid and amine acid in the liver mainly participated in oxidation and energy supply when SARA occurred, which possibly consumed more precursors involved in milk protein and milk fat synthesis. These results suggest new candidate proteins that may contribute to a better understanding of the mechanisms that mediate liver adaptation to SARA.

Renal angiotensin-converting enzyme is essential for the hypertension induced by nitric oxide synthesis inhibition

The kidney is an important source of angiotensin-converting enzyme (ACE) in many species, including humans. However, the specific effects of local ACE on renal function and, by extension, BP control are not completely understood. We previously showed that mice lacking renal ACE, are resistant to the hypertension induced by angiotensin II infusion. Here, we examined the responses of these mice to the low-systemic angiotensin II hypertensive model of nitric oxide synthesis inhibition with L-NAME. In contrast to wild-type mice, mice without renal ACE did not develop hypertension, had lower renal angiotensin II levels, and enhanced natriuresis in response to L-NAME. During L-NAME treatment, the absence of renal ACE was associated with blunted GFR responses; greater reductions in abundance of proximal tubule Na(+)/H(+) exchanger 3, Na(+)/Pi co-transporter 2, phosphorylated Na(+)/K(+)/Cl(-) cotransporter, and phosphorylated Na(+)/Cl(-) cotransporter; and greater reductions in abundance and processing of the γ isoform of the epithelial Na(+) channel. In summary, the presence of ACE in renal tissue facilitates angiotensin II accumulation, GFR reductions, and changes in the expression levels and post-translational modification of sodium transporters that are obligatory for sodium retention and hypertension in response to nitric oxide synthesis inhibition.

Angiotensin-converting enzyme overexpression in myelomonocytes prevents Alzheimer's-like cognitive decline

Cognitive decline in patients with Alzheimer's disease (AD) is associated with elevated brain levels of amyloid β protein (Aβ), particularly neurotoxic Aβ(1-42). Angiotensin-converting enzyme (ACE) can degrade Aβ(1-42), and ACE overexpression in myelomonocytic cells enhances their immune function. To examine the effect of targeted ACE overexpression on AD, we crossed ACE(10/10) mice, which overexpress ACE in myelomonocytes using the c-fms promoter, with the transgenic APP(SWE)/PS1(ΔE9) mouse model of AD (AD⁺). Evaluation of brain tissue from these AD⁺ACE(10/10) mice at 7 and 13 months revealed that levels of both soluble and insoluble brain Aβ(1-42) were reduced compared with those in AD⁺ mice. Furthermore, both plaque burden and astrogliosis were drastically reduced. Administration of the ACE inhibitor ramipril increased Aβ levels in AD⁺ACE(10/10) mice compared with the levels induced by the ACE-independent vasodilator hydralazine. Overall, AD⁺ACE(10/10) mice had less brain-infiltrating cells, consistent with reduced AD-associated pathology, though ACE-overexpressing macrophages were abundant around and engulfing Aβ plaques. At 11 and 12 months of age, the AD⁺ACE(10/WT) and AD⁺ACE(10/10) mice were virtually equivalent to non-AD mice in cognitive ability, as assessed by maze-based behavioral tests. Our data demonstrate that an enhanced immune response, coupled with increased myelomonocytic expression of catalytically active ACE, prevents cognitive decline in a murine model of AD.

Myeloid expression of angiotensin-converting enzyme facilitates myeloid maturation and inhibits the development of myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells which accumulate in cancer, infection and chronic inflammation. These cells suppress T-cell function and the immune response. Angiotensin-converting enzyme (ACE) is a peptidase that is now known to regulate aspects of myelopoiesis. Here, we show that ACE expression correlates with myeloid maturation in vitro. Forced ACE overexpression in monocytic cells reduces the generation of MDSCs. In vivo, mice with a genetic change resulting in myeloid cell ACE overexpression have reduced numbers of blood and splenic MDSCs in a tumor model and in a model of chronic inflammation induced by complete Freund's adjuvant. In contrast, ACE-null mice produce large numbers of MDSCs during chronic inflammation. Macrophages from mice with myeloid ACE overexpressing are more pro-inflammatory and have more tumor-killing activity than cells from wild-type mice. Thus, manipulating myeloid ACE activity can interfere with MDSC development and the maturation of myeloid cells.

Renal angiotensin-converting enzyme and blood pressure control

PURPOSE OF REVIEW

This review presents novel findings regarding the renal angiotensin-converting enzyme (ACE) and its role in blood pressure (BP) control.

RECENT FINDINGS

The textbook flow diagram of the renin-angiotensin system (RAS) shows the pulmonary endothelium as the main source of the ACE that converts angiotensin I to angiotensin II. However, ACE is made in large quantities by the kidneys, which raises the important question of what precisely is the function of renal ACE? Recent studies in gene-targeted mice indicates that renal ACE plays a dominant role in regulating the response of the kidney to experimental hypertension. In particular, renal ACE and locally generated angiotensin II affect the activity of several key sodium transporters and the induction of sodium and water retention resulting in the elevation of BP.

SUMMARY

New experimental data link the renal ACE/angiotensin II pathway and the local regulation of sodium transport as key elements in the development of hypertension.

Rediscovering ACE: novel insights into the many roles of the angiotensin-converting enzyme

Angiotensin-converting enzyme (ACE) is best known for the catalytic conversion of angiotensin I to angiotensin II. However, the use of gene-targeting techniques has led to mouse models highlighting many other biochemical properties and actions of this enzyme. This review discusses recent studies examining the functional significance of ACE tissue-specific expression and the presence in ACE of two independent catalytic sites with distinct substrates and biological effects. It is these features which explain why ACE makes important contributions to many different physiological processes including renal development, blood pressure control, inflammation, and immunity.

Abstract 87: The Accumulation of Myeloid-derived Suppressor Cells Is a Compensatory Response to the Development of Hypertension

The immune system plays a critical role in the development of hypertension. The immune response consists of pro-inflammatory cells, but also immunosuppressive cells that reduce T cell function. An important category of natural immunosuppressive cell is myeloid-derived suppressor cells (MDSC). We now show that blood and spleen CD11b+ Gr1+ myeloid cells are elevated 2-fold in both angiotensin II and L-NAME induced hypertension. These increased myeloid cells are MDSC in that they elevate IL-4R expression and suppress T cell proliferation. When hypertensive mice were depleted of MDSC, using either anti-Gr1 antibody or gemcitabine, there was a 15 mmHg rise in blood pressure and aggravation of T cells activation with increased production of IFN-γ, TNFα and IL-17 in both spleen and kidney. In contrast, adoptive transfer of MDSC reduced blood pressure in angiotensin-II induced hypertension by 25 mmHg (see Figure). These data suggest a new concept, that the accumulation of MDSC is a compensatory response to the inflammation induced by hypertension. They also indicate that MDSC play an important role in regulating blood pressure.

Abstract 59: Targeted Angiotensin Converting Enzyme Overexpression in Myelomonocytic Cells Prevents Cognitive Decline in Alzheimer’s Disease

The cognitive decline in Alzheimer's disease (AD) is associated with elevated brain levels of amyloid β-protein (Aβ), particularly Aβ 1-42 . Angiotensin-converting enzyme (ACE) can enzymatically degrade Aβ 1-42 and its overexpression in myelomonocytic cells enhances their immune function. To examine the effect of targeted ACE overexpression on AD, we crossed ACE 10/10 mice, which over express ACE in myelomonocytic cells, with the double-transgenic APP SWE /PS1 ΔE9 mouse model of AD (AD + ). At 7 months, soluble Aβ 1-42 was reduced by 44% (136 vs 245 pg/mg) and Aβ 1-40 was reduced by 32% (21 vs 31 pg/mg). Plaque burden was reduced by as much as 79% (13 vs 62 10 3 mm 2 ) and insoluble Aβ 1-42 by 64% (189 vs 521 pg/mg). There was also a substantial reduction in astrogliosis (49-57% at 7 months, 50% at 13 months). AD + ACE 10/10 mice demonstrated less overall brain infiltrating cells, consistent with less AD pathology, though ACE-overexpressing monocytes and macrophages were increasingly abundant surrounding and engulfing Aβ plaque. At 11 and 12 months, AD + ACE 10/WT and AD + ACE 10/10 mice were virtually equivalent to non-AD mice in cognitive ability as assessed by maze-based behavioral tests. This study shows that an enhanced immune response, coupled with increased myelomonocytic cell expression of ACE, resulted in essentially complete prevention of the cognitive decline observed in a murine model of AD.

Angiotensin-converting enzyme and the tumor microenvironment: mechanisms beyond angiogenesis

The renin angiotensin system (RAS) is a network of enzymes and peptides that coalesce primarily on the angiotensin II type 1 receptor (AT1R) to induce cell proliferation, angiogenesis, fibrosis, and blood pressure control. Angiotensin-converting enzyme (ACE), the key peptidase of the RAS, is promiscuous in that it cleaves other substrates such as substance P and bradykinin. Accumulating evidence implicates ACE in the pathophysiology of carcinogenesis. While the role of ACE and its peptide network in modulating angiogenesis via the AT1R is well documented, its involvement in shaping other aspects of the tumor microenvironment remains largely unknown. Here, we review the role of ACE in modulating the immune compartment of the tumor microenvironment, which encompasses the immunosuppressive, cancer-promoting myeloid-derived suppressor cells, alternatively activated tumor-associated macrophages, and T regulatory cells. We also discuss the potential roles of peptides that accumulate in the setting of chronic ACE inhibitor use, such as bradykinin, substance P, and N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP), and how they may undercut the gains of anti-angiogenesis from ACE inhibition. These emerging mechanisms may harmonize the often-conflicting results on the role of ACE inhibitors and ACE polymorphisms in various cancers and call for further investigations into the potential benefit of ACE inhibitors in some neoplasms.

A modern understanding of the traditional and nontraditional biological functions of angiotensin-converting enzyme

Angiotensin-converting enzyme (ACE) is a zinc-dependent peptidase responsible for converting angiotensin I into the vasoconstrictor angiotensin II. However, ACE is a relatively nonspecific peptidase that is capable of cleaving a wide range of substrates. Because of this, ACE and its peptide substrates and products affect many physiologic processes, including blood pressure control, hematopoiesis, reproduction, renal development, renal function, and the immune response. The defining feature of ACE is that it is composed of two homologous and independently catalytic domains, the result of an ancient gene duplication, and ACE-like genes are widely distributed in nature. The two ACE catalytic domains contribute to the wide substrate diversity of ACE and, by extension, the physiologic impact of the enzyme. Several studies suggest that the two catalytic domains have different biologic functions. Recently, the X-ray crystal structure of ACE has elucidated some of the structural differences between the two ACE domains. This is important now that ACE domain-specific inhibitors have been synthesized and characterized. Once widely available, these reagents will undoubtedly be powerful tools for probing the physiologic actions of each ACE domain. In turn, this knowledge should allow clinicians to envision new therapies for diseases not currently treated with ACE inhibitors.

Abstract 455: Decreased Experimental Hypertension and Inflammation in the Absence of Prolylendopeptidase Activity

Objective: Previously, we showed that inhibition of prolyloligopeptidase eliminated the differences in macrophage TNFα expression and BP response in mice lacking N-domain activity of ACE. Thus, functional studies of BP and inflammatory response in a model lacking prolylendopeptidase activity are performed.

Results: After a 14 day high-dose AngII infusion (980 ng/kg-min), POP-KO(n=12) BP was 130±3 mmHg and 147±4 mmHg for POP-WT(n=12). After 14 days of low-dose AngII infusion(490 ng/kg-min), POP-KO(n=8) BP was 126±4 mmHg and 139±3 mmHg for POP-WT(n=8). To investigate differences in the inflammatory response, we examined peritoneal macrophage cytokine expression in response to AngII. The percentage of F4/80+/TNFαhigh cells vs. total F4/80+ was 17%±4.7% for POP-KO (n=8) and 49%±2.8% for POP-WT (n=8)[p<0.005]. The percentage of F4/80+/IL-6high cells vs. total F4/80+ was 15%±3.2% for POP-KO(n=8) and 39%±4.8% for POP-WT(n=8)[p<0.01]. To investigate whether there were baseline differences, TNFalpha secretion was measured in POP-KO(8%) vs. POP-WT(16%) without AngII stimulation. Baseline bone marrow analysis by flow shows 48% CD11b+Ly6ghi cells in POP-KO (n=6) vs. 39% in POP-WT (n=4). Moreover, F4/80hiLy6cintermediate cells were 1.19% in the POP-KO (n=6) vs. 1.75% in POP-WT(n=4).

Conclusion: Inflammation is an emerging player in hypertension and prolylendopeptidase inhibition may play a role in reducing that inflammation. In the POP-KO mouse model, baseline differences in quantity and quality of inflammatory cells may contribute to the phenotypic differences found in vivo .