Immunoproteasomal Processing of IsoLG-Adducted Proteins Is Essential for Hypertension

BACKGROUND

Hypertension is characterized by CD8+ T cell activation and infiltration into peripheral tissues. CD8+ T cell activation requires proteasomal processing of antigenic proteins. It has become clear that isoLG (isolevuglandin)-adduced peptides are antigenic in hypertension; however, IsoLGs inhibit the constitutive proteasome. We hypothesized that immunoproteasomal processing of isoLG-adducts is essential for CD8+ T cell activation and inflammation in hypertension.

METHODS

IsoLG adduct processing was studied in murine dendritic cells (DCs), endothelial cells (ECs), and B8 fibroblasts. The role of the proteasome and the immunoproteasome in Ang II (angiotensin II)-induced hypertension was studied in C57BL/6 mice treated with bortezomib or the immunoproteasome inhibitor PR957 and by studying mice lacking 3 critical immunoproteasome subunits (triple knockout mouse). We also examined hypertension in mice lacking the critical immunoproteasome subunit LMP7 specifically in either DCs or ECs.

RESULTS

We found that oxidant stress increases the presence of isoLG adducts within MHC-I (class I major histocompatibility complex), and immunoproteasome overexpression augments this. Pharmacological or genetic inhibition of the immunoproteasome attenuated hypertension and tissue inflammation. Conditional deletion of LMP7 in either DCs or ECs attenuated hypertension and vascular inflammation. Finally, we defined the role of the innate immune receptors stimulator of interferon genes and TLR7/8 (toll-like receptor 7/8) as drivers of LMP7 expression in ECs.

CONCLUSIONS

These studies define a previously unknown role of the immunoproteasome in DCs and ECs in CD8+ T cell activation. The immunoproteasome in DCs and ECs is critical for isoLG-adduct presentation to CD8+ T cells, and in the endothelium, this guides homing and infiltration of T cells to specific tissues.

The presence of xanthine dehydrogenase is crucial for the maturation of the rat kidneys

The development of the kidney involves essential cellular processes, such as cell proliferation and differentiation, which are led by interactions between multiple signaling pathways. Xanthine dehydrogenase (XDH) catalyzes the reaction producing uric acid in the purine catabolism, which plays a multifaceted role in cellular metabolism. Our previous study revealed that the genetic ablation of the Xdh gene in rats leads to smaller kidneys, kidney damage, decline of renal functions, and failure to thrive. Rats, unlike humans, continue their kidney development postnatally. Therefore, we explored whether XDH plays a critical role in kidney development using SS-/- rats during postnatal development phase. XDH expression was significantly increased from postnatal day 5 to 15 in wild-type but not homozygote rat kidneys. The transcriptomic profile of renal tissue revealed several dysregulated pathways due to the lack of Xdh expression with the remodeling in inflammasome, purinergic signaling, and redox homeostasis. Further analysis suggested that lack of Xdh affects kidney development, likely via dysregulation of epidermal growth factor and its downstream STAT3 signaling. The present study showed that Xdh is essential for kidney maturation. Our data, alongside the previous research, suggests that loss of Xdh function leads to developmental issues, rendering them vulnerable to kidney diseases in adulthood.

LNK/SH2B3 loss of function increases susceptibility to murine and human atrial fibrillation

AIMS

The lymphocyte adaptor protein (LNK) is a negative regulator of cytokine and growth factor signaling. The rs3184504 variant in SH2B3 reduces LNK function and is linked to cardiovascular, inflammatory, and hematologic disorders including stroke. In mice, deletion of Lnk causes inflammation and oxidative stress. We hypothesized that Lnk-/- mice are susceptible to atrial fibrillation (AF) and that rs3184504 is associated with AF and AF-related stroke in humans. During inflammation, reactive lipid dicarbonyls are a major component of oxidative injury, and we further hypothesized that these mediators are critical drivers of the AF substrate in Lnk-/- mice.

METHODS AND RESULTS

Lnk-/- or wild-type (WT) mice were treated with vehicle or 2-hydroxybenzylamine (2-HOBA), a dicarbonyl scavenger, for 3 months. Compared to WT, Lnk-/- mice displayed increased AF duration that was prevented by 2-HOBA. In the Lnk-/- atria, action potentials were prolonged with reduced transient outward K+ current, increased late Na+ current, and reduced peak Na+ current, proarrhythmic effects that were inhibited by 2-HOBA. Mitochondrial dysfunction, especially for complex I, was evident in Lnk-/- atria, while scavenging lipid dicarbonyls prevented this abnormality. Tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) were elevated in Lnk-/- plasma and atrial tissue, respectively, both of which caused electrical and bioenergetic remodeling in vitro. Inhibition of soluble TNF-α prevented electrical remodeling and AF susceptibility, while IL-1β inhibition improved mitochondrial respiration but had no effect on AF susceptibility. In a large database of genotyped patients, rs3184504 was associated with AF, as well as AF-related stroke.

CONCLUSIONS

These findings identify a novel role for LNK in the pathophysiology of AF in both experimental mice and in humans. Moreover, reactive lipid dicarbonyls are critical to the inflammatory AF substrate in Lnk-/- mice and mediate the proarrhythmic effects of pro-inflammatory cytokines, primarily through electrical remodeling.

A novel functional role for the classic CNS neurotransmitters, GABA, glycine, and glutamate, in the kidney: potent and opposing regulators of the renal vasculature

The presence of a renal GABA/glutamate system has previously been described; however, its functional significance in the kidney remains undefined. We hypothesized, given its extensive presence in the kidney, that activation of this GABA/glutamate system would elicit a vasoactive response from the renal microvessels. The functional data here demonstrate, for the first time, that activation of endogenous GABA and glutamate receptors in the kidney significantly alters microvessel diameter with important implications for influencing renal blood flow. Renal blood flow is regulated in both the renal cortical and medullary microcirculatory beds via diverse signaling pathways. GABA- and glutamate-mediated effects on renal capillaries are strikingly similar to those central to the regulation of central nervous system capillaries, that is, exposing renal tissue to physiological concentrations of GABA, glutamate, and glycine led to alterations in the way that contractile cells, pericytes, and smooth muscle cells, regulate microvessel diameter in the kidney. Since dysregulated renal blood flow is linked to chronic renal disease, alterations in the renal GABA/glutamate system, possibly through prescription drugs, could significantly impact long-term kidney function.NEW & NOTEWORTHY Functional data here offer novel insight into the vasoactive activity of the renal GABA/glutamate system. These data show that activation of endogenous GABA and glutamate receptors in the kidney significantly alters microvessel diameter. Furthermore, the results show that these antiepileptic drugs are as potentially challenging to the kidney as nonsteroidal anti-inflammatory drugs.

Endothelial mechanical stretch regulates the immunological synapse interface of renal endothelial cells in a sex-dependent manner

Increased mechanical endothelial cell stretch contributes to the development of numerous cardiovascular and renal pathologies. Recent studies have shone a light on the importance of sex-dependent inflammation in the pathogenesis of renal disease states. The endothelium plays an intimate and critical role in the orchestration of immune cell activation through upregulation of adhesion molecules and secretion of cytokines and chemokines. While endothelial cells are not recognized as professional antigen-presenting cells, in response to cytokine stimulation, endothelial cells can express both major histocompatibility complex (MHC) I and MHC II. MHCs are essential to forming a part of the immunological synapse interface during antigen presentation to adaptive immune cells. Whether MHC I and II are increased under increased mechanical stretch is unknown. Due to hypertension being multifactorial, we hypothesized that increased mechanical endothelial stretch promotes the regulation of MHCs and key costimulatory proteins on mouse renal endothelial cells (MRECs) in a stretch-dependent manner. MRECs derived from both sexes underwent 5%, 10%, or 15% uniaxial cyclical stretch, and immunological synapse interface proteins were determined by immunofluorescence microscopy, immunoblot analysis, and RNA sequencing. We found that increased endothelial mechanical stretch conditions promoted downregulation of MHC I in male MRECs but upregulation in female MRECs. Moreover, MHC II was upregulated by mechanical stretch in both male and female MRECs, whereas CD86 and CD70 were regulated in a sex-dependent manner. By bulk RNA sequencing, we found that increased mechanical endothelial cell stretch promoted differential gene expression of key antigen processing and presentation genes in female MRECs, demonstrating that females have upregulation of key antigen presentation pathways. Taken together, our data demonstrate that mechanical endothelial stretch regulates endothelial activation and immunological synapse interface formation in renal endothelial cells in a sex-dependent manner.NEW & NOTEWORTHY Endothelial cells contribute to the development of renal inflammation and have the unique ability to express antigen presentation proteins. Whether increased endothelial mechanical stretch regulates immunological synapse interface proteins remains unknown. We found that antigen presentation proteins and costimulatory proteins on renal endothelial cells are modulated by mechanical stretch in a sex-dependent manner. Our data provide novel insights into the sex-dependent ability of renal endothelial cells to present antigens in response to endothelial mechanical stimuli.

Immunoproteasomal Processing of Isolevuglandin Adducts in Hypertension

Isolevuglandins (isoLGs) are lipid aldehydes that form in the presence of reactive oxygen species (ROS) and drive immune activation. We found that isoLG-adducts are presented within the context of major histocompatibility complexes (MHC-I) by an immunoproteasome dependent mechanism. Pharmacologic inhibition of LMP7, the chymotrypsin subunit of the immunoproteasome, attenuates hypertension and tissue inflammation in the angiotensin II (Ang II) model of hypertension. Genetic loss of function of all immunoproteasome subunits or conditional deletion of LMP7 in dendritic cell (DCs) or endothelial cells (ECs) attenuated hypertension, reduced aortic T cell infiltration, and reduced isoLG-adduct MHC-I interaction. Furthermore, isoLG adducts structurally resemble double-stranded DNA and contribute to the activation of STING in ECs. These studies define a critical role of the immunoproteasome in the processing and presentation of isoLG-adducts. Moreover they define a role of LMP7 as a regulator of T cell activation and tissue infiltration in hypertension.

Cardiac and vascular complications in lupus: Is there a role for sex?

Systemic lupus erythematosus (SLE) is a common systemic autoimmune disorder and is characterized by autoantibody formation and subsequent immune complex deposition into target organs. SLE affects nearly nine women to every one man worldwide. Patients with SLE are at an enhanced risk for cardiovascular disease (CVD) morbidity and mortality. CVD is the leading cause of death worldwide and includes heart and blood vessel disorders, cerebrovascular disease, and rheumatic heart disease. Specific mechanisms by which cardiac and vascular pathophysiology develops in patients with SLE are still not fully known. Not only do we not understand this correlation between SLE and CVD, but there is also a critical gap in scientific knowledge on the contribution of sex. In this review, we will discuss the cardiac and vascular pathological disease states that are present in some patients with SLE. More importantly, we will discuss the potential mechanisms for the role of sex and sex hormones in the development of CVD with SLE.

Novel Concepts in Nephron Sodium Transport: A Physiological and Clinical Perspective

The kidneys play a critical role in maintaining total body sodium (Na⁺) balance across a wide range of dietary intake, accomplished by a concerted effort involving multiple Na⁺ transporters along the nephron. Furthermore, nephron Na⁺ reabsorption and urinary Na⁺ excretion are closely linked to renal blood flow and glomerular filtration such that perturbations in either of them can modify Na⁺ transport along the nephron, ultimately resulting in hypertension and other Na⁺-retentive states. In this article, we provide a brief physiological overview of nephron Na⁺ transport and illustrate clinical syndromes and therapeutic agents that affect Na⁺ transporter function. We highlight recent advances in kidney Na⁺ transport, particularly the role of immune cells, lymphatics, and interstitial Na⁺ in regulating Na⁺ reabsorption, the emergence of potassium (K⁺) as a regulator of Na⁺ transport, and the evolution of the nephron to modulate Na⁺ transport.

Role of Axl in target organ inflammation and damage due to hypertensive aortic remodeling

We have shown that excessive endothelial cell stretch causes release of growth arrest-specific 6 (GAS6), which activates the tyrosine kinase receptor Axl on monocytes and promotes immune activation and inflammation. We hypothesized that GAS6/Axl blockade would reduce renal and vascular inflammation and lessen renal dysfunction in the setting of chronic aortic remodeling. We characterized a model of aortic remodeling in mice following a 2-wk infusion of angiotensin II (ANG II). These mice had chronically increased pulse wave velocity, and their aortas demonstrated increased mural collagen. Mechanical testing revealed a marked loss of Windkessel function that persisted for 6 mo following ANG II infusion. Renal function studies showed a reduced ability to excrete a volume load, a progressive increase in albuminuria, and tubular damage as estimated by periodic acid Schiff staining. Treatment with the Axl inhibitor R428 beginning 2 mo after ANG II infusion had a minimal effect on aortic remodeling 2 mo later but reduced the infiltration of T cells, γ/δ T cells, and macrophages into the aorta and kidney and improved renal excretory capacity, reduced albuminuria, and reduced evidence of renal tubular damage. In humans, circulating Axl+/Siglec6+ dendritic cells and phospho-Axl+ cells correlated with pulse wave velocity and aortic compliance measured by transesophageal echo, confirming chronic activation of the GAS6/Axl pathway. We conclude that brief episodes of hypertension induce chronic aortic remodeling, which is associated with persistent low-grade inflammation of the aorta and kidneys and evidence of renal dysfunction. These events are mediated at least in part by GAS6/Axl signaling and are improved with Axl blockade.NEW & NOTEWORTHY In this study, a brief, 2-wk period of hypertension in mice led to progressive aortic remodeling, an increase in pulse wave velocity, and evidence of renal injury, dysfunction, and albuminuria. This end-organ damage was associated with persistent renal and aortic infiltration of CD8+ and γ/δ T cells. We show that this inflammatory response is likely due to GAS6/Axl signaling and can be ameliorated by blocking this pathway. We propose that the altered microvascular mechanical forces caused by increased pulse wave velocity enhance GAS6 release from the endothelium, which in turn activates Axl on myeloid cells, promoting the end-organ damage associated with aortic stiffening.

Abstract P236: Role Of Axl In Target Organ Inflammation And Damage Due To Hypertensive Aortic Remodeling

Background: Aortic remodeling enhances arterial pulsatility in the microcirculation and we have shown that excessive endothelial stretch increases release of Growth Arrest Specific 6 (GAS6), which activates Axl on monocytes causing immune activation and inflammation.

Hypothesis: GAS6/Axl blockade reduces renal and vascular inflammation and lessens renal dysfunction caused by aortic remodeling.

Methods and Results: Three month old male C57Bl/6 mice received osmotic minipumps containing vehicle or ang II for 2 weeks and the pumps removed. Aortas demonstrated increased collagen and an 80% loss of Windkessel function that persisted for 6 months following ang II. Renal function studies showed reduced ability to excrete a volume load, a progressive increase in albuminuria and tubular damage as estimated by Periodic Acid Schiff staining. Treatment with the Axl inhibitor R428 beginning 2 months after ang II had minimal effect on aortic remodeling 2 months later, but reduced aortic and renal infiltration of T cells, gamma/delta T cells and macrophages as measured by flow cytometry (Figure). R428 also improved renal excretory capacity, decreased urinary NGAL, reduced albuminuria, and attenuated renal tubular damage. Interestingly, macrophage/T cell complexes were present in aortas of mice previously exposed to hypertension, and were reduced by R428.

Conclusion: Brief episodes of hypertension induce chronic aortic remodeling which increases Axl signaling and transformation of monocytes to inflammatory antigen presenting cells that activate T cells. Axl blockade might serve as a therapeutic option to improve end-organ damage after an episode of hypertension.

Abstract 015: Hypertensive Stretch On The Regulation Of The Immunological Synapse And Secretomes Of Male And Female Renal Endothelial Cells

Immune cells and inflammation contribute to the development of hypertension and renal injury. While endothelial cells are recognized as professional antigen presenting cells, they can express both Major Histocompatibility Complex (MHC) I and II and possess antigen-presenting functions. Endothelial cell activation and inflammation are critical in the development of hypertension. However, the mechanisms by which inflammatory hypertensive stimuli regulate renal endothelial immunological synapse proteins remains unknown. We hypothesize that inflammatory hypertensive mechanical stretch promotes the regulation of MHC I and II and costimulatory molecules on mouse renal endothelial cells (MRECs) in a sex-dependent manner. MRECs derived from both sexes underwent normotensive (5%; 1 Hz), hypertensive (10%, 1 Hz), and supra-hypertensive (15% 1 Hz) uniaxial cyclical stretch for 48 hours. We then assessed CD80, CD86, MHC II, MHC I, CD70, and CD40 by immunoblot analysis. A proteome multiplex assay was used to analyze male and female MREC secretomes during 5%, 10%, and 15% stretch. Hypertensive 10% stretch significantly increased only CD40 expression in males, while it upregulated CD80 and CD70 expression in females (p<0.05). Under 15% stretch, males significantly upregulated MHC I, CD70, and CD40 compared to I-Ab, CD80, CD86, and CD70 in females MRECs (p<0.05). We investigated sex differences and found that females significantly increased CD70 in both 10% and 15% stretch compared to males MRECs (p<0.05). We compared sex differences from our secretome proteomics in male and female MRECs at 10% and 15% stretch. We found that pathways associated with wound healing, Th17 activation, IL-6, and NF-κB signaling were upregulated in male MRECs undergoing 10% stretch. Interestingly, Th17 activation, natural killer cell signaling, and IL-23 signaling were downregulated in female MRECs undergoing 10% stretch. Under 15% stretch, IL-13 signaling, HMBG1 signaling, B cell signaling, and IL-13 signaling were downregulated in MRECs from both sexes. Our data provides novel insights into how inflammatory hypertensive stretch regulates immunological synapse proteins and secretomes in renal endothelial cells by stretch and sex-dependent manner.

Isolevuglandins disrupt PU.1-mediated C1q expression and promote autoimmunity and hypertension in systemic lupus erythematosus

We describe a mechanism responsible for systemic lupus erythematosus (SLE). In humans with SLE and in 2 SLE murine models, there was marked enrichment of isolevuglandin-adducted proteins (isoLG adducts) in monocytes and dendritic cells. We found that antibodies formed against isoLG adducts in both SLE-prone mice and humans with SLE. In addition, isoLG ligation of the transcription factor PU.1 at a critical DNA binding site markedly reduced transcription of all C1q subunits. Treatment of SLE-prone mice with the specific isoLG scavenger 2-hydroxybenzylamine (2-HOBA) ameliorated parameters of autoimmunity, including plasma cell expansion, circulating IgG levels, and anti-dsDNA antibody titers. 2-HOBA also lowered blood pressure, attenuated renal injury, and reduced inflammatory gene expression uniquely in C1q-expressing dendritic cells. Thus, isoLG adducts play an essential role in the genesis and maintenance of systemic autoimmunity and hypertension in SLE.

Endothelial cells: potential novel regulators of renal inflammation

Substantial evidence has supported the role of endothelial cell (EC) activation and dysfunction in the development of hypertension, chronic kidney disease (CKD), and lupus nephritis (LN). In both humans and experimental models of hypertension, CKD, and LN, ECs become activated and release potent mediators of inflammation including cytokines, chemokines, and reactive oxygen species that cause EC dysfunction, tissue damage, and fibrosis. Factors that activate the endothelium include inflammatory cytokines, mechanical stretch, and pathological shear stress. These signals can activate the endothelium to promote upregulation of adhesion molecules, such as intercellular adhesion molecule-1 and vascular cell adhesion molecule-1, which promote leukocyte adhesion and migration to the activated endothelium. More importantly, it is now recognized that some of these signals may in turn promote endothelial antigen presentation through major histocompatibility complex II. In this review, we will consider in-depth mechanisms of endothelial activation and the novel mechanism of endothelial antigen presentation. Moreover, we will discuss these proinflammatory events in renal pathologies and consider possible new therapeutic approaches to limit the untoward effects of endothelial inflammation in hypertension, CKD, and LN.

Growth Arrest Specific-6 and Axl Coordinate Inflammation and Hypertension

[Figure: see text].

Abstract 04: Growth Arrest Specific 6 And Axl Signaling Coordinate Endothelial Cell And Immune Cell Activation To Promote Inflammation And Hypertension

Endothelial cells (ECs) activated by hypertensive (10%) cyclical stretch releases factors including IL-6 and hydrogen peroxide that stimulate the conversion of human monocytes to an intermediate inflammatory phenotype. A novel subset of DCs in humans has been identified that express Axl and Sigelc-6 + (AS DCs) which drive T cells proliferation and produce inflammatory cytokines. The interplay between ECs and AS DCs in hypertension is unkown. We assessed AS DCs by flow cytometry in normotensive (n=23) and hypertensive (n=11) subjects and found a significant increase in AS DCs in hypertensive compared to normotensive subjects (297 ± 73 vs. 108 ± 26/ml; p =0.0304). When moncoytes were exposed to human aortic endothelial cells (HAECs) undergoing 10% stretch, the formation of AS DCs was markedly enhanced compared to 5%. The ligand for Axl is growth arrest specific 6 (GAS6), and we found that 10% HAEC stretch caused a 50% increase in the release of GAS6 by ECs comapred to 5%. We knocked down either EC GAS6 or Axl using siRNA and either of these abrogated the ability of ECs to promote AS DC formation. Using flow cytometry to analyze venous ECs that had been harvested from 23 volunteers to quantify EC activation and GAS6 secretion in vivo, we found a positive association between GAS6 and ICAM-1 (R 2 =0.39, p =0.0012). We found a positive association between pulse pressure and plasma GAS6 (R 2 =0.25, p =0.0079) ands systolic blood pressure and GAS6 (R 2 =0.19, p=0.0025) in volunteers. We found that plasma GAS6 is increased in Ang II hypertension and that either genetic deletion or pharmacological inhibition of Axl lowered blood pressure in reposne to Ang II and reduced renal inflammation. To investigate the role of immunological vs. stromal Axl in vivo, we perfomed bone marrow transplant studies and found that both Axl WT/WT ->Axl -/- and Axl -/- ->Axl W/WT had a significant reduction in blood pressure by 20 mmHg compared to the Axl WT/WT -> Axl WT/WT control. These data show that both immunological and stromal Axl contribute to hypertension and inflammation and GAS6/Axl signlaing may be a novel therapeutic target in this disease.

Hypertension: Do Inflammation and Immunity Hold the Key to Solving this Epidemic?

Elevated cardiovascular risk including stroke, heart failure, and heart attack is present even after normalization of blood pressure in patients with hypertension. Underlying immune cell activation is a likely culprit. Although immune cells are important for protection against invading pathogens, their chronic overactivation may lead to tissue damage and high blood pressure. Triggers that may initiate immune activation include viral infections, autoimmunity, and lifestyle factors such as excess dietary salt. These conditions activate the immune system either directly or through their impact on the gut microbiome, which ultimately produces chronic inflammation and hypertension. T cells are central to the immune responses contributing to hypertension. They are activated in part by binding specific antigens that are presented in major histocompatibility complex molecules on professional antigen-presenting cells, and they generate repertoires of rearranged T-cell receptors. Activated T cells infiltrate tissues and produce cytokines including interleukin 17A, which promote renal and vascular dysfunction and end-organ damage leading to hypertension. In this comprehensive review, we highlight environmental, genetic, and microbial associated mechanisms contributing to both innate and adaptive immune cell activation leading to hypertension. Targeting the underlying chronic immune cell activation in hypertension has the potential to mitigate the excess cardiovascular risk associated with this common and deadly disease.

The role of inflammation in hypertension: novel concepts

Hypertension remains the most important modifiable risk factor for the development of cardiovascular disease. While it is clear that inflammation plays a pivotal role in the development and maintenance of hypertension, several novel discoveries have been made within the past decade that have advanced the field and have provided new mechanistic insights. First, recent studies have identified a central role of sodium-induced immune cell activation in the pathogenesis of hypertension by altering the gut microbiome and formation of products of lipid oxidation known as isolevuglandins. Second, cytokine elaboration by the inflammasome leading to end-organ dysfunction and immune activation has been found to play a role in the genesis of hypertension. Third, novel techniques have identified previously uncharacterized immune cell populations that may play a functional role in these processes. Finally, the role of inflammation in hypertension may be an important mediator of severe COVID-19 infections. In this review, we discuss these recent advances in the study of inflammation and hypertension and highlight topics for future studies.

Abstract MP41: A Role Of Isolevuglandins In Systemic Lupus Erythematosus Associated Autoimmunity And Hypertension

Essential hypertension and systemic lupus erythematosus (SLE) are devastating conditions that disproportionately affect women. SLE has heterogeneous manifestations and treatment is limited to the use of non-specific global immunosuppression. Importantly, there is an increased prevalence of hypertension in women with SLE compared to healthy controls. Isolevuglandins (IsoLGs) are oxidation products of fatty acids that form as a result of reactive oxygen species. These molecules adduct covalently to lysine residues of proteins. Adducted proteins are then presented as autoantigens to T-cells resulting in immune cell activation. Previous studies have shown an essential role of IsoLGs in immune cell activation and the development of hypertension in animal models. We hypothesize that isoLGs are important for the development of hypertension and systemic immune activation in SLE. We first examined isoLG adduct accumulation within monocytes of human subjects with SLE compared to healthy controls. By flow cytometry, we found marked accumulation of isoLG adducts within CD14 + monocytes (34.2% ± 12.4% vs 3.81% ± 2.1% of CD14 + , N = 10-11, P <0.05). We confirmed this increase in isoLG adducts by mass spectrometry. To determine a causative role of isoLG adducts in immune activation and hypertension in SLE, we employed the B6.SLE123 and NZBWF1 mouse models of SLE. Animals were treated with the isoLG scavenger 2-hydroxybenzylamine (2-HOBA) or vehicle beginning at 7 weeks and were sacrificed at 32 weeks of age. C57BL/6 and NZW were used as controls. Importantly, treatment with 2-HOBA attenuated blood pressure in both mouse models (systolic BP 136.2 ± 5.6 mmHg for B6.SLE123 vs 120.9 ± 4.46 mmHg for B6.SLE123 +2HOBA; 164.7 ± 24.4 mmHg for NZBWF1 vs 136.9 ± 14.9 mmHg for NZBWF1 +2HOBA, N = 6-8, P < 0.05). Moreover, treatment with 2-HOBA reduced albuminuria and renal injury in the B6.SLE123 model (albumin/creatinine ratio 33.8 ± 2.0 x 10 -2 μg/mg for B6.SLE123 vs 5.5 ± 0.9 x 10 -2 μg/mg for B6.SLE123 +2HOBA, N = 7-9, P < 0.05). Finally, immune cell accumulation in primary and secondary lymphoid organs is significantly attenuated by 2-HOBA. These studies suggest a critical role of isoLG adduct accumulation in both systemic immune activation and hypertension in SLE.

Abstract MP27: Human Hypertension And Endothelial Cell Activation Promote The Formation And Activation Of Axl + Siglec-6 + Dendritic Cells Via Endothelial Release Of Growth Arrest Specific 6

We have shown that dendritic cells (DCs) from hypertensive mice convey hypertension when adoptively transferred to recipients. Recently a novel subset of DCs in humans that express Axl and Sigelc-6 + (AS DCs) have been identified which drive T cell proliferation and produce IL-1β, IL-6 and IL-23, consistent with DCs we have observed in hypertension. We hypothesized that AS cells are increased in hypertension and contribute to immune activation in this disease. We quantified circulating AS DCs by flow cytometry in normotensive (n=23) and hypertensive (n=11) subjects and found a more than 2-fold increase in circulating AS DCs in hypertensive compared to normotensive subjects (297 ± 73 vs. 108 ± 26/ml; p =0.0304). To investigate the mechanism by which AS DCs are formed in hypertension, we co-cultured human aortic endothelial cells (HAECs) undergoing either normotensive (5%) or hypertensive (10%) cyclical stretch for 48 hours with CD14 + monocytes from normotensive donors. Co-culture of monocytes with HAECs exposed to 10% stretch significantly increased AS DCs and AS DC IL-1β production when compared to 5% stretch alone as assessed by flow cytometry (21 ± 5 vs. 131 ± 32 IL-1β + AS DCs). Moreover, inhibition of Axl signaling with R248, completely abolished the production of IL-1β in AS DCs (34 ± 8 IL-1β + AS DCs). In additional experiments we found that 10% stretch caused a 50% increase in release of growth arrest 6 (GAS6), the ligand for Axl, from HAECs compared to 5% stretch. Treatment of human monocytes with GAS6 mimicked the effect of 10% stretch in promoting AS cell formation and IL-1β production. Based on the increased secretion of GAS6 from HAECs, we used a J-wire to harvest human endothelial cells from 23 additional volunteers to assess endothelial cell activation and GAS6 secretion in vivo. We found a positive association between pulse pressure and plasma GAS6 (R 2 =0.25, p =0.0079) and a striking positive association between GAS6 and ICAM-1 (R 2 =0.39, p =0.0012). These data show that secretion of GAS6 by an activated endothelial seems to promote the formation and activation of AS DCs. Thus, the interplay between endothelial-derived GAS6 and AS DCs seem to be an important mechanism in human hypertension and might be a novel therapeutic target for this disease.

ENaC in Salt-Sensitive Hypertension: Kidney and Beyond

PURPOSE OF REVIEW

The main goal of this article is to discuss the role of the epithelial sodium channel (ENaC) in extracellular fluid and blood pressure regulation.

RECENT FINDINGS

Besides its role in sodium handling in the kidney, recent studies have found that ENaC expressed in other cells including immune cells can influence blood pressure via extra-renal mechanisms. Dendritic cells (DCs) are activated and contribute to salt-sensitive hypertension in an ENaC-dependent manner. We discuss recent studies on how ENaC is regulated in both the kidney and other sites including the vascular smooth muscles, endothelial cells, and immune cells. We also discuss how this extra-renal ENaC can play a role in salt-sensitive hypertension and its promise as a novel therapeutic target. The role of ENaC in blood pressure regulation in the kidney has been well studied. Recent human gene sequencing efforts have identified thousands of variants among the genes encoding ENaC, and research efforts to determine if these variants and their expression in extra-renal tissue play a role in hypertension will advance our understanding of the pathogenesis of ENaC-mediated cardiovascular disease and lead to novel therapeutic targets.

Antagonism of major histocompatibility complex class II invariant chain peptide during chronic lipopolysaccharide treatment rescues autoregulatory behavior

Toll-like receptor 4 (TLR4) activation contributes to vascular dysfunction in pathological conditions such as hypertension and diabetes, but the role of chronic TLR4 activation on renal autoregulatory behavior is unknown. We hypothesized that subclinical TLR4 stimulation with low-dose lipopolysaccharide (LPS) infusion increases TLR4 activation and blunts renal autoregulatory behavior. We assessed afferent arteriolar autoregulatory behavior in male Sprague-Dawley rats after prolonged LPS (0.1 mg·kg^-1·day^-1 sq) infusion via osmotic minipump for 8 or 14 days. Some rats also received daily cotreatment with either anti-TLR4 antibody (1 μg ip), competitive antagonist peptide (CAP; 3 mg/kg ip) or tempol (2 mmol/l, drinking water) throughout the 8-day LPS treatment period. Autoregulatory behavior was assessed using the in vitro blood-perfused juxtamedullary nephron preparation. Selected physiological measures, systolic blood pressure and baseline diameters were normal and similar across groups. Pressure-dependent vasoconstriction averaged 72 ± 2% of baseline in sham rats, indicating intact autoregulatory behavior. Eight-day LPS-treated rats exhibited significantly impaired pressure-mediated vasoconstriction (96 ± 1% of baseline), whereas it was preserved in rats that received anti-TLR4 antibody (75 ± 3%), CAP (84 ± 2%), or tempol (82 ± 2%). Using a 14-day LPS (0.1 mg·kg^-1·day^-1 sq) intervention protocol, CAP treatment started on day 7, where autoregulatory behavior is already impaired. Systolic blood pressures were normal across all treatment groups. Fourteen-day LPS treatment retained the autoregulatory impairment (95 ± 2% of baseline). CAP intervention starting on day 7 rescued pressure-mediated vasoconstriction with diameters decreasing to 85 ± 1% of baseline. These data demonstrate that chronic subclinical TLR4 activation impairs afferent arteriolar autoregulatory behavior through mechanisms involving reactive oxygen species and major histocompatibility complex class II activation.

High Salt Activates CD11c+ Antigen-Presenting Cells via SGK (Serum Glucocorticoid Kinase) 1 to Promote Renal Inflammation and Salt-Sensitive Hypertension

Salt-sensing mechanisms in hypertension involving the kidney, vasculature, and central nervous system have been well studied; however, recent studies suggest that immune cells can sense sodium (Na+). Antigen-presenting cells (APCs) including dendritic cells critically modulate inflammation by activating T cells and producing cytokines. We recently found that Na+ enters dendritic cells through amiloride-sensitive channels including the α and γ subunits of the epithelial sodium channel (ENaC) and mediates nicotinamide adenine dinucleotide phosphate oxidase-dependent formation of immunogenic IsoLG (isolevuglandin)-protein adducts leading to inflammation and hypertension. Here, we describe a novel pathway in which the salt-sensing kinase SGK1 (serum/glucocorticoid kinase 1) in APCs mediates salt-induced expression and assembly of ENaC-α and ENaC-γ and promotes salt-sensitive hypertension by activation of the nicotinamide adenine dinucleotide phosphate oxidase and formation of IsoLG-protein adducts. Mice lacking SGK1 in CD11c+ cells were protected from renal inflammation, endothelial dysfunction, and developed blunted hypertension during the high salt feeding phase of the N-Nitro-L-arginine methyl ester hydrochloride/high salt model of salt-sensitive hypertension. CD11c+ APCs treated with high salt exhibited increased expression of ENaC-γ which coimmunoprecipitated with ENaC-α. This was associated with increased activation and expression of various nicotinamide adenine dinucleotide phosphate oxidase subunits. Genetic deletion or pharmacological inhibition of SGK1 in CD11c+ cells prevented the high salt-induced expression of ENaC and nicotinamide adenine dinucleotide phosphate oxidase. These studies indicate that expression of SGK1 in CD11c+ APCs contributes to the pathogenesis of salt-sensitive hypertension.

High dietary salt-induced dendritic cell activation underlies microbial dysbiosis-associated hypertension

Excess dietary salt contributes to inflammation and hypertension via poorly understood mechanisms. Antigen presenting cells including dendritic cells (DCs) play a key role in regulating intestinal immune homeostasis in part by surveying the gut epithelial surface for pathogens. Previously, we found that highly reactive γ-ketoaldehydes or isolevuglandins (IsoLGs) accumulate in DCs and act as neoantigens, promoting an autoimmune-like state and hypertension. We hypothesized that excess dietary salt alters the gut microbiome leading to hypertension and this is associated with increased immunogenic IsoLG-adduct formation in myeloid antigen presenting cells. To test this hypothesis, we performed fecal microbiome analysis and measured blood pressure of healthy human volunteers with salt intake above or below the American Heart Association recommendations. We also performed 16S rRNA analysis on cecal samples of mice fed normal or high salt diets. In humans and mice, high salt intake was associated with changes in the gut microbiome reflecting an increase in Firmicutes, Proteobacteria and genus Prevotella bacteria. These alterations were associated with higher blood pressure in humans and predisposed mice to vascular inflammation and hypertension in response to a sub-pressor dose of angiotensin II. Mice fed a high salt diet exhibited increased intestinal inflammation including the mesenteric arterial arcade and aorta, with a marked increase in the B7 ligand CD86 and formation of IsoLG-protein adducts in CD11c+ myeloid cells. Adoptive transfer of fecal material from conventionally housed high salt-fed mice to germ-free mice predisposed them to increased intestinal inflammation and hypertension. These findings provide novel insight into the mechanisms underlying inflammation and hypertension associated with excess dietary salt and may lead to interventions targeting the microbiome to prevent and treat this important disease.

Critical role of Interleukin 21 and T follicular helper cells in hypertension and vascular dysfunction

T and B cells have been implicated in hypertension, but the mechanisms by which they produce a coordinated response is unknown. T follicular helper (Tfh) cells that produce interleukin 21 (IL21) promote germinal center (GC) B cell responses leading to immunoglobulin (Ig) production. Here we investigate the role of IL21 and Tfh cells in hypertension. In response to angiotensin (Ang) II-induced hypertension, T cell IL21 production is increased, and Il21-/- mice develop blunted hypertension, attenuated vascular end-organ damage, and decreased interleukin 17A (IL17A) and interferon gamma production. Tfh-like cells and GC B cells accumulate in the aorta and plasma IgG1 is increased in hypertensive WT but not Il21-/-mice. Furthermore, Tfh cell deficient mice develop blunted hypertension and vascular hypertrophy in response to Ang II infusion. Importantly, IL21 neutralization reduces blood pressure (BP) and reverses endothelial dysfunction and vascular inflammation. Moreover, recombinant IL21 impairs endothelium-dependent relaxation ex vivo and decreases nitric oxide production from cultured endothelial cells. Finally, we show in humans that peripheral blood T cell production of IL21 correlates with systolic BP and IL17A production. These data suggest that IL21 may be a novel therapeutic target for the treatment of hypertension and its micro- and macrovascular complications.

Isolation and Adoptive Transfer of High Salt Treated Antigen-presenting Dendritic Cells

Excess dietary salt intake contributes to inflammation and plays a vital role in the development of hypertension. We previously found that antigen-presenting dendritic cells (DCs) can sense elevated extracellular sodium leading to the activation of the NADPH oxidase and formation of isolevuglandin (IsoLG)-protein adducts. These IsoLG-protein adducts react with self-proteins and promote an autoimmune-like state and hypertension. We have developed and optimized state-of-the-art methods to study DC function in hypertension. Here, we provide a detailed protocol for isolation, in vitro treatment with elevated sodium, and adoptive transfer of murine splenic CD11c⁺ cells into recipient mice to study their role in hypertension.

LNK deficiency promotes acute aortic dissection and rupture

Aortic dissection (AD) is a life-threatening vascular disease with limited treatment strategies. Here, we show that loss of the GWAS-identified SH2B3 gene, encoding lymphocyte adaptor protein LNK, markedly increases susceptibility to acute AD and rupture in response to angiotensin (Ang) II infusion. As early as day 3 following Ang II infusion, prior to the development of AD, Lnk-/- aortas display altered mechanical properties, increased elastin breaks, collagen thinning, enhanced neutrophil accumulation, and increased MMP-9 activity compared with WT mice. Adoptive transfer of Lnk-/- leukocytes into Rag1-/- mice induces AD and rupture in response to Ang II, demonstrating that LNK deficiency in hematopoietic cells plays a key role in this disease. Interestingly, treatment with doxycycline prevents the early accumulation of aortic neutrophils and significantly reduces the incidence of AD and rupture. PrediXcan analysis in a biobank of more than 23,000 individuals reveals that decreased expression of SH2B3 is significantly associated with increased frequency of AD-related phenotypes (odds ratio 0.81). Thus, we identified a role for LNK in the pathology of AD in experimental animals and humans and describe a new model that can be used to inform both inherited and acquired forms of this disease.

Hypertension and increased endothelial mechanical stretch promote monocyte differentiation and activation: roles of STAT3, interleukin 6 and hydrogen peroxide

Aims

Monocytes play an important role in hypertension. Circulating monocytes in humans exist as classical, intermediate, and non-classical forms. Monocyte differentiation can be influenced by the endothelium, which in turn is activated in hypertension by mechanical stretch. We sought to examine the role of increased endothelial stretch and hypertension on monocyte phenotype and function.

Methods and results

Human monocytes were cultured with confluent human aortic endothelial cells undergoing either 5% or 10% cyclical stretch. We also characterized circulating monocytes in normotensive and hypertensive humans. In addition, we quantified accumulation of activated monocytes and monocyte-derived cells in aortas and kidneys of mice with Angiotensin II-induced hypertension. Increased endothelial stretch enhanced monocyte conversion to CD14++CD16+ intermediate monocytes and monocytes bearing the CD209 marker and markedly stimulated monocyte mRNA expression of interleukin (IL)-6, IL-1β, IL-23, chemokine (C-C motif) ligand 4, and tumour necrosis factor α. STAT3 in monocytes was activated by increased endothelial stretch. Inhibition of STAT3, neutralization of IL-6 and scavenging of hydrogen peroxide prevented formation of intermediate monocytes in response to increased endothelial stretch. We also found evidence that nitric oxide (NO) inhibits formation of intermediate monocytes and STAT3 activation. In vivo studies demonstrated that humans with hypertension have increased intermediate and non-classical monocytes and that intermediate monocytes demonstrate evidence of STAT3 activation. Mice with experimental hypertension exhibit increased aortic and renal infiltration of monocytes, dendritic cells, and macrophages with activated STAT3.

Conclusions

These findings provide insight into how monocytes are activated by the vascular endothelium during hypertension. This is likely in part due to a loss of NO signalling and increased release of IL-6 and hydrogen peroxide by the dysfunctional endothelium and a parallel increase in STAT activation in adjacent monocytes. Interventions to enhance bioavailable NO, reduce IL-6 or hydrogen peroxide production or to inhibit STAT3 may have anti-inflammatory roles in hypertension and related conditions.

Abstract P214: Serum Glucocorticoid Kinase 1 and Sympathetic Nerve Activity in Salt-Sensitive Hypertension

Salt-sensitive hypertension affects nearly 50% of the population and reducing salt intake decreases blood pressure and cardiovascular events in the general population. The precise mechanism of how dietary salt contributes to blood pressure (BP) elevation, renal injury, and cardiovascular disease remains unclear. Substantial evidence supports a role of increased sympathetic output in salt-dependent hypertension and this promotes renal inflammation and dysfunction. It has been shown that salt accumulates in the interstitium of hypertensive humans and animals and drives immune cells toward a proinflammatory phenotype through the salt sensing kinase serum/glucocorticoid kinase 1 (SGK1). We have also shown an important role of monocytes and monocyte-derived dendritic cells in hypertension. In this study, we tested the hypothesis that SGK1 in myeloid CD11c + cells promote salt-sensitive hypertension by increasing sympathetic outflow. To test this hypothesis, we created mice lacking SGK1 in CD11c + cells (SGK1 CreCD11c mice) and used SGK1 fl/fl mice as controls. To induce salt-sensitivity, mice received 0.5 mg/ml of N-Nitro-L-arginine methyl ester hydrochloride (L-NAME) in the drinking water for 2 weeks. This was followed by a 2-week washout period and then a 4% high salt diet for 3 weeks. BP was monitored using telemetry. We found that BP elevation during high salt feeding was significantly attenuated in SGK1 CreCD11c mice compared to SGK1 fl/fl mice (125 ± 1 vs. 141 ± 1 mmHg; p < 0.01). SGK1 CreCD11c mice had a significant reduction in CD45 + , CD3 + , CD4 + CD8 + and CD19 + cells in the kidney compared to SGK1 fl/fl mice as assessed by flow cytometry (p < 0.05). Interestingly, on high salt, SGK1 CreCD11c mice had a significant reduction in heart rate (HR) compared to SGK1 fl/fl mice (528 ± 2 vs. 592 ± 7 bpm; p = 0.006). Microglial cells of the brain express CD11c, and we found that the reduction in HR was associated with a marked reduction in HR variability in SGK1 CreCD11c mice compared to SGK1 fl/fl mice (1.65 ± 0.38 vs. 3.00 ± 0.57; p = 0.0018), indicating a reduction in sympathetic outflow. Our data indicate that SGK1 in CD11c + myeloid cells and likely those of the central nervous system, modulate BP and sympathetic outflow promoting the pathogenesis of salt-sensitive hypertension.

Abstract 127: Axl + Siglec6 + Dendritic Cells: the Role of Salt, Stretch, and Hypertension

We have shown that monocyte-derived dendritic cells (DCs) are activated in hypertension to produce large amounts of cytokines and to activate T cells. DCs from hypertensive mice can convey hypertension when adoptively transferred to recipients. Single cell sequencing has recently identified a novel subset of DCs in humans that express Axl and Sigelc6 + (AS DCs). These cells have been reported to potently drive T cell proliferation and to produce large amounts of IL-8 and IL12. The role of AS DCs in hypertension remains unknown. We isolated total peripheral blood mononuclear cells (PBMCs) from normotensive (n=23) and hypertensive (n=12) patients and assessed DC populations, including AS DCs, using flow cytometry. We found a significant increase in the AS DCs in hypertensive compared to normotensive patients (297 ± 73 vs. 108 ± 26/ml; P=0.0304). In contrast, there were no differences in CD1c + DCs (3398 ± 776 vs. 5245 ± 122/ml) or CD141 + DCs (164 ± 20 vs. 218 ± 49/ml) between normotensive and hypertensive subjects. To investigate the mechanism by which AS DCs are formed in hypertension, we used two in vitro hypertensive stimuli: exposure to salt and hypertensive stretch of adjacent human endothelial cells. Human PBMCs were cultured in either normal NaCl (NS, 150 mM) or high NaCl (HS, 190 mM) for 48 hours. Flow cytometry indicated a striking increase in AS DCs by exposure to HS compared to NS (516 ± 181 vs 201 ± 57/ml) and this was prevented by co-treatment of cells with the salt-sensing Serum Glucocorticoid Kinase 1 inhibitor GSK650394. As a second approach, we co-cultured human aortic endothelial cells (HAECs) with PBMCs from normotensive donors and exposed the HAEC monolayer to either normal (5%) or hypertensive cyclical stretch (10%) for 24 hours. Co-culture of PBMCs with HAECs exposed to 10% stretch doubled AS DCs as compared to PBMCs cultured with HAECs undergoing 5% stretch (1.4 ± 0.5 vs 0.7 ± 0.3%; P=0.0217). These data show that AS DC population are increased in hypertensive patients and that known hypertensive stimuli in vitro promote formation of AS DCs. Thus, AS DCs seem to be an important immune cell subset in human hypertension and might be a novel therapeutic target for this disease.

Pentosan polysulfate preserves renal microvascular P2X1 receptor reactivity and autoregulatory behavior in DOCA-salt hypertensive rats

Inflammation contributes to ANG II-associated impairment of renal autoregulation and microvascular P2X1 receptor signaling, but its role in renal autoregulation in mineralocorticoid-induced hypertension is unknown. Autoregulatory behavior was assessed using the blood-perfused juxtamedullary nephron preparation. Hypertension was induced in uninephrectomized control rats (UNx) by subcutaneous implantation of a DOCA pellet plus administration of 1% NaCl in the drinking water (DOCA-salt) for 3 wk. DOCA-salt rats developed hypertension that was unaltered by anti-inflammatory treatment with pentosan polysulfate (DOCA-salt+PPS) but was suppressed with "triple therapy" (hydrochlorothiazide, hydralazine, and reserpine; DOCA-salt+TTx). Baseline arteriolar diameters were similar across all groups. UNx rats exhibited pressure-dependent vasoconstriction with diameters declining to 69 ± 2% of control at 170 mmHg, indicating intact autoregulation. DOCA-salt treatment significantly blunted this pressure-mediated vasoconstriction. Diameters remained between 91 ± 4 and 98 ± 3% of control over 65-170 mmHg, indicating impaired autoregulation. In contrast, pressure-mediated vasoconstriction was preserved in DOCA-salt+PPS and DOCA-salt+TTx rats, reaching 77 ± 7 and 75 ± 3% of control at 170 mmHg, respectively. ATP is required for autoregulation via P2X1 receptor activation. ATP- and β,γ-methylene ATP (P2X1 receptor agonist)-mediated vasoconstriction were markedly attenuated in DOCA-salt rats compared with UNx (P < 0.05), but significantly improved by PPS or TTx (P < 0.05 vs. DOCA-salt) treatment. Arteriolar responses to adenosine and UTP (P2Y2 receptor agonist) were unaffected by DOCA-salt treatment. PPS and TTx significantly reduced MCP-1 and protein excretion in DOCA-salt rats. These results support the hypothesis that hypertension triggers inflammatory cascades but anti-inflammatory treatment preserves renal autoregulation in DOCA-salt rats, most likely by normalizing renal microvascular reactivity to P2X1 receptor activation.

Abstract 286: Acute Toll-like Receptors 4 Activiation by Lipopolysaccharide Attenuates Afferent Arteriolar Autoregulatory Behavior

Pathogen associated molecular patterns (PAMPs) and damage associated molecular patterns (DAMPs) activate toll like receptors (TLRs) that stimulate the innate immune system. Immune system activation is linked to blunted renal autoregulatory behavior. Lipopolysaccharide (LPS), a component of the bacterial wall of gram-negative bacteria, is a ligand for TLR4. Preliminary experiments indicates that TLR4 protein expression is increased approximately by 28% (n=2) in small intrarenal arteries after 4 hours of acute LPS treatment versus control. Accordingly, we hypothesize that acute LPS treatment blunts afferent arteriolar autoregulatory behavior through TLR4 activation. Rats received a bolus injection of LPS (1mg/kg I.P.) and kidneys were harvested 4 hours later for juxtamedullary nephron studies. At a perfusion pressure of 100 mmHg, baseline arteriolar diameters in LPS treated kidneys averaged 11.9 ± 0.5μm (n=15) compared to 14.5 ± 0.7μm (n=14) in untreated controls (P < 0.05). Autoregulatory behavior was assessed in these same groups by increasing perfusion pressure in 15 mmHg increments from 65 to 170 mmHg. In control kidneys, afferent arteriolar diameter decreased by 29 ± 5 % (n=6) as perfusion pressure increased from 65 to 170 mmHg. In LPS treated kidneys, afferent arteriolar diameter actually increased by 3 ± 8% (P < 0.05; n=7) over the same pressure range, indicating marked blunting of pressure-induced vasoconstriction. P2 receptors have been implicated in autoregulatory resistance adjustments. Therefore, we assessed afferent arteriolar responsiveness to P2 receptor activation in vitro. In control kidneys, log concentrations of ATP (10 -8 - 10 -4 mol/L) reduced arteriolar diameter by 4 ± 1, 10 ± 2, 17 ± 4, 26 ± 5, and 32 ± 5% respectively (P < 0.05; n=8). In LPS treated kidneys, ATP reduced arteriolar diameter similarly by 6 ± 1, 11 ± 2, 15 ± 3, 18 ± 4, and 21 ± 5% respectively (P < 0.05; n=8). No significant difference in afferent arteriolar reactivity to ATP was found between the two groups. These data support the hypothesis that TLR4 activation by acute LPS treatment attenuates afferent arteriolar autoregulatory behavior. Accordingly, these data may open novel therapeutic approaches for prevention of inflammatory kidney disease.