Angiotensin II Directly Increases Endothelial Calcium and Nitric Oxide in Kidney and Brain Microvessels In Vivo With Reduced Efficacy in Hypertension

BACKGROUND

The vasoconstrictor effects of angiotensin II via type 1 angiotensin II receptors in vascular smooth muscle cells are well established, but the direct effects of angiotensin II on vascular endothelial cells (VECs) in vivo and the mechanisms how VECs may mitigate angiotensin II-mediated vasoconstriction are not fully understood. The present study aimed to explore the molecular mechanisms and pathophysiological relevance of the direct actions of angiotensin II on VECs in kidney and brain microvessels in vivo.

METHODS AND RESULTS

Changes in VEC intracellular calcium ([Ca2+]i) and nitric oxide (NO) production were visualized by intravital multiphoton microscopy of cadherin 5-Salsa6f mice or the endothelial uptake of NO-sensitive dye 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate, respectively. Kidney fibrosis by unilateral ureteral obstruction and Ready-to-use adeno-associated virus expressing Mouse Renin 1 gene (Ren1-AAV) hypertension were used as disease models. Acute systemic angiotensin II injections triggered >4-fold increases in VEC [Ca2+]i in brain and kidney resistance arterioles and capillaries that were blocked by pretreatment with the type 1 angiotensin II receptor inhibitor losartan, but not by the type 2 angiotensin II receptor inhibitor PD123319. VEC responded to acute angiotensin II by increased NO production as indicated by >1.5-fold increase in 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate fluorescence intensity. In mice with kidney fibrosis or hypertension, the angiotensin II-induced VEC [Ca2+]i and NO responses were significantly reduced, which was associated with more robust vasoconstrictions, VEC shedding, and microthrombi formation.

CONCLUSIONS

The present study directly visualized angiotensin II-induced increases in VEC [Ca2+]i and NO production that serve to counterbalance agonist-induced vasoconstriction and maintain residual organ blood flow. These direct and endothelium-specific angiotensin II effects were blunted in disease conditions and linked to endothelial dysfunction and the development of vascular pathologies.

Neuronally differentiated macula densa cells regulate tissue remodeling and regeneration in the kidney

Tissue regeneration is limited in several organs including the kidney, contributing to the high prevalence of kidney disease globally. However, evolutionary and physiological adaptive responses and the presence of renal progenitor cells suggest existing remodeling capacity. This study uncovered endogenous tissue remodeling mechanisms in the kidney that were activated by the loss of body fluid and salt and regulated by a unique niche of a minority renal cell type called the macula densa (MD). Here we identified neuronal differentiation features of MD cells that sense the local and systemic environment, secrete angiogenic, growth and extracellular matrix remodeling factors, cytokines and chemokines, and control resident progenitor cells. Serial intravital imaging, MD nerve growth factor receptor and Wnt mouse models and transcriptome analysis revealed cellular and molecular mechanisms of these MD functions. Human and therapeutic translation studies illustrated the clinical potential of MD factors including CCN1 as a urinary biomarker and therapeutic target in chronic kidney disease. The concept that a neuronally differentiated key sensory and regulatory cell type responding to organ-specific physiological inputs controls local progenitors to remodel or repair tissues may be applicable to other organs and diverse tissue regenerative therapeutic strategies.

Physiological Mechanisms of Dietary Salt Sensing in the Brain, Kidney, and Gastrointestinal Tract

Excess dietary salt (NaCl) intake is strongly correlated with cardiovascular disease and is a major contributing factor to the pathogenesis of hypertension. NaCl-sensitive hypertension is a multisystem disorder that involves renal dysfunction, vascular abnormalities, and neurogenically-mediated increases in peripheral resistance. Despite a major research focus on organ systems and these effector mechanisms causing NaCl-induced increases in arterial blood pressure, relatively less research has been directed at elucidating how NaCl is sensed by various tissues to elicit these downstream effects. The purpose of this review is to discuss how the brain, kidney, and gastrointestinal tract sense NaCl including key cell types, the role of NaCl versus osmolality, and the underlying molecular and electrochemical mechanisms.

Abstract 057: Macula Densa Stimulation Acutely Increases Afferent Renal Nerve Activity And Blood Pressure

Macula densa (MD) cells in the kidney are known to regulate renal hemodynamics and the renin-angiotensin system, and indirectly systemic blood pressure (BP). However, neuron-like differentiation and activity as non-traditional MD functions are emerging. This study addressed the hypothesis that MD cells function similarly to peripheral ganglia, form neuronal networks that are part of the peripheral (renal) nervous system and synapse with renal afferent/efferent nerves as a new pathway for the direct control of sympathetic tone and BP. Single cell MD Ca 2+ signaling was analyzed in vivo using intravital multiphoton microscopy (MPM) of MD-G6 mice that selectively express the ratiometric Ca 2+ reporter GCaMP6f/tdTomato in MD cells. Afferent renal nerve activity (ARNA) was isolated and measured via recording electrodes. Systemic BP was monitored via the cannulated carotid artery. Optogenetic MD stimulation was induced by blue light (470nm) exposure of the whole left kidney of MD-Ai27 mice that selectively express the depolarizing channelrhodopsin ChR2 in MD cells. Pacemaker-like regular Ca 2+ oscillations (4-fold elevations in baseline Ca 2+ and frequency of 0.03 Hz) and their cell-to-cell propagation via long, axon-like processes were exclusively confined to the MD area. Bulk and scRNA seq and MD transcriptome analysis identified the high expression of genes related to synaptic transmission that was validated by immunohistochemistry. Acute intra-renal infusion of arginine-vasopressin (AVP) produced 3-fold increase in MD Ca 2+ firing frequency (via the MD-specific AVPR1a) and a dose-dependent increase in ARNA and BP (saline: -1±1; 0.01ug/mL: 2±1; 0.1ug/mL: 7±2; 0.25ug/mL: 7±3; 0.5ug/mL: 10±3; 1.0ug/mL: 23±13). IV administration of AVP (0.25ug/mL) did not significantly alter ARNA (108±3%, n=3) but produced a significant increase in arterial blood pressure (40±6mmHg, n=3). Blue light exposure of MD-Ai27 mouse kidneys acutely and reversibly increased systemic BP by 22±5mmHg (P<0.05, n=5). In summary, MD cells send interoceptive signals to the brain via renal sensory afferent nerves to directly control BP. Targeting of novel MD mechanisms may result in exciting new therapeutic opportunities for renal and cardiovascular diseases and hypertension.

Abstract P323: Direct Vascular Endothelial Actions Of Angiotensin II Via At 1 R And No Signaling Revealed By Intravital Multiphoton Microscopy

The renin-angiotensin system (RAS) controls blood pressure and body fluid balance. The classic vasoactive effects of RAS are mediated by the binding of angiotensin II (ANGII) to ANGII type 1 receptors (AT 1 R) in vascular smooth muscle cells leading to vasoconstriction, or to opposing ANGII type 2 receptors (AT 2 R). However, only few studies investigated the direct effects of ANGII on vascular endothelial cells (VEC) in vivo and the mechanisms how VECs may mitigate ANGII-mediated vasoconstriction. The present study aimed to explore the molecular mechanisms and pathophysiological relevance of the direct actions of ANGII on VEC in the kidney. VEC calcium dynamics and NO synthesis were visualized by using intravital multiphoton microscopy (MPM) of Cdh5-G6 mice that selectively express the ratiometric Ca 2+ reporter GCaMP6f/tdTomato in VECs, or the endothelial uptake of iv injected nitric oxide (NO) sensitive dye DAF-FM, respectively. Bolus injection of ANGII (400 ng/kg, ia.) triggered a >4-fold increase in VEC calcium in afferent (AA) arterioles and glomerular capillaries, but not in peritubular capillaries. These responses were blocked by pretreatment with the AT 1 R inhibitor Losartan (60mg/kg ip.), but not by the AT 2 R inhibitor PD123319 (25mg/kg ip.)(1.2+/-0.4 p<0.001 and 5.6+/-0.9-fold, p=0.3, respectively). VEC responded to acute ANGII by increased NO synthesis as indicated by >1.5-fold increase in DAF-FM fluorescence intensity as compared to baseline (p<0.0001). In mice with unilateral ureteral obstruction (UUO), a well-known high ANGII and vasoconstrictor state associated with endothelial dysfunction, the ANGII induced calcium increase in VECs was significantly reduced (2.8+/-0.3-fold) as compared to control (4.6+/-0.4-fold, p<0.01). These results correlated with the significantly reduced AA diameter in UUO compared to control (8.2+/-0.4 and 10.43+/-0.3 μm, respectively, p<0.001). In summary, ANGII has major direct effects on VECs NO production that counterbalances agonist-induced vasoconstriction. These effects are diminished in conditions with endothelial dysfunction leading to increased vascular contractility. Cell-specific targeting of ANGII actions may represent exciting future therapeutic opportunities.

A new view of macula densa cell protein synthesis

Macula densa (MD) cells, a chief sensory cell type in the nephron, are endowed with unique microanatomic features including a high density of protein synthetic organelles and secretory vesicles in basal cell processes ("maculapodia") that suggest a so far unknown high rate of MD protein synthesis. This study aimed to explore the rate and regulation of MD protein synthesis and their effects on glomerular function using novel transgenic mouse models, newly established fluorescence cell biology techniques, and intravital microscopy. Sox2-tdTomato kidney tissue sections and an O-propargyl puromycin incorporation-based fluorescence imaging assay showed that MD cells have the highest level of protein synthesis within the kidney cortex followed by intercalated cells and podocytes. Genetic gain of function of mammalian target of rapamycin (mTOR) signaling specifically in MD cells (in MD-mTORgof mice) or their physiological activation by low-salt diet resulted in further significant increases in the synthesis of MD proteins. Specifically, these included both classic and recently identified MD-specific proteins such as cyclooxygenase 2, microsomal prostaglandin E2 synthase 1, and pappalysin 2. Intravital imaging of the kidney using multiphoton microscopy showed significant increases in afferent and efferent arteriole and glomerular capillary diameters and blood flow in MD-mTORgof mice coupled with an elevated glomerular filtration rate. The presently identified high rate of MD protein synthesis that is regulated by mTOR signaling is a novel component of the physiological activation and glomerular hemodynamic regulatory functions of MD cells that remains to be fully characterized.NEW & NOTEWORTHY This study discovered the high rate of protein synthesis in macula densa (MD) cells by applying direct imaging techniques with single cell resolution. Physiological activation and mammalian target of rapamycin signaling played important regulatory roles in this process. This new feature is a novel component of the tubuloglomerular cross talk and glomerular hemodynamic regulatory functions of MD cells. Future work is needed to elucidate the nature and (patho)physiological role of the specific proteins synthesized by MD cells.

Intravital imaging reveals glomerular capillary distension and endothelial and immune cell activation early in Alport syndrome

Alport syndrome (AS) is a genetic disorder caused by mutations in type IV collagen that lead to defective glomerular basement membrane, glomerular filtration barrier (GFB) damage, and progressive chronic kidney disease. While the genetic basis of AS is well known, the molecular and cellular mechanistic details of disease pathogenesis have been elusive, hindering the development of mechanism-based therapies. Here, we performed intravital multiphoton imaging of the local kidney tissue microenvironment in a X-linked AS mouse model to directly visualize the major drivers of AS pathology. Severely distended glomerular capillaries and aneurysms were found accompanied by numerous microthrombi, increased glomerular endothelial surface layer (glycocalyx) and immune cell homing, GFB albumin leakage, glomerulosclerosis, and interstitial fibrosis by 5 months of age, with an intermediate phenotype at 2 months. Renal histology in mouse or patient tissues largely failed to detect capillary aberrations. Treatment of AS mice with hyaluronidase or the ACE inhibitor enalapril reduced the excess glomerular endothelial glycocalyx and blocked immune cell homing and GFB albumin leakage. This study identified central roles of glomerular mechanical forces and endothelial and immune cell activation early in AS, which could be therapeutically targeted to reduce mechanical strain and local tissue inflammation and improve kidney function.

New Endothelial Mechanisms in Glomerular (Patho)biology and Proteinuria Development Captured by Intravital Multiphoton Imaging

In the past two decades, intravital imaging using multiphoton microscopy has provided numerous new visual and mechanistic insights into glomerular biology and disease processes including the function of glomerular endothelial cells (GEnC), podocytes, and the development of proteinuria. Although glomerular endothelial injury is known to precede podocyte damage in several renal diseases, the primary role of GEnCs in proteinuria development received much less attention compared to the vast field of podocyte pathobiology. Consequently, our knowledge of GEnC mechanisms in glomerular diseases is still emerging. This review highlights new visual clues on molecular and cellular mechanisms of GEnCs and their crosstalk with podocytes and immune cells that were acquired recently by the application of multiphoton imaging of the intact glomerular microenvironment in various proteinuric disease models. New mechanisms of glomerular tissue remodeling and regeneration are discussed based on results of tracking the fate and function of individual GEnCs using serial intravital multiphoton imaging over several days and weeks. The three main topics of this review include (i) the role of endothelial injury and microthrombi in podocyte detachment and albumin leakage via hemodynamic and mechanical forces, (ii) the alterations of the endothelial surface layer (glycocalyx) and its interactions with circulating immune cells in lupus nephritis, and (iii) the structural and functional remodeling and regeneration of GEnCs in hypertension, diabetes, and other experimental injury conditions. By the comprehensive visual portrayal of GEnCs and the many other contributing glomerular cell types, this review emphasizes the complexity of pathogenic mechanisms that result in proteinuria development.

FC 016SPARSENTAN IMPROVES GLOMERULAR BLOOD FLOW AND AUGMENTS PROTECTIVE TISSUE REMODELING IN MOUSE MODELS OF FOCAL SEGMENTAL GLOMERULOSCLEROSIS (FSGS)

Background and Aims

Preliminary preclinical and emerging clinical evidence indicates strong antiproteinuric actions of dual endothelin type A (ETA) and angiotensin II type 1 (AT1) receptor antagonism with sparsentan. These nephroprotective effects have been more pronounced in different experimental and clinical settings compared to current standard of care using an AT1 receptor blocker (ARB). Considering the broad spectrum of renal actions of endothelin (ET) and angiotensin II (Ang II), inhibition of both pathways using sparsentan is postulated to target multiple renal cell types via a variety of renoprotective mechanisms. The aim of this study was to determine glomerular action of sparsentan as compared to the ARB losartan (Los) by direct visualization of effects on renal hemodynamics and tissue remodeling in the intact living kidney.

Method

Intravital multiphoton microscopy (MPM) of the glomerular vasculature and filtration barrier structure and function was performed in genetically engineered mice combined with traditional urinalysis and histology-based phenotyping. Glomerular hemodynamic parameters (afferent and efferent arteriole (AA and EA) diameters and single nephron glomerular filtration rate (SNGFR)) and podocyte calcium entry, as a measure of cell injury, were quantitatively visualized in the FSGS model Pod-GCaMP5/Tomato TRPC6 transgenic mice (1.5 years of age), in which TRPC6 is overexpressed together with the calcium reporter GCaMP5 in podocytes. Single cell identification and fate tracking of cells of the renin lineage (CoRL) was performed over time using a second physiologic control mouse model, Ren1d-Confetti mice that feature a multicolor CFP/GFP/YFP/FP reporter. Three groups of mice in each model received treatment with either vehicle (CTRL), the ARB losartan (Los; 10 mg/kg/day), or sparsentan (120 mg/kg/day) for 6 weeks (FSGS model) or 2 weeks (control physiology model).

Results

Both Los and sparsentan treatment attenuated the acute ET + Ang II-induced elevation of podocyte calcium by ∼80%, and the development of albuminuria, and glomerulosclerosis and tissue fibrosis in the FSGS model. Notably, sparsentan prevented the ET + Ang II increases in podocyte calcium more than Los and was significantly more effective in dilating both AA and EA (Fig. 1A, B), increasing SNGFR (Fig. 1C), increasing capillary blood flow (2-fold; p&lt;0.0001 vs. CTRL), and decreasing albuminuria (20%; p&lt;0.05 vs. CTRL). Sparsentan also preserved p57+ podocyte number by 50% compared to Los (p&lt;0.0001 vs. Los). Similarly, pretreatment with sparsentan was more effective in preventing glomerular arteriolar vasoconstriction induced by acute ET + Ang II iv injection compared to Los (p&lt;0.05 vs. Los). Following a 2-week treatment in control healthy Ren1d-Confetti mice, sparsentan resulted in a more robust increase compared to Los in the number of Confetti+ cells, clones, and individual cells per clone in the glomeruli and AA (Fig. 1D-F). Renal tubule segments also showed active cellular remodeling in response to sparsentan.

Conclusion

Serial MPM imaging directly visualized several mechanisms underlying beneficial antiproteinuric and structural effects of sparsentan in both FSGS and in the normal mouse kidney and differences between dual ETA/AT1 receptor antagonism of sparsentan and a mono-selective ARB. The sparsentan-induced glomerular hemodynamic pattern was driven by both AA and EA dilation resulting in an increase in capillary blood flow. Compared to Los, sparsentan was more effective in attenuating ET/Ang II-induced podocyte injury and in activation of resident progenitor cells and tissue remodeling. These findings suggest multiple layers of renal protective actions by dual ETA and AT1 receptor antagonism.

Serial intravital imaging captures dynamic and functional endothelial remodeling with single-cell resolution

Endothelial cells are important in the maintenance of healthy blood vessels and in the development of vascular diseases. However, the origin and dynamics of endothelial precursors and remodeling at the single-cell level have been difficult to study in vivo owing to technical limitations. Therefore, we aimed to develop a direct visual approach to track the fate and function of single endothelial cells over several days and weeks in the same vascular bed in vivo using multiphoton microscopy (MPM) of transgenic Cdh5-Confetti mice and the kidney glomerulus as a model. Individual cells of the vascular endothelial lineage were identified and tracked owing to their unique color combination, based on the random expression of cyan/green/yellow/red fluorescent proteins. Experimental hypertension, hyperglycemia, and laser-induced endothelial cell ablation rapidly increased the number of new glomerular endothelial cells that appeared in clusters of the same color, suggesting clonal cell remodeling by local precursors at the vascular pole. Furthermore, intravital MPM allowed the detection of distinct structural and functional alterations of proliferating endothelial cells. No circulating Cdh5-Confetti⁺ cells were found in the renal cortex. Moreover, the heart, lung, and kidneys showed more significant clonal endothelial cell expansion compared with the brain, pancreas, liver, and spleen. In summary, we have demonstrated that serial MPM of Cdh5-Confetti mice in vivo is a powerful technical advance to study endothelial remodeling and repair in the kidney and other organs under physiological and disease conditions.

A new view of macula densa cell microanatomy

Although macula densa (MD) cells are chief regulatory cells in the nephron with unique microanatomical features, they have been difficult to study in full detail due to their inaccessibility and limitations in earlier microscopy techniques. The present study used a new mouse model with a comprehensive imaging approach to visualize so far unexplored microanatomical features of MD cells, their regulation, and functional relevance. MD-GFP mice with conditional and partial induction of green fluorescent protein (GFP) expression, which specifically and intensely illuminated only single MD cells, were used with fluorescence microscopy of fixed tissue and live MD cells in vitro and in vivo with complementary electron microscopy of the rat, rabbit, and human kidney. An elaborate network of major and minor cell processes, here named maculapodia, were found at the cell base, projecting toward other MD cells and the glomerular vascular pole. The extent of maculapodia showed upregulation by low dietary salt intake and the female sex. Time-lapse imaging of maculapodia revealed highly dynamic features including rapid outgrowth and an extensive vesicular transport system. Electron microscopy of rat, rabbit, and human kidneys and three-dimensional volume reconstruction in optically cleared whole-mount MD-GFP mouse kidneys further confirmed the presence and projections of maculapodia into the extraglomerular mesangium and afferent and efferent arterioles. The newly identified dynamic and secretory features of MD cells suggest the presence of novel functional and molecular pathways of cell-to-cell communication in the juxtaglomerular apparatus between MD cells and between MD and other target cells.NEW & NOTEWORTHY This study illuminated a physiologically regulated dense network of basal cell major and minor processes (maculapodia) in macula densa (MD) cells. The newly identified dynamic and secretory features of these microanatomical structures suggest the presence of novel functional and molecular pathways of cell-to-cell communication in the juxtaglomerular apparatus between MD and other target cells. Detailed characterization of the function and molecular details of MD cell intercellular communications and their role in physiology and disease warrant further studies.

Essential role and therapeutic targeting of the glomerular endothelial glycocalyx in lupus nephritis

Lupus nephritis (LN) is a major organ complication and cause of morbidity and mortality in patients with systemic lupus erythematosus (SLE). There is an unmet medical need for developing more efficient and specific, mechanism-based therapies, which depends on improved understanding of the underlying LN pathogenesis. Here we present direct visual evidence from high-power intravital imaging of the local kidney tissue microenvironment in mouse models showing that activated memory T cells originated in immune organs and the LN-specific robust accumulation of the glomerular endothelial glycocalyx played central roles in LN development. The glomerular homing of T cells was mediated via the direct binding of their CD44 to the hyaluronic acid (HA) component of the endothelial glycocalyx, and glycocalyx-degrading enzymes efficiently disrupted homing. Short-course treatment with either hyaluronidase or heparinase III provided long-term organ protection as evidenced by vastly improved albuminuria and survival rate. This glycocalyx/HA/memory T cell interaction is present in multiple SLE-affected organs and may be therapeutically targeted for SLE complications, including LN.

A combined immunology and renal pathophysiology study of the local kidney tissue microenvironment in lupus identifies a key role of glomerular endothelial glycocalyx in disease development.

Renomedullary Interstitial Cell Endothelin A Receptors Regulate BP and Renal Function

BACKGROUND

The physiologic role of renomedullary interstitial cells, which are uniquely and abundantly found in the renal inner medulla, is largely unknown. Endothelin A receptors regulate multiple aspects of renomedullary interstitial cell function in vitro.

METHODS

To assess the effect of targeting renomedullary interstitial cell endothelin A receptors in vivo, we generated a mouse knockout model with inducible disruption of renomedullary interstitial cell endothelin A receptors at 3 months of age.

RESULTS

BP and renal function were similar between endothelin A receptor knockout and control mice during normal and reduced sodium or water intake. In contrast, on a high-salt diet, compared with control mice, the knockout mice had reduced BP; increased urinary sodium, potassium, water, and endothelin-1 excretion; increased urinary nitrite/nitrate excretion associated with increased noncollecting duct nitric oxide synthase-1 expression; increased PGE₂ excretion associated with increased collecting duct cyclooxygenase-1 expression; and reduced inner medullary epithelial sodium channel expression. Water-loaded endothelin A receptor knockout mice, compared with control mice, had markedly enhanced urine volume and reduced urine osmolality associated with increased urinary endothelin-1 and PGE₂ excretion, increased cyclooxygenase-2 protein expression, and decreased inner medullary aquaporin-2 protein content. No evidence of endothelin-1-induced renomedullary interstitial cell contraction was observed.

CONCLUSIONS

Disruption of renomedullary interstitial cell endothelin A receptors reduces BP and increases salt and water excretion associated with enhanced production of intrinsic renal natriuretic and diuretic factors. These studies indicate that renomedullary interstitial cells can modulate BP and renal function under physiologic conditions.

Novel fluorescence techniques to quantitate renal cell biology

Fluorescence microscopy techniques are powerful tools to study tissue dynamics, cellular function and biology both in vivo and in vitro. These tools allow for functional assessment and quantification along with qualitative analysis, thus providing a comprehensive understanding of various cellular processes under normal physiological and disease conditions. The main focus of this chapter is the recently developed method of serial intravital multiphoton microscopy that has helped shed light on the dynamic alterations of the spatial distribution and fate of single renal cells or cell populations and their migration patterns in the same tissue region over several days in response to various stimuli within the living kidney. This technique is very useful for studying in vivo the molecular and cellular mechanisms of tissue remodeling and repair after injury. In addition, complementary in vitro imaging tools are also described and discussed, like tissue clearing techniques and protein synthesis measurement in tissues in situ that provide an in depth assessment of changes at the cellular level. Thus, these novel fluorescence techniques can be effectively leveraged for different tissue types, experimental conditions as well as disease models to improve our understanding of renal cell biology.

Advances in Renal Cell Imaging

A great variety of cell imaging technologies are used routinely every day for the investigation of kidney cell types in applications ranging from basic science research to drug development and pharmacology, clinical nephrology, and pathology. Quantitative visualization of the identity, density, and fate of both resident and nonresident cells in the kidney, and imaging-based analysis of their altered function, (patho)biology, metabolism, and signaling in disease conditions, can help to better define pathomechanism-based disease subgroups, identify critical cells and structures that play a role in the pathogenesis, critically needed biomarkers of disease progression, and cell and molecular pathways as targets for novel therapies. Overall, renal cell imaging has great potential for improving the precision of diagnostic and treatment paradigms for individual acute kidney injury or chronic kidney disease patients or patient populations. This review highlights and provides examples for some of the recently developed renal cell optical imaging approaches, mainly intravital multiphoton fluorescence microscopy, and the new knowledge they provide for our better understanding of renal pathologies.

The macula densa prorenin receptor is essential in renin release and blood pressure control

The prorenin receptor (PRR) was originally proposed to be a member of the renin-angiotensin system (RAS); however, recent work questioned their association. The present paper describes a functional link between the PRR and RAS in the renal juxtaglomerular apparatus (JGA), a classic anatomical site of the RAS. PRR expression was found in the sensory cells of the JGA, the macula densa (MD), and immunohistochemistry-localized PRR to the MD basolateral cell membrane in mouse, rat, and human kidneys. MD cell PRR activation led to MAP kinase ERK1/2 signaling and stimulation of PGE₂ release, the classic pathway of MD-mediated renin release. Exogenous renin or prorenin added to the in vitro microperfused JGA-induced acute renin release, which was inhibited by removing the MD or by the administration of a PRR decoy peptide. To test the function of MD PRR in vivo, we established a new mouse model with inducible conditional knockout (cKO) of the PRR in MD cells based on neural nitric oxide synthase-driven Cre-lox recombination. Deletion of the MD PRR significantly reduced blood pressure and plasma renin. Challenging the RAS by low-salt diet + captopril treatment caused further significant reductions in blood pressure, renal renin, cyclooxygenase-2, and microsomal PGE synthase expression in cKO vs. wild-type mice. These results suggest that the MD PRR is essential in a novel JGA short-loop feedback mechanism, which is integrated within the classic MD mechanism to control renin synthesis and release and to maintain blood pressure.

ORAI1 Activates Proliferation of Lymphatic Endothelial Cells in Response to Laminar Flow Through Krüppel-Like Factors 2 and 4

RATIONALE

Lymphatic vessels function to drain interstitial fluid from a variety of tissues. Although shear stress generated by fluid flow is known to trigger lymphatic expansion and remodeling, the molecular basis underlying flow-induced lymphatic growth is unknown.

OBJECTIVE

We aimed to gain a better understanding of the mechanism by which laminar shear stress activates lymphatic proliferation.

METHODS AND RESULTS

Primary endothelial cells from dermal blood and lymphatic vessels (blood vascular endothelial cells and lymphatic endothelial cells [LECs]) were exposed to low-rate steady laminar flow. Shear stress-induced molecular and cellular responses were defined and verified using various mutant mouse models. Steady laminar flow induced the classic shear stress responses commonly in blood vascular endothelial cells and LECs. Surprisingly, however, only LECs showed enhanced cell proliferation by regulating the vascular endothelial growth factor (VEGF)-A, VEGF-C, FGFR3, and p57/CDKN1C genes. As an early signal mediator, ORAI1, a pore subunit of the calcium release-activated calcium channel, was identified to induce the shear stress phenotypes and cell proliferation in LECs responding to the fluid flow. Mechanistically, ORAI1 induced upregulation of Krüppel-like factor (KLF)-2 and KLF4 in the flow-activated LECs, and the 2 KLF proteins cooperate to regulate VEGF-A, VEGF-C, FGFR3, and p57 by binding to the regulatory regions of the genes. Consistently, freshly isolated LECs from Orai1 knockout embryos displayed reduced expression of KLF2, KLF4, VEGF-A, VEGF-C, and FGFR3 and elevated expression of p57. Accordingly, mouse embryos deficient in Orai1, Klf2, or Klf4 showed a significantly reduced lymphatic density and impaired lymphatic development.

CONCLUSIONS

Our study identified a molecular mechanism for laminar flow-activated LEC proliferation.

Night shift work and stomach cancer risk in the MCC-Spain study

OBJECTIVES

Night shift work has been classified as a probable human carcinogen by the International Agency for Research on Cancer, based on experimental studies and limited evidence on human breast cancer risk. Evidence at other cancer sites is scarce. We evaluated the association between night shift work and stomach cancer risk in a population-based case-control study.

METHODS

A total of 374 incident stomach adenocarcinoma cases and 2481 population controls were included from the MCC-Spain study. Detailed data on lifetime night shift work were collected including permanent and rotating shifts, and their cumulative duration (years). Adjusted unconditional logistic regression models were used in analysis.

RESULTS

A total of 25.7% of cases and 22.5% of controls reported ever being a night shift worker. There was a weak positive, non-significant association between ever having had worked for at least 1 year in permanent night shifts and stomach cancer risk compared to never having worked night shifts (OR=1.2, 95% CI 0.9 to 1.8). However, there was an inverse 'U' shaped relationship with cumulative duration of permanent night shifts, with the highest risk observed in the intermediate duration category (OR 10-20 years=2.0, 95% CI 1.1 to 3.6) (p for trend=0.19). There was no association with ever having had worked in rotating night shifts (OR=0.9, 95% CI 0.6 to 1.2) and no trend according to cumulative duration (p for trend=0.68).

CONCLUSION

We found no clear evidence concerning an association between night shift work and stomach cancer risk.

[Utility of B-type natriuretic peptide in children]

Serum brain natriuretic peptide (BNP) has been reported to indicate ventricular dysfunction, however, in children it has not been studied yet in our country.

PURPOSE

157 BNP tests were performed in 107 children, on the one hand, to evaluate its clinical value, to assess LV or systemic RV function in patients with transposition of great arteries after Senning operation, on the other hand, to prove the relation between BNP, MRI and echocardiographic ventricular function parameters. PATIENTS' AGE: 4 months-20 years, mean 12.5 yrs. Group I: Senning patients, Groups II and III: patients with dilated or hypertrophic cardiomyopathy, Group IV: patients with aortic insufficiency.

METHODS

BNP was determined using the electrochemiluminesce method (Elycsys-10 Roche). During the functional MRI Mass- Medis software RV LV EF, end-diastolic, end-systolic volumes were calculated. Echo M-mode, TEI index were calculated.

RESULTS

BNPs were significantly as higher compared to normal in each group of patients. Group I: 318 +/- 285 pg/ml, p < 0.01, Group II: 7262 +/- 10970 pg/ml, p < 0.01, Group III: 1558 +/- 2765 pg/ml, p < 0.01, Group IV: 1076 +/- 2791 pg/ml, p < 0.00l, vs 58 +/- 31 pg/ml. BNP were negatively correlated with MRI RV EF (r: -0.51, p < 0.05) and showed good correlation with TEI index (0.43 +/- 0.18, p < 0.05). After 3 weeks of medical or surgical treatment BNP decreased significantly. 4 patients died during the follow-up period, these had the highest BNP levels in each patients group.

CONCLUSIONS

BNP is a useful, prognostically valuable method in children to monitor ventricular function. BNP levels reflect the severity of the impairment of systemic RV function in Senning patients in whom a complex RV geometry is present causing the assessment of RV function more difficult, so we recommend BNP measurements as a longitudinal test in this patient group.

[Quantification of right and left ventricular function with magnetic resonance imaging after Senning operation for complete transposition of the great arteries]

INTRODUCTION

The different non-invasive examinations do not result in unambigous results about the long-term determination of right ventricular function providing systemic circulation in children with transposition of the great arteries operated with Senning procedure.

AIM

The goal of study was to determine the application of MRI for the observation of right and left ventricular morphology and function, for the recognition of the progression of the disease, and for the necessity of reoperation.

METHODS

The authors have observed the morphology and function of the right and left ventricule by ECG triggered short axis MR pictures. For the analysis of MR pictures MASS 5.0 software was used. Authors have determined the end systolic and end diastolic volume, the ejection fraction, the mass, and the stroke volume of the right ventricule, the end systolic and end diastolic volume, ejection fraction, the mass, and the stroke volume of the left ventricle, and the shunt volume. The values of these data corrected to body mass have been calculated.

PATIENTS

176 Senning operations took place between 1980 and 1996. MRI exploration at 21 of the 118 analyzed patients were carried out.

RESULTS

The right ventricular ejection fraction value at Senning operated patients is significantly different (49 +/- 9% vs. 70 +/- 4%) from those of healthy children (P < 0.01). Right ventricular stroke volume/m2 and right ventricular end systolic volume/m2 were significantly different compared to normal (43 +/- 10 ml/m2 vs. 48 +/- 7 ml/mn and 46 +/- 16 ml/m2 vs. 21 +/- 5 ml/m2, p < 0.05). Authors found also significant differences in left ventricular ejection fraction in Senning patients as compared to normal (60 +/- 9% vs. 70 +/- 6%, p < 0.01).

CONCLUSION

MRI, which is a reliable method of objective determination of right ventricular function, became an available method in Hungary. According to the results, authors might presume that the development of right ventricular dysfunction is expected even among Senning operated children without clinical symptoms, so more frequent control is required. The pathological left ventricular parameters may be explained by ventricular interactions. Authors find MRI an important part of the complex follow-up protocol of Senning operations. MRI data extended by results of other non-invasive explorations are appropriate for the follow-up of right ventricular dysfunction.

[Medicine at the crossroads]

This article is based in the book by Dr M Konner "Medicine at the crossroads". Medicine must be analyzed in three levels: the structure of the global society and its relationship to the population's health; the institutions dedicated to health protection and promotion; and health related professions. The commented book is specifically focused on medical profession. The main problems of the profession and its role in society are analyzed. The excessively hierarchical and technological, and thus dehumanized, relationship between physicians and patients. The high volume of surgical procedures and the exaggerated dependence on medications. The lack of preoccupation for mental disorders, the artificial prolongation of life and several other problems. The problems that arise when medical profession is inserted in market economy are analyzed, based on Chilean experience. That debilitates its trusteeship virtue, that is the basis of its social and political status. The contradictions that are generated by this new tendency of the profession and the strategies to face them are depicted.

[Health, power, and democracy. Notes for a primary care theory]

Health services are relentlessly deteriorating due to the persistent increase in their costs. This deterioration not only affects people's health. This service is directly linked to personal and family security and populations social equity expectatives. Thus, its failure inevitably leads to a gradual loss of State and public authorities legitimacy, threatening the stability of the democratic system. In the long run, it also affects the legitimacy of medical profession. To overcome this problem, considering the limited possibilities of a relatively poor country, a new health services model is proposed, based on a massive strengthening of primary care, organized in a way in which the community assumes an important part of the responsibility for the health of its members. To achieve this purpose the use of the concept of "empowerment" is proposed, practically applied through the "pedagogic investigation-action". As a result a noticeable increase in the general health level of the population is expected. At the same time, one of the serious threatens to the legitimacy of the Democratic State will be eliminated.