Normal Renal Physiology Research Articles

The renal renin-angiotensin system

The renin-angiotensin system (RAS) is a critical regulator of sodium balance, extracellular fluid volume, vascular resistance, and, ultimately, arterial blood pressure. In the kidney, angiotensin II exerts its effects to conserve salt and water through a combination of the hemodynamic control of renal blood flow and glomerular filtration rate and tubular epithelial cell sodium chloride and water transport mechanisms. Pharmacological inhibition of the actions of the RAS are widely used in the treatment of patients with hypertension, congestive heart failure, left ventricular dysfunction, pulmonary and systemic edema, diabetic nephropathy, cirrhosis of the liver, scleroderma, and migraines. Therefore, a thorough understanding of the influences of the RAS on normal renal physiology is of major importance for first-year medical students.

A novel role for uric acid in acute kidney injury associated with tumour lysis syndrome

Tumour lysis syndrome (TLS) is a complication associated with the treatment of tumour types with high proliferative rate, large tumour burden or high sensitivity to cytotoxic therapy. The implementation of risk stratification strategies [1], appropriate prophylactic measures, vigilant monitoring of laboratory parameters and active interventions to reduce risk factors has dramatically decreased the incidence of clinically significant morbidity that results in end organ damage and mortality. Despite these advances, 5–6% of atrisk paediatric and adult patients undergoing chemotherapy develop acute kidney injury (AKI), and 40–50% of these patients will require dialysis therapies with associated allcause mortality in excess of 50% [2–4]. Similar outcomes are reported with spontaneous TLS [5]. The lack of standardized definitions and outcome measures has hampered appreciation of the extent of adverse renal outcomes in TLS. Recent adoption of a uniform definition of AKI (increase in serum creatinine of 0.3 mg/dL from baseline or a 50% increase in serum creatinine from baseline values within 48 h) [6] and the recognition that the development of in-hospital AKI have significant implications for long-term mortality [7] underscores the need to understand the mechanisms involved in AKI associated with TLS. Furthermore, the effect of chronic kidney disease (CKD) on renal outcomes in TLS requires a study, as clinical tumour lysis occurs more frequently in patients with pretreatment renal impairment [8]. One study examining risk factors for in-hospital AKI of diverse aetiologies reported that CKD increases the risk of AKI 40-fold with a 20-fold increased risk for dialysis [9]. Here, we will briefly review the current understanding of the pathogenesis of TLS-induced AKI. In particular, a recent literature suggests that AKI and nephropathy are not simply due to intrarenal crystal deposition of urate and phosphate. Mechanism of AKI associated with intrarenal deposition of uric acid crystals TLS is a group of metabolic complications that occur after the treatment of large volume, rapidly proliferating haematological cancers including not only acute leukaemia and aggressive lymphomas but also some solid tumours. Metabolic alterations that result include hyperkalaemia, hyperphosphataemia, hyperuricaemia and hyperuricosuria, hypocalcaemia and consequent AKI. Specifically, AKI associated with TLS has been considered to be exclusively a crystal-dependent process caused by the massive and abrupt release of intracellular metabolites from chemosensitive, rapidly proliferating tumour cells that undergo rapid lysis and release nucleic acid breakdown products, phosphorus and potassium. Both urate and calcium phosphate crystals may cause crystal-dependent injury of the kidney which overwhelms the normal homeostatic mechanism(s) autoregulating normal renal physiology [10]. One of the most important mediators of AKI resulting from TLS is uric acid. When dying cells release DNA and RNA, they are degraded in the liver and other sites with the rapid production of uric acid. Serum uric acid rises acutely, resulting in marked uricosuria. Such cell death and degradation also results in acid generation, often with volume depletion, resulting in acidic urine that decreases the solubility of uric acid. When levels of urinary uric acid exceed its solubility, both micro- and macrocrystal formations occur in the distal tubules and collecting ducts with obstruction of the tubular lumen. The prevention of AKI resulting from TLS includes initiating prophylactic measures prior to and during chemotherapy, including hydration, alkalinization of the urine, use of the xanthine oxidase inhibitor allopurinol, as well as the urate oxidase inhibitor, rasburicase or its derivatives.

Principles of Physiology for the Anaesthetist, Second Edition.

Principles of Physiology for the Anaesthetist, Second Edition. By Ian Power, M.D., and Peter Kam, M.D. London, United Kingdom, Hodder Education, 2008. Pages: 472. Price: $65.00.Attuned to subtleties, the anesthesia provider is accustomed to observing a twitch of the hand or a quickening of the pulse and perceiving through such a detail several important implications about the body's dynamics. The submicroscopic saturation of receptors, the complex equilibration of the body's fluid, a glitch in the heart's circuitry—all of these are germane to our practice. Anesthesia as a specialty has earned respect in the House of Medicine for its ability to perceive and respond to such subtle trends. It is thus a fitting reception for the anesthetic field to welcome the second edition of Principles of Physiology for the Anesthetist, by Drs. Ian Power and Peter Kam. In this conveniently sized, soft-back textbook, the authors offer a concise and targeted resource for the anesthesia provider to refine or refresh an understanding of pertinent physiology.First published in Britain in 2001, the second edition adds over 70 pages of material and marks several updates and improvements. Students of anesthesia preparing for certifying exams will be pleased to find that the book has retained its earlier helpful figures and illustrations, and has added a valuable Reflections section to each chapter. These summaries are helpful as overviews in prereading chapters and, combined with the new Key Equations and Tables glossary, form a useful resource for students seeking a quick review for test preparation.The scope and depth of the text are excellent—it touches on the broad canvas of human physiology, but most of the content is dedicated to topics of most pertinence to anesthesia. Cardiac, respiratory, renal, and neurophysiologic issues take the forefront, but other topics important to anesthesia such as immune, liver, and metabolic physiology are also handled in depth. The authors have included helpful chapters on the physiology of pain and the physiology of aging, as well as a compelling Special Environments chapter that discusses the physiology of diving, altitude, and even space travel. The Learning Point and Reflections sections help the book to maintain a comprehensive focus without miring the reader in minutiae. However, the discussions are detailed enough to satisfy even a veteran seeking a refresher on the cell-level functioning of N -methyl-d-aspartate receptors or the formulation of the Nernst equation.Principles of Physiology for the Anesthetist has few drawbacks and favors well in comparison to similar texts. It provides even more figures and reader-friendly summaries than Stoelting and Hillier's Pharmacology & Physiology in Anesthetic Practice, and is more focused and concise than general texts such as Guyton and Hall's superb Textbook of Medical Physiology .1,2If the book has a drawback, it is the extent to which the principles of physiology are discussed in the context of clinical anesthesia. For instance, a detailed and graceful description of the determinants of venous return to the heart deals with standard physiology but would benefit from a discussion of how positive pressure ventilation, anesthetic agents, and surgical positioning affect the venous return (pp. 157 and 158). The discussion of normal renal physiology is comprehensive and helpful, but particular concerns for an anesthesia provider such as renal failure and the effects of vasopressors or volatile agents on the kidneys are not discussed. Elsewhere, neuromuscular blockade is described with memorable references to snake toxins and antiquated pharmacology but with only general reference to drugs current in clinical practice (pp. 19 and 24). While not always overtly treating anesthetic issues in physiology, the selected content of the book never strays too far from topics central to anesthesia, and does so with a reader-friendly format.Drs. Power and Kam have produced an excellent text that will help perpetuate the expertise in physiology that belongs to the field of anesthesia. Whether the reader is a student of anesthetic practice or a veteran looking for a reference to refresh the fundamentals, Principles of Physiology for the Anesthetist offers a concise and authoritative resource.*Mayo Clinic Rochester, Rochester, Minnesota. shakespeare.william@mayo.edu

Endothelin receptor selectivity in chronic renal failure

Chronic kidney diseases are increasing worldwide at an alarming rate, and they are emerging as a major public health problem. Treatments that slow the progression of chronic kidney disease are needed. Endothelin-1 (ET-1) is a potent vasoconstrictor with proinflammatory, mitogenic and profibrotic effects that is closely involved in both normal renal physiology and pathology. Increasing evidence suggests that ET-1 and its cognate receptors are involved in a variety of progressive renal disorders to the extent that renal ET-1 expression correlates with disease severity and renal function impairment. Endothelin receptor antagonists have been used in renoprotection studies owing to their capacity of improving renal hemodynamics and reducing proteinuria. Whether selective ET(A) or non-selective ET(A)/ET(B) receptor antagonists are preferable is still a matter of debate. As angiotensin II blockers are not invariably effective in retarding disease progression when treatment is started late in the course of the disease, it is foreseeable that an ET-1 antagonist in addition to angiotensin-converting enzyme inhibitors could represent a combined treatment for progressive nephropathies. The focus of this review is to examine the role endothelin-1 plays in kidney diseases and to determine the ideal setting for antagonizing its biological activity in chronic nephropathies.

Mitogen activated protein kinases in renal fibrosis

The mitogen-activated protein (MAP) kinases are involved in both normal renal physiology and in the pathology of various forms of kidney injury, including renal fibrosis. In vitro studies have shown a role for all three MAP kinase (ERK, p38 and JNK) in the production of the major pro-fibrotic factor, transforming growth factor-beta1 (TGF-beta1) by intrinsic renal cell types. There is also considerable cross-talk between TGF-beta1 and MAP kinase signalling pathways in the synthesis and turnover of extracellular matrix by fibroblast-like cells in the kidney. In addition, MAP kinase signalling contributes to TGF-beta1 induced transition of tubular epithelial cells into myofibroblasts. Administration of specific inhibitors of individual MAP kinases has identified a pathogenic role for both p38 and JNK pathways in animal models of renal fibrosis. There is also evidence to suggest that MAP kinases are activated in human renal fibrosis. Thus, blockade of p38 and JNK pathways may have therapeutic potential for the treatment of chronic renal fibrosis.

The normal ageing kidney – morphology and physiology

This paper will review some fundamentals of normal renal physiology necessary to understand the changes occurring with age and enable the reader to distinguish between chronic renal insufficiency and the consequences of normal ageing on kidney function.

Aliskiren Improves Nitric Oxide Bioavailability and Limits Atherosclerosis

Inhibition of the renin-angiotensin system (RAS), with angiotensin-converting enzyme inhibitor- (ACEI) and angiotensin receptor blocker (ARB)–based treatment approaches, has emerged as the cornerstone of contemporary cardiovascular risk reduction. These therapies offer robust reductions in cardiovascular mortality in patients postmyocardial infarction, those with systolic heart failure, and in high-risk patients with atherosclerosis. Furthermore, interruption of the RAS system has emerged as a critical modulator of normal and aberrant renal physiology, and interruption of RAS signaling is linked to improved renal structure and function.

Role of endothelin and endothelin receptor antagonists in renal disease

Endothelin (ET)-1 is a potent vasoconstrictor peptide with pro-inflammatory, mitogenic, and pro-fibrotic properties that is closely involved in both normal renal physiology and pathology. ET-1 exerts a wide variety of biological effects, including constriction of cortical and medullary vessels, mesangial cell contraction, stimulation of extracellular matrix production, and inhibition of sodium and water reabsorption along the collecting duct, effects that are primarily mediated in an autocrine/paracrine manner. Increasing evidence indicates that the ET system is involved in an array of renal disorders. These comprise chronic proteinuric states associated with progressive glomerular and tubulointerstitial fibrosis, including diabetic and hypertensive nephropathy, glomerulonephritis and others. In addition, ET-1 is causally linked to renal disorders characterized by increased renal vascular resistance, including acute ischaemic renal failure, calcineurin inhibitor toxicity, endotoxaemia, hepatorenal syndrome and others. Furthermore, derangement of the ET system may be involved in conditions associated with inappropriate sodium and water retention; for example, in congestive heart failure and hepatic cirrhosis. Both selective and non-selective ET receptor antagonist have been developed and tested in animal models with promising results. As key events in progressive renal injury like inflammation and fibrosis are mediated via both ET(A) and ET(B) receptors, while constrictor effects are primarily transduced by ET(A) receptors, dual ET receptor blockade may be superior over selective ET(A) antagonism. Several compounds have been developed with remarkable effects in several models of acute and progressive renal injury. Thus, clinical studies are required to assess whether these results can be confirmed in humans, hopefully leading to novel and effective therapeutic options with few side effects.

DEVELOPMENT OF A NOVEL EX-VIVO RENAL PERFUSION CIRCUIT WITH NORMOTHERMIC BLOOD

The shortage of organs is a major limitation in transplantation. A possible solution to this problem is to improve the procurement techniques and to develop new methods to preserve and store organs. We developed an ex vivo renal perfusion system in which resuscitation of the organs was attempted with the ultimate goal of mimicking normal renal physiology, overcoming the ischemic barriers in organ retrieval and storage. Methods: Excised swine kidneys were placed in a plastic ex-vivo circuit attached to the femoral vessels of the donor with a mini-roller pump to regulate perfusion flows at 100 ml/min to avoid high perfusion pressures. Organs were studied during 4 hours of reperfusion and compared to control organs (in-situ), with temperature maintained at 37.5 °C. The reperfusion parameters studied include perfusion pressures, renal artery blood flows (RAF), vascular resistances (RVR), urine output (UO) and histologic evaluations. Results: RAF was restored early after reperfusion and maintained at 60–70% of baseline. UO was re-established during the first 10min of reperfusion and maintained during the full experiment, with lower values for the study group. RVR was maintained at the same value during reperfusion, with slightly higher values for the study group. Conclusion: With this system, diuresis was restored and the resuscitated ex vivo organs exhibited ongoing metabolism rather than being inhibited by traditional methods. The ability to quantify and analyze urine during reperfusion and preservation facilitates the assessment of organ function and viability before transplantation.

Protecting Calcium and Phosphate Balance in Chronic Renal Disease

In its earliest stages, chronic kidney disease (CKD) is associated with a failure to regulate phosphate balance optimally. Multiple aspects of normal renal physiology—from maintenance of an adequate GFR to responsiveness of the nephron to systemic and local signals that regulate phosphate secretion—underlie the deterioration in phosphate control as CKD progresses. The human organism is endowed with several adaptive mechanisms that attempt to counter the kidneys’ early and continuous decline in the functioning pathways that are normally involved in the regulation of phosphate excretion (1). Two components are central to these adaptive mechanisms. The first is the inexorable increase in circulating parathyroid hormone (PTH) prompted by minimally perceived increases in phosphate levels. Increased PTH concentrations stimulate the remaining nephrons to excrete phosphate more efficiently in the face of a continually decreasing nephron mass as CKD progresses. The second is the role of calcium in facilitating phosphate removal via nonrenal mechanisms. In the intestine, available free calcium binds readily with ingested phosphate to form a less soluble salt that is removed easily via normal bowel function. In soft tissue, free calcium binds with excessive phosphate and is deposited within the tissue. Although effective in the short-term, this adaptive response ultimately leads to progressive soft tissue calcification, a trade-off that is associated with a significant increase in cardiovascular risk. It follows that a secondary adaptive response that is intended to protect calcium homeostasis ensues. PTH mobilizes needed calcium from bone reserves, producing another unfavorable trade-off, ubiquitous metabolic bone disease in patients with CKD and ESRD. Why would the adaptive, compensatory mechanisms that protect phosphate and calcium homeostasis have such ultimately devastating consequences for these patients? Tight control of both phosphate and calcium homeostasis is essential to the normal functioning of virtually all life-sustaining, physiologic processes. Cell phosphate is at the core of all energydependent physiologic processes. Cell calcium and its ubiquitous binding protein are the triggers that initiate virtually all cellular functions. Thus, compromising the tight regulation of these two ions, even short term, carries an immediate risk to the highly integrated physiologic systems that are critical to sustaining essentially all biologic process. Viewed in that context, a trade-off that maintains biologic systems for years but ultimately leads to life-threatening conditions later in patients with CKD and ESRD is understandable. Unfortunately for the patient with early CKD, these adaptive mechanisms are so successful that even though GFR is significantly compromised, serum phosphate does not become elevated until the late stages of renal disease, at which time health care providers recognize the need to respond. By that time, parathyroid hyperplasia is irreversible, bone loss is significant, and soft tissue calcification, even if not grossly evident, is already well established. Historically, the foundation of the therapeutic approach to this clinical situation has been the use of calcium-containing phosphate binders (CCPB). Although not typically appreciated, this traditional approach when viewed in the context of the origins and consequences of the hyperphosphatemia of CKD and ESRD as outlined above is both logical and physiologically appropriate. Using CCPB to control phosphate provides the biologically appropriate agent to bind phosphate in the intestine while ensuring sufficient calcium systemically to downregulate PTH secretion and avoid mobilization of the organism’s endogenous calcium reserves from bones. Unfortunately, in the past few years, the logic and appropriateness of using CCPB in the management of phosphate balance in ESRD and CKD have been challenged. Essentially one study (2) and its putative documentation that using CCPB in dialysis patients actually contributes to coronary calcifications

The role of vascular endothelial growth factor (VEGF) in renal pathophysiology

Vascular endothelial growth factor (VEGF) is an endothelial-specific growth factor that promotes endothelial cell proliferation, differentiation and survival, mediates endothelium-dependent vasodilatation, induces microvascular hyperpermeability and participates in interstitial matrix remodeling. In the kidney, VEGF expression is most prominent in glomerular podocytes and in tubular epithelial cells, while VEGF receptors are mainly found on preglomerular, glomerular, and peritubular endothelial cells. The role of VEGF in normal renal physiology is essentially unknown. The absence of prominent effects of VEGF blockade in normal experimental animals suggests a limited function during homeostasis, although a role in the formation and maintenance of glomerular capillary endothelial fenestrations has been suggested. VEGF and its receptors are up-regulated in experimental animals and humans with type 1 and type 2 diabetes. Inhibition of VEGF has beneficial effects on diabetes-induced functional and structural alterations, suggesting a deleterious role for VEGF in the pathophysiology of diabetic nephropathy. VEGF is required for glomerular and tubular hypertrophy and proliferation in response to nephron reduction, and loss of VEGF is associated with the development of glomerulosclerosis and tubulointerstitial fibrosis in the remnant kidney. No firm conclusions on the role of VEGF in minimal change or membranous glomerulonephritis can be drawn. VEGF may be an essential mediator of glomerular recovery in proliferative glomerulonephritis. Glomerular and tubulointerstitial repair in thrombotic microangiopathy and cyclosporin nephrotoxicity may also be VEGF-dependent. In conclusion, VEGF is required for growth and proliferation of glomerular and peritubular endothelial cells. While deleterious in some, it may contribute to recovery in other forms of renal diseases.

CD40-induced transcriptional activation of vascular endothelial growth factor involves a 68-bp region of the promoter containing a CpG island.

Vascular endothelial growth factor (VEGF) is produced by several cell types in the kidney, and its expression is tightly regulated for the maintenance of normal renal physiology. Increases or decreases in its expression are associated with proteinuria and renal disease. Recently, we found that the expression of VEGF is markedly induced following interactions between CD40 ligand (CD40L) and CD40. Here, endothelial cells (EC) or Jurkat T cell lines were transiently transfected with luciferase reporter constructs under the control of the human VEGF promoter and were treated with human soluble CD40L (sCD40L). We identified a CD40-responsive 68-bp region (bp -50 to +18) of the promoter and 43 bp within this region (bp -25 to +18) that have 97% homology to a sequence of CpG dinucleotides. A computerized search revealed that the CpG region has putative binding domains for the transcriptional repressor protein methyl CpG binding protein-2 (MeCP2). In EMSA, we found that the 43-bp methylated sequence formed four complex(es) with nuclear extracts from untreated EC and reduced binding of at least one complex when nuclear lysates from sCD40L-activated EC (30 min) were used. Supershift analysis using anti-MeCP2 demonstrated that most of the complex(es) in both untreated and sCD40L-activated EC involved interactions between the 43-bp DNA and MeCP2. In addition, we found that other CpG binding proteins may also interact with this region of the promoter. Taken together, this is the first demonstration that CpG binding transcriptional repressor proteins including MeCP2 may be of importance in VEGF biology.

Beta(2)-Adrenoceptor activation attenuates endotoxin-induced acute renal failure.

Abnormalities in the beta(2)-adrenergic control of organ function have been implicated in the pathogenesis of several disease states, such as septic shock. The objectives of the present study were to define the contribution of beta(2)-adrenoceptors (beta(2)-AR) to normal renal physiology and to investigate whether overexpression of renal beta(2)-AR might be potentially beneficial in preventing progressive renal damage associated with endotoxemia. Adenoviral transgenes containing the human beta(2)-AR (Adeno-beta(2)-AR) were constructed and delivered into the rat kidney by means of intraparenchymal injections. Administration of 10(9) total viral particles of Adeno-beta(2)-AR induced an approximately threefold increase in beta(2)-AR density in the renal tissue, which 2 wk after delivery, enhanced GFR and sodium reabsorption compared with control rats. The enhanced GFR was abolished by the addition of the beta(2)-AR antagonist, ICI 118,551. Administration of lipopolysaccharide (LPS) caused a reduction in GFR, beta(2)-AR density, and cAMP together with enhanced TNF-alpha mRNA in the kidney. In rats overexpressing beta(2)-AR, the reduction in baseline GFR and elevation of TNF-alpha mRNA and leukocyte infiltration into the kidney associated with the endotoxin were blocked. These findings suggested the possibility that a renal-specific overexpression of beta(2)-AR preserves basal renal function in response to a ligand-independent beta(2)-AR activation and that the delivery of Adeno-beta(2)-AR gene is a potential novel therapeutic strategy for treatment of acute renal failure associated with sepsis.

Proinflammatory cytokines enhance COX-1 gene expression in cultured rat glomerular mesangial cells

Glomerular mesangial cells (GMC) exert an essential maintaining effect on hemodynamic integrity and immune competence of the kidney through arachidonate metabolism. To clarify this, cultured rat GMC were measured for the expression and production of cyclooxygenase (COX) and excretion of prostaglandin (PG). The rat GMC spontaneously expressed type 1 cyclooxygenase (COX-1), but not COX-2. The PGE2 and thromboxane B2 (TXB2) were spontaneously produced by the cells. Interleukin (IL)-1β (25 ng/ml), IL-8 (25 ng/ml), growth-related oncogene-α (GRO, 50 ng/ml) and tumor necrosis factor-α (TNF-α, 25 ng/ml) stimulated the COX-1 protein production as demonstrated by Western blot and enhanced PGE2 synthesis in GMC, beginning on 2 h of incubation, and steadily enhanced TXB2 synthesis over a 24-h period. Lipopolysaccharide (LPS, 100 ng/ml) enhanced both PGE2 and TXB2 syntheses from 2 h to at least 24 h of incubation. Collectively, the proinflammatory cytokines could enhance COX-1 but not COX-2 expression in GMC leading to increased PGE2 and TXB2 production. These biochemical events may be implicated in normal renal physiology as well as in pathogenesis of glomerular diseases.

Cisplatin up-regulates the adenosine A 1 receptor in the rat kidney

Cisplatin, a widely used anticancer drug, produces significant oto- and nephrotoxicity. Previous data from our laboratory, using cultured cell lines, indicated that cisplatin increases the expression of the adenosine A 1 receptor subtype through generation of reactive oxygen species and activation of nuclear factor-κB (NF-κB). Since the adenosine A 1 receptor plays an important role in normal renal physiology, this study was performed to determine whether cisplatin modulates adenosine A 1 receptor expression in vivo and whether these receptors play a role in the nephrotoxicity. Male Sprague–Dawley rats, treated with cisplatin (8 mg/kg), developed nephrotoxicity within 3 days, as demonstrated by increased serum creatinine and blood urea nitrogen. Cisplatin also produced a significant increase in malondialdehyde, apoptosis and necrosis in the kidney. The above changes were associated with a time-dependent increase in the expression of adenosine A 1 receptor, as determined by radioligand binding assays, Western blotting and immunocytochemistry, and an increase in adenosine A 1 receptor transcripts. Administration of selective and nonselective antagonists of the adenosine A 1 receptor produced either no change or exacerbated the nephrotoxicity produced by cisplatin. These data indicate that cisplatin can regulate the adenosine A 1 receptor in the kidney and suggest a cytoprotective role of this receptor subtype against cisplatin-induced nephrotoxicity.

Expression of the membrane-associated carbonic anhydrase isozyme XII in the human kidney and renal tumors.

Carbonic anhydrase isozyme XII (CA XII) is a novel membrane-associated protein with a potential role in von Hippel-Lindau carcinogenesis. Although Northern blotting has revealed positive signal for CA XII in normal human kidney, this is the first study to demonstrate its cellular and subcellular localization along the human nephron and collecting duct. Immunohistochemistry with a polyclonal antibody (PAb) raised against truncated CA XII revealed distinct staining in the basolateral plasma membrane of the epithelial cells in the thick ascending limb of Henle and distal convoluted tubules, and in the principal cells of the collecting ducts. A weak basolateral signal was also detected in the epithelium of the proximal convoluted tubules. In addition to the normal kidney specimens, this immunohistochemical study included 31 renal tumors. CA XII showed moderate or strong plasma membrane-associated expression in most oncocytomas and clear-cell carcinomas. The segmental, cellular, and subcellular distribution of CA XII along the human nephron and collecting duct suggests that it may be one of the key enzymes involved in normal renal physiology, particularly in the regulation of water homeostasis. High expression of CA XII in some renal carcinomas may contribute to its role in von Hippel-Lindau carcinogenesis.

The C5a receptor is expressed in normal renal proximal tubular but not in normal pulmonary or hepatic epithelial cells.

C5a, a 74 amino acid peptide cleaved from the complement protein C5, is an extremely potent anaphylatoxin. Expression of the receptor for the anaphylatoxin C5a (C5aR) has been thought to be restricted to cells of myeloid origin. However, recent evidence suggests that the C5aR is also expressed in hepatocytes as well as in pulmonary epithelial, endothelial and smooth muscle cells. In the present study, we investigated the tissue distribution of C5aR by immunohistochemistry in normal human lung, liver, intestine and kidney using well-defined monoclonal antibodies (mAbs) directed against the extracellular N-terminus of the receptor. In all tissues examined, macrophages displayed an abundant expression of C5aR protein. However, in the normal human lung, C5aR expression was not detectable in bronchial and alveolar epithelial cells or in vascular smooth muscle or endothelial cells. In the normal human liver, no C5aR protein was detected in hepatocytes, whereas Kupffer cells strongly expressed the C5aR. In normal human kidney, the C5aR was detectable only in proximal tubular cells. C5aR gene transcription in Kupffer cells and proximal tubular cells was confirmed by in situ hybridization. Thus, our results point to an as yet unknown role of the C5aR in normal renal physiology. In the normal lung and liver, however, previous evidence for the ubiquitous expression of C5aR in epithelial, endothelial and smooth muscle cells in situ should be re-evaluated.

Analysis of segmental renal gene expression by laser capture microdissection

Analysis of segmental renal gene expression by laser capture microdissection. The study of normal renal physiology has been greatly aided by microdissection techniques that have delineated the exceptional functional and cellular heterogeneity both along the nephron and between different nephron populations. These techniques are not widely used to study renal injury as microdissection is difficult because of tissue necrosis or fibrosis. We developed a procedure to detect specific gene expression in specific locations of the kidney in histologic sections. The anatomic specificity of laser capture microdissection (LCM) was employed with the sensitivity of reverse transcriptase-polymerase chain reaction (RT-PCR). LCM/RT-PCR detected mRNA for podoplanin in 2% of a single glomerulus, rat basic amino acid transporter in 6% of a single cross-section of proximal straight tubule, and renin in eight proximal convoluted tubule cross-sections. LCM/RT-PCR could isolate pure populations of proximal convoluted tubules, proximal straight tubules, and thick ascending limbs from renal histologic sections, although pure collecting ducts could not be isolated. LCM/RT-PCR localized ischemia-reperfusion-induced induction of KC/interleukin-8 primarily to the medullary thick ascending limb, and detected transforming growth factor-beta (TGF-beta) mRNA in glomeruli of a patient with membranous glomerulonephropathy. When used with an appropriate laser spot size, LCM/RT-PCR can measure gene expression in glomeruli or specific parts of the nephron and can study alterations in steady-state mRNA levels in animal models of renal disease. The applications, limitations, and refinements of this approach are discussed.

C-met proto-oncogene expression in benign and malignant human renal tissues.

Hepatocyte growth factor/scatter factor (HGF/SF) is a potent mitogen to renal epithelial cells in vitro and in vivo. HGF/SF signals through its receptor which is coded by the c-met proto-oncogene. We hypothesized that altered expression of the HGF/SF receptor, c-met, may be involved in the pathogenesis of certain renal cell carcinomas. Our objectives were to 1) assess the presence and localization of c-met protein in benign and malignant human renal tissues, and 2) correlate the presence of c-met protein with renal carcinoma histological subtype, tumor stage and tumor grade. Immunohistochemical analysis of c-met protein was performed in 41 normal and malignant human renal samples. c-met Immunostaining was detected in the normal kidney tissue in all 41 samples. In the normal kidney c-met immunostaining was limited to the cell membrane and/or cytoplasm of epithelial cells in specific tubular segments, including the proximal convoluted tubule, thin and thick limbs of the loop of Henle, and the collecting duct. The glomeruli, distal convoluted tubule and stroma were consistently negative for c-met staining. c-met Immunostaining was detected in 68% of renal cell carcinomas and was more common in higher nuclear grade cancers (p < 0.034). The c-met receptor is present in specific tubular segments in the normal kidney and is frequently expressed in higher nuclear grade renal cancers, suggesting a role in renal carcinoma progression. Future studies should evaluate the biological significance of the HGF/ SF-c-met pathway in normal renal physiology, and renal cancer growth and progression.

C-Met Proto-Oncogene Expression in Benign and Malignant Human Renal Tissues

Purpose Hepatocyte growth factor/scatter factor (HGF/SF) is a potent mitogen to renal epithelial cells in vitro and in vivo. HGF/SF signals through its receptor which is coded by the c-met proto-oncogene. We hypothesized that altered expression of the HGF/SF receptor, c-met, may be involved in the pathogenesis of certain renal cell carcinomas. Our objectives were to 1) assess the presence and localization of c-met protein in benign and malignant human renal tissues, and 2) correlate the presence of c-met protein with renal carcinoma histological subtype, tumor stage and tumor grade. Materials and Methods Immunohistochemical analysis of c-met protein was performed in 41 normal and malignant human renal samples. Results c-met Immunostaining was detected in the normal kidney tissue in all 41 samples. In the normal kidney c-met immunostaining was limited to the cell membrane and/or cytoplasm of epithelial cells in specific tubular segments, including the proximal convoluted tubule, thin and thick limbs of the loop of Henle, and the collecting duct. The glomeruli, distal convoluted tubule and stroma were consistently negative for c-met staining. c-met Immunostaining was detected in 68% of renal cell carcinomas and was more common in higher nuclear grade cancers (p <0.034). Conclusions The c-met receptor is present in specific tubular segments in the normal kidney and is frequently expressed in higher nuclear grade renal cancers, suggesting a role in renal carcinoma progression. Future studies should evaluate the biological significance of the HGF/SF-c-met pathway in normal renal physiology, and renal cancer growth and progression.