Growth factors in monoclonal light-chain--related renal diseases

Glomerulopathic Light Chain-Mesangial Cell Interactions: Sortilin-Related Receptor (SORL1) and Signaling

INTRODUCTION

Deciphering the intricacies of the interactions of glomerulopathic Ig light chains with mesangial cells is key to delineate signaling events responsible for the mesangial pathologic alterations that ensue.

METHODS

Human mesangial cells, caveolin 1 (CAV1), wild type (WT) ,and knockout (KO), were incubated with glomerulopathic light chains purified from the urine of patients with light chain-associated (AL) amyloidosis or light chain deposition disease. Associated signaling events induced by surface interactions of glomerulopathic light chains with caveolins and other membrane proteins, as well as the effect of epigallocatechin-3-gallate (EGCG) on the capacity of mesangial cells to intracellularly process AL light chains were investigated using a variety of techniques, including chemical crosslinking with mass spectroscopy, immunofluorescence, and ultrastructural immunolabeling.

RESULTS

Crosslinking experiments provide evidence suggesting that sortilin-related receptor (SORL1), a transmembrane sorting receptor that regulates cellular trafficking of proteins, is a component of the receptor on mesangial cells for glomerulopathic light chains. Colocalization of glomerulopathic light chains with SORL1 in caveolae and also in lysosomes when light chain internalization occurred, was documented using double immunofluorescence and immunogold labeling ultrastructural techniques. It was found that EGCG directly blocks c-Fos cytoplasmic to nuclei signal translocation after interactions of AL light chains with mesangial cells, resulting in a decrease in amyloid formation.

CONCLUSION

Our findings document for the first time a role for SORL1 linked to glomerular pathology and signaling events that take place when certain monoclonal light chains interact with mesangial cells. This finding may lead to novel therapies for treating renal injury caused by glomerulopathic light chains.

Renal amyloidosis with emphasis on the diagnostic role of electron microscopy

Our understanding of renal diseases with structured deposits has improved in the last two decades with the development of new diagnostic techniques that also changed the role of ultrastructural pathology in diagnostic decision-making. This review article addresses the current role of electron microscopy in the evaluation of structured deposits and discusses the impact of new developments. The diagnosis in a subset of structured deposits, amyloidosis, relies on morphologic and tinctorial characteristics at the light microscopic level. Congo red staining of tissue with demonstrable birefringence upon polarization has been regarded as the mainstay during tissue evaluation; however, there are pitfalls that must be considered, and electron microscopy remains a crucial adjunct investigative tool. Ultrastructurally the amyloid fibrils are unique with their characteristic appearance. They are randomly arranged, rigid, criss-crossing, non-branching, 7-15 nm (0.07-0.15 um) in diameter and of variable length. The morphology of fibrils is very similar in the different types of amyloidosis. By scanning electron microscopy amyloid fibrils appear artfully displayed. Immunofluorescence and immunohistochemical stains can be used to characterize the type of amyloidosis while mass spectroscopy is extremely useful in cases where typing of the amyloid using the above-mentioned techniques is difficult or equivocal.

Pathophysiology and management of monoclonal gammopathy of renal significance

Recent years have witnessed a rapid growth in our understanding of the pathogenic property of monoclonal proteins. It is evident that some of these small monoclonal proteins are capable of inducing end-organ damage as a result of their intrinsic physicochemical properties. Hence, an umbrella term, monoclonal gammopathy of clinical significance (MGCS), has been coined to include myriad conditions attributed to these pathogenic proteins. Because kidneys are the most commonly affected organ (but skin, peripheral nerves, and heart can also be involved), we discuss MGRS exclusively in this review. Mechanisms of renal damage may involve direct or indirect effects. Renal biopsy is mandatory and demonstration of monoclonal immunoglobulin in kidney, along with the corresponding immunoglobulin in serum or urine, is key to establish the diagnosis. Pitfalls exist at each diagnostic step, and a high degree of clinical suspicion is required to diagnose MGRS. Recognition of MGRS by hematologists and nephrologists is important, because timely clone-directed therapy improves renal outcomes. Autologous stem cell transplant may benefit selected patients.

Understanding Mesangial Pathobiology in AL-Amyloidosis and Monoclonal Ig Light Chain Deposition Disease

Patients with plasma cell dyscrasias produce free abnormal monoclonal Ig light chains that circulate in the blood stream. Some of them, termed glomerulopathic light chains, interact with the mesangial cells and trigger, in a manner dependent of their structural and physicochemical properties, a sequence of pathological events that results in either light chain–derived (AL) amyloidosis (AL-Am) or light chain deposition disease (LCDD). The mesangial cells play a key role in the pathogenesis of both diseases. The interaction with the pathogenic light chain elicits specific cellular processes, which include apoptosis, phenotype transformation, and secretion of extracellular matrix components and metalloproteinases. Monoclonal light chains associated with AL-Am but not those producing LCDD are avidly endocytosed by mesangial cells and delivered to the mature lysosomal compartment where amyloid fibrils are formed. Light chains from patients with LCDD exert their pathogenic signaling effect at the cell surface of mesangial cells. These events are generic mesangial responses to a variety of adverse stimuli, and they are similar to those characterizing other more frequent glomerulopathies responsible for many cases of end-stage renal disease. The pathophysiologic events that have been elucidated allow to propose future therapeutic approaches aimed at preventing, stopping, ameliorating, or reversing the adverse effects resulting from the interactions between glomerulopathic light chains and mesangium.

The pathogenesis of renal injury and treatment in light chain deposition disease

Light chain deposition disease (LCDD) is a rare clinical disorder. The deposition of light chain immunoglobulins mainly affects the kidneys, which have different characteristics than other tissues. To date, the therapeutic approach for the treatment of LCDD has no evidence-based consensus, and clinical experience of reported cases guides current disease management strategies. The present systematic review investigates and summarizes the pathological mechanisms of renal injury and the subsequent treatments for LCDD.

Healing the damaged mesangium in nodular glomerulosclerosis using mesenchymal stem cells (MSCs): Expectations and challenges

It has been shown experimentally that mesenchymal stem cells (MSCs) can be delivered to the mesangium in some conditions such as amyloidosis to clear debris and foreign material, and eventually transform into functional mesangial cells (MCs) and change the altered mesangial areas into normal collagen IV-rich matrix. A more challenging situation is when the matrix is rich in abnormal extracellular matrix proteins, especially those difficult to destroy such as tenascin, and, as a result, assumes a nodular appearance - what is known in pathology jargon as nodular glomerulosclerosis. MSCs find it difficult to dispose of the altered mesangial constituents, an initial step required for mesangial repair to occur successfully. The ability of MSCs to repair damaged mesangium represents a novel therapeutic intervention to reverse mesangial injury and is potentially a powerful and unique approach to prevent progression ending in end-stage renal disease (ESRD). This review will highlight progress that has been made in glomerular, and more specifically mesangial, repair, and will address future expectations and challenges to be confronted as the use of MSCs continues to be explored as a potential application for clinical practice.

Paraprotein-Related Kidney Disease: Kidney Injury from Paraproteins-What Determines the Site of Injury?

Disorders of plasma and B cells leading to paraproteinemias are associated with a variety of renal diseases. Understanding the mechanisms of injury and associated nephropathies provides a framework that aids clinicians in prompt diagnosis and appropriate adjunctive treatment of these disorders. Glomerular diseases that may be associated with paraproteinemias include amyloid deposition, monoclonal Ig deposition disease, proliferative GN with monoclonal Ig deposits, C3 glomerulopathy caused by alterations in the complement pathway, immunotactoid glomerulopathy, fibrillary GN, and cryoglobulinemia. Tubular lesions include the classic Fanconi syndrome, light-chain proximal tubulopathy, interstitial fibrosis, and cast nephropathy. These paraproteinemic renal diseases are distinct in their pathogenesis as well as their urinary and kidney biopsy findings. Renal pathology is usually initiated by deposition and direct involvement of the intact monoclonal Ig or Ig fragments with resident cells of the nephron. Our review summarizes current insights into the underlying molecular pathogenesis of these interesting kidney lesions.

Animal Models of Light Chain Deposition Disease Provide a Better Understanding of Nodular Glomerulosclerosis

BACKGROUND

Light chain deposition disease (LCDD) is a model of glomerulosclerosis. The mature lesion of LCDD mimics nodular glomerulosclerosis in diabetic nephropathy. The pathogenetic mechanisms involved are similar in both disorders, though the causative factors are entirely different. This fact highlights the generic response of the mesangium to varied stimuli. In-vitro work has provided much insight into the pathogenesis of glomerulosclerosis in LCDD where the mesangium is the main target for initiation and progression of the disease. The lack of animal models has prevented the development of further therapeutic approaches to be tested in platforms such as ex-vivo and in-vivo preparing the way for human studies.

METHODS

Light chains (LCs) obtained from the urine of patients with renal biopsy proven LCDD were delivered to glomeruli using ex-vivo and in-vivo approaches to address whether in-vitro information could be validated in-vivo. Selected in-vitro studies were conducted to address specific issues dealing with mesangial cell (MC) differentiation and composition of extracellular matrix to add additional data to the existing vast literature. Using light, electron and scanning microscopy together with immunohistochemistry and ultrastructural immunolabeling, MCs incubated in Matrigel with LCDD LCs, as well as delivery of such LCs by perfusion via renal artery (ex-vivo) and penile dorsal vein (in-vivo) to the kidneys, validation of pathogenetic pathways previously suggested in in-vitro experiments were tested and confirmed.

RESULTS

The animal models described in this manuscript provide validation for the in-vitro data that have been previously published and expand our appreciation of the important role that caveolin-1 plays in signaling events essential for the downstream sequence of events that eventually leads to the pathological alterations centered in the mesangium characterized by an increase in matrix production and formation of mesangial nodules.

CONCLUSIONS

The same findings observed in renal biopsies of patients with LCDD (mesangial expansion with increased matrix) were documented in the ex-vivo and in-vivo platforms. In-vivo understanding of the pathogenesis of mesangial glomerulosclerosis, as accomplished in the reported research, is crucial for the design of novel therapeutic approaches to treat a number of glomerulopathies with similar pathogenetic mechanisms. Inhibiting interactions between glomerulopathic LCs and MCs or interrupting the protein production/secretion pathways are potentially effective therapeutic maneuvers. The results obtained with caveolin-1 knockout mice emphasized the importance of caveolin-1 in signaling events essential to effect downstream mesangial alterations.

A mouse model recapitulating human monoclonal heavy chain deposition disease evidences the relevance of proteasome inhibitor therapy

Randall-type heavy chain deposition disease (HCDD) is a rare disorder characterized by glomerular and peritubular amorphous deposits of a truncated monoclonal immunoglobulin heavy chain (HC) bearing a deletion of the first constant domain (CH1). We created a transgenic mouse model of HCDD using targeted insertion in the immunoglobulin κ locus of a human HC extracted from a HCDD patient. Our strategy allows the efficient expression of the human HC in mouse B and plasma cells, and conditional deletion of the CH1 domain reproduces the major event underlying HCDD. We show that the deletion of the CH1 domain dramatically reduced serum HC levels. Strikingly, even with very low serum level of truncated monoclonal HC, histologic studies revealed typical Randall-type renal lesions that were absent in mice expressing the complete human HC. Bortezomib-based treatment resulted in a strong decrease of renal deposits. We further demonstrated that this efficient response to proteasome inhibitors mostly relies on the presence of the isolated truncated HC that sensitizes plasma cells to bortezomib through an elevated unfolded protein response (UPR). This new transgenic model of HCDD efficiently recapitulates the pathophysiologic features of the disease and demonstrates that the renal damage in HCDD relies on the production of an isolated truncated HC, which, in the absence of a LC partner, displays a high propensity to aggregate even at very low concentration. It also brings new insights into the efficacy of proteasome inhibitor-based therapy in this pathology.

Renal lesions associated with plasma cell dyscrasias: practical approach to diagnosis, new concepts, and challenges

CONTEXT

Patients with plasma cell dyscrasias (myeloma) may exhibit a variety of renal manifestations as a result of damage from circulating light- and heavy-chain immunoglobulin components produced by the neoplastic plasma cells. The renal alterations can occur in any of the renal compartments, and in a significant number of the cases more than one compartment is affected. Research in the laboratory has helped considerably in providing a solid conceptual understanding of how renal damage occurs.

OBJECTIVES

To detail advances that have been made in the diagnosis of these conditions and to provide an account of research accomplishments that have solidified diagnostic criteria. The new knowledge that has been acquired serves to provide a solid platform for the future design of new therapeutic interventions aimed at ameliorating or abolishing the progressive renal damage that typically takes place.

DATA SOURCES

Translational efforts have substantially contributed to elucidate mechanistically the molecular events responsible for the renal damage. The spectrum of renal manifestations associated with plasma cell dyscrasias has expanded significantly in the last 10 years. Diagnostic criteria have also been refined. This information has been summarized from work done at several institutions.

CONCLUSIONS

A number of significant challenges remain in the diagnosis of these conditions, some of which will be discussed in this article. Dealing with these challenges will require additional translational efforts and close cooperation between basic researchers, clinicians, and pathologists in order to improve the diagnostic tools available to renal pathologists and to acquire a more complete understanding of clinical and pathologic manifestations associated with these conditions.

Salt: its role in chronic kidney disease

Few controversies in medicine have such a long history as that of whether salt is identifiably dangerous or not dangerous. The most common reported association between excess dietary salt intake and clinical outcome has been in the field of hypertension, but dietary sodium intake mediates effects that go far beyond, and are independent of, extracellular fluid expansion and elevation in blood pressure. For nephrologists, clinical trials that demonstrate no negative outcome of a high salt diet in the general population are thus not particularly assuasive, because patients with chronic kidney disease (CKD) represent an entity that is by no means comparable to the general population. This review takes a look at the challenges associated with salt balance in CKD patients (particularly at K/DOQI stage 5), followed by a summary of current concepts believed to play a part in salt-mediated pathophysiology, and the conclusion, based on the present state of scientific knowledge, that it appears advisable to advocate low dietary salt intake in this patient population.

Role of translational research advancing the understanding of the pathogenesis of light chain-mediated glomerulopathies

Glomerulopathic light chains engage in pathological interactions with mesangial cells resulting in alterations in glomerular homeostasis. The crucial pathological events are centered in the mesangium and, therefore, research dealing with pathogenesis of these disorders is focused on this glomerular compartment. Particular physicochemical characteristics of these light chains are responsible for their ability to alter mesangial milieu leading to glomerular damage. An in vitro model has been used to dissect the processes involved. This model has been instrumental in providing a solid platform from which to observe in a dynamic fashion how mesangial cells handle pathogenic light chains and the sequential steps that are involved in the progressive glomerular damage. Key steps amenable to possible modulation have been defined and should provide a solid platform to design and test therapeutic interventions. In the past significant difficulties have been encountered in the development of animal models of light chain-induced glomerular damage. However, in the last few years a new generation of animal models has emerged to address whether what has been documented in vitro retains significance in vivo. Preliminary observations appear to substantiate this.

Expression of basic fibroblast growth factor in rat liver fibrosis and hepatic stellate cells

The expression of basic fibroblast growth factor (bFGF) in rat liver fibrosis and hepatic stellate cells (HSCs) and the relationship between the expression of bFGF and rat liver fibrogenesis were studied. Sixty male SD rats (230-260 g) were divided into 4 groups randomly (the 0 week group, 1 week group, 4 week group and 8 week group). Liver fibrosis was induced by subcutaneous injection of carbon tetrachloride. The sections of rats' liver in each group were tested by Van-Gieson (V-G) staining and immunohistochemistry. The expression of bFGF mRNA was detected by reverse transcription polymerase chain reaction (RT-PCR). HSCs were isolated by the combined methods of collagenase IV perfusion and density gradient centrifugation. The expression of bFGF protein in cultured HSCs was detected by Western blot. Images of immunohistochemistry detection, agarose gel electrophoresis of RT-PCR and SDS-polyacrylamide gel electrophoresis of Western blot were analyzed semiquantitatively by image-analyzing system. The results were analyzed by statistics. The results showed that the fibers were gradually increased in the sections of rat liver with the prolongation of the model induction. At the end of the 8th weeks, liver fibrosis was formed. The expression of bFGF detected by immunohistochemistry showed a similar tendency of gradual increase. At the end of the 8th weeks, the bFGF expression could be observed in many regions in sections and the strongest expression was in interstitial cells including HSCs and some hepatocytes in regions around the portal area and central veins. Also there was moderate expression widely in extracellular matrix (ECM). In RT-PCR detection and Western blot detection of HSCs cultured in vitro, the similar tendency of gradual increase was evident either. It is suggested that bFGF is related with liver fibrosis of rats closely and may be a fibrogenesis factor of liver. bFGF possibly regulates liver fibrogenesis through regulating metabolism of extracellular matrix (ECM) by autocrine and paracrine stimulation.

Salt intake, endothelial cell signaling, and progression of kidney disease

It has been known for decades that increased dietary intake of salt (NaCl) shortens the life span of rats in a dose-dependent fashion. This review focuses specifically on the recently described biological effect and consequences of increased salt ingestion on the endothelium through a mechanism that is independent of blood pressure. Changes in salt intake are recognized by endothelial cells in the vascular tree and glomeruli through a physical process that promotes a series of signaling events involved in transcriptional regulation of genes that include transforming growth factor-beta1 (TGF-beta1) and the endothelial isoform of nitric oxide synthase (NOS3). A balance is struck between TGF-beta1 and NOS3 as salt intake varies and creates a negative feedback loop, because TGF-beta1 increased expression of NOS3 and NO inhibited production of TGF-beta1 in healthy rats. Changes in this feedback system have been observed in salt-sensitive hypertension and appear to impact end-organ damage, particularly the kidney. The data support an important benefit to reduction of salt intake in the setting of chronic kidney disease.

Renal monoclonal immunoglobulin deposition disease: the disease spectrum

This study reports the clinicopathologic findings and outcome in 34 patients with renal monoclonal immunoglobulin deposition disease (MIDD), which included 23 light-chain DD (LCDD), 5 light- and heavy-chain DD (LHCDD), and 6 heavy-chain DD (HCDD). A total of 23 patients had pure MIDD, whereas 11 patients had LCDD with coexistent myeloma cast nephropathy (LCDD & MCN). Renal biopsy diagnosis preceded clinical evidence of dysproteinemia in 68% of all cases. By immunofluorescence, the composition of deposits included 11kappa/1lambda (LCDD), 3IgGkappa/2IgGlambda (LHCDD), 5gamma/1alpha (HCDD), and 10kappa/1lambda (LCDD & MCN). Patients with pure MIDD presented with mean serum creatinine of 4.2 mg/dl, nephrotic proteinuria, and hypertension. Cases of HCDD were associated with a CH1 deletion and frequently had hypocomplementemia and a positive hepatitis C virus antibody but negative hepatitis C virus PCR. LCDD & MCN is a morphologically and clinically distinct entity from pure MIDD, presenting with higher creatinine (mean, 7.8 mg/dl; P = 0.01), greater dialysis dependence (64 versus 26%; P = 0.053), subnephrotic proteinuria, and less nodular glomerulopathy (18 versus 100%; P < 0.0001). Multiple myeloma was more frequently diagnosed in LCDD & MCN than in pure MIDD (91 versus 31%; P = 0.025). Renal and patient survivals were significantly worse in patients with LCDD & MCN (mean, 4 and 22 mo, respectively), compared with patients with pure MIDD (mean, 22 and 54 mo). Chemotherapy stabilized or improved renal function in 10 of 15 patients (67%) with pure MIDD who presented with creatinine of <5.0 mg/dl, emphasizing the importance of early detection. On multivariate analysis, initial creatinine was the only predictor of renal and patient survival in pure MIDD, underscoring the prognostic significance of the renal involvement.

Monoclonal light chain--mesangial cell interactions: early signaling events and subsequent pathologic effects

Glomerulopathic monoclonal light chains (G-LC) interact with mesangial cells (MC), resulting in alterations of mesangial homeostasis. Early signaling events control mitogenic activities and cytokine production, which in turn participate in the subsequent pathologic events. Mesangial homeostasis is affected in two very different ways, depending on whether the G-LC is from a patient with light chain deposition disease (LCDD) or light chain-related amyloidosis (AL-Am). In contrast, tubulopathic (T)-LC chains from patients with myeloma cast nephropathy do not significantly interact with MC and result in no alterations in mesangial homeostasis. Therefore, understanding early events in the monoclonal LC-MC interactions is fundamental. MC in culture were exposed to LC obtained and purified from the urine of patients with plasma cell dyscrasias and biopsy-proven renal disease, including LCDD, AL-Am, and myeloma cast nephropathy. Incubation of MC with G-LC, but not T-LC, resulted in cytoskeletal and cell shape changes, activation of platelet-derived growth factor-beta (PDGF-beta) and its corresponding receptor, cytoplasmic to nuclear migration of c-fos and NF-kappa beta signals, and production of monocyte chemoattractant protein-1 (MCP-1), as well as increased expression of Ki-67, a proliferation marker. Although NF-kappa beta activation was directly related to MCP-1 production, c-fos activation regulated proliferative signals and cytoskeletal changes in MC. Amyloidogenic LC were avidly internalized by the MC, whereas LCDD-LC effector targets were located at the MC surface. These cellular events are likely initiated as a result of interactions of the G-LC with yet-uncharacterized MC surface receptors. Dissecting the events taking place when G-LC interact with MC may define potential important targets for selective therapeutic manipulation to ameliorate or prevent the glomerular injury that ensues.

Renal manifestations of plasma cell dyscrasias: an appraisal from the patients' bedside to the research laboratory

One of the most prominent features of plasma cell dyscrasias is the frequent occurrence of renal dysfunction. Renal insufficiency is a common finding with elevated serum creatinine in more than 50% of patients with multiple myeloma at the time of diagnosis. Renal failure is the second most common cause of death in myeloma surpassed only by infections. The reasons for renal failure are multifactorial and early accurate diagnosis of the renal alterations may significantly impact morbidity and survival. Renal failure may result from selective glomerular, tubular interstitial, or vascular pathology or from a combination of pathologic events. The disorders associated with plasma cell dyscrasias include those characterized by monoclonal light chain deposition, encompassing AL-amyloidosis, in addition to the less well-characterized entities, such as heavy chain deposition disease and heavy chain amyloidosis. Therefore, it is more accurate to refer to them as monoclonal immunoglobulin deposition diseases. Staining of renal biopsy specimens for kappa and lambda light chains using immunofluorescence techniques and more sophisticated advanced diagnostic techniques such as immunoelectron microscopy permit detailed characterization of the various renal pathologic manifestations. Renal biopsies can identify monoclonal immunoglobulin deposition, and nephrologists have an opportunity to detect an underlying plasma cell dyscrasia early in its clinical course before overt hematologic alterations become manifest and irreversible renal damage has occurred. The overall spectrum of clinical and pathologic manifestations of monoclonal immunoglobulin deposition renal diseases has expanded considerably in recent years. Recent developments in the research arena promise new therapeutic interventions aimed at avoiding or ameliorating renal damage and even promoting reversal of some of the pathologic alterations. Currently, the 5-year survival rate in myeloma is 29% in white patients and 30% in African-American patients, a rather modest improvement from 24% in the 1970s. Bone marrow ablation followed by transplantation is available as an alternative mode of therapy that may be extraordinarily helpful in a subset of patients with early myeloma.

In vitro modulation of AL-amyloid formation by human mesangial cells exposed to amyloidogenic light chains

We have shown in vitro AL-amyloid formation by human mesangial cells (HMCs). AL-amyloid formation may require lysosomal processing of the light chains (LCs) by HMCs for amyloidogenesis to occur. Chloroquine inhibits lysosomal activity. TGF-beta mediates extracellular matrix formation in many glomerulopathies. Thrombospondin (TSP) has been proposed as a mediator of cell proliferation and a marker of early fibrosis. We investigated amyloid formation by HMCs exposed to AL-LCs in the absence of amyloid enhancing factor (AEF). The effects of TGF-beta, TSP and chloroquine on in vitro amyloid formation were studied. HMCs were incubated with two AL-LCs, a light chain deposition disease (LCDD)-LC, or one of two tubulopathic LCs (T-LCs). Additional cells were treated with an AL-LC and chloroquine, TGF-beta, or TSP. Amyloid formation was evaluated microscopically using hematoxylin and eosin, Congo red and Thioflavin-T stains, as well as ultrastructurally. Amyloid was formed only when HMCs were incubated with AL-LCs. Addition of TSP significantly enhanced amyloid formation. In contrast, exogenous TGF-beta and chloroquine significantly attenuated amyloid formation. These findings show that some AL-LCs do not require AEF for amyloidogenesis to occur, and that chloroquine, TGF-beta and sTSP modulate in vitro AL-amyloidosis.

Fibronectin synthesis by human tubular epithelial cells in culture: effects of PDGF and TGF-beta on synthesis and splicing

BACKGROUND

Enhanced synthesis of extracellular matrix proteins including fibronectin (FN) is associated with the development of sclerosis. In this context we studied FN synthesis by tubular epithelial cells in response to transforming growth factor-beta (TGF-beta) and platelet-derived growth factor (PDGF).

METHODS

FN protein synthesis by human tubular epithelial cells in culture (TEC) was measured by biosynthetic labeling and ELISA. Splicing of FN was assessed by RT-PCR and by Northern blotting.

RESULTS

Cultivated TEC synthesized and released FN, the majority of which was deposited as an unsoluble protein and a minor portion (10 to 15%) was released into the supernatant. TGF-beta and, to a lesser degree, PDGF, up-regulated FN synthesis. All three FN splice variants (EDA, EDB, and IIICS) were produced. PDGF did not influence the splicing. TGF-beta preferentially up-regulated the EDA splice variant, but had no effect on the splicing of the other domains.

CONCLUSIONS

PDGF and TGF-beta both up-regulate FN synthesis of TEC. TGF-beta, but not PDGF, also changed the quality of the de novo synthesized FN, and thus has a different role in the development of sclerosis.

Dietary salt modulates renal production of transforming growth factor-beta in rats

Transforming growth factors (TGF) are potent multifunctional polypeptides that are involved in renal function and glomerular sclerosis. We postulated that dietary salt modified renal production of TGF-beta. An increase in dietary salt produced sustained increases in steady-state levels of mRNA for TGF-beta 1, -beta 2, and -beta 3 in the rat kidney. While serum concentration of TGF-beta 1 did not change, the 8.0% NaCl diet increased urinary excretion of TGF-beta 1, indicating enhanced renal production was the source of TGF-beta 1. Increasing urinary flow rates with diuretics did not further increase synthesis of TGF-beta 1 in animals receiving the 8.0% NaCl diet. The 8.0% NaCl diet increased production of TGF-beta 1 in both glomeruli and tubules, although active TGF-beta 1 was secreted in greater amounts only from glomeruli. Enhanced glomerular production of both inactive and active TGF-beta 1 induced by the 8.0% NaCl diet was inhibited by tetraethylammonium (TEA) and not glybenclamide. Cardiac production of TGF-beta 1 also increased on the 8.0% NaCl diet but was not affected by TEA. The results demonstrated that increased dietary salt augmented glomerular TGF-beta production by a mechanism that included a TEA-sensitive potassium channel. Dietary salt, by facilitating glomerular expression of TGF-beta, may directly promote development of glomerulosclerosis.

Demonstration of the proliferation marker Ki-67 in renal biopsies: correlation to clinical findings

Assessment of cell proliferation in renal biopsy samples is a potentially promising analytical tool to evaluate disease activity. So far no information is available on the correlation between proliferative activity in different anatomic compartments of the kidney and clinical symptoms. To elucidate this issue, we examined renal biopsy specimens from 20 patients with systemic vasculitis (15 Wegener's granulomatosis, five microscopic polyangiitis), 20 patients with immunoglobulin (Ig) A nephropathy (IgAN), 13 patients with minimal-change disease (MCD), 11 patients with tubulointerstitial nephritis, and five patients with diabetes mellitus. The streptavidin-biotin-peroxidase complex technique was applied to autoclave-pretreated, formalin-fixed, paraffin-embedded tissue sections to label different cell types with the antibody MIB1 directed against the Ki-67 antigen. Proliferation index (PI) was estimated as the number of positively stained nuclei per glomerular cross-section or per square millimeter section area. The interstitial cells were discriminated by additional staining of Ki-67-processed samples with specific immune markers. In patients with vasculitis, PI was considerably elevated in the extracapillary glomerular compartment (0.86), in proximal tubules (6.24), and in the interstitium (8.62). High proliferative activity was also noted in interstitium (3.98) and proximal tubules (1.35) of patients with IgAN. Of particular interest was the increased interstitial proliferative activity (15.0) in diabetic patients. Resident renal cells, but not infiltrating cells, seemed to constitute the majority of the proliferating cell population in the interstitium. In systemic vasculitis, clinical disease activity was significantly correlated to endocapillary (r(s) = 0.58), extracapillary (r(s) = 0.67), proximal tubular (r(s) = 0.67), and interstitial PI (r(s) = 0.61). By multiple linear regression analysis, proximal tubular PI was correlated to the presence of hematuria (beta = 0.72) and to interstitial fibrosis score (beta = 0.59). Interstitial PI was independently correlated to antineutrophil cytoplasmic antibodies (ANCA) titer (beta = 0.7) and interstitial fibrosis score (beta = 0.55), and it was the only one PI correlated to serum creatinine concentration (beta = 0.53). The independent association between interstitial PI and serum creatinine (beta = 0.64) was also found in IgAN. Proximal tubular PI was correlated to interstitial fibrosis score (beta = 0.59) and proteinuria (beta = 0.54). In MCD, high PI values were noted in proximal tubular cells (1.42) but not in glomeruli and the interstitium. In conclusion, assessment of proliferation activity by immunohistology provides additional information beyond conventional pathological techniques to evaluate disease activity and prognosis in renal biopsies.

Immunolocalization of acidic fibroblast growth factor and receptors in the tubulointerstitial compartment of chronically rejected human renal allografts

Tubular damage and loss associated with interstitial inflammation and fibrosis may be the most important determinants in chronic renal allograft rejection. To elucidate potential pathophysiologic mechanisms associated with tubulointerstitial lesions, we examined the expression of a fibrogenic cytokine, acidic fibroblast growth factor (FGF-1) and its high-affinity receptors, in both relevant renal transplant controls (n=5) and tissue from patients (n=19) who underwent nephrectomy after graft loss, secondary to chronic rejection. In situ hybridization and immunohistochemical analyses demonstrated minimal expression of FGF-1 mRNA and protein in the tubulointerstitial compartment of the normal human kidney. In contrast, tubulointerstitial lesions in kidney allografts experiencing chronic rejection demonstrated the exaggerated appearance of both FGF-1 protein and mRNA in resident inflammatory and tubular epithelial cells. Patterns of staining were consistent throughout tubular compartments and did not appear to be localized to any particular region. The tubulointerstitium in kidneys with findings of chronic rejection also exhibited increased immunodetection of proliferating cell nuclear antigen in the tubular epithelium, inflammatory cell infiltrate, and neovascular structures. The enhanced appearance of FGF-1 and readily detectable fibroblast growth factor receptors suggests that this polypeptide mitogen may serve as an important mediator of growth and repair responses, associated with development of angiogenesis and tubulointerstitial lesions during chronic rejection of human renal allografts.

Biology and therapy of immunoglobulin deposition diseases

All forms of MIDD represent pathologic deposition of immunoglobulin as amorphous casts, crystals, congophilic fibrils (in AL amyloid), or punctate noncongophilic deposits (in LCDD/HCDD/LHCDD). Diagnosis is based on identification and immunohistochemical characterization of deposits and Congo red staining. Current information including development of novel in vitro and in vivo models suggests a contributory role of both protein and host factors in the pathogenesis of these disorders. In particular, primary structural features of the VL portions of the light chain molecule may affect not only the extent but also the morphologic type of protein deposits. Thus, certain types of light chains may be particularly pathogenic, although the nature or extent of proteolysis/processing involved in the pathogenesis of these deposits is yet unclear. Recent data also point to the importance of accessory molecules, cytokines, and host factors in this process. Newer therapeutic approaches using high-dose therapy with cytotoxic agents or dexamethasone appear promising, although these data need to be confirmed in a larger number of patients. The serendipitous discovery of I-DOX as an agent capable of promoting amyloid resorption provides another novel approach in patients with AL amyloidosis. Continued research on the mechanisms of deposition and resorption of these immunoglobulin deposits should provide important information that can be used to design strategies for more effective therapy and, ultimately, prevention of MIDD.

Immunolocalization of FGF-1 and receptors in glomerular lesions associated with chronic human renal allograft rejection

Glomerular lesions are considered one of the more detrimental pathologic changes associated with chronic rejection of renal allografts. To elucidate potential pathophysiologic mechanisms associated with transplant glomerulopathy, we examined the expression of acidic fibroblast growth factor (FGF-1) and its high-affinity receptors (FGFR) in both relevant renal transplant controls (n=5) and tissue from patients (n=19) who underwent nephrectomy following graft loss secondary to chronic rejection. In situ immunohistochemical analyses demonstrated minimal staining and distribution of FGFR and FGF-1, which was localized to the mesangial matrix in glomeruli from normal human kidneys. In situ hybridization failed to detect the presence of FGF-1 mRNA in control tissue. In contrast, each stage of the developing glomerular lesion associated with chronic rejection demonstrated the exaggerated appearance of FGF-1 protein in visceral and parietal epithelial cells. Intense staining for FGF-1 protein did not correlate with the increased appearance of FGF-1 mRNA, which was restricted to circulating inflammatory cells. Glomeruli in kidneys with findings of chronic rejection also exhibited increased immunodetection of both FGFR and PCNA in mesangial and epithelial cells. Immunogold labeling of chronically rejected visceral epithelial cells revealed both cytoplasmic and nuclear/localization of FGF-1, thereby establishing mitogenic potential of the growth factor. The enhanced appearance of both biologically active FGF-1 and FGFR suggests that this polypeptide may serve as an important mediator of growth responses associated with glomerular lesion development during chronic rejection.