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

Renal amyloidosis: Pathogenesis

For many years amyloidosis was considered an extremely rare, somewhat mysterious disease. However, in the last 2-3 decades its pathogenesis, particularly that of renal amyloidosis has been carefully dissected in the research laboratory using in-vitro and, to a lesser extent, in-vivo models. These have provided a molecular understanding of sequential events that take place in the renal mesangium leading to the formation of amyloid fibrils and eventual extrusion into the mesangial matrix, which itself becomes seriously damaged and, in due time, replaced by the fibrillary material. Amyloid, once considered to be an "inert" substance, has been proven to be involved in crucial biological processes that result in the destruction and eventual replacement of normal renal constituents. This review centers on mechanisms involved in the renal glomerular amyloidosis to understand its pathogenesis.

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.

Phenotypic plasticity of mesenchymal stem cells is crucial for mesangial repair in a model of immunoglobulin light chain-associated mesangial damage

Mesangiopathies produced by glomerulopathic monoclonal immunoglobulin light chains (GLCs) acting on the glomerular mesangium produce two characteristic lesions: AL-amyloidosis (AL-Am) and light chain deposition disease (LCDD). In both cases, the pathology is centered in the mesangium, where initial and progressive damage occurs. In AL-Am the mesangial matrix is destroyed and replaced by amyloid fibrils and in LCDD, the mesangial matrix is increased and remodeled. The collagen IV rich matrix is replaced by tenascin. In both conditions, mesangial cells (MCs) become apoptotic as a direct effect of the GLCs. MCs were incubated in-vitro with GLCs and animal kidneys were perfused ex-vivo via the renal artery with GLCs, producing expected lesions, and then mesenchymal stem cells (MSCs) were added to both platforms. Each of the two platforms provided unique information that when put together created a comprehensive evaluation of the processes involved. A "cocktail" with growth and differentiating factors was used to study its effect on mesangial repair. MSCs displayed remarkable phenotypic plasticity during the repair process. The first role of the MSCs after migrating to the affected areas was to dispose of the amyloid fibrils (in AL-Am), the altered mesangial matrix (in LCDD) and apoptotic MCs/debris. To accomplish this task, MSCs transformed into facultative macrophages acquiring an abundance of lysosomes and endocytotic capabilities required to engage in phagocytic functions. Once the mesangial cleaning was completed, MSCs transformed into functional MCs restoring the mesangium to normal. "Cocktail" made the repair process more efficient.

Light chain amyloidosis: Where are the light chains from and how they play their pathogenic role?

Amyloid light-chain (AL) amyloidosis is a plasma-cell dyscrasia, as well as the most common type of systematic amyloidosis. Pathogenic plasma cells that have distinct cytogenetic and molecular properties secrete an excess amount of amyloidogenic light chains. Assisted by post-translational modifications, matrix components, and other environmental factors, these light chains undergo a conformational change that triggers the formation of amyloid fibrils that overrides the extracellular protein quality control system. Moreover, the amyloidogenic light-chain itself is cytotoxic. As a consequence, organ dysfunction is caused by both organ architecture disruption and the direct cytotoxic effect of amyloidogenic light chains. Here, we reviewed the molecular mechanisms underlying this sequence of events that ultimately leads to AL amyloidosis and also discuss current in vitro and in vivo models, as well as relevant novel therapeutic approaches.

Bronchoscopic Diagnosis and Treatment of Primary Tracheobronchial Amyloidosis: A Retrospective Analysis from China

Objective. To assess the value of bronchoscopy in the diagnosis and treatment of primary tracheobronchial amyloidosis (TBA), in order to reduce misdiagnosis rates and improve prognosis. Methods. Clinical data of 107 patients with TBA reported from 1981 to 2015 in China were retrospectively analyzed for clinical features, bronchoscopic manifestations, pathologies, treatments, and outcomes. Results. 105 of 107 TBA patients were pathologically confirmed by bronchoscopy. Main bronchoscopic manifestations of TBA were single or multiple nodules and masses within tracheobronchial lumens; local or diffuse luminal stenosis and obstruction; luminal wall thickening and rigidity; rough or uneven inner luminal walls; congestion and edema of mucosa, which was friable and prone to bleeding upon touch; and so forth. 53 patients were treated with bronchoscopic interventions, like Nd-YAG laser, high-frequency electrotome cautery, freezing, resection, clamping, argon plasma coagulation (APC), microwaving, stent implantation, drug spraying, and other treatments. 51 patients improved, 1 patient worsened, and 1 died. Conclusion. Bronchoscopic biopsy is the primary means of diagnosing TBA. A variety of bronchoscopic interventions have good short-term effects on TBA. Bronchoscopy has important value in the diagnosis, severity assessment, treatment, efficacy evaluation, and prognosis of TBA.

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: Glomerular Diseases Associated with Paraproteinemias

Paraproteins are monoclonal Igs that accumulate in blood as a result of abnormal excess production. These circulating proteins cause a diversity of kidney disorders that are increasingly being comanaged by nephrologists. In this review, we discuss paraprotein-related diseases that affect the glomerulus. We provide a broad overview of diseases characterized by nonorganized deposits, such as monoclonal Ig deposition disease (MIDD), proliferative GN with monoclonal Ig deposits (PGNMID), and C3 glomerulopathy, as well as those characterized by organized deposits, such as amyloidosis, immunotactoid glomerulopathy, fibrillary GN, and cryoglobulinemic GN, and rarer disorders, such as monoclonal crystalline glomerulopathies, paraprotein-related thrombotic microangiopathies, and membranous-like glomerulopathy with masked IgGκ deposits. This review will provide the nephrologist with an up to date understanding of these entities and highlight the areas of deficit in evidence and future lines of research.

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.

Proximal tubulopathies associated with monoclonal light chains: the spectrum of clinicopathologic manifestations and molecular pathogenesis

CONTEXT

Lesions associated with monoclonal light and heavy chains display a variety of glomerular, tubular interstitial, and vascular manifestations. While some of the entities are well recognized, including light and heavy chain deposition diseases, AL (light chain) and AH (heavy chain) amyloidosis, and light chain ("myeloma") cast nephropathy, other lesions centered on proximal tubules are much less accurately identified, properly diagnosed, and adequately understood in terms of pathogenesis and molecular mechanisms involved. These proximal tubule-centered lesions are typically associated with monoclonal light chains and have not been reported in patients with circulating monoclonal heavy chains.

OBJECTIVE

To determine the incidence of proximal tubulopathies in a series of patients with monoclonal light chain-related renal lesions and characterize them with an emphasis on clinical correlations and elucidation of molecular mechanisms involved in their pathogenesis.

DESIGN

A study of 5410 renal biopsies with careful evaluation of light microscopic, immunofluorescence, and electron microscopic findings was conducted to identify these monoclonal light/heavy chain-related lesions. In selected cases, ultrastructural immunolabeling was performed to better illustrate and understand molecular mechanisms involved or to resolve specific diagnostic difficulties.

RESULTS

In all, 2.5% of the biopsies were diagnosed as demonstrating renal pathology associated with monoclonal light or heavy chains. Of these, approximately 46% were classified as proximal tubule-centered lesions, also referred to as monoclonal light chain-associated proximal tubulopathies. These proximal tubulopathies were divided into 4 groups defined by characteristic immunomorphologic manifestations associated with specific clinical settings.

CONCLUSIONS

These are important lesions whose recognition in the different clinical settings is extremely important for patients' clinical management, therapeutic purposes, and prognosis. These entities have been segregated into 4 distinct variants, conceptualized morphologically and clinically. Specific mechanisms involved in their pathogenesis are proposed.

Renal Amyloidosis

Amyloidosis is an uncommon group of diseases in which soluble proteins aggregate and deposit extracellularly in tissue as insoluble fibrils, leading to tissue destruction and progressive organ dysfunction. More than 25 proteins have been identified as amyloid precursor proteins. Amyloid fibrils have a characteristic appearance on ultrastructural examination and generate anomalous colors under polarized light. Amyloidosis can be systemic or localized. The kidney is a prime site for amyloid deposition. Immunofluorescence, immunoperoxidase, and more recently laser microdissection and mass spectrometry are important tools used in the typing of renal amyloidosis.

Renal diseases with organized deposits: an algorithmic approach to classification and clinicopathologic diagnosis

CONTEXT

Most renal diseases with organized deposits are relatively uncommon conditions, and proper pathologic characterization determines the specific diagnosis. Different entities with specific clinical correlates have been recognized, and their correct diagnosis has an impact on patient management, treatment options, and determination of prognosis.

OBJECTIVE

The diagnosis of these conditions depends on careful evaluation of the findings by light microscopy together with immunofluorescence and electron microscopy. The objective of this manuscript is to delineate an algorithmic approach helpful in the pathologic assessment of these conditions at the light microscopic level. In some diseases, the immunomorphologic parameters short of electron microscopy provide solid information to suggest or make a definitive diagnosis. Nevertheless, electron microscopy plays a crucial role, because the criteria to separate these entities often are heavily influenced by the electron microscopic findings. Accepted diagnostic criteria for each of these conditions are discussed.

DESIGN

Information used for this manuscript is gathered from published data and the authors' experience.

RESULTS

The most common of these conditions is amyloidosis, which may account for as many as 5% to 8% of all renal biopsies in some renal pathology practices. Fibrillary, immunotactoid, and cryoglobulinemic glomerulopathies together represent, at most, 1% of all renal biopsies performed for medical renal diseases. Diabetic fibrillosis also is uncommon. Glomerulopathies associated with fibronectin deposits and collagenofibrotic glomerulopathy are extremely rare.

CONCLUSIONS

A systematic, algorithmic approach to the evaluation of the renal biopsies from patients with these disorders is very helpful to rule out certain conditions in the early stages of the evaluation of the biopsies. However, it is not uncommon for the final definitive diagnosis to be reached only after electron microscopic evaluation.

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.