Zebrafish model of amyloid light chain cardiotoxicity: regeneration versus degeneration

Mechanisms of damage and therapies for cardiac amyloidosis: a role for inflammation?

The term cardiac amyloidosis (CA) refers to the accumulation of extracellular amyloid deposits in the heart because of different conditions often affecting multiple organs including brain, kidney and liver. Notably, cardiac involvement significantly impacts prognosis of amyloidosis, with cardiac biomarkers playing a pivotal role in prognostic stratification. Therapeutic management poses a challenge due to limited response to conventional heart failure therapies, necessitating targeted approaches aimed at preventing, halting or reversing amyloid deposition. Mechanisms underlying organ damage in CA are multifactorial, involving proteotoxicity, oxidative stress, and mechanical interference. While the role of inflammation in CA remains incompletely understood, emerging evidence suggests its potential contribution to disease progression as well as its utility as a therapeutic target. This review reports on the cardiac involvement in systemic amyloidosis, its prognostic role and how to assess it. Current and emerging therapies will be critically discussed underscoring the need for further efforts aiming at elucidating CA pathophysiology. The emerging evidence suggesting the contribution of inflammation to disease progression and its prognostic role will also be reviewed possibly offering insights into novel therapeutic avenues for CA.

Cardio-Hepatic Interaction in Cardiac Amyloidosis

Background: Congestion is associated with poor prognosis in cardiac amyloidosis (CA). The cardio-hepatic interaction and the prognostic impact of secondary liver affection by cardiac congestion in CA are poorly understood and require further characterisation. Methods: Participants of the amyloidosis cohort study AmyKoS at the Interdisciplinary Amyloidosis Centre of Northern Bavaria with proven transthyretin (ATTR-CA) and light chain CA (AL-CA) underwent serial work-up including laboratory tests, echocardiography, and in-depth hepatic assessment by vibration-controlled transient elastography (VCTE) and 13C-methacetin breath test. Results: In total, 74 patients with AL-CA (n = 17), ATTR-CA (n = 26) and the controls (n = 31) were analysed. ATTR-CA patients showed decreased microsomal liver function expressed by maximal percentage of dose rate (PDRpeak) related to hepatic congestion. Reduced PDRpeak in AL-CA could result from altered pharmacokinetics due to changed hepatic blood flow. Liver stiffness as a combined surrogate of chronic liver damage and congestion was identified as a predictor of all-cause mortality. Statistical modelling of the cardio-hepatic interaction revealed septum thickness, NT-proBNP and PDRpeak as predictors of liver stiffness in both CA subtypes; dilatation of liver veins and the fibrosis score FIB-4 were only significant for ATTR-CA. Conclusions: Non-invasive methods allow us to characterise CA-associated hepatic pathophysiology. Liver stiffness might be promising for risk stratification in CA.

Amyloidogenic light chains impair plasma cell survival

Systemic light chain amyloidosis (AL) is a clonal plasma cell disorder characterized by the deposition of misfolded immunoglobulin light chains (LC) as insoluble fibrils in organs. The lack of suitable models has hindered the investigation of the disease mechanisms. Our aim was to establish AL LC-producing plasma cell lines and use them to investigate the biology of the amyloidogenic clone. We used lentiviral vectors to generate cell lines expressing LC from patients suffering from AL amyloidosis. The AL LC-producing cell lines showed a significant decrease in proliferation, cell cycle arrest, and an increase in apoptosis and autophagy as compared with the multiple myeloma LC-producing cells. According to the results of RNA sequencing the AL LC-producing lines showed higher mitochondrial oxidative stress, and decreased activity of the Myc and cholesterol pathways. The neoplastic behavior of plasma cells is altered by the constitutive expression of amyloidogenic LC causing intracellular toxicity. This observation may explain the disparity in the malignant behavior of the amyloid clone compared to the myeloma clone. These findings should enable future in vitro studies and help delineate the unique cellular pathways of AL, thus expediting the development of specific treatments for patients with this disorder.

Role of the mechanisms for antibody repertoire diversification in monoclonal light chain deposition disorders: when a friend becomes foe

The adaptive immune system of jawed vertebrates generates a highly diverse repertoire of antibodies to meet the antigenic challenges of a constantly evolving biological ecosystem. Most of the diversity is generated by two mechanisms: V(D)J gene recombination and somatic hypermutation (SHM). SHM introduces changes in the variable domain of antibodies, mostly in the regions that form the paratope, yielding antibodies with higher antigen binding affinity. However, antigen recognition is only possible if the antibody folds into a stable functional conformation. Therefore, a key force determining the survival of B cell clones undergoing somatic hypermutation is the ability of the mutated heavy and light chains to efficiently fold and assemble into a functional antibody. The antibody is the structural context where the selection of the somatic mutations occurs, and where both the heavy and light chains benefit from protective mechanisms that counteract the potentially deleterious impact of the changes. However, in patients with monoclonal gammopathies, the proliferating plasma cell clone may overproduce the light chain, which is then secreted into the bloodstream. This places the light chain out of the protective context provided by the quaternary structure of the antibody, increasing the risk of misfolding and aggregation due to destabilizing somatic mutations. Light chain-derived (AL) amyloidosis, light chain deposition disease (LCDD), Fanconi syndrome, and myeloma (cast) nephropathy are a diverse group of diseases derived from the pathologic aggregation of light chains, in which somatic mutations are recognized to play a role. In this review, we address the mechanisms by which somatic mutations promote the misfolding and pathological aggregation of the light chains, with an emphasis on AL amyloidosis. We also analyze the contribution of the variable domain (V_L) gene segments and somatic mutations on light chain cytotoxicity, organ tropism, and structure of the AL fibrils. Finally, we analyze the most recent advances in the development of computational algorithms to predict the role of somatic mutations in the cardiotoxicity of amyloidogenic light chains and discuss the challenges and perspectives that this approach faces.

Understanding AL amyloidosis with a little help from in vivo models

Monoclonal immunoglobulin (Ig) light chain amyloidosis (AL) is a rare but severe disease that may occur when a B or plasma cell clone secretes an excess of free Ig light chains (LCs). Some of these LCs tend to aggregate into organized fibrils with a β-sheet structure, the so-called amyloid fibrils, and deposit into the extracellular compartment of organs, such as the heart or kidneys, causing their dysfunction. Recent findings have confirmed that the core of the amyloid fibrils is constituted by the variable (V) domain of the LCs, but the mechanisms underlying the unfolding and aggregation of this fragment and its deposition are still unclear. Moreover, in addition to the mechanical constraints exerted by the massive accumulation of amyloid fibrils in organs, the direct toxicity of these variable domain LCs, full-length light chains, or primary amyloid precursors (oligomers) seems to play a role in the pathogenesis of the disease. Many in vitro studies have focused on these topics, but the variability of this disease, in which each LC presents unique properties, and the extent and complexity of affected organs make its study in vivo very difficult. Accordingly, several groups have focused on the development of animal models for years, with some encouraging but mostly disappointing results. In this review, we discuss the experimental models that have been used to better understand the unknowns of this pathology with an emphasis on in vivo approaches. We also focus on why reliable AL amyloidosis animal models remain so difficult to obtain and what this tells us about the pathophysiology of the disease.

Molecular Mechanism of Pathogenesis and Treatment Strategies for AL Amyloidosis

In amyloid light-chain (AL) amyloidosis, small B-cell clones (mostly plasma cell clones) present in the bone marrow proliferate and secrete unstable monoclonal free light chains (FLCs), which form amyloid fibrils that deposit in the interstitial tissue, resulting in organ injury and dysfunction. AL amyloidosis progresses much faster than other types of amyloidosis, with a slight delay in diagnosis leading to a marked exacerbation of cardiomyopathy. In some cases, the resulting heart failure is so severe that chemotherapy cannot be administered, and death sometimes occurs within a few months. To date, many clinical studies have focused on therapeutics, especially chemotherapy, to treat this disease. Because it is necessary to promptly lower FLC, the causative protein of amyloid, to achieve a hematological response, various anticancer agents targeting neoplastic plasma cells are used for the treatment of this disease. In addition, many basic studies using human specimens to elucidate the pathophysiology of AL have been conducted. Gene mutations associated with AL, the characteristics of amyloidogenic LC, and the structural specificity of amyloid fibrils have been clarified. Regarding the mechanism of cellular and tissue damage, the mass effect due to amyloid deposition, as well as the toxicity of pre-fibrillar LC, is gradually being elucidated. This review outlines the pathogenesis and treatment strategies for AL amyloidosis with respect to its molecular mechanisms.

Light Chain Stabilization: A Therapeutic Approach to Ameliorate AL Amyloidosis

Non-native immunoglobulin light chain conformations, including aggregates, appear to cause light chain amyloidosis pathology. Despite significant progress in pharmacological eradication of the neoplastic plasma cells that secrete these light chains, in many patients impaired organ function remains. The impairment is apparently due to a subset of resistant plasma cells that continue to secrete misfolding-prone light chains. These light chains are susceptible to the proteolytic cleavage that may enable light chain aggregation. We propose that small molecules that preferentially bind to the natively folded state of full-length light chains could act as pharmacological kinetic stabilizers, protecting light chains against unfolding, proteolysis and aggregation. Although the sequence of the pathological light chain is unique to each patient, fortunately light chains have highly conserved residues that form binding sites for small molecule kinetic stabilizers. We envision that such stabilizers could complement existing and emerging therapies to benefit light chain amyloidosis patients.

Dissecting the Molecular Features of Systemic Light Chain (AL) Amyloidosis: Contributions from Proteomics

Amyloidoses are characterized by aggregation of proteins into highly ordered amyloid fibrils, which deposit in the extracellular space of tissues, leading to organ dysfunction. In AL (amyloid light chain) amyloidosis, the most common form in Western countries, the amyloidogenic precursor is a misfolding-prone immunoglobulin light chain (LC), which, in the systemic form, is produced in excess by a plasma cell clone and transported to target organs though blood. Due to the primary role that proteins play in the pathogenesis of amyloidoses, mass spectrometry (MS)-based proteomic studies have gained an established position in the clinical management and research of these diseases. In AL amyloidosis, in particular, proteomics has provided important contributions for characterizing the precursor light chain, the composition of the amyloid deposits and the mechanisms of proteotoxicity in target organ cells and experimental models of disease. This review will provide an overview of the major achievements of proteomic studies in AL amyloidosis, with a presentation of the most recent acquisitions and a critical discussion of open issues and ongoing trends.

Future Perspectives

Opportunities and challenges in the field of systemic amyloidosis can be grouped into 4 categories. First, a deeper understanding of the pathogenesis of the disease is required. Second, a greater awareness of the disease, which will lead to an earlier diagnosis, is imperative. Third, end points for interventional trials are required to convey us to our fourth aspirations, which are novel therapies for patients with light chain amyloidosis.

Preclinical Models of Cancer Therapy-Associated Cardiovascular Toxicity: A Scientific Statement From the American Heart Association

Although cardiovascular toxicity from traditional chemotherapies has been well recognized for decades, the recent explosion of effective novel targeted cancer therapies with cardiovascular sequelae has driven the emergence of cardio-oncology as a new clinical and research field. Cardiovascular toxicity associated with cancer therapy can manifest as a broad range of potentially life-threatening complications, including heart failure, arrhythmia, myocarditis, and vascular events. Beyond toxicology, the intersection of cancer and heart disease has blossomed to include discovery of genetic and environmental risk factors that predispose to both. There is a pressing need to understand the underlying molecular mechanisms of cardiovascular toxicity to improve outcomes in patients with cancer. Preclinical cardiovascular models, ranging from cellular assays to large animals, serve as the foundation for mechanistic studies, with the ultimate goal of identifying biologically sound biomarkers and cardioprotective therapies that allow the optimal use of cancer treatments while minimizing toxicities. Given that novel cancer therapies target specific pathways integral to normal cardiovascular homeostasis, a better mechanistic understanding of toxicity may provide insights into fundamental pathways that lead to cardiovascular disease when dysregulated. The goal of this scientific statement is to summarize the strengths and weaknesses of preclinical models of cancer therapy-associated cardiovascular toxicity, to highlight overlapping mechanisms driving cancer and cardiovascular disease, and to discuss opportunities to leverage cardio-oncology models to address important mechanistic questions relevant to all patients with cardiovascular disease, including those with and without cancer.

Caenorhabditis elegans Models to Investigate the Mechanisms Underlying Tau Toxicity in Tauopathies

The understanding of the genetic, biochemical, and structural determinants underlying tau aggregation is pivotal in the elucidation of the pathogenic process driving tauopathies and the design of effective therapies. Relevant information on the molecular basis of human neurodegeneration in vivo can be obtained using the nematode Caenorhabditis elegans (C. elegans). To this end, two main approaches can be applied: the overexpression of genes/proteins leading to neuronal dysfunction and death, and studies in which proteins prone to misfolding are exogenously administered to induce a neurotoxic phenotype. Thanks to the easy generation of transgenic strains expressing human disease genes, C. elegans allows the identification of genes and/or proteins specifically associated with pathology and the specific disruptions of cellular processes involved in disease. Several transgenic strains expressing human wild-type or mutated tau have been developed and offer significant information concerning whether transgene expression regulates protein production and aggregation in soluble or insoluble form, onset of the disease, and the degenerative process. C. elegans is able to specifically react to the toxic assemblies of tau, thus developing a neurodegenerative phenotype that, even when exogenously administered, opens up the use of this assay to investigate in vivo the relationship between the tau sequence, its folding, and its proteotoxicity. These approaches can be employed to screen drugs and small molecules that can interact with the biogenesis and dynamics of formation of tau aggregates and to analyze their interactions with other cellular proteins.

Prognostic implications of pericardial and pleural effusion in patients with cardiac amyloidosis

BACKGROUND

Pericardial and pleural effusion are common findings in patients with cardiac amyloidosis (CA). It is not known, whether effusions correlate with right ventricular (RV) function in these patients. Furthermore, data on the prognostic significance of pleural and pericardial effusion in CA is scarce.

METHODS

Patients with transthyretin (ATTR) and light chain (AL) CA were included in a clinical registry. All patients underwent transthoracic echocardiography at baseline. The presence of pericardial and pleural effusion was determined in every patient. The clinical endpoint was defined as cardiac death or heart failure hospitalization.

RESULTS

In total, 143 patients were analysed. Of these, 85 patients were diagnosed with ATTR and 58 patients with AL. Twenty-four patients presented with isolated pericardial effusion and 35 with isolated pleural effusion. In 19 patients, both pericardial and pleural effusion were found and in 65 patients no effusion was present at baseline. The presence of pleural effusion correlated well with poor RV function, measured by global RV free-wall strain (p = 0.007) in patients with AL, but not in ATTR. No such correlation could be found for pericardial effusion in either amyloidosis subtype. Patients with AL presenting with pleural effusion had worse outcomes compared to patients with pericardial effusion alone or no effusion at baseline. In the ATTR group, there was no difference in outcomes according to presence and type of effusion.

CONCLUSION

More than 50% of patients with CA presented with pleural and/or pericardial effusions. While pleural effusion was clearly associated with poor RV function in AL, we were not able to detect this association with pericardial effusion.

Amyloidosis in Heart Failure

PURPOSE

Amyloidosis represents an increasingly recognized but still frequently missed cause of heart failure. In the light of many effective therapies for light chain (AL) amyloidosis and promising new treatment options for transthyretin (ATTR) amyloidosis, awareness among caregivers needs to be raised to screen for amyloidosis as an important and potentially treatable differential diagnosis. This review outlines the diversity of cardiac amyloidosis, its relation to heart failure, the diagnostic algorithm, and therapeutic considerations that should be applied depending on the underlying type of amyloidosis.

RECENT FINDINGS

Non-biopsy diagnosis is feasible in ATTR amyloidosis in the absence of a monoclonal component resulting in higher detection rates of cardiac ATTR amyloidosis. Biomarker-guided staging systems have been updated to facilitate risk stratification according to currently available biomarkers independent of regional differences, but have not yet prospectively been tested. Novel therapies for hereditary and wild-type ATTR amyloidosis are increasingly available. The complex treatment options for AL amyloidosis are improving continuously, resulting in better survival and quality of life. Mortality in advanced cardiac amyloidosis remains high, underlining the importance of early diagnosis and treatment initiation. Cardiac amyloidosis is characterized by etiologic and clinical heterogeneity resulting in a frequently delayed diagnosis and an inappropriately high mortality risk. New treatment options for this hitherto partially untreatable condition have become and will become available, but raise challenges regarding their implementation. Referral to specialized centers providing access to extensive and targeted diagnostic investigations and treatment initiation may help to face these challenges.

Autophagy Activation in Zebrafish Heart Regeneration

Autophagy is an evolutionarily conserved process that plays a key role in the maintenance of overall cellular health. While it has been suggested that autophagy may elicit cardioprotective and pro-survival modulating functions, excessive activation of autophagy can also be detrimental. In this regard, the zebrafish is considered a hallmark model for vertebrate regeneration, since contrary to adult mammals, it is able to faithfully regenerate cardiac tissue. Interestingly, the role that autophagy may play in zebrafish heart regeneration has not been studied yet. In the present work, we hypothesize that, in the context of a well-established injury model of ventricular apex resection, autophagy plays a critical role during cardiac regeneration and its regulation can directly affect the zebrafish regenerative potential. We studied the autophagy events occurring upon injury using electron microscopy, in vivo tracking of autophagy markers, and protein analysis. Additionally, using pharmacological tools, we investigated how rapamycin, an inducer of autophagy, affects regeneration relevant processes. Our results show that a tightly regulated autophagic response is triggered upon injury and during the early stages of the regeneration process. Furthermore, treatment with rapamycin caused an impairment in the cardiac regeneration outcome. These findings are reminiscent of the pathophysiological description of an injured human heart and hence put forward the zebrafish as a model to study the poorly understood double-sword effect that autophagy has in cardiac homeostasis.