Proteotoxicity in cardiac amyloidosis: amyloidogenic light chains affect the levels of intracellular proteins in human heart cells

Abstract

AL amyloidosis is characterized by widespread deposition of immunoglobulin light chains (LCs) as amyloid fibrils. Cardiac involvement is frequent and leads to life-threatening cardiomyopathy.Besides the tissue alteration caused by fibrils, clinical and experimental evidence indicates that cardiac damage is also caused by proteotoxicity of prefibrillar amyloidogenic species. As in other amyloidoses, the damage mechanisms at cellular level are complex and largely undefined. We have characterized the molecular changes in primary human cardiac fibroblasts (hCFs) exposed in vitro to soluble amyloidogenic cardiotoxic LCs from AL cardiomyopathy patients. To evaluate proteome alterations caused by a representative cardiotropic LC, we combined gel-based with label-free shotgun analysis and performed bioinformatics and data validation studies. To assess the generalizability of our results we explored the effects of multiple LCs on hCF viability and on levels of a subset of cellular proteins. Our results indicate that exposure of hCFs to cardiotropic LCs translates into proteome remodeling, associated with apoptosis activation and oxidative stress. The proteome alterations affect proteins involved in cytoskeletal organization, protein synthesis and quality control, mitochondrial activity and metabolism, signal transduction and molecular trafficking. These results support and expand the concept that soluble amyloidogenic cardiotropic LCs exert toxic effects on cardiac cells.Amyloidoses are protein misfolding diseases defined by the presence of extracellular protein aggregates as cross-β-sheet amyloid fibrils. The ability to form amyloid fibrils in vivo is a common feature of at least 36 distinct human proteins, which are otherwise different in terms of sequence, native structure, function and localization 1 . Light chain amyloidosis (AL amyloidosis) is the most frequent systemic form, and is characterized by widespread fibril deposition in target tissues 2,3 . Causal agents of this form are misfolding-prone immunoglobulin

Impact of minimal residual negativity using next generation flow cytometry on outcomes in light chain amyloidosis

“…This suggests that even low level of light chains produced by residual plasma cells can be cardiotoxic. This finding is supported by pre‐clinical studies in amyloidosis showing that cardiotropic light chains induce oxidative stress and protein remodeling, even in the absence of fibril deposits . Along the same lines as our findings, Palladini et al demonstrated that patients who achieved MRD negativity have a higher likelihood of developing future organ response .…”

Systemic immunoglobulin light chain amyloidosis

“…In addition, amyloid fibrils cause cytotoxicity and promote the misfolding of light chains and further oligomer formation 34 . Soluble prefibrillar species, mainly oligomers, also contribute to organ damage through proteotoxicity, increased cellular oxidative stress resulting in mitochondrial damage and reduced cell viability [37][38][39] (Figure 1).…”

“…Cardiac involvement is a key determinant of patient survival, therefore several investigators have studied the mechanisms of cardiac damage caused by misfolded light chain [37][38][39] . Cardiac dysfunction can result from amyloid deposits causing widespread disruption of tissue architecture and from proteotoxicity of the light chains 7 .…”

Immunoglobulin light chain amyloidosis: 2020 update on diagnosis, prognosis, and treatment

“…This insoluble protein deposits in tissues and interferes with organ function. Circulating soluble light chains may also be directly toxic to tissues such as the heart 5 . The β‐pleated sheet configuration is responsible for positive staining with Congo red when viewed under polarized light; this staining is required for the diagnosis of AL amyloidosis 6 .…”