Mass spectrometry characterization of light chain fragmentation sites in cardiac AL amyloidosis:insights into the timing of proteolysis.

Molecular mechanism of amyloidogenic mutations in hypervariable regions of antibody light chains.

/pdf/how-i-treat-al-amyloidosis-3i9icorx.pdf

How I treat AL amyloidosis

Light chain (AL) amyloidosis is characterized by deposition of immunoglobulin light chains (LC) as fibrils in target organs. Alongside the full-length protein, abundant LC fragments are always present in AL deposits. Herein, by combining gel-based and mass spectrometry analyses, we identified and compared the fragmentation sites of amyloid LCs from multiple organs of an AL λ amyloidosis patient (AL-55). The positions pinpointed here in kidney and subcutaneous fat, alongside those previously detected in heart of the same patient, were aligned and mapped on the LC's dimeric and fibrillar states. All tissues contain fragmented LCs along with the full-length protein; the fragment pattern is coincident across organs, although microheterogeneity exists. Multiple cleavage positions were detected; some are shared, whereas some are organ-specific, likely due to a complex of proteases. Cleavage sites are concentrated in "proteolysis-prone" regions, common to all tissues. Several proteolytic sites are not accessible on native dimers, while they are compatible with fibrils. Overall, data suggest that the heterogeneous ensemble of LC fragments originates in tissues, and is consistent with digestion of preformed fibrils, or with the hypothesis that initial proteolytic cleavage of the constant domain triggers the amyloidogenic potential of LCs, followed by subsequent proteolytic degradation. This work provides a unique set of molecular data on proteolysis from ex vivo amyloid, which allows discussing hypotheses on role and timing of proteolytic events occurring along amyloid formation and accumulation in AL patients.

/pdf/protease-sensitive-regions-in-amyloid-light-chains-what-a-4ecj66ebau.pdf

Protease-sensitive regions in amyloid light chains: what a common pattern of fragmentation across organs suggests about aggregation

In systemic light chain amyloidosis (AL), pathogenic monoclonal immunoglobulin light chains (LC) form toxic aggregates and amyloid fibrils in target organs. Prompt diagnosis is crucial to avoid permanent organ damage, but delayed diagnosis is common because symptoms usually appear only after strong organ involvement. Here we present LICTOR, a machine learning approach predicting LC toxicity in AL, based on the distribution of somatic mutations acquired during clonal selection. LICTOR achieves a specificity and a sensitivity of 0.82 and 0.76, respectively, with an area under the receiver operating characteristic curve (AUC) of 0.87. Tested on an independent set of 12 LCs sequences with known clinical phenotypes, LICTOR achieves a prediction accuracy of 83%. Furthermore, we are able to abolish the toxic phenotype of an LC by in silico reverting two germline-specific somatic mutations identified by LICTOR, and by experimentally assessing the loss of in vivo toxicity in a Caenorhabditis elegans model. Therefore, LICTOR represents a promising strategy for AL diagnosis and reducing high mortality rates in AL. Systemic light chain amyloidosis (AL) is caused by the production of toxic light chains and can be fatal, yet effective treatments are often not possible due to delayed diagnosis. Here the authors show that a machine learning platform analyzing light chain somatic mutations allows the prediction of light chain toxicity to serve as a possible tool for early diagnosis of AL.

/pdf/machine-learning-analyses-of-antibody-somatic-mutations-20le5ar9ed.pdf

Machine learning analyses of antibody somatic mutations predict immunoglobulin light chain toxicity.

Inherent biophysical properties modulate the toxicity of soluble amyloidogenic light chains

Light chain (LC) amyloidosis (AL) is caused by the overproduction, misfolding and aggregation of immunoglobulin LCs that tend to deposit as amyloid fibrils in the cardiac tissue [1]. Nowadays, the ...

/pdf/modulating-the-cardiotoxic-behaviour-of-immunoglobulin-light-2wlb8rxmdl.pdf

Arianna Ambrosetti

Papers

Inherent biophysical properties modulate the toxicity of soluble amyloidogenic light chains

Modulating the cardiotoxic behaviour of immunoglobulin light chain dimers through point mutations