Abstract
Primary amyloidosis (AL) results from overproduction of unstable monoclonal immunoglobulin light chains (LCs) and the deposition of insoluble fibrils in tissues, leading to fatal organ disease. Glycosaminoglycans (GAGs) are associated with AL fibrils and have been successfully targeted in the treatment of other forms of amyloidosis. We investigated the role of GAGs in LC fibrillogenesis. Ex vivo tissue amyloid fibrils were extracted and examined for structure and associated GAGs. The GAGs were detected along the length of the fibril strand, and the periodicity of heparan sulfate (HS) along the LC fibrils generated in vitro was similar to that of the ex vivo fibrils. To examine the role of sulfated GAGs on AL oligomer and fibril formation in vitro, a κ1 LC purified from urine of a patient with AL amyloidosis was incubated in the presence or absence of GAGs. The fibrils generated in vitro at physiologic concentration, temperature, and pH shared morphologic characteristics with the ex vivo κ1 amyloid fibrils. The presence of HS and over-O-sulfated-heparin enhanced the formation of oligomers and fibrils with HS promoting the most rapid transition. In contrast, GAGs did not enhance fibril formation of a non-amyloidogenic κ1 LC purified from urine of a patient with multiple myeloma. The data indicate that the characteristics of the full-length κ1 amyloidogenic LC, containing post-translational modifications, possess key elements that influence interactions of the LC with HS. These findings highlight the importance of the variable and constant LC regions in GAG interaction and suggest potential therapeutic targets for treatment.
Highlights
Other studies have examined light chains (LCs) structure and the effect of GAGs on fibril formation, most were performed with recombinant LCs that contained only the VL domain and did not possess post-translational modifications (27–29)
The present study indicates that the specific posttranslational modifications present within full-length LC dramatically influence the effects of heparan sulfate (HS) on fibril formation
We hypothesize that the modifications, present throughout the LC, create distinct regions that provide unique interaction sites that may be essential to the process of fibrillogenesis
Summary
GAGs and LC fibrils may allow the development of drugs to interfere with those interactions and retard LC fibrillogenesis. We demonstrate that a post-translationally modified, full-length (containing variable, VL and constant, CL domains), amyloidogenic LC protein (AL-00131), purified from AL patient urine, can form oligomers and fibrils under physiologic conditions (concentration, temperature, and pH) in vitro. The transitions that occur are promoted by the presence of sulfated GAGs such as HS and may depend on differences in pI between VL and CL regions (19) Both HS and heparin caused enhanced formation when compared with dermatan sulfate (DS) and CS. The rate and extent of oligomer and fibril formation varied with different post-assembly modifications of GAGs. The response and association of amyloidogenic LC with GAGs are specific and are not generated with a non-amyloidogenic LC protein (MM-96100, derived from the urine of a patient with myeloma and no amyloid disease)
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