Collagen Plays an Active Role in the Aggregation of β2-Microglobulin under Physiopathological Conditions of Dialysis-related Amyloidosis

Abstract

Dialysis-related amyloidosis is characterized by the deposition of insoluble fibrils of ␤ 2 -microglobulin (␤ 2 -m) in the musculoskeletal system. Atomic force microscopy inspection of ex vivo amyloid material reveals the presence of bundles of fibrils often associated to collagen fibrils. Aggregation experiments were undertaken in vitro with the aim of reproducing the physiopathological fibrillation process. To this purpose, atomic force microscopy, fluorescence techniques, and NMR were employed. We found that in temperature and pH conditions similar to those occurring in periarticular tissues in the presence of flogistic processes, ␤ 2 -m fibrillogenesis takes place in the presence of fibrillar collagen, whereas no fibrils are obtained without collagen. Moreover, the morphology of ␤ 2 -m fibrils obtained in vitro in the presence of collagen is extremely similar to that observed in the ex vivo sample. This result indicates that collagen plays a crucial role in ␤ 2 -m amyloid deposition under physiopathological conditions and suggests an explanation for the strict specificity of dialysis-related amyloidosis for the tissues of the skeletal system. We hypothesize that positively charged regions along the collagen fiber could play a direct role in ␤ 2 -m fibrillogenesis. This hypothesis is sustained by aggregation experiments performed by replacing collagen with a poly-L-lysine-coated mica surface. As shown by NMR measurements, no similar process occurs when poly-L-lysine is dissolved in solution with ␤ 2 -m. Overall, the findings are consistent with the estimates resulting from a simplified collagen model whereby electrostatic effects can lead to high local concentrations of oppositely charged species, such as ␤ 2 -m, that decay on moving away from the fiber surface.The deposition of ␤ 2 -microglobulin (␤ 2 -m) 2 into amyloid fibrils is the hallmark of dialysis-related amyloidosis (DRA), a disease arising as a complication of long-term hemodialysis. ␤ 2 -m is a 99-residue protein (molecular mass 11.7 kDa) that represents the light chain of the major histocompatibility complex class I (MHCI), an integral membrane protein involved in the immune response. As a result of normal MHCI catabolism, ␤ 2 -m is released in the serum from the cell surface and carried to the kidney for clearance. In the presence of kidney failure, the concentration of free circulating ␤ 2 -m can increase by up to 50-fold; the persistent increase in ␤ 2 -m concentration results in amyloid deposition, preferentially localized in the musculoskeletal system. The accumulation of ␤ 2 -m deposits has been shown to cause arthralgias, destructive osteoarthropathies, and carpal tunnel syndrome (1). Although a high concentration of ␤ 2 -m is a necessary condition for the onset of the disease, there is not a strict correlation between the disease severity and ␤ 2 -m levels (2), suggesting that other factors might be involved in ␤ 2 -m amyloid deposition.The aggregation process of ␤ 2 -m has been the object of extensive investigation for many years. Severa...

Heparin Strongly Enhances the Formation of β2-Microglobulin Amyloid Fibrils in the Presence of Type I Collagen

“…The aggregation process was investigated as a function of the incubation time by tapping mode atomic force microscopy. In a previous study (4) we demonstrated that ␤ 2 -m fibrillation under these conditions is strictly localized and associated with the presence of the collagen surface. In the absence of collagen, aggregation experiments performed in the presence of heparin did not give rise to fibril formation.…”

“…Incubation of ␤ 2 -m in the presence of fibrillar collagen yielded amyloid fibrils, the morphology of which was similar to that of ex vivo fibrils extracted from the amyloid deposits of patients affected by DRA. We hypothesized that the positively charged patches distributed over the collagen surface could promote an increase of ␤ 2 -m concentration in the solvent surrounding the collagen fiber and also the proper orientation of ␤ 2 -m that facilitates an ordered polymerization (4). Type I collagen must assume its highly ordered fiber conformation, typical of bones and ligaments, to promote amyloid formation and deposition.…”

Nucleation of protein fibrillation by nanoparticles

“…Fibril formation of ␤ 2 m has also been observed at neutral pH where the protein is predominantly native (29,41). At this pH, fibrillation of the wild-type protein requires the addition of seeds (29) and is enhanced by SDS (42), glycosaminoglycans (28,29), and collagen (27). However, the precise molecular mechanism(s) by which these highly charged molecules stimulate assembly is not known.…”

“…These diseases involve self-assembly of soluble proteins into large insoluble fibrils through nucleation-dependent assembly, often via the formation of oligomeric structures that possess toxic properties (24,25). It has been shown that surfaces presented by lipid bilayers (26), collagen fibers (27), polysaccharides (28,29), and other liquid-air, liquid-solid, or liquidliquid interfaces (30,31) can have specific and significant effects in promoting amyloid formation. These observations suggest that interactions with different surfaces could promote protein self-assembly into amyloid fibrils and enhance protein conformational changes associated with other protein misfolding diseases.…”

Interruptions in the collagen repeating tripeptide pattern can promote supramolecular association

“…[44][45][46][47][48][49] Type XXV collagen (CLAC) was discovered as a component of Alzheimer amyloid plaque, 45 and its amino acid sequence contains two long interruption sequences and three short imperfections within its triple-helix domain. There is evidence that Type XXV collagen inhibits amyloid fibril elongation, 46,49 and that a highly hydrophobic 8-residue sequence within the large 26-residue interruption may be involved in this inhibition.…”