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Summary Multinucleated giant cells (MGCs) form by fusion of macrophages and are presumed to contribute to the removal of debris from tissues. In a systematic in vitro analysis, we show that IL-4-induced MGCs phagocytosed large and complement-opsonized materials more effectively than their unfused M2 macrophage precursors. MGC expression of complement receptor 4 (CR4) was increased, but it functioned primarily as an adhesion integrin. In contrast, although expression of CR3 was not increased, it became functionally activated during fusion and was located on the extensive membrane ruffles created by excess plasma membrane arising from macrophage fusion. The combination of increased membrane area and activated CR3 specifically equips MGCs to engulf large complement-coated targets. Moreover, we demonstrate these features in vivo in the recently described complement-dependent therapeutic elimination of systemic amyloid deposits by MGCs. MGCs are evidently more than the sum of their macrophage parts. [ABSTRACT FROM AUTHOR]

Misfolding and aggregation of normally soluble proteins into amyloid fibrils and their deposition and accumulation underlies a variety of clinically significant diseases. Fibrillar aggregates with amyloid-like properties can also be generated in vitro from pure proteins and peptides, including those not known to be associated with amyloidosis. Whereas biophysical studies of amyloid-like fibrils formed in vitro have provided important insights into the molecular mechanisms of amyloid generation and the structural properties of the fibrils formed, amyloidogenic proteins are typically exposed to mild or more extreme denaturing conditions to induce rapid fibril formation in vitro. Whether the structure of the resulting assemblies is representative of their natural in vivo counterparts, thus, remains a fundamental unresolved issue. Here we show using Fourier transform infrared spectroscopy that amyloid-like fibrils formed in vitro from natively folded or unfolded β2-microglobulin (the protein associated with dialysis-related amyloidosis) adopt an identical β-sheet architecture. The same α-strand signature is observed whether fibril formation in vitro occurs spontaneously or from seeded reactions. Comparison of these spectra with those of amyloid fibrils extracted from patients with dialysis-related amyloidosis revealed an identical amide I′ absorbance maximum, suggestive of a characteristic and conserved amyloid fold. Our results endorse the relevance of biophysical studies for the investigation of the molecular mechanisms of β2-microglobulin fibrillogenesis, knowledge about which may inform understanding of the pathobiology of this protein. [ABSTRACT FROM AUTHOR]

One of the most fascinating features of amyloid fibrils is their generic cross-β architecture that can be formed from many different and completely unrelated proteins. Nonetheless, amyloid fibrils with diverse structural and phenotypic properties can form, both in vivo and in vitro, from the same protein sequence. Here, we have exploited the power of RNA selection techniques to isolate small, structured, single-stranded RNA molecules known as aptamers that were targeted specifically to amyloid-like fibrils formed in vitro from β2-microglobulin (β2m), the amyloid fibril protein associated with dialysis-related amyloidosis. The aptamers bind with high affinity (apparent KD ∼ nM) to β2m fibrils with diverse morphologies generated under different conditions in vitro, as well as to amyloid fibrils isolated from tissues of dialysis-related amyloidosis patients, demonstrating that they can detect conserved epitopes between different fibrillar species of β2m. Interestingly, the aptamers also recognize some other, but not all, amyloid fibrils generated in vitro or isolated from ex vivo sources. Based on these observations, we have shown that although amyloid fibrils share many common structural properties, they also have features that are unique to individual fibril types. [ABSTRACT FROM AUTHOR]

We report a family with autosomal-dominant hereditary systemic amyloidosis in three generations, presenting with renal involvement. Two members of the current generation received renal transplants for end-stage renal failure 16 and 18 years ago, and remain very well clinically despite massive visceral amyloidosis. Two other members of this generation, aged 32 and 47 years, have massive systemic amyloid but no clinical disability. Individuals known to be affected in previous generations died of renal failure in early adult life. Amyloid deposits in the proband, one of the transplanted individuals, were composed of apolipoprotein A-I (apoA-I), and among living family members there was complete concordance between amyloidosis and the presence of a novel 9 base pair in-frame deletion mutation in exon 4 of the apoA-I gene, causing a loss of residues Glu70Phe71Trp72. This predicts the acquisition of a single extra positive charge by mature apoA-I, and this variant was detected in the plasma of all carriers. All the previously reported amyloidogenic variants of apoA-I also carry an extra positive charge, indicating that this electrostatic change is likely to be relevant to the amyloidogenicity of apoA-I. [ABSTRACT FROM AUTHOR]