Characterization of the Response of Primary Cells Relevant to Dialysis-Related Amyloidosis to β2-Microglobulin Monomer and Fibrils

Abstract

The formation of insoluble amyloid fibrils is associated with an array of devastating human diseases. Dialysis-related amyloidosis (DRA) is a severe complication of hemodialysis that results in the progressive destruction of the bones and joints. Elevated concentrations of β2-microglobulin (β2m) in the serum of subjects on hemodialysis promote the formation of amyloid fibrils in the osteoarticular tissues, but the cellular basis for the destruction of these tissues in DRA is poorly understood. In this study we performed a systematic analysis of the interaction of monomeric and fibrillar β2m with primary human cells of the types present in the synovial joints of subjects with DRA. Building upon observations that macrophages infiltrate β2m amyloid deposits in vivo we demonstrate that monocytes, the precursors of macrophages, cannot degrade β2m fibrils, and that both monomeric β2m and fibrillar β2m are cytotoxic to these cells. β2m fibrils also impair the formation of bone resorbing osteoclasts from monocytes and reduce the viability of osteoblasts, the cell type that produces bone. As a consequence, we predict that β2m amyloid will disrupt the remodelling of the bone, which is critical for the maintenance of this tissue. Moreover, we show that β2m fibrils reduce the viability of chondrocytes, rationalizing the loss of cartilage in DRA. Together, our observations demonstrate that β2m cytotoxicity has multiple cellular targets in the osteoarticular tissues and is likely to be a key factor in the bone and joint destruction characteristic of DRA.

Direct three-dimensional visualization of membrane disruption by amyloid fibrils

“…Fibril samples were stored at 25°C and used within 3 mo. To prepare fibrils for confocal imaging, β 2 m monomers were labeled with TMR, as described in Porter et al (49) and as detailed in SI Methods. Liposome Preparation.…”

pH-induced molecular shedding drives the formation of amyloid fibril-derived oligomers

“…In addition, β 2 m fibrils formed under acidic conditions are structurally similar to those formed in vitro at near-neutral pH from the N-terminally truncated β 2 m variant, ΔN6 (21). They also display similar effects (internalization into the endo-lysosomal pathway and the inhibition of cellular reduction of MTT) when incubated with cell lines and with primary cells relevant to the pathology of dialysisrelated amyloidosis (DRA) (monocytes, chondrocytes, and osteoblasts) (9,10,23,24). Moreover, fibrils formed from ΔN6, but seeded with wild-type β 2 m fibrils formed at low pH, have been shown to inhibit osteoclast formation from primary human monocytes, rationalizing the osteoarticular pathology associated with DRA (23).…”

“…pH values of 7.4 and 6.4 were chosen to mimic the environments encountered by fibrils in the extracellular milieu and in early endosomes, respectively. In previous experiments we have shown that β 2 m fibrils are taken up into endosomes and lysosomes in a lengthdependent manner, wherein they persist as protease-resistant material that retains a cross-β structure and results in the perturbation of lysosome function (10,23,24). pH-induced changes in fibril yield and conformation were monitored by ThT fluorescence and SDS-PAGE (Methods).…”

Ferritin in dialysis-related arthropathy: could it be a possible biochemical indicator of articular chronic pain?

“…After ten years of dialysis, 80% of patients show stiffness in large joints, 64% show a restriction in movements, and 43% show carpal tunnel syndrome [7,8]. Less frequent is cubital tunnel syndrome [9]. The known main causes of this condition are beta-2 microglobulin deposits in the joints of patients due to insufficient elimination of this protein during therapy [10].…”