No abstract

No abstract

In beta(2)-microglobulin-related (Abeta2M) amyloidosis, partial unfolding of beta(2)-microglobulin (beta2-m) is believed to be prerequisite to its assembly into Abeta2M amyloid fibrils in vivo. Although low pH or 2,2,2-trifluoroethanol at a low concentration has been reported to induce partial unfolding of beta2-m and subsequent amyloid fibril formation in vitro, factors that induce them under near physiological conditions have not been determined. Using fluorescence spectroscopy with thioflavin T, circular dichroism spectroscopy, and electron microscopy, we here show that at low concentrations, sodium dodecyl sulfate (SDS) converts natively folded beta2-m monomers into partially folded, alpha-helix-containing conformers. Surprisingly, this results in the extension of Abeta2M amyloid fibrils at neutral pH, which could be explained basically by a first-order kinetic model. At low concentrations, SDS also stabilized the fibrils at neutral pH. These SDS effects were concentration-dependent and maximal at approximately 0.5 mM, around the critical micelle concentration of SDS (0.67 mM). As the concentration of SDS was increased above 1 mM, the alpha-helix content of beta2-m rose to approximately 10%, while the beta-sheet content decreased to approximately 20%, a change paralleled by a complete cessation of fibril extension and the destabilization of the fibrils. Detergents of other classes had no significant effect on the extension of fibrils. These findings are consistent with the hypothesis that in vivo, specific factors (e.g., phospholipids) that affect the conformation and stability of beta2-m and amyloid fibrils will have significant effects on the kinetics of Abeta2M fibril formation.

These findings suggest that abnormal HDL capacity to mediate cholesterol efflux is a key driver of excess CVD in patients on chronic hemodialysis and may explain why statins have limited effect to decrease CV events. The findings also suggest cellular cholesterol transporters as potential therapeutic targets to decrease CV risk in this population.

The presence of a normal IS/OS junction was associated with good visual acuity after ERM surgery. A normal IS/OS junction probably indicates morphological and functional recovery of the photoreceptors.

Abstract. ␤ 2 -Microglobulin-related (A␤2M) amyloidosis is a frequent and serious complication in patients on long-term dialysis, and ␤ 2 -microglobulin is a major structural component of A␤2M amyloid fibrils. Several biologic molecules inhibiting the depolymerization of A␤2M amyloid fibrils at a neutral pH were found recently. The effect of trifluoroethanol and glycosaminoglycans (GAG) on the extension of the fibrils at a neutral pH was investigated with the use of fluorescence spectroscopy with thioflavin T, circular dichroism spectroscopy, and electron microscopy. Trifluoroethanol at concentrations of up to 20% (vol/vol) caused fibril extension of heparin-stabilized seeds, inducing a subtle change in the tertiary structure of ␤ 2 -microglobulin and stabilizing the fibrils at a neutral pH. This extension reaction followed a first-order kinetic model. In addition, some GAG, especially heparin, dose-dependently enhanced the fibril extension. These results suggest that some GAG, especially heparin, may bind to the fibrils and enhance their deposition in vivo. Thus, the experimental system described here should be useful to search for the factors that accelerate A␤2M amyloid deposition in vivo. In addition, the interference of the binding of GAG to A␤2M amyloid fibrils may be an attractive therapeutic modality.␤ 2 -Microglobulin-related (A␤2M) amyloidosis is a frequent and serious complication in patients on long-term dialysis (1). Carpal tunnel syndrome and destructive arthropathy associated with cystic bone lesions are the major clinical manifestations of A␤2M amyloidosis (2,3). Several biochemical and cell biologic studies have revealed that intact ␤ 2 -microglobulin (␤2-m) is a major structural component of amyloid fibrils deposited in the synovial membrane of the carpal tunnel (4 -7), but the mechanism of the deposition of these amyloid fibrils is still incompletely understood. Although the retention of ␤2-m in the plasma seems to be prerequisite (8), other factors, such as the age of the patient, the duration of dialysis, and the type of dialysis membrane used, may also be involved (9 -11).We and other groups have proposed that a nucleationdependent polymerization model could explain the general mechanism of amyloid fibril formation in vitro, in various types of amyloidosis (12)(13)(14)(15)(16)(17). This model consists of two phases: a nucleation phase and an extension phase. Nucleus formation requires a series of association steps of monomers, which are thermodynamically unfavorable, representing the rate-limiting step in amyloid fibril formation in vitro. Once the nucleus (n-mer) has been formed, further addition of monomers becomes thermodynamically favorable, resulting in rapid extension of amyloid fibrils according to a first-order kinetic model (12,14,16).The extension of A␤2M amyloid fibrils, as well as the formation of the fibrils from ␤2-m, is greatly dependent on the pH of the reaction mixture, with the optimum pH at approximately 2.0 to 3.0 (16,17). However, they readily depolymerize into monomeri...

No abstract

The normal IS/OS junction observed in OCT3 images is associated with good visual recovery after MH closure. The presence of normal IS/OS junction may be important for visual recovery after MH repair.