Amyloid aggregation and deposition of human islet amyloid polypeptide at membrane interfaces

Abstract

Amyloid deposition of human islet amyloid polypeptide (hIAPP) within the islets of Langerhans is a pathological feature of type 2 diabetes mellitus. Substantial evidence indicates that the membrane-mediated aggregation and subsequent deposition of hIAPP are linked to dysfunction and death of pancreatic b-cells, but the molecular processes of hIAPP deposition are poorly understood. In this study, we examined the membranemediated aggregation and deposition of hIAPP at supported planar lipid bilayers with and without raft components (i.e. cholesterol and sphingomyelin) to provide insight into hIAPP-induced membrane dysfunction. The adsorption of hIAPP onto the bilayers was studied using a quartz crystal microbalance with dissipation monitoring, which showed enhanced accumulation of the peptide onto the bilayer containing raft components. Microscope observations demonstrated the growth of the aggregates formed from the membrane-adsorbed hIAPP. The examination of the membrane interfaces revealed that hIAPP aggregates retained the ability to associate with the membranes during the aggregation process, resulting in insertion of the aggregates into the bilayers. We also report the inhibitory effect of insulin on the hIAPP deposition. These findings demonstrate the aggregation of hIAPP at the membrane interfaces leading to amyloid deposits associated with the membrane and suggest a role for insulin in hIAPP deposition. A presumed mechanism regulating hIAPP deposition at the membrane interfaces is discussed.

An Equilibrium Model for the Combined Effect of Macromolecular Crowding and Surface Adsorption on the Formation of Linear Protein Fibrils

“…Previous theoretical and experimental studies from our laboratory and others (12)(13)(14) have demonstrated that the tendency of a dilute protein to form fibrils is significantly enhanced in solutions containing high concentrations of nominally inert polymers and proteins, a phenomenon that is attributed primarily to excluded volume or macromolecular crowding (15)(16)(17). Other theoretical and experimental studies from our laboratory and others (18)(19)(20) have demonstrated that the presence of adsorbing surfaces can significantly enhance the tendency of dilute proteins to form adsorbed linear and nonlinear aggregates. For these reasons, we speculated that the presence of both high concentrations of inert macromolecules and surfaces to which the fiber-forming protein can adsorb might have a cumulative effect on fiber formation by the dilute protein that is greater than the sum of the separate effects of crowding and adsorption.…”

Elucidation of insulin assembly at acidic and neutral pH: Characterization of low molecular weight oligomers

“…Aberrant aggregation of proteins into amyloid deposits is a hallmark of many human pathologies, for example, Alzheimer's disease, Parkinson's disease, and type 2 diabetes . Amyloid deposits contain amyloid fibrils characterized by cross‐β structure consisting of stacked β‐sheets held together by interpeptide hydrogen bonding along the long fibrillar axis .…”

The Role of Calcium, Lipid Membranes and Islet Amyloid Polypeptide in the Onset of Type 2 Diabetes: Innocent Bystanders or Partners in a Crime?

“…From a molecular point of view, obesity leads to calcium dyshomeostasis ( 30 ), increased concentration of free fatty acids (FFA) ( 42 ), and cholesterol ( 43 , 44 ). All of these effects have been shown to be involved in the molecular mechanisms leading to hIAPP-induced disruption of Langerhans’ β-cells ( 11 , 25 , 45 , 46 ). Thus, these metabolic effects could all represent a common link between environmental factors and molecular mechanisms.…”