Human SAA1-derived amyloid deposition in cell culture: a consistent model utilizing human peripheral blood mononuclear cells and serum-free medium

Abstract

Amyloid A (AA) amyloidosis is a fatal disease caused by extracellular deposition of fibrils derived from serum AA (SAA). AA amyloid fibril formation has previously been modeled in macrophage cultures using highly amyloidogenic mouse SAA1.1, but attempts to do the same with human SAA invariably failed. Our objective was to define conditions that support human SAA-derived amyloid formation in peripheral blood mononuclear cell (PBMC) cultures. Two conditions were found to be critical – omission of fetal calf serum and use of StemPro34, a lipid-enriched medium formulated for hematopoietic progenitor cells. Cultures maintained in serum-free StemPro34 and provided with recombinant human SAA1 in the complete absence of amyloid-enhancing factor exhibited amyloid deposition within 7 d. Amyloid co-localized with cell clusters that characteristically included cells of fibrocytic/dendritic morphology as well as macrophages. These cells formed networks that appeared to serve as scaffolding within and upon which amyloid accumulated. Cells in amyloid-forming cultures demonstrated increased adherence, survival and expression of extracellular matrix components. Of the three human SAA1 isoforms, SAA1.3 showed the most extensive amyloid deposition, consistent with it being the most prevalent isoform in Japanese patients with AA amyloidosis. Attesting to the reproducibility and general applicability of this model, amyloid formation has been documented in cultures established from eight PBMC donors.