| Primary systemic AL amyloidosis is caused by clonal bone marrow plasma cells that secrete an immunoglobulin whose light chain (LC) forms amyloid. Amyloid is a general term for misfolded proteins that polymerize and form fibrils with a cross beta-sheet structure. In the systemic amyloidoses, these fibrils deposit extracellularly in various target organs, particularly the heart and kidneys in AL amyloidosis. Recent evidence has challenged the dogma that tissue damage is solely the result of amyloid fibril deposition. To examine whether amyloidogenic human immunoglobulin light chains may cause acute toxic effects prior to the development of fibrillar tissue deposits in vivo, amyloidogenic LC-expressing cell lines were generated and transplanted into mice. A lambda6 LC gene was cloned from a patient with aggressive multi-organ AL amyloidosis and stably expressed in SP2/0 plasmacytoma cells, which were injected into syngeneic Balb/c and RAG-/- mice. Four to six weeks later, echocardiograms were performed and the mice were euthanized and serum, urine, and tissues were collected. Mice injected with LC-producing cells had detectable circulating human LC in their serum and some mice excreted LC and albumin in the urine, whereas mice injected with untransfected cells did not. In the kidney, there were amorphous protein deposits and early glomerulopathy by electron microscopy in two mice examined, but no mature fibril deposition. These mice had bradycardia and upregulation of the cell stress marker heme oxygenase-1 in the heart. Therefore, short-term expression of human amyloidogenic LC in mice in vivo produces alterations in kidney and heart function prior to the development of fibrillar deposits. However, the tumor model is unsuitable for long-term studies because of overgrowth of the plasmacytoma cells. To circumvent this problem, a transgenic model was developed in which the same lambda6 LC gene was expressed using a CMV promoter. In three transgenic lines, LC is expressed in epithelial cells and found in serum and urine. Thus, these mice will be useful for the study of accessory factors in amyloidogenesis and for the development of novel therapeutic approaches. |
