Glomerulopathic light chain-mesangial cell interactions modulate in vitro extracellular matrix remodeling and reproduce mesangiopathic findings documented in vivo.

Glomerulopathic light chains (LCs) are associated with two distinct mesangiopathies: AL (light-chain-related) amyloidosis and light-chain deposition disease (LCDD) with immunomorphologic features that are well documented in the literature. Even though both conditions are caused by monoclonal LCs, these entities differ dramatically in their morphologic expressions. In AL amyloidosis the mesangial matrix is replaced by amyloid fibrils, while in LCDD the matrix increases as a consequence of deposition of excess extracellular matrix (ECM). The immunomorphologic mesangial alterations observed in biopsy material are closely reproduced in vitro when mesangial cells grown on an artificial matrix are incubated with monoclonal light chains obtained from the urine of patients with either condition. This article summarizes previously reported data, reports new findings, and focuses on integrating all the available information on the subject. When mesangial cells are incubated with LCDD-LCs, production of ECM proteins (collagen IV, laminin, fibronectin, and tenascin) is increased, with maximum effect at 72 hours post LC treatment. A concomitant decrease in collagenase IV activity further accentuates the accumulation of mesangial matrix. These effects are mediated through transforming growth factor-beta (TGF-beta) activation. In contrast, when mesangial cells are incubated with Am-LCs, a decrease in ECM protein production and a stimulatory effect on collagenase IV is observed, which results in matrix degradation and facilitates amyloid deposition. The decreased TGF-beta documented in the literature in this setting precludes adequate matrix repair. These findings substantiate the morphologic alterations observed in renal biopsy specimens and in the in vitro model. Using this in vitro model, it is then possible to delineate the LC interactions with putative receptors at the mesangial cell surface that regulate mesangial cell pathobiologic responses and mesangial matrix homeostasis.

In vitro AL-amyloid formation by rat and human mesangial cells.

AA-amyloid has been produced experimentally in animal models, allowing the study of mechanisms involved in AA-amyloidogenesis, but those involved in renal AL-amyloidogenesis have not been adequately investigated due, in part, to lack of appropriate in vitro models. Rat and human mesangial cells were grown on a human extracellular matrix (Amgel) derived from normal tissues and on coverslips in the presence of 10 microliters of amyloid enhancing factor (AEF) per milliliter of media and 10 micrograms/ml monoclonal lambda light chains (LCs) obtained from two patients with AL-amyloidosis. Two additional lambda LCs derived from the urine of patients with myeloma and tubulointerstitial renal disease were used as controls. To verify amyloid deposition, light and electron microscopic examination, as well as Congo red and thioflavin T staining, were performed on samples incubated under different experimental conditions. Intracellular and extracellular amyloid was identified in samples incubated for 24 hours with human mesangial cells (for 48 hours with rat mesangial cells), amyloidogenic monoclonal LCs, and AEF. The amount of amyloid detected, which increased with longer incubation times, was found to be most abundant at 14 days. Amyloid was not present in cultures of mesangial cells incubated with amyloidogenic LCs alone or in the absence of mesangial cells. Likewise, incubation of mesangial cells with amyloidogenic LC or AEF separately or amyloidogenic LC in the presence of AEF but without mesangial cells did not result in amyloid formation. Amyloid was not seen when LCs obtained from the urine of patients with tubulointerstitial renal disease were incubated with AEF and mesangial cells. AL-amyloid production requires all three components--mesangial cells, amyloidogenic LCs, and AEF. In addition, amyloid was detected intracellular in mesangial cells, supporting the hypothesis that the production of AL-amyloid in the kidney requires intracellular processing by these cells. This system provides a unique experimental model to study renal AL-amyloidogenesis and a platform to explore mesangial cell-matrix interactions.