An in vitro model of light chain deposition disease

Abstract

Nodular glomerulosclerosis results from increased deposition of extracellular matrix proteins and monotypic light chains. The inability of mesangial cells to degrade abnormal levels of tenascin-C--along with the increased expression of some growth factors such as platelet-derived growth factor (PDGF) and transforming growth factor-beta (TGF-beta)--is crucial to the pathogenesis of light chain deposition disease (LCDD). In order to study the molecular processes contributing to LCDD, we grew mesangial cells in three-dimensional matrices and incubated the cells with free light chains purified from the urine of patients with biopsy-proven LCDD, immunoglobulin-associated amyloid deposits, or myeloma cast nephropathy. Light chains of the latter two cohorts served as controls. Mesangial cells incubated with light chains from patients with LCDD show a significant increase in tenascin-C expression, centrally located within newly formed nodules, along with increased expression of PDGF and TGF-betas, compared to mesangial cells incubated with control light chains. There was less extracellular MMP-7 even though its intracellular expression is markedly increased compared to the control. Addition of active MMP-7 degraded this excess tenascin-C in vitro, a process that could be prevented by an exogenous MMP inhibitor. Our in vitro model recapitulates in vivo findings in patients with LCDD, thus allowing definition of the sequential pathologic processes associated with glomerulopathic light chain interactions with mesangial cells.

A mouse model recapitulating human monoclonal heavy chain deposition disease evidences the relevance of proteasome inhibitor therapy

“…[50][51][52] Whether backcrossing of our HCDD mouse model to nephropathy-prone genetic background like DBA/2J could overcome this issue remains to be confirmed. 51 Nevertheless, gHC deposits were accompanied by glomerular accumulation of tenascin-C, a typical marker of ECM remodeling that precedes development of nodular glomeruloscerosis in LCDD.28 Consequently, our model remains relevant to accurately study in vivo the early phenotypic modifications of mesangial cells (induction of transforming growth factor b, matrix metalloproteinase 7 activity, etc) 25,[27][28][29] and to test new therapeutic approaches to prevent glomerular injury in MIDD.It was previously demonstrated that the ER resident chaperone protein BiP/GRP78 retains free HC by stable interaction with the CH1 domain, until a LC displaces this association and allows secretion of an entire immunoglobulin. 42 Monoclonal gHC lacking the CH1 domain was consequently supposed to be freely secreted by plasma cells.…”

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“…However, while amyloidogenic light chains are avidly internalized into the mesangial cells ( Figure 3B) using a clathrin-mediated mechanism (Figure 4), this is not the case with LCDD-light chains which activate cellular mechanisms when they interact with the surface receptors but are only minimally internalized [13,14]. Interaction with the surface receptors is responsible for their pathogenic effects downstream (Figures 3-5).…”

“…These light chains manifest morphologically as punctate electron dense material that is sometimes (if not electron dense enough) difficult to identify, as it tends to blend with the increased mesangial matrix (Figure 14). While in the initial phases of LCDD there are proliferative mesangial changes mediated by PDGF-β, as the disease progresses and matures, mesangial matrix deposition dominates the pathologic picture, driven by TGF-β, which in turn exerts a negative feedback on mesangial cellular proliferative activity resulting in the formation of mesangial nodules and progressive loss of mesangial cells as a direct effect of the glomerulopathic light chains [14,17]. Depending on which growth factor predominates in the mesangial milieu at the time of the renal biopsy, the morphologic findings will vary accordingly with either more or less mesangial cell proliferation and/or matrix deposition [19].…”

“…Genes normally quiescent in normal mesangial cells were activated leading to the production of abnormal extracellular matrix with fibrillary collagens, and most importantly, tenascin. Tenascin is a tenacious protein with an octopus-like appearance which binds strongly to integrins and matrix constituents [14]. It is a very difficult matrix protein to destroy and dispose of.…”

“…The various platforms allowed for complete reproduction of the two disease processes [14,15,30,[34][35][36][37]. Mesangial nodularity with increased extracellular matrix proteins, predominantly tenascin ( Figure 17) and replacement of the normal mesangial matrix by amyloid fibrils was observed in the in-vitro, ex-vivo and in-vivo models using LCDD and amyloidogenic light chains, respectively.…”