Sublytic C5b‐9 complexes induce proliferative changes of glomerular mesangial cells in rat Thy‐1 nephritis through TRAF6‐mediated PI3K‐dependent Akt1 activation

Abstract

The proliferation of glomerular mesangial cells (GMCs) and secretion of extracellular matrix (ECM) in rat Thy-1 nephritis (Thy-1N), resembling human mesangioproliferative glomerulonephritis (MsPGN), have been studied for many years, but the mechanisms, especially the role of signalling pathway activation and its regulation in GMCs triggered by sublytic C5b-9 complexes in Thy-1N rats remain largely unclear. In the study, the proliferation of GMCs and production of ECM as well as the role of PI3K/Akt and its regulation, both in GMCs induced by sublytic C5b-9 (in vitro) and in the renal tissues of rats with Thy-1N (in vivo), were determined and the results revealed that GMCs proliferation and ECM secretion, both in vitro and in vivo, were notably increased, and that PI3K/Akt1 activation and its regulation, such as TNF receptor-associated factor 6 (TRAF6)-mediated Akt1 ubiquitination and PI3K-dependent Akt1 phosphorylation, were involved in the process of Thy-1N induction. On the other hand, silence of the TRAF6, PI3K or Akt1 genes could obviously diminish the proliferative damages and urinary protein secretion of Thy-1N rats. Together, these data implicated that sublytic C5b-9 complexes in Thy-1N rats could promote GMCs proliferation and ECM production through TRAF6-mediated PI3K-dependent Akt1 activation, in which the ubiquitination and phosphorylation of the Akt1 signal molecule played an important role in the initiation and development of the proliferative changes in the rats with Thy-1N.

Sublytic C5b-9 Induces Glomerular Mesangial Cell Apoptosis Through miR-3546/SOX4/Survivin Axis in Rat Thy-1 Nephritis

“…In order to solve above-mentioned problems of human MsPGN, we used the rat model of Thy-1N to perform a series of experiments. Reportedly, in the process of Thy-1N induction, rat GMCs showed different pathological changes such as cell apoptosis and proliferation as well as inflammatory cytokine secretion [10,11,30,31]. Our previous experiments have proved that the GMC injury in the rats with Thy-1N is sublytic C5b-9-dependent [10,18,30].…”

“…GMCs culture and sublytic C5b-9 determination Rat GMCs were cultured in modified Eagle's medium (MEM) supplemented with 10% fetal bovine serum (FBS) as previously described [13,15]. Rabbit Thy-1 Ab and normal human sera (NHS, provide heterologous complement) were used to assemble C5b-9 on rat GMC membrane to avoid homologous restriction factors such as CD59 [29], which can disrupt C5b-9 formation on the cell membrane [10,30,31].…”

Complement—here, there and everywhere, but what about the transplanted organ?

“…A number of other stress-related factors such as interferon-γ (IFNγ), lipopolysaccharide (LPS) and IL-1 may also increase the production of complement generating C5a and C5b-C9 and consequent graft dysfunction. Complement activation on endothelial and epithelial cells in turn can upregulate or mediate the release of pro-inflammatory and fibrotic factors including tumour necrosis factor (TNF), interleukin-6 (IL-6), intercellular adhesion molecule-1 (ICAM-1) and collagen causing chronic tissue damage if they remain unregulated [38][39][40]. The presence of complement factors in human donor kidneys pre-transplantation have previously been reported with poor allograft function 3 years later [19].…”

“…C3 downstream products C3a and C5a have been shown to be important in antigen presentation thus further stimulating T cell responses against alloantigens, inducing rejection [10,14,39,41,47,53,73,74]. Recipient T cells are known to be primed within the first 24 hours following transplantation as donor APCs migrate to the recipient lymphoid system.…”

“…Studies have reported the susceptibility of APCs to complement products generated through cleavage of C3 [10,75]. In addition, APCs stimulated with C3a or C5a increased their ability to effectively stimulate alloreactive T cells via nuclear factor-ĸB (NF-ĸB) signalling [39,41]. APCs such as macrophages and dendritic cells (DC) are known to produce C3 and C5 [76].…”