Targeting tubulointerstitial remodeling in experimental proteinuric nephropathy

Abstract

Proteinuria is an important cause of tubulointerstitial damage. Anti-proteinuric interventions are not always successful, and residual proteinuria often leads to renal failure. This indicates the need for additional treatment modalities by targeting the harmful downstream consequences of proteinuria. We previously showed that proteinuria triggers renal lymphangiogenesis before the onset of interstitial inflammation and fibrosis. However, the interrelationship of these interstitial events in proteinuria is not yet clear. To this end, we specifically blocked lymphangiogenesis (anti-VEGFR3 antibody), monocyte/macrophage influx (clodronate liposomes) or lymphocyte and myofibroblast influx (S1P agonist FTY720) separately in a rat model to investigate the role and the possible interaction of each of these phenomena in tubulointerstitial remodeling in proteinuric nephropathy. Proteinuria was induced in 3-month old male Wistar rats by adriamycin injection. After 6 weeks, when proteinuria has developed, rats were treated for another 6 weeks by anti-VEGFR3 antibody, clodronate liposomes or FTY720 up to week 12. In proteinuric rats, lymphangiogenesis, influx of macrophages, T cells and myofibroblasts, and collagen III deposition and interstitial fibrosis significantly increased at week 12 vs week 6. Anti-VEGFR3 antibody prevented lymphangiogenesis in proteinuric rats, however, without significant effects on inflammatory and fibrotic markers or proteinuria. Clodronate liposomes inhibited macrophage influx and partly reduced myofibroblast expression; however, neither significantly prevented the development of lymphangiogenesis, nor fibrotic markers and proteinuria. FTY720 prevented myofibroblast accumulation, T-cell influx and interstitial fibrosis, and partially reduced macrophage number and proteinuria; however, it did not significantly influence lymphangiogenesis and collagen III deposition. This study showed that proteinuria-induced interstitial fibrosis cannot be halted by blocking lymphangiogenesis or the influx of macrophages. On the other hand, FTY720 treatment did prevent T-cell influx, myofibroblast accumulation and interstitial fibrosis, but not renal lymphangiogenesis and proteinuria. We conclude that tubulointerstitial fibrosis and inflammation are separate from lymphangiogenesis, at least under proteinuric conditions.

Urinary collagen degradation products as early markers of progressive renal fibrosis

“…The effects of ADR on proteinuria and tubulointerstitial remodeling have been described in detail before [30]. In short a summary of the relevant results for our study: 6 weeks after ADR injection proteinuria was increased eightfold up to 146 [77–230] mg/24 h (P < 0.001) compared to controls (18 [13–27] mg/24 h).…”

“…At 6 weeks, we did not see any significant changes for collagen type III expression, α-SMA positive myofibroblasts and tubulointerstitial fibrosis (PAS) in the renal tissue, which has been published before by our group and is needed to interpret our most recent findings [30]. …”

“…Previously published results on collagen type III expression, α-SMA positive myofibroblasts and tubulointerstitial expression (PAS), showed that treatment with FTY720 had different effects on these markers, even though all are known to reflect renal fibrosis [30]. The role of the extracellular matrix as a mere scaffold to uphold tissue integrity is being questioned, and it is becoming increasingly clear that it may be considered as a complex paracrine/endocrine entity [33].…”

Connective tissue growth factor regulates fibrosis-associated renal lymphangiogenesis

“…45 Interestingly, Yazdani et al reported that specifically blocking lymphangiogenesis by anti-VEGFR-3 antibody did not prevent inflammation, interstitial fibrosis, or proteinuria in a rat model of proteinuric nephropathy. 46 They also showed that depletion of macrophages by clodronate liposome treatment did not prevent lymphangiogenesis in this model. This is in stark contrast to another study showing that treatment with clodronate liposomes markedly reduced the number of macrophages and lymphangiogenesis induced by UUO.…”

Roles of the TGF-β–VEGF-C Pathway in Fibrosis-Related Lymphangiogenesis

“…In renal transplantation models, the mTOR inhibitor sirolimus inhibited lymphangiogenesis in association with an attenuated development of chronic kidney allograft injury [ 53 ]. However, the specific blocking of lymphangiogenesis by an anti-VEGFR-3 antibody did not prevent inflammation, interstitial fibrosis, and proteinuria in a rat adriamycin-induced proteinuric nephropathy model [ 54 ]. In contrast, the further induction of lymphangiogenesis by VEGF-C treatment suppressed inflammatory infiltrates and reduced inflammatory cytokines and TGF-β1 expression, leading to attenuate renal fibrosis in the mouse model of unilateral ureteral obstruction [ 55 ].…”