Regulation of renal proximal tubular epithelial cell fibroblast growth factor-2 generation by heparin

Heparin-based hydrogels induce human renal tubulogenesis in vitro

Dialysis or kidney transplantation is the only therapeutic option for end stage renal disease. Accordingly, there is a large unmet clinical need for new causative therapeutic treatments. Obtaining robust models that mimic the complex nature of the human kidney is a critical step in the development of new therapeutic strategies. Here we establish a synthetic in vitro human renal tubulogenesis model based on a tunable glycosaminoglycan-hydrogel platform. In this system, renal tubulogenesis can be modulated by the adjustment of hydrogel mechanics and degradability, growth factor signaling, and the presence of insoluble adhesion cues, potentially providing new insights for regenerative therapy. Different hydrogel properties were systematically investigated for their ability to regulate renal tubulogenesis. Hydrogels based on heparin and matrix metalloproteinase cleavable peptide linker units were found to induce the morphogenesis of single human proximal tubule epithelial cells into physiologically sized tubule structures. The generated tubules display polarization markers, extracellular matrix components, and organic anion transport functions of the in vivo renal proximal tubule and respond to nephrotoxins comparable to the human clinical response. The established hydrogel-based human renal tubulogenesis model is thus considered highly valuable for renal regenerative medicine and personalized nephrotoxicity studies.

STATEMENT OF SIGNIFICANCE

The only cure for end stage kidney disease is kidney transplantation. Hence, there is a huge need for reliable human kidney models to study renal regeneration and establish alternative treatments. Here we show the development and application of an in vitro human renal tubulogenesis model using heparin-based hydrogels. To the best of our knowledge, this is the first system where human renal tubulogenesis can be monitored from single cells to physiologically sized tubule structures in a tunable hydrogel system. To validate the efficacy of our model as a drug toxicity platform, a chemotherapy drug was incubated with the model, resulting in a drug response similar to human clinical pathology. The established model could have wide applications in the field of nephrotoxicity and renal regenerative medicine and offer a reliable alternative to animal models.

Role of circulating fibroblast growth factor-2 in lipopolysaccharide-induced acute kidney injury in mice

Fibroblast growth factor-2 (FGF-2) is an angiogenic growth factor involved in renal growth and regeneration. Previous studies in rodents revealed that single intrarenal injections of FGF-2 improved the outcome of acute kidney injury (AKI). Septic children usually show elevated plasma levels of FGF-2, and are at risk of developing AKI. However, the role of circulating FGF-2 in the pathogenesis of AKI is not well understood. We have developed a mouse model to determine how FGF-2 released into the circulation modulates the outcome of AKI induced by lipopolysaccharide (LPS). Young FVB/N mice were infected with adenoviruses carrying a secreted form of human FGF-2 or control LacZ vectors. Subsequently, when the circulating levels of FGF-2 were similar to those seen in septic children, mice were injected with a non-lethal dose of LPS or control buffer. All mice injected with LPS developed hypotension and AKI, from which they recovered after 5 days. FGF-2 did not improve the outcome of AKI, and induced more significant renal proliferative and apoptotic changes during the recovery phase. These findings suggest that circulating FGF-2 may not necessarily prevent the development or improve the outcome of AKI. Moreover, the renal accumulation of FGF-2 might cause further renal damage.

Expression of P311, a transforming growth factor beta latency-associated protein-binding protein, in human kidneys with IgA nephropathy

Background

In cultured NIH3T3 cells, P311 binds to the transforming growth factor-beta (TGF-β)-1 latency-associated protein (LAP) and induces the myofibroblast phenotype. In this study, we determined the levels of P311 and TGF-β1 proteins in tubulointerstitial tissue of patients with different severities of immunoglobulin-A nephropathy (IgAN), and analyzed the relationships between P311 protein expression and clinical data.

Methods

A total of 57 patients with IgAN and 5 controls (from partial nephrectomy) were included. P311 and TGF-β1 protein expression were measured by immunohistochemistry and clinical data (proteinuria, serum creatinine (Scr), eGFR and biopsy index) were recorded. The relationship between P311, TGF-β1, and clinical data was analyzed.

Results

P311 expression was significantly higher in the kidneys of IgAN patients than in controls and was higher in patients with advanced pathological grades of IgAN. P311 protein expression in tubulointerstitial tissue correlated with TGF-β1 and proteinuria. P311 expression was higher in patients with Scr > 133 μmol/L than in patients with Scr < 133 μmol/L.

Conclusion

P311 protein expression in the kidneys of IgAN patients correlates with TGF-β1 expression and with proteinuria. P311 might be a key cytokine in renal fibrosis and be involved in the progression of IgAN.

Novel cystogenic role of basic fibroblast growth factor in developing rodent kidneys

Basic fibroblast growth factor (bFGF) is a heparin-binding growth factor that is accumulated in human dysplastic and cystic renal diseases. Previous studies have shown that bFGF can modulate the growth of developing renal tubules; however, its role in the pathogenesis of renal cyst formation is not clearly understood. Here, we tested the hypothesis that overexpression of bFGF in developing rodent kidneys induces cyst formation in vivo. We used two different adenoviral-mediated gene-transferring approaches to overexpress bFGF in developing rodent kidneys. Initially, metanephric kidney (MK) explants harvested from embryonic day 15 Sprague-Dawley rats were infected with adenoviral vectors (rAd) encoding human bFGF or LacZ genes and transplanted under the renal capsule of adult female rats. Subsequently, to determine whether bFGF could induce renal cysts in developing kidneys with an intact renal collecting system, we injected rAd-bFGF or LacZ vectors in the retroorbital plexus of newborn mice. Basic FGF induced a more efficient integration of the MK explants into the host kidneys and increased the vascularization and proliferation of developing tubules, leading to tubular dilatation and rapid formation of renal cysts. In addition, we successfully expressed human bFGF in the kidney of newborn mice in vivo and induced tubular dilatation and renal cysts. In contrast, mice injected with rAd-lacZ did not develop tubular dilatation or renal cysts. To the best of our knowledge, these experiments show for the first time that overexpression of bFGF in developing rodent kidneys can induce the formation of renal cysts in vivo.