Repeated treatment with bone marrow cell secretory products maintains long-term renoprotection in experimental chronic kidney disease: a placebo-controlled trial

Progenitor cell secretory products exert additive renoprotective effects when combined with ace inhibitors in experimental CKD

Hypothesis/introduction:

Renal fibrovascular injury often persists in chronic kidney disease patients treated with renin-angiotensin system blockers. Intriguingly, early outgrowth cell-derived factor infusion also inhibits chronic renal injury. We sought to determine whether early outgrowth cell-derived factor administration provides further renoprotection when added to renin-angiotensin system blockade.

Materials and methods:

Conditioned medium was generated by incubating rat early outgrowth cells with serum-free endothelial basal medium-2 to collect their secreted factors. Subtotal nephrectomy rats received enalapril 0.5 mg/L in drinking water or placebo, beginning 8 weeks post-surgery. Four weeks later, enalapril-treated rats received intravenous injections of either conditioned medium or control endothelial basal medium-2 for 2 weeks. Glomerular filtration rate, urinary protein excretion and renal structure were assessed 4 weeks later at 16 weeks post-surgery.

Results:

Enalapril-treated subtotal nephrectomy rats receiving control endothelial basal medium-2 injections experienced only partial renoprotection when compared to vehicle-treated subtotal nephrectomy rats. In contrast, conditioned medium infusion, when administered in addition to enalapril, attenuated the progression of renal dysfunction in subtotal nephrectomy rats, improving glomerular filtration rate and reducing proteinuria without affecting blood pressure.

Conclusions:

Early outgrowth cell-derived factors exert additive renoprotective effects on top of angiotensin-converting enzyme inhibitor therapy in experimental chronic kidney disease, providing the rationale for clinical trials of early outgrowth cell-based therapies for chronic kidney disease.

YAP/TAZ Are Mechanoregulators of TGF-β-Smad Signaling and Renal Fibrogenesis

Like many organs, the kidney stiffens after injury, a process that is increasingly recognized as an important driver of fibrogenesis. Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are related mechanosensory proteins that bind to Smad transcription factors, the canonical mediators of profibrotic TGF-β responses. Here, we investigated the role of YAP/TAZ in the matrix stiffness dependence of fibroblast responses to TGF-β In contrast to growth on a stiff surface, fibroblast growth on a soft matrix led to YAP/TAZ sequestration in the cytosol and impaired TGF-β-induced Smad2/3 nuclear accumulation and transcriptional activity. YAP knockdown or treatment with verteporfin, a drug that was recently identified as a potent YAP inhibitor, elicited similar changes. Furthermore, verteporfin reduced YAP/TAZ levels and decreased the total cellular levels of Smad2/3 after TGF-β stimulation. Verteporfin treatment of mice subjected to unilateral ureteral obstruction similarly reduced YAP/TAZ levels and nuclear Smad accumulation in the kidney, and attenuated renal fibrosis. Our data suggest that organ stiffening cooperates with TGF-β to induce fibrosis in a YAP/TAZ- and Smad2/3-dependent manner. Interference with this YAP/TAZ and TGF-β/Smad crosstalk likely underlies the antifibrotic activity of verteporfin. Finally, through repurposing of a clinically used drug, we illustrate the therapeutic potential of a novel mechanointerference strategy that blocks TGF-β signaling and renal fibrogenesis.

Recombinant N-Terminal Slit2 Inhibits TGF-β-Induced Fibroblast Activation and Renal Fibrosis

Fibrosis and inflammation are closely intertwined injury pathways present in nearly all forms of CKD for which few safe and effective therapies exist. Slit glycoproteins signaling through Roundabout (Robo) receptors have been described to have anti-inflammatory effects through regulation of leukocyte cytoskeletal organization. Notably, cytoskeletal reorganization is also required for fibroblast responses to TGF-β Here, we examined whether Slit2 also controls TGF-β-induced renal fibrosis. In cultured renal fibroblasts, which we found to express Slit2 and Robo-1, the bioactive N-terminal fragment of Slit2 inhibited TGF-β-induced collagen synthesis, actin cytoskeletal reorganization, and Smad2/3 transcriptional activity, but the inactive C-terminal fragment of Slit2 did not. In mouse models of postischemic renal fibrosis and obstructive uropathy, treatment with N-terminal Slit2 before or after injury inhibited the development of renal fibrosis and preserved renal function, whereas the C-terminal Slit2 had no effect. Our data suggest that administration of recombinant Slit2 may be a new treatment strategy to arrest chronic injury progression after ischemic and obstructive renal insults by not only attenuating inflammation but also, directly inhibiting renal fibrosis.