Deleting the TGF-β receptor in proximal tubules impairs HGF signaling

Inhibition of Transforming Growth Factor-β Improves Primary Renal Tubule Cell Differentiation in Long-Term Culture

Patient-oriented applications of cell culture include cell therapy of organ failure like chronic renal failure. Clinical deployment of a cell-based device for artificial renal replacement requires qualitative and quantitative fidelity of a cultured cell to its in vivo counterpart. Active specific apicobasal ion transport reabsorbs 90-99% of the filtered load of salt and water in the kidney. In a bioengineered kidney, tubular transport concentrates wastes and eliminates the need for hemodialysis, but renal tubule cells in culture transport little or no salt and water due to dedifferentiation that mammalian cells undergo in vitro thereby losing important cell-type specific functions. We previously identified transforming growth factor-β (TGF-β) as a signaling pathway necessary for in vitro differentiation of renal tubule cells. Inhibition of TGF-β receptor-1 led to active and inhibitable electrolyte and water transport by primary human renal tubule epithelial cells in vitro. Addition of metformin increased transport, in the context of a transient effect on 5'-AMP-activated kinase phosphorylation. These data motivated us to examine whether increased transport was an idiosyncratic effect of SB431542, probe pathways downstream of TGF-β receptors possibly responsible for the improved differentiation, evaluate whether TGF-β inhibition induced a range of differentiated tubule functions, and to explore crosstalk between the effects of SB431542 and metformin. In this study, we use multiple small-molecule inhibitors of canonical and noncanonical pathways to confirm that inhibition of canonical TGF-β signaling caused the increased apicobasal transport. Hallmarks of proximal tubule cell function, including sodium reabsorption, para-amino hippurate excretion, and glucose uptake increased with TGF-β inhibition, and the specificity of the response was shown using inhibitors of each transport protein. We did not find any evidence of crosstalk between metformin and SB431542. These data suggest that the TGF-β signaling pathway governs multiple features of differentiation in renal proximal tubule cells in vitro. Inhibition of TGF-β by pharmacologic or genome engineering approaches may be a viable approach to enhancing differentiated function of tubule cells in vitro. Impact statement Cell therapy of renal failure requires qualitative and quantitative fidelity between in vitro and in vivo phenotypes, which has been elusive. We show that control of transforming growth factor-β signaling can promote differentiation of renal tubule cells grown in artificial environments. This is a key enabling step for cell therapy of renal failure.

cMet agonistic antibody prevents acute kidney injury to chronic kidney disease transition by suppressing Smurf1 and activating Smad7

We aimed to investigate the role of cMet agonistic antibody (cMet Ab) in preventing kidney fibrosis during acute kidney injury (AKI) to chronic kidney disease (CKD) transition. Additionally, we explored the effect of cMet Ab on TGF-β1/Smad pathway during the pathogenesis of kidney fibrosis. A unilateral ischemia-reperfusion injury (UIRI) mouse model was established to induce AKI-to-CKD transition. Furthermore, we incubated human proximal tubular epithelial cells (hPTECs) under hypoxic conditions as in vitro model of kidney fibrosis. We analyzed the soluble plasma cMet level in patients with AKI requiring dialysis. Patients who did not recover kidney function and progressed to CKD presented a higher increase in the cMet level. The kidneys of mice treated with cMet Ab showed fewer contractions and weighed more than the controls. The mice in the cMet Ab-treated group showed reduced fibrosis and significantly decreased expression of fibronectin and α-smooth muscle actin. cMet Ab treatment decreased inflammatory markers (MCP-1, TNF-α, and IL-1β) expression, reduced Smurf1 and Smad2/3 level, and increased Smad7 expressions. cMet Ab treatment increased cMet expression and reduced the hypoxia-induced increase in collagen-1 and ICAM-1 expression, thereby reducing apoptosis in the in vitro cell model. After cMet Ab treatment, hypoxia-induced expression of Smurf1, Smad2/3, and TGF-β1 was reduced, and suppressed Smad7 was activated. Down-regulation of Smurf1 resulted in suppression of hypoxia-induced fibronectin expression, whereas treatment with cMet Ab showed synergistic effects. cMet Ab can successfully prevent fibrosis response in UIRI models of kidney fibrosis by decreasing inflammatory response and inhibiting the TGF-β1/Smad pathway.

Substrate Elasticity Governs Differentiation of Renal Tubule Cells in Prolonged Culture

IMPACT STATEMENT

Successful clinical tissue engineering requires functional fidelity of the cultured cell to its in vivo counterpart, but this has been elusive in renal tissue engineering. Typically, renal proximal tubule cells in culture have a flattened morphology and do not express key transporters essential to their function. In this article, we show for the first time that in vitro substrate mechanical properties dictate differentiation of cultured renal proximal tubule cells. Remarkably, this effect was only discernable after 4 weeks in culture, longer than usually reported for this cell type. These results demonstrate a new tunable parameter to optimize cell differentiation in renal tissue engineering.

Implementing Reverse Phase Protein Array Profiling as a Sensitive Method for the Early Pre-Clinical Detection of Off-Target Toxicities Associated with Sunitinib Malate

PURPOSE

The tyrosine kinase inhibitor (TKI) sunitinib is a multi-targeted agent approved across multiple cancer indications. Nevertheless, since approval, data has emerged to describe a worrisome side effect profile including hypertension, hand-foot syndrome, fatigue, diarrhea, mucositis, proteinuria, and (rarely) congestive heart failure. It has been hypothesized that the observed multi-parameter toxicity profile is related to "on-target" kinase inhibition in "off-target" tissues.

EXPERIMENTAL DESIGN

To interrogate off-target effects in pre-clinical studies, a reverse phase protein array (RPPA) approach is employed. Mice are treated with sunitinib (40 mg kg^-1 ) for 4 weeks, following which critical organs are removed. The Zeptosens RPPA platform is employed for protein expression analysis.

RESULTS

Differentially expressed proteins associated with damage and/or stress are found in the majority of organs from treated animals. Proteins differentially expressed in the heart are associated with myocardial hypertrophy, ischaemia/reperfusion, and hypoxia. However, hypertrophy is not evidenced on histology. Mild proteinuria is observed; however, no changes in renal glomerular structure are visible via electron microscopy. In skin, proteins associated with cutaneous inflammation, keratinocyte hyper-proliferation, and increased inflammatory response are differentially expressed.

CONCLUSIONS AND CLINICAL RELEVANCE

It is posited that pre-clinical implementation of a combined histopathological/RPPA approach provides a sensitive method to mechanistically elucidate the early manifestation of TKI on-target/organ off-target toxicities.

A Glimpse of the Mechanisms Related to Renal Fibrosis in Diabetic Nephropathy

Diabetic nephropathy (DN) is a common kidney disease in people with diabetes, which is also a serious microvascular complication of diabetes and the main cause of end-stage renal disease (ESRD) in developed and developing countries. Renal fibrosis is a finally pathological change in DN. Nevertheless, the relevant mechanism of cause to renal fibrosis in DN is still complex. In this review, we summarized that the role of cell growth factors, epithelial-mesenchymal transition (EMT) in the renal fibrosis of DN, we also highlighted the miRNA and inflammatory cells, such as macrophage, T lymphocyte, and mastocyte modulate the progression of DN. In addition, there are certain other mechanisms that may yet be conclusively defined. Recent studies demonstrated that some of the new signaling pathways or molecules, such as Notch, Wnt, mTOR, Epac-Rap-1 pathway, may play a pivotal role in the modulation of ECM accumulation and renal fibrosis in DN. This review aims to elucidate the mechanism of renal fibrosis in DN and has provided new insights into possible therapeutic interventions to inhibit renal fibrosis and delay the development of DN.

Proteinase-Activated Receptor 2 May Drive Cancer Progression by Facilitating TGF-β Signaling

The G protein-coupled receptor proteinase-activated receptor 2 (PAR2) has been implicated in various aspects of cellular physiology including inflammation, obesity and cancer. In cancer, it usually acts as a driver of cancer progression in various tumor types by promoting invasion and metastasis in response to activation by serine proteinases. Recently, we discovered another mode through which PAR2 may enhance tumorigenesis: crosstalk with transforming growth factor-β (TGF-β) signaling to promote TGF-β1-induced cell migration/invasion and invasion-associated gene expression in ductal pancreatic adenocarcinoma (PDAC) cells. In this chapter, we review what is known about the cellular TGF-β responses and signaling pathways affected by PAR2 expression, the signaling activities of PAR2 required for promoting TGF-β signaling, and the potential molecular mechanism(s) that underlie(s) the TGF-β signaling-promoting effect. Since PAR2 is activated through various serine proteinases and biased agonists, it may couple TGF-β signaling to a diverse range of other physiological processes that may or may not predispose cells to cancer development such as local inflammation, systemic coagulation and pathogen infection.

Blocking TGF-β and β-Catenin Epithelial Crosstalk Exacerbates CKD

The TGF-β and Wnt/β-catenin pathways have important roles in modulating CKD, but how these growth factors affect the epithelial response to CKD is not well studied. TGF-β has strong profibrotic effects, but this pleiotropic factor has many different cellular effects depending on the target cell type. To investigate how TGF-β signaling in the proximal tubule, a key target and mediator of CKD, alters the response to CKD, we injured mice lacking the TGF-β type 2 receptor specifically in this epithelial segment. Compared with littermate controls, mice lacking the proximal tubular TGF-β receptor had significantly increased tubular injury and tubulointerstitial fibrosis in two different models of CKD. RNA sequencing indicated that deleting the TGF-β receptor in proximal tubule cells modulated many growth factor pathways, but Wnt/β-catenin signaling was the pathway most affected. We validated that deleting the proximal tubular TGF-β receptor impaired β-catenin activity in vitro and in vivo Genetically restoring β-catenin activity in proximal tubules lacking the TGF-β receptor dramatically improved the tubular response to CKD in mice. Deleting the TGF-β receptor alters many growth factors, and therefore, this ameliorated response may be a direct effect of β-catenin activity or an indirect effect of β-catenin interacting with other growth factors. In conclusion, blocking TGF-β and β-catenin crosstalk in proximal tubules exacerbates tubular injury in two models of CKD.