The epidermal growth factor receptor axis and kidney fibrosis

Effect of the plasma metabolites, biomarkers, and inflammatory proteins on urolithiasis: insights from Mendelian randomization and mediation analysis

Urolithiasis represents a systemic disorder characterized by metabolic circulation issues and ongoing inflammation. The purpose of this research is to explore the relationships of causation among plasma metabolites, biomarkers, inflammatory proteins, and stones within the urinary system. We initially carried out a two-sample Mendelian randomization (MR) analysis to evaluate possible causal connections between 233 plasma metabolites and 35 biomarkers related to urolithiasis. The genetic association study (GWAS) data concerning plasma metabolites were derived from a 2024 publication in Nature, while data for biomarkers were collected from the UK Biobank. To determine causal relationships, we utilized several analytical techniques, including inverse variance weighting (IVW), MR-Egger, weighted median, and weighted mode. Furthermore, we conducted analyses for pleiotropy and heterogeneity to ensure the findings' robustness. A Steiger analysis was used to explore the presence of any reverse causal relationships. Lastly, we conducted mediation analysis to elucidate how inflammatory proteins mediate the associations between plasma metabolites, biomarkers, and stones in the urinary system. Our research demonstrates causal connections between six plasma metabolites and six biomarkers related to upper urinary tract stones. Furthermore, we identified causal associations between ten plasma metabolites and four biomarkers linked to lower urinary tract stones. Most of these metabolites belong to lipid and lipoprotein classes, indicating that changes in blood lipid levels may influence stone formation. Finally, mediation analysis revealed 13 mediating relationships, including the mediating effects of six inflammatory proteins. Our results provide evidence for the causal links among plasma metabolites, biomarkers, and inflammatory proteins associated with urolithiasis. This provides new insights into the potential mechanisms underlying urinary system stone formation, contributing to their prevention, diagnosis, and treatment.

CD148 agonistic antibody alleviates renal injury induced by chronic angiotensin II infusion in mice

BACKGROUND

Angiotensin II (Ang II) plays a critical role in the progression of kidney disease. In addition to its direct signaling events, Ang II transactivates epidermal growth factor receptor (EGFR) and causes renal injury. CD148 is a transmembrane protein tyrosine phosphatase that dephosphorylates EGFR and strongly inhibits its activity. In this study, we have asked if CD148 agonistic antibody 18E1 mAb attenuates renal injury induced by chronic Ang II infusion to explore its therapeutic application.

METHODS

Hypertensive nephropathy was induced in mice subjected to unilateral nephrectomy (UNx) by infusing Ang II (1.4 mg/kg per day) for 6 weeks using an osmotic minipump. The 18E1 mAb or isotype control IgG were intraperitoneally injected (15 mg/kg, three times per week) to the UNx + Ang II mice for 6 weeks, and their renal phenotype was investigated.

RESULTS

Chronic Ang II infusion induced evident hypertension and renal injury that is indicated by elevation of plasma creatinine, urinary albumin excretion, renal hypertrophy, podocyte injury, macrophage infiltration, and the expression of alpha smooth muscle actin and collagen deposition. As compared with isotype control antibody, 18E1 mAb significantly reduced these renal changes, while it showed no effects on blood pressure. Furthermore, phospho-EGFR immunohistochemistry and immunoblotting demonstrated renal EGFR is activated in the mice that were subjected to UNx and Ang II infusion and 18E1 mAb significantly reduces EGFR phosphorylation in these kidneys as compared with isotype control treatment.

CONCLUSION

Agonistic CD148 antibody attenuates UNx + Ang II-induced renal injury, in part by reducing EGFR activity.

CD133+CD24+ Renal Tubular Progenitor Cells Drive Hypoxic Injury Recovery via Hypoxia-Inducible Factor-1A and Epidermal Growth Factor Receptor Expression

CD133+CD24+ renal tubular progenitor cells play a crucial role in the repair and regeneration of renal tubules after acute kidney injury. The aim of this study is to investigate the responses of the human renal tubular precursor TERT (HRTPT) CD133+CD24+ cells and human renal epithelial cell 24 TERT (HREC24T) CD133-CD24+ cells to hypoxic stress, as well as their gene expression profiles. Whole transcriptome sequencing and functional network analysis identified distinct molecular characteristics of HRTPT cells as they were enriched with hypoxia-inducible factor-1A (HIF1A), epidermal growth factor (EGF), and endothelin-1 (EDN1). Our in vitro experiments demonstrated that, under hypoxia (2.5% oxygen), HRTPT cells showed minimal cell death and a 100-fold increase in HIF1A protein levels. In contrast, HREC24T cells exhibited significant cell death and only a two-fold increase in HIF1A protein level. These results indicate that CD133+CD24+ renal tubular progenitor cells have enhanced survival mechanisms under hypoxic stress, enabling them to survive and proliferate to replace damaged tubular cells. This study provides novel insights into the protective role of CD133+CD24+ renal tubular progenitor cells in hypoxic renal injury and identifies their potential survival mechanisms.

GALNT3 in Ischemia-Reperfusion Injury of the Kidney

Key Points

N -acetylgalactosaminyltransferase-3 (GALNT3) was downregulated in both ischemic AKI and cisplatin nephrotoxicity. GALNT3 played a protective role in renal tubular cells, and its downregulation contributed to AKI. Mechanistically, GALNT3 protected kidney tubular cells at least partially through O-glycosylation of EGF receptor.

Background

Damages to subcellular organelles, such as mitochondria and endoplasmic reticulum, are well recognized in tubular cell injury and death in AKI. However, the changes and involvement of Golgi apparatus are much less known. In this study, we report the regulation and role of N -acetylgalactosaminyltransferase-3 (GALNT3), a key enzyme for protein glycosylation in Golgi apparatus, in AKI.

Methods

AKI was induced in mice by renal ischemia–reperfusion injury or cisplatin. In vitro , rat kidney proximal tubular cells were subjected to hypoxia/reoxygenation (H/R) injury. To determine the role of GALNT3, its specific inhibitor T3inh-1 was tested in mice, and the effects of GALNT3 overexpression as well as knockdown were examined in the rat renal proximal tubular cells. EGF receptor (EGFR) activation was induced by recombinant EGF or by overexpressing EGFR.

Results

GALNT3 was significantly decreased in both in vivo and in vitro models of AKI induced by renal ischemia–reperfusion injury and cisplatin. T3Inh-1, a specific GALNT3 inhibitor, exacerbated ischemic AKI and suppressed tubular cell proliferation in mice. Moreover, knockdown of GALNT3 increased apoptosis during H/R treatment in rat renal proximal tubular cells, whereas overexpression of GALNT3 attenuated H/R-induced apoptosis, further supporting a protective role of GALNT3. Mechanistically, GALNT3 contributed to O-glycosylation of EGFR and associated EGFR signaling. Activation or overexpression of EGFR suppressed the proapoptotic effect of GALNT3 knockdown in H/R-treated rat renal proximal tubular cells.

Conclusions

GALNT3 protected kidney tubular cells in AKI at least partially through O-glycosylation of EGFR.

Survivin inhibition attenuates EGF-induced epithelial mesenchymal transformation of human RPE cells via the EGFR/MAPK pathway

PURPOSE

The abnormal growth factors-induced epithelial-mesenchymal transition (EMT) in retinal pigment epithelial (RPE) cells was known as a vital pathogenesis of proliferative vitreoretinopathy (PVR). This study aims to explore how survivin inhibition affects EMT induced by epidermal growth factor (EGF) in RPE cells.

METHODS

Human primary RPE cells were identified in vitro. EMT in RPE cells was induced by EGF. Inhibition of survivin in RPE cells was accomplished through the use of a survivin inhibitor (YM155) and survivin siRNA. The viability, proliferation and migration of RPE cells was detected by methylthiazol tetrazolium assay, bromodeoxyuridine labeling assay, and wound healing assay, respectively. The EGF receptor /mitogen-activated protein kinase (EGFR/MAPK) proteins and EMT-related proteins were measured by western blot and immunofluorescence assay.

RESULTS

EGF induced significant EMT in RPE cells, activated the phosphorylation of EGFR/MAPK signaling proteins, and caused changes to EMT-related proteins. YM155 suppressed RPE cells' viability, proliferation, and migration; induced the phosphorylation of EGFR, JNK, and P38MAPK; and down regulated EGFR and phosphorylated ERK. YM155 also increased expression of E-cadherin and ZO-1 proteins and reduced expression of N-cadherin, Vimentin, and α-SMA proteins. The EGF-induced increase of RPE cell proliferation and migration was constrained by survivin inhibition. Moreover, survivin inhibition in RPE cells suppressed the EGF-caused phosphorylation of EGFR/MAPK proteins and attenuated the EGF-induced reduction of E-cadherin and ZO-1 proteins and increase of N-cadherin, Vimentin, and α-SMA proteins.

CONCLUSIONS

Survivin inhibition attenuates EGF-induced EMT of RPE cells by affecting the EGFR/MAPK signaling pathway. Survivin might be a promising target for preventing PVR.

Targeting the epidermal growth factor receptor (EGFR/ErbB) for the potential treatment of renal pathologies

Epidermal growth factor receptor (EGFR), which is referred to as ErbB1/HER1, is the prototype of the EGFR family of receptor tyrosine kinases which also comprises ErbB2 (Neu, HER2), ErbB3 (HER3), and ErbB4 (HER4). EGFR, along with other ErbBs, is expressed in the kidney tubules and is physiologically involved in nephrogenesis and tissue repair, mainly following acute kidney injury. However, its sustained activation is linked to several kidney pathologies, including diabetic nephropathy, hypertensive nephropathy, glomerulonephritis, chronic kidney disease, and renal fibrosis. This review aims to provide a summary of the recent findings regarding the consequences of EGFR activation in several key renal pathologies. We also discuss the potential interplay between EGFR and the reno-protective angiotensin-(1-7) (Ang-(1-7), a heptapeptide member of the renin-angiotensin-aldosterone system that counter-regulates the actions of angiotensin II. Ang-(1-7)-mediated inhibition of EGFR transactivation might represent a potential mechanism of action for its renoprotection. Our review suggests that there is a significant body of evidence supporting the potential inhibition of EGFR/ErbB, and/or administration of Ang-(1-7), as potential novel therapeutic strategies in the treatment of renal pathologies. Thus, EGFR inhibitors such as Gefitinib and Erlinotib that have an acceptable safety profile and have been clinically used in cancer chemotherapy since their FDA approval in the early 2000s, might be considered for repurposing in the treatment of renal pathologies.

Renal toxicity of Aconitum plants? A study based on a new mass spectrometry scanning strategy and computer virtual screening

BACKGROUND

Radix Aconiti Lateralis (Fuzi), a mono-herbal preparation of Aconitum herbs in the genus Aconitum, is commonly used in traditional Chinese medicine (TCM) to treat critical illnesses. The curative effect of Fuzi is remarkable. However, the toxic effects of Fuzi are still a key clinical focus, and the substances inducing nephrotoxicity are still unclear. Therefore, this study proposes a research model combining "in vitro and in vivo component mining-virtual multi-target screening-active component prediction-literature verification" to screen potential nephrotoxic substances rapidly.

METHOD

The UHPLC-Q-Exactive-Orbitrap MS analysis method was used for the correlation analysis of Fuzi's in vitro-in vivo chemical substance groups. On this basis, the key targets of nephrotoxicity were screened by combining online disease databases and a protein-protein interaction (PPI) network. The computer screening technique was used to verify the binding mode and affinity of Fuzi's components with nephrotoxic targets. Finally, the potential material basis of Fuzi-induced nephrotoxicity was screened.

RESULTS

Eighty-one Fuzi components were identified. Among them, 35 components were absorbed into the blood. Based on the network biology method, 21 important chemical components and three potential key targets were screened. Computer virtual screening revealed that mesaconine, benzoylaconine, aconitine, deoxyaconitine, hypaconitine, benzoylhypaconine, benzoylmesaconine, and hypaconitine may be potential nephrotoxic substances of Fuzi.

CONCLUSIONS

Fuzi may interact with multiple components and targets in the process of inducing nephrotoxicity. In the future, experiments can be designed to explore further. This study provides a reference for screening Fuzi nephrotoxic components and has certain significance for the safe use of Fuzi.

Emodin inhibits M1 macrophage activation that related to acute and chronic kidney injury through EGFR/MAPK pathway

BACKGROUND

Macrophages are the main inflammatory cells involved in kidney injury and play a significant role in the development of acute kidney injury (AKI) and progression of chronic kidney disease (CKD). Emodin is believed to stabilize macrophage homeostasis under pathological conditions. The objective of this study aimed to explore the underlying mechanisms and effects of Emodin on M1 macrophages.

METHODS

Network pharmacology methods were used to predict target proteins associated with renal injury and identify the pathways affected by emodin. RAW264.7 macrophages were induced into M1 polarization using LPS and then treated with emodin at 20, 40, and 80 µM. The effects of emodin on cell viability, cytokines (IL-1β, IL-6, TNF-α), M1 macrophage markers (F4/80 + CD86+), and the EGFR/MAPK pathway were evaluated. Additionally, we transfected RAW264.7 cells with an EGFR shRNA interference lentivirus to assess its effects on RAW264.7 cells function and MAPK pathway. After RAW264.7 cells were passaged to expanded culture and transfected with EGFR-interfering plasmid, macrophages were induced to polarize towards M1 with LPS and then treated with 80 µM emodin. CKD modeling was performed to test how emodin is regulated during CKD.

RESULTS

There are 15 common targets between emodin and kidney injury, of which the EGFR/MAPK pathway is the pathway through which emodin affects macrophage function. Emodin significantly reduced the levels of IL-6, IL-1β and TNF-α (p < 0.05) and the ratio of M1 macrophage surface markers F4/80 + CD86+ (p < 0.01) in the supernatant of RAW264.7 cells in a dose-dependent manner. Furthermore, the inhibitory effect of emodin on RAW264.7 cells was achieved by interfering with the EGFR/MAPK pathway. Moreover, emodin also affected the mRNA and protein expression of EGFR and Ras, leading to a decrease in the rate of M1 macrophages, thus inhibiting the pro-inflammatory effect of M1 macrophages. The addition of emodin reduced the rate of M1 macrophages in CKD and inhibited the further polarization of M1 macrophages, thus maintaining the pro-inflammatory and anti-inflammatory homeostasis in CKD, and these effects were achieved by emodin through the control of the EGRF/ERK pathway.

CONCLUSION

Emodin attenuates M1 macrophage polarization and pro-inflammatory responses via the EGFR/MAPK signalling pathway. And the addition of emodin maintains pro- and anti-inflammatory homeostasis, which is important for maintaining organ function and tissue repair.

TGFβ overcomes FGF-induced transinhibition of EGFR in lens cells to enable fibrotic secondary cataract

To cause vision-disrupting fibrotic secondary cataract (PCO), lens epithelial cells that survive cataract surgery must migrate to the posterior of the lens capsule and differentiate into myofibroblasts. During this process, the cells become exposed to the FGF that diffuses out of the vitreous body. In normal development, such relatively high levels of FGF induce lens epithelial cells to differentiate into lens fiber cells. It has been a mystery as to how lens cells could instead undergo a mutually exclusive cell fate, namely epithelial to myofibroblast transition, in the FGF-rich environment of the posterior capsule. We and others have reported that the ability of TGFβ to induce lens cell fibrosis requires the activity of endogenous ErbBs. We show here that lens fiber-promoting levels of FGF induce desensitization of ErbB1 (EGFR) that involves its phosphorylation on threonine 669 mediated by both ERK and p38 activity. Transinhibition of ErbB1 by FGF is overcome by a time-dependent increase in ErbB1 levels induced by TGFβ, the activation of which is increased after cataract surgery. Our studies provide a rationale for why TGFβ upregulates ErbB1 in lens cells and further support the receptor as a therapeutic target for PCO.

Glutamyl-prolyl-tRNA synthetase (EPRS1) drives tubulointerstitial nephritis-induced fibrosis by enhancing T cell proliferation and activity

Toxin- and drug-induced tubulointerstitial nephritis (TIN), characterized by interstitial infiltration of immune cells, frequently necessitates dialysis for patients due to irreversible fibrosis. However, agents modulating interstitial immune cells are lacking. Here, we addressed whether the housekeeping enzyme glutamyl-prolyl-transfer RNA synthetase 1 (EPRS1), responsible for attaching glutamic acid and proline to transfer RNA, modulates immune cell activity during TIN and whether its pharmacological inhibition abrogates fibrotic transformation. The immunological feature following TIN induction by means of an adenine-mixed diet was infiltration of EPRS1high T cells, particularly proliferating T and γδ T cells. The proliferation capacity of both CD4+ and CD8+ T cells, along with interleukin-17 production of γδ T cells, was higher in the kidneys of TIN-induced Eprs1+/+ mice than in the kidneys of TIN-induced Eprs1+/- mice. This discrepancy contributed to the fibrotic amelioration observed in kidneys of Eprs1+/- mice. TIN-induced fibrosis was also reduced in Rag1-/- mice adoptively transferred with Eprs1+/- T cells compared to the Rag1-/- mice transferred with Eprs1+/+ T cells. The use of an EPRS1-targeting small molecule inhibitor (bersiporocin) under clinical trials to evaluate its therapeutic potential against idiopathic pulmonary fibrosis alleviated immunofibrotic aggravation in TIN. EPRS1 expression was also observed in human kidney tissues and blood-derived T cells, and high expression was associated with worse patient outcomes. Thus, EPRS1 may emerge as a therapeutic target in toxin- and drug-induced TIN, modulating the proliferation and activity of infiltrated T cells.

Urinary Epidermal Growth Factor Level as a Noninvasive Indicator of Tubular Repair in Patients with Acute Kidney Injury

Epidermal growth factor (EGF), an essential factor for the proliferation and survival of renal tubular cells, is expressed by distal tubules and normally excreted via urine. Previous studies in rats demonstrated that acute tubular injury reduces urinary EGF levels. However, it is unclear whether urinary EGF is a suitable monitoring marker of tubular repair status after acute kidney injury (AKI) in humans. To address this question, we measured serum and urinary EGF in patients with AKI (n = 99) using ELISA and investigated whether urinary EGF levels were associated with the severity of tubular injury and renal prognosis. Urinary EGF was abundant in healthy controls but showed a significant decrease in AKI patients (14,522 ± 2190 pg/mL vs. 3201 ± 459.7 pg/mL, p < 0.05). The urinary EGF level in patients with renal AKI was notably lower than that in patients with pre-renal AKI. Furthermore, the urinary EGF level in patients with AKI stage 3 was significantly lower than that in patients with AKI stage 1. Urinary EGF levels were negatively correlated with urinary β-2MG and serum creatinine levels but positively correlated with hemoglobin levels and eGFR. Urinary EGF was not significantly correlated with urinary NAG, α-1MG, L-FABP, NGAL, KIM-1, or urinary protein concentrations. No significant correlation was observed between serum and urinary EGF levels, suggesting that urinary EGF is derived from the renal tubules rather than the blood. In living renal transplantation donors, the urinary EGF/Cr ratio was approximately half the preoperative urinary EGF/Cr ratio after unilateral nephrectomy. Collectively, these data suggest that urinary EGF is a suitable noninvasive indicator of not only the volume of functional normal renal tubules but also the status of tubular repair after AKI.

Cytoplasmic retention of the DNA/RNA-binding protein FUS ameliorates organ fibrosis in mice

Uncontrolled accumulation of extracellular matrix leads to tissue fibrosis and loss of organ function. We previously demonstrated in vitro that the DNA/RNA-binding protein fused in sarcoma (FUS) promotes fibrotic responses by translocating to the nucleus, where it initiates collagen gene transcription. However, it is still not known whether FUS is profibrotic in vivo and whether preventing its nuclear translocation might inhibit development of fibrosis following injury. We now demonstrate that levels of nuclear FUS are significantly increased in mouse models of kidney and liver fibrosis. To evaluate the direct role of FUS nuclear translocation in fibrosis, we used mice that carry a mutation in the FUS nuclear localization sequence (FUSR521G) and the cell-penetrating peptide CP-FUS-NLS that we previously showed inhibits FUS nuclear translocation in vitro. We provide evidence that FUSR521G mice or CP-FUS-NLS-treated mice showed reduced nuclear FUS and fibrosis following injury. Finally, differential gene expression analysis and immunohistochemistry of tissues from individuals with focal segmental glomerulosclerosis or nonalcoholic steatohepatitis revealed significant upregulation of FUS and/or collagen genes and FUS protein nuclear localization in diseased organs. These results demonstrate that injury-induced nuclear translocation of FUS contributes to fibrosis and highlight CP-FUS-NLS as a promising therapeutic option for organ fibrosis.

Comprehensive strategy for identifying extracellular vesicle surface proteins as biomarkers for chronic kidney disease

Chronic kidney disease (CKD) poses a significant health burden worldwide. Especially, obesity-induced chronic kidney disease (OCKD) is associated with a lack of accuracy in disease diagnostic methods. The identification of reliable biomarkers for the early diagnosis and monitoring of CKD and OCKD is crucial for improving patient outcomes. Extracellular vesicles (EVs) have emerged as potential biomarkers in the context of CKD. In this review, we focused on the role of EVs as potential biomarkers in CKD and OCKD and developed a comprehensive list of EV membrane proteins that could aid in the diagnosis and monitoring of the disease. To assemble our list, we employed a multi-step strategy. Initially, we conducted a thorough review of the literature on EV protein biomarkers in kidney diseases. Additionally, we explored papers investigating circulating proteins as biomarkers in kidney diseases. To further refine our list, we utilized the EV database Vesiclepedia.org to evaluate the qualifications of each identified protein. Furthermore, we consulted the Human Protein Atlas to assess the localization of these candidates, with a particular focus on membrane proteins. By integrating the information from the reviewed literature, Vesiclepedia.org, and the Human Protein Atlas, we compiled a comprehensive list of potential EV membrane protein biomarkers for CKD and OCKD. Overall, our review underscores the potential of EVs as biomarkers in the field of CKD research, providing a foundation for future studies aimed at improving CKD and OCKD diagnosis and treatment.

Pharmacological inhibition of the mixed lineage leukemia 1-menin interaction aggravates acute kidney injury induced by folic acid and ischemia-reperfusion in mice

Mixed lineage leukemia 1 (MLL1) is a methyltransferase that induces histone H3 lysine 4 trimethylation (H3K4me3) and partially exerts its untoward functional effects by interacting with multiple subunits including menin and WD repeat-containing protein 5 (WDR5). In this study, we investigated the role and mechanisms of MLL1 in murine models of acute kidney injury induced by folic acid (FA) and ischemia-reperfusion. Injury to the kidney elevated the expression of MLL1, menin, WDR5, and H3K4Me3, which was accompanied by increased serum creatinine and blood urea nitrogen, renal tubular injury, and apoptosis. Pharmacological inhibition of MLL1 activity with MI503 to disrupt the interaction between MLL1 with menin further increased serum creatinine and blood urea nitrogen levels, enhanced expression of neutrophil gelatinase-associated lipocalin and kidney injury molecule-1, and induced more apoptosis in the kidney following FA and ischemia-reperfusion injury. In contrast, MI503 treatment decreased the expression of vimentin and proliferating cell nuclear antigens. Similarly, treatment with MM102 to disrupt the interaction between MLL1 and WDR5 also worsened renal dysfunction, aggravated tubular cell injury, increased apoptosis, and inhibited cellular dedifferentiation and proliferation in mice following FA injection. Moreover, MI503 inhibited FA-induced phosphorylation of epidermal growth factor receptor, signal transducer and activator of transcription 3, and extracellular signal-regulated kinase-1/2 in injured kidneys. Collectively, these data suggest that MLL1 contributes to renal protection and functional recovery and promotes renal regeneration through a mechanism associated with activation of the epidermal growth factor receptor signaling pathway.NEW & NOTEWORTHY Mixed lineage leukemia 1 (MLL1) is a methyltransferase that induces histone H3 lysine 4 trimethylation and exerts its functional roles by interacting with multiple subunits. In this study, we demonstrated that inhibition of MLL1 activity by MI503 or MM102 aggravated renal injury and apoptosis and suppressed renal tubular cell dedifferentiation and proliferation, suggesting that MLL1 activation during acute kidney injury acts as an intrinsic protective mechanism to mediate renal tubular cell survival and regeneration.

Tubular cell transcriptional intermediary factor 1γ deficiency exacerbates kidney injury-induced tubular cell polyploidy and fibrosis

Tubulointerstitial fibrosis is considered the final convergent pathway of progressive chronic kidney diseases (CKD) regardless of etiology. However, mechanisms underlying kidney injury-induced fibrosis largely remain unknown. Recent studies have indicated that transcriptional intermediary factor 1γ (TIF1γ) inhibits the progression of fibrosis in other organs. Here, we found that TIF1γ was highly expressed in the cytoplasm and nucleus of the kidney proximal tubule. Interestingly, we found tubular TIF1γ expression was decreased in patients with CKD, including those with diabetes, hypertension, and IgA nephropathy, and in mouse models with experimental kidney fibrosis (unilateral ureteral obstruction [UUO], folic acid nephropathy [FAN], and aristolochic acid-induced nephrotoxicity). Tubule-specific knock out of TIF1γ in mice exacerbated UUO- and FAN-induced tubular cell polyploidy and subsequent fibrosis, whereas overexpression of kidney TIF1γ protected mice against kidney fibrosis. Mechanistically, in tubular epithelial cells, TIF1γ exerted an antifibrotic role via transforming growth factor-β (TGF-β)-dependent and -independent signaling. TIF1γ hindered TGF-β signaling directly by inhibiting the formation and activity of the transcription factor Smad complex in tubular cells, and we discovered that TIF1γ suppressed epidermal growth factor receptor (EGFR) signaling upstream of TGF-β signaling in tubular cells by ubiquitylating EGFR at its lysine 851/905 sites thereby promoting EGFR internalization and lysosomal degradation. Pharmacological inhibition of EGFR signaling attenuated exacerbated polyploidization and the fibrotic phenotype in mice with tubule deletion of TIF1γ. Thus, tubular TIF1γ plays an important role in kidney fibrosis by suppressing profibrotic EGFR and TGF-β signaling. Hence, our findings suggest that maintaining homeostasis of tubular TIF1γ may be a new therapeutic option for treating tubulointerstitial fibrosis and subsequent CKD.

The Role of the Epidermal Growth Factor Receptor in Diabetic Kidney Disease

The epidermal growth factor receptor (EGFR) is expressed in numerous cell types in the adult mammalian kidney and is activated by a family of EGF-like ligands. EGFR activation has been implicated in a variety of physiologic and pathophysiologic functions. There is increasing evidence that aberrant EGFR activation is a mediator of progressive kidney injury in diabetic kidney disease. This review will highlight recent studies indicating its potential role and mechanisms of injury of both glomerular and tubular cells in development and progression of diabetic kidney disease.