Regulation of kidney development by the Mdm2/Mdm4-p53 axis

Machine learning algorithm-based identification and verification of characteristic genes in acute kidney injury

Background

Acute kidney injury is a common renal disease with high incidence and mortality. Early identification of high-risk acute renal injury patients following renal transplant could improve their prognosis, however, no biomarker exists for early detection.

Methods

The GSE139061 dataset was used to identify hub genes in 86 DEGs between acute kidney injury and control samples using three machine learning algorithms (LASSO, random forest, and support vector machine-recursive feature elimination). We used GSEA to identify the related signal pathways of six hub genes. Finally, we validated these potential biomarkers in an in vitro hypoxia/reoxygenation injury cell model using RT-qPCR.

Results

Six hub genes (MDFI, EHBP1L1, FBXW4, MDM4, RALYL, and ESM1) were identified as potentially predictive of an acute kidney injury. The expression of ESM1 and RALYL were markedly increased in control samples, while EHBP1L1, FBXW4, MDFI, and MDM4 were markedly increased in acute kidney injury samples.

Conclusion

We screened six hub genes related to acute kidney injury using three machine learning algorithms and identified genes with potential diagnostic utility. The hub genes identified in this study might play a significant role in the pathophysiology and progression of AKI. As such, they might be useful for the early diagnosis of AKI and provide the possibility of improving the prognosis of AKI patients.

Cigarette smoke extract mediates cell premature senescence in chronic obstructive pulmonary disease patients by up-regulating USP7 to activate p300-p53/p21 pathway

OBJECTIVES

Tobacco hazard is one of the most severe public health issues in the world. It is believed that smoking is the most important factor leading to chronic obstructive pulmonary disease (COPD). Endothelial progenitor cells (EPCs) originate from the bone marrow and can effectively repair vascular endothelial damage and improve vascular endothelial function. Current studies suggest that EPCs senescence and EPCs depletion exist in smoking-related COPD, but the molecular mechanism remains unclear.

METHODS

Co-immunoprecipitation was used to detect the interaction between USP7 and p300. EPCs from smoking COPD patients were isolated, and the expressions of USP7 and p300 were detected by RT-PCR and Western Blot. Different concentrations of cigarette smoke extract (CSE) and USP7 or p300 inhibitors were used to treat EPCs, then the expression of p53, p53 target genes and aging-related genes were detected. Cell Counting Kit - 8 (CCK8) was used to detect cell proliferation, flow cytometry was used to detect cell cycle distribution, β-galactosidase (β-gal) staining and Lamp1 immunofluorescence was used to detect the proportion of aging cells. COPD mouse models were used to confirm the molecular mechanism.

RESULTS

USP7 and p300 interacted with each other, and USP7 affected the protein stability of p300 by regulating the ubiquitination of p300. There existed high expressions of USP7 and p300 proteins in EPCs of smoking COPD patients and COPD mouse model. CSE promoted the high expressions of USP7 and p300 in EPCs. Further studies showed that CSE mediated the USP7/p300-dependent high expression of p53 and activated the expression of p53 target genes especially p21. Activation of p53 - p21 pathway finally inhibited cell activity, led to cell cycle arrest and premature senescence of EPCs.

CONCLUSION

CSE mediated up-regulation of USP7 and p300 activated p53 - p21 pathway was a molecular mechanism that might lead to COPD.

Dlx3 Ubiquitination by Nuclear Mdm2 Is Essential for Dentinogenesis in Mice

Dentin is a major mineralized component of teeth. Odontoblasts are responsible for synthesis and secretion of dentin matrix. Previously, it has been demonstrated in a cell culture system that the E3 ubiquitin ligase, murine double minute 2 (Mdm2), promotes odontoblast-like differentiation of mouse dental papilla cells (mDPCs) by ubiquitinating p53 and the odontoblast-specific substrate Dlx3. However, whether Mdm2 plays an essential role in vivo in odontoblast differentiation and dentin formation remains unknown. In this study, we investigated the in vivo functions of Mdm2 using Dmp1-Cre;Mdm2 flox/flox mice combined with multiple histological and molecular biological methods. The results showed that Mdm2 deletion in the odontoblast layer led to defects in odontoblast differentiation and dentin formation. Unexpectedly, specific inhibition of the Mdm2-p53 axis in wild-type mice by injection of a small-molecule inhibitor Nutlin-3a indicated that the role of Mdm2 in dentinogenesis was p53 independent, which was inconsistent with the previous in vitro study. In situ proximity ligation assay (PLA) showed that Mdm2 interacted with and ubiquitinated Dlx3 in the odontoblast nucleus of mouse molars. Dlx3 promoted the translocation of Mdm2 to the nucleus, and in turn, the nuclear Mdm2 mediated ubiquitination of Dlx3 and promoted the odontoblast-like differentiation of mDPCs. Dlx3 interacted with Mdm2 through its C-terminal domain. Deletion of the C-terminal domain of Dlx3 reversed the enhanced odontoblast-like differentiation and the activation of Dspp promoter mediated by overexpression of wild-type or nuclear Mdm2. Our findings suggest that nuclear Mdm2 mediates ubiquitination of the transcription factor Dlx3, which is essential for Dlx3 transcriptional activity on Dspp as well as subsequent odontoblast differentiation and dentin formation.

Angiotensin II biphasically regulates cell differentiation in human iPSC-derived kidney organoids

Human kidney organoid technology holds promise for novel kidney disease treatment strategies and utility in pharmacological and basic science. Given the crucial roles of the intrarenal renin-angiotensin system (RAS) and angiotensin II (ANG II) in the progression of kidney development and injury, we investigated the expression of RAS components and effects of ANG II on cell differentiation in human kidney organoids. Human induced pluripotent stem cell-derived kidney organoids were induced using a modified 18-day Takasato protocol. Gene expression analysis by digital PCR and immunostaining demonstrated the formation of renal compartments and expression of RAS components. The ANG II type 1 receptor (AT1R) was strongly expressed in the early phase of organoid development (around day 0), whereas ANG II type 2 receptor (AT2R) expression levels peaked on day 5. Thus, the organoids were treated with 100 nM ANG II in the early phase on days 0-5 (ANG II-E) or during the middle phase on days 5-10 (ANG II-M). ANG II-E was observed to decrease levels of marker genes for renal tubules and proximal tubules, and the downregulation of renal tubules was inhibited by an AT1R antagonist. In contrast, ANG II-M increased levels of markers for podocytes, the ureteric tip, and the nephrogenic mesenchyme, and an AT2R blocker attenuated the ANG II-M-induced augmentation of podocyte formation. These findings demonstrate RAS expression and ANG II exertion of biphasic effects on cell differentiation through distinct mediatory roles of AT1R and AT2R, providing a novel strategy to establish and further characterize the developmental potential of human induced pluripotent stem cell-derived kidney organoids.NEW & NOTEWORTHY This study demonstrates angiotensin II exertion of biphasic effects on cell differentiation through distinct mediatory roles of angiotensin II type 1 receptor and type 2 receptor in human induced pluripotent stem cell-derived kidney organoids, providing a novel strategy to establish and further characterize the developmental potential of the human kidney organoids.

The roles of histone deacetylases in kidney development and disease

Histone deacetylases (HDACs) are important epigenetic regulators that mediate deacetylation of both histone and non-histone proteins. HDACs, especially class I HDACs, are highly expressed in developing kidney and subject to developmental control. HDACs play an important role in kidney formation, especial nephron progenitor maintenance and differentiation. Several lines of evidence support the critical role of HDACs in the development and progression of various kidney diseases. HDAC inhibitors (HDACis) are very effective in the prevention and treatment of kidney diseases (including kidney cancer). A better understanting of the molecular mechanisms underlying the role(s) of HDACs in the pathogenesis and progression of renal disease are likely to be of great help in developing more effective and less toxic selective HDAC inhibitors and combinatorial therapeutics.

Targeting MDMX for Cancer Therapy: Rationale, Strategies, and Challenges

The oncogene MDMX, also known as MDM4 is a critical negative regulator of the tumor suppressor p53 and has been implicated in the initiation and progression of human cancers. Increasing evidence indicates that MDMX is often amplified and highly expressed in human cancers, promotes cancer cell growth, and inhibits apoptosis by dampening p53-mediated transcription of its target genes. Inhibiting MDMX-p53 interaction has been found to be effective for restoring the tumor suppressor activity of p53. Therefore, MDMX is becoming one of the most promising molecular targets for developing anticancer therapeutics. In the present review, we mainly focus on the current MDMX-targeting strategies and known MDMX inhibitors, as well as their mechanisms of action and in vitro and in vivo anticancer activities. We also propose other potential targeting strategies for developing more specific and effective MDMX inhibitors for cancer therapy.

Aquaporin 2 Expression in Human Fetal Kidney Development

Introduction: The metanephrogenic zone, renal cortex and renal pyramids develop into their final form by week 13. The metanephric kidney produces large quantities of diluted urine in order to maintain volumes of amniotic fluid. Aquaporins are transmembrane protein channels that enable water transport through biological membranes. Aquaporin 2 (AQP2) is a water channel found in the supranuclear region and apical area of the cell membrane of the kidneys collecting tubule cells. Its main function is reabsorption of water through vasopressin stimulation.

Materials and methods: Immunohistochemistry was used to study fetal renal tissue of 34 post-mortem fetuses of 9 weeks to 24 weeks gestational age.

Results: AQP2 expression is present in connecting tubules and collecting tubules during the targeted time period. From week 9 to 12, the expression is cytoplasmic. From week 13 to 20 the enhancement of expression in the apical cell membrane occurs with the advancement of fetal age. At the end of the studied period, from week 21 to 24, both cytoplasmic and apical expression were observed. In animal studies AQP2 expression has an increasing trend during development. In contradiction with these results, other authors described low AQP2 levels in the human fetal kidney.

Conclusions: This study helps to understand the amniotic fluid’s homeostasis during pregnancy. In the beginning of the fetal period AQP2 protein is present in the cytoplasm of epithelial cells of the collecting duct and distal connecting duct. During the fetal period, AQP2 expression in collecting ducts becomes more enhanced in the apical membrane of the cells.

TGF-β1/p53 signaling in renal fibrogenesis

Fibrotic disorders of the renal, pulmonary, cardiac, and hepatic systems are associated with significant morbidity and mortality. Effective therapies to prevent or curtail the advancement to organ failure, however, remain a major clinical challenge. Chronic kidney disease, in particular, constitutes an increasing medical burden affecting >15% of the US population. Regardless of etiology (diabetes, hypertension, ischemia, acute injury, urologic obstruction), persistently elevated TGF-β1 levels are causatively linked to the activation of profibrotic signaling networks and disease progression. TGF-β1 is the principal driver of renal fibrogenesis, a dynamic pathophysiologic process that involves tubular cell injury/apoptosis, infiltration of inflammatory cells, interstitial fibroblast activation and excess extracellular matrix synthesis/deposition leading to impaired kidney function and, eventually, to chronic and end-stage disease. TGF-β1 activates the ALK5 type I receptor (which phosphorylates SMAD2/3) as well as non-canonical (e.g., src kinase, EGFR, JAK/STAT, p53) pathways that collectively drive the fibrotic genomic program. Such multiplexed signal integration has pathophysiological consequences. Indeed, TGF-β1 stimulates the activation and assembly of p53-SMAD3 complexes required for transcription of the renal fibrotic genes plasminogen activator inhibitor-1, connective tissue growth factor and TGF-β1. Tubular-specific ablation of p53 in mice or pifithrin-α-mediated inactivation of p53 prevents epithelial G₂/M arrest, reduces the secretion of fibrotic effectors and attenuates the transition from acute to chronic renal injury, further supporting the involvement of p53 in disease progression. This review focuses on the pathophysiology of TGF-β1-initiated renal fibrogenesis and the role of p53 as a regulator of profibrotic gene expression.

Mdm proteins: critical regulators of embry ogenesis and homeostasis

Mdm2 and Mdm4 are negative regulators of the tumor suppressor p53; hence, this relationship is the focus of many cancer related studies. A multitude of experiments across various developmental stages have been conducted to explore the tissue-specific roles of these proteins in the mouse. When Mdm2 or Mdm4 are deleted in the germline or specific tissues, they display different phenotypic defects, some of which lead to embryonic lethality. Mdm2 loss is often more deleterious than loss of its homolog Mdm4 All tissues experience activation of p53 target genes upon loss of Mdm2 or Mdm4; however, the degree to which the p53 pathway is perturbed is highly tissue-specific and does not correlate to the severity of the morphological phenotypes. Therefore, a need for further understanding of how these proteins regulate p53 activity is warranted, as therapeutic targeting of the p53 pathway is rapidly evolving and gaining attention in the field of cancer research. In this review, we discuss the tissue-specificity of Mdm proteins in regulating p53 and expose the need for investigation at the cell-specific level.