The importance of proinflammatory failed-repair tubular epithelia as a predictor of diabetic kidney disease progression.

The immense public health burden of diabetic kidney disease (DKD) has led to an increase in research on the pathophysiology of advanced DKD. The present study focused on the significance of proinflammatory vascular cell adhesion molecule 1 (VCAM1)+ tubules in DKD progression. A retrospective cohort study of DKD patients showed that the percentage of VCAM1+ tubules in kidney samples was correlated with poor renal outcomes. We established an advanced DKD model by partial resection of the kidneys of db/db mice and demonstrated that it closely resembled the human advanced DKD phenotype, with tissue hypoxia, tubular DNA damage, tissue inflammation, and high tubular VCAM1 expression. Luseogliflozin ameliorated tissue hypoxia and proinflammatory responses, including VCAM1+ expression, in tubules. These findings suggest the potential of tubular VCAM1 as a histological marker for poor DKD outcomes. SGLT2 inhibitors may attenuate tissue hypoxia and subsequent tissue inflammation in advanced DKD, thereby ameliorating tubular injury.

Diverse Receptor Tyrosine Kinase Phosphorylation in Urine-Derived Tubular Epithelial Cells from Autosomal Dominant Polycystic Kidney Disease Patients.

BACKGROUNDS: The clinical features of autosomal dominant polycystic kidney disease (ADPKD) differ among patients even if they have the same gene mutation in PKD1 or PKD2. This suggests that there is diversity in the expression of other modifier genes or in the underlying molecular mechanisms of ADPKD, but these are not well understood. METHODS: We primarily cultured solute carrier family 12 member 3 (SLC12A3)-positive urine-derived distal tubular epithelial cells from 6 ADPKD patients and 4 healthy volunteers and established immortalized cell lines. The diversity in receptor tyrosine kinase (RTK) phosphorylation by phospho-RTK array in immortalized tubular epithelial cells was analyzed. RESULTS: We noted diversity in the activation of several molecules, including Met, a receptor of hepatocyte growth factor (HGF). Administration of golvatinib, a selective Met inhibitor, or transfection of small interfering RNA for Met suppressed cell proliferation and downstream signaling only in the cell lines in which hyperphosphorylation of Met was observed. In three-dimensional culture of Madin-Darby canine kidney (MDCK) cells as a cyst formation model of ADPKD, HGF activated Met, resulting in an increased total cyst number and total cyst volume. Administration of golvatinib inhibited these phenotypes in MDCK cells. CONCLUSION: Analysis of urine-derived tubular epithelial cells demonstrated diverse RTK phosphorylation in ADPKD, and Met phosphorylation was noted in some patients. Considering the difference in the effects of golvatinib on immortalized tubular epithelial cells among patients, this analysis may aid in selecting suitable drugs for individual ADPKD patients.

Intratubular epithelial-mesenchymal transition and tubular atrophy after kidney injury in mice.

Tubular atrophy is a common pathological feature of kidney fibrosis. Although fibroblasts play a predominant role in tissue fibrosis, the role of repairing tubular epithelia in tubular atrophy is unclear. We demonstrated the essential role of focal adhesion kinase (FAK)-mediated intratubular epithelial-mesenchymal transition (EMT) in the pathogenesis of tubular atrophy after severe ischemia-reperfusion injury (IRI). Actively proliferating tubular epithelia undergoing intratubular EMT were noted in the acute phase of severe IRI, resulting in tubular atrophy in the chronic phase, reflecting failed tubular repair. Furthermore, FAK was phosphorylated in the tubular epithelia in the acute phase of severe IRI, and its inhibition ameliorated both tubular atrophy and interstitial fibrosis in the chronic phase after injury. In vivo clonal analysis of single-labeled proximal tubular epithelial cells after IRI using proximal tubule reporter mice revealed substantial clonal expansion after IRI, reflecting active epithelial proliferation during repair. The majority of these proliferating epithelia were located in atrophic and nonfunctional tubules, and FAK inhibition was sufficient to prevent tubular atrophy. In vitro, transforming growth factor-ß induced FAK phosphorylation and an EMT phenotype, which was also prevented by FAK inhibition. In an in vitro tubular epithelia gel contraction assay, transforming growth factor-ß treatment accelerated gel contraction, which was suppressed by FAK inhibition. In conclusion, injury-induced intratubular EMT is closely related to tubular atrophy in a FAK-dependent manner.

Pharmacological inhibition of ataxia-telangiectasia mutated exacerbates acute kidney injury by activating p53 signaling in mice.

The DNA damage response after kidney injury induces cell cycle arrest in renal tubular epithelial cells, resulting in the secretion of pro-fibrotic cytokines, thereby promoting interstitial fibrosis in a paracrine manner. Phosphorylation of ataxia-telangiectasia mutated (ATM) is the initial step in the DNA damage response and subsequent cell cycle arrest; however, the effects of ATM inhibition on the injured kidney have not been explored. Pharmacological ATM inhibition by KU55933 in cisplatin-treated mice did not ameliorate, but instead exacerbated cisplatin-induced DNA damage and tubular injury, thereby increasing mortality. Analysis of isolated tubular epithelia by FACS from bigenic SLC34a1-CreERt2; R26tdTomato proximal tubular-specific reporter mice revealed that KU55933 upregulated p53 and subsequent pro-apoptotic signaling in tubular epithelia of cisplatin-treated mice, leading to marked mitochondrial injury and apoptosis. In addition, KU55933 attenuated several DNA repair processes after cisplatin treatment, including single-strand DNA repair and Fanconi anemia pathways, suggesting that DNA repair after dual treatment of cisplatin and KU55933 was not sufficient to prevent the cisplatin-induced tubular injury. Our study suggested that ATM inhibition does not increase DNA repair after cisplatin-induced DNA damage and exacerbates tubular injury through the upregulation of p53-dependent pro-apoptotic signaling. Acute kidney injury must be carefully monitored when ATM inhibitors become available in clinical practice in the future.