Xiaowen Yu

Renal fibrosis is the common outcome of practically all progressive forms of chronic kidney disease (CKD), a significant societal health concern. Glutamate dehydrogenase (GDH) 1 is one of key enzymes in glutamine metabolism to catalyze the reversible conversion of glutamate to α‐ketoglutarate and ammonia. However, its function in renal fibrosis has not yet been proven. In this study, GDH1 expression was significantly downregulated in kidney tissues of both children with kidney disease and animal models of CKD. In vivo, the use of R162 (a GDH1 inhibitor) significantly improved renal fibrosis, as indicated by Sirius red and Masson trichrome staining. These findings are consistent with the impaired expression of fibrosis indicators in kidneys from both the unilateral ureteral obstruction (UUO) and 5/6 nephrectomy (5/6 Nx) models. In vitro, silencing GDH1 or pretreatment with R162 inhibited the induction of fibrosis indicators in tissue kidney proximal tubular cells (TKPTS) treated with Transforming growth factor Beta 1 (TGF‐β1), whereas activating GDH1 worsened TGF‐β1's induction impact. Using RNA‐sequence, luciferase reporter assays and Biacore analysis, we demonstrated that GDH1 interacts with Peroxisome proliferator‐activated receptor gamma (PPARγ) and blocks its transcriptional activity, independent of the protein's expression. Additionally, R162 treatment boosted PPARγ transcriptional activity, and blocking of this signaling pathway reversed R162's protective effect. Finally, we discovered that R162 treatment or silencing GDH1 greatly lowered reactive oxygen species (ROS) and lipid accumulation. These findings concluded that suppressing GDH1 or R162 treatment could prevent renal fibrosis by augmenting PPARγ transcriptional activity to control lipid accumulation and redox balance.

Profibrotic proximal tubules (PT) were identified as a unique phenotype of proximal tubule cells (PTCs) in renal fibrosis by single-cell RNA sequencing (scRNA-seq). Controlling the process of renal fibrosis requires understanding how to manage the S1 subset’s branch to the S3 subset rather than to the profibrotic PT subset. Insulin-induced gene 1 (Insig1) is one of the branch-dependent genes involved in controlling this process, although its role in renal fibrosis is unknown. Here, we discovered that tubular Insig1 deficiency, rather than fibroblast Insig1 deficiency, plays a detrimental role in the pathogenesis of renal fibrosis in vivo and in vitro. Overexpression of Insig1 profoundly inhibited renal fibrosis. Mechanistically, Insig1 deletion in PTCs boosted SREBP1 nuclear localization, increasing Aldh1a1 transcriptional activity, causing excessive NAD ⁺ consumption and ER enlargement, as well as accelerating renal fibrosis. We also identified nicardipine as a selective inhibitor of Aldh1a1, which could restore NAD ⁺ and maintain ER homeostasis, as well as improve renal fibrosis. Together, our findings support tubular Insig1 as a new therapeutic target for chronic kidney disease (CKD).

Profibrotic proximal tubules (PTs) were identified as a unique phenotype of PTCs in renal fibrosis. Controlling the process of renal fibrosis requires understanding how to manage the S1 subset's branch to the S3 subset rather than to the profibrotic PT subset. Insig1 is one of the branch-dependent genes involved in controlling this process, although its role in renal fibrosis is unknown. Here, we discovered the pathogenic effect of PTC-specific Insig1 deficiency on renal fibrosis in vivo and in vitro. Overexpression of Insig1 profoundly inhibited renal fibrosis. Insig1 deletion boosted SREBP1 nuclear localization, increasing Aldh1a1 transcriptional activity, causing excessive NAD⁺ consumption and ER enlargement, and accelerating renal fibrosis. We identified nicardipine as a selective inhibitor of Aldh1a1-restored NAD⁺ and ER homeostasis, which attenuated renal fibrosis. Together, our findings support Insig1 as a new therapeutic target for CKD.

Nephrotoxicity is a major side effect of cisplatin. Apoptosis, oxidative stress, inflammation, and the MAPK signaling pathway activation are concerned with the pathophysiology of cisplatin‐induced acute kidney injury (AKI). Madecassoside (MA), an active constituent of Centella asiatica , has anti‐oxidative and anti‐inflammatory effects. The present research aim to investigate the underlying protective mechanisms of MA on cisplatin nephrotoxicity. Pretreatment of mice with MA markedly ameliorated cisplatin‐induced renal tubular cell injury evidenced by the improvement of kidney function and kidney morphology and blocked upregulation of kidney injury biomarkers (kidney injury molecule 1 (KIM‐1) and neutrophil gelatinase‐associated lipocalin (NGAL)). Cisplatin‐induced renal cell apoptosis, inflammation, and oxidative stress were also prevented by MA treatment. Consistent with the in vivo results, MA pretreatment attenuated cisplatin‐induced renal cell apoptosis, oxidative stress, and inflammation. Transcriptome analysis using RNA‐sequencing suggested that the MAPK signaling pathway was the most affected, and MA could inhibit cisplatin‐induced MAPK signaling pathway activation in vivo and in vitro. In summary, MA treatment ameliorated cisplatin‐induced renal tubular damage possibly by decreasing activation of the MAPK signaling pathway, suggesting its potential for the treatment of AKI.

The nuclear pregnane X receptor protects against bilateral renal ischemia/reperfusion-induced acute kidney injury in mice.

Acute kidney injury (AKI) is a worldwide public health problem with no specific and satisfactory therapies in clinic. The nuclear pregnane X receptor (PXR) is involved in the progression of multiple diseases, including metabolic diseases, atherosclerosis, hypertension, liver injury, etc. However, its role in kidney injury remains to be understood. In this study, we have investigated the role of PXR in AKI and underlying mechanism(s) involved in its function. PXR was robustly down-regulated and negatively correlated with renal dysfunction in human and animal kidneys with AKI. Silencing PXR in rats enhanced cisplatin-induced AKI and induced severe mitochondrial abnormalities, whereas activating PXR protected against AKI. Using luciferase reporter assays, genomic manipulation, and proteomics data analysis on the kidneys of PXR^−/− rats, we determined that PXR targeted Aldo-keto reductase family 1, member B7 (AKR1B7) to improve mitochondrial function, thereby ameliorating AKI. We confirmed the protective role of PXR against kidney injury using genomic and pharmacologic approaches in an ischemia/reperfusion model of AKI. These findings demonstrate that disabling the PXR/AKR1B7/mitochondrial metabolism axis is an important factor that can contribute to AKI, whereas reestablishing this axis can be useful for treating AKI.

DT‐13 combined with topotecan (TPT) showed stronger antitumour effects in mice subcutaneous xenograft model compared with their individual effects in our previous research. Here, we further observed the synergistically effect in mice orthotopic xenograft model. Metabolomics analysis showed DT‐13 combined with TPT alleviated metabolic disorders induced by tumour and synergistically inhibited the activity of the aerobic glycolysis‐related enzymes in vivo and in vitro. Mechanistic studies revealed that the combination treatment promoted epidermal growth factor receptor (EGFR) degradation through non‐muscle myosin IIA (NM IIA)‐induced endocytosis of EGFR, further inhibited the activity of hexokinase II (HK II), and eventually promoted the aerobic glycolysis inhibition activity more efficiently compared with TPT or DT‐13 monotherapy. The combination therapy also inhibited the specific binding of HK II to mitochondria. When using the NM II inhibitor (‐)002Dblebbistatin or MYH‐9 shRNA, the synergistic inhibition effect of DT‐13 and TPT on aerobic glycolysis was eliminated in BGC‐823 cells. Immunohistochemical analysis revealed selective up‐regulation of NM IIA while specific down‐regulation of p‐CREB, EGFR, and HK II by the combination therapy. Collectively, these findings suggested that this regimen has significant clinical implications, warranted further investigation.

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