Collecting Duct-Specific CR6-Interacting Factor-1-Deletion Aggravates Renal Inflammation and Fibrosis Induced by Unilateral Ureteral Obstruction

Integrated network analysis and experimental verification of the mechanisms employed by Compound Jixuecao Decoction to improve endoplasmic reticulum stress and apoptosis in chronic renal failure

ETHNOPHARMACOLOGICAL RELEVANCE

Compound Jixuecao Decoction (CJD) is a traditional Chinese herbal medicine prescribed in China to treat chronic renal failure (CRF). Previous studies have shown that CJD affects cell apoptosis and proliferation. However, the mechanism of its renal protective action has not been characterized.

AIM OF THE STUDY

To explore the mechanism(s) underlying the effect of CJD on endoplasmic reticulum stress (ERS) and apoptosis in the treatment of CRF using network pharmacology, molecular docking, molecular dynamics simulations, and in vivo studies.

MATERIALS AND METHODS

The compounds comprising CJD were extracted from the Traditional Chinese Medicine Systems Pharmacology Database. A Swiss target prediction database and similarity integration approach were employed to identify potential targets of these components. The GeneCards and DisGeNET databases were used to identify targets associated with CRF, apoptosis, and ERS. The STRING database was employed to analyze the protein-protein interactions (PPIs) associated with drug-disease crossover. A chemical composition-shared target network was established, and critical pathways were identified through gene ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses. The Protein Data Bank database was used to search key proteins, while molecular docking and dynamics simulations were performed between the top four CJD active ingredients and proteins involved in apoptosis and ERS in CRF. Subsequent in vivo studies using a 5/6 nephrectomy rat model of CRF were performed to verify the findings.

RESULTS

The 80 compounds identified in CJD yielded 875 target genes, of which 216 were potentially related to CRF. PPI network analysis revealed key targets via topology filtering. Enrichment analysis, molecular docking, and molecular dynamics simulation results suggested that CJD primarily targets mitofusin-2 (MFN2), B-cell lymphoma-2 (BCL2), BAX, protein kinase RNA-like ER kinase (PERK), and C/EBP homologous protein (CHOP) during CRF treatment. In vivo, CJD significantly increased the abundance of MFN2, BCL2, and significantly reduced the abundance of BAX, PERK, CHOP proteins in kidney tissues, indicating that CJD could improve apoptosis and ERS in CRF rats.

CONCLUSIONS

This study provides evidence that CJD effectively delays CFR through modulation of the MFN2 and PERK-eIF2α-ATF4-CHOP signaling pathways.

Omega-3 Fatty Acids Attenuate Renal Fibrosis via AMPK-Mediated Autophagy Flux Activation

The unilateral ureteral obstruction (UUO) injury model is well-known to mimic human chronic kidney disease, promoting the rapid onset and development of kidney injury. ω3-poly unsaturated fatty acids (PUFAs) have been observed to protect against tissue injury in many disease models. In this study, we assessed the efficacy of ω3-PUFAs in attenuating UUO injury and investigated their mechanism of action. The immortalized human proximal tubular cells human kidney-2 (HK2) were incubated for 72 h with docosahexaenoic acid (DHA) or eicosapentaenoic acid (EPA) in various concentrations, in the presence or absence of transforming growth factor (TGF)-β. DHA/EPA reduced the epithelial-mesenchymal transition in the TGF-β-treated HK2 cells by enhancing autophagy flux and adenosine monophosphate-activated protein kinase (AMPK) phosphorylation. C57BL/6 mice were divided into four groups and treated as follows: sham (no treatment, n = 5), sham + ω3-PUFAs (n = 5), UUO (n = 10), and UUO + ω3-PUFAs (n = 10). Their kidneys and blood were harvested on the seventh day following UUO injury. The kidneys of the ω3-PUFAs-treated UUO mice showed less oxidative stress, inflammation, and fibrosis compared to those of the untreated UUO mice. Greater autophagic flux, higher amounts of microtubule-associated protein 1A/1B-light chain 3 (LC3)-II, Beclin-1, and Atg7, lower amounts of p62, and higher levels of cathepsin D and ATP6E were observed in the kidneys of the omega-3-treated UUO mice compared to those of the control UUO mice. In conclusion, ω3-PUFAs enhanced autophagic activation, leading to a renoprotective response against chronic kidney injury.

PCK1 Protects against Mitoribosomal Defects in Diabetic Nephropathy in Mouse Models

SIGNIFICANCE STATEMENT

Renal gluconeogenesis plays an important role in the pathogenesis of diabetic nephropathy (DN). Proximal tubular phosphoenolpyruvate carboxykinase1 (PEPCK1) is the rate-limiting enzyme in gluconeogenesis. However, the functions of PEPCK1 have not been elucidated. We describe the novel role of PEPCK1 as a mitoribosomal protector using Pck1 transgenic (TG) mice and knockout mice. Pck1 blocks excessive glycolysis by suppressing the upregulation of excess HK2 (the rate-limiting enzyme of glycolysis). Notably, Pck1 overexpression retains mitoribosomal function and suppresses renal fibrosis. The renal and mitoribosomal protective roles of Pck1 may provide important clues for understanding DN pathogenesis and provide novel therapeutic targets.

BACKGROUND

Phosphoenolpyruvate carboxykinase (PEPCK) is part of the gluconeogenesis pathway, which maintains fasting glucose levels and affects renal physiology. PEPCK consists of two isoforms-PEPCK1 and PEPCK2-that the Pck1 and Pck2 genes encode. Gluconeogenesis increases in diabetic nephropathy (DN), escalating fasting and postprandial glucose levels. Sodium-glucose cotransporter-2 inhibitors increase hepatic and renal gluconeogenesis. We used genetically modified mice to investigate whether renal gluconeogenesis and Pck1 activity are renoprotective in DN.

METHODS

We investigated the expression of Pck1 in the proximal tubule (PTs) of streptozotocin (STZ)-treated diabetic mice. We studied the phenotypic changes in PT-specific transgenic (TG) mice and PT-specific Pck1 conditional knockout (CKO) mice.

RESULTS

The expression of Pck1 in PTs was downregulated in STZ-treated diabetic mice when they exhibited albuminuria. TG mice overexpressing Pck1 had improved albuminuria, concomitant with the mitigation of PT cell apoptosis and deposition of peritubular type IV collagen. Moreover, CKO mice exhibited PT cell apoptosis and type IV collagen deposition, findings also observed in STZ-treated mice. Renal fibrotic changes in CKO mice were associated with increasing defects in mitochondrial ribosomes (mitoribosomes). The TG mice were protected against STZ-induced mitoribosomal defects.

CONCLUSION

PCK1 preserves mitoribosomal function and may play a novel protective role in DN.

Oxidative Stress and Mitochondrial Dysfunction in Chronic Kidney Disease

The kidney contains many mitochondria that generate ATP to provide energy for cellular processes. Oxidative stress injury can be caused by impaired mitochondria with excessive levels of reactive oxygen species. Accumulating evidence has indicated a relationship between oxidative stress and kidney diseases, and revealed new insights into mitochondria-targeted therapeutics for renal injury. Improving mitochondrial homeostasis, increasing mitochondrial biogenesis, and balancing mitochondrial turnover has the potential to protect renal function against oxidative stress. Although there are some reviews that addressed this issue, the articles summarizing the relationship between mitochondria-targeted effects and the risk factors of renal failure are still few. In this review, we integrate recent studies on oxidative stress and mitochondrial function in kidney diseases, especially chronic kidney disease. We organized the causes and risk factors of oxidative stress in the kidneys based in their mitochondria-targeted effects. This review also listed the possible candidates for clinical therapeutics of kidney diseases by modulating mitochondrial function.

Gene expression profile and injury sites in mice treated with Shiga toxin 2 and lipopolysaccharide as a Shiga toxin-associated hemolytic uremic syndrome model

Shiga toxin 2 (Stx2) and lipopolysaccharide (LPS) contribute to the development of hemolytic uremic syndrome (HUS). Mouse models of HUS induced by LPS/Stx2 have been used for elucidating HUS pathophysiology and for therapeutic development. However, the underlying molecular mechanisms and detailed injury sites in this model remain unknown. We analyzed mouse kidneys after LPS/Stx2 administration using microarrays. Decreased urinary osmolality and urinary potassium were observed after LPS/Stx2 administration, suggestive of distal nephron disorders. A total of 1212 and 1016 differentially expressed genes were identified in microarrays at 6 and 72 h after LPS/Stx2 administration, respectively, compared with those in controls. Ingenuity pathway analysis revealed activation of TNFR1/2, iNOS, and IL-6 signaling at both time points, and inhibition of pathways associated with lipid metabolism at 72 h only. The strongly downregulated genes in the 72-h group were expressed in the distal nephrons. In particular, genes associated with distal convoluted tubule (DCT) 2 /connecting tubule (CNT) and principal cells of the cortical collection duct (CCD) were downregulated to a greater extent than those associated with DCT1 and intercalated cells. Stx receptor globotriaosylceramide 3 (Gb3) revealed no colocalization with DCT1-specific Pvalb and intercalated cell-specific Slc26a4 but did present colocalization with Slc12a3 (present in both DCT1 and DCT2), and Aqp2 in principal cells. Gb3 localization tended to coincide with the segment in which the downregulated genes were present. Thus, the LPS/Stx2-induced kidney injury model represents damage to DCT2/CNT and principal cells in the CCD, based on molecular, biological, and physiological findings.