Cobaltosic oxide-polyethylene glycol-triphenylphosphine nanoparticles ameliorate the acute-to-chronic kidney disease transition by inducing BNIP3-mediated mitophagy.

Accumulating evidence highlights mitochondrial dysfunction as a crucial factor in the pathogenesis of acute kidney injury (AKI); thus, novel therapeutic strategies maintaining mitochondrial homeostasis are highly anticipated. Recent studies have shown that cobaltosic oxide has peroxidase-like catalytic activities, although its role and mechanism remain elusive in AKI. In the present study, we synthesized and identified cobaltosic oxide-polyethylene glycol-triphenylphosphine (COPT) nanoparticles by conjugating cobaltosic oxide with polyethylene glycol and triphenylphosphine, to improve its biocompatibility and mitochondria-targeting property. We found that COPT preferentially accumulated in the kidney proximal tubule cells, and significantly alleviated ischemic AKI in mouse models and gentamicin induced-AKI in the zebrafish model. COPT also inhibited the transition from AKI to chronic kidney disease (CKD), with few side effects. Further studies demonstrated that COPT localized in the mitochondria, and ameliorated hypoxia-reoxygenation-mediated mitochondrial damage through enhancing mitophagy in vitro and in vivo. Mechanistically, COPT dose-dependently induced the expression of Bcl-2/adenovirus E1B 19-kDa interacting protein (BNIP3), while knockdown of BNIP3 attenuated COPT-induced mitophagic flux and mitochondrial protection. Thus, our findings suggest that COPT nanoparticles ameliorate AKI and its progression to CKD through inducing BNIP3-mediated mitophagy, indicating that COPT may serve as a promising mitochondria-targeting therapeutic agent against AKI.

Molecular cloning, expression analysis, and the immune-related role of a thymosin ß in the goldfish, Carassius auratus.

ß-Thymosins play critical roles in the regulation of many important physiological processes, but their function in teleost fishes remains poorly understood. In this study, the full-length cDNA coding for a thymosin ß (Tß) was cloned and identified in goldfish, Carassius auratus (gfTß). The gfTß cDNA consisted of 653 bp with an open reading frame of 135 bp that encodes a 44 amino acid polypeptide. Sequence analysis revealed one thymosin domain and a highly conserved actin-binding motif (18LKKTET23). Expression of gfTß transcript was detected ubiquitously in all tissues examined, with relatively higher levels in the brain, intestine, spleen, gill, skin, kidney, and testis. Cadmium and H2O2 exposure induced increases in gfTß transcript levels in the liver and spleen. Moreover, gfTß transcription was upregulated in response to LPS challenge in the spleen while Poly I:C treatment did not affect gfTß expression. In vivo injection of recombinant gfTß generated from an Escherichia coli system induced expression of T lymphocyte-related genes (RAG1 and CD8α). These results suggest that gfTß may be involved in the immune response of teleost fishes via modulation of T lymphocyte development.

Self-Assembling P38 Peptide Inhibitor Nanoparticles Ameliorate the Transition from Acute to Chronic Kidney Disease by Suppressing Ferroptosis.

Accumulating evidence highlights p38 as a crucial factor highly activated during the process of acute kidney injury (AKI), but the application of p38 inhibitor in AKI is quite limited due to the low efficiency and poor kidney-targeting ability. Herein, a novel self-assembling peptide nanoparticle with specific p38-inhibiting activity is constructed, which linked mitogen-activated protein kinase kinase 3b (MKK3b), the functional domain of p38, with the cell-penetrating TAT sequence, ultimately self-assembling into TAT-MKK3b nanoparticles (TMNPs) through tyrosinase oxidation. Subsequent in vitro and in vivo studies demonstrated that TMNPs preferably accumulated in the renal tubular epithelial cells (RTECs) through forming protein coronas by binding to albumin, and strongly improved the reduced renal function of ischemia-reperfusion injury (IRI)-induced AKI and its transition to chronic kidney disease (CKD). Mechanically, TMNPs inhibited ferroptosis via its solute carrier family 7 member 11 (SLC7A11)/glutathione peroxidase 4 (GPX4) axis-inducing capacity and synergistic potent antioxidant property in AKI. The findings indicated that the multifunctional TMNPs exhibited renal targeting, ROS-scavenging, and ferroptosis-mitigating capabilities, which may serve as a promising therapeutic agent for the treatment of AKI and its progression to CKD.

IL-37 Ameliorates Renal Fibrosis by Restoring CPT1A-Mediated Fatty Acid Oxidation in Diabetic Kidney Disease.

Introduction: Diabetic kidney disease (DKD) is a major source of chronic kidney disease and end-stage renal disease. The injury of glomerulus in DKD is the primary focus; however, proximal tubulopathy also is an indispensable factor in the progression of DKD. Interleukin-37 (IL-37), an anti-inflammatory cytokine of IL-1 family member, has been demonstrated to be associated with diabetes and its relative complications in recent years, but the effect of IL-37 on renal fibrosis in DKD is unclear. Methods: We established streptozotocin plus high fat diet-induced DKD mice model with wild type or IL-37 transgenic mice. Masson and HE staining, immunostaining, and Western blot were used to observe renal fibrosis. In addition, RNA-sequencing was applied to explore the potential mechanisms of IL-37. In vitro, treatment of human proximal tubular (HK-2) cells with 30 mmol/L high glucose or 300 ng/mL recombinant IL-37 further elucidated the possible mechanism of IL-37 inhibition of DKD renal fibrosis. Results: In this work, we first verified the decreased expression of IL-37 in kidney of DKD patient and its correlation with clinical features of renal impairment. Moreover, IL-37 expression markedly attenuated proteinuria and renal fibrosis in DKD mice. Using RNA-sequencing, we found and confirmed a novel role of IL-37 in ameliorating fatty acid oxidation (FAO) reduction of renal tubular epithelial cells both in vivo and in intro. In addition, further mechanistic studies showed that IL-37 alleviated the FAO reduction in HK-2 cells and renal fibrosis in DKD mice through upregulating carnitine palmitoyl-transferase 1A (CPT1A), an important catalyzer for FAO pathway. Conclusion: These data suggest that IL-37 attenuates renal fibrosis via regulating FAO in renal epithelial cells. Upregulation of IL-37 levels might be an effective therapeutic avenue for DKD.

REST contributes to AKI-to-CKD transition through inducing ferroptosis in renal tubular epithelial cells.

Ischemic-reperfusion injury (IRI) is a major pathogenic factor in acute kidney injury (AKI), which directly leads to the hypoxic injury of renal tubular epithelial cells (RTECs). Although emerging studies suggest repressor element 1-silencing transcription factor (REST) as a master regulator of gene repression under hypoxia, its role in AKI remains elusive. Here, we found that REST was upregulated in AKI patients, mice, and RTECs, which was positively associated with the degree of kidney injury, while renal tubule-specific knockout of Rest significantly alleviated AKI and its progression to chronic kidney disease (CKD). Subsequent mechanistic studies indicated that suppression of ferroptosis was responsible for REST-knockdown-induced amelioration of hypoxia-reoxygenation injury, during which process Cre-expressing adenovirus-mediated REST downregulation attenuated ferroptosis through upregulating glutamate-cysteine ligase modifier subunit (GCLM) in primary RTECs. Further, REST transcriptionally repressed GCLM expression via directly binding to its promoter region. In conclusion, our findings revealed the involvement of REST, a hypoxia regulatory factor, in AKI-to-CKD transition and identified the ferroptosis-inducing effect of REST, which may serve as a promising therapeutic target for ameliorating AKI and its progression to CKD.

The molecular mechanisms and intervention strategies of mitophagy in cardiorenal syndrome.

Cardiorenal syndrome (CRS) is defined as a disorder of the heart and kidney, in which acute or chronic injury of one organ may lead to acute or chronic dysfunction of the other. It is characterized by high morbidity and mortality, resulting in high economic costs and social burdens. However, there is currently no effective drug-based treatment. Emerging evidence implicates the involvement of mitophagy in the progression of CRS, including cardiovascular disease (CVD) and chronic kidney disease (CKD). In this review, we summarized the crucial roles and molecular mechanisms of mitophagy in the pathophysiology of CRS. It has been reported that mitophagy impairment contributes to a vicious loop between CKD and CVD, which ultimately accelerates the progression of CRS. Further, recent studies revealed that targeting mitophagy may serve as a promising therapeutic approach for CRS, including clinical drugs, stem cells and small molecule agents. Therefore, studies focusing on mitophagy may benefit for expanding innovative basic research, clinical trials, and therapeutic strategies for CRS.

Oroxylin A ameliorates AKI-to-CKD transition through maintaining PPARα-BNIP3 signaling-mediated mitochondrial homeostasis.

Background: Acute kidney injury (AKI) occurs in approximately 7-18% of all hospitalizations, but there are currently no effective drug therapy for preventing AKI or delaying its progression to chronic kidney disease (CKD). Recent studies have shown that Scutellaria baicalensis, a traditional Chinese herb, could attenuate cisplatin-induced AKI, although the mechanism remains elusive. Further, it is unknown whether its major active component, Oroxylin A (OA), can alleviate kidney injury. Methods: The therapeutic effect of OA was evaluated by using ischemia-reperfusion (IR) and cisplatin mediated-AKI mice and HK-2 cells under hypoxia-reoxygenation (HR) conditions. HE staining, transmission electron microscopy, flow cytometry, immunofluorescence, qPCR, Western blot, PPARα inhibitor, BNIP3 siRNA and ChIP assay were used to explore the role and mechanism of OA in AKI. Results: OA ameliorated tubular damage and dramatically decreased serum creatinine (Scr) and urea nitrogen (BUN), and the expressions of renal injury markers (Kim-1, Ngal) in AKI mice induced by both IR injury and cisplatin, as well as attenuating AKI-to-CKD transition. In vitro experiments showed that OA alleviated HR-induced mitochondrial homeostasis imbalance in renal tubular epithelial cells. Mechanistically, OA dose-dependently induced the expression of Bcl-2/adenovirus E1B 19-kDa interacting protein (BNIP3), while knockdown of BNIP3 expression reversed the protection of OA against HR-mediated mitochondrial injury. Network pharmacological analysis and experimental validation suggested that OA enhanced BNIP3 expression via upregulating the expression of peroxisome proliferator activated receptor alpha (PPARα), which induced the transcription of BNIP3 via directly binding to its promoter region. Both in vitro and in vivo experiments confirmed that the renoprotective effect of OA was dramatically reduced by GW6471, a PPARα antagonist. Conclusion: Our findings revealed that OA ameliorates AKI-to-CKD transition by maintaining mitochondrial homeostasis through inducing PPARα-BNIP3 signaling pathway, indicating that OA may serve as a candidate therapeutic strategy for alleviating AKI and CKD.

Activation of EP4 alleviates AKI-to-CKD transition through inducing CPT2-mediated lipophagy in renal macrophages.

Acute kidney injury (AKI) is a common clinical syndrome with complex pathogenesis, characterized by a rapid decline in kidney function in the short term. Worse still, the incomplete recovery from AKI increases the risk of progression to chronic kidney disease (CKD). However, the pathogenesis and underlying mechanism remain largely unknown. Macrophages play an important role during kidney injury and tissue repair, but its role in AKI-to-CKD transition remains elusive. Herein, single nucleus RNA sequencing (snRNA-Seq) and flow cytometry validations showed that E-type prostaglandin receptor 4 (EP4) was selectively activated in renal macrophages, rather than proximal tubules, in ischemia-reperfusion injury (IRI)-induced AKI-to-CKD transition mouse model. EP4 inhibition aggravated AKI-to-CKD transition, while EP4 activation impeded the progression of AKI to CKD though regulating macrophage polarization. Mechanistically, network pharmacological analysis and subsequent experimental verifications revealed that the activated EP4 inhibited macrophage polarization through inducing Carnitine palmitoyltransferase 2 (CPT2)-mediated lipophagy in macrophages. Further, CPT2 inhibition abrogated the protective effect of EP4 on AKI-to-CKD transition. Taken together, our findings demonstrate that EP4-CPT2 signaling-mediated lipophagy in macrophages plays a pivotal role in the transition of AKI to CKD and targeting EP4-CPT2 axis could serve as a promising therapeutic approach for retarding AKI and its progression to CKD.

Identification of three selenoprotein T paralogs in goldfish (Carassius auratus) and expression analysis in response to environmental stressors.

Selenoproteins, which contain the selenocysteine (Sec), play crucial roles in antioxidant protection. In the present study, we have identified and characterized three selenoprotein T paralogs (designated as gfSelT1a, gfSelT1b and gfSelT2) in goldfish, Carassius auratus. The SECIS element was found in the 3'-UTRs of gfSelT1a, gfSelT1b and gfSelT2 mRNA. Sequence analysis showed that they all possess the CxxU motif (where U represents Sec) in the N-terminal. Constitutive expressions of gfSelT1a, gfSelT1b and gfSelT2 were observed in all tissues studied. In liver, gfSelT1a, gfSelT1b and gfSelT2 mRNA expression levels significantly decreased when fasting and increased after re-feeding. The expressions of gfSelT1a, gfSelT1b and gfSelT2 were all inducible by cadmium exposure and H2O2-mediated oxidative stress, except the transcripts of gfSelT1b decreasing with H2O2 stimulation in brain. Furthermore, the expressions of gfSelT1a, gfSelT1b and gfSelT2 consistently increased in spleen but decreased in brain in response to heat stress. However, in liver only gfSelT1a mRNA expression significantly increased. In a word, this is the first report of the presence of three SelT genes in goldfish and their distinct expression patterns in response to environmental stressors. Our results suggest a potential involvement of gfSelT1a, gfSelT1b and gfSelT2 in host protection against environmental stressors including heavy mental, oxidative stress and heat stress in goldfish.