Metabolomic and biochemical characterization of a new model of the transition of acute kidney injury to chronic kidney disease induced by folic acid

Ameliorating role of co-administration of granulocyte colony stimulating factor and sodium bicarbonate on the skeletal muscle of a rat model of chronic kidney disease (A histological and immunohistochemical study)

Over half million individuals suffer from chronic kidney disease (CKD) worldwide. In addition to raising the possibility of cardiovascular diseases, skeletal myopathy remains a challenging complication that is highly correlated with mortality and a lower quality of life. Granulocyte-colony stimulating factor (G-CSF) is an active cytokine for mobilization of immunological and hematopoietic stem cells that can replace exogenous stem cell infusions. So, it is seen as a less expensive and noninvasive tool for regenerative medicine. Sixty three rats were divided into 4 groups: I control, II CKD induced, IIIa, IIIb treated and IV recovery groups. After induction of CKD in all rats, group II were sacrificed after 4 weeks. Rats of group IIIa received NaHCO3. Group IIIb rats were injected subcutaneously by G-CSF as 100 µg/kg/day for 5 successive days in addition to NaHCO3 as group IIIa. Group IV rats were housed for 4 weeks without treatment. Serum urea, creatinine, tissue MDA& TNF-α were assessed. Renal and gastrocnemius muscle sections were evaluated for histological structure, CD34 and myogenin immune expression, morphometric and statistical analyses. The CKD group revealed a significant increase in MDA and TNF-α. Furthermore, features of renal injury, muscle degenerative changes, increased collagen and decreased CD34 and myogenin expression were observed. Alterations were partially attenuated by NaHCO3, while GCSF remarkably improved most parameters. The current results indicated that co-administration of GCSF and NaHCO3 could ameliorate CKD myopathy via attenuating oxidative stress, immunomodulation, pro-angiogenic ability, myocyte regeneration. In addition to the reduction of mitochondrial stress and maintenance of cellular homeostasis.

Adenine-induced animal model of chronic kidney disease: current applications and future perspectives

Chronic kidney disease (CKD) with high morbidity and mortality all over the world is characterized by decreased kidney function, a condition which can result from numerous risk factors, including diabetes, hypertension and obesity. Despite significant advances in our understanding of the pathogenesis of CKD, there are still no treatments that can effectively combat CKD, which underscores the urgent need for further study into the pathological mechanisms underlying this condition. In this regard, animal models of CKD are indispensable. This article reviews a widely used animal model of CKD, which is induced by adenine. While a physiologic dose of adenine is beneficial in terms of biological activity, a high dose of adenine is known to induce renal disease in the organism. Following a brief description of the procedure for disease induction by adenine, major mechanisms of adenine-induced CKD are then reviewed, including inflammation, oxidative stress, programmed cell death, metabolic disorders, and fibrillation. Finally, the application and future perspective of this adenine-induced CKD model as a platform for testing the efficacy of a variety of therapeutic approaches is also discussed. Given the simplicity and reproducibility of this animal model, it remains a valuable tool for studying the pathological mechanisms of CKD and identifying therapeutic targets to fight CKD.

ULK1-regulated AMP sensing by AMPK and its application for the treatment of chronic kidney disease

Adenosine monophosphate (AMP)-activated protein kinase (AMPK) is a central kinase involved in energy homeostasis. Increased intracellular AMP levels result in AMPK activation through the binding of AMP to the γ-subunit of AMPK. Recently, we reported that AMP-induced AMPK activation is impaired in the kidneys in chronic kidney disease (CKD) despite an increase in the AMP/ATP ratio. However, the mechanisms by which AMP sensing is disrupted in CKD are unclear. Here, we identified mechanisms of energy homeostasis in which Unc-51-like kinase 1 (ULK1)-dependent phosphorylation of AMPKγ1 at Ser260/Thr262 promoting AMP sensitivity of AMPK. AMPK activation by AMP was impaired in Ulk1 knockout mice despite an increased AMP/ATP ratio. ULK1 expression is markedly downregulated in CKD kidneys, leading to AMP sensing failure. Additionally, MK8722, an allosteric AMPK activator, stimulated AMPK in the kidneys of a CKD mouse model (5/6th nephrectomy) via a pathway that is independent of AMP sensing. Thus, our study shows that MK8722 treatment significantly attenuates the deterioration of kidney function in CKD and may be a potential therapeutic option in CKD therapeutics.

Oleoylethanolamide attenuates acute-to-chronic kidney injury: in vivo and in vitro evidence of PPAR-α involvement

Chronic kidney disease (CKD) development after acute kidney injury (AKI) involves multiple mechanisms, including inflammation, epithelial-mesenchymal transition (EMT), and extracellular matrix deposition, leading to progressive tubulointerstitial fibrosis. Recently, a central role for peroxisome-proliferator activated receptor (PPAR)-α has been addressed in preserving kidney function during AKI. Among endogenous lipid mediators, oleoylethanolamide (OEA), a PPAR-α agonist, has been studied for its metabolic and anti-inflammatory effects. Here, we have investigated OEA effects on folic acid (FA)-induced kidney injury in mice and the underlying mechanisms. OEA improved kidney function, normalized urine output, and reduced serum BUN, creatinine, and albuminuria. Moreover, OEA attenuated tubular epithelial injury, as shown by histological analysis, and decreased expression of neutrophil gelatinase-associated lipocalin and kidney injury molecule-1. Gene expression analysis of kidney tissue indicated that OEA limited immune cell infiltration and inflammation. Moreover, OEA significantly inhibited Wnt7b and Catnb1 gene transcription and α-smooth muscle actin expression, indicating suppression of EMT. Accordingly, OEA exhibited an anti-fibrotic effect, as shown by Masson staining and the reduced levels of transforming growth factor (TGF)-β1, fibronectin, and collagen IV. Mechanistically, the nephroprotective effect of OEA was related to PPAR-α activation since OEA failed to exert its beneficial activity in FA-insulted PPAR-α-/- mice. PPAR-α involvement was also confirmed in HK2 cells where GW6471, a PPAR-α antagonist, blunted OEA activity on the TGF-β1 signalling pathway and associated pro-inflammatory and fibrotic patterns. Our findings revealed that OEA counteracts kidney injury by controlling inflammation and fibrosis, making it an effective therapeutic tool for limiting AKI to CKD progression.

HDAC3 aberration-incurred GPX4 suppression drives renal ferroptosis and AKI-CKD progression

Acute kidney injury (AKI) progression to chronic kidney disease (CKD) represents a unique renal disease setting characterized by early renal cellular injury and regulated cell death, and later renal fibrosis, of which the critical role and nature of ferroptosis are only partially understood. Here, we report that renal tubular epithelial ferroptosis caused by HDAC3 (histone deacetylase 3) aberration and the resultant GPX4 suppression drives AKI-CKD progression. In mouse models of AKI-CKD transition induced by nephrotoxic aristolochic acid (AA) and folic acid (FA), renal tubular epithelial ferroptosis occurred early that coincided with preferential HDAC3 elevation and marked suppression of a core anti-ferroptosis enzyme GPX4 (glutathione peroxidase 4). Intriguingly, genetic Hdac3 knockout or administration of a HDAC3-selective inhibitor RGFP966 effectively mitigated the GPX4 suppression, ferroptosis and the fibrosis-associated renal functional loss. In cultured tubular epithelial cells, HDAC3 over-expression or inhibition inversely affected GPX4 abundances. Further analysis revealed that Gpx4 promoter contains a typical binding motif of transcription factor KLF5 (Kruppel-like factor 5). HDAC3 and KLF5 inducibly associated and bound to Gpx4 promoter upon AA treatment, leading to local histone hypoacetylation and GPX4 transactivation inhibition, which was blocked by RGFP966 and a KLF5 inhibitor ML264, respectively, suggesting that KLF5 co-regulated the HDAC3-incurred Gpx4 transcription inhibition. More importantly, in AKI-CKD mice receiving a GPX4 inactivator RSL3, the anti-ferroptosis and renoprotective effects of RGFP966 were largely abrogated, indicating that GPX4 is an essential downstream mediator of the HDAC3 aberration and renal ferroptosis during AKI-CKD transition. Together, our study identified a critical epigenetic pathway of ferroptosis during AKI-CKD transition and suggested that the strategies preserving GPX4 by HDAC3 inhibition are potentially effective to reduce renal ferroptosis and slow AKI-CKD progression.

Animal Models of Kidney Disease: Challenges and Perspectives

Kidney disease is highly prevalent and affects approximately 850 million people worldwide. It is also associated with high morbidity and mortality, and current therapies are incurable and often ineffective. Animal models are indispensable for understanding the pathophysiology of various kidney diseases and for preclinically testing novel remedies. In the last two decades, rodents continue to be the most used models for imitating human kidney diseases, largely because of the increasing availability of many unique genetically modified mice. Despite many limitations and pitfalls, animal models play an essential and irreplaceable role in gaining novel insights into the mechanisms, pathologies, and therapeutic targets of kidney disease. In this review, we highlight commonly used animal models of kidney diseases by focusing on experimental AKI, CKD, and diabetic kidney disease. We briefly summarize the pathological characteristics, advantages, and drawbacks of some widely used models. Emerging animal models such as mini pig, salamander, zebrafish, and drosophila, as well as human-derived kidney organoids and kidney-on-a-chip are also discussed. Undoubtedly, careful selection and utilization of appropriate animal models is of vital importance in deciphering the mechanisms underlying nephropathies and evaluating the efficacy of new treatment options. Such studies will provide a solid foundation for future diagnosis, prevention, and treatment of human kidney diseases.

Identifying disease progression in chronic kidney disease using proton magnetic resonance spectroscopy

Chronic kidney disease (CKD) affects approximately 10% of the world population, higher still in some developing countries, and can cause irreversible kidney damage eventually leading to kidney failure requiring dialysis or kidney transplantation. However, not all patients with CKD will progress to this stage, and it is difficult to distinguish between progressors and non-progressors at the time of diagnosis. Current clinical practice involves monitoring estimated glomerular filtration rate and proteinuria to assess CKD trajectory over time; however, there remains a need for novel, validated methods that differentiate CKD progressors and non-progressors. Nuclear magnetic resonance techniques, including magnetic resonance spectroscopy and magnetic resonance imaging, have the potential to improve our understanding of CKD progression. Herein, we review the application of magnetic resonance spectroscopy both in preclinical and clinical settings to improve the diagnosis and surveillance of patients with CKD.

Impact of Vancomycin Loading Doses and Dose Escalation on Glomerular Function and Kidney Injury Biomarkers in a Translational Rat Model

Vancomycin-induced kidney injury is common, and outcomes in humans are well predicted by animal models. This study employed our translational rat model to investigate temporal changes in the glomerular filtration rate (GFR) and correlations with kidney injury biomarkers related to various vancomycin dosing strategies. First, Sprague-Dawley rats received allometrically scaled loading doses or standard doses. Rats that received a loading dose had low GFRs and increased urinary injury biomarkers (kidney injury molecule 1 [KIM-1] and clusterin) that persisted through day 2 compared to those that did not receive a loading dose. Second, we compared low and high allometrically scaled vancomycin doses to a positive acute kidney injury control of high-dose folic acid. Rats in both the low- and high-dose vancomycin groups had higher GFRs on all dosing days than the positive-control group. When the two vancomycin groups were compared, rats that received the low dose had significantly higher GFRs on days 1, 2, and 4. Compared to low-dose vancomycin, the KIM-1 was elevated among rats in the high-dose group on dosing day 3. The GFR correlated most closely with the urinary injury biomarker KIM-1 on all experimental days. Vancomycin loading doses were associated with significant losses of kidney function and elevations of urinary injury biomarkers. In our translational rat model, both the degree of kidney function decline and urinary biomarker increases corresponded to the magnitude of the vancomycin dose (i.e., a higher dose resulted in worse outcomes).

IL-18 deficiency ameliorates the progression from AKI to CKD

Inflammation is an important factor in the progression from acute kidney injury (AKI) to chronic kidney disease (CKD). The role of interleukin (IL)-18 in this progression has not been examined. We aimed to clarify whether and how IL-18 limits this progression. In a folic acid induced renal injury mouse model, we studied the time course of kidney injury and renal IL-18 expression. In wild-type mice following injection, renal IL-18 expression increased. In parallel, we characterized other processes, including at day 2, renal tubular necroptosis assessed by receptor-interacting serine/threonine-protein kinase1 (RIPK1) and RIPK3; at day 14, transdifferentiation (assessed by transforming growth factor β1, vimentin and E-cadherin); and at day 30, fibrosis (assessed by collagen 1). In IL-18 knockout mice given folate, compared to wild-type mice, tubular damage and necroptosis, transdifferentiation, and renal fibrosis were attenuated. Importantly, IL-18 deletion decreased numbers of renal M1 macrophages and M1 macrophage cytokine levels at day 14, and reduced M2 macrophages numbers and macrophage cytokine expression at day 30. In HK-2 cells, IL-18 knockdown attenuated necroptosis, transdifferentiating and fibrosis.In patients with tubulointerstitial nephritis, IL-18 protein expression was increased on renal biopsies using immunohistochemistry. We conclude that genetic IL-18 deficiency ameliorates renal tubular damage, necroptosis, cell transdifferentiation, and fibrosis. The renoprotective role of IL-18 deletion in the progression from AKI to fibrosis may be mediated by reducing a switch in predominance from M1 to profibrotic M2 macrophages during the process of kidney repair.

A regulatory miRNA-mRNA network is associated with transplantation response in acute kidney injury

Background

Acute kidney injury (AKI) is a life-threatening complication characterized by rapid decline in renal function, which frequently occurs after transplantation surgery. However, the molecular mechanism underlying the development of post-transplant (post-Tx) AKI still remains unknown. An increasing number of studies have demonstrated that certain microRNAs (miRNAs) exert crucial functions in AKI. The present study sought to elucidate the molecular mechanisms in post-Tx AKI by constructing a regulatory miRNA–mRNA network.

Results

Based on two datasets (GSE53771 and GSE53769), three key modules, which contained 55 mRNAs, 76 mRNAs, and 151 miRNAs, were identified by performing weighted gene co-expression network analysis (WGCNA). The miRDIP v4.1 was applied to predict the interactions of key module mRNAs and miRNAs, and the miRNA–mRNA pairs with confidence of more than 0.2 were selected to construct a regulatory miRNA–mRNA network by Cytoscape. The miRNA–mRNA network consisted of 82 nodes (48 mRNAs and 34 miRNAs) and 125 edges. Two miRNAs (miR-203a-3p and miR-205-5p) and ERBB4 with higher node degrees compared with other nodes might play a central role in post-Tx AKI. Additionally, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis indicated that this network was mainly involved in kidney-/renal-related functions and PI3K–Akt/HIF-1/Ras/MAPK signaling pathways.

Conclusion

We constructed a regulatory miRNA–mRNA network to provide novel insights into post-Tx AKI development, which might help discover new biomarkers or therapeutic drugs for enhancing the ability for early prediction and intervention and decreasing mortality rate of AKI after transplantation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40246-021-00363-y.

Folic acid-induced animal model of kidney disease

The kidneys are a vital organ that is vulnerable to both acute kidney injury (AKI) and chronic kidney disease (CKD) which can be caused by numerous risk factors such as ischemia, sepsis, drug toxicity and drug overdose, exposure to heavy metals, and diabetes. In spite of the advances in our understanding of the pathogenesis of AKI and CKD as well AKI transition to CKD, there is still no available therapeutics that can be used to combat kidney disease effectively, highlighting an urgent need to further study the pathological mechanisms underlying AKI, CKD, and AKI progression to CKD. In this regard, animal models of kidney disease are indispensable. This article reviews a widely used animal model of kidney disease, which is induced by folic acid (FA). While a low dose of FA is nutritionally beneficial, a high dose of FA is very toxic to the kidneys. Following a brief description of the procedure for disease induction by FA, major mechanisms of FA-induced kidney injury are then reviewed, including oxidative stress, mitochondrial abnormalities such as impaired bioenergetics and mitophagy, ferroptosis, pyroptosis, and increased expression of fibroblast growth factor 23 (FGF23). Finally, application of this FA-induced kidney disease model as a platform for testing the efficacy of a variety of therapeutic approaches is also discussed. Given that this animal model is simple to create and is reproducible, it should remain useful for both studying the pathological mechanisms of kidney disease and identifying therapeutic targets to fight kidney disease.