Metformin Improves the Senescence of Renal Tubular Epithelial Cells in a High-Glucose State Through E2F1

To target cellular senescence in diabetic kidney disease: the known and the unknown

Cellular senescence represents a condition of irreversible cell cycle arrest, characterized by heightened senescence-associated beta-galactosidase (SA-β-Gal) activity, senescence-associated secretory phenotype (SASP), and activation of the DNA damage response (DDR). Diabetic kidney disease (DKD) is a significant contributor to end-stage renal disease (ESRD) globally, with ongoing unmet needs in terms of current treatments. The role of senescence in the pathogenesis of DKD has attracted substantial attention with evidence of premature senescence in this condition. The process of cellular senescence in DKD appears to be associated with mitochondrial redox pathways, autophagy, and endoplasmic reticulum (ER) stress. Increasing accumulation of senescent cells in the diabetic kidney not only leads to an impaired capacity for repair of renal injury, but also the secretion of pro-inflammatory and profibrotic cytokines and growth factors causing inflammation and fibrosis. Current treatments for diabetes exhibit varying degrees of renoprotection, potentially via mitigation of senescence in the diabetic kidney. Targeting senescent cell clearance through pharmaceutical interventions could emerge as a promising strategy for preventing and treating DKD. In this paper, we review the current understanding of senescence in DKD and summarize the possible therapeutic interventions relevant to senescence in this field.

mTOR in metabolic homeostasis and disease

The ability to maintain cellular metabolic homeostasis is critical to life, in which mTOR plays an important role. This kinase integrates upstream nutrient signals and performs essential functions in physiology and metabolism by increasing metabolism and suppressing autophagy. Thus, dysregulation of mTOR activity leads to diseases, especially metabolic diseases such as cancer, type 2 diabetes and neurological disorders. Therefore, inhibition of overactivated mTOR becomes a rational approach to treat a variety of metabolic diseases. In this review, we discuss how mTOR responds to upstream signals and how mTOR regulates metabolic processes, including protein, nucleic acid, and lipid metabolism. Furthermore, we discuss the possible causes and consequences of dysregulated mTOR signaling activity, and summarize relevant applications, such as inhibition of mTOR activity to treat these diseases. This review will advance our comprehensive knowledge of the association between mTOR and metabolic homeostasis, which has significant ramifications for human health.

Targeting senescence to prevent diabetic kidney disease: Exploring molecular mechanisms and potential therapeutic targets for disease management

BACKGROUND/AIMS

As a microvascular complication, diabetic kidney disease is the leading cause of chronic kidney disease and end-stage renal disease worldwide. While the underlying pathophysiology driving transition of diabetic kidney disease to renal failure is yet to be fully understood, recent studies suggest that cellular senescence is central in disease development and progression. Consequently, understanding the molecular mechanisms which initiate and drive senescence in response to the diabetic milieu is crucial in developing targeted therapies that halt progression of renal disease.

METHODS

To understand the mechanistic pathways underpinning cellular senescence in the context of diabetic kidney disease, we reviewed the literature using PubMed for English language articles that contained key words related to senescence, inflammation, fibrosis, senescence-associated secretory phenotype (SASP), autophagy, and diabetes.

RESULTS

Aberrant accumulation of metabolically active senescent cells is a notable event in the progression of diabetic kidney disease. Through autocrine- and paracrine-mediated mechanisms, resident senescent cells potentiate inflammation and fibrosis through increased expression and secretion of pro-inflammatory cytokines, chemoattractants, recruitment of immune cells, myofibroblast activation, and extracellular matrix remodelling. Compounds that eliminate senescent cells and/or target the SASP - including senolytic and senomorphics drugs - demonstrate promising results in reducing the senescent cell burden and associated pro-inflammatory effect.

CONCLUSIONS

Here we evidence the link between senescence and diabetic kidney disease and highlight underlying molecular mechanisms and potential therapeutic targets that could be exploited to delay disease progression and improve outcomes for individuals with the disease. Trials are now required to translate their therapeutic potential to a clinical setting.

Integrating serum pharmacochemistry and network pharmacology to explore potential compounds and mechanisms of Alpiniae oxyphyllae fructus in the treatment of cellular senescence in diabetic kidney disease

Background

Diabetic kidney disease (DKD), one of the microvascular complications in patients with diabetes mellitus, is a common cause of end-stage renal disease. Cellular senescence is believed to be an essential participant in the pathogenesis of DKD. Although there is evidence that Alpiniae oxyphyllae fructus (AOF) can ameliorate DKD progression and organismal senescence, its ability to ameliorate renal cellular senescence in DKD as well as active components and molecular mechanisms remain to be explored.

Purpose

This study aimed to investigate the role of AOF in the treatment of cellular senescence in DKD and to explore its active components and potential molecular mechanisms.

Methods

The pharmacological efficacy of AOF in ameliorating cellular senescence in DKD was assessed by establishing DKD mouse models and HK-2 cells under high glucose stress. UHPLC-QTOF-MS was used to screen the active compounds in AOF, which were used in conjunction with network pharmacology to predict the molecular mechanism of AOF in the treatment of cellular senescence in DKD.

Results

In vivo experiments showed that AOF reduced GLU, mAlb, Scr, BUN, MDA, SOD levels, and ameliorated renal pathological damage and renal cell senescence in DKD mice. In vitro experiments showed that AOF-containing serum improved the decline in HK-2 cell viability and alleviated cellular senescence under high glucose intervention. The results of the UHPLC-QTOF-MS screened 26 active compounds of AOF. The network pharmacological analyses revealed that Cubebin, 2',6'-dihydroxy-4'-methoxydihydrochalcone, Chalcone base + 3O,1Prenyl, Batatasin IV, and Lucidenolactone were the five core compounds and TP53, SRC, STAT3, PIK3CA, and AKT1 are the five core targets of AOF in the treatment of DKD. Molecular docking simulation results showed that the five core compounds had good binding ability to the five core targets. Western blot validated the network pharmacological prediction results and showed that AOF and AOF-containing serum down-regulate the expression of TP53, and phosphorylation of SRC, STAT3, PIK3CA, and AKT.

Conclusion

Our study shows that AOF may delay the development of cellular senescence in DKD by down-regulating the levels of TP53, and phosphorylation of SRC, STAT3, PIK3CA, and AKT.

Effects of metformin on knee joint capsule fibrosis in a diabetic mouse model

Aims

The antidiabetic agent metformin inhibits fibrosis in various organs. This study aims to elucidate the effects of hyperglycaemia and metformin on knee joint capsule fibrosis in mice.

Methods

Eight-week-old wild-type (WT) and type 2 diabetic (db/db) mice were divided into four groups without or with metformin treatment (WT met(-/+), Db met(-/+)). Mice received daily intraperitoneal administration of metformin and were killed at 12 and 14 weeks of age. Fibrosis morphology and its related genes and proteins were evaluated. Fibroblasts were extracted from the capsules of 14-week-old mice, and the expression of fibrosis-related genes in response to glucose and metformin was evaluated in vitro.

Results

The expression of all fibrosis-related genes was higher in Db met(-) than in WT met(-) and was suppressed by metformin. Increased levels of fibrosis-related genes, posterior capsule thickness, and collagen density were observed in the capsules of db/db mice compared with those in WT mice; these effects were suppressed by metformin. Glucose addition increased fibrosis-related gene expression in both groups of mice in vitro. When glucose was added, metformin inhibited the expression of fibrosis-related genes other than cellular communication network factor 2 (Ccn2) in WT mouse cells.

Conclusion

Hyperglycaemia promotes fibrosis in the mouse knee joint capsule, which is inhibited by metformin. These findings can help inform the development of novel strategies for treating knee joint capsule fibrosis.

Ablation of Brg1 in fibroblast/myofibroblast lineages attenuates renal fibrosis in mice with diabetic nephropathy

AIMS

Diabetic nephropathy (DN) is one of the most common complications of diabetes and represents a prototypical form of chronic kidney disease (CKD). Interstitial fibrosis is a key pathological feature of DN. During DN-associated renal fibrosis, resident fibroblasts trans-differentiate into myofibroblasts to remodel the extracellular matrix, the underlying epigenetic mechanism of which is not entirely clear.

METHODS

Diabetic nephropathy was induced in C57B6/j mice by a single injection with streptozotocin (STZ). Gene expression was examined by quantitative PCR and Western blotting. Renal fibrosis was evaluated by PicroSirius Red staining.

RESULTS

We report that expression of Brg1, a chromatin remodeling protein, in renal fibroblasts was up-regulated during DN pathogenesis as assessed by single-cell RNA-seq. Treatment with high glucose similarly augmented Brg1 expression in primary renal fibroblasts in vitro. Importantly, Brg1 ablation in quiescent renal fibroblasts or in mature myofibroblasts equivalently attenuated renal fibrosis in the context of diabetic nephropathy in mice. Additionally, administration with a small-molecule Brg1 inhibitor PFI-3 ameliorated renal fibrosis and improved renal function in mice induced to develop DN.

SIGNIFICANCE

In conclusion, our data provide novel genetic evidence that links Brg1 to fibroblast-myofibroblast transition and renewed rationale for targeting Brg1 in the intervention of DN-associated renal fibrosis.

The chromatin remodeling protein BRG1 mediates Ang II induced pro-fibrogenic response in renal fibroblasts

AIMS

Renal fibrosis is an important pathophysiological process commonly observed in patients chronic kidney disease (CKD). Angiotensin II (Ang II) is a major risk factor for CKD in part by promoting renal fibrosis. In the present study we investigated Brahma-Related Gene 1 (BRG1, encoded by Smarca4) in Ang II induced pro-fibrogenic response in renal fibroblasts.

METHODS AND MATERIALS

CKD was induced by chronic angiotensin II infusion. Fibroblast- and myofibroblast-specific BRG1 deletion was achieved by crossing the BRG1f/f mice to the Col1a1-CreERT2 mice and the Postn-CreERT2 mice, respectively.

KEY FINDINGS

BRG1 expression was up-regulated when fibroblasts were exposed to Ang II in vitro and in vivo. BRG1 silencing in primary renal fibroblasts blocked transition to myofibroblasts as evidenced by down-regulation of myofibroblast marker genes and reduction in cell proliferation, migration, and contraction. Consistently, deletion of BRG1 from fibroblasts or from myofibroblasts significantly attenuated renal fibrosis in mice subjected to chronic Ang II infusion. Transcriptomic analysis indicated that BRG1 primarily regulated expression of genes involved in cell migroproliferative behavior and extracellular matrix remodeling. Importantly, administration of PFI-3, a small-molecule BRG1 inhibition, markedly ameliorated Ang II induced renal fibrosis in mice.

SIGNIFICANCE

Our data support a role for BRG1 in Ang II induced fibrogenic response in renal fibroblasts and suggest that targeting BRG1 could be considered as a reasonable approach for the intervention of CKD.

Transcriptional mechanism of E2F1/TFAP2C/NRF1 in regulating KANK2 gene in nephrotic syndrome

The mortality rate linked with nephrotic syndrome (NS) is quite high. The renal tubular injury influences the response of NS patients to steroid treatment. KN motif and ankyrin repeat domains 2 (KANK2) regulates actin polymerization, which is required for renal tubular cells to maintain their function. In this study, we found that the levels of KANK2 in patients with NS were considerably lower than those in healthy controls, especially in NS patients with acute kidney injury (AKI). To get a deeper understanding of the KANK2 transcriptional control mechanism, the core promoter region of the KANK2 gene was identified. KANK2 was further found to be positively regulated by E2F Transcription Factor 1 (E2F1), Transcription Factor AP-2 Gamma (TFAP2C), and Nuclear Respiratory Factor 1 (NRF1), both at mRNA and protein levels. Knocking down E2F1, TFAP2C, or NRF1 deformed the cytoskeleton of renal tubular cells and reduced F-actin content. EMSA and ChIP assays confirmed that all three transcription factors could bind to the upstream promoter transcription site of KANK2 to transactivate KANK2 in renal tubular epithelial cells. Our study suggests that E2F1, TFAP2C, and NRF1 play essential roles in regulating the KANK2 transcription, therefore shedding fresh light on the development of putative therapeutic options for the treatment of NS patients.

The Comparation of Renal Anti-Senescence Effects and Blood Metabolites between Dapagliflozin and Metformin in Non-Diabetes Environment

Delaying kidney senescence process will benefit renal physiologic conditions, and prompt the kidney recovering from different pathological states. The renal anti-senescence effects of sodium-glucose cotransporter-2 inhibitors (SGLT2i) and metformin have been proven in diabetic settings, but the roles of each one and combination of two drugs in natural kidney aging process remain undefined and deserve further research. Senescence-accelerated mouse prone 8 (SAMP8) were orally administered dapagliflozin, metformin, and a combination of them for 16 weeks. Dapagliflozin exhibits better effects than metformin in lowering senescence related markers, and the combination therapy shows the best results. In vitro experiments demonstrate the same results that the combination of dapagliflozin and metformin can exert a better anti-senescence effect. Blood metabolites detection in vivo shows dapagliflozin mainly leads to the change of blood metabolites enriched in choline metabolism, and metformin tends to induce change of blood metabolites enriched in purine metabolism. In conclusion, the results suggest dapagliflozin may have a better renal anti-senescence effect than metformin in non-diabetes environment, and the combination of the two drugs can strengthen the effect. The two drugs can lead to different blood metabolites alteration, which may lead to different systemic effects.

Tubular injury in diabetic kidney disease: molecular mechanisms and potential therapeutic perspectives

Diabetic kidney disease (DKD) is a chronic complication of diabetes and the leading cause of end-stage renal disease (ESRD) worldwide. Currently, there are limited therapeutic drugs available for DKD. While previous research has primarily focused on glomerular injury, recent studies have increasingly emphasized the role of renal tubular injury in the pathogenesis of DKD. Various factors, including hyperglycemia, lipid accumulation, oxidative stress, hypoxia, RAAS, ER stress, inflammation, EMT and programmed cell death, have been shown to induce renal tubular injury and contribute to the progression of DKD. Additionally, traditional hypoglycemic drugs, anti-inflammation therapies, anti-senescence therapies, mineralocorticoid receptor antagonists, and stem cell therapies have demonstrated their potential to alleviate renal tubular injury in DKD. This review will provide insights into the latest research on the mechanisms and treatments of renal tubular injury in DKD.

All-trans retinoic acid inhibits oxidative stress via ACE2/Ang (1-7)/MasR pathway in renal tubular epithelial cells stimulated with high glucose

The aim of this study was to investigate the effects of all-trans retinoic acid (atRA) on oxidative stress in renal tubular epithelial cells induced by high glucose (HG) and its potential mechanism. We investigated the effects of atRA in HG-induced renal epithelial cell line HK-2. Seven groups were designed for this experiment: negative control, mannitol, high-glucose (HG), HG combined with a low concentration of atRA, HG combined with a middle concentration of atRA, HG combined with a high concentration of atRA, and HG combined with captopril. After 48 h of incubation, oxidative stress factor expression in the supernatant was detected by enzyme-linked immunosorbent assay. Reactive oxygen species and cell apoptosis expression were assessed by flow cytometry. NADPH oxidase, fibrosis factor, and angiotensin-converting enzyme 2/angiotensin (1-7)/mas receptor (ACE2/Ang (1-7)/MasR) pathway-related protein expressions were determined by western blot analysis. The expressions of oxidative stress factors, NADPH oxidase components, and fibrosis factors were significantly higher after HG treatment. Apoptosis of HK2 cells in the HG group was also significantly higher. AtRA could reverse the above abnormal changes in a concentration-dependent manner. HG significantly promoted the expression of ACE, Ang II, and Ang II type 1 receptor (AT1R), whereas it inhibited the expression of ACE2, Ang (1-7), and MasR. With the elevation of concentration, atRA could gradually suppress the expression of ACE, Ang II, and AT1R, but facilitate ACE2, Ang (1-7), and MasR. These results were statistically significant. AtRA could significantly inhibit oxidative stress and apoptosis of renal tubular epithelial cells induced by HG. The mechanism may inhibit the ACE/Ang II/AT1R pathway and/or activate ACE2/Ang (1-7)/MasR pathway.

Mitochondria in cell senescence: A Friend or Foe?

Cell senescence denotes cell growth arrest in response to continuous replication or stresses damaging DNA or mitochondria. Mounting research suggests that cell senescence attributes to aging-associated failing organ function and diseases. Conversely, it participates in embryonic tissue maturation, wound healing, tissue regeneration, and tumor suppression. The acute or chronic properties and microenvironment may explain the double faces of senescence. Senescent cells display unique characteristics. In particular, its mitochondria become elongated with altered metabolomes and dynamics. Accordingly, mitochondria reform their function to produce more reactive oxygen species at the cost of low ATP production. Meanwhile, destructed mitochondrial unfolded protein responses further break the delicate proteostasis fostering mitochondrial dysfunction. Additionally, the release of mitochondrial damage-associated molecular patterns, mitochondrial Ca²⁺ overload, and altered NAD⁺ level intertwine other cellular organelle strengthening senescence. These findings further intrigue researchers to develop anti-senescence interventions. Applying mitochondrial-targeted antioxidants reduces cell senescence and mitigates aging by restoring mitochondrial function and attenuating oxidative stress. Metformin and caloric restriction also manifest senescent rescuing effects by increasing mitochondria efficiency and alleviating oxidative damage. On the other hand, Bcl2 family protein inhibitors eradicate senescent cells by inducing apoptosis to facilitate cancer chemotherapy. This review describes the different aspects of mitochondrial changes in senescence and highlights the recent progress of some anti-senescence strategies.

Cellular senescence of renal tubular epithelial cells in renal fibrosis

Renal fibrosis (RF) is the common pathological manifestation of virtually all chronic kidney diseases (CKD) and one of the major causes of end-stage renal disease (ESRD), but the pathogenesis of which is still unclear. Renal tubulointerstitial lesions have been identified as a key pathological hallmark of RF pathology. Renal tubular epithelial cells are the resident cells of the tubulointerstitium and play an important role in kidney recovery versus renal fibrosis following injury. Studies in recent years have shown that senescence of renal tubular epithelial cells can accelerate the progression of renal fibrosis. Oxidative stress(OS), telomere attrition and DNA damage are the major causes of renal tubular epithelial cell senescence. Current interventions and therapeutic strategies for cellular senescence include calorie restriction and routine exercise, Klotho, senolytics, senostatics, and other related drugs. This paper provides an overview of the mechanisms and the key signaling pathways including Wnt/β-catenin/RAS, Nrf2/ARE and STAT-3/NF-κB pathway involved in renal tubular epithelial cell senescence in RF and therapies targeting renal tubular epithelial cell senescence future therapeutic potential for RF patients. These findings may offer promise for the further treatment of RF and CKD.

Inhibition of IGF2BP1 attenuates renal injury and inflammation by alleviating m6A modifications and E2F1/MIF pathway

Septic acute kidney injury (AKI) is characterized by inflammation. Pyroptosis often occurs during AKI and is associated with the development of septic AKI. This study found that induction of insulin-like growth factor 2 mRNA binding protein 1 (IGF2BP1) to a higher level can induce pyroptosis in renal tubular cells. Meanwhile, macrophage migration inhibitory factor (MIF), a subunit of NLRP3 inflammasomes, was essential for IGF2BP1-induced pyroptosis. A putative m6A recognition site was identified at the 3'-UTR region of E2F transcription factor 1 (E2F1) mRNA via bioinformatics analyses and validated using mutation and luciferase experiments. Further actinomycin D (Act D) chase experiments showed that IGF2BP1 stabilized E2F1 mRNA dependent on m6A. Electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) indicated that E2F1 acted as a transcription factor to promote MIF expression. Thus, IGF2BP1 upregulated MIF through directly upregulating E2F1 expression via m6A modification. Experiments on mice with cecum ligation puncture (CLP) surgery verified the relationships between IGF2BP1, E2F1, and MIF and demonstrated the significance of IGF2BP1 in MIF-associated pyroptosis in vivo. In conclusion, IGF2BP1 was a potent pyroptosis inducer in septic AKI through targeting the MIF component of NLRP3 inflammasomes. Inhibiting IGF2BP1 could be an alternate pyroptosis-based treatment for septic AKI.