Mitochondrial dysfunction and mitophagy: the beginning and end to diabetic nephropathy?

Mitochondrial dysfunction and NLRP3 inflammasome: key players in kidney stone formation

The mitochondrion serves as a critical intracellular organelle, engaging in essential roles in the regulation of energy production, oxidative stress management, calcium homeostasis, and apoptosis. One such disease that has been particularly associated with these functions is kidney stone disease (KSD), specifically calcium oxalate (CaOx). It is underpinned by oxidative stress and tissue inflammation. Recent studies have shed light on the vital involvement of mitochondrial dysfunction, the nucleotide-binding domain and leucine-rich repeat containing protein 3 (NLRP3) inflammasome, endoplasmic reticulum stress and subsequent cell death in CaOx crystal retention and aggregation. These processes are pivotal in the pathogenesis of kidney stone formation. This review focuses on the pivotal roles of mitochondria in renal cell functions and provides an overview of the intricate interconnectedness between mitochondrial dysfunction and NLRP3 inflammasome activation in the context of KSD. It is essential to recognise the utmost significance of gaining a comprehensive understanding of the mechanisms that safeguard mitochondrial function and regulate the NLRP3 inflammasome. Such knowledge carries significant scientific implications and opens up promising avenues for the development of innovative strategies to prevent the formation of kidney stones.

The role of mitochondrial dysfunction in kidney injury and disease

Mitochondria are the main sites of aerobic respiration in the cell and mainly provide energy for the organism, and play key roles in adenosine triphosphate (ATP) synthesis, metabolic regulation, and cell differentiation and death. Mitochondrial dysfunction has been identified as a contributing factor to a variety of diseases. The kidney is rich in mitochondria to meet energy needs, and stable mitochondrial structure and function are essential for normal kidney function. Recently, many studies have shown a link between mitochondrial dysfunction and kidney disease, maintaining mitochondrial homeostasis has become an important target for kidney therapy. In this review, we integrate the role of mitochondrial dysfunction in different kidney diseases, and specifically elaborate the mechanism of mitochondrial reactive oxygen species (mtROS), autophagy and ferroptosis involved in the occurrence and development of kidney diseases, providing insights for improved treatment of kidney diseases.

Combined associations of visceral adipose tissue and adherence to a Mediterranean lifestyle with T2D and diabetic microvascular complications among individuals with prediabetes

BACKGROUND

It's unclear if excess visceral adipose tissue (VAT) mass in individuals with prediabetes can be countered by adherence to a Mediterranean lifestyle (MEDLIFE). We aimed to examine VAT mass, MEDLIFE adherence, and their impact on type 2 diabetes (T2D) and diabetic microvascular complications (DMC) in individuals with prediabetes.

METHODS

11,267 individuals with prediabetes from the UK Biobank cohort were included. VAT mass was predicted using a non-linear model, and adherence to the MEDLIFE was evaluated using the 25-item MEDLIFE index, encompassing categories such as "Mediterranean food consumption," "Mediterranean dietary habits," and "Physical activity, rest, social habits, and conviviality." Both VAT and MEDLIFE were categorized into quartiles, resulting in 16 combinations. Incident cases of T2D and related DMC were identified through clinical records. Cox proportional-hazards regression models were employed to examine associations, adjusting for potential confounding factors.

RESULTS

Over a median follow-up of 13.77 years, we observed 1408 incident cases of T2D and 714 cases of any DMC. High adherence to the MEDLIFE, compared to the lowest quartile, reduced a 16% risk of incident T2D (HR: 0.84, 95% CI: 0.71-0.98) and 31% for incident DMC (0.69, 0.56-0.86). Conversely, compared to the lowest quartile of VAT, the highest quartile increased the risk of T2D (5.95, 4.72-7.49) and incident any DMC (1.79, 1.36-2.35). We observed an inverse dose-response relationship between MEDLIFE and T2D/DMC, and a dose-response relationship between VAT and all outcomes (P for trend < 0.05). Restricted cubic spline analysis confirmed a nearly linear dose-response pattern across all associations. Compared to individuals with the lowest MEDLIFE quartile and highest VAT quartile, those with the lowest T2D risk had the lowest VAT and highest MEDLIFE (0.12, 0.08-0.19). High MEDLIFE was linked to reduced T2D risk across all VAT categories, except in those with the highest VAT quartile. Similar trends were seen for DMC.

CONCLUSION

High adherence to MEDLIFE reduced T2D and MDC risk in individuals with prediabetes, while high VAT mass increases it, but MEDLIFE adherence may offset VAT's risk partly. The Mediterranean lifestyle's adaptability to diverse populations suggests promise for preventing T2D.

Renal aging and mitochondrial quality control

Mitochondria are dynamic organelles that participate in different cellular process that control metabolism, cell division, and survival, and the kidney is one of the most metabolically active organs that contains abundant mitochondria. Perturbations in mitochondrial homeostasis in the kidney can accelerate kidney aging, and maintaining mitochondrial homeostasis can effectively delay aging in the kidney. Kidney aging is a degenerative process linked to detrimental processes. The significance of aberrant mitochondrial homeostasis in renal aging has received increasing attention. However, the contribution of mitochondrial quality control (MQC) to renal aging has not been reviewed in detail. Here, we generalize the current factors contributing to renal aging, review the alterations in MQC during renal injury and aging, and analyze the relationship between mitochondria and intrinsic renal cells. We also introduce MQC in the context of renal aging, and discuss the study of mitochondria in the intrinsic cells of the kidney, which is the innovation of our paper. In addition, during kidney injury and repair, the specific functions and regulatory mechanisms of MQC systems in resident and circulating cell types remain unclear. Currently, most of the studies we reviewed are based on animal and cellular models, the relationship between renal tissue aging and mitochondria has not been adequately investigated in clinical studies, and there is still a long way to go.

Chinese botanical drugs targeting mitophagy to alleviate diabetic kidney disease, a comprehensive review

Diabetic kidney disease (DKD) is one of the chronic microvascular complications caused by diabetes, which is characterized by persistent albuminuria and/or progressive decline of estimated glomerular filtration rate (eGFR), and has been the major cause of dialysis around the world. At present, although the treatments for DKD including lifestyle modification, glycemic control and even using of Sodium-glucose cotransporter 2 (SGLT2) inhibitors can relieve kidney damage caused to a certain extent, there is still a lack of effective treatment schemes that can prevent DKD progressing to ESRD. It is urgent to find new complementary and effective therapeutic agents. Growing animal researches have shown that mitophagy makes a great difference to the pathogenesis of DKD, therefore, exploration of new drugs that target the restoration of mitophagy maybe a potential perspective treatment for DKD. The use of Chinese botanical drugs (CBD) has been identified to be an effective treatment option for DKD. There is growing concern on the molecular mechanism of CBD for treatment of DKD by regulating mitophagy. In this review, we highlight the current findings regarding the function of mitophagy in the pathological damages and progression of DKD and summarize the contributions of CBD that ameliorate renal injuries in DKD by interfering with mitophagy, which will help us further explain the mechanism of CBD in treatment for DKD and explore potential therapeutic strategies for DKD.

Fangji Huangqi decoction ameliorates membranous nephropathy through the upregulation of BNIP3-mediated mitophagy

ETHNOPHARMACOLOGICAL RELEVANCE

Fangji Huangqi Decoction (FJHQ), a traditional Chinese medicinal formula outlined in Zhang Zhongjing's "Jin Gui Yao Lue" during the Han Dynasty, is often used to treat conditions characterized by symptoms like edema and dysuria, including membranous nephropathy (MN). Despite its proven clinical effectiveness, the exact mechanisms through which FJHQ acts on MN remain elusive.

AIM OF THE STUDY

This study aimed to investigate whether FJHQ enhances BNIP3-mediated mitophagy in podocytes by promoting BNIP3 expression and whether this improvement leads to the amelioration of MN.

MATERIALS AND METHODS

In this study, by establishing passive Heymann nephritis (PHN) rats, an experimental rat model of MN induced by sheep anti-rat Fx1A serum, we evaluated the effects of FJHQ in vivo. In vitro experiments were carried out by treating primary podocytes with experimental rat serum. Furthermore, the potential mechanism by which FJHQ acts through BNIP3 was further examined by transfecting primary podocytes with the siRNA of BNIP3 or the corresponding control vector.

RESULTS

After 4 weeks, significant kidney damage was observed in the rats in the model group, comparatively, FJHQ markedly decreased urine volume, 24-h urinary protein, blood urea nitrogen (BUN), creatinine (Scr), and increased serum total albumin (ALB). Histology showed that FJHQ caused significant improvements in glomerular hyperplasia, and IgG immune complex deposition in MN rats. JC-1 fluorescence labelling and flow cytometry analysis showed that FJHQ could significantly increase mitochondrial membrane potential in vivo. In the mitochondria of MN model rats, FJHQ was able to down-regulate the expression of P62 and up-regulate the expression of BNIP3, LC3B, and LC3 II/LC3 I, according to Western blot and immunofluorescence studies. Furthermore, FJHQ has been shown to significantly up-regulate mitochondrial membrane potential, down-regulate P62 expression in mitochondria, and up-regulate the expression of BNIP3, LC3B, and LC3 II/LC3 I in mitochondria at the cellular level. After the administration of the autophagy inhibitor chloroquine, the serum of rats treated with FJHQ further increased the expression of LC3 II/LC3 I in primary podocytes, showing higher autophagy flow. After the interference of BNIP3 in podocytes, the effect of FJHQ on mitochondrial membrane potential and autophagy-related proteins almost disappeared.

CONCLUSION

FJHQ enhanced mitophagy in podocytes by promoting the expression of BNIP3, thereby contributing to the amelioration of MN. This work reveals the possible underlying mechanism by which FJHQ improves MN and provides a new avenue for MN treatment.

An aldose reductase inhibitor, WJ-39, ameliorates renal tubular injury in diabetic nephropathy by activating PINK1/Parkin signaling

Renal tubular injury is a critical factor during the early stages of diabetic nephropathy (DN). Proximal tubular epithelial cells, which contain abundant mitochondria essential for intracellular homeostasis, are susceptible to disruptions in the intracellular environment, making them especially vulnerable to diabetic state disorders, which may be attributed to their elevated energy requirements and reliance on aerobic metabolism. It is widely thought that overactivation of the polyol pathway is implicated in DN pathogenesis, and inhibition of aldose reductase (AR), the rate-limiting enzyme in this pathway, represents a promising therapeutic avenue. WJ-39, a novel aldose reductase inhibitor, was investigated in this study for its protective effects on renal tubules in DN and the underlying mechanisms. Our findings revealed that WJ-39 significantly ameliorated the renal tubular morphology in high-fat diet (HFD)/streptozotocin (STZ)-induced DN rats, concurrently inhibiting fibrosis. Notably, WJ-39 safeguarded the structure and function of renal tubular mitochondria by enhancing mitochondrial dynamics. This involved the regulation of mitochondrial fission and fusion proteins and the promotion of PTEN-induced putative kinase 1 (PINK1)/Parkin-mediated mitophagy. Furthermore, WJ-39 demonstrated the inhibition of endogenous apoptosis by mitigating the production of mitochondrial reactive oxygen species (ROS). The protective effects of WJ-39 on mitochondria and apoptosis were countered in high glucose-treated HK-2 cells upon transfection with PINK1 siRNA. Overall, our findings suggest that WJ-39 protects the structural and functional integrity of renal tubules in DN, which may be attributed to its capacity to inhibit aldose reductase activity, activate the PINK1/Parkin signaling pathway, promote mitophagy, and alleviate apoptosis.

Ameliorative effect of montelukast against STZ induced diabetic nephropathy: targeting HMGB1, TLR4, NF-κB, NLRP3 inflammasome, and autophagy pathways

Diabetic nephropathy (DN) is reported as one of the most serious microvascular diabetic complications and the trigger of end-stage renal disease (ESRD), underscoring the concern of any therapeutic intervention directed at ameliorating the development and progression of DN. The current study explored the renoprotective impact of montelukast (Mon) against streptozotocin (STZ)-induced DN in rats compared to a standard anti-hyperglycemic insulin (Ins) treatment. Diabetes was induced by a single dose of STZ (55 mg/kg). Diabetic rats were treated with Mon (10 and 20 mg/kg, oral gavage) for eight weeks. Mon administration for 8 weeks after induction of diabetes conferred significant dose-dependent renoprotection, independent of blood glucose levels (unlike Ins), as evidenced by the improvement in serum creatinine, and blood urea nitrogen (BUN), and ameliorated STZ-induced renal necrotic, inflammatory alterations, and renal fibrosis. Additionally, Mon treatment in diabetic rats significantly restored redox hemostasis as evidenced by malondialdehyde (MDA) and total antioxidant capacity (TAC) levels; significantly reduced the renal expression of high mobility group box (HMGB) 1, toll-like receptor (TLR) 4, nuclear factor kappa B (NF-κB) (in the nucleus), NOD-like receptor family pyrin domain containing (NLRP) 3, and interleukin (IL)-1β. Moreover, Mon administration ameliorated the dysregulation in autophagy as evidenced by p62 and microtubule-associated protein 1A/1B-light chain 3 (LC3)-II levels. In conclusion, the renoprotective effect of Mon is potentially associated with its modulatory effect on inflammatory cytokines, antioxidant properties, and autophagy.

CD36 deletion ameliorates diabetic kidney disease by restoring fatty acid oxidation and improving mitochondrial function

Renal tubular epithelial cells (TECs) are vulnerable to mitochondrial dysregulation, which is an integral part of diabetic kidney disease (DKD). We found that CD36 knockout ameliorated mitochondrial dysfunction and diabetic kidney injury in mice, improved renal function, glomerular hypertrophy, tubular injury, tubulointerstitial fibrosis, and kidney cell apoptosis. Furthermore, CD36 knockout conferred protection against diabetes-induced mitochondrial dysfunction and restored renal tubular cells and mitochondrial morphology. CD36 knockout also restored mitochondrial fatty acid oxidation (FAO) and enhanced FAO-associated respiration in diabetic TECs. CD36 was found to alter cellular metabolic pathways in diabetic kidneys partly via PDK4 the -AMPK axis inactivation. Because CD36 protects against DKD by improving mitochondrial function and restoring FAO, it can serve as a potential therapeutic target.

Urinary mitochondrial DNA may be useful in diagnosing early diabetic nephropathy

The present study aimed to determine whether urinary mitochondrial (mt)DNA could be combined as a non-invasive biomarker with other clinical findings of kidney injury to help diagnose early diabetic nephropathy (DN). A total of 165 patients with type 2 diabetes mellitus (T2DM) were enrolled in the present study and the mtDNA levels in urine were measured using quantitative PCR. The diagnostic value of urinary mtDNA levels in patients with T2DM was compared using estimated glomerular filtration rate (eGFR) or albumin-to-creatinine ratio staging. Spearman correlation analysis was used to analyze the correlation between urinary mtDNA and other clinical findings. Correlation factors for early DN were assessed using univariate logistic regression analysis. Urinary leukocyte and glucose levels do not interfere with urinary mtDNA levels. In patients with T2DM, the level of urinary mtDNA increases in the early stages of kidney injury and further increases with the severity of kidney injury. Urinary mtDNA levels in patients with eGFR 60-90 ml/min/1.73 m2 were higher than that in patients with eGFR >90 ml/min/1.73 m2. The levels of urinary mt89DNA and mt349DNA were negatively correlated with the eGFR level (ρ=-0.437; P<0.001; ρ=-0.390; P<0.001) and positively correlated with the level of cystatin C (ρ=0.177; P=0.025; ρ=0.144; P=0.070). Urinary mtDNA is positively correlated with early DN occurrence [odds ratio (OR), 1.330; 95% confidence interval (CI), 1.175-1.507; P<0.001; OR, 1.328; 95% CI, 1.156-1.525; P<0.001]. In conclusion, urinary mtDNA combined with other clinical indicators of kidney injury may help the diagnosis of early DN.

Minnelide Markedly Reduces Proteinuria in Mice with Adriamycin Nephropathy by Protecting Against Podocyte Injury

Minimal change disease (MCD) is the most common cause of idiopathic nephrotic syndrome in children. The current major therapy is hormones for most steroid-sensitive patients. However, many patients have recurrent relapses of the disease and require long-term immunosuppression, leading to significant morbidity due to the side effects of the drugs. Therefore, better drugs need to be urgently explored to treat nephrotic syndrome while avoiding the side effects of drugs. Minnelide, a water-soluble prodrug of triptolide, has been proved to be effective in treating cancers in many clinical trials. This study aimed to investigate the therapeutic effect of minnelide in mice with adriamycin (ADR) nephropathy, its underlying protection mechanisms, and its reproductive toxicity. Minnelide was administered intraperitoneally to 6-8-week female mice with adriamycin nephropathy for 2 weeks, and the urine, blood, and kidney tissues were taken to analyze the therapeutic effect. In addition, we evaluated reproductive toxicity by measuring the levels of gonadal hormones and observing the histological changes in ovaries and testes. Primary mouse podocytes were exposed to puromycin (PAN) to damage the cytoskeleton and induce apoptosis, and then, triptolide was used to evaluate the therapeutic effect and underlying protection mechanisms in vitro. It was observed that minnelide dramatically alleviated proteinuria and apoptosis in mice with adriamycin nephropathy. In vitro, triptolide ameliorated puromycin-induced cytoskeletal rearrangement and apoptosis via reactive oxygen species-mediated mitochondrial pathway. In addition, minnelide caused no reproductive toxicity to male and female mice. The results suggested that minnelide might be a promising drug for nephrotic syndrome.

Correction to: YY1 inactivated transcription co-regulator PGC-1α to promote mitochondrial dysfunction of early diabetic nephropathy-associated tubulointerstitial fibrosis

The development of diabetic nephropathy (DN) could be promoted by the occurrence of tubulointerstitial fibrosis (TIF), which has a close relationship with mitochondrial dysfunction of renal tubular epithelial cells (RTECs). As a key regulator of metabolic homeostasis, Yin Yang 1 (YY1) plays an important role not only in regulating the fibrosis process but also in maintaining the mitochondrial function of pancreatic β-cells. However, it was not clear whether YY1 participated in maintaining mitochondrial function of RTECs in early DN-associated TIF. In this study, we dynamically detected mitochondrial functions and protein expression of YY1 in db/db mice and high glucose (HG)-cultured HK-2 cells. Our results showed that comparing with the occurrence of TIF, the emergence of mitochondrial dysfunction of RTECs was an earlier even, besides the up-regulated and nuclear translocated YY1. Correlation analysis showed YY1 expressions were negatively associated with PGC-1α in vitro and in vivo. Further mechanism research demonstrated the formation of mTOR-YY1 heterodimer induced by HG up-regulated YY1, the nuclear translocation of which inactivated PGC-1α by binding to the PGC-1α promoter. Overexpression of YY1 induced mitochondrial dysfunctions in normal glucose-cultured HK-2 cells and 8-weeks-old db/m mice. While, dysfunctional mitochondria induced by HG could be improved by knockdown of YY1. Finally, downregulation of YY1 could retard the progression of TIF by preventing mitochondrial functions, resulting in the improvement of epithelial-mesenchymal transition (EMT) in early DN. These findings suggested that YY1 was a novel regulator of mitochondrial function of RTECs and contributed to the occurrence of early DN-associated TIF.

Sinensetin ameliorates high glucose-induced diabetic nephropathy via enhancing autophagy in vitro and in vivo

Diabetic nephropathy (DN) affects around 40% of people with diabetes, the final outcome of which is end-stage renal disease. The deficiency of autophagy and excessive oxidative stress have been found to participate in the pathogenesis of DN. Sinensetin (SIN) has been proven to have strong antioxidant capability. However, the effect of SIN on DN has not been studied. We examined the effect of SIN on cell viability and autophagy in the podocyte cell line, MPC5 cells, treated with high glucose (HG). For in vivo studies, DN mice models were established by intraperitoneal injected with streptozotocin (40 mg/kg) for 5 consecutive days and fed with a 60% high-fat diet, and SIN was given (10, 20, and 40 mg/kg) for 8 weeks via intraperitoneal injection. The results showed that SIN could protect MPC5 cells against HG-induced damage and significantly improve the renal function of DN mice. Moreover, SIN remarkably restored the autophagy activity of MPC5 cells which was inhibited under HG conditions. Consistent with this, SIN efficiently improved autophagy in the kidney tissue of DN mice. In brief, our findings demonstrated the protective effect of SIN on DN via restoring the autophagic function, which might provide a basis for drug development.

RNA-Seq transcriptome analysis of renal tissue from spontaneously hypertensive rats revealed renal protective effects of dapagliflozin, an inhibitor of sodium-glucose cotransporter 2

Hypertensive nephropathy (HTN) is a common complication of hypertension. Although various agents for treatment of hypertension exert significant effects, there is currently no effective treatment for hypertensive nephropathy. Sodium-glucose cotransporter 2 (SGLT2) inhibitors, such as dapagliflozin (DAPA), are a new class of hypoglycemic agents shown to improve the prognosis of patients with chronic kidney disease and diabetes mellitus. However, the mechanisms underlying the protective effects of DAPA remain unclear. RNA-sequencing (RNA-Seq)-based computational analysis was conducted to explore the transcriptomic changes to spontaneously hypertensive rats (SHRs) treated with DAPA for 8 weeks. Differentially expressed genes in SHRs were related to dysregulation of lipid metabolism, oxidation-reduction reaction, immunity and inflammation in HTN. Transcriptome analysis showed that 8 weeks of DAPA therapy exerted protective effects on the renal tissues of SHRs through the lysosomal, phagosomal, and autophagic pathways. VENN diagram analysis identified Zinc finger and BTB domain-containing 20 (Zbtb20) as the potential target of DAPA therapy. Consistent with the RNA-Seq findings, real-time quantitative PCR and immunohistochemical analyses revealed increased expression of Zbtb20 in the renal tissues of SHRs, whereas expression was decreased following 8 weeks of DAPA administration. The results of this study clarified the transcriptome signature of HTN and the beneficial effects of DAPA on renal tissues by alleviating dysregulation of metabolic processes and reducing inflammation.

Mitochondrial dysfunction and oxidative stress: Role in chronic kidney disease

Chronic kidney disease (CKD) is associated with a variety of distinct disease processes that permanently change the function and structure of the kidney across months or years. CKD is characterized as a glomerular filtration defect or proteinuria that lasts longer than three months. In most instances, CKD leads to end-stage kidney disease (ESKD), necessitating kidney transplantation. Mitochondrial dysfunction is a typical response to damage in CKD patients. Despite the abundance of mitochondria in the kidneys, variations in mitochondrial morphological and functional characteristics have been associated with kidney inflammatory responses and injury during CKD. Despite these variations, CKD is frequently used to define some classic signs of mitochondrial dysfunction, including altered mitochondrial shape and remodeling, increased mitochondrial oxidative stress, and a marked decline in mitochondrial biogenesis and ATP generation. With a focus on the most significant developments and novel understandings of the involvement of mitochondrial remodeling in the course of CKD, this article offers a summary of the most recent advances in the sources of procured mitochondrial dysfunction in the advancement of CKD. Understanding mitochondrial biology and function is crucial for developing viable treatment options for CKD.

Mitophagy, Inflammasomes and Their Interaction in Kidney Diseases: A Comprehensive Review of Experimental Studies

Mitophagy is an important mechanism for mitochondrial quality control by regulating autophagosome-specific phagocytosis, degradation and clearance of damaged mitochondria, and involved in cell damage and diseases. Inflammasomes are important inflammation-related factors newly discovered in recent years, which are involved in cell innate immunity and inflammatory response, and play an important role in kidney diseases. Based on the current studies, we reviewed the progress of mitophagy, inflammasomes and their interaction in kidney diseases.

Placental Mesenchymal Stem Cells Alleviate Podocyte Injury in Diabetic Kidney Disease by Modulating Mitophagy via the SIRT1-PGC-1alpha-TFAM Pathway

The use of mesenchymal stem cells (MSCs) has become a new strategy for treating diabetic kidney disease (DKD). However, the role of placenta derived mesenchymal stem cells (P-MSCs) in DKD remains unclear. This study aims to investigate the therapeutic application and molecular mechanism of P-MSCs on DKD from the perspective of podocyte injury and PINK1/Parkin-mediated mitophagy at the animal, cellular, and molecular levels. Western blotting, reverse transcription polymerase chain reaction, immunofluorescence, and immunohistochemistry were used to detect the expression of podocyte injury-related markers and mitophagy-related markers, SIRT1, PGC-1α, and TFAM. Knockdown, overexpression, and rescue experiments were performed to verify the underlying mechanism of P-MSCs in DKD. Mitochondrial function was detected by flow cytometry. The structure of autophagosomes and mitochondria were observed by electron microscopy. Furthermore, we constructed a streptozotocin-induced DKD rat model and injected P-MSCs into DKD rats. Results showed that as compared with the control group, exposing podocytes to high-glucose conditions aggravated podocyte injury, represented by a decreased expression of Podocin along with increased expression of Desmin, and inhibited PINK1/Parkin-mediated mitophagy, manifested as a decreased expression of Beclin1, the LC3II/LC3I ratio, Parkin, and PINK1 associated with an increased expression of P62. Importantly, these indicators were reversed by P-MSCs. In addition, P-MSCs protected the structure and function of autophagosomes and mitochondria. P-MSCs increased mitochondrial membrane potential and ATP content and decreased the accumulation of reactive oxygen species. Mechanistically, P-MSCs alleviated podocyte injury and mitophagy inhibition by enhancing the expression of the SIRT1-PGC-1α-TFAM pathway. Finally, we injected P-MSCs into streptozotocin-induced DKD rats. The results revealed that the application of P-MSCs largely reversed the markers related to podocyte injury and mitophagy and significantly increased the expression of SIRT1, PGC-1α, and TFAM compared with the DKD group. In conclusion, P-MSCs ameliorated podocyte injury and PINK1/Parkin-mediated mitophagy inhibition in DKD by activating the SIRT1-PGC-1α-TFAM pathway.

Treatment of tubular damage in high-fat-diet-fed obese mice using sodium-glucose co-transporter inhibitors

A long-term high-fat diet (HFD) causes obesity and changes in renal lipid metabolism and lysosomal dysfunction in mice, causing renal damage. Sodium-glucose co-transporter inhibitors, including phlorizin, exert nephroprotective effects in patients with chronic kidney disease, but the underlying mechanism remains unclear. A HFD or standard diet was fed to adult C57BL/6J male mice, and phlorizin was administered. Lamellar body components of the proximal tubular epithelial cells (PTECs) were investigated. After phlorizin administration in HFD-fed mice, sphingomyelin and ceramide in urine and tissues were assessed and label-free quantitative proteomics was performed using kidney tissue samples. Mitochondrial elongation by fusion was effective in the PTECs of HFD-fed obese mice under phlorizin administration, and many lamellar bodies were found in the apical portion of the S2 segment of the proximal tubule. Phlorizin functioned as a diuretic, releasing lamellar bodies from the apical membrane of PTECs and clearing the obstruction in nephrons. The main component of the lamellar bodies was sphingomyelin. On the first day of phlorizin administration in HFD-fed obese mice, the diuretic effect was increased, and more sphingomyelin was excreted through urine than in vehicle-treated mice. The expressions of three peroxisomal β-oxidation proteins involved in fatty acid metabolism were downregulated after phlorizin administration in the kidneys of HFD-fed mice. Fatty acid elongation protein levels increased with phlorizin administration, indicating an increase in long-chain fatty acids. Lamellar bodies accumulated in the proximal renal tubule of the S2 segment of the HFD-fed mice, indicating that the urinary excretion of lamellar bodies has nephroprotective effects.

The Mitochondrion: A Promising Target for Kidney Disease

Mitochondrial dysfunction is important in the pathogenesis of various kidney diseases and the mitochondria potentially serve as therapeutic targets necessitating further investigation. Alterations in mitochondrial biogenesis, imbalance between fusion and fission processes leading to mitochondrial fragmentation, oxidative stress, release of cytochrome c and mitochondrial DNA resulting in apoptosis, mitophagy, and defects in energy metabolism are the key pathophysiological mechanisms underlying the role of mitochondrial dysfunction in kidney diseases. Currently, various strategies target the mitochondria to improve kidney function and kidney treatment. The agents used in these strategies can be classified as biogenesis activators, fission inhibitors, antioxidants, mPTP inhibitors, and agents which enhance mitophagy and cardiolipin-protective drugs. Several glucose-lowering drugs, such as glucagon-like peptide-1 receptor agonists (GLP-1-RA) and sodium glucose co-transporter-2 (SGLT-2) inhibitors are also known to have influences on these mechanisms. In this review, we delineate the role of mitochondrial dysfunction in kidney disease, the current mitochondria-targeting treatment options affecting the kidneys and the future role of mitochondria in kidney pathology.

GDF11, a target of miR-32-5p, suppresses high-glucose-induced mitochondrial dysfunction and apoptosis in HK-2 cells through PI3K/AKT signaling activation

PURPOSE

To investigate the role and underlying mechanism of GDF11 on diabetic nephropathy (DN)-related mitochondrial dysfunction and apoptosis.

METHODS

A DN model of rats was established in this study. Human Kidney-2 (HK-2) cells were cultured under high-glucose (HG) condition with or without recombinant GDF11 (rGDF11). Mitochondrial morphology of HK-2 cells was analyzed by transmission electron microscope and MitoTracker Red CMXRos staining. Mitochondrial membrane potential (MMP) and ROS production were monitored using JC-1 assay kit and MitoSOX staining, respectively. Cell apoptosis was detected by TUNEL or flow cytometry assays.

RESULTS

Herein, we observed that GDF11 was down-regulated in renal cortex and serum of DN rats, which was accompanied by renal mitochondrial morphological abnormalities. In line with the findings in vivo, HK-2 cells exposed to HG presented with mitochondrial morphological alterations and further apoptosis accompanied by GDF11 reduction. In addition, HG promoted a decrease in MMP while an increase in mitochondrial ROS production. Conversely, rGDF11 treatment significantly alleviated these HG-induced mitochondrial defects in HK-2 cells. Meanwhile, HK-2 cell apoptosis induced by HG was simultaneously suppressed by rGDF11. Mechanistically, the decreased levels of p-AKT induced by HG were attenuated after rGDF11 administration. Inhibition of the PI3K/AKT pathway resisted the effects of rGDF11 on the MMP and apoptosis of HK-2 cells. In addition, we identified that GDF11 is a target of miR-32-5p. Up-regulation of miR-32-5p could inhibit the expression of GDF11.

CONCLUSION

rGDF11 treatment rescued HG-induced HK-2 cell mitochondrial dysfunction and apoptosis, which may be dependent on the activation of the PI3K/AKT pathway.

Klotho, Oxidative Stress, and Mitochondrial Damage in Kidney Disease

Reducing oxidative stress stands at the center of a prevention and control strategy for mitigating cellular senescence and aging. Kidney disease is characterized by a premature aging syndrome, and to find a modulator targeting against oxidative stress, mitochondrial dysfunction, and cellular senescence in kidney cells could be of great significance to prevent and control the progression of this disease. This review focuses on the pathogenic mechanisms related to the appearance of oxidative stress damage and mitochondrial dysfunction in kidney disease. In this scenario, the anti-aging Klotho protein plays a crucial role by modulating signaling pathways involving the manganese-containing superoxide dismutase (Mn-SOD) and the transcription factors FoxO and Nrf2, known antioxidant systems, and other known mitochondrial function regulators, such as mitochondrial uncoupling protein 1 (UCP1), B-cell lymphoma-2 (BCL-2), Wnt/β-catenin, peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1 alpha), transcription factor EB, (TFEB), and peroxisome proliferator-activated receptor gamma (PPAR-gamma). Therefore, Klotho is postulated as a very promising new target for future therapeutic strategies against oxidative stress, mitochondria abnormalities, and cellular senescence in kidney disease patients.

Protective effect of natural products in the metabolic-associated kidney diseases via regulating mitochondrial dysfunction

Metabolic syndrome (MS) is a complex group of metabolic disorders syndrome with hypertension, hyperuricemia and disorders of glucose or lipid metabolism. As an important organ involved in metabolism, the kidney is inevitably attacked by various metabolic disorders, leading to abnormalities in kidney structure and function. Recently, an increasing number of studies have shown that mitochondrial dysfunction is actively involved in the development of metabolic-associated kidney diseases. Mitochondrial dysfunction can be used as a potential therapeutic strategy for the treatment of metabolic-associated kidney diseases. Many natural products have been widely used to improve the treatment of metabolic-associated kidney diseases by inhibiting mitochondrial dysfunction. In this paper, by searching several authoritative databases such as PubMed, Web of Science, Wiley Online Library, and Springer Link. We summarize the Natural Products Protect Against Metabolic-Associated Kidney Diseases by Regulating Mitochondrial Dysfunction. In this review, we sought to provide an overview of the mechanisms by which mitochondrial dysfunction impaired metabolic-associated kidney diseases, with particular attention to the role of mitochondrial dysfunction in diabetic nephropathy, gouty nephropathy, hypertensive kidney disease, and obesity-related nephropathy, and then the protective role of natural products in the kidney through inhibition of mitochondrial disorders, thus providing a systematic understanding of the targets of mitochondrial dysfunction in metabolic-associated kidney diseases, and finally a review of promising therapeutic targets and herbal candidates for metabolic-associated kidney diseases through inhibition of mitochondrial dysfunction.

Identification of hsa_circRNA_100632 as a novel molecular biomarker for fulminant type 1 diabetes

Objective

Circular RNAs (circRNAs) are associated with diabetes, but their role in fulminant type 1 diabetes (FT1D) is unclear. Thus, we characterized the role of circRNAs in FT1D.

Research design and methods

CircRNA expression profiles were detected in peripheral blood mononuclear cells (PBMCs) of five FT1D patients and five controls using a circRNA microarray. An independent cohort comprised of 40 FT1D cases, 75 type 1 diabetes (T1D) cases, and 115 controls was used to verify the circRNAs using quantitative real-time polymerase chain reaction (qRT-PCR). Spearman's correlation analysis and receiver operating characteristic (ROC) curve analysis were performed to determine the clinical diagnostic capability of circRNAs. Bioinformatics was used to identify potential biological functions and circRNA-miRNA-mRNA interactions.

Results

There were 13 upregulated and 13 downregulated circRNAs in PBMCs of patients with FT1D. Five circRNAs were further verified in a second cohort. Hsa_circRNA_100632 was significantly upregulated in the FT1D and T1D groups. Hsa_circRNA_100632 was differentiated between patients with FT1D and controls [area under the curve (AUC) 0.846; 95% CI 0.776-0.916; P<0.0001] as well as between patients with FT1D and patients with T1D (AUC 0.726; 95% CI 0.633-0.820; P<0.0001). Bioinformatics analysis showed that hsa_circRNA_100632 may be involved in 47 circRNA-miRNA-mRNA signaling pathways associated with diabetes.

Conclusions

CircRNAs were aberrantly expressed in PBMCs of patients with FT1D, and hsa_circRNA_100632 may be a diagnostic marker of FT1D.

Melatonin Attenuates Mitochondrial Damage in Aristolochic Acid-Induced Acute Kidney Injury

Aristolochic acid (AA), extracted from Aristolochiaceae plants, plays an essential role in traditional herbal medicines and is used for different diseases. However, AA has been found to be nephrotoxic and is known to cause aristolochic acid nephropathy (AAN). AA-induced acute kidney injury (AKI) is a syndrome in AAN with a high morbidity that manifests mitochondrial damage as a key part of its pathological progression. Melatonin primarily serves as a mitochondria-targeted antioxidant. However, its mitochondrial protective role in AA-induced AKI is barely reported. In this study, mice were administrated 2.5 mg/kg AA to induce AKI. Melatonin reduced the increase in Upro and Scr and attenuated the necrosis and atrophy of renal proximal tubules in mice exposed to AA. Melatonin suppressed ROS generation, MDA levels and iNOS expression and increased SOD activities in vivo and in vitro. Intriguingly, the in vivo study revealed that melatonin decreased mitochondrial fragmentation in renal proximal tubular cells and increased ATP levels in kidney tissues in response to AA. In vitro, melatonin restored the mitochondrial membrane potential (MMP) in NRK-52E and HK-2 cells and led to an elevation in ATP levels. Confocal immunofluorescence data showed that puncta containing Mito-tracker and GFP-LC3A/B were reduced, thereby impeding the mitophagy of tubular epithelial cells. Furthermore, melatonin decreased LC3A/B-II expression and increased p62 expression. The apoptosis of tubular epithelial cells induced by AA was decreased. Therefore, our findings revealed that melatonin could prevent AA-induced AKI by attenuating mitochondrial damage, which may provide a potential therapeutic method for renal AA toxicity.

Qing-Re-Xiao-Zheng-Yi-Qi formula relieves kidney damage and activates mitophagy in diabetic kidney disease

Introduction: Qing-Re-Xiao-Zheng-Yi-Qi Formula is an effective prescription in diabetic kidney disease treatment, we have confirmed the efficacy of Qing-Re-Xiao-Zheng therapy in diabetic kidney disease through clinical trials. In this study, we investigated the mechanisms of Qing-Re-Xiao-Zheng-Yi-Qi Formula in the treatment of diabetic kidney disease. Methods: We used Vanquish UHPLC^TM to analyze the chemical profiling of Qing-Re-Xiao-Zheng-Yi-Qi Formula freeze-dried powder. We constructed diabetic kidney disease rat models induced by unilateral nephrectomy and high-dose streptozocin injection. We examined blood urea nitrogen, serum creatinine, serum glucose, total cholesterol, triglyceride, serum total protein, albumin, alanine aminotransferase, aspartate aminotransferase and 24 h urinary total protein in diabetic kidney disease rats. The renal pathological changes were observed by HE, Masson, PAS stanning and transmission electron microscopy. The levels of fibrosis-related proteins and mitophagy-related proteins were detected by western blot analysis. We also conducted an immunofluorescence co-localization analysis on podocytes to further investigate the effect of Qing-Re-Xiao-Zheng-Yi-Qi Formula treatment on mitophagy. Results: A total of 27 constituents in Qing-Re-Xiao-Zheng-Yi-Qi Formula were tentatively identified. We found PINK1/Parkin-mediated mitophagy was inhibited in diabetic kidney disease. Qing-Re-Xiao-Zheng-Yi-Qi Formula treatment could raise body weight and reduce renal index, reduce proteinuria, improve glycolipid metabolic disorders, ameliorate renal fibrosis, and reduce the expression of Col Ⅳ and TGF-β1 in diabetic kidney disease rats. Qing-Re-Xiao-Zheng-Yi-Qi Formula treatment could also increase the expression of nephrin, activate mitophagy and protect podocytes in diabetic kidney disease rats and high glucose cultured podocytes. Conclusion: PINK1/Parkin-mediated mitophagy was inhibited in diabetic kidney disease, and Qing-Re-Xiao-Zheng-Yi-Qi Formula treatment could not only ameliorate pathological damage, but also promote mitophagy to protect podocytes in diabetic kidney disease.

Effects of Elamipretide on Autophagy in Renal Cells of Pigs with Metabolic Syndrome

Autophagy eliminates excessive nutrients and maintains homeostasis. Obesity and metabolic syndrome (MetS) dysregulate autophagy, possibly partly due to mitochondria injury and inflammation. Elamipretide (ELAM) improves mitochondrial function. We hypothesized that MetS blunts kidney autophagy, which ELAM would restore. Domestic pigs were fed a control or MetS-inducing diet for 16 weeks. During the 4 last weeks, MetS pigs received subcutaneous injections of ELAM (0.1 mg/kg/day, MetS + ELAM) or vehicle (MetS), and kidneys were then harvested to measure protein expression of autophagy mediators and apoptosis. Systemic and renal venous levels of inflammatory cytokines were measured to calculate renal release. The function of isolated mitochondria was assessed by oxidative stress, energy production, and pro-apoptotic activity. MetS slightly downregulated renal expression of autophagy mediators including p62, ATG5-12, mTOR, and AMPK vs. control. Increased mitochondrial H₂O₂ production accompanied decreased ATP production, elevated apoptosis, and renal fibrosis. In MetS + ELAM, mito-protection restored autophagic protein expression, improved mitochondrial energetics, and blunted renal cytokine release and fibrosis. In vitro, mitoprotection restored mitochondrial membrane potential and reduced oxidative stress in injured proximal tubular epithelial cells. Our study suggests that swine MetS mildly affects renal autophagy, possibly secondary to mitochondrial damage, and may contribute to kidney structural damage in MetS.

Hypoxia-Inducible Factors and Diabetic Kidney Disease—How Deep Can We Go?

Diabetes is one of the leading causes of chronic kidney disease (CKD), and multiple underlying mechanisms involved in pathogenesis of diabetic nephropathy (DN) have been described. Although various treatments and diagnosis applications are available, DN remains a clinical and economic burden, considering that about 40% of type 2 diabetes patients will develop nephropathy. In the past years, some research found that hypoxia response and hypoxia-inducible factors (HIFs) play critical roles in the pathogenesis of DN. Hypoxia-inducible factors (HIFs) HIF-1, HIF-2, and HIF-3 are the main mediators of metabolic responses to the state of hypoxia, which seems to be the one of the earliest events in the occurrence and progression of diabetic kidney disease (DKD). The abnormal activity of HIFs seems to be of crucial importance in the pathogenesis of diseases, including nephropathies. Studies using transcriptome analysis confirmed by metabolome analysis revealed that HIF stabilizers (HIF-prolyl hydroxylase inhibitors) are novel therapeutic agents used to treat anemia in CKD patients that not only increase endogenous erythropoietin production, but also could act by counteracting the metabolic alterations in incipient diabetic kidney disease and relieve oxidative stress in the renal tissue. In this review, we present the newest data regarding hypoxia response and HIF involvement in the pathogenesis of diabetic nephropathy and new therapeutic insights, starting from improving kidney oxygen homeostasis.

The Nicotinamide/Streptozotocin Rodent Model of Type 2 Diabetes: Renal Pathophysiology and Redox Imbalance Features

Diabetic nephropathy (DN) is a common complication of diabetes mellitus. While there has been a great advance in our understanding of the pathogenesis of DN, no effective managements of this chronic kidney disease are currently available. Therefore, continuing to elucidate the underlying biochemical and molecular mechanisms of DN remains a constant need. In this regard, animal models of diabetes are indispensable tools. This review article highlights a widely used rodent model of non-obese type 2 diabetes induced by nicotinamide (NA) and streptozotocin (STZ). The mechanism underlying diabetes induction by combining the two chemicals involves blunting the toxic effect of STZ by NA so that only a percentage of β cells are destroyed and the remaining viable β cells can still respond to glucose stimulation. This NA-STZ animal model, as a platform for the testing of numerous antidiabetic and renoprotective materials, is also discussed. In comparison with other type 2 diabetic animal models, such as high-fat-diet/STZ models and genetically engineered rodent models, the NA-STZ model is non-obese and is less time-consuming and less expensive to create. Given that this unique model mimics certain pathological features of human DN, this model should continue to find its applications in the field of diabetes research.

Metabolic reprogramming: A novel therapeutic target in diabetic kidney disease

Diabetic kidney disease (DKD) is one of the most common microvascular complications of diabetes mellitus. However, the pathological mechanisms contributing to DKD are multifactorial and poorly understood. Diabetes is characterized by metabolic disorders that can bring about a series of changes in energy metabolism. As the most energy-consuming organs secondary only to the heart, the kidneys must maintain energy homeostasis. Aberrations in energy metabolism can lead to cellular dysfunction or even death. Metabolic reprogramming, a shift from mitochondrial oxidative phosphorylation to glycolysis and its side branches, is thought to play a critical role in the development and progression of DKD. This review focuses on the current knowledge about metabolic reprogramming and the role it plays in DKD development. The underlying etiologies, pathological damages in the involved cells, and potential molecular regulators of metabolic alterations are also discussed. Understanding the role of metabolic reprogramming in DKD may provide novel therapeutic approaches to delay its progression to end-stage renal disease.

A Review of the Potential Effects of Melatonin in Compromised Mitochondrial Redox Activities in Elderly Patients With COVID-19

Melatonin, an endogenous indoleamine, is an antioxidant and anti-inflammatory molecule widely distributed in the body. It efficiently regulates pro-inflammatory and anti-inflammatory cytokines under various pathophysiological conditions. The melatonin rhythm, which is strongly associated with oxidative lesions and mitochondrial dysfunction, is also observed during the biological process of aging. Melatonin levels decline considerably with age and are related to numerous age-related illnesses. The signs of aging, including immune aging, increased basal inflammation, mitochondrial dysfunction, significant telomeric abrasion, and disrupted autophagy, contribute to the increased severity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. These characteristics can worsen the pathophysiological response of the elderly to SARS-CoV-2 and pose an additional risk of accelerating biological aging even after recovery. This review explains that the death rate of coronavirus disease (COVID-19) increases with chronic diseases and age, and the decline in melatonin levels, which is closely related to the mitochondrial dysfunction in the patient, affects the virus-related death rate. Further, melatonin can enhance mitochondrial function and limit virus-related diseases. Hence, melatonin supplementation in older people may be beneficial for the treatment of COVID-19.

Erythropoietin Mitigates Diabetic Nephropathy by Restoring PINK1/Parkin-Mediated Mitophagy

Diabetic nephropathy (DN), one of the most detrimental microvascular complications of diabetes, is the leading cause of end-stage renal disease. The pathogenesis of DN is complicated, including hemodynamic changes, inflammatory response, oxidative stress, among others. Recently, many studies have demonstrated that mitophagy, especially PINK1/Parkin-mediated mitophagy, plays an important role in the pathogenesis of DN. Erythropoietin (EPO), a glycoprotein hormone mainly secreted by the kidney, regulates the production of erythrocytes. This research intends to explore the beneficial effects of EPO on DN and investigate related mechanisms. In in vitro experiments, we found that EPO promoted autophagic flux and alleviated mitochondrial dysfunction in terms of mitochondrial fragmentation, elevated mitochondrial ROS as well as the loss of mitochondrial potential, and lowered the apoptosis level in high-glucose-treated mesangial cells. Moreover, EPO increased protein expressions of PINK1 and Parkin, enhanced the co-localization of LC3 with mitochondria, Parkin with mitochondria as well as LC3 with Parkin, and increased the number of GFP-LC3 puncta, resulting in increased level of PINK1/Parkin-mediated mitophagy in mesangial cells. The knockdown of PINK1 abrogated the effect of EPO on mitophagy. In addition, in vivo experiments demonstrated that EPO attenuated renal injury, reduced oxidative stress, and promoted expressions of genes related to PINK1/Parkin-mediated mitophagy in the kidneys of DN mice. In summary, these results suggest that PINK1/Parkin-mediated mitophagy is involved in the development of DN and EPO mitigates DN by restoring PINK1/Parkin-mediated mitophagy.

Formononetin Attenuates Renal Tubular Injury and Mitochondrial Damage in Diabetic Nephropathy Partly via Regulating Sirt1/PGC-1α Pathway

Mitochondrial abnormality is one of the main factors of tubular injury in diabetic nephropathy (DN). Formononetin (FMN), a novel isoflavonoid isolated from Astragalus membranaceus, has diverse pharmacological activities. However, the beneficial effects of FMN on renal tubular impairment and mitochondrial dysfunction in DN have yet to be studied. In this study, we performed in vivo tests in Streptozotocin (STZ) -induced diabetic rats to explore the therapeutic effects of FMN on DN. We demonstrated that FMN could ameliorate albuminuria and renal histopathology. FMN attenuated renal tubular cells apoptosis, mitochondrial fragmentation and restored expression of mitochondrial dynamics-associated proteins, such as Drp1, Fis1 and Mfn2, as well as apoptosis-related proteins, such as Bax, Bcl-2 and cleaved-caspase-3. Moreover, FMN upregulated the protein expression of Sirt1 and PGC-1α in diabetic kidneys. In vitro studies further demonstrated that FMN could inhibit high glucose-induced apoptosis of HK-2 cells. FMN also reduced the production of mitochondrial superoxide and alleviated mitochondrial membrane potential (MMP) loss. Furthermore, FMN partially restored the protein expression of Drp1, Fis1 and Mfn2, Bax, Bcl-2, cleaved-caspase-3, Sirt1 and PGC-1α in HK-2 cells exposure to high glucose. In conclusion, FMN could attenuate renal tubular injury and mitochondrial damage in DN partly by regulating Sirt1/PGC-1α pathway.

A Deep Insight Into Regulatory T Cell Metabolism in Renal Disease: Facts and Perspectives

Kidney disease encompasses a complex set of diseases that can aggravate or start systemic pathophysiological processes through their complex metabolic mechanisms and effects on body homoeostasis. The prevalence of kidney disease has increased dramatically over the last two decades. CD4⁺CD25⁺ regulatory T (Treg) cells that express the transcription factor forkhead box protein 3 (Foxp3) are critical for maintaining immune homeostasis and preventing autoimmune disease and tissue damage caused by excessive or unnecessary immune activation, including autoimmune kidney diseases. Recent studies have highlighted the critical role of metabolic reprogramming in controlling the plasticity, stability, and function of Treg cells. They are also likely to play a vital role in limiting kidney transplant rejection and potentially promoting transplant tolerance. Metabolic pathways, such as mitochondrial function, glycolysis, lipid synthesis, glutaminolysis, and mammalian target of rapamycin (mTOR) activation, are involved in the development of renal diseases by modulating the function and proliferation of Treg cells. Targeting metabolic pathways to alter Treg cells can offer a promising method for renal disease therapy. In this review, we provide a new perspective on the role of Treg cell metabolism in renal diseases by presenting the renal microenvironment、relevant metabolites of Treg cell metabolism, and the role of Treg cell metabolism in various kidney diseases.

PACS-2 Ameliorates Tubular Injury by Facilitating Endoplasmic Reticulum-Mitochondria Contact and Mitophagy in Diabetic Nephropathy

Mitochondria-associated endoplasmic reticulum membrane (MAM) may have a role in tubular injury in diabetic nephropathy (DN), but the precise mechanism remains unclear. Here, we demonstrate that the expression of phosphofurin acidic cluster sorting protein 2 (PACS-2), a critical regulator of MAM formation, is significantly decreased in renal tubules of patients with DN, and PACS-2 expression is positively correlated with renal function and negatively correlated with degrees of tubulointerstitial lesions. Conditional deletion of Pacs-2 in proximal tubules (PTs) aggravates albuminuria and tubular injury in a streptozotocin-induced mouse model of diabetes. Mitochondrial fragmentation, MAM disruption, and defective mitophagy accompanied by altered expression of mitochondrial dynamics and mitophagic proteins, including Drp1 and Becn1, are observed in tubules of diabetic mice; these changes are more pronounced in PT-specific Pacs-2 knockout mice. In vitro, overexpression of PACS-2 in HK-2 cells alleviates excessive mitochondrial fission induced by high glucose concentrations through blocking mitochondrial recruitment of DRP1 and subsequently restores MAM integrity and enhances mitophagy. Mechanistically, PACS-2 binds to BECN1 and mediates the relocalization of BECN1 to MAM, where it promotes the formation of mitophagosome. Together, these data highlight an important but previously unrecognized role of PACS-2 in ameliorating tubular injury in DN by facilitating MAM formation and mitophagy.

Administration of mesenchymal stem cells in diabetic kidney disease: mechanisms, signaling pathways, and preclinical evidence

Diabetic kidney disease (DKD) is a serious microvascular complication of diabetes. Currently, the prevalence and mortality of DKD are increasing annually. However, with no effective drugs to prevent its occurrence and development, the primary therapeutic option is to control blood sugar and blood pressure. Therefore, new and effective drugs/methods are imperative to prevent the development of DKD in patients with diabetes. Mesenchymal stem cells (MSCs) with multi-differentiation potential and paracrine function have received extensive attention as a new treatment option for DKD. However, their role and mechanism in the treatment of DKD remain unclear, and clinical applications are still being explored. Given this, we here provide an unbiased review of recent advances in MSCs for the treatment of DKD in the last decade from the perspectives of the pathogenesis of DKD, biological characteristics of MSCs, and different molecular and signaling pathways. Furthermore, we summarize information on combination therapy strategies using MSCs. Finally, we discuss the challenges and prospects for clinical application.

YY1 inactivated transcription co-regulator PGC-1α to promote mitochondrial dysfunction of early diabetic nephropathy-associated tubulointerstitial fibrosis

The development of diabetic nephropathy (DN) could be promoted by the occurrence of tubulointerstitial fibrosis (TIF), which had a closely relationship with mitochondrial dysfunction of renal tubular epithelial cells (RTECs). As a key regulator of metabolic homeostasis, Yin Yang 1 (YY1) played an important role not only in regulating fibrosis process, but also in maintaining mitochondrial function of pancreatic β cells. However, it was not clear whether YY1 participated in maintaining mitochondrial function of RTECs in early DN-associated TIF. In this study, we dynamically detected mitochondrial functions and protein expression of YY1 in db/db mice and high glucose (HG)-cultured HK-2 cells. Our results showed that comparing with the occurrence of TIF, the emergence of mitochondrial dysfunction of RTECs was an earlier even, besides the up-regulated and nuclear translocated YY1. Correlation analysis showed YY1 expressions were negatively associated with PGC-1α in vitro and in vivo. Further mechanism research demonstrated the formation of mTOR-YY1 heterodimer induced by HG upregulated YY1, the nuclear translocation of which inactivated PGC-1α by binding to the PGC-1α promoter. Overexpression of YY1 induced mitochondrial dysfunctions in normal glucose cultured HK-2 cells and 8-week-old db/m mice. While, dysfunctional mitochondria induced by HG could be improved by knockdown of YY1. Finally, downregulation of YY1 could retard the progression of TIF by preventing mitochondrial functions, resulting in the improvement of epithelial-mesenchymal transition (EMT) in early DN. These findings suggested that YY1 was a novel regulator of mitochondrial function of RTECs and contributed to the occurrence of early DN-associated TIF .

Mitophagy and mitochondrial dynamics in type 2 diabetes mellitus treatment

The prevalence of type 2 diabetes is associated with inflammatory bowels diseases, nonalcoholic steatohepatitis and even a spectrum of cancer such as colon cancer and liver cancer, resulting in a substantial healthcare burden on our society. Autophagy is a key regulator in metabolic homeostasis such as lipid metabolism, energy management and the balance of cellular mineral substances. Mitophagy is selective autophagy for clearing the damaged mitochondria and dysfunctional mitochondria. A myriad of evidence has demonstrated a major role of mitophagy in the regulation of type 2 diabetes and metabolic homeostasis. It is well established that defective mitophagy has been linked to the development of insulin resistance. Moreover, insulin resistance is further progressed to various diseases such as nephropathy, retinopathy and cardiovascular diseases. Concordantly, restoration of mitophagy will be a reliable and therapeutic target for type 2 diabetes. Recently, various phytochemicals have been proved to prevent dysfunctions of β-cells by mitophagy inductions during diabetes developments. In agreement with the above phenomenon, mitophagy inducers should be warranted as potential and novel therapeutic agents for treating diabetes. This review focuses on the role of mitophagy in type 2 diabetes relevant diseases and the pharmacological basis and therapeutic potential of autophagy regulators in type 2 diabetes.

AMPK Activator O304 Protects Against Kidney Aging Through Promoting Energy Metabolism and Autophagy

Aging is an important risk factor for kidney injury. Energy homeostasis plays a key role in retarding aging, and mitochondria are responsible for energy production. In the kidney, renal tubular cells possess high abundance of mitochondria to meet the high energy consumption. AMPK is an evolutionarily conserved serine/threonine kinase which plays a central role in maintaining energy homeostasis and mitochondrial homeostasis. Besides that, AMPK also commands autophagy, a clearing and recycling process to maintain cellular homeostasis. However, the effect of AMPK activators on kidney aging has not been fully elucidated. To this end, we testified the effects of O304, a novel direct AMPK activator, in naturally aging mice model and D-Galactose (D-Gal)-treated renal tubular cell culture. We identified that O304 beneficially protects against cellular senescence and aged-related fibrosis in kidneys. Also, O304 restored energy metabolism, promoted autophagy and preserved mitochondrial homeostasis. Transcriptomic sequencing also proved that O304 induced fatty acid metabolism, mitochondrial biogenesis and ATP process, and downregulated cell aging, DNA damage response and collagen organization. All these results suggest that O304 has a strong potential to retard aged kidney injury through regulating AMPK-induced multiple pathways. Our results provide an important therapeutic approach to delay kidney aging.

Green tea peptides ameliorate diabetic nephropathy by inhibiting the TGF-β/Smad signaling pathway in mice

Diabetic nephropathy (DN) is the most important cause of middle and late-stage chronic kidney disease. Green tea polypeptides are extracted from tea pomace, and exhibit various pharmacological effects. In this study, we analyzed the reno-protective effects of green tea peptides in diabetic db/db mice, and explored the underlying mechanisms. Peptide treatment for 5 weeks significantly reduced the blood glucose levels and other indices of diabetes, and alleviated renal injury measured in terms of blood creatinine, urea nitrogen and urinary albumin/urinary creatinine levels. Mechanistically, the green tea peptides downregulated p-Smad2/3, α-SMA, ZO-1 and vimentin proteins in the kidney tissues, and elevated Smad7. Thus, green tea peptides inhibited the deposition of ECM proteins by suppressing excessive activation of the TGF-β/Smad signaling pathway and reducing fibronectin levels. On the other hand, tea peptides ameliorated renal injury by inhibiting the production of inflammatory factors (iNOS and TNF-α) by suppressing the NF-κB signaling pathway. In addition, we confirmed the inhibitory effect of green tea peptides on the TGF-β/Smad signaling pathway in TGF-β1-stimulated HK-2 cells. Therefore, tea peptides can be considered as an effective candidate for alleviating DN.

Antioxidant effect of nicotinamide mononucleotide in tendinopathy

Background

A link between tendinopathy and oxidative stress has been recently reported. Nicotinamide mononucleotide (NMN) is a precursor of nicotinamide adenine dinucleotide, which plays an important role in cell redox homeostasis. The aim of this study was to evaluate the antioxidant effect of NMN on tendinopathy in vitro and in vivo.

Methods

Tenocytes from healthy Sprague-Dawley rats were cultured in regular glucose (RG) and high-glucose (HG) conditions with or without NMN, and were divided into four groups: RG NMN(−), RG NMN(+), HG NMN(−), and HG NMN(+). Cell viability, reactive oxygen species (ROS) accumulation, apoptotic rate, and mRNA expression of nicotinamide adenine dinucleotide phosphate oxidase (NOX)1, NOX4, interleukin (IL)6, sirtuin (SIRT)1, and SIRT6 were investigated. In addition, rats with collagenase-induced tendinopathy were treated with or without NMN. Immunostaining of NOX1 and NOX4; mRNA expression of SIRT1, SIRT6, and IL6; and superoxide dismutase (SOD) activity measurements in the Achilles tendon were performed.

Results

NMN increased the expression of SIRT1 and SIRT6 in rat tenocytes, but decreased the levels of NOX1, NOX4, IL6, ROS, and apoptosis. In Achilles tendons with collagenase-induced tendinopathy, NMN increased the mRNA expression of SIRT1 and SIRT6, as well as SOD activity; while suppressing protein expression of NOX1 and NOX4, and mRNA expression of IL6.

Conclusion

The in vitro and in vivo results of this study show that NMN exerts an antioxidant effect on tendinopathy by promoting the expression of SIRT while inhibiting that of NOX.

Renoprotective potential of myo-inositol on diabetic kidney disease: Focus on the role of the PINK1/Parkin pathway and mitophagy receptors

Recent studies have emphasized the role of mitochondria in renal function as well as in renal injury. Poor mitochondrial quality control mechanisms including mitochondrial fusion, fission and mitophagy are major contributors for progression of diabetic renal injury. The current study is aimed to evaluate the protective role of myo-inositol (MI) against diabetic nephropathy (DN) by utilizing high glucose exposed NRK 52E cell and streptozotocin (STZ) induced DN model. MI supplementation (at doses 37.5 and 75 mg/kg) ameliorated albuminuria and enhanced the renal function as indicated significant improvement in urinary creatinine and urea levels. On the other hand, the western blot analysis of both in vitro and in vivo studies has revealed poor mitophagy in renal cells which was reversed upon myo-inositol treatment. Apart from targeting the canonical PINK1/Parkin pathway, we also focused on the role mitophagy receptors prohibitin (PHB) and NIP3-like protein (NIX). A significant reduction in expression of NIX and PHB2 was observed in renal tissue of diabetic control rats and high glucose exposed NRK 52E cells. Myo-inositol treatment resulted in positive modulation of PINK1/Parkin pathway as well as PHB2 and NIX. Myo-inositol also enhanced the mitochondrial biogenesis in renal tissue of diabetic rat by upregulating Nrf2/SIRT1/PGC-1α axis. The current study thus underlines the renoprotective effect myo-inositol, upregulation of mitophagy proteins and mitochondrial biogenesis upon myo-inositol treatment.

HIF-1α Alleviates High-Glucose-Induced Renal Tubular Cell Injury by Promoting Parkin/PINK1-Mediated Mitophagy

It is well-established that mitophagy leads to Diabetic Nephropathy (DN) and renal failure. Mitophagy mediated by a Hypoxia-inducible factor-1α (HIF-1α) plays a beneficial role in many diseases. Nevertheless, the mechanisms underlying HIF-1α-mediated mitophagy in DN remain unclear. This study defines the role of HIF-1α mediated mitophagy in DN. The expression of HIF-1α was upregulated in HK-2 cells in an High-Glucose (HG) environment, and the YC-1 (a specific inhibitor of HIF-1α) further exacerbated the hypoxia-induced mitochondrial dysfunction. Conversely, the HIF-1α-mediated protective effect was strengthened by scavenger N-acetylcysteine (NAC), a type of reactive oxygen species. Moreover, HIF-1α-Parkin/PINK1-mediated mitophagy prevented apoptosis and ROS production in HK-2 cells subjected to HG exposure. In summary, HIF-1α mediated mitophagy on HK-2 cells under HG conditions could alleviate DN, suggesting that it has huge prospects for DN treatment.

Mitochondrial Pathophysiology on Chronic Kidney Disease

In healthy kidneys, interstitial fibroblasts are responsible for the maintenance of renal architecture. Progressive interstitial fibrosis is thought to be a common pathway for chronic kidney diseases (CKD). Diabetes is one of the boosters of CKD. There is no effective treatment to improve kidney function in CKD patients. The kidney is a highly demanding organ, rich in redox reactions occurring in mitochondria, making it particularly vulnerable to oxidative stress (OS). A dysregulation in OS leads to an impairment of the Electron transport chain (ETC). Gene deficiencies in the ETC are closely related to the development of kidney disease, providing evidence that mitochondria integrity is a key player in the early detection of CKD. The development of novel CKD therapies is needed since current methods of treatment are ineffective. Antioxidant targeted therapies and metabolic approaches revealed promising results to delay the progression of some markers associated with kidney disease. Herein, we discuss the role and possible origin of fibroblasts and the possible potentiators of CKD. We will focus on the important features of mitochondria in renal cell function and discuss their role in kidney disease progression. We also discuss the potential of antioxidants and pharmacologic agents to delay kidney disease progression.

Upregulation of TIPE1 in tubular epithelial cell aggravates diabetic nephropathy by disrupting PHB2 mediated mitophagy

Renal tubular epithelial cells (RTECs) are one of the most mitochondria-rich cell types, and are thus vulnerable to mitochondrial dysregulation, which is defined as a pivotal event in tubular damage in diabetic nephropathy (DN). However, the underlying mechanisms remain largely unknown. Here, we investigated the role and mechanisms of tumor necrosis factor alpha-induced protein 8-like 1 (TNFAIP8L1/TIPE1) in high glucose (HG)-induced mitochondrial dysfunction in RTECs and DN progression. TIPE1 expression was predominantly upregulated in RTECs in patients with DN and mice with streptozotocin (STZ)-induced DN. Conditional knockout of Tipe1 in RTECs significantly decreased the urine protein creatinine ratio, renal tubular damage, epithelial-mesenchymal transition, and interstitial fibrosis in STZ-induced mice. RNA sequencing revealed that citrate cycle-related genes were positively enriched in the renal tissues of RTEC-specific Tipe1 knockout mice. Tipe1 deficiency upregulated ATP levels, mitochondrial membrane potential, and respiration rate, but downregulated mitochondrial ROS levels in RTECs. Furthermore, Tipe1 ablation led to enhanced mitophagy in RTECs, indicative of increased LC3II, PINK1, and Parkin expression, but decreased p62 expression in mitochondria. Mechanistically, mass spectrometry screening and co-immunoprecipitation assays revealed the interaction of TIPE1 with prohibitin 2 (PHB2), a crucial mitophagy receptor. Intriguingly, TIPE1 promoted the ubiquitination and proteasomal degradation of PHB2. Subsequently, PHB2 knockdown almost abrogated the improvement of Tipe1 loss on HG-induced tubular cell mitophagy and damage. Thus, TIPE1 disrupts mitochondrial homeostasis in RTECs and promotes tubular damage by destabilizing PHB2 under HG conditions. Hence, TIPE1 may act as a potential therapeutic target to prevent DN progression.

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TIPE1 is highly expressed in RTECs of DN.

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TIPE1 aggravates diabetic renal injury and fibrosis.

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TIPE1 disrupts the mitochondria homeostasis of RTECs by inhibiting mitophagy.

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TIPE1 interacts with and promotes the proteasomal degradation of PHB2.

Podocyte Bioenergetics in the Development of Diabetic Nephropathy: The Role of Mitochondria

Diabetic nephropathy (DN) is the leading cause of kidney failure, with an increasing incidence worldwide. Mitochondrial dysfunction is known to occur in DN and has been implicated in the underlying pathogenesis of disease. These complex organelles have an array of important cellular functions and involvement in signaling pathways, and understanding the intricacies of these responses in health, as well as how they are damaged in disease, is likely to highlight novel therapeutic avenues. A key cell type damaged early in DN is the podocyte, and increasing studies have focused on investigating the role of mitochondria in podocyte injury. This review will summarize what is known about podocyte mitochondrial dynamics in DN, with a particular focus on bioenergetic pathways, highlighting key studies in this field and potential opportunities to target, enhance or protect podocyte mitochondrial function in the treatment of DN.

Therapeutic potential of resveratrol in diabetic nephropathy according to molecular signaling

BACKGROUND

Diabetic nephropathy (DN) as a severe complication of diabetes mellitus (DM), is a crucial menace for human health and survival and remarkably elevates the healthcare systems' costs. Therefore, it is worth noting to identify novel preventive and therapeutic strategies to alleviate the disease conditions. Resveratrol, as a well-defined anti-diabetic/ antioxidant agent has capabilities to counteract diabetic complications. It has been predicted that resveratrol will be a fantastic natural polyphenol for diabetes therapy in the next few years.

OBJECTIVE

Accordingly, the current review aims to depict the role of resveratrol in the regulation of different signaling pathways that are involved in the reactive oxygen species (ROS) production, inflammatory processes, autophagy, and mitochondrial dysfunction, as critical contributors to DN pathophysiology.

RESULTS

The pathogenesis of DN can be multifactorial; hyperglycemia is one of the prominent risk factors of DN development that is closely related to oxidative stress. Resveratrol, as a well-defined polyphenol, has various biological and medicinal properties, including anti-diabetic, anti-inflammatory, and anti-oxidative effects.

CONCLUSION

Resveratrol prevents kidney damages that are caused by oxidative stress, enhances antioxidant capacity, and attenuates the inflammatory and fibrotic responses. For this reason, resveratrol is considered an interesting target in DN research due to its therapeutic possibilities during diabetic disorders and renal protection.

Mitochondrial dynamics and diabetic kidney disease: Missing pieces for the puzzle of therapeutic approaches

Diabetic kidney disease (DKD) is a common microvascular complication among diabetic patients. Once the DKD has developed, most of the patients inevitably progress to the end‐stage renal disease (ESRD). Although many new therapeutic strategies have attempted to demolish the root of the pathogenesis of DKD, the residual risks of ESRD still remained. Alteration of mitochondrial dynamics towards mitochondrial fission concurrent with the mitochondrial dysfunction is the characteristic that is usually seen in various diseases, including DKD. It has been proposed that those perturbation and their cooperative networks could be responsible for the residual risk of ESRD in DKD patients. In this review, the collective evidence of alteration in mitochondrial dynamics and their associations with the mitochondrial function from in vitro, in vivo and clinical reports of DKD are comprehensively summarized and discussed. In addition, both basic and clinical reports regarding the pharmacological interventions that showed an impact on the mitochondrial dynamics, and the correlation with the renal parameters in DKD is presented. Understanding these complex mechanisms in combination with the existing therapeutic modalities could bring a new opportunity to overcome the unresolvable problem of DKD.

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.

Therapeutic potential of pro-resolving mediators in diabetic kidney disease

Renal microvascular disease associated with diabetes [Diabetic kidney disease - DKD] is the leading cause of chronic kidney disease. In DKD, glomerular basement membrane thickening, mesangial expansion, endothelial dysfunction, podocyte cell loss and renal tubule injury contribute to progressive glomerulosclerosis and tubulointerstitial fibrosis. Chronic inflammation is recognized as a major pathogenic mechanism for DKD, with resident and circulating immune cells interacting with local kidney cell populations to provoke an inflammatory response. The onset of inflammation is driven by the release of well described proinflammatory mediators, and this is typically followed by a resolution phase. Inflammation resolution is achieved through the bioactions of endogenous specialized pro-resolving lipid mediators (SPMs). As our understanding of SPMs advances 'resolution pharmacology' based approaches using these molecules are being explored in DKD.