Roles of Mitochondrial DNA Damage in Kidney Diseases: A New Biomarker

The emerging role of mtDNA release in sepsis: Current evidence and potential therapeutic targets

Sepsis is a systemic inflammatory reaction caused by infection, and severe sepsis can develop into septic shock, eventually leading to multiorgan dysfunction and even death. In recent years, studies have shown that mitochondrial damage is closely related to the occurrence and development of sepsis. Recent years have seen a surge in concern over mitochondrial DNA (mtDNA), as anomalies in this material can lead to cellular dysfunction, disruption of aerobic respiration, and even death of the cell. In this review, we discuss the latest findings on the mechanisms of mitochondrial damage and the molecular mechanisms controlling mitochondrial mtDNA release. We also explored the connection between mtDNA misplacement and inflammatory activation. Additionally, we propose potential therapeutic targets of mtDNA for sepsis treatment.

Genetic determinants of renal scarring in children with febrile UTI

BACKGROUND

Febrile urinary tract infections (UTIs) are among the most severe bacterial infections in infants, in which a subset of patients develops complications. Identifying infants at risk of recurrent infections or kidney damage based on clinical signs is challenging. Previous observations suggest that genetic factors influence UTI outcomes and could serve as predictors of disease severity. In this study, we conducted a nationwide survey of infant genotypes to develop a strategy for infection management based on individual genetic risk. Our aims were to identify genetic susceptibility variants for renal scarring (RS) and genetic host factors predisposing to dilating vesicoureteral reflux (VUR) and recurrent UTIs.

METHODS

To assess genetic susceptibility, we collected and analyzed DNA from blood using exome genotyping. Disease-associated genetic variants were identified through bioinformatics analysis, including allelic frequency tests and odds ratio calculations. Kidney involvement was defined using dimercaptosuccinic acid (DMSA) scintigraphy.

RESULTS

In this investigation, a cohort comprising 1087 infants presenting with their first episode of febrile UTI was included. Among this cohort, a subset of 137 infants who underwent DMSA scanning was subjected to gene association analysis. Remarkable genetic distinctions were observed between patients with RS and those exhibiting resolved kidney involvement. Notably, the genetic signature indicative of renal scarring prominently featured mitochondrial genes.

CONCLUSIONS

In this nationwide study of genetic susceptibility to RS after febrile UTIs in infancy, we identified a profile dominated by mitochondrial polymorphisms. This profile can serve as a predictor of future complications, including RS and recurrent UTIs.

Mitochondrial dysfunction in the pathophysiology of renal diseases

Mitochondria are essential organelles in the human body, serving as the metabolic factory of the whole organism. When mitochondria are dysfunctional, it can affect all organs of the body. The kidney is rich in mitochondria, and its function is closely related to the development of kidney diseases. Studying the relationship between mitochondria and kidney disease progression is of great interest. In the past decade, scientists have made inspiring progress in investigating the role of mitochondria in the pathophysiology of renal diseases. This article discusses various mechanisms for maintaining mitochondrial quality, including mitochondrial energetics, mitochondrial biogenesis, mitochondrial dynamics, mitochondrial DNA repair, mitochondrial proteolysis and the unfolded protein response, mitochondrial autophagy, mitochondria-derived vesicles, and mitocytosis. The article also highlights the cross talk between mitochondria and other organelles, with a focus on kidney diseases. Finally, the article concludes with an overview of mitochondria-related clinical research.

Association between blood metals mixture and chronic kidney disease in adults: NHANES 2013-2016

BACKGROUND

The association between single metal exposure and chronic kidney disease (CKD) has been established. However, there is limited research on the effects of multi-metal mixtures and their potential age-specific associations with kidney injury. This study aimed to examine the relationship between metal mixtures and kidney function in adults, while also exploring the modifying effects of age.

METHODS

We included a subset (n = 4250) of a nationally representative adult population in the National Health and Nutrition Examination Survey (NHANES) 2013-2016. Kidney function was assessed using the glomerular filtration rate (eGFR) and creatinine albumin ratio (ACR). The individual and combined effects of lead (Pb), cadmium (Cd), mercury, and manganese on kidney injury and the risk of CKD were evaluated.

RESULTS

Pb and Cd were found to be positively associated with decreased kidney function. For a one Ln-unit increase in lead and cadmium, the adjusted ORs of CKD were 1.60 (95% CI: 1.35, 1.90) and 1.41 (95% CI:1.12, 1.77), respectively. We also observed an interaction between lead and cadmium for ACR. We also observed the joint effect between Pb and Cd on eGFR, ACR and CKD. Stratified analysis found a higher risk of decreased kidney function among older individuals. The quantile-g calculation model further showed that metal mixture was associated with decreased kidney function and the risk of CKD (OR = 1.53, 95% CI: 1.22, 1.90). And lead and cadmium were the main contributors. And Pb and Cd were the major components that increased the risk of CKD.

CONCLUSION

Co-exposure to metal mixture were associated with reduced kidney function in adults, especially in older. Our findings support co-exposure to lead and cadmium as risk factors of CKD in adults.

Mitochondrial metabolism and targeted treatment strategies in ischemic-induced acute kidney injury

Ischemia-reperfusion injury (IRI) is a common cause of acute kidney injury (AKI). The kidney is susceptible to IRI under several clinical conditions, including hypotension, sepsis, and surgical procedures, such as partial nephrectomy and kidney transplantation. Extensive research has been conducted on the mechanism and intervention strategies of renal IRI in past decades; however, the complex pathophysiology of IRI-induced AKI (IRI-AKI) is not fully understood, and there remains a lack of effective treatments for AKI. Renal IRI involves several processes, including reactive oxygen species (ROS) production, inflammation, and apoptosis. Mitochondria, the centers of energy metabolism, are increasingly recognized as substantial contributors to the early phases of IRI. Multiple mitochondrial lesions have been observed in the renal tubular epithelial cells (TECs) of IRI-AKI mice, and damaged or dysfunctional mitochondria are toxic to the cells because they produce ROS and release cell death factors, resulting in TEC apoptosis. In this review, we summarize the recent advances in the mitochondrial pathology in ischemic AKI and highlight promising therapeutic approaches targeting mitochondrial dysfunction to prevent or treat human ischemic AKI.

Exploring the Role of Mitochondrial Hydrogen Sulfide in Maintaining Polarity and mtDNA Integrity with a Multichannel Fluorescent Probe

Abnormal mitochondrial state has been implicated in the pathogenesis of various diseases including neurodegenerative disorders, myopathies, cardiovascular diseases, and cancers. Assessing mitochondrial functionality can be achieved by monitoring alterations in mitochondrial polarity and mitochondrial DNA (mtDNA) integrity, which serve as valuable biomarkers. Hydrogen sulfide (H2S), a gaseous signaling molecule, plays a regulatory role in mitochondrial respiratory chain activity, ATP synthesis, and calcium ion balance, thereby influencing cellular metabolism and signal transduction. Investigating the interplay between mitochondrial H2S, polarity, and mtDNA can enhance our understanding of the underlying regulatory mechanisms involved in H2S-mediated mitochondrial functions. To address this, we designed a mitochondria-targeted multichannel fluorescent probe, HNA, capable of cascaded detection of H2S and polarity, as well as parallel detection of mtDNA. The probe exhibited a significant turn-on response to H2S, emitting at approximately 604 nm, while the product HNAP demonstrated high sensitivity to polarity within the wavelength range of 526-591 nm. Additionally, the probe was able to bind to DNA, resulting in an enhanced long-wave emission at 668 nm. Facilitated by HNA, our study provides novel insights into the role of mitochondrial H2S in maintaining mitochondrial polarity and validates its protective effect on mtDNA through antioxidative mechanisms. Overall, this work proposes a potential therapeutic strategy for modulating the inflammatory process in mitochondrial-related diseases.

Mitochondrial DNA Variants at Low-Level Heteroplasmy and Decreased Copy Numbers in Chronic Kidney Disease (CKD) Tissues with Kidney Cancer

The human mitochondrial genome (mtDNA) is a circular DNA molecule with a length of 16.6 kb, which contains a total of 37 genes. Somatic mtDNA mutations accumulate with age and environmental exposure, and some types of mtDNA variants may play a role in carcinogenesis. Recent studies observed mtDNA variants not only in kidney tumors but also in adjacent kidney tissues, and mtDNA dysfunction results in kidney injury, including chronic kidney disease (CKD). To investigate whether a relationship exists between heteroplasmic mtDNA variants and kidney function, we performed ultra-deep sequencing (30,000×) based on long-range PCR of DNA from 77 non-tumor kidney tissues of kidney cancer patients with CKD (stages G1 to G5). In total, this analysis detected 697 single-nucleotide variants (SNVs) and 504 indels as heteroplasmic (0.5% ≤ variant allele frequency (VAF) < 95%), and the total number of detected SNVs/indels did not differ between CKD stages. However, the number of deleterious low-level heteroplasmic variants (pathogenic missense, nonsense, frameshift and tRNA) significantly increased with CKD progression (p < 0.01). In addition, mtDNA copy numbers (mtDNA-CNs) decreased with CKD progression (p < 0.001). This study demonstrates that mtDNA damage, which affects mitochondrial genes, may be involved in reductions in mitochondrial mass and associated with CKD progression and kidney dysfunction.

Mitochondrial Impairment: A Link for Inflammatory Responses Activation in the Cardiorenal Syndrome Type 4

Cardiorenal syndrome type 4 (CRS type 4) occurs when chronic kidney disease (CKD) leads to cardiovascular damage, resulting in high morbidity and mortality rates. Mitochondria, vital organelles responsible for essential cellular functions, can become dysfunctional in CKD. This dysfunction can trigger inflammatory responses in distant organs by releasing Damage-associated molecular patterns (DAMPs). These DAMPs are recognized by immune receptors within cells, including Toll-like receptors (TLR) like TLR2, TLR4, and TLR9, the nucleotide-binding domain, leucine-rich-containing family pyrin domain-containing-3 (NLRP3) inflammasome, and the cyclic guanosine monophosphate (cGMP)-adenosine monophosphate (AMP) synthase (cGAS)-stimulator of interferon genes (cGAS-STING) pathway. Activation of these immune receptors leads to the increased expression of cytokines and chemokines. Excessive chemokine stimulation results in the recruitment of inflammatory cells into tissues, causing chronic damage. Experimental studies have demonstrated that chemokines are upregulated in the heart during CKD, contributing to CRS type 4. Conversely, chemokine inhibitors have been shown to reduce chronic inflammation and prevent cardiorenal impairment. However, the molecular connection between mitochondrial DAMPs and inflammatory pathways responsible for chemokine overactivation in CRS type 4 has not been explored. In this review, we delve into mechanistic insights and discuss how various mitochondrial DAMPs released by the kidney during CKD can activate TLRs, NLRP3, and cGAS-STING immune pathways in the heart. This activation leads to the upregulation of chemokines, ultimately culminating in the establishment of CRS type 4. Furthermore, we propose using chemokine inhibitors as potential strategies for preventing CRS type 4.

The Activation of cGAS-STING in Acute Kidney Injury

The activation of the cGAS-STING pathway is associated with many sterile inflammatory and inflammatory conditions, including acute kidney injury. As a cytoplasmic DNA sensor, sensitization of the cGAS-STING pathway can ignite the innate immune response in vivo and trigger a series of biological effects. In recent years, there is increasing evidence showing that the cGAS-STING pathway plays a vital role in acute kidney injury, a non-inflammatory disease induced by activation of innate immune cells, and closely related to intracellular reactive oxygen species, mitochondrial DNA, and the cGAS-STING pathway. This review provides a prospect of the cGAS-STING pathway and its relationship to acute kidney injury.

Urinary exosomes: a promising biomarker of drug-induced nephrotoxicity

Drug-induced nephrotoxicity (DIN) is a big concern for clinical medication, but the clinical use of certain nephrotoxic drugs is still inevitable. Current testing methods make it hard to detect early renal injury accurately. In addition to understanding the pathogenesis and risk factors of drug-induced nephrotoxicity, it is crucial to identify specific renal injury biomarkers for early detection of DIN. Urine is an ideal sample source for biomarkers related to kidney disease, and urinary exosomes have great potential as biomarkers for predicting DIN, which has attracted the attention of many scholars. In the present paper, we will first introduce the mechanism of DIN and the biogenesis of urinary exosomes. Finally, we will discuss the changes in urinary exosomes in DIN and compare them with other predictive indicators to enrich and boost the development of biomarkers of DIN.

Wasp venom-induced acute kidney injury: current progress and prospects

Wasp venom can trigger local and systemic reactions, with the kidneys being commonly affected, potentially causing acute kidney injury (AKI). Despite of the recent advances, our knowledge on the underlying mechanisms of toxicity and targeted therapies remain poor. AKI can result from direct nephrotoxic effects of the wasp venom or secondary rhabdomyolysis and intravascular hemolysis, which will release myoglobin and free hemoglobin. Inflammatory responses play a central role in these pathological mechanisms. Noteworthily, the successful establishment of a suitable experimental model can assist in basic research and clinical advancements related to wasp venom-induced AKI. The combination of therapeutic plasma exchange and continuous renal replacement therapy appears to be the preferred treatment for wasp venom-induced AKI. In addition, studies on cilastatin and varespladib for wasp venom-induced AKI treatment have shown their potential as therapeutic agents. This review summarizes the available evidence on the mechanisms and treatment of wasp venom-induced AKI, with a particular focus on the role of inflammatory responses and potential targets for therapeutic drugs, and, therefore, aiming to support the development of clinical treatment against wasp venom-induced AKI.

Association of mitochondrial DNA copy number with chronic kidney disease in older adults

BACKGROUND

Mitochondrial dysfunction in kidney cells has been implicated in the pathogenesis of chronic kidney disease (CKD). Estimation of mitochondrial DNA copy number (mtDNA-CN) is considered a convenient method for representing mitochondrial function in large samples. However, no study has investigated the association between mtDNA-CN and CKD in older adults with the highest prevalence. The objective is to examine cross-sectional and prospective associations between mtDNA-CN values and CKD risk in older adults to determine whether mtDNA-CN represents a novel potential biomarker for the recognition of CKD risk.

PATIENTS AND METHODS

In a Chinese community-based cohort of over 65-year-olds, we included 14,467 participants (52.6% females). CKD was defined by eGFR < 60 mL/min/1.73 m2 or ICD-10 codes (patients = 3831 (26.5%)). Participants had peripheral blood levels of mtDNA-CN calculated from probe intensities of the Axiom CAS Array.

RESULTS

The risk of CKD prevalence decreased with mtDNA-CN per 1-SD increment, independent of established risk factors for older CKD (odds ratio [OR] per SD 0.90, 95% confidence interval [CI] 0.86, 0.93, P < 0.001), and has comparable strength of association with these established risk factors. Furthermore, the progression of kidney function was stratified according to the worsening of eGFR categories. The risk of kidney function progression to a more severe stage gradually decreased as the mtDNA-CN increased (P trend < 0.001). Non-CKD participants in the highest quartile of mtDNA-CN had a lower risk of developing CKD compared to the lowest quartile within 2 years of follow-up, reducing the risk of CKD by 36% (95% CI 0.42, 0.97; P = 0.037).

CONCLUSIONS

Based on the analysis of the largest sample to date investigating the association between mtDNA-CN and CKD in older adults, higher levels of mtDNA-CN were found to be associated with a lower risk of CKD, suggesting that a reduced level of mtDNA-CN is a potential risk factor for CKD.

Accumulation of Renal Fibrosis in Hyperuricemia Rats Is Attributed to the Recruitment of Mast Cells, Activation of the TGF-β1/Smad2/3 Pathway, and Aggravation of Oxidative Stress

Renal fibrosis is relentlessly progressive and irreversible, and a life-threatening risk. With the continuous intake of a high-purine diet, hyperuricemia has become a health risk factor in addition to hyperglycemia, hypertension, and hyperlipidemia. Hyperuricemia is also an independent risk factor for renal interstitial fibrosis. Numerous studies have reported that increased mast cells (MCs) are closely associated with kidney injury induced by different triggering factors. This study investigated the effect of MCs on renal injury in rats caused by hyperuricemia and the relationship between MCs and renal fibrosis. Our results reveal that hyperuricemia contributes to renal injury, with a significant increase in renal MCs, leading to renal fibrosis, mitochondrial structural disorders, and oxidative stress damage. The administration of the MCs membrane stabilizer, sodium cromoglycate (SCG), decreased the expression of SCF/c-kit, reduced the expression of α-SMA, MMP2, and inhibited the TGF-β1/Smad2/3 pathway, thereby alleviating renal fibrosis. Additionally, SCG reduced renal oxidative stress and mitigated mitochondrial structural damage by inhibiting Ang II production and increasing renal GSH, GSH-Px, and GR levels. Collectively, the recruitment of MCs, activation of the TGF-β1/Smad2/3 pathway, and Ang II production drive renal oxidative stress, ultimately promoting the progression of renal fibrosis in hyperuricemic rats.