Persistent DNA damage underlies tubular cell polyploidization and progression to chronic kidney disease in kidneys deficient in the DNA repair protein FAN1

Single-cell analysis of proximal tubular cells with different DNA content reveals functional heterogeneity in the acute kidney injury to chronic kidney disease transition

INTRODUCTION

Proximal tubular epithelial cells with different DNA contents emerge after acute kidney injury (AKI). However, their heterogeneity and roles in the acute kidney injury-to-chronic kidney disease (AKI-to-CKD) transition remain incompletely understood.

METHODS

Proximal tubular epithelial cells with different DNA contents were isolated at days 3 and 14 post-AKI following ischemia reperfusion injury for single-cell RNA sequencing.

RESULTS

Here, we found that proximal tubular epithelial cells with different DNA contents have existing and distinct bulk transcriptome profiles, especially those cells over 4N (polyploid cells with more than four chromosome sets) with upregulated profibrotic signatures. Heterogeneity existed within four distinct functional clusters. In particular, the polyploid cells demonstrated a preferential enrichment within specific proinflammatory and profibrotic clusters post-AKI. Polyploid cells within these specific clusters displayed the profibrotic trajectory, accompanied by increased fibrosis-driving regulon activity and very strong cell-cell interactions. This suggests polyploidy cells have an intrinsic role in promoting the AKI-to-CKD transition. Furthermore, we identified that secreted phosphoprotein 1 (SPP1) as the pivotal hub of polyploid cells and may be involved in various profibrotic signaling pathways. Genetic knockdown of SPP1 in the proximal tubule in vivo dramatically ameliorated kidney fibrosis.

CONCLUSIONS

Overall, our findings reveal the heterogeneity of proximal tubular epithelial cells with different DNA contents and identify intrinsic factors of polyploid cells such as SPP1 expression in promoting kidney fibrosis. Our study provides novel insights into potential therapeutic target of preventing the AKI-to-CKD transition.

Intercellular Communication Network of CellChat Uncovers Mechanisms of Kidney Fibrosis Based on Single-Cell RNA Sequencing

BACKGROUND

Chronic kidney disease (CKD) is a global health concern, with renal fibrosis being a major pathological feature. Empagliflozin (Empa), a sodium-glucose co-transporter-2 inhibitor, has shown promise in protecting the kidney. This study aimed to investigate the effects of Empa on renal fibrosis in a nondiabetic CKD model and to elucidate the underlying mechanisms.

METHODS

We established a CKD model using 5/6 nephrectomy (5/6 Nx) rats and divided them into three groups: placebo-treated sham surgery rats, placebo-treated 5/6 Nx rats, and Empa-treated 5/6 Nx rats. Kidney function was assessed by measuring blood urea nitrogen, serum creatinine, and urinary albumin-to-creatinine ratio. Renal fibrosis was evaluated histologically. Single-cell RNA sequencing (scRNA-seq) was performed to analyze intercellular communication networks and identify alterations in ligand-receptor pairs and signaling pathways involved in fibrosis.

RESULTS

Empa treatment significantly improved kidney function and reduced renal interstitial fibrosis in 5/6 Nx rats. scRNA-seq revealed that Empa modulated the TGF-β signaling pathway, inhibited intercellular communication, and reduced the expression of fibrotic genes such as COLLAGEN, FN1, THBS, and LAMININ. Furthermore, Empa downregulated GRN gene expression, weakened signal transmission in the MIF pathway, consequently reduced the interaction between M2 macrophages and other cell types, such as endothelial cells, fibroblasts, and mesangial cells.

CONCLUSION

This study elucidates the potential mechanisms by which Empa slows the progression of renal fibrosis in nondiabetic CKD. By reducing the number of M2 macrophages and inhibiting signal transduction in both pro-inflammatory and fibrotic pathways, Empa modulates the intercellular communication network in renal cells, offering a promising therapeutic strategy for CKD management.

The unexpected diagnosis of karyomegalic interstitial nephritis in a presumed case of Mesoamerican Nephropathy: a case report

Background

Chronic kidney disease of unknown etiology (CKDu) is a form of chronic kidney disease commonly found in certain rural populations globally. This condition is characterized by chronic tubulointerstitial nephropathy, yet it lacks specific signature lesions and is believed to have a multifactorial etiology, often associated with environmental toxins. Karyomegalic Interstitial Nephritis (KIN), although a rare form of chronic interstitial nephropathy leading to end-stage kidney disease, is not classified under CKDu.

Case presentation

In this case report, we explore the diagnostic journey of a 40-year-old male farmer from Guatemala. He presented with headache, fever, and facial pain, but laboratory tests revealed significant kidney impairment and liver dysfunction. The pivotal point in his diagnostic workup was a kidney biopsy, which showed severe chronic tubulointerstitial scarring and enlarged, hyperchromatic nuclei in the tubular epithelial cells, confirming KIN. This diagnosis marked a departure from the initial suspicion of Mesoamerican Nephropathy (MEN).

Conclusion

This case underscores the critical need for a comprehensive evaluation in atypical presentations of chronic kidney disease, particularly emphasizing the importance of being vigilant for KIN in areas where MEN is commonly diagnosed.

Canagliflozin inhibits hedgehog interacting protein (Hhip) induction of tubulopathy in diabetic Akita mice

Renal hedgehog interacting protein (Hhip) activates sodium-glucose cotransporter 2 (Sglt2) expression and promotes tubular senescence in murine diabetic kidney disease (DKD), yet its underlying mechanism(s) are poorly understood. Here we study the effect of the SGLT2 inhibitor, canagliflozin on tubulopathy (fibrosis and apoptosis) in Akita/HhipRPTC-transgenic (Tg) mice with overexpression of Hhip in their renal proximal tubular cells (RPTCs) and its relevant mechanisms. The DKD-tubulopathy with pronounced Sglt2 expression was aggravated in the kidney of Akita/HhipRPTC-Tg cf. Akita/non-Tg mice. A strong association was observed between Hhip and tubular senescence in Nephroseq from the Nakagawa chronic kidney disease study. Both in vivo and in vitro, excessive Hhip in RPTCs triggered RPTC senescence (polyploidization and cytoskeleton destabilization) and released extracellular vesicles (EVs) carrying Hhip (EVsHhip), most of which were apoptotic bodies (ABsHhip) or microvesicles (MVsHhip) and little exosomes (EXOsHhip). Further, Hhip stimulated β2-microglobulin, which further interacts with EVsHhip, together facilitating RPTC turn-over from cellular senescence to fibrosis and/or apoptosis, ultimately leading to advanced tubulopathy. In contrast, canagliflozin administration offset the action of Hhip in RPTCs, thereby preventing DKD progression. In conclusion, canagliflozin prevented excessive Hhip-mediated tubulopathy, possibly via the inhibition of excessive Hhip carried by extracellular vehicles in DKD.

Fanconi syndrome with karyomegalic interstitial nephritis after ifosfamide treatment for osteosarcoma: a case report

Patients with ifosfamide-induced renal damage present with Fanconi syndrome. Karyomegalic nephropathy/interstitial nephritis (KNIN) is a rare form of chronic tubulo-interstitial nephritis that was initially considered a type of familial nephropathy. However, several reports of drug-induced KNIN, i.e., KNIN-like nephropathy, have been reported in recent years. We present the case of an 18-year-old man who presented with Fanconi syndrome and progressive renal dysfunction after receiving chemotherapy including ifosfamide and cisplatin for right femoral osteosarcoma. Renal biopsy revealed numerous atrophied tubular epithelial cells with large, polymorphic nuclei, and the definitive diagnosis was KNIN. Most patients with KNIN-like nephropathy who receive ifosfamide are concomitantly treated with cisplatin, indicating that ifosfamide and cisplatin might act synergistically to increase the risk for KNIN-like nephropathy. Further investigation in case series is warranted to reveal potential treatment approaches and to evaluate prognosis.

FAN1 Deletion Variant in Basenji Dogs with Fanconi Syndrome

Background: Fanconi syndrome is a disorder of renal proximal tubule transport characterized by metabolic acidosis, amino aciduria, glucosuria, and phosphaturia. There are acquired and hereditary forms of this disorder. A late-onset form of Fanconi syndrome in Basenjis was first described in 1976 and is now recognized as an inherited disease in these dogs. In part because of the late onset of disease signs, the disorder has not been eradicated from the breed by selective mating. A study was therefore undertaken to identify the molecular genetic basis of the disease so that dogs could be screened prior to breeding in order to avoid generating affected offspring. Methods: Linkage analysis within a large family of Basenjis that included both affected and unaffected individuals was performed to localize the causative variant within the genome. Significant linkage was identified between chromosome 3 (CFA3) makers and the disease phenotype. Fine mapping restricted the region to a 2.7 Mb section of CFA3. A whole genome sequence of a Basenji affected with Fanconi syndrome was generated, and the sequence data were examined for the presence of potentially deleterious homozygous variants within the mapped region. Results: A homozygous 317 bp deletion was identified in the last exon of FAN1 of the proband. 78 Basenjis of known disease status were genotyped for the deletion variant. Among these dogs, there was almost complete concordance between genotype and phenotype. The only exception was one dog that was homozygous for the deletion variant but did not exhibit signs of Fanconi syndrome. Conclusions: These data indicate that the disorder is very likely the result of FAN1 deficiency. The mechanism by which this deficiency causes the disease signs remains to be elucidated. FAN1 has endonuclease and exonuclease activity that catalyzes incisions in regions of double-stranded DNA containing interstrand crosslinks. FAN1 inactivation may cause Fanconi syndrome in Basenjis by sensitization of kidney proximal tubule cells to toxin-mediated DNA crosslinking, resulting in the accumulation of genomic and mitochondrial DNA damage in the kidney. Differential exposure to environmental toxins that promote DNA crosslink formation may explain the wide age-at-onset variability for the disorder in Basenjis.

Investigation of the acute effect of the synthetic hemodialysis membrane on the expression of XRCC1 and PARP1 in chronic hemodialysis patients

OBJECTIVE

The interaction between blood from end-stage renal failure patients undergoing hemodialysis treatment and the hemodialysis (HD) membranes used may lead to DNA damage, contingent upon the biocompatibility of the membranes. Given that this process could impact the disease's course, it is crucial to assess the efficacy of DNA repair mechanisms.

METHODS

In our study, we investigated the gene expression levels of XRCC1 and PARP1 enzymes, which are involved in the base excision repair (BER) repair mechanism crucial for repairing oxidative DNA damage, in 20 end-stage renal disease (ESRD) patients undergoing HD treatment both before and after dialysis sessions. Additionally, we compared our findings with those from 20 healthy controls. We assessed gene expression levels using real-time polymerase chain reaction (qRT-PCR).

RESULTS

We observed that the HD process utilizing a polysulfone membrane did not impact the expression levels of genes. However, we noted a lower expression level of the PARP1 gene in ESRD patients undergoing HD compared to the control group (0.021 ± 0.005 vs 0.0019 ± 0.0013, p = 0.0001).

CONCLUSION

Although our study findings indicate that HD membranes do not affect gene expression overall, the specific decrease in PARPI gene expression suggests that the effectiveness of the BER DNA repair mechanism is impaired in ESRD patients, which may play a significant role in the progression of the disease.

Identification of Differentially Expressed Genes in Cold Storage-associated Kidney Transplantation

BACKGROUND

Although it is acknowledged that ischemia-reperfusion injury is the primary pathology of cold storage-associated kidney transplantation, its underlying mechanism is not well elucidated.

METHODS

To extend the understanding of molecular events and mine hub genes posttransplantation, we performed bulk RNA sequencing at different time points (24 h, day 7, and day 14) on a murine kidney transplantation model with prolonged cold storage (10 h).

RESULTS

In the present study, we showed that genes related to the regulation of apoptotic process, DNA damage response, cell cycle/proliferation, and inflammatory response were steadily elevated at 24 h and day 7. The upregulated gene profiling delicately transformed to extracellular matrix organization and fibrosis at day 14. It is prominent that metabolism-associated genes persistently took the first place among downregulated genes. The gene ontology terms of particular note to enrich are fatty acid oxidation and mitochondria energy metabolism. Correspondingly, the key enzymes of the above processes were the products of hub genes as recognized. Moreover, we highlighted the proximal tubular cell-specific increased genes at 24 h by combining the data with public RNA-Seq performed on proximal tubules. We also focused on ferroptosis-related genes and fatty acid oxidation genes to show profound gene dysregulation in kidney transplantation.

CONCLUSIONS

The comprehensive characterization of transcriptomic analysis may help provide diagnostic biomarkers and therapeutic targets in kidney transplantation.

Phenotypic and Genotypic Features of the FAN1 Mutation-Related Disease in a Large Hungarian Family

Pathogenic variants in the FAN1 gene lead to a systemic disease with karyomegalic interstitial nephritis (KIN) at the forefront clinically. The phenotypic-genotypic features of a FAN1 mutation-related disease involving five members of a Hungarian Caucasian family are presented. Each had adult-onset chronic kidney disease of unknown cause treated with renal replacement therapy and elevated liver enzymes. Short stature, emaciation, latte-colored skin, freckles, and a hawk-like nose in four patients, a limited intellect in two patients, and chronic restrictive lung disease in one patient completed the phenotype. Severe infections occurred in four patients. All five patients had ceased. Four patients underwent autopsy. KIN and extrarenal karyomegaly were observed histologically; the livers showed no specific abnormality. The genotyping using formalin-fixed tissue samples detected a hitherto undescribed homozygous FAN1 mutation (c.1673_1674insT/p.Met558lfs*4; exon 5) in three of these patients and a heterozygous FAN1 mutation in one patient. The reason for the heterozygosity is discussed. In addition, 56 family members consented to the screening for FAN1 mutation from which 17 individuals proved to be heterozygous carriers; a blood chemistry evaluation of their kidney and liver function did not find any abnormality. The clinical presentation of FAN1-related disease was multifaceted, and not yet described manifestations were observed besides kidney and liver disease. Mutation in this gene should be suspected in adults with small kidneys of unknown cause, elevated liver enzymes, and recurrent infections, even without a family history.

Chronic exposure to tris(1,3-dichloro-2-propyl) phosphate: Effects on intestinal microbiota and serum metabolism in rats

Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) is a widely used organophosphate ester that can adversely affect animal or human health. The intestinal microbiota is critical to human health. High-dose exposure to TDCIPP can markedly affect the intestinal ecosystem of mice, but the effects of long-term exposure to lower concentrations of TDCIPP on the intestinal flora and body metabolism remain unclear. In this study, TDCIPP was administered to Sprague-Dawley rats by gavage at a dose of 13.3 mg/kg bw/day for 90 days. TDCIPP increased the relative weight of the kidneys (P = 0.017), but had no effect on the relative weight of the heart, liver, spleen, lungs, testes, and ovaries (P > 0.05). 16 S rRNA gene sequencing revealed that long-term TDCIPP exposure affected the diversity, relative abundance, and functions of rat gut microbes. The serum metabolomics of the rats showed that TDCIPP can disrupt the serum metabolic profiles, result in the up-regulation of 26 metabolites and down-regulation of 3 metabolites, and affect multiple metabolic pathways in rat sera. In addition, the disturbed genera and metabolites were correlated. The functions of some disturbed gut microbes were consistent with the affected metabolic pathways in the sera, and these metabolic pathways were all associated with kidney disease, suggesting that TDCIPP may cause kidney injury in rats by affecting the intestinal flora and serum metabolism.

Polyploid tubular cells: a shortcut to stress adaptation

Tubular epithelial cells (TCs) compose the majority of kidney parenchyma and play fundamental roles in maintaining homeostasis. Like other tissues, mostly immature TC with progenitor capabilities are able to replace TC lost during injury via clonal expansion and differentiation. In contrast, differentiated TC lack this capacity. However, as the kidney is frequently exposed to toxic injuries, evolution positively selected a response program that endows differentiated TC to maintain residual kidney function during kidney injury. Recently, we and others have described polyploidization of differentiated TC, a mechanism to augment the function of remnant TC after injury by rapid hypertrophy. Polyploidy is a condition characterized by >2 complete sets of chromosomes. Polyploid cells often display an increased functional capacity and are generally more resilient to stress as evidenced by being conserved across many plants and eukaryote species from flies to mammals. Here, we discuss the occurrence of TC polyploidy in different contexts and conditions and how this integrates into existing concepts of kidney cell responses to injury. Collectively, we aim at stimulating the acquisition of novel knowledge in the kidney field as well as accelerating the translation of this basic response mechanism to the clinical sphere.

Why is chronic kidney disease progressive? Evolutionary adaptations and maladaptations

Despite significant advances in renal physiology, the global prevalence of chronic kidney disease (CKD) continues to increase. The emergence of multicellular organisms gave rise to increasing complexity of life resulting in trade-offs reflecting ancestral adaptations to changing environments. Three evolutionary traits shape CKD over the lifespan: 1) variation in nephron number at birth, 2) progressive nephron loss with aging, and 3) adaptive kidney growth in response to decreased nephron number. Although providing plasticity in adaptation to changing environments, the cell cycle must function within constraints dictated by available energy. Prioritized allocation of energy available through the placenta can restrict fetal nephrogenesis, a risk factor for CKD. Moreover, nephron loss with aging is a consequence of cell senescence, a pathway accelerated by adaptive nephron hypertrophy that maintains metabolic homeostasis at the expense of increased vulnerability to stressors. Driven by reproductive fitness, natural selection operates in early life but diminishes thereafter, leading to an exponential increase in CKD with aging, a product of antagonistic pleiotropy. A deeper understanding of the evolutionary constraints on the cell cycle may lead to manipulation of the balance between progenitor cell renewal and differentiation, regulation of cell senescence, and modulation of the balance between cell proliferation and hypertrophy. Application of an evolutionary perspective may enhance understanding of adaptation and maladaptation by nephrons in the progression of CKD, leading to new therapeutic advances.

Minichromosome maintenance 6 protects against renal fibrogenesis by regulating DUSP6-mediated ERK/GSK-3β/Snail1 signaling

Minichromosome maintenance 6 (MCM6) has been implicated in the progression of various malignant tumors; however, its exact physiological function in kidney diseases remains unclear. Here, we demonstrated that MCM6 levels showed a significant increase in the proximal tubular cells during progressive renal fibrosis in two unrelated in vivo fibrotic models, including unilateral ureteral obstruction (UUO) and unilateral ischemia-reperfusion injury (UIRI). Depletion of MCM6 aggravated partial epithelial-mesenchymal transition, extracellular matrix accumulation, and myofibroblast activation in the kidneys of UUO or UIRI mice. Conversely, overexpression of MCM6 promoted the recovery of E-cadherin and retarded UUO- or UIRI-induced renal fibrosis. In addition, DUSP6 expression substantially decreased in fibrotic kidneys, and it might be involved in MCM6-induced renal fibrosis by regulating the activation of ERK/GSK-3β/Snail1 signaling. In conclusion, our results highlight the significance of MCM6 in renal fibrosis, providing a potential therapeutic target for patients with chronic kidney disease.

Chronic kidney disease in children: an update

Chronic kidney disease (CKD) is a major healthcare issue worldwide. However, the prevalence of pediatric CKD has never been systematically assessed and consistent information is lacking in this population. The current definition of CKD is based on glomerular filtration rate (GFR) and the extent of albuminuria. Given the physiological age-related modification of GFR in the first years of life, the definition of CKD is challenging per se in the pediatric population, resulting in high risk of underdiagnosis in this population, treatment delays and untailored clinical management. The advent and spreading of massive-parallel sequencing technology has prompted a profound revision of the epidemiology and the causes of CKD in children, supporting the hypothesis that CKD is much more frequent than currently reported in children and adolescents. This acquired knowledge will eventually converge in the identification of the molecular pathways and cellular response to damage, with new specific therapeutic targets to control disease progression and clinical features of children with CKD. In this review, we will focus on recent innovations in the field of pediatric CKD and in particular those where advances in knowledge have become available in the last years, with the aim of providing a new perspective on CKD in children and adolescents.

Polyploid tubular cells initiate a TGF-β1 controlled loop that sustains polyploidization and fibrosis after acute kidney injury

Polyploidization of tubular cells (TC) is triggered by acute kidney injury (AKI) to allow survival in the early phase after AKI, but in the long run promotes fibrosis and AKI-chronic kidney disease (CKD) transition. The molecular mechanism governing the link between polyploid TC and kidney fibrosis remains to be clarified. In this study, we demonstrate that immediately after AKI, expression of cell cycle markers mostly identifies a population of DNA-damaged polyploid TC. Using transgenic mouse models and single-cell RNA sequencing we show that, unlike diploid TC, polyploid TC accumulate DNA damage and survive, eventually resting in the G1 phase of the cell cycle. In vivo and in vitro single-cell RNA sequencing along with sorting of polyploid TC shows that these cells acquire a profibrotic phenotype culminating in transforming growth factor (TGF)-β1 expression and that TGF-β1 directly promotes polyploidization. This demonstrates that TC polyploidization is a self-sustained mechanism. Interactome analysis by single-cell RNA sequencing revealed that TGF-β1 signaling fosters a reciprocal activation loop among polyploid TC, macrophages, and fibroblasts to sustain kidney fibrosis and promote CKD progression. Collectively, this study contributes to the ongoing revision of the paradigm of kidney tubule response to AKI, supporting the existence of a tubulointerstitial cross talk mediated by TGF-β1 signaling produced by polyploid TC following DNA damage.NEW & NOTEWORTHY Polyploidization in tubular epithelial cells has been neglected until recently. Here, we showed that polyploidization is a self-sustained mechanism that plays an important role during chronic kidney disease development, proving the existence of a cross talk between infiltrating cells and polyploid tubular cells. This study contributes to the ongoing revision of kidney adaptation to injury, posing polyploid tubular cells at the center of the process.

Modeling of FAN1-Deficient Kidney Disease Using a Human Induced Pluripotent Stem Cell-Derived Kidney Organoid System

Karyomegalic interstitial nephritis (KIN) is a genetic kidney disease caused by mutations in the FANCD2/FANCI-Associated Nuclease 1 (FAN1) gene on 15q13.3, which results in karyomegaly and fibrosis of kidney cells through the incomplete repair of DNA damage. The aim of this study was to explore the possibility of using a human induced pluripotent stem cell (hiPSC)-derived kidney organoid system for modeling FAN1-deficient kidney disease, also known as KIN. We generated kidney organoids using WTC-11 (wild-type) hiPSCs and FAN1-mutant hiPSCs which include KIN patient-derived hiPSCs and FAN1-edited hiPSCs (WTC-11 FAN1+/-), created using the CRISPR/Cas9 system in WTC-11-hiPSCs. Kidney organoids from each group were treated with 20 nM of mitomycin C (MMC) for 24 or 48 h, and the expression levels of Ki67 and H2A histone family member X (H2A.X) were analyzed to detect DNA damage and assess the viability of cells within the kidney organoids. Both WTC-11-hiPSCs and FAN1-mutant hiPSCs were successfully differentiated into kidney organoids without structural deformities. MMC treatment for 48 h significantly increased the expression of DNA damage markers, while cell viability in both FAN1-mutant kidney organoids was decreased. However, these findings were observed in WTC-11-kidney organoids. These results suggest that FAN1-mutant kidney organoids can recapitulate the phenotype of FAN1-deficient kidney disease.

Karyomegalic interstitial nephritis as a rare cause of kidney graft dysfunction: case report and review of literature

Karyomegalic interstitial nephritis (KIN) is a rare cause of chronic interstitial nephritis characterized by enlarged renal tubular epithelial nuclei. The first case of KIN reported in a kidney graft was in 2019. Here, we report the first case of KIN in 2 brothers receiving kidneys from 2 different unrelated living donors. A male kidney transplant recipient with focal segmental glomerulosclerosis as the original kidney disease presented with graft impairment and proteinuria, and graft biopsy revealed KIN. This patient had a brother who was also a kidney transplant recipient and had one episode of graft impairment and was diagnosed with KIN as well.

Mitochondrial ROS Triggers KIN Pathogenesis in FAN1-Deficient Kidneys

Karyomegalic interstitial nephritis (KIN) is a genetic adult-onset chronic kidney disease (CKD) characterized by genomic instability and mitotic abnormalities in the tubular epithelial cells. KIN is caused by recessive mutations in the FAN1 DNA repair enzyme. However, the endogenous source of DNA damage in FAN1/KIN kidneys has not been identified. Here we show, using FAN1-deficient human renal tubular epithelial cells (hRTECs) and FAN1-null mice as a model of KIN, that FAN1 kidney pathophysiology is triggered by hypersensitivity to endogenous reactive oxygen species (ROS), which cause chronic oxidative and double-strand DNA damage in the kidney tubular epithelial cells, accompanied by an intrinsic failure to repair DNA damage. Furthermore, persistent oxidative stress in FAN1-deficient RTECs and FAN1 kidneys caused mitochondrial deficiencies in oxidative phosphorylation and fatty acid oxidation. The administration of subclinical, low-dose cisplatin increased oxidative stress and aggravated mitochondrial dysfunction in FAN1-deficient kidneys, thereby exacerbating KIN pathophysiology. In contrast, treatment of FAN1 mice with a mitochondria-targeted ROS scavenger, JP4-039, attenuated oxidative stress and accumulation of DNA damage, mitigated tubular injury, and preserved kidney function in cisplatin-treated FAN1-null mice, demonstrating that endogenous oxygen stress is an important source of DNA damage in FAN1-deficient kidneys and a driver of KIN pathogenesis. Our findings indicate that therapeutic modulation of kidney oxidative stress may be a promising avenue to mitigate FAN1/KIN kidney pathophysiology and disease progression in patients.

Tubular-specific expression of HIV protein Vpr leads to severe tubulointerstitial damage accompanied by progressive fibrosis and cystic development

Chronic kidney disease (CKD) is a common cause of morbidity in human immunodeficiency virus (HIV)-positive individuals. HIV infection leads to a wide spectrum of kidney cell damage, including tubular epithelial cell (TEC) injury. Among the HIV-1 proteins, the pathologic effects of viral protein R (Vpr) are well established and include DNA damage response, cell cycle arrest, and cell death. Several in vitro studies have unraveled the molecular pathways driving the cytopathic effects of Vpr in tubular epithelial cells. However, the in vivo effects of Vpr on tubular injury and CKD pathogenesis have not been thoroughly investigated. Here, we use a novel inducible tubular epithelial cell-specific Vpr transgenic mouse model to show that Vpr expression leads to progressive tubulointerstitial damage, interstitial inflammation and fibrosis, and tubular cyst development. Importantly, Vpr-expressing tubular epithelial cells displayed significant hypertrophy, aberrant cell division, and atrophy; all reminiscent of tubular injuries observed in human HIV-associated nephropathy (HIVAN). Single-cell RNA sequencing analysis revealed the Vpr-mediated transcriptomic responses in specific tubular subsets and highlighted the potential multifaceted role of p53 in the regulation of cell metabolism, proliferation, and death pathways in Vpr-expressing tubular epithelial cells. Thus, our study demonstrates that HIV Vpr expression in tubular cells is sufficient to induce HIVAN-like tubulointerstitial damage and fibrosis, independent of glomerulosclerosis and proteinuria. Additionally, as this new mouse model develops progressive CKD with diffuse fibrosis and kidney failure, it can serve as a useful tool to examine the mechanisms of kidney disease progression and fibrosis in vivo.

Mobile Phone Use, Genetic Susceptibility and New-Onset Chronic Kidney Diseases

Objective: To examine the associations of mobile phone use and its use characteristics with new-onset CKD. Methods: 408,743 participants without prior CKD in the UK Biobank were included. The primary outcome was new-onset CKD. Results: During a median follow-up of 12.1 years, 10,797 (2.6%) participants occurred CKD. Compared with mobile phone non-users, a significantly higher risk of new-onset CKD was found in mobile phone users (HR = 1.07; 95% CI: 1.02-1.13). Moreover, among mobile phone users, compared with participants with weekly usage time of mobile phone making or receiving calls <30 min, a significantly higher risk of new-onset CKD was observed in those with usage time ≥30 min (HR = 1.12; 95% CI: 1.07-1.18). Moreover, participants with both high genetic risks of CKD and longer weekly usage time of mobile phones had the highest risk of CKD. Similar results were found using the propensity score matching methods. However, there were no significant associations of length of mobile phone use, and hands-free device/speakerphone use with new-onset CKD among mobile phone users. Conclusion: Mobile phone use was significantly associated with a higher risk of new-onset CKD, especially in those with longer weekly usage time of mobile phones making or receiving calls. Our findings and the underlying mechanisms should be further investigated.

Polyploid tubular cells and chronic kidney disease

Defective DNA repair drives chronic kidney disease (CKD), but mechanisms are unclear. Airik and colleagues use a genetic model of defective DNA repair mimicking karyomegalic nephritis, a form of CKD characterized by tubular epithelial cells (TEC) with large nuclei and tubulointerstitial nephritis. They show that DNA damage in TEC triggers endoreplication leading to polyploid TEC and CKD. Blocking endoreplication preserved kidney function, suggesting that DNA damage triggers CKD via TEC polyploidization, questioning the concept of G2/M-arrest.