NDUFS4 regulates cristae remodeling in diabetic kidney disease.

The mitochondrial electron transport chain (ETC) is a highly adaptive process to meet metabolic demands of the cell, and its dysregulation has been associated with diverse clinical pathologies. However, the role and nature of impaired ETC in kidney diseases remains poorly understood. Here, we generate diabetic mice with podocyte-specific overexpression of Ndufs4, an accessory subunit of mitochondrial complex I, as a model investigate the role of ETC integrity in diabetic kidney disease (DKD). We find that conditional male mice with genetic overexpression of Ndufs4 exhibit significant improvements in cristae morphology, mitochondrial dynamics, and albuminuria. By coupling proximity labeling with super-resolution imaging, we also identify the role of cristae shaping protein STOML2 in linking NDUFS4 with improved cristae morphology. Together, we provide the evidence on the central role of NDUFS4 as a regulator of cristae remodeling and mitochondrial function in kidney podocytes. We propose that targeting NDUFS4 represents a promising approach to slow the progression of DKD.

Immune Checkpoint Inhibitor-Associated Nephrotoxicity.

CONTEXT: The clinical indications for immune checkpoint inhibitors (ICIs) are rapidly expanding. However, adverse events affecting multiple organs, including kidneys leading to ICI-associated acute kidney injury (AKI), remain a significant challenge with ICI therapy. Although AKI is considered a rare complication, it can be severe and result in treatment interruption or discontinuation of ICIs. Despite a generally favorable kidney prognosis, the possibility of re-challenging ICI therapy remains a subject of debate, particularly for patients who have exhausted other treatment options or experienced severe AKI. Subject of Review: In a recent review article, Sprangers et al. provide a comprehensive overview of the possible mechanisms and clinical manifestations of ICI-associated AKI [Nat Rev Nephrol. 2022;18(12):794-805]. The authors propose a practical strategy for diagnosing and managing suspected cases of ICI-associated AKI, which includes identifying a subset of eligible patients who may be re-exposed to ICIs following an episode of AKI. Second Opinion: The authors of the review article offer several recommendations on the diagnosis and treatment of ICI-associated nephrotoxicity. While we generally agree with the recommendations proposed by the authors, it is important to acknowledge that the available data primarily rely on small retrospective studies, as the authors have recognized. In addition, there are two key questions that need be carefully addressed in future studies: (1) the optimal dose and duration of corticosteroids and the use of alternative immunosuppressive agents in patients with ICI-associated nephrotoxicity and (2) a clear guideline for restarting ICI treatment in patients with AKI who have not fully recovered their kidney function.

The transcription factor ChREBP links mitochondrial lipidomes to mitochondrial morphology and progression of diabetic kidney disease.

A substantial body of evidence has established the contributions of both mitochondrial dynamics and lipid metabolism to the pathogenesis of diabetic kidney disease (DKD). However, the precise interplay between these two key metabolic regulators of DKD is not fully understood. Here, we uncover a link between mitochondrial dynamics and lipid metabolism by investigating the role of carbohydrate-response element-binding protein (ChREBP), a glucose-responsive transcription factor and a master regulator of lipogenesis, in kidney podocytes. We find that inducible podocyte-specific knockdown of ChREBP in diabetic db/db mice improves key biochemical and histological features of DKD in addition to significantly reducing mitochondrial fragmentation. Because of the critical role of ChREBP in lipid metabolism, we interrogated whether and how mitochondrial lipidomes play a role in ChREBP-mediated mitochondrial fission. Our findings suggest a key role for a family of ether phospholipids in ChREBP-induced mitochondrial remodeling. We find that overexpression of glyceronephosphate O-acyltransferase, a critical enzyme in the biosynthesis of plasmalogens, reverses the protective phenotype of ChREBP deficiency on mitochondrial fragmentation. Finally, our data also points to Gnpat as a direct transcriptional target of ChREBP. Taken together, our results uncover a distinct mitochondrial lipid signature as the link between ChREBP-induced mitochondrial dynamics and progression of DKD.

NDUFS4 Regulates Cristae Remodeling in Diabetic Kidney Disease.

The mitochondrial electron transport chain (ETC) is a highly adaptive process to meet metabolic demands of the cell, and its dysregulation has been associated with diverse clinical pathologies. However, the role and nature of impaired ETC in kidney diseases remains poorly understood. Here, we generated diabetic mice with podocyte-specific overexpression of Ndufs4, an accessory subunit of mitochondrial complex I, as a model to investigate the role of ETC integrity in diabetic kidney disease (DKD). We find that these conditional mice exhibit significant improvements in cristae morphology, mitochondrial dynamics, and albuminuria. By coupling proximity labeling with super-resolution imaging, we also identify the role of cristae shaping proteins in linking NDUFS4 with improved cristae morphology. Taken together, we discover the central role of NDUFS4 as a powerful regulator of cristae remodeling, respiratory supercomplexes assembly, and mitochondrial ultrastructure in vitro and in vivo. We propose that targeting NDUFS4 represents a promising approach to slow the progression of DKD.

Mitochondrial Regulation of Diabetic Kidney Disease.

The role and nature of mitochondrial dysfunction in diabetic kidney disease (DKD) has been extensively studied. Yet, the molecular drivers of mitochondrial remodeling in DKD are poorly understood. Diabetic kidney cells exhibit a cascade of mitochondrial dysfunction ranging from changes in mitochondrial morphology to significant alterations in mitochondrial biogenesis, biosynthetic, bioenergetics and production of reactive oxygen species (ROS). How these changes individually or in aggregate contribute to progression of DKD remain to be fully elucidated. Nevertheless, because of the remarkable progress in our basic understanding of the role of mitochondrial biology and its dysfunction in DKD, there is great excitement on future targeted therapies based on improving mitochondrial function in DKD. This review will highlight the latest advances in understanding the nature of mitochondria dysfunction and its role in progression of DKD, and the development of mitochondrial targets that could be potentially used to prevent its progression.

PGC1α is required for the renoprotective effect of lncRNA Tug1 in vivo and links Tug1 with urea cycle metabolites.

lncRNA taurine-upregulated gene 1 (Tug1) is a promising therapeutic target in the progression of diabetic nephropathy (DN), but the molecular basis of its protection remains poorly understood. Here, we generate a triple-mutant diabetic mouse model coupled with metabolomic profiling data to interrogate whether Tug1 interaction with peroxisome proliferator-activated receptor gamma coactivator 1α (PGC1α) is required for mitochondrial remodeling and progression of DN in vivo. We find that, compared with diabetic conditional deletion of Pgc1α in podocytes alone (db/db; Pgc1αPod-f/f), diabetic Pgc1α knockout combined with podocyte-specific Tug1 overexpression (db/db; TugPodTg; Pgc1αPod-f/f) reverses the protective phenotype of Tug1 overexpression, suggesting that PGC1α is required for the renoprotective effect of Tug1. Using unbiased metabolomic profiling, we find that altered urea cycle metabolites and mitochondrial arginase 2 play an important role in Tug1/PGC1α-induced mitochondrial remodeling. Our work identifies a functional role of the Tug1/PGC1α axis on mitochondrial metabolic homeostasis and urea cycle metabolites in experimental models of diabetes.

Long Noncoding RNAs and Their Therapeutic Promise in Diabetic Nephropathy.

Recent advances in large-scale RNA sequencing and genome-wide profiling projects have unraveled a heterogeneous group of RNAs, collectively known as long noncoding RNAs (lncRNAs), which play central roles in many diverse biological processes. Importantly, an association between aberrant expression of lncRNAs and diverse human pathologies has been reported, including in a variety of kidney diseases. These observations have raised the possibility that lncRNAs may represent unexploited potential therapeutic targets for kidney diseases. Several important questions regarding the functionality of lncRNAs and their impact in kidney diseases, however, remain to be carefully addressed. Here, we provide an overview of the main functions and mechanisms of actions of lncRNAs, and their promise as therapeutic targets in kidney diseases, emphasizing on the role of some of the best-characterized lncRNAs implicated in the pathogenesis and progression of diabetic nephropathy.

KDIGO Controversies Conference on onco-nephrology: kidney disease in hematological malignancies and the burden of cancer after kidney transplantation.

The bidirectional relationship between cancer and chronic kidney disease (CKD) is complex. Patients with cancer, particularly those with hematological malignancies such as multiple myeloma and lymphoma, are at increased risk of developing acute kidney injury and CKD. On the other hand, emerging evidence from large observational registry analyses have consistently shown that cancer risk is increased by at least 2- to 3-fold in kidney transplant recipients, and the observed increased risk occurs not only in those who have received kidney transplants but also in those on dialysis and with mild- to moderate-stage CKD. The interactions between cancer and CKD have raised major therapeutic and clinical challenges in the management of these patients. Given the magnitude of the problem and uncertainties, and current controversies within the existing evidence, Kidney Disease: Improving Global Outcomes (KDIGO) assembled a global panel of multidisciplinary clinical and scientific expertise for a controversies conference on onco-nephrology to identify key management issues in nephrology relevant to patients with malignancy. This report covers the discussed controversies in kidney disease in hematological malignancies, as well as cancer after kidney transplantation. An overview of future research priorities is also discussed.

KDIGO Controversies Conference on onco-nephrology: understanding kidney impairment and solid-organ malignancies, and managing kidney cancer.

The association between kidney disease and cancer is multifaceted and complex. Persons with chronic kidney disease (CKD) have an increased incidence of cancer, and both cancer and cancer treatments can cause impaired kidney function. Renal issues in the setting of malignancy can worsen patient outcomes and diminish the adequacy of anticancer treatments. In addition, the oncology treatment landscape is changing rapidly, and data on tolerability of novel therapies in patients with CKD are often lacking. Caring for oncology patients has become more specialized and interdisciplinary, currently requiring collaboration among specialists in nephrology, medical oncology, critical care, clinical pharmacology/pharmacy, and palliative care, in addition to surgeons and urologists. To identify key management issues in nephrology relevant to patients with malignancy, KDIGO (Kidney Disease: Improving Global Outcomes) assembled a global panel of multidisciplinary clinical and scientific expertise for a controversies conference on onco-nephrology in December 2018. This report covers issues related to kidney impairment and solid organ malignancies as well as management and treatment of kidney cancer. Knowledge gaps, areas of controversy, and research priorities are described.

Role for carbohydrate response element-binding protein (ChREBP) in high glucose-mediated repression of long noncoding RNA Tug1.

Long noncoding RNAs (lncRNAs) have been shown to play key roles in a variety of biological activities of the cell. However, less is known about how lncRNAs respond to environmental cues and what transcriptional mechanisms regulate their expression. Studies from our laboratory have shown that the lncRNA Tug1 (taurine upregulated gene 1) is crucial for the progression of diabetic kidney disease, a major microvascular complication of diabetes. Using a combination of proximity labeling with the engineered soybean ascorbate peroxidase (APEX2), ChIP-qPCR, biotin-labeled oligonucleotide pulldown, and classical promoter luciferase assays in kidney podocytes, we extend our initial observations in the current study and now provide a detailed analysis on a how high-glucose milieu downregulates Tug1 expression in podocytes. Our results revealed an essential role for the transcription factor carbohydrate response element binding protein (ChREBP) in controlling Tug1 transcription in the podocytes in response to increased glucose levels. Along with ChREBP, other coregulators, including MAX dimerization protein (MLX), MAX dimerization protein 1 (MXD1), and histone deacetylase 1 (HDAC1), were enriched at the Tug1 promoter under high-glucose conditions. These observations provide the first characterization of the mouse Tug1 promoter's response to the high-glucose milieu. Our findings illustrate a molecular mechanism by which ChREBP can coordinate glucose homeostasis with the expression of the lncRNA Tug1 and further our understanding of dynamic transcriptional regulation of lncRNAs in a disease state.

Shaping Up Mitochondria in Diabetic Nephropathy.

Mitochondrial medicine has experienced significant progress in recent years and is expected to grow significantly in the near future, yielding many opportunities to translate novel bench discoveries into clinical medicine. Multiple lines of evidence have linked mitochondrial dysfunction to a variety of metabolic diseases, including diabetic nephropathy (DN). Mitochondrial dysfunction presumably precedes the emergence of key histologic and biochemical features of DN, which provides the rationale to explore mitochondrial fitness as a novel therapeutic target in patients with DN. Ultimately, the success of mitochondrial medicine is dependent on a better understanding of the underlying biology of mitochondrial fitness and function. To this end, recent advances in mitochondrial biology have led to new understandings of the potential effect of mitochondrial dysfunction in a myriad of human pathologies. We have proposed that molecular mechanisms that modulate mitochondrial dynamics contribute to the alterations of mitochondrial fitness and progression of DN. In this comprehensive review, we highlight the possible effects of mitochondrial dysfunction in DN, with the hope that targeting specific mitochondrial signaling pathways may lead to the development of new drugs that mitigate DN progression. We will outline potential tools to improve mitochondrial fitness in DN as a novel therapeutic strategy. These emerging views suggest that the modulation of mitochondrial fitness could serve as a key target in ameliorating progression of kidney disease in patients with diabetes.

Summary of the International Conference on Onco-Nephrology: an emerging field in medicine.

Onco-nephrology is an emerging field in medicine. Patients with cancer may suffer from kidney diseases because of the cancer itself and cancer-related therapy. It is critical for nephrologists to be knowledgeable of cancer biology and therapy in order to be fully integrated in the multidisciplinary team and optimally manage patients with cancer and kidney diseases. In a recent international meeting, the key issues in this challenging clinical interface were addressed, including many unresolved basic science questions, such as the high tumor incidence in kidney transplant recipients. To this end, 70 highly qualified faculty members were gathered from all over the world to discuss these issues in 8 plenary sessions, including 5 keynote lectures. In addition, 48 young nephrologists and oncologists were invited to present their original observations that were highlighted in 2 large poster sessions.

MTHFD2 links RNA methylation to metabolic reprogramming in renal cell carcinoma.

One-carbon metabolism plays a central role in a broad array of metabolic processes required for the survival and growth of tumor cells. However, the molecular basis of how one-carbon metabolism may influence RNA methylation and tumorigenesis remains largely unknown. Here we show MTHFD2, a mitochondrial enzyme involved in one-carbon metabolism, contributes to the progression of renal cell carcinoma (RCC) via a novel epitranscriptomic mechanism that involves HIF-2α. We found that expression of MTHFD2 was significantly elevated in human RCC tissues, and MTHFD2 knockdown strongly reduced xenograft tumor growth. Mechanistically, using an unbiased methylated RNA immunoprecipitation sequencing (meRIP-Seq) approach, we found that MTHFD2 plays a critical role in controlling global N6-methyladenosine (m6A) methylation levels, including the m6A methylation of HIF-2α mRNA, which results in enhanced translation of HIF-2α. Enhanced HIF-2α translation, in turn, promotes the aerobic glycolysis, linking one-carbon metabolism to HIF-2α-dependent metabolic reprogramming through RNA methylation. Our findings also suggest that MTHFD2 and HIF-2α form a positive feedforward loop in RCC, promoting metabolic reprograming and tumor growth. Taken together, our results suggest that MTHFD2 links RNA methylation status to the metabolic state of tumor cells in RCC.

Drp1S600 phosphorylation regulates mitochondrial fission and progression of nephropathy in diabetic mice.

Phosphorylation of Dynamin-related protein1 (Drp1) represents an important regulatory mechanism for mitochondrial fission. Here we established the role of Drp1 Serine 600 (S600) phosphorylation on mitochondrial fission in vivo, and assessed the functional consequences of targeted elimination of the Drp1S600 phosphorylation site in progression of diabetic nephropathy (DN). We generated a knockin mouse in which S600 was mutated to alanine (Drp1S600A). We found that diabetic Drp1S600A mice exhibited improved biochemical and histological features of DN along with reduced mitochondrial fission and diminished mitochondrial ROS in vivo. Importantly, we observed that the effect of Drp1S600 phosphorylation on mitochondrial fission in the diabetic milieu was stimulus- but not cell type-dependent. Mechanistically, we showed that mitochondrial fission in high glucose conditions occurs through concomitant binding of phospho-Drp1S600 with mitochondrial fission factor (Mff) and actin-related protein 3 (Arp3), ultimately leading to accumulation of F-actin and Drp1 on the mitochondria. Taken together, these findings establish that a single phosphorylation site in Drp1 can regulate mitochondrial fission and progression of DN in vivo, and highlight the stimulus-specific consequences of Drp1S600 phosphorylation on mitochondrial dynamics.

PTEN-induced partial epithelial-mesenchymal transition drives diabetic kidney disease.

Epithelial-mesenchymal transition (EMT) contributes significantly to interstitial matrix deposition in diabetic kidney disease (DKD). However, detection of EMT in kidney tissue is impracticable, and anti-EMT therapies have long been hindered. We reported that phosphatase and tensin homolog (PTEN) promoted transforming growth factor beta 1 (TGF-ß), sonic hedgehog (SHH), connective tissue growth factor (CTGF), interleukin 6 (IL-6), and hyperglycemia-induced EMT when PTEN was modified by a MEX3C-catalyzed K27-linked polyubiquitination at lysine 80 (referred to as PTENK27-polyUb). Genetic inhibition of PTENK27-polyUb alleviated Col4a3 knockout-, folic acid-, and streptozotocin-induced (STZ-induced) kidney injury. Serum and urine PTENK27-polyUb concentrations were negatively correlated with glomerular filtration rate (GFR) for diabetic patients. Mechanistically, PTENK27-polyUb facilitated dephosphorylation and protein stabilization of TWIST, SNAI1, and YAP in renal epithelial cells, leading to enhanced EMT. We identified that a small molecule, triptolide, inhibited MEX3C-catalyzed PTENK27-polyUb and EMT of renal epithelial cells. Treatment with triptolide reduced TWIST, SNAI1, and YAP concurrently and improved kidney health in Col4a3 knockout-, folic acid-injured disease models and STZ-induced, BTBR ob/ob diabetic nephropathy models. Hence, we demonstrated the important role of PTENK27-polyUb in DKD and a promising therapeutic strategy that inhibited the progression of DKD.