Extracellular signal-regulated kinase 1/2 regulates NAD metabolism during acute kidney injury through microRNA-34a-mediated NAMPT expression

MC16 promotes mitochondrial biogenesis and ameliorates acute and diabetic nephropathy

BACKGROUND AND PURPOSE

Kidney disease (KD) is a leading cause of mortality worldwide, affecting 〉10% of the global population. Two of the most common causes of KD are diabetes and acute kidney injury (AKI), both of which induce mitochondrial dysfunction resulting in renal proximal tubular damage/necrosis. Thus, pharmacological induction of mitochondrial biogenesis (MB) may provide a therapeutic strategy to block the onset/progression of KD. Here, we evaluated the pharmacological and potential therapeutic effects of a novel MB-inducing oxindole agent, MC16.

EXPERIMENTAL APPROACH

Primary cultures of rabbit renal proximal tubule cells (RPTCs) were used to evaluate the cellular signalling and MB-inducing effects of MC16. Mice were used to determine the MB-inducing effects of MC16 in vivo, and the metabolic effects of MC16 on the renal cortical metabolome. Mouse models of AKI and diabetic kidney disease (DKD) were used to demonstrate the therapeutic potential of MC16 to ameliorate acute and diabetic nephropathy.

KEY RESULTS

MC16 activated the PI3K-AKT-eNOS-FOXO1 axis and induced MB in RPTCs. MC16 induced MB and altered the renal cortical metabolome of mice. MC16 accelerated renal recovery, reduced vascular permeability, and diminished mitochondrial dysfunction following AKI. MC16 decreased diabetes-induced renal swelling, improved renal and mitochondrial function, and diminished interstitial fibrosis in DKD mouse models.

CONCLUSION AND IMPLICATIONS

MC16 is a novel compound that induces MB and ameliorates acute and diabetic nephropathy in mice. This study underscores that targeting MB following the onset of renal/metabolic insults may provide a therapeutic strategy to mitigate the onset and/or progression of KD.

Trametinib ameliorated Adriamycin-induced podocyte injury by inhibiting METTL3 modified m6A RCAN1 RNA methylation

N6-methyladenosine (m6A) plays a crucial role in kidney diseases. Methyltransferase-like 3 (METTL3) as a key m6A writer can be regulated by trametinib. However, the epigenetic regulation of trametinib in focal segmental glomerulosclerosis (FSGS) remains unclear. We investigated whether trametinib protects podocytes by modulating METTL3-methylated target RNAs. Regulator of calcineurin 1 (RCAN1) was predicted as a target binding RNA of METTL3 by THEW database. Immunostaining of METTL3 and RCAN1 with podocyte marker Wilm's tumor-1 (WT-1) confirmed their localization within podocytes in renal biopsy from FSGS patients. Transfection METTL3 to human podocytes reduced WT-1, synaptopodin (SYNPO), and RCAN1 protein levels. Total m6A, m6A methylated RNA of RCAN1 increased and total RCAN1 mRNA decreased. Inhibition of METTL3 using siRNA or trametinib reversed these changes and attenuated the ADR-induced downregulation of WT-1 and SYNPO in vitro. In ADR-induced FSGS mice, trametinib ameliorated proteinuria, hypoalbuminemia, renal dysfunction, glomerulosclerosis and podocyte foot process effacement. Additionally, trametinib preserved podocyte function assessed by WT-1 and SYNPO as well as delayed renal fibrosis assessed by α-smooth muscle actin and fibronectin. Consistent with results in vitro, trametinib also decreased the ADR-induced upregulation of METTL3 and reversed the changed levels of total m6A, m6A methylated Rcan1 and total Rcan1 in FSGS mice. In conclusion, trametinib may serve as a renal protective agent for FSGS by regulating METTL3-dependent RCAN1 methylation levels.

Lasmiditan induces mitochondrial biogenesis in primary mouse renal peritubular endothelial cells and augments wound healing and tubular network formation

Kidney disease (KD) is a progressive and life-threatening illness that has manifested into a global health crisis, impacting >10% of the general population. Hallmarks of KD include tubular interstitial fibrosis, renal tubular cell atrophy/necrosis, glomerulosclerosis, persistent inflammation, microvascular endothelial cell (MV-EC) dysfunction/rarefaction, and mitochondrial dysfunction. Following acute kidney injury (AKI), and/or during KD onset/progression, MV-ECs of the renal peritubular endothelial capillaries (RPECs) are highly susceptible to injury, dysfunction, and rarefaction. Pharmacological induction of mitochondrial biogenesis (MB) via 5-hydroxytryptamine receptor 1F (HTR1F) agonism has been shown to enhance mitochondrial function and renal vascular recovery post-AKI in mice; however, little is known about MB in relation to renal MV-ECs and RPEC repair mechanisms. To address this gap in knowledge, the in vitro effects of the potent and selective FDA-approved HTR1F agonist lasmiditan were tested on primary mouse renal peritubular endothelial cells (MRPECs). Lasmiditan increased mitochondrial maximal respiration rates, mRNA and protein expression of MB-related genes, and mitochondrial number in MRPECs. MRPECs were then exposed to pro-inflammatory agents associated with renal MV-EC dysfunction, AKI, and KD (i.e., lipopolysaccharides, transforming growth factor-β1, and tumor necrosis factor-α), in the presence/absence of lasmiditan. Lasmiditan treatment augmented MRPEC wound healing, endothelial tubular network formation (ETNF), enhanced barrier integrity, and blunted inflammatory-induced MV-EC dysfunctions. Together, these data suggest that lasmiditan induces MB and improves wound healing and ETNF of primary MRPECs in the presence/absence of pro-inflammatory agents, highlighting a potential therapeutic role for lasmiditan treatment in renal MV-EC dysfunction, AKI, and/or KD.NEW & NOTEWORTHY Lasmiditan, an FDA-approved HTR1F agonist, induces mitochondrial biogenesis (MB) and enhances recovery following acute kidney injury in mice. Renal microvascular endothelial cells (MV-ECs) are highly susceptible to dysfunction/rarefaction postinjury. The effect of MB on MV-EC repair/recovery is unknown. We show that lasmiditan induces MB in primary mouse renal peritubular endothelial cells and improves wound healing, endothelial tubular network formation, and barrier integrity after inflammatory-induced dysfunction, indicative of its potential for the treatment of kidney diseases.

Twist2 knockdown alleviates renal ischemia-reperfusion injury by maintaining mitochondrial function and enhancing mitophagy through Bnip3

Renal ischemia-reperfusion injury (IRI) is a major cause of acute kidney injury (AKI). Twist-related protein 2 (Twist2) is a basic helix/loop/helix transcription factor. However, the underlying effects of Twist2 in IRI remain to be elucidated. Herein, we found that the expression of Twist2 was significantly upregulated in renal tissues of mice induced by ischemia/reperfusion (I/R) and in human renal tubular epithelial cell HK-2 exposed to hypoxia-reoxygenation. We silenced Twist2 with RNAi technology. Twist2 knockdown alleviated renal pathological damage in mice. Twist2 depletion ameliorated IRI-induced mitochondrial dysfunction, such as increasing ATP content and mitochondrial DNA copy number and restoring mitochondrial membrane potential in the kidneys of mice, and similar results were observed in in vitro experiments. Twist2 interference increased the expression of LC3B and decreased the expression of p62 and mitochondrial membrane proteins TIMM23 and TOMM20 both in vivo and in vitro. Electron microscope and the co-localization of LC3B and mitotracker DsRed suggested the induction of autophagy and mitophagy after Twist2 knockdown in kidneys or cells. Mechanism studies revealed that Twist2 exerted a direct inhibitory effect on BCL2 interacting protein 3 (Bnip3) transcriptional activity by targeting the Bnip3 promoter. In hypoxia/reoxygenation-induced renal tubular epithelial cells, the interference of Bnip3 reversed the effect of Twist2 depletion on mitochondrial function and mitophagy. In conclusion, our findings suggest that the depletion of Twist2 exerts renoprotective effect in I/R-induced AKI. Twist2 regulates mitochondrial function and mitophagy in part by targeting and downregulating Bnip3. Our study provides new insights into the pathological mechanisms of I/R-induced AKI.

Targeting NAD Metabolism for the Therapy of Age-Related Neurodegenerative Diseases

As the aging population continues to grow rapidly, age-related diseases are becoming an increasing burden on the healthcare system and a major concern for the well-being of elderly individuals. While aging is an inevitable process for all humans, it can be slowed down and age-related diseases can be treated or alleviated. Nicotinamide adenine dinucleotide (NAD) is a critical coenzyme or cofactor that plays a central role in metabolism and is involved in various cellular processes including the maintenance of metabolic homeostasis, post-translational protein modifications, DNA repair, and immune responses. As individuals age, their NAD levels decline, and this decrease has been suggested to be a contributing factor to the development of numerous age-related diseases, such as cancer, diabetes, cardiovascular diseases, and neurodegenerative diseases. In pursuit of healthy aging, researchers have investigated approaches to boost or maintain NAD levels. Here, we provide an overview of NAD metabolism and the role of NAD in age-related diseases and summarize recent progress in the development of strategies that target NAD metabolism for the treatment of age-related diseases, particularly neurodegenerative diseases.

MicroRNAs as Biomarkers and Therapeutic Targets for Acute Kidney Injury

Acute kidney injury (AKI) is a clinical syndrome where a rapid decrease in kidney function and/or urine output is observed, which may result in the imbalance of water, electrolytes and acid base. It is associated with poor prognosis and prolonged hospitalization. Therefore, an early diagnosis and treatment to avoid the severe AKI stage are important. While several biomarkers, such as urinary L-FABP and NGAL, can be clinically useful, there is still no gold standard for the early detection of AKI and there are limited therapeutic options against AKI. miRNAs are non-coding and single-stranded RNAs that silence their target genes in the post-transcriptional process and are involved in a wide range of biological processes. Recent accumulated evidence has revealed that miRNAs may be potential biomarkers and therapeutic targets for AKI. In this review article, we summarize the current knowledge about miRNAs as promising biomarkers and potential therapeutic targets for AKI, as well as the challenges in their clinical use.

Mitochondrial quality control in acute kidney disease

Acute kidney disease (AKD) involves multiple pathogenic mechanisms,  including maladaptive repair of renal cells that are rich in mitochondria. Maintenance of mitochondrial homeostasis and quality control is crucial for normal kidney function. Mitochondrial quality control serves to maintain mitochondrial function under various conditions, including mitochondrial bioenergetics, mitochondrial biogenesis, mitochondrial dynamics (fusion and fission) and mitophagy. To date, increasing evidence indicates that mitochondrial quality control is disrupted when acute kidney disease develops. This review describes the mechanisms of mitochondria quality control in acute kidney disease, aiming to provide clues to help design new clinical treatments.

Induced pluripotent stem cells-podocytes promote repair in acute kidney injury is dependent on Mafb/CCR5/Nampt axis-mediated M2 macrophage polarization

Induced pluripotent stem cells (iPSCs) have been the focus of cellular therapy studies. The use of iPSCs in regenerative medicine is limited by their tumorigenic potential. This study sought to determine whether iPSCs-derived podocytes attenuate acute kidney injury (AKI) and the molecular mechanism. Inoculation of iPSCs-podocytes significantly promoted the repair of kidney injury in AKI mice, reduced the levels of kidney injury factors Scr, BUN, and urinary NAG, and alleviated the inflammatory response. Histological analysis revealed a significant increase in the number of M2 macrophages and a significant decrease in M1 macrophages in the kidney tissues. Subsequently, the genes and signaling pathways that may be associated with kidney injury repair in mice were analyzed by RNA-seq and bioinformatics prediction. The polarization of M2 macrophages was promoted by MAF bZIP transcription factor B (Mafb)-mediated activation of C-C motif chemokine receptor 5 (Ccr5) and nicotinamide phosphoribosyltransferase (Nampt) signaling pathway. Taken together, these results show that iPSCs-podocytes depend on Mafb to activate the Nampt signaling pathway through transcriptional activation of Ccr5, thereby promoting the repair of AKI caused by ischemia-reperfusion.

The Stress-Responsive microRNA-34a Alters Insulin Signaling and Actions in Adipocytes through Induction of the Tyrosine Phosphatase PTP1B

Metabolic stresses alter the signaling and actions of insulin in adipocytes during obesity, but the molecular links remain incompletely understood. Members of the microRNA-34 (miR-34 family play a pivotal role in stress response, and previous studies showed an upregulation of miR-34a in adipose tissue during obesity. Here, we identified miR-34a as a new mediator of adipocyte insulin resistance. We confirmed the upregulation of miR-34a in adipose tissues of obese mice, which was observed in the adipocyte fraction exclusively. Overexpression of miR-34a in 3T3-L1 adipocytes or in fat pads of lean mice markedly reduced Akt activation by insulin and the insulin-induced glucose transport. This was accompanied by a decreased expression of VAMP2, a target of miR-34a, and an increased expression of the tyrosine phosphatase PTP1B. Importantly, PTP1B silencing prevented the inhibitory effect of miR-34a on insulin signaling. Mechanistically, miR-34a decreased the NAD⁺ level through inhibition of Naprt and Nampt, resulting in an inhibition of Sirtuin-1, which promoted an upregulation of PTP1B. Furthermore, the mRNA expression of Nampt and Naprt was decreased in adipose tissue of obese mice. Collectively, our results identify miR-34a as a new inhibitor of insulin signaling in adipocytes, providing a potential pathway to target to fight insulin resistance.

MicroRNAs in kidney injury and disease

MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression by degrading or repressing the translation of their target messenger RNAs. As miRNAs are critical regulators of cellular homeostasis, their dysregulation is a crucial component of cell and organ injury. A substantial body of evidence indicates that miRNAs are involved in the pathophysiology of acute kidney injury (AKI), chronic kidney disease and allograft damage. Different subsets of miRNAs are dysregulated during AKI, chronic kidney disease and allograft rejection, which could reflect differences in the physiopathology of these conditions. miRNAs that have been investigated in AKI include miR-21, which has an anti-apoptotic role, and miR-214 and miR-668, which regulate mitochondrial dynamics. Various miRNAs are downregulated in diabetic kidney disease, including the miR-30 family and miR-146a, which protect against inflammation and fibrosis. Other miRNAs such as miR-193 and miR-92a induce podocyte dedifferentiation in glomerulonephritis. In transplantation, miRNAs have been implicated in allograft rejection and injury. Further work is needed to identify and validate miRNAs as biomarkers of graft function and of kidney disease development and progression. Use of combinations of miRNAs together with other molecular markers could potentially improve diagnostic or predictive power and facilitate clinical translation. In addition, targeting specific miRNAs at different stages of disease could be a promising therapeutic strategy.

Mechanism of miR-34a in the metabolism of extracellular matrix in fibroblasts of stress urinary incontinence via Nampt-mediated autophagy

Stress urinary incontinence (SUI) is a troublesome hygienic problem that afflicts the female population and is associated with extracellular matrix (ECM). Herein, we investigated the effects of microRNA (miR)-34a on ECM metabolism in fibroblasts of SUI via mediating nicotinamide phosphoribosyl transferase (Nampt/NAmPRTase) and hope to find novel insights in the treatment of SUI. Firstly, the anterior vaginal wall tissues of SUI patients and the female vaginal wall fibroblasts (FVWFs) of non-SUI subjects were collected and identified. Then, FVWFs were treated with 10 ng/mL of interleukin 1 beta (IL-1β) to establish SUI cell models. Subsequently, miR-34a and Nampt expressions in both types of cells were detected via RT-qPCR. It was found that miR-34a was poorly expressed, while Nampt was highly expressed in SUI. Subsequently, IL-1β-treated FVWFs were transfected with miR-34a-mimic and pcDNA3.1-Nampt, respectively. Thereafter, RT-qPCR and Western blot detected that miR-34a overexpression increased COL1A, ACAN, and TIMP-1; decreased MMP-2 and MMP-9; and elevated LC3 II/I ratio, Beclin-1 expression, and the autophagosome number in IL-1β-treated FVWFs, while Nampt upregulation reversed the above outcomes. Then, dual-luciferase reporter gene assay detected that Nampt is a downstream target of miR-34a. Together, miR-34a overexpression promoted autophagy, inhibited ECM degradation in IL-1β-treated FVWFs, and ameliorated SUI via suppressing Nampt.

The Impact of General Anesthesia on Redox Stability and Epigenetic Inflammation Pathways: Crosstalk on Perioperative Antioxidant Therapy

Worldwide, the prevalence of surgery under general anesthesia has significantly increased, both because of modern anesthetic and pain-control techniques and because of better diagnosis and the increased complexity of surgical techniques. Apart from developing new concepts in the surgical field, researchers and clinicians are now working on minimizing the impact of surgical trauma and offering minimal invasive procedures due to the recent discoveries in the field of cellular and molecular mechanisms that have revealed a systemic inflammatory and pro-oxidative impact not only in the perioperative period but also in the long term, contributing to more difficult recovery, increased morbidity and mortality, and a negative financial impact. Detailed molecular and cellular analysis has shown an overproduction of inflammatory and pro-oxidative species, responsible for augmenting the systemic inflammatory status and making postoperative recovery more difficult. Moreover, there are a series of changes in certain epigenetic structures, the most important being the microRNAs. This review describes the most important molecular and cellular mechanisms that impact the surgical patient undergoing general anesthesia, and it presents a series of antioxidant therapies that can reduce systemic inflammation.

The Significance of NAD+ Biosynthesis Alterations in Acute Kidney Injury

Acute kidney injury (AKI) is a serious and highly prevalent disease, yet only supportive treatment is available. Nicotinamide adenine dinucleotide (NAD+) is a cofactor necessary for adenosine triphosphate (ATP) production and cell survival. Changes in renal NAD+ biosynthesis and energy utilization are features of AKI. Targeting NAD+ as an AKI therapy shows promising potential. However, the pursuit of NAD+-based treatments requires deeper understanding of the unique drivers and effects of the NAD+ biosynthesis derangements that arise in AKI. This article summarizes the NAD+ biosynthesis alterations in the kidney in AKI, chronic disease, and aging. To enhance this understanding, we explore instances of NAD+ biosynthesis alterations outside the kidney in inflammation, pregnancy, and cancer. In doing so, we seek to highlight that the different NAD+ biosynthesis pathways are not interconvertible and propose that the way in which NAD+ is synthesized may be just as important as the NAD+ produced.

Emerging early diagnostic methods for acute kidney injury

Many factors such as trauma and COVID-19 cause acute kidney injury (AKI). Late AKI have a very high incidence and mortality rate. Early diagnosis of AKI provides a critical therapeutic time window for AKI treatment to prevent progression to chronic renal failure. However, the current clinical detection based on creatinine and urine output isn't effective in diagnosing early AKI. In recent years, the early diagnosis of AKI has made great progress with the advancement of information technology, nanotechnology, and biomedicine. These emerging methods are mainly divided into two aspects: First, predicting AKI through models construct by machine learning; Second, early diagnosis of AKI through detection of newly-discovered early biomarkers. Currently, these methods have shown great potential and become an attractive tool for the early diagnosis of AKI. Therefore, it is very important to discuss and summarize these methods for the early diagnosis of AKI. In this review, we first systematically summarize the application of machine learning in AKI prediction algorithms and specific scenarios. In addition, we introduce the key role of early biomarkers in the progress of AKI, and then comprehensively summarize the application of emerging detection technologies for early AKI. Finally, we discuss current challenges and prospects of machine learning and biomarker detection. The review is expected to provide new insights for early diagnosis of AKI, and provided important inspiration for the design of early diagnosis of other major diseases.

Mitochondrial Dysfunction: An Emerging Link in the Pathophysiology of Cardiorenal Syndrome

The crosstalk between the heart and kidney is carried out through various bidirectional pathways. Cardiorenal syndrome (CRS) is a pathological condition in which acute or chronic dysfunction in the heart or kidneys induces acute or chronic dysfunction of the other organ. Complex hemodynamic factors and biochemical and hormonal pathways contribute to the development of CRS. In addition to playing a critical role in generating metabolic energy in eukaryotic cells and serving as signaling hubs during several vital processes, mitochondria rapidly sense and respond to a wide range of stress stimuli in the external environment. Impaired adaptive responses ultimately lead to mitochondrial dysfunction, inducing cell death and tissue damage. Subsequently, these changes result in organ failure and trigger a vicious cycle. In vitro and animal studies have identified an important role of mitochondrial dysfunction in heart failure (HF) and chronic kidney disease (CKD). Maintaining mitochondrial homeostasis may be a promising therapeutic strategy to interrupt the vicious cycle between HF and acute kidney injury (AKI)/CKD. In this review, we hypothesize that mitochondrial dysfunction may also play a central role in the development and progression of CRS. We first focus on the role of mitochondrial dysfunction in the pathophysiology of HF and AKI/CKD, then discuss the current research evidence supporting that mitochondrial dysfunction is involved in various types of CRS.

BMAL1 regulates mitochondrial homeostasis in renal ischaemia-reperfusion injury by mediating the SIRT1/PGC-1α axis

The regulation of renal function by circadian gene BMAL1 has been recently recognized; however, the role and mechanism of BMAL1 in renal ischaemia‐reperfusion injury (IRI) are still unknown. The purpose of this study was to clarify the pathophysiological role of BMAL1 in renal IRI. We measured the levels of BMAL1 and mitochondrial biogenesis‐related proteins, including SIRT1, PGC‐1α, NRF1 and TFAM, in rats with renal IRI. In rats, the level of BMAL1 decreased significantly, resulting in inhibition of SIRT1 expression and mitochondrial biogenesis. In addition, under hypoxia and reoxygenation (H/R) stimulation, BMAL1 knockdown decreased the level of SIRT1 and exacerbated the degree of mitochondrial damage and apoptosis. Overexpression of BMAL1 alleviated H/R‐induced injury. Furthermore, application of the SIRT1 inhibitor EX527 not only reduced the activities of SIRT1 and PGC‐1α but also further aggravated mitochondrial dysfunction and partially reversed the protective effect of BMAL1 overexpression. Moreover, whether in vivo or in vitro, the application of SIRT1 agonist resveratrol rescued the mitochondrial dysfunction caused by H/R or IRI by activating mitochondrial biogenesis. These results indicate that BMAL1 is a key circadian gene that mediates mitochondrial homeostasis in renal IRI through the SIRT1/PGC‐1α axis, which provides a new direction for targeted therapy for renal IRI.

NAD+ ameliorates endotoxin-induced acute kidney injury in a sirtuin1-dependent manner via GSK-3β/Nrf2 signalling pathway

Acute kidney injury (AKI) is a substantial worldwide public health concern with no specific and effective therapies in clinic. NAD⁺ is a pivotal determinant of cellular energy metabolism involved in the progression of AKI; however, its mechanism in kidney injury remains poorly understood. Sirtuin 1 (SIRT1) is an NAD⁺‐dependent deacetylase associated with renal protection and acute stress resistance. In this study, we have investigated the role of NAD⁺ in AKI and the potential mechanism(s) involved in its renoprotective effect. NAD⁺ was notably decreased and negatively correlated with kidney dysfunction in AKI, restoring NAD⁺ with NMN significantly ameliorates LPS‐induced oxidative stress and apoptosis and attenuates renal damage. We also found that the protection of NAD⁺ is associated with SIRT1 expressions and performs in a SIRT1‐dependent manner. Inhibition of SIRT1 blunted the protective effect of NAD⁺ and up‐regulated the activity of glycogen synthase kinase‐3β (GSK‐3β) that was concomitant with mitigated Nrf2 nuclear accumulation, thereby exacerbates AKI. These findings suggest that NAD⁺/SIRT1/GSK‐3β/Nrf2 axis is an important mechanism that can protect against AKI which might be a potential therapeutic target for the treatment of AKI.

Potential of Polyphenols to Restore SIRT1 and NAD+ Metabolism in Renal Disease

SIRT1 is an NAD⁺-dependent class III histone deacetylase that is abundantly expressed in the kidney, where it modulates gene expression, apoptosis, energy homeostasis, autophagy, acute stress responses, and mitochondrial biogenesis. Alterations in SIRT1 activity and NAD⁺ metabolism are frequently observed in acute and chronic kidney diseases of diverse origins, including obesity and diabetes. Nevertheless, in vitro and in vivo studies and clinical trials with humans show that the SIRT1-activating compounds derived from natural sources, such as polyphenols found in fruits, vegetables, and plants, including resveratrol, quercetin, and isoflavones, can prevent disease and be part of treatments for a wide variety of diseases. Here, we summarize the roles of SIRT1 and NAD⁺ metabolism in renal pathophysiology and provide an overview of polyphenols that have the potential to restore SIRT1 and NAD⁺ metabolism in renal diseases.

Tourniquet-induced lower limb ischemia/reperfusion reduces mitochondrial function by decreasing mitochondrial biogenesis in acute kidney injury in mice

The mechanisms by which lower limb ischemia/reperfusion induces acute kidney injury (AKI) remain largely uncharacterized. We hypothesized that tourniquet-induced lower limb ischemia/reperfusion (TILLIR) would inhibit mitochondrial function in the renal cortex. We used a murine model to show that TILLIR of the high thigh regions inflicted time-dependent AKI as determined by renal function and histology. This effect was associated with decreased activities of mitochondrial complexes I, II, V and citrate synthase in the kidney cortex. Moreover, TILLIR reduced mRNA levels of a master regulator of mitochondrial biogenesis PGC-1α, and its downstream genes NDUFS1 and ATP5o in the renal cortex. TILLIR also increased serum corticosterone concentrations. TILLIR did not significantly affect protein levels of the critical regulators of mitophagy PINK1 and PARK2, mitochondrial transport proteins Tom20 and Tom70, or heat-shock protein 27. TILLIR had no significant effect on mitochondrial oxidative stress as determined by mitochondrial ability to generate reactive oxygen species, protein carbonylation, or protein levels of MnSOD and peroxiredoxin1. However, TILLIR inhibited classic autophagic flux by increasing p62 protein abundance and preventing the conversion of LC3-I to LC3-II. TILLIR increased phosphorylation of cytosolic and mitochondrial ERK1/2 and mitochondrial AKT1, as well as mitochondrial SGK1 activity. In conclusion, lower limb ischemia/reperfusion induces distal AKI by inhibiting mitochondrial function through reducing mitochondrial biogenesis. This AKI occurs without significantly affecting PINK1-PARK2-mediated mitophagy or mitochondrial oxidative stress in the kidney cortex.

Molecular Changes in miRNA in Irradiated Rat Kidneys: Role of miR-34a and its Vascular Targets in the Notch Pathway

The mechanism(s) of vascular regression in adult organs remains an unexplored gap. Irradiation to the kidney results in vascular regression and renal failure. The goal of this work was to determine molecular mechanism(s) of radiation-induced vascular regression and its mitigation by the drug lisinopril. Female WAG/RijCmcr rats received either 13 Gy X-ray irradiation, sparing one leg, or no irradiation, the latter serving as age-matched controls. Some irradiated animals received lisinopril. Kidney miRNA-seq was performed 35 days postirradiation, before symptoms of nephropathy. MicroRNA expression profiles were compared with data from humans. MicroRNA targets were predicted using TargetScan and confirmed by qRT-PCR and Western blot. Renal vascular endothelial cell density was evaluated at 100 days to confirm vascular regression. The normal rat kidney microRNA profile resembled that of humans. MiR-34a was increased >7-fold and emerged as the predominant rat microRNA altered by radiation. Expression of Jagged1, a ligand in the Notch pathway of vascular development and a target of miR-34a-5p was decreased by radiation but not in irradiated rats receiving lisinopril. Radiation decreased endothelial cells in the kidneys at 100 days, confirming vascular regression. In conclusion, the results of this study showed that radiation greatly increased miRNA34-a in rat kidneys, while lisinopril mitigated radiation-induced decrease of the Notch ligand, Jagged1, a molecular target of miRNA34-a.

New insights into the important roles of tumor cell-intrinsic PD-1

PD-1 (Programmed cell death protein-1) is mainly expressed in various immune cells, while its ligands PD-L1/PD-L2 (Programmed death ligand-1/Programmed death ligand-2) are mostly expressed in tumor cells. Generally, the binding of PD-L1/PD-L2 and PD-1 could lead to the tumor immune evasion. However, some recent studies showed that PD-1 could also be expressed in tumor cells and could activate mTOR (Mammalian Target of Rapamycin) or Hippo signaling pathway, therefore facilitating tumor proliferation independent of the immune system. While there was evidence that tumor cell-intrinsic PD-1 inhibited the activation of AKT and ERK1/2 pathways, thereby inhibiting tumor cell growth. Based on TCGA and CCLE database, we found that PD-1 was expressed in a variety of tumors and was associated with patient's prognosis. Besides, we found that PD-1 may be involved in many carcinogenic signaling pathway on the basis of PD-1 gene enrichment analysis of cancer tissues and cancer cells. Our understanding of the tumor cell-intrinsic PD-1 function is still limited. This review is aimed at elaborating the potential effects of tumor cell-intrinsic PD-1 on carcinogenesis, providing a novel insight into the effects of anti-PD-1/PD-L1 immunotherapy, and helping to open a major epoch of combination therapy.

MiR-34a suppression targets Nampt to ameliorate bone marrow mesenchymal stem cell senescence by regulating NAD+-Sirt1 pathway

BACKGROUND

Expansion-mediated replicative senescence and age-related natural senescence have adverse effects on mesenchymal stem cell (MSC) regenerative capability and functionality, thus severely impairing the extensive applications of MSC-based therapies. Emerging evidences suggest that microRNA-34a (miR-34a) has been implicated in the process of MSC senescence; however, the molecular mechanisms with regard to how miR-34a influencing MSC senescence remain largely undetermined.

METHODS

MiR-34a expression in MSCs was evaluated utilizing RT-qPCR. The functional effects of miR-34a exerting on MSC senescence were investigated via gene manipulation. Relevant gene and protein expression levels were analyzed by RT-qPCR and western blot. Luciferase reporter assays were applied to confirm that Nampt is a direct target of miR-34a. The underlying regulatory mechanism of miR-34a targeting Nampt in MSC senescence was further explored by measuring intracellular NAD⁺ content, NAD⁺/NADH ratio and Sirt1 activity.

RESULTS

In contrast to Nampt expression, miR-34a expression incremented in senescent MSCs. MiR-34a overexpression in young MSCs resulted in senescence-associated characteristics as displayed by senescence-like morphology, prolonged cell proliferation, declined osteogenic differentiation potency, heightened senescence-associated-β-galactosidase activity, and upregulated expression levels of the senescence-associated factors. Conversely, miR-34a suppression in replicative senescent and natural senescent MSCs contributed to diminished senescence-related phenotypic features. We identified Nampt as a direct target gene of miR-34a. In addition, miR-34a repletion resulted in prominent reductions in Nampt expression levels, NAD⁺ content, NAD⁺/NADH ratio, and Sirt1 activity, whereas anti-miR-34a treatment exerted the opposite effects. Furthermore, miR-34a-mediated MSC senescence was evidently rescued following the co-treatment with Nampt overexpression.

CONCLUSION

This study identifies a significant role of miR-34a playing in MSC replicative senescence and natural senescence via targeting Nampt and further mediating by NAD⁺-Sirt1 pathway, carrying great implications for optimal strategies for MSC therapeutic applications.

Mitochondrial quality control in kidney injury and repair

Mitochondria are essential for the activity, function and viability of eukaryotic cells and mitochondrial dysfunction is involved in the pathogenesis of acute kidney injury (AKI) and chronic kidney disease, as well as in abnormal kidney repair after AKI. Multiple quality control mechanisms, including antioxidant defence, protein quality control, mitochondrial DNA repair, mitochondrial dynamics, mitophagy and mitochondrial biogenesis, have evolved to preserve mitochondrial homeostasis under physiological and pathological conditions. Loss of these mechanisms may induce mitochondrial damage and dysfunction, leading to cell death, tissue injury and, potentially, organ failure. Accumulating evidence suggests a role of disturbances in mitochondrial quality control in the pathogenesis of AKI, incomplete or maladaptive kidney repair and chronic kidney disease. Moreover, specific interventions that target mitochondrial quality control mechanisms to preserve and restore mitochondrial function have emerged as promising therapeutic strategies to prevent and treat kidney injury and accelerate kidney repair. However, clinical translation of these findings is challenging owing to potential adverse effects, unclear mechanisms of action and a lack of knowledge of the specific roles and regulation of mitochondrial quality control mechanisms in kidney resident and circulating cell types during injury and repair of the kidney.

Molecular pathophysiology of acute kidney injury: The role of sirtuins and their interactions with other macromolecular players

Acute kidney injury (AKI), a rapid drop in kidney function, displays high mortality and morbidity, and its repeated or severe status can shift into chronic kidney disease or even end-stage renal disease. How and which events cause AKI still is controversial. In addition, no specific therapies have emerged that can attenuate AKI or expedite recovery. Some central mechanisms including tubular epithelial cells injury, endothelial injury, renal cell apoptosis, and necrosis signaling cascades, and inflammation have been reported in the pathophysiology of AKI. However, the timing of the activation of each pathway, their interactions, and the hierarchy of these pathways remain unknown. The main molecular mechanisms that might be complicated in this process are the mitochondrial impairment and alteration/shifting of cellular metabolites (e.g., acetyl-CoA and NAD⁺ /NADH) acting as cofactors to alter the activities of many enzymes, for instance, sirtuins. Moreover, alteration of mitochondrial structure over the fusion and fission mechanisms can regulate cellular signaling pathways by modifying the rate of reactive oxygen species generation and metabolic activities. The aim of this review is to better understand the underlying pathophysiological and molecular mechanisms of AKI. In addition, we predicted the main other molecular players in interaction with sirtuins as energy/stresses monitoring proteins for the development of future approaches in the treatment or prevention of ischemic AKI.