Prohibitin 2-mediated mitophagy attenuates renal tubular epithelial cells injury by regulating mitochondrial dysfunction and NLRP3 inflammasome activation

A novel mechanism of PHB2-mediated mitophagy participating in the development of Parkinson's disease

JOURNAL/nrgr/04.03/01300535-202408000-00037/figure1/v/2023-12-16T180322Z/r/image-tiff Endoplasmic reticulum stress and mitochondrial dysfunction play important roles in Parkinson's disease, but the regulatory mechanism remains elusive. Prohibitin-2 (PHB2) is a newly discovered autophagy receptor in the mitochondrial inner membrane, and its role in Parkinson's disease remains unclear. Protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) is a factor that regulates cell fate during endoplasmic reticulum stress. Parkin is regulated by PERK and is a target of the unfolded protein response. It is unclear whether PERK regulates PHB2-mediated mitophagy through Parkin. In this study, we established a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse model of Parkinson's disease. We used adeno-associated virus to knockdown PHB2 expression. Our results showed that loss of dopaminergic neurons and motor deficits were aggravated in the MPTP-induced mouse model of Parkinson's disease. Overexpression of PHB2 inhibited these abnormalities. We also established a 1-methyl-4-phenylpyridine (MPP+)-induced SH-SY5Y cell model of Parkinson's disease. We found that overexpression of Parkin increased co-localization of PHB2 and microtubule-associated protein 1 light chain 3, and promoted mitophagy. In addition, MPP+ regulated Parkin involvement in PHB2-mediated mitophagy through phosphorylation of PERK. These findings suggest that PHB2 participates in the development of Parkinson's disease by interacting with endoplasmic reticulum stress and Parkin.

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

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

The neuroprotective effect of Chinese herbal medicine for cerebral ischemia reperfusion injury through regulating mitophagy

The incidence of ischemic stroke has been increasing annually with an unfavorable prognosis. Cerebral ischemia reperfusion injury can exacerbate nerve damage. Effective mitochondrial quality control including mitochondrial fission, fusion and autophagy, is crucial for maintaining cellular homeostasis. Several studies have revealed the critical role of mitophagy in Cerebral ischemia reperfusion injury. Cerebral ischemia and hypoxia induce mitophagy, and mitophagy exhibits positive and negative effects in cerebral ischemia reperfusion injury. Studies have shown that Chinese herbal medicine can alleviate Cerebral ischemia reperfusion injury and serve as a neuroprotective agent by inhibiting or promoting mitophagy-mediated pathways. This review focuses on the mitochondrial dynamics and mitophagy-related pathways, as well as the role of mitophagy in ischemia reperfusion injury. Additionally, it discusses the therapeutic potential and benefits of Chinese herbal monomers and decoctions in the treatment of ischemic stroke.

Prohibitions in the meta-inflammatory response: a review

Prohibitins are the central regulatory element of cellular homeostasis, especially by modulating the response at different levels: Nucleus, mitochondria and membranes. Their localization and interaction with various proteins, homons, transcription and nuclear factors, and mtDNA indicate the globality and complexity of their pleiotropic properties, which remain to be investigated. A more detailed deciphering of cellular metabolism in relation to prohibitins under normal conditions and in various metabolic diseases will allow us to understand the precise role of prohibitins in the signaling cascades of PI3K/Akt, Raf/MAP/ERK, STAT3, p53, and others and to fathom their mutual influence. A valuable research perspective is to investigate the role of prohibitins in the molecular and cellular interactions between the two major players in the pathogenesis of obesity-adipocytes and macrophages - that form the basis of the meta-inflammatory response. Investigating the subtle intercellular communication and molecular cascades triggered in these cells will allow us to propose new therapeutic strategies to eliminate persistent inflammation, taking into account novel molecular genetic approaches to activate/inactivate prohibitins.

Anesthesia/surgery-induced learning and memory dysfunction by inhibiting mitophagy-mediated NLRP3 inflammasome inactivation in aged mice

Postoperative cognitive dysfunction (POCD) is a common postoperative complication, not only affects the quality of life of the elderly and increases the mortality rate, but also brings a greater burden to the family and society. Previous studies demonstrated that Nod-like receptor protein 3 (NLRP3) inflammasome participates in various inflammatory and neurodegenerative diseases. However, possible mitophagy mechanism in anesthesia/surgery-elicited NLRP3 inflammasome activation remains to be elucidated. Hence, this study clarified whether mitophagy dysfunction is related to anesthesia/surgery-elicited NLRP3 inflammasome activation. POCD model was established in aged C57BL/6 J mice by tibial fracture fixation under isoflurane anesthesia. Morris Water Maze (MWM) was used to evaluate learning and memory abilities. We found that in vitro experiments, lipopolysaccharide (LPS) significantly facilitated NLRP3 inflammasome activation and mitophagy inhibition in BV2 cells. Rapamycin restored mitophagy and improved mitochondrial function, and inhibited NLRP3 inflammasome activation induced by LPS. In vivo experiments, anesthesia and surgery caused upregulation of hippocampal NLRP3, caspase recruitment domain (ASC) and interleukin-1β (IL-1 β), and downregulation of microtubule-associated protein light chain 3II (LC3II) and Beclin1 in aged mice. Olaparib inhibited anesthesia/surgery-induced NLRP3, ASC, and IL-1β over-expression in the hippocampus, while upregulated the expression of LC3II and Beclin1. Furthermore, Olaparib improved cognitive impairment in older mice. These results revealed that mitophagy was involved in NLRP3 inflammasome-mediated anesthesia/surgery-induced cognitive deficits in aged mice. Overall, our results suggested that mitophagy was related in NLRP3 inflammasome-induced cognitive deficits after anesthesia and surgery in aged mice. Activating mitophagy may have clinical benefits in the prevention of cognitive impairment induced by anesthesia and surgery in elderly patients.

Prohibitin 2: A key regulator of cell function

The PHB2 gene is located on chromosome 12p13 and encodes prohibitin 2, a highly conserved protein of 37 kDa. PHB2 is a dimer with antiparallel coils, possessing a unique negatively charged region crucial for its mitochondrial molecular chaperone functions. Thus, PHB2 plays a significant role in cell life activities such as mitosis, mitochondrial autophagy, signal transduction, and cell death. This review discusses how PHB2 inhibits transcription factors or nuclear receptors to maintain normal cell functions; how PHB2 in the cytoplasm or membrane ensures normal cell mitosis and regulates cell differentiation; how PHB2 affects mitochondrial structure, function, and cell apoptosis through mitochondrial intimal integrity and mitochondrial autophagy; how PHB2 affects mitochondrial stress and inhibits cell apoptosis by regulating cytochrome c migration and other pathways; how PHB2 affects cell growth, proliferation, and metastasis through a mitochondrial independent mechanism; and how PHB2 could be applied in disease treatment. We provide a theoretical basis and an innovative perspective for a comprehensive understanding of the role and mechanism of PHB2 in cell function regulation.

Myeloid-derived grancalcin instigates obesity-induced insulin resistance and metabolic inflammation in male mice

The crosstalk between the bone and adipose tissue is known to orchestrate metabolic homeostasis, but the underlying mechanisms are largely unknown. Herein, we find that GCA + (grancalcin) immune cells accumulate in the bone marrow and release a considerable amount of GCA into circulation during obesity. Genetic deletion of Gca in myeloid cells attenuates metabolic dysfunction in obese male mice, whereas injection of recombinant GCA into male mice causes adipose tissue inflammation and insulin resistance. Mechanistically, we found that GCA binds to the Prohibitin-2 (PHB2) receptor on adipocytes and activates the innate and adaptive immune response of adipocytes via the PAK1-NF-κB signaling pathway, thus provoking the infiltration of inflammatory immune cells. Moreover, we show that GCA-neutralizing antibodies improve adipose tissue inflammation and insulin sensitivity in obese male mice. Together, these observations define a mechanism whereby bone marrow factor GCA initiates adipose tissue inflammation and insulin resistance, showing that GCA could be a potential target to treat metainflammation.

Prohibitin2/PHB2, Transcriptionally Regulated by GABPA, Inhibits Cell Growth via PRKN/Parkin-dependent Mitophagy in Endometriosis

Endometriosis (EMS) is a common benign gynecological disease affecting women of reproductive age. It is characterized by abnormal growth of endometrial tissue outside the uterine cavity, resulting in chronic pelvic pain and infertility. Endometrial physiological and pathological processes are intimately connected to autophagy. Mitophagy is an essential selective mode that protects cells from metabolic stress and hypoxia. Mitochondrial autophagy mediated by prohibitin 2 (PHB2) is dependent on the PRKN/Parkin pathway and is involved in numerous human diseases. Uncertainty remains as to whether mitophagy regulation by PHB2 contributes to the occurrence and progression of EMS. This study aims to investigate the mechanism underlying the role of PHB2 in EMS. This study detected the protein and mRNA expression of PHB2 in ectopic and normal endometrial tissues of ovarian EMS, in addition to ectopic endometrial cell line 12Z and endometrial stromal cell line KC02-44D for gene overexpression or knockdown. Cell function experiments and mitochondrial function experiments were conducted to investigate the role of PHB2 in the endometrium. Bioinformatic analysis and experiments were also used to investigate the upstream transcription factors that influence PHB2 expression. PHB2 was downregulated in ectopic endometrium, and PHB2 overexpression inhibited cell proliferation, migration, and invasion and promoted apoptosis. The upregulation of mitophagy markers, including Parkin and LC3II/I, and the downregulation of autophagy degradation markers P62 and TOMM20 in EMS suggest that PHB2 may contribute to cell proliferation, migration, invasion, and apoptosis via PRKN/Parkin-mediated mitophagy. Analysis and validation of bioinformatics data revealed that the transcription factor GABPA binds directly to the PHB2 promoter region and controls the transcriptional expression of PHB2. This study investigated the role of PHB2 in the onset of EMS. It inhibits EMS growth via PRKN/Parkin-mediated mitophagy, and GABPA controls the transcriptional disorder of PHB2. This study's findings suggest a novel method for investigating the clinical potential of PHB2 in EMS.

Mitochondrial F-ATP Synthase Co-Migrating Proteins and Ca2+-Dependent Formation of Large Channels

Monomers, dimers, and individual FOF1-ATP synthase subunits are, presumably, involved in the formation of the mitochondrial permeability transition pore (PTP), whose molecular structure, however, is still unknown. We hypothesized that, during the Ca2+-dependent assembly of a PTP complex, the F-ATP synthase (subunits) recruits mitochondrial proteins that do not interact or weakly interact with the F-ATP synthase under normal conditions. Therefore, we examined whether the PTP opening in mitochondria before the separation of supercomplexes via BN-PAGE will increase the channel stability and channel-forming capacity of isolated F-ATP synthase dimers and monomers in planar lipid membranes. Additionally, we studied the specific activity and the protein composition of F-ATP synthase dimers and monomers from rat liver and heart mitochondria before and after PTP opening. Against our expectations, preliminary PTP opening dramatically suppressed the high-conductance channel activity of F-ATP synthase dimers and monomers and decreased their specific "in-gel" activity. The decline in the channel-forming activity correlated with the reduced levels of as few as two proteins in the bands: methylmalonate-semialdehyde dehydrogenase and prohibitin 2. These results indicate that proteins co-migrating with the F-ATP synthase may be important players in PTP formation and stabilization.

Mitochondrial dysfunction and oxidative stress: Role in chronic kidney disease

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

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

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

Rutin Attenuates Oxidative Stress Via PHB2-Mediated Mitophagy in MPP+-Induced SH-SY5Y Cells

Oxidative stress plays a crucial role in the occurrence and development of Parkinson's disease (PD). Rutin, a natural botanical ingredient, has been shown to have antioxidant properties. Therefore, the aim of this study was to investigate the neuroprotective effects of rutin on PD and the underlying mechanisms. MPP⁺(1-methyl-4-phenylpyridinium ions)-treated SH-SY5Y cells were used as an in vitro model of PD. Human PHB2-shRNA lentiviral particles were transfected into SH-SY5Y cells to interfere with the expression of Prohibitin2 (PHB2). The oxidative damage of cells was analyzed by detecting intracellular reactive oxygen species (ROS), malondialdehyde (MDA), and mitochondrial membrane potential (MMP). Western blotting was used to detect the protein expression of antioxidant factors such as nuclear factor E2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1), NADPH quinone oxidoreductase-1 (NQO-1), and mitophagy factors PHB2, translocase of outer mitochondrial membrane 20 (TOM20), and LC3II/LC3I (microtubule-associated protein II light chain 3 (LC3II) to microtubule-associated protein I light chain 3 (LC3I)). In addition, we also examined the expression of PHB2 and LC3II/LC3I by immunofluorescence staining. MPP⁺ treatment significantly increased the generation of ROS and MDA and the level of MMP depolarization and decreased the protein expression of Nrf2, HO-1, NQO1, TOM20, PHB2, and LC3II/LC3I. In MPP⁺-treated SH-SY5Y cells, rutin significantly decreased the generation of ROS and MDA and the level of MMP depolarization and increased the protein expression of Nrf2, HO-1, NQO-1, TOM20, PHB2, and LC3II/LC3I. However, the protective role of rutin was inhibited in PHB2-silenced cells. Rutin attenuates oxidative damage which may be associated with PHB2-mediated mitophagy in MPP⁺-induced SH-SY5Y cells. Rutin might be used as a potential drug for the prevention and treatment of PD.

Atorvastatin reduces contrast media-induced pyroptosis of renal tubular epithelial cells by inhibiting the TLR4/MyD88/NF-κB signaling pathway

BACKGROUND

Contrast-induced acute kidney injury (CI-AKI) is the third most common cause of hospital-acquired renal failure. However, there is no effective treatment of CI-AKI, and its mechanism is unknown. Interestingly, atorvastatin has been reported to be effective in renal injury. Therefore, the aim of this study was to explore the effect and possible molecular mechanism of atorvastatin in CI-AKI.

METHODS

On the CI-AKI in vitro model, rat tubular epithelial cells (NRK-52E) were treated with 18 mg I/ml meglumine diatrizoate (MEG) and then pretreated with atorvastatin. pcDNA3.1-TLR4 treatment was performed to overexpress toll-like receptor 4 (TLR4) in NRK-52E cells. Cell Counting Kit-8 (CCK-8) and lactate dehydrogenase (LDH) kits were used to detect NRK-52E cell viability as well as LDH release in each group, respectively; qRT-PCR to determine mRNA expression of TLR4 in cells; western blot to detect protein expression levels of pyroptosis-related proteins (NLRP3, caspase-1, ASC, and GSDMD) and TLR4/MyD88/NF-κB signaling pathway-related proteins (TLR4, MyD88, NF-κBp65, and p-NF-κB p65) in cells.

RESULTS

MEG treatment significantly inhibited the viability of NRK-52E cells, increased pro-inflammatory factor levels and promoted pyroptosis, representing successful establishment of a rat tubular epithelial cell (NRK-52E) CI-AKI in vitro model. Notably, atorvastatin increased the activity of MEG-treated NRK-52E cells and alleviated cell injury in a concentration-dependent manner. In addition, atorvastatin significantly down-regulated the expression of TLR4 in MEG-treated NRK-52E cells. However, overexpression of TLR4 inhibited the effects of atorvastatin on increasing cell viability, alleviating cell injury, reducing pro-inflammatory factors (IL-1β, IL-6, and TNF-α) levels, and inhibiting apoptosis (by down-regulating the expression of NLRP3, caspase-1, ASC, and GSDMD). Furthermore, atorvastatin also inhibited the expression of TLR4/MyD88/NF-κB pathway-related proteins (TLR4, MyD88, and p-NF-κB p65).

CONCLUSION

Atorvastatin can attenuate CI-AKI through increasing the activity of MEG-treated renal tubular epithelial cells, relieving cell injury, as well as inhibiting pyroptosis and inflammation. More importantly, the mechanism was achieved by inhibiting the TLR4//MyD88/NF-κB signaling pathway.

Artemisinin Alleviates Cerebral Ischemia/Reperfusion-Induced Oxidative Damage via Regulating PHB2-Mediated Autophagy in the Human Neuroblastoma SH-SY5Y Cell Line

Oxidative stress plays a key role in cerebral ischemia/reperfusion injury. Artemisinin (ART) has antioxidative stress activity in addition to its powerful antimalarial effects. In this article, we investigated the effect of ART on OGD/R-induced oxidative stress injury and its underlying mechanisms. We used oxygen-glucose deprivation/reoxygenation (OGD/R) to establish an in vitro model of cerebral ischemia/reperfusion (I/R) injury. CCK-8 and lactate dehydrogenase (LDH) release were used to assess cellular damage. Measurement of reactive oxygen species (ROS), malondialdehyde (MDA), superoxide dismutase (SOD), glutathione (GSH), and mitochondrial membrane potential (MMP) estimates oxidative stress-induced damage and protection from ART effect. OGD/R treatment aggravated oxidative stress damage, whereas ART reversed the effects of OGD/R. Autophagy is closely related to oxidative stress; in order to confirm whether the antioxidative stress effect of ART is related to PHB2-mediated autophagy, we examined the protein expression of prohibitin 2 (PHB2), TOMM20, p62, and the conversion of microtubule-associated protein light chain 3I (LC3I) to LC3II and found that the protein expression of PHB2, TOMM20, p62, and LC3II/LC3I was significantly correlated with OGD/R treatment. The colocalization of PHB2 and LC3, TOMM20, and LC3 was reduced after OGD/R treatment, and ART reversed this change. After silencing PHB2, the protective effect of ART against OGD/R-induced oxidative stress injury was reduced, the protein expressions of PHB2, TOMM20 and LC3II/LC3I and the colocalization of PHB2 and LC3, TOMM20, and LC3 were decreased. We used chloroquine to block the lysosomal pathway and found that ART increased the conversion of LC3I to LC3II, silencing PHB2 which inhibited the conversion of LC3I to LC3II, and impaired mitophagy. Our findings showed that ART attenuated OGD/R-induced oxidative stress damage through PHB2-mediated mitophagy. To the current knowledge, our study is the first to demonstrate that ART attenuates OGD/R-induced oxidative stress injury through PHB2-mediated autophagy in the human neuroblastoma SH-SY5Y cell line, which provided new insights into the treatment of OGD/R injury.

Non-classical ferroptosis inhibition by a small molecule targeting PHB2

Ferroptosis is a new type of programmed cell death characterized by iron-dependent lipid peroxidation. Ferroptosis inhibition is thought as a promising therapeutic strategy for a variety of diseases. Currently, a majority of known ferroptosis inhibitors belong to either antioxidants or iron-chelators. Here we report a new ferroptosis inhibitor, termed YL-939, which is neither an antioxidant nor an iron-chelator. Chemical proteomics revealed the biological target of YL-939 to be prohibitin 2 (PHB2). Mechanistically, YL-939 binding to PHB2 promotes the expression of the iron storage protein ferritin, hence reduces the iron content, thereby decreasing the susceptibility to ferroptosis. We further showed that YL-939 could substantially ameliorate liver damage in a ferroptosis-related acute liver injury model by targeting the PHB2/ferritin/iron axis. Overall, we identified a non-classical ferroptosis inhibitor and revealed a new regulation mechanism of ferroptosis. These findings may present an attractive intervention strategy for ferroptosis-related diseases.

Augmenter of liver regeneration reduces mitochondria-derived ROS and NLRP3 inflammasome activation through PINK1/Parkin-mediated mitophagy in ischemia-reperfusion-induced renal tubular injury

Ischemia-reperfusion (IR) injury is one of the main causes of acute kidney disease (AKI). Several studies have shown that mitochondrial damage, which leads to increased production of reactive oxygen species (ROS), plays a vital role in the pathogenesis of IR-induced AKI. Increased ROS production can cause oxidative damage and activate the inflammasome in renal tubular cells, ultimately resulting in apoptosis or necrosis. Mitophagy is a type of selective autophagy that plays a protective role in AKI by regulating the quality of mitochondria and reducing the production of ROS. We previously reported that the augmenter of liver regeneration (ALR) exhibits antiapoptotic and antioxidant functions, although the precise mechanisms of action need to be studied further. In the current study, ALR was overexpressed and an in vitro model of IR injury was constructed. The overexpression of ALR reduced the production of mitochondria-derived ROS (mtROS), the activation of the NLRP3 inflammasome, and the rate of apoptosis. Moreover, this suppression of mtROS production and inflammasome activation was mediated through the PTEN-induced kinase 1 (PINK1)/Parkin pathway of mitophagy. These results suggest that ALR can alleviate IR-induced apoptosis via the PINK1/Parkin mitophagy pathway to reduce the production of mtROS and limit the activation of the NLRP3 inflammasome.

Nonreceptor Tyrosine Kinase c-Abl-Mediated PHB2 Phosphorylation Aggravates Mitophagy Disorder in Parkinson’s Disease Model

Mitophagy and oxidative stress play important roles in Parkinson's disease (PD). Dysregulated mitophagy exacerbates mitochondrial oxidative damage; however, the regulatory mechanism of mitophagy is unclear. Here, we provide a potential mechanistic link between c-Abl, a nonreceptor tyrosine kinase, and mitophagy in PD progression. We found that c-Abl activation reduces the interaction of prohibitin 2 (PHB2) and microtubule-associated protein 1 light chain 3 (LC3) and decreases the expressive level of antioxidative stress proteins, including nuclear factor erythroid 2-related factor 2 (Nrf2), NADPH quinone oxidoreductase-1 (NQO-1), and the antioxidant enzyme heme oxygenase-1 (HO-1) in 1-methyl-4-phenylpyridinium- (MPP⁺-) lesioned SH-SY5Y cells. Importantly, we found that MPP⁺ can increase the expression of phosphorylated proteins at the tyrosine site of PHB2 and the interaction of c-Abl with PHB2. We showed for the first time that PHB2 by changing tyrosine (Y) to aspartate (D) at site 121 resulted in impaired binding of PHB2 and LC3 in vitro. Moreover, silencing of PHB2 can decrease the interaction of PHB2 and LC3 and exacerbate the loss of dopaminergic neurons. We also found that STI 571, a c-Abl family kinase inhibitor, can decrease dopaminergic neuron damage and ameliorate MPTP-induced behavioral deficits in PD mice. Taken together, our findings highlight a novel molecular mechanism for aberrant PHB2 phosphorylation as an inhibitor of c-Abl activity and suggest that c-Abl and PHB2 are potential therapeutic targets for the treatment of individuals with PD. However, these results need to be further validated in PHB2 Y121D mice.

The molecular mechanisms and intervention strategies of mitophagy in cardiorenal syndrome

Cardiorenal syndrome (CRS) is defined as a disorder of the heart and kidney, in which acute or chronic injury of one organ may lead to acute or chronic dysfunction of the other. It is characterized by high morbidity and mortality, resulting in high economic costs and social burdens. However, there is currently no effective drug-based treatment. Emerging evidence implicates the involvement of mitophagy in the progression of CRS, including cardiovascular disease (CVD) and chronic kidney disease (CKD). In this review, we summarized the crucial roles and molecular mechanisms of mitophagy in the pathophysiology of CRS. It has been reported that mitophagy impairment contributes to a vicious loop between CKD and CVD, which ultimately accelerates the progression of CRS. Further, recent studies revealed that targeting mitophagy may serve as a promising therapeutic approach for CRS, including clinical drugs, stem cells and small molecule agents. Therefore, studies focusing on mitophagy may benefit for expanding innovative basic research, clinical trials, and therapeutic strategies for CRS.

The multifaceted role of kidney tubule mitochondrial dysfunction in kidney disease development

More than 800 million people suffer from kidney disease. Genetic studies and follow-up animal models and cell biological experiments indicate the key role of proximal tubule metabolism. Kidneys have one of the highest mitochondrial densities. Mitochondrial biogenesis, mitochondrial fusion and fission, and mitochondrial recycling, such as mitophagy are critical for proper mitochondrial function. Mitochondrial dysfunction can lead to an energetic crisis, orchestrate different types of cell death (apoptosis, necroptosis, pyroptosis, and ferroptosis), and influence cellular calcium levels and redox status. Collectively, mitochondrial defects in renal tubules contribute to epithelial atrophy, inflammation, or cell death, orchestrating kidney disease development.

Receptor-mediated mitophagy: An emerging therapeutic target in acute kidney injury

Acute kidney injury (AKI) is a global health concern associated with high morbidity and mortality. AKI etiology is linked to mitochondrial dysfunction along with oxidative stress and inflammation. The defective mitochondria are removed via mitophagy for maintaining cellular integrity. The main regulatory mechanisms of mitophagy in response to different stressors are Phosphatase and tensin homolog-induced kinase 1 (PINK1)/Parkin and receptor-mediated. Receptors like B-cell lymphoma 2/adenovirus E1B-interacting protein (BNIP3), BNIP3L, prohibitin2, tacrolimus (FK506)-binding protein8 (FKBP8), autophagy-beclin1-regulator1 (AMBRA1) and SMAD-ubiquitination regulatory factor1 (SMURF1), etc. participate in receptor-mediated mitophagy. In recent studies, receptor-mediated mitophagy showed protective effects in AKI. This review summarizes the evidence related to mitophagy in AKI and outlines the significance of receptor-mediated mitophagy modulation as a possible therapeutic approach in AKI.

Prohibitins: A Key Link between Mitochondria and Nervous System Diseases

Prohibitins (PHBs) are conserved proteins in eukaryotic cells, which are mainly located in the inner mitochondrial membrane (IMM), cell nucleus, and cell membrane. PHBs play crucial roles in various cellular functions, including the cell cycle regulation, tumor suppression, immunoglobulin M receptor binding, and aging. In addition, recent in vitro and in vivo studies have revealed that PHBs are important in nervous system diseases. PHBs can prevent apoptosis, inflammation, mitochondrial dysfunction, and autophagy in neurological disorders through different molecules and pathways, such as OPA-1, PINK1/Parkin, IL6/STAT3, Tau, NO, LC3, and TDP43. Therefore, PHBs show great promise in the protection of neurological disorders. This review summarizes the relevant studies on the relationship between PHBs and neurological disorders and provides an update on the molecular mechanisms of PHBs in nervous system diseases.

Leonurine attenuates cisplatin nephrotoxicity by suppressing the NLRP3 inflammasome, mitochondrial dysfunction, and endoplasmic reticulum stress

PURPOSE

Cisplatin has been widely accepted as an effective chemotherapy drug with various side effects, including nephrotoxicity. The mechanisms of cisplatin-induced acute kidney injury (AKI) are complex, and there are limited renoprotective approaches. Leonurine is the main active compound of a Chinese herb and has recently been reported to have a protective effect on the kidneys. This study aimed to verify the renoprotective effect of leonurine in attenuating cisplatin-induced AKI and explore the potential associated mechanisms.

METHODS

C57BL/6 mice were divided into four groups (Sham, Cisplatin, Leonurine, and Cisplatin + Leonurine). Mice in the leonurine-treated groups were pretreated with a daily intraperitoneal injection of 25 mg/kg leonurine. AKI was induced by injecting cisplatin once intraperitoneally at 20 mg/kg body weight. Mice were killed on day 5. Kidney injury was assessed using a serum biochemical and histological assay. Apoptosis was evaluated using a terminal deoxyribonucleotide transferase-mediated dUTP nick-end labeling (TUNEL) staining assay and Western blot. Antioxidant enzymes were detected using commercial kits. The improvement in inflammasome activation, mitochondrial dysfunction, and endoplasmic reticulum stress (ERS) were assessed by polymerase chain reaction (PCR) and Western blot, respectively.

RESULTS

Leonurine treatment improved kidney function by preventing renal tubular injury and apoptosis. Expression of nucleotide-binding leucine-rich repeat and pyrin domain containing protein 3 (NLRP3) inflammasome components and inflammatory cytokines, mitochondrial dysfunction, and ERS were all alleviated by leonurine.

CONCLUSION

The results indicate that leonurine plays a protective role in cisplatin-induced AKI and may represent an effective multi-targeted intervention strategy.

PGC-1α inhibits the NLRP3 inflammasome via preserving mitochondrial viability to protect kidney fibrosis

The NLRP3 inflammasome is activated by mitochondrial damage and contributes to kidney fibrosis. However, it is unknown whether PGC-1α, a key mitochondrial biogenesis regulator, modulates NLRP3 inflammasome in kidney injury. Primary renal tubular epithelial cells (RTECs) were isolated from C57BL/6 mice. The NLRP3 inflammasome, mitochondrial dynamics and morphology, oxidative stress, and cell injury markers were examined in RTECs treated by TGF-β1 with or without Ppargc1a plasmid, PGC-1α activator (metformin), and siPGC-1α. In vivo, adenine-fed and unilateral ureteral obstruction (UUO) mice were treated with metformin. In vitro, TGF-β1 treatment to RTECs suppressed the expressions of PGC-1α and mitochondrial dynamic-related genes. The NLRP3 inflammasome was also activated and the expression of fibrotic and cell injury markers was increased. PGC-1α induction with the plasmid and metformin improved mitochondrial dynamics and morphology and attenuated the NLRP3 inflammasome and cell injury. The opposite changes were observed by siPGC-1α. The oxidative stress levels, which are inducers of the NLRP3 inflammasome, were increased and the expression of TNFAIP3, a negative regulator of NLRP3 inflammasome regulated by PGC-1α, was decreased by TGF-β1 and siPGC-1α. However, PGC-1α restoration reversed these alterations. In vivo, adenine-fed and UUO mice models showed suppression of PGC-1α and TNFAIP3 and dysregulated mitochondrial dynamics. Moreover, the activation of oxidative stress and NLRP3 inflammasome, and kidney fibrosis were increased in these mice. However, these changes were significantly reversed by metformin. This study demonstrated that kidney injury was ameliorated by PGC-1α-induced inactivation of the NLRP3 inflammasome via modulation of mitochondrial viability and dynamics.

Autophagy in Cisplatin Nephrotoxicity during Cancer Therapy

Cisplatin is a widely used chemotherapeutic agent but its clinical use is often limited by nephrotoxicity. Autophagy is a lysosomal degradation pathway that removes protein aggregates and damaged or dysfunctional cellular organelles for maintaining cell homeostasis. Upon cisplatin exposure, autophagy is rapidly activated in renal tubule cells to protect against acute cisplatin nephrotoxicity. Mechanistically, the protective effect is mainly related to the clearance of damaged mitochondria via mitophagy. The role and regulation of autophagy in chronic kidney problems after cisplatin treatment are currently unclear, despite the significance of research in this area. In cancers, autophagy may prevent tumorigenesis, but autophagy may reduce the efficacy of chemotherapy by protecting cancer cells. Future research should focus on developing drugs that enhance the anti-tumor effects of cisplatin while protecting kidneys during cisplatin chemotherapy.

Mechanism of Mitophagy and Its Role in Sepsis Induced Organ Dysfunction: A Review

Autophagy, an evolutionarily conserved process, plays an important role in maintaining cellular homeostasis under physiological and pathophysiological conditions. It is widely believed that mitochondria influence the development of disease by regulating cellular metabolism. When challenged by different stimuli, mitochondria may experience morphological disorders and functional abnormalities, leading to a selective form of autophagy-mitophagy, which can clear damaged mitochondria to promote mitochondrial quality control. Sepsis is a complex global problem with multiple organ dysfunction, often accompanied by manifold mitochondrial damage. Recent studies have shown that autophagy can regulate both innate and acquired immune processes to protect against organ dysfunction in sepsis. Sepsis-induced mitochondrial dysfunction may play a pathophysiological role in the initiation and progression of sepsis-induced organ failure. Mitophagy is reported to be beneficial for sepsis by eliminating disabled mitochondria and maintaining homeostasis to protect against organ failure. In this review, we summarize the recent findings and mechanisms of mitophagy and its involvement in septic organ dysfunction as a potential therapeutic target.

Mitochondrial dysfunction as a driver of NLRP3 inflammasome activation and its modulation through mitophagy for potential therapeutics

The NLR family pyrin domain containing 3 (NLRP3) inflammasome is responsible for the sensation of various pathogenic and non-pathogenic damage signals and has a vital role in neuroinflammation and neural diseases. Various stimuli, such as microbial infection, misfolded protein aggregates, and aberrant deposition of proteins can induce NLRP3 inflammasome in neural cells. Once triggered, the NLRP3 inflammasome leads to the activation of caspase-1, which in turn activates inflammatory cytokines, such as interleukin-1β and interleukin -18, and induces pyroptotic cell death. Mitochondria are critically involved in diverse cellular processes and are involved in regulating cellular redox status, calcium levels, inflammasome activation, and cell death. Mitochondrial dysfunction and subsequent accumulation of mitochondrial reactive oxygen species, mitochondrial deoxyribonucleic acid, and other mitochondria-associated proteins and lipids play vital roles in the instigation of the NLRP3 inflammasome. In addition, the processes of mitochondrial dynamics, such as fission and fusion, are essential in the maintenance of mitochondrial integrity and their imbalance also promotes NLRP3 inflammasome activation. In this connection, mitophagy-mediated maintenance of mitochondrial homeostasis restricts NLRP3 inflammasome hyperactivation and its consequences in various neurological disorders. Hence, mitophagy can be exploited as a potential strategy to target damaged mitochondria induced NLRP3 inflammasome activation and its lethal consequences. Therefore, the identification of novel mitophagy modulators has promising therapeutic potential for NLRP3 inflammasome-associated neuronal diseases.

Receptor-mediated mitophagy regulates EPO production and protects against renal anemia

Erythropoietin (EPO) drives erythropoiesis and is secreted mainly by the kidney upon hypoxic or anemic stress. The paucity of EPO production in renal EPO-producing cells (REPs) causes renal anemia, one of the most common complications of chronic nephropathies. Although mitochondrial dysfunction is commonly observed in several renal and hematopoietic disorders, the mechanism by which mitochondrial quality control impacts renal anemia remains elusive. In this study, we showed that FUNDC1, a mitophagy receptor, plays a critical role in EPO-driven erythropoiesis induced by stresses. Mechanistically, EPO production is impaired in REPs in Fundc1^-/- mice upon stresses, and the impairment is caused by the accumulation of damaged mitochondria, which consequently leads to the elevation of the reactive oxygen species (ROS) level and triggers inflammatory responses by up-regulating proinflammatory cytokines. These inflammatory factors promote the myofibroblastic transformation of REPs, resulting in the reduction of EPO production. We therefore provide a link between aberrant mitophagy and deficient EPO generation in renal anemia. Our results also suggest that the mitochondrial quality control safeguards REPs under stresses, which may serve as a potential therapeutic strategy for the treatment of renal anemia.

Activation of the angiotensin II receptor promotes autophagy in renal proximal tubular cells and affords protection from ischemia/reperfusion injury

Roles of the renin-angiotensin system in autophagy and ischemia/reperfusion (I/R) injury in the kidney have not been fully characterized. Here we examined the hypothesis that modest activation of the angiotensin II (Ang II) receptor upregulates autophagy and increases renal tolerance to I/R injury. Sprague-Dawley rats were assigned to treatment with a vehicle or a non-pressor dose of Ang II (200 ng/kg/min) for 72 h before 30-min renal I/R. LC3-immunohistochemistry showed that Ang II treatment increased autophagosomes in proximal tubular cells by 2.7 fold. In Ang II-pretreated rats, autophagosomes were increased by 2.5 fold compared to those in vehicle-treated rats at 4 h after I/R, when phosphorylation of Akt and S6 was suppressed and ULK1-Ser555 phosphorylation was increased. Serum creatinine and urea nitrogen levels, incidence of oliguria, and histological score of tubular necrosis at 24 h after I/R were attenuated by Ang II-pretreatment. In NRK-52E cells, Ang II induced LC3-II upregulation, which was inhibited by losartan but not by A779. The results indicate that a non-pressor dose of Ang-II promotes autophagy via ULK1-mediated signaling in renal tubular cells and attenuates renal I/R injury. The AT1 receptor, but not the Mas receptor, contributes to Ang-II-induced autophagy and presumably also to the renoprotection.

Arsenic induces hepatic insulin resistance via mtROS-NLRP3 inflammasome pathway

Hepatic insulin resistance (IR) is the key event for arsenic-caused type 2 diabetes (T2D). However, the unequivocal mechanism of arsenic-induced hepatic IR remains unclear. The current study determined the role of NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome activation in arsenic-induced IR and revealed the underlying mechanism. Three-month NaAsO₂ gavage led to glucose intolerance and insulin insensitivity, impaired hepatic insulin signaling. Additionally, NaAsO₂ upregulated the level of oxidized mitochondrial DNA (ox-mtDNA) and mitophagy, thereby activating the NLRP3 inflammasome in SD rat liver. In vitro, we demonstrated that NaAsO₂-induced IR depended upon the NLRP3 inflammasome activation. Moreover, inhibiting mitophagy mitigated the NLRP3 inflammasome activation and impaired insulin signaling induced by NaAsO₂. Furthermore, mitochondrial reactive oxygen species (mtROS) scavenger alleviated the upregulated ox-mtDNA and mitophagy, thereby inhibiting the NLRP3 inflammasome activation, and improving insulin signaling. Taken together, these data demonstrated that mtROS-triggered ox-mtDNA, mitophagy, and the activation of NLRP3 inflammasome was involved in arsenic-induced hepatic IR.

The mitochondrial-targeted peptide SBT-20 ameliorates inflammation and oxidative stress in chronic renal failure

Chronic renal failure (CRF) is the final outcome of the development of chronic kidney disease with different causes. Although CRF is a common clinical disease, its pathogenesis remains to be improved. SBT-20 belongs to a class of cell-permeable peptides that target the inner mitochondrial membrane, reduce reactive oxygen species (ROS), normalize electron transport chain function, and ATP generation. Our experiment was to evaluate whether SBT-20 affected the oxidative stress and inflammatory process of CRF. The levels of ROS production, mitochondrial membrane potential, NF- κB-p65, TNF-α, Drp1, and mfn2 were measured before and after SBT-20 treatment. We observed that SBT-20 treatment inhibited H2O2-induced mitochondrial ROS production. SBT-20 could also restore the mitochondrial membrane potential and reduce the elevated levels of NF-κB-p65 and TNF-α in HK-2 cells. In vivo, the renal function of CRF mice recovered after treating with SBT-20, the levels of necrotic cells and inflammation decreased, and the morphology of mitochondria recovered. The results showed that SBT-20 had a protective effect on CRF by reducing oxidative stress, inflammation progression via down-regulating of NF-κB-p65, TNF-α, and Drp1 and upregulating of Mfn2. These data support SBT-20 could be used as a potential preparation for CRF.

Mitophagy Receptors and Mediators: Therapeutic Targets in the Management of Cardiovascular Ageing

Mitophagy serves as a cardinal regulator in the maintenance of mitochondrial integrity, function, and cardiovascular homeostasis, through the fine control and governance of cellular metabolism, ATP production, redox balance, and mitochondrial quality and quantity control. As a unique form of selective autophagy, mitophagy specifically recognizes and engulfs long-lived or damaged (depolarized) mitochondria through formation of the double-membraned intracellular organelles - mitophagosomes, ultimately resulting in lysosomal degradation. Levels of mitophagy are reported to be altered in pathological settings including cardiovascular diseases and biological ageing although the precise nature of mitophagy change in ageing and ageing-associated cardiovascular deterioration remains poorly defined. Ample clinical and experimental evidence has depicted a convincing tie between cardiovascular ageing and altered mitophagy. In particular, ageing perturbs multiple enigmatic various signal machineries governing mitophagy, mitochondrial quality, and mitochondrial function, contributing to ageing-elicited anomalies in the cardiovascular system. This review will update novel regulatory mechanisms of mitophagy especially in the perspective of advanced ageing, and discuss how mitophagy dysregulation may be linked to cardiovascular abnormalities in ageing. We hope to pave the way for development of new therapeutic strategies against the growing health and socieconomical issue of cardiovascular ageing through targeting mitophagy.

Autophagy in kidney homeostasis and disease

Autophagy is a conserved lysosomal pathway for the degradation of cytoplasmic components. Basal autophagy in kidney cells is essential for the maintenance of kidney homeostasis, structure and function. Under stress conditions, autophagy is altered as part of the adaptive response of kidney cells, in a process that is tightly regulated by signalling pathways that can modulate the cellular autophagic flux - mammalian target of rapamycin, AMP-activated protein kinase and sirtuins are key regulators of autophagy. Dysregulated autophagy contributes to the pathogenesis of acute kidney injury, to incomplete kidney repair after acute kidney injury and to chronic kidney disease of varied aetiologies, including diabetic kidney disease, focal segmental glomerulosclerosis and polycystic kidney disease. Autophagy also has a role in kidney ageing. However, questions remain about whether autophagy has a protective or a pathological role in kidney fibrosis, and about the precise mechanisms and signalling pathways underlying the autophagy response in different types of kidney cells and across the spectrum of kidney diseases. Further research is needed to gain insights into the regulation of autophagy in the kidneys and to enable the discovery of pathway-specific and kidney-selective therapies for kidney diseases and anti-ageing strategies.

Prohibitin 2 is Involved in Parkin-Mediated Mitophagy in Urothelial Cells of Cattle Infected with Bovine Papillomavirus

Prohibitin 2 (PHB2), an inner mitochondrial membrane (IMM) protein, has recently been identified as a novel receptor involved in parkin-mediated mitophagy. In the field of veterinary medicine, the role of PHB2 in parkin-mediated mitophagy was described, for the first time, in urothelial cells of cattle, naturally infected with bovine papillomavirus (BPV). The BPV2 and BPV13 E5 oncoprotein, responsible for abortive infections in urothelial cells, was detected by RT-PCR. Severe ultrastructural abnormalities of the inner mitochondrial membrane were detected using transmission electron microscopy. PHB2 formed a functional complex with PHB1. PHB2 was significantly overexpressed in mitochondrial fractions from urothelial mucosa samples taken from cattle harbouring BPV infection. PHB2 overexpression could be attributed to mitochondrial dysfunction, as its expression levels in the cytosolic, microsomal, and nuclear fractions were seen to be unmodified. Immunoprecipitation studies revealed the interaction between PHB2 and phosphorylated forms of both PINK1 and parkin. Furthermore, PHB2 interacted with LC3-II, a marker of autophagosomal membranes and autophagy receptors, such as p62 and optineurin. PHB2 was shown to interact with transcription factor EB (TFEB), which is activated following parkin-mediated mitophagy, and embryonic stem cell-expressed Ras (ERAS), a constitutive protein coded by ERas. Western blot analysis revealed a significant overexpression of unphosphorylated TFEB in mitochondrial and nuclear fractions from urothelial mucosa samples from cattle suffering from BPV infection. Finally, PHB2 interacted with ERAS, believed to be involved in mitophagosome maturation. Taken together, the molecular and ultrastructural findings of this study suggested that BPV infection is responsible for parkin-dependent mitophagy, in the pathway of which PHB2 plays a crucial role.

Inflammasome and Mitophagy Connection in Health and Disease

The inflammasome is a large intracellular protein complex that activates inflammatory caspase-1 and induces the maturation of interleukin (IL)-1β and IL-18. Mitophagy plays an essential role in the maintenance of mitochondrial homeostasis during stress. Previous studies have indicated compelling evidence of the crosstalk between inflammasome and mitophagy. Mitophagy regulation of the inflammasome, or vice versa, is crucial for various biological functions, such as controlling inflammation and metabolism, immune and anti-tumor responses, and pyroptotic cell death. Uncontrolled regulation of the inflammasome often results in pathological inflammation and pyroptosis, and causes a variety of human diseases, including metabolic and inflammatory diseases, infection, and cancer. Here, we discuss how improved understanding of the interactions between inflammasome and mitophagy can lead to novel therapies against various disease pathologies, and how the inflammasome-mitophagy connection is currently being targeted pharmacologically by diverse agents and small molecules. A deeper understanding of the inflammasome-mitophagy connection will provide new insights into human health and disease through the balance between mitochondrial clearance and pathology.

Drp1-regulated PARK2-dependent mitophagy protects against renal fibrosis in unilateral ureteral obstruction

Mitophagy is a principle mechanism to degrade damaged mitochondria through PARK2-dependent or PARK2-independent pathway. Mitophagy has been identified to play an important role in acute kidney disease, whereas its role in renal fibrosis remains ill-defined. We sought to investigate the involvement and regulation of mitophagy in renal tubular epithelial cell(RTEC) injury and renal fibrosis after unilateral ureteral obstruction(UUO). Mitochondrial damageand mitochondrial reactive oxygen species (ROS) production was increased in kidney after obstruction of the left ureter. Mitophagy was increased in kidneys following UUO and HK-2 cells under hypoxia exposure, assessed by electron microscopy of mitophagosome, colocalization of MitotrackerRed-stained mitochondria and LC3 staining. The upregulation of PINK1, PARK2, and LC3 II in mitochondrial fraction was observed in the obstructed kidney and hypoxia-exposed HK-2 cells. Pink1 or Park2 gene deletion markedly increased mtROS production, mitochondrial damage, TGFβ1 expression in RTEC, and renal fibrosis in UUO. Mitochondrial recruitment of Drp1 was also induced after UUO. The Drp1 inhibitor, Mdivi-1, decreased mitochondrial PINK1, PARK2 and LC3II level, increased mtROS production both in vivo and in vitro, activated TGFβ1-Smad2/3 signaling in HK-2 cells under hypoxia and worsened renal fibrosis following UUO. The upregulation of TGFβ1 signaling in hypoxia-treated HK-2 cells due to PINK1 or PARK2 silencing, or worsened renal fibrosis after UUO due to Pink1-or Park2-KO mice was rescued by mitoTEMPO, a mitochondria-targeted antioxidant. The findings of this study suggest that Drp1-regulated PARK2-dependent mitophagy plays a critical role in hypoxia-induced renal tubular epithelial cell injury and renal fibrosis in UUO.

Role of Parkin-mediated mitophagy in the protective effect of polydatin in sepsis-induced acute kidney injury

BACKGROUND

We have reported that polydatin (PD) alleviates mitochondrial dysfunction in rat models of sepsis-induced acute kidney injury (SI-AKI), but the mechanism is not well understood. Here, we investigated the role of Parkin-mediated mitophagy in the protective effects of PD in SI-AKI in mice.

METHODS

Sepsis was induced in the mice by caecal ligation and puncture. Mitophagy was determined by mitochondrial mass. NLRP3 inflammasome activation was determined by NLRP3, ASC and caspase-1. Mitophagy was blocked by treatment with mitochondrial division inhibitor-1 and Parkin knockout.

KEY RESULTS

PD treatment increased the sepsis-induced loss of mitochondrial mass, indicating the upregulation of mitophagy. Furthermore, PD treatment mediated Parkin translocation from the cytoplasm to the mitochondria. This suggests that Parkin-mediated mitophagy is an underlying mechanism. This was confirmed by the suppression of PD-induced mitophagy in Parkin-/- mice and in mice that were treated with a mitophagy inhibitor. PD-induced Parkin translocation and mitophagy were blocked by inhibiting SIRT1; thus, activation of SIRT1 might be an important molecular mechanism that is triggered by PD. Additionally, PD treatment protected against sepsis-induced kidney injury. These effects were blocked by inhibition of Parkin-dependent mitophagy. Furthermore, PD also protected against mitochondrial dysfunction and mitochondria-dependent apoptosis, and the effect was blocked when Parkin-dependent mitophagy was inhibited. Finally, PD suppressed NLRP3 inflammasome activation that was also dependent on Parkin-mediated mitophagy.

CONCLUSIONS

These findings indicate that Parkin-mediated mitophagy is important for the protective effect of PD in SI-AKI, and the underlying mechanisms include the inhibition of mitochondrial dysfunction and NLRP3 inflammasome activation.

Bax inhibitor 1 preserves mitochondrial homeostasis in acute kidney injury through promoting mitochondrial retention of PHB2

Bax inhibitor-1 (BI1) conveys anti-apoptotic signals for mitochondria while prohibitin 2 (PHB2) is implicated in sustaining mitochondrial morphology and function. However, their regulatory roles in acute kidney injury (AKI) are largely unknown. Methods: In human patients with AKI, levels of BI1 in urine and plasma were determined using ELISA. An experimental model of AKI was established using ATP depletion-mediated metabolic stress and ischemia-reperfusion injury (IRI) in primary tubule cells and BI1 transgenic mice, respectively. Western blots, ELISA, qPCR, immunofluorescence, RNA silencing, and domain deletion assay were employed to evaluate the roles of BI1 and PHB2 in the preservation of mitochondrial integrity. Results: Levels of BI1 in urine and plasma were decreased in patients with AKI and its expression correlated inversely with renal function. However, reconstitution of BI1 in a murine AKI model was capable of alleviating renal failure, inflammation and tubular death. Further molecular scrutiny revealed that BI1 preserved mitochondrial genetic integrity, reduced mitochondrial oxidative stress, promoted mitochondrial respiration, inhibited excessive mitochondrial fission, improved mitophagy and suppressed mitochondrial apoptosis. Intriguingly, levels of the mitochondria-localized PHB2 were sustained by BI1 and knockdown of PHB2 abolished the mitochondrial- and renal- protective properties of BI1. Furthermore, BI1 promoted PHB2 retention within mitochondria through direct interaction with cytoplasmic PHB2 to facilitate its mitochondrial import. This was confirmed by the observation that the C-terminus of BI1 and the PHB domain of PHB2 were required for the BI1-PHB2 cross-linking. Conclusion: Our data have unveiled an essential role of BI1 as a master regulator of renal tubule function through sustaining mitochondrial localization of PHB2, revealing novel therapeutic promises against AKI.

Disturbance of mitochondrial dynamics and mitophagy in sepsis-induced acute kidney injury

AIMS

The renal tubule cells require a large number of mitochondria to supply ATP due to their high-energy demand during reabsorption and secretion against chemical gradients and result in mitochondria susceptible to disorder and injury during stress conditions. Injured mitochondria are eventually degraded by mitophagy, and disturbances in mitophagy are associated with the pathogenesis of acute kidney injury (AKI) such as diabetic nephropathy and glomerulosclerosis. However, whether a disturbance in mitophagy has occurred and the role it plays in (SAKI) is still unclear. Therefore, the aim of this study was to investigate the key features of mitophagy and mitochondrial dynamics in sepsis-induced acute kidney injury (SAKI).

MAIN METHODS

In this study, a murine septic AKI model induced by cecal ligation and puncture (CLP) was built; mitophagy and mitochondrial dynamics were measured in mice kidney in different time point.

KEY FINDINGS

The results showed that mitochondrial dynamics were characterized by fission/fusion aberrant, however more inclined to fission, and mitochondrial associated apoptosis was elevated over-time during SAKI. Furthermore, mitophagy was impaired in the later phase of SAKI, although elevated in early stage of SAKI. The results indicate that the underlying mechanisms of impaired mitophagy may associate with the cleavage of Parkin via caspases activated by NLRP3, at least partly.

SIGNIFICANCE

It is conceivable that this selective autophagic process and quality control machinery was impaired, leading to the accumulation of damaged mitochondria, oxidative stress, and cell death. Therefore, a targeted approach, by enhancing mitophagy during SAKI, may be a promising therapeutic strategy.

PINK1-parkin pathway of mitophagy protects against contrast-induced acute kidney injury via decreasing mitochondrial ROS and NLRP3 inflammasome activation

Contrast-induced acute kidney injury (CI-AKI) occurs in more than 30% of patients after intravenous iodinated contrast media and causes serious complications, including renal failure and mortality. Recent research has demonstrated that routine antioxidant and alkaline therapy failed to show benefits in CI-AKI patients with high risk for renal complications. Mitophagy is a mechanism of selective autophagy, which controls mitochondrial quality and mitochondrial reactive oxygen species (ROS) through degradation of damaged mitochondria. The role of mitophagy and its regulation of apoptosis in CI-AKI are poorly understood. In this study, we demonstrated that mitophagy was induced in renal tubular epithelial cells (RTECs) during CI-AKI, both in vivo and in vitro. Meanwhile, contrast media-induced mitophagy was abolished when silencing PINK1 or PARK2 (Parkin), indicating a dominant role of the PINK1-Parkin pathway in mitophagy. Moreover, mitochondrial damage, mitochondrial ROS, RTEC apoptosis, and renal injury under contrast exposure were more severe in PINK1- or PARK2-deficient cells and mice than in wild-type groups. Functionally, PINK1-Parkin-mediated mitophagy prevented RTEC apoptosis and tissue damage in CI-AKI through reducing mitochondrial ROS and subsequent NLRP3 inflammasome activation. These results demonstrated that PINK1-Parkin-mediated mitophagy played a protective role in CI-AKI by reducing NLRP3 inflammasome activation.