Mitochondrial composition and function under the control of hypoxia

Sirtuin‑1 protects hair follicle stem cells from TNFα-mediated inflammatory stress via activating the MAPK-ERK-Mfn2 pathway

OBJECTIVE

Stem cell transplantation is a promising tool to treat burn injuries. However, the inflammatory microenvironment in damaged skin limits the efficiency of stem cell-based therapy via poorly understood mechanisms. The aim of our study is to explore the contribution and mechanism of Sirtuin-1 (Sirt1) in TNFα-mediated inflammatory stress in hair follicle stem cells (HFSCs).

METHODS

Cellular viability was determined using the MTT assay, TUNEL staining, western blot analysis and LDH release assay. Adenovirus-loaded Sirt1 was transduced into HFSCs to overexpress Sirt1 in the presence of TNFα. Mitochondrial function was determined using JC-1 staining, mitochondrial ROS staining, immunofluorescence staining and western blotting.

RESULTS

Sirt1 was downregulated in response to the TNFα treatment. Additionally, TNFα stress reduced the viability, mobility and proliferation of HFSCs, and these effects were reversed by the overexpression of Sirt1. At the molecular level, Sirt1 overexpression attenuated TNFα-mediated mitochondrial damage, as evidenced by increased mitochondrial energy metabolism, decreased mitochondrial ROS generation, stabilized mitochondrial potential and blockage of the mitochondrial apoptotic pathway. Furthermore, Sirt1 modulated mitochondrial homeostasis by activating the MAPK-ERK-Mfn2 axis; inhibition of this pathway abrogated the protective effects of Sirt1 on HFSC survival, migration and proliferation.

SIGNIFICANCE

Based on our results, the inflammatory stress-mediated HFSC injury may be associated with a decrease in Sirt1 expression and subsequent mitochondrial dysfunction. Accordingly, strategies designed to enhance Sirt1 expression would be an effective approach to enhance the survival of HFSCs in the inflammatory microenvironment.

Particulate matter exposure increases JC polyomavirus replication in the human host

BACKGROUND

Human polyomaviruses (HPyVs) asymptomatically infect the human population during childhood and establish latency in the host. Viral reactivation and urinary excretion can occur when the immune system is impaired. Exposure to particulate air pollution, including the PM₁₀/PM_2.5 components, is a public health problem and has been linked to several disorders. Studies assessing the relationship between PM₁₀/PM_2.5 exposure and viral replication are lacking.

OBJECTIVES

To investigate the relationship between HPyVs viruria and PM₁₀/PM_2.5 exposures.

METHODS

Individual environmental exposure was assessed in 50 healthy adult volunteers using a chemical transport model (CTM) with a municipality resolution for daily PM₁₀ and monitoring stations data for daily PM_2.5 exposures. For each subject, a urine sample was collected, and HPyVs (JCPyV, BKPyV, MCPyV, HPyV6, HPyV7 and HPyV9) loads were determined. Zero-inflated negative binomial (ZINB) regression was used to model the count data, as it contained excessive zeros. Covariates were chosen by stepwise selection.

RESULTS

HPyVs DNA was detected in 54% (median:87.6*10⁵ copies/ml) of the urine samples. JCPyV was the prevalent (48%, (median viral load:126*10⁵ copies/ml). Considering the load of the most frequently measured HPyVs, JCPyV, in the count-part of the ZINB model, every unitary in PM measured 2 days before urine collection (PM Day -2) was associated with an increase in JCPyV load (PM₁₀: +4.0%, p-value = 0.002; PM_2.5: +3.6%, p-value = 0.005). In the zero-part, the significant predictor was the PM₁₀ measured 5 days before urine collection (+3%, p-value = 0.03).

CONCLUSIONS

The environmental levels of PM₁₀/PM_2.5 increase the JCPyV viruria. Our findings emphasize the need for studies assessing the influence of air pollution exposure on the risk of viral reactivation.

Markers of Mitochondrial Metabolism in Tumor Hypoxia, Systemic Inflammation, and Adverse Outcome of Rectal Cancer

Tumor hypoxia contributes to therapy resistance and metastatic progression of locally advanced rectal cancer (LARC). We postulated that the tumor mitochondrial metabolism, manifested by reactive oxygen species (ROS) and mitochondrial DNA (mtDNA) damage, reflects how hypoxic conditions connect to cancer-induced systemic inflammation and poor outcome. Levels of ROS and mtDNA damage were analyzed in three colorectal cancer (CRC) cell lines cultured for 24 hours under normoxia (21% O₂) or hypoxia (0.2% O₂) and serum sampled at the time of diagnosis from 35 LARC patients participating in a prospective therapy study. Compared with normoxia, ROS were significantly repressed and mtDNA damage was significantly enhanced in the hypoxic CRC cell lines; hence, a low ratio of ROS to mtDNA damage was an indicator of hypoxic conditions. In the LARC patients, low serum ROS were associated with elevated levels of circulating carcinoembryonic antigen and tumor choline concentration, both indicative of unfavorable biology, as well as adverse progression-free and overall survival. A low ratio of ROS to mtDNA damage in serum was associated with poor local tumor response to the neoadjuvant treatment and, of note, elevated systemic inflammation factors (C-reactive protein, the interleukin-1 receptor antagonist, and factors involved in tumor necrosis factor signaling), indicating that deficient treatment response locally and detrimental inflammation systemically link to a hypoxic mitochondrial metabolism. In conclusion, serum ROS and damaged mtDNA may be markers of the mitochondrial metabolism driven by the state of oxygenation of the primary tumor and possibly implicated in systemic inflammation and adverse outcome of LARC.

The Living Dead: Mitochondria and Metabolic Arrest

Mitochondria are not just the powerhouses of the cell; these 'end of function' organelles are crucial components of cellular physiology and influence many central metabolic and signaling pathways that support complex multicellular life. Not surprisingly, these organelles play vital roles in adaptations for extreme survival strategies including hibernation and freeze tolerance, both of which are united by requirements for a strong reduction and reprioritization of metabolic processes. To facilitate metabolic rate depression, adaptations of all aspects of mitochondrial function are required, including; energetics, physiology, abundance, gene regulation, and enzymatic controls. This review discusses these factors with a focus on the stress-specific nature of mitochondrial genes and transcriptional regulators, and processes including apoptosis and chaperone protein responses. We also analyze the regulation of glutamate dehydrogenase and pyruvate dehydrogenase, central mitochondrial enzymes involved in coordinating the shifts in metabolic fuel use associated with extreme survival strategies. Finally, an emphasis is given to the novel mitochondrial research areas of microRNAs, peptides, epigenetics, and gaseous mediators and their potential roles in facilitating hypometabolism. © 2018 IUBMB Life, 70(12):1260-1266, 2018.

Sirt3 attenuates post-infarction cardiac injury via inhibiting mitochondrial fission and normalization of AMPK-Drp1 pathways

Mitochondrial damage is involved in the pathogenesis of post-infarction cardiac injury. However, the upstream regulators of mitochondrial damage have not yet been identified. The aim of our study is to explore the role of Sirt3 in post-infarction cardiac injury with a particular focus on mitochondrial fission and AMPK-Drp1 pathways. Our results indicated that Sirt3 was downregulated in the progression of post-infarction cardiac injury. Overexpression of Sirt3 attenuated cardiac fibrosis, sustained myocardial function, inhibited the inflammatory response, and reduced cardiomyocyte death. Functional studies illustrated that chronic post-infarction cardiac injury was characterized by increased mitochondrial fission, which triggered mitochondrial oxidative stress, metabolic disorders, mitochondrial potential reduction and caspase-9 apoptosis in cardiomyocytes. However, Sirt3 overexpression attenuated mitochondrial fission and thus preserved mitochondrial homeostasis and cardiomyocyte viability. Furthermore, our results confirmed that Sirt3 repressed mitochondrial fission via normalizing AMPK-Drp1 pathways. Inhibition of AMPK activity re-activated Drp1 and thus abrogated the inhibitory effect of Sirt3 on mitochondrial fission. Altogether, our results indicate that Sirt3 enhancement could be an effective approach to retard the development of post-infarction cardiac injury via disrupting mitochondrial fission and normalizing the AMPK-Drp1 axis.

BI1 alleviates cardiac microvascular ischemia-reperfusion injury via modifying mitochondrial fission and inhibiting XO/ROS/F-actin pathways

Pathogenesis of cardiac microvascular ischemia-reperfusion (IR) injury is associated with excessive mitochondrial fission. However, the upstream mediator of mitochondrial fission remains obscure. Bax inhibitor 1 (BI1) is linked to multiple mitochondrial functions, and there have been no studies investigating the contribution of BI1 on mitochondrial fission in the setting of cardiac microvascular IR injury. This study was undertaken to establish the action of BI1 on the cardiac microvascular reperfusion injury and figure out whether BI1 sustained endothelial viability via inhibiting mitochondrial fission. Our observation indicated that BI1 was downregulated in reperfused hearts and overexpression of BI1 attenuated microvascular IR injury. Mechanistically, reperfusion injury elevated the levels of xanthine oxidase (XO), an effect that was followed by increased reactive oxygen species (ROS) production. Subsequently, oxidative stress mediated F-actin depolymerization and the latter promoted mitochondrial fission. Aberrant fission caused mitochondrial dysfunction and ultimately activated mitochondrial apoptosis in cardiac microvascular endothelial cells. By comparison, BI1 overexpression repressed XO expression and thus neutralized ROS, interrupting F-actin-mediated mitochondrial fission. The inhibitory effect of BI1 on mitochondrial fission sustained endothelial viability, reversed endothelial barrier integrity, attenuated the microvascular inflammation response, and maintained microcirculation patency. Altogether, we conclude that BI1 is essential in maintaining mitochondrial homeostasis and alleviating cardiac microvascular IR injury. Deregulated BI1 via the XO/ROS/F-actin pathways plays a causative role in the development of cardiac microvascular reperfusion injury.

Sirt3-mediated mitochondrial fission regulates the colorectal cancer stress response by modulating the Akt/PTEN signalling pathway

Sirtuin-3 (Sirt3), a sub-family member of the nicotinamide adenine dinucleotide-dependent histone deacetylases, has been reported to be involved in mitochondrial oxidative stress regulation, mitochondrial calcium management, mitophagy activation, and mitochondrial energy metabolism. The aim of our study was to explore the functional role of Sirt3 in colorectal cancer stress, focusing particularly on its effects on mitochondrial fission. Our study demonstrated that Sirt3 was highly upregulated in colorectal cancer cells compared to normal rectal mucosa cells. However, the genetic ablation of Sirt3 reduced colorectal cancer cell viability, mobility and proliferation. At the molecular level, we found that Sirt3 knockdown suppressed the expression of adhesive factors and cyclins. Furthermore, Sirt3 deletion was also associated with mitochondrial membrane potential reduction, ROS overproduction, mPTP opening, mitochondrial pro-apoptotic upregulation, and caspase-9-related death programme activation. Furthermore, we determined that Sirt3 regulated the colorectal cancer stress response by modulating mitochondrial fission. The loss of Sirt3 triggered fatal mitochondrial fission by suppressing the Akt/PTEN pathway. Re-activation of the Akt/PTEN pathway combatted mitochondrial fission and promoted colorectal cancer mobility, survival, and growth. Altogether, these findings provide an additional rationale for the function of Sirt3 in supporting the growth and survival of colorectal cancer.

NR4A1 Promotes Cerebral Ischemia Reperfusion Injury by Repressing Mfn2-Mediated Mitophagy and Inactivating the MAPK-ERK-CREB Signaling Pathway

Mitochondrial dysfunction has been acknowledged as the key pathogenic mechanism in cerebral ischemia-reperfusion (IR) injury. Mitophagy is the protective system used to sustain mitochondrial homeostasis. However, the upstream regulator of mitophagy in response to brain IR injury is not completely understood. Nuclear receptor subfamily 4 group A member 1 (NR4A1) has been found to be associated with mitochondrial protection in a number of diseases. The aim of our study is to explore the functional role of NR4A1 in cerebral IR injury, with a particular focus on its influence on mitophagy. Wild-type mice and NR4A1-knockout mice were used to generate cerebral IR injury in vivo. Mitochondrial function and mitophagy were detected via immunofluorescence assays and western blotting. Cellular apoptosis was determined via MTT assays, caspase-3 activity and western blotting. Our data revealed that NR4A1 was significantly increased in the reperfused brain tissues. Genetic ablation of NR4A1 reduced the cerebral infarction area and repressed neuronal apoptosis. The functional study demonstrated that NR4A1 modulated cerebral IR injury by inducing mitochondrial damage. Higher NR4A1 promoted mitochondrial potential reduction, evoked cellular oxidative stress, interrupted ATP generation, and initiated caspase-9-dependent apoptosis. Mechanistically, NR4A1 induced mitochondrial damage by disrupting Mfn2-mediated mitophagy. Knockdown of NR4A1 elevated Mfn2 expression and therefore reversed mitophagic activity, sending a prosurvival signal for mitochondria in the setting of cerebral IR injury. Further, we demonstrated that NR4A1 modulated Mfn2 expression via the MAPK-ERK-CREB signaling pathway. Blockade of the ERK pathway could abrogate the permissive effect of NR4A1 deletion on mitophagic activation, contributing to neuronal mitochondrial apoptosis. Overall, our results demonstrate that the pathogenesis of cerebral IR injury is closely associated with a drop in protective mitophagy due to increased NR4A1 through the MAPK-ERK-CREB signaling pathway.

Endoplasmic reticulum stress-dependent ROS production mediates synovial myofibroblastic differentiation in the immobilization-induced rat knee joint contracture model

Joint contracture is a common complication for people with joint immobility that involves fibrosis structural alteration in the joint capsule. Considering that endoplasmic reticulum (ER) stress plays a prominent role in the promotion of tissue fibrosis, we investigated whether the unfolded protein response (UPR) contributes to the fibrotic development in immobilization-induced knee joint contractures. Using a non-traumatic rat knee joint contracture model, twelve female Sprague-Dawley rats received knee joint immobilization for a period of 8 weeks. We found that fibrosis protein markers (type I collagen, α-SMA) and UPR (GRP78, ATF6α, XBP1s) markers were parallelly upregulated in rat primary cultured synovial myofibroblasts. In the same cell types, pre-treatment with an ER stress inhibitor, 4-phenylbutyric acid (4-PBA), not only abrogated cytokine TGFβ1 stimulation but also reduced the protein level of UPR. Additionally, high reactive oxygen species (ROS) generation was detected in synovial myofibroblasts through flow cytometry, as expected. Notably, TGFβ1-induced UPR was significantly reduced through the inhibition of ROS with antioxidants. These data suggest that ER stress act as a pro-fibrotic stimulus through the overexpression of ROS in synovial fibroblasts. Interestingly, immunohistochemical results showed an increase in the UPR protein levels both in human acquired joint contractures capsule tissue and in animal knee joint contracture tissue. Together, our findings suggest that ER stress contributes to synovial myofibroblastic differentiation in joint capsule fibrosis and may also serve as a potential therapeutic target in joint contractures.

TAZ inhibition promotes IL-2-induced apoptosis of hepatocellular carcinoma cells by activating the JNK/F-actin/mitochondrial fission pathway

Background

Cytokine-based cancer therapies have attracted a great deal of attention in recent years. Unfortunately, resistance to treatment limits the efficacy of these therapeutics. Therefore, the aim of our study was to explore the mechanism of IL-2-based therapy for hepatocellular carcinoma in an attempt to increase the efficiency of this treatment option.

Methods

HepG2 cells were treated with IL-2. Then, siRNA against TZA was used to transfected into HepG2 cells. Cellular apoptosis was measured via MTT assay, TUNEL assay and caspase-3 activity. Cellular proliferation was evaluated via EdU assay and western blotting. Cellular migration was detected via Transwell assay. Mitochondrial function was monitored by mitochondrial potential analysis, ROS staining, immunofluorescence and western blotting. Pathway blocker and activator were used to establish the role of JNK/F-actin/mitochondrial fission signaling pathway in HepG2 cells stress response.

Results

Our study found that IL-2 treatment significantly reduced the viability, mobility and proliferation of HepG2 cells in vitro. We also demonstrated that IL-2 treatment was accompanied by an increase in the expression of transcriptional co-activator with PDZ-binding motif (TAZ). Interestingly, genetic ablation of TAZ in the presence of IL-2 further promoted apoptosis, inhibited mobility, and arrested proliferation in HepG2 cells. At the molecular level, IL-2 administration activated excessive mitochondrial fission via the JNK/F-actin pathway; these effects were further enhanced by TAZ deletion. Mechanistically, TAZ knockdown further increased the expression of mitochondrial fission-related proteins such as Drp1, Mff and Fis. The augmented mitochondrial fission stimulated ROS overproduction, mediated redox imbalance, interrupted mitochondrial energy generation, reduced mitochondrial membrane potential, promoted leakage of the pro-apoptotic molecule cyt-c into the nucleus, and initiated caspase-9-related mitochondrial death. Further, we demonstrated that the anti-proliferative and anti-metastatic effects of IL-2 in HepG2 cells were enhanced by TAZ deletion, suggesting that IL-2 sensitizes HepG2 cells to IL-2-based cytokine therapy. However, JNK/F-actin pathway blockade could abrogate the inhibitory effects of TAZ deletion on HepG2 migration, proliferation and survival.

Conclusions

Taken together, our data indicate that the anti-tumor effects of IL-2-based therapies may be enhanced by TAZ deletion in a JNK/F-actin pathway-dependent manner. This finding provides a novel combinatorial therapeutic approach for treating hepatocellular carcinoma that might significantly increase the efficacy of cytokine-based therapies in a clinical setting.

Electronic supplementary material

The online version of this article (10.1186/s12935-018-0615-y) contains supplementary material, which is available to authorized users.

Degradation of the mitochondrial complex I assembly factor TMEM126B under chronic hypoxia

Cell stress such as hypoxia elicits adaptive responses, also on the level of mitochondria, and in part is mediated by the hypoxia-inducible factor (HIF) 1α. Adaptation of mitochondria towards acute hypoxic conditions is reasonably well understood, while regulatory mechanisms, especially of respiratory chain assembly factors, under chronic hypoxia remains elusive. One of these assembly factors is transmembrane protein 126B (TMEM126B). This protein is part of the mitochondrial complex I assembly machinery. We identified changes in complex I abundance under chronic hypoxia, in association with impaired substrate-specific mitochondrial respiration. Complexome profiling of isolated mitochondria of the human leukemia monocytic cell line THP-1 revealed HIF-1α-dependent deficits in complex I assembly and mitochondrial complex I assembly complex (MCIA) abundance. Of all mitochondrial MCIA members, we proved a selective HIF-1-dependent decrease of TMEM126B under chronic hypoxia. Mechanistically, HIF-1α induces the E3-ubiquitin ligase F-box/WD repeat-containing protein 1A (β-TrCP1), which in turn facilitates the proteolytic degradation of TMEM126B. Attenuating a functional complex I assembly appears critical for cellular adaptation towards chronic hypoxia and is linked to destruction of the mitochondrial assembly factor TMEM126B.

Targeting Oxidative Stress and Mitochondrial Dysfunction in the Treatment of Impaired Wound Healing: A Systematic Review

Wound healing is a well-tuned biological process, which is achieved via consecutive and overlapping phases including hemostasis, inflammatory-related events, cell proliferation and tissue remodeling. Several factors can impair wound healing such as oxygenation defects, aging, and stress as well as deleterious health conditions such as infection, diabetes, alcohol overuse, smoking and impaired nutritional status. Growing evidence suggests that reactive oxygen species (ROS) are crucial regulators of several phases of healing processes. ROS are centrally involved in all wound healing processes as low concentrations of ROS generation are required for the fight against invading microorganisms and cell survival signaling. Excessive production of ROS or impaired ROS detoxification causes oxidative damage, which is the main cause of non-healing chronic wounds. In this context, experimental and clinical studies have revealed that antioxidant and anti-inflammatory strategies have proven beneficial in the non-healing state. Among available antioxidant strategies, treatments using mitochondrial-targeted antioxidants are of particular interest. Specifically, mitochondrial-targeted peptides such as elamipretide have the potential to mitigate mitochondrial dysfunction and aberrant inflammatory response through activation of nucleotide-binding oligomerization domain (NOD)-like family receptors, such as the pyrin domain containing 3 (NLRP3) inflammasome, nuclear factor-kappa B (NF-κB) signaling pathway inhibition, and nuclear factor (erythroid-derived 2)-like 2 (Nrf2).

ER-Mitochondria Microdomains in Cardiac Ischemia-Reperfusion Injury: A Fresh Perspective

The mitochondrial and endoplasmic reticulum (ER) homeostasis is pivotal to the maintenance of an array of physiological processes. The physical contact and association between ER and mitochondria, known as the ER–mitochondria microdomains or mitochondria-associated ER membrane (MAM), temporally and spatially regulates the mitochondria/ER structure and function. More evidence suggests a role for MAMs in energy production, cellular contraction and mobility, and normal extracellular signal transmission. In pathological states, such as cardiac ischemia–reperfusion (I/R injury), this ER–mitochondria microdomains may act to participate in the cellular redox imbalance, ER stress, mitochondrial injury, energy deletion, and programmed cell death. From a therapeutic perspective, a better understanding of the cellular and molecular mechanisms of the pathogenic ER–mitochondria contact should help to identify potential therapeutic target for cardiac I/R injury and other cardiovascular diseases and also pave the road to new treatment modalities pertinent for the treatment of reperfusion damage in clinical practice. This review will mainly focus on the possible signaling pathways involved in the regulation of the ER–mitochondria contact. In particular, we will summarize the downstream signaling modalities influenced by ER–mitochondria microdomains, for example, mitochondrial fission, mitophagy, calcium balance, oxidative stress, and programmed cell death in details.

Zearalenone regulates endometrial stromal cell apoptosis and migration via the promotion of mitochondrial fission by activation of the JNK/Drp1 pathway

Increased endometrial stromal cell (ESC) survival and migration is responsible for the development and progression of endometriosis. However, little is known about the mechanisms underlying ESC survival and migration, and limited therapeutic strategies that are able to reverse these abnormalities are available. The present study investigated the effects of zearalenone (ZEA) on ESC survival and migration, particularly focusing on mitochondrial fission and the c‑Jun N‑terminal kinase (JNK)/dynamin‑related protein 1 (Drp1) pathway. The results revealed that ZEA induced ESC apoptosis in a dose‑dependent manner. Furthermore, ZEA treatment triggered excessive mitochondrial fission resulting in structural and functional mitochondrial damage, leading to the collapse of the mitochondrial membrane potential and subsequent leakage of cytochrome c into the cytoplasm. This triggered the mitochondrial pathway of apoptosis. Additionally, ZEA‑induced mitochondrial fission decreased ESC migration through F‑actin/G‑actin homeostasis dysregulation. ZEA also increased JNK phosphorylation and subsequently Drp1 phosphorylation at the serine 616 position, resulting in Drp1 activation. JNK/Drp1 pathway inhibition abolished the inhibitory effects of ZEA on ESC survival and migration. In summary, the present study demonstrated that ZEA reduced ESC survival and migration through the stimulation of mitochondrial fission by activation of the JNK/Drp1 pathway.

Empagliflozin rescues diabetic myocardial microvascular injury via AMPK-mediated inhibition of mitochondrial fission

Impaired cardiac microvascular function contributes to diabetic cardiovascular complications although effective therapy remains elusive. Empagliflozin, a sodium-glucose cotransporter 2 (SGLT2) inhibitor recently approved for treatment of type 2 diabetes, promotes glycosuria excretion and offers cardioprotective actions beyond its glucose-lowering effects. This study was designed to evaluate the effect of empagliflozin on cardiac microvascular injury in diabetes and the underlying mechanism involved with a focus on mitochondria. Our data revealed that empagliflozin improved diabetic myocardial structure and function, preserved cardiac microvascular barrier function and integrity, sustained eNOS phosphorylation and endothelium-dependent relaxation, as well as improved microvessel density and perfusion. Further study suggested that empagliflozin exerted its effects through inhibition of mitochondrial fission in an adenosine monophosphate (AMP)-activated protein kinase (AMPK)-dependent manner. Empagliflozin restored AMP-to-ATP ratio to trigger AMPK activation, suppressed Drp1S616 phosphorylation, and increased Drp1S637 phosphorylation, ultimately leading to inhibition of mitochondrial fission. The empagliflozin-induced inhibition of mitochondrial fission preserved cardiac microvascular endothelial cell (CMEC) barrier function through suppressed mitochondrial reactive oxygen species (mtROS) production and subsequently oxidative stress to impede CMEC senescence. Empagliflozin-induced fission loss also favored angiogenesis by promoting CMEC migration through amelioration of F-actin depolymerization. Taken together, these results indicated the therapeutic promises of empagliflozin in the treatment of pathological microvascular changes in diabetes.

Cyclosporine A induces endothelin-converting enzyme-1: Studies in vivo and in vitro

AIM

Cyclosporine A (CsA) induces renal vasoconstriction and hypoxia and enhances the expression of endothelin-1 (ET-1) pro-hormone (pre-pro-ET-1), plausibly leading to a feed-forward loop of renal vasoconstriction, hypoxia and enhanced synthesis of the potent vasoconstrictor ET-1. Endothelin-converting enzyme (ECE)-1 cleaves big endothelin to generate endothelin (ET)-1 and is upregulated by hypoxia via hypoxia-inducible factor (HIF). We hypothesized that in addition to the direct induction of ET-1 synthesis, CsA might also intensify renal ECE-1 expression, thus contributing to enhanced ET-1 synthesis following CsA.

METHODS

CsA was administered to Sprague Dawley rats (120 mg/kg/SC) for 4 days, and renal HIF and ECE-1 expression were assessed with Western blots and immunostaining. Human umbilical vein endothelial cells (HUVEC) and proximal tubular cell line (HK-2) were subjected to CsA, and ECE-1 induction was evaluated using real-time mRNA PCR and Western blots.

RESULTS

Cyclosporine A intensified renal parenchymal ECE-1 expression in the rat kidney, particularly in distal nephron segments, along with renal hypoxia (detected by pimonidazole adducts) and HIF expression, in line with our recent observations showing episodic hypoxia in mice subjected to CsA. Furthermore, in cultured normoxic HUVEC and HK-2 cells, CsA dose-dependently induced both pre-pro-ET-1 and ECE-1 mRNA and protein expression, with enhanced ET-1 generation.

CONCLUSION

CsA induces ECE-1 via both hypoxic and non-hypoxic pathways. ECE-1 may contribute to increased renal ET-1 generation following CsA, participating in a feed-forward loop of renal parenchymal hypoxia and ET synthesis.

miR-125a induces apoptosis, metabolism disorder and migrationimpairment in pancreatic cancer cells by targeting Mfn2-related mitochondrial fission

Mitochondrial fission is important for the development and progression of pancreatic cancer (PC). However, little is known regarding its role in pancreatic cancer apoptosis, metabolism and migration. In the current study, the mechanism by which mitochondrial fission modifies the biological characteristics of PC was explored. MicroRNA-125a (miR-125a) had the ability to inhibit mitochondrial fission and contributed to cellular survival. Suppressed mitochondrial fission led to a reduction in mitochondrial debris, preserved the mitochondrial membrane potential, inhibited mitochondrial permeability transition pore opening, ablated cytochrome c leakage into the cytoplasm and reduced the pro-apoptotic protein contents, finally blocking mitochondria related apoptosis pathways. Furthermore, defective mitochondrial fission induced by miR-125a enhanced mitochondria-dependent energy metabolism by promoting activity of electron transport chain complexes. Furthermore, suppressed mitochondrial fission also contributed to PANC-1 cell migration by preserving the F-actin balance. Furthermore, mitofusin 2 (Mfn2), the key defender of mitochondrial fission, is involved in inhibition of miR125a-mediated mitochondrial fission. Low contents of miR-125a upregulated Mfn2 transcription and expression, leading to inactivation of mitochondrial fission. Ultimately, the current study determined that miR-125a and Mfn2 are regulated by hypoxia-inducible factor 1 (HIF1). Knockdown of HIF1 reversed miR-125a expression, and therefore, inhibited Mfn2 expression, leading to activation of mitochondrial fission. Collectively, the present study demonstrated mitochondrial fission as a tumor suppression process that is regulated by the HIF/miR-125a/Mfn2 pathways, acting to restrict PANC-1 cell survival, energy metabolism and migration, with potential implications for novel approaches for PC therapy.

Mitochonic acid 5 activates the MAPK-ERK-yap signaling pathways to protect mouse microglial BV-2 cells against TNFα-induced apoptosis via increased Bnip3-related mitophagy

BACKGROUND

The regulation of microglial function via mitochondrial homeostasis is important in the development of neuroinflammation. The underlying mechanism for this regulatory function remains unclear. In this study, we investigated the protective role of mitochonic acid 5 (MA-5) in microglial mitochondrial apoptosis following TNFα-induced inflammatory injury.

METHODS

TNFα was used to induce inflammatory injury in mouse microglial BV-2 cells with and without prior MA-5 treatment. Cellular apoptosis was assessed using the MTT and TUNEL assays. Mitochondrial functions were evaluated via mitochondrial membrane potential JC-1 staining, ROS flow cytometry analysis, mPTP opening assessment, and immunofluorescence of cyt-c. Mitophagy was examined using western blots and immunofluorescence. The pathways analysis was carried out using western blots and immunofluorescence with a pathway blocker.

RESULTS

Our results demonstrated that TNFα induced apoptosis in the microglial BV-2 cell line by activating the caspase-9-dependent mitochondrial apoptotic pathway. Mechanistically, inflammation reduced mitochondrial potential, induced ROS production, and contributed to the leakage of mitochondrial pro-apoptotic factors into the cytoplasm. The inflammatory response reduced cellular energy metabolism and increased oxidative stress. By contrast, treatment with MA-5 reduced mitochondrial apoptosis via upregulation of mitophagy. Increased mitophagy degraded damaged mitochondria, disrupting mitochondrial apoptosis, neutralizing ROS overproduction, and improving cellular energy production. We also identified that MA-5 regulated mitophagy via Bnip3 through the MAPK-ERK-Yap signaling pathway. Inhibiting this signaling pathway or knocking down Bnip3 expression prevented MA-5 from having beneficial effects on mitochondrial homeostasis and increased microglial apoptosis.

CONCLUSIONS

After TNFα-induced inflammatory injury, MA-5 affects microglial mitochondrial homeostasis in a manner mediated via the amplification of protective, Bnip3-related mitophagy, which is mediated via the MAPK-ERK-Yap signaling pathway.

Protective role of melatonin in cardiac ischemia-reperfusion injury: From pathogenesis to targeted therapy

Acute myocardial infarction (MI) is a major cause of mortality and disability worldwide. In patients with MI, the treatment option for reducing acute myocardial ischemic injury and limiting MI size is timely and effective myocardial reperfusion using either thombolytic therapy or primary percutaneous coronary intervention (PCI). However, the procedure of reperfusion itself induces cardiomyocyte death, known as myocardial reperfusion injury, for which there is still no effective therapy. Recent evidence has depicted a promising role of melatonin, which possesses powerful antioxidative and anti-inflammatory properties, in the prevention of ischemia-reperfusion (IR) injury and the protection against cardiomyocyte death. A number of reports explored the mechanism of action behind melatonin-induced beneficial effects against myocardial IR injury. In this review, we summarize the research progress related to IR injury and discuss the unique actions of melatonin as a protective agent. Furthermore, the possible mechanisms responsible for the myocardial benefits of melatonin against reperfusion injury are listed with the prospect of the use of melatonin in clinical application.

Yap regulates gastric cancer survival and migration via SIRT1/Mfn2/mitophagy

Gastric cancer is the fifth most common cancer worldwide and Hippo-Yap is the novel signaling pathway which plays an important role in gastric cancer tumor development and progression. However, little insight is available to date regarding the specific role of Yes-associated protein (Yap) in gastric cancer. In the present study, we identified the mechanism through which Yap sustains gastric cancer viability and migration. Yap was greatly upregulated in gastric cancer cells and its expression promoted cellular migration and survival. Functional studies found that knockdown of Yap reduced the mitophagy activity, which subsequently caused mitochondrial apoptosis and cellular oxidative stress. The latter impaired adhesive protein expression, alleviated F-actin expression, blunted lamellipodium formation, leading to inhibition of cancer cell motility. Mechanistically, Yap preserved Sirtuin 1 (SIRT1) activity which manipulated mitofusin 2 (Mfn2) expression and subsequent mitophagy. Loss of Yap reduced SIRT1 expression and inhibited Mfn2-mediated mitophagy. Collectively, our results identified Hippo-Yap as a tumor promoter in gastric cancer that was mediated via activation of the SIRT1/Mfn2/mitophagy axis, with potential applications to gastric cancer therapy involving cancer survival and migration.

HIF1α deletion facilitates adipose stem cells to repair renal fibrosis in diabetic mice

Adipose stem cell (ASC) transplantation is a promising therapeutic strategy for diabetic renal fibrosis. Hypoxia-inducible factor 1α (HIF1α) is a negative regulatory factor of mitochondrial function. In the current study, we aimed to explore if HIF1α deletion protects against hyperglycemia-induced ASC damage and enhances the therapeutic efficiency of ASCs in diabetic renal fibrosis. Our data indicated that HIF1α was upregulated in ASCs in response to high glucose stimulation. Higher HIF1α expression was associated with ASC apoptosis and proliferation arrest. Loss of HIF1α activated mitophagy protecting ASCs against high glucose-induced apoptosis via preserving mitochondrial function. Transplanting HIF1α-deleted ASCs in db/db mice improved the abnormalities in glucose metabolic parameters, including the levels of glucose, insulin, C-peptide, HbA1c, and inflammatory markers. In addition, the engraftment of HIF1α-modified ASCs also reversed renal function, decreased renal hypertrophy, and ameliorated renal histological changes in db/db mice. Functional studies confirmed that HIF1α-modified ASCs reduced renal fibrosis. Collectively, our results demonstrate that ASCs may be a promising therapeutic treatment for ameliorating diabetes and the development of renal fibrosis and that the loss of HIF1α in ASCs may further increase the efficiency of stem cell-based therapy. These findings provide a new understanding about the protective effects of HIF1α silencing on ASCs and offer a new strategy for promoting the therapeutic efficacy of ASCs in diabetic renal fibrosis.

MITF acts as an anti-oxidant transcription factor to regulate mitochondrial biogenesis and redox signaling in retinal pigment epithelial cells

There is increasing evidence that the mechanisms protecting the retinal pigment epithelium (RPE) against oxidative stress are important for preventing retinal degenerative diseases. Little, however, is known about these mechanisms. Here we show that MITF, a transcription factor responsible for RPE development and function, regulates redox signaling by acting through PGC1α, a master regulator of mitochondrial biogenesis. Mitf deficiency in mice leads to significantly higher levels of reactive oxygen species (ROS) in both RPE and retina, suggesting that Mitf dysfunction might lead to oxidative damage in the RPE and, by extension, in the retina. Furthermore, overexpression of MITF in the human RPE cell line ARPE-19 indicates that MITF up-regulates antioxidant gene expression and mitochondrial biogenesis by regulating PGC1α and protects cells against oxidative stress. Our findings provide new insights into understanding the redox function of MITF in RPE cells and its potential contribution to prevention of RPE-associated retinal degenerations.

Redox-signals and macrophage biology

Macrophages are known for their versatile role in biology. They sense and clear structures that contain exogenous or endogenous pathogen-associated molecular patterns. This process is tightly linked to the production of a mixture of potentially harmful oxidants and cytokines. Their inherent destructive behavior is directed against foreign material or structures of 'altered self', which explains the role of macrophages during innate immune reactions and inflammation. However, there is also another side of macrophages when they turn into a tissue regenerative, pro-resolving, and healing phenotype. Phenotype changes of macrophages are termed macrophage polarization, representing a continuum between classical and alternative activation. Macrophages as the dominating producers of superoxide/hydrogen peroxide and nitric oxide are not only prone to oxidative modifications but also to more subtle signaling properties of redox-active molecules conveying redox regulation. We review basic concepts of the enzymatic nitric oxide and superoxide production within macrophages, refer to their unique chemical reactions and outline biological consequences not only for macrophage biology but also for their communication with cells in the microenvironment. These considerations link hypoxia to the NO system, addressing feedforward as well as feedback circuits. Moreover, we summarize the role of redox-signaling affecting epigenetics and reflect the central role of mitochondrial-derived oxygen species in inflammation. To better understand the diverse functions of macrophages during initiation as well as resolution of inflammation and to decode their versatile roles during innate and adaptive immunity with the entire spectrum of cell protective towards cell destructive activities we need to appreciate the signaling properties of redox-active species. Herein we discuss macrophage responses in terms of nitric oxide and superoxide formation with the modulating impact of hypoxia.

Interspecific variation in brain mitochondrial complex I and II capacity and ROS emission in marine sculpins

Environmental hypoxia presents a metabolic challenge for animals because it inhibits mitochondrial respiration and can lead to the generation of reactive oxygen species (ROS). We investigated the interplay between O2 use for aerobic respiration and ROS generation among sculpin fishes (Cottidae, Actinopterygii) that are known to vary in whole-animal hypoxia tolerance. We hypothesized that mitochondria from hypoxia tolerant sculpins would show more efficient O2 use with a higher phosphorylation efficiency and lower ROS emission. We showed that brain mitochondria from more hypoxia tolerant sculpins had lower complex I and higher complex II flux capacities compared with less hypoxia tolerant sculpins, but these differences were not related to variation in phosphorylation efficiency (ADP/O) or mitochondrial coupling (respiratory control ratio). The hypoxia tolerant sculpin had higher mitochondrial H2O2 emission per O2 consumed (H2O2/O2) under oligomycin-induced state 4 conditions compared to less hypoxia tolerant sculpin. An in vitro redox challenge experiment revealed species differences in how well mitochondria defend their glutathione redox status when challenged with high levels of reduced glutathione, but the redox challenge elicited the same H2O2/O2 in all species. Furthermore, in vitro anoxia-recovery lowered absolute H2O2 emission (H2O2/mg mitochondrial protein) in all species and negatively impacted state 3 respiration rates in some species, but the responses were not related to hypoxia tolerance. Overall, we clearly demonstrate a relationship between hypoxia tolerance and complex I and II flux capacities in sculpins, but the differences in complex flux capacity do not appear to be directly related to variation in ROS metabolism.

Effects of melatonin on fatty liver disease: The role of NR4A1/DNA-PKcs/p53 pathway, mitochondrial fission, and mitophagy

Mitochondrial dysfunction has been implicated in the pathogenesis of nonalcoholic fatty liver disease (NAFLD) through poorly defined mechanisms. Melatonin supplementation has been found to protect liver function in diabetes and obesity. Here, we intensively explored the role and mechanism of melatonin in the development of NAFLD. We demonstrated that the onset of diet-induced NAFLD greatly caused NR4A1 upregulation in hepatocytes, leading to the activation of DNA-PKcs and p53. On the one hand, p53 aided Drp1 migration in the mitochondria and consequently drove mitochondrial fission. On the other hand, p53 repressed Bnip3 transcription and expression, resulting in mitophagy arrest. The excessive fission and deficient mitophagy dramatically mediated mitochondrial dysfunction, including extensive mPTP opening, reduction in mitochondrial potential, oxidative stress, calcium overload, mitochondrial respiratory collapse, and ATP shortage. However, genetic deletion of NR4A1 or DNA-PKcs could definitively reverse NAFLD progression and the mitochondrial dysfunction. Similarly, melatonin supplementation could robustly reduce the damage to liver and mitochondrial structure and function in NAFLD. Mechanistically, melatonin halted fission but recovered mitophagy via blockade of NR4A1/DNA-PKcs/p53 pathway, finally improving mitochondrial and liver function in the setting of NAFLD. Our results identify NR4A1/DNA-PKcs/p53 pathway as the novel molecular mechanism underlying the pathogenesis of NAFLD via regulation of Drp1-mediated mitochondrial fission and Bnip3-related mitophagy. Meanwhile, we also confirm that melatonin has the ability to cut off the NR4A1/DNA-PKcs/p53 pathway, which confers a protective advantage to hepatocytes and mitochondria. The manipulation of NR4A1/DNA-PKcs/p53 pathway by melatonin highlights a new entry point for treating NAFLD.

Melatonin suppresses platelet activation and function against cardiac ischemia/reperfusion injury via PPARγ/FUNDC1/mitophagy pathways

Platelet activation is a major (patho-) physiological mechanism that underlies ischemia/reperfusion (I/R) injury. In this study, we explored the molecular signals for platelet hyperactivity and investigated the beneficial effects of melatonin on platelet reactivity in response to I/R injury. After reperfusion, peroxisome proliferator-activated receptor γ (PPARγ) was progressively downregulated in patients with acute myocardial infarction undergoing coronary artery bypass grafting (CABG) surgery and in mice with I/R injury model. Loss of PPARγ was closely associated with FUN14 domain containing 1 (FUNDC1) dephosphorylation and mitophagy activation, leading to increased mitochondrial electron transport chain complex (ETC.) activity, enhanced mitochondrial respiratory function, and elevated ATP production. The improved mitochondrial function strongly contributed to platelet aggregation, spreading, expression of P-selectin, and final formation of micro-thromboses, eventually resulting in myocardial dysfunction and microvascular structural destruction. However, melatonin powerfully suppressed platelet activation via restoration of the PPARγ content in platelets, which subsequently blocked FUNDC1-required mitophagy, mitochondrial energy production, platelet hyperactivity, and cardiac I/R injury. In contrast, genetic ablation of PPARγ in platelet abolished the beneficial effects of melatonin on mitophagy, mitochondrial ATP supply, and platelet activation. Our results lay the foundation for the molecular mechanism of platelet activation in response to I/R injury and highlight that the manipulation of the PPARγ/FUNDC1/mitophagy pathway by melatonin could be a novel strategy for cardioprotection in the setting of cardiac I/R injury.

Yap promotes hepatocellular carcinoma metastasis and mobilization via governing cofilin/F-actin/lamellipodium axis by regulation of JNK/Bnip3/SERCA/CaMKII pathways

Despite the increasingly important role of Hippo-Yap in hepatocellular carcinoma (HCC) development and progression, little insight is available at the time regarding the specifics interaction of Yap and cancer cells migration. Here, we identified the mechanism by which tumor-intrinsic Yap deletion resulted in HCC migratory inhibition. Yap was greatly upregulated in HCC and its expression promoted the cells migration. Functional studies found that knockdown of Yap induced JNK phosphorylation which closely bound to the Bnip3 promoter and contributed to Bnip3 expression. Higher Bnip3 employed excessive mitophagy leading to mitochondrial dysfunction and ATP shortage. The insufficient ATP inactivated SERCA and consequently triggered intracellular calcium overload. As the consequence of calcium oscillation, Ca/calmodulin-dependent protein kinases II (CaMKII) was signaled and subsequently inhibited cofilin activity via phosphorylated modification. The phosphorylated cofilin failed to manipulate F-actin polymerization and lamellipodium formation, resulting into the impairment of lamellipodium-based migration. Collectively, our results identified Hippo-Yap as the tumor promoter in hepatocellular carcinoma that mediated via activation of cofilin/F-actin/lamellipodium axis by limiting JNK-Bnip3-SERCA-CaMKII pathways, with potential application to HCC therapy involving cancer metastasis.

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Yap is upregulated in the hepatocellular carcinoma and promotes cancer cell migration.

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Loss of Yap impairs cell mobility via inhibiting cofilin/F-actin/lamellipodium by activation of JNK-Bnip3-SERCA-CaMKII.

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Loss of Yap enhances JNK phosphorylation which triggers Bnip3-required mitophagy.

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Excessive mitophagy induces mitochondrial energy disorder which blunts SERCA and causes calcium overload.

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The calcium overload drives CaMKII which inactivates cofilin, leading to F-actin degradation and lamellipodium collapse.

Non-electron transfer chain mitochondrial defects differently regulate HIF-1α degradation and transcription

Mitochondria are the main consumers of molecular O2 in a cell as well as an abundant source of reactive oxygen species (ROS). Both, molecular oxygen and ROS are powerful regulators of the hypoxia-inducible factor-1α-subunit (HIF-α). While a number of mechanisms in the oxygen-dependent HIF-α regulation are quite well known, the view with respect to mitochondria is less clear. Several approaches using pharmacological or genetic tools targeting the mitochondrial electron transport chain (ETC) indicated that ROS, mainly formed at the Rieske cluster of complex III of the ETC, are drivers of HIF-1α activation. However, studies investigating non-ETC located mitochondrial defects and their effects on HIF-1α regulation are scarce, if at all existing. Thus, in the present study we examined three cell lines with non-ETC mitochondrial defects and focused on HIF-1α degradation and transcription, target gene expression, as well as ROS levels. We found that cells lacking the key enzyme 2-enoyl thioester reductase/mitochondrial enoyl-CoA reductase (MECR), and cells lacking manganese superoxide dismutase (MnSOD) showed a reduced induction of HIF-1α under long-term (20h) hypoxia. By contrast, cells lacking the mitochondrial DNA depletion syndrome channel protein Mpv17 displayed enhanced levels of HIF-1α already under normoxic conditions. Further, we show that ROS do not exert a uniform pattern when mediating their effects on HIF-1α, although all mitochondrial defects in the used cell types increased ROS formation. Moreover, all defects caused a different HIF-1α regulation via promoting HIF-1α degradation as well as via changes in HIF-1α transcription. Thereby, MECR- and MnSOD-deficient cells showed a reduction in HIF-1α mRNA levels whereas the Mpv17 lacking cells displayed enhanced HIF-1α mRNA levels under normoxia and hypoxia. Altogether, our study shows for the first time that mitochondrial defects which are not related to the ETC and Krebs cycle contribute differently to HIF-1α regulation by affecting HIF-1α degradation and HIF-1α transcription where ROS play not a major role.

Maintenance of redox homeostasis by hypoxia-inducible factors

Oxidative phosphorylation enables cells to generate the large amounts of ATP required for development and maintenance of multicellular organisms. However, under conditions of reduced O₂ availability, electron transport becomes less efficient, leading to increased generation of superoxide anions. Hypoxia-inducible factors switch cells from oxidative to glycolytic metabolism, to reduce mitochondrial superoxide generation, and increase the synthesis of NADPH and glutathione, in order to maintain redox homeostasis under hypoxic conditions.

[Empagliflozin alleviates cardiac microvascular ischemia/reperfusion injury by maintaining myocardial mitochondrial homeostasis]

OBJECTIVE

To evaluate the effect of empagliflozin (EMPA) in mitigating microvascular and endothelial damage induced by myocardial ischemia-reperfusion (I/R) injury.

METHODS

Fifteen male C57BL/6J mice were randomized into shamoperated group, I/R group and I/R+EMPA group, and in the latter two groups, myocardial I/R injury was induced by ligating the left anterior descending coronary artery followed by reperfusion for 2 h. EMPA treatment was administered at the daily dose of 10 mg/kg for 7 days. After the treatment, the changes in myocardial microvascular structure of the mice were observed under electron microscopy. In the cell experiment, cultured human coronary artery endothelial cells (HCAECs) were treated with 10 μmol/L EMPA before exposure to hypoxia for 45 min followed normoxic culture for 2 h. Western blotting and immunofluorescence assay were performed to observe fibrin accumulation and endothelial cell protein expressions in the myocardial tissues of the mice and in HCAECs, and RT-qPCR was used to detect the expressions of pro-inflammatory cytokines.

RESULTS

Electron microscopy revealed significant myocardial microvascular wall thickening and lumen narrowing in mice with myocardial I/R injury. Fibrin accumulation and ICAM1 expression in the microvessels were more pronounced in I/R group than in the sham-operated and I/R + EMPA groups (P < 0.05). EMPA treatment obviously alleviated microvascular occlusion and microthrombus formation induced by I/R injury. At the cellular level, the protein levels of p-eNOS, Fak, and Src kinases in hypoxic exposure group were significantly lower than those in the control and EMPA treatment groups (P < 0.05). Hypoxic exposure significantly reduced mitochondrial DNA replication and transcription and lowered the expression levels of Cox-Ⅰ and Cox-Ⅱ in HCAECs, and these changes were obviously improved by EMPA treatment (P < 0.05).

CONCLUSION

EMPA can alleviate myocardial I/R injury by maintaining mitochondrial homeostasis to protect the microvascular system.