HAX1-Overexpression Augments Cardioprotective Efficacy of Stem Cell-Based Therapy Through Mediating Hippo-Yap Signaling

Although stem/progenitor cell therapy shows potential for myocardial infarction repair, enhancing the therapeutic efficacy could be achieved through additional genetic modifications. HCLS1-associated protein X-1 (HAX1) has been identified as a versatile modulator responsible for cardio-protective signaling, while its role in regulating stem cell survival and functionality remains unknown. In this study, we investigated whether HAX1 can augment the protective potential of Sca1+ cardiac stromal cells (CSCs) for myocardial injury. The overexpression of HAX1 significantly increased cell proliferation and conferred enhanced resistance to hypoxia-induced cell death in CSCs. Mechanistically, HAX1 can interact with Mst1 (a prominent conductor of Hippo signal transduction) and inhibit its kinase activity for protein phosphorylation. This inhibition led to enhanced nuclear translocation of Yes-associated protein (YAP) and activation of downstream therapeutic-related genes. Notably, HAX1 overexpression significantly increased the pro-angiogenic potential of CSCs, as demonstrated by elevated expression of vascular endothelial growth factors. Importantly, implantation of HAX1-overexpressing CSCs promoted neovascularization, protected against functional deterioration, and ameliorated cardiac fibrosis in ischemic mouse hearts. In conclusion, HAX1 emerges as a valuable and efficient inducer for enhancing the effectiveness of cardiac stem or progenitor cell therapeutics.

Structure-guided discovery of protein and glycan components in native mastigonemes

Mastigonemes, the hair-like lateral appendages lining cilia or flagella, participate in mechanosensation and cellular motion, but their constituents and structure have remained unclear. Here, we report the cryo-EM structure of native mastigonemes isolated from Chlamydomonas at 3.0 Å resolution. The long stem assembles as a super spiral, with each helical turn comprising four pairs of anti-parallel mastigoneme-like protein 1 (Mst1). A large array of arabinoglycans, which represents a common class of glycosylation in plants and algae, is resolved surrounding the type II poly-hydroxyproline (Hyp) helix in Mst1. The EM map unveils a mastigoneme axial protein (Mstax) that is rich in heavily glycosylated Hyp and contains a PKD2-like transmembrane domain (TMD). Mstax, with nearly 8,000 residues spanning from the intracellular region to the distal end of the mastigoneme, provides the framework for Mst1 assembly. Our study provides insights into the complexity of protein and glycan interactions in native bio-architectures.

Hyperbaric Oxygen Upregulates Mst1 to Activate Keap1/Nrf2/HO-1 Pathway Resisting Oxidative Stress in a Rat Model of Acute Myocardial Infarction

This study aimed to investigate the protective effects and mechanisms of hyperbaric oxygen (HBO) preconditioning in a rat model of acute myocardial infarction (MI) established by ligation of the left anterior descending (LAD) coronary artery. Microarray, real-time PCR, and western blotting (WB) results demonstrated that the Mst1 gene was downregulated in the heart tissue of the MI rat model. HBO preconditioning significantly increased Mst1 expression in cardiac tissues of rats after MI modeling. Lentiviral infection was used to silence the Mst1 gene in rats treated with HBO to probe the effect of Mst1 on HBO cardioprotection. HBO preconditioning decreased heart infarct size and ameliorated cardiac function in MI rats, whereas Mst1 silencing reversed the effect of HBO administration, as indicated after heat infarct size determination via TTC staining, histological examination via HE staining, and measurements of cardiac function. HBO preconditioning reduced oxidative stress and inflammation in cardiac tissue of MI rat model, evidenced by alteration of malondialdehyde (MDA), 8-hydroxy-2-deoxyguanosine (8-OHdG), and protein carbonyl contents, as well as production of inflammation-associated myeloperoxidase (MPO), IL-1β, and TNF-α. These findings provide a new signaling mechanism through which HBO preconditioning can protect against acute MI injury through the Mst1-mediating Keap1/Nrf2/HO-1-dependent antioxidant defense system.

Transcription factor TOX maintains the expression of Mst1 in controlling the early mouse NK cell development

Rationale: TOX is a DNA-binding factor required for the development of multiple immune cells and the formation of lymph nodes. However, the temporal regulation mode of TOX on NK cell development and function needs to be further explored. Methods: To investigate the role of TOX in NK cells at distinct developmental phases, we deleted TOX at the hematopoietic stem cell stage (Vav-Cre), NK cell precursor (CD122-Cre) stage and late NK cell developmental stage (Ncr1-Cre), respectively. Flow cytometry was used to detect the development and functional changes of NK cell when deletion of TOX. RNA-seq was used to assess the differences in transcriptional expression profile of WT and TOX-deficient NK cells. Published Chip-seq data was exploited to search for the proteins directly interact with TOX in NK cells. Results: The deficiency of TOX at the hematopoietic stem cell stage severely retarded NK cell development. To a less extent, TOX also played an essential role in the physiological process of NKp cells differentiation into mature NK cells. Furthermore, the deletion of TOX at NKp stage severely impaired the immune surveillance function of NK cells, accompanied by down-regulation of IFN-γ and CD107a expression. However, TOX is dispensable for mature NK cell development and function. Mechanistically, by combining RNA-seq data with published TOX ChIP-seq data, we found that the inactivation of TOX at NKp stage directly repressed the expression of Mst1, an important intermediate kinase in Hippo signaling pathway. Mst1 deficient at NKp stage gained the similar phenotype with Toxfl/flCD122Cre mice. Conclusion: In our study, we conclude that TOX coordinates the early mouse NK cell development at NKp stage by maintaining the expression of Mst1. Moreover, we clarify the different dependence of the transcription factor TOX in NK cells biology.

Mst1 attenuates myocardial ischemia/reperfusion injury following heterotopic heart transplantation in mice through regulating Keap1/Nrf2 axis

Ischemia reperfusion (I/R) injury remains a frequent adverse event that accompanies heart transplantation. Oxidative stress and aberrant production of free radicals were regarded as the culprit of cell death and tissue damage in post-transplant IR injury. Mst1 has been identified as a mediator of oxidative stress and Nrf2 regulates anti-oxidative enzymes, however, the interaction between Mst1 and Nrf2 anti-oxidative stress pathway remains to be clarified in the event of cardiac IR injury. Herein, the model of ischemia-reperfusion injury in heterotopic heart transplantation mice was firstly established.. We observed that cardiac IR induced upregulation of Mst1 and activation of Nrf2/HO-1pathway in mice receiving heterotopic heart transplantation. Further Cobalt dichloride-induced oxidative stress model of RAW264.7 macrophage cells were then established to mimic cardiac I/R injury, results showed that exposure to CoCl₂ induced the upregulation of Mst1 and activation of Keap1/Nrf2 pathway, and genetic ablation of Mst-1 and inhibition of Keap1/Nrf2 pathway aggravated oxidative damage in those cells. Additional in vivo study showed that transfection of Mst1 shRNA spurred ROS generation and worsened cardiac damage in IR mice. Meanwhile, Mst1-KD mice receiving heart transplantation showed markedly downregulation of Nrf2, HO-1 yet upregulation of Keap1, indicating diminished protective effect against tissue damage caused by IR probably owing to the frustration of Keap1/Nrf2 pathway. Taken together, our findings demonstrated the protective effect of Mst1 from cardiac IR injury via triggering Keap1/Nrf2 axis and suppressing ROS generation, which shed light on the promising role of Mst1 in transitional management of IR injury resulted from cardiac transplantation.

The role of the Hippo pathway in autophagy in the heart

The Hippo pathway, an evolutionarily conserved signalling mechanism, controls organ size and tumourigenesis. Increasing lines of evidence suggest that autophagy, an important mechanism of lysosome-mediated cellular degradation, is regulated by the Hippo pathway, which thereby profoundly affects cell growth and death responses in various cell types. In the heart, Mst1, an upstream component of the Hippo pathway, not only induces apoptosis but also inhibits autophagy through phosphorylation of Beclin 1. YAP/TAZ, transcription factor co-factors and the terminal effectors of the Hippo pathway, affect autophagy through transcriptional activation of TFEB, a master regulator of autophagy and lysosomal biogenesis. The cellular abundance of YAP is negatively regulated by autophagy and suppression of autophagy induces accumulation of YAP, which, in turn, acts as a feedback mechanism to induce autophagosome formation. Thus, the Hippo pathway and autophagy regulate each other, thereby profoundly affecting cardiomyocyte survival and death. This review discusses the interaction between the Hippo pathway and autophagy and its functional significance during stress conditions in the heart and the cardiomyocytes therein.

Rab10 protects against DOX-induced cardiotoxicity by alleviating the oxidative stress and apoptosis of cardiomyocytes

Doxorubicin (DOX) is a widely used anticancer drug, but its clinical application is limited by cardiotoxicity. As a member of the Rab family, Rab10 has multiple subcellular localizations and carries out a wide variety of functions. Here, we explored the role of Rab10 on DOX-induced cardiotoxicity. Cardiac-specific Rab10 transgenic mice were constructed and treated with DOX or saline. We found that cardiac-specific overexpression of Rab10 alleviated cardiac dysfunction and attenuated cytoplasmic vacuolization and mitochondrial damage in DOX-treated mouse heart tissues. Immunofluorescence staining and Western blot analysis showed that Rab10 alleviated DOX-induced apoptosis and oxidative stress in cardiomyocytes in mouse heart tissues. We demonstrated that DOX mediated apoptosis, oxidative stress and depolarization of the mitochondrial membrane potential in H9c2 cells, while overexpression and knockdown of Rab10 attenuated and aggravated these effects, respectively. Furthermore, we found that Mst1, a serine-threonine kinase, was cleaved and translocated into the nucleus in H9c2 cells after DOX treatment, and knockdown of Mst1 alleviated DOX-induced cardiomyocyte apoptosis. Overexpression of Rab10 inhibited the cleavage of Mst1 mediated by DOX treatment in vivo and in vitro. Together, our findings demonstrated that cardiac-specific overexpression of Rab10 alleviated DOX-induced cardiac dysfunction and injury via inhibiting oxidative stress and apoptosis of cardiomyocytes, which may be partially ascribed to the inhibition of Mst1 activity.

Mst1-mediated phosphorylation of Nur77 improves the endometrial receptivity in human and mice

BACKGROUND

Successful embryo implantation requires the attachment of a blastocyst to the receptive endometrial epithelium, which was disturbed in the women with recurrent implantation failure (RIF). Endometrial β3-integrin was the most important adhesion molecule contributing to endometrial receptivity in both humans and mice. Nur77 has been proven indispensable for fertility in mice, here we explore the role of Nur77 on embryo-epithelial adhesion and potential treatment to embryo implantation failure.

METHODS

The expression and location of Mst1 and Nur77 in endometrium from fertile women and RIF patients were examined by IHC, qRT-PCR and Western blotting. In vitro kinase assay following with LC-MS/MS were used to identify the phosphorylation site of Nur77 activated by Mst1. The phosphorylated Nur77 was detected by phos-tag SDS-PAGE assay and specific antibody against phospho-Nur77-Thr366. The effect of embryo-epithelium interaction was determined in the BeWo spheroid or mouse embryo adhesion assay, and delayed implantation mouse model. RNA-seq was used to explore the mechanism by which Nur77 derived peptide promotes endometrial receptivity.

FINDINGS

Endometrial Mammalian sterile 20 (STE20)-like kinase 1 (Mst1) expression level was decreased in the women with RIF than that in the fertile control group, while Mst1 activation in the epithelial cells promoted trophoblast-uterine epithelium adhesion. The effect of Nur77 mediated trophoblast-uterine epithelium adhesion was facilitated by active Mst1. Mechanistically, mst1 promotes the transcription activity of Nur77 by phosphorylating Nur77 at threonine 366 (T366), and consequently increased downstream target β3-integrin expression. Furthermore, a Nur77-derived peptide containing phosphorylated T366 markedly promoted mouse embryo attachment to Ishikawa cells ([4 (2-4)] vs [3 (2-4)]) and increased the embryo implantation rate (4 vs 1.4) in a delayed implantation mouse model by regulating integrin signalling. Finally, it is observed that the endometrial phospho-Nur77 (T366) level is decreased by 80% in the women with RIF.

INTERPRETATION

In addition to uncovering a potential regulatory mechanism of Mst1/Nur77/β3-integrin signal axis involved in the regulation of embryo-epithelium interaction, our finding provides a novel marker of endometrial receptivity and a potential therapeutic agent for embryo implantation failure.

FUNDING

National Key Research and Development Program of China (2018YFC1004400), the National Natural Science Foundation of China (82171653, 82271698, 82030040, 81971387 and 30900727), and National Institutes of Health grants (R01HL103869).

Melatonin activates the Mst1-Nrf2 signaling to alleviate cardiac hypertrophy in pulmonary arterial hypertension

Among pulmonary arterial hypertension (PAH) patients, right ventricular (RV) functioning has been considered a major determining factor for cardiac capacity and survival. However, despite the recognition of the clinical importance for preserving RV functioning, no effective treatments are currently available for RV failure. This study aims to suggest one such possible treatment, through investigating the cardio-protective capabilities of the anti-oxidant, melatonin (Mel), for treating adverse RV remodeling in PAH, along with its underlying mechanisms. Arginine vasopressin induced neonatal rat cardiomyocyte hypertrophy in vitro; in vivo, PAH was induced in rats through intraperitoneal monocrotaline (MCT) injections, and Mel was administered intraperitoneally 24 h prior to MCT. Mel reduced rat cardiomyocyte hypertrophy and mitochondrial oxidative stress in vitro by activating the Mst1-Nrf2 pathway, which were all reversed upon siRNA knockdown of Mst1. Likewise, in vivo, Mel pre-treatment significantly ameliorated MCT-induced deterioration in cardiac function, RV hypertrophy, fibrosis and dilation. These beneficial effects were also associated with Mst1-Nrf2 pathway up regulation and its associated reduction in oxidative stress, as evidenced by the decrease in RV malondialdehyde content. Notably, results from Mel treatment were similar, or even superior, to those obtained from N-acetyl cysteine (NAC), which has already been-confirmed as an anti-oxidative treatment for PAH. By contrast, co-treatment with the Mst1 inhibitor XMU-MP-1 reversed all of those Mel-associated beneficial effects. Our findings thus identified Mel as a potent cardio-protective agent against the onset of maladaptive RV remodeling, through enhancement of the anti-oxidative response via Mst1-Nrf2 pathway activation.

Neuroprotective effect of L-deprenyl on the expression level of the Mst1 gene and inhibition of apoptosis in rat-model spinal cord injury

Objectives

After primary tissue damage as a result of spinal cord injury (SCI), there is a period of secondary damage, which includes several cellular and inflammatory biochemical cascades. As a novel pro-apoptotic kinase, Mst1 (serine/threonine kinase 4) promotes programmed cell death in an inflammatory disease model. This study aimed to evaluate Mst1 gene expression levels in rats with spinal cord injury treated with L- deprenyl.

Materials and Methods

The rats were divided into control (contusion), laminectomy, sham-operated (contused rats received 1 ml normal saline intraperitoneal), and treatment (contused rats received 5 mg/kg of L-deprenyl intraperitoneal; once a day for 7 days). The BBB (Basso, Beattie, and Bresnahan) scales were performed to assess motor function following SCI. Rats were sacrificed 28 days after SCI and the spinal cord lesion area was removed. Apoptosis and cavity formation in the spinal cord were determined by H&E staining and TUNEL assay, respectively. The mRNA levels of the Mst1, Nrf2, Bcl-2, and PGC1 α genes were analyzed using real-time quantitative PCR.

Results

The results showed significant improvement in motor function in the L- deprenyl group compared with the untreated group. Histological analysis showed a significant reduction in the number of tunnel-positive cells after injection of L-deprenyl, as well as a decrease in the volume of the cavity. In addition, L-deprenyl treatment increased the expression of the Nrf2, Bcl-2, and PGC1 α genes, while reducing the expression of the Mst1 gene in the spinal nerves.

Conclusion

These results suggest that L-deprenyl is a promising treatment for spinal cord injury.

Physiological Role of Bile Acids Modified by the Gut Microbiome

Bile acids (BAs) are produced from cholesterol in the liver and are termed primary BAs. Primary BAs are conjugated with glycine and taurine in the liver and then released into the intestine via the gallbladder. After the deconjugation of glycine or taurine by the gut microbiome, primary BAs are converted into secondary BAs by the gut microbiome through modifications such as dehydroxylation, oxidation, and epimerization. Most BAs in the intestine are reabsorbed and transported to the liver, where both primary and secondary BAs are conjugated with glycine or taurine and rereleased into the intestine. Thus, unconjugated primary Bas, as well as conjugated and unconjugated secondary BAs, have been modified by the gut microbiome. Some of the BAs reabsorbed from the intestine spill into the systemic circulation, where they bind to a variety of nuclear and cell-surface receptors in tissues, whereas some of the BAs are not reabsorbed and bind to receptors in the terminal ileum. BAs play crucial roles in the physiological regulation of various tissues. Furthermore, various factors, such as diet, age, and antibiotics influence BA composition. Here, we review recent findings regarding the physiological roles of BAs modified by the gut microbiome in the metabolic, immune, and nervous systems.

Glycogen accumulation and phase separation drives liver tumor initiation

Glucose consumption is generally increased in tumor cells to support tumor growth. Interestingly, we report that glycogen accumulation is a key initiating oncogenic event during liver malignant transformation. We found that glucose-6-phosphatase (G6PC) catalyzing the last step of glycogenolysis is frequently downregulated to augment glucose storage in pre-malignant cells. Accumulated glycogen undergoes liquid-liquid phase separation, which results in the assembly of the Laforin-Mst1/2 complex and consequently sequesters Hippo kinases Mst1/2 in glycogen liquid droplets to relieve their inhibition on Yap. Moreover, G6PC or another glycogenolysis enzyme-liver glycogen phosphorylase (PYGL) deficiency in both human and mice results in glycogen storage disease along with liver enlargement and tumorigenesis in a Yap-dependent manner. Consistently, elimination of glycogen accumulation abrogates liver growth and cancer incidence, whereas increasing glycogen storage accelerates tumorigenesis. Thus, we concluded that cancer-initiating cells adapt a glycogen storing mode, which blocks Hippo signaling through glycogen phase separation to augment tumor incidence.

Valproic Acid Ameliorates Locomotor Function in the Rat Model of Contusion via Alteration of Mst1, Bcl-2, and Nrf2 Gene Expression

Background:

In animal models of inflammatory diseases, Mst1 facilitates the programmed cell death as a novel pro-apoptotic kinase. This research aimed to determine the expression level of Mst1 gene in a rat model of SCI treated with VPA.

Methods:

Severe rat model contusion was used for evaluation of the neuroprotective effect of valproic acid. The BBB test, was performed to determine locomotor functions. H&E staining and TUNEL assay were performed to detect cavity formation and apoptosis, respectively. The mRNA levels of the genes Mst1, Nrf2, and Bcl-2 were evaluated, using quantitative RT-PCR.

Results:

The results revealed that Mst1 gene expression and TUNEL-positive cells in the VPA-treated group were significantly reduced as compared to the untreated group (p ≤ 0.05).

Conclusion:

Our findings indicate that VPA has therapeutic potential and can be a candidate for the treatment of neurodegenerative disorders and traumatic injury as a promising drug.

Schizosaccharomyces pombe KAT5 contributes to resection and repair of a DNA double-strand break

Chromatin remodeling is essential for effective repair of a DNA double-strand break (DSB). KAT5 (Schizosaccharomyces pombe Mst1, human TIP60) is a MYST family histone acetyltransferase conserved from yeast to humans that coordinates various DNA damage response activities at a DNA DSB, including histone remodeling and activation of the DNA damage checkpoint. In S. pombe, mutations in mst1+ causes sensitivity to DNA damaging drugs. Here we show that Mst1 is recruited to DSBs. Mutation of mst1+ disrupts recruitment of repair proteins and delays resection. These defects are partially rescued by deletion of pku70, which has been previously shown to antagonize repair by homologous recombination (HR). These phenotypes of mst1 are similar to pht1-4KR, a nonacetylatable form of histone variant H2A.Z, which has been proposed to affect resection. Our data suggest that Mst1 functions to direct repair of DSBs toward HR pathways by modulating resection at the DSB.

Mst1 Knockout Alleviates Mitochondrial Fission and Mitigates Left Ventricular Remodeling in the Development of Diabetic Cardiomyopathy

The disruption of mitochondrial dynamics is responsible for the development of diabetic cardiomyopathy (DCM). However, the mechanisms that regulate the balance of mitochondrial fission and fusion are not well-understood. Wild-type, Mst1 transgenic and Mst1 knockout mice were induced with experimental diabetes by streptozotocin injection. In addition, primary neonatal cardiomyocytes were isolated and cultured to simulate diabetes to explore the mechanisms. Echocardiograms and hemodynamic measurements revealed that Mst1 knockout alleviated left ventricular remodeling and cardiac dysfunction in diabetic mice. Mst1 knockdown significantly decreased the number of TUNEL-positive cardiomyocytes subjected to high-glucose (HG) medium culture. Immunofluorescence study indicated that Mst1 overexpression enhanced, while Mst1 knockdown mitigated mitochondrial fission in DCM. Mst1 participated in the regulation of mitochondrial fission by upregulating the expression of Drp1, activating Drp1^S616 phosphorylation and Drp1^S637 dephosphorylation, as well as promoting Drp1 recruitment to the mitochondria. Furthermore, Drp1 knockdown abolished the effects of Mst1 on mitochondrial fission, mitochondrial membrane potential and mitochondrial dysfunction in cardiomyocytes subjected to HG treatment. These results indicated that Mst1 knockout inhibits mitochondrial fission and alleviates left ventricular remodeling thus prevents the development of DCM.

Dissecting molecular mechanisms underlying H2O2-induced apoptosis of mouse bone marrow mesenchymal stem cell: role of Mst1 inhibition

BACKGROUND

Bone marrow mesenchymal stem cell (BM-MSC) has been shown to treat pulmonary arterial hypertension (PAH). However, excessive reactive oxygen species (ROS) increases the apoptosis of BM-MSCs, leading to poor survival and engraft efficiency. Thus, improving the ability of BM-MSCs to scavenge ROS may considerably enhance the effectiveness of transplantation therapy. Mammalian Ste20-like kinase 1 (Mst1) is a pro-apoptotic molecule which increases ROS production. The aim of this study is to uncover the underlying mechanisms the effect of Mst1 inhibition on the tolerance of BM-MSCs under H₂O₂ condition.

METHODS

Mst1 expression in BM-MSCs was inhibited via transfection with adenoviruses expressing a short hairpin (sh) RNA directed against Mst1 (Ad-sh-Mst1) and exposure to H₂O₂. Cell viability was detected by Cell Counting Kit 8 (CCK-8) assay, and cell apoptosis was analyzed by Annexin V-FITC/PI, Caspase 3 Activity Assay kits, and pro caspase 3 expression. ROS level was evaluated by the ROS probe DCFH-DA, mitochondrial membrane potential (ΔΨm) assay, SOD1/2, CAT, and GPx expression. Autophagy was assessed using transmission electron microscopy, stubRFP-sensGFP-LC3 lentivirus, and autophagy-related protein expression. The autophagy/Keap1/Nrf2 signal in H₂O₂-treated BM-MSC/sh-Mst1 was also measured.

RESULTS

Mst1 inhibition reduced ROS production; increased antioxidant enzyme SOD1/2, CAT, and GPx expression; maintained ΔΨm; and alleviated cell apoptosis in H₂O₂-treated BM-MSCs. In addition, this phenomenon was closely correlated with the autophagy/Keap1/Nrf2 signal pathway. Moreover, the antioxidant pathway Keap1/Nrf2 was also blocked when autophagy was inhibited by the autophagy inhibitor 3-MA. However, Keap1 or Nrf2 knockout via siRNA had no effect on autophagy activation or suppression.

CONCLUSION

Mst1 inhibition mediated the cytoprotective action of mBM-MSCs against H₂O₂-induced oxidative stress injury. The underlying mechanisms involve autophagy activation and the Keap1/Nrf2 signal pathway.

LncRNA SNHG17 knockdown promotes Parkin-dependent mitophagy and reduces apoptosis of podocytes through Mst1

LncRNAs play important roles in the regulation of podocyte apoptosis in diabetic nephropathy (DN). However, the role of lncRNA SNHG17 in controlling mitophagy-induced apoptosis of podocytes in DN is unknown. This study aims to elucidate the underlying mechanism of lncRNA SNHG17 in the regulation of mitophagy-induced apoptosis of podocytes in DN. LncRNA SNHG17 and Mammalian Sterile 20-like kinase 1 (Mst1) expression were upregulated in glomeruli and podocytes of DM mice and high glucose-treated podocytes, whereas Parkin expression was downregulated. LncRNA SNHG17 overexpression suppressed mitophagy and induced apoptosis of podocytes while silencing lncRNA SNHG17 promoted mitophagy and reduced the apoptosis of podocytes. In addition, lncRNA SNHG17 interacted with Mst1 and regulated the degradation of Mst1. We further found lncRNA SNHG17 regulated Parkin expression through Mst1. Mechanistically, lncRNA SNHG17 regulated Parkin-dependent mitophagy and apoptosis of podocytes through regulating Mst1. Finally, silencing lncRNA SNHG17 promoted mitophagy and relieved DNin vivo. In conclusion, lncRNA SNHG17 knockdown promotes Parkin-dependent mitophagy and reduces apoptosis of podocytes through regulating the degradation of Mst1.

Mst1 promotes mitochondrial dysfunction and apoptosis in oxidative stress-induced rheumatoid arthritis synoviocytes

In this study, we investigated the role of macrophage stimulating 1 (Mst1) and the AMPK-Sirt1 signaling pathway in the oxidative stress-induced mitochondrial dysfunction and apoptosis seen in rheumatoid arthritis-related fibroblast-like synoviocytes (RA-FLSs). Mst1 mRNA and protein expression was significantly higher in hydrogen peroxide (H₂O₂)-treated RA-FLSs than untreated controls. H₂O₂ treatment induced the mitochondrial apoptotic pathway by activating caspase3/9 and Bax in the RA-FLSs. Moreover, H₂O₂ treatment significantly reduced mitochondrial membrane potential and mitochondrial state-3 and state-4 respiration, but increased reactive oxygen species (ROS). Mst1 silencing significantly reduced oxidative stress-induced mitochondrial dysfunction and apoptosis in RA-FLSs. Sirt1 expression was significantly reduced in the H₂O₂-treated RA-FLSs, but was higher in the H₂O₂-treated Mst1-silenced RA-FLSs. Pretreatment with selisistat (Sirt1-specific inhibitor) or compound C (AMPK antagonist) significantly reduced the viability and mitochondrial function in H₂O₂-treated Mst1-silenced RA-FLSs by inhibiting Sirt1 function or Sirt1 expression, respectively. These findings demonstrate that oxidative stress-related upregulation and activation of Mst1 promotes mitochondrial dysfunction and apoptosis in RA-FLSs by inhibiting the AMPK-Sirt1 signaling pathway. This suggests the Mst1-AMPK-Sirt1 axis is a potential target for RA therapy.

Long non-coding RNA ROR sponges miR-138 to aggravate hypoxia/reoxygenation-induced cardiomyocyte apoptosis via upregulating Mst1

BACKGROUND

Hypoxia/reoxygenation (H/R) injury of cardiomyocytes causes an irreversible damage to heart and largely results in acute myocardial infarction. Study has indicated lncRNA ROR aggravates myocardial ischemia/reperfusion (I/R) injury. Also, lncRNA ROR sponges miR-138 to promote osteogenesis. MiR-138 involves in hypoxic pulmonary vascular remodelling by targeting Mst1. However, the interaction between lncRNA ROR, miR-138 and Mst1 involved in myocardial H/R injury is still unknown.

METHODS

H9C2 cells were used to establish H/R injury model. The expression levels of lncRNA ROR and miR-138 were modified by transfection with the miR-138 mimics or lncRNA ROR overexpression plasmid. MTT and flow cytometry analysis were performed to detect cell proliferation and apoptosis. Dual luciferase reporter assay was used to determine interaction between lncRNA ROR and miR-138 or miR-138 and Mst1. Expression levels of lncRNA ROR, miR-138, Mst1 and apoptosis-related markers were determined by qRT-PCR or western blotting.

RESULTS

LncRNA ROR was significantly up-regulated, while miR-138 was obviously down-regulated in H/R-induced injury of H9C2 cells. Furthermore, miR-138 overexpression alleviated cardiac cell apoptosis induced by H/R injury. Mst1 was revealed to be a target of miR-138 and negatively regulated by miR-138. Mst1 overexpression reversed the protective effects of miR-138 on H/R injury of H9C2 cells. LncRNA ROR was identified as a sponge for miR-138. MiR-138 could protect H9C2 cells form H/R injury induced by lncRNA ROR overexpression.

CONCLUSION

Our study provides that lncRNA ROR sponges miR-138 to aggravate H/R-induced myocardial cell injury by upregulating the expression of Mst1.

Macrophage stimulating 1-induced inflammation response promotes aortic aneurysm formation through triggering endothelial cells death and activating the NF-κB signaling pathway

Aortic aneurysm formation is associated with endothelial cells dysfunction through an undefined mechanism. Macrophage stimulating 1 (Mst1) and NF-κB signaling pathway have been found to be related to inflammation response in endothelial cell damage. The goal of our study is to explore the role of Mst1 in regulating endothelial cell viability with a focus on NF-κB signaling pathway and inflammation response. Endothelial cell viability and death were determined via immunofluorescence and ELISA. Agonist of NF-κB signaling pathway and siRNA against Mst1 were used. The results in our study demonstrated that Mst1 transcription and expression were significantly elevated after exposure to oxidative stress in endothelial cells. Once loss of Mst1 through transfection of siRNA (si-Mst1), endothelial cell viability and survival rate were rapidly increased in response to oxidative stress. In addition, we also found that Mst1 controlled inflammation response and mitochondrial function in endothelial cells. Re-activation of NF-κB signaling pathway was followed by an activation of inflammation response and mitochondrial dysfunction, as evidenced by increased expression of inflammation factors and decreased ATP synthesis. Altogether, our results identify Mst1 as the primary factors responsible for endothelial cells dysfunction in aneurysms formation through inducing inflammation response, endothelial apoptosis, and NF-κB signaling pathway activation.

Cerebral ischemia-reperfusion is modulated by macrophage-stimulating 1 through the MAPK-ERK signaling pathway

Cerebral ischemia-reperfusion (IR) injury is associated with mitochondrial damage. Macrophage-stimulating 1 (MST1) reportedly stimulates mitochondrial apoptosis by suppressing BCL-2. We investigated whether MST1 promotes the progression of cerebral IR injury by inducing mitochondrial dysfunction in vivo and in vitro. Western blot analysis, quantitative polymerase chain reaction, immunofluorescence, and mitochondrial function assays were conducted in cells from wild-type and Mst1-knockout mice subjected to cerebral IR injury. MST1 expression in wild-type glial cells increased following cerebral IR injury. Cerebral IR injury reduced the mitochondrial membrane potential and mitochondrial metabolism in glial cells, while it enhanced mitochondrial reactive oxygen species generation and mitochondrial calcium levels in these cells. The deletion of Mst1 attenuated cerebral IR injury by improving mitochondrial function and reducing mitochondrial damage. The mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathway was suppressed in wild-type glial cell upon cerebral IR injury but was reactivated in Mst1-knockout glial cell. Accordingly, blocking the MAPK/ERK pathway abolished the beneficial effects of Mst1 deletion during cerebral IR injury by inducing mitochondrial damage in glial cells. Our results suggest that cerebral IR injury is associated with MST1 upregulation in the brain, while the genetic ablation of Mst1 can attenuate mitochondrial damage and sustain brain function following cerebral IR injury.

Lin28a protects against diabetic cardiomyopathy through Mst1 inhibition

Lin28a has been found to enhance glucose uptake and insulin sensitivity. Lin28a alleviates cardiac dysfunction under various pathological conditions. However, the effects and underlying mechanisms of Lin28a on diabetic cardiomyopathy (DCM) are not well-understood. The aim of this study was to determine whether Lin28a protects against DCM and the potential mechanisms. Two to three days old mouse neonatal primary cardiomyocytes were randomized for treatment with adenoviruses harboring Lin28a and mammalian sterile 20-like kinase 1 (Mst1) short hairpin RNA, 48 hr before culturing in normal or high glucose medium. Cardiomyocyte apoptosis, autophagy, mitochondrial morphology, adenosine triphosphate content, and cytokine levels in the high glucose or normal conditions were observed between all groups. Either Lin28a overexpression or Mst1 knockdown alleviated mitochondrial ultrastructure impairment, decreased cytokine levels, inhibited apoptosis, and enhanced autophagy in primary neonatal mouse cardiomyocytes treated with high glucose. Importantly, the protective effects of Lin28a and Mst1 disappeared after treatment with 3-methyladenine, an autophagy inhibitor. Interestingly, in Mst1 knockdown cardiomyocytes, Lin28a overexpression failed to further enhance autophagy and alleviate high glucose-induced cardiomyocyte injury, which implies the protective roles of Lin28a counteracting high glucose-induced cardiomyocyte injury are dependent on Mst1 inhibition. Furthermore, co-immunoprecipitation and immunofluorescence double staining suggested that there were no direct interactions between Mst1 and Lin28a. Lin28a increased the expression of Akt, which inhibited the activation of Mst1-mediated apoptotic pathways.

Mst1-Deficiency Induces Hyperactivation of Monocyte-Derived Dendritic Cells via Akt1/c-myc Pathway

Mst1 is a multifunctional serine/threonine kinase that is highly expressed in several immune organs. The role of Mst1 in the activation of dendritic cells (DCs), a key player of adaptive immunity, is poorly understood. In this study, we investigated the role of Mst1 in GM-CSF-induced bone marrow-derived DCs and the underlying mechanisms. Mst1^−/− DCs in response to GM-CSF expressed higher levels of activation/maturation-related cell surface molecules, such as B7 and MHC class II than Mst1^+/+ DCs. Furthermore, the expression of proinflammatory cytokines, such as IL-23, TNF-α, and IL-12p40, was increased in Mst1^−/− DCs, indicating that Mst1-deficiency may induce the hyperactivation of DCs. Additionally, Mst1^−/− DCs exhibited a stronger capacity to activate allogeneic T cells than Mst1^+/+ DCs. Silencing of Mst1 in DCs promoted their hyperactivation, similar to the phenotypes of Mst1^−/− DCs. Mst1^−/− DCs exhibited an increase in Akt1 phosphorylation and c-myc protein levels. In addition, treatment with an Akt1 inhibitor downregulated the protein level of c-myc increased in Mst1-deficient DCs, indicating that Akt1 acts as an upstream inducer of the de novo synthesis of c-myc. Finally, Akt1 and c-myc inhibitors downregulated the increased expression of IL-23p19 observed in Mst1-knockdown DCs. Taken together, these data demonstrate that Mst1 negatively regulates the hyperactivation of DCs through downregulation of the Akt1/c-myc axis in response to GM-CSF, and suggest that Mst1 is one of the endogenous factors that determine the activation status of GM-CSF-stimulated inflammatory DCs.

Hippo/Mst1 overexpression induces mitochondrial death in head and neck squamous cell carcinoma via activating β-catenin/Drp1 pathway

Mammalian Ste20-like kinase 1 (Mst1) is associated with cell apoptosis. In the current study, we explored the regulatory effects of Mst1 on squamous cell carcinoma of the head and neck (SCCHN) in vitro. SCCHN Cal27 cells and Tu686 cells were transfected with adenovirus-loaded Mst1 to detect the role of Mst1 in cell viability. Then, siRNA against Drp1 was transfected into cells to evaluate the influence of mitochondrial fission in cancer survival. Our data illustrated that Mst1 overexpression promoted SCCHN Cal27 cell and Tu686 cell death via activating mitochondria-related apoptosis. Cells transfected with adenovirus-loaded Mst1 have increased expression of DRP1 and higher DRP1 promoted mitochondrial fission. Active mitochondrial fission mediated mitochondrial damage, as evidenced by increased mitochondrial oxidative stress, decreased mitochondrial energy production, and reduced mitochondrial respiratory complex function. Moreover, Mst1 overexpression triggered mitochondria-dependent cell apoptosis via DRP1-related mitochondrial fission. Further, we found that Mst1 overexpression controlled mitochondrial fission via the β-catenin/DRP1 pathways; inhibition of β-catenin and/or knockdown of DRP1 abolished the pro-apoptotic effects of Mst1 overexpression on SCCHN Cal27 cells and Tu686 cells, leading to the survival of cancer cells in vitro. In sum, our results illustrate that Mst1/β-catenin/DRP1 axis affects SCCHN Cal27 cell and Tu686 cell viability via controlling mitochondrial dynamics balance. This finding identifies Mst1 activation might be an effective therapeutic target for the treatment of SCCHN.

Inhibitory effect of melatonin on Mst1 ameliorates myocarditis through attenuating ER stress and mitochondrial dysfunction

Viral myocarditis has been found to be one of the leading causes of sudden death in young adults. However, no effective drugs have been developed to intervene the progression of myocarditis. Accordingly, the present study is carried out to explore the protective role played by melatonin in the setting of viral myocarditis with a focus on Mst1-Hippo pathway, mitochondrial dysfunction and ER stress. Cardiac function was determined via echocardiographic examination. Mitochondrial function and ER stress were detected via ELISA, western blots, and immunofluorescence. Our data demonstrated that virus injection induced cardiac dysfunction as evidenced by reduced contractile function in myocardium. Besides, LDH release assay and western blotting analysis demonstrated that cardiomyocyte death was activated by virus injection. Interestingly, melatonin treatment improved cardiac function and repressed virus-mediated cardiomyocyte apoptosis. At the molecular levels, mitochondrial dysfunction was induced by virus infection, as indicated by mitochondrial membrane potential reduction, mPTP opening rate elevation and caspase-9-related apoptosis activation. Besides, ER stress parameters were also elevated in virus-treated cardiomyocytes. Interestingly, melatonin treatment maintained mitochondrial dysfunction and repressed ER stress. To the end, we found that Mst1 was upregulated by virus infection; this effect was attenuated through supplementation with melatonin. However, Mst1 overexpression reduced the beneficial impact exerted by melatonin on cardiomyocyte viability, mitochondrial function and ER homeostasis. Our study illustrated that melatonin treatment attenuated viral myocarditis via sustaining cardiomyocyte viability, repressing mitochondrial dysfunction and inhibiting ER stress in a manner dependent on Mst1 inhibition.

Mst1 deletion reduces septic cardiomyopathy via activating Parkin-related mitophagy

Cardiomyocyte function and viability are highly modulated by mammalian Ste20-like kinase 1 (Mst1)-Hippo pathway and mitochondria. Mitophagy, a kind of mitochondrial autophagy, is a protective program to attenuate mitochondrial damage. However, the relationship between Mst1 and mitophagy in septic cardiomyopathy has not been explored. In the present study, Mst1 knockout mice were used in a lipopolysaccharide (LPS)-induced septic cardiomyopathy model. Mitophagy activity was measured via immunofluorescence, Western blotting, and enzyme-linked immunosorbent assay. Pathway blocker and small interfering RNA were used to perform the loss-of-function assay. The results demonstrated that Mst1 was rapidly increased in response to LPS stress. Knockout of Mst1 attenuated LPS-mediated inflammation damage, reduced cardiomyocyte death, and improved cardiac function. At the molecular levels, LPS treatment activated mitochondrial damage, such as mitochondrial respiratory dysfunction, mitochondrial potential reduction, mitochondrial ATP depletion, and caspase family activation. Interestingly, in response to mitochondrial damage, Mst1 deletion activated mitophagy which attenuated LPS-mediated mitochondrial damage. However, inhibition of mitophagy via inhibiting parkin mitophagy abolished the protective influences of Mst1 deletion on mitochondrial homeostasis and cardiomyocyte viability. Overall, our results demonstrated that septic cardiomyopathy is linked to Mst1 upregulation which is followed by a drop in the protective mitophagy.

Mst1 deletion reduces hyperglycemia-mediated vascular dysfunction via attenuating mitochondrial fission and modulating the JNK signaling pathway

Diabetes is a leading cause of microvascular complications, such as nephropathy and retinopathy. Recent studies have proposed that hyperglycemia-induced endothelial cell dysfunction is modulated by mitochondrial stress. Therefore, our experiment was to detect the upstream mediator of mitochondrial stress in hyperglycemia-treated endothelial cells with a focus on macrophage-stimulating 1 (Mst1) and mitochondrial fission. Our data illuminated that hyperglycemia incubation reduced cell viability, as well as increased apoptosis ratio in endothelial cell, and this alteration seemed to be associated with Mst1 upregulation. Inhibition of Mst1 via transfection of Mst1 siRNA into an endothelial cell could sustain cell viability and maintain mitochondrial function. At the molecular levels, endothelial cell death was accompanied with the activation of mitochondrial oxidative stress, mitochondrial apoptosis, and mitochondrial fission. Genetic ablation of Mst1 could reduce mitochondrial oxidative injury, block mitochondrial apoptosis, and repress mitochondrial fission. Besides, we also found Mst1 triggered mitochondrial dysfunction as well as endothelial cell damage through augmenting JNK pathway. Suppression of JNK largely ameliorated the protective actions of Mst1 silencing on hyperglycemia-treated endothelial cells and sustain mitochondrial function. The present study identifies Mst1 as a primary key mediator for hyperglycemia-induced mitochondrial damage and endothelial cell dysfunction. Increased Mst1 impairs mitochondrial function and activates endothelial cell death via opening mitochondrial death pathway through JNK.

Mst1 contributes to nasal epithelium inflammation via augmenting oxidative stress and mitochondrial dysfunction in a manner dependent on Nrf2 inhibition

Nasal epithelium inflammation plays an important role in transmitting and amplifying damage signals for the lower airway. However, the molecular basis of nasal epithelium inflammation damage has not been fully addressed. Mst1 is reported to modulate inflammation via multiple effects. Thus, the aim of our study is to understand the pathological mechanism underlying Mst1-related nasal epithelium inflammation in vitro. Our result indicated that Mst1 expression was rapidly increased in response to tumor necrosis factor-α (TNF-α) treatment in vitro and this effect was a dose-dependent manner. Interestingly, knockdown of Mst1 via transfecting small interfering RNA markedly reversed cell viability in the presence of TNF-α. Further, we found that Mst1 deficiency reduced cellular oxidative stress and attenuated mitochondrial dysfunction, as evidenced by reversed mitochondrial complex-I activity, decreased mitochondrial permeability transition pore opening rate, and stabilized mitochondrial membrane potential. Besides, we found that Nrf2 expression was increased after deletion of Mst1 whereas silencing of Nrf2 abolished the protective effects of Mst1 deletion on nasal epithelium survival and mitochondrial homeostasis. Moreover, Nrf2 overexpression also protected nasal epithelium against TNF-α-induced inflammation damage. Altogether, our data confirm that the Mst1 activation and Nrf2 downregulation seem to be the potential mechanisms responsible for the inflammation-mediated injury in nasal epithelium via mediating mitochondrial damage and cell oxidative stress.

Suramin protects hepatocytes from LPS-induced apoptosis by regulating mitochondrial stress and inactivating the JNK-Mst1 signaling pathway

An uncontrolled inflammatory response has been implicated in the progression of acute liver failure through poorly understood mechanisms. The aim of our study was to investigate whether suramin attenuates inflammation-mediated hepatocyte apoptosis by modulating mitochondrial homeostasis. Primary hepatocytes were isolated from mice and treated with LPS in vitro in the presence or absence of suramin. Western blotting, immunofluorescence staining, and ELISAs were used to evaluate the mitochondrial stress. The LPS treatment caused hepatocyte death via apoptosis. Interestingly, suramin supplementation attenuated LPS-mediated hepatocyte death by reducing Mst1 expression; the overexpression of Mst1 abolished the anti-apoptotic effects of suramin on LPS-treated hepatocytes. At the molecular level, suramin treatment repressed mitochondrial oxidative stress, sustained mitochondrial dynamics and blocked the caspase-9-mediated mitochondrial apoptosis pathway; these effects of suramin were achieved by reversing Mst1 expression. Furthermore, our study found that suramin modulated Mst1 expression via the JNK signaling pathway. Activation of JNK prevented the suramin-mediated Mst1 downregulation and concomitantly increased hepatocyte apoptosis and mitochondrial dysfunction. Taken together, our results confirmed the anti-apoptotic and anti-inflammatory effects of suramin on LPS-challenged hepatocytes. Suramin sustained hepatocyte viability and attenuated mitochondrial stress via repressing the JNK-Mst1 signaling pathway.

The NuA4 acetyltransferase and histone H4 acetylation promote replication recovery after topoisomerase I-poisoning

BACKGROUND

Histone acetylation plays an important role in DNA replication and repair because replicating chromatin is subject to dynamic changes in its structures. However, its precise mechanism remains elusive. In this report, we describe roles of the NuA4 acetyltransferase and histone H4 acetylation in replication fork protection in the fission yeast Schizosaccharomyces pombe.

RESULTS

Downregulation of NuA4 subunits renders cells highly sensitive to camptothecin, a compound that induces replication fork breakage. Defects in NuA4 function or mutations in histone H4 acetylation sites lead to impaired recovery of collapsed replication forks and elevated levels of Rad52 DNA repair foci, indicating the role of histone H4 acetylation in DNA replication and fork repair. We also show that Vid21 interacts with the Swi1-Swi3 replication fork protection complex and that Swi1 stabilizes Vid21 and promotes efficient histone H4 acetylation. Furthermore, our genetic analysis demonstrates that loss of Swi1 further sensitizes NuA4 and histone H4 mutant cells to replication fork breakage.

CONCLUSION

Considering that Swi1 plays a critical role in replication fork protection, our results indicate that NuA4 and histone H4 acetylation promote repair of broken DNA replication forks.

Overexpression of macrophage stimulating 1 enhances the anti-tumor effects of IL-24 in esophageal cancer via inhibiting ERK-Mfn2 signaling-dependent mitophagy

Although cytokine-based therapy is a promising tool to control the progression of esophageal cancer, low therapeutic responses largely compromise treatment efficacy through unidentified mechanisms. The goal of our study was to explore the roles of macrophage stimulating 1 (Mst1) and mitophagy in enhancing IL-24-based cytokine therapy in esophageal cancer. Our data demonstrated that IL-24 application promoted cancer death by inducing mitochondrial stress, as manifested by mitochondrial ROS overproduction, mitochondrial potential dissipation, cellular ATP deprivation and mitochondrial death activation. Overexpression of Mst1 enhanced IL-24-mediated mitochondrial damage and further augmented IL-24-induced death in esophageal cancer. Molecular investigations illustrated that the IL-24-activated mitochondrial response is accompanied by activation of mitophagy, a protective mechanism to attenuate mitochondrial damage. However, Mst1 overexpression inhibited mitophagy activity, which was achieved by inactivating the ERK-Mfn2 signaling pathway. The re-activation of mitophagy abolished the cancer-killing effects of Mst1 overexpression on esophageal cancer. Altogether, our data demonstrate that IL-24-related therapeutic resistance is associated with mitophagy activation. Mst1 overexpression inhibits mitophagy activity via suppressing the ERK-Mfn2 pathway, ultimately augmenting IL-24-inducd esophageal cancer death via enhanced mitochondrial stress.

Mammalian STE20-like Kinase 1 Knockdown Attenuates TNFα-Mediated Neurodegenerative Disease by Repressing the JNK Pathway and Mitochondrial Stress

Neuroinflammation has been acknowledged as a primary factor contributing to the pathogenesis of neurodegenerative disease. However, the molecular mechanism underlying inflammation stress-mediated neuronal dysfunction is not fully understood. The aim of our study was to explore the influence of mammalian STE20-like kinase 1 (Mst1) in neuroinflammation using TNFα and CATH.a cells in vitro. The results of our study demonstrated that the expression of Mst1 was dose-dependently increased after TNFα treatment. Interestingly, knockdown of Mst1 using siRNA transfection significantly repressed TNFα-induced neuronal death. We also found that TNFα treatment was associated with mitochondrial stress, including mitochondrial ROS overloading, mitochondrial permeability transition pore (mPTP) opening, mitochondrial membrane potential reduction, and mitochondrial pro-apoptotic factor release. Interestingly, loss of Mst1 attenuated TNFα-triggered mitochondrial stress and sustained mitochondrial function in CATH.a cells. We found that Mst1 modulated mitochondrial homeostasis and cell viability via the JNK pathway in a TNFα-induced inflammatory environment. Inhibition of the JNK pathway abolished TNFα-mediated CATH.a cell death and mitochondrial malfunction, similar to the results obtained via silencing of Mst1. Taken together, our results indicate that inflammation-mediated neuronal dysfunction is implicated in Mst1 upregulation, which promotes mitochondrial stress and neuronal death by activating the JNK pathway. Accordingly, our study identifies the Mst1-JNK-mitochondria axis as a novel signaling pathway involved in neuroinflammation.

Mst1-Hippo pathway triggers breast cancer apoptosis via inducing mitochondrial fragmentation in a manner dependent on JNK-Drp1 axis

BACKGROUND AND OBJECTIVE

Mst1-Hippo pathway and mitochondrial fragmentation participate in the progression of several types of cancers. However, their roles in breast cancer requires investigation. The aim of our study is to determine whether Mst1 overexpression regulates the viability of breast cancer cells via modulating mitochondrial fragmentation.

MATERIALS AND METHODS

TUNEL staining, MTT assay and Western blotting were used to detect cancer cell death. Adenovirus-loaded Mst1 was transfected into cells to overexpress Mst1. Mitochondrial fragmentation was observed via immunofluorescence staining and Western blotting. Pathway blocker was used to detect whether Mst1 modulated cell death and mitochondrial fragmentation via JNK signaling pathway.

RESULTS

Our data showed that Mst1 overexpression promoted breast cancer cell death in a manner dependent on mitochondrial apoptosis. Mitochondrial oxidative stress, energy metabolism disorder, mitochondrial cyt-c liberation and mitochondrial apoptosis activation were observed after Mst1 overexpression. Furthermore, we demonstrated that Mst1 overexpression activated mitochondrial stress via triggering Drp1-related mitochondrial fragmentation, and that inhibition of Drp1-related mitochondrial fragmentation abrogated the proapoptotic effect of Mst1 overexpression on breast cancer cells. To this end, we found that Mst1 modulated Drp1 expression via the JNK signaling pathway, and that blockade of the JNK pathway attenuated mitochondrial stress and repressed apoptosis in Mst1-overexpressed cells.

CONCLUSION

Altogether, our results identified a tumor suppressive role for Mst1 overexpression in breast cancer via activation of the JNK-Drp1 axis and subsequent initiation of fatal mitochondrial fragmentation. Given these findings, strategies to enhance Mst1 activity and elevate the JNK-Drp1-mitochondrial fragmentation cascade have clinical benefits for patients with breast cancer.

Mst1 inhibition attenuates non-alcoholic fatty liver disease via reversing Parkin-related mitophagy

Obesity-related non-alcoholic fatty liver disease (NAFLD) is connected with mitochondrial stress and hepatocyte apoptosis. Parkin-related mitophagy sustains mitochondrial homeostasis and hepatocyte viability. However, the contribution and regulatory mechanisms of Parkin-related mitophagy in NAFLD are incompletely understood. Macrophage stimulating 1 (Mst1) is a novel mitophagy upstream regulator which excerbates heart and cancer apoptosisn via repressing mitophagy activity. The aim of our study is to explore whether Mst1 contributes to NAFLD via disrupting Parkin-related mitophagy. A NAFLD model was generated in wild-type (WT) mice and Mst1 knockout (Mst1-KO) mice using high-fat diet (HFD). Cell experiments were conducted via palmitic acid (PA) treatment in the primary hepatocytes. The results in our study demonstrated that Mst1 was significantly upregulated in HFD-treated livers. Genetic ablation of Mst1 attenuated HFD-mediated hepatic injury and sustained hepatocyte viability. Functional studies illustrated that Mst1 knockdown reversed Parkin-related mitophagy and the latter protected mitochondria and hepatocytes against HFD challenge. Besides, we further figured out that Mst1 modulated Parkin expression via the AMPK pathway; blockade of AMPK repressed Parkin-related mitophagy and recalled hepatocytes mitochondrial apoptosis. Altogether, our data identified that NAFLD was closely associated with the defective Parkin-related mitophagy due to Mst1 upregulation. This finding may pave the road to new therapeutic modalities for the treatment of fatty liver disease.

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Mst1 deletion prevents diet-induced NAFLD.

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Mst1 deficiency increases Parkin expression and thus reverses mitophagy activity.

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Loss of Parkin-related mitophagy abrogates the protective effect of Mst1 deletion on hepatocyte mitochondrial stress.

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Mst1 modulates Parkin via activating AMPK pathway.

Recombinant asialoerythropoetin protects HL-1 cardiomyocytes from injury via suppression of Mst1 activation

Background

Recombinant human erythropoietin (rhuEPO) and asialoerythropoietin (asialo-rhuEPO) are cardioprotective. However, the protective effects of rhuEPO could not be translated into clinical practice because of its hematopoiesis-associated side effects while non-erythropoietic asialo-rhuEPO is unavailable in large quantities for clinical studies. This study was designed to investigate the cardiomyocyte protective potential of plant-produced asialo-rhuEPO (asialo-rhuEPO^P) against staurosporine (STS)-induced injury in HL-1 murine cardiomyocytes and identify cellular pathway(s) responsible for its cardioprotection.

Methods

HL-1 cardiomyocytes were simultaneously treated with STS and asialo-rhuEPO^P. Cellular injury, apoptosis, and cell viabilities were measured by LDH assay, Hoechst staining and trypan blue exclusion method, respectively while western blotting was used to study its effects on apoptosis and autophagy hallmarks.

Results

Our results showed that 20 IU/ml asialo-rhuEPO^P provided 39% protection to cardiomyocytes compared to STS-treated cells, which is 2-fold better than that of mammalian cell-produce rhuEPO (rhuEPO^M). Asialo-rhuEPO^P was found to suppress activation of proapoptotic kinase Mst1 (mammalian Sterile-20-like kinase 1) and FOXO3, leading to inhibition of apoptotic pathway and restoration of autophagy as indicated by the reduction of fragmented/condensed nuclei, altered ratios of Bax/Bcl2, p-Bad/Bad, cytosol/mitochondrial cyt c and caspase-3 activation, and the restored levels of autophagy markers Beclin1, p62 and LC3B-II. Additionally, Akt was found to be activated and FOXO3 was phosphorylated on Ser253, suggesting inhibition of FOXO3 transcriptional function.

Conclusions

Asialo-rhuEPO^P-mediated cardioprotection occurs through activation of PI3K/Akt pathway leading to suppression of Mst1 activation and promoting cardiomyocyte survival.

General significance

Asialo-rhuEPO^P could be used to modulate Mst1 activity elevated under numerous pathological states.

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Recombinant asialo-rhuEPO protect HL-1 cardiomyocytes against STS-induced injury.

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Protective effect of recombinant asialo-rhuEPO is superior to sialylated EPO.

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Asialo-rhuEPO suppresses activation of proapoptotic kinase MSt1 by activating Akt.

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Asialo-rhuEPO restores autophagy and inhibits apoptosis to promote cell survival.

Sepsis-related myocardial injury is associated with Mst1 upregulation, mitochondrial dysfunction and the Drp1/F-actin signaling pathway

LPS-induced septic cardiomyopathy has been found to be connected with mitochondrial stress through unknown mechanisms. Mitochondrial fission is an early event in mitochondrial dysfunction. The aim of our study was to determine the role and regulatory mechanism of mitochondrial fission in the progression of LPS-induced septic cardiomyopathy, with a particular focus on Mst1 and F-actin. Our data demonstrated that Mst1 expression was rapidly upregulated in LPS-treated hearts and that increased Mst1 promoted cardiomyocyte death by inducing mitochondrial stress. Mechanistically, elevated expression of Mst1 upregulated Drp1, and the latter initiated mitochondrial fission. Excessive mitochondrial fission caused mitochondrial oxidative injury, mitochondrial membrane potential reduction, mitochondrial proapoptotic element translocation into the cytoplasm/nucleus, mitochondrial energy dysfunction and mitochondrial apoptosis activation. Inhibition of mitochondrial fission sustained mitochondrial function and favored cardiomyocyte survival. Furthermore, we identified F-actin degradation as an apparent downstream event of mitochondrial fission activation in the context of LPS-induced septic cardiomyopathy. Stabilization of F-actin attenuated fission-mediated cardiomyocyte death. Altogether, our results define the Mst1/Drp1/mitochondrial fission/F-actin axis as a new signaling pathway that mediates LPS-related septic cardiomyopathy by inducing mitochondrial stress and cardiomyocyte death. Therefore, Mst1 expression, mitochondrial fission modification and F-actin stabilization may serve as potential therapeutic targets for sepsis-related myocardial injury.

Mst1 promotes cardiac ischemia-reperfusion injury by inhibiting the ERK-CREB pathway and repressing FUNDC1-mediated mitophagy

Cardiac ischemia-reperfusion (I/R) injury results mainly from mitochondrial dysfunction and cardiomyocyte death. Mitophagy sustains mitochondrial function and exerts a pro-survival effect on the reperfused heart tissue. Mammalian STE20-like kinase 1 (Mst1) regulates chronic cardiac metabolic damage and autophagic activity, but its role in acute cardiac I/R injury, especially its effect on mitophagy, is unknown. The aim of this study is to explore whether Mst1 is involved in reperfusion-mediated cardiomyocyte death via modulation of FUN14 domain containing 1 (FUNDC1)-related mitophagy. Our data indicated that Mst1 was markedly increased in reperfused hearts. However, genetic ablation of Mst1 in Mst1-knockout (Mst1-KO) mice significantly reduced the expansion of the cardiac infarction area, maintained myocardial function and abolished I/R-mediated cardiomyocyte death. At the molecular level, upregulation of Mst1 promoted ROS production, reduced mitochondrial membrane potential, facilitated the leakage of mitochondrial pro-apoptotic factors into the nucleus, and activated the caspase-9-related apoptotic pathway in reperfused cardiomyocytes. Mechanistically, Mst1 activation repressed FUNDC1 expression and consequently inhibited mitophagy. However, deletion of Mst1 was able to reverse FUNDC1 expression and thus re-activate protective mitophagy, effectively sustaining mitochondrial homeostasis and blocking mitochondrial apoptosis in reperfused cardiomyocytes. Finally, we demonstrated that Mst1 regulated FUNDC1 expression via the MAPK/ERK-CREB pathway. Inhibition of the MAPK/ERK-CREB pathway prevented FUNDC1 activation caused by Mst1 deletion. Altogether, our data confirm that Mst1 deficiency sends a pro-survival signal for the reperfused heart by reversing FUNDC1-related mitophagy and thus reducing cardiomyocyte mitochondrial apoptosis, which identifies Mst1 as a novel regulator for cardiac reperfusion injury via modulation of mitochondrial homeostasis.

Mst1 facilitates hyperglycemia-induced retinal pigmented epithelial cell apoptosis by evoking mitochondrial stress and activating the Smad2 signaling pathway

Hyperglycemia induces retinal pigmented epithelial cell apoptosis and mitochondrial stress via poorly understood mechanisms. The goal of our current study is to explore whether mammalian sterile 20-like kinase 1 (Mst1) is involved in the pathogenesis of hyperglycemia-mediated retinal pigmented epithelial cell apoptosis by triggering mitochondrial abnormalities and activating the Smad2 signaling pathway. Retinal pigmented epithelial ARPE-19 cells were presented with a high-glucose challenge in vitro. Cell viability and apoptosis were measured via western blotting, ELISAs, and immunofluorescence assays. Mitochondrial function was detected via JC-1 staining, mitochondrial ROS flow cytometry, western blotting, and ELISAs. Loss- and gain-of-function assays were performed via cell transfection and transduction with Mst1 siRNA and Smad2 adenovirus, respectively. The results indicated that hyperglycemia treatment upregulated the levels of Mst1, an effect that was accompanied by an increase in ARPE-19 cell apoptosis. Loss of Mst1 attenuated hyperglycemia-induced cell apoptosis, and this effect seemed to be associated with mitochondrial protection. In response to hyperglycemia stimulus, mitochondrial stress was noted in ARPE-19 cells, including mitochondrial ROS overproduction, mitochondrial respiratory metabolism dysfunction, mitochondrial fission/fusion imbalance, and mitochondrial apoptosis activation. Further, we provided evidence to support the crucial role played by Smad2 in promoting Mst1-mediated cell apoptosis and mitochondrial stress. Overexpression of Smad2 abrogated the beneficial effects of Mst1 deletion on ARPE-19 cell viability and mitochondrial protection. Altogether, our results identified Mst1 as a novel mediator controlling the fate of retinal pigmented epithelial cells and mitochondrial homeostasis via the Smad2 signaling pathway. Based on this finding, strategies to repress Mst1 upregulation and block Smad2 activation are vital to alleviate hyperglycemia-mediated retinal pigmented epithelial cell damage.

Overexpression of Mst1 reduces gastric cancer cell viability by repressing the AMPK-Sirt3 pathway and activating mitochondrial fission

BACKGROUND AND OBJECTIVE

Mammalian sterile 20-like kinase 1 (Mst1) plays a critical role in regulating cell survival and apoptosis. However, its influence on gastric cancer cell viability is not understood. Our study aims to explore the specific role of Mst1 in gastric cancer.

MATERIALS AND METHODS

Cellular viability was measured via TUNEL staining, MTT assays, and Western blotting. Immunofluorescence was performed to observe mitochondrial fission. Mst1 overexpression assays were conducted to observe the regulatory mechanisms of Mst1 in mitochondrial fission and cell apoptosis.

RESULTS

The results demonstrated that Mst1 was downregulated in AGS cells when compared with GES-1 cells. However, overexpression of Mst1 reduced cell viability and increased apoptosis in AGS cells. Molecular experiments showed that Mst1 overexpression mediated mitochondrial damage, as evidenced by decreased ATP production, increased ROS generation, more cyt-c translocation from the mitochondria into the cytoplasm and nucleus, and activated the caspase-9-related apoptotic pathway. Furthermore, we found that mitochondrial fission was required for Mst1-induced mitochondrial dysfunction; inhibition of mitochondrial fission sustained mitochondrial homeostasis in response to Mst1 overexpression. In addition, our data revealed that Mst1 controlled mitochondrial fission via repressing the AMPK-Sirt3 pathway. Activation of the AMPK-Sirt3 pathway negated the promoting effect of Mst1 overexpression on mitochondrial fission.

CONCLUSION

Altogether, our data identified Mst1 as a novel tumor-suppressive factor in promoting cell death in gastric cancer cells by triggering mitochondrial fission and blocking the AMPK-Sirt3 axis.

Mst1: Function and Mechanism in Brain and Myocardial Ischemia Reperfusion Injury

Mammalian STE20-like kinase-1 (Mst1) is a generally expressed apoptosis-promoting kinase and a key bridgebuilder of apoptotic signaling in the etiology of tissue injury. Despite the fact that the biological function of Mst1 and its role in the cell's signalling network have yet to be determined, however, there is a lot of evidence that Mst1 plays an important role in cell death which results from tissue injury. Previous studies have shown that Mst1 is not only a target for some apoptosis- related molecules such as caspase 3 and P53, but also act as an activator of these proteinases to magnify apoptosis signal pathways. This article reviews the role of Mst1 in the signaling pathways which is related with the neuronal cell apoptosis or microglia activation following myocardial and brain injury. Therefore, this work contributes to better understanding of the pathological process of myocardial and brain injury.

Liraglutide protects against glucolipotoxicity-induced RIN-m5F β-cell apoptosis through restoration of PDX1 expression

Prolonged exposure to high levels of glucose and fatty acid (FFA) can induce tissue damage commonly referred to as glucolipotoxicity and is particularly harmful to pancreatic β-cells. Glucolipotoxicity-mediated β-cell failure is a critical causal factor in the late stages of diabetes, which suggests that mechanisms that prevent or reverse β-cell death may play a critical role in the treatment of the disease. Transcription factor PDX1 was recently reported to play a key role in maintaining β-cell function and survival, and glucolipotoxicity can activate mammalian sterile 20-like kinase 1 (Mst1), which, in turn, stimulates PDX1 degradation and causes dysfunction and apoptosis of β-cells. Interestingly, previous research has demonstrated that increased glucagon-like peptide-1 (GLP-1) signalling effectively protects β cells from glucolipotoxicity-induced apoptosis. Unfortunately, few studies have examined the related mechanism in detail, especially the role in Mst1 and PDX1 regulation. In the present study, we investigate the toxic effect of high glucose and FFA levels on rat pancreatic RINm5F β-cells and demonstrate that the GLP-1 analogue liraglutide restores the expression of PDX1 by inactivating Mst1, thus ameliorating β-cell impairments. In addition, liraglutide also upregulates mitophagy, which may help restore mitochondrial function and protect β-cells from oxidative stress damage. Our study suggests that liraglutide may serve as a potential agent for developing new therapies to reduce glucolipotoxicity.

Cardiac-specific Mst1 deficiency inhibits ROS-mediated JNK signalling to alleviate Ang II-induced cardiomyocyte apoptosis

Apoptosis is associated with various myocardial diseases. Angiotensin II (Ang II) plays a central role in the pathogenesis of RAAS‐triggered cardiac apoptosis. Our previous studies showed that mammalian Ste20‐like kinase 1 (Mst1) aggravates cardiac dysfunction in cardiomyocyte under pathological conditions, but its role in Ang II‐mediated cardiomyocyte apoptosis is not known. We addressed this in the present study by investigating whether cardiac‐specific Mst1 knockout can alleviate Ang II‐induced cardiomyocyte apoptosis along with the underlying mechanisms. In vitro and in vivo experiments showed that Ang II increased intracellular reactive oxygen species (ROS) production and cardiomyocyte apoptosis; these were reversed by administration of the ROS scavenger N‐acetylcysteine and by Mst1 deficiency, which suppressed c‐Jun N‐terminal kinase (JNK) phosphorylation and downstream signaling. Interestingly, Mst1 knockout failed to alleviate Ang II‐induced phosphorylation of extracellular signal‐regulated kinase 1/2, and inactivated apoptosis signal‐regulating kinase1 (ASK1) by promoting its association with thioredoxin (Trx), which reversed the Ang II‐induced activation of the ASK1–JNK pathway and suppressed Ang II‐induced cardiomyocyte apoptosis. Thus, cardiac‐specific Mst1 knockout inhibits ROS‐mediated JNK signalling to block Ang II‐induced cardiomyocyte apoptosis, suggesting Mst1 as a potential therapeutic target for treatment of RAAS‐activated heart failure.

Neuroprotective effect of lovastatin through down-regulation of pro-apoptotic Mst1 gene expression in rat model pilocarpine epilepsy

OBJECTIVE

Statins as inhibitors of HMG-CoA reductase have been recently recognized as anti-inflammatory and neuroprotective drugs. In this paper, we studied anti-apoptotic and regulatory effects of lovastatin using Pilocarpine rat model through downregulation of Mst1 (Mammalian sterile 20-like kinase 1) as a novel pro-apoptotic gene.

METHODS

The rats were divided into four groups: non-treated epileptic rats, lovastatin treated, and two vehicle groups. Racine scale was used for behavioral assessment and animals with a score of 4-5 were selected for the study. After 3 days, epileptic rats received intraperitoneal injections of lovastatin, followed by treating for 14 days. Next, they were sacrificed (28 post-first seizure) and prepared for histopathological analysis and Real-time RT-PCR.

RESULTS

The results showed that lovastatin protects Pilocarpine-induced cell death via a regulatory effect on pro-apoptotic and anti-apoptotic gene expression. The real-time PCR results showed that in the epileptic lovastatin treated group, the expression level of Mst1 significantly decreased while Nrf2 and Bcl-2 genes increased. Furthermore, histological analysis of neurodegeneration in the brain sections showed that the number of hippocampal apoptotic cells significantly decreased in the treatment groups. The results showed that the numerical density of neurons per area was significantly higher in the treated than the untreated group.

CONCLUSION

Overall, the results of this study showed that lovastatin attenuates hippocampal cell death in Pilocarpine-induced status epilepticus rat model through downregulation of the pro-apoptotic Mst1 gene.

ABBREVIATIONS

Mst1: Mammalian sterile 20-like kinase 1; Nrf2: nuclear factor erythroid 2-related factor 2; Bcl-2: B-cell lymphoma 2; HMG-CoA: 3-hydroxy-3-methylglutaryl-coenzyme A; RT-PCR: reverse transcription-polymerase chain reaction; TLE: Temporal Lobe Epilepsy; SE: status epilepticus.

Mst1 regulates post-infarction cardiac injury through the JNK-Drp1-mitochondrial fission pathway

Background

Post-infarction cardiac injury is closely associated with cardiac remodeling and heart dysfunction. Mammalian STE20-like kinase 1 (Mst1), a regulator of cellular apoptosis, is involved in cardiac remodeling in post-infarction heart, but the mechanisms remain poorly defined. We aimed to explore the role of Mst1 in regulating chronic post-infarction cardiac injury, with a focus on mitochondrial homoeostasis.

Methods

Wild-type (WT) and Mst1-knockout mice were as the cardiac myocardial infarction model. Cardiac fibrosis, myocardial inflammation response, heart dysfunction and cardiomyocyte death were measured in vivo using immunohistochemistry, immunofluorescence, western blot, qPCR and TUNEL assays. Cardiomyocytes were isolated from WT and Mst1-knockout mice, and a chronic hypoxia model was used to induce damage. Mitochondrial function was determined via JC1 staining, ROS measurement, cyt-c leakage detection and mitochondrial apoptotic pathways analysis. Mitochondrial fission was observed using immunofluorescence. A pathway activator and inhibitor were applied to establish the signaling pathways involved in regulating mitochondrial homeostasis.

Results

Our study demonstrated that Mst1 expression was significantly upregulated in the heart post-infarction. Activated Mst1 induced cardiac fibrosis, an excessive inflammatory response, and cardiomyocyte death, whereas the genetic ablation of Mst1 protected the myocardium against chronic post-infarction injury. Function assays showed that upregulation of Mst1 activity contributed to JNK pathway activation, which led to Drp1 migration from the cytoplasm onto the surface of the mitochondria, indicative of mitochondrial fission activation. Excessive mitochondrial fission caused mitochondrial fragmentation, resulting in mitochondrial potential collapse, ROS overproduction, mitochondrial pro-apoptotic leakage into the cytoplasm, and the initiation of caspase-9-mediated mitochondrial apoptosis. By contrast, Mst1 deletion helped to maintain mitochondrial structure and function, sending pro-survival signals to the cardiomyocytes.

Conclusions

Our results identify Mst1 as a malefactor in the development of post-infarction cardiac injury and that it acts through the JNK-Drp1-mitochondrial fission pathway.

Effect of Mst1 on Endometriosis Apoptosis and Migration: Role of Drp1-Related Mitochondrial Fission and Parkin-Required Mitophagy

BACKGROUND/AIMS

Mitochondrial homeostasis is implicated in the development and progression of endometriosis through poorly defined mechanisms. Mst1 is the major growth suppressor related to cancer migration, apoptosis and proliferation. However, whether Mst1 is involved in endometriosis apoptosis and migration via regulating the mitochondrial function remains to be elucidated.

METHODS

Expression of Mst1 in endometriosis was examined via western blots. Cellular apoptosis was detected via MTT and TUNEL assay. Gain of function assay about Mst1 was conducted via adenovirus over-expression. Mitochondrial functions were evaluated via mitochondrial membrane potential JC-1 staining, ROS flow cytometry analysis, mPTP opening assessment and immunofluorescence of HtrA2/Omi. The mitophagy activity were examined via western blots and immunofluorescence.

RESULTS

First, we found that Mst1 was significantly downregulated in the ectopic endometrium of endometriosis compared to the normal endometrium. However, the recovery of Mst1 function was closely associated with the inability of endometrial stromal cells (ESCs) to migrate and survive. A functional study indicated that regaining Mst1 enhanced Drp1 post-transcriptional phosphorylation at Ser616 and repressed Parkin transcription activity via p53, leading to mitochondrial fission activation and mitophagy inhibition. Excessive Drp1-related fission forced the mitochondria to liberate HtrA2/Omi into the cytoplasm. Moreover, Mst1-induced defective mitophagy evoked cellular oxidative stress, energy metabolism and calcium overload. Through excessive mitochondrial fission and aberrant mitophagy, Mst1 launched caspase 9-related mitochondrial apoptosis and abrogated F-actin/lamellipodium-dependent cellular migration. Notably, we also defined NR4A/miR181c as the upstream signal for Mst1 dysfunction in endometriosis.

CONCLUSION

Collectively, our results comprehensively described the important role of the NR4A-miR181c-Mst1 pathway in endometriosis, which handled mitochondrial apoptosis and F-actin/ lamellipodium-based migration via the regulation of Drp1-related mitochondrial fission and Parkin-required mitophagy, with a potential application in endometriosis therapy by limiting ESCs migration and promoting apoptosis.

Mst1 regulates colorectal cancer stress response via inhibiting Bnip3-related mitophagy by activation of JNK/p53 pathway

The Hippo-Mst1 pathway is associated with tumor development and progression. However, little evidence is available for its role in colorectal cancer (CRC) stress response via mitochondrial homeostasis. In this study, we conducted gain-of function assay about Mst1 in CRC via adenovirus transfection. Then, cellular viability and apoptosis were measured via MTT, TUNEL assay, and typan blue staining. Mitochondrial function was detected via JC1 staining, mPTP opening assay, and immunofluorescence of cyt-c. Mitophagy was observed via western blots and immunofluorescence. Cell migration and proliferation were evaluated via Transwell and BrdU assay. Western blots were used to analyze the signaling pathways with JNK inhibitors or p53 siRNA. We found that Mst1 was down-regulated in CRC. Overexpression of Mst1 induced CRC apoptosis and impaired cell proliferation and migration. Functional studies have illustrated that recovery of Mst1 could activate JNK pathway which upregulated the p53 expression. The latter repressed Bnip3 transcription and activity, leading to the mitophagy arrest. The defective mitophagy impaired mitochondrial homeostasis, evoked cellular oxidative stress, and initiated the mitochondrial apoptosis. Meanwhile, bad-structured mitophagy also hindered the cancer proliferation via CyclinD/E. Moreover, Mst1-suppressed mitophagy was associated with CRC migration inhibition via regulation of CXCR4/7 expression. Collectively, our data described the comprehensive role of Mst1 in colorectal cancer stress response involving apoptosis, mobilization, and growth via handling mitophagy by JNK/p53/Bnip3 pathways.

Deletion of Mst1 attenuates neuronal loss and improves neurological impairment in a rat model of traumatic brain injury

Neuronal cell death following traumatic brain injury (TBI) is a considerable contributor to neurological deficits. In our work, we explored the functions of Mammalian STE20-like kinase-1 (Mst1), a apoptosis-promoting kinase and also a pivotal bridgebuilder of apoptotic signaling, in the etiopathogenesis of an experimental rat model of TBI. We found that the phosphorylation level of Mst1 in injured area was significantly increased after TBI. Furthermore, we discovered that inhibition of Mst1 phosphorylation can effectively reduce neuronal cell death by inhibiting the activation of caspase 3 and suppressing the damage of DNA during TBI. In addition, the decreased of Mst1 phosphorylation level, not only reduced brain edema and blood-brain barrier (BBB) damage in injured region but also weakened the impairment of neurologic behavior during TBI. In conclusion, our work demonstrates that Mst1 plays an important role in TBI-induced neuronal cell death, suggesting that Mst1 is expected to be a potential therapeutic target for TBI.

Genetic ablation of the mammalian sterile-20 like kinase 1 (Mst1) improves cell reprogramming efficiency and increases induced pluripotent stem cell proliferation and survival

Adult fibroblasts can be reprogrammed into induced pluripotent stem cells (iPSC) for use in various applications. However, there are challenges in iPSC generation including low reprogramming efficiency, yield, cell survival and viability. Since the Hippo signalling pathway is a key pathway involved in regulating cell proliferation and survival, we here test whether modification of the Hippo pathway will enhance the efficiency of iPSC generation and improve their survival.

The Hippo pathway was modified by genetic ablation of the mammalian sterile-20 like kinase 1 (Mst1), a major component of the pathway. Using adult skin fibroblasts isolated from Mst1 knockout mice (Mst1^−/−) as a source of iPSC we found that genetic ablation of Mst1 leads to significantly increased reprogramming efficiency by 43.8%. Moreover, Mst1^−/− iPSC displayed increase proliferation by 12% as well as an increase in cell viability by 20% when treated with a chemical hypoxic inducer. Mechanistically, we found higher activity of YAP, the main downstream effector of the Hippo pathway, in iPSC lacking Mst1.

In conclusion, our data suggests that Mst1 can be targeted to improve the efficiency of adult somatic cell reprogramming as well as to enhance iPSC proliferation and survival.

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Genetic deletion of Mst1 increases the efficiency of cell reprogramming.

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iPSC lacking Mst1 displays higher proliferation rate than WT iPSC.

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In response to chemical hypoxia Mst1^−/− iPSC demonstrates higher survival.

Mst1 shuts off cytosolic antiviral defense through IRF3 phosphorylation

Here, Meng et al. investigated how interferon regulatory factor 3 (IRF3) activation, a key signal mediator/transcriptional factor of the antiviral-sensing pathway, is regulated. They demonstrate that Mst1, a stress response kinase, represses cytosolic antiviral sensing and defense through the repression of RNA virus-induced activation of TBK1 and interference with the IRF3 homodimerization and chromatin binding via direct phosphorylation of IRF3 Thr253 and Thr75 residues.

Cytosolic RNA/DNA sensing elicits primary defense against viral pathogens. Interferon regulatory factor 3 (IRF3), a key signal mediator/transcriptional factor of the antiviral-sensing pathway, is indispensible for interferon production and antiviral defense. However, how the status of IRF3 activation is controlled remains elusive. Through a functional screen of the human kinome, we found that mammalian sterile 20-like kinase 1 (Mst1), but not Mst2, profoundly inhibited cytosolic nucleic acid sensing. Mst1 associated with IRF3 and directly phosphorylated IRF3 at Thr75 and Thr253. This Mst1-mediated phosphorylation abolished activated IRF3 homodimerization, its occupancy on chromatin, and subsequent IRF3-mediated transcriptional responses. In addition, Mst1 also impeded virus-induced activation of TANK-binding kinase 1 (TBK1), further attenuating IRF3 activation. As a result, Mst1 depletion or ablation enabled an enhanced antiviral response and defense in cells and mice. Therefore, the identification of Mst1 as a novel physiological negative regulator of IRF3 activation provides mechanistic insights into innate antiviral defense and potential antiviral prevention strategies.

Mst1 regulates hepatic lipid metabolism by inhibiting Sirt1 ubiquitination in mice

Previous study showed mammalian Ste20-like kinase (Mst1) may serve as target for the development of new therapies for diabetes. However, the function of Mst1 involved in liver lipid metabolism has remained elusive. In this study, we report that the liver of Mst1 knockout (Mst1(-/-)) mice showed more severe liver metabolic damage under fasting and high-fat diet than that of control mice. And fasting induced hepatic Mst1 expression. Mst1 overexpression inhibited Srebp-1c expression and increased the expression of antioxidant genes in primary hepatocytes. We also found that fasting-induced expression of hepatic Sirt1 was attenuated in Mst1(-/-) mice. Mst1 overexpression promoted Sirt1 expression, probably due to inhibiting Sirt1 ubiquitination. In summary, our study suggests that Mst1 regulates hepatic lipid metabolism by inhibiting Sirt1 ubiquitination in mice.