Metformin rescues Parkin protein expression and mitophagy in high glucose-challenged human renal epithelial cells by inhibiting NF-κB via PP2A activation

Sodium butyrate ameliorates high glucose-suppressed neuronal mitophagy by restoring PRKN expression via inhibiting the RELA-HDAC8 complex

Damaged mitochondria accumulation in diabetes is one of the main features that contribute to increased incidence of cognitive impairment by inducing apoptosis. Butyrate is a major metabolite produced by microbiota that has neuroprotective effects by regulating mitochondrial function. However, detailed mechanisms underlying how butyrate can regulate neuronal mitophagy remain unclear. Here, we examined the regulatory effects of sodium butyrate (NaB) on high glucose-induced mitophagy dysregulation, neuronal apoptosis, and cognitive impairment and its underlying mechanisms in human-induced pluripotent stem cell-derived neurons, SH-SY5Ys, and streptozotocin (STZ)-induced diabetic mice. In our results, diabetic mice showed gut-microbiota dysbiosis, especially a decreased number of butyrate-producing bacteria and reduced NaB plasma concentration. NaB ameliorated high glucose-induced neuronal mitochondrial dysfunction by recovering PRKN/Parkin-mediated mitophagy. High glucose-induced reactive oxygen species (ROS) and -inhibited PRKAA/AMPKα stimulated the RELA/p65-HDAC8 complex, which downregulated PRKN protein expression by binding to the PRKN promoter region. NaB restored PRKN expression by blocking RELA nuclear translocation and directly inhibiting HDAC8 in the nucleus. In addition, HDAC8 overexpression inhibited the positive effect of NaB on high glucose-induced mitophagy dysfunction and neuronal apoptosis. Oral administration of NaB improved cognitive impairment in diabetic mice by restoring mitophagy in the hippocampus. Taken together, NaB ameliorates neuronal mitophagy through PRKN restoration by inhibiting RELA-HDAC8 complexes, suggesting that NaB is an important substance for protecting neuronal apoptosis in diabetes-associated cognitive impairment.

Mitophagy in neurodegenerative disease pathogenesis

Mitochondria are critical cellular energy resources and are central to the life of the neuron. Mitophagy selectively clears damaged or dysfunctional mitochondria through autophagic machinery to maintain mitochondrial quality control and homeostasis. Mature neurons are postmitotic and consume substantial energy, thus require highly efficient mitophagy pathways to turn over damaged or dysfunctional mitochondria. Recent evidence indicates that mitophagy is pivotal to the pathogenesis of neurological diseases. However, more work is needed to study mitophagy pathway components as potential therapeutic targets. In this review, we briefly discuss the characteristics of nonselective autophagy and selective autophagy, including ERphagy, aggrephagy, and mitophagy. We then introduce the mechanisms of Parkin-dependent and Parkin-independent mitophagy pathways under physiological conditions. Next, we summarize the diverse repertoire of mitochondrial membrane receptors and phospholipids that mediate mitophagy. Importantly, we review the critical role of mitophagy in the pathogenesis of neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. Last, we discuss recent studies considering mitophagy as a potential therapeutic target for treating neurodegenerative diseases. Together, our review may provide novel views to better understand the roles of mitophagy in neurodegenerative disease pathogenesis.

Parkin-Mediated Mitophagy by TGF-β Is Connected with Hepatic Stellate Cell Activation

Hepatic stellate cells (HSCs) are the main contributors to the development and progression of liver fibrosis. Parkin is an E3 ligase involved in mitophagy mediated by lysosomes that maintains mitochondrial homeostasis. Unfortunately, there is little information regarding the regulation of parkin by transforming growth factor-β (TGF-β) and its association with HSC trans-differentiation. This study showed that parkin is upregulated in fibrotic conditions and elucidated the underlying mechanism. Parkin was observed in the cirrhotic region of the patient liver tissues and visualized using immunostaining and immunoblotting of mouse fibrotic liver samples and primary HSCs. The role of parkin-mediated mitophagy in hepatic fibrogenesis was examined using TGF-β-treated LX-2 cells with mitophagy inhibitor, mitochondrial division inhibitor 1. Parkin overexpression and its colocalization with desmin in human tissues were found. Increased parkin in fibrotic liver homogenates of mice was observed. Parkin was expressed more abundantly in HSCs than in hepatocytes and was upregulated under TGF-β. TGF-β-induced parkin was due to Smad3. TGF-β facilitated mitochondrial translocation, leading to mitophagy activation, reversed by mitophagy inhibitor. However, TGF-β did not change mitochondrial function. Mitophagy inhibitor suppressed profibrotic genes and HSC migration mediated by TGF-β. Collectively, parkin-involved mitophagy by TGF-β facilitates HSC activation, suggesting mitophagy may utilize targets for liver fibrosis.

Chemical mitophagy modulators: Drug development strategies and novel regulatory mechanisms

Maintaining mitochondrial homeostasis is a potential therapeutic strategy for various diseases, including neurodegenerative diseases, cardiovascular diseases, metabolic disorders, and cancer. Selective degradation of mitochondria by autophagy (mitophagy) is a fundamental mitochondrial quality control mechanism conserved from yeast to humans. Indeed, small-molecule modulators of mitophagy are valuable pharmaceutical tools that can be used to dissect complex biological processes and turn them into potential drugs. In the past few years, pharmacological regulation of mitophagy has shown promising therapeutic efficacy in various disease models. However, with the increasing number of chemical mitophagy modulator studies, frequent methodological flaws can be observed, leading some studies to draw unreliable or misleading conclusions. This review attempts (a) to summarize the molecular mechanisms of mitophagy; (b) to propose a Mitophagy Modulator Characterization System (MMCS); (c) to perform a comprehensive analysis of methods used to characterize mitophagy modulators, covering publications over the past 20 years; (d) to provide novel targets for pharmacological intervention of mitophagy. We believe this review will provide a panorama of current research on chemical mitophagy modulators and promote the development of safe and robust mitophagy modulators with therapeutic potential by introducing high methodological standards.

Hydrogen peroxide activates APE1/Ref-1 via NF-κB and Parkin: A role in liver cancer resistance to oxidative stress

Cancer cells exhibit an altered redox balance and aberrant redox signaling due to genetic, metabolic, and microenvironment-associated reprogramming. Persistently elevated levels of reactive oxygen species (ROS) contribute to many aspects of tumor development and progression. Emerging studies demonstrated the vital role of apurinic/apyrimidinic endonuclease 1 or reduction/oxidation (redox) factor 1(APE1/Ref-1) in the oxidative stress response and survival of cancer cells. APE1/Ref-1 is a multifunctional enzyme involved in the DNA damage response and functions as a redox regulator of transcription factors. We herein demonstrated that basal hydrogen peroxide (H₂O₂) and APE1/Ref-1 expression levels were markedly higher in cancer cell lines than in non-cancerous cells. Elevated APE1/Ref-1 levels were associated with shorter survival in liver cancer patients. Mechanistically, we showed that H₂O₂ activated nuclear factor-κB (NF-κB). RelA/p65 inhibited the expression of the E3 ubiquitin ligase Parkin, possibly by interfering with ATF4 activity. Parkin was responsible for the ubiquitination and proteasomal degradation of APE1/Ref-1; therefore, the H₂O₂-induced suppression of Parkin expression increased APE1/Ref-1 levels. The probability of survival was lower in liver cancer patients with low Parkin and high RelA expression levels. Additionally, Parkin and RelA expression levels negatively and positively correlated with APE1/Ref-1 levels, respectively, in the TCGA liver cancer cohort. We concluded that increases in APE1/Ref-1 via the NF-κB and Parkin pathways are critical for cancer cell survival under oxidative stress. The present results show the potential of the NF-κB-Parkin-APE1/Ref-1 axis as a prognostic factor and therapeutic strategy to eradicate liver cancer.

The molecular mechanisms and intervention strategies of mitophagy in cardiorenal syndrome

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

Upregulation of Wilms' Tumor 1 in epicardial cells increases cardiac fibrosis in dystrophic mice

Cardiomyopathy is a primary cause of mortality in Duchenne muscular dystrophy (DMD) patients. Mechanistic understanding of cardiac fibrosis holds the key to effective DMD cardiomyopathy treatments. Here we demonstrate that upregulation of Wilms' tumor 1 (Wt1) gene in epicardial cells increased cardiac fibrosis and impaired cardiac function in 8-month old mdx mice lacking the RNA component of telomerase (mdx/mTR-/-). Levels of phosphorylated IƙBα and p65 significantly rose in mdx/mTR-/- dystrophic hearts and Wt1 expression declined in the epicardium of mdx/mTR-/- mice when nuclear factor κB (NF-κB) and inflammation were inhibited by metformin. This demonstrates that Wt1 expression in epicardial cells is dependent on inflammation-triggered NF-κB activation. Metformin effectively prevented cardiac fibrosis and improved cardiac function in mdx/mTR-/- mice. Our study demonstrates that upregulation of Wt1 in epicardial cells contributes to fibrosis in dystrophic hearts and metformin-mediated inhibition of NF-κB can ameliorate the pathology, and thus showing clinical potential for dystrophic cardiomyopathy. Translational Perspective: Cardiomyopathy is a major cause of mortality in Duchenne muscular dystrophy (DMD) patients. Promising exon-skipping treatments are moving to the clinic, but getting sufficient dystrophin expression in the heart has proven challenging. The present study shows that Wilms' Tumor 1 (Wt1) upregulation in epicardial cells is primarily responsible for cardiac fibrosis and dysfunction of dystrophic mice and likely of DMD patients. Metformin effectively prevents cardiac fibrosis and improves cardiac function in dystrophic mice, thus representing a treatment option for DMD patients on top of existing therapies.

A signature constructed with mitophagy-related genes to predict the prognosis and therapy response for breast cancer

Over the past decades, the incidence and mortality rates of breast cancer (BC) have increased rapidly; however, molecular biomarkers that can reliably detect BC are yet to be discovered. Our study aimed to identify a novel signature that can predict the prognosis of patients with BC. Data from the TCGA-BRCA cohort were analyzed using univariate Cox regression analysis, and least absolute shrinkage and selection operator (LASSO) analysis was performed to build a stable prognostic model. Subsequently, Kaplan–Meier (K–M) and receiver operating characteristic (ROC) analyses were performed to demonstrate the predictive power of our gene signature. Each patient was assigned to either a low- or high-risk group. Patients with high-risk BC had poorer survival than those with low-risk BC. Cox regression analysis suggested that our signature was an independent prognostic factor. Additionally, decision curve analysis and calibration accurately predicted the capacity of our nomogram. Thus, based on the differentially expressed genes (DEGs) of mitophagy-related tumor classification, we established a 13-gene signature and robust nomogram for predicting BC prognosis, which can be beneficial for the diagnosis and treatment of BC.

The role of AMPK-dependent pathways in cellular and molecular mechanisms of metformin: a new perspective for treatment and prevention of diseases

Metformin can suppress gluconeogenesis and reduce blood sugar by activating adenosine monophosphate-activated protein kinase (AMPK) and inducing small heterodimer partner (SHP) expression in the liver cells. The main mechanism of metformin’s action is related to its activation of the AMPK enzyme and regulation of the energy balance. AMPK is a heterothermic serine/threonine kinase made of a catalytic alpha subunit and two subunits of beta and a gamma regulator. This enzyme can measure the intracellular ratio of AMP/ATP. If this ratio is high, the amino acid threonine 172 available in its alpha chain would be activated by the phosphorylated liver kinase B1 (LKB1), leading to AMPK activation. Several studies have indicated that apart from its significant role in the reduction of blood glucose level, metformin activates the AMPK enzyme that in turn has various efficient impacts on the regulation of various processes, including controlling inflammatory conditions, altering the differentiation pathway of immune and non-immune cell pathways, and the amelioration of various cancers, liver diseases, inflammatory bowel disease (IBD), kidney diseases, neurological disorders, etc. Metformin’s activation of AMPK enables it to control inflammatory conditions, improve oxidative status, regulate the differentiation pathways of various cells, change the pathological process in various diseases, and finally have positive therapeutic effects on them. Due to the activation of AMPK and its role in regulating several subcellular signalling pathways, metformin can be effective in altering the cells’ proliferation and differentiation pathways and eventually in the prevention and treatment of certain diseases.

A Clinical Perspective of the Multifaceted Mechanism of Metformin in Diabetes, Infections, Cognitive Dysfunction, and Cancer

In type 2 diabetes, ecological and lifecourse factors may interact with the host microbiota to influence expression of his/her genomes causing perturbation of interconnecting biological pathways with diverse clinical course. Metformin is a plant-based or plant-derived medicinal product used for the treatment of type 2 diabetes for over 60 years and is an essential drug listed by the World Health Organization. By reducing mitochondrial oxidative phosphorylation and adenosine triphosphate (ATP) production, metformin increased AMP (adenosine monophosphate)-activated protein kinase (AMPK) activity and altered cellular redox state with reduced glucagon activity, endogenous glucose production, lipogenesis, and protein synthesis. Metformin modulated immune response by directly reducing neutrophil to lymphocyte ratio and improving the phagocytic function of immune cells. By increasing the relative abundance of mucin-producing and short-chain-fatty-acid-producing gut microbes, metformin further improved the host inflammatory and metabolic milieu. Experimentally, metformin promoted apoptosis and reduced proliferation of cancer cells by reducing their oxygen consumption and modulating the microenvironment. Both clinical and mechanistic studies support the pluripotent effects of metformin on reducing cardiovascular–renal events, infection, cancer, cognitive dysfunction, and all-cause death in type 2 diabetes, making this low-cost medication a fundamental therapy for individualization of other glucose-lowering drugs in type 2 diabetes. Further research into the effects of metformin on cognitive function, infection and cancer, especially in people without diabetes, will provide new insights into the therapeutic value of metformin in our pursuit of prevention and treatment of ageing-related as well as acute and chronic diseases beyond diabetes.

Dioscin relieves diabetic nephropathy via suppressing oxidative stress and apoptosis, and improving mitochondrial quality and quantity control

Dioscin is a steroidal saponin isolated from various kinds of vegetables and herbs and possesses various biological activities. In this study, the protective effect of dioscin on diabetic nephropathy (DN) was explored. Dioscin and metformin (positive control) were administered orally to diabetic rats daily for 8 weeks. The biochemistry parameters, pancreas and kidney histological changes, oxidative stress, inflammation, apoptosis, autophagy, and mitochondrial quality and quantity control (mitophagy and mitochondrial fission/fusion) were measured. Our results showed that dioscin effectively reduced blood glucose, pancreatic injury, renal function markers and renal pathological changes in DN rat kidneys. Dioscin reduced O^2- and H₂O₂ levels, decreased MDA levels, enhanced antioxidant enzyme (SOD, CAT) activities, and reduced inflammatory factor expressions. Moreover, NOX4 expression and the disorder of the mitochondrial respiratory chain were reversed by dioscin. Furthermore, apoptosis mediated by the mitochondria and ER stress was inhibited by dioscin through downregulating the expressions of Bax, CytC, Apaf-1, caspase 9, p-PERK, p-EIF2α, IRE1, p-IRE1, XBP1s, ATF4, p-CHOP and caspase 12. In addition, autophagy was enhanced by dioscin via an AMPK-mTOR pathway. Mitophagy and mitochondrial fission/fusion belong to the mitochondrial quality and quantity control process, which was improved by dioscin via regulating Parkin, PINK1, DRP1, p-DRP1 and MFN2 expressions. Collectively, these results suggested that dioscin protected against DN through inhibiting oxidative stress, inflammation, and apoptosis mediated by the mitochondria and ER stress. Autophagy and mitochondrial quality and quantity control (mitophagy and mitochondrial fission/fusion) were also improved by dioscin.

Mitophagy in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the most common cause of end-stage kidney disease worldwide and is the main microvascular complication of diabetes. The increasing prevalence of diabetes has increased the need for effective treatment of DKD and identification of new therapeutic targets for better clinical management. Mitophagy is a highly conserved process that selectively removes damaged or unnecessary mitochondria via the autophagic machinery. Given the important role of mitophagy in the increased risk of DKD, especially with the recent surge in COVID-19-associated diabetic complications, in this review, we provide compelling evidence for maintaining homeostasis in the glomeruli and tubules and its underlying mechanisms, and offer new insights into potential therapeutic approaches for treatment of DKD.

AMPK agonist alleviate renal tubulointerstitial fibrosis via activating mitophagy in high fat and streptozotocin induced diabetic mice

Renal tubulointerstitial fibrosis was a crucial pathological feature of diabetic nephropathy (DN), and renal tubular injury might associate with abnormal mitophagy. In this study, we investigated the effects and molecular mechanisms of AMPK agonist metformin on mitophagy and cellular injury in renal tubular cell under diabetic condition. The high fat diet (HFD) and streptozotocin (STZ)-induced type 2 diabetic mice model and HK-2 cells were used in this study. Metformin was administered in the drinking water (200 mg/kg/d) for 24 weeks. Renal tubulointerstitial lesions, oxidative stress and some indicators of mitophagy (e.g., LC3II, Pink1, and Parkin) were examined both in renal tissue and HK-2 cells. Additionally, compound C (an AMPK inhibitor) and Pink1 siRNA were applied to explore the molecular regulation mechanism of metformin on mitophagy. We found that the expression of p-AMPK, Pink1, Parkin, LC3II, and Atg5 in renal tissue of diabetic mice was decreased obviously. Metformin reduced the levels of serum creatinine, urine protein, and attenuated renal oxidative injury and fibrosis in HFD/STZ induced diabetic mice. In addition, Metformin reversed mitophagy dysfunction and the over-expression of NLRP3. In vitro pretreatment of HK-2 cells with AMPK inhibitor compound C or Pink1 siRNA negated the beneficial effects of metformin. Furthermore, we noted that metformin activated p-AMPK and promoted the translocation of Pink1 from the cytoplasm to mitochondria, then promoted the occurrence of mitophagy in HK-2 cells under HG/HFA ambience. Our results suggested for the first time that AMPK agonist metformin ameliorated renal oxidative stress and tubulointerstitial fibrosis in HFD/STZ-induced diabetic mice via activating mitophagy through a p-AMPK-Pink1-Parkin pathway.

Relieving Cellular Energy Stress in Aging, Neurodegenerative, and Metabolic Diseases, SIRT1 as a Therapeutic and Promising Node

The intracellular energy state will alter under the influence of physiological or pathological stimuli. In response to this change, cells usually mobilize various molecules and their mechanisms to promote the stability of the intracellular energy status. Mitochondria are the main source of ATP. Previous studies have found that the function of mitochondria is impaired in aging, neurodegenerative diseases, and metabolic diseases, and the damaged mitochondria bring lower ATP production, which further worsens the progression of the disease. Silent information regulator-1 (SIRT1) is a multipotent molecule that participates in the regulation of important biological processes in cells, including cellular metabolism, cell senescence, and inflammation. In this review, we mainly discuss that promoting the expression and activity of SIRT1 contributes to alleviating the energy stress produced by physiological and pathological conditions. The review also discusses the mechanism of precise regulation of SIRT1 expression and activity in various dimensions. Finally, according to the characteristics of this mechanism in promoting the recovery of mitochondrial function, the relationship between current pharmacological preparations and aging, neurodegenerative diseases, metabolic diseases, and other diseases was analyzed.

Mitophagy: A Novel Therapeutic Target for Treating DN

Diabetic nephropathy (DN) is a common microvascular complication of diabetes and one of the leading causes of end-stage renal disease. Tubular damage is an early change and characteristic of DN, and mitochondrial dysfunction plays an important role in the development of DN. Therefore, the timely removal of damaged mitochondria in tubular cells is an effective treatment strategy for DN. Mitophagy is a type of selective autophagy that ensures the timely elimination of damaged mitochondria to protect cells from oxidative stress. In this review, we summarize our understanding of mitochondrial dysfunction and dynamic disorders in tubular cells in DN and the molecular mechanism of mitophagy. Finally, the role of mitophagy in DN and its feasibility as a therapeutic target for DN are discussed.

Regulation of Parkin expression as the key balance between neural survival and cancer cell death

Parkin is a cytosolic E3 ubiquitin ligase that plays an important role in neuroprotection by targeting several proteins to be degraded by the 26S proteasome. Its dysfunction has been associated not only with Parkinson's disease (PD) but also with other neurodegenerative pathologies, such as Alzheimer's disease and Huntington's disease. More recently, Parkin has been identified as a tumor suppressor gene implicated in cancer development. Due to the important roles that this E3 ubiquitin ligase plays in cellular homeostasis, its expression, activity, and turnover are tightly regulated. Several reviews have addressed Parkin regulation; however, genetic and epigenetic regulation have been excluded. In addition to posttranslational modifications (PTMs), this review examines the regulatory mechanisms that control Parkin function through gene expression, epigenetic regulation, and degradation. Furthermore, the consequences of disrupting these regulatory processes on human health are discussed.

Mitophagy in Human Diseases

Mitophagy is a selective autophagic process, essential for cellular homeostasis, that eliminates dysfunctional mitochondria. Activated by inner membrane depolarization, it plays an important role during development and is fundamental in highly differentiated post-mitotic cells that are highly dependent on aerobic metabolism, such as neurons, muscle cells, and hepatocytes. Both defective and excessive mitophagy have been proposed to contribute to age-related neurodegenerative diseases, such as Parkinson’s and Alzheimer’s diseases, metabolic diseases, vascular complications of diabetes, myocardial injury, muscle dystrophy, and liver disease, among others. Pharmacological or dietary interventions that restore mitophagy homeostasis and facilitate the elimination of irreversibly damaged mitochondria, thus, could serve as potential therapies in several chronic diseases. However, despite extraordinary advances in this field, mainly derived from in vitro and preclinical animal models, human applications based on the regulation of mitochondrial quality in patients have not yet been approved. In this review, we summarize the key selective mitochondrial autophagy pathways and their role in prevalent chronic human diseases and highlight the potential use of specific interventions.

Possible treatment for UVB-induced skin injury: Anti-inflammatory and cytoprotective role of metformin in UVB-irradiated keratinocytes

BACKGROUND

Excessive inflammation and cell death induced by ultraviolet (UV) cause skin photodamage. Metformin possesses anti-inflammatory and cytoprotective effects. However, whether metformin inhibits inflammation and cell death in UVB-induced acute skin damage is unclear.

OBJECTIVE

To evaluate the anti-inflammatory and cytoprotective effects of metformin in vitro and in vivo. Furthermore, its potential mechanism has been explored.

METHODS

Transcriptome sequencing and multiplex cytokines analysis were used to evaluate the validity of in vitro UVB-induced acute damage keratinocyte model and anti-inflammatory effects of metformin. We also determined the expression and nuclear translocation of CCAAT/enhancer-binding protein beta (C/EBPβ), an important transcriptional factor of Interleukin-1beta (IL-1β). Cell viability and cell death of keratinocytes were evaluated upon UVB irradiation in the presence or absence of metformin. 0.6% metformin cream was applied on UVB-irradiated mice to explore its pharmacological effects in vivo.

RESULTS

Transcriptional landscape of 50 mJ/cm² UVB-irradiated HaCaT cells is typical of UVB-induced acute damage keratinocyte model in vitro. Metformin alleviated transcription and secretion of IL-1β, Tumor Necrosis Factor-alpha, and Fibroblast Growth Factor 2, expression and nuclear translocation of C/EBPβ in this model. Metformin also protected keratinocytes from cell death caused by UVB-induced cellular secretions, which contributed to its cytoprotective effects. Topical administration of 0.6% metformin cream alleviated UVB-induced skin damage in mice.

CONCLUSION

We proved the protective roles of metformin in UVB-challenged keratinocytes and UVB-irradiated mice, which indicated the potential value of metformin in topical therapy against skin photodamage.

Antidiabetic compounds 8a, 8b, 8k, and 9h enhance insulin secretion: activity and mechanism

PURPOSE

This study primarily investigated the effects of hypoglycemic compounds (Imeglimin derivatives) on insulin secretion in type 2 diabetes mellitus (T2DM), and further explored the possible mechanism underlying these effects.

METHODS

Firstly, Metformin was used as the initiating compound to synthesize three sets of derivatives which contained Imeglimin structure core. At the cellular level, we screened compounds with better effect on the activity of insulin receptor tyrosine protein kinase (IFcTPK) after the islet β cells were treated with the compounds of different concentrations. The insulin secretion was assessed using radioimmunoassay and the cytotoxicity to islet β cells was evaluated by means of MTT assay following treatment with the compounds. The Ca²⁺-related mechanism by which these compounds promote insulin secretion was elucidated with whole cell recordings from current-clamp mode.

RESULTS

Totally, 48 synthesized compounds were generated, wherein 10 compounds could increase the activity of IFcTPK in HIT-T15 cells better among these compounds. The modified Imeglimin, especially in the structure of hydrophilic hydroxyl or piperidine rings, could improve the activity of the compound to promote insulin secretion. Furthermore, the compounds 8a, 8b, 8k, and 9h revealed high insulin secretion-promoting activity. These compounds enhanced insulin secretion in islet β cells by repressing the ATP-sensitive K(+) and voltage-gated K+ pathway.

CONCLUSIONS

Our findings indicate that the hypoglycemic compounds 8a, 8b, 8k, and 9h confer better promotive effect on insulin secretion, which provides a reference for the development of drugs with better hypoglycemic activity.

Metformin ameliorates brain damage caused by cardiopulmonary resuscitation via targeting endoplasmic reticulum stress-related proteins GRP78 and XBP1

Cerebral damage after cardiac arrest (CA) and cardiopulmonary resuscitation (CPR) is a primary cause of death. Endoplasmic reticulum stress (ERS) is very important during these situations. This study aimed to explore the role of metformin in protecting brain endoplasmic reticulum post CA/CPR. Male SD rats (n = 132) were treated with 6-min CA-posted asphyxia and sham surgery. Before CA/CPR, metformin (200 mg/kg/day) or a vehicle (0.9% saline) were administered randomly for two weeks. The neurological deficit scores were assessed 24 h, 48 h, 72 h, and 7 days after CA/CPR, and the rat brains were analyzed by Western blotting and qRT-PCR. Apoptosis was detected by the TUNEL assay according to the mitochondrial membrane potential (MMP). Oxidative stress and ERS-related protein expression were also investigated. The Western blotting and qRT-PCR results revealed that the resuscitated animals had time-dependent elevated GRP78 and XBP1 levels compared with the sham operative rats. Moreover, our results showed that the rats treated with metformin had increased neurological deficit scores (NDS), an improved seven-day survival rate, decreased cell apoptosis within the hippocampus CA1 area, and less oxidative stress compared with the CA/CPR group. Furthermore, metformin inhibited the mRNA and protein expressions of glucose-regulated protein 78 (GRP78) and X-box binding protein 1 (XBP1) in the CA/CPR rat model. We confirmed that CA/CPR can induce ERS-related apoptosis and oxidative stress in the brain; moreover, inhibiting ERS-related proteins GRP78 and XBP1 with metformin might attenuate cerebral injury post CA/CPR.

Metformin Increases Protein Phosphatase 2A Activity in Primary Human Skeletal Muscle Cells Derived from Lean Healthy Participants

OBJECTIVE

To investigate if PP2A plays a role in metformin-induced insulin sensitivity improvement in human skeletal muscle cells. Participants. Eight lean insulin-sensitive nondiabetic participants (4 females and 4 males; age: 21.0 ± 1.0 years; BMI: 22.0 ± 0.7 kg/m²; 2-hour OGTT: 97.0 ± 6.0 mg/dl; HbA1c: 5.3 ± 0.1%; fasting plasma glucose: 87.0 ± 2.0 mg/dl; M value; 11.0 ± 1.0 mg/kgBW/min).

DESIGN

A hyperinsulinemic-euglycemic clamp was performed to assess insulin sensitivity in human subjects, and skeletal muscle biopsy samples were obtained. Primary human skeletal muscle cells (shown to retain metabolic characteristics of donors) were cultured from these muscle biopsies that included 8 lean insulin-sensitive participants. Cultured cells were expanded, differentiated into myotubes, and treated with 50 μM metformin for 24 hours before harvesting. PP2Ac activity was measured by a phosphatase activity assay kit (Millipore) according to the manufacturer's protocol.

RESULTS

The results indicated that metformin significantly increased the activity of PP2A in the myotubes for all 8 lean insulin-sensitive nondiabetic participants, and the average fold increase is 1.54 ± 0.11 (P < 0.001).

CONCLUSIONS

These results provided the first evidence that metformin can activate PP2A in human skeletal muscle cells derived from lean healthy insulin-sensitive participants and may help to understand metformin's action in skeletal muscle in humans.

Metformin: Metabolic Rewiring Faces Tumor Heterogeneity

Tumor heterogeneity impinges on all the aspects of tumor history, from onset to metastasis and relapse. It is growingly recognized as a propelling force for tumor adaptation to environmental and micro-environmental cues. Metabolic heterogeneity perfectly falls into this process. It strongly contributes to the metabolic plasticity which characterizes cancer cell subpopulations—capable of adaptive switching under stress conditions, between aerobic glycolysis and oxidative phosphorylation—in both a convergent and divergent modality. The mitochondria appear at center-stage in this adaptive process and thus, targeting mitochondria in cancer may prove of therapeutic value. Metformin is the oldest and most used anti-diabetic medication and its relationship with cancer has witnessed rises and falls in the last 30 years. We believe it is useful to revisit the main mechanisms of action of metformin in light of the emerging views on tumor heterogeneity. We first analyze the most consolidated view of its mitochondrial mechanism of action and then we frame the latter in the context of tumor adaptive strategies, cancer stem cell selection, metabolic zonation of tumors and the tumor microenvironment. This may provide a more critical point of view and, to some extent, may help to shed light on some of the controversial evidence for metformin’s anticancer action.

LDHB inhibition induces mitophagy and facilitates the progression of CSFV infection

Cellular metabolism caters to the energy and metabolite needs of cells. Although the role of the terminal metabolic enzyme LDHB (lactate dehydrogenase B) in the glycolysis pathway has been widely studied in cancer cells, its role in viral infection is relatively unknown. In this study, we found that CSFV (classical swine fever virus) infection reduces pyruvate levels while promotes lactate release in pigs and in PK-15 cells. Moreover, using a yeast two-hybrid screening system, we identified LDHB as a novel interacting partner of CSFV non-structural protein NS3. These results were confirmed via co-immunoprecipitation, glutathione S-transferase and confocal assays. Furthermore, knockdown of LDHB via interfering RNA induced mitochondrial fission and mitophagy, as detected reduced mitochondrial mass. Upon inhibition of LDHB, expression of the mitophagy proteins TOMM20 and VDAC1 decreased and the ubiquitination of MFN2, a mitochondrial fusion mediator, was promoted. In addition, a sensitive dual fluorescence reporter (mito-mRFP-EGFP) was utilized to analyze the delivery of autophagosomes to lysosomes in LDHB inhibition cells. Furthermore, LDHB inhibition promoted NFKB signaling, which was regulated by mitophagy; meanwhile, infection with CSFV negated these NFKB anti-viral responses. Inhibition of LDHB also inhibited apoptosis, providing an environment conducive to persistent viral infection. Finally, we demonstrated that LDHB inhibition promoted CSFV growth via mitophagy, whereas its overexpression decreased CSFV replication. Our data revealed a novel mechanism through which LDHB, a metabolic enzyme, mediates CSFV infection, and provides new avenues for the development of anti-viral strategies.Abbreviations: 3-MA:3-methyladenine; CCCP:carbonyl cyanide 3-chlorophenylhydrazone; CCK-8:cell counting kit-8; CSFV:classical swine fever virus; DAPI:4',6-diamidino-2-phenylindole; DMSO:dimethyl sulfoxide; EGFP:enhanced green fluorescent protein; FBS:fetal bovine serum; FITC:fluorescein isothiocyanate; GST:glutathione-S-transferase; HCV:hepatitis C virus; IFN:interferon; LDH:lactate dehydrogenase; MAP1LC3/LC3:microtubule associated protein 1 light chain 3; MFN2:mitofusin 2; MOI:multiplicity of infection; NFKB:nuclear factor kappa B subunit 1; NFKBIA:nuclear factor inhibitor alpha; NS3:nonstructural protein 3; NKIRAS2:NFKB inhibitor interacting Ras like 2; PRKN:parkin E3 ubiquitin protein ligase; PBS:phosphate-buffered saline; qRT-PCR:real-time quantitative reverse transcriptase polymerase chain reaction; RELA:RELA proto-oncogene, NF-kB subunit; shRNA: short hairpin RNA; siRNA: small interfering RNA; TCID50:50% tissue culture infectious doses; TEM:transmission electron microscopy; TNF:tumor necrosis factor; TOMM20:translocase of outer mitochondrial membrane 20; VDAC1:voltage dependent anion channel 1.

Diabetes Mellitus, Mitochondrial Dysfunction and Ca2+-Dependent Permeability Transition Pore

Diabetes mellitus is one of the most common metabolic diseases in the developed world, and is associated either with the impaired secretion of insulin or with the resistance of cells to the actions of this hormone (type I and type II diabetes, respectively). In both cases, a common pathological change is an increase in blood glucose—hyperglycemia, which eventually can lead to serious damage to the organs and tissues of the organism. Mitochondria are one of the main targets of diabetes at the intracellular level. This review is dedicated to the analysis of recent data regarding the role of mitochondrial dysfunction in the development of diabetes mellitus. Specific areas of focus include the involvement of mitochondrial calcium transport systems and a pathophysiological phenomenon called the permeability transition pore in the pathogenesis of diabetes mellitus. The important contribution of these systems and their potential relevance as therapeutic targets in the pathology are discussed.