Metformin Enhances Autophagy and Provides Cardioprotection in δ-Sarcoglycan Deficiency-Induced Dilated Cardiomyopathy

Metformin Lysosomal Targeting: A Novel Aspect to Be Investigated for Metformin Repurposing in Neurodegenerative Diseases?

Metformin is a widely employed drug in type 2 diabetes. In addition to warranting good short- and long-term glycemic control, metformin displays many intriguing properties as protection against cardiovascular and neurodegenerative diseases, anti-tumorigenic and longevity promotion. In addition to being a low-cost drug, metformin is generally well tolerated. However, despite the enthusiastic drive to aliment these novel studies, many contradictory results suggest the importance of better elucidating the complexity of metformin action in different tissues/cells to establish its possible employment in neurodegenerative diseases. This review summarises recent data identifying lysosomal-dependent processes and lysosomal targets, such as endosomal Na+/H+ exchangers, presenilin enhancer 2 (PEN2), the lysosomal pathway leading to AMP-activated protein kinase (AMPK) activation, and the transcription factor EB (TFEB), modulated by metformin. Lysosomal dysfunctions resulting in autophagic and lysosomal acidification and biogenesis impairment appear to be hallmarks of many inherited and acquired neurodegenerative diseases. Lysosomes are not yet seen as a sort of cellular dump but are crucial in determining key signalling paths and processes involved in the clearance of aggregated proteins. Thus, the possibility of pharmacologically modulating them deserves great interest. Despite the potentiality of metformin in this context, many additional important issues, such as dosing, should be addressed in the future.

Pharmacokinetic Profile and Comparative Bioavailability of an Oral Fixed-Dose Combination of Metformin and Acetylsalicylic Acid (Aspirin)

Patients with diabetes face a 2-4-fold greater cardiovascular risk compared to those without diabetes. Both metformin and acetylsalicylic acid (aspirin) treatment have demonstrated a significant reduction in this risk. This single-center, open-label, sequence randomized, 2 × 2 crossover, single-dose clinical trial evaluated the pharmacokinetics profile and comparative bioavailability of a novel oral fixed-dose combination (FDC) of metformin/acetylsalicylic acid (500/100 mg tablet) versus the reference mono-drugs administered concomitantly, metformin 500 mg tablet and acetylsalicylic acid 100 mg tablet, in 22 healthy Mexican adult volunteers under fasting conditions. Blood samples were collected predose and at specified intervals across a 24-hour period following administration and were analyzed for metformin and salicylic acid using high-performance liquid chromatography coupled with tandem mass spectrometry. Test products were considered to have comparative bioavailability if confidence intervals of natural log-transformed (maximum plasma drug concentration (Cmax), (area under the plasma drug concentration-time curve form 0 up to last sampling time (AUC0 -t), and (area under the plasma drug concentration-time cruve from 0 up to infinity (AUC0 ∞) data were within the range of 80%-125%. The results obtained from the present clinical study demonstrate the comparative bioavailability of the FDC when compared with the coadministration of reference mono-drugs. There were no adverse events or adverse reactions reported throughout the study.

Pharmacological Treatments and Therapeutic Targets in Muscle Dystrophies Generated by Alterations in Dystrophin-Associated Proteins

Muscular dystrophies (MDs) are a heterogeneous group of diseases of genetic origin characterized by progressive skeletal muscle degeneration and weakness. There are several types of MDs, varying in terms of age of onset, severity, and pattern of the affected muscles. However, all of them worsen over time, and many patients will eventually lose their ability to walk. In addition to skeletal muscle effects, patients with MDs may present cardiac and respiratory disorders, generating complications that could lead to death. Interdisciplinary management is required to improve the surveillance and quality of life of patients with an MD. At present, pharmacological therapy is only available for Duchene muscular dystrophy (DMD)-the most common type of MD-and is mainly based on the use of corticosteroids. Other MDs caused by alterations in dystrophin-associated proteins (DAPs) are less frequent but represent an important group within these diseases. Pharmacological alternatives with clinical potential in patients with MDs and other proteins associated with dystrophin have been scarcely explored. This review focuses on drugs and molecules that have shown beneficial effects, mainly in experimental models involving alterations in DAPs. The mechanisms associated with the effects leading to promising results regarding the recovery or maintenance of muscle strength and reduction in fibrosis in the less-common MDs (i.e., with respect to DMD) are explored, and other therapeutic targets that could contribute to maintaining the homeostasis of muscle fibers, involving different pathways, such as calcium regulation, hypertrophy, and maintenance of satellite cell function, are also examined. It is possible that some of the drugs explored here could be used to affordably improve the muscular function of patients until a definitive treatment for MDs is developed.

Mapping the interplay of immunoproteasome and autophagy in different heart failure phenotypes

Proper protein degradation is required for cellular protein homeostasis and organ function. Particularly, in post-mitotic cells, such as cardiomyocytes, unbalanced proteolysis due to inflammatory stimuli and oxidative stress contributes to organ dysfunction. To ensure appropriate protein turnover, eukaryotic cells exert two main degradation systems, the ubiquitin-proteasome-system and the autophagy-lysosome-pathway. It has been shown that proteasome activity affects the development of cardiac dysfunction differently, depending on the type of heart failure. Studies analyzing the inducible subtype of the proteasome, the immunoproteasome (i20S), demonstrated that the i20S plays a double role in diseased hearts. While i20S subunits are increased in cardiac hypertrophy, atrial fibrillation and partly in myocarditis, the opposite applies to diabetic cardiomyopathy and ischemia/reperfusion injury. In addition, the i20S appears to play a role in autophagy modulation depending on heart failure phenotype. This review summarizes the current literature on the i20S in different heart failure phenotypes, emphasizing the two faces of i20S in injured hearts. A selection of established i20S inhibitors is introduced and signaling pathways linking the i20S to autophagy are highlighted. Mapping the interplay of the i20S and autophagy in different types of heart failure offers potential approaches for developing treatment strategies against heart failure.

Targeting autophagy with natural products as a potential therapeutic approach for diabetic microangiopathy

As the quality of life improves, the incidence of diabetes mellitus and its microvascular complications (DMC) continues to increase, posing a threat to people's health and wellbeing. Given the limitations of existing treatment, there is an urgent need for novel approaches to prevent and treat DMC. Autophagy, a pivotal mechanism governing metabolic regulation in organisms, facilitates the removal of dysfunctional proteins and organelles, thereby sustaining cellular homeostasis and energy generation. Anomalous states in pancreatic β-cells, podocytes, Müller cells, cardiomyocytes, and Schwann cells in DMC are closely linked to autophagic dysregulation. Natural products have the property of being multi-targeted and can affect autophagy and hence DMC progression in terms of nutrient perception, oxidative stress, endoplasmic reticulum stress, inflammation, and apoptosis. This review consolidates recent advancements in understanding DMC pathogenesis via autophagy and proposes novel perspectives on treating DMC by either stimulating or inhibiting autophagy using natural products.

Platelet Membrane-Encapsulated Nanocomplexes Based on Profundity Scavenging ROS Strategy for Myocardial Infarction Therapy

Ischemia-induced myocardial injury has become a serious threat to human health, and its treatment remains a challenge. The occurrence of ischemic events leads to a burst release of reactive oxygen species (ROS), which triggers extensive oxidative damage and leads to dysfunctional autophagy, making it difficult for cells to maintain homeostasis. Antioxidants and modulation of autophagy have thus become promising strategies for the treatment of ischemic myocardial injury. This study proposes an antioxidant-activated autophagy therapeutic regimen based on combining melanin (Mel), an excellent antioxidant with metformin mimetic ploymetformin via electrostatic interactions, to obtain a nanocomplex (Met-Mel). The nanocomplex is finally encapsulated with platelet membranes (PMN) to construct a biomimetic nanoparticle (PMN@Met-Mel) capable of targeting injured myocardium. The prepared PMN@Met-Mel has good Mel loading capacity and optimal biosafety. It exhibits excellent antioxidant activity and autophagy activation, rapidly restoring mitochondrial function. Moreover, RNA sequencing (RNA-seq) analysis reveals that PMN@Met-Mel operates mechanistically by triggering the activation of the autophagy pathway. Subsequent in vivo experiments showcase promising cardioprotective effects of these nanoparticles. These discoveries present a newly devised nanoplatform with promising potential for the effective treatment of myocardial infarction.

Systematic Investigation of Dose-Dependent Protein Thermal Stability Changes to Uncover the Mechanisms of the Pleiotropic Effects of Metformin

Metformin is a widely used drug to treat type II diabetes. Beyond lowering blood sugar, it has been reported to have pleiotropic effects such as suppressing cancer growth and attenuating cell oxidative stress and inflammation. However, the underlying mechanisms of these effects remain to be explored. Here, we systematically study the thermal stability changes of proteins in liver cells (HepG2) induced by a wide dosage range of metformin by using the proteome integral solubility alteration (PISA) assay. The current results demonstrate that, besides the most accepted target of metformin (complex I), low concentrations of metformin (such as 0.2 μM) stabilize the complex IV subunits, suggesting its important role in the sugar-lowering effect. Low-dose metformin also results in stability alterations of ribosomal proteins, correlating with its inhibitive effect on cell proliferation. We further find that low-concentration metformin impacts mitochondrial cargo and vesicle transport, while high-concentration metformin affects cell redox responses and cell membrane protein sorting. This study provides mechanistic insights into the molecular mechanisms of lowering blood sugar and the pleiotropic effects of metformin.

Effect of Metformin on Oxidative Stress and Left Ventricular Geometry in Nondiabetic Heart Failure Patients: A Randomized Controlled Trial

Introduction: There is an increasing interest in using metformin in cardiovascular diseases and its potential new roles. Only two randomized controlled trials investigated the effect of metformin in nondiabetic heart failure (HF) patients. However, none of these studies assess the role of metformin in reducing oxidative stress. We hypothesized that metformin might improve oxidative stress and left ventricular remodeling in nondiabetic HF patients with reduced ejection fraction (HFrEF). Methods and Methods: Seventy HFrEF patients (EF 37% ± 8%; median age 66 years) were randomized to metformin (n = 35) or standard of care (SOC) for HF (n = 35) for 6 months in addition to standard therapy. Outcomes included the difference in the change (Δ) in total antioxidant capacity (TAC) and malondialdehyde (MDA), both assessed colorimetrically and left ventricular mass index (LVMI) assessed through transthoracic echocardiography. Results: Compared with the SOC, metformin treatment increased TAC [Δ = 0.12 mmol/L, confidence intervals (95% CIs): 0.03-0.21; P = 0.007]. TAC increased significantly only in the metformin group (0.90 ± 0.08 mmol/L at baseline vs. 1.04 ± 0.99 mmol/L at 6 months, P < 0.05). Metformin therapy preserved LVMI (Δ = -23 g/m2, 95% CI: -42.91 to -4.92; P = 0.014) and reduced fasting plasma glucose (Δ = -6.16, 95% CI: -12.31 to -0.02, P = 0.047) compared with the SOC. Results did not change after adjusting for baseline values. Changes in MDA left ventricular ejection fraction (LVEF) and blood pressure were not significantly different between groups. Conclusion: Metformin treatment in HF patients with reduced LVEF improved TAC and prevented the increase in LVMI compared with the SOC. These effects of metformin warrant further research in HF patients without diabetes to explore the potential benefits of metformin. Trial Registration Number: This protocol was registered in ClinicalTrials.gov under the number NCT05177588.

Pharmacotherapeutic Approaches to Treatment of Muscular Dystrophies

Muscular dystrophies are a heterogeneous group of genetic muscle-wasting disorders that are subdivided based on the region of the body impacted by muscle weakness as well as the functional activity of the underlying genetic mutations. A common feature of the pathophysiology of muscular dystrophies is chronic inflammation associated with the replacement of muscle mass with fibrotic scarring. With the progression of these disorders, many patients suffer cardiomyopathies with fibrosis of the cardiac tissue. Anti-inflammatory glucocorticoids represent the standard of care for Duchenne muscular dystrophy, the most common muscular dystrophy worldwide; however, long-term exposure to glucocorticoids results in highly adverse side effects, limiting their use. Thus, it is important to develop new pharmacotherapeutic approaches to limit inflammation and fibrosis to reduce muscle damage and promote repair. Here, we examine the pathophysiology, genetic background, and emerging therapeutic strategies for muscular dystrophies.

Autophagy in Heart Failure: Insights into Mechanisms and Therapeutic Implications

Autophagy, a dynamic and complex process responsible for the clearance of damaged cellular components, plays a crucial role in maintaining myocardial homeostasis. In the context of heart failure, autophagy has been recognized as a response mechanism aimed at counteracting pathogenic processes and promoting cellular health. Its relevance has been underscored not only in various animal models, but also in the human heart. Extensive research efforts have been dedicated to understanding the significance of autophagy and unravelling its complex molecular mechanisms. This review aims to consolidate the current knowledge of the involvement of autophagy during the progression of heart failure. Specifically, we provide a comprehensive overview of published data on the impact of autophagy deregulation achieved by genetic modifications or by pharmacological interventions in ischemic and non-ischemic models of heart failure. Furthermore, we delve into the intricate molecular mechanisms through which autophagy regulates crucial cellular processes within the three predominant cell populations of the heart: cardiomyocytes, cardiac fibroblasts, and endothelial cells. Finally, we emphasize the need for future research to unravel the therapeutic potential associated with targeting autophagy in the management of heart failure.

Effects of Metformin on Ischemia/Reperfusion Injury: New Evidence and Mechanisms

The search for new drugs with the potential to ensure therapeutic success in the treatment of cardiovascular diseases has become an essential pathway to follow for health organizations and committees around the world. In June 2021, the World Health Organization listed cardiovascular diseases as one of the main causes of death worldwide, representing 32% of them. The most common is coronary artery disease, which causes the death of cardiomyocytes, the cells responsible for cardiac contractility, through ischemia and subsequent reperfusion, which leads to heart failure in the medium and short term. Metformin is one of the most-used drugs for the control of diabetes, which has shown effects beyond the control of hyperglycemia. Some of these effects are mediated by the regulation of cellular energy metabolism, inhibiting apoptosis, reduction of cell death through regulation of autophagy and reduction of mitochondrial dysfunction with further reduction of oxidative stress. This suggests that metformin may attenuate left ventricular dysfunction induced by myocardial ischemia; preclinical and clinical trials have shown promising results, particularly in the setting of acute myocardial infarction. This is a review of the molecular and pharmacological mechanisms of the cardioprotective effects of metformin during myocardial ischemia-reperfusion injury.

Cardiovascular Protection by Metformin: Latest Advances in Basic and Clinical Research

BACKGROUND

Metformin is among the most frequently prescribed antidiabetic drugs worldwide and remains the first-line therapy for type 2 diabetes due to its well-established glucose-lowering efficacy and favorable safety profile.

SUMMARY

Studies over the past decades show that metformin also exerts many other beneficial effects independent of its glucose-lowering effect both in experimental models and human subjects. Among them, the most notable is its cardiovascular protective effect. In this review, we discuss the latest cutting-edge research findings on metformin's cardiovascular protection from both preclinical studies and randomized clinical trials. We focus on describing novel basic research discoveries reported in influential journals and discussing their implications in the context of latest clinical trial findings related to common cardiovascular and metabolic disorders, including atherosclerosis and dyslipidemia, myocardial injury, and heart failure.

KEY MESSAGES

While substantial preclinical and clinical evidence suggests metformin as a potential cardiovascular protectant, large-scale randomized controlled trials are warranted to establish its clinical efficacy in treating patients with atherosclerotic cardiovascular disease and heart failure.

Metformin-induced TTP mediates communication between Kupffer cells and hepatocytes to alleviate hepatic steatosis by regulating lipophagy and necroptosis

OBJECTIVE

Emerging evidence suggests that crosstalk between Kupffer cells (KCs) and hepatocytes protects against non-alcoholic fatty liver disease (NAFLD). However, the underlying mechanisms that lead to the reduction of steatosis in NAFLD remain obscure.

METHODS

Ttp^+/+ and Ttp^-/- mice were fed with a high-fat diet. Hepatic steatosis was analyzed by Nile Red staining and measurement of inflammatory cytokines. Lipid accumulation and cell death were evaluated in co-culture systems with primary hepatocytes and KCs derived from either Ttp^+/+ or Ttp^-/- mice.

RESULTS

Tristetraprolin (TTP), an mRNA binding protein, was essential for the protective effects of metformin in NAFLD. Metformin activated TTP via the AMPK-Sirt1 pathway in hepatocytes and KCs. TTP inhibited TNF-α production in KCs, which in turn decreased hepatocyte necroptosis. Downregulation of Rheb expression by TTP promoted hepatocyte lipophagy via mTORC1 inhibition and increased nuclear translocation of transcription factor-EB (TFEB). Consistently, TTP-deficient NAFLD mice failed to respond to metformin with respect to alleviation of hepatic steatosis, protection of hepatocyte necroptosis, or induction of lipophagy.

CONCLUSIONS

TTP, which is essential for the protective effects of metformin, may represent a novel primary therapeutic target in NAFLD.

Metformin Inhibits Autophagy, Mitophagy and Antagonizes Doxorubicin-Induced Cardiomyocyte Death

The antidiabetic drug metformin has been shown to reduce cardiac injury under various pathological conditions, including anticancer drug doxorubicin (DOX)-induced cardiotoxicity, which makes metformin a prime candidate for repurposing. However, the mechanisms that mediate the cardioprotective effects of metformin remain highly controversial. In this study, we tested a prevailing hypothesis that metformin activates autophagy/mitophagy to reduce DOX cardiotoxicity. FVB/N mice and H9C2 cardiac myoblasts were treated with metformin, respectively. Autophagy/mitophagy was determined by Western blot analysis of microtubule-associated protein light chain 3, form-II (LC3-II), a well-established marker of autophagic vesicles. Although metformin had minimal effects on basal LC3-II levels, it significantly inhibited the accumulation of LC3-II levels by the lysosomal protease inhibitors pepstatin A and E64d in both total cell lysates and mitochondrial fractions. Also, dual fluorescent autophagy/mitophagy reporters demonstrated that metformin slowed the degradation rate of autophagic cargos or mitochondrial fragments in the lysosomes. These surprising results suggest that metformin inhibits rather than stimulates autophagy/mitophagy, sharply contrasting the popular belief. In addition, metformin diminished DOX-induced autophagy/mitophagy as well as cardiomyocyte death. Together, these results suggest that the cardioprotective effects of metformin against DOX cardiotoxicity may be mediated by its ability to inhibit autophagy and mitophagy, although the underlying molecular mechanisms remain to be determined.

Experimental diabetes exacerbates autophagic flux impairment during myocardial I/R injury through calpain-mediated cleavage of Atg5/LAMP2

To explore the role of autophagic flux in the increased susceptibility of the experimental diabetic heart to ischaemia-reperfusion (I/R) injury, we established STZ-induced diabetic mice and performed I/R. In vitro, neonatal mouse cardiomyocytes were subjected to high glucose and hypoxia/reoxygenation challenge to mimic diabetic I/R injury. We found that experimental diabetes aggravated I/R-induced injury than compared with nondiabetic mice. Autophagic flux was impaired in I/R hearts, and the impairment was exacerbated in diabetic mice subjected to I/R with defective autophagosome formation and clearance. Calpains, calcium-dependent thiol proteases, were upregulated and highly activated after I/R of diabetes, while calpain inhibition attenuated cardiac function and cell death and partially restored autophagic flux. The expression levels of Atg5 and LAMP2, two crucial autophagy-related proteins, were significantly degraded in diabetic I/R hearts, alterations that were associated with calpain activation and could be reversed by calpain inhibition. Co-overexpression of Atg5 and LAMP2 reduced myocardial injury and normalized autophagic flux. In conclusion, experimental diabetes exacerbates autophagic flux impairment of cardiomyocytes under I/R stress, resulting in worse I/R-induced injury. Calpain activation and cleavage of Atg5 and LAMP2 at least partially account for the deterioration of autophagic flux impairment.

The Role of MicroRNAs in Dilated Cardiomyopathy: New Insights for an Old Entity

Dilated cardiomyopathy (DCM) is a clinical diagnosis characterized by left ventricular or biventricular dilation and systolic dysfunction. In most cases, DCM is progressive, leading to heart failure (HF) and death. This cardiomyopathy has been considered a common and final phenotype of several entities. DCM occurs when cellular pathways fail to maintain the pumping function. The etiology of this disease encompasses several factors, such as ischemia, infection, autoimmunity, drugs or genetic susceptibility. Although the prognosis has improved in the last few years due to red flag clinical follow-up, early familial diagnosis and ongoing optimization of treatment, due to its heterogeneity, there are no targeted therapies available for DCM based on each etiology. Therefore, a better understanding of the mechanisms underlying the pathophysiology of DCM will provide novel therapeutic strategies against this cardiac disease and their different triggers. MicroRNAs (miRNAs) are a group of small noncoding RNAs that play key roles in post-transcriptional gene silencing by targeting mRNAs for translational repression or, to a lesser extent, degradation. A growing number of studies have demonstrated critical functions of miRNAs in cardiovascular diseases (CVDs), including DCM, by regulating mechanisms that contribute to the progression of the disease. Herein, we summarize the role of miRNAs in inflammation, endoplasmic reticulum (ER) stress, oxidative stress, mitochondrial dysfunction, autophagy, cardiomyocyte apoptosis and fibrosis, exclusively in the context of DCM.

Metformin protects against vascular calcification through the selective degradation of Runx2 by the p62 autophagy receptor

Vascular calcification is associated with aging, type 2 diabetes, and atherosclerosis, and increases the risk of cardiovascular morbidity and mortality. It is an active, highly regulated process that resembles physiological bone formation. It has previously been established that pharmacological doses of metformin alleviate arterial calcification through adenosine monophosphate-activated protein kinase (AMPK)-activated autophagy, however the specific pathway remains elusive. In the present study we hypothesized that metformin protects against arterial calcification through the direct autophagic degradation of runt-related transcription factor 2 (Runx2). Calcification was blunted in vascular smooth muscle cells (VSMCs) by metformin in a dose-dependent manner (0.5-1.5 mM) compared to control cells (p < 0.01). VSMCs cultured under high-phosphate (Pi) conditions in the presence of metformin (1 mM) showed a significant increase in LC3 puncta following bafilomycin-A1 (Baf-A; 5 nM) treatment compared to control cells (p < 0.001). Furthermore, reduced expression of Runx2 was observed in the nuclei of metformin-treated calcifying VSMCs (p < 0.0001). Evaluation of the functional role of autophagy through Atg3 knockdown in VSMCs showed aggravated Pi-induced calcification (p < 0.0001), failure to induce autophagy (punctate LC3) (p < 0.001) and increased nuclear Runx2 expression (p < 0.0001) in VSMCs cultured under high Pi conditions in the presence of metformin (1 mM). Mechanistic studies employing three-way coimmunoprecipitation with Runx2, p62, and LC3 revealed that p62 binds to both LC3 and Runx2 upon metformin treatment in VSMCs. Furthermore, immunoblotting with LC3 revealed that Runx2 specifically binds with p62 and LC3-II in metformin-treated calcified VSMCs. Lastly, we investigated the importance of the autophagy pathway in vascular calcification in a clinical setting. Ex vivo clinical analyses of calcified diabetic lower limb artery tissues highlighted a negative association between Runx2 and LC3 in the vascular calcification process. These studies suggest that exploitation of metformin and its analogues may represent a novel therapeutic strategy for clinical intervention through the induction of AMPK/Autophagy Related 3 (Atg3)-dependent autophagy and the subsequent p62-mediated autophagic degradation of Runx2.

Autophagy activation can partially rescue proteasome dysfunction-mediated cardiac toxicity

The ubiquitin-proteasome pathway and its functional interplay with other proteostatic and/or mitostatic modules are crucial for cell viability, especially in post-mitotic cells like cardiomyocytes, which are constantly exposed to proteotoxic, metabolic, and mechanical stress. Consistently, treatment of multiple myeloma patients with therapeutic proteasome inhibitors may induce cardiac failure; yet the effects promoted by heart-targeted proteasome dysfunction are not completely understood. We report here that heart-targeted proteasome knockdown in the fly experimental model results in increased proteome instability and defective mitostasis, leading to disrupted cardiac activity, systemic toxicity, and reduced longevity. These phenotypes were partially rescued by either heart targeted- or by dietary restriction-mediated activation of autophagy. Supportively, activation of autophagy by Rapamycin or Metformin administration in flies treated with proteasome inhibitors reduced proteome instability, partially restored mitochondrial function, mitigated cardiotoxicity, and improved flies' longevity. These findings suggest that autophagic inducers represent a novel promising intervention against proteasome inhibitor-induced cardiovascular complications.

Enhanced nuclear localization of phosphorylated MLKL predicts adverse events in patients with dilated cardiomyopathy

AIMS

The role of necroptosis in dilated cardiomyopathy (DCM) remains unclear. Here, we examined whether phosphorylation of mixed lineage kinase domain-like protein (MLKL), an indispensable event for execution of necroptosis, is associated with the progression of DCM.

METHODS AND RESULTS

Patients with DCM (n = 56, 56 ± 15 years of age; 68% male) were enrolled for immunohistochemical analyses of biopsies. Adverse events were defined as a composite of death or admission for heart failure or ventricular arrhythmia. Compared with the normal myocardium, increased signals of MLKL phosphorylation were detected in the nuclei, cytoplasm, and intercalated discs of cardiomyocytes in biopsy samples from DCM patients. The phosphorylated MLKL (p-MLKL) signal was increased in enlarged nuclei or nuclei with bizarre shapes in hypertrophied cardiomyocytes. Nuclear p-MLKL level was correlated negatively with septal peak myocardial velocity during early diastole (r = -0.327, P = 0.019) and was correlated positively with tricuspid regurgitation pressure gradient (r = 0.339, P = 0.023), while p-MLKL level in intercalated discs was negatively correlated with mean left ventricular wall thickness (r = -0.360, P = 0.014). During a median follow-up period of 3.5 years, 10 patients (18%) had adverse events. To examine the difference in event rates according to p-MLKL expression levels, patients were divided into two groups by using the median value of nuclear p-MLKL or intercalated disc p-MLKL. A group with high nuclear p-MLKL level (H-nucMLKL group) had a higher adverse event rate than did a group with low nuclear p-MLKL level (L-nucMLKL group) (32% vs. 4%, P = 0.012), and Kaplan-Meier survival curves showed that the adverse event-free survival rate was lower in the H-nucMLKL group than in the L-nucMLKL group (P = 0.019 by the log-rank test). Such differences were not detected between groups divided by a median value of intercalated disc p-MLKL. In δ-sarcoglycan-deficient (Sgcd-/- ) mice, a model of DCM, total p-MLKL and nuclear p-MLKL levels were higher than in wild-type mice.

CONCLUSION

The results suggest that increased localization of nuclear p-MLKL in cardiomyocytes is associated with left ventricular diastolic dysfunction and future adverse events in DCM.

Machine learning and bioinformatics to identify 8 autophagy-related biomarkers and construct gene regulatory networks in dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is a condition of impaired ventricular remodeling and systolic diastole that is often complicated by arrhythmias and heart failure with a poor prognosis. This study attempted to identify autophagy-related genes (ARGs) with diagnostic biomarkers of DCM using machine learning and bioinformatics approaches. Differential analysis of whole gene microarray data of DCM from the Gene Expression Omnibus (GEO) database was performed using the NetworkAnalyst 3.0 platform. Differentially expressed genes (DEGs) matching (|log2FoldChange ≥ 0.8, p value < 0.05|) were obtained in the GSE4172 dataset by merging ARGs from the autophagy gene libraries, HADb and HAMdb, to obtain autophagy-related differentially expressed genes (AR-DEGs) in DCM. The correlation analysis of AR-DEGs and their visualization were performed using R language. Gene Ontology (GO) enrichment analysis and combined multi-database pathway analysis were served by the Enrichr online enrichment analysis platform. We used machine learning to screen the diagnostic biomarkers of DCM. The transcription factors gene regulatory network was constructed by the JASPAR database of the NetworkAnalyst 3.0 platform. We also used the drug Signatures database (DSigDB) drug database of the Enrichr platform to screen the gene target drugs for DCM. Finally, we used the DisGeNET database to analyze the comorbidities associated with DCM. In the present study, we identified 23 AR-DEGs of DCM. Eight (PLEKHF1, HSPG2, HSF1, TRIM65, DICER1, VDAC1, BAD, TFEB) molecular markers of DCM were obtained by two machine learning algorithms. Transcription factors gene regulatory network was established. Finally, 10 gene-targeted drugs and complications for DCM were identified.

Modulation of autophagy, apoptosis and oxidative stress: a clue for repurposing metformin in photoaging

Long-term sun exposure is the commonest cause of photoaging, where mutual interplay between autophagy, oxidative stress, and apoptosis is incriminated. In combating photoaging, pharmacological approaches targeted to modulate autophagy are currently gaining more ground. This study aimed to examine repurposing metformin use in such context with or without the antioxidant coenzyme Q10 (coQ10) in ultraviolet A (UVA) irradiation-induced skin damage. The study was conducted on 70 female CD1 mice that were randomly assigned into seven groups (10/group): normal control, vehicle-treated-UVA-exposed mice, three metformin UVA-exposed groups (Topical 1 and 10%, and oral 300 mg/kg), topical coQ10 (1%)-treated mice, and combined oral metformin with topical coQ10-treated UVA-exposed mice. After UVA-exposure for 10 weeks (3 times/week), macroscopic signs of photoaging were evaluated. Mice were then euthanized, and the skin was harvested for biochemical estimation of markers for oxidative stress, inflammation, matrix breakdown, and lysosomal function. Histopathological signs of photoaging were also evaluated with immunohistochemical detection of associated changes in autophagic and apoptotic markers. Metformin, mainly by topical application, improved clinical and histologic signs of photoaging. This was associated with suppression of the elevated oxidative stress, IL-6, matrix metalloproteinase 1, and caspase, with induction of cathepsin D and subsequent change in anti-LC3 and P62 staining in skin tissue. In addition to metformin antioxidant, anti-inflammatory, and antiapoptotic activities, its anti-photoaging effect is mainly attributed to enhancing autophagic flux by inducing cathepsin D. Its protective effect is boosted by coQ10, which supports their potential use in photoaging.

Metformin treatment is associated with improved outcome in patients with diabetes and advanced heart failure (HFrEF)

The role of metformin (MET) in the treatment of patients with advanced HFrEF and type 2 diabetes mellitus (DM) is not firmly established. We studied the impact of MET on metabolic profile, quality of life (QoL) and survival in these patients. A total of 847 stable patients with advanced HFrEF (57.4 ± 11.3 years, 67.7% NYHA III/IV, LVEF 23.6 ± 5.8%) underwent clinical and laboratory evaluation and were prospectively followed for a median of 1126 (IQRs 410; 1781) days for occurrence of death, urgent heart transplantation or mechanical circulatory support implantation. A subgroup of 380 patients (44.9%) had DM, 87 of DM patients (22.9%) were treated with MET. Despite worse insulin sensitivity and more severe DM (higher BMI, HbA1c, worse insulin resistance), MET-treated patients exhibited more stable HF marked by lower BNP level (400 vs. 642 ng/l), better LV and RV function, lower mitral and tricuspid regurgitation severity, were using smaller doses of diuretics (all p < 0.05). Further, they had higher eGFR (69.23 vs. 63.34 ml/min/1.73 m2) and better QoL (MLHFQ: 36 vs. 48 points, p = 0.002). Compared to diabetics treated with other glucose-lowering agents, MET-treated patients had better event-free survival even after adjustment for BNP, BMI and eGFR (p = 0.035). Propensity score-matched analysis with 17 covariates yielded 81 pairs of patients and showed a significantly better survival for MET-treated subgroup (p = 0.01). MET treatment in patients with advanced HFrEF and DM is associated with improved outcome by mechanisms beyond the improvement of blood glucose control.

Recent Advances on Drug Development and Emerging Therapeutic Agents Through Targeting Cellular Homeostasis for Ageing and Cardiovascular Disease

Ageing is a progressive physiological process mediated by changes in biological pathways, resulting in a decline in tissue and cellular function. It is a driving factor in numerous age-related diseases including cardiovascular diseases (CVDs). Cardiomyopathies, hypertension, ischaemic heart disease, and heart failure are some of the age-related CVDs that are the leading causes of death worldwide. Although individual CVDs have distinct clinical and pathophysiological manifestations, a disturbance in cellular homeostasis underlies the majority of diseases which is further compounded with aging. Three key evolutionary conserved signalling pathways, namely, autophagy, mitophagy and the unfolded protein response (UPR) are involved in eliminating damaged and dysfunctional organelle, misfolded proteins, lipids and nucleic acids, together these molecular processes protect and preserve cellular homeostasis. However, amongst the numerous molecular changes during ageing, a decline in the signalling of these key molecular processes occurs. This decline also increases the susceptibility of damage following a stressful insult, promoting the development and pathogenesis of CVDs. In this review, we discuss the role of autophagy, mitophagy and UPR signalling with respect to ageing and cardiac disease. We also highlight potential therapeutic strategies aimed at restoring/rebalancing autophagy and UPR signalling to maintain cellular homeostasis, thus mitigating the pathological effects of ageing and CVDs. Finally, we highlight some limitations that are likely hindering scientific drug research in this field.

Combining the HSP90 inhibitor TAS-116 with metformin effectively degrades the NLRP3 and attenuates inflammasome activation in rats: A new management paradigm for ulcerative colitis

Ulcerative colitis (UC) is a prevalent type of inflammatory bowel diseases that may predispose patients to acquire colitis-related cancer if treatment was not effective. Despite the presence of an array of established treatment options, current modalities are not successful for a substanial number of patients. The activation of the NLRP3 inflammasome is critical in the development of inflammatory processes in the colon. Additionally, the regulation of NLRP3 via HSP90 inhibition is a potential target to treat UC. Moreover, during inflammation, autophagy allows the turnover of malfunctioning proteins and therefore stands as a viable strategy for inactivating NLRP3 inflammasomes and halting hyperinflammation. Herein, we evaluated the effect of autophagy induction using metformin in the context of HSP90 inhibition by TAS-116 in the dextran sodium sulfate (DSS)-induced UC in rats. We revealed that TAS-116-induced interruption of the protein complex containing HSP90 and NLRP3 might hamper and delay the start of the inflammatory cascade ensued by the NLRP3 inflammasome oligomerization. In such circumstances, the unprotected NLRP3 is subjected to autophagic degradation in an environment of metformin-promoted autophagic signaling. As a result, such dynamic synergy was efficient in combating colon damage and immune-cell infiltration. This was confirmed by the macroscopic and microscopic investigations. Further, biochemical analysis revealed subdued inflammation cascade and oxidative injury. Therefore, simultaneous administration of TAS-116 and metformin is a new management paradigm aimed at inducing malfunction in the NLRP3 followed by augmenting its autophagic degradation, respectively. However, further studies should be conducted to assess the reliability and consistency of this novel approach.

Metformin attenuates cadmium-induced degeneration of spiral ganglion neuron via restoring autophagic flux in primary culture

Cadmium (Cd), a common environmental and occupational toxicant, is an important risk factor for hearing loss. After exposure, Cd accumulates in the inner ear and induces spiral ganglion neuron (SGN) degeneration; however, the underlying mechanisms are poorly understood. Dysfunctional autophagy has been implicated in many neurodegenerative diseases, including Cd-induced neurotoxicity. Metformin has been validated to confer not only anti-hyperglycaemic but also neuroprotective effects. However, the relationship between autophagy dysfunction, SGN degeneration, and the effect of metformin on Cd-induced SGN neurotoxicity has not yet been established. In this study, we demonstrate that metformin notably attenuates Cd-evoked SGN degeneration by restoring impaired autophagy flux, as evidenced by the suppression of Cd-induced elevation of autophagy markers microtubule-associated protein 1A/1B-light chain 3-II (LC3-II) and autophagy substrate protein p62 in degenerated SGN. Blockage of autophagy flux by chloroquine abolished metformin-induced neuroprotection against Cd-induced neurotoxicity in SGN. The results of this study reveal that autophagy dysfunction is an important component of Cd-induced SGN degeneration, and metformin may be a potential protective agent for attenuating SGN degeneration following Cd exposure.

Impact of Autophagy on Prognosis of Patients With Dilated Cardiomyopathy

BACKGROUND

Autophagy is a cellular process that degrades a cell's own cytoplasmic components for energy provision and to maintain a proper intracellular environment. Left ventricular reverse remodeling (LVRR) promises a better prognosis for patients with dilated cardiomyopathy (DCM).

OBJECTIVES

The authors tested the hypothesis that autophagy is involved in LVRR and has prognostic value in the human failing heart.

METHODS

Using left ventricular endomyocardial biopsy specimens from 42 patients with DCM (21 LVRR-positive and 21 LVRR-negative) and 7 patients with normal cardiac function (control), the authors performed immunohistochemistry and immunofluorescent labeling of LC3 and cathepsin D and electron microscopic observation in addition to general morphometry under light microscopy.

RESULTS

The clinical characteristics of LVRR-positive patients were similar to those of the LVRR-negative patients, except for pulmonary artery pressure and left atrial dimension. Morphometry under light microscopy did not differ among specimens from DCM patients, regardless of their LVRR status. Electron microscopy revealed that autophagic vacuoles (autophagosomes and autolysosomes) and lysosomes were abundant within cardiomyocytes from DCM patients. Moreover, cardiomyocytes from LVRR-positive patients contained significantly more autophagic vacuoles with higher autolysosome ratios and cathepsin D expression levels than cardiomyocytes from LVRR-negative patients. Logistic regression analysis adjusted for age showed that increases in autophagic vacuole number and cathepsin D expression were predictive of LVRR. DCM patients who achieved LVRR experienced fewer cardiovascular events during the follow-up period.

CONCLUSIONS

The authors show that autophagy is a useful marker predictive of LVRR in DCM patients. This provides novel pathologic insight into a strategy for treating the failing DCM heart.

Metformin: Expanding the Scope of Application-Starting Earlier than Yesterday, Canceling Later

Today the area of application of metformin is expanding, and a wealth of data point to its benefits in people without carbohydrate metabolism disorders. Already in the population of people leading an unhealthy lifestyle, before the formation of obesity and prediabetes metformin smooths out the adverse effects of a high-fat diet. Being prescribed at this stage, metformin will probably be able to, if not prevent, then significantly reduce the progression of all subsequent metabolic changes. To a large extent, this review will discuss the proofs of the evidence for this. Another recent important change is a removal of a number of restrictions on its use in patients with heart failure, acute coronary syndrome and chronic kidney disease. We will discuss the reasons for these changes and present a new perspective on the role of increasing lactate in metformin therapy.

Exacerbated post-infarct pathological myocardial remodelling in diabetes is associated with impaired autophagy and aggravated NLRP3 inflammasome activation

Background

Diabetes mellitus (DM) patients surviving myocardial infarction (MI) have substantially higher mortality due to the more frequent development of subsequent pathological myocardial remodelling and concomitant functional deterioration. This study investigates the molecular pathways underlying accelerated cardiac remodelling in a well‐established mouse model of diabetes exposed to MI.

Methods and results

Myocardial infarction in DM mice was established by ligating the left anterior descending coronary artery. Cardiac function was assessed by echocardiography. Myocardial hypertrophy and cardiac fibrosis were determined histologically 6 weeks post‐MI or sham operation. Autophagy, the NLRP3 inflammasome, and caspase‐1 were evaluated by western blotting or immunofluorescence. Echocardiographic imaging revealed significantly increased left ventricular dilation in parallel with increased mortality after MI in DM mice (53.33%) compared with control mice (26.67%, P < 0.05). Immunoblotting, electron microscopy, and immunofluorescence staining for LC3 and p62 indicated impaired autophagy in DM + MI mice compared with control mice (P < 0.05). Furthermore, defective autophagy was associated with increased NLRP3 inflammasome and caspase‐1 hyperactivation in DM + MI mouse cardiomyocytes (P < 0.05). Consistent with NLRP3 inflammasome and caspase‐I hyperactivation, cardiomyocyte death and IL‐1β and IL‐18 secretion were increased in DM + MI mice (P < 0.05). Importantly, the autophagy inducer and the NLRP3 inhibitor attenuated the cardiac remodelling of DM mice after MI.

Conclusion

In summary, our results indicate that DM aggravates cardiac remodelling after MI through defective autophagy and associated exaggerated NLRP3 inflammasome activation, proinflammatory cytokine secretion, suggesting that restoring autophagy and inhibiting NLRP3 inflammasome activation may serve as novel targets for the prevention and treatment of post‐infarct remodelling in DM.

The gut-cardiovascular connection: new era for cardiovascular therapy

Our gut microbiome is constituted by trillions of microorganisms including bacteria, archaea and eukaryotic microbes. Nowadays, gut microbiome has been gradually recognized as a new organ system that systemically and biochemically interact with the host. Accumulating evidence suggests that the imbalanced gut microbiome contributes to the dysregulation of immune system and the disruption of cardiovascular homeostasis. Specific microbiome profiles and altered intestinal permeability are often observed in the pathophysiology of cardiovascular diseases. Gut-derived metabolites, toxins, peptides and immune cell-derived cytokines play pivotal roles in the induction of inflammation and the pathogenesis of dysfunction of heart and vasculature. Impaired crosstalk between gut microbiome and multiple organ systems, such as gut-vascular, heart-gut, gut-liver and brain-gut axes, are associated with higher cardiovascular risks. Medications and strategies that restore healthy gut microbiome might therefore represent novel therapeutic options to lower the incidence of cardiovascular and metabolic disorders.

SGLT2 Inhibitors as Calorie Restriction Mimetics: Insights on Longevity Pathways and Age-Related Diseases

Sodium-glucose cotransporter-2 (SGLT2) inhibitors induce glycosuria, reduce insulin levels, and promote fatty acid oxidation and ketogenesis. By promoting a nutrient deprivation state, SGLT2 inhibitors upregulate the energy deprivation sensors AMPK and SIRT1, inhibit the nutrient sensors mTOR and insulin/IGF1, and modulate the closely linked hypoxia-inducible factor (HIF)-2α/HIF-1α pathways. Phosphorylation of AMPK and upregulation of adiponectin and PPAR-α favor a reversal of the metabolic syndrome which have been linked to suppression of chronic inflammation. Downregulation of insulin/IGF1 pathways and mTOR signaling from a reduction in glucose and circulating amino acids promote cellular repair mechanisms, including autophagy and proteostasis which confer cellular stress resistance and attenuate cellular senescence. SIRT1, another energy sensor activated by NAD+ in nutrient-deficient states, is reciprocally activated by AMPK, and can deacetylate and activate transcription factors, such as PCG-1α, mitochondrial transcription factor A (TFAM), and nuclear factor E2-related factor (NRF)-2, that regulate mitochondrial biogenesis. FOXO3 transcription factor which target genes in stress resistance, is also activated by AMPK and SIRT1. Modulation of these pathways by SGLT2 inhibitors have been shown to alleviate metabolic diseases, attenuate vascular inflammation and arterial stiffness, improve mitochondrial function and reduce oxidative stress-induced tissue damage. Compared with other calorie restriction mimetics such as metformin, rapamycin, resveratrol, and NAD+ precursors, SGLT2 inhibitors appear to be the most promising in the treatment of aging-related diseases, due to their regulation of multiple longevity pathways that closely resembles that achieved by calorie restriction and their established efficacy in reducing cardiovascular events and all-cause mortality. Evidence is compelling for the role of SGLT2 inhibitors as a calorie restriction mimetic in anti-aging therapeutics.

Effects of omega-3 fatty acids and metformin combination on diabetic cardiomyopathy in rats through autophagic pathway

Diabetic cardiomyopathy is a primary cause of increased morbidity and mortality in diabetics. Evidence has suggested a pivotal role for interrupted mitochondrial dynamics and quality control machinery in the onset and development of diabetic cardiomyopathy. Sequestosome 1 (SQSTM1) is a major reporter of selective autophagic activity. Other than controlling the expression of genes involved in mitochondrial biogenesis, recently peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC-1α) was reported to directly affect SQSTM1 gene expression. Calcineurin, a pivotal mediator of cardiac hypertrophy, has been also linked to enhanced expression of SQSTM1. This study aimed to test the cardioprotective effects of adding ω-3 polyunsaturated fatty acids (PUFAs) to metformin in a rat model of type 2 diabetes mellitus and to evaluate the molecular mechanisms underlying their effects on mitochondrial quality. Diabetes was induced in male Sprague Dawley rats by a high-fat diet for 6 weeks, followed by a low-dose streptozotocin (35 mg/kg). Diabetic rats were either treated with metformin (150 mg/kg/d), ω-3 PUFAs (300 mg/kg/d), or their combination in the same doses for further 8 weeks. Along with metabolic and pathological derangements, we report that correlating with electron microscopic evidence of mitochondrial degeneration, gene expression of the autophagic indicators SQSTM1, PGC-1α, and calcineurin were decreased in the hearts of diabetic rats. Independent of its anti-hyperglycemic effects, metformin successfully preserved mitochondrial integrity and upregulated myocardial PGC-1α, calcineurin, and SQSTM1 gene expression. ω-3 PUFAs possess synergistic cardioprotection when added to metformin, suggested by improvements in myocardial ultrastructure, autophagic activity, and SQSTM1 gene expression.

Autophagy-targeted therapy to modulate age-related diseases: Success, pitfalls, and new directions

Autophagy is a critical metabolic process that supports homeostasis at a basal level and is dynamically regulated in response to various physiological and pathological processes. Autophagy has some etiologic implications that support certain pathological processes due to alterations in the lysosomal-degradative pathway. Some of the conditions related to autophagy play key roles in highly relevant human diseases, e.g., cardiovascular diseases (15.5%), malignant and other neoplasms (9.4%), and neurodegenerative conditions (3.7%). Despite advances in the discovery of new strategies to treat these age-related diseases, autophagy has emerged as a therapeutic option after preclinical and clinical studies. Here, we discuss the pitfalls and success in regulating autophagy initiation and its lysosome-dependent pathway to restore its homeostatic role and mediate therapeutic effects for cancer, neurodegenerative, and cardiac diseases. The main challenge for the development of autophagy regulators for clinical application is the lack of specificity of the repurposed drugs, due to the low pharmacological uniqueness of their target, including those that target the PI3K/AKT/mTOR and AMPK pathway. Then, future efforts must be conducted to deal with this scenery, including the disclosure of key components in the autophagy machinery that may intervene in its therapeutic regulation. Among all efforts, those focusing on the development of novel allosteric inhibitors against autophagy inducers, as well as those targeting autolysosomal function, and their integration into therapeutic regimens should remain a priority for the field.

Metformin ameliorates bladder dysfunction in a rat model of partial bladder outlet obstruction

Alteration of bladder morphology and function was the most important consequence of bladder outlet obstruction (BOO). Using a rat model of partial BOO (pBOO), we found that rats treated with metformin showed lower baseline pressures with a reduced inflammatory reaction in the early phase (2 wk) after pBOO. The NLR family pyrin domain containing 3 inflammasome pathway was inhibited in pBOO rat bladders with treatment of metformin in the early phase. Metformin reduced the activity of NLR family pyrin domain containing 3 in primary urothelial cells. In the chronic phase (9 wk after pBOO), metformin treatment ameliorated bladder fibrosis and improved the reduced compliance. Treatment with metformin suppressed the activation of Smad3 and compensated the diminished autophagy in 9-wk pBOO rat bladders. Autophagy was inhibited with upregulation of profibrotic proteins in primary fibroblasts from chronic pBOO bladders, which could be restored by administration of metformin. The antifibrotic effects of metformin on fibroblasts were diminished after silencing of AMP-activated protein kinase or light chain 3B. In summary, this study elucidates that oral administration of metformin relieves inflammation in the bladder during the early phase of pBOO. Long-term oral administration of metformin can prevent functional and histological changes in the pBOO rat bladder. The current study suggests that metformin might be used to prevent the development of bladder dysfunction secondary to BOO.NEW & NOTEWORTHY The present study in a rat model showed that oral administration of metformin alleviated inflammation following partial bladder outlet obstruction in the early phase and ameliorated bladder fibrosis as well as bladder dysfunction by long-term treatment. Our study indicated that metformin is a potential drug to inhibit bladder remodeling and alleviate bladder dysfunction. Clinical trials are needed to validate the effect of metformin on the bladder dysfunction and bladder fibrosis in the future.

The effects of metformin on autophagy

Metformin is the first-line option for treating newly diagnosed diabetic patients and also involved in other pharmacological actions, including antitumor effect, anti-aging effect, polycystic ovarian syndrome prevention, cardiovascular action, and neuroprotective effect, etc. However, the mechanisms of metformin actions were not fully illuminated. Recently, increasing researches showed that autophagy is a vital medium of metformin playing pharmacological actions. Nevertheless, results on the effects of metformin on autophagy were inconsistent. Apart from few clinical evidences, more data focused on kinds of no-clinical models. First, many studies showed that metformin could induce autophagy via a number of signaling pathways, including AMPK-related signaling pathways (e.g. AMPK/mTOR, AMPK/CEBPD, MiTF/TFE, AMPK/ULK1, and AMPK/miR-221), Redd1/mTOR, STAT, SIRT, Na⁺/H⁺ exchangers, MAPK/ERK, PK2/PKR/AKT/ GSK3β, and TRIB3. Secondly, some signaling pathways were involved in the process of metformin inhibiting autophagy, such as AMPK-related signaling pathways (AMPK/NF-κB and other undetermined AMPK-related signaling pathways), Hedgehog, miR-570-3p, miR-142-3p, and MiR-3127-5p. Thirdly, two types of signaling pathways including PI3K/AKT/mTOR and endoplasmic reticulum (ER) stress could bidirectionally impact the effectiveness of metformin on autophagy. Finally, multiple signal pathways were reviewed collectively in terms of affecting the effectiveness of metformin on autophagy. The pharmacological effects of metformin combining its actions on autophagy were also discussed. It would help better apply metformin to treat diseases in term of mediating autophagy.

Metformin Reverses the Enhanced Myocardial SR/ER-Mitochondria Interaction and Impaired Complex I-Driven Respiration in Dystrophin-Deficient Mice

Besides skeletal muscle dysfunction, Duchenne muscular dystrophy (DMD) exhibits a progressive cardiomyopathy characterized by an impaired calcium (Ca²⁺) homeostasis and a mitochondrial dysfunction. Here we aimed to determine whether sarco-endoplasmic reticulum (SR/ER)–mitochondria interactions and mitochondrial function were impaired in dystrophic heart at the early stage of the pathology. For this purpose, ventricular cardiomyocytes and mitochondria were isolated from 3-month-old dystrophin-deficient mice (mdx mice). The number of contacts points between the SR/ER Ca²⁺ release channels (IP3R1) and the porine of the outer membrane of the mitochondria, VDAC1, measured using in situ proximity ligation assay, was greater in mdx cardiomyocytes. Expression levels of IP3R1 as well as the mitochondrial Ca²⁺ uniporter (MCU) and its regulated subunit, MICU1, were also increased in mdx heart. MICU2 expression was however unchanged. Furthermore, the mitochondrial Ca²⁺ uptake kinetics and the mitochondrial Ca²⁺ content were significantly increased. Meanwhile, the Ca²⁺-dependent pyruvate dehydrogenase phosphorylation was reduced, and its activity significantly increased. In Ca²⁺-free conditions, pyruvate-driven complex I respiration was decreased whereas in the presence of Ca²⁺, complex I-mediated respiration was boosted. Further, impaired complex I-mediated respiration was independent of its intrinsic activity or expression, which remains unchanged but is accompanied by an increase in mitochondrial reactive oxygen species production. Finally, mdx mice were treated with the complex I modulator metformin for 1 month. Metformin normalized the SR/ER-mitochondria interaction, decreased MICU1 expression and mitochondrial Ca²⁺ content, and enhanced complex I-driven respiration. In summary, before any sign of dilated cardiomyopathy, the DMD heart displays an aberrant SR/ER-mitochondria coupling with an increase mitochondrial Ca²⁺ homeostasis and a complex I dysfunction. Such remodeling could be reversed by metformin providing a novel therapeutic perspective in DMD.

ICS II protects against cardiac hypertrophy by regulating metabolic remodelling, not by inhibiting autophagy

Cardiac hypertrophy is characterized by a shift in metabolic substrate utilization. Therefore, the regulation of ketone body uptake and metabolism may have beneficial effects on heart injuries that induce cardiac remodelling. In this study, we investigated whether icariside II (ICS II) protects against cardiac hypertrophy in mice and cardiomyocytes. To create cardiac hypertrophy animal and cell models, mice were subjected to transverse aortic constriction (TAC), and embryonic rat cardiomyocytes (H9C2) were stimulated with angiotensin II, a neurohumoral stressor. Both the in vivo and in vitro results suggest that ICS II treatment ameliorated pressure overload–induced cardiac hypertrophy and preserved heart function. In addition, apoptosis and oxidative stress were reduced in the presence of ICS II. Moreover, ICS II inhibited excess autophagy in TAC‐induced hearts and angiotensin II–stimulated cardiomyocytes. Mechanistically, we found that ICS II administration regulated SIRT3 expression in cardiac remodelling. SIRT3 activation increased ketone body transportation and utilization. Collectively, our data show that ICS II attenuated cardiac hypertrophy by modulating ketone body and fatty acid metabolism, and that this was likely due to the activation of the SIRT3‐AMPK pathway. ICS II treatment may provide a new therapeutic strategy for improving myocardial metabolism in cardiac hypertrophy and heart failure.

Metformin and Fibrosis: A Review of Existing Evidence and Mechanisms

Fibrosis is a physiological response to organ injury and is characterized by the excessive deposition of connective tissue components in an organ, which results in the disruption of physiological architecture and organ remodeling, ultimately leading to organ failure and death. Fibrosis in the lung, kidney, and liver accounts for a substantial proportion of the global burden of disability and mortality. To date, there are no effective therapeutic strategies for controlling fibrosis. A class of metabolically targeted chemicals, such as adenosine monophosphate-activated protein kinase (AMPK) activators and peroxisome proliferator-activated receptor (PPAR) agonists, shows strong potential in fighting fibrosis. Metformin, which is a potent AMPK activator and is the only recommended first-line drug for the treatment of type 2 diabetes, has emerged as a promising method of fibrosis reduction or reversion. In this review, we first summarize the key experimental and clinical studies that have specifically investigated the effects of metformin on organ fibrosis. Then, we discuss the mechanisms involved in mediating the antifibrotic effects of metformin in depth.

Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition)1

In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for bona fide autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field.

Mechanisms of action of metformin and its regulatory effect on microRNAs related to angiogenesis

Angiogenesis is rapidly initiated in response to pathological conditions and is a key target for pharmaceutical intervention in various malignancies. Anti-angiogenic therapy has emerged as a potential and effective therapeutic strategy for treating cancer and cardiovascular-related diseases. Metformin, a first-line oral antidiabetic agent for type 2 diabetes mellitus (T2DM), not only reduces blood glucose levels and improves insulin sensitivity and exerts cardioprotective effects but also shows benefits against cancers, cardiovascular diseases, and other diverse diseases and regulates angiogenesis. MicroRNAs (miRNAs) are endogenous noncoding RNA molecules with a length of approximately 19-25 bases that are widely involved in controlling various human biological processes. A large number of miRNAs are involved in the regulation of cardiovascular cell function and angiogenesis, of which miR-21 not only regulates vascular cell proliferation, migration and apoptosis but also plays an important role in angiogenesis. The relationship between metformin and abnormal miRNA expression has gradually been revealed in the context of numerous diseases and has received increasing attention. This paper reviews the drug-target interactions and drug repositioning events of metformin that influences vascular cells and has benefits on angiogenesis-mediated effects. Furthermore, we use miR-21 as an example to explain the specific molecular mechanism underlying metformin-mediated regulation of the miRNA signaling pathway controlling angiogenesis and vascular protective effects. These findings may provide a new therapeutic target and theoretical basis for the clinical prevention and treatment of cardiovascular diseases.

Clinical perspectives and concerns of metformin as an anti-aging drug

As percentages of elderly people rise in many societies, age-related diseases have become more prevalent than ever. Research interests have been shifting to delaying age-related diseases by delaying or reversing aging itself. We use metformin as an entry point to talk about the important molecular and genetic longevity-regulating mechanisms that have been extensively studied with it. Then we review a number of observational studies, animal studies, and clinical trials to reflect the clinical potentials of the mechanisms in lifespan extension, cardiovascular diseases, tumors, and neurodegeneration. Finally, we highlight remaining concerns that are related to metformin and future anti-aging research.

Morphological characteristics in diabetic cardiomyopathy associated with autophagy

Diabetic cardiomyopathy, clinically diagnosed as ventricular dysfunction in the absence of coronary atherosclerosis or hypertension in diabetic patients, is a cardiac muscle-specific disease that increases the risk of heart failure and mortality. Its clinical course is characterized initially by diastolic dysfunction, later by systolic dysfunction, and eventually by clinical heart failure from an uncertain mechanism. Light microscopic features such as interstitial fibrosis, inflammation, and cardiomyocyte hypertrophy are observed in diabetic cardiomyopathy, but are common to failing hearts generally and are not specific to diabetic cardiomyopathy. Electron microscopic studies of biopsy samples from diabetic patients with heart failure have revealed that the essential mechanism underlying diabetic cardiomyopathy involves thickening of the capillary basement membrane, accumulation of lipid droplets, and glycogen as well as increased numbers of autophagic vacuoles within cardiomyocytes. Autophagy is a conserved mechanism that contributes to maintaining intracellular homeostasis by degrading long-lived proteins and damaged organelles and is observed more often in cardiomyocytes within failing hearts. Diabetes mellitus (DM) impairs cardiac metabolism and leads to dysregulation of energy substrates that contribute to cardiac autophagy. However, a "snapshot" showing greater numbers of autophagic vacuoles within cardiomyocytes may indicate that autophagy is activated into phagophore formation or is suppressed due to impairment of the lysosomal degradation step. Recent in vivo studies have shed light on the underlying molecular mechanism governing autophagy and its essential meaning in the diabetic heart. Autophagic responses to diabetic cardiomyopathy differ between diabetic types: they are enhanced in type 1 DM, but are suppressed in type 2 DM. This difference provides important insight into the pathophysiology of diabetic cardiomyopathy. Here, we review recent advances in our understanding of the pathophysiology of diabetic cardiomyopathy, paying particular attention to autophagy in the heart, and discuss the therapeutic potential of interventions modulating autophagy in diabetic cardiomyopathy.

The CnB1 p.D102A variant is linked to dilated cardiomyopathy via impaired Calcineurin activity

BACKGROUND

The role of calcineurin (protein phosphatase 2B (PP2B)) in the pathogenesis of human dilated cardiomyopathy (DCM) has not been fully elucidated. We determined the potential involvement of calcineurin in the pathogenesis of DCM caused by mutations in CnB1, a subunit of calcineurin.

METHODS

By whole-exome sequencing, we identified a new CnB1 variant in a Han Chinese proband with cardiomyopathy from a 3-generation family with 2 normal individuals and 3 individuals with familial dilated cardiomyopathy. The potential pathogenic variant was validated by Sanger sequencing. We performed functional and mechanistic experiments in a CnB1-knockin (KI) mouse model and at the cellular level.

RESULTS

We detected a rare heterozygous CnB1 variant (p.D102A) in a proband with dilated cardiomyopathy. This variant was localized to the EF hand 3 region of CnB1, where no variants have been previously reported. KI mice harboring the p.D102A variant exhibited decreased cardiac function and cardiac dilatation. Immunoblotting, RT-PCR and immunofluorescence results showed decreased cardiomyocyte size and heart failure-related protein expression. A calcineurin activity assay demonstrated decreased calcineurin activity in the KI mice, accompanied by the decreased ability of CnB1 to bind CnA.

CONCLUSIONS

CnB1 p.D102A is a disease-associated variant that confers susceptibility to cardiac dilatation. This variant is associated with impaired calcineurin activity and a subsequent decrease in the ability of CnB1 to bind CnA.

The ties that bind: functional clusters in limb-girdle muscular dystrophy

The limb-girdle muscular dystrophies (LGMDs) are a genetically pleiomorphic class of inherited muscle diseases that are known to share phenotypic features. Selected LGMD genetic subtypes have been studied extensively in affected humans and various animal models. In some cases, these investigations have led to human clinical trials of potential disease-modifying therapies, including gene replacement strategies for individual subtypes using adeno-associated virus (AAV) vectors. The cellular localizations of most proteins associated with LGMD have been determined. However, the functions of these proteins are less uniformly characterized, thus limiting our knowledge of potential common disease mechanisms across subtype boundaries. Correspondingly, broad therapeutic strategies that could each target multiple LGMD subtypes remain less developed. We believe that three major "functional clusters" of subcellular activities relevant to LGMD merit further investigation. The best known of these is the glycosylation modifications associated with the dystroglycan complex. The other two, mechanical signaling and mitochondrial dysfunction, have been studied less systematically but are just as promising with respect to the identification of significant mechanistic subgroups of LGMD. A deeper understanding of these disease pathways could yield a new generation of precision therapies that would each be expected to treat a broader range of LGMD patients than a single subtype, thus expanding the scope of the molecular medicines that may be developed for this complex array of muscular dystrophies.

First Reports of Effects of Insulin, Human-like Insulin Receptors and Adapter Proteins in Acanthamoeba castellanii

The insulin receptor (IR) and insulin-like growth factor 1 receptor (IGF1-R) play key roles in growth, regulation of nutrient metabolism and carbohydrate homeostasis. Insulin-like molecules in prokaryotes and other early life have been reported. However, an account of metabolic effects of insulin, transcriptomic evidence of expression of glucose transporting channels (GLUT) and homology modelling of IR and IGF1-R like proteins in unicellular life-forms have yet to be established. Acanthamoeba spp. has existed for about 2 billion years and is one of the earliest mitochondriate unicellular eukaryotic cells on Earth. Despite Acanthamoeba spp. being grown in a medium called peptone-yeast-glucose (PYG) for over 50 years, the mechanism and regulation of glucose uptake by IR or IGF1-R molecules in this microbe has not yet been reported. Several methods were utilized to validate the effects of insulin on trophozoites of A. castellanii, including: growth assays with insulin, estimation of glucose and potassium (K+) entry into the cell, and histology showing anabolic effects on proteins. Bioinformatic computational tools and homology modeling demonstrated the involvement of IR like proteins, GLUT, and adapter proteins in mediating the IR cascade. Growth assays showed proliferative effects in a dose range of 2.98-5.97 µmol/mL of insulin. After insulin exposure, A. castellanii trophozoites displayed enhanced Periodic acid-Sciff (PAS) staining. Amino acid sequence similarities and homology modelling revealed ACA1_163470 in Acanthamoeba spp. to be a homolog of human-IR. Acanthamoeba protein ACA1_336150 shares similarities with IGF1-R. Additionally, some proteins like ACA1_060920 have attributes of GLUT like channels on homology modelling and show similarity with human GLUT. Knowledge of IR and insulin effects in Acanthamoeba spp. contributes to its biology and advances current understanding behind the evolution of IR and IGF1-R signalling cascade.

Benefits of Metformin in Attenuating the Hallmarks of Aging

Biological aging involves an interplay of conserved and targetable molecular mechanisms, summarized as the hallmarks of aging. Metformin, a biguanide that combats age-related disorders and improves health span, is the first drug to be tested for its age-targeting effects in the large clinical trial-TAME (targeting aging by metformin). This review focuses on metformin's mechanisms in attenuating hallmarks of aging and their interconnectivity, by improving nutrient sensing, enhancing autophagy and intercellular communication, protecting against macromolecular damage, delaying stem cell aging, modulating mitochondrial function, regulating transcription, and lowering telomere attrition and senescence. These characteristics make metformin an attractive gerotherapeutic to translate to human trials.

circPAN3 exerts a profibrotic role via sponging miR-221 through FoxO3/ATG7-activated autophagy in a rat model of myocardial infarction

BACKGROUND

Cardiovascular disease (CVD) is the leading cause of mortality worldwide. Cardiac fibrosis is the scarring process occurs commonly with CVDs impairing the function and structure of heart. Herein, we investigated the role of circPAN3 in the pathogenesis of cardiac fibrosis.

METHODS

A rat myocardial infarction (MI) model was constructed to evaluate the role of circPAN3. Expression of circPAN3 in MI was determined, and si-circPAN3 was applied to verify its profibrotic effects. With an in vitro model, cardiac fibroblasts were stimulated by transforming growth factor beta 1 (TGFβ1). Immunofluorescent staining was employed to assess the fibrosis-related markers, as well as autophagy activity. CCK-8 and transwell assays were performed to determine cell proliferation and migration. Luciferase reporter assay and RNA pull-down were subjected to verify the interaction of circPAN3/miR-221. The enrichment of FoxO3 on the promoter region of ATG7 was detected using CHIP assay.

RESULTS

Elevated circPAN3 was found in rat MI heart tissue, of which knockdown attenuated cardiac fibrosis after MI. In an in vitro model exposing with TGFβ1, increasing cell proliferation and migration were observed, whereas these effects were abolished by circPAN3 knockdown, as well as autophagy activity. miR-221 was identified as a target to be involved in circPAN3-mediated cardiac fibrosis after MI. miR-221 negatively regulated FoxO3, thus causing the inhibition of ATG7 transcription. The regulatory network of circPAN3/miR-221/FoxO3/ATG7 in cardiac fibrosis was further determined in vivo.

CONCLUSION

circPAN3 exhibited profibrotic effects during autophagy-mediated cardiac fibrosis via miR-221/FoxO3/ATG7 axis, which may serve as potential biomarkers for cardiac fibrosis therapeutics.