MitoNEET prevents iron overload-induced insulin resistance in H9c2 cells through regulation of mitochondrial iron.

Iron overload (IO) induces insulin resistance in H9c2 cardiomyoblast cells. Here, we used H9c2 cells overexpressing MitoNEET to examine the potential for protection against iron accumulation in the mitochondria and subsequent insulin resistance. In control H9c2 cells, IO was observed to increase mitochondrial iron content, reactive oxygen species (ROS) production, mitochondrial fission, and reduced insulin-stimulated Akt and ERK1/2 phosphorylation. IO did not significantly affect mitophagy, or mitochondrial content, however, an increase in peroxisome-proliferator-activated receptor gamma coactivator 1 alpha (PGC1α) protein expression, a key regulator of mitochondrial biogenesis, was observed. MitoNEET overexpression was able to attenuate the effects of IO on mitochondrial iron content, reactive oxygen species, mitochondrial fission, and insulin signaling. MitoNEET overexpression also upregulated levels of PGC1α protein. The mitochondria-targeted antioxidant, Skq1, prevented IO-induced ROS production and insulin resistance in control cells, indicating mitochondrial ROS plays a causal role in the onset of insulin resistance. The selective mitochondrial fission inhibitor, Mdivi-1, prevented IO-induced mitochondrial fission, however, it did not alleviate IO-induced insulin resistance. Collectively, IO causes insulin resistance in H9c2 cardiomyoblasts and this can be averted by reduction of mitochondrial iron accumulation and ROS production by overexpression of the MitoNEET protein.

MitoNEET Provides Cardioprotection via Reducing Oxidative Damage and Conserving Mitochondrial Function.

Cardiometabolic diseases exert a significant health impact, leading to a considerable economic burden globally. The metabolic syndrome, characterized by a well-defined cluster of clinical parameters, is closely linked to an elevated risk of cardiovascular disease. Current treatment strategies often focus on addressing individual aspects of metabolic syndrome. We propose that exploring novel therapeutic approaches that simultaneously target multiple facets may prove more effective in alleviating the burden of cardiometabolic disease. There is a growing body of evidence suggesting that mitochondria can serve as a pivotal target for the development of therapeutics aimed at resolving both metabolic and vascular dysfunction. MitoNEET was identified as a binding target for the thiazolidinedione (TZD) class of antidiabetic drugs and is now recognized for its role in regulating various crucial cellular processes. Indeed, mitoNEET has demonstrated promising potential as a therapeutic target in various chronic diseases, encompassing cardiovascular and metabolic diseases. In this review, we present a thorough overview of the molecular mechanisms of mitoNEET, with an emphasis on their implications for cardiometabolic diseases in more recent years. Furthermore, we explore the potential impact of these findings on the development of novel therapeutic strategies and discuss potential directions for future research.

Importance of Autophagy in Mediating Cellular Responses to Iron Overload in Cardiomyocytes.

Both iron overload and deficiency can promote development of cardiomyopathy. Advances in our knowledge from recent research have indicated numerous potential cellular mechanisms. Regulation of myocardial autophagy by iron is of particular interest and will be reviewed here. Autophagy is already well established to play a significant role in regulating the development of heart failure. This review will focus on regulation of autophagy by iron, crosstalk between autophagy and other cellular process which have also already been implicated in heart failure (oxidative stress, mitochondrial dysfunction, endoplasmic reticulum stress, ferroptosis) and the therapeutic potential of targeting these interactions.

MitoNEET preserves muscle insulin sensitivity during iron overload by regulating mitochondrial iron, reactive oxygen species and fission.

Iron overload (IO) is known to contribute to metabolic dysfunctions such as type 2 diabetes and insulin resistance. Using L6 skeletal muscle cells overexpressing the CDGSH iron-sulfur domain-containing protein 1 (CISD1, also known as mitoNEET) (mitoN) protein, we examined the potential role of MitoN in preventing IO-induced insulin resistance. In L6 control cells, IO resulted in insulin resistance which could be prevented by MitoN as demonstrated by western blot of p-Akt and Akt biosensor cells. Mechanistically, IO increased; mitochondrial iron accumulation, mitochondrial reactive oxygen species (ROS), Fis1-dependent mitochondrial fission, mitophagy, FUN14 domain-containing protein 1 (FUNDC1) expression, and decreased Parkin. MitoN overexpression was able to reduce increases in mitochondrial iron accumulation, mitochondrial ROS, mitochondrial fission, mitophagy and FUNDC1 upregulation due to IO. MitoN did not have any effect on the IO-induced downregulation of Parkin. MitoN alone also upregulated peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC1α) protein levels, a master regulator of mitochondrial biogenesis. The use of mitochondrial antioxidant, Skq1, or fission inhibitor, Mdivi-1, prevented IO-induced insulin resistance implying both mitochondrial ROS and fission play a causal role in the development of insulin resistance. Taken together, MitoN is able to confer protection against IO-induced insulin resistance in L6 skeletal muscle cells through regulation of mitochondrial iron content, mitochondrial ROS, and mitochondrial fission.

Autophagy deficiency exacerbated hypoxia-reoxygenation induced inflammation and cell death via a mitochondrial DNA/STING/IRF3 pathway.

AIMS: Autophagy is an important cellular process for maintaining physiological homeostasis and is known to protect against cardiovascular diseases including ischemia reperfusion (I/R) injury. The underlying mechanisms behind its protection require further characterization. MATERIALS AND METHODS: Atg7 knock out (AKO) mice were generated and subjected to I/R injury, complemented by Atg7 KO in a H9c2 cardiomyoblast cellular model ± hypoxia-reoxygenation. Subsequently, in both models, inflammation and cell death were studied. KEY FINDINGS: We confirmed that Atg7 KO led to autophagy, including mitophagy, deficiency. Upon H/R, Atg7 KO cells exhibited increased cell death compared to WT cells. Notably, we found that autophagy deficiency increased stress-induced mitochondrial fission, release of mitochondrial DNA, and sterile inflammation, namely activation of a STING/IRF3 axis leading to elevated interferon-α. Following I/R injury, AKO mice showed elevated cell death which correlated with a gene expression profile indicative of decreased anti-inflammatory responses. SIGNIFICANCE: Autophagy deficiency in the cardiomyocyte setting results in detrimental effects during I/R injury in mice or H/R injury in cells, mediated in part via mtDNA/IRF3/STING pathway. As such, modulation of this pathway may yield novel and promising therapeutics to treat or prevent I/R injury.

Role of Mitochondrial Iron Overload in Mediating Cell Death in H9c2 Cells.

Iron overload (IO) is associated with cardiovascular diseases, including heart failure. Our study's aim was to examine the mechanism by which IO triggers cell death in H9c2 cells. IO caused accumulation of intracellular and mitochondrial iron as shown by the use of iron-binding fluorescent reporters, FerroOrange and MitoFerroFluor. Expression of cytosolic and mitochondrial isoforms of Ferritin was also induced by IO. IO-induced iron accumulation and cellular ROS was rapid and temporally linked. ROS accumulation was detected in the cytosol and mitochondrial compartments with CellROX, DCF-DA and MitoSOX fluorescent dyes and partly reversed by the general antioxidant N-acetyl cysteine or the mitochondrial antioxidant SkQ1. Antioxidants also reduced the downstream activation of apoptosis and lytic cell death quantified by Caspase 3 cleavage/activation, mitochondrial Cytochrome c release, Annexin V/Propidium iodide staining and LDH release of IO-treated cells. Finally, overexpression of MitoNEET, an outer mitochondrial membrane protein involved in the transfer of Fe-S clusters between mitochondrial and cytosol, was observed to lower iron and ROS accumulation in the mitochondria. These alterations were correlated with reduced IO-induced cell death by apoptosis in MitoNEET-overexpressing cells. In conclusion, IO mediates H9c2 cell death by causing mitochondrial iron accumulation and subsequent general and mitochondrial ROS upregulation.

Surgical treatment of a Morgagni hernia causing intermittent gastric outlet obstruction.

A Morgagni hernia is a rare diaphragmatic hernia which develops through a congenital defect in the retrosternal area, usually on the right hand side. Because of its congenital aetiology, Morgagni hernias are rarely considered in the differential diagnosis of gastric outlet obstruction symptoms in adults. We present a patient with an incarcerated Morgagni hernia who presented with gastric outlet obstruction. A 77-year-old woman presented with symptoms and signs of gastric outlet obstruction, dehydration and acute renal impairment. She was treated by fluid resuscitation and nasogastric tube insertion. Radiological imaging showed a Morgagni hernia containing stomach, omentum and colon. This was treated surgically via an abdominal approach and the defect was closed with mesh. The patient recovered well from this procedure and was discharged. We discuss the anatomy, clinical presentation and surgical treatment of this rare diaphragmatic hernia to raise awareness among surgeons and surgical trainees.