Regulation of Na+-K+-ATPase effected high glucose-induced myocardial cell injury through c-Src dependent NADPH oxidase/ROS pathway

DR region of NKAα1 is a target to ameliorate hepatic lipid metabolism disturbance in obese mice

BACKGROUND

Na⁺/K⁺-ATPase (NKA), an ion pumping enzyme ubiquitously expressed in various cells, is critically involved in cellular ion homeostasis and signal transduction. However, the role of NKA in hepatic lipid homeostasis has yet to be fully characterized.

METHODS

The activity of NKA and NKAα1 expression were determined in steatotic cells, mice and patients. The roles of NKAα1 in hepatosteatosis were detected using hepatocyte knockout or specific overexpression of NKAα1 in mice.

RESULTS

Herein, we demonstrated that the expression and activity of α1 subunit of NKA (NKAα1) were lowered in the livers of nonalcoholic fatty liver disease (NAFLD) patients, high-fat diet (HFD)-induced obese mice, and genetically obese (ob/ob, db/db) mice, as well as oleic acid-induced hepatocytes. Hepatic deficiency of NKAα1 exacerbated, while adeno-associated virus-mediated liver specific overexpression of NKAα1 alleviated hepatic steatosis through regulation of fatty acid oxidation (FAO) and lipogenesis. Mechanistically, we revealed that NKAα1 upregulated sirtuin 1 (SIRT1) via interacting with ubiquitin specific peptidase 22 (USP22), a deubiquitinating enzyme for the stabilization and deubiquitination of SIRT1, thus activating the downstream autophagy signaling. Blockade of the SIRT1/autophagy signaling pathway eliminated the protective effects of NKAα1 against lipid deposition in hepatocytes. Importantly, we found that an antibody against the DR region (⁸⁹⁷DVEDSYGQQWTYEQR⁹¹¹) of NKAα1 subunit (DR-Ab) ameliorated hepatic steatosis through maintaining the membrane density of NKAα1 and inducing its activation.

CONCLUSIONS

Collectively, this study renews the functions of NKAα1 in liver lipid metabolism and provides a new clue for gene therapy or antibody treatment of hepatic lipid metabolism disturbance by targeting NKAα1.

Contributions of SGK3 to transporter-related diseases

Serum- and glucocorticoid-induced kinase 3 (SGK3), which is ubiquitously expressed in mammals, is regulated by estrogens and androgens. SGK3 is activated by insulin and growth factors through signaling pathways involving phosphatidylinositol-3-kinase (PI3K), 3-phosphoinositide-dependent kinase-1 (PDK-1), and mammalian target of rapamycin complex 2 (mTORC2). Activated SGK3 can activate ion channels (TRPV5/6, SOC, Kv1.3, Kv1.5, Kv7.1, BKCa, Kir2.1, Kir2.2, ENaC, Nav1.5, ClC-2, and ClC Ka), carriers and receptors (Npt2a, Npt2b, NHE3, GluR1, GluR6, SN1, EAAT1, EAAT2, EAAT4, EAAT5, SGLT1, SLC1A5, SLC6A19, SLC6A8, and NaDC1), and Na+/K+-ATPase, promoting the transportation of calcium, phosphorus, sodium, glucose, and neutral amino acids in the kidney and intestine, the absorption of potassium and neutral amino acids in the renal tubules, the transportation of glutamate and glutamine in the nervous system, and the transportation of creatine. SGK3-sensitive transporters contribute to a variety of physiological and pathophysiological processes, such as maintaining calcium and phosphorus homeostasis, hydro-salinity balance and acid-base balance, cell proliferation, muscle action potential, cardiac and neural electrophysiological disturbances, bone density, intestinal nutrition absorption, immune function, and multiple substance metabolism. These processes are related to kidney stones, hypophosphorous rickets, multiple syndromes, arrhythmia, hypertension, heart failure, epilepsy, Alzheimer's disease, amyotrophic lateral sclerosis, glaucoma, ataxia idiopathic deafness, and other diseases.

Predictive Value of Fasting Blood Glucose for Microvascular Obstruction in Nondiabetic Patients with ST-Segment Elevation Myocardial Infarction after Primary Percutaneous Coronary Intervention

Background

The relationship between fasting blood glucose (FBG) and microvascular obstruction (MVO) after primary percutaneous coronary intervention (PCI) remains unclear in nondiabetic patients with ST-segment elevation myocardial infarction (STEMI). This study aimed to determine the predictive value of FBG in MVO in nondiabetic STEMI patients.

Methods

A total of 108 nondiabetic STEMI patients undergoing primary PCI were enrolled in this study. The patients were classified into either the MVO group or non-MVO group based on cardiac magnetic resonance imaging (CMR).

Results

FBG in the MVO group was higher than in the non-MVO group. Univariate analysis showed that FBG, peak high-sensitive troponin T (TnT), pre-PCI thrombolysis in myocardial infarction (pre-PCI TIMI) flow, left ventricular ejection fraction (LVEF), infarction size, left ventricular end-diastolic diameter (LVEDd), left ventricular end-diastolic volume (LVEDV), and global longitudinal strain (GLS) were likely predictive factors of MVO. After adjustment for other parameters, FBG, peak TnT, LVEF, and LVEDV remained independent predictors for MVO.

Conclusion

FBG was independently associated with MVO in nondiabetic STEMI patients.

Role of Deranged Energy Deprivation Signaling in the Pathogenesis of Cardiac and Renal Disease in States of Perceived Nutrient Overabundance

Sodium-glucose cotransporter 2 inhibitors reduce the risk of serious heart failure and adverse renal events, but the mechanisms that underlie this benefit are not understood. Treatment with SGLT2 inhibitors is distinguished by 2 intriguing features: ketogenesis and erythrocytosis. Both reflect the induction of a fasting-like and hypoxia-like transcriptional paradigm that is capable of restoring and maintaining cellular homeostasis and survival. In the face of perceived nutrient and oxygen deprivation, cells activate low-energy sensors, which include sirtuin-1 (SIRT1), AMP-activated protein kinase (AMPK), and hypoxia inducible factors (HIFs; especially HIF-2α); these enzymes and transcription factors are master regulators of hundreds of genes and proteins that maintain cellular homeostasis. The activation of SIRT1 (through its effects to promote gluconeogenesis and fatty acid oxidation) drives ketogenesis, and working in concert with AMPK, it can directly inhibit inflammasome activation and maintain mitochondrial capacity and stability. HIFs act to promote oxygen delivery (by stimulating erythropoietin and erythrocytosis) and decrease oxygen consumption. The activation of SIRT1, AMPK, and HIF-2α enhances autophagy, a lysosome-dependent degradative pathway that removes dangerous constituents, particularly damaged mitochondria and peroxisomes, which are major sources of oxidative stress and triggers of cellular dysfunction and death. SIRT1 and AMPK also act on sodium transport mechanisms to reduce intracellular sodium concentrations. It is interesting that type 2 diabetes mellitus, obesity, chronic heart failure, and chronic kidney failure are characterized by the accumulation of intracellular glucose and lipid intermediates that are perceived by cells as indicators of energy overabundance. The cells respond by downregulating SIRT1, AMPK, and HIF-2α, thus leading to an impairment of autophagic flux and acceleration of cardiomyopathy and nephropathy. SGLT2 inhibitors reverse this maladaptive signaling by triggering a state of fasting and hypoxia mimicry, which includes activation of SIRT1, AMPK, and HIF-2α, enhanced autophagic flux, reduced cellular stress, decreased sodium influx into cells, and restoration of mitochondrial homeostasis. This mechanistic framework clarifies the findings of large-scale randomized trials and the close association of ketogenesis and erythrocytosis with the cardioprotective and renoprotective benefits of these drugs.

DR-region of Na+/K+-ATPase is a target to ameliorate hepatic insulin resistance in obese diabetic mice

Reduced hepatic Na⁺/K⁺-ATPase (NKA) activity and NKAα1 expression are engaged in the pathologies of metabolism diseases. The present study was designed to investigate the potential roles of NKAα1 in hepatic gluconeogenesis and glycogenesis in both hepatocytes and obese diabetic mice.

Methods: Insulin resistance was mimicked by glucosamine (GlcN) in either human hepatocellular carcinoma (HepG2) cells or primary mouse primary hepatocytes. Obese diabetic mice were induced by high-fat diet (HFD) feeding for 12 weeks.

Results: We found that both NKA activity and NKAα1 protein level were downregulated in GlcN-treated hepatocytes and in the livers of obese diabetic mice. Pharmacological inhibition of NKA with ouabain worsened, while activation of NKAα1 with an antibody against an extracellular DR region of NKAα1 subunit (DR-Ab) prevented GlcN-induced increase in gluconeogenesis and decrease in glycogenesis. Likewise, the above results were also corroborated by the opposite effects of genetic knockout/overexpression of NKAα1 on both gluconeogenesis and glycogenesis. In obese diabetic mice, hepatic activation or overexpression of NKAα1 stimulated the PI3K/Akt pathway to suppress hyperglycemia and improve insulin resistance. More importantly, loss of NKA activities in NKAα1^+/- mice was associated with more susceptibility to insulin resistance following HFD feeding.

Conclusions: Our findings suggest that NKAα1 is a physiological regulator of glucose homoeostasis and its DR-region is a novel target to treat hepatic insulin resistance.

Stimulation of Na+/K+-ATPase with an Antibody against Its 4th Extracellular Region Attenuates Angiotensin II-Induced H9c2 Cardiomyocyte Hypertrophy via an AMPK/SIRT3/PPARγ Signaling Pathway

Activation of the renin-angiotensin system (RAS) contributes to the pathogenesis of cardiovascular diseases. Sodium potassium ATPase (NKA) expression and activity are often regulated by angiotensin II (Ang II). This study is aimed at investigating whether DR-Ab, an antibody against 4^th extracellular region of NKA, can protect Ang II-induced cardiomyocyte hypertrophy. Our results showed that Ang II treatment significantly reduced NKA activity and membrane expression. Pretreatment with DR-Ab preserved cell size in Ang II-induced cardiomyopathy by stabilizing the plasma membrane expression of NKA and restoring its activity. DR-Ab reduced intracellular ROS generation through inhibition of NADPH oxidase activity and protection of mitochondrial functions in Ang II-treated H9c2 cardiomyocytes. Pharmacological manipulation and Western blotting analysis demonstrated the cardioprotective effects were mediated by the activation of the AMPK/Sirt-3/PPARγ signaling pathway. Taken together, our results suggest that dysfunction of NKA is an important mechanism for Ang II-induced cardiomyopathy and DR-Ab may be a novel and promising therapeutic approach to treat cardiomyocyte hypertrophy.

Halofuginone protects against advanced glycation end products‑induced injury of H9C2 cells via alleviating endoplasmic reticulum stress‑associated apoptosis and inducing autophagy

Advanced glycation end products (AGEs) have been reported to serve an important role in the stiffening of cardiac tissues and myocardial cell injury. Serious myocardial cell injury can result in various heart diseases with high mortality. Halofuginone (HF), which possesses marked anti-inflammatory and antifibrotic effects, has recently been applied to inhibit the effects of cardiac stress. The present study aimed to investigate the potential effects of HF and its underlying mechanism in the treatment of AGEs-induced H9C2 cardiomyocyte damage. The western blot results of the present study demonstrated that HF may reduce the expression levels of myocardial injury markers, including myoglobin, creatine kinase MB and cardiac troponin I. In addition, flow cytometric analysis indicated that the production of reactive oxygen species (ROS) was significantly decreased by HF. Additionally, endoplasmic reticulum (ER) stress was suppressed in response to treatment with HF, as observed by low expression levels of ER stress-associated proapoptotic proteins (CCAAT/enhancer-binding protein homologous protein and cleaved caspase-12); overexpression of prosurvival proteins (growth arrest and DNA damage-inducible protein GADD34 and binding immunoglobulin protein) was also reported. Furthermore, the expression levels of microtubule-associated proteins 1A/1B light chain 3B (LC3)II/LC3I and Beclin 1 were elevated, whereas P62 expression levels were reduced following treatment with HF. These findings, together with immunofluorescence staining of LC3, indicated that HF may induce autophagy. Finally, the protective effects of HF on AGEs-treated H9C2 cells were reversed following treatment with the inhibitor 3-methyladenine, as indicated by inhibition of autophagy, and increases in apoptosis, ROS production and the ER stress response. Collectively, the findings of the present study suggested that the protective effects of HF against AGEs-induced myocardial cell injury may be associated with the induction of autophagy and amelioration of ROS-mediated ER stress and apoptosis. These findings may contribute to the development of a novel therapeutic method to inhibit the progression of myocardial cell injury.

Effect of photobiomodulation therapy on neuronal injuries by ouabain: the regulation of Na, K-ATPase; Src; and mitogen-activated protein kinase signaling pathway

BACKGROUND

To determine whether photobiomodulation (PBM) rescued the disruption of Na⁺/Ca²⁺ homeostasis and mitochondrial membrane potential by ouabain; the Na, K-ATPase inhibitor. For PBM in this study, a 660 nm LED array was used at energy densities of 0.78, 1.56, 3.12, 6.24, and 9.36 J/cm².

RESULTS

HCN-2 neuronal cells treated with ouabain showed loss of cell polarity, disrupted cell morphology, and decreased cell viability, which were improved after PBM treatment. We found that ouabain-induced Na, K-ATPase inhibition promoted activation of downstream signaling through Src, Ras, and mitogen-activated protein kinase (MAPK), which were suppressed after PBM treatment. This provided evidence of Na, K-ATPase α-subunit inactivation and intracellular Ca²⁺ increase. In response to ouabain, we observed activation of Src and MAPK by Na, K-ATPase, decreased mitochondrial membrane potential, and Na⁺-dependent Ca²⁺ increases, which were restored by PBM treatment.

CONCLUSIONS

This study demonstrated that Na⁺/K⁺ imbalance could be regulated by PBM treatment in neuronal cells, and we suggest that PBM is a potential therapeutic tool for Na, K-ATPase targeted neuronal diseases.

Mechanistic insights into the augmented effect of bone marrow mesenchymal stem cells and thiazolidinediones in streptozotocin-nicotinamide induced diabetic rats

This study was designed to assess whether the protective effects of bone marrow-derived mesenchymal stem cells (MSCs) against diabetes could be enhanced by pioglitazone (PIO), a PPARγ agonist. Combined MSCs and PIO treatments markedly improved fasting blood glucose, body weight, lipid profile levels, insulin level, insulin resistance, β cell function. Those protective effects also attenuated both pancreatic lesions and fibrosis in diabetic rats and decreased the depletion of pancreatic mediators of glycemic and lipid metabolism including peroxisome proliferator-activated receptor alpha (PPARα), PGC-1α, GLP-1 and IRS-2. Cardiac biogenesis of diabetic groups was also improved with MSCs and/or PIO treatments as reflected by the enhanced up-regulation of the expressions of cardiac IRS1, Glucose transporter 4, PGC-1, PPARα and CPT-1 genes and the down-regulated expression of lipogenic gene SREBP. The combination of MSCs and PIO also potentiated the decrease of abnormal myocardial pathological lesions in diabetic rats. Similarly, the inhibitory effects of MSCs on diabetic cardiac fibrosis and on the up regulations of TGF-β, collagen I and III gene expressions were partial but additive when combined with PIO. Therefore, combined therapy with PIO and BMCs transplantation could further potentiate the protective benefit of MSCs against diabetes and cardiac damage compared to MSCs monotherapy.

Cardiac glycoside bufalin blocks cancer cell growth by inhibition of Aurora A and Aurora B activation via PI3K-Akt pathway

In our previous study, cardiac glycosides including bufalin, a group of sodium pump (Na+/K+-ATPase) inhibitors widely used to treat heart failure for many years, have been demonstrated to induce a delay of mitotic entry and mitotic arrest in many cancer cells. However, the underlying mechanism remains poorly understood. Here, we reported for the first time that cardiac glycoside bufalin induced mitotic entry delay and prometaphase arrest by inhibition of activation of Aurora A/B. Furthermore, cardiac glycoside bufalin prevented Aurora A recruitment to mitotic centrosomes and Aurora B recruitment to unattached kinetochores. Mechanistically, bufalin and knockdown of sodium pump inhibited PI3K-Akt pathway, which in turn inhibit the activation of Aurora A/B, followed by a delay in mitotic entry and mitotic arrest. These actions were reversed by overexpression of Akt. In addition, ERK, mTOR, and ROS are not involved in bufalin-mediated downregulation of active form of Aurora A/B. Taken together, cardiac glycoside bufalin induces mitotic entry delay and mitotic arrest in cancer cells through inhibition of Aurora A/B activation via PI3K-Akt pathway. Based on this novel finding we could suggest that targeting PI3K-Akt pathway may have therapeutic value for the treatment of cancers associated with sodium pump overexpression.