Protein kinase B (PKB/Akt)--a key regulator of glucose transport?

Enhanced Insulin Secretion Through Upregulation of Transcription Factors by Hydroalcoholic Extract of Securigera securidaca Seeds in Diabetic Animal Model

AIM

In previous studies, the researchers observed an increase in insulin secretion in STZ-treated diabetic rats following treatment with the hydroalcoholic extract of Securigera securidaca (HESS) seeds. This study focuses on the relationship between the antioxidant properties of HESS with changes in diabetic pancreatic tissue and the gene expression of factors that impact insulin secretion.

METHODS

In this controlled experimental study, three varying doses of HESS were administered to three groups of diabetic rats induced by STZ. Oxidative stress indicators like total antioxidant capacity (TAC), total oxidant status (TOS) and malondialdehyde were assessed in both pancreatic and liver tissues. Pancreatic histology was studied post-haematoxylin staining. Insulin and FGF21 levels in the blood were measured using the ELISA method. The expression of Nrf2 and FGF21 genes in the pancreas and liver, along with MafA and PDX-1 genes in the pancreas, was quantified using real-time PCR.

RESULTS

The administration of HESS in varying doses led to a dose-dependent rise in blood insulin levels and a decrease in blood glucose levels and oxidative stress. By reducing oxidative stress, HESS treatment lowered the heightened levels of NRF2 and FGF21 in the liver and pancreas of diabetic rats, improving pancreatic tissue health. As oxidative stress decreased, the expression of MafA and PDX1 genes in the pancreas approached levels seen in healthy rats.

CONCLUSION

HESS elicits an increase in insulin secretion through the mitigation of oxidative stress and tissue damage, as well as the modulation of gene expression related to the insulin transcription factors PDX-1 and MafA.

Biological functions and therapeutic potential of CKS2 in human cancer

The incidence of cancer is increasing worldwide and is the most common cause of death. Identification of novel cancer diagnostic and prognostic biomarkers is important for developing cancer treatment strategies and reducing mortality. Cyclin-dependent kinase subunit 2 (CKS2) is involved in cell cycle and proliferation processes, and based on these processes, CKS2 was identified as a cancer gene. CKS2 is expressed in a variety of tissues in the human body, but its abnormal expression is associated with cancer in a variety of systems. CKS2 is generally elevated in cancer, plays a role in almost all aspects of cancer biology (such as cell proliferation, invasion, metastasis, and drug resistance) through multiple mechanisms regulating certain important genes, and is associated with clinicopathological features of patients. In addition, CKS2 expression patterns are closely related to cancer type, stage and other clinical variables. Therefore, CKS2 is considered as a tool for cancer diagnosis and prognosis and may be a promising tumor biomarker and therapeutic target. This article reviews the biological function, mechanism of action and potential clinical significance of CKS2 in cancer, in order to provide a new theoretical basis for clinical molecular diagnosis, molecular targeted therapy and scientific research of cancer.

A zebrafish model of diabetic nephropathy shows hyperglycemia, proteinuria and activation of the PI3K/Akt pathway

Diabetic nephropathy (DN), as a complication of diabetes, is a substantial healthcare challenge owing to the high risk of morbidity and mortality involved. Although significant progress has been made in understanding the pathogenesis of DN, more efficient models are required to develop new therapeutics. Here, we created a DN model in zebrafish by crossing diabetic Tg(acta1:dnIGF1R-EGFP) and proteinuria-tracing Tg(l-fabp::VDBP-GFP) lines, named zMIR/VDBP. Overfed adult zMIR/VDBP fish developed severe hyperglycemia and proteinuria, which were not observed in wild-type zebrafish. Renal histopathology revealed human DN-like characteristics, such as glomerular basement membrane thickening, foot process effacement and glomerular sclerosis. Glomerular dysfunction was restored upon calorie restriction. RNA sequencing analysis demonstrated that DN zebrafish kidneys exhibited transcriptional patterns similar to those seen in human DN pathogenesis. Notably, the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) signaling pathway was activated, a phenomenon observed in the early phase of human DN. In addition, metformin improved hyperglycemia and proteinuria in DN zebrafish by modulating Akt phosphorylation. Our results indicate that zMIR/VDBP fish are suitable for elucidating the mechanisms underlying human DN and could be a powerful tool for therapeutic discovery.

KIF2A Upregulates PI3K/AKT Signaling through Polo-like Kinase 1 (PLK1) to Affect the Proliferation and Apoptosis Levels of Eriocheir sinensis Spermatogenic Cells

E. sinensis is an animal model for studying the reproduction and development of crustaceans. In this study, we knocked down the Es-Kif2a gene by injecting dsRNA into E. sinensis and inhibited Es-Plk1 gene expression by injecting PLK1 inhibitor BI6727 into E. sinensis. Then, the cell proliferation level, apoptosis level, and PI3K/AKT signaling expression level were detected. Our results showed that the proliferation level of spermatogenic cells decreased, while the apoptosis level increased after Es-Kif2a knockdown or Es-Plk1 inhibition. In order to verify whether these changes are caused by regulating the PI3K/AKT pathway, we detected the expression of PI3K and AKT proteins after Es-Kif2a knockdown or Es-Plk1 inhibition. Western Blot showed that in both the Es-Kif2a knockdown group and the Es-Plk1 inhibition group, the expression of PI3K and AKT proteins decreased. In addition, immunofluorescence showed that Es-KIF2A and Es-PLK1 proteins were co-localized during E. sinensis spermatogenesis. To further explore the upstream and downstream relationship between Es-KIF2A and Es-PLK1, we detected the expression level of Es-PLK1 after Es-Kif2a knockdown as well as the expression level of Es-KIF2A after Es-Plk1 inhibition. Western Blot showed that the expression of Es-PLK1 decreased after Es-Kif2a knockdown, while there was no significant change of Es-KIF2A after Es-Plk1 inhibition, indicating that Es-PLK1 may be a downstream factor of Es-KIF2A. Taken together, these results suggest that Es-KIF2A upregulates the PI3K/AKT signaling pathway through Es-PLK1 during the spermatogenesis of E. sinensis, thereby affecting the proliferation and apoptosis levels of spermatogenic cells.

Revving the engine: PKB/AKT as a key regulator of cellular glucose metabolism

Glucose metabolism is of critical importance for cell growth and proliferation, the disorders of which have been widely implicated in cancer progression. Glucose uptake is achieved differently by normal cells and cancer cells. Even in an aerobic environment, cancer cells tend to undergo metabolism through glycolysis rather than the oxidative phosphorylation pathway. Disordered metabolic syndrome is characterized by elevated levels of metabolites that can cause changes in the tumor microenvironment, thereby promoting tumor recurrence and metastasis. The activation of glycolysis-related proteins and transcription factors is involved in the regulation of cellular glucose metabolism. Changes in glucose metabolism activity are closely related to activation of protein kinase B (PKB/AKT). This review discusses recent findings on the regulation of glucose metabolism by AKT in tumors. Furthermore, the review summarizes the potential importance of AKT in the regulation of each process throughout glucose metabolism to provide a theoretical basis for AKT as a target for cancers.

Circulating Sphingolipids in Insulin Resistance, Diabetes and Associated Complications

Sphingolipids play an important role in the development of diabetes, both type 1 and type 2 diabetes, as well as in the development of both micro- and macro-vascular complications. Several reviews have been published concerning the role of sphingolipids in diabetes but most of the emphasis has been on the possible mechanisms by which sphingolipids, mainly ceramides, contribute to the development of diabetes. Research on circulating levels of the different classes of sphingolipids in serum and in lipoproteins and their importance as biomarkers to predict not only the development of diabetes but also of its complications has only recently emerged and it is still in its infancy. This review summarizes the previously published literature concerning sphingolipid-mediated mechanisms involved in the development of diabetes and its complications, focusing on how circulating plasma sphingolipid levels and the relative content carried by the different lipoproteins may impact their role as possible biomarkers both in the development of diabetes and mainly in the development of diabetic complications. Further studies in this field may open new therapeutic avenues to prevent or arrest/reduce both the development of diabetes and progression of its complications.

Hypoglycemic effects of dendrobium officinale leaves

Introduction: Numerous studies have demonstrated that the stems of D. officinale have the effect of lowering blood glucose, but the leaves of D. officinale have seldom been investigated. In this study, we mainly studied the hypoglycemic effect and mechanism of D. officinale leaves. Methods: Initially in vivo, male C57BL/6 mice were administered either standard feed (10 kcal% fat) or high-fat feed (60 kcal% fat) along with either normal drinking water or drinking water containing 5 g/L water extract of D. officinale leaves (EDL) for 16 weeks, and changes in body weight, food intake, blood glucose, etc., were monitored weekly. Next in vitro, C2C12 myofiber precursor cells which were induced to differentiate into myofibroblasts and cultured with EDL to detect the expression of insulin signaling pathway related proteins. HEPA cells were also cultured with EDL to detect the expression of hepatic gluconeogenesis or hepatic glycogen synthesis related proteins. Eventually after separating the components from EDL by ethanol and 3 kDa ultrafiltration centrifuge tube, we conducted animal experiments using the ethanol-soluble fraction of EDL (ESFE), ethanol-insoluble fraction of EDL (EIFE), ESFE with a molecular weight of >3 kDa (>3 kDa ESFE), and ESFE with a molecular weight of <3 kDa (<3 kDa ESFE) for intensive study. Results: The results in vivo revealed that the mice fed the high-fat diet exhibited significantly decreased blood glucose levels and significantly increased glucose tolerance after the EDL treatment, whereas the mice fed the low-fat diet did not. The results in vitro showed that EDL activated the expression of protein kinase B (AKT), the phosphorylation of AKT, and the expression of downstream GSK3β in the insulin signaling pathway. EDL treatment of HEPA cells confirmed that EDL did not affect hepatic gluconeogenesis or hepatic glycogen synthesis. In the experiment of studying the composition of EDL, we found that the >3 kDa ESFE displayed the effect of lowering blood glucose. In summary, the effect of EDL in lowering blood glucose may bethanole achieved by activating the insulin signaling pathway to increase insulin sensitivity, and the main functional substance was contained within the >3 kDa ESFE. Discussion: The findings of this study represent a reference point for further exploration of the hypoglycemic effects of D. officinale leaves and may assist in both the identification of new molecular mechanisms to improve insulin sensitivity and the isolation of monomeric substances that lower blood glucose. Furthermore, the obtained results may provide a theoretical basis for the development of hypoglycemic drugs with D. officinale leaves as the main component.

Simultaneous SGLT2 inhibition and caloric restriction improves insulin resistance and kidney function in OLETF rats

SGLT2 inhibitors (SGLT2i) are emerging as a novel therapy for type 2 diabetes due to their effective hypoglycemic and potential cardio- and nephroprotective effects, while caloric restriction (CR) is a common behavioral modification to improve adiposity and insulin resistance. Therefore, both interventions simultaneously may potentially further improve metabolic syndrome by enhancing carbohydrate metabolism. To test this hypothesis, cohorts of 10-week old, male Long Evans Tokushima Otsuka (LETO) and Otsuka Long Evans Tokushima Fatty (OLETF) rats were treated with SGLT2i (10 mg luseoglifozin/kg/day x 4 wks) (OLETF only) and/or 30% CR (2 wks at 12 weeks of age). CR maintained body mass in both strains while SGLT2i alone did not have any effect on body mass. Simultaneous treatments decreased SBP in OLETF vs SGLT2i alone, decreased insulin resistance index (IRI), and increased creatinine clearance vs OLETF ad lib. Conversely, CR decreased albuminuria independent of SGLT2i. In conclusion, SGLT2i treatment by itself did not elicit significant improvements in insulin resistance, kidney function or blood pressure. However, when combined with CR, these changes where more profound than with CR alone without inducing chronic hypoglycemia.

Maresin 1 Alleviates Diabetic Kidney Disease via LGR6-Mediated cAMP-SOD2-ROS Pathway

BACKGROUND

Chronic hyperglycemia-induced inflammation is recognized as the most important pathophysiological process in diabetic kidney disease (DKD). As maresin 1 (MaR1) is an extensive anti-inflammatory lipid mediator, the present study investigated the protective role of MaR1 in the pathogenesis of DKD and its clinical relevance.

METHODS

Serum MaR1 concentrations were analyzed in 104 subjects with normal glucose tolerant, type 2 diabetes (T2DM), or DKD. Streptozotocin (STZ) together with high fat diet was used to induce male C57BL/6 J mice into diabetic mice which were treated with MaR1. Human renal tubule epithelial cells (HK-2 cells) were treated by high glucose for glucotoxicity cell model and transfected with LGR6 siRNA for knockdown with MaR1 added，and detected oxidative stress and inflammatory related factors.

RESULTS

Serum MaR1 concentrations were significant decreased in T2DM with or without kidney disease compared with normal participant and were lowest in patients with DKD. Serum MaR1 concentrations were negatively correlated with hemoglobin A1c (HbA1c), duration of diabetes, urinary albumin to creatinine ratio (UACR), neutrophil, and neutrophil-lymphocyte ratio and were positively correlated with high-density lipoprotein-cholesterol (HDL-C) and estimated glomerular filtration rate (eGFR). In mouse model, MaR1 injection alleviated hyperglycemia, UACR and the pathological progression of DKD. Interestingly, the renal expression of LGR6 was down-regulated in DKD and high glucose treated HK-2 cells but up-regulated by MaR1 treatment. Mechanistically, MaR1 alleviated inflammation via LGR6-mediated cAMP-SOD2 antioxidant pathway in DKD mice and high glucose treated HK-2 cells.

CONCLUSIONS

Our study demonstrates that decreased serum MaR1 levels were correlated with the development of DKD. MaR1 could alleviate DKD and glucotoxicity-induced inflammation via LGR6-mediated cAMP-SOD2 antioxidant pathway. Thus, our present findings identify MaR1 as a predictor and a potential therapeutic target for DKD.

LIN28A enhances regenerative capacity of human somatic tissue stem cells via metabolic and mitochondrial reprogramming

Developing methods to improve the regenerative capacity of somatic stem cells (SSCs) is a major challenge in regenerative medicine. Here, we propose the forced expression of LIN28A as a method to modulate cellular metabolism, which in turn enhances self-renewal, differentiation capacities, and engraftment after transplantation of various human SSCs. Mechanistically, in undifferentiated/proliferating SSCs, LIN28A induced metabolic reprogramming from oxidative phosphorylation (OxPhos) to glycolysis by activating PDK1-mediated glycolysis-TCA/OxPhos uncoupling. Mitochondria were also reprogrammed into healthy/fused mitochondria with improved functional capacity. The reprogramming allows SSCs to undergo cell proliferation more extensively with low levels of oxidative and mitochondrial stress. When the PDK1-mediated uncoupling was untethered upon differentiation, LIN28A-SSCs differentiated more efficiently with an increase of OxPhos by utilizing the reprogrammed mitochondria. This study provides mechanistic and practical approaches of utilizing LIN28A and metabolic reprogramming in order to improve SSCs utility in regenerative medicine.

The Metastasis Suppressor NDRG1 Directly Regulates Androgen Receptor Signaling in Prostate Cancer

N-myc-downregulated gene 1 (NDRG1) has potent anticancer effects and inhibits cell growth, survival, metastasis, and angiogenesis. Previous studies suggested that NDRG1 is linked to the androgen signaling network, but this mechanistic relationship is unclear. Considering the crucial role of the androgen receptor (AR) in prostate cancer (PCa) progression, here we examined for the first time the effect of NDRG1 on AR expression, activation, and downstream signaling in LNCaP, 22Rv1, and C4-2B PCa cell types. We demonstrate that NDRG1 effectively promotes interaction of AR with the chaperone HSP90, which in turn stabilizes the AR while decreasing its androgen-mediated activation. The expression of NDRG1 suppressed: (1) AR activation, as measured by p-AR^Ser213 and p-AR^Ser81; (2) expression of a major AR transcriptional target, prostate-specific antigen (PSA); and (3) AR transcriptional activity, probably via inhibiting the c-Jun-AR interaction by reducing c-Jun phosphorylation (p-c-Jun^Ser63). NDRG1 was also demonstrated to inhibit multiple key molecules involved in androgen-dependent and -independent signaling (namely EGFR, HER2, HER3, PI3K, STAT3, and NF-κB), which promote the development of castration-resistant prostate cancer. We also identified the cysteine-rich secretory protein/antigen 5/pathogenesis related-1 (CAP) domain of NDRG1 as vital for inhibition of AR activity. Examining NDRG1 and p-NDRG1 in PCa patient specimens revealed a significant negative correlation between NDRG1 and PSA levels in prostatectomy patients that went on to develop metastasis. These results highlight a vital role for NDRG1 in androgen signaling and its potential as a key therapeutic target and biomarker in PCa.

Molecular mechanisms underlying hepatitis C virus infection-related diabetes

Diabetes is a noncommunicable widespread disease that poses the risk of severe complications in patients, with certain complications being life-threatening. Hepatitis C is an infectious disease that mainly causes liver damage, which is also a profound threat to human health. Hepatitis C virus (HCV) infection has many extrahepatic manifestations, including diabetes. Multiple mechanisms facilitate the strong association between HCV and diabetes. HCV infection can affect the insulin signaling pathway in liver and pancreatic tissue and change the profiles of circulating microRNAs, which may further influence the occurrence and development of diabetes. This review describes how HCV infection causes diabetes and discusses the current research progress with respect to HCV infection-related diabetes.

Exosomal microRNAs in hepatocellular carcinoma

Hepatocellular carcinoma is one of the most common malignant tumors worldwide and the fourth leading cause of cancer-related deaths. The prognosis of hepatocellular carcinoma patients is extremely poor due to the occult onset and high metastasis of hepatocellular carcinoma. Therefore, biomarkers with high specificity and sensitivity are of great importance in early screening, diagnosis prognosis, and treatment of hepatocellular carcinoma patients. Exosomes are tiny vesicles secreted by various types of cells, which can serve as mediators of intercellular communication to regulate the tumor microenvironment, and play a key role in the occurrence, development, prognosis, monitor and treatment of hepatocellular carcinoma. As microRNA deliverer, exosomes are involved in multiple life activities by regulating target genes of recipient cells such as proliferation, invasion, metastasis and apoptosis of cancer cells. In this review, we summarized the composition, active mechanism and function of exosomal microRNAs in hepatocellular carcinoma, and elaborated on their potential application value of early diagnosis and treatment in hepatocellular carcinoma.

SGK1 signaling promotes glucose metabolism and survival in extracellular matrix detached cells

Loss of integrin-mediated attachment to extracellular matrix (ECM) proteins can trigger a variety of cellular changes that affect cell viability. Foremost among these is the activation of anoikis, caspase-mediated cell death induced by ECM detachment. In addition, loss of ECM attachment causes profound alterations in cellular metabolism, which can lead to anoikis-independent cell death. Here, we describe a surprising role for serum and glucocorticoid kinase-1 (SGK1) in the promotion of energy production when cells are detached. Our data demonstrate that SGK1 activation is necessary and sufficient for ATP generation during ECM detachment and anchorage-independent growth. More specifically, SGK1 promotes a substantial elevation in glucose uptake because of elevated GLUT1 transcription. In addition, carbon flux into the pentose phosphate pathway (PPP) is necessary to accommodate elevated glucose uptake and PPP-mediated glyceraldehyde-3-phosphate (G3P) is necessary for ATP production. Thus, our data show SGK1 as master regulator of glucose metabolism and cell survival during ECM-detached conditions.

RF-amide related peptide-3 (RFRP-3): a novel neuroendocrine regulator of energy homeostasis, metabolism, and reproduction

A hypothalamic neuropeptide, RF-amide related peptide-3 (RFRP-3), the mammalian ortholog of the avian gonadotropin-inhibitory hormone (GnIH) has inhibitory signals for reproductive axis via G-protein coupled receptor 147 in mammals. Moreover, RFRP-3 has orexigenic action but the mechanism involved in energy homeostasis and glucose metabolism is not yet known. Though, the RFRP-3 modulates orexigenic action in co-operation with other neuropeptides, which regulates metabolic cues in the hypothalamus. Administration of GnIH/RFRP-3 suppresses plasma luteinizing hormone, at the same time stimulates feeding behavior in birds and mammals. Likewise, in the metabolically deficient conditions, its expression is up-regulated suggests that RFRP-3 contributes to the integration of energy balance and reproduction. However, in many other metabolic conditions like induced diabetes and high-fat diet obesity, etc. its role is still not clear while, RFRP-3 induces the glucose homeostasis by adipocytes is reported. The physiological role of RFRP-3 in metabolic homeostasis and the metabolic effects of RFRP-3 signaling in pharmacological studies need a detailed discussion. Further studies are required to find out whether RFRP-3 is associated with restricted neuroendocrine function observed in type II diabetes mellitus, aging, or sub-fertility. In this context, the current review is focused on the role of RFRP-3 in the above-mentioned mechanisms. Studies from search engines including PubMed, Google Scholar, and science.gov are included after following set inclusion/exclusion criteria. As a developing field few mechanisms are still inconclusive, however, based on the available information RFRP-3 seems to be a putative tool in future treatment strategies towards metabolic disease.

Metabolic Consequences of Neuronal HIF1α-Deficiency in Mediobasal Hypothalamus in Mice

OBJECTIVE

This study aims to investigate whether hypoxia-inducible factor 1α (HIF1α) in the neurons of the mediobasal hypothalamus is involved in the regulation of body weight, glucose, and lipid metabolism in mice and to explore the underlying molecular mechanisms.

METHODS

HIF1α ^flox/flox mice were used. The adeno-associated virus that contained either cre, GFP and syn, or GFP and syn (controls) was injected into the mediobasal hypothalamus to selectively knock out HIF1α in the neurons of the mediobasal hypothalamus. The body weight and food intake were weighed daily. The levels of blood glucose, insulin, total cholesterol (TC), triglyceride (TG), free fatty acid (FFA), high-density lipoprotein (HDL), and low-density lipoprotein (LDL)were tested. Intraperitoneal glucose tolerance test (IPGTT) was performed. The insulin-stimulated Akt phosphorylation in the liver, epididymal fat, and skeletal muscle were examined. Also, the mRNA expression levels of HIF1α, proopiomelanocortin (POMC), neuropeptide Y (NPY), and glucose transporter protein 4 (Glut4) in the hypothalamus were checked.

RESULTS

After selectively knocking out HIF1α in the neurons of the mediobasal hypothalamus (HIF1αKOMBH), the body weights and food intake of mice increased significantly compared with the control mice (p < 0.001 at 4 weeks). Compared with that of the control group, the insulin level of HIF1αKOMBH mice was 3.5 times higher (p < 0.01). The results of the IPGTT showed that the blood glucose level of the HIF1αKOMBH group at 20-120 min was significantly higher than that of the control group (p < 0.05). The serum TC, FFA, HDL, and LDL content of the HIF1αKOMBH group was significantly higher than those of the control group (p < 0.05). Western blot results showed that compared with those in the control group, insulin-induced AKT phosphorylation levels in liver, epididymal fat, and skeletal muscle in the HIF1αKOMBH group were not as significantly elevated as in the control group. Reverse transcription-polymerase chain reaction (RT-PCR) results in the whole hypothalamus showed a significant decrease in Glut4 mRNA expression. And the mRNA expression levels of HIF1α, POMC, and NPY of the HIF1αKOMBH group decreased significantly in ventral hypothalamus.

CONCLUSIONS

The hypothalamic neuronal HIF1α plays an important role in the regulation of body weight balance in mice under normoxic condition. In the absence of hypothalamic neuronal HIF1α, the mice gained weight with increased appetite, accompanied with abnormal glucose and lipid metabolism. POMC and Glut4 may be responsible for this effect of HIF1α.

Sphingolipids as a Culprit of Mitochondrial Dysfunction in Insulin Resistance and Type 2 Diabetes

Insulin resistance is defined as a complex pathological condition of abnormal cellular and metabolic response to insulin. Obesity and consumption of high-fat diet lead to ectopic accumulation of bioactive lipids in insulin-sensitive tissues. Intracellular lipid accumulation is regarded as one of the major factors in the induction of insulin resistance and type 2 diabetes (T2D). A significant number of studies have described the involvement of ceramides and other sphingolipids in the inhibition of insulin-signaling pathway in both skeletal muscles and the liver. Adverse effects of sphingolipid accumulation have recently been linked to the activation of protein kinase Cζ (PKCζ) and protein phosphatase 2A (PP2A), which, in turn, negatively affect phosphorylation of serine/threonine kinase Akt [also known as protein kinase B (PKB)], leading to decreased glucose uptake in skeletal muscles as well as increased gluconeogenesis and glycogenolysis in the liver. Sphingolipids, in addition to their direct impact on the insulin signaling pathway, may be responsible for other negative aspects of diabetes, namely mitochondrial dysfunction and deficiency. Mitochondrial health, which is characterized by appropriate mitochondrial quantity, oxidative capacity, controlled oxidative stress, undisturbed respiratory chain function, adenosine triphosphate (ATP) production and mitochondrial proliferation through fission and fusion, is impaired in the skeletal muscles and liver of T2D subjects. Recent findings suggest that impaired mitochondrial function may play a key role in the development of insulin resistance. Mitochondria stay in contact with the endoplasmic reticulum (ER), Golgi membranes and mitochondria-associated membranes (MAM) that are the main places of sphingolipid synthesis. Moreover, mitochondria are capable of synthesizing ceramide though ceramide synthase (CerS) activity. Recently, ceramides have been demonstrated to negatively affect mitochondrial respiratory chain function and fission/fusion activity, which is also a hallmark of T2D. Despite a significant correlation between sphingolipids, mitochondrial dysfunction, insulin resistance and T2D, this subject has not received much attention compared to the direct effect of sphingolipids on the insulin signaling pathway. In this review, we focus on the current state of scientific knowledge regarding the involvement of sphingolipids in the induction of insulin resistance by inhibiting mitochondrial function.

Maresin 1 regulates insulin signaling in human adipocytes as well as in adipose tissue and muscle of lean and obese mice

Maresin 1 (MaR1) is a DHA-derived pro-resolving lipid mediator. The present study aimed to characterize the ability of MaR1 to prevent the alterations induced by TNF-α on insulin actions in glucose uptake and Akt phosphorylation in cultured human adipocytes from overweight/obese subjects, as well as to investigate the effects of MaR1 acute and chronic administration on Akt phosphorylation in absence/presence of insulin in white adipose tissue (WAT) and skeletal muscle from lean and diet-induced obese (DIO) mice. MaR1 (0.1 nM) prevented the inhibitory effect of TNF-α on insulin-stimulated 2-Deoxy-D-glucose uptake and Akt phosphorylation in human adipocytes. Acute treatment with MaR1 (50 μg/kg, 3 h, i.p.) induced Akt phosphorylation in WAT and skeletal muscle of lean mice. However, MaR1 did not further increase the stimulatory effect of insulin on Akt activation. Interestingly, intragastric chronic treatment with MaR1 (50 μg/kg, 10 days) in DIO mice reduced the hyperglycemia induced by the high fat diet (HFD) and improved systemic insulin sensitivity. In parallel, MaR1 partially restored the impaired insulin response in skeletal muscle of DIO mice and reversed HFD-induced lower Akt phosphorylation in WAT in non-insulin-stimulated DIO mice while did not restore the defective Akt activation in response to acute insulin observed in DIO mice. Our results suggest that MaR1 attenuates the impaired insulin signaling and glucose uptake induced by proinflammatory cytokines. Moreover, the current data support that MaR1 treatment could be useful to reduce the hyperglycemia and the insulin resistance associated to obesity, at least in part by improving Akt signaling.

Sphingolipid Metabolism and Signaling in Skeletal Muscle: From Physiology to Physiopathology

Sphingolipids represent one of the major classes of eukaryotic lipids. They play an essential structural role, especially in cell membranes where they also possess signaling properties and are capable of modulating multiple cell functions, such as apoptosis, cell proliferation, differentiation, and inflammation. Many sphingolipid derivatives, such as ceramide, sphingosine-1-phosphate, and ganglioside, have been shown to play many crucial roles in muscle under physiological and pathological conditions. This review will summarize our knowledge of sphingolipids and their effects on muscle fate, highlighting the role of this class of lipids in modulating muscle cell differentiation, regeneration, aging, response to insulin, and contraction. We show that modulating sphingolipid metabolism may be a novel and interesting way for preventing and/or treating several muscle-related diseases.

Protein kinase Akt2/PKBβ is involved in blastomere proliferation of preimplantation mouse embryos

Activation of Akt/Protein Kinase B (PKB) by phosphatidylinositol-3-kinase (PI3K) controls several cellular functions largely studied in mammalian cells, including preimplantation embryos. We previously showed that early mouse embryos inherit active Akt from oocytes and that the intracellular localization of this enzyme at the two-cell stage depends on the T-cell leukemia/lymphoma 1 oncogenic protein, Tcl1. We have now investigated whether Akt isoforms, namely Akt1, Akt2 and Akt3, exert a specific role in blastomere proliferation during preimplantation embryo development. We show that, in contrast to other Akt family members, Akt2 enters male and female pronuclei of mouse preimplantation embryos at the late one-cell stage and thereafter maintains a nuclear localization during later embryo cleavage stages. Depleting one-cell embryos of single Akt family members by microinjecting Akt isoform-specific antibodies into wild-type zygotes, we observed that: (a) Akt2 is necessary for normal embryo progression through cleavage stages; and (b) the specific nuclear targeting of Akt2 in two-cell embryos depends on Tcl1. Our results indicate that preimplantation mouse embryos have a peculiar regulation of blastomere proliferation based on the activity of the Akt/PKB family member Akt2, which is mediated by the oncogenic protein Tcl1. Both Akt2 and Tcl1 are essential for early blastomere proliferation and embryo development.

Effect of Long-term Administration of Oral Magnesium Sulfate and Insulin to Reduce Streptozotocin-Induced Hyperglycemia in Rats: the Role of Akt2 and IRS1 Gene Expressions

The effects of long-term oral administration of magnesium sulfate and insulin on hyperglycemia were investigated using Akt2 and IRS1 gene expression methods in streptozotocin-induced diabetic rats. Fifty rats were randomly divided into five experimental groups: 1, non-diabetic control (NDC); 2, Mg²⁺-treated non-diabetic control (Mg-NDC); 3, chronic diabetic (CD); 4, Mg²⁺-treated chronic diabetic (Mg-CD); and 5, insulin-treated chronic diabetic (Ins-CD). Streptozotocin was used to induce diabetes. The Mg-CD and Mg-NDC groups received 10 g/l of MgSO₄ added to drinking water. The Ins-CD group received 2.5 U/kg of insulin twice a day. Blood glucose level and body weight were measured every week. The intraperitoneal glucose tolerance test (IPGTT) was performed after 16 weeks. MgSO₄ administration improved the blood glucose level and IPGTT. It also increased Akt2 and IRS1 genes as well as protein expression. Insulin lowered the blood glucose level and increased IRS1 gene and protein expression, but did not affect Akt2 gene and protein expression. Glucose reduction after Mg therapy may be mediated, at least partially, via IRS1 and Akt2 genes and protein stimulation. In insulin-treated rats, insulin resistance was not significant due to the absence of Akt2 gene expression.

Azoramide improves mitochondrial dysfunction in palmitate-induced insulin resistant H9c2 cells

Azoramide is identified as a new compound with the dual properties for the improvement of ER-folding capacity in various cells as well as for the treatment of T2DM. Although the effect of azoramide in glucose-homeostasis in mammalians is not known very well, a limited number of experimental studies showed that it could improve the insulin sensitivity in genetically obese mice. Therefore, here, we aimed to investigate the direct effect of azoramide on insulin signaling in insulin-resistant (IR) cardiomyocytes using IR-modelled ventricular cardiomyocytes. This model was established in H9c2 cells using palmitic acid incubation (50-μM for 24-h). The development of IR in cells was verified by monitoring the cellular 2-DG6P uptake assays in these treated cells. The 2-DG6P uptake was 50% less in the IR-cells compared to the control cells, while azoramide treatment (20-μM for 48-h) could prevent fully that decrease. In addition, azoramide treatment markedly preserved the IR-induced less ATP production and high-ROS production in these IR-cells. Furthermore, this treatment prevented the functional changes in mitochondria characterized by depolarized mitochondrial membrane potential and mitochondrial fusion or fusion-related protein levels as well as cellular ATP level. Moreover, this treatment provided marked protection against IR-associated changes in the insulin signaling pathway in cells, including recovery in the phosphorylation of IRS1 and Akt as well as the protein level of GLUT4 and Akt. Our present results, for the first time, demonstrated that azoramide plays an important protective role in IR-cardiomyocytes, at most, protective action on mitochondria. Therefore, one can suggest that azoramide, as a novel regulator, can provide direct cardioprotection in the IR-heart, at most, via affecting mitochondria and can be a good candidate as a new drug for the treatment of IR-associated cardiovascular disorders in mammalians with systemic IR.

Effects of puerarin on the AKT signaling pathway in bovine preadipocyte differentiation

Objective

Puerarin has the potential of regulating the differentiation of preadipocytes, but its mechanism of action has not yet been elucidated. Adipocytes found in adipose tissue, the main endocrine organ, are the main sites of lipid deposition, and are widely used as a cell model in the study of in vitro fat deposition. This study aimed to investigate the effects of puerarin on adipogenesis in vitro.

Methods

Puerarin was added to the culture medium during the process of adipogenesis. The proliferation and differentiation of bovine preadipocytes was measured through cell viability and staining with Oil Red O. The content of triacylglycerol (TG) was measured using a triglyceride assay kit. The mRNA and protein expression levels of adipogenic genes, peroxisome proliferator-activated receptor-γ (PPARγ) and CCAAT/enhancer-binding protein-α (C/EBPα), were measured using quantitative real-time polymerase chain reaction (qRT-PCR) and western blotting, respectively.

Results

The addition of puerarin significantly increased adipogenesis of bovine preadipocytes and enhanced the mRNA and protein level expression of PPARγ (p<0.01). The expression of P-Akt increased after adipogenic hormonal induction, whereas puerarin significantly increased PPARγ expression by promoting the Akt signaling component, P-Akt. The mechanism of adipogenesis was found to be related to the phosphorylation level of Ser473, which may activate the downstream signaling of the Akt pathway.

Conclusion

Puerarin was able to promote the differentiation of preadipocytes and improve fat deposition in cattle. The mechanism of adipogenesis was found to be related to the phosphorylation level of Ser473.

γ-Tocotrienol Suppression of the Warburg Effect Is Mediated by AMPK Activation in Human Breast Cancer Cells

Cancer cell metabolism is characterized by aerobic glycolysis or the "Warburg effect". Enhanced Akt signaling is associated with activation of various downstream enzymes involved in the glycolytic process, whereas activation of 5'-AMP-activated kinase (AMPK) acts to terminate energy expending mechanisms and decrease glycolytic enzyme expression. Studies were conducted to determine if the anticancer effects of γ-tocotrienol, are mediated through a suppression in aerobic glycolysis. Results show that treatment with 0-7 μM γ-tocotrienol throughout a 4-day culture period resulted in a dose-responsive increase in AMPK activation, and corresponding decrease in Akt activity in human MCF-7 and MDA-MB-231 breast cancer cells. γ-Tocotrienol treatment was also found to induce a dose-responsive decrease in phosphorylated-Fox03 (inactivated), a transcription factor that acts to inhibit in the levels of glycolytic enzyme, and this decrease was associated with a reduction in glycolytic enzyme levels and activity, as well as glucose consumption in these cells. PCR microarray analysis shows that γ-tocotrienol treatment decreases the expression of genes associate with metabolic signaling and glycolysis in MCF-7 and MDA-MB-231 breast cancer cells. In summary, these findings demonstrate that the anticancer effects of γ-tocotrienol are mediated, at least in part, by a suppression in the Warburg effect.

Mechanisms of statin-associated skeletal muscle-associated symptoms

Statins lower the serum low-density lipoprotein cholesterol and prevent cardiovascular events by inhibiting 3-hydroxy-3-methyl-glutaryl-CoA reductase. Although the safety of statins is documented, many patients ingesting statins may suffer from skeletal muscle-associated symptoms (SAMS). Importantly, SAMS are a common reason for stopping the treatment with statins. Statin-associated muscular symptoms include fatigue, weakness and pain, possibly accompanied by elevated serum creatine kinase activity. The most severe muscular adverse reaction is the potentially fatal rhabdomyolysis. The frequency of SAMS is variable but in up to 30% of the patients ingesting statins, depending on the population treated and the statin used. The mechanisms leading to SAMS are currently not completely clarified. Over the last 15 years, several research articles focused on statin-induced mitochondrial dysfunction as a reason for SAMS. Statins can impair the function of the mitochondrial respiratory chain, thereby reducing ATP and increasing ROS production. This can induce mitochondrial membrane permeability transition, release of cytochrome c into the cytosol and induce apoptosis. In parallel, statins inhibit activation of Akt, mainly due to reduced function of mTORC2, which may be related to mitochondrial dysfunction. Mitochondrial dysfunction by statins is also responsible for activation of AMPK, which is associated with impaired activation of mTORC1. Reduced activation of mTORC1 leads to increased skeletal muscle protein degradation, impaired protein synthesis and stimulation of apoptosis. In this paper, we discuss some of the different hypotheses how statins affect skeletal muscle in more detail, focusing particularly on those related to mitochondrial dysfunction and the impairment of the Akt/mTOR pathway.

Lack of muscle mTOR kinase activity causes early onset myopathy and compromises whole-body homeostasis

BACKGROUND

The protein kinase mechanistic target of rapamycin (mTOR) controls cellular growth and metabolism. Although balanced mTOR signalling is required for proper muscle homeostasis, partial mTOR inhibition by rapamycin has beneficial effects on various muscle disorders and age-related pathologies. Besides, more potent mTOR inhibitors targeting mTOR catalytic activity have been developed and are in clinical trials. However, the physiological impact of loss of mTOR catalytic activity in skeletal muscle is currently unknown.

METHODS

We have generated the mTORmKOKI mouse model in which conditional loss of mTOR is concomitant with expression of kinase inactive mTOR in skeletal muscle. We performed a comparative phenotypic and biochemical analysis of mTORmKOKI mutant animals with muscle-specific mTOR knockout (mTORmKO) littermates.

RESULTS

In striking contrast with mTORmKO littermates, mTORmKOKI mice developed an early onset rapidly progressive myopathy causing juvenile lethality. More than 50% mTORmKOKI mice died before 8 weeks of age, and none survived more than 12 weeks, while mTORmKO mice died around 7 months of age. The growth rate of mTORmKOKI mice declined beyond 1 week of age, and the animals showed profound alterations in body composition at 4 weeks of age. At this age, their body weight was 64% that of mTORmKO mice (P < 0.001) due to significant reduction in lean and fat mass. The mass of isolated muscles from mTORmKOKI mice was remarkably decreased by 38-56% (P < 0.001) as compared with that from mTORmKO mice. Histopathological analysis further revealed exacerbated dystrophic features and metabolic alterations in both slow/oxidative and fast/glycolytic muscles from mTORmKOKI mice. We show that the severity of the mTORmKOKI as compared with the mild mTORmKO phenotype is due to more robust suppression of muscle mTORC1 signalling leading to stronger alterations in protein synthesis, oxidative metabolism, and autophagy. This was accompanied with stronger feedback activation of PKB/Akt and dramatic down-regulation of glycogen phosphorylase expression (0.16-fold in tibialis anterior muscle, P < 0.01), thus causing features of glycogen storage disease type V.

CONCLUSIONS

Our study demonstrates a critical role for muscle mTOR catalytic activity in the regulation of whole-body growth and homeostasis. We suggest that skeletal muscle targeting with mTOR catalytic inhibitors may have detrimental effects. The mTORmKOKI mutant mouse provides an animal model for the pathophysiological understanding of muscle mTOR activity inhibition as well as for mechanistic investigation of the influence of skeletal muscle perturbations on whole-body homeostasis.

Sphingolipid Metabolism: New Insight into Ceramide-Induced Lipotoxicity in Muscle Cells

Insulin-resistance is a characteristic feature of type 2 diabetes (T2D) and plays a major role in the pathogenesis of this disease. Skeletal muscles are quantitatively the biggest glucose users in response to insulin and are considered as main targets in development of insulin-resistance. It is now clear that circulating fatty acids (FA), which are highly increased in T2D, play a major role in the development of muscle insulin-resistance. In healthy individuals, excess FA are stored as lipid droplets in adipocytes. In situations like obesity and T2D, FA from lipolysis and food are in excess and eventually accumulate in peripheral tissues. High plasma concentrations of FA are generally associated with increased risk of developing diabetes. Indeed, ectopic fat accumulation is associated with insulin-resistance; this is called lipotoxicity. However, FA themselves are not involved in insulin-resistance, but rather some of their metabolic derivatives, such as ceramides. Ceramides, which are synthetized de novo from saturated FA like palmitate, have been demonstrated to play a critical role in the deterioration of insulin sensitivity in muscle cells. This review describes the latest progress involving ceramides as major players in the development of muscle insulin-resistance through the targeting of selective actors of the insulin signaling pathway.

TXNIP regulates AKT-mediated cellular senescence by direct interaction under glucose-mediated metabolic stress

Aging is associated with an inevitable and universal loss of cell homeostasis and restricts an organism's lifespan by an increased susceptibility to diseases and tissue degeneration. The glucose uptake associated with producing energy for cell survival is one of the major causes of ROS production under physiological conditions. However, the overall mechanisms by which glucose uptake results in cellular senescence remain mysterious. In this study, we found that TXNIP deficiency accelerated the senescent phenotypes of MEF cells under high glucose condition. TXNIP^‐/‐ MEF cells showed greater induced glucose uptake and ROS levels than wild‐type cells, and N‐acetylcysteine (NAC) treatment rescued the cellular senescence of TXNIP^‐/‐ MEF cells. Interestingly, TXNIP^‐/‐ MEF cells showed continuous activation of AKT during long‐term subculture, and AKT signaling inhibition completely blocked the cellular senescence of TXNIP^‐/‐ MEF cells. In addition, we found that TXNIP interacted with AKT via the PH domain of AKT, and their interaction was increased by high glucose or H₂O₂ treatment. The inhibition of AKT activity by TXNIP was confirmed using western blotting and an in vitro kinase assay. TXNIP deficiency in type 1 diabetes mice (Akita) efficiently decreased the blood glucose levels and finally increased mouse survival. However, in normal mice, TXNIP deficiency induced metabolic aging of mice and cellular senescence of kidney cells by inducing AKT activity and aging‐associated gene expression. Altogether, these results suggest that TXNIP regulates cellular senescence by inhibiting AKT pathways via a direct interaction under conditions of glucose‐derived metabolic stress.

Human Plasmablast Migration Toward CXCL12 Requires Glucose Oxidation by Enhanced Pyruvate Dehydrogenase Activity via AKT

Migration of human plasmablast to the bone marrow is essential for the final differentiation of plasma cells and maintenance of effective humoral immunity. This migration is controlled by CXCL12/CXCR4-mediated activation of the protein kinase AKT. Herein, we show that the CXCL12-induced migration of human plasmablasts is dependent on glucose oxidation. Glucose depletion markedly inhibited plasmablast migration by 67%, and the glucose analog 2-deoxyglucose (2-DG) reduced the migration by 53%; conversely, glutamine depletion did not reduce the migration. CXCL12 boosted the oxygen consumption rate (OCR), and 2-DG treatment significantly reduced the levels of all measured tricarboxylic acid (TCA) cycle intermediates. AKT inhibitors blocked the CXCL12-mediated increase of OCR. CXCL12 enhanced the pyruvate dehydrogenase (PDH) activity by 13.5-fold in an AKT-dependent manner to promote mitochondrial oxidative phosphorylation. The knockdown and inhibition of PDH confirmed its indispensable role in CXCL12-induced migration. Cellular ATP levels fell by 91% upon exposure to 2-DG, and the mitochondrial ATP synthase inhibitor oligomycin inhibited CXCL12-induced migration by 85%. Low ATP levels inhibited the CXCL12-induced activation of AKT and phosphorylation of myosin light chains by 42%, which are required for cell migration. Thus, we have identified a mechanism that controls glucose oxidation via AKT signaling and PDH activation, which supports the migration of plasmablasts. This mechanism can provide insights into the proper development of long-lived plasma cells and is, therefore, essential for optimal humoral immunity. To our knowledge, this study is the first to investigate metabolic mechanisms underlying human plasmablast migration toward CXCL12.

RNA-Seq Analysis Reveals a Positive Role of HTR2A in Adipogenesis in Yan Yellow Cattle

In this study, we performed high throughput RNA sequencing at the primary bovine preadipocyte (Day-0), mid-differentiation (Day-4), and differentiated adipocyte (Day-9) stages in order to characterize the transcriptional events regulating differentiation and function. The preadipocytes were isolated from subcutaneous fetal bovine adipose tissues and were differentiated into mature adipocytes. The adipogenic characteristics of the adipocytes were detected during various stages of adipogenesis (Day-0, Day-4, and Day-9). We used RNA sequencing (RNA-seq) to investigate a comprehensive transcriptome information of adipocytic differentiation. Compared to the pre-differentiation stage (Day-0), 2510 genes were identified as differentially expressed genes (DEGs) at the mid-differentiation stage (Day-4). We found 2446 DEGs in the mature adipocytic stage relative to the mid-differentiation stage. Some adipogenesis-related transcription factors, CCAAT-enhancer-binding protein α (C/EBPα) and peroxisome proliferator-activated receptor γ (PPARγ) were differentially expressed at Day-0, Day-4, and Day-9. We further investigated the adipogenic function of 5-hydroxytryptamine receptor 2A (HTR2A) in adipogenesis. Overexpression of HTR2A stimulated the differentiation of preadipocytes, and knockdown of HTR2A had opposite effects. Furthermore, functional enrichment analysis of DEGs revealed that the PI3K-Akt signaling pathway was the significantly enriched pathway, and HTR2A regulated adipogenesis by activating or inhibiting phosphorylation of phospho-AKT (Ser473). In summary, the present study provides the first comparative transcription of various periods of adipocytes in cattle, which presents a solid foundation for further study into the molecular mechanism of fat deposition and the improvement of beef quality in cattle.

Exendin-4 protects INS-1 cells against palmitate-induced apoptosis through the IRE1α-Xbp1 signaling pathway

The anti-apoptotic effect of the incretin analog, exendin-4 (EX-4) on pancreatic β cells is mediated via the activation of protein kinase B (Akt) signaling, and its effect is partly produced through the inhibition of endoplasmic reticulum (ER) stress. However, the molecular mechanisms that underlie the effect of EX-4 on the suppression of ER stress and the upregulation of Akt signaling are poorly understood. Inositol-requiring enzyme 1 (IRE1), a member of the ER-localized transmembrane protein family, activates its downstream transcription factor X-box binding protein 1 (XBP1) to mediate a key part of the cellular unfolded protein response in order to cope with ER stress. Using the clonal rat pancreatic β cell line INS-1, the present study produced an in vitro model of ER stress using palmitate (PA) in order to determine whether the beneficial effect of EX-4 under ER stress was regulated by the IRE1α-Xbp1 signaling pathway. The results demonstrated that the reduction in ER stress and the activation Akt by EX-4 may be associated with the upregulation of IRE1α phosphorylation and the splicing of Xbp1 mRNA, which improved PA-reduced cell viability. This effect was partially abrogated by the knockdown of IRE1α with small interfering RNA. Additionally, cellular IRE1α was phosphorylated by the protein kinase A (PKA) associated with EX-4 and the activation of IRE1α, as IRE1α phosphorylation was attenuated by the inhibition of PKA with its inhibitor. In conclusion, the data identified the IRE1α-Xbp1 signaling pathway as an essential mediator that associates EX-4 with the intracellular mechanism that inhibits ER stress and activates Akt in order to regulate β cell survival. This may provide important evidence for the use of EX-4 in treatments for type 2 diabetes.

Drosophila melanogaster as a Model for Diabetes Type 2 Progression

Drosophila melanogaster has been used as a very versatile and potent model in the past few years for studies in metabolism and metabolic disorders, including diabetes types 1 and 2. Drosophila insulin signaling, despite having seven insulin-like peptides with partially redundant functions, is very similar to the human insulin pathway and has served to study many different aspects of diabetes and the diabetic state. Yet, very few studies have addressed the chronic nature of diabetes, key for understanding the full-blown disease, which most studies normally explore. One of the advantages of having Drosophila mutant viable combinations at different levels of the insulin pathway, with significantly reduced insulin pathway signaling, is that the abnormal metabolic state can be studied from the onset of the life cycle and followed throughout. In this review, we look at the chronic nature of impaired insulin signaling. We also compare these results to the results gleaned from vertebrate model studies.

Expression analysis of candidate genes for fatty acid composition in adipose tissue and identification of regulatory regions

The aim of this work was to study the genetic basis of the backfat expression of lipid-related genes associated with meat quality traits in pigs. We performed a genome-wide association study with the backfat gene expression measured in 44 genes by qPCR and the PorcineSNP60 BeadChip genotypes in 115 Iberian x Landrace backcross animals. A total of 193 expression-associated SNPs located in 19 chromosomal regions were associated with expression levels of ACSM5, ELOVL6, FABP4, FADS2, and SLC27A4 genes. Three expression quantitative trail loci (eQTLs) corresponding to ACSM5, FABP4, and FADS2 were classified as cis-acting eQTLs, whereas the remaining 16 eQTLs have trans-regulatory effects. Remarkably, a SNP in the ACSM5 promoter region and a SNP in the 3′UTR region of FABP4 were the most associated polymorphisms with the ACSM5 and FABP4 expression levels, respectively. Moreover, relevant lipid-related genes mapped in the trans-eQTLs regions associated with the ACSM5, FABP4, FADS2, and SLC27A4 genes. Interestingly, a trans-eQTL hotspot on SSC13 regulating the gene expression of ELOVL6, ELOLV5, and SCD, three important genes implicated in the elongation and desaturation of fatty acids, was identified. These findings provide new data to further understand the functional regulatory mechanisms implicated in the variation of fatty acid composition in pigs.

Regulation of Serine-Threonine Kinase Akt Activation by NAD+-Dependent Deacetylase SIRT7

The Akt pathway is a central regulator that promotes cell survival in response to extracellular signals. Depletion of SIRT7, an NAD⁺-dependent deacetylase that is the least-studied sirtuin, is known to significantly increase Akt activity in mice through unknown mechanisms. In this study, we demonstrate that SIRT7 depletion in breast cancer cells results in Akt hyper-phosphorylation and increases cell survival following genotoxic stress. Mechanistically, SIRT7 specifically interacts with and deacetylates FKBP51 at residue lysines 28 and 155 (K28 and K155), resulting in enhanced interactions among FKBP51, Akt, and PHLPP, as well as Akt dephosphorylation. Mutating both lysines to arginines abolishes the effect of SIRT7 on Akt activity through FKBP51 deacetylation. Finally, energy stress strengthens SIRT7-mediated effects on Akt dephosphorylation through FKBP51 and thus sensitizes cancer cells to cytotoxic agents. These results reveal a direct role of SIRT7 in Akt regulation and raise the possibility of using the glucose analog 2-deoxy-D-glucose (2DG) as a chemo-sensitizing agent.

Phosphatase and tensin homologue: a therapeutic target for SMA

Spinal muscular atrophy (SMA) is one of the most common juvenile neurodegenerative diseases, which can be associated with child mortality. SMA is caused by a mutation of ubiquitously expressed gene, Survival Motor Neuron1 (SMN1), leading to reduced SMN protein and the motor neuron death. The disease is incurable and the only therapeutic strategy to follow is to improve the expression of SMN protein levels in motor neurons. Significant numbers of motor neurons in SMA mice and SMA cultures are caspase positive with condensed nuclei, suggesting that these cells are prone to a process of cell death called apoptosis. Searching for other potential molecules or signaling pathways that are neuroprotective for central nervous system (CNS) insults is essential for widening the scope of developmental medicine. PTEN, a Phosphatase and Tensin homologue, is a tumor suppressor, which is widely expressed in CNS. PTEN depletion activates anti-apoptotic factors and it is evident that the pathway plays an important protective role in many neurodegenerative disorders. It functions as a negative regulator of PIP3/AKT pathway and thereby modulates its downstream cellular functions through lipid phosphatase activity. Moreover, previous reports from our group demonstrated that, PTEN depletion using viral vector delivery system in SMN delta7 mice reduces disease pathology, with significant rescue on survival rate and the body weight of the SMA mice. Thus knockdown/depletion/mutation of PTEN and manipulation of PTEN medicated Akt/PKB signaling pathway may represent an important therapeutic strategy to promote motor neuron survival in SMA.

Protective effect of crocin on BPA-induced liver toxicity in rats through inhibition of oxidative stress and downregulation of MAPK and MAPKAP signaling pathway and miRNA-122 expression

Bisphenol A (BPA) is an artificial environmental endocrine disrupting chemical and commonly used as a monomer of polycarbonate plastics and epoxy resins. The aim of the present study is to investigate the hepatoprotective effects of crocin, a constituent of saffron, against BPA-induced liver toxicity. We showed that treatment of male Wistar rats with 0.5 mg/kg BPA for 30 days increased the level of 8-isoprostane, decreased the level of reduced glutathione, elevated serum levels of aspartate aminotransferase, lactate dehydrogenase, triglyceride, and glucose, and induced periportal inflammation. Western blot results revealed that BPA increased the phosphorylation of c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK1/2), and mitogen-activated protein kinase-activated protein kinase (MAPKAPK), but not p38. BPA also reduced the Akt signaling activation and upregulated microRNA (miR-122) expression. Moreover, we showed here that crocin 20 mg/kg administration ameliorated liver damage and improved elevated levels of TG and liver enzymes of BPA-treated rats possibly though antioxidant activity, downregulation of miR-122 transcript level and lowering the phosphorylation of JNK, ERK1/2, and MAPKAPK and subsequently their activities. Overall, the findings suggest that crocin possesses hepatoprotective effects against BPA-induced liver toxicity by enhancing the antioxidative defense system and regulation of important signaling pathway activities and miR-122 expression.

Glucose variability aggravates cardiac fibrosis by altering AKT signalling path

OBJECTIVE

To study the effect of blood glucose variability on cardiac fibrosis and its mechanism in a model of diabetic cardiomyopathy.

METHODS

A total of 45 Sprague Dawley rats were randomly divided into three groups: control, control diabetes mellitus and fluctuated blood glucose groups. Fluctuated blood glucose was induced by daily subcutaneous insulin and intraperitoneal glucose injections at different time points. Blood lipids and glycosylated haemoglobin A1c were assessed. Super oxide dismutase activity and malondialdehyde level in rat heart homogenates were determined by assay kit. Structural cardiac tissue changes were observed by haematoxylin and eosin staining and Masson's trichrome staining. Collagen type 3, fibronectin, phosphorylated Ser/Thr protein kinase, phosphorylated glycogen synthase kinase-3 beta, glycogen synthase kinase-3 beta, nuclear factor kappa-light-chain-enhancer of activated B cells, cleaved-cysteinyl aspartate-specific proteinase-3 (caspase-3) and tumour necrosis factor-α levels were determined by western blot.

RESULTS

Compared with the control group, cardiac fibrosis and oxidative stress in heart tissue were aggravated in diabetic rats, which were more pronounced in glucose variability rats. However, the expression levels of AKT and glycogen synthase kinase-3 beta were not significantly different in three groups, but the expression levels of phosphorylated Ser/Thr protein kinase and phosphorylated glycogen synthase kinase-3 beta were significantly decreased in the control diabetes mellitus and fluctuated blood glucose groups compared to control group, and levels in the fluctuated blood glucose group were significantly less than in the control diabetes mellitus group. In addition, the expression levels of nuclear factor kappa B and caspase-3 in both the control diabetes mellitus and fluctuated blood glucose groups were higher than in the control group, with the highest levels measured in the fluctuated blood glucose group.

CONCLUSION

Blood glucose variability can aggravate heart tissue fibrosis, possibly involving oxidative stress by inhibiting AKT signalling path.

Antibody to human α-fetoprotein inhibits cell growth of human hepatocellular carcinoma cells by resuscitating the PTEN molecule: in vitro experiments

It has been proposed that α-fetoprotein (AFP) is a new member of the intracellular signaling molecule family of the phosphoinositide 3-kinase (PI3K)/AKT signaling pathway via interaction with the phosphatase and tensin homolog (PTEN). In this study, the effects of anti-human AFP antibody on the functions of PTEN were examined using an AFP-producing human hepatoma cell line. The antibody caused significant inhibition of cell growth, compared to a normal IgG control, with the accumulation of intracellular immune complexes followed by significant reduction of cytosolic functional AFP. Decrease in the amount of AKT phosphorylated on serine (S) 473 indicated that PI3K/AKT signaling was suppressed in the cells. S380-phosphorylated PTEN increased markedly by the second day after antibody treatment, with slight but significant increase in the PTEN protein level. Since phosphorylation at S380 is critical for PTEN stability, the increase in S380-phosphorylated PTEN indicated maintenance of the number of PTEN molecules and the related potential to control PI3K/AKT signaling. p53 protein (P53) significantly, but slightly increased during antibody treatment, because PTEN expression increased the stability and function of P53 via both molecular interactions. P53 phosphorylated at S20 or at S392 dramatically increased, suggesting an increase in the stability, accumulation and activation of P53. Glucose transporter 1 (GLUT1) increased immediately after antibody treatment, pointing to a deficiency of glucose in the cells. Immunofluorescence cytology revealed that antibody-treatment re-distributed GLUT1 molecules throughout the cytoplasm with a reduction of their patchy localization on the cell surface. This suggested that translocation of GLUT1 depends on the PI3K/AKT pathway, in particular on PTEN expression. Antibody therapy targeted at AFP-producing tumor cells showed an inhibitory effect on the PI3K/AKT pathway via the liberation, restoration and functional stabilization of PTEN. PTEN simultaneously induced both P53 activation and intracellular translocation of GLUT1, since these are closely associated with PTEN.

Salt-inducible kinase 2 and -3 are downregulated in adipose tissue from obese or insulin-resistant individuals: implications for insulin signalling and glucose uptake in human adipocytes

AIMS/HYPOTHESIS

Salt-inducible kinases (SIKs) are related to the metabolic regulator AMP-activated protein kinase (AMPK). SIK2 is abundant in adipose tissue. The aims of this study were to investigate the expression of SIKs in relation to human obesity and insulin resistance, and to evaluate whether changes in the expression of SIKs might play a causal role in the development of disturbed glucose uptake in human adipocytes.

METHODS

SIK mRNA and protein was determined in human adipose tissue or adipocytes, and correlated to clinical variables. SIK2 and SIK3 expression and phosphorylation were analysed in adipocytes treated with TNF-α. Glucose uptake, GLUT protein levels and localisation, phosphorylation of protein kinase B (PKB/Akt) and the SIK substrate histone deacetylase 4 (HDAC4) were analysed after the SIKs had been silenced using small interfering RNA (siRNA) or inhibited using a pan-SIK-inhibitor (HG-9-91-01).

RESULTS

We demonstrate that SIK2 and SIK3 mRNA are downregulated in adipose tissue from obese individuals and that the expression is regulated by weight change. SIK2 is also negatively associated with in vivo insulin resistance (HOMA-IR), independently of BMI and age. Moreover, SIK2 protein levels and specific kinase activity display a negative correlation to BMI in human adipocytes. Furthermore, SIK2 and SIK3 are downregulated by TNF-α in adipocytes. Silencing or inhibiting SIK1-3 in adipocytes results in reduced phosphorylation of HDAC4 and PKB/Akt, less GLUT4 at the plasma membrane, and lower basal and insulin-stimulated glucose uptake in adipocytes.

CONCLUSION/INTERPRETATION

This is the first study to describe the expression and function of SIKs in human adipocytes. Our data suggest that SIKs might be protective in the development of obesity-induced insulin resistance, with implications for future treatment strategies.

Jiangzhi Capsule improves fructose-induced insulin resistance in rats: Association with repair of the impaired sarcolemmal glucose transporter-4 recycling

ETHNOPHARMACOLOGICAL RELEVANCE

Jiangzhi Capsule, originated from an experienced formula in traditional Chinese Medicine, has been listed and used for the management of metabolic abnormalities in Australia for a long time. To better understand Jiangzhi Capsule, this study investigated its effect on insulin resistance.

MATERIALS AND METHODS

Male rats were treated with liquid fructose in their drinking water over 14 weeks. Jiangzhi Capsule was co-administered (once daily, by oral gavage) during the last 7 weeks. Indexes of lipid and glucose homeostasis were determined enzymatically, by ELISA and/or histologically. Gene expression was analyzed by real-time PCR, Western blot and/or immunohistochemistry.

RESULTS

Treatment with Jiangzhi Capsule (100mg/kg) attenuated fructose overconsumption-induced increases in basal plasma insulin concentrations, the homeostasis model assessment of insulin resistance index and the adipose tissue insulin resistance index in rats. The increased plasma glucose concentrations during oral glucose tolerance test were also inhibited. Furthermore, Jiangzhi Capsule had a trend to attenuate the decreased ratios of glucose and non-esterified fatty acids to plasma insulin concentrations. Mechanistically, this insulin-sensitizing action was accompanied by normalization of the downregulated sarcolemmal glucose transporter (GLUT)-4 protein expression and the decreased phosphorylated Akt to total Akt protein ratio in gastrocnemius.

CONCLUSIONS

These results suggest that Jiangzhi Capsule ameliorates fructose-induced insulin resistance with a link to repair of the impaired sarcolemmal GLUT-4 recycling through modulation of the ratio of phosphorylated Akt to total Akt in gastrocnemius. Our findings provide an evidence-based and mechanistic understanding of Jiangzhi Capsule for the management of insulin resistance-associated disorders.

Adeno-associated virus-mediated expression of myostatin propeptide improves the growth of skeletal muscle and attenuates hyperglycemia in db/db mice

Inhibition of myostatin, a negative growth modulator for muscle, can functionally enhance muscle mass and improve glucose and fat metabolism in myostatin propeptide (MPRO) transgenic mice. This study was to investigate whether myostatin inhibition by adeno-associated virus (AAV)-mediated gene delivery of MPRO could improve muscle mass and achieve therapeutic effects on glucose regulation and lipid metabolism in the db/db mice and the mechanisms involved in that process. Eight-week-old male db/db mice were administered saline, AAV-GFP and AAV-MPRO/Fc vectors and monitored random blood glucose levels and body weight for 36 weeks. Body weight gain was not different during follow-up among the groups, but AAV-MPRO/Fc vectors resulted high level of MPRO in the blood companied by an increase in skeletal muscle mass and muscle hypertrophy. In addition, AAV-MPRO/Fc-treated db/db mice showed significantly lower blood glucose and insulin levels and significantly increased glucose tolerance and insulin sensitivity compared with the control groups (P<0.05). Moreover, these mice exhibited lower triglyceride (TG) and free fatty acid (FFA) content in the skeletal muscle, although no difference was observed in fat pad weights and serum TG and FFA levels. Finally, AAV-MPRO/Fc-treated mice had enhanced insulin signaling in the skeletal muscle. These data suggest that AAV-mediated MPRO therapy may provide an important clue for potential clinical applications to prevent type II diabetes, and these studies confirm that MPRO is a therapeutic target for type II diabetes.

Tuberous sclerosis complex inactivation disrupts melanogenesis via mTORC1 activation

Tuberous sclerosis complex (TSC) is an autosomal dominant tumor-suppressor gene syndrome caused by inactivating mutations in either TSC1 or TSC2, and the TSC protein complex is an essential regulator of mTOR complex 1 (mTORC1). Patients with TSC develop hypomelanotic macules (white spots), but the molecular mechanisms underlying their formation are not fully characterized. Using human primary melanocytes and a highly pigmented melanoma cell line, we demonstrate that reduced expression of either TSC1 or TSC2 causes reduced pigmentation through mTORC1 activation, which results in hyperactivation of glycogen synthase kinase 3β (GSK3β), followed by phosphorylation of and loss of β-catenin from the nucleus, thereby reducing expression of microphthalmia-associated transcription factor (MITF), and subsequent reductions in tyrosinase and other genes required for melanogenesis. Genetic suppression or pharmacological inhibition of this signaling cascade at multiple levels restored pigmentation. Importantly, primary melanocytes isolated from hypomelanotic macules from 6 patients with TSC all exhibited reduced TSC2 protein expression, and 1 culture showed biallelic mutation in TSC2, one of which was germline and the second acquired in the melanocytes of the hypomelanotic macule. These findings indicate that the TSC/mTORC1/AKT/GSK3β/β-catenin/MITF axis plays a central role in regulating melanogenesis. Interventions that enhance or diminish mTORC1 activity or other nodes in this pathway in melanocytes could potentially modulate pigment production.

HSD1 and AQP7 short-term gene regulation by cortisone in 3T3-L1 adipocytes

Adipose Tissue (AT) is a complex organ with a crucial regulatory role in energy metabolism and in the development of obesity and the Metabolic Syndrome (MS). Modified responses and the metabolism of hormones have been observed in visceral adiposity during obesity, specifically as related with cortisone. The objective of this study was to assess, in the 3T3-L1 adipocyte cell line, the short-term effect of cortisone on the expression of 11β-Hydroxysteroid dehydrogenase 1 (Hsd1), which is responsible for activation of cortisone into cortisol, and for Aquaporin 7 (Aqp7), involved in glycerol transport through the cell membrane. Total RNA (tRNA) and complementary DNA (cDNA) were obtained from cell samples treated with cortisone (0.1, 1, and 10 μM) during different times (0, 5, 10, 15, and 20 min, and 48 h) to quantify the expression of the aforementioned genes by real time PCR employing MnSOD and Ppia as housekeeping genes. There was a time-dependent response of Aqp7, a dose-dependent response of Hsd1, and an increase observed in the expression of both genes during min 1 of treatment (5- and 6-fold, respectively), followed by a decrease during the following 5-10 min (P < 0.05). With the 1-μM cortisone treatment, both genes showed cubic tendencies in their expression; the Hsd1 tendency is described by the equation y = 0.18×(3)-1.65×(2)+3.59x+1.31, while the Aqp7 tendency is described by y = 0.33×(3)-2.67×(2)+4.93x+1.84. There are immediate and quantitatively important actions of cortisone on the expression of Aqp7 and Hsd1 in 3T3-L1 adipocytes.