PI3K/Akt pathway mediates high glucose-induced lipid accumulation in human renal proximal tubular cells via spliced XBP-1

Mangiferin, a component of Mangifera indica leaf extracts, inhibits lipid synthesis in human sebocytes

Inhibition of lipid synthesis in sebocytes is essential for acne treatments. The effects of natural product-derived substances on lipid synthesis are unknown. This study investigated the effects of water extract of Mangifera indica leaves (WEML) on lipid synthesis in human sebocytes. Sebocyte differentiation in low serum conditions increased lipid accumulation and proliferator-activated receptor γ expression. WEML treatment significantly inhibited lipid accumulation and adipogenic mRNA expression in sebocytes. Mangiferin, a bioactive compound in WEML, also reduced lipid accumulation and adipogenic mRNA expression via the AKT pathway. Thus, WEML and mangiferin effectively inhibit lipid synthesis in sebocytes, showing promise for acne treatment.

LncRNA HOX transcript antisense RNA mediates hyperglycemic-induced injury in the renal tubular epithelial cell via the miR-126-5pAkt axis

OBJECTIVE

To investigate the involvement of HOX transcript antisense RNA (HOTAIR) in the injury of renal tubular epithelial cells induced by high glucose. Results: In high glucose-induced HK-2 cells, the expression of HOTAIR was upregulated, resulting in suppressed cell proliferation. Meanwhile, HOTAIR upregulates the expression of pro-apoptotic proteins Bax and cleaved caspase-3, while downregulating the expression of the anti-apoptotic protein Bcl-2. Luciferase reporter assays revealed that HOTAIR could target miR-126-5p. Additionally, it was found that the PI3K/Akt signaling pathway serves as a downstream target of miR-126-5p. Knockdown of HOTAIR relieved apoptosis, whereas further inhibition of miR-126-5p led to apoptosis in HK-2 cells. Conclusions: HOTAIR plays a regulatory role in mediating high glucose-induced injuries in HK-2 cells, specifically affecting apoptosis and cell viability, via the miR-126-5p/PI3K/Akt signaling pathway.

Effect of Thymoquinone on Renal Damage Induced by Hyperlipidemia in LDL Receptor-Deficient (LDL-R-/-) Mice

Hyperlipidemia is a well-established risk factor for kidney injury, which can lead to chronic kidney disease (CKD). Thymoquinone (TQ) is one of the most active ingredients in Nigella sativa seeds. It has various beneficial properties, including antioxidant and anti-inflammatory activities. TQ also exerts positive effects on doxorubicin- (DOX-) induced nephropathy and ischemia-reperfusion-induced kidney injury in rats. Therefore, in this study, we investigated the possible protective effects of TQ against kidney injury in low-density lipoprotein receptor-deficient (LDL-R^-/^-) mice. Eight-week-old male LDL-R^-/^- mice were randomly divided into the following three groups: normal diet (ND group), high-fat diet (HFD group), and HFD combined with TQ (HFD+TQ group). The mice were fed the same diet for eight weeks. After eight weeks, we performed serological analysis of the mice in all three groups. We histologically analyzed the kidney tissue and also investigated the expression of proinflammatory cytokines in the kidney tissue. Metabolic characteristics, including total cholesterol (TC), low-density lipoprotein-cholesterol (LDL-C), and creatinine (CRE) levels, were lower in the LDL-R^-/^- HFD+TQ mice than in the HFD mice. Periodic acid-Schiff (PAS) and Masson's trichrome staining revealed excessive lipid deposition and collagen accumulation in the kidneys of the LDL-R^-/^- HFD mice, which were significantly reduced in the LDL-R^-/^- HFD+TQ mice. Furthermore, macrophages and levels of proinflammatory cytokines were lower in the kidney tissues of the LDL-R^-/^- HFD+TQ mice than in those of the LDL-R^-/^- HFD mice. Moreover, profibrosis- and oxidative stress-related protein expression was lower in the kidney tissues of the LDL-R^-/^- HFD+TQ mice than in those of the LDL-R^-/^- HFD mice. These results indicate that TQ may be a potential therapeutic agent for kidney damage caused by hyperlipidemia.

Placental lipid transport and content in response to maternal overweight and gestational diabetes mellitus in human term placenta

BACKGROUND AND AIMS

Placental lipid transport is altered in women with high prepregnancy body mass index (pre-BMI) or gestational diabetes (GDM), which consequently affects foetal growth. However, the interaction of maternal overweight (OW) and GDM on placental lipid metabolism and possible adaptations are less studied. We aimed to examine whether maternal OW or GDM is the main factor disrupting placental lipid processing in human term placenta.

METHODS AND RESULTS

A total of 152 lean (18.5 ≤ pre-BMI ≤ 23.9 kg/m²) and OW (24 ≤ pre-BMI ≤ 27.9 kg/m²) pregnant women with or without GDM with a scheduled delivery by caesarean section were recruited. Maternal venous blood samples were used to measure metabolic parameters during pregnancy. Term placentas and cord blood were collected at delivery to determine placental lipid metabolism and foetal circulating lipid levels. Maternal OW significantly increased the placental mRNA expression of genes involved in lipid metabolism (FAT/CD36, FATP1, FATP4, FATP6, and PPAR-α), elevated placental lipid content (triglyceride, cholesterol), enhanced placental mTORC1-rpS6 and ERK1/2 signalling, increased cord blood insulin levels and birth weight. Neonatal birth weight was positively correlated with maternal pre-BMI, placental ERK1/2 signalling and cord blood insulin. There was an interaction between OW and GDM in regulating key placental fuel transport and storage gene expression (LPL, FATP6, FABP7, PPAR-α, PPAR-β, PPAR-γ, IR-β, GLUT1, SNAT2, SNAT4, and LAT1).

CONCLUSION

Maternal OW mainly affects placental lipid metabolism, which may contribute to foetal overgrowth and may impact long-term offspring health. GDM plays a less significant role in affecting placental lipid transfer and other mechanisms may be involved.

MicroRNA 1228 Mediates the Viability of High Glucose-Cultured Renal Tubule Cells through Targeting Thrombospondin 2 and PI3K/AKT Signaling Pathway

AIM

The present study aimed to elucidate the potential function of microRNA 1228 (miR-1228) on the high glucose (HG)-damaged human renal proximal tubule cells (HK-2) and the underlying mechanism.

METHODS

The datasets GSE47185 and GSE51674 were downloaded from the Gene Expression Omnibus database for mining differently expressed mRNAs and miRNAs, respectively. Bioinformatics online tools were applied to predict the binding sites between miR-1228 and thrombospondin 2 (THBS2), which was confirmed by dual-luciferase assay. Real-time quantitative polymerase chain reaction was used to detect the mRNA level of miR-1228/THBS2. Western blot was used to detect the protein level of THBS2 and the PI3K/AKT signaling pathway-associated markers. HK-2 cells were cultured in HG (30 mM) to mimic hyperglycemia. Cell counting kit 8 and flow cytometry assays were utilized to determine the cell proliferation and apoptosis.

RESULTS

The expression of THBS2 was significantly upregulated in diabetic nephropathy (DN) based on bioinformatics tools and identified as a direct target of miR-1228. miR-1228 was downregulated in DN and HG-damaged HK-2 cells. HG notably reduced HK-2 cell proliferation. This negative effect was attenuated by transfecting with an miR-1228 mimic and aggravated by transfecting with an miR-1228 inhibitor. However, under basal condition, there was no significant effect on the HK-2 cell proliferation among blank control, mimic, and inhibitor groups. Overexpression of THBS2 abolished the elevating effect of the miR-1228 mimic on the HG-damaged HK-2 cell proliferation, while restored the inhibitory effects of the miR-1228 mimic on the cell apoptosis. On the contrary, the suppressive effects on the proliferation and the enhancive effects on the apoptosis by silencing miR-1228 in HK-2 cells stimulated with HG can be weakened by recommendation of THBS2 small interference RNAs. Furthermore, we also found that HG significantly enhanced the phosphorylation levels of PI3K and AKT. In terms of overexpression and knockdown experiments, Western blot analysis further revealed that miR-1228 inhibited the activation of the PI3K/AKT signaling pathway in HG-damaged HK-2 cells by regulating THBS2.

CONCLUSION

The findings illustrated that miR-1228 improved survivability and inhibited apoptosis in HK-2 cells stimulated with HG partly by restraining the activation of the PI3K/AKT signaling pathway.

Momordica charantia silver nanoparticles modulate S/JAK/STAT and P13K/Akt/PTEN signalling pathways in the kidney of streptozotocin-induced diabetic rats

Objectives

Diabetes nephropathy (DN) is one of the complications of diabetes mellitus (DM) marked by gradual progressive loss of renal function. SOCS/JAK/STAT and PI3K/Akt/PTEN signalling pathways are among the chain of interactions implicated in the onset, progression and pathology of DN. Momordica charantia (bitter melon) is often used in folk medicine as therapy for DM due to its hypoglycemic properties. This study was designed to evaluate M. charantia silver nanoparticles' therapeutic effect on DN-induced by streptozotocin (STZ) in Wistar rats.

Methods

The M. charantia nanoparticles used was synthesized using the filtrate from the plant methanolic extract added to 1 mM concentration of aqueous silver nitrate. DM was induced in Wistar rats by intraperitoneal injection of STZ (65 mg/kg). The animals' treatment groups were divided into; Diabetic control (65 mg/kg STZ), Control, and groups treated with silver nitrate (10 mg/kg), M. charantia nanoparticles (50 mg/kg), metformin (100 mg/kg), and plant extract (100 mg/kg). Treatment was terminated after 11 days. RT-PCR determined renal mRNA expression of Akt, PI3k, PTEN, TGF-β, JAK2, STAT3, STAT5, SOCS3, SOCS4 and glucokinase (GCK). Consequently, characterized compounds from M. charantia identified from literatures were docked with PI3K, JAK2 and TGF-β and STAT3 to retrieve potential hits.

Results

Oral administration of M. charantia nanoparticles (50 mg/kg) to STZ-induced diabetic untreated rats significantly ((p < 0.05) down-regulated the mRNA expression of Akt, PI3k, TGF-β, JAK2, STAT3 and upregulated the mRNA expression of PTEN, SOCS3 and SOCS4, thus establishing the role of M. charantia nanoparticles in alleviating DN in diabetic rats. Additionally, there was a significant up-regulation of glucose metabolizing gene (glucokinase) upon administering M. charantia nanoparticles. Molecular docking results showed 12 compounds from bitter melon with docking score ranging from -6.114 kcal/mol to -8.221 kcal/mol that are likely to exert anti-diabetic properties.

Conclusion

Observation drawn from this study suggests that M. charantia nanoparticles ameliorate DN through regulation of SOCS/JAK/STAT and PI3K/Akt/PTEN signalling pathways.

METTL14-regulated PI3K/Akt signaling pathway via PTEN affects HDAC5-mediated epithelial-mesenchymal transition of renal tubular cells in diabetic kidney disease

Histone deacetylase 5 (HDAC5) belongs to class II HDAC subfamily and is reported to be increased in the kidneys of diabetic patients and animals. However, little is known about its function and the exact mechanism in diabetic kidney disease (DKD). Here, we found that HDAC5 was located in renal glomeruli and tubular cells, and significantly upregulated in diabetic mice and UUO mice, especially in renal tubular cells and interstitium. Knockdown of HDAC5 ameliorated high glucose-induced epithelial–mesenchymal transition (EMT) of HK2 cells, indicated in the increased E-cadherin and decreased α-SMA, via the downregulation of TGF-β1. Furthermore, HDAC5 expression was regulated by PI3K/Akt signaling pathway and inhibition of PI3K/Akt pathway by LY294002 treatment or Akt phosphorylation mutation reduced HDAC5 and TGF-β1 expression in vitro high glucose-cultured HK2 cells. Again, high glucose stimulation downregulated total m6A RNA methylation level of HK2 cells. Then, m6A demethylase inhibitor MA2 treatment decreased Akt phosphorylation, HDAC5, and TGF-β1 expression in high glucose-cultured HK2 cells. In addition, m6A modification-associated methylase METTL3 and METTL14 were decreased by high glucose at the levels of mRNA and protein. METTL14 not METTL3 overexpression led to PI3K/Akt pathway inactivation in high glucose-treated HK2 cells by enhancing PTEN, followed by HDAC5 and TGF-β1 expression downregulation. Finally, in vivo HDACs inhibitor TSA treatment alleviated extracellular matrix accumulation in kidneys of diabetic mice, accompanied with HDAC5, TGF-β1, and α-SMA expression downregulation. These above data suggest that METTL14-regulated PI3K/Akt signaling pathway via PTEN affected HDAC5-mediated EMT of renal tubular cells in diabetic kidney disease.

Identification of Biological Pathways Contributing to Marbling in Skeletal Muscle to Improve Beef Cattle Breeding

Red meat is an important dietary source that provides part of the nutritional requirements. Intramuscular fat, known as marbling, is located throughout skeletal muscle. Marbling is a trait of major economic relevance that positively influences sensory quality aspects. The aim of the present study was to identify and better understand biological pathways defining marbling in beef cattle. Pathway analysis was performed in PathVisio with publicly available transcriptomic data from semitendinosus muscle of well-marbled and lean-marbled beef. Moreover, for Bos taurus we created a gene identifier mapping database with bridgeDb and a pathway collection in WikiPathways. The regulation of marbling is possibly the result of the interplay between signaling pathways in muscle, fat, and intramuscular connective tissue. Pathway analysis revealed 17 pathways that were significantly different between well-marbled and lean-marbled beef. The MAPK signaling pathway was enriched, and the signaling pathways that play a role in tissue development were also affected. Interestingly, pathways related to immune response and insulin signaling were enriched.

Inhibition of TREM-1 attenuates inflammation and lipid accumulation in diet-induced nonalcoholic fatty liver disease

In the liver tissues of obese diabetic or nondiabetic patients, triggering receptor expressed on myeloid cells-1 (TREM-1) is usually found to be upregulated, thus leading to upregulation of various inflammatory cytokines and lipid accumulation. On the other hand, nonalcoholic fatty liver disease (NAFLD), characterized by excess lipid accumulation, and inflammatory injury in liver, is becoming an epidemic disease, globally. In the present study, we aimed to investigate the biological role and the underlying mechanisms of TREM-1 in NAFLD. upregulation of TREM-1 occurred in high-fat diet (HFD)-induced mice NAFLD model and oleic acid-treated HepG2 and primary mouse hepatocytes cell model at messenger RNA and protein levels. Functional studies established that overexpression of TREM-1 displayed hyperlipidemia, and increased in inflammatory indicators and lipid accumulation-related genes, which was ameliorated by knockdown of TREM-1. Our results also showed that obvious lipid accumulation and inflammatory injury occurred in the liver tissue of HFD-fed mice, while treatment with lentiviral vector short hairpin TREM showed marked improvement in tissue morphology and architecture and less lipid accumulation, thus deciphering the mechanism through which knockdown of TREM-1 ameliorated the inflammatory response and lipid accumulation of NAFLD mice through inactivation of the nuclear factor-κB (NF-κB) and PI3K/AKT signal pathways, respectively. In conclusion, TREM-1/NF-κB and TREM-1/PI3K/AKT axis could be an important mechanism in ameliorating the inflammatory response and lipid accumulation, respectively, thus shedding light on the development of novel therapeutics to the treatment of NAFLD.

Upregulated long noncoding RNA LOC105375913 induces tubulointerstitial fibrosis in focal segmental glomerulosclerosis

Tubulointerstitial fibrosis impacts renal prognosis of focal segmental glomerulosclerosis (FSGS). Based on transcriptomic analysis, we found that the level of LOC105375913 was increased in tubular cells of FSGS patients. C3a induced the expression of LOC105375913, which promoted the expression of fibronectin and collagen I in tubular cells. Silence of snail reversed the level of fibronectin and collagen I in cells overexpressing LOC105375913. MiR-27b was predicted and confirmed to regulate the expression of snail in tubular cells, and LOC105375913 contained the response element of miR-27b. The competitive binding between LOC105375913 and miR-27b increased the level of snail and promoted fibrogenesis in tubular cells. Upstream, p38 and XBP-1s regulated the expression of LOC105375913. Inhibition of p38 or silence of XBP-1s decreased the level of LOC105375913, and suppressed the expression of snail, fibronectin and collagen I in tubular cells treated with C3a. Overexpression of LOC105375913 decreased the level of miR-27b, increased the level of snail and caused tubulointerstitial fibrosis in mice. In conclusion, the activation of C3a/p38/XBP-1s pathway induces the expression of LOC105375913 in tubular cells, and LOC105375913 increases the level of snail and induces tubulointerstitial fibrosis through competitive binding of miR-27b in tubular cells of FSGS patients.

Oxidative stress mediated by lipid metabolism contributes to high glucose-induced senescence in retinal pigment epithelium

Retinal pigment epithelium (RPE) dysfunction is thought to increase the risk of the development and progression of diabetic retinopathy (DR), the leading cause of blindness. However, the molecular mechanism behind high glucose-induced RPE cell damage is still blurred. We reported that ARPE-19 exposed to 25 mM glucose for 48 h did not induce apoptosis, but senescence validated by SA-β-Gal staining, p21 expression and cell cycle distribution. High glucose also increased oxidant species that exerted a pivotal role in senescence, which could be relieved by the treatment with antioxidant N-acetylcysteine (NAC). The accumulation of lipid droplets and the increase of lipid oxidation were also observed in ARPE-19 treated with high glucose. And the supplementation of free fatty acids (FFAs) indicated that lipid metabolism was associated with the generation of hydrogen peroxide (H₂O₂) and subsequent senescence in ARPE-19. PI3K/Akt/mTOR signaling pathway was shown to be responsible for the accumulation of intracellular lipids by regulating fatty acid synthesis, which in turn controlled senescence. Furthermore, high glucose induced autophagy in ARPE-19 with the treatment of glucose for 48 h, and autophagy inhibitor hydroxychloroquine (HCQ) or bafilomycin further aggravated the senescence, accompanying by an increase in oxidant species. Whereas, prolonged high glucose exposure inhibited autophagy and increased apoptotic cells. Experiments above provide evidence that lipid metabolism plays an important role in oxidative stressed senescence of RPE.

Effect of Qufengtongluo Decoction on PI3K/Akt Signaling Pathway in the Kidney of Type 2 Diabetes Mellitus Rat (GK Rat) with Diabetic Nephropathy

Qufengtongluo (QFTL) decoction is an effective treatment for diabetic nephropathy (DN). However, the underlying molecular mechanism is still unclear. In this study, we try to investigate whether QFTL decoction acts via inhibiting PI3K/Akt signaling pathway. Twenty-four GK rats were randomly divided into 3 groups: blank group, sham-operated group, and QFTL group. After model establishment, rats in QFTL group were given QFTL decoction by gavage, while the rest were given pure water. During the 8-week intervention, 24 hr urinal protein was measured every 2-3 weeks. After intervention, kidneys were removed for pathological smear, quantitative real-time PCR, and western blotting to detect expression levels of p-PI3K, p-Akt, PTEN, TGF-β, PI3K mRNA, Akt mRNA, PTEN mRNA, and TGF-β mRNA. QFTL group showed a slighter degree of renal fibrosis in Masson and PASM staining and a greater reduction of 24 hr urinal protein than blank group. Compared to blank group, expression levels of p-PI3K, p-Akt, PI3K mRNA, and Akt mRNA were lower in QFTL group, while expression levels of PTEN and PTEN mRNA were higher. Besides, TGF-β was downregulated by QFTL decoction. In conclusion, this study suggests that QFTL decoction might inhibit PI3K/Akt signaling pathway via activating PTEN and inhibiting TGF-β.

Human Peritoneal Mesothelial Cell Death Induced by High-Glucose Hypertonic Solution Involves Ca2+ and Na+ Ions and Oxidative Stress with the Participation of PKC/NOX2 and PI3K/Akt Pathways

Chronic peritoneal dialysis (PD) therapy is equally efficient as hemodialysis while providing greater patient comfort and mobility. Therefore, PD is the treatment of choice for several types of renal patients. During PD, a high-glucose hyperosmotic (HGH) solution is administered into the peritoneal cavity to generate an osmotic gradient that promotes water and solutes transport from peritoneal blood to the dialysis solution. Unfortunately, PD has been associated with a loss of peritoneal viability and function through the generation of a severe inflammatory state that induces human peritoneal mesothelial cell (HPMC) death. Despite this deleterious effect, the precise molecular mechanism of HPMC death as induced by HGH solutions is far from being understood. Therefore, the aim of this study was to explore the pathways involved in HGH solution-induced HPMC death. HGH-induced HPMC death included influxes of intracellular Ca²⁺ and Na⁺. Furthermore, HGH-induced HPMC death was inhibited by antioxidant and reducing agents. In line with this, HPMC death was induced solely by increased oxidative stress. In addition to this, the cPKC/NOX2 and PI3K/Akt intracellular signaling pathways also participated in HGH-induced HPMC death. The participation of PI3K/Akt intracellular is in agreement with previously shown in rat PMC apoptosis. These findings contribute toward fully elucidating the underlying molecular mechanism mediating peritoneal mesothelial cell death induced by high-glucose solutions during peritoneal dialysis.

Endoplasmic Reticulum Stress in the Diabetic Kidney, the Good, the Bad and the Ugly

Diabetic kidney disease is the leading worldwide cause of end stage kidney disease and a growing public health challenge. The diabetic kidney is exposed to many environmental stressors and each cell type has developed intricate signaling systems designed to restore optimal cellular function. The unfolded protein response (UPR) is a homeostatic pathway that regulates endoplasmic reticulum (ER) membrane structure and secretory function. Studies suggest that the UPR is activated in the diabetic kidney to restore normal ER function and viability. However, when the cell is continuously stressed in an environment that lies outside of its normal physiological range, then the UPR is known as the ER stress response. The UPR reduces protein synthesis, augments the ER folding capacity and downregulates mRNA expression of genes by multiple pathways. Aberrant activation of ER stress can also induce inflammation and cellular apoptosis, and modify signaling of protective processes such as autophagy and mTORC activation. The following review will discuss our current understanding of ER stress in the diabetic kidney and explore novel means of modulating ER stress and its interacting signaling cascades with the overall goal of identifying therapeutic strategies that will improve outcomes in diabetic nephropathy.

Phosphorylation of PRAS40-Thr246 involved in renal lipid accumulation of diabetes

Lipid accumulation of kidney is a threat to renal physiological function of diabetes. The previous studies on diabetic nephropathy have demonstrated that activated Akt was involved in renal lipogenesis through enhancing transcription factor SREBP-1. PRAS40 is one of the downstream targets of activated Akt that was reported to involve in lipid metabolism in hepatic cells. However, it is still not clear whether PRAS40 is also involved in the renal lipogenesis of diabetes. Our study revealed that phosphorylation of PRAS40-Thr246 known as inactivated style increased in renal tubular cells of diabetic rats accompanied with over-expression of phospho-Akt, SREBP-1, and ADRP. In addition, in vitro experiment also found that high glucose enhanced expression of phospho-PRAS40-Thr246 followed by increased SREBP-1 and lipid droplets in HKC cells. After treated with LY294002, high glucose-induced HKC cells showed decreased phospho-PRAS40-Thr246, phospho-Akt-Ser473, and SREBP-1. Furthermore, wild type PRAS40 vector-caused increased phospho-PRAS40-Thr246 exaggerated lipid deposits in high glucose-treated HKC cells, which was effectively prevented in cells transfected with mutant PRAS40 vector (T246A). These above data suggested that phosphorylation of PRAS40-Thr246 mediated abnormal lipid metabolism in kidney of diabetes and might be the potential target for treating lipogenesis of diabetic nephropathy.

Tetramethylpyrazine reduces glucose and insulin-induced activation of hepatic stellate cells by inhibiting insulin receptor-mediated PI3K/AKT and ERK pathways

Hepatic stellate cell (HSC) activation is the central event during liver fibrogenesis. Metabolic syndrome characterized by hyperglycemia and hyperinsulinemia contributes to nonalcoholic steatohepatitis-associated liver fibrosis. This study was to investigate the effects of tetramethylpyrazine (TMP) on HSC activation induced by glucose and insulin (Glu/Ins) and the underlying mechanisms. Results showed that Glu/Ins significantly stimulated proliferation, invasion, adhesion, and extracellular matrix (ECM) production in HSCs. TMP inhibited HSC proliferation, invasion and adhesion, and reduced the expression of marker genes related to HSC activation in Glu/Ins-activated HSCs. Mechanistic evidence revealed that TMP reduced insulin receptor (InsR) expression and blocked the downstream phosphatidylinositol-3-kinase (PI3K)/AKT and extracellular signal-regulated kinase (ERK) cascades, which was required for TMP attenuation of HSC activation. Moreover, TMP modulated the genes relevant to ECM homeostasis favoring ECM degradation. It could be concluded that TMP inhibited Glu/Ins-stimulated HSC activation and ECM production by inhibiting InsR-mediated PI3K/AKT and ERK pathways.

Phospho-mTOR: a novel target in regulation of renal lipid metabolism abnormality of diabetes

The activation of Akt has been proved to involve in the lipogenesis of diabetic nephropathy. However, it's still not clear whether mTOR, another main gene in PI3K/Akt pathway, is also involved in the renal lipogenesis of diabetes. In the present study, it was revealed that the phosphorylation of mTOR was up-regulated in the renal tubular cells of diabetic rats, followed by the over-expression of SREBP-1, ADRP and lipogenesis. Again, high glucose increased the expression of phospho-mTOR accompanied with SREBP-1 and ADRP up-regulation and lipid accumulation in HKC cells. Rapamycin, known as mTOR inhibitor, was used to inhibit the activation of mTOR, which prevented effectively high glucose-induced SREBP-1 up-regulation and lipogenesis in HKC cells. Furthermore, high glucose-stimulated HKC cells transfected with wild-type mTOR vector showed the enhanced SREBP-1 and lipid droplets, however, TE mTOR vector (kinase dead)-transfected HKC cells presented resistance to high glucose and decreased SREBP-1 expression and lipogenesis. These above data suggested that phospho-mTOR mediated lipid accumulation in renal tubular cells of diabetes and might be the potential targets for treating lipogenesis of diabetic nephropathy.

Intermittent injections of osteocalcin reverse autophagic dysfunction and endoplasmic reticulum stress resulting from diet-induced obesity in the vascular tissue via the NFκB-p65-dependent mechanism

The osteoblast-specific secreted molecule osteocalcin behaves as a hormone-regulating glucose and lipid metabolism, but the role of osteocalcin in cardiovascular disease (CVD) is not fully understood. In the present study, we investigated the effect of osteocalcin on autophagy and endoplasmic reticulum (ER) stress secondary to diet-induced obesity in the vascular tissue of mice and in vascular cell models and clarified the intracellular events responsible for osteocalcin-mediated effects. The evidences showed that intermittent injections of osteocalcin in mice fed the high-fat diet were associated with a reduced body weight gain, decreased blood glucose and improved insulin sensitivity compared with mice fed the high-fat diet receiving vehicle. Simultaneously, the administration of osteocalcin not only attenuated autophagy and ER stress but also rescued impaired insulin signaling in vascular tissues of mice fed a high-fat diet. Consistent with these results in vivo, the addition of osteocalcin reversed autophagy and ER stress and restored defective insulin sensitivity in vascular endothelial cells (VECs) and vascular smooth muscle cells (VSMCs) in the presence of tunicamycin or in knockout XBP-1 (a transcription factor which mediates ER stress response) cells or in Atg7(-/-) cells. The protective effects of osteocalcin were nullified by suppression of Akt, mammalian target of rapamycin (mTOR) or nuclear factor kappa B (NFκB), suggesting that osteocalcin inhibits autophagy, ER stress and improves insulin signaling in the vascular tissue and cells under insulin resistance in a NFκB-dependent manner, which may be a promising therapeutic strategies of cardiovascular dysfunction secondary to obesity.

Osteocalcin reverses endoplasmic reticulum stress and improves impaired insulin sensitivity secondary to diet-induced obesity through nuclear factor-κB signaling pathway

Osteocalcin, a synthetic osteoblast-specific protein, has recently emerged as an important regulator of energy metabolism, but the underlying mechanisms are not fully understood. In the present study, mice fed a high-fat diet and receiving osteocalcin showed reduced body weight gain, less fat pad gain, and improved insulin sensitivity as well as increased energy expenditure compared with mice fed a high-fat diet and receiving vehicle. Meanwhile, increased endoplasmic reticulum (ER) stress, defective insulin signaling, and mitochondrial dysfunction induced by obesity were also effectively alleviated by treatment with osteocalcin. Consistent with these findings, the addition of osteocalcin to the culture medium of 3T3-L1 adipocytes, Fao liver cells, and L6 muscle cells markedly reduced ER stress and restored insulin sensitivity. These effects were nullified by blockade of nuclear factor-κB (NF-κB) or phosphatidylinositol 3-kinase but not by U0126, a mitogen-activated protein kinase inhibitor, indicating the causative role of phosphatidylinositol 3-kinase/NF-κB in action of osteocalcin. In addition, the reversal effects of osteocalcin in cells deficient in X-box-binding protein-1, a transcription factor that modulates ER stress response, further confirmed its protective role against ER stress and insulin resistance. Our findings suggest that osteocalcin attenuates ER stress and rescues impaired insulin sensitivity in insulin resistance via the NF-κB signaling pathway, which may offer novel opportunities for treatment of obesity and diabetes.