Yujia Yuan

Regulation of SIRT1 in aging: Roles in mitochondrial function and biogenesis

Aging is a degenerative process associated with cumulative damage, which leads to cellular dysfunction, tissue failure, and disorders of body function. Silent information regulator-1, also known as sirtuin 1 (SIRT1), has been reported to be involved in the regulation of various important biological processes, including inflammation, mitochondrial biogenesis, as well as cell senescence and consequent aging. The level of SIRT1 is decreased in both transcriptional and postranscriptional conditions during aging, accompanied by attenuated mitochondrial biogenesis, an important component of aging-related diseases. Over the last decade, extensive studies have demonstrated that SIRT1 can activate several transcriptional factors, such as peroxisome proliferator activated receptor γ co-activator 1α (PGC-1α) and hypoxia-inducible factor 1α (HIF-1α) resulting in ameliorated mitochondria biogenesis and extended life span. In this review, we focus on the molecular regulation of SIRT1 and its role in mitochondrial biogenesis during in the context of aging and aging-related diseases.

Serum metabolic variables associated with impaired glucose tolerance induced by high-fat-high-cholesterol diet in Macaca mulatta

Dyslipidemia caused by ‘Western-diet pattern’ is a strong risk factor for the onset of diabetes. This study aimed to disclose the relationship between the serum metabolite changes induced by habitual intake of high-fat and high-cholesterol (HFHC) diet and the development of impaired glucose tolerance (IGT) and insulin resistance through animal models of Macaca mulatta. Sixteen M. mulatta (six months old) were fed a control diet or a HFHC diet for 18 months. The diet effect on serum metabolic profiles was investigated by longitudinal research. Islet function was assessed by intravenous glucose tolerance and hyperinsulinemic-euglycemic clamp test. Metabonomics were determined by 1 H proton nuclear magnetic resonance spectroscopy. Prolonged diet-dependent hyperlipidemia facilitated visceral fat accumulation in liver and skeletal muscle and disorder of glucose homeostasis in juvenile monkeys. Glucose disappearance rate (KGlu) and insulin response to the glucose challenge effects in HFHC monkeys were significantly lower than in control monkeys. Otherwise, serum trimethylamine-N-oxide (TMAO), lactate and leucine/isoleucine were significantly higher in HFHC monkeys. Sphingomyelin and choline were the most positively correlated with KGlu (R2 = 0.778), as well as negative correlation (R2 = 0.64) with total cholesterol. The HFHC diet induced visceral fat, abnormal lipid metabolism and IGT prior to weight gain and body fat content increase in juvenile monkeys. We suggest that increased serum metabolites, such as TMAO, lactate, branched-chain amino acids and decreased sphingomyelin and choline, may serve as possible predictors for the evaluation of IGT and insulin resistance risks in the prediabetic state.

Mesenchymal stem cell-conditioned media ameliorate diabetic endothelial dysfunction by improving mitochondrial bioenergetics via the Sirt1/AMPK/PGC-1α pathway

Vasculopathy is a major complication of diabetes. Impaired mitochondrial bioenergetics and biogenesis due to oxidative stress are a critical causal factor for diabetic endothelial dysfunction. Sirt1, an NAD+-dependent enzyme, is known to play an important protective role through deacetylation of many substrates involved in oxidative phosphorylation and reactive oxygen species generation. Mesenchymal stem cell-conditioned medium (MSC-CM) has emerged as a promising cell-free therapy due to the trophic actions of mesenchymal stem cell (MSC)-secreted molecules. In the present study, we investigated the therapeutic potential of MSC-CMs in diabetic endothelial dysfunction, focusing on the Sirt1 signalling pathway and the relevance to mitochondrial function. We found that high glucose-stimulated MSC-CM attenuated several glucotoxicity-induced processes, oxidative stress and apoptosis of endothelial cells of the human umbilical vein. MSC-CM perfusion in diabetic rats ameliorated compromised aortic vasodilatation and alleviated oxidative stress in aortas. We further demonstrated that these effects were dependent on improved mitochondrial function and up-regulation of Sirt1 expression. MSC-CMs activated the phosphorylation of phosphoinositide 3-kinase (PI3K) and protein kinase B (Akt), leading to direct interaction between Akt and Sirt1, and subsequently enhanced Sirt1 expression. In addition, both MSC-CM and Sirt1 activation could increase the expression of peroxisome proliferator-activated receptor γ co-activator-1α (PGC-1α), as well as increase the mRNA expression of its downstream, mitochondrial, biogenesis-related genes. This indirect regulation was mediated by activation of AMP-activated protein kinase (AMPK). Overall our findings indicated that MSC-CM had protective effects on endothelial cells, with respect to glucotoxicity, by ameliorating mitochondrial dysfunction via the PI3K/Akt/Sirt1 pathway, and Sirt1 potentiated mitochondrial biogenesis, through the Sirt1/AMPK/PGC-1α pathway.

Mesenchymal Stem Cells Ameliorated Glucolipotoxicity in HUVECs through TSG-6

Glucolipotoxicity is one of the critical causal factors of diabetic complications. Whether mesenchymal stem cells (MSCs) have effects on glucolipotoxicity in human umbilical vein endothelial cells (HUVECs) and mechanisms involved are unclear. Thirty mM glucose plus 100 μM palmitic acid was used to induce glucolipotoxicity in HUVECs. MSCs and HUVECs were co-cultured at the ratio of 1:5 via Transwell system. The mRNA expressions of inflammatory factors were detected by RT-qPCR. The productions of reactive oxygen species (ROS), cell cycle and apoptosis were analyzed by flow cytometry. The tumor necrosis factor-α stimulated protein 6 (TSG-6) was knockdown in MSCs by RNA interference. High glucose and palmitic acid remarkably impaired cell viability and tube formation capacity, as well as increased the mRNA expression of inflammatory factors, ROS levels, and cell apoptosis in HUVECs. MSC co-cultivation ameliorated these detrimental effects in HUVECs, but no effect on ROS production. Moreover, TSG-6 was dramatically up-regulated by high glucose and fatty acid stimulation in both MSCs and HUVECs. TSG-6 knockdown partially abolished the protection mediated by MSCs. MSCs had protective effects on high glucose and palmitic acid induced glucolipotoxicity in HUVECs, and TSG-6 secreted by MSCs was likely to play an important role in this process.

Phloretin attenuates hyperuricemia-induced endothelial dysfunction through co-inhibiting inflammation and GLUT9-mediated uric acid uptake

Hyperuricemia is an important risk factor for cardiovascular and renal diseases. Phloretin had shown antioxidant and anti‐inflammatory properties, but its role in endothelial injury is rarely reported. In this study, we aimed to investigate the protective effect of phloretin on UA‐induced injury in human umbilical vein endothelial cells. The effects of UA and phloretin on cell viability, inflammation, THP‐1 monocyte adhesion, endothelial cell tube formation, GLUT9 expression and UA uptake in human umbilical vein endothelial cells were evaluated. The changes of nuclear factor‐kappa B/extracellular regulated protein kinases signalling were also analysed. Our results showed that UA reduced cell viability and tube formation, and increased inflammation and monocytes adhesion in human umbilical vein endothelial cells in a dose‐dependent manner. In contrast, phloretin significantly attenuated pro‐inflammatory factors expression and endothelial injury induced by UA. Phloretin inhibited the activation of extracellular regulated protein kinases/nuclear factor‐kappa B pathway, and reduced GLUT9 and it mediated UA uptake in human umbilical vein endothelial cells. These results indicated that phloretin attenuated UA‐induced endothelial injury via a synergic mechanism including direct anti‐inflammatory effect and lowering cellular UA uptake. Our study suggested that phloretin might be a promising therapy for hyperuricemia‐related cardiovascular diseases.

A preclinical evaluation of alternative site for islet allotransplantation

The bone marrow cavity (BMC) has recently been identified as an alternative site to the liver for islet transplantation. This study aimed to compare the BMC with the liver as an islet allotransplantation site in diabetic monkeys. Diabetes was induced in Rhesus monkeys using streptozocin, and the monkeys were then divided into the following three groups: Group1 (islets transplanted in the liver with immunosuppressant), Group 2 (islets transplanted in the tibial BMC), and Group 3 (islets transplanted in the tibial BMC with immunosuppressant). The C-peptide and blood glucose levels were preoperatively measured. An intravenous glucose tolerance test (IVGTT) was conducted to assess graft function, and complete blood cell counts were performed to assess cell population changes. Cytokine expression was measured using an enzyme-linked immune sorbent assay (ELISA) and MILLIPLEX. Five monkeys in Group 3 exhibited a significantly increased insulin-independent time compared with the other groups (Group 1: 78.2 ± 19.0 days; Group 2: 58.8 ± 17.0 days; Group 3: 189.6 ± 26.2 days) and demonstrated increases in plasma C-peptide 4 months after transplantation. The infusion procedure was not associated with adverse effects. Functional islets in the BMC were observed 225 days after transplantation using the dithizone (DTZ) and insulin/glucagon stains. Our results showed that allogeneic islets transplanted in the BMC of diabetic Rhesus monkeys remained alive and functional for a longer time than those transplanted in the liver. This study was the first successful demonstration of allogeneic islet engraftment in the BMC of non-human primates (NHPs).

Polyacetylene glycoside attenuates ischemic kidney injury by co-inhibiting inflammation, mitochondria dysfunction and lipotoxicity

Aims: Ischemic acute kidney injury (AKI) is a serious clinical problem and no efficient therapeutics is available in clinic now. Natural polyacetylene glycosides (PGAs) had shown antioxidant and anti‐inflammatory properties, but their effects on kidney injury have not been evaluated. This study aimed to investigate the protective effect of PGA on ischemic kidney injury in renal tubular epithelial cells (TECs) and mice. Main methods: Hypoxic HK‐2 cells and renal ischemia/reperfusion injury (IRI) mice were treated with PGA from Coreopsis tinctoria, and the cell viability, renal function, apoptosis, inflammation, mitochondrial injury, lipids metabolism were analyzed. Key findings: In vitro results showed that PGA improved cell viability and reduced oxidative stress, pro‐apoptotic/pro‐inflammatory factors expression and NF&kgr;B activation in TECs under hypoxia/reperfusion (H/R). Moreover, PGA reduced mitochondria oxidative stress and improved ATP production, &Dgr;&PSgr;m and mitochondria biogenesis, and inhibited lipids uptake, biosynthesis and accumulation in hypoxic TECs. In vivo, PGA significantly attenuated kidney injury and reduced blood urea nitrogen (BUN), serum creatinine (CREA) and urinary albumin (Alb), and increased creatinine clearance (CC) in IRI mice. PGA also decreased cell apoptosis, mitochondria oxidative stress, inflammatory response and lipid droplets accumulation, and promoted ATP generation in kidney of IRI mice. Significance: Our results proved that PGA ameliorated ischemic kidney injury via synergic anti‐inflammation, mitochondria protection and anti‐lipotoxicity actions, and it might be a promising multi‐target therapy for ischemic AKI. Graphical abstract: Figure. No caption available.

MSCs protect endothelial cells from inflammatory injury partially by secreting STC1

&NA; Inflammatory factors play an important role in the pathogenesis of diabetic vascular complications. Considerable interest in the therapeutic potential of mesenchymal stem cells (MSCs) has recently arisen. The purposes of this study were to investigate the effects of MSCs on endothelial cells under inflammatory conditions and to determine the relevant mechanism underlying these effects. In vitro, after TNF‐&agr; stimulation, MSCs‐CM treatment significantly restored cell viability, reduced THP‐1 cell adhesion and enhanced tube formation capacity via inhibiting ROS overproduction and NF‐&kgr;B activation, subsequently down‐regulating adhesion molecules and chemokines. These effects may be partially due to the up‐regulation of uncoupling protein 2 (UCP2) in HUVECs that was induced by the secretion of stanniocalcin 1 (STC1) from MSCs. In vivo, MSCs transplantation ameliorated the progression of diabetes‐associated vascular dysfunction by reducing ROS production and down‐regulating the expression of adhesion molecules. These results suggest that MSCs protect HUVECs from inflammatory injury partially by secreting STC1. MSCs may be a potential therapeutic approach for the treatment of diabetic vascular complications. HighlightsMSCs ameliorate inflammatory factor induced endothelial damage.MSCs protect HUVECs from inflammatory injury partially by secreting STC1.STC1 up‐regulated UCP2 in HUVECs and subsequently reduced ROS accumulation and inflammation cascade.MSCs may be potential for diabetic vascular complications therapy.

Mesenchymal stem cells ameliorate hyperglycemia-induced endothelial injury through modulation of mitophagy

Mitochondrial dysfunction and excessive mitochondrial reactive oxygen species (ROS) are fundamental contributors to endothelial injury in diabetic states. Mesenchymal stem cells (MSCs) have exhibited an extraordinary cytoprotective effect that extends to the modulation of mitochondrial homeostasis. However, the underlying mechanisms have not been clearly defined. Emerging evidence has suggested that mitophagy could counteract mitochondrial-derived oxidative stress through the selective elimination of impaired or dysfunctional mitochondria. Therefore, we investigated whether MSCs could ameliorate high-glucose-induced endothelial injury through the modulation of mitophagy. We observed that exposure of human umbilical vein endothelial cells (HUVECs) to high glucose triggers mitochondrial impairment with excessive mitochondrial fragmentation and ROS generation, loss of membrane potential and reduced ATP production. Furthermore, mitophagy was blunted upon high glucose insult, which accelerated dysfunctional mitochondrial accumulation, initiating the mitochondrial apoptotic pathway and, eventually, endothelial dysfunction. MSCs treatment notably attenuated these perturbations accompanied by an enhancement of Pink1 and Parkin expression, whereas these beneficial effects of MSCs were abolished when either Pink1 or Parkin was knocked down. In aortas of diabetic rats, defective mitophagy was observed, which coincided with marked mitochondrial dysfunction. Ultrastructurally, RAECs from diabetic rats revealed a significant reduction in autophagic vacuoles and a marked increase in fragmented mitochondria. Importantly, the infusion of MSCs restored Pink1/Parkin-mediated mitophagy, ameliorated mitochondrial dysfunction and attenuated apoptosis in endothelial cells in diabetic rats. These results suggest that MSCs may protect endothelial cells from hyperglycemia-induced injury by ameliorating mitochondrial dysfunction via Pink1/Parkin –mediated mitophagy

Glucocorticoid treatment facilitates development of a metabolic syndrome in ovariectomized Macaca Mulatta fed a high fat diet

HighlightsWe reported for the first time that the endocrine and physiological changes in response to chronic and high dose of GCs in non‐human primates, and the effects of withdrawal of a long‐term treatment, which led to recovery from metabolic disorders.We used ovariectomized monkeys to mimic the situation of perimenopausal and postmenopausal women, and might be used as potential models of Cushing’s syndrome or MetS in non‐human primates.The lipid and glucose related factors including leptin and GLUT4 play important roles in the GCs effect. Abstract Metabolic syndrome (MetS) is characterized by a cluster of key features, which include abdominal obesity, insulin resistance, hypertension, and dyslipidemia. The aim of this study was to assess the impact of elevated glucocorticoid levels on the development of MetS in middle‐aged female rhesus monkeys (Macaca Mulatta) after ovariectomy. Six female ovariectomized rhesus monkeys (9–13 years) were randomly assigned to either a control group (normal diet, n = 3) or a group in which MetS was facilitated (n = 3). The MetS group fed with HFD (15% fat) and received oral prednisone acetate treatment (50 mg/day). After 24 months, the GCs treatment was withdrawn with continuation of high‐fat feeding for a further 12 months. After 24 months, the MetS group displayed a significant increase in body weight and abdominal circumference. Additionally, the MetS animals displayed abnormal serum lipids, insulin resistance and impaired glucose tolerance. Histology of liver biopsies indicated marked accumulation of lipid droplets in hepatocytes of MetS animals. Withdrawal of GCs treatment led to recovery from above‐mentioned metabolic disorders. Whereas GCs treatment increased leptin expression, it lowered expression of adiponectin and other factors in adipose tissue. Expression of Hydroxy‐steroid dehydrogenase‐1 and glucose transporter type‐4 in the livers of MetS animals were reduced. We conclude that in the context of high fat diet, high levels of exogenous GCs contribute to the development of MetS in non‐human primates.