Guangjie Wu

BACKGROUND AND PURPOSE: Recent reports have suggested that salidroside could protect cardiomyocytes from oxidative injury and stimulate glucose uptake in skeletal muscle cells by activating AMP-activated protein kinase (AMPK). The aim of this study was to evaluate the therapeutic effects of salidroside on diabetic mice and to explore the underlying mechanisms. EXPERIMENTAL APPROACH: The therapeutic effects of salidroside on type 2 diabetes were investigated. Increasing doses of salidroside (25, 50 and 100 mg·kg(-1) ·day(-1)) were administered p.o. to db/db mice for 8 weeks. Biochemical analysis and histopathological examinations were conducted to evaluate the therapeutic effects of salidroside. Primary cultured mouse hepatocytes were used to further explore the underlying mechanisms in vitro. KEY RESULTS: Salidroside dramatically reduced blood glucose and serum insulin levels and alleviated insulin resistance. Hypolipidaemic effects and amelioration of liver steatosis were observed after salidroside administration. In vitro, salidroside dose-dependently induced an increase in the phosphorylations of AMPK and PI3K/Akt, as well as glycogen synthase kinase 3β (GSK3β) in hepatocytes. Furthermore, salidroside-stimulated AMPK activation was found to suppress the expression of PEPCK and glucose-6-phosphatase. Salidroside-induced AMPK activation also resulted in phosphorylation of acetyl CoA carboxylase, which can reduce lipid accumulation in peripheral tissues. In isolated mitochondria, salidroside inhibited respiratory chain complex I and disturbed oxidation/phosphorylation coupling and moderately depolarized the mitochondrial membrane potential, resulting in a transient increase in the AMP/ATP ratio. CONCLUSIONS AND IMPLICATIONS: Salidroside exerts an antidiabetic effect by improving the cellular metabolic flux through the activation of a mitochondria-related AMPK/PI3K/Akt/GSK3β pathway.

Diabetes is a recognized high-risk factor for the development of atherosclerosis, in which macroautophagy/autophagy is emerging to play essential roles. The retention of low-density lipoprotein (LDL) particles in subendothelial space following transcytosis across the endothelium is the initial step of atherosclerosis. Here, we identified that high glucose could promote atherosclerosis by stimulating transcytosis of LDL. By inhibiting AMPK-MTOR-PIK3C3 pathway, high glucose suppresses the CAV-CAVIN-LC3B-mediated autophagic degradation of CAV1; therefore, more CAV1 is accumulated in the cytosol and utilized to form more caveolae in the cell membrane and facilitates the LDL transcytosis across endothelial cells. For a proof of concept, higher levels of lipids were accumulated in the subendothelial space of umbilical venous walls from pregnant women with gestational diabetes mellitus (GDM), compared to those of pregnant women without GDM. Our results reveal that high glucose stimulates LDL transcytosis by a novel CAV1-CAVIN1-LC3B signaling-mediated autophagic degradation pathway. ABBREVIATIONS: ; CAV1: caveolin-1; CAVIN1: caveolae associated protein 1; CSD: the CAV1 scaffolding domain; GDM: gestational diabetes mellitus; IMD: intramembrane domain; LIR: LC3-interacting region; MAP1LC3/LC3: microtubule- associated protein 1 light chain 3; MFI: mean fluorescence intensity; MTOR: mechanistic target of rapamycin kinase; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; SQSTM1/p62: sequestosome 1.

Oxidized low density of lipoprotein (oxLDL) is the major lipid found in atherosclerotic lesion and elevated plasma oxLDL is recognized to be a risk factor of atherosclerosis. Whether plasma oxLDL could be transported across endothelial cells and initiate atherosclerotic changes remains unknown. In an established in vitro cellular transcytosis model, the present study found that oxLDL could traffic across vascular endothelial cells and further that the regulation of endogenous ceramide production by ceramide metabolizing enzyme inhibitors significantly altered the transcytosis of oxLDL across endothelial cells. It was found that acid sphingomyelinase inhibitor, desipramine (DES), and de novo ceramide synthesis inhibitor, myriocin (MYR), both decreasing the endogenous ceramide production, significantly inhibited the transcytosis of oxLDL. Ceramidase inhibitor, N-oleoylethanolamine (NOE), and sphingomyelin synthase inhibitor, O-Tricyclo[5.2.1.02,6]dec-9-yl dithiocarbonate potassium salt (D609), both increasing the endogenous ceramide production, significantly upregulated the transcytosis of oxLDL. In vivo, injection of fluorescence labeled oxLDL into mice body also predisposed to the subendothelial retention of these oxidized lipids. The observations provided in the present study demonstrate that endogenous ceramide contributes to the transcytosis of oxLDL across endothelial cells and promotes the initiating step of atherosclerosis-the subendothelial retention of lipids in vascular wall.