A novel endothelium-independent effect of insulin on basal vascular tone in cafeteria diet-induced hypertensive rats

Hydrogen sulfide ameliorates hypertension and vascular dysfunction induced by insulin resistance in rats by reducing oxidative stress and activating eNOS

Hydrogen sulfide (H2S) is a gasotransmitter implied in metabolic diseases, insulin resistance, obesity, and type 2 Diabetes Mellitus. This study aimed to determine the effect of chronic administration of sodium hydrosulfide (NaHS; inorganic H2S donor), L-Cysteine (L-Cys; substrate of H2S producing enzymes) and DL-Propargylglycine (DL-PAG; cystathionine-gamma-lyase inhibitor) on the vascular dysfunction induced by insulin resistance in rat thoracic aorta. For this purpose, 72 animals were divided into two main sets that received: 1) tap water (control group; n = 12); and 2) fructose 15% w/v in drinking water [insulin resistance group (IR); n = 60] for 20 weeks. After 16 weeks, the group 2 was divided into five subgroups (n = 12 each), which received daily i. p. injections during 4 weeks of: 1) non-treatment (control); 2) vehicle (phosphate buffer saline; PBS, 1 ml/kg); 3) NaHS (5.6 mg/kg); 4) L-Cys (300 mg/kg); and (5) DL-PAG (10 mg/kg). Hemodynamic variables, metabolic variables, vascular function, ROS levels and the expression of p-eNOS and eNOS were determined. IR induced: 1) hyperinsulinemia; 2) increased HOMA-index; 3) decreased Matsuda index; 4) hypertension, vascular dysfunction, increased ROS levels; 5) increased iNOS, and 6) decreased CSE, p-eNOS and eNOS expression. Furthermore, IR did not affect contractile responses to norepinephrine. Interestingly, NaHS and L-Cys treatment, reversed IR-induced impairments and DL-PAG treatment decreased and increased the HOMA and Matsuda index, respectively. Taken together, these results suggest that NaHS and L-Cys decrease the metabolic and vascular alterations induced by insulin resistance by reducing oxidative stress and activating eNOS. Thus, hydrogen sulfide may have a therapeutic application.

Rictor maintains endothelial integrity under shear stress

Background: Endothelial injury induced by low shear stress (LSS) is an initiating factor in the pathogenesis of various cardiovascular diseases, including atherosclerosis, hypertension, and thrombotic diseases. Low shear stress activates the mammalian target of rapamycin complex 2 (mTORC2) signaling pathway. Rictor, the main constituent protein of mTORC2, is involved in vascular development. However, the impact of conditional Rictor ablation on endothelial homeostasis, especially on endothelial-specific markers, such as vascular endothelial-cadherin (VE-cadherin) and von Willebrand factor (VWF), under blood flow stimulation is unclear.

Objective: We aimed to investigate whether endothelial Rictor is involved in maintaining vascular endothelial integrity and the potential role of Rictor in atheroprone blood flow-mediated endothelial injury.

Methods and results: Immunofluorescence staining showed that endothelial Rictor was successfully knocked out in a mouse model. Scanning electron microscopy (EM) detection revealed disruption of the endothelial monolayer in the thoracic aorta of Rictor-deficient mice. Furthermore, scanning electron microscopy and transmission electron microscopy showed that Rictor deletion disrupted endothelial integrity and expanded cell junctions in the left common carotid artery region. In vitro, low shear stress disrupted actin filament polarity and the promoted the translocation of vascular endothelial-cadherin, the key component of adherens junctions (AJs) in human umbilical vein endothelial cells. After Rictor downregulation by small interfering RNA, the translocation of vascular endothelial-cadherin and stress fibers increased. Rictor knockdown inhibited low shear stress-induced von Willebrand factor upregulation, and downregulation of vascular endothelial-cadherin decreased low shear stress-induced von Willebrand factor expression. These results suggest that vascular endothelial-cadherin/von Willebrand factor is a possible mechanism mediated by Rictor in the pathological process of low shear stress-induced endothelial injury.

Conclusion: Rictor is a key protein that regulates endothelial integrity under vascular physiological homeostasis, and Rictor mediates low shear stress-induced endothelial injury by regulating adherens junctions and von Willebrand factor.