Suppression of Endothelial AGO1 Promotes Adipose Tissue Browning and Improves Metabolic Dysfunction

Abstract

Background: Metabolic disorders such as obesity and diabetes mellitus can cause dysfunction of endothelial cells (ECs) and vascular rarefaction in adipose tissues. However, the modulatory role of ECs in adipose tissue function is not fully understood. Other than vascular endothelial growth factor–vascular endothelial growth factor receptor-mediated angiogenic signaling, little is known about the EC-derived signals in adipose tissue regulation. We previously identified Argonaute 1 (AGO1; a key component of microRNA-induced silencing complex) as a crucial regulator in hypoxia-induced angiogenesis. In this study, we intend to determine the AGO1-mediated EC transcriptome, the functional importance of AGO1-regulated endothelial function in vivo, and the relevance to adipose tissue function and obesity. Methods: We generated and subjected mice with EC-AGO1 deletion (EC-AGO1-knockout [KO]) and their wild-type littermates to a fast food–mimicking, high-fat high-sucrose diet and profiled the metabolic phenotypes. We used crosslinking immunoprecipitation- and RNA-sequencing to identify the AGO1-mediated mechanisms underlying the observed metabolic phenotype of EC-AGO1-KO. We further leveraged cell cultures and mouse models to validate the functional importance of the identified molecular pathway, for which the translational relevance was explored using human endothelium isolated from healthy donors and donors with obesity/type 2 diabetes mellitus. Results: We identified an antiobesity phenotype of EC-AGO1-KO, evident by lower body weight and body fat, improved insulin sensitivity, and enhanced energy expenditure. At the organ level, we observed the most significant phenotype in the subcutaneous and brown adipose tissues of KO mice, with greater vascularity and enhanced browning and thermogenesis. Mechanistically, EC-AGO1 suppression results in inhibition of thrombospondin-1 ( THBS1 /TSP1), an antiangiogenic and proinflammatory cytokine that promotes insulin resistance. In EC-AGO1-KO mice, overexpression of TSP1 substantially attenuated the beneficial phenotype. In human endothelium isolated from donors with obesity or type 2 diabetes mellitus, AGO1 and THBS1 are expressed at higher levels than the healthy controls, supporting a pathological role of this pathway. Conclusions: Our study suggests a novel mechanism by which ECs, through the AGO1-TSP1 pathway, control vascularization and function of adipose tissues, insulin sensitivity, and whole-body metabolic state.

Stress-induced RNA–chromatin interactions promote endothelial dysfunction

“…Single-cell RNA-seq was performed in human mesenteric arterial ECs in two healthy and two T2D donors, following the procedures we recently described 57 . Briefly, the arterial intima was gently dissociated from the arterial wall using a scalpel.…”

Angiogenesis in Adipose Tissue: The Interplay Between Adipose and Endothelial Cells

“…The suppression of argonaute (AGO1), a regulator of the endothelial hypoxia response, leads to a desuppression of VEGFA and thereby contributing to hypoxia-induced angiogenesis ( Chen et al, 2013 ). The EC-specific AGO1 knockout in mice resulted in lower body weight gain under a high-fat high-sucrose diet, which could be explained by the lower SAT and BAT mass ( Tang et al, 2020 ; Figure 2 ). The knockout mice had lower fasting glucose level and higher insulin sensitivity, as confirmed by oGTT, ITT, and higher phosphorylation levels of AKT and AMPK, hallmarks of insulin sensitivity, in SAT and BAT.…”

Capillary Rarefaction in Obesity and Metabolic Diseases—Organ-Specificity and Possible Mechanisms

“…In addition to individual miRNAs, Argonaute 1 (AGO1), one of the miRNA-induced silencing complex components, has been shown to regulate AT vascular density and browning [ 85 ]. EC-specific Ago1 -KO mice gained less fat mass, exhibited improved insulin sensitivity and energy metabolism concurrent with higher vascular density in sWAT and BAT when fed with a HFHS diet.…”

“…EC-specific Ago1 -KO mice gained less fat mass, exhibited improved insulin sensitivity and energy metabolism concurrent with higher vascular density in sWAT and BAT when fed with a HFHS diet. These mice also had enhanced browning of sWAT and improved thermogenesis in BAT [ 85 ].…”

“…Interestingly, the suppression of Vegfa expression in mice also led to a browning phenotype in WAT, suggesting that further studies are required to conclude the exact role of VEGFA in this phenomenon. Recently, endothelial protein argonaute-1 (AGO1) suppression was also shown to increase vascular density and AT browning [ 85 ].…”