ROLE OF ASGR1 IN METABOLIC SYNDROME, OBESITY, AND ATHEROSCLEROSIS

Background and aim: Asialoglycoprotein receptor 1 (ASGR1), is primarily expressed on the surface of the hepatocytes where it recognizes glycoproteins with exposed galactose or N-acetylgalactoseamine as terminal glycan moiety. Following recognition, the receptor binds to the glycoproteins and removes them from circulation through endocytosis. ASGR1 loss-of-function mutations have been linked to a lower cardiovascular risk of 34%. Thus, the aim of this Ph.D. project was to investigate, in vivo, the impact of ASGR1 deficiency on modulating glycans and glycoproteins and lipid metabolism on cardiometabolic disorders such as obesity and atherosclerosis. Methods: Male mice, 2-month-old WT and ASGR1 knockout (ASGR1-/-), were fed with a high-fat diet for 20 weeks (HFD). In those mice, extensive metabolic analysis and immunophenotyping were performed. Furthermore, total plasma N-glycome and untargeted liver proteomics were carried out for functional analysis. Second, to evaluate the lipid metabolism and atherosclerosis, we backcrossed ASGR1-/- with LDL-R-/- and ApoE-/- mice, generating DKO mice lacking ASGR1-/-/LDL-R-/- or ASGR1-/-/ApoE-/-. Female and male, 2-month-old LDL-R-/- and ApoE-/- mice were fed with a high-cholesterol diet (WTD, western-type diet) for 16 weeks. In DKO mice models lipid profile, plaque formation, and composition were assessed. Additionally, the circulating immunophenotype was measured. Results: ASGR1-/- present similar trends with the WT mice for galactosylation in complex glycans as well as α-2,3-linked sialylation, on mono-/diantennary glycans and in tri-/tetrantennary glycans while they present an increased sialic acid O-acetylation. Upon HFD, the circulating metabolic profile of ASGR1 deficient was similar to the WT mice, in terms of lipid, glucose, and immunoinflammatory profile. However, ASGR1-deficient mice presented an inflamed liver and adipose tissue compared to WT. Additionally, the main ATP-production pathways such as β-oxidation, glycolysis, and gluconeogenesis were dysfunctional in ASGR1-/- compared to the controls. DKO mice ASGR1-/-/LDL-R-/- and ASGR1-/-/ApoE-/- compared to their controls, upon WTD diet present a significantly lower level of cholesterol with increased collagen content and without any change in immunoinflammatory profile. Those mice do not show changes in liver morphology. Conclusion and discussion: Total plasma N-glycome remains stable in ASGR1 deficient mice suggesting that there is no increase in circulating glycoproteins. Thus, other redundant mechanisms should take over the glycoprotein endocytosis. ASGR1 deficiency upon high fat diet is associated with liver and adipose tissue inflammation without modulating the systemic one. In contrast, in high-cholesterol diet, ASGR1 deficiency lowers the lipid profile, reduces the plaque area size, and increases the collagen content, compared with the WT mice. These results indicate that the improved lipid profile reduces plaque progression and increases plaque stability. These changes did not alter liver morphology, nor the immunoinflammatory profile in circulating in DKO compared to their counterparts LDL-R-/-, ApoE-/- mice, respectively. These results indicate that ASGR1 might be a potential pharmacological target as target lowering therapy.