Potential Involvement of SRB1 in Type 1 Diabetes Associated Dyslipidemia: Characterizing SRB1 Antisense

Background: One of the main complications of type 1 diabetes is cardiovascular disease associated with dyslipidemia, characterized by abnormally high levels of triglyceride-rich lipoproteins in the bloodstream. This imbalance could eventually lead to complications such as atherosclerosis. Liver Scavenger Receptor Class B Type 1 (SRB1) is currently being investigated for its role in type 1 diabetes induced dyslipidemia. We aim to characterize the effects of using a liver specific SRB1 antisense (GalNAc-SRB1 ASO) in non-diabetic and diabetic mice. We hypothesize that triglyceride and cholesterol levels will increase to a greater extent in diabetic mice injected with GalNAc-SRB1 ASO than in non-diabetic mice. Methods: Diabetic and non-diabetic LDL receptor-deficient (Ldlr-/-) mice were injected with GalNac-SRB1 ASO to silence liver SRB1 expression. Each week, triglyceride levels, cholesterol levels, blood glucose levels, and body weight were recorded. After four weeks, the liver, testis, kidneys, and brown fat were collected. Expression of the SRB1 receptor was measured via Reverse Transcriptase Polymerase Chain Reaction (RT-PCR). The specificity of the ASO was also tested by measuring the expression of both Lrp1 and CD36 receptors in the liver via RT-PCR. The SRB1 protein was then visualized in the liver using immunohistochemistry. Results: In non-diabetic mice, triglyceride and cholesterol levels increased as the concentration of GalNAc-SRB1 ASO increased. GalNAc-SRB1 ASO decreased mRNA SRB1 expression in the liver of non-diabetic mice by 90%, whereas there was no major decrease in SRB1 expression in the other tissues such as the kidney, testis, and brown fat. High concentrations of the GalNAc-SRB1 ASO decreased mRNA expression of Lrp1 and Cd36 receptors in the liver, showing other receptors may be targeted in high concentrations of the ASO. After 2 weeks of GalNAc-SRB1 ASO injections, the ASO increased triglyceride and cholesterol levels in diabetic mice and non-diabetic mice similarly, although absolute levels were higher in diabetic mice. Conclusion: Our data show that the GalNAc-SRB1 ASO specifically silences expression of liver SRB1, increasing lipid levels in both diabetic and non-diabetic mice. Further studies will use this SRB1 ASO to help determine the role that liver SRB1 plays in dyslipidemia associated with type 1 diabetes.