Development Of Adipose-Specific VEGFB₁₈₆-Expressing Animal Models And Functional Study In Adipose Development And Energy Metabolism

Obesity can cause a variety of physical and psychological diseases,and the incidence has been rising sharply.When the energy stored in the body is greater than the energy consumption,the accumulation of fat tissue is excessive.Endocrine disorders of fat cells can induce obesity and other complications as well.Adipose tissue is divided into white fat tissue?WAT?responsible for energy storage and brown fat tissue?BAT?responsible for maintaining body temperature by heat generation,as well as the intermediate beige fat tissue discovered in recent years.Vascular endothelial growth factor VEGFB includes two isoforms,VEGFB₁₈₆ and VEGFB₁₆₇,through alternative splicing.The two isoforms are significantly different in structure and function.At present,it is found that VEGFB can affect the development of adipose tissue and transportation of fatty acids between tissues of energy storage and energy consumption.More and more studies are focusing on VEGFB in adipose development and energy metabolism although there are very few studies on these two isoforms.Whether the two play differently important roles and which one is more important than the other are not clear.There are not many animal models available so far.In this study,we take advantage of VEGFB deletion mouse(VEGFB^-/-)established in the laboratory and the adipose-specific AP2-driven VEGFB₁₈₆overexpression transgenic mice to generate AP2-VEGFB₁₈₆/VEGFB^-/-double transgenic mice.AP2-VEGFB₁₈₆ was successfully transferred into VEGFB^-/-mouse background in order to study the role of VEGFB₁₈₆ in adipose development and energy metabolism.It has been reported that the AP2 promoter is expressed in some non-adipocytes besides adipose tissues.To improve the specificity,we used another adipocyte-specific promoter from adiponectin gene?AdipoQ?to construct a recombinant expression construct AdipoQ-VEGFB₁₈₆.Through microinjection of AdipoQ-VEGFB₁₈₆86 plasmid into one-cell stage pronuclei,we successfully obtained AdipoQ-VEGFB₁₈₆ overexpression mouse.The study found that these two mouse models are similar but different.We have compared AdipoQ-VEGFB₁₈₆ with AP2-VEGFB₁₈₆ mice in study of VEGFB₁₈₆'s role in adipose development and energy metabolism.Experimental results found that the three transgenic mice AP2-VEGFB₁₈₆,AdipoQ-VEGFB₁₈₆,and AP2-VEGFB₁₈₆/VEGFB^-/-all have reduced body weight compared with the wild type.WAT size is decreased and became lighter.The size and number of adipocytes are smaller and there is an obvious browning of WAT.Adipose tissue development in transgenic mice is accompanied by changes in gene expression in the adipose tissues.Expression of WAT development-related factors such as LEPTIN is down regulated and the expression of BAT-associated genes is increased,such as UCP-1.Results indicate the tendency of adipose tissue browning.In addition,compared with the control group,the expression of fatty acid transporter FATP is down regulated and the fatty acid content in adipose tissue are reduced,indicating a reduced accumulation of adipose tissue.This may be one of the important reasons for the weight loss of mice.In terms of energy metabolism,the body temperature of transgenic mice is increased and metabolism is accelerated.The content of serum triglycerides and cholesterol has decreased,indicating that blood lipid levels have decreased although they are within the normal range.The sensitivity of mice to glucose and insulin is increased and metabolic level is improved.Comparing AdipoQ-VEGFB₁₈₆ and AP2-VEGFB₁₈₆ overexpressing mice,the expression level of VEGFB₁₈₆ in WAT was significantly higher in AdipoQ-VEGFB₁₈₆,same as the body temperature.All the results indicate that VEGFB₁₈₆ has a strong regulatory effect on adipose tissue development and energy metabolism.