Apolipoprotein A-IV (ApoA-IV) exists in relatively high levels in the circulation systems of animals, but its roles are not fully elucidated. It is known that the Apoa4 gene resides in the cluster Apoa1/Apoc3/Apoa4. Because of a short intergenic sequence between Apoc3 and Apoa4, a previous ApoA-IV knockout mouse model by gene targeting had an accompanying deficiency in ApoC-III expression, which limited its application in investigating the precise roles of ApoA-IV. To solve this problem, we created a specific knockout of ApoA-IV in Sprague-Dawlay rats by TALEN approach.

Age-matched knockout rats and their wild-type littermate controls maintained on a standard rodent diet were studied and blood metabolic parameters were measured. Glucose, insulin, olive oil, and intralipid tolerance tests were performed to study the glucose and lipid metabolism of rats. Quantitative real-time PCR and RNA-seq analysis in liver and inguinal white adipose tissue (iWAT) of rats at three ages (18 weeks, 45 weeks and 90 weeks) were performed to identify the genes altered by ApoA-IV knockout.

ApoA-IV knockout rats were apparently normal and fertile, but exhibited improved glucose clearance when challenged with glucose tolerance test. In addition, fasting-induced hepatic steatosis was more pronounced in ApoA-IV knockout rats. Further analysis identified that a set of hepatic genes involved in glycolysis, gluconeogenesis and de novo lipogenesis were altered in the absence of ApoA-IV, which induced enhanced glycolysis, attenuated gluconeogenesis and elevated de novo lipogenesis. And the RNA-seq results also confirmed that almost all the genes mentioned in the phenotyping section were highly consistent throughout the three studied ages.

ApoA-IV functions in an age-independent manner in the modulation of glucose and lipid metabolism of rats, and may serve as a potential linker between hepatic glucose and lipid metabolism.