Tissue Distribution and Regulation of the Small Sar1b GTPase in Mice

Abstract

Background/Aims: Sar1b GTPase (Sar1b) represents an obligatory component of COPII vesicles that bud from the endoplasmic reticulum to transport proteins to the Golgi apparatus. Its genetic mutations lead to a severe disorder known as chylomicron retention disease. Despite growing knowledge on Sar1b, little is known about it tissue distribution and regulation, which constitute the aims of the present study. We aimed to determine the Sar1b tissue distribution and modulation by a high-fat diet and gene forcing using transgenic mice in comparison to wild-type mice. Methods: The expression pattern of Sar1b was studied in different organs of wild-type and Sar1b transgenic mice by qRT-PCR and Western blot. The effect of transgenesis and insulin resistance induced by a 12-week high-fat diet on Sar1b gene expression was also assessed by qRT-PCR. Results: Evaluation of Sar1b mRNA revealed the skeletal muscle as the tissue with the highest Sar1b expression, followed by the heart and liver, the organs composing the digestive tract, the brain and finally the lung and the adipose tissue. Sar1b protein expression levels follow a similar pattern among the organs, except for its lower expression in the heart. While the high-fat diet did not exert any significant alterations, Sar1b transgenic mice displayed higher gene expression in the liver, ileum, jejunum, proximal and distal colon compared to wild-type mice. Conclusion: Our study supports the importance of Sar1b in organs involved in lipid transport and/or calcium trafficking such as the liver, intestine, skeletal muscle and heart.