Effects of low-protein diet and feed restriction on mRNA expression of cationic amino acid transporters in porcine skeletal muscles

Abstract

We investigated the effects of a low-protein diet and feed restriction on the mRNA expression of cationic amino acid transporters (CATs) in porcine skeletal muscles, specifically, the longissimus dorsi (LD), rhomboideus (RH), and biceps femoris (BF) muscles. Eighteen piglets were randomly divided into three groups: a control (CP21%, ad libitum), low-protein diet (LP, CP16%, ad libitum), and feed-restricted diet (FR, CP21%, 76% feed intake of control pigs) groups. The expression levels of CAT-1 in the LD and BF muscles of LP pigs were higher than that of control pigs, whereas that of FR pigs did not differ from that of control pigs. The CAT-2A expression levels in the RH muscle of FR pigs was higher than that of control pigs. The concentrations of free lysine in all muscles of LP and FR pigs were lower than that of control pigs. The concentrations of free arginine in the LD and RH muscles of LP and FR pigs were lower than that of control pigs. To examine the factors involved in the regulation of CATs mRNA expression, we evaluated the in vitro effects of lysine, arginine, insulin-like growth factor-1, and dexamethasone on the expression of CAT-1, CAT-2A, and CAT-2B in C2C12 myotubes. CAT-1 expression levels increased in response to lysine and/or arginine deprivation. We show, for the first time, that CAT-1 and CAT-2 expression levels in skeletal muscles differ in response to dietary treatments and CAT-1 expression in skeletal muscles appears to increase in response to low free lysine concentrations.