Enhanced small neutral but not branched chain amino acid transport after epigenetic sodium coupled neutral amino acid transporter‐2 (SNAT2) cDNA expression in myoblasts

Abstract

Background Skeletal muscle mass and function are partly maintained by the supply of amino acids, altered amino acid transport is an important cause of frailty that can lead to decreased independence with increasing age and slow trauma recovery. The system‐A sodium coupled neutral amino acid transporter (SNAT)‐2 coded by gene family SLC38A2 generates a 506 amino acid 56 kDa protein that is an important transporter of amino acids in skeletal muscle. Ageing is associated with a decrease in expression of SNAT2 transporters. Methods In this study, we used the C2C12 cell line, using myoblast cells and cells differentiated into myotubes. We investigated if the expression of SNAT2 DNA would enhance intracellular amino acid levels and increase their availability for protein synthesis. Results In control myoblasts and myotubes, we found significantly decreased expression of SNAT2 (6.5× decrease, n = 4 per group, P < 0.05) in myotubes than found in myoblasts. After transfection with a SNAT2‐eGFP cDNA plasmid, C2C12 myoblasts significantly increased perinuclear punctate SNAT2‐eGFP expression that persisted and was more cytoplasmic after differentiation into myotubes. Interestingly, transfected cells were significantly more responsive to the hormone 5α‐dihydrotestosterone (DHT, 4.5 nM, by 1.6×, n = 3 per group, P < 0.04). Starvation significantly enhanced the amino acid C14‐MeAIB transport (1.7×, n = 3 per group, P < 0.05) indicating increased function of SNAT2. Inhibiting SNAT2 with high concentrations of MeAIB (3.3 or 5 mM) significantly reduced C14‐Isoleucine transport by L‐type amino acid transporter (LAT2, 52.8% and 77%, respectively, n = 3 per group, P < 0.05). However, there was no increase in the LAT2 transport of C14‐isoleucine detectable in SNAT2‐eGFP transfected cells after DHT (4.5 nM) exposure. This indicated that small amino acid availability was not rate limiting to LAT2 function in myoblasts. Conclusions Overall, these data show that transfection of SNAT2‐eGFP expression enhanced its function following starvation and treatment with physiological levels of DHT. Enhanced SNAT2 expression in muscle cells offers a viable epigenetic target in pathological conditions associated with altered amino acid transport.

Comparative analysis of amino acid content and protein synthesis-related genes expression levels in breast muscle among different duck breeds/strains

“…SLC38A2 could transport small amino acid (such as Glu) with one sodium ion into muscle fibers, and then exchange them into larger amino acids by SLC7A5 , which was essential for protein synthesis ( Hundal and Taylor, 2009 ). Decreased SLC38A2 expression could inhibit the availability of small amino acids, leading to reduced transport by SLC7A5 of branched chain amino acids ( Pearson et al, 2021 ). PAT1 was involved in the absorption of small amino acids and their derivatives at the apical membrane of intestinal epithelial cells ( Boll et al, 2004 ).…”

Potential nutritional healthy-aging strategy: enhanced protein metabolism by balancing branched-chain amino acids in a finishing pig model

“…13,14 Besides, the transport of BCAAs requires the aid of AA transporters such as sodium-dependent neutral AA transporter 2 (SNAT2), L-type AA transporter 1 (LAT1), and protonassisted amino acid transporter 1 (PAT1). 15,16 These transporters exhibit a dual transporter and receptor function, sensing BCAA availability, relaying nutrient signals to the cell interior, regulating the uptake and efflux of BCAAs, and regulating the dynamic balance of protein synthesis and deposition in mammals, subsequently affecting the growth of muscle fibers, increasing skeletal muscle mass, and ultimately playing the role of anti-aging agents in skeletal muscles.…”