Effects of oral phosphatidic acid feeding with or without whey protein on muscle protein synthesis and anabolic signaling in rodent skeletal muscle

Abstract

BackgroundPhosphatidic acid (PA) is a diacyl-glycerophospholipid that acts as a signaling molecule in numerous cellular processes. Recently, PA has been proposed to stimulate skeletal muscle protein accretion, but mechanistic studies are lacking. Furthermore, it is unknown whether co-ingesting PA with other leucine-containing ingredients can enhance intramuscular anabolic signaling mechanisms. Thus, the purpose of this study was to examine if oral PA feeding acutely increases anabolic signaling markers and muscle protein synthesis (MPS) in gastrocnemius with and without whey protein concentrate (WPC).MethodsOvernight fasted male Wistar rats (~250 g) were randomly assigned to four groups: control (CON, n = 6-13), PA (29 mg; n = 8), WPC (197 mg; n = 8), or PA + WPC (n = 8). Three hours post-feeding, gastrocnemius muscle was removed for markers of Akt-mTOR signaling, gene expression patterns related to skeletal muscle mass regulation and metabolism, and MPS analysis via the SUnSET method.ResultsCompared to CON rats, PA, WPC and PA + WPC resulted in a significant elevation in the phosphorylation of mTOR (Ser2481) and rps6 (Ser235/236) (p < 0.05) in the gastrocnemius though there were no differences between the supplemented groups. MPS levels in the gastrocnemius were significantly (p < 0.05) elevated in WPC versus CON rats, and tended to be elevated in PA versus CON rats (p = 0.08), though MPS was less in PA + WPC versus WPC rats (p < 0.05) in spite of robust increases in mTOR pathway activity markers in the former group. C2C12 myoblast data agreed with the in vivo data herein showing that PA increased MPS levels 51 % (p < 0.001) phosphorylated p70s6k (Thr389) levels 67 % (p < 0.001).ConclusionsOur results are the first in vivo evidence to demonstrate that PA tends to increases MPS 3 h post-feeding, though PA may delay WPC-mediated MPS kinetics within a 3 h post-feeding window.

The mechanistic and ergogenic effects of phosphatidic acid in skeletal muscle

“…Previous in vitro cell culture and in vivo animal studies demonstrate that the presence of exogenous PA enhances mTORmediated signalling (Mobley et al 2015;Winter et al 2010;Yoon et al 2011;You et al 2012). This response appears to act through a PI3K-independent mechanism, as provision of exogenous PA to C2C12 myoblasts and PA feeding in rats results in p70S6K but not Akt phosphorylation (Mobley et al 2015;O'Neil et al 2009). Moreover, Wortmannin administration does not prevent exogenous PA-induced phosphorylation of p70S6K in this same cell model.…”

“…PA is found in a number of commonly consumed food sources (Tanaka et al 2012), such as cabbage, tomato, and cucumber (ϳ0.55, 0.25, and 0.2 mg/g wet weight, respectively), although the method by which these foods are prepared (i.e., boiling) can reduce the PA content, potentially because of inactivation of PA synthesising enzymes (Tanaka et al 2012). Previous in vitro cell culture and in vivo animal studies demonstrate that the presence of exogenous PA enhances mTORmediated signalling (Mobley et al 2015;Winter et al 2010;Yoon et al 2011;You et al 2012). This response appears to act through a PI3K-independent mechanism, as provision of exogenous PA to C2C12 myoblasts and PA feeding in rats results in p70S6K but not Akt phosphorylation (Mobley et al 2015;O'Neil et al 2009).…”

New strategies in sport nutrition to increase exercise performance

“…In a subsequent study from the same group, Joy et al (2014) reported that in contrast to their previous study [183], PA supplementation (750mg/day) during 8 weeks resistance training lead to significant increases in lean body mass (+2.4 kg), skeletal muscle cross sectional area (+1.0 cm), and leg press strength (+51.9 kg) when compared to placebo [184]. Finally, Mobley et al (2015) recently examined the effect of PA, whey protein concentrate (WPC) and a combination of PA+WPC administration on acute signaling responses in rat skeletal muscle [185]. Interestingly, WPC ingestion was the only intervention that significantly increased MPS 3h post administration, whilst PA actually lead to an ~50% reduction in the WPC-mediated MPS response.…”

Molecular Regulation of Exercise-Induced Muscle Fiber Hypertrophy

“…Further interrogation suggests that PA-mTORC1 signaling axis may be localized to hybrid organelles consisting of late endosomes coupled to lysozomes (LELs) (Jacobs et al 2014). PA treatment indeed increases muscle protein synthesis and mTOR signaling in vivo (Mobley et al 2015). Translating these findings to human RT, supplementation with PAwas recently found to drive greater RT-induced muscle hypertrophy than placebo (Joy et al 2014).…”