Safdar A, Yardley NJ, Snow R, Melov S, Tarnopolsky MA. Global and targeted gene expression and protein content in skeletal muscle of young men following short-term creatine monohydrate supplementation. Physiol Genomics 32: 219-228, 2008. First published October 23, 2007 doi:10.1152/physiolgenomics.00157.2007.-Creatine monohydrate (CrM) supplementation has been shown to increase fat-free mass and muscle power output possibly via cell swelling. Little is known about the cellular response to CrM. We investigated the effect of short-term CrM supplementation on global and targeted mRNA expression and protein content in human skeletal muscle. In a randomized, placebocontrolled, crossover, double-blind design, 12 young, healthy, nonobese men were supplemented with either a placebo (PL) or CrM (loading phase, 20 g/day ϫ 3 days; maintenance phase, 5 g/day ϫ 7 days) for 10 days. Following a 28-day washout period, subjects were put on the alternate supplementation for 10 days. Muscle biopsies of the vastus lateralis were obtained and were assessed for mRNA expression (cDNA microarrays ϩ real-time PCR) and protein content (Kinetworks KPKS 1.0 Protein Kinase screen). CrM supplementation significantly increased fat-free mass, total body water, and body weight of the participants (P Ͻ 0.05). Also, CrM supplementation significantly upregulated (1.3-to 5.0-fold) the mRNA content of genes and protein content of kinases involved in osmosensing and signal transduction, cytoskeleton remodeling, protein and glycogen synthesis regulation, satellite cell proliferation and differentiation, DNA replication and repair, RNA transcription control, and cell survival. We are the first to report this large-scale gene expression in the skeletal muscle with short-term CrM supplementation, a response that suggests changes in cellular osmolarity. ergogenic aid; osmosensing; cell signaling; cDNA microarray; realtime PCR CREATINE MONOHYDRATE (CrM) supplementation has a number of biochemical and physiological effects and enhances muscle performance in humans (89). Intracellular phosphocreatine (PCr) functions as an energy buffer to prevent ATP depletion in the skeletal muscle, especially during short-duration repetitive high-intensity exercise bouts (22,43,75,89). Following the intake of 20 g CrM/day for 4 -7 days (2, 29, 33) or 3 g CrM/day for 4 -12 wk (4,46,91,94), skeletal muscle total creatine and PCr increase by 10 -20%. Short-term CrM supplementation increases muscle force and/or power (2,3,7,8,10,18,29,59,96), whereas chronic CrM supplementation in conjunction with weight training increases maximal muscle strength and power, fat-free mass (FFM), muscle fiber size, total body water, and total body weight (47, 91, 94) compared with placebo. The increase in FFM and total body weight is partly due to fluid retention in myocytes caused by the osmotic potential of high intracellular CrM abundance (45,47,60). Whether the aforementioned phenotypic effects are due to energy buffering, physiochemical attributes of the compound, cell volume regulation, ...
