Author(s): VANDECAUTER, J., D’HOE, B., VAN DER STEDE, T., VAN DE LOOCK, A., VAN DE CASTEELE, F., VAN VOSSEL, K., LIEVENS, E., DERAVE, W., Institution: GHENT UNIVERSITY, Country: BELGIUM, Abstract-ID: 2233

INTRODUCTION:
Carnosine and creatine are highly abundant metabolites in skeletal muscle, where they play crucial roles in energy metabolism and homeostasis, making them popular supplements for sports performance. Pooled single fiber analysis has shown that both carnosine (+70%) and creatine (+20%) have higher concentrations in fast fibers compared to slow fibers [1-2]. However, it remains unknown whether genes encoding enzymes and transporters involved in their metabolism differ between both fiber types and whether their expression interindividually correlates with carnosine and creatine levels in skeletal muscle. Since it is generally believed that beta-alanine (the rate-limiting precursor of carnosine) and creatine availability are dependent on extramuscular synthesis (in liver/kidney) and diet, we hypothesized that transporters would primarily explain interindividual and inter-fiber type differences.
METHODS:
In study one, 1050 single fibers were isolated from vastus lateralis biopsies of 12 males and two females (75 fibers per individual), while in study two, bulk muscle biopsies were obtained from 30 males and 29 females. Pooled single fibers and bulk samples underwent RNA sequencing as previously described [3]. Seven carnosine- and five creatine-related genes were detected in muscle tissue and selected for further analysis. Furthermore, proton magnetic resonance spectroscopy was performed on the same participants of study two using our in-house developed technique to quantify carnosine in the soleus and gastrocnemius muscle (i.e., mean carnosine), and creatine in the soleus. Paired t-tests compared gene expression between fiber types, and Pearson correlations linked the bulk gene expression with the metabolite concentrations (significance set at p<0.05).
RESULTS:
In study one, fast-twitch fibers had significantly higher expression of the main carnosine synthesis enzyme carnosine synthase (CARNS1; +57%) and of GADL1 (+127%), a synthesis enzyme for its main precursor, beta-alanine. Conversely, the putative main beta-alanine transporter (TauT, SLC6A6; -41%) and carnosine transporter (PHT1, SLC15A4; -12%) were significantly lower expressed in fast fibers. Similarly, the key creatine synthesis enzymes arginine:glycine amidinotransferase (AGAT/GATM; +46%) and guanidinoacetate methyltransferase (GAMT; +9%) showed higher expression in fast fibers compared to slow fibers. In study two, we found that mean muscle carnosine concentration was positively correlated with CARNS1 (r=0.257; p=0.049) and GADL1 (r=0.373; p=0.004) expression from bulk biopsies, but this was not the case between soleus creatine and GATM or GAMT expression (p>0.05).
CONCLUSION:
Although it is generally believed that carnosine and creatine are mainly synthesized in liver/kidney and transported into muscle, our findings suggest local expression of synthesis enzymes, coinciding with elevated carnosine and creatine content in fast fibers.

References:
[1] Hill et al. (2007)
[2] Tesch et al. (1989)
[3] Van der Stede et al. (2024)