Flögel Svenja, Strater Miriam, Fischer Dietmar, Gründemann Dirk
Department of Pharmacology, Faculty of Medicine and University Hospital Cologne, University of Cologne, Germany.
FEBS J. 2025 Mar;292(5):1124-1140. doi: 10.1111/febs.17382. Epub 2025 Jan 10.
Creatine is essential for ATP regeneration in energy-demanding cells. Creatine deficiency results in severe neurodevelopmental impairments. In the brain, creatine is synthesized locally by oligodendrocytes to supply neighboring neurons. Neuronal uptake is mediated by SLC6A8. However, it is still unknown how creatine is released from the producing cells. Here, we investigated the function of the transporter SLC22A15, which exhibits strikingly high amino acid sequence conservation. The release of substrates from 293 cells via heterologously expressed human and rat SLC22A15 was analyzed by mass spectrometry. A number of zwitterions were identified as substrates, with similar efflux transport efficiencies. However, in absolute numbers, the efflux of creatine far outweighed all other substrates. In contrast to the permanent creatine efflux mediated by SLC16A12 and SLC16A9, SLC22A15 was, by default, completely inactive, thereby preventing continuous creatine loss from producing cells. External substrates such as guanidinoacetic acid, GABA, or MPP trigger creatine release through a one-to-one exchange. Human and mouse mRNA profiles indicate that SLC22A15 expression is highest in oligodendrocytes and bone marrow. Single-cell RNA sequencing data substantiate the hypothesis that SLC22A15 depends on high intracellular creatine concentrations: high SLC22A15 counts, as in oligodendrocytes and macrophages, correlate with high counts of the creatine synthesis enzymes AGAT and GAMT in both humans and mice, whereas in proximal tubular cells and hepatocytes, AGAT counts are high, but SLC22A15 is absent. Our findings establish SLC22A15 as the pivotal transporter for controlled creatine release from oligodendrocytes, filling a critical gap in understanding creatine metabolism in the brain.
肌酸对于能量需求高的细胞中ATP的再生至关重要。肌酸缺乏会导致严重的神经发育障碍。在大脑中，少突胶质细胞可在局部合成肌酸以供应邻近的神经元。神经元摄取由SLC6A8介导。然而，肌酸如何从产生细胞中释放仍不清楚。在此，我们研究了转运蛋白SLC22A15的功能，该转运蛋白具有极高的氨基酸序列保守性。通过质谱分析了经由异源表达的人和大鼠SLC22A15从293细胞中释放底物的情况。鉴定出多种两性离子作为底物，其外排转运效率相似。然而，就绝对数量而言，肌酸的外排远远超过所有其他底物。与由SLC16A12和SLC16A9介导的持续性肌酸外排不同，SLC22A15默认情况下完全无活性，从而防止了产生细胞中肌酸的持续流失。诸如胍基乙酸、GABA或MPP等外部底物通过一对一交换触发肌酸释放。人和小鼠的mRNA谱表明，SLC22A15在少突胶质细胞和骨髓中表达最高。单细胞RNA测序数据证实了SLC22A15依赖于高细胞内肌酸浓度这一假设：在人和小鼠中，少突胶质细胞和巨噬细胞中高计数的SLC22A15与肌酸合成酶AGAT和GAMT的高计数相关，而在近端肾小管细胞和肝细胞中，AGAT计数高，但不存在SLC22A15。我们的研究结果确立了SLC22A15作为少突胶质细胞中控制肌酸释放的关键转运蛋白，填补了理解大脑中肌酸代谢的关键空白。
