Creatine transporter deficiency leads to increased whole-body and cellular metabolism

摘要

Creatine (Cr) is a guanidino compound required for rapid replenishment of ATP in cells with a high-energy demand. In humans, mutations in the Cr transporter (CRT;SLC6A8) prevent Cr entry into tissue and result in significant intellectual impairment, epilepsy, and aphasia. The lack of Cr on both whole body and cellular metabolism was evaluated in Crt knockout (Crt^−/y) mice, a high-fidelity model of human CRT deficiency. Crt^−/y mice have reduced body mass however show a two-fold increase in body fat. There was increased energy expenditure in a homecage environment and during treadmill running in Crt^−/y mice. Consistent with the increases in whole-body metabolic function, Crt^−/y mice show increases in cellular metabolism as well. Mitochondrial respiration increased in skeletal muscle fibers and hippocampal lysates from Crt^−/y mice. In addition, Crt^−/y mice had increased citrate synthase activity, suggesting a higher number of mitochondria instead of an increase in mitochondrial activity. In order to determine if the increase in respiration was due to increased mitochondrial numbers, we measured oxygen consumption in an equal number of mitochondria from Crt^+/y and Crt^−/y mice. There were no changes in mitochondrial respiration when normalized to mitochondrial number, suggesting that the increase in respiration observed could be to higher mitochondrial content in Crt^−/y mice.