Developmental changes in the expression of creatine synthesizing enzymes and creatine transporter in a precocial rodent, the spiny mouse.
BACKGROUND
Creatine synthesis takes place predominately in the kidney and liver via a two-step process involving AGAT (L-arginine:glycine amidinotransferase) and GAMT (guanidinoacetate methyltransferase). Creatine is taken into cells via the creatine transporter (CrT), where it plays an essential role in energy homeostasis, particularly for tissues with high and fluctuating energy demands. Very little is known of the fetal requirement for creatine and how this may change with advancing pregnancy and into the early neonatal period. Using the spiny mouse as a model of human perinatal development, the purpose of the present study was to comprehensively examine the development of the creatine synthesis and transport systems.


RESULTS
The estimated amount of total creatine in the placenta and brain significantly increased in the second half of pregnancy, coinciding with a significant increase in expression of CrT mRNA. In the fetal brain, mRNA expression of AGAT increased steadily across the second half of pregnancy, although GAMT mRNA expression was relatively low until 34 days gestation (term is 38-39 days). In the fetal kidney and liver, AGAT and GAMT mRNA and protein expression were also relatively low until 34-37 days gestation. Between mid-gestation and term, neither AGAT or GAMT mRNA or protein could be detected in the placenta.


CONCLUSIONS
Our results suggest that in the spiny mouse, a species where, like the human, considerable organogenesis occurs before birth, there appears to be a limited capacity for endogenous creatine synthesis until approximately 0.9 of pregnancy. This implies that a maternal source of creatine, transferred across the placenta, may be essential until the creatine synthesis and transport system matures in preparation for birth. If these results also apply to the human, premature birth may increase the risk of creatine deficiency.
Ireland
Zoe
Z
Department of Physiology, Monash University, Clayton, Australia 3800. zoe.ireland@med.monash.edu.au
Russell
Aaron P
AP
Wallimann
Theo
T
Walker
David W
DW
Snow
Rod
R
D000579:Amidinotransferases / Q000235:genetics*; D000818:Animals; D000831:Animals, Newborn; D001921:Brain / Q000201:enzymology / Q000378:metabolism; D003401:Creatine / Q000378:metabolism*; D005260:Female; D005333:Fetus / Q000201:enzymology / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D050937:Guanidinoacetate N-Methyltransferase / Q000235:genetics*; D015151:Immunoblotting; D007668:Kidney / Q000201:enzymology; D008099:Liver / Q000201:enzymology; D026901:Membrane Transport Proteins / Q000235:genetics*; D051379:Mice; D010920:Placenta / Q000201:enzymology / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011247:Pregnancy; D012333:RNA, Messenger / Q000235:genetics
D026901:Membrane Transport Proteins; D012333:RNA, Messenger; C080679:creatine transporter; D050937:Guanidinoacetate N-Methyltransferase; D000579:Amidinotransferases; C020681:glycine amidinotransferase; D003401:Creatine