Hexokinase I expression and activity in embryonic mouse heart during early and late organogenesis.
Hexokinase (HK) catalyzes the first step in glucose metabolism, that is, the conversion of glucose to glucose-6-phosphate (G6P). Four HK isoforms have been identified, of which HK-I is predominant in embryonic and fetal tissues. HK-I has been studied in preimplantation embryos and in fetal stages, but little is known about its activity or expression in the early postimplantation embryo. We evaluated HK-I expression, HK-I activity, and glycolytic metabolism in the embryonic mouse heart during early [gestational day (gd) 9.5] and late (gd 13.5) organogenesis. Immunohistochemistry demonstrated that HK-I is localized mainly in the heart at both stages, with stronger expression on gd 13.5. Densitometry after SDS-PAGE/western analysis confirmed higher immunodetectable HK-I protein levels in hearts on gd 13.5 vs gd 9.5. By contrast, RT-PCR demonstrated higher HK-I mRNA expression on gd 9.5 vs gd 13.5. Similarly, cardiac HK-I activity (conversion of glucose to G6P) and glycolysis (conversion of glucose to lactate) were higher on gd 9.5 than on gd 13.5. These results suggest a complex regulation of HK-I expression and activity in the embryonic heart during organogenesis, involving a change in the intrinsic activity of the enzyme with development. HK-I appears to play an important role in glucose metabolism during this critical stage of cardiogenesis.
Fritz
H L
HL
Department of Anatomy, Physiological Sciences, and Radiology, College of Veterinary Medicine, North Carolina State University, 4700 Hillsborough Street, Raleigh, NC 27606 USA.
Smoak
I W
IW
Branch
S
S
D000818:Animals; D015153:Blotting, Western; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D005865:Gestational Age; D006019:Glycolysis; D006321:Heart / Q000196:embryology*; D006593:Hexokinase / Q000096:biosynthesis*; D007150:Immunohistochemistry; D051379:Mice; D009206:Myocardium / Q000201:enzymology*; D011247:Pregnancy; D012333:RNA, Messenger / Q000096:biosynthesis; D020133:Reverse Transcriptase Polymerase Chain Reaction
D012333:RNA, Messenger; D006593:Hexokinase