Abstract
GLUT1 is essential for human brain development and function, as evidenced by the severe epileptic encephalopathy observed in children with GLUT1 deficiency syndrome resulting from inherited loss-of-function mutations in the gene encoding this facilitative glucose transporter. To further elucidate the pathophysiology of this disorder, the zebrafish orthologue of human GLUT1 was identified, and expression of this gene was abrogated during early embryonic development, resulting in a phenotype of aberrant brain organogenesis consistent with the observed expression of Glut1 in the embryonic tectum and specifically rescued by human GLUT1 mRNA. Affected embryos displayed impaired glucose uptake concomitant with increased neural cell apoptosis and subsequent ventricle enlargement, trigeminal ganglion cell loss, and abnormal hindbrain architecture. Strikingly, inhibiting expression of the zebrafish orthologue of the proapoptotic protein Bad resulted in complete rescue of this phenotype, and this occurred even in the absence of restoration of apparent glucose uptake. Taken together, these studies describe a tractable system for elucidating the cellular and molecular mechanisms of Glut1 deficiency and provide compelling in vivo genetic evidence directly linking nutrient availability and activation of mitochondria-dependent apoptotic mechanisms during embryonic brain development.
Highlights
Abundant in the extracellular milieu, the cellular uptake of glucose is precisely regulated by specific growth factors and signaling pathways [4]
Cell culture studies reveal that inhibition of cellular glucose uptake dramatically increases apoptosis under conditions of growth factor restriction and that cell survival under such circumstances is dependent upon the regulation of glucose uptake and metabolism by the proto-oncogene Akt [5,6,7]
The data in this study reveal a critical role for Glut1 in the development of the embryonic vertebrate brain
Summary
Abundant in the extracellular milieu, the cellular uptake of glucose is precisely regulated by specific growth factors and signaling pathways [4]. A biochemical link between glucose homeostasis and apoptosis was further suggested by studies demonstrating an interaction between the proapoptotic protein, Bad, and the glycolytic enzyme, glucokinase [8]. In support of these findings, a recent study demonstrates a direct link between glucose metabolism and apoptosis in Xenopus laevis oocytes mediated by activation of caspase-2 [9]. Our findings reveal the first in vivo data linking impaired nutrient availability and activation of apoptosis during early vertebrate development and provide new mechanistic insights relevant to the pathogenesis and treatment of affected patients
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