Overexpression of liver-type phosphofructokinase (PFKL) in transgenic-PFKL mice: implication for gene dosage in trisomy 21

Abstract

The human liver-type subunit of the key glycolytic enzyme, phosphofructokinase (PFKL), is encoded by a gene residing on chromosome 21. This chromosome, when triplicated, causes the phenotypic expression of Down's syndrome (trisomy 21). Increased phosphofructokinase activity, a result of gene dosage, is commonly found in erythrocytes and fibroblasts from Down's syndrome patients. We describe the construction of transgenic mice overexpressing PFKL for use as a well-defined model system, in which the effects of PFKL overexpression in various tissues, and throughout development, can be studied. Mice transgenic for a murine PFKL 'gene cDNA' hybrid construct were found to overexpress PFKL in a tissue-specific manner resembling that of the endogenous enzyme. Although unchanged in adult brain, PFK specific activity was found to have been almost doubled in brains of embryonic transgenic-PFKL mice, suggesting that the extra copies of the PFKL gene are expressed during the developmental period. This pattern of overexpression of PFKL in brains of transgenic-PFKL mice suggests that gene-dosage effects may be temporally separated from some of their consequences, adding an additional layer of complexity to the analysis of gene dosage in trisomy 21.

Effects of overexpression of the liver subunit of 6-phosphofructo-1-kinase on the metabolism of a cultured mammalian cell line

“…What, then, is the explanation for the metabolic changes observed in the tissues of Down's syndrome patients [12,13,15] and in the previous studies that have characterized the effects of overexpressing PFK-1 in cultured mammalian cells [16] and in transgenic mice [18][19][20] ? In Down's syndrome, many genes will be overexpressed, and therefore it is impossible to assign any of the metabolic effects observed specifically to the overexpression of PFK-1.…”

“…These cells also showed a 20-40 % increase in glycolytic flux, compared with cells from controls, when flux in the pathway was stimulated by treatment of the cells with Methylene Blue [15]. In a series of experiments [16][17][18][19][20], Groner and co-workers have overexpressed, in cells and transgenic mice, some of the genes located on the long arm of chromosome 21, including the gene for PFK-L. Transfection of PC12 cells with a vector expressing PFK-L resulted in clones with " 50 % increases in PFK-L activity and " 40 % increases in glycolytic flux [16]. Similarly, in transgenic mice overexpressing PFK-L, a 60 % increase in the specific activity of brain PFK-1 was associated with a 58 % increase in the rate of glucose metabolism [19].…”

Is it possible to improve neurodevelopmental abnormalities in Down syndrome?

“…Several mouse models were created, including models for over-expression of App ( Harris-Cerruti et al, 2004 ), Sod1 (Gahtan et al, 1998 ), Sim2 (Chrast et al, 2000 ), Synj1 (Voronov et al, 2008 ), S100 β (Gerlai and Roder, 1995 ), Pfk1 (Elson et al, 1994 ), Hmg14 (Bustin et al, 1995 ), Dyrk1a (Altafaj et al, 2001 ), Ets2 (Sumarsono et al, 1996 ), DSCR1 (Baek et al, 2009 ), and BACE2 (Azkona et al, 2010a ). Recent work focused on the role of Dyrk1a triplication in the cognitive defi cit of DS, showing that transgenic mice (TgDyrk1a) exhibit various, but not all, learning defects of Ts65Dn mice (Altafaj et al, 2001 ).…”

Gene-Dosage Effect on Chromosome 21 Transcriptome in Trisomy 21: Implication in Down Syndrome Cognitive Disorders

“…In red blood cells, substrate and product levels of PFKL are decreased and increased, respectively (Magnani et al, 1987). Transgenic mice overexpressing PFKL showed faster utilization of glucose in brain, paralleling the observations on DS patients (Elson et al, 1994;Peled-Kamar et al, 1998). However, there is no evidence that these effects would have pathological consequences.…”