Itpase-Deficient Mice Show Growth Retardation and Die Before Weaning

Cell Death and Differentiation (2009) 16, 1315–1322 & 2009 Macmillan Publishers Limited All rights reserved 1350-9047/09 $32.00 www.nature.com/cdd ITPase-deficient mice show growth retardation and die before weaning M Behmanesh1,2, K Sakumi*,1, N Abolhassani1, S Toyokuni3, S Oka1, YN Ohnishi1, D Tsuchimoto1 and Y Nakabeppu1 Inosine triphosphate pyrophosphatase (ITPase), the enzyme that hydrolyzes ITP and other deaminated purine nucleoside triphosphates to the corresponding purine nucleoside monophosphate and pyrophosphate, is encoded by the Itpa gene. In this study, we established Itpa knockout (KO) mice and used them to show that ITPase is required for the normal organization of sarcomeres in the heart. ItpaÀ/À mice died about 2 weeks after birth with features of growth retardation and cardiac myofiber disarray, similar to the phenotype of the cardiac a-actin KO mouse. Inosine nucleotides were found to accumulate in both the nucleotide pool and RNA of ItpaÀ/À mice. These data suggest that the role of ITPase in mice is to exclude ITP from the ATP pool, and the main target substrate of this enzyme is rITP. Our data also suggest that cardiomyopathy, which is mainly caused by mutations in sarcomeric protein-encoding genes, is also caused by a defect in maintaining the quality of the ATP pool, which is an essential requirement for sarcomere function. Cell Death and Differentiation (2009) 16, 1315–1322; doi:10.1038/cdd.2009.53; published online 5 June 2009 Nucleotide and polynucleotide molecules are spontaneously repair of alkylation-induced DNA damage, and increased damaged under the physiological conditions.1–3 These sensitivity to methyl methanesulfonate and streptozotocin- modifications often cause a nucleotide to pair with an alternate induced diabetes.20,21 However, there is no report regarding partner nucleotide in DNA.4,5 For example, 8-oxo-dGTP, an ITPase and endonuclease V knockout mouse as yet. oxidized product of dGTP, can pair with adenine as well as The enzyme activity of ITPase (EC 3.6.1.19) was first cytosine during replication, resulting in a transversion muta- described in 1969.22 ITPase, which is encoded by the Itpa tion.4 8-Oxoguanine in DNA appears through two indepen- gene in mammals, hydrolyzes deaminated purine nucleoside dent pathways, either by an incorporation of the oxidized triphosphates, such as dITP and ITP, to the corresponding precursor, 8-oxo-dGTP during DNA synthesis, or by the direct purine nucleoside monophosphate and pyrophosphate.16,23 oxidation of a guanine base in DNA.6,7 To prevent the former The enzyme was identified as a novel NTP pyrophosphatase pathway from being used, mammals possess the oxidized by a protein structure-based approach in 1999.24 We have purine nucleoside triphosphatase encoded by the Mth1 gene, reported the genomic organization and expression of the that degrades 8-oxo-dGTP into 8-oxo-dGMP and pyropho- mouse Itpa gene in 2005.23 In this study to elucidate the sphate,8,9 and to protect against the latter pathway, biological significance of ITPase in mice, we produced an Itpa 8-oxoguanine-DNA glycosylase, encoded by the Ogg1 gene, knockout. These ItpaÀ/À mice died about 2 weeks after birth removes the oxidized base from the DNA.10–15 To evaluate with features of growth retardation and cardiac myofiber the roles of these enzymes in mouse, we produced Ogg1 and disarray. Mth1 single-knockout mice, as well as Ogg1 plus Mth1 double-knockout mice, and showed their tumor susceptibility 6 and the accumulation of 8-oxoguanine in their DNA. Results Similar to oxidation, deamination is also a common chemical modification that nucleotides may undergo under Biological features of ItpaÀ/À mice. To disrupt the Itpa 1,2 physiological conditions. In the case of deaminated purine gene, exons 2–4 that encode V23-I88 of mouse ITPase were bases, such as hypoxanthine, it is considered that inosine replaced with the polII-neo cassette (Figure 1a). Two triphosphate pyrophosphatase (ITPase), endonuclease V and independently targeted ES clones were obtained and used hypoxanthine-DNA glycosylase have a role in eliminating the to establish the knockout (KO) mouse strains. The Itpa gene- 16–19 19 deaminated bases from DNA. Saparbaev and Laval disrupted ES cells were injected into C57BL/6J blastocysts to reported that alkylpurine-DNA glycosylases engage in hypox- produce Itpa KO mice. Disruption of the Itpa gene was anthine-DNA glycosylase activity both in Escherichia coli and confirmed by Southern blotting (ES clone, Figure 1b) as well mammalian cells. The alkylpurine-DNA glycosylase-deficient as by genomic PCR (KO mice, Figure 1c). When we (Mpg knockout) mouse has features of impaired base excision analyzed the expression of the Itpa gene in Itpa KO mice, 1Division of Neurofunctional Genomics, Department of Immunobiology and Neuroscience, Medical Institute of Bioregulation, Kyushu University, Fukuoka 812-8582, Japan; 2Department of Genetics, School of Sciences, Tarbiat Modares University, PO Box 14115-175, Tehran, Iran and 3Department of Pathology and Biological Responses, Graduate School of Medicine, Nagoya University, Nagoya 466-8550, Japan *Correspondence: K Sakumi, Division of Neurofunctional Genomics, Department of Immunobiology and Neuroscience, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-Ku, Fukuoka, Fukuoka 812-8582, Japan. Tel: þ 81 92 642 68 02; Fax: þ 81 92 642 68 04; E-mail: [email protected] Keywords: ITPase; nucleotide pool; ATP; mouse mutant; cardiomyopathy Abbreviations: ITPase, inosine triphosphate pyrophosphatase; RBCs, red blood cells; KO, knockout Received 24.9.08; revised 10.3.09; accepted 15.4.09; Edited by M Piacentini; published online 05.6.09 ITPase-deficient mice M Behmanesh et al 1316 Figure 1 Generation of the ItpaÀ/À mouse. (a) Schematic representation of a partial restriction map of the mouse Itpa locus, targeting vector and targeted allele. PCR primers to detect the wild type and knockout alleles are indicated by open and closed triangles, respectively. ‘p’ indicates the probe fragment used in Southern blot analysis. As there are several Itpa pseudogenes in the mouse genome,23 we cloned the exact Itpa gene located on chromosome 2 and used it to construct a targeting vector. (b) Southern blot analysis of Itpa þ /À ES cells. The 50-flanking probe (p) was used to distinguish the EcoRI-digested targeted allele. An approximate 6 kb targeted allele (KO) was found only in the lane of Itpa þ /À ES cells. (c) Targeted allele confirmed by the genomic PCR of mouse tail DNA. Amplified DNAs derived from wild type (WT) and knockout (KO) alleles are indicated by open and closed triangles, respectively we detected a shorter length of cDNA in the RT-PCR product About 10% of offspring obtained by the mating of Itpa þ /À mice of Itpa KO mouse RNAs using primer sets positioned in showed the ItpaÀ/À genotype (Figure 4a). The birth ratio exons 1 and 8 (Figure 2a). The shorter length of cDNA was indicates that more than half of the ItpaÀ/À mice died before detected in both KO mouse strains. The unexpected cDNA birth. Although there was a significant amount of milk in the contained a sequence corresponding to exons 1, 5, 6, 7 and stomach of ItpaÀ/À newborn mice, these mice showed growth 8, with one G insertion between exons 1 and 5 (Figure 2b). retardation and died about 14 days after birth (Figure 4b-d). This abnormally spliced RNA encodes a polypeptide Prior to death, the ItpaÀ/À mouse showed ataxia, abnormal composed of 29 amino acids, that is, the first 22 amino breathing (Supplemental Movie 1) and heart abnormalities. acids encoded by exon 1 of the Itpa gene and an additional 7 These phenotypes were common in the two knockout mouse misframed amino acids derived from the exon 5 sequence. lines, independently established from different Itpa þ /À ES The aberrant translation product lacks the major portion of cells. On pathological analysis, the ItpaÀ/À mouse showed ITPase (176 a.a./198 a.a.), including the residues thought to such features as immature hair follicles, hyperkeratosis of the interact with ITP (Figure 2c).16 The null expression of the forestomach, decreased extramedullary hematopoiesis in ITPase protein in the ItpaÀ/À mouse was confirmed by liver and spleen, and germ cell hypoplasia in testis (data not western blotting using a rabbit anti-ITPase antiserum. We did shown), in addition to hypoplasia of the heart (Figure 5a-c). not detect any signal corresponding to the expected size of The heart of the ItpaÀ/À mouse was smaller and immature, ITPase (MW, 21.9 kDa) in ItpaÀ/À mouse samples especially the ventricle regions. Analysis of a 10 days old (Figure 3a). A 3.1 kDa peptide, the expected translation ItpaÀ/À mouse heart showed that both ventricular chamber product of abnormally spliced RNA, was not detected in our walls were thinner than those of the Itpa þ / þ mouse heart system, perhaps because of an instability of the peptide or (Figure 5d-f). The striated staining of desmin corresponding to the detection limit of the antiserum (Supplementary Figure). the Z-disc was absent in the ItpaÀ/À heart and disorganization Finally, no ITPase activity was detected in the erythrocyte of myocardial fiber was observed (Figure 5g-i). By ultra- extract of the ItpaÀ/À mouse (Figure 3b), and we concluded structural analysis of ItpaÀ/À mouse cardiomyocytes, it was that the gene disruption had succeeded. evident that the number of sarcomeres was decreased and The Itpa þ /À mouse was indistinguishable from its Itpa þ / þ that the sarcomere structure was broken and disorganized. littermates with respect to size, viability, fertility and behavior. The shape of mitochondria was changed, although the inner Cell Death and Differentiation ITPase-deficient mice M Behmanesh et al 1317 Figure 2 RT-PCR analysis of ItpaÀ/À mouse RNA.

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