Lifelong impact of ENPP1 Deficiency and the early onset form of ABCC6 Deficiency from patient or caregiver perspective

The ectonucleotide pyrophosphatase/phosphodiesterase family member 1 (ENPP1) and ATP-binding cassette subfamily C member 6 (ABCC6) proteins play a prominent role in inhibiting ectopic calcification and arterial stenosis. Patients with ENPP1 Deficiency or infant onset ABCC6 Deficiency often present with pathological calcification, narrowed blood vessels, multiorgan dysfunction and high infant mortality. The heterogenous presentation and progression is well documented. Our objective was to characterize how these morbidities lead to burden of illness and poor quality of life across ages from the patient/caregiver perspective. Patients/caregivers were interviewed via phone using Institutional Review Board–approved questionnaires. Patient-reported outcomes were collected via validated instruments. Thirty-one caregivers and 7 patients participated: infant onset ABCC6 Deficiency, n = 6 (infants/children); ENPP1 Deficiency, n = 32 (13 infants, 12 children, 7 adults). ENPP1 and ABCC6-deficient children aged <8 years and aged 8–18 years reported poor school functioning (0.69 vs 0.72 effect size, respectively) and poor physical health (0.88 vs 1, respectively). In the total ENPP1 cohort, 72% (23/32) reported bone/joint pain and/or mobility/fatigue issues. Three of seven ENPP1-deficient adults reported moderate to severe pain (>4), as measured by the Brief Pain Inventory (BPI), that interfered with daily activities despite pain medication. Top reported burdens for caregivers of infants with ABCC6/ENPP1 Deficiencies included heart-related issues and hospitalizations. Treatment/medications, and hearing loss were the highest burdens reported by caregivers/families of the pediatric ENPP1 Deficiency cohort, whereas adults reported bone/joint pain and mobility impairment as the greatest burdens. Individuals with ENPP1 Deficiency or infant onset ABCC6 Deficiency experience lifelong morbidity causing substantial physical and emotional burden to patients/caregivers.

Osteoblast-specific deficiency of ectonucleotide pyrophosphatase or phosphodiesterase-1 engenders insulin resistance in high-fat diet fed mice

Supraphysiological levels of the osteoblast-enriched mineralization regulator ectonucleotide pyrophosphatase or phosphodiesterase-1 (NPP1) is associated with type 2 diabetes mellitus. We determined the impact of osteoblast-specific Enpp1 ablation on skeletal structure and metabolic phenotype in mice. Female, but not male, 6-week-old mice lacking osteoblast NPP1 expression (osteoblast-specific knockout [KO]) exhibited increased femoral bone volume or total volume (17.50% vs. 11.67%; p < .01), and reduced trabecular spacing (0.187 vs. 0.157 mm; p < .01) compared with floxed (control) mice. Furthermore, an enhanced ability of isolated osteoblasts from the osteoblast-specific KO to calcify their matrix in vitro compared to fl/fl osteoblasts was observed (p < .05). Male osteoblast-specific KO and fl/fl mice showed comparable glucose and insulin tolerance despite increased levels of insulin-sensitizing under-carboxylated osteocalcin (195% increase; p < .05). However, following high-fat-diet challenge, osteoblast-specific KO mice showed impaired glucose and insulin tolerance compared with fl/fl mice. These data highlight a crucial local role for osteoblast NPP1 in skeletal development and a secondary metabolic impact that predominantly maintains insulin sensitivity.

The high expression of NUDT5 indicates poor prognosis of breast cancer by modulating AKT / Cyclin D signaling

NUDIX hydrolase type 5 (NUDT5) is a kind of ADP-ribose pyrophosphatase and nucleotide metabolizing enzyme in cell metabolism. Previous studies have shown NUDT5 expression affected chromosome remodeling, involved in cell adhesion, cancer stem cell maintenance and epithelial to mesenchyme transition in breast cancer cells. Nevertheless, the role of NUDT5 in breast cancer progression and prognosis has not yet been systematically studied. This study explored the association of NUDT5 with the tumor development and poor prognosis in patients with breast cancer. Our results show that the levels of NUDT5 were upregulated in breast cancer cell lines and breast tumor tissues, and the expression of NUDT5 in breast tumor tissues increased significantly when compared with adjacent non-tumorous tissues by immunohistochemical staining of tissue microarrays. Breast cancer patients with high NUDT5 expression had a worse prognosis than those with low expression of NUDT5. In addition, the knockdown of NUDT5 suppressed breast cancer cell lines proliferation, migration and invasion, and dramatically inhibited the AKT phosphorylation at Thr308 and expression of Cyclin D1. The opposite effects were observed in vitro following NUDT5 rescue. Our findings indicated that the high expression of NUDT5 is probably involved in the poor prognosis of breast cancer via the activation of the AKT / Cyclin D pathways, which could be a prognostic factor and potential target in the diagnosis and treatment of breast cancer.

ITPase deficiency causes a Martsolf-like syndrome with a lethal infantile dilated cardiomyopathy

Typical Martsolf syndrome is characterized by congenital cataracts, postnatal microcephaly, developmental delay, hypotonia, short stature and biallelic hypomorphic mutations in either RAB3GAP1 or RAB3GAP2. Genetic analysis of 85 unrelated "mutation negative" probands with Martsolf or Martsolf-like syndromes identified two individuals with different homozygous null mutations in ITPA, the gene encoding inosine triphosphate pyrophosphatase (ITPase). Both probands were from multiplex families with a consistent, lethal and highly distinctive disorder; a Martsolf-like syndrome with infantile-onset dilated cardiomyopathy. Severe ITPase-deficiency has been previously reported with infantile epileptic encephalopathy (MIM 616647). ITPase acts to prevent incorporation of inosine bases (rI/dI) into RNA and DNA. In Itpa-null cells dI was undetectable in genomic DNA. dI could be identified at a low level in mtDNA without detectable mitochondrial genome instability, mtDNA depletion or biochemical dysfunction of the mitochondria. rI accumulation was detectable in proband-derived lymphoblastoid RNA. In Itpa-null mouse embryos rI was detectable in the brain and kidney with the highest level seen in the embryonic heart (rI at 1 in 385 bases). Transcriptome and proteome analysis in mutant cells revealed no major differences with controls. The rate of transcription and the total amount of cellular RNA also appeared normal. rI accumulation in RNA-and by implication rI production-correlates with the severity of organ dysfunction in ITPase deficiency but the basis of the cellulopathy remains cryptic. While we cannot exclude cumulative minor effects, there are no major anomalies in the production, processing, stability and/or translation of mRNA.

ITPA deficiency and ribavirin level are still predictive of anaemia in HCV-HIV-coinfected patients receiving ribavirin combined with a first-generation DAA (ANRS HC27 study)

BACKGROUND

We aimed to determine the impact of inosine triphosphatase (ITPA) deficiency on ribavirin (RBV)-induced anaemia in HIV-HCV-coinfected patients receiving a triple therapy including the haematotoxic direct-acting antiviral agent boceprevir (BOC).

METHODS

Patients of the ANRS HC27 BocepreVIH study were genotyped for two ITPA single nucleotide polymorphisms involved in ITPA deficiency. RBV trough concentration (Ctrough) was determined at week (W)4 and W8. Impact of ITPA deficiency on anaemia, RBV Ctrough, response and haematotoxicity (grade 3/4 anaemia, erythropoietin [EPO] use, RBV dose reduction or transfusion between day [D]0 and W8) was evaluated. Impact of RBV Ctrough on anaemia was also studied.

RESULTS

Among the 63 genotyped patients, 33% had a predicted ITPA deficiency. ITPA deficiency was associated with a lower haemoglobin (Hb) decline both at W4 (-1.0 g/dl versus -2.1 g/dl; P=0.02) and W8 (-2.7 g/dl versus -4.1 g/dl; P=0.05). None of the patients with ITPA deficiency received EPO between D0-W8 versus 26% of patients without ITPA deficiency (P=0.01). RBV Ctrough was associated with Hb decrease both at W4 and W8 and an RBV Ctrough cutoff value of 2 µg/ml was significantly associated with a W4 Hb decline >2 g/dl. Haematotoxicity was significantly associated with a lower W4 Hb level (P=0.017), absence of ITPA deficiency (P=0.018) and higher RBV Ctrough (P=0.012). ITPA deficiency, W4 RBV Ctrough and gender were independent predictors of anaemia at W4. ITPA deficiency was not associated with virological response.

CONCLUSIONS

ITPA deficiency and RBV Ctrough are still predictive of RBV-induced anaemia in HIV-HCV-coinfected patients treated with RBV combined with a first-generation direct antiviral agent.

Mineralisation of collagen rich soft tissues and osteocyte lacunae in Enpp1(-/-) mice

Ecto-nucleotide pyrophosphatase/phosphodiesterases (NPPs) hydrolyse nucleotide triphosphates to the corresponding nucleotide monophosphates and the mineralisation inhibitor, pyrophosphate (PPi). This study examined the role of NPP1 in osteocytes, osteoclasts and cortical bone, using a mouse model lacking NPP1 (Enpp1(-/-)). We used microcomputed tomography (μCT) to investigate how NPP1 deletion affects cortical bone structure; excised humerus bones from 8, 15 and 22-week old mice were scanned at 0.9 μm. Although no changes were evident in the cortical bone of 8-week old Enpp1(-/-) mice, significant differences were observed in older animals. Cortical bone volume was decreased 28% in 22-week Enpp1(-/-) mice, whilst cortical porosity was reduced 30% and 60% at 15 and 22-weeks, respectively. This was accompanied by up to a 15% decrease in closed pore diameter and a 55% reduction in the number of pores. Cortical thickness was reduced up to 35% in 15 and 22-week Enpp1(-/-) animals and the endosteal diameter was increased up to 23%. Thus, the cortical bone from Enpp1(-/-) mice was thinner and less porous, with a larger marrow space. Scanning electron microscopy (SEM) revealed a decrease in the size and number of blood vessel channels in the cortical bone as well as a 40% reduction in the mean plan area of osteocyte lacunae. We noted that the number of viable osteocytes isolated from the long bones of Enpp1(-/-) mice was decreased ≤50%. In contrast, osteoclast formation and resorptive activity were unaffected by NPP1 deletion. μCT and histological analysis of Enpp1(-/-) mice also revealed calcification of the joints and vertebrae as well as soft tissues including the whisker follicles, ear pinna and trachea. This calcification worsened as the animals aged. Together, these data highlight the key role of NPP1 in regulating calcification of both soft and skeletal tissues.

ITPA genotype protects against anemia during peginterferon and ribavirin therapy but does not influence virological response

On-treatment anemia is associated with higher sustained virological response (SVR) rates during peginterferon plus ribavirin (RBV) therapy. Inosine triphosphatase (ITPA) variants causing ITPase deficiency have been shown to protect against RBV-induced anemia. However, ITPase activity has not been associated with SVR. To study this discrepancy, we examined the relationships between ITPase activity, on-treatment anemia, SVR, and RBV levels in hepatitis C virus genotype 1 (HCV-1) patients from the CHARIOT study. ITPA genotype (rs7270101, rs1127354) was used to define ITPase activity in 546 patients. Plasma RBV levels were measured using high-performance liquid chromatography (HPLC). Relationships between ITPase activity, on-treatment hemoglobin (Hb) levels, RBV levels, and SVR were tested using regression modeling, survival analysis, and locally weighted scatterplot smoothing (LOWESS) plot analysis. Hb decline was independently associated with SVR (P<0.0001). ITPase deficiency was present in 35%. ITPase deficiency strongly protected against Hb decline (P<0.0001), but was not associated with SVR (P=0.28). The probability of SVR increased with lower nadir Hb for both wild-type and deficient ITPase activity, but the association curve shifted to describe a parallel relationship at higher Hb levels in patients with ITPase deficiency. In a subset (n=203), we tested the hypothesis that the association between Hb decline and SVR reflected RBV levels rather than actual Hb level. RBV levels were associated with on-treatment Hb decline and SVR, but not ITPase activity. In regression models, adjustment for RBV levels attenuated the association between Hb decline and SVR.

CONCLUSION

ITPase deficiency protects against RBV-induced anemia, but is not associated with SVR. Our data suggest that the relationship between Hb decline and SVR is not mechanistic, but is linked to RBV levels.

Upregulation of IGF2 expression during vascular calcification

The process of vascular calcification shares many similarities with that of skeletal mineralisation and involves the deposition of hydroxyapatite crystals in arteries and cardiac valves. However, the cellular mechanisms responsible have yet to be fully elucidated. In this study, we employed microarray analysis to demonstrate the upregulation of more than >9000 genes during the calcification of murine vascular smooth muscle cells (VSMCs), of which the most significantly, differentially expressed gene was Igf2. Following the validation of increased IGF2 expression by RT-qPCR and immunoblotting in calcifying murine VSMCs, IGF2 expression was further demonstrated in the calcified aorta of the Enpp1(-/-) mouse model of medial aortic calcification. Having confirmed that IGF1R and IGF2R were expressed in cultured murine VSMCs, cell-signalling studies in these cells revealed that IGF2 (50 ng/ml) significantly stimulated the phosphorylation of Akt and Erk1/2 (P<0.05). These results potentially indicate that IGF2 may mediate VSMC calcification via the stimulation of Erk1/2 and Akt signalling. This study suggests that the increased IGF2 expression in calcifying VSMCs may reflect the well-established prenatal role of IGF2, particularly as the osteogenic phenotypic transition of VSMCs in a calcified environment recapitulates many of the events occurring during embryonic development. A full understanding of the importance of IGF2 in this pathological process will lead to a better understanding of the aetiology of vascular calcification.

Mono-allelic and bi-allelic ENPP1 deficiency promote post-injury neointimal hyperplasia associated with increased C/EBP homologous protein expression

OBJECTIVE

Bi-allelic function-inactivating ENPP1 mutations cause artery media calcification (AMC) with associated severe myointimal hyperplasia in generalized arterial calcification of infancy (GACI), whereas mono-allelic ENPP1 deficiency is phenotypically normal. Here, we tested if ENPP1 deficiency promotes abnormal vascular smooth muscle cell (VSMC)-driven responses to injury, with or without calcification. The ER stress mediator C/EBP homologous protein (CHOP) affects neointimal hyperplasia and atherosclerosis, and has paradoxical effects on bone formation. Hence, we assessed relationships between ENPP1 and CHOP in VSMCs.

METHODS

We studied ENPP1-deficient mice and control littermates subjected to left carotid artery ligation, and isolated and studied VSMCs from these and Chop-/- mice, or with CHOP siRNA treatment.

RESULTS

Normal Enpp1-/+ mice, in addition to Enpp1-/- mice prior to AMC development, had accelerated neointimal hyperplasia in response to carotid artery ligation at 7-8 weeks age. Neointimal hyperplasia was linked with robust artery media CHOP expression in situ, but with marked AMC only in injured Enpp1-/- arteries. Cultured, ENPP1-deficient and CHOP-deficient VSMCs had increased migration and proliferation to PDGF. Cultured Chop-/- VSMCs demonstrated increased Pi donor-induced calcification. CHOP was significantly increased in Pi donor treated Enpp1-/- and Enpp1-/+ cultured VSMCs. CHOP siRNA treatment of Enpp1-/- VSMCs increased calcification, associated with elevated expression of tissue nonspecific alkaline phosphatase and the master osteoblastic transcription factor RUNX2.

CONCLUSIONS

Both mono-allelic and bi-allelic ENPP1 deficiency promote dysregulated VSMC function, with robust lesion CHOP expression and enhanced neointimal hyperplasia after injury in vivo, but marked post-injury calcification limited to Enpp1-/- mice. Intimal hyperplasia in GACI appears regulated by biologic effects of ENPP1 deficiency other than calcification, including ER stress. VSMC CHOP excess in ENPP1 deficiency may primarily function to limit VSMC calcification.

The human ITPA polymorphic variant P32T is destabilized by the unpacking of the hydrophobic core

Inosine triphosphate pyrophosphatase (ITPA), a key enzyme involved in maintaining the purity of cellular nucleoside triphosphate pools, specifically recognizes inosine triphosphate and xanthosine triphosphate (including the deoxyribose forms) and detoxifies them by catalyzing the hydrolysis of a phosphoanhydride bond, releasing pyrophosphate. This prevents their inappropriate use as substrates in enzymatic reactions utilizing (d)ATP or (d)GTP. A human genetic polymorphism leads to the substitution of Thr for Pro32 (P32T) and causes ITPA deficiency in erythrocytes, with heterozygotes having on average 22.5% residual activity, and homozygotes having undetectable activity. This polymorphism has been implicated in modulating patients' response to mercaptopurines and ribavirin. Human fibroblasts containing this variant have elevated genomic instability upon treatment with base analogs. We find that the wild-type and P32T forms are dimeric in solution and in the crystal structure. This abolishes the previous speculation that the P32T change disrupts dimerization as a mechanism of inactivation. The only difference in structure from the wild-type protein is that the area surrounding Thr32 is disrupted. Phe31 is flipped from the hydrophobic core out into the solvent, leaving a hole in the hydrophobic core of the protein which likely accounts for the reduced thermal stability of P32T ITPA and ultimately leads to its susceptibility to degradation in human cells. Circular dichroism and thermal denaturation studies confirm these structural results. We propose that the dimer of P32T variant subunit with wild-type subunit is degraded in cells similarly to the P32T homodimer explaining the level of loss of ITPA activity in heterozygotes.

Central role of pyrophosphate in acellular cementum formation

BACKGROUND

Inorganic pyrophosphate (PP(i)) is a physiologic inhibitor of hydroxyapatite mineral precipitation involved in regulating mineralized tissue development and pathologic calcification. Local levels of PP(i) are controlled by antagonistic functions of factors that decrease PP(i) and promote mineralization (tissue-nonspecific alkaline phosphatase, Alpl/TNAP), and those that increase local PP(i) and restrict mineralization (progressive ankylosis protein, ANK; ectonucleotide pyrophosphatase phosphodiesterase-1, NPP1). The cementum enveloping the tooth root is essential for tooth function by providing attachment to the surrounding bone via the nonmineralized periodontal ligament. At present, the developmental regulation of cementum remains poorly understood, hampering efforts for regeneration. To elucidate the role of PP(i) in cementum formation, we analyzed root development in knock-out ((-/-)) mice featuring PP(i) dysregulation.

RESULTS

Excess PP(i) in the Alpl(-/-) mouse inhibited cementum formation, causing root detachment consistent with premature tooth loss in the human condition hypophosphatasia, though cementoblast phenotype was unperturbed. Deficient PP(i) in both Ank and Enpp1(-/-) mice significantly increased cementum apposition and overall thickness more than 12-fold vs. controls, while dentin and cellular cementum were unaltered. Though PP(i) regulators are widely expressed, cementoblasts selectively expressed greater ANK and NPP1 along the root surface, and dramatically increased ANK or NPP1 in models of reduced PP(i) output, in compensatory fashion. In vitro mechanistic studies confirmed that under low PP(i) mineralizing conditions, cementoblasts increased Ank (5-fold) and Enpp1 (20-fold), while increasing PP(i) inhibited mineralization and associated increases in Ank and Enpp1 mRNA.

CONCLUSIONS

Results from these studies demonstrate a novel developmental regulation of acellular cementum, wherein cementoblasts tune cementogenesis by modulating local levels of PP(i), directing and regulating mineral apposition. These findings underscore developmental differences in acellular versus cellular cementum, and suggest new approaches for cementum regeneration.

Altered bone development and an increase in FGF-23 expression in Enpp1(-/-) mice

Nucleotide pyrophosphatase phosphodiesterase 1 (NPP1) is required for the conversion of extracellular ATP into inorganic pyrophosphate (PP(i)), a recognised inhibitor of hydroxyapatite (HA) crystal formation. A detailed phenotypic assessment of a mouse model lacking NPP1 (Enpp1(-/-)) was completed to determine the role of NPP1 in skeletal and soft tissue mineralization in juvenile and adult mice. Histopathological assessment of Enpp1(-/-) mice at 22 weeks of age revealed calcification in the aorta and kidney and ectopic cartilage formation in the joints and spine. Radiographic assessment of the hind-limb showed hyper-mineralization in the talocrural joint and hypo-mineralization in the femur and tibia. MicroCT analysis of the tibia and femur disclosed altered trabecular architecture and bone geometry at 6 and 22 weeks of age in Enpp1(-/-) mice. Trabecular number, trabecular bone volume, structure model index, trabecular and cortical thickness were all significantly reduced in tibiae and femurs from Enpp1(-/-) mice (P<0.05). Bone stiffness as determined by 3-point bending was significantly reduced in Enpp1(-/-) tibiae and femurs from 22-week-old mice (P<0.05). Circulating phosphate and calcium levels were reduced (P<0.05) in the Enpp1(-/-) null mice. Plasma levels of osteocalcin were significantly decreased at 6 weeks of age (P<0.05) in Enpp1(-/-) mice, with no differences noted at 22 weeks of age. Plasma levels of CTx (Ratlaps™) and the phosphaturic hormone FGF-23 were significantly increased in the Enpp1(-/-) mice at 22 weeks of age (P<0.05). Fgf-23 messenger RNA expression in cavarial osteoblasts was increased 12-fold in Enpp1(-/-) mice compared to controls. These results indicate that Enpp1(-/-) mice are characterized by severe disruption to the architecture and mineralization of long-bones, dysregulation of calcium/phosphate homeostasis and changes in Fgf-23 expression. We conclude that NPP1 is essential for normal bone development and control of physiological bone mineralization.

The appearance and modulation of osteocyte marker expression during calcification of vascular smooth muscle cells

Background

Vascular calcification is an indicator of elevated cardiovascular risk. Vascular smooth muscle cells (VSMCs), the predominant cell type involved in medial vascular calcification, can undergo phenotypic transition to both osteoblastic and chondrocytic cells within a calcifying environment.

Methodology/Principal Findings

In the present study, using in vitro VSMC calcification studies in conjunction with ex vivo analyses of a mouse model of medial calcification, we show that vascular calcification is also associated with the expression of osteocyte phenotype markers. As controls, the terminal differentiation of murine calvarial osteoblasts into osteocytes was induced in vitro in the presence of calcifying medium (containing ß-glycerophosphate and ascorbic acid), as determined by increased expression of the osteocyte markers DMP-1, E11 and sclerostin. Culture of murine aortic VSMCs under identical conditions confirmed that the calcification of these cells can also be induced in similar calcifying medium. Calcified VSMCs had increased alkaline phosphatase activity and PiT-1 expression, which are recognized markers of vascular calcification. Expression of DMP-1, E11 and sclerostin was up-regulated during VSMC calcification in vitro. Increased protein expression of E11, an early osteocyte marker, and sclerostin, expressed by more mature osteocytes was also observed in the calcified media of Enpp1^−/− mouse aortic tissue.

Conclusions/Significance

This study has demonstrated the up-regulation of key osteocytic molecules during the vascular calcification process. A fuller understanding of the functional role of osteocyte formation and specifically sclerostin and E11 expression in the vascular calcification process may identify novel potential therapeutic strategies for clinical intervention.

Arterial calcification is driven by RAGE in Enpp1-/- mice

BACKGROUND/AIMS

Ectopic osteochondral differentiation, driven by ENPP1-catalyzed generation of the chondrogenesis and calcification inhibitor inorganic pyrophosphate (PP(i)), promotes generalized arterial calcification of infancy. The multiligand receptor for advanced glycation end-products (RAGE), which promotes atherosclerosis and diabetic cardiovascular and renal complications, also mediates chondrocyte differentiation in response to RAGE ligand calgranulins such as S100A11. Here, we tested RAGE involvement in ENPP1 deficiency-associated arterial calcification.

METHODS

Because ectopic artery calcification in Enpp1-/- mice is P(i)-dependent and mediated by PP(i) deficiency, in vitro studies on effects of S100A11 and RAGE on mouse aortic explants were conducted using exogenous P(i), as well as alkaline phosphatase to hydrolyze ambient PP(i).

RESULTS

S100A11 induced cartilage-specific collagen IX/XI expression and calcification dependent on RAGE in mouse aortic explants that was inhibited by the endogenous RAGE signaling inhibitor soluble RAGE (sRAGE). Enpp1-/- aortic explants demonstrated decreased P(i)-stimulated release of sRAGE, and increased calcification and type IX/XI collagen expression that were suppressed by exogenous sRAGE and by Rage knockout. Last, Rage knockout suppressed spontaneous aortic calcification in situ in Enpp1-/- mice.

CONCLUSION

Cultured Enpp1-/- aortic explants have decreased P(i)-stimulated release of sRAGE, and RAGE promotes ectopic chondrogenic differentiation and arterial calcification in Enpp1-/- mice.

[Animal models for vascular calcification]

Analysis of animal models is indispensable to elucidate the molecular mechanism in vascular calcification (VC) as well as to develop new therapies for VC. Various gene-modified mice that show VC have been reported, and considerable progress has been made through the analyses of these animals. Mice of which bone-calcification regulatory factors were modified are the representative animal models for VC, indicating that these factors certainly regulate VC as well as bone-calcification. Inducible VC in wild-type animals is also an important research tool for developing preventive and therapeutic approach for VC.

Association between inosine triphosphate pyrophosphohydrolase deficiency and azathioprine-related adverse drug reactions in the Chinese kidney transplant recipients

Azathioprine (AZA) is a thiopurine prodrug commonly used in patients with kidney transplantation. The aim of this study is to explore in patients with kidney transplantation whether AZA-related side effects can be explained by the inosine triphophate pyrophosphatase (ITPA) or thiopurine S-methyltransferase (TPMT) polymorphisms using both pheno-and genotyping. Erythrocyte ITPA and TPMT activity of 155 patients with kidney transplantation and AZA therapy was determined by HPLC. The frequencies of ITPA and TPMT polymorphisms were detected. Among 155 patients, three cases with zero activity were homozygote for 94C>A. The allele frequency of the 94C>A polymorphism was 0.12. Allele for the IVS2+21A>C mutation in the patients of this study was not found. Thirty-five cases had stopped azathioprine medication or were on reduced dose due to AZA-related side effects, including hematotoxicity (n = 12), hepatotoxicity (n = 18), gastrointestinal toxicity (n = 5, one patient developed hepatotoxicity simultaneously) and flu-like symptoms (n = 1). No statistical significant associations between ITPA 94C>A phenotype or genotype and AZA-related hematotoxicity or hepatotoxicity could be detected. However, five patients who developed gastrointestinal disturbance, two patients were homozygote for 94C>A and other three patients had 94C>A heterozygous allele. The patient who experienced flu-like symptoms were the remaining homozygote for 94C>A. This study demonstrates that ITPA activity reduced in patients with 94C>A mutation (P < 0.01). Patients with ITPA 94C>A homozygous allele are at high risk to develop AZA-related gastrointestinal toxicity and flu-like symptoms (P < 0.01). TPMT wild-type/ITPA variant (homozygote) is closely related to the AZA-induced side effects (P < 0.01).

ITPA gene variants protect against anaemia in patients treated for chronic hepatitis C

Chronic infection with the hepatitis C virus (HCV) affects 170 million people worldwide and is an important cause of liver-related morbidity and mortality. The standard of care therapy combines pegylated interferon (pegIFN) alpha and ribavirin (RBV), and is associated with a range of treatment-limiting adverse effects. One of the most important of these is RBV-induced haemolytic anaemia, which affects most patients and is severe enough to require dose modification in up to 15% of patients. Here we show that genetic variants leading to inosine triphosphatase deficiency, a condition not thought to be clinically important, protect against haemolytic anaemia in hepatitis-C-infected patients receiving RBV.

The SOS screen in Arabidopsis: a search for functions involved in DNA metabolism

The SOS screen, as originally described by Perkins et al. (1999) [7], was setup with the aim of identifying Arabidopsis functions that might potentially be involved in the DNA metabolism. Such functions, when expressed in bacteria, are prone to disturb replication and thus trigger the SOS response. Consistently, expression of AtRAD51 and AtDMC1 induced the SOS response in bacteria, even affecting E. coli viability. 100 SOS-inducing cDNAs were isolated from a cDNA library constructed from an Arabidopsis cell suspension that was found to highly express meiotic genes. A large proportion of these SOS(+) candidates are clearly related to the DNA metabolism, others could be involved in the RNA metabolism, while the remaining cDNAs encode either totally unknown proteins or proteins that were considered as irrelevant. Seven SOS(+) candidate genes are induced following gamma irradiation. The in planta function of several of the SOS-inducing clones was investigated using T-DNA insertional mutants or RNA interference. Only one SOS(+) candidate, among those examined, exhibited a defined phenotype: silenced plants for DUT1 were sensitive to 5-fluoro-uracil (5FU), as is the case of the leaky dut-1 mutant in E. coli that are affected in dUTPase activity. dUTPase is essential to prevent uracil incorporation in the course of DNA replication.

ITPase-deficient mice show growth retardation and die before weaning

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. Itpa(-/-) mice died about 2 weeks after birth with features of growth retardation and cardiac myofiber disarray, similar to the phenotype of the cardiac alpha-actin KO mouse. Inosine nucleotides were found to accumulate in both the nucleotide pool and RNA of Itpa(-/-) 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.

Pharmacogenetic significance of inosine triphosphatase

Inosine triphosphatase (ITPase) is the enzyme that catalyzes the conversion of inosine triphosphate (ITP) and deoxy-inosine triphosphate (dITP) to inosine monophosphate and deoxy-inosine monophosphate, respectively, thereby maintaining low intracellular concentrations of ITP and dITP. Individuals deficient in ITPase activity were first recognized over 30 years ago. For decades, no clinical significance could be attributed to this inborn error of metabolism whatsoever. In recent years, evidence has started to accumulate that polymorphisms in the gene encoding ITPase are associated with potentially severe adverse drug reactions towards the thiopurine drugs azathioprine and 6-mercaptopurine. The pharmacogenetic significance is presently being debated in the literature. However, the present state of knowledge is still insufficient to definitively determine the pharmacogenetic significance of ITPase. This article aims to review the current knowledge on the role of ITPase in thiopurine metabolism.

Crystal structure of human inosine triphosphatase. Substrate binding and implication of the inosine triphosphatase deficiency mutation P32T

Inosine triphosphatase (ITPA) is a ubiquitous key regulator of cellular non-canonical nucleotide levels. It breaks down inosine and xanthine nucleotides generated by deamination of purine bases. Its enzymatic action prevents accumulation of ITP and reduces the risk of incorporation of potentially mutagenic inosine nucleotides into nucleic acids. Here we describe the crystal structure of human ITPA in complex with its prime substrate ITP, as well as the apoenzyme at 2.8 and 1.1A, respectively. These structures show for the first time the site of substrate and Mg2+ coordination as well as the conformational changes accompanying substrate binding in this class of enzymes. Enzyme substrate interactions induce an extensive closure of the nucleotide binding grove, resulting in tight interactions with the base that explain the high substrate specificity of ITPA for inosine and xanthine over the canonical nucleotides. One of the dimer contact sites is made up by a loop that is involved in coordinating the metal ion in the active site. We predict that the ITPA deficiency mutation P32T leads to a shift of this loop that results in a disturbed affinity for nucleotides and/or a reduced catalytic activity in both monomers of the physiological dimer.

The ITPA c.94C>A and g.IVS2+21A>C sequence variants contribute to missplicing of the ITPA gene

Inosine triphosphate pyrophosphatase (ITPase) catalyzes the conversion of inosine triphosphate (ITP) to the correspondent monophosphate. The ITPA c.94C>A and g.IVS2+21A>C allelic variants are associated with decreased red cell enzyme activity. The ITPA c.94C>A [P32T] sequence variant is associated with an increased risk of adverse drug reactions in patients treated with the thiopurine drug azathioprine. The aim of this study was to explore the molecular mechanisms of ITPase deficiency. ITPA mRNA was extracted from peripheral blood leukocytes (PBL), Epstein-Barr virus transformed lymphoblast cell cultures, reticulocytes, and cultured fibroblast from patients with known ITPA genotypes. ITPA mRNA was reversed transcribed, sequenced and the relative amounts of misspliced transcripts quantitated from three independent experiments. The ITPA g.IVS2+21A>C sequence variant resulted in missplicing of exon 3. The ITPA c.94C>A allelic variant resulted in missplicing of exons 2 and 3 representing, in PBL samples, 61% of the total mRNA expressed in ITPA c.94C>A homozygotes. We proposed that the ITPA c.94C>A allelic variant destroys an exonic splicing silencing (ESS) element in exon 2, resulting in the activation of two nearby upstream 5' splice sites and missplicing of the exons 2 and 3 cassette causing structural changes to the enzyme and contributing to ITPase deficiency.

Genetic basis of inosine triphosphate pyrophosphohydrolase deficiency in the Japanese population

Inosine triphosphate pyrophosphohydrolase (ITPase) is an enzyme that catalyzes the conversion of inosine triphosphate (ITP) to inosine monophosphate and pyrophosphate. In Caucasian populations it is reported that the frequency of cases showing decreased ITPase activity is 5%. The structure of ITPA gene along with five single nucleotide polymorphisms has been reported in Caucasians. We examined ITPase activity and frequency of two polymorphisms (94C>A and IVS2+21A>C) in 100 Japanese individuals. Among these individuals, we observed that three cases with zero activity were homozygote for 94C>A, and were accompanied by abnormal accumulation of ITP in erythrocytes. The cases included in the low ITPase activity group were heterozygote for 94C>A polymorphism. The activity of the heterozygote cases was approximately 27% of the mean value of the wild type. The allele frequency of the 94C>A polymorphism was 0.155, which was 2.6 times higher than that of the Caucasians (0.06). The IVS2+21A>C was not detected in Japanese cases, although it occurred with a frequency of 0.130 in Caucasians. Furthermore, we identified a novel mutation IVS2+68T>G in intron 2 in the case with the lowest enzyme activity in the 94C>A wild type. Since the frequency of ITPA 94C>A polymorphism is higher in the Japanese population than that in Caucasians, it is more important to examine ITPA 94C>A polymorphism in the Japanese population to prevent thiopurine drug toxicity. Pretherapeutic screening of individuals for ITPA polymorphisms should be considered for safer and more tolerable treatment with thiopurine drugs.

Azathioprine and 6-mercaptopurine pharmacogenetics and metabolite monitoring in inflammatory bowel disease

The thiopurine drugs azathioprine and 6-mercaptopurine (6-MP) are well-established in the treatment of inflammatory bowel disease (IBD). However, there is a wide inter- and intra-patient variation in the concentrations of active and toxic metabolites due to their complex metabolism and genetic polymorphisms in metabolizing enzymes. Serious drug toxicity leads to cessation of therapy in 9-25% of patients, and there is failure to achieve efficacy in approximately 15% of cases. Advances in the understanding of thiopurine drug metabolism have led to new genetic and metabolite tests to help clinicians optimize thiopurine use. Thiopurine methyltransferase (TPMT) enzyme activity can predict life-threatening myelotoxicity in the one in 300 patients who are TPMT-deficient. However, myelotoxicity can also occur in the presence of normal TPMT activity so blood count monitoring should remain standard practice. TPMT testing may also aid in dose individualization. 6-Thioguanine nucleotides (6-TGN) are thought to be the predominant active metabolites of the thiopurines. 6-thioguanine nucleotide concentration is correlated with bone marrow toxicity and may also correlate with efficacy in IBD. Measurement of 6-TGN and 6-methylmercaptopurine (6-MMP) concentration is most useful in determining why a patient is not responding to a standard dose of a thiopurine drug and may help in avoiding myelosuppression. The ratio of these metabolites can help distinguish non-compliance, under-dosing, thiopurine-resistant and thiopurine-refractory disease. Some of these investigations are entering routine clinical practice but more research is required to determine their optimal use in patients with IBD.

Sustained osteomalacia of long bones despite major improvement in other hypophosphatasia-related mineral deficits in tissue nonspecific alkaline phosphatase/nucleotide pyrophosphatase phosphodiesterase 1 double-deficient mice

We have shown previously that the hypomineralization defects of the calvarium and vertebrae of tissue nonspecific alkaline phosphatase (TNAP)-deficient (Akp2-/-) hypophosphatasia mice are rescued by simultaneous deletion of the Enpp1 gene, which encodes nucleotide pyrophosphatase phosphodiesterase 1 (NPP1). Conversely, the hyperossification in the vertebral apophyses typical of Enpp1-/- mice is corrected in [Akp2-/-; Enpp1-/-] double-knockout mice. Here we have examined the appendicular skeletons of Akp2-/-, Enpp1-/-, and [Akp2-/-; Enpp1-/-] mice to ascertain the degree of rescue afforded at these skeletal sites. Alizarin red and Alcian blue whole mount analysis of the skeletons from wild-type, Akp2-/-, and [Akp2-/-; Enpp1-/-] mice revealed that although calvarium and vertebrae of double-knockout mice were normalized with respect to mineral deposition, the femur and tibia were not. Using several different methodologies, we found reduced mineralization not only in Akp2-/- but also in Enpp1-/- and [Akp2-/-; Enpp1-/-] femurs and tibias. Analysis of calvarial- and bone marrow-derived osteoblasts for mineralized nodule formation in vitro showed increased mineral deposition by Enpp1-/- calvarial osteoblasts but decreased mineral deposition by Enpp1-/- long bone marrow-derived osteoblasts in comparison to wild-type cells. Thus, the osteomalacia of Akp2-/- mice and the hypomineralized phenotype of the long bones of Enpp1-/- mice are not rescued by simultaneous deletion of TNAP and NPP1 functions.

Idiopathic infantile arterial calcification and persistent pulmonary hypertension

Idiopathic infantile arterial calcification is a rare and usually fatal disorder, which is characterized by widespread vaso-occlusive disease. Presentation is variable, but refractory hypertension is typical, with symptoms of cardiorespiratory failure. Some present in utero with evidence of fetal compromise, which may manifest as hydrops fetalis and premature delivery or stillbirth. Presentation otherwise is usually in the neonatal period with 85% of cases being fatal within the first 6 months. Coronary artery involvement is a poor prognostic feature. The pathophysiology of this disorder is well documented but the underlying etiology remains unknown. An autosomal recessive metabolic disorder is thought likely and this is supported in this case. Pulmonary hypertension has not previously been reported to be a primary feature of this disease. Here we describe such a case in which a newborn underwent extracorporeal membrane oxygenation, and during this time a diagnosis of idiopathic arterial calcification was made.

Deficiencies of physiologic calcification inhibitors and low-grade inflammation in arterial calcification: lessons for cartilage calcification

Apart from clinical parallels, similarities in the pathogenesis of arterial and articular cartilage calcification have come to light in recent years. These include the roles of aging, of chronic low-grade inflammation and of genetic and acquired dysregulation of inorganic pyrophosphate (PP(i)) metabolism. This review focuses on recent developments in understanding the pathogenesis of artery calcification pertinent to interpretation of the mechanistic basis for articular cartilage calcification in aging and osteoarthritis.

Concerted regulation of inorganic pyrophosphate and osteopontin by akp2, enpp1, and ank: an integrated model of the pathogenesis of mineralization disorders

Tissue-nonspecific alkaline phosphatase (TNAP) hydrolyzes the mineralization inhibitor inorganic pyrophosphate (PP(i)). Deletion of the TNAP gene (Akp2) in mice results in hypophosphatasia characterized by elevated levels of PP(i) and poorly mineralized bones, which are rescued by deletion of nucleotide pyrophosphatase phosphodiesterase 1 (NPP1) that generates PP(i). Mice deficient in NPP1 (Enpp1(-/-)), or defective in the PP(i) channeling function of ANK (ank/ank), have decreased levels of extracellular PP(i) and are hypermineralized. Given the similarity in function between ANK and NPP1 we crossbred Akp2(-/-) mice to ank/ank mice and found a partial normalization of the mineralization phenotypes and PP(i) levels. Examination of Enpp1(-/-) and ank/ank mice revealed that Enpp1(-/-) mice have a more severe hypermineralized phenotype than ank/ank mice and that NPP1 but not ANK localizes to matrix vesicles, suggesting that failure of ANK deficiency to correct hypomineralization in Akp2(-/-) mice reflects the lack of ANK activity in the matrix vesicle compartment. We also found that the mineralization inhibitor osteopontin (OPN) was increased in Akp2(-/-), and decreased in ank/ank mice. PP(i) and OPN levels were normalized in [Akp2(-/-); Enpp1(-/-)] and [Akp2(-/-); ank/ank] mice, at both the mRNA level and in serum. Wild-type osteoblasts treated with PP(i) showed an increase in OPN, and a decrease in Enpp1 and Ank expression. Thus TNAP, NPP1, and ANK coordinately regulate PP(i) and OPN levels. The hypomineralization observed in Akp2(-/-) mice arises from the combined inhibitory effects of PP(i) and OPN. In contrast, NPP1 or ANK deficiencies cause a decrease in the PP(i) and OPN pools that leads to hypermineralization.

Adverse drug reactions to azathioprine therapy are associated with polymorphism in the gene encoding inosine triphosphate pyrophosphatase (ITPase)

Adverse drug reactions to azathioprine (AZA), the pro-drug of 6-mercaptopurine (6-MP), occur in 15% to 28% of patients and the majority are not explained by thiopurine methyltransferase (TPMT) deficiency. Inosine triphosphate pyrophosphatase (ITPase) deficiency results in the benign accumulation of the inosine nucleotide ITP. 6-MP is activated through a 6-thio-IMP intermediate and, in ITPase deficient patients, potentially toxic 6-thio-ITP is predicted to accumulate. The association between polymorphism in the ITPA gene and adverse drug reactions to AZA therapy was studied in patients treated for inflammatory bowel disease. Sixty-two patients with inflammatory bowel disease suffering adverse drug reactions to AZA therapy were genotyped for ITPA 94C>A and IVS2 + 21A>C polymorphisms, and TPMT*3A, *3C, *2 polymorphisms. Genotype frequencies were compared to a consecutive series of 68 controls treated with AZA for a minimum of 3 months without adverse effect. The ITPA 94C>A deficiency-associated allele was significantly associated with adverse drug reactions [odds ratio (OR) 4.2, 95% confidence interval (CI) 1.6-11.5, P = 0.0034]. Significant associations were found for flu-like symptoms (OR 4.7, 95% CI 1.2-18.1, P = 0.0308), rash (OR 10.3, 95% CI 4.7-62.9, P = 0.0213) and pancreatitis (OR 6.2,CI 1.1-32.6, P = 0.0485). Overall, heterozygous TPMT genotypes did not predict adverse drug reactions but were significantly associated with a subgroup of patients experiencing nausea and vomiting as the predominant adverse reaction to AZA therapy (OR 5.5, 95% CI 1.4-21.3, P = 0.0206). Polymorphism in the ITPA gene predicts AZA intolerance. Alternative immunosuppressive drugs, particularly 6-thioguanine, should be considered for AZA-intolerant patients with ITPase deficiency.

A Japanese case with inosine triphosphate pyrophosphohydrolase deficiency attributable to an enzymatic defect in white blood cells

Inosine triphosphate pyrophosphohydrolase (ITPase) deficiency is characterized by abnormal accumulation of inosine triphosphate. We describe the first Japanese case with ITPase deficiency and demonstrate that the deficiency of ITPase activity is not only found in erythrocytes but also in white blood cells.

Linked deficiencies in extracellular PP(i) and osteopontin mediate pathologic calcification associated with defective PC-1 and ANK expression

Osteopontin and PP(i) both suppress hydroxyapatite deposition. Extracellular PP(i) deficiency causes spontaneous hypercalcification, yet unchallenged osteopontin knockout mice have only subtle mineralization abnormalities. We report that extracellular PP(i) deficiency promotes osteopontin deficiency and correction of osteopontin deficiency prevents hypercalcification, suggesting synergistic inhibition of hydroxyapatite deposition. Nucleotide pyrophosphatase phosphodiesterase (NPP) isozymes including PC-1 (NPP1) function partly to generate PP(i), a physiologic calcification inhibitor. PP(i) transport is modulated by the membrane channel protein ANK. Spontaneous articular cartilage calcification, increased vertebral cortical bone formation, and peripheral joint and intervertebral ossific ankylosis are associated with both PC-1 deficiency and expression of truncated ANK in ank/ank mice. To assess how PC-1, ANK, and PP(i) regulate both calcification and cell differentiation, we studied cultured PC-1 -/- and ank/ank mouse calvarial osteoblasts. PC-1 -/- osteoblasts demonstrated approximately 50% depressed NPP activity and markedly lowered extracellular PP(i) associated with hypercalcification. These abnormalities were rescued by transfection of PC-1 but not of the NPP isozyme B10/NPP3. PC-1 -/- and ank/ank cultured osteoblasts demonstrated not only comparable extracellular PP(i) depression and hypercalcification but also marked reduction in expression of osteopontin (OPN), another direct calcification inhibitor. Soluble PC-1 (which corrected extracellular PP(i) and OPN), and OPN itself (> or = 15 pg/ml), corrected hypercalcification by PC-1 -/- and ank/ank osteoblasts. Thus, linked regulatory effects on extracellular PP(i) and OPN expression mediate the ability of PC-1 and ANK to regulate calcification.

Genetic basis of inosine triphosphate pyrophosphohydrolase deficiency

Inosine triphosphate pyrophosphohydrolase (ITPase) deficiency is a common inherited condition characterized by the abnormal accumulation of inosine triphosphate (ITP) in erythrocytes. The genetic basis and pathological consequences of ITPase deficiency are unknown. We have characterized the genomic structure of the ITPA gene, showing that it has eight exons. Five single nucleotide polymorphisms were identified, three silent (138G-->A, 561G-->A, 708G-->A) and two associated with ITPase deficiency (94C-->A, IVS2+21A-->C). Homozygotes for the 94C-->A missense mutation (Pro32 to Thr) had zero erythrocyte ITPase activity, whereas 94C-->A heterozygotes averaged 22.5% of the control mean, a level of activity consistent with impaired subunit association of a dimeric enzyme. ITPase activity of IVS2+21A-->C homozygotes averaged 60% of the control mean. In order to explore further the relationship between mutations and enzyme activity, we examined the association between genotype and ITPase activity in 100 healthy controls. Ten subjects were heterozygous for 94C-->A (allele frequency: 0.06), 24 were heterozygotes for IVS2+21A-->C (allele frequency: 0.13) and two were compound heterozygous for these mutations. The activities of IVS2+21A-->C heterozygotes and 94C-->A/IVS2+21A-->C compound heterozygotes were 60% and 10%, respectively, of the normal control mean, suggesting that the intron mutation affects enzyme activity. In all cases when ITPase activity was below the normal range, one or both mutations were found. The ITPA genotype did not correspond to any identifiable red cell phenotype. A possible relationship between ITPase deficiency and increased drug toxicity of purine analogue drugs is proposed.

Tissue-nonspecific alkaline phosphatase and plasma cell membrane glycoprotein-1 are central antagonistic regulators of bone mineralization

Osteoblasts mineralize bone matrix by promoting hydroxyapatite crystal formation and growth in the interior of membrane-limited matrix vesicles (MVs) and by propagating the crystals onto the collagenous extracellular matrix. Two osteoblast proteins, tissue-nonspecific alkaline phosphatase (TNAP) and plasma cell membrane glycoprotein-1 (PC-1) are involved in this process. Mutations in the TNAP gene result in the inborn error of metabolism known as hypophosphatasia, characterized by poorly mineralized bones, spontaneous fractures, and elevated extracellular concentrations of inorganic pyrophosphate (PP(i)). PP(i) suppresses the formation and growth of hydroxyapatite crystals. PP(i) is produced by the nucleoside triphosphate pyrophosphohydrolase activity of a family of isozymes, with PC-1 being the only member present in MVs. Mice with spontaneous mutations in the PC-1 gene have hypermineralization abnormalities that include osteoarthritis and ossification of the posterior longitudinal ligament of the spine. Here, we show the respective correction of bone mineralization abnormalities in knockout mice null for both the TNAP (Akp2) and PC-1 (Enpp1) genes. Each allele of Akp2 and Enpp1 has a measurable influence on mineralization status in vivo. Ex vivo experiments using cultured double-knockout osteoblasts and their MVs demonstrate normalization of PP(i) content and mineral deposition. Our data provide evidence that TNAP and PC-1 are key regulators of the extracellular PP(i) concentrations required for controlled bone mineralization. Our results suggest that inhibiting PC-1 function may be a viable therapeutic strategy for hypophosphatasia. Conversely, interfering with TNAP activity may correct pathological hyperossification because of PP(i) insufficiency.

Animal models of pathologic calcification

Recent progress in genetics and mouse genomics enables researchers to unveil the molecular basis for mouse phenotypes that express pathologic calcification in soft tissue and/or articular tissues. A newly identified multipass transmembrane protein, ANK, appears to function as an inorganic pyrophosphate (PPi) transporter or regulator of PPi transport. Abnormal extracellular PPi (ePPi) metabolism has been implicated in abnormal calcification, decreased concentrations predisposing to basic calcium phosphate (BCP) deposition, and increased concentrations promoting calcium pyrophosphate dihydrate (CPPD) crystal deposition in articular tissues. The chromosomal location of human ANK overlaps the locus identified in several kindreds affected with familial chondrocalcinosis. Deficient generation of ePPi by the ectoenzyme nucleoside triphosphate pyrophosphohydrolase also results in excessive ossification and ectopic deposition of BCP crystals in tiptoe-walking mice and PC-1 null mice. Recent studies reinforce the important regulatory role of ePPi in pathologic and physiologic calcification.

DNA polymorphisms in ITPA including basis of inosine triphosphatase deficiency

Intracellular concentrations of the nucleotide inosine triphosphate (ITP) are regulated by ITP-ase (EC 3.6.1.19), which is encoded by ITPA on chromosome 20p. Subjects with complete deficiency of ITP-ase activity (MIM 147520) have elevated ITP concentrations in erythrocytes, but no obvious clinical abnormalities. Based on biochemical screening, complete ITP-ase deficiency has been postulated to result from homozygosity for a dysfunctional allele, with an estimated frequency of 0.05 in Caucasians. ITP-ase deficiency has not yet been characterized at the molecular genetic level. Sequencing of the genomic DNA from a Caucasian subject with complete ITP-ase deficiency revealed homozygosity for missense mutation 198C>A, which predicted a threonine for proline substitution at codon 32 (P32T), whereas among 125 normal Caucasians, there were no homozygotes for P32T (P = 0.0079). The P32T allele frequency of 0.07 in Caucasians was similar to the estimates derived from earlier biochemical studies. P32T was found to be present at varying frequency in other ethnic groups. Two common synonymous single-nucleotide polymorphisms were also identified. These ITPAmarkers, including P32T, provide tools for further study of association with clinical and biochemical phenotypes.

Osteoblast tissue-nonspecific alkaline phosphatase antagonizes and regulates PC-1

Tissue-nonspecific alkaline phosphatase (TNAP) is essential for bone matrix mineralization, but the central mechanism for TNAP action remains undefined. We observed that ATP-dependent (45)Ca precipitation was decreased in calvarial osteoblast matrix vesicle (MV) fractions from TNAP-/- mice, a model of infantile hypophosphatasia. Because TNAP hydrolyzes the mineralization inhibitor inorganic pyrophosphate (PP(i)), we assessed phosphodiesterase nucleotide pyrophosphatase (PDNP/NTPPPH) activity, which hydrolyzes ATP to generate PP(i). Plasma cell membrane glycoprotein-1 (PC-1), but not the isozyme B10 (also called PDNP3) colocalized with TNAP in osteoblast MV fractions and pericellular matrix. PC-1 but not B10 increased MV fraction PP(i) and inhibited (45)Ca precipitation by MVs. TNAP directly antagonized inhibition by PC-1 of MV-mediated (45)Ca precipitation. Furthermore, the PP(i) content of MV fractions was greater in cultured TNAP-/- than TNAP+/+ calvarial osteoblasts. Paradoxically, transfection with wild-type TNAP significantly increased osteoblast MV fraction NTPPPH. Specific activity of NTPPPH also was twofold greater in MV fractions of osteoblasts from TNAP+/+ mice relative to TNAP-/- mice. Thus TNAP attenuates PC-1/NTPPPH-induced PP(i) generation that would otherwise inhibit MV-mediated mineralization. TNAP also paradoxically regulates PC-1 expression and NTPPPH activity in osteoblasts.

Study of immunogenicity and virulence of bovine herpesvirus 1 mutants deficient in the UL49 homolog, UL49.5 homolog and dUTPase genes in cattle

We previously reported that the bovine herpesvirus 1 (BHV 1) gene homologous to herpes simplex virus gene UL49 is dispensable; nevertheless, a mutant with the UL49 homolog (UL49 h) gene deletion exhibited significantly impaired growth in cell culture. To further evaluate the role of the UL49 h in virus infectivity in the natural host of BHV 1, the pathogenesis of the UL49 h negative mutant was studied in cattle. An additional mutant with a combined defect in UL49 h, UL49.5 h and dUTPase genes was also studied in parallel. We found that both mutants were avirulent in cattle inasmuch as intranasal (i.n.) administration of either mutants induced no apparent clinical disease, nor did animals receiving the mutants shed virus. Following i.n. inoculation with the mutants animals developed low levels of serum neutralizing (SN) antibodies, and were partially protected against wild-type BHV 1 challenge. Intramuscular immunizations with either mutant induced good SN titers, and moreover, they induced nearly complete protection against respiratory challenge with wild-type virus. The results from this study establish that BHV 1 UL49 h is an important virulence factor, and also suggest that deletion of the nonessential viral genes UL49 h, UL49.5 h and dUTPase may be useful in developing recombinant BHV 1 vaccines or BHV 1-based vaccine vectors.

dUTPase-minus caprine arthritis-encephalitis virus is attenuated for pathogenesis and accumulates G-to-A substitutions

The importance of the virally encoded dUTPase for CAEV replication, invasiveness, pathogenesis, and genetic stability was investigated in goats infected by viruses with single point (DU-G) and deletion (DU-1) mutations of the dUTPase gene (DU gene). The DU gene was found to be dispensable for CAEV replication in vivo as judged by times taken to seroconvert, frequencies of viral isolation, and tissue distribution of viral RNAs. DU- reversion at week 34 in one of three goats infected with the single point mutant DU-G, however, suggested that the viral dUTPase confers some advantages for replication in vivo. Moreover, we show that dUTPase is necessary for the timely development of bilateral arthritic lesions of the carpus. Finally, dUTPase was shown to efficiently prevent accumulation of G-to-A transitions in the viral genome.

Attenuation of dUTPase-deficient pseudorabies virus for the natural host

Pseudorabies virus (PrV) is the causative agent of Aujeszky's disease which results in significant losses in pig husbandry. Recently we identified the gene encoding the deoxyuridine-triphosphatase (dUTPase) of PrV as the homolog of the UL50 gene of herpes simplex virus type 1. The PrV UL50 gene product was characterized and a UL50 negative PrV mutant (PrV UL50-) was generated by insertion of a lacZ expression cassette into the UL50 open reading frame (Jöns and Mettenleiter, J. Virol. 70, 1242-1245). Here we show that replication of PrV UL50- in cell culture was only slightly impaired as compared to wild-type PrV strain Ka. After intranasal infection of young pigs PrV UL50- proved to be substantially attenuated, whereas severe clinical signs and death occurred after infection with wild-type PrV. Challenge infection with the highly virulent NIA-3 strain of PrV showed that prior infection with PrV UL50- conferred protection against Aujeszky's disease. Innocuity and efficacy make UL50-negative PrV an attractive candidate for a live PrV vaccine.

Replication in vitro and in vivo of an equine infectious anemia virus mutant deficient in dUTPase activity

As an important enzyme in DNA synthesis, dUTPase is present in a wide variety of organisms and viruses and has been identified as a component of the equine infectious anemia virus (EIAV) pol gene. The role of EIAV dUTPase, designated DU, in virus replication in vitro and in vivo was investigated with a recently described infectious molecular clone of EIAV. A deletion mutant that was deficient in dUTPase activity was constructed, and its replication kinetics was examined in fetal equine kidney (FEK) cells and primary equine bone marrow macrophage (EBMM) cells. In FEK cells, which are permissive for EIAV replication, the mutant virus replicated as well as the parental virus. In primary cultures of EBMM cells, which are primary targets of EIAV infection in vivo, the DU mutant showed delayed replication kinetics and replicated to a lower extent than did the parental virus. As the multiplicity of infection decreased, the difference between the parental and mutant viruses increased, such that at the lowest multiplicity of infection tested, there was over a 100-fold difference in virus production. The mutant virus was also much less cytopathic. The role of DU in replication in vivo was examined using a Shetland pony model of EIAV infection. Shetland ponies that were infected with the parental and mutant viruses showed transient virus RNA levels in plasma approximately 5 to 10 days postinfection. The peak virus levels in plasma (as measured by a quantitative reverse transcriptase PCR assay) were 10- to 100-fold lower in the mutant virus-infected animals than in the animals infected with the parental virus. However, ponies infected with the mutant virus mounted similar antibody responses despite the marked differences in virus replication. These studies demonstrate that EIAV DU is important for the efficient replication of the virus in macrophages in vitro and in vivo and suggests that variations in the DU sequence could markedly affect the biological and pathogenic properties of EIAV.

Characterization of equine infectious anemia virus dUTPase: growth properties of a dUTPase-deficient mutant

The putative dUTPase domain was deleted from the polymerase (pol) gene of equine infectious anemia virus (EIAV) to produce a recombinant delta DUpol Escherichia coli expression cassette and a delta DU proviral clone. Expression of the recombinant delta DUpol polyprotein yielded a properly processed and enzymatically active reverse transcriptase, as determined by immunoblot analysis and DNA polymerase activity gels. Transfection of delta DU provirus into feline (FEA) cells resulted in production of virus that replicated to wild-type levels in both FEA cells and fetal equine kidney cells. In contrast, the delta DU virus replicated poorly (less than 1% of wild-type levels) in primary equine macrophage cultures, as measured by reverse transcriptase assays. Preparations of delta DU virus contained negligible dUTPase activity, which confirms that virion-associated dUTPase is encoded in the pol gene region between the RNase H domain and integrase, as has been demonstrated previously for feline immunodeficiency virus (J. H. Elder, D. L. Lerner, C. S. Hasselkus-Light, D. J. Fontenot, E. Hunter, P. A. Luciw, R. C. Montelaro, and T. R. Phillips, J. Virol. 66:1791-1794, 1992). Our results suggest that virus-encoded dUTPase is dispensable for virus replication in dividing cells in vitro but may be required for efficient replication of EIAV in nondividing equine macrophages, the natural host cells for this virus.

Inosine triphosphate pyrophosphohydrolase deficiency in a kindred with adenosine deaminase deficiency

A complete deficiency of inosine triphosphate pyrophosphohydrolase (ITPase) has been identified, together with high concentrations (mean 157 mumol/l) of the unusual nucleotide ITP, in the erythrocytes of 3 members of a consanguineous United Kingdom kindred. The defect has been noted previously in North America and Sweden, but even in presumed homozygotes some residual ITPase activity was reported. Homozygosity for the defect has not been associated previously with any clinical abnormality. In this kindred it was co-existent with adenosine deaminase (ADA) deficient severe combined immunodeficiency. Since the genes for both ITPase and ADA are localised on the same chromosome, segregation analysis of ITPase and ADA activity was undertaken in available kindred members. The results confirmed an autosomal recessive mode of inheritance for ITPase deficiency, but suggested that the co-existence with ADA deficiency was coincidental.

Purine metabolism in normal and ITP-pyrophosphohydrolase-deficient human erythrocytes

Fresh and stored erythrocytes from normal and ITP-pyrophosphohydrolase (ITP-ase, EC 3.6.1.19) deficient individuals were incubated with hypoxanthine, guanine, allopurinol, and inosine. Differences in the purine metabolism between the normal and the ITP-ase deficient erythrocytes were observed only in the IMP-ITP cycle. Hypoxanthine, guanine and allopurinol were converted to nucleotides at the same rate. Hypoxanthine (2.5 mumol/l) inhibited the salvage of allopurinol (40 mumol/l). A slow decrease (0.7%/day) in salvage rate was observed in both types of cells upon storage at +4 degrees C. Erythrocyte ITP-ase activity was measured in a reference sample group of 48 healthy volunteers. Two distinct groups were found with mean activities equal to 48.3 +/- 13.1 nkat/g Hb (means +/- SD, n = 38) and 11.4 +/- 4.3 nkat/g Hb (n = 10). In two previously selected subjects, the ITP-ase activity was 0.2 and 2.4 nkat/g Hb. A hypothetical genetic mechanism is discussed. The maximal energy turnover in the IMP-ITP cycle during hypoxanthine incubation was found to be less than 10% of the basal erythrocyte energy turnover.

Purine metabolism in normal and high-ITP human erythrocytes. Attempts to evaluate the ability to store the cells

Storage of erythrocyte units from donors with ITP pyrophosphohydrolase deficiency have been studied and compared with units from normal donors. Verifying other investigations the incidence of this genetic disorder was found to be as high as about 3%. Hemolysis in the units was higher than in other units and there was a tendency to low total adenylate concentration. It is suggested that blood centers should organize a quality assurance program where one of the aims should be to detect genetic disorders that make the erythrocytes from the donors less suitable for long term liquid storage.

[Congenital hypophosphatasia]

Hypophosphatasia represents an inborn enzymatic deficiency characterized by a reduced activity of alkaline phosphatase in serum and tissue and an increased urinary excretion of phosphoethanolamine. 278 cases have been described until the end of 1980. Based on the age of manifestation and the predominant clinical findings the following classification is possible: The prenatal form (49 cases) with caput membranaceum, skeletal deformities and respiratory distress has a mortality of 100%. The early infantile form (94 cases) shows rickets-like osseous anomalies, dystrophy, craniostenosis, nephrocalcinosis, mortality amounting to 40%. Diagnostic features of the infantile-juvenile form (112 cases) are premature loss of deciduous teeth, bone deformities, rickets-like findings, and short stature. Mortality is only 1%. The adult form (23 cases) often remains undiscovered and has a good prognosis. It presents with pseudofractures and pains in the bones as chief symptoms. Heredity is autosomal recessive in all four types of hypophosphatasia. Possibly in the adult form there is an additional autosomal dominant inheritance. Alkaline phosphatase deficiency affects all tissues excepting the intestinal isoenzyme. Urinary excretion of phosphoethanolamine is elevated. Values for calcium and inorganic phosphorus in serum are usually normal or only slightly increased. Marked hypercalcemia is observed in severely diseased patients affected by the early infantile form. In these cases hypercalcemia often leads to nephrocalcinosis and renal insufficiency. Since alkaline phosphatase is equally active as pyrophosphatase, reduced phosphatase activity induces an accumulation of pyrophosphate in serum and its increased excretion in urine. The precise pathogenetic mechanisms of hypophosphatasia are still unknown. Possibly, the accumulation of pyrophosphate implies a disorder of calcification. Postnatal diagnosis is based on clinical findings in association with decreased alkaline phosphatase activity and increased phosphoethanolamine excretion. For the detection of heterozygotes additional biochemical markers should be tested. These include the determination of alkaline phosphatase in leucocytes and cultured skin fibroblasts, the calculation of tubular phosphate reabsorption and the analysis of pyrophosphate and pyrophosphatases. The difficulty in ascertaining the carrier state is that the measurement of a single parameter may give normal results.(ABSTRACT TRUNCATED AT 400 WORDS)