Role of GALNT2 in the modulation of ENPP1 expression, and insulin signaling and action: GALNT2: a novel modulator of insulin signaling.

Ectonucleotide pyrophosphatase phosphodiesterase 1 (ENPP1) inhibits insulin signaling and action. Understanding the mechanisms underlying ENPP1 expression may help unravel molecular mechanisms of insulin resistance. Recent data suggest a role of ENPP1-3'untraslated region (UTR), in controlling ENPP1 expression. We sought to identify trans-acting ENPP1-3'UTR binding proteins, and investigate their role on insulin signaling. By RNA pull-down, 49 proteins bound to ENPP1-3'UTR RNA were identified by mass spectrometry (MS). Among these, in silico analysis of genome wide association studies and expression profile datasets pointed to N-acetylgalactosaminyltransferase 2 gene (GALNT2) for subsequent investigations. Gene expression levels were evaluated by RT-PCR. Protein expression levels, IRS-1 and Akt phosphorylation were evaluated by Western blot. Insulin receptor (IR) autophosphorylation was evaluated by ELISA. GALNT2 down-regulation increased while GALNT2 over-expression reduced ENPP1 expression levels. In addition, GALNT2 down-regulation reduced insulin stimulation of IR, IRS-1 and Akt phosphorylation and insulin inhibition of phosphoenolpyruvate carboxykinase (PEPCK) expression, a key neoglucogenetic enzyme. Our data point to GALNT2 as a novel factor involved in the modulation of ENPP1 expression as well as insulin signaling and action in human liver HepG2 cells.

Role of somatomedin-B-like domains on ENPP1 inhibition of insulin signaling.

The exact mechanism by which ectonucleotide pyrophosphatase phosphodiesterase 1 (ENPP1) inhibits insulin signaling is not known. ENPP1 contains two somatomedin-B-like domains (i.e. SMB 1 and 2) involved in ENPP1 dimerization in animal cells. The aim of the present study was to investigate if these domains modulate ENPP1 inhibitory activity on insulin signaling in human insulin target cells (HepG2). ENPP1 (ENPP1-3'myc), ENPP1 deleted of SMB 1 (ENPP1-ΔI-3'myc) or of SMB 2 (ENPP1-ΔII-3'myc) domain were cloned in frame with myc tag in mammalian expression vector pRK5. Plasmids were transiently transfected in human liver HepG2 cells. ENPP1 inhibitory activity on insulin signaling, dimerization and protein-protein interaction with insulin receptor (IR), reported to mediate the modulation of ENPP1 inhibitory activity, were studied. As compared to untransfected cells, a progressive increase of ENPP1 inhibitory activity on insulin-induced IR ß-subunit autophosphorylation and on Akt-S(473) phosphorylation was observed in ENPP1-3'myc, ENPP1-ΔI-3'myc and ENPP1-ΔII-3'myc cells. Under non reducing conditions a 260 kDa homodimer, indicating ENPP1 dimerization, was observed. The ratio of non reduced (260 kDa) to reduced (130 kDa) ENPP1 was significantly decreased by two thirds in ENPP1-ΔII-3'myc vs. ENPP1-3'myc but not in ENPP1-ΔI-3'myc. A similar ENPP1/IR interaction was detectable by co-immunoprecipitation in ENPP1-3'myc, ENPP1-ΔI-3'myc and ENPP1-ΔII-3'myc cells. In conclusion, SMB 1 and SMB 2 are negative modulators of ENPP1 inhibitory activity on insulin signaling. For SMB 2 such effect might be mediated by a positive role on protein dimerization.

Pharmacogenetics of dabigatran etexilate interindividual variability.

INTRODUCTION: Dabigatran etexilate is given in fixed doses without coagulation monitoring for the prevention of blood clots in at risk adults. A high inter-individual variability in blood concentrations of the active metabolite of dabigatran has been reported. ABCB1 and CES1 exert an important effect in the metabolism of dabigatran etexilate and allele variants at these two loci are likely to play a pivotal role. To investigate whether screening for polymorphisms within the ABCB1 and the CES1 genes would explain a portion of the inter-individual variability in blood concentrations of the active metabolite of dabigatran. MATERIAL AND METHODS: In a cohort of patients who had atrial fibrillation and on anticoagulant prophylaxis with dabigatran etexilate, we investigated whether genotypes at rs4148738 (ABCB1), rs8192935 (CES1), and rs2244613 (CES1) loci would affect plasma dabigatran trough and peak concentrations. RESULTS AND DISCUSSION: Among 92 patients (median age: 72.0years, range: 52-92) analyzed, no clinical variable or genotype was associated with a significant difference in dabigatran peak concentrations. As for trough concentrations, in addition to creatinine clearance, and sex a significant association with the CES1 SNP rs8192935 (p=0.023) was detected. The mean adjusted plasma levels were higher among patients with the CC genotype (86.3ng/dl) than in those carrying the T allele (62.1ng/dl). No significant effect was found for the ABCB1 SNP rs4148738. The CES1 SNP rs8192935 significantly influenced the dabigatran trough concentrations and carriers of the T allele showed significantly lower concentrations than did carriers of the CC genotype.

Phenylalanine hydroxylase deficiency in south Italy: Genotype-phenotype correlations, identification of a novel mutant PAH allele and prediction of BH4 responsiveness.

We investigated the mutation spectrum of the phenylalanine hydroxylase gene (PAH) in a cohort of patients from 33 Italian PKU families. Mutational screening of the known coding region, including conventional intron splice sites, was performed by direct sequencing of the patients' genomic DNA. Thirty-three different disease causing mutations were identified in our patient group, including 19 missense, 6 splicing, 3 nonsense, 5 deletions, with a detection rate of 100%. The most prevalent mutation was the IVS10-11G>A, accounting for 12.1% of PKU alleles studied. Other frequent mutations were: p.R261Q (9.1%), p.P281L (7.6%), and p.R408W (6.1%). We also identified one novel missense mutation, p.H290Q. A spectrum of 31 different genotypes was observed and a genotype based predictions of BH4-responsiveness were assessed. Among all genotypes, 13 were predicted to be BH4-responsive represented by thirteen PKU families. In addition, genotype-phenotype correlations were performed. This study reveals the importance of a full genotyping of PKU patients and the prediction of BH4-responsiveness, not only because of the definitive diagnosis and prediction of the optimal diet, but also to point out those patients that could benefit from new therapeutic approach. They may potentially benefit from BH4 therapy which, combined with a less strict diet, or eventually in special cases as monotherapy, may contribute to reduce nutritional deficiencies and minimize neurological and psychological dysfunctions.

Intra-familiar discordant PKU phenotype explained by mutation analysis in three pedigrees.

Classical phenylketonuria (PKU) and mild hyperphenylalaninemia (MHP) are two phenotypes of phenylalanine hydroxylase (PAH) deficiency with different degrees of severity. We have analyzed three families in which classical PKU, MHP and a normal phenotype occurred within each family due to the different combinations of three mutations segregating within the family. Indeed, sequence PAH analysis revealed three different alleles segregating in each family. This report suggests that when discordant phenotypes occur in a family, complete analysis of the PAH gene may be performed in order to support the diagnosis and assist in accurate genetic counseling and patient management. We further support the marked heterogeneity of hyperphenylalaninemia primarily due to allelic heterogeneity at the PAH locus.

Mutation analysis in hyperphenylalaninemia patients from South Italy.

BACKGROUND: Mutations in the gene encoding phenylalanine hydroxylase (PAH, EC 1.14.16.1) are associated with various degrees of hyperphenylalaninemia (HPA), including classical phenylketonuria (PKU). OBJECTIVE: The aim of the study was to determine the mutations responsible for mild forms of HPA and to relate different clinical phenotypes of HPA patients to their PAH genotypes in order to better predict the clinical phenotype and implement optimal dietary therapy and prognosis in newborns with the disease. METHODS: Phenylalanine hydroxylase (PAH) gene mutations have been analyzed by direct DNA sequencing in 30 HPA patients (Phe levels ranging from 2 to 6mg/dL) from Southern Italy who were identified in a neonatal screening program and a genotype-phenotype correlation was performed. RESULTS: PAH gene mutation was identified in 39 out of 60 alleles with a mutation detection rate of 65%. Eighteen mutations, 2 undescribed, were observed (13 missense mutations, 1 deletion, 4 splice site mutations). Using the "in vitro" predicted residual activity, a good genotype-phenotype correlation was obtained also in a new mild HPA case, a PAH compound heterozygote, previously undetected. CONCLUSION: A marked genetic heterogeneity was found in HPA patients from Southern Italy and a good genotype-phenotype correlation was obtained. Identification of PAH gene mutations responsible for PAH deficiency will therefore be useful in the prediction of biochemical and clinical phenotypes in HPA patients.

ENPP1 affects insulin action and secretion: evidences from in vitro studies.

The aim of this study was to deeper investigate the mechanisms through which ENPP1, a negative modulator of insulin receptor (IR) activation, plays a role on insulin signaling, insulin secretion and eventually glucose metabolism. ENPP1 cDNA (carrying either K121 or Q121 variant) was transfected in HepG2 liver-, L6 skeletal muscle- and INS1E beta-cells. Insulin-induced IR-autophosphorylation (HepG2, L6, INS1E), Akt-Ser(473), ERK1/2-Thr(202)/Tyr(204) and GSK3-beta Ser(9) phosphorylation (HepG2, L6), PEPCK mRNA levels (HepG2) and 2-deoxy-D-glucose uptake (L6) was studied. GLUT 4 mRNA (L6), insulin secretion and caspase-3 activation (INS1E) were also investigated. Insulin-induced IR-autophosphorylation was decreased in HepG2-K, L6-K, INS1E-K (20%, 52% and 11% reduction vs. untransfected cells) and twice as much in HepG2-Q, L6-Q, INS1E-Q (44%, 92% and 30%). Similar data were obtained with Akt-Ser(473), ERK1/2-Thr(202)/Tyr(204) and GSK3-beta Ser(9) in HepG2 and L6. Insulin-induced reduction of PEPCK mRNA was progressively lower in untransfected, HepG2-K and HepG2-Q cells (65%, 54%, 23%). Insulin-induced glucose uptake in untransfected L6 (60% increase over basal), was totally abolished in L6-K and L6-Q cells. GLUT 4 mRNA was slightly reduced in L6-K and twice as much in L6-Q (13% and 25% reduction vs. untransfected cells). Glucose-induced insulin secretion was 60% reduced in INS1E-K and almost abolished in INS1E-Q. Serum deficiency activated caspase-3 by two, three and four folds in untransfected INS1E, INS1E-K and INS1E-Q. Glyburide-induced insulin secretion was reduced by 50% in isolated human islets from homozygous QQ donors as compared to those from KK and KQ individuals. Our data clearly indicate that ENPP1, especially when the Q121 variant is operating, affects insulin signaling and glucose metabolism in skeletal muscle- and liver-cells and both function and survival of insulin secreting beta-cells, thus representing a strong pathogenic factor predisposing to insulin resistance, defective insulin secretion and glucose metabolism abnormalities.