http://repub.eur.nl/res/aut/1980/ List of Publications en http://repub.eur.nl/static-eur/img/logo.png http://repub.eur.nl http://repub.eur.nl/res/pub/27299/ 2010-04-01T00:00:00Z Context: It has been shown that mitochondrial DNA (mtDNA) content is associated with type 2 diabetes (T2D) and related traits. However, empirical data, often based on small samples, did not confirm this observation in all studies. Therefore, the role of mtDNA content in T2D remains elusive. Objective: In this study, we assessed the heritability of mtDNA content in buccal cells and analyzed the association of mtDNA content in blood with prevalent and incident T2D. Design and Setting: mtDNA content from cells from buccal and blood samples was assessed using a real-time PCR-based assay. Heritability of mtDNA content was estimated in 391 twins from the Netherlands Twin Register. The association with prevalent T2D was tested in a case control study from The Netherlands (n = 329). Incident T2D was analyzed using prospective samples from Finland (n = 444) and The Netherlands (n = 238). Main Outcome Measures: We measured the heritability of mtDNA content and the association of mtDNA content in blood with prevalent and incident T2D. Results: A heritability of mtDNA content of 35% (19-48%) was estimated in the twin families. We did not observe evidence of an association between mtDNA content and prevalent or incident T2D and related traits. Furthermore, we observed a decline in mtDNA content with increasing age that was male specific (P = 0.001). Conclusion: In this study, we show that mtDNA content has a heritability of 35% in Dutch twins. There is no association between mtDNA content in blood and prevalent or incident T2D and related traits in our study samples. Copyright http://repub.eur.nl/res/pub/25595/ 2010-01-01T00:00:00Z Aims/hypothesis: LARS2 has been previously identified as a potential type 2 diabetes susceptibility gene through the low-frequency H324Q (rs71645922) variant (minor allele frequency [MAF] 3.0%). However, this association did not achieve genome-wide levels of significance. The aim of this study was to establish the true contribution of this variant and common variants in LARS2 (MAF>5%) to type 2 diabetes risk. Methods: We combined genome-wide association data (n=10,128) from the DIAGRAM consortium with independent data derived from a tagging single nucleotide polymorphism (SNP) approach in Dutch individuals (n=999) and took forward two SNPs of interest to replication in up to 11,163 Dutch participants (rs17637703 and rs952621). In addition, because inspection of genome-wide association study data identified a cluster of low-frequency variants with evidence of type 2 diabetes association, we attempted replication of rs9825041 (a proxy for this group) and the previously identified H324Q variant in up to 35,715 participants of European descent. Results: No association between the common SNPs in LARS2 and type 2 diabetes was found. Our replication studies for the two low-frequency variants, rs9825041 and H324Q, failed to confirm an association with type 2 diabetes in Dutch, Scandinavian and UK samples (OR 1.03 [95% CI 0.95-1.12], p=0.45, n=31,962 and OR 0.99 [0.90-1.08], p=0.78, n=35,715 respectively). Conclusions/interpretation: In this study, the largest study examining the role of sequence variants in LARS2 in type 2 diabetes susceptibility, we found no evidence to support previous data indicating a role in type 2 diabetes susceptibility. http://repub.eur.nl/res/pub/15750/ 2009-02-12T00:00:00Z Mitochondria play an important role in many processes, like glucose metabolism, fatty acid oxidation and ATP synthesis. In this study, we aimed to identify association of common polymorphisms in nuclear-encoded genes involved in mitochondrial protein synthesis and biogenesis with type II diabetes mellitus (T2DM) using a two-stage design. In the first stage, we analyzed 62 tagging single nucleotide polymorphisms (SNPs) in the Hoorn study (n=999 participants) covering all common variation in 13 biological candidate genes. These 13 candidate genes were selected from four clusters regarded essential for correct mitochondrial protein synthesis and biogenesis: aminoacyl tRNA synthetases, translation initiation factors, tRNA modifying enzymes and mitochondrial DNA transcription and replication. SNPs showing evidence for association with T2DM were measured in second stage genotyping (n=10164 participants). After a meta-analysis, only one SNP in SIRT4 (rs2522138) remained significant (P=0.01). Extending the second stage with samples from the Danish Steno Study (n=1220 participants) resulted in a common odds ratio (OR) of 0.92 (0.85-1.00), P=0.06. Moreover, in a large meta-analysis of three genome-wide association studies, this SNP was also not associated with T2DM (P=0.72). In conclusion, we did not find evidence for association of common variants in 13 nuclear-encoded mitochondrial proteins with T2DM.European Journal of Human Genetics advance online publication, 11 February 2009; doi:10.1038/ejhg.2009.4. http://repub.eur.nl/res/pub/10387/ 2005-01-01T00:00:00Z Previously, we have shown that a mutation in the mitochondrial DNA-encoded tRNA(Leu(UUR)) gene is associated with type 2 diabetes. One of the consequences of this mutation is a reduced aminoacylation of tRNA(Leu(UUR)). In this study, we have examined whether variants in the leucyl tRNA synthetase gene (LARS2), involved in aminoacylation of tRNA(Leu(UUR)), associate with type 2 diabetes. Direct sequencing of LARS2 cDNA from 25 type 2 diabetic subjects revealed eight single nucleotide polymorphisms. Two of the variants were examined in 7,836 subjects from four independent populations in the Netherlands and Denmark. A -109 g/a variant was not associated with type 2 diabetes. Allele frequencies for the other variant, H324Q, were 3.5% in type 2 diabetic and 2.7% in control subjects, respectively. The common odds ratio across all four studies was 1.40 (95% CI 1.12-1.76), P = 0.004. There were no significant differences in clinical variables between carriers and noncarriers. In this study, we provide evidence that the LARS2 gene may represent a novel type 2 diabetes susceptibility gene. The mechanism by which the H324Q variant enhances type 2 diabetes risk needs to be further established. This is the first report of association between an aminoacyl tRNA synthetase gene and disease. Our results further highlight the important role of mitochondria in glucose homeostasis. http://repub.eur.nl/res/pub/5941/ 2004-01-01T00:00:00Z IGFs are important regulators of pancreatic beta-cell development, growth, and maintenance. Mutations in the IGF genes have been found to be associated with type 2 diabetes, myocardial infarction, birth weight, and obesity. These associations could result from changes in insulin secretion. We have analyzed glucose-stimulated insulin secretion using hyperglycemic clamps in carriers of a CA repeat in the IGF-I promoter and an ApaI polymorphism in the IGF-II gene. Normal and impaired glucose-tolerant subjects (n = 237) were independently recruited from three different populations in the Netherlands and Germany to allow independent replication of associations. Both first- and second-phase insulin secretion were not significantly different between the various IGF-I or IGF-II genotypes. Remarkably, noncarriers of the IGF-I CA repeat allele had both a reduced insulin sensitivity index (ISI) and disposition index (DI), suggesting an altered balance between insulin secretion and insulin action. Other diabetes-related parameters were not significantly different for both the IGF-I and IGF-II gene variant. We conclude that gene variants in the IGF-I and IGF-II genes are not associated with detectable variations in glucose-stimulated insulin secretion in these three independent populations. Further studies are needed to examine the exact contributions of the IGF-I CA repeat alleles to variations in ISI and DI. http://repub.eur.nl/res/pub/8810/ 1998-01-01T00:00:00Z Human Intestine 407 cells respond to hypo-osmotic stress with a rapid stimulation of compensatory ionic conductances accompanied by a transient increase in the activity of the extracellular-signal-regulated protein kinases Erk-1 and Erk-2. In this study, we examined the upstream regulators of hypotonicity-induced Erk-1/Erk-2 activation and their possible role in cell-volume regulation. The hypotonicity-provoked Erk-1/Erk-2 activation was greatly reduced in cells pretreated with the specific mitogen-activated/Erk-activating kinase inhibitor PD098059 and was preceded by a transient stimulation of Raf-1. Pretreatment of the cells with PMA, GF109203X, wortmannin or Clostridium botulinum C3 exoenzyme did not appreciably affect the hypotonicity-provoked Erk-1/Erk-2 stimulation, suggesting the osmosensitive signalling pathway to be largely independent of protein kinase C and p21(rho). In contrast, expression of dominant negative RasN17 completely abolished the hypotonicity-induced Erk-1/Erk-2 activation. Stimulation of the swelling-induced ion efflux was independent of activation of these mitogen-activated protein kinases, as revealed by hypotonicity-provoked isotope efflux from 125I-- and 86Rb+-loaded cells after pretreatment with PD098059 and after expression of RasN17. In addition, the epidermal-growth-factor-induced potentiation of the hypotonicity-provoked anionic response did not depend on the increase in Erk-1/Erk-2 activity but, instead, was found to depend on Ca2+ influx. Taken together, these results indicate that hypotonic stress induces Erk-1/Erk-2 activation through the Ras/Raf-signalling pathway, and argue against a direct role for this pathway in cell-volume control.