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Inferring a person's smoking habit and history from blood is relevant for complementing or replacing self-reports in epidemiological and public health research, and for forensic applications. However, a finite DNA methylation marker set and a validated statistical model based on a large dataset are not yet available. Employing 14 epigenome-wide association studies for marker discovery, and using data from six population-based cohorts (N = 3764) for model building, we identified 13 CpGs most suitable for inferring smoking versus non-smoking status from blood with a cumulative Area Under the Curve (AUC) of 0.901. Internal fivefold cross-validation yielded an average AUC of 0.897 +/- 0.137, while external model validation in an independent population-based cohort (N = 1608) achieved an AUC of 0.911. These 13 CpGs also provided accurate inference of current (average AUC(crossvalidation) 0.925 +/- 0.021, AUC(externalvalidation)0.914), former (0.766 +/- 0.023, 0.699) and never smoking (0.830 +/- 0.019, 0.781) status, allowed inferring pack-years in current smokers (10 pack-years 0.800 +/- 0.068, 0.796; 15 pack-years 0.767 +/- 0.102, 0.752) and inferring smoking cessation time in former smokers (5 years 0.774 +/- 0.024, 0.760; 10 years 0.766 +/- 0.033, 0.764; 15 years 0.767 +/- 0.020, 0.754). Model application to children revealed highly accurate inference of the true non- smoking status (6 years of age: accuracy 0.994, N = 355; 10 years: 0.994, N = 309), suggesting prenatal and passive smoking exposure having no impact on model applications in adults. The finite set of DNA methylation markers allow accurate inference of smoking habit, with comparable accuracy as plasma cotinine use, and smoking history from blood, which we envision becoming useful in epidemiology and public health research, and in medical and forensic applications.

International audience; Aim: Homocysteine (Hcy) is a sensitive marker of one-carbon metabolism. Higher Hcy levels have been associated with global DNA hypomethylation. We investigated the association between plasma Hcy and epigenome-wide DNA methylation in leukocytes.Methods: Methylation was measured using Illumina 450 k arrays in 2035 individuals from six cohorts. Hcy-associated differentially methylated positions and regions were identified using meta-analysis.Results: Three differentially methylated positions cg21607669 (SLC27A1), cg26382848 (AJUBA) and cg10701000 (KCNMA1) at chromosome 19, 14 and 10, respectively, were significantly associated with Hcy. In addition, we identified 68 Hcy-associated differentially methy-lated regions, the most significant of which was a 1.8-kb spanning domain (TNXB/ATF6B) at chromosome 6.Conclusion: We identified novel epigenetic loci associated with Hcy levels, of which specific role needs to be further validated.

In the first part of this thesis we focus on the genetic determinants of lipid metabolism as atherogenic dyslipidemia is major component of cardiometabolic disease and consequently of CVD. In the second part of the thesis, we study the age-related changes of cardiometabolic risk factors over the life course across four generations. In this thesis, we aimed to gain new insights into the underlying pathophysiology of cardiometabolic disease and the long-term and cumulative exposure of its risk factors over the life course, thereby facilitating the search for preventive and curative strategies of cardiometabolic disease. In the first part of this thesis, we focused on the genetic determinants of lipid metabolism during both fasting and postprandial states. In the second part, we studied the age-related changes of cardiometabolic risk factors, in particular of body weight, overweight and obesity, over the life course across four generations. An important finding of the thesis is that obesity has worsened in the younger generations, reaching almost double the prevalence of older generations. However, after midlife the levels of obesity levelled off, which could be a reason why the adverse shift in obesity was not associated with unfavourable changes in cardiometabolic risk factors. We also found out that some genes effect body weight differently at different ages, which suggests that gene-environment interactions play an important role in body weight and consequently in obesity.

In the first part of this thesis we focus on the genetic determinants of lipid metabolism as atherogenic dyslipidemia is major component of cardiometabolic disease and consequently of CVD. In the second part of the thesis, we study the age-related changes of cardiometabolic risk factors over the life course across four generations. In this thesis, we aimed to gain new insights into the underlying pathophysiology of cardiometabolic disease and the long-term and cumulative exposure of its risk factors over the life course, thereby facilitating the search for preventive and curative strategies of cardiometabolic disease. In the first part of this thesis, we focused on the genetic determinants of lipid metabolism during both fasting and postprandial states. In the second part, we studied the age-related changes of cardiometabolic risk factors, in particular of body weight, overweight and obesity, over the life course across four generations. An important finding of the thesis is that obesity has worsened in the younger generations, reaching almost double the prevalence of older generations. However, after midlife the levels of obesity levelled off, which could be a reason why the adverse shift in obesity was not associated with unfavourable changes in cardiometabolic risk factors. We also found out that some genes effect body weight differently at different ages, which suggests that gene-environment interactions play an important role in body weight and consequently in obesity.

This thesis aims to increase the understanding of human osteoarthritis pathophysiology by developing reliable biomimetic ex vivo human osteochondral explant models and focussing on the role of osteoarthritis-relevant triggers (mechanical stress) and interacting genetic factors for developing treatment targets. Human aged joint tissues were collected in the Research in Articular Osteoarthritis Cartilage (RAAK) biobank. To add knowledge of the osteoarthritis pathophysiological processes, aged human ex vivo osteochondral explants were subject to three osteoarthritis-relevant triggers, being inflammation, hypertrophy and injurious mechanical stress. Next, knowledge on early initiating processes occurring in mechano-pathology was investigated by applying RNA-sequencing to cartilage of aged human osteochondral explants subjected to mechanical stress. In addition, to show that the human osteochondral explant model could also be used for genetic interaction studies, we investigated expression of the osteoarthritis risk gene MGP in relation to rs1800801 genotypes. By combining information from RNA-sequencing datasets of cartilage and bone with osteoarthritis-relevant triggers in cartilage and bone explants we investigated the role of MGP and vitamin K in osteoarthritis. Lastly, the injurious mechanical explant model was exploited to determine the effectivity of inhibiting the osteoarthritis risk gene DIO2 by iopanoic acid treatment either by burst or prolonged release from PLGA-PEG nanoparticles.

The studies described in this thesis provides the field with valuable data on the potential therapeutic effects of fatty acids and specialized pro-resolving lipid mediators in rheumatoid arthritis and osteoarthritis. The omega-6 fatty acid AdA shows potent pro-resolving effects on the production of pro-inflammatory chemoattractantLTB4 with great promise to limit RA disease progression. In contrast to the promising potential therapeutic effects of AdA in RA, the evidence for pro-resolving effects in OA is still scarce. The results of the studies from this thesis show that neither LXA4, LXB4, RvE2 or Mar-1 were able to reduce OA disease activity in the experimental set-up we used. Finally, the studies described in this thesis show the utmost critical importance of the right sample preparation and storage for the intended subsequent analysis.