Most human tumours have genetic mutations in their Rb and p53 pathways, but retinoblastoma is thought to be an exception. Studies suggest that retinoblastomas, which initiate with mutations in the gene retinoblastoma 1 (RB1), bypass the p53 pathway because they arise from intrinsically death-resistant cells during retinal development. In contrast to this prevailing theory, here we show that the tumour surveillance pathway mediated by Arf, MDM2, MDMX and p53 is activated after loss of RB1 during retinogenesis. RB1-deficient retinoblasts undergo p53-mediated apoptosis and exit the cell cycle. Subsequently, amplification of the MDMX gene and increased expression of MDMX protein are strongly selected for during tumour progression as a mechanism to suppress the p53 response in RB1-deficient retinal cells. Our data provide evidence that the p53 pathway is inactivated in retinoblastoma and that this cancer does not originate from intrinsically death-resistant cells as previously thought. In addition, they support the idea that MDMX is a specific chemotherapeutic target for treating retinoblastoma.

Disease incidences increase with age, but the molecular characteristics of ageing that lead to increased disease susceptibility remain inadequately understood. Here we perform a whole-blood gene expression meta-analysis in 14,983 individuals of European ancestry (including replication) and identify 1,497 genes that are differentially expressed with chronological age. The age-associated genes do not harbor more age-associated CpG-methylation sites than other genes, but are instead enriched for the presence of potentially functional CpG-methylation sites in enhancer and insulator regions that associate with both chronological age and gene expression levels. We further used the gene expression profiles to calculate the ‘transcriptomic age' of an individual, and show that differences between transcriptomic age and chronological age are associated with biological features linked to ageing, such as blood pressure, cholesterol levels, fasting glucose, and body mass index. The transcriptomic prediction model adds biological relevance and complements existing epigenetic prediction models, and can be used by others to calculate transcriptomic age in external cohorts.

Cyclin-dependent kinase 5 (cdk5) is highly homologous to other members of the cdk family that are known to function in proliferating cells. Despite the structural similarity, cdk5-associated histone H1 kinase activity is only detectable in postmitotic neurons of the central nervous system (CNS). p35 is a neuronal-specific cdk5 regulator that activates cdk5 kinase activity upon association. The cdk5/p35 kinase activity increases during the progression of CNS neurogenesis, suggesting a function of cdk5 in neuronal differentiation. Here we show that both cdk5 and p35 proteins are present in the growth cones of developing neurons. The staining pattern of cdk5 in the growth cones is similar to that of actin filaments but not microtubules. To address the functional significance of the cdk5/p35 kinase in neurogenesis, we ectopically expressed wild-type or mutant kinases in cortical cultures. Expression of dominant-negative mutants of cdk5 (cdk5N 144 and cdk5T 33) inhibited neurite outgrowth, which was rescued by coexpression of the wild-type proteins. A similar extent of neurite outgrowth inhibition was obtained by transfection of an antisense p35 construct, which in turn was only rescued by p35 but not cdk5 coexpression. In contrast, longer neurites were elaborated in neurons that coexpressed exogenous cdk5 and p35. These observations suggest that the cdk5/p35 kinase plays a critical role in neurite outgrowth during neuronal differentiation.

Thyroid dysfunction is an important public health problem, which affects 10% of the general population and increases the risk of cardiovascular morbidity and mortality. Many aspects of thyroid hormone regulation have only partly been elucidated, including its transport, metabolism, and genetic determinants. Here we report a large meta-analysis of genome-wide association studies for thyroid function and dysfunction, testing 8 million genetic variants in up to 72,167 individuals. One-hundred-and-nine independent genetic variants are associated with these traits. A genetic risk score, calculated to assess their combined effects on clinical end points, shows significant associations with increased risk of both overt (Graves’ disease) and subclinical thyroid disease, as well as clinical complications. By functional follow-up on selected signals, we identify a novel thyroid hormone transporter (SLC17A4) and a metabolizing enzyme (AADAT). Together, these results provide new knowledge about thyroid hormone physiology and disease, opening new possibilities for therapeutic targets.

ObjectiveIdentify gene expression profiles associated with OA processes in articular cartilage and determine pathways changing during the disease process.MethodsGenome wide gene expression was determined in paired samples of OA affected and preserved cartilage of the same joint using microarray analysis for 33 patients of the RAAK study. Results were replicated in independent samples by RT-qPCR and immunohistochemistry. Profiles were analyzed with the online analysis tools DAVID and STRING to identify enrichment for specific pathways and protein-protein interactions.ResultsAmong the 1717 genes that were significantly differently expressed between OA affected and preserved cartilage we found significant enrichment for genes involved in skeletal development (e.g. TNFRSF11B and FRZB). Also several inflammatory genes such as CD55, PTGES and TNFAIP6, previously identified in within-joint analyses as well as in analyses comparing preserved cartilage from OA affected joints versus healthy cartilage were among the top genes. Of note was the high up-regulation of NGF in OA cartilage. RT-qPCR confirmed differential expression for 18 out of 19 genes with expression changes of 2-fold or higher, and immunohistochemistry of selected genes showed a concordant change in protein expression. Most of these changes associated with OA severity (Mankin score) but were independent of joint-site or sex.ConclusionWe provide further insights into the ongoing OA pathophysiological processes in cartilage, in particular into differences in macroscopically intact cartilage compared to OA affected cartilage, which seem relatively consistent and independent of sex or joint. We advocate that development of treatment could benefit by focusing on these similarities in gene expression changes and/or pathways.