[Complex diseases: the importance of genetics]. / Les maladies complexes: l'importance de la génétique.

Complex diseases usually harbour hereditary factors linked with multiple susceptibility genes. The additive effects of genetic and environmental factors are responsible for the pathology. The impact of heredity has been demonstrated through family studies, but also, and mostly, through the study of adopted people and twins. Recently, genome wide association studies (GWAS) allowed the identification of many susceptibility genes for most complex diseases. However, a large part of the heritability is still missing, probably because of insufficient exploration of rare genetic variants and/or epigenetic factors. The ultimate goal of these genetic studies is the definition of an individual risk leading to specific preventive measures (model "predict and prevent"), but this purpose remains very remote for the majority of complex diseases.

[Genomics of inflammatory bowel diseases: basis for a new molecular classification and new therapeutic strategies of these diseases]. / Génomique des maladies inflammatoires intestinales. Base pour une nouvelle classification moléculaire de ces maladies et source de nouvelles stratégies thérapeutiques.

Inflammatory Bowel Disease, Crohn's disease and ulcerative colitis, are complex, multifactorial, polygenic diseases. Huge progresses in the knowledge of human genome and genotyping techniques have allowed the identifications of dozens of genes and loci associated with these diseases. These discoveries set the path for a new molecular classification of these diseases and let us see new therapeutic possibilities. The present paper highlights, in the setting of the Synthèse CHU 2009 meeting, the contributions of the team of the CHU and university of Liège in this field.

Effect of high osmolarity acclimation on tolerance to hyperosmotic shocks in L929 cultured cells.

Application of abrupt, large hyperosmotic shocks induces in L929 cultured cells changes similar to those previously described in other cell types, notably a hypercondensation of the nuclear chromatin. This paper shows that; 1) this phenomenon is concomitant with a complete disappearance of deoxyribonucleic acid, as visualized by immunogold labelling, from the nucleoplasmic spaces; 2) acclimation to high osmolarities (600 mOsm) by addition to the culture medium of NaCl, sorbitol or proline protects the cells from these effects, which appear to be largely attenuated-acclimated cells also survive much better to the osmotic shock than do control cells and; 3) the best protection seems to be provided by sorbitol and NaCl. Proline acclimation is less effective. These effects are discussed in terms of increased tolerance to NaCl load induced at the level of different macromolecules by so-called 'compensatory' organic compounds.

The role of the Toll receptor pathway in susceptibility to inflammatory bowel diseases.

The intestinal flora has long been thought to play a role either in initiating or in exacerbating the inflammatory bowel diseases (IBD). Host defenses, such as those mediated by the Toll-like receptors (TLR), are critical to the host/pathogen interaction and have been implicated in IBD pathophysiology. To explore the association of genetic variation in TLR pathways with susceptibility to IBD, we performed a replication study and pooled analyses of the putative IBD risk alleles in NFKB1 and TLR4, and we performed a haplotype-based screen for association to IBD in the TLR genes and a selection of their adaptor and signaling molecules. Our genotyping of 1539 cases of IBD and pooled analysis of 4805 cases of IBD validates the published association of a TLR4 allele with risk of IBD (odds ratio (OR): 1.30, 95% confidence interval (CI): 1.15-1.48; P=0.00017) and Crohn's disease (OR: 1.33, 95% CI: 1.16-1.54; P=0.000035) but not ulcerative colitis. We also describe novel suggestive evidence that TIRAP (OR: 1.16, 95% CI: 1.04-1.30; P=0.007) has a modest effect on risk of IBD. Our analysis, therefore, offers additional evidence that the TLR4 pathway - in this case, TLR4 and its signaling molecule TIRAP - plays a role in susceptibility to IBD.

Protein patterns, osmolytes, and aldose reductase of L-929 cells exposed to hyperosmotic media.

L-929 cells acclimated to media made hyperosmotic (600 mosmol/kgH2O) by addition of NaCl, sorbitol, or mannitol show, on SDS-polyacrylamide gels, a markedly enhanced protein band at 40 kDa, most likely corresponding to the enzyme aldose reductase. The effect was not observed in cells acclimated to a medium rendered hyperosmotic by addition of proline. The major organic osmolyte accumulated is sorbitol in cells acclimated to high-sorbitol or high-NaCl medium, proline in cells acclimated to high-proline medium. Cells acclimated to any of these hyperosmotic media display unaltered Na+ levels and similarly increased K+ levels and decreased Cl-levels. These results are interpreted in terms of the mechanisms involved in aldose reductase induction and in regulation of the enzyme activity in long-term acclimation to hyperosmotic media.

Changes in major intracellular osmolytes in L-929 cells following rapid and slow application of hyperosmotic media.

Cultured L-929 cells respond to media-made hyperosmotic (600 mOsmol/kg H2O) by addition of NaCl, sorbitol or proline by adjusting successively their intracellular level in different osmolytes: Na+, K+, amino acids and sorbitol. In the NaCl medium, Na+ and K+ are first to increase. Their concentration is then down-regulated while they are replaced by less disrupting osmolytes: amino acids and sorbitol. The amino-acid level is also adjusted with respect to the increase in sorbitol which starts only after 24 h, depending on the induction of aldose reductase. A similar evolution in the amount of these osmolytes is observed, with different time scales and amplitudes, depending on whether the osmotic shocks are applied abruptly or slowly, in a more physiological way. The interplay between the osmolytes is also different depending on their availability in the external medium. Such complex evolutions indicate that a cascade of interacting signals must be considered to account for the overall regulation process. It can hardly be fitted into a model implicating a single primary signalling event (early increase in ions or decrease in cell volume) as usually postulated. Also, the volume up-regulation is not significantly different in the different conditions, showing that it is not primarily dependent on the adjustment of the intracellular osmolarity which is reached immediately upon cell shrinkage and is maintained all over, independently of the availability and changes in nature of the osmolytes.

Purification, characterization, and nucleotide sequence of the thermolabile alpha-amylase from the antarctic psychrotroph Alteromonas haloplanctis A23.

The alpha-amylase excreted by the antarctic bacterium Alteromonas haloplanctis was purified and the corresponding amy gene was cloned and sequenced. N- and C-terminal amino acid sequencing were used to establish the primary structure of the mature A. haloplanctis alpha-amylase which is composed of 453 amino acids with a predicted Mr of 49,340 and a pI of 5.5. Three Ca2+ ions are bound per molecule and its activity is modulated by chloride ions. Within the four consensus sequences, Asp-174, Glu-200, and Asp-264 are the proposed catalytic residues. The psychrotrophic A. haloplanctis alpha-amylase is characterized by a high amylolytic activity at low temperatures, a reduced apparent optimal temperature, and typical thermodynamic activation parameters A. haloplanctis alpha-amylase has also a low thermal stability as demonstrated by the temperature effect on both activity and secondary structure. It is suggested that structure flexibility and lower sensitivity of secondary structure to temperature variations in the low temperature range are the main structural adaptations of the psychrotrophic enzyme. The unusual stacking of small amino acids around the catalytic residues is proposed as a factor inducing active site flexibility and concomitant high activity of the enzyme at low temperatures.