Gene-environment interactions in Inflammatory Bowel Disease:Emphasis on smoking and autophagy

Inflammatoire darmziekten (IBD), bestaande uit de ziekte van Crohn (ZvC) en colitis ulcerosa (CU) worden gekenmerkt door chronische ontsteking van het darmslijmvlies. Er ligt een genetische gevoeligheid ter grondslag aan het ontstaan van IBD, maar het zijn juist omgevingsfactoren die deze gevoeligheid voor en het beloop van de ziekte kunnen beïnvloeden. Een belangrijke omgevingsfactor die aantoonbaar van invloed is op IBD is roken. Roken verergert de mate van ontstekingen bij de ZvC, maar opvallend genoeg blijken patiënten met CU juist een gunstig effect te hebben op de ontstekingen bij deze ziekte. Als we darmepitheel cellen en T-lymfocyten bloot te stellen aan sigarettenrook, zien we dat het inflammatie-geïnduceerde apoptose remt wat de ZvC verergerd, maar in CU juist gunstig is. Heat shock eiwitten lijken hierin een belangrijke rol te spelen en dan met name HSPA6. We laten zien dat sigarettenrook het HSPA6 expressie verhoogt (op zowel RNA als eiwit niveau) en het anti-apoptotisch eiwit, Bcl-Xl stabiliseert. Deze bevindingen samen met de significante associatie in het HSPA6 gen met CU suggereren dat HSPA6 bijdraagt aan het anti-apoptotisch effect van sigarettenrook in CU. Welke componenten in sigarettenrook precies verantwoordelijk zijn voor dit effect, en hoe deze aangrijpen, is nog onduidelijk. De T300A variant van het ATG16L1 gen is één van de bekendste en sterkste ZvC-geassocieerde risicovarianten en een mogelijke interactie met sigarettenrook is nog niet eerder aangetoond. ATG16L1 is essentieel is voor (niet-selectieve) autofagie, een proces dat een rol speelt in de overleving van de cel, maar het is ook belangrijk voor de afbraak van bacteriën. We laten zien dat de opname van E. coli en pathogene E. coli (AIEC) in monocyten met de T300A mutatie, significant is verhoogt. Sigarettenrook onderdrukt deze verhoogde opname van E. coli, maar niet van AIEC. Verder laten we zien dat monocyten met de T300A mutatie die zijn gestimuleerd met inflammatoire triggers of sigarettenrook minder goed in staat zijn AIEC af te breken, resulterend in een verstoorde balans van de darmflora en verergering van de ZvC

Role of defective autophagia and the intestinal flora in Crohn disease

The precise mechanisms underlying the development of Crohn disease (CD) remain controversial, but sufficient data have been collected to suggest that an uncontrolled immune response within the intestinal mucosa leads to inflammation in a genetically susceptible host. Although lack of mucosal regulatory T cells causes colitis in humans and experimental rodents, patients with CD have more rather than less regulatory activity in the intestine, apparently excluding defects in tolerance as the cause of CD. Genome-wide association studies have identified many gene variants that confer susceptibility and which seem associated to diminished functioning of especially innate immunity. In apparent agreement, CD patients are impaired with respect to innate immune responses and controlling bacterial flora in the intestine. Furthermore, severe genetic deficiencies in innate immunity, like e.g., lack of NADP oxidase activity or diminished function of the Wiskott Aldrich syndrome protein are associated with colitis in mice and men, and are often mistakenly diagnosed as CD. Thus we favor the view that the primary defect in CD is a lack in innate immunity, causing second tier immunological defenses to combat otherwise easily controlled bacterial breaches of the mucosal barrier.</p

Role of defective autophagia and the intestinal flora in Crohn disease

The precise mechanisms underlying the development of Crohn disease (CD) remain controversial, but sufficient data have been collected to suggest that an uncontrolled immune response within the intestinal mucosa leads to inflammation in a genetically susceptible host. Although lack of mucosal regulatory T cells causes colitis in humans and experimental rodents, patients with CD have more rather than less regulatory activity in the intestine, apparently excluding defects in tolerance as the cause of CD. Genome-wide association studies have identified many gene variants that confer susceptibility and which seem associated to diminished functioning of especially innate immunity. In apparent agreement, CD patients are impaired with respect to innate immune responses and controlling bacterial flora in the intestine. Furthermore, severe genetic deficiencies in innate immunity, like e.g., lack of NADP oxidase activity or diminished function of the Wiskott Aldrich syndrome protein are associated with colitis in mice and men, and are often mistakenly diagnosed as CD. Thus we favor the view that the primary defect in CD is a lack in innate immunity, causing second tier immunological defenses to combat otherwise easily controlled bacterial breaches of the mucosal barrier.</p

Arginine 357 of SecY is needed for SecA-dependent initiation of preprotein translocation

The Escherichia coli SecYEG complex forms a transmembrane channel for both protein export and membrane protein insertion. Secretory proteins and large periplasmic domains of membrane proteins require for translocation in addition the SecA ATPase. The conserved arginine 357 of SecY is essential for a yet unidentified step in the SecA catalytic cycle. To further dissect its role, we have analysed the requirement for R357 in membrane protein insertion. Although R357 substitutions abolish post-translational translocation, they allow the translocation of periplasmic domains targeted co-translationally by an N-terminal transmembrane segment. We propose that R357 is essential for the initiation of SecA-dependent translocation only.

Mice defective in p53 nuclear localization signal 1 exhibit exencephaly

p53 is a major suppressor of human malignancy. The protein levels and activity are tightly regulated in cells. Early experiments identified nuclear localization signal 1 (NLS1) as a regulator of p53 localization. We have generated mice bearing a mutation in p53 ( NLS1 ), designated p53 ( NLS1 ). Our experiments confirm a role for NLS1 in regulating p53 function. Murine embryonic fibroblasts generated from homozygous p53 ( NLS1 ) animals are partially defective in cell cycle arrest and do not respond to inhibitory signals from oncogenic Ras. In addition, p53-dependent apoptosis is abrogated in thymocytes. Contrary to predicted results, fibroblasts from homozygous p53 ( NLS1 ) animals have a greater rate of proliferation than p53-null cells. In addition, p53 ( NLS1 ) cells are more resistant to UV-induced death. Surprisingly, the homozygous p53 ( NLS1 ) animals exhibit embryonic and peri-natal lethality, with a significant portion of the animals developing exencephaly. Thus, p53 ( NLS1/NLS1 ) embryos exhibit a reduced viability relative to p53-null mice. These studies indicate that the NLS1 is a major regulator of p53 activity in vivo