The ADAM family

Didier Cataldo and his team at GIGA-research, have for several years focussed on certain genes involved in asthma, notably those coding for enzymatic proteins in the ADAMs family (A Disintegrin And Metalloproteinases) and ADAMTS (the same, with particular repeated motifs referred to as “thrombospondines-like”). To cut a long story short, these metalloproteinases consisting of a zinc ion are closely related to proteases in snake venom, which forms another part of the family of adamalysines. This strange detail has no connection to asthma, but highlights the extent to which ADAMs and ADAMTS are ubiquitous in the animal kingdom. Around forty of them have been identified to date, 25 of which are present in the human species and 35 in mice. They play a crucial role in processes ranging from membrane fusion during fertilisation of an egg by a sperm, activation of specific growth factors during embryonic brain development, amyloid protein deposits in Alzheimer's disease, tumoral aggression in breast cancer, the degeneration of cartilage in arthrosis, and the release of cytokines and other inflammatory factors in asthma. Hence our current position.

The protease which Geneviève Paulissen, post-doctoral student in Didier Cataldo's team, is working upon goes by the acronym of ADAMTS-12. The first publication establishing a potential link between this protease and asthma dates back to 2006 (1); a study showing that the gene from this enzyme had been localised in the genome in the region associated with vulnerability to asthma. At the time, Geneviève Paulissen was working on her final dissertation in Biomedical Sciences, with Professor Cataldo as supervisor. The dissertation focused on ADAMs in asthmatic pathology. 'Following this publication, we thought it might be interesting to study ADAMTS-12 in an experimental model' she says, 'because we had mice available which were deficient in this gene. We wanted to verify and confirm the role of this protease in asthma with an in vivo experimental model. ' It should be noted that there had been unfortunate precedents, notably ADAM-33, another protease whose gene had been clearly recognised in 2002 as being a gene also likely to indicate susceptibility to asthma. However the suppression of this gene in knock out mice provoked no particular signs of asthma in animals! The challenge was therefore to succeed in identifying evidence of differences of asthma phenotype in animals without the ADAMTS-12 protease and then to be able through these signs to decipher the role of the protease in the pathogenesis of the disease.

Wild type and knock out mice

With this in mind, Geneviève Paulissen developed two experimental models exposing mice deficient in ADAMTS-12 to two allergens. Her choice focused on ovalbumine, a protein which is inert but which is capable of triggering asthma attacks after allergisation, and the House Dust Mite -HDM), which is responsible for most of human allergies. In the ovalbumine experimental model, mice were simply placed in plexiglass enclosures where they inhaled a solution containing the allergen in aerosol form for 30 minutes. In the second model, the solution containing the HDM allergen was instilled directly into the naval cavities of sleeping mice. By means of comparison, the wild type mice were subject to the same protocol as their knock out cousins for ADAMTS-12. Bronchial responsiveness was then measured in all the mice, similar to the tests conducted on humans to diagnose asthma.  'We saw that the mice which were deficient in the ADAMTS-12 gene had bronchial reactiveness which was much higher than the wild type mice who were exposed to the same allergen. This reactiveness is the principal characteristic of asthma', explains the young researcher. The mice were then sacrificed to analyse the inflammation markers present in their lungs. 'We observed that mice which were deficient in ADAMTS-12 showed a significant increase in the two populations of key cells in asthma, polynuclear eosinophils (characteristic in allergic reactions) and mast cells (responsible for releasing histamine, the main intermediary for allergic manifestations). Then we examined the bronchial tissues under the microscope and saw that peribronchial inflammation had also increased in these mice. Delving a little deeper, we wanted to know whether the cytokines were connected with these inflammatory signals, using a cytokine-array (a procedure to identify a panel of cytokines known to be involved in inflammatory phenomena) and we then confirmed their presence using Elisa tests. Most of them were also increased. ' All these increases were significant; in all cases, they had at least doubled in comparison with the wild type mice. 

(1) Kurtz et al, J allergy Clin Immunol Vol 118, 2, 396-402