[Stigmatisation : a widespread problem with multiple consequences]. / La stigmatisation : un problem fréquent aux conséquences multiples.

Stigmatisation is a well known social phenomenon based on the discrimination of an individual or a sub-group of individuals by a dominant or majority group. Often discussed in the frame of psychiatry, it is also observed in other domains of medicine. It impacts not only patients, but their relatives and their children, as well as the health professionals taking care of them. Moreover, it is detrimental to the implementation of preventive strategies and induces depressive reactions, loss of self esteem and reduction of patients' quality of life. Finally, it keeps researchers away from certain domains of medicine and has a negative impact on funding for research and treatment. It is therefore important to understand its underlying mechanisms in order to fight it more efficiently.

La stigmatisation est un phénomène social très commun, basé sur la discrimination d'un individu ou d'un sous-groupe d'individus par un groupe dominant ou majoritaire. Discuté habituellement dans le contexte spécifique de la psychiatrie, ce phénomène existe aussi dans d'autres domaines de la médecine. Il touche non seulement les patients mais également leurs proches, leurs enfants, et parfois les soignants qui s'en occupent. De plus, il nuit à l'implantation de stratégies de prévention, induit des réactions dépressives, une perte d'estime de soi et une détérioration de la qualité de vie chez les patients. Enfin, il freine l'intérêt des scientifiques et restreint les fonds qui sont alloués à la recherche dans les domaines qui en font l'objet. Il est donc important d'en comprendre les mécanismes afin de mieux le combattre.

Cytochrome P450 CYP89A9 is involved in the formation of major chlorophyll catabolites during leaf senescence in Arabidopsis.

Nonfluorescent chlorophyll catabolites (NCCs) were described as products of chlorophyll breakdown in Arabidopsis thaliana. NCCs are formyloxobilin-type catabolites derived from chlorophyll by oxygenolytic opening of the chlorin macrocycle. These linear tetrapyrroles are generated from their fluorescent chlorophyll catabolite (FCC) precursors by a nonenzymatic isomerization inside the vacuole of senescing cells. Here, we identified a group of distinct dioxobilin-type chlorophyll catabolites (DCCs) as the major breakdown products in wild-type Arabidopsis, representing more than 90% of the chlorophyll of green leaves. The molecular constitution of the most abundant nonfluorescent DCC (NDCC), At-NDCC-1, was determined. We further identified cytochrome P450 monooxygenase CYP89A9 as being responsible for NDCC accumulation in wild-type Arabidopsis; cyp89a9 mutants that are deficient in CYP89A9 function were devoid of NDCCs but accumulated proportionally higher amounts of NCCs. CYP89A9 localized outside the chloroplasts, implying that FCCs occurring in the cytosol might be its natural substrate. Using recombinant CYP89A9, we confirm FCC specificity and show that fluorescent DCCs are the products of the CYP89A9 reaction. Fluorescent DCCs, formed by this enzyme, isomerize to the respective NDCCs in weakly acidic medium, as found in vacuoles. We conclude that CYP89A9 is involved in the formation of dioxobilin-type catabolites of chlorophyll in Arabidopsis.