Tricho-hepato-enteric syndrome : from abnormal RNA decay to disease – THE-RNA

The Tricho-HepatoEnteric syndrome (THE) is a rare congenital disease associating intractable diarrhea, facial dysmorphism with hair abnormalities, intrauterine growth restriction, immunological defects and hepatic disease. The Ski complex is a heterotetramer identified in yeast and composed of Ski2, Ski3 and two copies of Ski8. It is a cofactor of the cytoplasmic exosome, a protein complex implicated in RNA decay and quality control. We have linked the THE syndrome to loss of function mutations in the SKIV2L or TTC37 genes (respectively human orthologs of the yeast SKI2 and SKI3 genes). How the dysfunction of a central RNA decay machinery translates into a specific syndrome remains is a mystery. Identifying and understanding the specific molecular dysfunctions associated with Ski defects will be of crucial importance to define the contribution of RNA degradation to human diseases and to optimize patient management. Several hypothetical mechanisms explaining THE phenotype can be proposed including the persistence of aberrant RNA(s) that would deregulate some cellular function(s), the translation of aberrant RNA leading to accumulation of aberrant proteins, or the alteration of the antiviral response. We will investigate these hypotheses by implementing a broad approach ranging from patients samples to animal models and from RNA to protein. Our consortium combines teams from different medical and scientific background and with specific expertise to allow a bench to bedside strategy. To better test our hypotheses, we will perform experiments aimed at clarifying the organization, function and localization of the human Ski complex. The creation of cellular and animal models will allow us to explore and describe the mechanisms affected in this syndrome. Indeed despite its description more than 20 years ago, several clinical features of THE syndrome are loosely known because of the rarity of the syndrome. The multicentric collaboration between French hospitals will include a large and better-defining cohort. These will allow have an accurate definition the phenotype of patients, with collection of clinical data (growth, symptom, neuropsychogical evaluation), samples (stools, blood, hair), and biological profile. A better understanding of the human Ski complex is necessary as available data on this assembly currently originates from yeast. Thus, we plan to confirm the human Ski complex composition and identify its partners. We will evaluate effects of known human mutation on complex formation and function using specific reporters to assay mRNA decay. As the Ski complex is evolutionary conserved in eukaryotes, we will develop an animal model to test our hypotheses. Due to easy handling, rapid generation time, and powerful genetic tools, drosophila will be used to get insights into the syndrome basis. Indeed it will allow creating models for all components of the Ski complex and cofactor and analysis spatio-temporal and sub-cellular localization of the three proteins in different organs in different conditions. Patient samples, cellular and animal models will allow us to identify molecular defects leading to the pathology. Hence, comparing RNA-Seq profiles will pinpoint pathways altered by Ski mutation. Hair abnormalities are an important feature of THE syndrome. Thus, easily available hair samples will be used to evaluate the existence of aberrant protein using mass spectrometry (MS)-based proteomic strategy. Finally, a better characterization of innate and adaptative immunity will be done on patients to elucidate how the Ski complex affects this function. The study of the microbiota composition in patients and anima models will help to determine a role of the interaction host/microbiota in disease. Models will also be used to study the effect of alteration of ski complex on viral infection. In summary, our project will allow a better understanding of the THE physiopathology and of the Ski complex function leading better treatment of patients.