Fundamental, genetic and clinical aspects of male infertility due to severe sperm flagellar abnormalities – FLAGEL-OME

Male infertility affects more than 20 million men worldwide and represents a major health concern. Although multifactorial, male infertility has a strong genetic basis, which has so far not been extensively studied. This project’s coordinating team and this consortium had a major contribution to the identification and characterization of severe sperm defects such as macrozoospermia, globozoospermia and severe forms of asthenozoospermia caused by multiple morphological abnormalities of the flagella (MMAF). A previous ANR funding (MAS-FLAGELLA; 2014-2019) allowed us to establish this consortium regrouping reproduction and bioinformatics specialists, human geneticists and fundamental researchers to elucidate the genetic basis of MMAF. This work which entailed the exome sequencing of a cohort of 176 MMAF subjects permitted to characterize and publish causative mutations in 9 genes and to identify another 14 candidate genes warranting further work. Overall this research program permitted the publication of 15 manuscripts in high ranking international journal and 5 more are currently under review.
Here, the same consortium will leverage the previously acquired expertise and tools to further investigate the molecular basis of flagellogenesis and to translate this knowledge into actionable information and strategies to improve diagnosis and care of infertile MMAF patients. The first four tasks of our project correspond to different approaches converging towards a single goal: to identify and characterize most actors of flagellogenesis. We will use two different models, the mouse and Trypanosoma brucei, to validate new genes and perform proteomic analyses to identify protein partners of identified flagellar MMAF proteins (tasks 1 and 2). Using public resources including protein-protein interactions from IMEx databases and gene expression data from GTEx, we will construct and analyze the “flagellogenesis biological network”, leading to the identification of key functional protein modules and new essential flagellogenesis participants (task 3). We will also include more patients in our cohort and improve our exome bioinformatics pipeline to increase our diagnosis efficiency following exome sequencing (task 4). Overall we aim to obtain a genetic diagnosis for 80% of MMAF patients upon exome sequencing. The objective of Task 5 is to perform a genotype-phenotype analysis in order to correlate the identified gene defects with the efficiency of in vitro fertilization (IVF) by intracytoplasmic sperm injection (ICSI), with the aim of improving the clinical care provided to the patients. Task 6 is the most ambitious and original of all tasks. Over the course of our previous project, using the CRISPR/Cas9 technology we created 5 knock out (KO) mouse lines for 5 distinct MMAF genes. Globally, all homozygous mutant male mice were infertile and recapitulated the human phenotype, while heterozygous animals presented no or minimal phenotypes. We will capitalize on our already established KO mouse lines to create multiple heterozygous animals. The study of these animals will permit to estimate the weight of the cumulative genetic burden in the aetiology of asthenozoospermia. The information gained from our project will ultimately allow reaching a genetic diagnosis not only for subjects with rare and severe sperm defects, but also for the large majority of infertile men with moderate alterations of sperm parameters.
Overall, building upon our experience, tools and knowledge, we propose a new and ambitious research program. Using an original approach combining human, mouse, T. brucei and computational modeling, we will characterise the flagella interactome, improve our understanding of flagella defects leading to infertility, and define the overall weight of multigenic transmission in male infertility. Moreover, this work will have a direct impact on the genetic diagnosis, prognosis and care of infertile men.