POIKTMP-DP

Poikiloderma with tendon contractures, myopathy and pulmonary fibrosis (POIKTMP [MIM 615704]) is a rare and severe multisystem disease caused by dominant variants in the FAM111B gene, described by the coordinating team in 2013. Studying POIKTMP is challenging due to the limited understanding of the biological function of the FAM111B protein and the absence of orthologs in most species, complicating the development of animal models. Nevertheless, our preliminary studies have demonstrated that introduction of the human FAM111B mutant into zebrafish and mouse models successfully reproduces a muscle phenotype similar to that observed in patients, indicating that the human FAM111B protein interacts with protein partners conserved across species. We also observed a dominant-negative effect of pathogenic variants in POIKTMP, consisting predominantly of missense variants in the FAM111B gene. Furthermore, we have recently demonstrated a dysfunction of the ubiquitin-proteasome system (UPS) in POIKTMP, as well as a loss of interactions of mutated FAM111B with other protein partners within a high molecular weight complex suggesting a central role of FAM111B in protein homeostasis via UPS regulation. The POIKTMP-DP project is led by four transdisciplinary teams with established collaborations, combining expertise in basic research, therapeutic innovation and clinical care to ensure an efficient transition to clinical application. Three main objectives structure this project: 1) Objective 1 (WP1): Identification of FAM111B protein partners and target regulatory sequences. WP1A includes high-resolution mapping of the FAM111B interactome by proximity labelling and mass spectrometry (APEX, SRET, BioID/TurboID), complemented by bioinformatic analysis of the protein partners and pathways involved in patient-derived fibroblasts and iPSC-derived muscle progenitors, as well as in isogenic control cells. WP1B aims to identify potential FAM111B chromatin binding sites and its regulatory role in POIKTMP pathogenesis by ChIP-Seq approach and RNASeq studies. 2) Objective 2 (WP2): In vitro and in vivo preclinical models. WP2A consists in developing a POIKTMP muscle organoid derived from patient iPSCs using MyoStretch technology. WP2B aims to set up a systemic mouse model using intraperitoneal injection of mutant rAAV-FAM111B vectors. These models will enable us to better explore the pathophysiology of the disease and, ultimately, to test therapeutic approaches. 3) Objective 3 (WP3): Development of targeted therapeutic approaches. WP3 includes the development of innovative gene therapies targeting dominant-negative effect variants, such as the allele-specific antisense oligonucleotide approach (WP3A) and pre-mRNA trans-splicing (WP3B), enabling allele-specific replacement of FAM111B exon 2 containing the two mutated hot-spot regions using a single therapeutic construct. In conclusion, we believe that POIKTMP-DP is a promising translational project, both original and pioneering, given the scarcity of research on POIKTMP and the FAM111B gene worldwide. Exploring therapeutic approaches is essential for these patients, who have an altered quality of life and reduced life expectancy, with no current treatment options. In the era of personalized genomic medicine, this project lays the foundations for two complementary targeted therapies to significantly improve the clinical outlook for POIKTMP patients. More broadly, POIKTMP-DP offers considerable potential as a study model for other monogenic diseases linked to dominant-negative variants.