Lamin-genome interactions in the development of Familial Partial Lipodystrophy

Mutasjoner i molekyler i membranen som beskytter kromosomer («lamin»), forårsaker en smelting av fettvev i nedre deler av kroppen, og samtidig en akkumulering av fett i magen samt alvorlige metabolske komplikasjoner som ofte forårsaker diabetes. Denne sykdommen en sjelden form av lipodystrofi. Vi har tidligere vist at et gen som heter MIR335 er deregulert av lamin-mutasjonen, og fant mekanismer bak dette. Deregulering av dette genet forårsaker et problem med fettcelle differensiering som kan kobles til lipodystrofien hos pasienter. Vi viser nå også at i celler fra disse pasientene, endres den 3-dimensjonale (3D) konformasjonen av kromosomer rundt MIR335-genet i forhold til kontroll friske personer: MIR335-genet interagerer fysisk med andre regioner i kromosomet hos pasienter enn hos friske individer. Dette betyr at deregulering av dette genet er knyttet til mer globale defekter i hvordan gener er organisert og regulert hos pasienter. Dette åpner for nye og spennende forskningsveier innen metabolske forstyrrelser og, kanskje enda viktigere, fedme.

-

Familial partial lipodystrophy of Dunnigan type (FPLD2) is a laminopathy that mainly affects adipose tissue, resulting in partial lipoatrophy and severe metabolic disorders. FPLD2 is caused by the p.R482W mutation in lamin A. The mutation impairs lamin A interaction with DNA and nucleosomes in vitro, and in patient cells results in dysmorphic nuclei. We rationalize that the p.R482W mutation causes tissue-specific alterations in lamin-genome contacts which reorganize chromatin, thereby mis-positioning developmental genes, deregulating transcription, and leading to defects in adipogenesis and fat tissue metabolism. We aim to uncover the role of the LMNA p.R482W mutation on the formation of lamina-associated domains (LADs) and the impact of defective mutant LADs on the commitment of progenitor cells to adipogenesis. Using FPLD2 patient cells, patient-derived iPS cells for disease modeling, and engineered adipose stem cells (ASCs), the project combines stem cell biology, high-throughput genomics (LMNA ChIP-seq, RNA-seq, bioinformatics) and a new dCas9-EGFP locus-specific tracking system in living cells for real-time analysis of gene positioning. OBJECTIVE 1 aims to determine how the p.R482W mutation affects the position and genomic composition of LADs and the lineage specificity of dissociation of genes from the lamina on differentiation. OBJECTIVE 2 uses FPLD2 patient-derived iPS cells to identify the developmental role of the LMNA p.R482W mutation on LAD formation and adipogenesis. OBJECTIVE 3 investigates the spatio-temporal dynamics of loci with respect to wild-type and mutated lamina, using a dCas9-EGFP gene tagging strategy (perhaps the most challenging development in this project). The results will bring our understanding of laminopathies to a new level. Impact of the work extends beyond the basics of lamin-genome interactions, and aims to open doors to new possibilities for alleviating tissue-specific symptoms of laminopathies.