Evidence for a fragile X messenger ribonucleoprotein 1 (FMR1) mRNA gain‐of‐function toxicity mechanism contributing to the pathogenesis of fragile X‐associated premature ovarian insufficiency

Abstract

Fragile X‐associated premature ovarian insufficiency (FXPOI) is among a family of disorders caused by expansion of a CGG trinucleotide repeat sequence located in the 5′ untranslated region (UTR) of the fragile X messenger ribonucleoprotein 1 (FMR1) gene on the X chromosome. Women with FXPOI have a depleted ovarian follicle population, resulting in amenorrhea, hypoestrogenism, and loss of fertility before the age of 40. FXPOI is caused by expansions of the CGG sequence to lengths between 55 and 200 repeats, known as a FMRI premutation, however the mechanism by which the premutation drives disease pathogenesis remains unclear. Two main hypotheses exist, which describe an mRNA toxic gain‐of‐function mechanism or a protein‐based mechanism, where repeat‐associated non‐AUG (RAN) translation results in the production of an abnormal protein, called FMRpolyG. Here, we have developed an in vitro granulosa cell model of the FMR1 premutation by ectopically expressing CGG‐repeat RNA and FMRpolyG protein. We show that expanded CGG‐repeat RNA accumulated in intranuclear RNA structures, and these aggregates were able to cause significant granulosa cell death independent of FMRpolyG expression. Using an innovative RNA pulldown, mass spectrometry‐based approach we have identified proteins that are specifically sequestered by CGG RNA aggregates in granulosa cells in vitro, and thus may be deregulated as consequence of this interaction. Furthermore, we have demonstrated reduced expression of three proteins identified via our RNA pulldown (FUS, PA2G4 and TRA2β) in ovarian follicles in a FMR1 premutation mouse model. Collectively, these data provide evidence for the contribution of an mRNA gain‐of‐function mechanism to FXPOI disease biology.

Insight and Recommendations for Fragile X-Premutation-Associated Conditions from the Fifth International Conference on FMR1 Premutation

“…The pathophysiology of FXTAS involves multiple mechanisms, including RNA toxicity [ 24 , 25 , 26 ], clogging of the proteasome [ 27 ], RAN translation [ 28 , 29 ], and mitochondrial dysfunction [ 30 , 31 , 32 ] (for more details, see Section 2 , ‘The molecular basis of FXPAC’). Recent papers have shown that males progress more rapidly in motor symptoms than females, presumably because of the protective effects in addition to the presence of the normal second X chromosome [ 33 ].…”

Ribosomal composition affects the noncanonical translation and toxicity of polyglycine-containing proteins in fragile X-associated conditions

“…The RNA-tagging approach allowed us to identify over a hundred and fifty proteins—including factors with translation regulatory properties. Some identified proteins overlapped with ones already described as binding to mutant FMR1 mRNA such as SRPK1 or TAR DNA-binding protein 43 (TDP-43) (Malik et al , 2021b; Rosario et al , 2022; Sellier et al , 2010; Jin et al , 2007; Cid-Samper et al , 2018; Sellier et al , 2017). Further, we described three new modifiers of RAN translation of this mRNA.…”

“…It is necessary for oocyte growth and follicle development, and its depletion causes changes in transcription and chromatin configuration, leading to premature ovarian failure (Liu et al, 2018). Our discovery that RPS26 regulates the level of FMRpolyG in cellular models sheds new light on the potential role of RPS26-related RAN translation in FXPOI, where FMRpolyG aggregates are detected in ovarian cells and contribute to the development and progression of fertility issues (Buijsen et al, 2016;Shelly et al, 2021;Rosario et al, 2022).…”