Interactome of FMRP-N-tat therapeutic unveils key interactions for cellular function in Fragile X neurons

Therapeutic protein replacement has demonstrated preclinical and clinical efficacy in neurological disorders but has not been used clinically for Fragile X syndrome (FXS), a genetic neurodevelopmental disorder caused by loss of Fragile X messenger ribonucleoprotein (FMRP). FXS results from a triplet repeat expansion of more than 200 CGG repeats in the 5'-UTR of the FMR1 gene leading to epigenetic silencing of FMRP. Currently, no clinically approved disease-modifying treatments for FXS exist. Recently, a tat-conjugated FMRP fragment encompassing residues 1 to 297 (FMRP N-tat) was shown to restore aspects of neuronal function in a mouse model of FXS. Promising in vivo data hinted to the therapeutic potential of FMRP N-tat. Herein, affinity purification mass spectrometry was used to identify the FMRP N-tat interactome in tsA-201 FMR1 knockout cells and FXS patient iPSC-derived neurons. The FMRP N-tat interactome included RNA binding proteins and constituents of the ribosome, which aligned closely with the known functions of FMRP. Further, the FMRP N-tat associated proteins included FXR2, STAU1, TRIM28, C1QBP, VDAC2, and several ribosomal proteins to regulate mRNA stability, cellular stress responses, mitochondrial function, and translation. The results highlight the potential of FMRP N-tat to orchestrate assembly of factors to correct lost function in FMRP deficient cells.