Piperine Modulates Protein Mediated Toxicity in Fragile X-Associated Tremor/Ataxia Syndrome through Interacting Expanded CGG Repeat (r(CGG) exp ) RNA.

An expansion of CGG tandem repeats in the 5' untranslated region (5'-UTR) of fragile X mental retardation 1 ( FMR1) gene causes fragile X-associated tremor/ataxia syndrome (FXTAS). The transcripts of these expanded repeats r(CGG) either form RNA foci or undergo the repeat-associated non-ATG (RAN) translation that produces toxic homopolymeric proteins in neuronal cells. The discovery of small molecule modulators that possess a strong binding affinity and high selectivity to these toxic expanded repeats RNA could be a promising therapeutic approach to cure the expanded repeat-associated neurological diseases. Therefore, here we sought to test the therapeutic potential of a natural alkaloid, piperine, by assessing its ability to bind and neutralize the toxicity of r(CGG) RNA motif. To accomplish this first, we have determined the affinity of piperine to r(CGG) RNA using fluorescence-based binding assay and isothermal titration calorimetry assay. These assays showed that piperine forms a thermodynamically favorable interaction with r(CGG) RNA with high selectivity to the G-rich RNA motif. Interaction of piperine with r(CGG) motif was further validated using several biophysical techniques such as CD, CD melting, NMR spectroscopy, and gel retardation assay. Moreover, piperine was also found to be effective for improving the r(CGG) associated splicing defects and RAN translation in a FXTAS cell model system. Our results effectively provided the evidence that piperine strongly interacts with r(CGG) RNA and could be used as a suitable candidate for therapeutic development against FXTAS.