Inhibition of Rho-Associated Kinases ROCK1 and ROCK2 as a Therapeutic Strategy to Reactivate the Repressed FXN Gene in Friedreich Ataxia

Abstract

Friedreich ataxia (FA) is an autosomal recessive disease characterized by progressive damage to the nervous system and severe cardiac abnormalities. The disease is caused by a GAA•TTC triplet repeat expansion in the first intron of the FXN gene, resulting in epigenetic repression of FXN transcription and reduction in FXN (frataxin) protein which results in mitochondrial dysfunction. Factors and pathways that promote FXN repression represent potential therapeutic targets whose inhibition would restore FXN transcription and frataxin protein levels. Here, we performed a candidate-based RNAi screen to identify kinases, a highly druggable class of proteins, that when knocked down upregulate FXN expression. Using this approach, we identified Rho kinase ROCK1 as a critical factor required for FXN repression. ShRNA-mediated knockdown of ROCK1, or the related kinase ROCK2, increases FXN mRNA and frataxin protein levels in FA patient-derived induced pluripotent stem cells (iPSCs) and differentiated neurons and cardiomyocytes to levels observed in normal cells. We demonstrate that small molecule ROCK inhibitors, including the FDA-approved drug belumosudil and fasudil, reactivate FXN expression in cultured FA iPSCs, neurons, cardiomyocytes, and FA patient primary fibroblasts and ameliorate the characteristic mitochondrial defects in these cell types. Remarkably, treatment of transgenic FA mice of both sexes with belumosudil or fasudil upregulates FXN expression, ameliorates the mitochondrial defects in the brain and heart tissues, and improves motor coordination and muscle strength. Collectively, our study identifies ROCK kinases as critical repressors of FXN expression and provides preclinical evidence that FDA-approved ROCK inhibitors may be repurposed for treatment of FA.

Keywords: Friedreich ataxia; ROCK kinases; frataxin; mitochondrial function; neurodegeneration; reactivation of FXN.