Valproic acid increases SMN2 expression and modulates SF2/ASF and hnRNPA1 expression in SMA fibroblast cell lines

Spinal muscular atrophy (SMA) is a common autosomal recessive neuromuscular disorder that is caused by loss of the survival motor neuron gene, SMN1. SMA treatment strategies have focused on production of the SMN protein from the almost identical gene, SMN2. Valproic acid (VPA) is a histone deacetylase inhibitor that can increase SMN levels in some SMA cells or SMA patients through activation of SMN2 transcription or splicing correction of SMN2 exon 7. It remains to be clarified what concentration of VPA is required and by what mechanisms the SMN production from SMN2 is elicited. We observed that in two fibroblast cell lines from Japanese SMA patients, more than 1mM of VPA increased SMN2 expression at both the transcript and protein levels. VPA increased not only full-length (FL) transcript level but also exon 7-excluding (Δ7) transcript level in the cell lines and did not change the ratio of FL/Δ7, suggesting that SMN2 transcription was mainly activated. We also found that VPA modulated splicing factor expression: VPA increased the expression of splicing factor 2/alternative splicing factor (SF2/ASF) and decreased the expression of heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1). In conclusion, more than 1mM of VPA activated SMN2 transcription and modulated the expression of splicing factors in our SMA fibroblast cell lines.