Valproic acid increases SMN levels in spinal muscular atrophy patient cells

Abstract

Spinal Muscular Atrophy (SMA) is caused by diminished Survival of Motor Neuron (SMN) protein, leading to neuromuscular junction (NMJ) dysfunction and spinal motor neuron (MN) loss. Here, we report that reduced SMN function impacts the action of a pertinent microRNA and its mRNA target in MNs. Loss of the C. elegans SMN ortholog, SMN-1, causes NMJ defects. We found that increased levels of the C. elegans Gemin3 ortholog, MEL-46, ameliorates these defects. Increased MEL-46 levels also restored perturbed microRNA (miR-2) function in smn-1(lf) animals. We determined that miR-2 regulates expression of the C. elegans M2 muscarinic receptor (m2R) ortholog, GAR-2. GAR-2 loss ameliorated smn-1(lf) and mel-46(lf) synaptic defects. In an SMA mouse model, m2R levels were increased and pharmacological inhibition of m2R rescued MN process defects. Collectively, these results suggest decreased SMN leads to defective microRNA function via MEL-46 misregulation, followed by increased m2R expression, and neuronal dysfunction in SMA.

Treatment of spinal muscular atrophy cells with drugs that upregulate SMN expression reveals inter- and intra-patient variability

“…In vitro experiments with phenylbutyrate (PBA) and valproic acid (VPA) -two well-known HDACi -have shown an increase in SMN mRNA and protein levels in SMA fibroblasts. [15][16][17] Similar studies with hydroxyurea (HU) in EBV-immortalized SMA lymphoblasts 18 have shown an increase in the FL-SMN/D7-SMN (FL/D7 ratio). Pilot trials with these drugs have been performed in SMA patients and results were promising, [19][20][21] leading to the development of placebo-controlled clinical trials.…”

“…34 Two to ten percent of genes are believed to be regulated by histone acetylation and deacetylation, 35 but we do not know whether these compounds upregulate SMN2 by increasing histone acetylation at the SMN promoter, or by activating the acetylation state of a critical transcription factor. 17 Kernochan et al 36 observed that even though acetylated H3 and H4 histones predominated in the transcriptional origin of the SMN gene, VPA treatment led to acetylation in farupstream regions where there are usually fewer acetylated H3 and H4 histones. Further research will help to clarify the mechanism of action and individual response to these compounds.…”

“…The number of SMN2 copies has been considered irrelevant for the in vitro positive response. 15,17 However, their orientation in the SMA locus, their methylation activity, 43 and the presence of mutations affecting their expression or splicing 28,44 could influence the final response. Individual metabolism appears to be associated with the differential response to VPA, as previously suggested by Brichta et al 20 These investigators studied the level of SMN expression in blood after the oral administration of VPA and found positive, negative and non-responder patients.…”

Severe SMA mice show organ impairment that cannot be rescued by therapy with the HDACi JNJ-26481585

“…Despite these promising experimental approaches, no readily available effective treatment for SMA exists to date. 19,20 Targeting SMN2 gene transcription by use of histone deacetylase inhibitors (HDACi) such as valproic acid (VPA), Trichostatin A, SAHA, sodium butyrate, LBH589 or M344 [21][22][23][24][25][26][27][28] is an approach with potentially fast clinical implementation. Moreover, HDACi treatment has previously been shown to increase SMN2 transcription and to ameliorate the phenotype in SMA mouse models.…”

Solving the puzzle of spinal muscular atrophy: What are the missing pieces?

“…HDAC-inhs have been tested in vitro and in vivo: hydroxybutyric acid was the first compound shown to increase SMN2 levels in lymphoblastoid cell lines from SMA patients and to also increase the lifespan of a SMA mice [Chang et al, 2001]. Since then, valproic acid, phenylbutyrate, trycostatin A, and SAHA have also been shown to increase SMN levels in vitro and/or to improve the survival of SMA models in pre-clinical studies [Brichta et al, 2003;Sumner et al, 2003;Andreassi et al, 2004;Hahnen et al, 2006;Avila et al, 2007;Narvel et al, 2008;Riessland et al, 2010]. Valproic acid and phenylbutyrate have been tested in patients with SMA but with discordant outcomes.…”