Increasing SMN levels using the histone deacetylase inhibitor SAHA ameliorates defects in skeletal muscle microvasculature in a mouse model of severe spinal muscular atrophy
Introduction
Spinal muscular atrophy (SMA) is a predominately childhood form of motor neuron disease in which the lower motor neurons in the ventral horns of the spinal cord degenerate, resulting in denervation and atrophy of trunk and limb muscles. With an incidence of approximately 1:6000 live births SMA is the leading genetic cause of infant mortality and with a carrier frequency of 1:35 the second most common autosomal recessive inherited disorder in humans [10], [17]. All SMA patients show a homozygous absence of the disease determining gene survival motor neuron 1 (SMN1), but carry different copies of the main disease modifying gene SMN2 which produces, due to alternative splicing compared to SMN1, only 10% of an identical, ubiquitously expressed SMN protein [15], and it is this low level of SMN which causes the SMA phenotype. While motor neurons appear particularly sensitive to low SMN levels, a growing number of studies in mouse models report the effects of decreased SMN levels in multiple tissues including brain [28], bone [24], heart [23], lung [14] and intestine [21]. In the vascular system, defects in heart function [3] and structure [13] respectively have been reported in mouse models of SMA, whilst congenital heart septal defects and peripheral necrosis are reported in severe SMA patients [1], [19], [20]. See [12] for a review of non neuromuscular phenotypes in SMA. Specifically, the vascular bed in skeletal muscle is significantly reduced in density at early symptomatic times in a mouse model of severe SMA [25], while the vessels which are present have an increased diameter but are poorly ramified within the muscle tissue. Similar, but more advanced changes are seen in a slightly longer-lived Taiwanese model of severe SMA [21] and other groups have described a capillary defect in the heart of SMA mice [22].
Modulation of SMN levels in SMA tissue has been achieved by a variety of methodologies including and for example adeno-associated viral transduction [11], [27], antisense RNA technologies [7], [8] and histone deacetylase (HDAC) inhibitors [2], [4], [21]. One such HDAC inhibitor, suberoylanilide hydroxamic acid (SAHA) significantly increases the level of SMN protein in SMA affected skeletal muscle [16], [18] and improves survival [18]. In addition, treatment with similar HDAC inhibitors has been shown to modestly improve the SMA phenotype [2], [6], [26]. Here we show that increasing SMN levels, via treatment with SAHA, is effective in significantly ameliorating this vascular defect.
Section snippets
Mice
Taiwanese: FVB.Cg-Tg(SMN2)2Hung Smn1tm1Hung/J mice were bred and maintained in micro-isolation chambers in Cologne [18], according to guidelines established by the Landesamt für Natur, Umwelt and Verbraucherschutz NRW in Germany. Litters of Taiwanese mice, including both SMA mice and control littermates, were treated orally via a feeding needle with the HDAC inhibitor suberolynalide hydroxamic acid (SAHA). Mice were dosed twice daily from birth with 25 mg/kg of SAHA dissolved in DMSO or the
Results
Here, we set out to test the effect of systemically increasing SMN levels post-natally on the vascular bed defect in skeletal muscle, in a severe mouse model of spinal muscular atrophy (SMA). The severity of SMA is inversely related to the amount of SMN protein present, and here we used a pharmacological means to increase the level of SMN protein, by dosing mice with the HDAC inhibitor suberolynalide hydroxamic acid (SAHA: 25 mg/kg) twice daily from birth, which increases SMN levels ~2 fold [16]
Discussion
We show that SAHA, a second generation HDAC inhibitor significantly ameliorates the severe skeletal muscle vascular defect in a mouse model of SMA. This is in addition to confirming its published rescue of motor performance and morphology [18].
It is now established that severe vascular defects are present in mouse models of severe SMA [21], [22], [25]. Here, vascular density in late symptomatic (P10) muscle from SMA animals was less than 20% of the levels in control littermates. This decrease
Conclusion
SMA affects a much wider range of tissues and organs than simply the motor system, particularly in severe and longer-lived patients, and therefore it is increasingly important that any potential therapy increases SMN levels ubiquitously and targets these non-motor phenotypes. Here we show that a second generation HDACi is able to significantly ameliorate vascular bed defects in skeletal muscle in a mouse model of SMA, in addition to ameliorating weight loss and motor function.
Acknowledgements
This work was supported by SBMS University of Edinburgh (E.S.), BDF Newlife Foundation, RS Macdonald Charitable Trust (S.H.P.), SMA Trust, Muscular Dystrophy Campaign (T.H.G.) and Deutsche Forschunsgemeinschaft (B.W.).
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2017, American Journal of Human GeneticsCitation Excerpt :Both SMA and SMA-Ncaldko/wt mice die at a mean age of 13 days and there is no difference in weight progression at this age (Figures S5A and S5B). Severe SMA mice show multi-organ failure27,43,67 due to very low SMN levels, which could not be rescued by heterozygous Ncald knockout alone. Nonetheless, we found that other hallmarks of SMA were improved upon heterozygous Ncald knockout: the size of the NMJs in the transversus abdominis muscle (TVA) was increased and the number of proprioceptive inputs on MN soma was elevated in SMA-Ncaldko/wt versus SMA mice (P10) (Figures 4B and 4C).
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2017, NeuronCitation Excerpt :Another way to increase SMN levels is to increase SMN2 transcription (d’Ydewalle and Sumner, 2015). We and others showed that histone deacetylase (HDAC) inhibitors can activate the SMN2 promoter, improving disease outcomes in SMA mice (Avila et al., 2007; Somers et al., 2013). HDAC inhibitors failed to show clinical efficacy in SMA patients, likely due to low potency and specificity (Kissel et al., 2011; Swoboda et al., 2010).
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2013, Biochimica et Biophysica Acta - Molecular Basis of DiseaseCitation Excerpt :However, higher doses of SAHA resulted in toxicity even in heterozygous mice [80]. A recent study with SAHA showed weight gain and improved motor function in Taiwanese type I SMA mice, although the effect on lifespan was not reported [97]. Treatment of Taiwanese type I SMA mice with JNJ-26481585, a novel second-generation HDAC inhibitor, did not provide any lifespan benefit [98].
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These authors contributed equally to the paper.