Abstract
Spinal muscular atrophy (SMA) is a neuromuscular disease caused by loss of the survival motor neuron (SMN) gene. While there are currently two approved gene-based therapies for SMA, availability, high cost, and differences in patient response indicate that alternative treatment options are needed. Optimal therapeutic strategies will likely be a combination of SMN-dependent and -independent treatments aimed at alleviating symptoms in the central nervous system and peripheral muscles. Krüppel-like factor 15 (KLF15) is a transcription factor that regulates key metabolic and ergogenic pathways in muscle. We have recently reported significant downregulation of Klf15 in muscle of presymptomatic SMA mice. Importantly, perinatal upregulation of Klf15 via transgenic and pharmacological methods resulted in improved disease phenotypes in SMA mice, including weight and survival. In the current study, we designed an adeno-associated virus serotype 8 (AAV8) vector to overexpress a codon-optimized Klf15 cDNA under the muscle-specific Spc5-12 promoter (AAV8-Klf15). Administration of AAV8-Klf15 to severe Taiwanese Smn−/−;SMN2 or intermediate Smn2B/− SMA mice significantly increased Klf15 expression in muscle. We also observed significant activity of the AAV8-Klf15 vector in liver and heart. AAV8-mediated Klf15 overexpression moderately improved survival in the Smn2B/− model but not in the Taiwanese mice. An inability to specifically induce Klf15 expression at physiological levels in a time- and tissue-dependent manner may have contributed to this limited efficacy. Thus, our work demonstrates that an AAV8-Spc5-12 vector induces high gene expression as early as P2 in several tissues including muscle, heart, and liver, but highlights the challenges of achieving meaningful vector-mediated transgene expression of Klf15.
Highlights
Spinal muscular atrophy (SMA) is a devastating childhood neuromuscular disease that leads to early death in the most severe cases [1, 2]
We have recently demonstrated that Krüppel-like factor 15 (Klf15) expression is significantly downregulated in muscle of presymptomatic SMA mice and that upregulating Klf15 expression via genetic or pharmacological approaches results in improved disease phenotypes [18]
We find that while neonatal administration of the associated virus serotype 8 (AAV8)-Klf15 construct leads to significant increased levels of Klf15 in muscle, this has no overt effect on survival or weight gain in the severe Taiwanese SMA mice, while we observe a small improvement in the lifespan of the intermediate Smn2B/− mice
Summary
Spinal muscular atrophy (SMA) is a devastating childhood neuromuscular disease that leads to early death in the most severe cases [1, 2]. The first genetic therapy for SMA, nusinersen/SpinrazaTM, was approved in December 2016 by the Food and Drug Administration (FDA) and in June 2017 by the European Medicines Agency (EMA) [8] This antisense oligonucleotide is delivered directly to the central nervous system (CNS) via a lumbar puncture and is aimed at promoting SMN2 exon 7 inclusion [9]. We set out to overexpress Klf in skeletal muscle of neonatal SMA mice via a self-complementary adeno-associated virus serotype 2/8 and the Spc promoter. While this strategy led to substantial Klf expression in skeletal muscle of SMA mice and control littermates, there were no associated significant improvements in disease phenotypes. AAV8-Klf injections resulted in pronounced expression as early as postnatal day 2 in several tissues, including muscle, liver, and heart, highlighting the potential of this specific viral construct for efficient perinatal delivery
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