Muscle overexpression of Klf15 via an AAV8-Spc5-12 construct does not provide benefits in spinal muscular atrophy mice

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 Smn(2B/−) 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 Smn(2B/−) 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.