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

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 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.

Protein Network Analysis Reveals a Functional Connectivity of Dysregulated Processes in ALS and SMA

“… 38 Moreover, an overexpression of KLF15 by muscle specific Adeno-associated virus (AAV) in SMA mice had only a partial effect on survival of intermediate SMA mice compared to control mice, while severe SMA mice did not show differences in survival compared to control mice. 23 Similar results were reported in studies with muscle-specific KLF15 overexpression in the SOD1 G93A ALS mouse model. Those mice did not show any difference in disease progression or muscle atrophy compared to control animals.…”

“…Moreover, network biology supports researchers to identify potential new treatment strategies for neurodegenerative diseases. 9 , 47 Here, we performed a network analysis on published studies that focus on fatty acid metabolism in SMA patients and mouse models, 10 KLF15 overexpression in an SMA mouse model 23 and B-Raf signaling in SMA. 22 Moreover, further proteins were added that are involved in actin and stress granules dynamics as well as the most common ALS-associated proteins ( Table 1 ).…”

“…As many skeletal muscles become atrophic in SMA, 15 , 21 we performed a PubMed search with the following terms: “ spinal muscular atrophy ” AND “ peripheral tissue ” AND “ pathway ” AND “ muscle ” AND “ therapy .” Six different papers matched with the keywords. 23 , 34 - 38 One focuses on spinal and bulbar muscular atrophy 35 and two address SMA. 23 , 38 Both SMA papers focus on the transcription factor Krüppel-like Factor 15 (KLF15).…”

“… 23 , 34 - 38 One focuses on spinal and bulbar muscular atrophy 35 and two address SMA. 23 , 38 Both SMA papers focus on the transcription factor Krüppel-like Factor 15 (KLF15). 23 , 38 Therefore, KLF15 and its interaction partners Signal transducer and activator of transcription 3 (STAT3) or Phosphoinositide-3-kinase regulatory subunit 3 (PIK3R3), respectively, were added to the list for STRING analysis ( Table 1 ).…”

“… 23 , 38 Both SMA papers focus on the transcription factor Krüppel-like Factor 15 (KLF15). 23 , 38 Therefore, KLF15 and its interaction partners Signal transducer and activator of transcription 3 (STAT3) or Phosphoinositide-3-kinase regulatory subunit 3 (PIK3R3), respectively, were added to the list for STRING analysis ( Table 1 ). KLF15 interactors were identified by STRING Interaction Network section on GeneCards website ( https://www.genecards.org/ ; evaluation date on June 3rd, 2021).…”