title: SMN Blood Levels in a Porcine Model of Spinal Muscular Atrophy.
abstract: Spinal Muscular Atrophy (SMA) is an autosomal recessive motor neuron disease that results in loss of spinal motor neurons, muscular weakness and, in severe cases, respiratory failure and death. SMA is caused by a deletion or mutation of the SMN1 gene and retention of the SMN2 gene that leads to low SMN expression levels.The measurement of SMN mRNA levels in peripheral blood samples has been used in SMA clinical studies as a pharmacodynamic biomarker for response to therapies designed to increase SMN levels. We recently developed a postnatal porcine model of SMA by the viral delivery of a short-hairpin RNA (shRNA) targeting porcine SMN (pSMN). scAAV9-mediated knockdown of pSMN mRNA at postnatal day 5 results in denervation, weakness and motor neuron and ventral root axon loss that begins 3-4 weeks after viral delivery, and this phenotype can be ameliorated by subsequent viral delivery of human SMN (hSMN).
  
  
  
  To determine if the effect of modulating SMN levels using gene therapy can be measured in blood.
  
  
  
  We measured expression of pSMN mRNA and hSMN mRNA by quantitative droplet digital PCR (ddPCR).
  
  
  
  We found that the endogenous expression of pSMN mRNA in blood increases in the first month of life. However, there were no significant differences in blood levels of pSMN mRNA after knock-down or of human SMN mRNA after gene therapy.
  
  
  
  Our results, obtained in a large animal model of SMA that is similar in size and anatomy to human infants, suggest that measurement of SMN mRNA levels in blood may not be informative in SMA clinical trials involving intrathecal delivery of SMN-modulating therapies.
authors.affiliation: Department of Biological Chemistry and Pharmacology, The Ohio State University Wexner Medical Center, Columbus, Oh, USA.
authors.forename: Chitra
authors.initials: CC
authors.lastname: Iyer
authors.affiliation: Department of Biological Chemistry and Pharmacology, The Ohio State University Wexner Medical Center, Columbus, Oh, USA.
authors.forename: Xueqian
authors.initials: X
authors.lastname: Wang
authors.affiliation: Department of Biological Chemistry and Pharmacology, The Ohio State University Wexner Medical Center, Columbus, Oh, USA.
authors.forename: Samantha R
authors.initials: SR
authors.lastname: Renusch
authors.affiliation: Department of Biological Chemistry and Pharmacology, The Ohio State University Wexner Medical Center, Columbus, Oh, USA.
authors.forename: Sandra I
authors.initials: SI
authors.lastname: Duque
authors.affiliation: Center for Biostatistics, The Ohio State University Wexner Medical Center, Columbus, Oh, USA.
authors.forename: Allison M
authors.initials: AM
authors.lastname: Wehr
authors.affiliation: Center for Biostatistics, The Ohio State University Wexner Medical Center, Columbus, Oh, USA.
authors.forename: Xiaokui-Molly
authors.initials: XM
authors.lastname: Mo
authors.affiliation: Department of Biological Chemistry and Pharmacology, The Ohio State University Wexner Medical Center, Columbus, Oh, USA.
authors.forename: Vicki L
authors.initials: VL
authors.lastname: McGovern
authors.affiliation: Department of Neurology, The Ohio State University Wexner Medical Center, Columbus, Oh, USA.|Department of Physical Medicine and Rehabilitation, The Ohio State University Wexner Medical Center, Columbus, Oh, USA.
authors.forename: W David
authors.initials: WD
authors.lastname: Arnold
authors.affiliation: Department of Biological Chemistry and Pharmacology, The Ohio State University Wexner Medical Center, Columbus, Oh, USA.
authors.forename: Arthur H M
authors.initials: AH
authors.lastname: Burghes
authors.affiliation: Department of Biological Chemistry and Pharmacology, The Ohio State University Wexner Medical Center, Columbus, Oh, USA.|Department of Neurology, The Ohio State University Wexner Medical Center, Columbus, Oh, USA.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Kolb
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D005260:Female; D055785:Gene Knockdown Techniques; D015316:Genetic Therapy; D005822:Genetic Vectors; D006801:Humans; D009134:Muscular Atrophy, Spinal / Q000097:blood / Q000235:genetics*; D012333:RNA, Messenger / Q000097:blood*; D034741:RNA, Small Interfering; D055533:Survival of Motor Neuron 1 Protein / Q000097:blood / Q000235:genetics*; D034421:Sus scrofa; D013552:Swine
chemical_list: D012333:RNA, Messenger; D034741:RNA, Small Interfering; C526471:SMN1 protein, human; D055533:Survival of Motor Neuron 1 Protein
keywords: SMA; SMN; ddPCR; gene-therapy; scAAV9-SMN; scAAV9-shRNA