Gene expression of nAChR, SNAP-25 and GAP-43 in skeletal muscles following botulinum toxin A injection: a study in rats.
OBJECTIVE
Botulinum toxin A (BoNT-A) is used to manage spasticity in cerebral palsy. BoNT-A cleaves SNAP-25 protein, blocking acetylcholine release and weakening the muscle. Nicotinic acetylcholine receptors (nAChR) including alpha, beta, delta, gamma, and epsilon subunits, and GAP-43 protein are associated with functional recovery of neuromuscular junctions (NMJ) following BoNT-A. To better understand the mechanism behind this functional recovery, this study attempted to (1) document changes in NMJ morphometry following BoNT-A, and (2) determine the gene expression of nAChR subunits, SNAP-25, and GAP-43 protein.


METHODS
In this rat study (46 rats), 6 units/kg body weight of BoNT-A was injected into the gastrocnimus. NMJ morphometry and the time course of gene expression of nAChR subunits, SNAP-25, and GAP-43 were evaluated up to 1year post-injection.


RESULTS
NMJ morphometry: gutter depth was reduced vs. the control side at two months, and normalizing by 6 months following BoNT. nAChR alpha mRNA and gamma mRNA increased by 3 days, peaked at 7 days and returned to control levels; delta mRNA peaked at 3 days. Epsilon mRNA peaked by 7 days. SNAP-25 mRNA increased from 60 to 90 days, returning to control levels by 6 months. GAP-43 mRNA was unchanged.


CONCLUSIONS
Specific nAChR subunit mRNA expression up-regulates and then returns to normal within two weeks, preceding changes in NMJ morphometry. Although GAP-43 participates in nerve sprouting, no increase of GAP-43 mRNA occurred following BoNT-A. Delayed up-regulation of SNAP-25 mRNA might be associated with muscle functional recovery.
Ma
Jianjun
J
Department of Orthopaedic Surgery, Wake Forest University Health Sciences, Winston-Salem, NC 27157-1070, USA.
Shen
Jian
J
Lee
Cassandra A
CA
Elsaidi
Gamal A
GA
Smith
Thomas L
TL
Walker
Francis O
FO
Rushing
Julia T
JT
Tan
Kim H
KH
Koman
L Andrew
LA
Smith
Beth P
BP
D000818:Animals; D019274:Botulinum Toxins, Type A / Q000633:toxicity*; D019922:GAP-43 Protein / Q000235:genetics*; D008565:Membrane Proteins / Q000235:genetics*; D018482:Muscle, Skeletal / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000235:genetics*; D009469:Neuromuscular Junction / Q000187:drug effects / Q000473:pathology; D021122:Protein Subunits; D012333:RNA, Messenger / Q000032:analysis*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011978:Receptors, Nicotinic / Q000235:genetics*; D050825:Synaptosomal-Associated Protein 25
D019922:GAP-43 Protein; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D021122:Protein Subunits; D012333:RNA, Messenger; D011978:Receptors, Nicotinic; C494210:Snap25 protein, rat; D050825:Synaptosomal-Associated Protein 25; D019274:Botulinum Toxins, Type A