Requirement of enhanced Survival Motoneuron protein imposed during neuromuscular junction maturation.
Spinal muscular atrophy is a common motor neuron disease caused by low survival motoneuron (SMN), a key protein in the proper splicing of genes. Restoring the protein is therefore a promising therapeutic strategy. Implementation of this strategy, however, depends on defining the temporal requirements for SMN. Here, we used controlled knockdown of SMN in transgenic mice to determine the precise postnatal stage requirements for this protein. Reducing SMN in neonatal mice resulted in a classic SMA-like phenotype. Unexpectedly, depletion of SMN in adults had relatively little effect. Insensitivity to low SMN emerged abruptly at postnatal day 17, which coincided with establishment of the fully mature neuromuscular junction (NMJ). Mature animals depleted of SMN eventually exhibited evidence of selective neuromuscular pathology that was made worse by traumatic injury. The ability to regenerate the mature NMJ in aged or injured SMN-depleted mice was grossly impaired, a likely consequence of the inability to meet the surge in demand for motoneuronal SMN that was seen in controls. Our results demonstrate that relative maturity of the NMJ determines the temporal requirement for the SMN protein. These observations suggest that the use of potent but potentially deleterious SMN-enhancing agents could be tapered in human patients once the neuromuscular system matures and reintroduced as needed to enhance SMN for remodeling aged or injured NMJs.
Shingo
S
Kariya
Teresa
T
Obis
Caterina
C
Garone
Turgay
T
Akay
Fusako
F
Sera
Shinichi
S
Iwata
Shunichi
S
Homma
Umrao R
UR
Monani
D000375:Aging; D000483:Alleles; D000818:Animals; D005260:Female; D055785:Gene Knockdown Techniques; D005838:Genotype; D006720:Homozygote; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D009046:Motor Neurons / Q000378:metabolism; D009048:Motor Skills; D018482:Muscle, Skeletal / Q000473:pathology; D009469:Neuromuscular Junction / Q000378:metabolism*; D010641:Phenotype; D055533:Survival of Motor Neuron 1 Protein / Q000378:metabolism*; D013569:Synapses; D013997:Time Factors; D019076:Transgenes
C526472:Smn1 protein, mouse; D055533:Survival of Motor Neuron 1 Protein