Increasing Agrin Function Antagonizes Muscle Atrophy and Motor Impairment in Spinal Muscular Atrophy.

Frontiers in Cellular Neuroscience , 30 January 2018
Increasing Agrin Function Antagonizes Muscle Atrophy and Motor Impairment in Spinal Muscular Atrophy

Marina Boido ¹ , Elena De Amicis ¹ , Valeria Valsecchi ¹ , Marco Trevisan ¹ , Ugo Ala ² , Markus A. Ruegg ³ , Stefan Hettwer ⁴ , Alessandro Vercelli ^1,5

Spinal muscular atrophy (SMA) is a pediatric genetic disease, characterized by motor neuron (MN) death, leading to progressive muscle weakness, respiratory failure, and, in the most severe cases, to death. Abnormalities at the neuromuscular junction (NMJ) have been reported in SMA, including neurofilament (NF) accumulation at presynaptic terminals, immature and smaller than normal endplates, reduced transmitter release, and, finally, muscle denervation. Here we have studied the role of agrin in SMAΔ7 mice, the experimental model of SMAII.

We observed a 50% reduction in agrin expression levels in quadriceps of P10 SMA mice compared to age-matched WT controls. To counteract such condition, we treated SMA mice from birth onwards with therapeutic agrin biological NT-1654, an active splice variant of agrin retaining synaptogenic properties, which is also resistant to proteolytic cleavage by neurotrypsin. Mice were analyzed for behavior, muscle and NMJ histology, and survival.

Motor behavior was significantly improved and survival was extended by treatment of SMA mice with NT-1654. At P10, H/E-stained sections of the quadriceps, a proximal muscle early involved in SMA, showed that NT-1654 treatment strongly prevented the size decrease of muscle fibers. Studies of NMJ morphology on whole-mount diaphragm preparations revealed that NT-1654-treated SMA mice had more mature NMJs and reduced NF accumulation, compared to vehicle-treated SMA mice.

We conclude that increasing agrin function in SMA has beneficial outcomes on muscle fibers and NMJs as the agrin biological NT-1654 restores the crosstalk between muscle and MNs, delaying muscular atrophy, improving motor performance and extending survival.

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Figure . Analysis of diaphragm NMJs. (A–C) Evaluation of NMJ maturation by BTX-immunostaining: NT-1654 injection partially stimulates NMJ maturation in treated SMA (B) compared to PBS SMA (A) , as quantified in (C) . Mature endplates are indicated by arrowheads. (D–F) Double immunostaining against BTX (red) and NF (green) is employed for analyzing NF accumulation into the plaques: NT-1654 SMA (E) display a significantly lower number of engulfed NMJs (arrows) compared to PBS SMA (D) , as also quantified in (F) . Unpaired T -test, * P < 0.05. Scale bar = 25 μm in (A,B,D,E) .

¹ Department of Neuroscience Rita Levi Montalcini, Neuroscience Institute Cavalieri Ottolenghi, University of Turin, Turin, Italy
² Department of Molecular Biotechnology and Health Sciences, University of Turin, Turin, Italy
³ Biozentrum, University of Basel, Basel, Switzerland
⁴ Neurotune AG, Schlieren, Switzerland
⁵ Department of Neuroscience Rita Levi Montalcini, National Institute of Neuroscience, Turin, Italy