Analysis of a read-through promoting compound in a severe mouse model of spinal muscular atrophy

Abstract

Spinal muscular atrophy (SMA) is the leading genetic cause of infantile death and caused by the loss of functional Survival Motor Neuron 1 (SMN1). The remaining copy gene, SMN2, is unable to rescue from disease because the primary gene product lacks the final coding exon, exon 7, due to an alternative splicing event. While SMNΔ7 is a rapidly degraded protein, exon 7 is not specifically required in a sequence-specific manner to confer increased functionality to this truncated protein. Based upon this molecular observation, aminoglycosides have been examined to artificially elongate the C-terminus of SMNΔ7 by "read-through" of the stop codon. An SMNΔ7 read-through event benefits intermediate mouse models of SMA. Here we demonstrate that delivery of a read-through inducing compound directly to the CNS can partially lessen the severity of a severe model of SMA (Smn(-/-); SMN2(+/+)), albeit not to the extent seen in the less severe model. This further demonstrates the utility of read-through inducing compounds in SMA.

Fig. 1

Lifespan of severe SMA mice with CNS administration of TC007 at p1 and p3 not significantly increased. (A) Kaplan-Meyer survival curve shown with TC007-treated SMA mice (solid black), and vehicle-treated SMA mice (dotted black). Arrows on X-axis indicates average lifespan of the SMA mice. (Mantel-Cox test p=0.1554; Vehicle-treated N=13, TC007-treated N=17) (B) Average lifespan of TC007-treated versus vehicle-treated SMA pups (Student’s T Test p=0.0846 and bars represent SEM).

Fig. 1

Lifespan of severe SMA mice with CNS administration of TC007 at p1 and p3 not significantly increased. (A) Kaplan-Meyer survival curve shown with TC007-treated SMA mice (solid black), and vehicle-treated SMA mice (dotted black). Arrows on X-axis indicates average lifespan of the SMA mice. (Mantel-Cox test p=0.1554; Vehicle-treated N=13, TC007-treated N=17) (B) Average lifespan of TC007-treated versus vehicle-treated SMA pups (Student’s T Test p=0.0846 and bars represent SEM).

Fig. 2

Gross-motor function of severe SMA TC007-treated mice not significantly increased as compared to vehicle-treated (Student’s T Test). (A) Each grey circle (vehicle) or black square (TC007) represents an individual mouse plotted per day, post-natal days 5 through 8 (N for each day TC007: 14, 14, 11, 5 and vehicle: 7, 7, 7, 1 respectively). Lines represent the average of each group (TC007: black bar, vehicle: grey dotted bar) and bars represent SEM. (B) TC007-treated mice (line) on average not significantly different than vehicle-treated (dotted) littermates. Error bars represent SEM. (C) TC007-treated (black line) mice are not significantly different in ability to right on average than vehicle-treated (grey dotted). Bars represent Standard Deviation.

Fig. 2

Gross-motor function of severe SMA TC007-treated mice not significantly increased as compared to vehicle-treated (Student’s T Test). (A) Each grey circle (vehicle) or black square (TC007) represents an individual mouse plotted per day, post-natal days 5 through 8 (N for each day TC007: 14, 14, 11, 5 and vehicle: 7, 7, 7, 1 respectively). Lines represent the average of each group (TC007: black bar, vehicle: grey dotted bar) and bars represent SEM. (B) TC007-treated mice (line) on average not significantly different than vehicle-treated (dotted) littermates. Error bars represent SEM. (C) TC007-treated (black line) mice are not significantly different in ability to right on average than vehicle-treated (grey dotted). Bars represent Standard Deviation.

Fig. 2

Gross-motor function of severe SMA TC007-treated mice not significantly increased as compared to vehicle-treated (Student’s T Test). (A) Each grey circle (vehicle) or black square (TC007) represents an individual mouse plotted per day, post-natal days 5 through 8 (N for each day TC007: 14, 14, 11, 5 and vehicle: 7, 7, 7, 1 respectively). Lines represent the average of each group (TC007: black bar, vehicle: grey dotted bar) and bars represent SEM. (B) TC007-treated mice (line) on average not significantly different than vehicle-treated (dotted) littermates. Error bars represent SEM. (C) TC007-treated (black line) mice are not significantly different in ability to right on average than vehicle-treated (grey dotted). Bars represent Standard Deviation.

Fig. 3

TC007-treated pups weigh significantly more at end-stages. The weights of the TC007-treated pups (squares) were significantly larger (as indicated on graph) at end-stages than vehicle-treated (circles). Asterisk represents (*) p=0.0460 by Student’s T Test and error bars represent SEM.