A large animal model of spinal muscular atrophy and correction of phenotype

Abstract

Objectives Spinal muscular atrophy (SMA) is caused by reduced levels of SMN which results in motoneuron loss. Therapeutic strategies to increase SMN levels including drug compounds, antisense oligonucleotides or scAAV9 gene therapy have proved effective in mice. We wished to determine whether reduction of SMN in postnatal motoneurons resulted in SMA in a large animal model, whether SMA could be corrected after development of muscle weakness and the response of clinically relevant biomarkers. Methods Using intrathecal delivery of scAAV9 expressing a shRNA targeting pig SMN1, SMN was knocked down in motoneurons postnatally to SMA levels. This resulted in an SMA phenotype representing the first large animal model of SMA. Restoration of SMN was performed at different time points with scAAV9 expressing human SMN (scAAV9-SMN) and electrophysiology measures and pathology were performed. Results Knockdown of SMN in postnatal motoneurons results in overt proximal weakness, fibrillations on electromyography (EMG) indicating active denervation, and reduced compound muscle action potential (CMAP) and motor unit number estimates (MUNE), like human SMA. Neuropathology showed loss of motoneurons and motor axons. Pre-symptomatic delivery of scAAV9-SMN prevented SMA symptoms indicating all changes are SMN dependent. Delivery of scAAV9-SMN after symptom onset had a marked impact on phenotype, electrophysiological measures and pathology. Interpretation High SMN levels are critical in postnatal motoneurons and reduction of SMN results in a SMA phenotype which is SMN dependent. Importantly, clinically relevant biomarkers including CMAP and MUNE are responsive to SMN restoration and abrogation of phenotype can be achieved even after symptom onset.

Intrathecal gene therapy rescues a model of demyelinating peripheral neuropathy

“…However, none of those previous studies focused specifically on myelinating Schwann cells, because ubiquitous promoters were used. Widespread expression was reported in some cases after AAV injection from the spinal cord to the brain in both adults and neonates (26,33), and even after AAV9 injection in large animal models (27,34). This is the first demonstration, to our knowledge, of a successful intrathecal approach to treating peripheral neuropathy by delivering a myelin-related gene and achieving widespread Schwann cell-specific expression.…”

Copackaged AAV9 Vectors Promote Simultaneous Immune Tolerance and Phenotypic Correction of Pompe Disease

“…[37][38][39] Early restoration of enzyme activity to both neural and skeletal muscle tissue is likely to have the greatest effect on physiological outcomes related to treatment strategies as our studies and those of others have demonstrated time-dependent arrests in functional decline after gene therapy. 11,74,75 Reliance upon liver-derived GAA to target neural tissues is dependent upon crosscorrection of neighboring cells through secretion and reuptake of GAA, yet the protein is too large to cross the blood-brain barrier and therefore does not address the neuropathology related to Pompe disease. 6,31 For these reasons, ERT or exclusively hepatic gene transfer would not address glycogen accumulation particularly in the motor neurons involved with ambulation or respiration as evidenced by patients continuing to be wheelchairand ventilator-dependent after long-term treatment of ERT.…”

Gene therapy for the CNS using AAVs: The impact of systemic delivery by AAV9

“…[89]. Very recently, AAV9-SMN1 intrathecal delivery has also successfully corrected the phenotype of a pig SMA model [98]. All of these successful reports culminated in the first clinical trial approved for the test of AAV9 in neurodegenerative disorders (NCT02122952) (see Table 2).…”