Characterization of a murine model of SMA

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disease, which is the leading genetic cause of mortality in children. To date no effective treatment exists for SMA. The genetic basis for SMA has been well documented as a mutation in the gene for survival of motor neuron (SMN). Because there is an understanding of which gene needs to be replaced (SMN) and where it needs to be replaced (spinal motor systems), SMA is an ideal target for gene replacement via gene therapy. While a variety of animal models for SMA exist, they are either too fulminant to realistically test most gene delivery strategies, or too mild to provide a robust read out of the therapeutic effect. The field, therefore, requires a robust model with a slower symptomatic progression. A conditional knockout of SMN in neuronal cell types, giving a phenotype of functional motor defects, weight loss and reduced life expectancy partially satisfies this need (Frugier, Tiziano et al. 2000). This Cre/LoxP mediated neuron specific model presents an attractive alternative. In the present manuscript, we characterize the functional motor deficits of the model. We observed a decline in locomotor ability, as assessed by open field testing. The finer functions of motor skills such as righting reflex and grip strength were also observed to degenerate in the SMA mice. The decline in motor function that we observed here correlates with the anatomical decline in motor neurons and motor axons presented in the literature (Ferri, Melki et al. 2004). This work adds to our understanding and knowledge base of this Cre/LoxP model and provides a basis from which functional recovery, following interventions can be assessed.

Pain in amyotrophic lateral sclerosis: a neglected aspect of disease

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder marked by progressive loss of motor neurons, muscle wasting, and respiratory dysfunction. With disease progression, secondary symptoms arise creating new problematic conditions for ALS patients. Amongst these is pain. Although not a primary consequence of disease, pain occurs in a substantial number of individuals. Yet, studies investigating its pathomechanistic properties in the ALS patient are lacking. Therefore, more exploratory efforts into its scope, severity, impact, and treatment should be initiated. Several studies investigating the use of Clostridial neurotoxins for the reduction of pain in ALS patients suggest the potential for a neural specific approach involving focal drug delivery. Gene therapy represents a way to accomplish this. Therefore, the use of viral vectors to express transgenes that modulate the nociceptive cascade could prove to be an effective way to achieve meaningful benefit in conditions of pain in ALS.

Follistatin gene delivery enhances muscle growth and strength in nonhuman primates

Antagonists of myostatin, a blood-borne negative regulator of muscle growth produced in muscle cells, have shown considerable promise for enhancing muscle mass and strength in rodent studies and could serve as potential therapeutic agents for human muscle diseases. One of the most potent of these agents, follistatin, is both safe and effective in mice, but similar tests have not been performed in nonhuman primates. To assess this important criterion for clinical translation, we tested an alternatively spliced form of human follistatin that affects skeletal muscle but that has only minimal effects on nonmuscle cells. When injected into the quadriceps of cynomolgus macaque monkeys, a follistatin isoform expressed from an adeno-associated virus serotype 1 vector, AAV1-FS344, induced pronounced and durable increases in muscle size and strength. Long-term expression of the transgene did not produce any abnormal changes in the morphology or function of key organs, indicating the safety of gene delivery by intramuscular injection of an AAV1 vector. Our results, together with the findings in mice, suggest that therapy with AAV1-FS344 may improve muscle mass and function in patients with certain degenerative muscle disorders.

Antioxidants attenuate multiple phases of formalin-induced nociceptive response in mice

An emerging theme in the study of the pathophysiology of chronic and persistent pain is the role of pro-oxidant substances. Reactive oxygen species (ROS) have been implicated in contributing to and/or maintaining conditions of chronic pain. Recent pre-clinical reports suggest that antioxidants are effective analgesics in neuropathic and inflammatory pain models. The present study extends this work by examining the effect of three antioxidants on tissue injury-induced nociception. C57BL6 mice (20-25 g) were pretreated with either phenyl-N-tert-butylnitrone (PBN; 50 mg/kg, i.p.), 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy (TEMPOL; 200 or 50 mg/kg, i.p.), N-acetyl-L-cysteine (NAC; 200 or 100mg/kg, i.p.), or vehicle (0.5 ml/100 g), 5 min before intraplantar formalin (10%, 20 microl) injection. Nociceptive responding, indicated by licking or biting the affected hindlimb, was quantified for 30 min after formalin injection. Each drug was effective in attenuating two or more phases (acute, quiescent, and tonic) of the formalin response. To assess putative site of action, intrathecal TEMPOL (380 nmol/5 microl, i.t.) was given 5 min before intraplantar formalin. Intrathecal TEMPOL produced a 83% reduction in nociceptive responding in the tonic phase, but no significant attenuation of the acute phase response. To confirm that the antioxidant property of intrathecal TEMPOL was responsible for its analgesic effect on the formalin-induced pain response, intrathecal TEMPOL was coadministered with the free radical donor tert-butylhydroperoxide (tert-BuOOH). Tert-BuOOH coadminstration reversed the TEMPOL-induced analgesia in the tonic intraplantar formalin response reduction. The data suggest that pro-oxidant species may be important mediators of tissue injury-induced algesia in rodents, and that a spinal site of action is implicated in the tonic response.