Remote adenoviral gene delivery to the spinal cord: contralateral delivery and reinjection

Strategic approaches to developing drug treatments for ALS

Significant progress in understanding the cellular mechanisms of motor neuron degeneration in amyotrophic lateral sclerosis (ALS) has not been matched with the development of therapeutic strategies to prevent disease progression. The multiple potential causes and relative rarity of the disease are two significant factors that make drug development and assessment in clinical trials extremely difficult. We review recent progress in promoting therapeutics into clinical trials and highlight the value of moderate throughput screening for the acceleration and improvement of drug design.

Cytoplasmic dynein mediates adenovirus binding to microtubules

During infection, adenovirus (Ad) capsids undergo microtubule-dependent retrograde transport as part of a program of vectorial transport of the viral genome to the nucleus. The microtubule-associated molecular motor, cytoplasmic dynein, has been implicated in the retrograde movement of Ad. We hypothesized that cytoplasmic dynein constituted the primary mode of association of Ad with microtubules. To evaluate this hypothesis, an Ad-microtubule binding assay was established in which microtubules were polymerized with taxol, combined with Ad in the presence or absence of microtubule-associated proteins (MAPs), and centrifuged through a glycerol cushion. The addition of purified bovine brain MAPs increased the fraction of Ad in the microtubule pellet from 17.3% +/- 3.5% to 80.7% +/- 3.8% (P < 0.01). In the absence of tubulin polymerization or in the presence of high salt, no Ad was found in the pellet. Ad binding to microtubules was not enhanced by bovine brain MAPs enriched for tau protein or by the addition of bovine serum albumin. Enhanced Ad-microtubule binding was also observed by using a fraction of MAPs purified from lung A549 epithelial cell lysate which contained cytoplasmic dynein. Ad-microtubule interaction was sensitive to the addition of ATP, a hallmark of cytoplasmic dynein-dependent microtubule interactions. Immunodepletion of cytoplasmic dynein from the A549 cell lysate abolished the MAP-enhanced Ad-microtubule binding. The interaction of Ad with both dynein and dynactin complexes was demonstrated by coimmunoprecipitation. Partially uncoated capsids isolated from cells 40 min after infection also exhibited microtubule binding. In summary, the primary mode of Ad attachment to microtubules occurs though cytoplasmic dynein-mediated binding.

Neurotrophin-3 expressed in situ induces axonal plasticity in the adult injured spinal cord

The mammalian CNS lacks the ability to effectively compensate for injury by the regeneration of damaged axons or axonal plasticity of intact axons. However, reports suggest that molecular or cellular manipulations can induce compensatory processes that could support regeneration or plasticity after trauma. We tested whether local, sustained release of the neurotrophic factor neurotrophin-3 (NT-3) would support axonal plasticity in the spinal cord distal to the site of injury in rats. The corticospinal tract (CST) was cut unilaterally at the level of the medulla. This avoided excessive inflammation, secondary cell death, vascular disruption, and the release of inhibitory molecules in the lumbar spinal cord. A replication-defective adenoviral vector (Adv) carrying the NT-3 gene (Adv.EFalpha-NT3) was delivered to the spinal motoneurons by retrograde transport through the sciatic nerve. Retrograde transport of the adenoviral vectors avoided the inflammatory response that would be associated with direct injection into the spinal cord. Transduction of spinal motoneurons with Adv.EFalpha-NT3 resulted in a significant increase in the concentration of NT-3 in the L3-L6 region of the spinal cord for up to 3 weeks. In animals with a CST lesion, this local expression of NT-3 induced growth of axons from the intact CST across the midline to the denervated side. If the CST remained intact, overexpression of NT-3 did not lead to an increase in the number of axons crossing the midline. These data demonstrate that local, sustained expression of NT-3 will support axonal plasticity of intact CST axons after trauma-induced denervation.