Molecular targets for neuroprotection

Neuronal matrix metalloproteinase-9 is a determinant of selective neurodegeneration

Selective neuronal loss is the hallmark of neurodegenerative diseases. In patients with amyotrophic lateral sclerosis (ALS), most motor neurons die but those innervating extraocular, pelvic sphincter, and slow limb muscles exhibit selective resistance. We identified 18 genes that show >10-fold differential expression between resistant and vulnerable motor neurons. One of these, matrix metalloproteinase-9 (MMP-9), is expressed only by fast motor neurons, which are selectively vulnerable. In ALS model mice expressing mutant superoxide dismutase (SOD1), reduction of MMP-9 function using gene ablation, viral gene therapy, or pharmacological inhibition significantly delayed muscle denervation. In the presence of mutant SOD1, MMP-9 expressed by fast motor neurons themselves enhances activation of ER stress and is sufficient to trigger axonal die-back. These findings define MMP-9 as a candidate therapeutic target for ALS. The molecular basis of neuronal diversity thus provides significant insights into mechanisms of selective vulnerability to neurodegeneration.

Axonal degeneration as a therapeutic target in the CNS

Degeneration of the axon is an important step in the pathomechanism of traumatic, inflammatory and degenerative neurological diseases. Increasing evidence suggests that axonal degeneration occurs early in the course of these diseases and therefore represents a promising target for future therapeutic strategies. We review the evidence for axonal destruction from pathological findings and animal models with particular emphasis on neurodegenerative and neurotraumatic disorders. We discuss the basic morphological and temporal modalities of axonal degeneration (acute, chronic and focal axonal degeneration and Wallerian degeneration). Based on the mechanistic concepts, we then delineate in detail the major molecular mechanisms that underlie the degenerative cascade, such as calcium influx, axonal transport, protein aggregation and autophagy. We finally concentrate on putative therapeutic targets based on the mechanistic prerequisites.

Preclinical trials--an update on translational research in ALS

Translational research has become a strategy which describes the steps from in vitro experimental therapy, its translation into experimental animals and finally to humans. However, this translation of hypotheses from one of these levels to another faces a number of difficulties which are currently of major interest for the development of therapeutics. In particular, in the previously untreatable motor neuron diseases, the steps from genes to transgenic animals and finally to the patient have proven difficult. High expectations have not met with the transfer of numerous therapies from experimental animals to men; there are many in- and outside the field which already question the value of animal models. It is the opinion of the authors that we should not dismiss the models before we have not defined generally accepted standards of protocols for therapeutic studies in experimental animals. Only if a generally agreed standardized and validated methodology in mice cannot predict the human response to therapeutics, an animal model should be abandoned. In contrast, the value of translating genetic findings to experimental animals and men is currently shown for motor proteins; in particular the functional impact of dynactin and dynein for the integrity of motor neurons of rodents and men are in the center of interest.

Clinical Trials in ALS: What Did We Learn from Recent Trials in Humans?

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease. No treatment is currently able to stop the disease process. In the absence of new active compounds there is an urgent need to develop new strategies based on the neuroprotective activity of available drugs. ALS is a heterogeneous disease. To build up these therapeutic trials, we need to have a better understanding of the prognostic factors in this disease. During the Phase IV Rilutek Trial in France, we developed in a large population of patients a prognostic score based on clinical parameters available at the bedside. The most significant variables are vital capacity, spasticity, fasciculations, swallowing, cough and creatininemia. This score proved to be very useful in daily use in the clinic and for planning disease management in ALS as in the design of therapeutic trials. In ALS clinical trials, efficacy can be evaluated using survival or functional parameters. In phase II trials, function remains the most commonly used. In phase III trials, the gold standard endpoint remains the survival rate at month 18. We analyzed the most recent ALS trials published in the literature. This review suggests that in these trials there is a discrepancy between drug effects on survival versus function. These results suggest that a reappraisal of strategies to identify therapeutic targets for ALS is required.

Gene-based treatment of motor neuron diseases

Motor neuron diseases (MND), such as amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA), are progressive neurodegenerative diseases that share the common characteristic of upper and/or lower motor neuron degeneration. Therapeutic strategies for MND are designed to confer neuroprotection, using trophic factors, anti-apoptotic proteins, as well as antioxidants and anti-excitotoxicity agents. Although a large number of therapeutic clinical trials have been attempted, none has been shown satisfactory for MND at this time. A variety of strategies have emerged for motor neuron gene transfer. Application of these approaches has yielded therapeutic results in cell culture and animal models, including the SOD1 models of ALS. In this study we describe the gene-based treatment of MND in general, examining the potential viral vector candidates, gene delivery strategies, and main therapeutic approaches currently attempted. Finally, we discuss future directions and potential strategies for more effective motor neuron gene delivery and clinical translation.