Neuroprotective Effects of Toll-Like Receptor 4 Antagonism in Spinal Cord Cultures and in a Mouse Model of Motor Neuron Degeneration

Abstract

Sustained inflammatory reactions are common pathological events associated with neuron loss in neurodegenerative diseases. Reported evidence suggests that Toll-like receptor 4 (TLR4) is a key player of neuroinflammation in several neurodegenerative diseases. However, the mechanisms by which TLR4 mediates neurotoxic signals remain poorly understood. We investigated the role of TLR4 in in vitro and in vivo settings of motor neuron degeneration. Using primary cultures from mouse spinal cords, we characterized both the proinflammatory and neurotoxic effects of TLR4 activation with lipopolysaccharide (activation of microglial cells, release of proinflammatory cytokines and motor neuron death) and the protective effects of a cyanobacteriaderived TLR4 antagonist (VB3323). With the use of TLR4-deficient cells, a critical role of the microglial component with functionally active TLR4 emerged in this setting. The in vivo experiments were carried out in a mouse model of spontaneous motor neuron degeneration, the wobbler mouse, where we preliminarily confirmed a protective effect of TLR4 antagonism. Compared with vehicle-and riluzole-treated mice, those chronically treated with VB3323 showed a decrease in microglial activation and morphological alterations of spinal cord neurons and a better performance in the paw abnormality and grip-strength tests. Taken together, our data add new understanding of the role of TLR4 in mediating neurotoxicity in the spinal cord and suggest that TLR4 antagonists could be considered in future studies as candidate protective agents for motor neurons in degenerative diseases.

The wobbler mouse, an ALS animal model

“…In a similar way, the systemic administration of a recombinant human TNF-binding protein-1 (rhTBP-1) delayed both symptom progression and motor neuron loss in the wobbler mouse by selectively inhibiting the expression of TNF-alpha and TNFR1 and phosphorylation of JNK and p38MAPK in affected motor neurons (Bigini et al 2008). The link between the inflammatory reaction and motor neuron damage in wobbler mice has been recently confirmed by a treatment with a cyanobacterium-derived toll-like receptor 4 (TLR4), VB3323 (De Paola et al 2012). In agreement with the results emerging from in vitro studies, in which VB3323 reduced motor neuron loss and microglial response after lipopolysaccharide (LPS) stimulation, a significant decrease in microglial activation and morphological alterations of motor neurons, associated with a significant improvement of motor performance was detected in VB3323-treated mice, as compared to both vehicle-treated and riluzole-treated wobbler individuals (Fumagalli et al 2006).…”

Role of Toll-like receptor/MYD88 signaling in neurodegenerative diseases

“…Nguyen et al found that closely associated with the severity of ALS was the stronger and restricted up-regulation of TLR2 and proinflammatory cytokines in the degenerating regions of the ventral spinal cord and efferent fiber tracts of the brain from the LPS-treated SOD1(G37R) mice ( Nguyen et al, 2004 ). For these reasons, researchers hold the idea that antagonists could be considered in future studies as candidate protective agents for motor neurons in degenerative diseases ( De Paola et al, 2012 ). However, it is not always the case because, in certain conditions, TLRs may be a protective factor for ALS.…”

Toll-like receptors in central nervous system injury and disease: A focus on the spinal cord

“…In the wobbler mouse, systemic, chronic administration of a TLR4 antagonist, VB3323, during the symptomatic phase improved behavioral outcomes including grip strength, and reduced chromatolysis, glial activation and TNF-a production in the cervical spinal cord (De Paola et al, 2012). It is not yet known whether the beneficial effects of the TLR4 antagonist are mediated by direct actions on spinal cord cells, or indirectly via systemic responses.…”