Contrasting effects of cerebrospinal fluid from motor neuron disease patients on the survival of primary motor neurons cultured with or without glia

40 Years of CSF Toxicity Studies in ALS: What Have We Learnt About ALS Pathophysiology?

Based on early evidence of in vitro neurotoxicity following exposure to serum derived from patients with amyotrophic lateral sclerosis (ALS), several studies have attempted to explore whether cerebrospinal fluid (CSF) obtained from people with ALS could possess similar properties. Although initial findings proved inconclusive, it is now increasingly recognized that ALS-CSF may exert toxicity both in vitro and in vivo. Nevertheless, the mechanism underlying CSF-induced neurodegeneration remains unclear. This review aims to summarize the 40-year long history of CSF toxicity studies in ALS, while discussing the various mechanisms that have been proposed, including glutamate excitotoxicity, proteotoxicity and oxidative stress. Furthermore, we consider the potential implications of a toxic CSF circulatory system in the pathophysiology of ALS, and also assess its significance in the context of current ALS research.

Defining novel functions for cerebrospinal fluid in ALS pathophysiology

Despite the considerable progress made towards understanding ALS pathophysiology, several key features of ALS remain unexplained, from its aetiology to its epidemiological aspects. The glymphatic system, which has recently been recognised as a major clearance pathway for the brain, has received considerable attention in several neurological conditions, particularly Alzheimer's disease. Its significance in ALS has, however, been little addressed. This perspective article therefore aims to assess the possibility of CSF contribution in ALS by considering various lines of evidence, including the abnormal composition of ALS-CSF, its toxicity and the evidence for impaired CSF dynamics in ALS patients. We also describe a potential role for CSF circulation in determining disease spread as well as the importance of CSF dynamics in ALS neurotherapeutics. We propose that a CSF model could potentially offer additional avenues to explore currently unexplained features of ALS, ultimately leading to new treatment options for people with ALS.

Cerebrospinal fluid cytotoxicity in amyotrophic lateral sclerosis: a systematic review of in vitro studies

Various studies have suggested that a neurotoxic cerebrospinal fluid profile could be implicated in amyotrophic lateral sclerosis. Here, we systematically review the evidence for cerebrospinal fluid cytotoxicity in amyotrophic lateral sclerosis and explore its clinical correlates. We searched the following databases with no restrictions on publication date: PubMed, Embase and Web of Science. All studies that investigated cytotoxicity in vitro following exposure to cerebrospinal fluid from amyotrophic lateral sclerosis patients were considered for inclusion. Meta-analysis could not be performed, and findings were instead narratively summarized. Twenty-eight studies were included in our analysis. Both participant characteristics and study conditions including cerebrospinal fluid concentration, exposure time and culture model varied considerably across studies. Of 22 studies assessing cell viability relative to controls, 19 studies reported a significant decrease following exposure to cerebrospinal fluid from patients with amyotrophic lateral sclerosis, while three early studies failed to observe any difference. Seven of eight studies evaluating apoptosis observed significant increases in the levels of apoptotic markers following exposure to cerebrospinal fluid from patients with amyotrophic lateral sclerosis, with the remaining study reporting a qualitative difference. Although five studies investigated the possible relationship between cerebrospinal fluid cytotoxicity and patient characteristics, such as age, gender and disease duration, none demonstrated an association with any of the factors. In conclusion, our analysis suggests that cerebrospinal fluid cytotoxicity is a feature of sporadic and possibly also of familial forms of amyotrophic lateral sclerosis. Further research is, however, required to better characterize its underlying mechanisms and to establish its possible contribution to amyotrophic lateral sclerosis pathophysiology.

Molecular pathways of motor neuron injury in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a genetically diverse disease. At least 15 ALS-associated gene loci have so far been identified, and the causative gene is known in approximately 30% of familial ALS cases. Less is known about the factors underlying the sporadic form of the disease. The molecular mechanisms of motor neuron degeneration are best understood in the subtype of disease caused by mutations in superoxide dismutase 1, with a current consensus that motor neuron injury is caused by a complex interplay between multiple pathogenic processes. A key recent finding is that mutated TAR DNA-binding protein 43 is a major constituent of the ubiquitinated protein inclusions in ALS, providing a possible link between the genetic mutation and the cellular pathology. New insights have also indicated the importance of dysregulated glial cell-motor neuron crosstalk, and have highlighted the vulnerability of the distal axonal compartment early in the disease course. In addition, recent studies have suggested that disordered RNA processing is likely to represent a major contributing factor to motor neuron disease. Ongoing research on the cellular pathways highlighted in this Review is predicted to open the door to new therapeutic interventions to slow disease progression in ALS.