Sporadic amyotrophic lateral sclerosis (SALS) – skeletal muscle response to cerebrospinal fluid from SALS patients in a rat model

Abstract

Skeletal muscle atrophy is the most prominent feature of amyotrophic lateral sclerosis (ALS), an adult-onset neurodegenerative disease of motor neurons. However, the contribution of skeletal muscle to disease progression remains elusive. Our previous studies have shown that intrathecal injection of cerebrospinal fluid from sporadic ALS patients (ALS-CSF) induces several degenerative changes in motor neurons and glia of neonatal rats. Here, we describe various pathologic events in the rat extensor digitorum longus muscle following intrathecal injection of ALS-CSF. Adenosine triphosphatase staining and electron microscopic (EM) analysis revealed significant atrophy and grouping of type 2 fibres in ALS-CSF-injected rats. Profound neuromuscular junction (NMJ) damage, such as fragmentation accompanied by denervation, were revealed by α-bungarotoxin immunostaining. Altered expression of key NMJ proteins, rapsyn and calpain, was also observed by immunoblotting. In addition, EM analysis showed sarcolemmal folding, Z-line streaming, structural alterations of mitochondria and dilated sarcoplasmic reticulum. The expression of trophic factors was affected, with significant downregulation of vascular endothelial growth factor (VEGF), marginal reduction in insulin-like growth factor-1 (IGF-1), and upregulation of brain-derived neurotrophic factor (BDNF) and glial-derived neurotrophic factor (GDNF). However, motor neurons might be unable to harness the enhanced levels of BDNF and GDNF, owing to impaired NMJs. We propose that ALS-CSF triggers motor neuronal degeneration, resulting in pathological changes in the skeletal muscle. Muscle damage further aggravates the motor neuronal pathology, because of the interdependency between them. This sets in a vicious cycle, leading to rapid and progressive loss of motor neurons, which could explain the relentless course of ALS.This article has an associated First Person interview with the first author of the paper.

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

“…These insights could arise from additional studies employing a proteomic approach, given that few such studies have been performed so far ( Varghese et al , 2013 ). In vitro results also need to be complemented by in vivo evidence, which have to date revealed various changes following CSF infusion, including neurofilament phosphorylation, endoplasmic reticulum stress, as well as motor dysfunction ( Deepa et al , 2011 ; Vijayalakshmi et al , 2011 ; Shanmukha et al , 2018 ). Although the observed changes have been reported to be histologically similar to sporadic ALS cases ( Gomez-Pinedo et al , 2018 ), whether CSF toxicity studies accurately capture the mechanisms involved in ALS pathophysiology, and could serve as an important model for ALS, is not yet clear.…”

“…Amongst the many lines of enquiry aiming to address this question, several studies have suggested that a neurotoxic cerebrospinal fluid (CSF) profile could be implicated in the disease process ( Shaw, 2002 ; Matias-Guiu et al , 2010 ; Sumitha et al , 2019 ; Tokuda et al , 2019 ). CSF from ALS patients has in fact been shown to exert cytotoxicity in vitro ( Tikka et al , 2002 ; Vijayalakshmi et al , 2009 ; Barber et al , 2011 ; Sumitha et al , 2019 ), and to provoke wide-ranging pathology, from neurofilament phosphorylation to musculoskeletal changes, when administered in vivo ( Shahani et al , 2004 ; Gomez-Pinedo et al , 2018 ; Shanmukha et al , 2018 ). While the cause of these findings remains unclear, they nevertheless suggest the presence of one or more potentially toxic factors in ALS–CSF, with possible involvement in disease spread ( Smith et al , 2015 ).…”

Defining novel functions for cerebrospinal fluid in ALS pathophysiology

“…ALS-CSF was also found to produce phenotypic changes, with rats subjected to intraventricular injections experiencing motor dysfunction [165]. Muscular atrophy was observed in a different study, possibly arising through motor neuron degeneration [173].…”

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

“…In addition to cellular changes, intrathecal and intraventricular infusion of ALS-CSF in rat models were also found to result in motor impairment and other musculoskeletal features ( Sankaranarayani et al, 2010 , 2014 ; Sumitha et al, 2014 ; Shanmukha et al, 2018 ). These could possibly be attributed to altered neuronal activity in the motor cortex, in which increased neuronal excitability was observed ( Sankaranarayani et al, 2010 , 2014 ; Shanmukha et al, 2018 ).…”