Increased ROS‐Dependent Fission of Mitochondria Causes Abnormal Morphology of the Cell Powerhouses in a Murine Model of Amyotrophic Lateral Sclerosis

Abstract

Amyotrophic lateral sclerosis (ALS) is the most common motor neuron disease in humans and remains to have a fatal prognosis. Recent studies in animal models and human ALS patients indicate that increased reactive oxygen species (ROS) play an important role in the pathogenesis. Considering previous studies revealing the influence of ROS on mitochondrial physiology, our attention was focused on mitochondria in the murine ALS model, wobbler mouse. The aim of this study was to investigate morphological differences between wild-type and wobbler mitochondria with aid of superresolution structured illumination fluorescence microscopy, TEM, and TEM tomography. To get an insight into mitochondrial dynamics, expression studies of corresponding proteins were performed. Here, we found significantly smaller and degenerated mitochondria in wobbler motor neurons at a stable stage of the disease. Our data suggest a ROS-regulated, Ox-CaMKII-dependent Drp1 activation leading to disrupted fission-fusion balance, resulting in fragmented mitochondria. These changes are associated with numerous impairments, resulting in an overall self-reinforcing decline of motor neurons. In summary, our study provides common pathomechanisms with other ALS models and human ALS cases confirming mitochondria and related dysfunctions as a therapeutic target for the treatment of ALS.

ROS scavengers decrease γH2ax spots in motor neuronal nuclei of ALS model mice in vitro

“…As mitochondria are physiologically the major producers of intracellular ROS, mitochondrial dysfunction can lead to many cell damaging processes including an excessive production of this harmful species (Smith et al, 2019 ). Since we demonstrated in a previous study that mitochondria in Wobbler motor neurons have abnormal morphology (Stein et al, 2021 ) and mitochondrial malfunction is known to be present in Wobbler animals (Xu et al, 2001 ; Dave et al, 2003 ; Santoro et al, 2004 ; Gonzalez Deniselle et al, 2012 ), it is tempting to assume an increased mitochondrial ROS production in a Wobbler phenotype. Therefore, an additional ROS scavenger, Mito-TEMPO, was used to specifically scavenge mitochondrially produced ROS.…”

“…SDS-gel electrophoresis and Western blotting were performed as previously described (Stein et al, 2021 ). For SDS-gel electrophoresis proteins were isolated from four to eight cervical spinal cord samples (p40) per genotype using Cell lysis buffer (#9803S, Cell Signaling Technology, Danvers, Massachusetts, USA) supplemented with protease inhibitor (#11697498001, Merck, Darmstadt, Germany).…”

“…Recent studies described the importance of oxidative stress for the pathogenesis, both in Wobbler mice and in ALS patients (Petrov et al, 2017 ; Röderer et al, 2018 ; Matschke et al, 2019 ; Tam et al, 2019 ; Wang et al, 2019 ; Zwilling et al, 2020 ; Stein et al, 2021 ). Our previous studies identified significantly increased levels of reactive oxygen species (ROS) as a marker for oxidative stress in the stable clinical phase (p40) of the Wobbler spinal cord (Röderer et al, 2018 ).…”

Mitochondrial dynamics in neurological diseases: a narrative review

“…VPS54 gene mutation has also been shown to cause ALS. In mutant mice, the researchers observed an abnormal distribution of mitochondria, in which the mitochondria became smaller and the mitochondrial cristae disappeared; moreover, the expression of MFN2 and OPA1 was lower, and the phosphorylation of Drp1 at ser616 was higher than that in the wild type mice ( 58 ). Tau is involved in the occurrence of ALS and has been shown to interact with Drp1, with a synchronous increase in phosphorylated tau and Drp1 leading to increased mitochondrial fission ( 59 ).…”

What Is the Role of Mitochondrial Fission in Neurologic Disease?

“…[97][98][99] In the wobbler mouse model of ALS, the presence of small and degenerated mitochondria reflected ROS-regulated, CaMKII-dependent DRP1 activation. 100 Preventing excessive fission by inhibiting DRP1/Fis1 interaction using a selective peptide inhibitor led to improvement in mitochondrial structure and function in fibroblasts derived from patients with several familial forms of ALS and in cultured motor neurons expressing SOD1 mutations, and improved motor performance and survival in mutant SOD1 mice. 101 Hyperphosphorylated tau was found to be mislocalized to synapses in postmortem motor cortex across ALS subtypes and interacts with DRP1, promoting mitochondrial fragmentation and oxidative stress.…”