Expression of collagen XVII and ubiquitin-binding protein p62 in motor neuron disease

Regulated cell death and its role in Alzheimer's disease and amyotrophic lateral sclerosis

Despite considerable research efforts, it is still not clear which mechanisms underlie neuronal cell death in neurodegenerative diseases. During the last 20 years, multiple pathways have been identified that can execute regulated cell death (RCD). Among these RCD pathways, apoptosis, necroptosis, pyroptosis, ferroptosis, autophagy-related cell death, and lysosome-dependent cell death have been intensively investigated. Although RCD consists of numerous individual pathways, multiple common proteins have been identified that allow shifting from one cell death pathway to another. Another layer of complexity is added by mechanisms such as the endosomal machinery, able to regulate the activation of some RCD pathways, preventing cell death. In addition, restricted axonal degeneration and synaptic pruning can occur as a result of RCD activation without loss of the cell body. RCD plays a complex role in neurodegenerative processes, varying across different disorders. It has been shown that RCD is differentially involved in Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS), among the most common neurodegenerative diseases. In AD, neuronal loss is associated with the activation of not only necroptosis, but also pyroptosis. In ALS, on the other hand, motor neuron death is not linked to canonical necroptosis, whereas pyroptosis pathway activation is seen in white matter microglia. Despite these differences in the activation of RCD pathways in AD and ALS, the accumulation of protein aggregates immunoreactive for p62/SQSTM1 (sequestosome 1) is a common event in both diseases and many other neurodegenerative disorders. In this review, we describe the major RCD pathways with clear activation in AD and ALS, the main interactions between these pathways, as well as their differential and similar involvement in these disorders. Finally, we will discuss targeting RCD as an innovative therapeutic concept for neurodegenerative diseases, such as AD and ALS. Considering that the execution of RCD or "cellular suicide" represents the final stage in neurodegeneration, it seems crucial to prevent neuronal death in patients by targeting RCD. This would offer valuable time to address upstream events in the pathological cascade by keeping the neurons alive.

Cooperation of cell adhesion and autophagy in the brain: Functional roles in development and neurodegenerative disease

Cellular adhesive connections directed by the extracellular matrix (ECM) and maintenance of cellular homeostasis by autophagy are seemingly disparate functions that are molecularly intertwined, each regulating the other. This is an emerging field in the brain where the interplay between adhesion and autophagy functions at the intersection of neuroprotection and neurodegeneration. The ECM and adhesion proteins regulate autophagic responses to direct protein clearance and guide regenerative programs that go awry in brain disorders. Concomitantly, autophagic flux acts to regulate adhesion dynamics to mediate neurite outgrowth and synaptic plasticity with functional disruption contributed by neurodegenerative disease. This review highlights the cooperative exchange between cellular adhesion and autophagy in the brain during health and disease. As the mechanistic alliance between adhesion and autophagy has been leveraged therapeutically for metastatic disease, understanding overlapping molecular functions that direct the interplay between adhesion and autophagy might uncover therapeutic strategies to correct or compensate for neurodegeneration.

Selective neuronal degeneration in MATR3 S85C knock-in mouse model of early-stage ALS

A missense mutation, S85C, in the MATR3 gene is a genetic cause for amyotrophic lateral sclerosis (ALS). It is unclear how the S85C mutation affects MATR3 function and contributes to disease. Here, we develop a mouse model that harbors the S85C mutation in the endogenous Matr3 locus using the CRISPR/Cas9 system. MATR3 S85C knock-in mice recapitulate behavioral and neuropathological features of early-stage ALS including motor impairment, muscle atrophy, neuromuscular junction defects, Purkinje cell degeneration and neuroinflammation in the cerebellum and spinal cord. Our neuropathology data reveals a loss of MATR3 S85C protein in the cell bodies of Purkinje cells and motor neurons, suggesting that a decrease in functional MATR3 levels or loss of MATR3 function contributes to neuronal defects. Our findings demonstrate that the MATR3 S85C mouse model mimics aspects of early-stage ALS and would be a promising tool for future basic and preclinical research.

Lack of collagen VI promotes neurodegeneration by impairing autophagy and inducing apoptosis during aging

Collagen VI is an extracellular matrix (ECM) protein with a broad distribution in different tissues and mostly deposited at the close periphery of the cell surface. Previous studies revealed that collagen VI protects neurons from the toxicity of amyloid-βpeptides and from UV-induced damage. However, the physiological role of this protein in the central nervous system (CNS) remains unknown. Here, we established primary neural cultures from murine cortex and hippocampus, and carried out in vitro and in vivo studies in wild-type and collagen VI null (Col6a1^−/−) mice. Col6a1^−/− neural cultures displayed an increased incidence of spontaneous apoptosis and higher vulnerability to oxidative stress, accompanied by altered regulation of autophagy with increased p62 protein levels and decreased LC3 lipidation. Analysis of brain sections confirmed increased apoptosis and abnormal regulation of autophagy in the CNS of collagen VI-deficient animals. To investigate the in vivo physiological consequences of these CNS defects, we carried out functional studies and found that motor and memory task performances were impaired in aged Col6a1^−/− mice. These findings indicate that lack of collagen VI leads to spontaneous apoptosis and defective autophagy in neural cells, and point at a protective role for this ECM protein in the CNS during physiological aging.

Rho guanine nucleotide exchange factor is an NFL mRNA destabilizing factor that forms cytoplasmic inclusions in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is an adult-onset progressive disorder of unknown etiology characterized by the selective degeneration of motor neurons. Recent evidence supports the hypothesis that alterations in RNA metabolism in motor neurons can explain the development of protein inclusions, including neurofilamentous aggregates, observed in this pathology. In mice, p190RhoGEF, a guanine nucleotide exchange factor, is involved in neurofilament protein aggregation in an RNA-triggered transgenic model of motor neuron disease. Here, we observed that rho guanine nucleotide exchange factor (RGNEF), the human homologue of p190RhoGEF, binds low molecular weight neurofilament mRNA and affects its stability via 3' untranslated region destabilization. We observed that the overexpression of RGNEF in a stable cell line significantly decreased the level of low molecular weight neurofilament protein. Furthermore, we observed RGNEF cytoplasmic inclusions in ALS spinal motor neurons that colocalized with ubiquitin, p62/sequestosome-1, and TAR (trans-active regulatory) DNA-binding protein 43 (TDP-43). Our results provide further evidence that RNA metabolism pathways are integral to ALS pathology. This is also the first described link between ALS and an RNA binding protein with aggregate formation that is also a central cell signaling pathway molecule.