Changes in the Expression of FUS/TLS in Spinal Cords of SOD1 G93A Transgenic Mice and Correlation with Motor-Neuron Degeneration

Pathological mechanisms of amyotrophic lateral Sclerosis

Amyotrophic lateral sclerosis refers to a neurodegenerative disease involving the motor system, the cause of which remains unexplained despite several years of research. Thus, the journey to understanding or treating amyotrophic lateral sclerosis is still a long one. According to current research, amyotrophic lateral sclerosis is likely not due to a single factor but rather to a combination of mechanisms mediated by complex interactions between molecular and genetic pathways. The progression of the disease involves multiple cellular processes and the interaction between different complex mechanisms makes it difficult to identify the causative factors of amyotrophic lateral sclerosis. Here, we review the most common amyotrophic lateral sclerosis-associated pathogenic genes and the pathways involved in amyotrophic lateral sclerosis, as well as summarize currently proposed potential mechanisms responsible for amyotrophic lateral sclerosis disease and their evidence for involvement in amyotrophic lateral sclerosis. In addition, we discuss current emerging strategies for the treatment of amyotrophic lateral sclerosis. Studying the emergence of these new therapies may help to further our understanding of the pathogenic mechanisms of the disease.

Distribution Features and Potential Effects of Serotonin in the Cerebrum of SOD1 G93A Transgenic Mice

Serotonin (5-HT) participates in the pathogenesis of amyotrophic lateral sclerosis (ALS), but its effects have not been completely clarified. Therefore, we observed the distribution features and potential effects of 5-HT in the cerebrum of G93A SOD1 transgenic (TG) and wild-type (WT) mice by fluorescence immunohistochemistry, Western blotting, ELISA, as well as motor function measurements. Both 5-HT and tryptophan hydroxylase-2 (TPH2) were mainly present in the limbic systems of the cerebrum, such as the glomerular layer of the olfactory bulb, nucleus accumbens, cingulate, fimbria of the hippocampus, mediodorsal thalamic nucleus, habenular nucleus, ventromedial hypothalamus nucleus, lateral hypothalamus area, dorsal raphe nucleus, and piriform cortex. TPH2 and 5-HT were expressed in cell bodies in the dorsal raphe nucleus and piriform cortex, while in other regions they were distributed as filaments and clump shapes in axons. The TPH2 distribution in the cerebrum of TG was significantly lower than that in WT in preset, onset, and progression stages. TPH2 expression in the fimbria of the hippocampus, mediodorsal thalamic nucleus, habenular nucleus, ventromedial hypothalamus nucleus and lateral hypothalamus area was increased in the onset stage and decreased in the progression stage, gradually decreased in the cingulate with disease progression and significantly decreased in the glomerular layer of the olfactory bulb and nucleus accumbens in the onset stage in TG. The number of mammalian achaete-scute homolog-1 in the subventricular zone (SVZ) in TG was significantly lower than that in WT, which was correlated with the TPH2 distribution. Double immunofluorescence staining showed that TPH2, mammalian achaete-scute homolog-1 and 5-HT were mainly expressed in neurons but rarely expressed in microglia or astrocytes in the piriform cortex. The relative fluorescence density of TPH2 in the cingulate region was negatively correlated with the disease severity. Our findings suggest that 5-HT plays a protective role in ALS, likely by regulating neural stem cells in the subventricular zone that might be involved in neuron development in the piriform cortex.

Astrocytes in Neurodegeneration: Inspiration From Genetics

Despite the discovery of numerous molecules and pathologies, the pathophysiology of various neurodegenerative diseases remains unknown. Genetics participates in the pathogenesis of neurodegeneration. Neural dysfunction, which is thought to be a cell-autonomous mechanism, is insufficient to explain the development of neurodegenerative disease, implying that other cells surrounding or related to neurons, such as glial cells, are involved in the pathogenesis. As the primary component of glial cells, astrocytes play a variety of roles in the maintenance of physiological functions in neurons and other glial cells. The pathophysiology of neurodegeneration is also influenced by reactive astrogliosis in response to central nervous system (CNS) injuries. Furthermore, those risk-gene variants identified in neurodegenerations are involved in astrocyte activation and senescence. In this review, we summarized the relationships between gene variants and astrocytes in four neurodegenerative diseases, including Alzheimer’s disease (AD), amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and Parkinson’s disease (PD), and provided insights into the implications of astrocytes in the neurodegenerations.

Phosphoinositide-3-kinase regulatory subunit 4 participates in the occurrence and development of amyotrophic lateral sclerosis by regulating autophagy

The development of amyotrophic lateral sclerosis (ALS) may be related to the abnormal alterations of multiple proteins. Our previous study revealed that the expression of phosphoinositide-3-kinase regulatory subunit 4 (PIK3R4) was decreased in ALS. However, the role of PIK3R4 in ALS pathogenesis remains unknown. This study was the first to find that transfection of PC12 cells with small interfering RNA against the PIK3R4 gene significantly decreased the expression levels of PIK3R4 and the autophagy-related proteins p62 and LC3. Additionally, in vivo experiments revealed that the PIK3R4 protein was extensively expressed in the anterior horn, posterior horn, central canal, and areas surrounding the central canal in cervical, thoracic, and lumbar segments of the spinal cord in adult mice. PIK3R4 protein was mainly expressed in the neurons within the spinal lumbar segments. PIK3R4 and p62 expression levels were significantly decreased at both the pre-onset and onset stages of ALS disease in Tg(SOD1*G93A)1Gur mice compared with control mice, but these proteins were markedly increased at the progression stage. LC3 protein expression did not change during progression of ALS. These findings suggest that PIK3R4 likely participates in the prevention of ALS progression. This study was approved by the Ethics Committee for Animal Care and Use of Jiangxi Provincial People's Hospital, Affiliated People's Hospital of Nanchang University (approval No. 2020025) on March 26, 2020.

Potential Common Genetic Risks of Sporadic Parkinson's Disease and Amyotrophic Lateral Sclerosis in the Han Population of Mainland China

Sporadic Parkinson’s disease (sPD) and sporadic amyotrophic lateral sclerosis (sALS) are neurodegenerative diseases characterized by progressive and selective neuron death, with some genetic similarities. In order to investigate the genetic risk factors common to both sPD and sALS, we carried out a screen of risk alleles for sALS and related loci in 530 sPD patients and 530 controls from the Han population of Mainland China (HPMC). We selected 27 single-nucleotide polymorphisms in 10 candidate genes associated with sALS, and we performed allelotyping and genotyping to determine their frequencies in the study population as well as bioinformatics analysis to assess their functional significance in these diseases. The minor alleles of rs17115303 in DAB adaptor protein 1 (DAB1) gene and rs6030462 in protein tyrosine phosphatase receptor type T (PTPRT) gene were correlated with increased risk of both sPD and sALS. Polymorphisms of rs17115303 and rs6030462 were associated with alterations in transcription factor binding sites, secondary structures, long non-coding RNA interactions, and nervous system regulatory networks; these changes involved biological processes associated with neural cell development, differentiation, neurogenesis, migration, axonogenesis, cell adhesion, and metabolism of phosphate-containing compounds. Thus, variants of DAB1 gene (rs17115303) and PTPRT gene (rs6030462) are risk factors common to sPD and sALS in the HPMC. These findings provide insight into the molecular pathogenesis of both diseases and can serve as a basis for the development of targeted therapies.

All-Trans Retinoic Acid Exerts Neuroprotective Effects in Amyotrophic Lateral Sclerosis-Like Tg (SOD1*G93A)1Gur Mice

All-trans retinoic acid (ATRA), a ligand of retinoic acid receptors, could regulate various biological processes by activating retinoic acid signals. Recent studies suggested that ATRA displays multiple neuroprotective effects and thereby alleviates the disease progression in a variety of neurological diseases. Our previous studies found that the impaired retinoic acid signal decreased ALDH1A2, an essential synthetase of ATRA, in the spinal cord of ALS mice. Here, we evaluated the neuroprotective and neurorestorative effects of ATRA in a SOD1-G93A transgenic mice model of ALS. We administrated ATRA(3 mg/kg) daily from the onset stage to the progression stage for 5 weeks. Behavioral tests showed that ATRA improved the forelimb grip strength in ALS mice and may slow the disease progression, but not the body weight. ATRA could completely reverse the impaired retinoic acid receptor alpha (RARα) signal in the spinal cord of ALS mice. This effect was accompanied by enhancing the degradation of misfolded proteins via the ubiquitin-proteasome system, regulating the oxidative stress, inhibiting the astrocyte activation, and promoting the neurotrophic signal recovery. Our findings are the first to indicate that the damaged retinoic acid signal is involved in the pathogenesis of ALS, and ATRA could induce the functional neuroprotection via repairing the damaged retinoic acid signal.