Emerging Roles for the RNA-Binding Protein HuD (ELAVL4) in Nervous System Diseases

HuD (ELAVL4) gain-of-function impairs neuromuscular junctions and induces apoptosis in in vitro and in vivo models of amyotrophic lateral sclerosis

Early defects at the neuromuscular junction (NMJ) are among the first hallmarks of the progressive neurodegenerative disease amyotrophic lateral sclerosis (ALS). According to the "dying back" hypothesis, disruption of the NMJ not only precedes, but is also a trigger for the subsequent degeneration of the motoneuron in both sporadic and familial ALS, including ALS caused by the severe FUS pathogenic variant P525L. However, the mechanisms linking genetic and environmental factors to NMJ defects remain elusive. By taking advantage of co-cultures of motoneurons and skeletal muscle derived from human induced pluripotent stem cells (iPSCs), we show that the neural RNA binding protein HuD (ELAVL4) may underlie NMJ defects and apoptosis in FUS-ALS. HuD overexpression in motoneurons phenocopies the severe FUSP525L mutation, while HuD knockdown in FUSP525L co-cultures produces phenotypic rescue. We validated these findings in vivo in a Drosophila FUS-ALS model. Neuronal-restricted overexpression of the HuD-related gene, elav, produces per se a motor phenotype, while neuronal-restricted elav knockdown significantly rescues motor dysfunction caused by FUS. Finally, we show that HuD levels increase upon oxidative stress in human motoneurons and in sporadic ALS patients with an oxidative stress signature. On these bases, we propose HuD as an important player downstream of FUS mutation in familial ALS, with potential implications for sporadic ALS related to oxidative stress.

Neurodegeneration: can metabolites from Eremurus persicus help?

The number of patients affected by neurodegenerative diseases is increasing worldwide, and no effective treatments have been developed yet. Although precision medicine could represent a powerful tool, it remains a challenge due to the high variability among patients. To identify molecules acting with innovative mechanisms of action, we performed a computational investigation using SAFAN technology, focusing specifically on HuD. This target belongs to the human embryonic lethal abnormal visual-like (ELAV) proteins and plays a key role in neuronal plasticity and differentiation. The results highlighted that the molecule able to bind the selected target was (R)-aloesaponol-III-8-methyl ether [(R)-ASME], a metabolite extracted from Eremurus persicus. Notably, this molecule is a TNF-α inhibitor, a cytokine involved in neuroinflammation. To obtain a suitable amount of (R)-ASME to confirm its activity on HuD, we optimized the extraction procedure. Together with ASME, another related metabolite, germichrysone, was isolated. Both ASME and germichrysone underwent biological investigation, but only ASME confirmed its ability to bind HuD. Given the multifactorial nature of neurodegenerative diseases, we decided to investigate ASME as a proteasome activator, being molecules endowed with this kind of activity potentially able to counteract aggregations of dysregulated proteins. ASME was able to activate the considered target both in enzymatic and cellular assays. Therefore, ASME may be considered a promising hit in the fight against neurodegenerative diseases.

Pathogenesis and immunopathology of paraneoplastic disorders

Paraneoplastic neurologic syndromes (PNS) represent a rare group of immune-mediated complications associated with an underlying tumor. Ectopic protein expression in neoplastic cells or an aberrant immune regulation in the course of hematooncologic diseases or thymomas trigger an autoimmune response that may affect any part of the central and/or peripheral nervous system. Recent advances in drug therapies as well as novel animal models and neuropathologic studies have led to further insights on the immune pathomechanisms of PNS. Although the syndromes share common paths in pathogenesis, they may differ in the disease course, prognosis, and therapy targets, depending on the localization and type of antibody epitope. Neuropathologic hallmarks of PNS associated with antibodies directed against intracellular epitopes are characterized by T cell-dominated inflammation, reactive gliosis including microglial nodules, and neuronal degeneration. By contrast, the neuropathology of cell surface antibody-mediated PNS strongly depends on the targeted antigen and varies from B cell/plasma cell-dominated inflammation and well-preserved neurons together with a reduced expression of the target antigen in anti-NMDAR encephalitis to irreversible Purkinje cell loss in anti-P/Q-type VGCC antibody-associated paraneoplastic cerebellar degeneration. The understanding of different pathomechanisms in PNS is important because they strongly correspond with therapy response and prognosis, and should guide treatment decisions.

The molecular genetics of nELAVL in brain development and disease

Embryonic development requires tight control of gene expression levels, activity, and localisation. This control is coordinated by multiple levels of regulation on DNA, RNA and protein. RNA-binding proteins (RBPs) are recognised as key regulators of post-transcriptional gene regulation, where their binding controls splicing, polyadenylation, nuclear export, mRNA stability, translation rate and decay. In brain development, the ELAVL family of RNA binding proteins undertake essential functions across spatiotemporal windows to help regulate and specify transcriptomic programmes for cell specialisation. Despite their recognised importance in neural tissues, their molecular roles and connections to pathology are less explored. Here we provide an overview of the neuronal ELAVL family, noting commonalities and differences amongst different species, their molecular characteristics, and roles in the cell. We bring together the available molecular genetics evidence to link different ELAVL proteins to phenotypes and disease, in both the brain and beyond, including ELAVL2, which is the least studied ELAVL family member. We find that ELAVL-related pathology shares a common neurological theme, but different ELAVL proteins are more strongly connected to different phenotypes, reflecting their specialised expression across time and space.

Short- and Long-Term Regulation of HuD: A Molecular Switch Mediated by Folic Acid?

The RNA-binding protein HuD has been shown to play a crucial role in gene regulation in the nervous system and is involved in various neurological and psychiatric diseases. In this study, through the creation of an interaction network on HuD and its potential targets, we identified a strong association between HuD and several diseases of the nervous system. Specifically, we focused on the relationship between HuD and the brain-derived neurotrophic factor (BDNF), whose protein is implicated in several neuronal diseases and is involved in the regulation of neuronal development, survival, and function. To better investigate this relationship and given that we previously demonstrated that folic acid (FA) is able to directly bind HuD itself, we performed in vitro experiments in neuron-like human SH-SY5Y cells in the presence of FA, also known to be a pivotal environmental factor influencing the nervous system development. Our findings show that FA exposure results in a significant increase in both HuD and BDNF transcripts and proteins after 2 and 4 h of treatment, respectively. Similar data were obtained after 2 h of FA incubation followed by 2 h of washout. This increase was no longer detected upon 24 h of FA exposure, probably due to a signaling shutdown mechanism. Indeed, we observed that following 24 h of FA exposure HuD is methylated. These findings indicate that FA regulates BDNF expression via HuD and suggest that FA can behave as an epigenetic modulator of HuD in the nervous system acting via short- and long-term mechanisms. Finally, the present results also highlight the potential of BDNF as a therapeutic target for specific neurological and psychiatric diseases.

RNA binding proteins in senescence: A potential common linker for age-related diseases?

Aging represents the major risk factor for the onset and/or progression of various disorders including neurodegenerative diseases, metabolic disorders, and bone-related defects. As the average age of the population is predicted to exponentially increase in the coming years, understanding the molecular mechanisms underlying the development of aging-related diseases and the discovery of new therapeutic approaches remain pivotal. Well-reported hallmarks of aging are cellular senescence, genome instability, autophagy impairment, mitochondria dysfunction, dysbiosis, telomere attrition, metabolic dysregulation, epigenetic alterations, low-grade chronic inflammation, stem cell exhaustion, altered cell-to-cell communication and impaired proteostasis. With few exceptions, however, many of the molecular players implicated within these processes as well as their role in disease development remain largely unknown. RNA binding proteins (RBPs) are known to regulate gene expression by dictating at post-transcriptional level the fate of nascent transcripts. Their activity ranges from directing primary mRNA maturation and trafficking to modulation of transcript stability and/or translation. Accumulating evidence has shown that RBPs are emerging as key regulators of aging and aging-related diseases, with the potential to become new diagnostic and therapeutic tools to prevent or delay aging processes. In this review, we summarize the role of RBPs in promoting cellular senescence and we highlight their dysregulation in the pathogenesis and progression of the main aging-related diseases, with the aim of encouraging further investigations that will help to better disclose this novel and captivating molecular scenario.

The Emerging Role of RNA in Diseases and Cancers

In recent years, there has been a growing interest in the role of RNA in diseases and cancers [...].

Evaluation of the concentration of growth associated protein-43 and glial cell-derived neurotrophic factor in degenerated intervertebral discs of the lumbosacral region of the spine

Important neurotrophic factors that are potentially involved in degenerative intervertebral disc (IVD) disease of the spine's lumbosacral (L/S) region include glial cell-derived neurotrophic factor (GDNF) and growth associated protein 43 (GAP-43). The aim of this study was to determine and compare the concentrations of GAP-43 and GDNF in degenerated and healthy IVDs and to quantify and compare the GAP-43-positive and GDNF-positive nerve fibers. The study group consisted of 113 Caucasian patients with symptomatic lumbosacral discopathy (confirmed by a specialist surgeon), an indication for surgical treatment. The control group included 81 people who underwent postmortem examination. GAP-43 and GDNF concentrations were significantly higher in IVD samples from the study group compared with the control group, and the highest concentrations were observed in the degenerated IVDs that were graded 4 on the Pfirrmann scale. In the case of GAP-43, it was found that as the degree of IVD degeneration increased, the number of GAP-43-positive nerve fibers decreased. In the case of GDNF, the greatest number of fibers per mm² of surface area was found in the IVD samples graded 3 on the Pfirrmann scale, and the number was found to be lower in samples graded 4 and 5. Hence, GAP-43 and GDNF are promising targets for analgesic treatment of degenerative IVD disease of the lumbosacral region of the spine.