Phosphorylation of the common neurotrophin receptor p75 by p38beta2 kinase affects NF-kappaB and AP-1 activities

A bibliometric analysis of rheumatology: knowledge structure and research trends of RNA-Binding proteins in rheumatic diseases

BACKGROUND

Rheumatic disease is a kind of disease dominated by inflammatory lesions of connective tissue and abnormal immune function. It mostly belongs to autoimmune diseases or connective tissue diseases affecting multiple organs. Meanwhile, understanding the role of RNA-binding proteins (RBPs) in pathogenesis is rapidly developing. This study aims at summarizing the hotspots in rheumatology studies related to RBPs.

METHODS

Scientific papers on RBPs related to rheumatology between 1982 and 2022 were gathered from the Web of Science database. The data analysis and visualization were obtained using the Bibliometrix package. Bibliometrix package was used to analyze bibliometric indicators and visualize the trends and hotspots of the research.

RESULTS

A total of 964 articles met the requirement. From 1982 to 2022, the USA and Anhui Medical University were the most productive country and institution, respectively, in this field. Arthritis and Rheumatism, Annals of the Rheumatic Diseases and Arthritis & Rheumatology were the top three periodicals obtained by Bradford's law. Co-word analysis divided the keywords into three clusters, focusing on diagnosis and classification of Systemic Lupus Erythematosus, pathogenesis of osteoarthritis and pathogenesis of Rheumatoid Arthritis, respectively. Trend topic analysis revealed that pathogenesis and classification of rheumatic diseases might be the research trend.

CONCLUSION

Focusing on RBPs in rheumatic diseases, we illustrated the evolution of this field and predicted future research hotspots. The research trend topics have evolved towards clinical classification and pathogenesis at the molecular and genetic level. The pathogenic mechanism in rheumatic diseases will continue to be a hotspot in the future. Besides, the classification of Systemic Lupus Erythematosus patients may be another hotspot. Researchers are recommended to pay more attention to hotspots demonstrated in the future. Key Points • Bibliometrix package was used to analyze bibliometric indicators and visualize the trends and hotspots of the research. • Focusing on RBPs in rheumatic diseases, we illustrated the evolution of this field and predicted future research hotspots. • The research trend topics have evolved towards clinical classification and the pathogenesis at the molecular and genetic level. • The pathogenic mechanism in rheumatic diseases will continue to be a hotspot in the future.

Equilibrium between monomers and dimers of the death domain of the p75 neurotrophin receptor in solution

p75 neurotrophin receptor (p75NTR) contains a C-terminal globular protein module known as the death domain (DD), which plays a central role in apoptotic and inflammatory signaling through the formation of oligomeric protein complexes. A monomeric state of the p75NTR-DD also exists depending on its chemical environment in vitro. However, studies on the oligomeric states of the p75NTR-DD have produced conflicting findings and sparked great controversy. Here we present new evidence from biophysical and biochemical studies to demonstrate the coexistence of symmetric and asymmetric dimers of the p75NTR-DD, which may equilibrate with the monomeric form in solution and in the absence of any other protein. The reversible close-open solution behavior may be important for the p75NTR-DD to serve as an intracellular signaling hub. This result supports an intrinsic ability of the p75NTR-DD to self-associate, in congruence with the oligomerization properties of all members of the DD superfamily.

Age-related changes in hippocampal-dependent synaptic plasticity and memory mediated by p75 neurotrophin receptor

The plasticity mechanisms in the nervous system that are important for learning and memory are greatly impacted during aging. Notably, hippocampal-dependent long-term plasticity and its associative plasticity, such as synaptic tagging and capture (STC), show considerable age-related decline. The p75 neurotrophin receptor (p75NTR ) is a negative regulator of structural and functional plasticity in the brain and thus represents a potential candidate to mediate age-related alterations. However, the mechanisms by which p75NTR affects synaptic plasticity of aged neuronal networks and ultimately contribute to deficits in cognitive function have not been well characterized. Here, we report that mutant mice lacking the p75NTR were resistant to age-associated changes in long-term plasticity, associative plasticity, and associative memory. Our study shows that p75NTR is responsible for age-dependent disruption of hippocampal homeostatic plasticity by modulating several signaling pathways, including BDNF, MAPK, Arc, and RhoA-ROCK2-LIMK1-cofilin. p75NTR may thus represent an important therapeutic target for limiting the age-related memory and cognitive function deficits.

Death domain of p75 neurotrophin receptor: a structural perspective on an intracellular signalling hub

The death domain (DD) is a globular protein motif with a signature feature of an all-helical Greek-key motif. It is a primary mediator of a variety of biological activities, including apoptosis, cell survival and cytoskeletal changes, which are related to many neurodegenerative diseases, neurotrauma, and cancers. DDs exist in a wide range of signalling proteins including p75 neurotrophin receptor (p75^NTR ), a member of the tumour necrosis factor receptor superfamily. The specific signalling mediated by p75^NTR in a given cell depends on the type of ligand engaging the extracellular domain and the recruitment of cytosolic interactors to the intracellular domain, especially the DD, of the receptor. In solution, the p75^NTR -DDs mainly form a symmetric non-covalent homodimer. In response to extracellular signals, conformational changes in the p75^NTR extracellular domain (ECD) propagate to the p75^NTR -DD through the disulfide-bonded transmembrane domain (TMD) and destabilize the p75^NTR -DD homodimer, leading to protomer separation and exposure of binding sites on the DD surface. In this review, we focus on recent advances in the study of the structural mechanism of p75^NTR -DD signalling through recruitment of diverse intracellular interactors for the regulation and control of diverse functional outputs.

The effect of P2X7 receptor activation on nuclear factor-κB phosphorylation induced by status epilepticus in the rat hippocampus

Nuclear factor-kappa B (NFκB) signal is essential for neuronal survival and its activation may protect neuron against various stimuli. Since purinergic signals activate NFκB through the P2X7 receptor, we investigated the distinct pattern of NF-κB phosphorylation in neurons by P2X7 receptor activation following status epilepticus (SE) in an effort to understand the role of P2X7 receptor in epileptogenic insult. In non-SE animals, 2'(3')-O-(4-benzoyl)benzoyl adenosine 5'-triphosphate (BzATP, a P2X7R agonist) treatment increased only p52-Ser869 NF-κB phosphorylation in neuron. Following SE, p52-Ser865, p52-Ser869, p65-Ser276, p65-Ser311, p65-Ser468, and p65-Ser529 NF-κB phosphorylation was significantly decreased in CA1 and CA3 neurons. However, BzATP treatment prevented reductions in p65-Ser276, p65-Ser311, p65-Ser529, and p52-Ser869 NF-κB phosphorylations in CA1 and/or CA3 neurons induced by SE. Furthermore, BzATP treatment reduced SE-induced p65-Ser311, p65-Ser468, p65-Ser536, and p52-Ser869 NF-κB phosphorylations in astrocytes. These findings indicate that P2X7 functions may be involved in the regulation of SE-induced reactive astrocytes and neuronal degeneration via NF-κB phosphorylations in response to pilocarpine-induced SE in the rat hippocampus.

Prediction of functional phosphorylation sites by incorporating evolutionary information

Protein phosphorylation is a ubiquitous protein post-translational modification, which plays an important role in cellular signaling systems underlying various physiological and pathological processes. Current in silico methods mainly focused on the prediction of phosphorylation sites, but rare methods considered whether a phosphorylation site is functional or not. Since functional phosphorylation sites are more valuable for further experimental research and a proportion of phosphorylation sites have no direct functional effects, the prediction of functional phosphorylation sites is quite necessary for this research area. Previous studies have shown that functional phosphorylation sites are more conserved than non-functional phosphorylation sites in evolution. Thus, in our method, we developed a web server by integrating existing phosphorylation site prediction methods, as well as both absolute and relative evolutionary conservation scores to predict the most likely functional phosphorylation sites. Using our method, we predicted the most likely functional sites of the human, rat and mouse proteomes and built a database for the predicted sites. By the analysis of overall prediction results, we demonstrated that protein phosphorylation plays an important role in all the enriched KEGG pathways. By the analysis of protein-specific prediction results, we demonstrated the usefulness of our method for individual protein studies. Our method would help to characterize the most likely functional phosphorylation sites for further studies in this research area.

Role of tyrosine phosphorylation in the antioxidant effects of the p75 neurotrophin receptor

The p75 neurotrophin receptor (p75NTR) is an α-and γ-secretase substrate expressed preferentially in the cholinergic neurons of the nucleus basalis of Meynert, the hippocampus, and the cerebellum of the adult brain. Mutations of the γ-secretase, presenilin, have been implicated in familial Alzheimer's disease. Furthermore, oxidative and inflammatory injury to the cholinergic neurons of the nucleus basalis of Meynert and hippocampus plays a critical role in the pathology of Alzheimer's disease. The intracellular domain of p75NTR (p75ICD) is the α- and γ-secretase cleavage fragment of the holoreceptor that functions as an antioxidant in PC12 rat pheochromocytoma cells. Phosphorylation of the receptor is thought to be necessary for many of its functions, and two tyrosines in p75ICD have been among the functionally important phosphorylation sites. Site-directed mutagenesis was used to generate three p75ICD mutants that cannot be phosphorylated at either or both tyrosines, respectively. Each of these mutants was expressed in p75NTR-deficient PC12 cells to determine the effects of blocking phosphorylation at specific sites on the antioxidant activity of p75ICD. Interfering with phosphorylation at tyrosine-337 impairs antioxidant function, while interfering with phosphorylation at tyrosine-366 does not, and may in fact impart protection from oxidant stress. Neither MAPK (i.e., p38, ERK1, ERK2) content nor NF-κB activation accounts for the differential sensitivity to oxidant stress among the differentially phosphorylated p75NTR cell lines. However, differences in the time course of ERK1,2 phosphorylation among the lines account in large measure for their differential oxidant sensitivity. The phosphorylation state of specific sites on p75ICD may modulate the resistance of neurons in Alzheimer's disease-relevant brain regions to oxidant stress.

Neurotrophins in healthy and diseased skin

Neurotrophins (NT) belong to a family of structurally and functionally related proteins that, depending on the tissue context and the receptors involved, promote either neuronal cell survival and differentiation or cell death. NT, and in particular NGF, were first identified as neurotrophic factors supporting the synthesis and development of sensory neurons in the central and peripheral nervous system. It is now widely accepted that NT also act as growth factors in non-neuronal cells, including the skin. In the skin, most cell types are able to secrete and/or to respond to stimulation by NT, creating a unique network of molecular signaling in the cutaneous microenvironment. Moreover, many skin diseases have been associated with an involvement of a number of neural factors including NT, but less attention has been given to the role of NT as growth factors in the development of skin pathologies. This review summarizes currently data on the expression and function of NT and their receptors in several cell types in the skin. Moreover it focuses on the role of the skin NT network in two cutaneous conditions, melanoma and psoriasis where NT are clearly involved.

p75NTR-mediated signaling promotes the survival of myoblasts and influences muscle strength

During muscle development, the p75(NTR) is expressed transiently on myoblasts. The temporal expression pattern of the receptor raises the possibility that the receptor is influencing muscle development. To test this hypothesis, p75(NTR)-deficient mutant mice were tested for muscle strength by using a standard wire gripe strength test and were found to have significantly decreased strength relative to that of normal mice. When normal mybolasts were examined in vivo for expression of NGF receptors, p75(NTR) was detected on myoblasts but the high affinity NGF receptor, trk A, was not co-expressed with p75(NTR). In vitro, proliferating C2C12 and primary myoblasts co-expressed the p75(NTR) and MyoD, but immunofluorescent analysis of primary myoblasts and RT-PCR analysis of C2C12 mRNA revealed that myoblasts were devoid of trk A. In contrast to the cell death functions that characterize the p75(NTR) in neurons, p75(NTR)-positive primary and C2C12 myoblasts did not differentiate or undergo apoptosis in response to neurotrophins. Rather, myoblasts survived and even proliferated when grown at subconfluent densities in the presence of the neurotrophins. Furthermore, when myoblasts treated with NGF were lysed and immunoprecipitated with antibodies against phosphorylated I-kappaB and AKT, the cells contained increased levels of both phospho-proteins, both of which promote cell survival. By contrast, neurotrophin-treated myoblasts did not induce phosphorylation of Map Kinase p42/44 or p38, indicating the survival was not mediated by the trk A receptor. Taken together, the data indicate that the p75(NTR) mediates survival of myoblasts prior to differentiation and that the activity of this receptor during myogenesis is important for developing muscle.

Ten years on: mediation of cell death by the common neurotrophin receptor p75(NTR)

The common neurotrophin receptor p75(NTR) remains one of the most enigmatic of the tumor necrosis factor receptor (TNFR) superfamily: on the one hand, it displays a death domain and has been shown to be capable of mediating programmed cell death (PCD) upon ligand binding; on the other hand, its death domain is of type II (unlike that of Fas or TNFR I), and it has also been shown to be capable of mediating cell death in response to the withdrawal of ligand. Thus, p75(NTR) may function as a death receptor-similar to Fas or TNFR I-or a dependence receptor-similar to deleted in colorectal cancer (DCC) or uncoordinated gene-5 homologues 1-3 (UNC5H1-3). Here, we review the data relating to the mediation of PCD by p75(NTR), and suggest that one reasonable model for the apparently paradoxical effects of p75(NTR) is that this receptor functions as a "quality control" in that it is capable of mediating PCD in at least four situations: (1). withdrawal of neurotrophins; (2). exposure to mismatched neurotrophins; (3). exposure to unprocessed neurotrophins; and (4). exposure of inappropriately immature cells to neurotrophins. Results to date suggest that these functions are mediated through different underlying mechanisms, and that their respective signaling pathways are cell type and co-receptor dependent.

PKA phosphorylates the p75 receptor and regulates its localization to lipid rafts

Although a large number of studies have been carried out on the diverse effects mediated by the common neurotrophin receptor p75(NTR), little is known about the molecular mechanisms by which p75(NTR) initiates intracellular signal transduction. We identified a variant of the beta catalytic subunit of cAMP-dependent protein kinase (PKACbeta) as a p75(NTR)-interacting protein, which phosphorylates p75(NTR) at Ser304. Intracellular cAMP in cerebellar neurons was accumulated transiently by ligand binding to p75(NTR). Activation of cAMP-PKA is required for translocation of p75(NTR) to lipid rafts, and for biochemical and biological activities of p75(NTR), such as inactivation of Rho and the neurite outgrowth. Proper recruitment of activated p75(NTR) to lipid rafts, structures that represent specialized signaling organelles, is of fundamental importance in determining p75(NTR) bioactivity.

The neurotrophin receptor p75(NTR): novel functions and implications for diseases of the nervous system

Neurotrophins have long been known to promote the survival and differentiation of vertebrate neurons. However, these growth factors can also induce cell death through the p75 neurotrophin receptor (p75(NTR)), a member of the tumor necrosis factor receptor superfamily. Consistent with a function in controlling the survival and process formation of neurons, p75(NTR) is mainly expressed during early neuronal development. In the adult, p75(NTR) is re-expressed in various pathological conditions, including epilepsy, axotomy and neurodegeneration. Potentially toxic peptides, including the amyloid beta- (Abeta-) peptide that accumulates in Alzheimer's disease, are ligands for p75(NTR). Recent work also implicates p75(NTR) in the regulation of both synaptic transmission and axonal elongation. It associates with the Nogo receptor, a binding protein for axonal growth inhibitors, and appears to be the transducing subunit of this receptor complex.