Different Aberrant Changes of mGluR5 and Its Downstream Signaling Pathways in the Scrapie-Infected Cell Line and the Brains of Scrapie-Infected Experimental Rodents

Post-translational modifications in prion diseases

More than 650 reversible and irreversible post-translational modifications (PTMs) of proteins have been listed so far. Canonical PTMs of proteins consist of the covalent addition of functional or chemical groups on target backbone amino-acids or the cleavage of the protein itself, giving rise to modified proteins with specific properties in terms of stability, solubility, cell distribution, activity, or interactions with other biomolecules. PTMs of protein contribute to cell homeostatic processes, enabling basal cell functions, allowing the cell to respond and adapt to variations of its environment, and globally maintaining the constancy of the milieu interieur (the body's inner environment) to sustain human health. Abnormal protein PTMs are, however, associated with several disease states, such as cancers, metabolic disorders, or neurodegenerative diseases. Abnormal PTMs alter the functional properties of the protein or even cause a loss of protein function. One example of dramatic PTMs concerns the cellular prion protein (PrPC), a GPI-anchored signaling molecule at the plasma membrane, whose irreversible post-translational conformational conversion (PTCC) into pathogenic prions (PrPSc) provokes neurodegeneration. PrPC PTCC into PrPSc is an additional type of PTM that affects the tridimensional structure and physiological function of PrPC and generates a protein conformer with neurotoxic properties. PrPC PTCC into PrPSc in neurons is the first step of a deleterious sequence of events at the root of a group of neurodegenerative disorders affecting both humans (Creutzfeldt-Jakob diseases for the most representative diseases) and animals (scrapie in sheep, bovine spongiform encephalopathy in cow, and chronic wasting disease in elk and deer). There are currently no therapies to block PrPC PTCC into PrPSc and stop neurodegeneration in prion diseases. Here, we review known PrPC PTMs that influence PrPC conversion into PrPSc. We summarized how PrPC PTCC into PrPSc impacts the PrPC interactome at the plasma membrane and the downstream intracellular controlled protein effectors, whose abnormal activation or trafficking caused by altered PTMs promotes neurodegeneration. We discussed these effectors as candidate drug targets for prion diseases and possibly other neurodegenerative diseases.

Different reactive profiles of calmodulin in the CSF samples of Chinese patients of four types of genetic prion diseases

Background and purpose

Calmodulin (CaM) levels exhibit significant elevation in the brain tissue of rodent and cell line models infected with prion, as well as in the cerebrospinal fluid (CSF) samples from patients diagnosed with sporadic Creutzfeldt-Jakob disease (sCJD). However, the status of CSF CaM in patients with genetic prion diseases (gPrDs) remains unclear. This study aims to assess the characteristics of CSF CaM in Chinese patients presenting four subtypes of gPrDs.

Methods

A total of 103 CSF samples from patients diagnosed with T188K-gCJD, E200K-gCJD, D178N-FFI, P102L-GSS were included in this study, along with 40 CSF samples from patients with non-prion diseases (non-PrDs). The presence of CSF CaM and 14-3-3 proteins was assessed using Western blots analysis, while levels of CSF 14-3-3 and total tau were measured using enzyme-linked immunosorbent assays (ELISAs). Statistical methods including multivariate logistic regression were employed to evaluate the association between CSF CaM positivity and relevant clinical, laboratory, and genetic factors.

Results

The positive rates of CSF CaM were significantly higher in cases of T188K-gCJD (77.1%), E200K-gCJD (86.0%), and P102-GSS (90.9%) compared to non-PrD cases (22.5%). In contrast, CSF CaM positivity was slightly elevated in D178N-FFI (34.3%). CSF CaM positivity was remarkably high in patients who tested positive for CSF 14-3-3 by Western blot and exhibited high levels of total tau (≥1400 pg/ml) as measures by ELISA. Multivariate logistic regression analysis confirmed a significant association between CSF CaM positivity and specific mutations in PRNP, as well as with CSF 14-3-3 positivity. Furthermore, the diagnostic performance of CaM surpassed that of 14-3-3 and tau when analyzing CSF samples from T188K-gCJD and E200K-gCJD patients.

Conclusion

Western blot analysis reveals significant variations in the positivity of CSF CaM among the four genotypes of gPrD cases, demonstrating a positive correlation with 14-3-3 positivity and elevated tau levels in CSF.

Metabotropic glutamate receptors (mGluRs) in epileptogenesis: an update on abnormal mGluRs signaling and its therapeutic implications

Epilepsy is a neurological disorder characterized by high morbidity, high recurrence, and drug resistance. Enhanced signaling through the excitatory neurotransmitter glutamate is intricately associated with epilepsy. Metabotropic glutamate receptors (mGluRs) are G protein-coupled receptors activated by glutamate and are key regulators of neuronal and synaptic plasticity. Dysregulated mGluR signaling has been associated with various neurological disorders, and numerous studies have shown a close relationship between mGluRs expression/activity and the development of epilepsy. In this review, we first introduce the three groups of mGluRs and their associated signaling pathways. Then, we detail how these receptors influence epilepsy by describing the signaling cascades triggered by their activation and their neuroprotective or detrimental roles in epileptogenesis. In addition, strategies for pharmacological manipulation of these receptors during the treatment of epilepsy in experimental studies is also summarized. We hope that this review will provide a foundation for future studies on the development of mGluR-targeted antiepileptic drugs.

Abnormal Changes of IL3/IL3R and Its Downstream Signaling Pathways in the Prion-Infected Cell Line and in the Brains of Scrapie-Infected Rodents

Interleukin 3 (IL-3) plays an important role in hematopoiesis and immune regulation, brain IL-3/IL-3R signaling has been shown to involve in the physiological and pathological processes of a variety of neurodegenerative diseases, but its role in prion diseases is rarely described. Here, the changes of IL-3/IL-3R and its downstream signaling pathways in a scrapie-infected cell line and in the brains of several scrapie-infected rodent models were evaluated by various methods. Markedly decreased IL-3Rα were observed in the brains of scrapie-infected rodents at terminal stage and in the prion-infected cell model, which showed increased in the brain samples collected at early and middle stage of infection. The IL-3 levels were almost unchanged in the brains of scrapie-infected mice and in the prion-infected cell line. Morphological assays identified close co-localization of the increased IL-3Rα signals with NeuN- and Iba1-positive cells, whereas co-localization of IL-3 signals with NeuN- and GFAP-positive cells in the scrapie-infected brain tissues. Some downstream components of IL-3/IL-3R pathways, including JAK2-STAT5 and PI3K/AKT/mTOR pathways, were downregulated in the brains of scrapie-infected rodents at terminal stage and in the prion-infected cells. Stimulation of recombinant IL-3 on the cultured cells showed prion that the prion-infected cells displayed markedly more reluctant responses of JAK2-STAT5 and PI3K/AKT/mTOR pathways than the normal partner cells. These data suggest that although prion infection or PrPSc accumulation in brain tissues does not affect IL-3 expression, it significantly downregulates IL-3R levels, thereby inhibiting the downstream pathways of IL-3/IL-3R and blocking the neuroregulatory and neuroprotective activities of IL-3.