Corruption and spread of pathogenic proteins in neurodegenerative diseases

Increased carbonylation, protein aggregation and apoptosis in the spinal cord of mice with experimental autoimmune encephalomyelitis

Previous work from our laboratory implicated protein carbonylation in the pathophysiology of both MS (multiple sclerosis) and its animal model EAE (experimental autoimmune encephalomyelitis). Subsequent in vitro studies revealed that the accumulation of protein carbonyls, triggered by glutathione deficiency or proteasome inhibition, leads to protein aggregation and neuronal cell death. These findings prompted us to investigate whether their association can be also established in vivo. In the present study, we characterized protein carbonylation, protein aggregation and apoptosis along the spinal cord during the course of MOG (myelin-oligodendrocyte glycoprotein)(35-55) peptide-induced EAE in C57BL/6 mice. The results show that protein carbonyls accumulate throughout the course of the disease, albeit by different mechanisms: increased oxidative stress in acute EAE and decreased proteasomal activity in chronic EAE. We also show a temporal correlation between protein carbonylation (but not oxidative stress) and apoptosis. Furthermore, carbonyl levels are significantly higher in apoptotic cells than in live cells. A high number of juxta-nuclear and cytoplasmic protein aggregates containing the majority of the oxidized proteins are present during the course of EAE. The LC3 (microtubule-associated protein light chain 3)-II/LC3-I ratio is significantly reduced in both acute and chronic EAE indicating reduced autophagy and explaining why aggresomes accumulate in this disorder. Taken together, the results of the present study suggest a link between protein oxidation and neuronal/glial cell death in vivo, and also demonstrate impaired proteostasis in this widely used murine model of MS.

Not only immunoglobulins, C-reactive protein too

The purpose of this letter is to expand a discussion, published recently in Molecular Immunology, on the post-secretion gain of function by immunoglobulins. It was reported that some circulating IgG molecules in all healthy individuals acquire novel antigen-binding specificity after exposure to conditions that change protein conformation, such as acidic pH. Another protein, C-reactive protein, also acquires novel ligand-binding specificity post-secretion after a switch from its native pentameric conformation to non-native pentameric conformation. Thus, that the functions of a protein depend upon its alternate structural states, and therefore on the surrounding milieu, is a more general phenomenon for some ancient molecules of the immune system than previously thought.

Amyloidosis: a clinical overview

Amyloidosis is the name for protein-folding diseases characterized by extracellular deposition of a specific soluble precursor protein that aggregates in the form of insoluble fibrils. The classification of amyloidosis is based on the chemical characterization of the precursor protein. Deposition of amyloid is localized or systemic. The 4 main types of systemic amyloidosis are AL, AA, ATTR, and Aβ2M type. A schematic approach is proposed for the clinical management of systemic amyloidosis. The importance of typing amyloid with confidence, the usefulness of imaging techniques, the principles of treatment, and the need for well-planned treatment monitoring during follow-up are discussed.

Protein aggregation and degradation mechanisms in neurodegenerative diseases

Neurodegenerative diseases are characterized by selective neuronal vulnerability and neurodegeneration in specific brain regions. The pathogenesis of these disorders centrally involves abnormal accumulation and aggregation of specific proteins, which are deposited in intracellular inclusions or extracellular aggregates that are characteristic for each disease. Increasing evidence suggests that genetic mutations or environmental factors can instigate protein misfolding and aggregation in these diseases. Consequently, neurodegenerative diseases are often considered as conformational diseases. This idea is further supported by studies implicating that impairment of the protein quality control (PQC) and clearance systems, such as the ubiquitin-proteasome system and autophagosome-lysosome pathway, may lead to the abnormal accumulation of disease-specific proteins. This suggests that similar pathological mechanisms may underlie the pathogenesis of the different neurodegenerative disorders. Interestingly, several proteins that are known to associate with neurodegenerative diseases have been identified as important regulators of PQC and clearance systems. In this review, we summarize the central features of abnormal protein accumulation in different common neurodegenerative diseases and discuss some aspects of specific disease-associated proteins regulating the PQC and clearance mechanisms, such as ubiquilin-1.