Endo-lysosomal proteins and ubiquitin CSF concentrations in Alzheimer's and Parkinson's disease.

BACKGROUND: Increasing evidence implicates dysfunctional proteostasis and the involvement of the autophagic and endo-lysosomal system and the ubiquitin-proteasome system in neurodegenerative diseases. In Alzheimer's disease (AD), there is an accumulation of autophagic vacuoles within the neurons. In Parkinson's disease (PD), susceptibility has been linked to genes encoding proteins involved in autophagy and lysosomal function, as well as mutations causing lysosomal disorders. Furthermore, both diseases are characterized by the accumulation of protein aggregates. METHODS: Proteins associated with endocytosis, lysosomal function, and the ubiquitin-proteasome system were identified in the cerebrospinal fluid (CSF) and targeted by combining solid-phase extraction and parallel reaction monitoring mass spectrometry. In total, 50 peptides from 18 proteins were quantified in three cross-sectional cohorts including AD (N = 61), PD (N = 21), prodromal AD (N = 10), stable mild cognitive impairment (N = 15), and controls (N = 68). RESULTS: A pilot study, including subjects selected based on their AD CSF core biomarker concentrations, showed increased concentrations of several targeted proteins in subjects with core biomarker levels indicating AD pathology compared to controls. Next, in a clinically characterized cohort, lower concentrations in CSF of proteins in PD were found compared to subjects with prodromal AD. Further investigation in an additional clinical study again revealed lower concentrations in CSF of proteins in PD compared to controls and AD. CONCLUSION: In summary, significantly different peptide CSF concentrations were identified from proteins AP2B1, C9, CTSB, CTSF, GM2A, LAMP1, LAMP2, TCN2, and ubiquitin. Proteins found to have altered concentrations in more than one study were AP2B1, CTSB, CTSF, GM2A, LAMP2, and ubiquitin. Interestingly, given the genetic implication of lysosomal function in PD, we did identify the CSF concentrations of CTSB, CTSF, GM2A, and LAMP2 to be altered. However, we also found differences in proteins associated with endocytosis (AP2B1) and the ubiquitin-proteasome system (ubiquitin). No difference in any peptide CSF concentration was found in clinically characterized subjects with AD compared to controls. In conclusion, CSF analyses of subjects with PD suggest a general lysosomal dysfunction, which resonates well with recent genetic findings, while such changes are minor or absent in AD.

Increased level of compleasomes in cerebrospinal fluid of patients with herpes simplex encephalitis.

Herpes simplex encephalitis (HSE) is a common cause of viral encephalitis (HSV-1) characterised by pronounced inflammation and elevated intracranial pressure. We have shown in a rat model that HSV-1 infection causes an interaction between complement factors and proteasomes, leading to formation of proteasome/complement complexes (compleasomes). Exposure of the proteasome regulatory subunit antisecretory factor 1 (AF1) leads to a decrease in intracranial pressure. The aim of this study was to evaluate the acute and prolonged formation of compleasomes in cerebrospinal fluid (CSF) from patients with HSE. Cerebrospinal fluid samples (n = 55) from 24 HSE patients were analysed for compleasome complexes. Samples from healthy controls (n = 23) and patient controls (n = 27) served as baseline information. Sandwich enzyme-linked immunosorbent assay (ELISA) for proteasomes and their complex formation with complement factor 3 or 4, and Western blot for C3 activation were performed on CSF samples. Increased compleasome formation, both presenting as an initial formation and showing exposure of subunit AF1 in the compleasomes, was found in CSF samples drawn from patients with HSE compared with samples from the control groups (p < 0.0005). The total protein CSF concentration was equal in all groups. The levels were higher in the acute phase compared with late in the disease course (p < 0.0005). Complement 3 breakdown product iC3b was detected in CSF samples of the HSE patients. The early increased formation of compleasomes in CSF suggests that this complex may be involved in host defence against HSE.

Reaction of complement factors and proteasomes in experimental encephalitis.

Herpes simplex virus type 1 (HSV-1) encephalitis causes a deleterious inflammation and elevated intracranial pressure. As a step towards examining the origin of the inflammation, we here report the response of circulating proteasomes and complement factors in blood and cerebrospinal fluid (CSF) in rats infected with HSV-1. Infection was via the nasal route, with 1.1 × 104 plaque-forming units of HSV-1 strain 2762 given in one or both nostrils. A sandwich enzyme-linked immunosorbent assay was used to study the level of 26S proteasomes and their complex formation with complement factors 3 and 4. HSV-1 infection in the rat causes a complex formation between complement factors and proteasomes, which we designate compleasomes. In the first experiment, with HSV-1 given in both nostrils, compleasomes containing complement factors 3 and 4 increased significantly in both blood plasma and CSF. The concentration of proteasomes in plasma was similar in controls and infected rats (320 ± 163 vs. 333 ± 125 ng/ml). In the second experiment, with HSV-1 given in one nostril, CSF levels were 1 ± 1 ng/ml in controls and 56 ± 22 ng/ml in the HSV-1 group, whereas the total protein concentration in CSF remained the same in the two groups. The compleasome response was limited to CSF, with a highly significant difference between infected rats and controls (n = 11, p < 0.001). It was possible to mimic the reaction between proteasomes and complements 3 and 4 in vitro in the presence of ATP.

[Proteasomes and their role in the extracellular space].

The presented review concerns the intracellular proteasome and their possible functions. The ubiquitin-proteasome system (UPS) is responsible for the common regulated proteolysis in the cell. 26S proteasome is a central proteolytic unit of UPS and is a multisubunit protein complex consisting of a core catalytic complex, called 20S proteasome, capped at one or both ends by 19S regulatory complex. Proteasomes have been shown in the extracellular space: in alveolar and cerebrospinal fluids, blood plasma. Extracellular proteasomes are intact intracellular particles that exhibit three types of specific peptidase activity. Extracellular proteasomes have been detected in both healthy people and patients with different diseases. Its concentration has been found to be increased in patients suffering from autoimmune diseases, malignant tumors, trauma or sepsis and to correlate with the disease progression, which has both diagnostic and prognostic value.

Circulating extracellular proteasome in the cerebrospinal fluid: a study on concentration and proteolytic activity.

Alterations of the intracellular ubiquitin-proteasome pathway are found in neurodegenerative and inflammatory disorders of the central nervous system, as well as in its malignancies. Inhibitory substrates of the proteasomes represent promising approaches to control autoimmune inflammations and induction of apoptosis in cancer cells. Extracellular circulating proteasomes are positively correlated to outcome prognosis in hematogenic neoplasias and the outcome in critically ill patients. Previously, we reported raised levels of proteolytic active 20S proteasomes in the extracellular alveolar space in patients with acute respiratory distress syndrome (ARDS). For the cerebrospinal fluid, we assumed that extracellular circulating proteasomes with enzymatic activity can be found, too. Cerebrospinal fluid (CSF) samples of twenty-six patients (14 females, 12 males), who underwent diagnostic spinal myelography, were analyzed for leukocyte cell count, total protein content, lactate and interleukine-6 (Il-6) concentrations. CSF samples were analyzed for concentration and enzymatic activity of extracellular 20S proteasomes (fluorescenic substrate cleavage; femtokatal). Blood samples were analyzed with respect to concentration of extracellular circulating proteasomes. Choroidal plexus was harvested at autopsies and examined with immunoelectron microscopy (EM) for identification of possible transportation mechanisms. Statistical analysis was performed using SPSS (18.0.3). In all patients, extracellular proteasome was found in the CSF. The mean concentration was 24.6 ng/ml. Enzymatic activity of the 20S subunits of proteasomes was positively identified by the fluorescenic subtrate cleavage at a mean of 8.5 fkat/ml. Concentrations of extracellular proteasomes in the CSF, total protein content and Il-6 were uncorrelated. Immunoelectron microscopy revealed merging vesicles of proteasomes with the outer cell membrane suggestive of an exozytic transport mechanism. For the first time, extracellular circulating 20S proteasome in the CSF of healthy individuals is identified and its enzymatic activity detected. A possible exozytic vesicle-bond transportation mechanism is suggested by immunoelectron microscopy. The present study raises more questions on the function of extracellular proteasome in the CSF and encourages further studies on the role of extracellular protesomes in pathological conditions of the central nervous system (tumor lesions and inflammatory processes).