Affinity purification and characterization of protein gene product 9.5 (PGP9.5) from retina

Blood Markers in Relation to a History of Traumatic Brain Injury Across Stages of Cognitive Impairment in a Diverse Cohort

BACKGROUND

Traumatic brain injury (TBI) has been linked to multiple pathophysiological processes that could increase risk for Alzheimer's disease and related dementias (ADRD). However, the impact of prior TBI on blood biomarkers for ADRD remains unknown.

OBJECTIVE

Using cross-sectional data, we assessed whether a history of TBI influences serum biomarkers in a diverse cohort (approximately 50% Hispanic) with normal cognition, mild cognitive impairment, or dementia.

METHODS

Levels of glial fibrillary acidic protein (GFAP), neurofilament light (NFL), total tau (T-tau), and ubiquitin carboxy-terminal hydrolase-L1 (UCHL1) were measured for participants across the cognitive spectrum. Participants were categorized based on presence and absence of a history of TBI with loss of consciousness, and study samples were derived through case-control matching. Multivariable general linear models compared concentrations of biomarkers in relation to a history of TBI and smoothing splines modelled biomarkers non-linearly in the cognitively impaired groups as a function of time since symptom onset.

RESULTS

Each biomarker was higher across stages of cognitive impairment, characterized by clinical diagnosis and Mini-Mental State Examination performance, but these associations were not influenced by a history of TBI. However, modelling biomarkers in relation to duration of cognitive symptoms for ADRD showed differences by history of TBI, with only GFAP and UCHL1 being elevated.

CONCLUSIONS

Serum GFAP, NFL, T-tau, and UCHL1 were higher across stages of cognitive impairment in this diverse clinical cohort, regardless of TBI history, though longitudinal investigation of the timing, order, and trajectory of the biomarkers in relation to prior TBI is warranted.

Thorough overview of ubiquitin C-terminal hydrolase-L1 and glial fibrillary acidic protein as tandem biomarkers recently cleared by US Food and Drug Administration for the evaluation of intracranial injuries among patients with traumatic brain injury

Traumatic brain injury (TBI) is a major cause of mortality and morbidity affecting all ages. It remains to be a diagnostic and therapeutic challenge, in which, to date, there is no Food and Drug Administration‐approved drug for treating patients suffering from TBI. The heterogeneity of the disease and the associated complex pathophysiology make it difficult to assess the level of the trauma and to predict the clinical outcome. Current injury severity assessment relies primarily on the Glasgow Coma Scale score or through neuroimaging, including magnetic resonance imaging and computed tomography scans. Nevertheless, such approaches have certain limitations when it comes to accuracy and cost efficiency, as well as exposing patients to unnecessary radiation. Consequently, extensive research work has been carried out to improve the diagnostic accuracy of TBI, especially in mild injuries, because they are often difficult to diagnose. The need for accurate and objective diagnostic measures led to the discovery of biomarkers significantly associated with TBI. Among the most well‐characterized biomarkers are ubiquitin C‐terminal hydrolase‐L1 and glial fibrillary acidic protein. The current review presents an overview regarding the structure and function of these distinctive protein biomarkers, along with their clinical significance that led to their approval by the US Food and Drug Administration to evaluate mild TBI in patients.

Interplay of proliferation and differentiation factors is revealed in the early human eye development

BACKGROUND

Eye development is a consequence of numerous epithelial-to-mesenchymal interactions between the prospective lens ectoderm, outpocketings of the forebrain forming optic vesicles, and surrounding mesenchyme. How different cell types forming eye structures differentiate from their precursors, and which factors coordinate complex human eye development remains largely unknown. Proper differentiation of photoreceptors is of special interest because of their involvement in the appearance of degenerative retinal diseases.

METHODS

Here we analyze the spatiotemporal expression of neuronal markers nestin, protein gene product 9.5 (PGP9.5), and calcium binding protein (S100), proliferation marker (Ki-67), markers for cilia (alpha-tubulin), and cell stemness marker octamer-binding transcription factor 4 (Oct-4) in histological sections of 5-12 -week human eyes using immunohistochemical and immunofluorescence methods.

RESULTS

While during the investigated developmental period nestin shows strong expression in all mesenchymal derivatives, lens, optic stalk and inner neuroblastic layer, PGP9.5 and S100 expression characterizes only neural derivatives (optic nerve and neural retina). PGP9.5 is co-localized with nestin and S100 in the differentiating cells of the inner neuroblastic layer. Initially strong proliferation in all parts of the developing eye gradually ceases, especially in the outer neuroblastic layer. Proliferating Ki-67 positive cells co-localize with nestin in the retina, lens, and choroid. Strong Oct-4 and alpha-tubulin immunoreactivity in the retina and optic nerve gradually decreases, while they co-localize in outer neuroblastic and nerve fiber layers.

CONCLUSIONS

The described expression of investigated markers indicates their importance in eye growth and morphogenesis, while their spatially and temporally restricted pattern coincides with differentiation of initially immature cells into specific retinal cell lineages. Alterations in their spatiotemporal interplay might lead to disturbances of visual function.

Winter hibernation and UCHL1-p34cdc2 association in toad oocyte maturation competence

Currently, it is believed that toad oocyte maturation is dependent on the physiological conditions of winter hibernation. Previous antibody-blocking experiments have demonstrated that toad ubiquitin carboxyl-terminal hydrolase L1 (tUCHL1) is necessary for germinal vesicle breakdown during toad oocyte maturation. In this paper, we first supply evidence that tUCHL1 is highly evolutionarily conserved. Then, we exclude protein availability and ubiquitin carboxyl-terminal hydrolase enzyme activity as factors in the response of oocytes to winter hibernation. In the context of MPF (maturation promoting factor) controlling oocyte maturation and to further understand the role of UCHL1 in oocyte maturation, we performed adsorption and co-immunoprecipitation experiments using toad oocyte protein extracts and determined that tUCHL1 is associated with MPF in toad oocytes. Recombinant tUCHL1 absorbed p34(cdc2), a component of MPF, in obviously larger quantities from mature oocytes than from immature oocytes, and p13(suc1) was isolated from tUCHL1 with a dependence on the ATP regeneration system, suggesting that still other functions may be involved in their association that require phosphorylation. In oocytes from hibernation-interrupted toads, the p34(cdc2) protein level was significantly lower than in oocytes from toads in artificial hibernation, providing an explanation for the different quantities isolated by recombinant tUCHL1 pull-down and, more importantly, identifying a mechanism involved in the toad oocyte's dependence on a low environmental temperature during winter hibernation. Therefore, in toads, tUCHL1 binds p34(cdc2) and plays a role in oocyte maturation. However, neither tUCHL1 nor cyclin B1 respond to low temperatures to facilitate oocyte maturation competence during winter hibernation.

Histology of symptomatic gastroesophageal reflux disease: is it predictive of response to proton pump inhibitors?

BACKGROUND AND AIM

To examine the differences in esophageal histopathology between non-erosive reflux disease (NERD) and reflux esophagitis (RE), and to investigate whether baseline esophageal histopathology can predict the therapeutic response to proton pump inhibitors (PPIs).

METHOD

The subjects comprised 94 patients with NERD (n = 71) or mild RE (n = 23). Tissue was biopsied from 5 cm above the squamo-columnar junction (SCJ), and the degree or presence of nine histopathological markers was assessed. The patients were treated with rabeprazole (RPZ) 10 mg once daily for 4 weeks. If complete heartburn relief was not achieved, RPZ was increased to 10 mg twice daily for another 2 weeks, and then to 20 mg twice daily for another 2 weeks if heartburn remained.

RESULTS

Features of esophageal histopathology 5 cm above the SCJ differed between NERD and RE patients. The esophageal histopathology in patients unresponsive to RPZ was characterized by Protein Gene Product (PGP) 9.5 negativity in those with NERD, and intraepithelial bleeding in those with RE. In addition, the combination of dilated intercellular spaces (DIS) (+)/PGP 9.5 (-) was indicative of strong resistance to PPI therapy in NERD patients.

CONCLUSION

The therapeutic efficacy of PPI can be predicted from the features of biopsied esophageal tissue. Factors predictive of resistance to treatment with PPI are negativity for PGP 9.5 in NERD patients and intraepithelial bleeding in RE patients.

The ubiquitin-proteasome system in retinal health and disease

The ubiquitin-proteasome system (UPS) is the main intracellular pathway for modulated protein turnover, playing an important role in the maintenance of cellular homeostasis. It also exerts a protein quality control through degradation of oxidized, mutant, denatured, or misfolded proteins and is involved in many biological processes where protein level regulation is necessary. This system allows the cell to modulate its protein expression pattern in response to changing physiological conditions and provides a critical protective role in health and disease. Impairments of UPS function in the central nervous system (CNS) underlie an increasing number of genetic and idiopathic diseases, many of which affect the retina. Current knowledge on the UPS composition and function in this tissue, however, is scarce and dispersed. This review focuses on UPS elements reported in the retina, including ubiquitinating and deubiquitinating enzymes (DUBs), and alternative proteasome assemblies. Known and inferred roles of protein ubiquitination, and of the related, SUMO conjugation (SUMOylation) process, in normal retinal development and adult homeostasis are addressed, including modulation of the visual cycle and response to retinal stress and injury. Additionally, the relationship between UPS dysfunction and human neurodegenerative disorders affecting the retina, including Alzheimer's, Parkinson's, and Huntington's diseases, are dealt with, together with numerous instances of retina-specific illnesses with UPS involvement, such as retinitis pigmentosa, macular degenerations, glaucoma, diabetic retinopathy (DR), and aging-related impairments. This information, though still basic and limited, constitutes a suitable framework to be expanded in incoming years and should prove orientative toward future therapy design targeting sight-affecting diseases with a UPS underlying basis.

Roles for the ubiquitin-proteasome pathway in protein quality control and signaling in the retina: implications in the pathogenesis of age-related macular degeneration

The accumulation of damaged or postsynthetically modified proteins and dysregulation of inflammatory responses and angiogenesis in the retina/RPE are thought be etiologically related to formation of drusen and choroidal neovascularization (CNV), hallmarks of age-related macular degeneration (AMD). The ubiquitin-proteasome pathway (UPP) plays crucial roles in protein quality control, cell cycle control and signal transduction. Selective degradation of aberrant proteins by the UPP is essential for timely removal of potentially cytotoxic damaged or otherwise abnormal proteins. Proper function of the UPP is thought to be required for cellular function. In contrast, age--or stress induced--impairment the UPP or insufficient UPP capacity may contribute to the accumulation of abnormal proteins, cytotoxicity in the retina, and AMD. Crucial roles for the UPP in eye development, regulation of signal transduction, and antioxidant responses are also established. Insufficient UPP capacity in retina and RPE can result in dysregulation of signal transduction, abnormal inflammatory responses and CNV. There are also interactions between the UPP and lysosomal proteolytic pathways (LPPs). Means that modulate the proteolytic capacity are making their way into new generation of pharmacotherapies for delaying age-related diseases and may augment the benefits of adequate nutrition, with regard to diminishing the burden of AMD.

Role of the ubiquitin-proteasome in protein quality control and signaling: implication in the pathogenesis of eye diseases

The ubiquitin-proteasome pathway (UPP) plays important roles in many cellular functions, such as protein quality control, cell cycle control, and signal transduction. The selective degradation of aberrant proteins by the UPP is essential for the timely removal of potential cytotoxic damaged or otherwise abnormal proteins. Conversely, accumulation of the cytotoxic abnormal proteins in eye tissues is etiologically associated with many age-related eye diseases such as retina degeneration, cataract, and certain types of glaucoma. Age- or stress-induced impairment or overburdening of the UPP appears to contribute to the accumulation of abnormal proteins in eye tissues. Cell cycle and signal transduction are regulated by the conditional UPP-dependent degradation of the regulators of these processes. Impairment or overburdening of the UPP could also result in dysregulation of cell cycle control and signal transduction. The consequences of the improper cell cycle and signal transduction include defects in ocular development, wound healing, angiogenesis, or inflammatory responses. Methods that enhance or preserve UPP function or reduce its burden may be useful strategies for preventing age-related eye diseases.

PTOV1 is associated with UCH-L1 and in response to estrogen stimuli during the mouse oocyte development

To investigate the biological significance of ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1) involvement in oocyte maturation, we screened for proteins that bound to UCH-L1 in mouse ovaries, and we found that the prostate tumor overexpressed-1 (PTOV1) protein was able to bind to UCH-L1. PTOV1 is highly expressed in prostate cancers and considered as a potential marker for carcinogenesis and the progress of prostate cancer. It was reported that PTOV1 plays an important role in cell cycle regulation, but its role in mammalian oocyte development and meiosis is still unclear. In this paper, it was found that the expression levels of PTOV1 in mouse ovaries progressively increased from prepubescence to adulthood. And we found by immunohistochemistry that PTOV1 spreaded in both the cytoplasm and nuclei of oocytes during prepuberty, but in normal adult mouse oocytes, it concentrated not only in nuclei but also on the plasma membrane, though in some oocytes with abnormal shapes, PTOV1 did not display the typical distribution patterns. In granulosa cells, however, it was found to locate in the cytoplasm at all the selected ages. In postnatal mouse ovaries (28 days), estradiol treatment induced the adult-specific distribution pattern of PTOV1 in oocytes. In addition, UCH-L1 was shown to be associated with CDK1, which participated in the regulation of cell cycle and oocyte maturation. Therefore, we propose that the distribution changes of PTOV1 are age-dependent, and significant for mouse oocyte development and maturation. Moreover, the discovery that PTOV1 is associated with UCH-L1 in mouse oocytes supports the explanations for that UCH-L1 is involved in oocyte development and maturation, especially under the regulation of estrogen.

Analysis of the neuronal marker protein gene product 9.5 in internal limiting membranes after indocyanine-green assisted peeling

BACKGROUND

Indocyanine green-assisted internal limiting membrane (ILM) peeling was suspected to disrupt the innermost layer of the neural retina. We examined whether surgically excised specimens contain remnants of neuronal tissue.

METHODS

Ten patients with macular hole underwent pars plana vitrectomy and indocyanine green-assisted ILM peeling. A total of 0.1 mL of a 0.5% indocyanine green solution was applied for 15 seconds. The ILM specimens were prepared for immunohistochemistry, using a polyclonal antibody against protein gene product 9.5. Protein gene product 9.5 is a pan-neuronal marker labeling human neuronal cells. Appropriate controls to show selectivity of the antibody were performed on neuronal tissue of donor eyes. One ILM was prepared for electron microscopy.

RESULTS

A selective expression of protein gene product 9.5 was found in neuronal fibers of the retina and optic nerve of donor eyes. Only 1 of the 10 surgical ILM specimens showed a minimal focal positivity for protein gene product 9.5. No neuronal tissue was detected on the ILM by electron microscopy.

CONCLUSION

Focal expression of protein gene product 9.5 in only 1 of 10 surgical ILM specimens argues against a general indocyanine green-related disruption of the innermost retinal layers. However, higher concentrations of the dye, longer incubation times or different solvents than used in this study may lead to different results.

The HIV Protease Inhibitors Nelfinavir and Saquinavir, but Not a Variety of HIV Reverse Transcriptase Inhibitors, Adversely Affect Human Proteasome Function

Background

In HIV-infected patients some clinical and immunological benefits of antiretroviral therapy, which frequently include a combination of HIV protease inhibitors (PIs) and reverse transcriptase inhibitors (RTIs), cannot be solely explained by the drugs’ action on viral enzymes. Proteasomes constitute the central protease of the ubiquitin ATP-dependent pathway involved in many cellular processes, as well as in HIV maturation and aggressiveness. Objective: To explore whether the PIs nelfinavir and saquinavir and the RTIs abacavir, nevirapine, delavirdine, stavudine and didanosine affect proteasome function in vitro and in vivo.

Methods

Peptidase activity of purified human 26S and 20S proteasomes was assayed with and without the drugs at different concentrations. Intracellular proteasome proteolytic activity was evaluated by searching for ubiquitin-tagged proteins in HL60 cells incubated with and without the drugs.

Results

At therapeutic dosages, nelfinavir and saquinavir inhibited proteasome peptidase activity and caused intracellular accumulation of polyubiquitinated proteins, a hallmark of proteasome proteolytic inhibition in vivo; the RTIs failed to evoke either effect.

Conclusion

Proteasomes are targeted by the two PIs but not the RTIs. Therefore, in HIV-infected patients the beneficial effect of a therapy including one of the two PIs should partly rely on inhibition of host proteasome function.

Function of the ubiquitin proteolytic pathway in the eye

The ubiquitin pathway (UP) is involved in regulation of many essential cellular processes usually by the degradation of regulators of these processes. For example the UP is involved in regulation of cell cycle, proliferation, differentiation, organogenesis, development, and signal transduction in the lens and retina. A functional UP has also been documented in the cornea. Upon aging or exposure to stress there is an accumulation of damaged proteins, including ubiquitinated proteins, in the lens and retina. Some of these proteins may be cytotoxic. Thus, an active UP may be required to avoid such age and disease-related accumulation of damaged proteins. In this review we will explain the biochemistry of the UP and we will document the most important studies regarding UP function in the lens, retina and cornea.

A novel ubiquitin carboxyl terminal hydrolase is involved in toad oocyte maturation

p28, a 28kD protein from toad (Bufo bufo gargarizans) oocytes, was identified by using p13(suc1)-agarose affinity chromatography. Sequence homology analysis of the full-length cDNA of p28 (Gene Bank accession number: AF 314091) indicated that it encodes a protein containing 224 amino-acids with about 55% identities and more than 70% positives to human, rat or mouse UCH-L1, and contains homological functional domains of UCH family. Anti-p28 monoclonal antibody, on injecting into the oocytes, could inhibit the progesterone-induced resumption of meiotic division in a dose-dependent manner. The recombinant protein p28 showed similar SDS/PAGE behaviors to the native one, and promoted ubiquitin ethyl ester hydrolysis, a classical catalytic reaction for ubiquitin carboxyl terminal hydrolases (UCHs). The results in this paper reveal that a novel protein, p28, exists in the toad oocytes, is a UCH L1 homolog, was engaged in the process of progesterone-induced oocyte maturation possibly through an involvement in protein turnover and degradation.

The human 26S proteasome is a target of antiretroviral agents

BACKGROUND

Proteasomes constitute the degradative machinery of the ubiquitin/adenosine triphosphate-dependent proteolytic pathway, which is involved in many cell functions, including immune response and apoptosis, and in HIV maturation and infectivity.

OBJECTIVE

To examine whether proteasomes are targeted by antiretroviral agents.

METHODS

Chymotrypsin-like, trypsin-like and peptidyl-glutamyl-peptide hydrolysing activities of purified human 26S and 20S proteasomes, the latter depleted or enriched in 11S regulator, were assayed after incubation with indinavir, lamivudine and zidovudine at 1-80 microM alone and in combination. To assess the drug effects on cellular functions regulated by proteasomes, the accumulation of ubiquitin-tagged proteins, the processing of the nuclear factor kappa B precursor p105, and the degradation of the inhibitor of nuclear factor kappa B, isoform alpha (IkappaBalpha) were evaluated by Western immunoblotting in Jurkat cells after incubation for 6 h with the drugs above.

RESULTS

Trypsin-like and mostly chymotrypsin-like activities of purified 26S proteasome were inhibited by each drug from 10 to 80 microM, more by double combinations and mostly by the triple combination. The peptidyl-glutamyl-peptide hydrolysing activity of the 26S proteasome and the three peptidase activities of the 20S proteasome, depleted or enriched in 11S regulator, were unaffected. The accumulation of ubiquitin-tagged proteins, reduced IkappaBalpha degradation and p105 processing were appreciable in intact cells with the triple drug combination.

CONCLUSION

The human 26S proteasome is a target of antiretroviral agents. This suggests that the antiviral action and some clinical and immunological benefits of combined antiretroviral therapy rely not only on its known effects on viral enzymes, but also on host cell components.

Abnormal ubiquitination of axons in normally myelinated white matter in multiple sclerosis brain

The hallmark of the lesions in multiple sclerosis (MS) is inflammatory demyelination with sparing of axons. Recent neuropathological and neuroradiological investigations show that structural changes of the axons occur, both in plaques and in the normal appearing white matter. A better understanding of the axonal damage in MS is important, since this may be responsible for permanent disability. We have investigated the immunoreactivity for ubiquitin, a sensitive method to detect axonal dystrophy and accumulation of abnormal proteins in pathological conditions of the nervous system, in the brains of six cases of MS (age range 39-66 years). Tissue blocks were fixed in formalin and embedded in paraffin. A panel of antibodies was used: anti-ubiquitin, anti-neurofilament (SMI-31 + SMI-32), anti-amyloid precursor protein and anti-PGP9.5. We focused our attention on chronic plaques, recognized by the absence of Luxol Fast Blue B-positive inclusions in macrophages. SMI-31 + SMI-32 showed the presence of a variable amount of axons within the plaques; the axonal network within the plaques was looser than outside. No ubiquitin reactivity was present in chronic plaques. In the normally myelinated white matter surrounding the plaques, a dense granular ubiquitin immunoreactivity was found both near and far from the plaque edge. No similar staining was found in control brains. Ubiquitination is the first step of a non-lysosomal degradation pathway of proteins. The present findings suggest a derangement of this proteolytic pathway in the axons outside the plaques, possibly as a consequence of chronic absence of myelin in the axonal segment inside the plaque. The spectrum of axonal changes in MS appears to be wider than expected and involves the apparently normal white matter.

Proteasomes are a target of the anti-tumour drug vinblastine

Proteasomes, the proteolytic machinery of the ubiquitin/ATP-dependent pathway, have a relevant role in many processes crucial for cell physiology and cell cycle progression. Proteasome inhibitors are used to block cell cycle progression and to induce apoptosis in certain cell lines. Here we examine whether proteasomal function is affected by the anti-tumour drug vinblastine, whose cytostatic action relies mainly on the disruption of mitotic spindle dynamics. The effects of vinblastine on the peptidase activities of human 20 S and 26 S proteasomes and on the proteolytic activity of 26 S proteasome were assessed in the presence of specific fluorogenic peptides and (125)I-lysozyme-ubiquitin conjugates respectively. The assays of ubiquitin-protein conjugates and of inhibitory kappa B alpha (I kappa B alpha), which are characteristic intracellular proteasome substrates, by Western blotting on lysates from HL60 cells incubated with or without vinblastine, illustrated the effects of vinblastine on proteasomes in vivo. We also evaluated the effects of vinblastine on the signal-induced degradation of I kappa B alpha. Vinblastine at 3--110 microM reversibly inhibited the chymotrypsin-like activity of the 20 S proteasome and the trypsin-like and peptidyl-glutamyl-peptide hydrolysing activities of both proteasomes, but only at 110 microM vinblastine was the chymotrypsin-like activity of the 26 S proteasome inhibited; furthermore, at 25--200 microM the drug inhibited the degradation of ubiquitinated lysozyme. In HL60 cells exposed for 6 h to 0.5--10 microM vinblastine, the drug-dose-related accumulation of polyubiquitinated proteins, as well as that of a high-molecular-mass form of I kappa B alpha, occurred. Moreover, vinblastine impaired the signal-induced degradation of I kappa B alpha. Cell viability throughout the test was approx. 95%. Proteasomes can be considered to be a new and additional vinblastine target.

Structural and functional characterization of 20S and 26S proteasomes from bovine brain

Two proteins were isolated, in a stable form, from bovine brain by ion exchange chromatography, gel filtration and ultracentrifugation on glycerol gradient. They were identified as 20S and 26S proteasomes on the basis of molecular mass, migration velocity on non-denaturing gels, immunoreactivity, multipeptidase activity and the 26S proteasome also for dependence on ATP for the degradation of short peptides and ubiquitinylated proteins. However, the 26S proteasome has some properties not yet described for its counterpart of other tissues and from brain of this and other species. In particular, the ATP concentration required by the 26S proteasome to reach maximal peptidase activity was approximately 40-fold lower than the one required for maximal proteolytic activity on polyubiquitinylated substrates. Moreover, plots of substrate concentration vs. velocity gave a saturation curve for the 26S proteasome only, which, for the trypsin-like and post-glutamyl peptide hydrolase activities fitted the Michaelis-Menten equation, whereas for the chymotrypsin-like activity indicated multibinding site kinetics with positive cooperativity (n = 2.32+/-0.38). As concerns the 20S proteasome, its electrophoretic pattern on native gel revealed a single protein band, a feature, to our knowledge, not yet described for the brain particle of any species.