Mass spectrometric characterization of gelsolin isoforms

LC-MS/MS: A sensitive and selective analytical technique to detect COVID-19 protein biomarkers in the early disease stage

INTRODUCTION

The COVID-19 outbreak has put enormous pressure on the scientific community to detect infection rapidly, identify the status of disease severity, and provide an immediate vaccine/drug for the treatment. Relying on immunoassay and a real-time reverse transcription polymerase chain reaction (rRT-PCR) led to many false-negative and false-positive reports. Therefore, detecting biomarkers is an alternative and reliable approach for determining the infection, its severity, and disease progression. Recent advances in liquid chromatography and mass spectrometry (LC-MS/MS) enable the protein biomarkers even at low concentrations, thus facilitating clinicians to monitor the treatment in hospitals.

AREAS COVERED

This review highlights the role of LC-MS/MS in identifying protein biomarkers and discusses the clinically significant protein biomarkers such as Serum amyloid A, Interleukin-6, C-Reactive Protein, Lactate dehydrogenase, D-dimer, cardiac troponin, ferritin, Alanine transaminase, Aspartate transaminase, gelsolin and galectin-3-binding protein in COVID-19, and their analysis by LC-MS/MS in the early stage.

EXPERT OPINION

Clinical doctors monitor significant biomarkers to understand, stratify, and treat patients according to disease severity. Knowledge of clinically significant COVID-19 protein biomarkers is critical not only for COVID-19 caused by the coronavirus but also to prepare us for future pandemics of other diseases in detecting by LC-MS/MS at the early stages.

HIV-1 Vpr Induces Degradation of Gelsolin, a Myeloid Cell-Specific Host Factor That Reduces Viral Infectivity by Inhibiting the Expression and Packaging of the HIV-1 Env Glycoprotein

Gelsolin (GSN) is a structural actin-binding protein that is known to affect actin dynamics in the cell. Using mass spectrometry, we identified GSN as a novel Vpr-interacting protein. Endogenous GSN protein was expressed at detectable levels in monocyte-derived macrophages (MDM) and in THP-1 cells, but it was undetectable at the protein level in other cell lines tested. The HIV-1 infection of MDM was associated with a reduction in GSN steady-state levels, presumably due to the Vpr-induced degradation of GSN. Indeed, the coexpression of GSN and Viral protein R (Vpr) in transiently transfected HEK293T cells resulted in the Vpr-dependent proteasomal degradation of GSN. This effect was observed for Vprs from multiple virus isolates. The overexpression of GSN in HEK293T cells had no effect on Gag expression or particle release, but it reduced the expression and packaging of the HIV-1 envelope (Env) glycoprotein and reduced viral infectivity. An analysis of the HIV-1 splicing patterns did not reveal any GSN-dependent differences, suggesting that the effect of GSN on Env expression was regulated at a posttranscriptional level. Indeed, the treatment of transfected cells with lysosomal inhibitors reversed the effect of GSN on Env stability, suggesting that GSN reduced Env expression via enhanced lysosomal degradation. Our data identify GSN as a macrophage-specific host antiviral factor that reduces the expression of HIV-1 Env. IMPORTANCE Despite dramatic progress in drug therapies, HIV-1 infection remains an incurable disease that affects millions of people worldwide. The virus establishes long-lasting reservoirs that are resistant to currently available drug treatments and allow the virus to rebound whenever drug therapy is interrupted. Macrophages are long-lived cells that are relatively insensitive to HIV-1-induced cytopathicity and thus could contribute to the viral reservoir. Here, we identified a novel host factor, gelsolin, that is expressed at high levels in macrophages and inhibits viral infectivity by modulating the expression of the HIV-1 Env glycoprotein, which is critical in the spread of an HIV-1 infection. Importantly, the viral protein Vpr induces the degradation of gelsolin and thus counteracts its antiviral activity. Our study provides significant and novel insights into HIV-1 virus-host interactions and furthers our understanding of the importance of Vpr in HIV-1 infection and pathogenesis.

HIV and Proteomics: What We Have Learned from High Throughput Studies

The accelerated development of technology over the last three decades has driven biological sciences to high-throughput profiling experiments, now broadly referred to as systems biology. The unprecedented improvement of analytical instrumentation has opened new avenues for more complex experimental designs and expands the knowledge in genomics, proteomics, and other omics fields. Despite the collective efforts of hundreds of researchers, gleaning all the expected information from omics experiments is still quite far. This paper summarizes what has been learned from high-throughput proteomics studies thus far, and what is believed should be done to reveal even more valuable information from such studies. It is drawn from the background in using proteomics to study human immunodeficiency virus 1 infection of macrophages and/or T cells, but it is believed that some conclusions will be more broadly applicable.

Gelsolin expression in sheep milk somatic cells during lactation

The identification of genes involved in phenotypes related to milk quality is important for both economic and health aspects in livestock production. The aim of this study was to assess the level of gelsolin gene expression in two breeds of dairy sheep - Sarda and Gentile - with pronounced differences in quantitative and qualitative milk traits. Gelsolin, a type of actin-modulating proteins is involved in the processes of actin remodeling during cell growth and apoptosis; therefore a role of this protein in mammary changes during lactation was here hypothesized. Individual milk samples were collected three times during lactation from 26 ewes of the two breeds. The differential gene expression of gelsolin in the two breeds and the three lactation times was estimated by quantitative PCR on RNA extracted from milk somatic cells. Correlations of gelsolin gene expression with milk yield and quality and days of lactation were also estimated. The results showed that gelsolin gene expression was significantly higher in the Sarda compared to the Gentile at each lactation stage, in agreement with the longer lactation duration and the higher daily milk yield of the first breed. Significant correlations of gelsolin gene expression were found with milk fat content in Sarda breed (-0.46, P<0.05). Gelsolin expression analysis confirmed the link between gelsolin gene function and milk fat content of sheep.

Antagonistic sepsis markers: Serum gelsolin and actin/gelsolin ratio

OBJECTIVES

For appropriate sepsis care, prognostic laboratory markers are mandatory. The aim of our study was to evaluate the predictive value of serum actin, gelsolin and the recently defined actin/gelsolin ratio during sepsis by comparison it to classical clinical and inflammatory laboratory parameters.

DESIGN & METHODS

We analyzed sera of severe septic (n=32) and SIRS (n=12) patients for 5days. Ophthalmologic patients (n=27) served as controls. Besides serum actin, gelsolin and actin/gelsolin ratios classical laboratory parameters (WBC count, serum procalcitonin, hsCRP) and clinical scores (APACHE II, SAPS II, SOFA), were also assessed.

RESULTS

Septic patients showed significantly decreased first-day gelsolin levels and increased actin/gelsolin ratios compared to SIRS patients (p<0.05), furthermore, non-survivors had significantly lower gelsolin levels compared to survivors (p<0.05). Non-survivors had 11.4-fold higher 2nd day actin/gelsolin ratios than survivors. Besides procalcitonin (PCT) and hsCRP, gelsolin and actin/gelsolin ratios also proved to be useful in discriminating SIRS from sepsis in the ICU (p<0.05). Gelsolin had similar prognostic value to PCT when assessing 7-day mortality and the predictive capacity of the first-day actin/gelsolin ratios was similar to that of APACHE II score regarding ICU mortality in severe sepsis.

CONCLUSIONS

Serum gelsolin and actin/gelsolin ratio might serve as efficient complementary prognostic markers in sepsis. However, for daily clinical usage, an automated laboratory assay of actin and gelsolin is still needed to be developed.

Using carboxyfluorescein diacetate succinimidyl ester to monitor intracellular protein glycation

Protein glycation is a ubiquitous process involved in vascular complications observed in diabetes. Glyoxal (GO), an intracellular reactive oxoaldehyde that is one of the most potent glycation agents, readily reacts with amines present on proteins to produce the lysine-derived adduct carboxymethyllysine, which is a prevalent advanced glycation end-product (AGE). Our group previously showed that cell exposure to GO leads to an alteration in the cell contractile activity that could occur as a result of the glycation of various proteins regulating the cell contractile machinery. Here, we measured the extent of glycation on three functionally distinct proteins known to participate in cell contraction and cytoskeletal organization-Rho-kinase (ROCK), actin, and gelsolin (GSN)-using an assay based on the reaction of the cell membrane-permeable fluorescent probe carboxyfluorescein diacetate succinimidyl ester (CFDA-SE), which reacts with primary amine groups of proteins. By combining CFDA-SE fluorescence and Western blot detection, we observed (following GO incubation) increased glycation of actin and ROCK as well as an increased interaction between actin and GSN as observed by co-immunoprecipitation. Thus, we conclude that the use of the fluorescent probe CFDA-SE offers an interesting alternative to perform a comparative analysis of the extent of intracellular protein glycation in live cells.

Plasma gelsolin protects HIV-1 gp120-induced neuronal injury via voltage-gated K+ channel Kv2.1

Plasma gelsolin (pGSN), a secreted form of gelsolin, is constitutively expressed throughout the central nervous system (CNS). The neurons, astrocytes and oligodendrocytes are the major sources of pGSN in the CNS. It has been shown that levels of pGSN in the cerebrospinal fluid (CSF) are decreased in several neurological conditions including HIV-1-associated neurocognitive disorders (HAND). Although there is no direct evidence that a decreased level of pGSN in CSF is causally related to the pathogenesis of neurological disorders, neural cells, if lacking pGSN, are more vulnerable to cell death. To understand how GSN levels relate to neuronal injury in HAND, we studied the effects of pGSN on HIV-1 gp120-activated outward K+ currents in primary rat cortical neuronal cultures. Incubation of rat cortical neurons with gp120 enhanced the outward K+ currents induced by voltage steps and resulted in neuronal apoptosis. Treatment with pGSN suppressed the gp120-induced increase of delayed rectifier current (IK) and reduced vulnerability to gp120-induced neuronal apoptosis. Application of Guangxitoxin-1E (GxTx), a Kv2.1 specific channel inhibitor, inhibited gp120 enhancement of IK and associated neuronal apoptosis, similar effects to pGSN. Western blot and PCR analysis revealed gp120 exposure to up-regulate Kv2.1 channel expression, which was also inhibited by treatment with pGSN. Taken together, these results indicate pGSN protects neurons by suppressing gp120 enhancement of IK through Kv2.1 channels and reduction of pGSN in HIV-1-infected brain may contribute to HIV-1-associated neuropathy.

2D DIGE analysis of the bursa of Fabricius reveals characteristic proteome profiles for different stages of chicken B-cell development

Antibody producing B-cells are an essential component of the immune system. In contrast to human and mice where B-cells develop in the bone marrow, chicken B-cells develop in defined stages in the bursa of Fabricius, a gut associated lymphoid tissue. In order to gain a better understanding of critical biological processes like immigration of B-cell precursors into the bursa anlage, their differentiation and final emigration from the bursa we analyzed the proteome dynamics of this organ during embryonic and posthatch development. Samples were taken from four representative developmental stages (embryonic day (ED) 10, ED18, day 2, and day 28) and compared in an extensive 2D DIGE approach comprising six biological replicates per time point. Cluster analysis and PCA demonstrated high reliability and reproducibility of the obtained data set and revealed distinctive proteome profiles for the selected time points, which precisely reflect the differentiation processes. One hundred fifty three protein spots with significantly different intensities were identified by MS. We detected alterations in the abundance of several proteins assigned to retinoic acid metabolism (e.g. retinal-binding protein 5) and the actin-cytoskeleton (e.g. vinculin and gelsolin). By immunohistochemistry, desmin was identified as stromal cell protein associated with the maturation of B-cell follicles. Strongest protein expression difference (10.8-fold) was observed for chloride intracellular channel 2. This protein was thus far not associated with B-cell biology but our data suggest an important function in bursa B-cell development.

Urinary proteome analysis of irritable bowel syndrome (IBS) symptom subgroups

Irritable bowel syndrome (IBS) is a functional gastrointestinal (GI) disorder characterized by chronic abdominal pain associated with alterations in bowel function. Given the heterogeneity of the symptoms, multiple pathophysiologic factors are suspected to play a role. We classified women with IBS into four subgroups based on distinct symptom profiles. In-depth shotgun proteomic analysis was carried out to profile the urinary proteomes to identify possible proteins associated with these subgroups. First void urine samples with urine creatinine level≥100 mg/dL were used after excluding samples that tested positive for blood. Urine from 10 subjects representing each symptom subgroup was pooled for proteomic analysis. The urine proteome was analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) using a data-independent method known as Precursor Acquisition Independent From Ion Count (PAcIFIC) that allowed extended detectable dynamic range. Differences in protein quantities were determined by peptide spectral counting followed by validation of select proteins with ELISA or a targeted single reaction monitoring (LC-SRM/MS) approach. Four IBS symptom subgroups were selected: (1) Constipation, (2) Diarrhea+Low Pain, (3) Diarrhea+High Pain, and (4) High Pain+High Psychological Distress. A fifth group consisted of Healthy Control subjects. From comparisons of quantitative spectral counting data among the symptom subgroups and controls, a total of 18 proteins that showed quantitative differences in relative abundance and possible physiological relevance to IBS were selected for further investigation. Three of the 18 proteins were chosen for validation by either ELISA or SRM. An elevated expression of gelsolin (GSN) was associated with the high pain groups. Trefoil Factor 3 (TFF3) levels were higher in IBS groups compared to controls. In this study, the IBS patients subclassified by predominant symptoms showed differences in urine proteome levels. Proteins showing distinctive changes are involved in homeostasis of intestinal function and inflammatory response. These findings warrant future studies with larger, independent cohorts to enable more extensive assessment and validation of urinary protein markers as a diagnostic tool in adults with IBS.

Plasma gelsolin accumulates in macrophage nodules in brains of simian immunodeficiency virus infected rhesus macaques

Plasma gelsolin (pGSN), an isoform 1, is secreted by various types of cells in the central nervous system (CNS) and periphery, but not by the liver. pGSN circulates in blood and cerebrospinal fluid (CSF); however, its concentration in CSF is approximately twenty times lower than in plasma. It has been shown that several types of cells such as oligodendrocytes, neurons, and/or astrocytes contribute to the overall pool of pGSN in the CNS. Further, it has been postulated that pGSN plays multiple roles during microbial infection and modulates inflammatory responses; however, the exact mechanism of regulation is not known. We previously showed that levels of pGSN in CSF of individuals with advanced neurocognitive impairment due to HIV infection of the brain are decreased. Here, we show that macrophages express significant amounts of pGSN in response to HIV infection in vitro. Using immunohistochemistry of simian immunodeficiency virus infected rhesus monkey brains, we show that increased levels of pGSN are present in macrophage nodules creating locally a high level of this protein within the brain. This may not be reflected by the overall decreased level in the distinct CSF compartment.

A cell model for conditional profiling of androgen-receptor-interacting proteins

Partial androgen insensitivity syndrome (PAIS) is associated with impaired male genital development and can be transmitted through mutations in the androgen receptor (AR). The aim of this study is to develop a cell model suitable for studying the impact AR mutations might have on AR interacting proteins. For this purpose, male genital development relevant mouse cell lines were genetically modified to express a tagged version of wild-type AR, allowing copurification of multiprotein complexes under native conditions followed by mass spectrometry. We report 57 known wild-type AR-interacting proteins identified in cells grown under proliferating and 65 under nonproliferating conditions. Of those, 47 were common to both samples suggesting different AR protein complex components in proliferating and proliferation-inhibited cells from the mouse proximal caput epididymus. These preliminary results now allow future studies to focus on replacing wild-type AR with mutant AR to uncover differences in protein interactions caused by AR mutations involved in PAIS.

Reduction of plasma gelsolin levels correlates with development of multiple organ dysfunction syndrome and fatal outcome in burn patients

Background

Depletion of the circulating actin-binding protein, plasma gelsolin (pGSN) has been described in critically ill surgical patients. We hypothesized that the extent of pGSN reduction might correlate with different outcome of burn patients. The study was performed to evaluate the prognostic implications of pGSN levels on the development of multiple organ dysfunction syndrome (MODS) and fatal outcome in a group of severely burn patients.

Methods and Findings

95 patients were included, and they were divided into three groups with different burn area: group I (n = 33), group II (n = 32) and group III (n = 30). According to whether there was development of MODS or not, patients were divided into MODS group (n = 28) and none-MODS group (n = 67); then the patients with MODS were further divided into non-survivor group (n = 17) and survivor group (n = 11). The peripheral blood samples were collected on postburn days (PBD) 1, 3, 7, 14, and 21. The levels of pGSN were determined and T cells were procured from the blood. The contents of cytokines (IL-2, IL-4 and IFN-γ) released by T cells were also measured. The related factors of prognosis were analyzed by using multivariate logistic regression analysis. The results showed that pGSN concentrations, as well as the levels of IL-2 and IFN-γ, decreased markedly on PBD 1–21, whereas, the levels of IL-4 increased markedly in all burn groups as compared with normal controls (P<0.05 or P<0.01), and there were obviously differences between group I and group III (P<0.05 or P<0.01). The similar results were found in MODS patients and the non-survivor group as compared with those without MODS and the survival group on days 3–21 postburn (P<0.05 or P<0.01). Moreover, as the pGSN levels decreased, the incidence of septic complication as well as MODS remarkably increased.

Conclusions

pGSN levels appear to be an early prognostic marker in patients suffering from major burns.

Searching for the noninvasive biomarker holy grail: are urine proteomics the answer?

Recently, biobehavioral nursing scientists have focused their attention on the search for biomarkers or biological signatures to identify patients at risk for various health problems and poor disease outcomes. In response to the national impetus for biomarker discovery, the measurement of biological fluids and tissues has become increasingly sophisticated. Urine proteomics, in particular, may hold great promise for biobehavioral focused nursing scientists for examination of symptom-and syndrome-related research questions. Urine proteins are easily accessible secreted proteins that provide direct and indirect windows into bodily functions. Advances in proteomics and biomarker discovery provide new opportunities to conduct research studies with banked and fresh urine to benefit diagnosis, prognosis, and evaluation of outcomes in various disease populations. This article provides a review of proteomics and a rationale for utilizing urine proteomics in biobehavioral research. It addresses as well some of the challenges involved in data collection and sample preparation.

Immunoreactivity of anti-gelsolin antibodies: implications for biomarker validation

Background

Proteomic-based discovery of biomarkers for disease has recently come under scrutiny for a variety of issues; one prominent issue is the lack of orthogonal validation for biomarkers following discovery. Validation by ELISA or Western blot requires the use of antibodies, which for many potential biomarkers are under-characterized and may lead to misleading or inconclusive results. Gelsolin is one such biomarker candidate in HIV-associated neurocognitive disorders.

Methods

Samples from human (plasma and CSF), monkey (plasma), monocyte-derived macrophage (supernatants), and commercial gelsolin (recombinant and purified) were quantitated using Western blot assay and a variety of anti-gelsolin antibodies. Plasma and CSF was used for immunoaffinity purification of gelsolin which was identified in eight bands by tandem mass spectrometry.

Results

Immunoreactivity of gelsolin within samples and between antibodies varied greatly. In several instances, multiple bands were identified (corresponding to different gelsolin forms) by one antibody, but not identified by another. Moreover, in some instances immunoreactivity depended on the source of gelsolin, e.g. plasma or CSF. Additionally, some smaller forms of gelsolin were identified by mass spectrometry but not by any antibody. Recombinant gelsolin was used as reference sample.

Conclusions

Orthogonal validation using specific monoclonal or polyclonal antibodies may reject biomarker candidates from further studies based on misleading or even false quantitation of those proteins, which circulate in various forms in body fluids.