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Objectives: Interferon regulatory factor 5 (IRF5) plays a central role in interferon-mediated inflammation and is implicated in autoimmune diseases, including systemic lupus erythematosus (SLE). Detecting IRF5 in plasma is challenging due to its low circulating levels, highlighting the need for a highly sensitive and quantitative assay. This study aimed to develop such an assay, validate the existence of previously identified IRF5 high and low subgroups in SLE, and support the potential of IRF5 as a biomarker in precision medicine.

Method: We established a solid-phase proximity ligation assay (SP-PLA) for IRF5 detection using a commercially available polyclonal antibody, which was benchmarked against two in-house recombinant antibodies. A linear calibration curve was generated using recombinant IRF5 protein (range 0.01-100 pg/μL), with a limit of detection between 0.01 and 0.05 pg/μL. EDTA-plasma samples from three SLE subgroups (n = 25 per group) were analysed.

Results: IRF5 was detectable in all SLE plasma samples using SP-PLA (mean 0.63 pg/μL; sd 1.92 pg/μL; maximum 13.54 pg/μL). The IRF5 high SLE subgroup showed significantly higher IRF5 plasma levels than the IRF5 low SLE subgroup (Dunn's post-hoc test, adjusted p < 0.05).

Conclusion: The SP-PLA enabled sensitive and specific detection of low-level IRF5 in plasma and confirmed the presence of IRF5 high and low subgroups in SLE using a quantitative method. These findings support the potential of IRF5 as a biomarker, but validation in independent cohorts is required. The assay may facilitate patient stratification in future research and precision medicine approaches targeting the interferon pathway.

Introduction: Pregnant women in sub-Saharan Africa face heightened susceptibility to Plasmodium falciparum malaria, with placental sequestration driving adverse outcomes. The infection may lead to pregnancy-associated malaria (PAM) because of the sequestration of Plasmodium falciparum-infected erythrocytes in the placental intervillous space. Although there are several tools for diagnosing malaria infection during pregnancy, including blood smear microscopic examination, rapid diagnostic tests, and PCR, there are no tools for detecting placental infection and, by extension, any dysfunction associated with PAM. Thus, PAM, specifically placental infection, can only be confirmed via postnatal placental histopathology. Therefore, there is an urgent need for specific plasma biomarkers of PAM.

Methods: Here, we used the high throughput proximity extension assay to screen plasma from malaria-exposed pregnant women for differentially expressed proteins that may serve as candidate biomarkers of Plasmodium falciparum infection during pregnancy, with future potential to inform diagnosis of PAM or adverse malaria outcomes. Such biomarkers may also elucidate the pathophysiology of PAM.

Results: Using proximity extension assay (PEA), we identified elevated IgG Fc receptor IIb (FCGR2B) and heme oxygenase-1 (HO-1) in malaria-positive pregnancies, while neurturin (NRTN) and IL-20 were downregulated.

Discussion: IL-20 emerged as a top candidate biomarker, warranting validation in large cohorts with placental histopathology.

Background

Gastric cancer (GC), the world’s fifth most common malignancy, remains a major cause of death, motivating minimally invasive protein measurements. Small extracellular vesicles (sEVs) mirror cellular state but are difficult to profile from limited material. Proximity extension assay (PEA) enables multiplex, sensitive detection. We developed a PEA-centred workflow to profile GC cell-line sEVs, benchmarked against cells and an EV-rich control, and nominate hypothesis-generating candidates.

Methodss

EVs from four GC cell lines (Kato III, AGS, MKN45, MKN7) were isolated by differential centrifugation/filtration and ultracentrifugation; prostasomes (seminal-fluid EVs; ethics-approved) were purified by ultracentrifugation, Superdex 200 size-exclusion, and sucrose gradient. EVs were characterized by TEM, NTA, and Western blot (CD9/CD63/CD81; Calnexin). Protein profiling used Olink PEA across five Target 96 panels, two commercial (Oncology, Inflammation) and three experimental (Cancer, Cellular Pathways, Neurology) with availability-based selection; single replicate per condition. NPX values were background/LOD-corrected in R, with PCA. STRING PPI used medium confidence (0.4) with FDR-adjusted enrichment. Selected proteins were validated by SP-PLA (qPCR), EV-PLA (flow cytometry), and WB.

Resultss

EVs and prostasomes were purified and characterized per MISEV2023 (TEM/NTA; CD9/CD63/CD81+, calnexin–). Using five Olink PEA panels, 460 proteins were profiled; principal component analysis separated sEVs from parental cells. We identified 71 proteins enriched in GC sEVs, including EphA2, cMet, IL-6, SCF, AXIN1, NOTCH1, and CAV1; 17 were unique to Kato III sEVs. STRING showed a highly connected network, with top pathways: Pathways in cancer, Cytokine–cytokine receptor interaction, and PI3K–Akt. Orthogonal assays (SP-PLA, EV-PLA, WB densitometry) confirmed the presence of EphA2 and cMet on GC sEVs.

Discussions

PEA-based profiling of GC cell-line sEVs nominates 71 enriched proteins (e.g., EphA2, cMet, NOTCH1, CAV1) as hypothesis-generating candidates that may reflect cell-type–specific cargo and tumor–microenvironment signaling. Key limitations include the in-vitro design, single replicates, preselected PEA panels, and the use of prostasomes rather than healthy plasma sEVs, which may affect generalizability and specificity. Translational relevance requires validation in patient biofluids with orthogonal assays and cohort-level evaluation.

A homogeneous PCR-based assay for sensitive and specific detection of antibodies in serum or dried blood spots (DBS) is presented and the method is used to monitor individuals infected with or vaccinated against SARS-CoV-2. Detection probes were prepared by conjugating the recombinant spike protein subunit 1 (S1), containing the receptor binding domain (RBD) of SARS-CoV-2, to each of a pair of specific oligonucleotides. The same was done for the nucleocapsid protein (NP). Upon incubation with serum or DBS samples, the bi- or multivalency of the antibodies (IgG, IgA or IgM) brings pairs of viral proteins with their conjugated oligonucleotides in proximity, allowing the antibodies to be detected by a modified proximity extension assay (PEA). Anti-S1 and anti-NP antibodies could be detected simultaneously from one incubation reaction. This Antibody PEA (AbPEA) test uses only 1 µl of neat or up to 100,000-fold diluted serum or one ø1.2 mm disc cut from a DBS. All 100 investigated sera and 21 DBS collected prior to the COVID-19 outbreak were negative, demonstrating a 100% specificity. The area under the curve, as evaluated by Receiver Operating Characteristic (ROC) analysis reached 0.998 (95%CI: 0.993–1) for samples taken from 11 days after symptoms onset. The kinetics of antibody responses were monitored after a first and second vaccination using serially collected DBS from 14 individuals. AbPEA offers highly specific and sensitive solution-phase antibody detection without requirement for secondary antibodies, no elution step when using DBS sample in a simple procedure that lends itself to multiplex survey of antibody responses.

Adenine nucleotide translocases (ANTs) and uncoupling proteins (UCPs) are known to facilitate proton leak across the inner mitochondrial membrane. However, it remains to be unravelled whether UCP2/3 contribute to significant amount of proton leak in vivo. Reports are indicative of UCP2 dependent proton-coupled efflux of C4 metabolites from the mitochondrial matrix. Previous studies have suggested that UCP2/3 knockdown (KD) contributes to increased ANT-dependent proton leak. Here we investigated the hypothesis that interaction exists between the UCP2 and ANT2 proteins, and that such interaction is regulated by the cellular metabolic demand. Protein-protein interaction was evaluated using reciprocal co-immunoprecipitation and in situ proximity ligation assay. KD of ANT2 and UCP2 was performed by siRNA in human embryonic kidney cells 293A (HEK293A) cells. Mitochondrial and cellular respiration was measured by high-resolution respirometry. ANT2-UCP2 interaction was demonstrated, and this was dependent on cellular metabolism. Inhibition of ATP synthase promoted ANT2-UCP2 interaction whereas high cellular respiration, induced by adding the mitochondrial uncoupler FCCP, prevented interaction. UCP2 KD contributed to increased carboxyatractyloside (CATR) sensitive proton leak, whereas ANT2 and UCP2 double KD reduced CATR sensitive proton leak, compared to UCP2 KD. Furthermore, proton leak was reduced in double KD compared to UCP2 KD. In conclusion, our results show that there is an interaction between ANT2-UCP2, which appears to be dynamically regulated by mitochondrial respiratory activity. This may have implications in the regulation of mitochondrial efficiency or cellular substrate utilization as increased activity of UCP2 may promote a switch from glucose to fatty acid metabolism.

Formation of the mouse cerebellum is initiated in the embryo and continues for a few weeks after birth. Double-mutant mice lacking platelet-derived growth factor C (PDGF-C) and that are heterozygous for platelet-derived growth factor receptor alpha (Pdgfc(-/-); Pdgfra(GFP/+)) develop cerebellar hypoplasia and malformation with loss of cerebellar lobes in the posterior vermis. This phenotype is similar to those observed in Foxc1 mutant mice and in a human neuroimaging pattern called Dandy Walker malformation. Pdgfc-Pdgfra mutant mice also display ependymal denudation in the fourth ventricle and gene expression changes in cerebellar meninges, which coincide with the first visible signs of cerebellar malformation. Here, we show that PDGF-C/PDGFR alpha signalling is a critical component in the network of molecular and cellular interactions that take place between the developing meninges and neural tissues, and which are required to build a fully functioning cerebellum.

Extracellular vesicles (EVs) are mediators of intercellular communication and a promising class of biomarkers. Surface proteins of EVs play decisive roles in establishing a connection with recipient cells, and they are putative targets for diagnostic assays. Analysis of the surface proteins can thus both illuminate the biological functions of EVs and help identify potential biomarkers. We developed a strategy combining high-resolution mass spectrometry (HRMS) and  proximity ligation assays (PLA) to first identify and then validate surface proteins discovered on EVs. We applied our workflow to investigate surface proteins of small EVs found in seminal fluid (SF-sEV). We identified 1,014 surface proteins and verified the presence of a subset of these on the surface of SF-sEVs. Our work demonstrates a general strategy for deep analysis of EVs' surface proteins across patients and pathological conditions, proceeding from unbiased screening by HRMS to ultra-sensitive targeted analyses via PLA.

To improve our ability to monitor cellular responses to e.g. cytokines or drugs, Lonn et al have developed a semi-automated system for large-scale in situ proximity ligation assays (isPLA) in HaCAT keratinocyte cells. Their approach expands the scope for image-based single cell analyses by combining observations of protein interactions and modifications with morphological details of individual cells at high throughput. Protein interactions and posttranslational modifications orchestrate cellular responses to e.g. cytokines and drugs, but it has been difficult to monitor these dynamic events in high-throughput. Here, we describe a semi-automated system for large-scale in situ proximity ligation assays (isPLA), combining isPLA in microtiter wells with automated microscopy and computer-based image analysis. Phosphorylations and interactions are digitally recorded along with subcellular morphological features. We investigated TGF-beta-responsive Smad2 linker phosphorylations and complex formations over time and across millions of individual cells, and we relate these events to cell cycle progression and local cell crowding via measurements of DNA content and nuclear size of individual cells, and of their relative positions. We illustrate the suitability of this protocol to screen for drug effects using phosphatase inhibitors. Our approach expands the scope for image-based single cell analyses by combining observations of protein interactions and modifications with morphological details of individual cells at high throughput.

Glioblastoma (GBM) is a brain malignancy characterized by invasiveness to the surrounding brain tissue and by stem-like cells, which propagate the tumor and may also regulate invasiveness. During brain development, polarity proteins, such as Par3, regulate asymmetric cell division of neuro-glial progenitors and neurite motility. We, therefore, studied the role of the Par3 protein (encoded by PARD3) in GBM. GBM patient transcriptomic data and patient-derived culture analysis indicated diverse levels of expression of PARD3 across and independent from subtypes. Multiplex immunolocalization in GBM tumors identified Par3 protein enrichment in SOX2-, CD133-, and NESTIN-positive (stem-like) cells. Analysis of GBM cultures of the three subtypes (proneural, classical, mesenchymal), revealed decreased gliomasphere forming capacity and enhanced invasiveness upon silencing Par3. GBM cultures with suppressed Par3 showed low expression of stemness (SOX2 and NESTIN) but higher expression of differentiation (GFAP) genes. Moreover, Par3 silencing reduced the expression of a set of genes encoding mitochondrial enzymes that generate ATP. Accordingly, silencing Par3 reduced ATP production and concomitantly increased reactive oxygen species. The latter was required for the enhanced migration observed upon silencing of Par3 as anti-oxidants blocked the enhanced migration. These findings support the notion that Par3 exerts homeostatic redox control, which could limit the tumor cell-derived pool of oxygen radicals, and thereby the tumorigenicity of GBM.