Leo Dahl

The microprotein p11 ( S100A10 ) is a ubiquitously expressed molecular scaffold that is known to be required for behavioral responses to certain antidepressants, presumably through its effect on G protein–coupled receptor (GPCR)–mediated signaling. Here, we demonstrate that p11 recruitment to GPCRs is promoted by an active receptor conformation. Furthermore, by mapping the GPCR-p11 interactome using a multiplexed suspension bead array (SBA) of 211 receptors, we identified more than two dozen high-confidence physical interactors across diverse GPCR signaling families. We define the functional significance of these interactions by focusing on a novel SBA screening hit, the protease-activated receptor 2 (PAR2). Transcriptomic fingerprinting and signaling assays in p11-knockout cells reveal that p11 acts as an amplifier of endogenous PAR2 signaling. PAR2 and p11 are specifically coexpressed in vivo in a subset of sensory neurons, and p11-deficient mice exhibit a blunted PAR2-mediated inflammatory response. Our results establish p11 as a widespread, activity-dependent modulator of GPCR-mediated signaling outcomes across diverse physiological processes.

Population-based studies of circulating blood proteins have provided profound insights into human biology. However, short-lived changes often remained undetected. To address this, we performed a comprehensive longitudinal dried blood spot (DBS) self-sampling study in 808 young adults of the BAMSE cohort during 2020-2022. We profiled serological, autoimmune, and proteomic phenotypes in relation to SARS-CoV-2 exposures (infection, vaccination), physiological traits, genetic variation, and blood counts. Data-driven seroclustering revealed dynamic immune response to both exposures, while analysis of anti-interferon autoantibodies (AAbs) uncovered associations of pre-existing stable AAbs with prolonged COVID-19 symptoms. Genome-wide mapping determined 664 pQTLs, with cis-pQTLs associated showing increased longitudinal stability. We also identified relationships between blood cell counts and DBS proteins beyond the hematocrit effects. Paired pre- and post-exposure highlighted transient alterations for infection (e.g. LAP3) and vaccinations (e.g. TIMP3). Multi-molecular phenotyping in self-sampling can capture dynamic immune trajectories, informing precision medicine efforts with clinically valuable insights on short-term variability in health phenotypes.

The recent COVID-19 pandemic has posed major health challenges. To expand our molecular understanding beyond those seeking medical care, we conducted a cross-sectional survey targeting random residents from Sweden’s two largest cities. Two thousand participants were invited during 2021 to self-sample dried blood spots (DBS) and provide health information. DBS samples were analysed for multiple anti-SARS-CoV-2 antibodies (Abs), auto-reactive antibodies (AAbs) against 23 interferons (IFNs), and for 502 circulating immune-related proteins. Data-driven methodologies characterised the DBS phenotypes in response to infections and vaccination. We received DBS samples from 437 (22%) volunteers aged 18-69, 60% females, and 50% per city. Multi-analyte serology distinguished self-reported infections (26%) and vaccination (40%), revealing a time-dependent discrepancy between reported and measured immunity. Anti-IFN Abs were detected in 21% of the donors and more frequent for type 1 IFNs alongside a natural infection. Integrating proteomics with antibody data provided additional insights into processes of cell-mediated immunity. Proteomics-centric analysis identified 24% of the participants to deviate in their phenotypes due to infection, immunity, respiratory distress, and age-related traits. Multi-molecular analysis of layperson samples uncovered heterogeneity and diversity of immunity and health phenotypes, complementing clinical investigations.

Receptor activity–modifying proteins (RAMPs) form complexes with G protein–coupled receptors (GPCRs) and may regulate their cellular trafficking and pharmacology. RAMP interactions have been identified for about 50 GPCRs, but only a few GPCR-RAMP complexes have been studied in detail. To elucidate a comprehensive GPCR-RAMP interactome, we created a library of 215 dual epitope-tagged (DuET) GPCRs representing all GPCR subfamilies and coexpressed each GPCR with each of the three RAMPs. Screening the GPCR-RAMP pairs with customized multiplexed suspension bead array (SBA) immunoassays, we identified 122 GPCRs that showed strong evidence for interaction with at least one RAMP. We screened for interactions in three cell lines and found 23 endogenously expressed GPCRs that formed complexes with RAMPs. Mapping the GPCR-RAMP interactome expands the current system-wide functional characterization of RAMP-interacting GPCRs to inform the design of selective therapeutics targeting GPCR-RAMP complexes.

Background: Self-sampling of dried blood spots (DBS) offers new routes to gather valuable health-related information from the general population. Yet, the utility of using deep proteome profiling from home-sampled DBS to obtain clinically relevant insights about SARS-CoV-2 infections remains largely unexplored.Methods: Our study involved 228 individuals from the general Swedish population who used a volumetric DBS sampling device and completed questionnaires at home during spring 2020 and summer 2021. Using multi-analyte COVID-19 serology, we stratified the donors by their response phenotypes, divided them into three study sets, and analyzed 276 proteins by proximity extension assays (PEA). After normalizing the data to account for variances in layman-collected samples, we investigated the association of DBS proteomes with serology and self-reported information.Results: Our three studies display highly consistent variance of protein levels and share associations of proteins with sex (e.g., MMP3) and age (e.g., GDF-15). Studying seropositive (IgG⁺) and seronegative (IgG^-) donors from the first pandemic wave reveals a network of proteins reflecting immunity, inflammation, coagulation, and stress response. A comparison of the early-infection phase (IgM⁺IgG^-) with the post-infection phase (IgM^-IgG⁺) indicates several proteins from the respiratory system. In DBS from the later pandemic wave, we find that levels of a virus receptor on B-cells differ between seropositive (IgG⁺) and seronegative (IgG^-) donors.Conclusions: Proteome analysis of volumetric self-sampled DBS facilitates precise analysis of clinically relevant proteins, including those secreted into the circulation or found on blood cells, augmenting previous COVID-19 reports with clinical blood collections. Our population surveys support the usefulness of DBS, underscoring the role of timing the sample collection to complement clinical and precision health monitoring initiatives.

Objective: Current breast cancer risk prediction scores and algorithms can potentially be further improved by including molecular markers. To this end, we studied the association of circulating plasma proteins using Proximity Extension Assay (PEA) with incident breast cancer risk. Subjects: In this study, we included 1577 women participating in the prospective KARMA mammographic screening cohort. Results: In a targeted panel of 164 proteins, we found 8 candidates nominally significantly associated with short-term breast cancer risk (P < 0.05). Similarly, in an exploratory panel consisting of 2204 proteins, 115 were found nominally significantly associated (P < 0.05). However, none of the identified protein levels remained significant after adjustment for multiple testing. This lack of statistically significant findings was not due to limited power, but attributable to the small effect sizes observed even for nominally significant proteins. Similarly, adding plasma protein levels to established risk factors did not improve breast cancer risk prediction accuracy. Conclusions: Our results indicate that the levels of the studied plasma proteins captured by the PEA method are unlikely to offer additional benefits for risk prediction of short-term overall breast cancer risk but could provide interesting insights into the biological basis of breast cancer in the future.

Biomarkers for early detection of breast cancer may complement population screening approaches to enable earlier and more precise treatment. The blood proteome is an important source for biomarker discovery but so far, few proteins have been identified with breast cancer risk. Here, we measure 2929 unique proteins in plasma from 598 women selected from the Karolinska Mammography Project to explore the association between protein levels, clinical characteristics, and gene variants, and to identify proteins with a causal role in breast cancer. We present 812 cis-acting protein quantitative trait loci for 737 proteins which are used as instruments in Mendelian randomisation analyses of breast cancer risk. Of those, we present five proteins (CD160, DNPH1, LAYN, LRRC37A2 and TLR1) that show a potential causal role in breast cancer risk with confirmatory results in independent cohorts. Our study suggests that these proteins should be further explored as biomarkers and potential drug targets in breast cancer.

Receptor activity-modifying proteins (RAMPs) can form complexes with G protein-coupled receptors (GPCRs) and regulate their cellular trafficking and pharmacology. RAMP interactions have been identified for about 50 GPCRs, but only a few GPCR-RAMP complexes have been studied in detail. To elucidate a complete interactome between GPCRs and the three RAMPs, we developed a customized library of 215 Dual Epitope-Tagged (DuET) GPCRs representing all GPCR subfamilies. Using a multiplexed suspension bead array (SBA) assay, we identified 122 GPCRs that showed strong evidence for interaction with at least one RAMP. We screened for native interactions in three cell lines and found 23 GPCRs that formed complexes with RAMPs. Mapping the GPCR-RAMP interactome expands the current system-wide functional characterization of RAMP-interacting GPCRs to inform the design of selective GPCR-targeted therapeutics. One-Sentence Summary: Novel complexes between G protein-coupled receptors and interacting proteins point to a system-wide regulation of GPCR function.

G protein–coupled receptors (GPCRs) control critical cellular signaling pathways. Therapeutic agents including anti-GPCR antibodies (Abs) are being developed to modulate GPCR function. However, validating the selectivity of anti-GPCR Abs is challenging because of sequence similarities among individual receptors within GPCR subfamilies. To address this challenge, we developed a multiplexed immunoassay to test >400 anti-GPCR Abs from the Human Protein Atlas targeting a customized library of 215 expressed and solubilized GPCRs representing all GPCR subfamilies. We found that ~61% of Abs tested were selective for their intended target, ~11% bound off-target, and ~28% did not bind to any GPCR. Antigens of on-target Abs were, on average, significantly longer, more disordered, and less likely to be buried in the interior of the GPCR protein than the other Abs. These results provide important insights into the immunogenicity of GPCR epitopes and form a basis for designing therapeutic Abs and for detecting pathological auto-Abs against GPCRs.

The blood proteome reflects homeostatic and dynamic cellular processes across human organs. However, few blood proteomics studies of sufficient depth and size have been reported in breast cancer. To comprehensively identify circulating proteins with a causal role in breast cancer we measured 2,929 unique proteins in plasma from 598 women selected from the Karolinska Mammography Project and explored associations between proteins levels, clinical characteristics, and gene variants. The analysis revealed 812 cis-acting protein quantitative trait loci (pQTL), which were used as instruments in Mendelian randomisation (MR) analysis of breast cancer. Five proteins (P < 1.7x10-5, Bonferroni-corrected) with a potential causal role in breast cancer risk were revealed (CD160, DNPH1, LAYN, LRRC37A2 and TLR1). Confirming the MR findings in independent cohorts (FinnGen R9 and the UK Biobank), our study suggests that these proteins should be further explored as potential drug targets in breast cancer.