Abstract Glycolysis is critical for NLRP3 inflammasome activation, yet the link between lactic acid metabolism and inflammasome signaling remains unclear. Here, we show that stimulation of macrophages with the NLRP3 activators nigericin or ATP induces lactic acid production and efflux via a lactate dehydrogenase–dependent pathway. Accumulation of intracellular lactic acid leads to cytoplasmic acidification, which promotes NLRP3 inflammasome activation. Concurrently, elevated extracellular lactic acid impairs lactate efflux, exacerbating intracellular acidification and amplifying ASC speck formation, caspase-1 activation, and IL-1β secretion. Alkalinization of the extracellular milieu prevents intracellular acidification and abolishes inflammasome activation. Mechanistically, intracellular lactic acidification promoted mitochondrial dysfunction and reactive oxygen species production, and concurrently induced phosphorylation of the stress kinase PKR, which facilitated PKR–NLRP3 interaction and inflammasome assembly through parallel pathways. Independently of inflammasome signaling, lactic acid also directly cleaves pro-IL-1β and pro-IL-18 into mature forms through a mechanism requiring its carboxyl group and mimicking caspase-1 substrate specificity. Mass spectrometry analysis revealed lactic acid–mediated cleavage of pro-IL-1β at Asp116, the canonical caspase-1 site. In a murine model of polymicrobial sepsis induced by cecal ligation and puncture, systemic lactate administration exacerbated inflammation, increased IL-1β levels and neutrophil infiltration, induced hypothermia, and worsened survival. Together, these findings identify intracellular lactic acidification as a metabolic signal that promotes inflammation predominantly through NLRP3 inflammasome activation, while also revealing a potential inflammasome-independent cytokine processing mechanism under conditions of severe metabolic stress.

Polyethylene glycol (PEG)-modified nanocomposites may induce acute hypersensitivity reactions (HSR), including complement activation and hypotension, followed by tachyphylaxis with an unknown mechanism. We tested a hypothesis that complement activation mediated hypotension induced by PEGylated magnetic nanoparticles (PEG-MNP) in a rodent model of acute HSR. Blood flow of renal/cremaster vasculature and aortic arch was measured in anesthetized rats using ultrasonic flowmetry or laser speckle contrast imaging. PEG-MNP (250 or 50 nm) induced a temporary reduction in arterial pressure by approximately 30 mmHg, with significant reduction in renal/cremaster blood flow and cardiac output, followed by tachyphylaxis and thrombocytopenia. PEG-MNP, but not pristine MNP, significantly increased renal vascular resistance (RVR) with a reduction in the calculated cross-sectional area of renal vessels, whereas the vasodilator acetylcholine decreased both blood pressure and RVR before and after administration of PEG-MNP. Complement depletion by cobra venom factor induced a transient reduction in blood flow and prevented PEG-MNP-induced hemodynamic effects. Proteomic analysis identified much higher complement protein ratio in the hard corona of PEG-MNP vs. MNP in plasma from rats; preexposure of the rats to PEG-MNP or MNP in vivo greatly reduced plasma proteins with high affinity for PEG-MNP. In conclusion, complement activation in the protein corona may mediate PEGylated nanocomposite-induced transient microvascular occlusion that entrains the reversible hemodynamic effects in HSR; complement depletion, at least in part, may mediate tachyphylaxis in response to the 2nd dose of PEGylated nanocomposite. The findings may facilitate predicting or preventing acute HSR to PEGylated nanomedicine or vaccines with growing clinical applications.

Background:Sodium-glucose cotransporter 2 (SGLT2) inhibitors reduce cardiovascular and cardiorenal events in people across the spectrum of heart failure. Using proteomics analysis, this study investigated the potential benefits of SGLT2 inhibitors in primary prevention at a protein level in patients without diabetes or heart failure. Methods:This is a sub-study of the EMPA-HEART 2 CardioLink-7 trial, which randomized people without diabetes or clinically overt heart failure but with risk factors for adverse cardiac remodeling to empagliflozin (10 mg/day) or placebo for 6 months. Blood samples were collected during the randomization visit and at the 6-month follow-up visit for proteomics analysis. Our investigation involved two phases of approach: discovery and verification. Results:Samples from individuals assigned to empagliflozin (n = 21) and placebo (n = 22) (median baseline N-terminal pro-B-type natriuretic peptide levels: 33.9 and 78.4 pg/ml, respectively) were analyzed. In the discovery phase, 28 of 1622 proteins fulfilled our threshold for being differentially expressed at 6 months. Ten proteins were verified, including calmodulin-like protein 5, desmoplakin, hornerin, peroxiredoxin-2, macrophage colony-stimulating factor 1 receptor, endosialin, high-temperature requirement serine protease A1, immunoglobulin epsilon heavy chain, proteasome subunit beta type-5, and cerebellin-4. Compared to the placebo group, the expression of these proteins from baseline to 6 months was all significantly decreased in the empagliflozin group. Their functions involved ion channel signaling, fibrosis, oxidative stress, inflammation, apoptosis, immune response, proteolysis, and neuromodulation. Conclusion:Empagliflozin modified multiple biologically relevant pathways in the nondiabetes and non-heart failure setting. These findings should be considered hypothesis-generating and warrant validation in larger, adequately powered studies.

Elevated plasma phenylalanine (PHE) is associated with adverse outcomes in heart failure (HF), but whether PHE is only a marker of systemic severity or can modify ischemic vulnerability remains unclear. We evaluated the prognostic value of the PHE–phenylpyruvate (PPA) axis and examined how PHE affects mitochondrial stress responses after ischemic injury and whether 5-methoxytryptophan (5-MTP) mitigates these effects. Plasma levels of PHE and PPA were analyzed in 191 patients with ischemic HF from the cardiac intensive care unit to assess 90-day mortality. A rat myocardial infarction (MI) model was used to assess PHE-related metabolites in infarct and peri-infarct-enriched left ventricular tissue during chronic post-MI remodeling. HL-1 cardiomyocytes were subjected to oxygen–serum–glucose deprivation (OSGD) with or without PHE and 5-MTP. Cell metabolic activity, ATP levels, mitochondrial respiration, extracellular acidification rate-defined glycolytic function, pyruvate supplementation, dichloroacetate response, cell-death patterns, intracellular PHE-related metabolites, and quantitative proteomics were analyzed. In the clinical cohort, elevated PHE was independently associated with 90-day mortality after adjustment for estimated glomerular filtration rate, C-reactive protein, and albumin, supporting PHE as a short-term prognostic and candidate risk-stratification biomarker. Post-MI myocardium showed tissue-level accumulation of PHE-related metabolites. In HL-1 cells, 20 mM PHE exacerbated OSGD-induced mitochondrial dysfunction, ATP reduction, glycolytic reserve exhaustion, and mixed cell-death signaling. Pyruvate failed to rescue ATP, while dichloroacetate partially restored ATP, suggesting pyruvate dehydrogenase-sensitive vulnerability. Proteomics revealed pathway-level suppression of oxidative phosphorylation; 5-MTP partially shifted mitochondrial and metabolic signatures toward recovery without uniformly lowering intracellular PHE. PHE is a short-term prognostic marker and, under high-dose experimental stress, a potential modifier of ischemic bioenergetic vulnerability. 5-MTP appears to act mainly through downstream mitochondrial stress resilience. These findings support PHE-related metabolic stress as a clinically relevant risk signal and experimental modifier of ischemic myocardial vulnerability, while further validation is required before PHE-guided therapeutic strategies can be proposed. Not applicable.

Metabolic enzyme compartmentalization is increasingly recognized as a regulatory strategy, yet its functional relevance in cancer remains incompletely understood. Here, we demonstrate that polymerization of cytidine triphosphate synthase (CTPS) into filaments is essential for tumor growth in vivo and for three-dimensional proliferation. Glutamine deprivation, a hallmark of the nutrient-poor core of solid tumors, promotes CTPS filament assembly, suppressing enzymatic activity and limiting phospholipid synthesis and autophagic flux. Using proximity labeling, we identify the chaperone HSPB8 as a filament-associated regulator. HSPB8 antagonizes CTPS filament assembly by facilitating clearance of misfolded proteins, thereby restoring CTPS activity. Filament disassembly enhances CTP production, elevates autophagy-related phosphatidylinositol and phosphatidylethanolamine synthesis, and accelerates autophagic flux. Disruption of CTPS filament formation impairs xenograft tumor growth. Consistently, analysis of patient datasets reveals that high CTPS and low HSPB8 expression correlate with poor survival across multiple cancers. These findings identify CTPS filament dynamics as a metabolic vulnerability in tumors. ### Competing Interest Statement The authors have declared no competing interest. Ministry of Science and Technology, Taiwan, MOST 111-2311-B-182-001, MOST 108-2321-B-182-004-MY3 Linkou Chang Gung Memorial Hospital, CMRPD1K0591-2, CMRPD1M0171

Background: Polyethylene glycol (PEG)-modified nanocomposites may induce acute hypersensitivity reactions (HSR), including complement activation and hypotension, followed by tachyphylaxis with an unknown mechanism. We established a rodent model of HSR, and hypothesized that the formation of protein corona with a composition specific to PEGylated nanoparticles induces an acute and transient microvascular occlusion that entrains the hemodynamic effects. Methods: Hemodynamic parameters of renal and cremaster vasculature were measured in anesthetized rats using ultrasonic flowmetry and laser speckle contrast imaging, respectively. Proteomic analysis on the hard corona of dextran-coated magnetic nanoparticles (MNP) with and without PEGylation was conducted after incubation of the nanoparticles with plasma from rats. Results: PEG-MNP iv. induced a temporary reduction by approximately 30 mmHg in arterial pressure, with significant reduction in renal/cremaster blood flow and cardiac output, followed by tachyphylaxis and thrombocytopenia. PEG-MNP, but not pristine MNP, significantly increased renal vascular resistance with a reduction in the calculated cross-sectional area of renal vessels, suggesting microvascular occlusion. In contrast, the vasodilator acetylcholine decreased both blood pressure and vascular resistance before and after administration of PEG-MNP, suggesting an intact endothelium. Complement depletion by cobra venom factor induced a transient reduction in blood flow and prevented PEG-MNP-induced hemodynamic effects, suggesting an important role of complement activation. Proteomic analysis identified much higher complement proteins in the hard corona of PEG-MNP vs. MNP in plasma from rats; preexposure of rats to PEG-MNP or MNP in vivo greatly reduced plasma proteins with high affinity for PEG-MNP. The results suggest that complement depletion may mediate tachyphylaxis in response to the 2nd dose of PEG-MNP. Conclusion: PEGylated nanocomposites-induced complement activation in the protein corona may trigger the hemodynamic effects and subsequent pathophysiological responses in HSR of rats. ### Competing Interest Statement The authors have declared no competing interest.

Oral cavity squamous cell carcinoma (OSCC), a leading subtype of head and neck cancer, exhibits high global incidence and mortality rates. Despite advancements in surgery and radiochemotherapy, approximately one-third of patients experience relapse. To improve current targeted and immunotherapy strategies for recurrent OSCC, we conducted multi-omics analyses on pretreatment OSCC samples (cohorts 1 and 2, n=137) and identified A3A and EGFR, both at the RNA and protein levels, as inversely expressed markers for patient stratification and response prediction. Survival analysis demonstrated that elevated A3A or PD-L1 expression levels correlated to improved responses to anti-PD-1 therapy in patients (cohort 3a, n=50, IHC). In contrast, high RRAS expression (cohort 4, n=252, qRT-PCR) was significantly associated with OSCC recurrence. Cell-based experiments revealed that RRAS was involved in radiotherapy and cisplatin resistance through the EGFR/RRAS/AKT/ERK signaling pathway. In OSCC patient-derived xenograft (PDX) mouse models, treatments with cisplatin and cetuximab (anti-EGFR) effectively reduced tumor size in EGFR-high-derived (#34) but not A3A-high-derived (#22) PDX tumors. Our study demonstrated that A3A-high tumors were immune-hot and responsive to anti-PD-1 therapy, whereas EGFR-high tumors exhibited chr.7p11.2 gains and DNA repair alterations. Additionally, RRAS-high tumors were associated with OSCC recurrence via AKT and ERK phosphorylation and demonstrate improved clinical outcomes with cetuximab therapy (cohort 3b, n=49, IHC). This study emphasizes the significance of A3A and EGFR expression levels in OSCC patient stratification and precision therapy, suggesting the use of anti-PD-1 or anti-EGFR treatments, respectively based on these biomarkers. Furthermore, RRAS emerges as a novel prognostic marker for local recurrence.

Clostridium innocuum, a member of the human gut microbiome with intrinsic resistance to vancomycin, has been increasingly associated with inflammatory bowel diseases (IBD). Clinical observations indicate that co-infection with Clostridioides difficile and C. innocuum could lead to poorer clinical remission in ulcerative colitis; however, the pathogenic mechanism of C. innocuum remains unclear. Here, we investigated the effects of vancomycin and C. difficile on C. innocuum secretomes and the functions of the modified secretomes on C. innocuum pathogenicity. The results indicated that, compared to co-culturing with C. difficile, vancomycin was more effective in stimulating the secretion of proteins without a signal peptide, whereas C. difficile was better at promoting the secretion of classical secretory proteins. Based on these results, we further analyzed the effects of three abundant classical secretory proteins on C. innocuum virulence utilizing recombinant proteins. The results demonstrated that the NlpC/P60-containing protein (NlpC/P60) can enhance C. innocuum biofilm formation and adherence to HT-29 cells. Additionally, NlpC/P60, D-Ala-D-Ala carboxypeptidase, and a polysaccharide deacetylase were able to stimulate IL-8 production of HT-29 cells and TNF-α production of Raw264.7 macrophages. Additionally, recombinant NlpC/P60 and polysaccharide deacetylase exhibited cytotoxicity on Raw264.7 cells at 48 h. As the production of IL-8 and TNF-α is closely associated with IBD development, it is suggested that C. innocuum secretomes, under the influence of vancomycin or C. difficile, could contribute to IBD progression by enhancing inflammation and host-pathogen interactions.

Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors have transformed lung adenocarcinoma (LUAD) treatment in EGFR-mutant (MT) patients, but strategies targeting wild-type (WT) EGFR tumors remain necessary. This study analyzed a diverse LUAD patient cohort with EGFR mutation statuses and wild-type profiles for ALK and KRAS to identify stage-specific biomarkers. Using quantitative proteomics and multiomics, we discovered 21 dysregulated proteins in early-stage EGFR-WT LUAD, identifying myeloid-derived growth factor (MYDGF) as a key candidate biomarker. Elevated MYDGF levels in tissue (n = 117) and serum (n = 196) correlated significantly with cancer stage in EGFR-WT patients but not EGFR-MT cases. Notably, a higher tumor-to-normal MYDGF ratio predicted a favorable prognosis in early-stage EGFR-WT LUAD. Functional studies demonstrated that MYDGF exerts distinct roles in cell viability and migration depending on its cellular localization and the invasive potential of cancer cells. Specifically, secreted MYDGF promoted a protumorigenic phenotype, whereas excess intracellular MYDGF appeared to suppress the oncogenic capacity of aggressive cancer cells. MYDGF knockdown and subsequent proteomic analysis provided further insights into these context-dependent functions. These findings highlight EGFR status- and stage-specific proteomic profiles in LUAD, emphasizing the importance of context-dependent biomarker assessment for personalized treatment strategies.

Background Tissue metabolomics analysis, alongside genomics and proteomics, offers crucial insights into the regulatory mechanisms of tumorigenesis. To enhance metabolite detection sensitivity, chemical isotope labeling (CIL) techniques, such as dansylation, have been developed to improve metabolite separation and ionization in mass spectrometry (MS). However, the dissolution of hydrophobic derivatized metabolites in solvents with high acetonitrile content limits the use of liquid chromatography (LC) systems with small-volume reversed-phase (RP) columns. In this study, we established a nano-LC-MS system with an online dilution design to address this issue, enabling sensitive analysis of oral cancer tissue metabolomes. Results Our nano-LC system features a flow path design with online sample dilution before an RP trap column and backflushing of the trap column before entering the analytical column. Compared to other nano-LC systems, both with and without online dilution designs, our system demonstrates the superiority of the T-connector-based dilution method. Using only 1/20th of the sample required for popular micro-LC systems, our nano-LC detects a larger number of peak pairs with similar recovery rates for both hydrophilic and hydrophobic metabolites, ensuring unbiased results. Thirty-two matched pairs of oral squamous cell carcinoma (OSCC) tissue samples and adjacent noncancerous tissues (ANTs) underwent high-throughput CIL-metabolome analysis using our nano-LC system. Compared to our previous micro-LC methods, the nano-LC-MS system exhibits enhanced detection sensitivity, significantly reducing sample requirements. Significance Our findings highlight the efficacy of our platform for metabolomic analysis with limited sample amounts. The nano-LC system’s ability to analyze samples dissolved in strong eluents suggests potential applications for handling other hydrophobic compounds using RPLC or other separation methods facing similar solvent incompatibility issues. This approach holds promise for identifying novel metabolite biomarkers for oral cancers, advancing our understanding of tumorigenesis, and enhancing clinical applications.

For decades, studies of snake venoms focused on the venom--ome--specific toxins (VSTs). VSTs are dominant soluble proteins believed to contribute to the main venomous effects and emerged into gene clusters for fast adaptation and diversification of snake venoms. However, the conserved minor venom components, such as snake venom phosphodiesterase (svPDE), remain largely unexplored. Here, we focus on svPDE by genomic and transcriptomic analysis across snake clades and demonstrate that soluble svPDE is co--opted from the ancestral membrane--attached ENPP3 (ectonucleotide pyrophosphatase/phosphodiesterase 3) gene by replacing the original 5' exon with the exon encoding a signal peptide. Notably, the exons, promoters, and transcription/ translation starts have been replaced multiple times during snake evolution, suggesting the evolutionary necessity of svPDE. The structural and biochemical analyses also show that svPDE shares the similar functions with ENPP family, suggesting its perturbation to the purinergic signaling and insulin transduction in venomous effects.

Clinical information of patients with breast cancer.

Supplementary materials and methods and supplementary figure legends.

This file contains 7 supplementary figures supporting that Flightless-I blocks p62-mediated recognition of LC3 to impede selective autophagy and promote breast cancer progression.

BackgroundPseudomonas aeruginosa intestinal carriage rates are significantly higher in immunosuppressed individuals and hospitalized patients who therefore have increased risk of infections and antibiotic-associated diarrhea. To combat intestinal dysbiosis and decolonize P. aeruginosa from gastrointestinal tract, we investigated the anti-adherence and gut microbiota modulation properties of marine prebiotic fucoidans.MethodsProteomic analysis of culture supernatant was performed by LC-MS/MS. Using lectin-based enzyme-linked immunosorbent assay, hemagglutinin domain interaction and inhibition with biomolecules were studied. We investigated the role of nutritional grade fucoidans in a mouse model and used 16S ribosomal RNA sequencing to examine fecal microbiota composition.ResultsAnalysis of culture supernatant proteins indicated the secretion of two-partner secretion (TPS) family proteins, including TpsA1/CdiA2 and TpsA2/CdiA1. Lectin like activity at the N-terminal of TpsA due to a conserved hemagglutinin domain (Pfam identifier [ID] PF05860) mediates binding to mucins that carry multiple fucosylated glycans. Fucose-rich sulfated polysaccharides (fucoidans) and sulfated dextrans were found to be potent inhibitors of the recombinant N-terminal hemagglutinin domain of TpsA (TpsA-NT-HAD) binding to mucins. In a mouse model, antibiotic-induced dysbiosis was essential for P. aeruginosa gastrointestinal colonization. After prophylactic oral fucoidans supplementation, a higher proportion (60%) of the mice were decolonized over time and resisted re-colonization, this was associated with remarkable expansion of Bacteroides (post-infection day-3 abundance, 29-50%) and consequential reductions in bloom of Enterobacteriaceae and Enterococcaceae populations. In the non-supplemented group, Parabacteroides mediated recovery from dysbiosis but failed to decolonize P. aeruginosa.ConclusionsSupplementing diet with marine prebiotic fucoidans can mediate earlier recovery from dysbiosis and decolonization of P. aeruginosa from gut by inhibiting secreted virulence factor (TpsA/CdiA) interaction with mucins and promoting the growth of beneficial Bacteroides population. We suggest the prophylactic use of nutritional grade fucoidans to decolonize P. aeruginosa from gastrointestinal tract of at-risk individuals to prevent infection and transmission of colonizing P. aeruginosa.

Enterovirus (EV) 71 caused episodes of outbreaks in China and Southeast Asia during the last few decades. We have previously reported that EV71 induces reactive oxygen species (ROS). However, the underlying mechanism remains elusive. Co-immunoprecipitation-proteomic analysis revealed that enteroviral 2B protein interacted with mitochondrial voltage-dependent anion channel 3 (VDAC3). Knockdown (KD) of VDAC3 expression specifically inhibited enteroviral replication. Single-round viral replication was also inhibited in KD cells, suggesting that VDAC3 plays an essential role in replication. Consistent with this, VDAC3 gene KD significantly reduced the EV71-induced mitochondrial ROS generation. Exogenous 2B expression could induce the mitochondrial ROS generation that was significantly reduced in VDAC3-KD cells or in the Mito-TEMPO-treated cells. Moreover, VDAC3 appears to be necessary for regulation of antioxidant metabolism. VDAC3 gene KD led to the enhancement of such pathways as hypotaurine/taurine synthesis in the infected cells. Taken together, these findings suggest that 2B and VDAC3 interact to enhance mitochondrial ROS generation, which promotes viral replication.

Reports of bite from Protobothrops mucrosquamatus (Pmu) are frequent in Taiwan, and its wide-spread distribution and diverse habitats drove us to investigate its envenoming effects and relevant venom variations. We used reversed-phase high-performance liquid chromatography and mass spectrometry to analyze 163 Pmu venom samples collected from northern and southeastern Taiwan. Twenty-two major protein fractions were separated and analyzed, and their contents were determined semi-quantitatively. The results showed that despite the trivial differences in the protein family, there is an existing variation in acidic phospholipases A2s, serine proteinases, metalloproteinases, C-type lectin-like proteins, and other less abundant components in the Pmu venoms. Moreover, clinical manifestations of 209 Pmu envenomed patients hospitalized in northern or southeastern Taiwan revealed significant differences in local symptoms, such as ecchymosis and blistering. The mechanism of these local effects and possibly relevant venom components were examined. Further analysis showed that certain venom components with inter-population variation might work alone or synergistically with others to aggravate the local effects. Therefore, our findings of the venom variation may help one to improve antivenom production and better understand and manage Pmu bites.

Pseudogenes (genes disrupted by frameshift or in-frame stop codons) are ubiquitously present in the bacterial genome and considered as nonfunctional fossil. Here, we used RNA-seq and mass-spectrometry technologies to measure the transcriptomes and proteomes of Salmonella enterica serovars Paratyphi A and Typhi. All pseudogenes' mRNA sequences remained disrupted, and were present at comparable levels to their intact homologs. At the protein level, however, 101 out of 161 pseudogenes suggested successful translation, with their low expression regardless of growth conditions, genetic background and pseudogenization causes. The majority of frameshifting detected was compensatory for -1 frameshift mutations. Readthrough of in-frame stop codons primarily involved UAG; and cytosine was the most frequent base adjacent to the codon. Using a fluorescence reporter system, fifteen pseudogenes were confirmed to express successfully in vivo in Escherichia coli. Expression of the intact copy of the fifteen pseudogenes in S. Typhi affected bacterial pathogenesis as revealed in human macrophage and epithelial cell infection models. The above findings suggest the need to revisit the nonstandard translation mechanism as well as the biological role of pseudogenes in the bacterial genome.

Metabolomics, which serves as a readout of biological processes and diseases monitoring, is an informative research area for disease biomarker discovery and systems biology studies. In particular, reversed-phase liquid chromatography-mass spectrometry (RPLC-MS) has become a powerful and popular tool for metabolomics analysis, enabling the detection of most metabolites. Very polar and ionic metabolites, however, are less easily detected because of their poor retention in RP columns. Dansylation of metabolites simplifies the sub-metabolome analysis by reducing its complexity and increasing both hydrophobicity and ionization ability. However, the various metabolite concentrations in clinical samples have a wide dynamic range with highly individual variation in total metabolite amount, such as in saliva. The bicarbonate buffer typically used in dansylation labeling reactions induces solvent stratification, resulting in poor reproducibility, selective sample loss and an increase in false-determined metabolite peaks. In this study, we optimized the dansylation protocol for samples with wide concentration range of metabolites, utilizing diisopropylethylamine (DIPEA) or tri-ethylamine (TEA) in place of bicarbonate buffer, and presented the results of a systemic investigation of the influences of individual processes involved on the overall performance of the protocol. In addition to achieving high reproducibility, substitution of DIPEA or TEA buffer resulted in similar labeling efficiency of most metabolites and more efficient labeling of some metabolites with a higher pKa. With this improvement, compounds that are only present in samples in trace amounts can be detected, and more comprehensive metabolomics profiles can be acquired for biomarker discovery or pathway analysis, making it possible to analyze clinical samples with limited amounts of metabolites.

Synaptic dopamine (DA) concentrations are largely determined by the activities of presynaptic D2 and D3 autoreceptors (D2R and D3R) and DA transporter (DAT). Furthermore, the activity of DAT is regulated by phosphorylation events and protein interactions that affect its surface expression. Because DA autoreceptors and DAT coordinately maintain synaptic DA homeostasis, we hypothesized that D3R might crosstalk with DAT to fine-tune synaptic DA concentrations. To test this hypothesis, we established [3H]DA uptake and DAT surface expression assays in hD3/rDAT-double-transfected HEK-293 cells or limbic forebrain synaptosomal preparations. Ropinirole, a preferential D3R agonist, reduced [3H]DA uptake in HEK-hD3/rDAT cells in a dose-dependent manner, an effect which could be blocked by the D2R/D3R antagonist, raclopride. Furthermore, ropinirole also reduced DAT surface expression in limbic forebrain synaptosomes, and this effect could be blocked by raclopride or the internalization inhibitor, concanavalin A. To identify potential mediators of this apparent D3R-DAT crosstalk, DAT-associated proteins were co-immunoprecipitated from limbic forebrain synaptosomes after D3R activation and identified by MALDI-TOF. From this analysis, the Hsc70 chaperone was identified as a DAT-associated protein. Interestingly, ropinirole induced the association of Hsc70/Hsp70 with DAT, and the Hsc70/Hsp70 inhibitor, apoptozole, prevented the ropinirole-induced reduction of DAT surface expression. Together, these results suggest that D3R negatively regulates DAT activity by promoting the association of DAT and Hsc70/Hsp70.