Youngsoo Kim

Galactokinase 1 (GALK1) is a metabolic kinase that phosphorylates galactose. Mutations in GALK1 cause type II galactosemia, which manifests as cataracts and extra‐ocular symptoms. The mechanisms underlying these symptoms are not fully understood. In this study, we explored a novel function of GALK1 beyond galactose phosphorylation. GALK1 is ubiquitously expressed across human tissues, regardless of developmental stage. GALK1 phosphorylates TIMM13 at the Y73 residue. The phosphorylated Y73 stabilizes TIMM13 by electrostatically interacting with two cationic residues, thereby enhancing its affinity for Zn ^{2 +} . This structural change ensures the mitochondrial translocation of TIMM13 in the correct conformation. Disruption of Y73 phosphorylation impairs mitochondrial bioenergetics and dissipates the mitochondrial membrane potential. Furthermore, galactose competitively inhibits GALK1‐mediated phosphorylation, suggesting that mitochondrial activity is modulated by carbohydrate availability. Galactosemia‐associated GALK1 mutations showed compromised activity in TIMM13 phosphorylation, subsequently repressing mitochondrial respiration. Collectively, the GALK1‐TIMM13 axis appears to provide a potential link between galactose metabolism and mitochondrial respiration.

Background: Blood plasma proteomics is a promising approach for biomarker discovery, but the broad dynamic range of plasma proteins limits the detection of low-abundance proteins. Depletion and enrichment platforms have been developed to address this challenge; however, most previous evaluations have relied on next-generation mass spectrometry instruments. Platform behavior therefore needs to be evaluated in more accessible liquid chromatography-mass spectrometry instrumentation. Methods: Seven plasma preparation platforms were evaluated using accessible LC-MS instrumentation and compared with recent next-generation mass spectrometry benchmarks. A commercial pooled plasma sample was processed using neat plasma, Multiple Affinity Removal System Human 14, perchloric acid precipitation with neutralization, ENRICH-iST, Mag-Net, Proteonano™, and Proteograph XT. Samples were analyzed by data-independent acquisition mode. Results: Depletion and enrichment platforms increased proteome coverage compared with neat plasma, which identified an average of 777 proteins. The depletion platforms identified an average of 1,278–1,468 proteins, whereas the enrichment platforms identified 1,891–6,060 proteins. Proteograph XT provided the greatest proteome coverage, with an average of 6,060 identified proteins, and showed the lowest missing value rate of 1.9%. However, greater proteome coverage did not always correlate with better quantitative precision. Platform choice significantly affected abundance profiles and clinically relevant protein coverage. These platform-specific differences reproduced recent next-generation mass spectrometry results. Conclusions: Findings in this study demonstrate that more accessible liquid chromatography-mass spectrometry setups can effectively capture key differences among plasma preparation platforms. This study supports the broader approach of plasma proteomics in settings where next-generation instrumentation is not routinely available.

Rhee SJ, et al. J Korean Med Sci. 2025 Jan;40(18):e66. https://doi.org/10.3346/jkms.2025.40.e66

The amyloid cascade hypothesis suggests that amyloid beta (Aβ) contributes to initiating subsequent tau pathology in Alzheimer’s disease (AD). However, the underlying mechanisms through which Aβ contributes to tau uptake and propagation remain poorly understood. Here, we show that preexisting amyloid pathology accelerates the uptake of extracellular tau into neurons. Using quantitative proteomic analysis of endocytic vesicles, we reveal that Aβ induces the internalization of fibroblast growth factor receptor 3 (FGFR3). Extracellular tau binds to the extracellular domain of FGFR3 and is internalized by the FGFR3 ligand, fibroblast growth factor 2 (FGF2). Aβ accelerates FGF2 secretion from neurons, thereby inducing the internalization of tau-attached FGFR3. Knockdown of FGFR3 in the hippocampus reduces tau aggregation by decreasing tau uptake and improving memory function in AD model mice. These data suggest FGFR3 in neurons as a novel tau receptor and a key mediator of Aβ-induced tau uptake in AD.

Psychiatric evaluation relies on subjective symptoms and behavioral observation, which sometimes leads to misdiagnosis. Despite previous efforts to utilize plasma proteins as objective markers, the depletion method is time-consuming. Therefore, this study aimed to enhance previous quantification methods and construct objective discriminative models for major psychiatric disorders using nondepleted plasma. Multiple reaction monitoring-mass spectrometry (MRM-MS) assays for quantifying 453 peptides in nondepleted plasma from 132 individuals [35 major depressive disorder (MDD), 47 bipolar disorder (BD), 23 schizophrenia (SCZ) patients, and 27 healthy controls (HC)] were developed. Pairwise discriminative models for MDD, BD, and SCZ, and a discriminative model between patients and HC were constructed by machine learning approaches. In addition, the proteins from nondepleted plasma-based discriminative models were compared with previously developed depleted plasma-based discriminative models. Discriminative models for MDD versus BD, BD versus SCZ, MDD versus SCZ, and patients versus HC were constructed with 11 to 13 proteins and showed reasonable performances (AUROC = 0.890-0.955). Most of the shared proteins between nondepleted and depleted plasma models had consistent directions of expression levels and were associated with neural signaling, inflammatory, and lipid metabolism pathways. These results suggest that multiprotein markers from nondepleted plasma have a potential role in psychiatric evaluation.

In many cases of traumatic brain injury (TBI), conspicuous abnormalities, such as scalp wounds and intracranial hemorrhages, abate over time. However, many unnoticeable symptoms, including cognitive, emotional, and behavioral dysfunction, often last from several weeks to years after trauma, even for mild injuries. Moreover, the cause of such persistence of symptoms has not been examined extensively. Recent studies have implicated the dysregulation of the molecular system in the injured brain, necessitating an in-depth analysis of the proteome and signaling pathways that mediate the consequences of TBI. Thus, in this study, the brain proteomes of two TBI models were examined by quantitative proteomics during the recovery period to determine the molecular mechanisms of TBI. Our results show that the proteomes in both TBI models undergo distinct changes. A bioinformatics analysis demonstrated robust activation and inhibition of signaling pathways and core proteins that mediate biological processes after brain injury. These findings can help determine the molecular mechanisms that underlie the persistent effects of TBI and identify novel targets for drug interventions.

Some individuals with mild traumatic brain injury (mTBI), also known as concussion, have neuropsychiatric and physical problems that last longer than a few months. Symptoms following mTBI are not only impacted by the kind and severity of the injury but also by the post-injury experience and the individual's responses to it, making the persistence of mTBI particularly difficult to predict. We aimed to identify prognostic blood-based protein biomarkers predicting 6-month outcomes, in light of the clinical course after the injury, in a longitudinal mTBI cohort (N = 42). Among 420 target proteins quantified by multiple-reaction monitoring-mass spectrometry assays of blood samples, 31, 43, and 15 proteins were significantly associated with the poor recovery of neuropsychological symptoms at < 72 h, 1 week, and 1 month after the injury, respectively. Sequential associations among clinical assessments (depressive symptoms and cognitive function) affecting the 6-month outcomes were evaluated. Then, candidate biomarker proteins indirectly affecting the outcome via neuropsychological symptoms were identified. Using the identified proteins, prognostic models that can predict the 6-month outcome of mTBI were developed. These protein biomarkers established in the context of the clinical course of mTBI may have potential for clinical application.

The conventional differentiation of affective disorders into major depressive disorder (MDD) and bipolar disorder (BD) has insufficient biological evidence. Utilizing multiple proteins quantified in plasma may provide critical insight into these limitations. In this study, the plasma proteomes of 299 patients with MDD or BD (aged 19–65 years old) were quantified using multiple reaction monitoring. Based on 420 protein expression levels, a weighted correlation network analysis was performed. Significant clinical traits with protein modules were determined using correlation analysis. Top hub proteins were determined using intermodular connectivity, and significant functional pathways were identified. Weighted correlation network analysis revealed six protein modules. The eigenprotein of a protein module with 68 proteins, including complement components as hub proteins, was associated with the total Childhood Trauma Questionnaire score (r = −0.15, p = 0.009). Another eigenprotein of a protein module of 100 proteins, including apolipoproteins as hub proteins, was associated with the overeating item of the Symptom Checklist-90-Revised (r = 0.16, p = 0.006). Functional analysis revealed immune responses and lipid metabolism as significant pathways for each module, respectively. No significant protein module was associated with the differentiation between MDD and BD. In conclusion, childhood trauma and overeating symptoms were significantly associated with plasma protein networks and should be considered important endophenotypes in affective disorders.