Comparative Proteomic Analysis Reveals the Effect of Selenoprotein W Deficiency on Oligodendrogenesis in Fear Memory

Selenium metabolism and selenoproteins function in brain and encephalopathy

Selenium (Se) is an essential trace element of the utmost importance to human health. Its deficiency induces various disorders. Se species can be absorbed by organisms and metabolized to hydrogen selenide for the biosynthesis of selenoproteins, selenonucleic acids, or selenosugars. Se in mammals mainly acts as selenoproteins to exert their biological functions. The brain ranks highest in the specific hierarchy of organs to maintain the level of Se and the expression of selenoproteins under the circumstances of Se deficiency. Dyshomeostasis of Se and dysregulation of selenoproteins result in encephalopathy such as Alzheimer's disease, Parkinson's disease, depression, amyotrophic lateral sclerosis, and multiple sclerosis. This review provides a summary and discussion of Se metabolism, selenoprotein function, and their roles in modulating brain diseases based on the most currently published literature. It focuses on how Se is utilized and transported to the brain, how selenoproteins are biosynthesized and function physiologically in the brain, and how selenoproteins are involved in neurodegenerative diseases. At the end of this review, the perspectives and problems are outlined regarding Se and selenoproteins in the regulation of encephalopathy.

Selenoprotein H mediates low selenium-related cognitive decline through impaired oligodendrocyte myelination with disrupted hippocampal lipid metabolism in female mice

Low selenium levels are closely associated with reduced cognitive performance and lipid dysregulation, yet the mechanism of action remains unclear. The physiological function of selenium is primarily mediated by selenoproteins. Selenoprotein H (SELENOH), as one of the selenium-containing proteins, has an unelucidated role in regulating cognitive status and lipid metabolism. In this study, we established a Selenoh gene knockout (HKO) mouse model to investigate whether Selenoh mediates the impact of selenium on cognitive function. We found that HKO mice showed a significant decline in cognition compared with the wild-type (HWT) littermates, and were not affected by deficient or excessive selenium, while no differences in anxiety and depression behavior were observed. HKO mice showed reduced myelin basic protein expression in hippocampal oligodendrocytes, with decreased glycolipid levels and increased phospholipid and sphingolipid levels in the hippocampus. Furthermore, the high-fat diet (HFD) exerted no effect on cognition and limited impact on the gene profile in the hippocampus of HKO mice. Compared with those of HWT mice, the myelination pathways in the hippocampus of HKO mice were downregulated as revealed by RNA-seq, which was further confirmed by the reduced expression levels of myelin-related proteins. Finally, HKO increased the expression of hippocampal fatty acid transporter (FATP) 4, and HFD increased the FATP4 expression in HWT mice but not in HKO mice. In summary, our study demonstrated that HKO induced cognitive decline by impairing myelination in oligodendrocytes with disrupted hippocampal lipid metabolism, which provided a novel viewpoint on the selenoprotein-mediated neurodegenerative diseases of selenium.

Selenoprotein W modulates tau homeostasis in an Alzheimer's disease mouse model

Lower selenium levels are observed in Alzheimer's disease (AD) brains, while supplementation shows multiple benefits. Selenoprotein W (SELENOW) is sensitive to selenium changes and binds to tau, reducing tau accumulation. However, whether restoration of SELENOW has any protective effect in AD models and its underlying mechanism remain unknown. Here, we confirm the association between SELENOW downregulation and tau pathology, revealing SELENOW's role in promoting tau degradation through the ubiquitin‒proteasome system. SELENOW competes with Hsp70 to interact with tau, promoting its ubiquitination and inhibiting tau acetylation at K281. SELENOW deficiency leads to synaptic defects, tau dysregulation and impaired long-term potentiation, resulting in memory deficits in mice. Conversely, SELENOW overexpression in the triple transgenic AD mice ameliorates memory impairment and tau-related pathologies, featuring decreased 4-repeat tau isoform, phosphorylation at Ser396 and Ser404, neurofibrillary tangles and neuroinflammation. Thus, SELENOW contributes to the regulation of tau homeostasis and synaptic maintenance, implicating its potential role in AD.

Knocking out Selenium Binding Protein 1 Induces Depressive-Like Behavior in Mice

Selenium binding protein 1 (SELENBP1) is involved in neurologic disorders, such as multiple sclerosis, spinal cord injury, Parkinson's disease, epilepsy, and schizophrenia. However, the role of SELENBP1 in the neurogenesis of depression, which is a neurologic disorder, and the underlying mechanisms of oxidative stress and inflammation in depression remain unknown. In this study, we evaluated the changes in the expression levels of SELENBP1 in the hippocampus of a mouse model of depression and in the serum of human patients with depression using the Gene Expression Omnibus database. These changes were validated using blood samples from human patients with depression and mouse models with chronic unpredictable mild stress (CUMS)-induced depressive-like behavior. We also investigated the effects of SELENBP1 knockout (KO) on inflammation, oxidative stress, and hippocampal neurogenesis in mice with CUMS-induced depression. Our results revealed that SELENBP1 levels was decreased in the blood of human patients with depression and in the hippocampus of mice with CUMS-induced depression. SELENBP1 KO increased CUMS-induced depressive behavior in mice and caused dysregulation of inflammatory cytokines and oxidative stress. This led to a decrease in the numbers of doublecortin- and Ki67-positive cells, which might aggravate CUMS-induced depressive symptoms. These findings suggest that SELENBP1 might be involved in the regulation of neurogenesis in mice with depression and could be served as a potential target for diagnosing and treating depression.

Biomarker and transcriptomics profiles of serum selenium concentrations in patients with heart failure are associated with immunoregulatory processes

BACKGROUND

Low selenium concentrations are associated with worse outcomes in heart failure (HF). However, the underlying pathophysiologic mechanisms remain incompletely understood. Therefore, we aimed to contrast serum selenium concentrations to blood biomarker and transcriptomic profiles in patients with HF.

METHODS

Circulating biomarkers, whole blood transcriptomics and serum selenium measurements in a cohort of 2328 patients with HF were utilized. Penalized linear regression and gene expression analysis were used to assess biomarker and transcriptomics profiles, respectively. As a proof-of-principle, potential causal effects of selenium on excreted cytokines concentrations were investigated using human peripheral blood mononuclear cells (PBMCs).

RESULTS

Mean selenium levels were 60.6 μg/L in Q1 and 122.0 μg/L in Q4. From 356 biomarkers and 20 clinical features, the penalized linear regression model yielded 44 variables with <5 % marginal false discovery rate as predictors of serum selenium. Biomarkers associated positively with selenium concentrations included: epidermal growth factor receptor (EGFR), IFN-gamma-R1, CD4, GDF15, and IL10. Biomarkers associated negatively with selenium concentrations included: PCSK9, TNFSF13, FGF21 and PAI. Additionally, 148 RNA transcripts were found differentially expressed between high and low selenium status (Padj.<0.05; log-fold-change<|0.25|). Enrichment analyses of the selected biomarkers and RNA transcripts identified similar enriched processes, including regulation processes of leukocyte differentiation and activation, as well as cytokines production. The mRNA expression of two selenoproteins (MSRB1 and GPX4) were strongly correlated with serum selenium, while GPX4, SELENOK, and SELENOS were associated with prognosis. In the in-vitro setting, PBMCs supplemented with selenium showed significantly lower abundance of several (pro-)inflammatory cytokines.

CONCLUSION

These data suggest that immunoregulation is an important mechanism through which selenium might have beneficial roles in HF. The beneficial effects of higher serum selenium concentrations are likely because of global immunomodulatory effects on the abundance of cytokines. MSRB1 and GPX4 are potential modulators of and should be pursued in future research.

Epigenome-Wide Association Study in Peripheral Tissues Highlights DNA Methylation Profiles Associated with Episodic Memory Performance in Humans

The decline in episodic memory (EM) performance is a hallmark of cognitive aging and an early clinical sign in Alzheimer’s disease (AD). In this study, we conducted an epigenome-wide association study (EWAS) using DNA methylation (DNAm) profiles from buccal and blood samples for cross-sectional (n = 1019) and longitudinal changes in EM performance (n = 626; average follow-up time 5.4 years) collected under the auspices of the Lifebrain consortium project. The mean age of participants with cross-sectional data was 69 ± 11 years (30−90 years), with 50% being females. We identified 21 loci showing suggestive evidence of association (p < 1 × 10−5) with either or both EM phenotypes. Among these were SNCA, SEPW1 (both cross-sectional EM), ITPK1 (longitudinal EM), and APBA2 (both EM traits), which have been linked to AD or Parkinson’s disease (PD) in previous work. While the EM phenotypes were nominally significantly (p < 0.05) associated with poly-epigenetic scores (PESs) using EWASs on general cognitive function, none remained significant after correction for multiple testing. Likewise, estimating the degree of “epigenetic age acceleration” did not reveal significant associations with either of the two tested EM phenotypes. In summary, our study highlights several interesting candidate loci in which differential DNAm patterns in peripheral tissue are associated with EM performance in humans.