Dietary selenium deficiency and supplementation differentially modulate the expression of two ER-resident selenoproteins (selenoprotein K and selenoprotein M) in the ovaries of aged mice: Preliminary data

Towards prolonging ovarian reproductive life: Insights into trace elements homeostasis

Ovarian aging is marked by a reduction in the quantity and quality of ovarian follicles, leading to a decline in female fertility and ovarian endocrine function. While the biological characteristics of ovarian aging are well-established, the exact mechanisms underlying this process remain elusive. Recent studies underscore the vital role of trace elements (TEs) in maintaining ovarian function. Imbalances in TEs can lead to ovarian aging, characterized by reduced enzyme activity, hormonal imbalances, ovulatory disorders, and decreased fertility. A comprehensive understanding of the relationship between systemic and cellular TEs balance and ovarian aging is critical for developing treatments to delay aging and manage age-related conditions. This review consolidates current insights into TEs homeostasis and its impact on ovarian aging, assesses how altered TEs metabolism affects ovarian aging, and suggests future research directions to prolong ovarian reproductive life. These studies are expected to offer novel approaches for mitigating ovarian aging.

SELENOM Knockout Induces Synaptic Deficits and Cognitive Dysfunction by Influencing Brain Glucose Metabolism

Selenium, a trace element associated with memory impairment and glucose metabolism, mainly exerts its function through selenoproteins. SELENOM is a selenoprotein located in the endoplasmic reticulum (ER) lumen. Our study demonstrates for the first time that SELENOM knockout decreases synaptic plasticity and causes memory impairment in 10-month-old mice. In addition, SELENOM knockout causes hyperglycaemia and disturbs glucose metabolism, which is essential for synapse formation and transmission in the brain. Further research reveals that SELENOM knockout leads to inhibition of the brain insulin signaling pathway [phosphatidylinositol 3-kinase (PI3K)/AKT/mTOR/p70 S6 kinase pathway], which may impair synaptic plasticity in mice. High-fat diet (HFD) feeding suppresses the brain insulin signaling pathway in SELENOM knockout mice and leads to earlier onset of cognitive impairment at 5 months of age. In general, our study demonstrates that SELENOM knockout induces synaptic deficits via the brain insulin signaling pathway, thus leading to cognitive dysfunction in mice. These data strongly suggest that SELENOM plays a vital role in brain glucose metabolism and contributes substantially to synaptic plasticity.

Selenoproteins and the senescence-associated epitranscriptome

Selenium is a naturally found trace element, which provides multiple benefits including antioxidant, anticancer, and antiaging, as well as boosting immunity. One unique feature of selenium is its incorporation as selenocysteine, a rare 21st amino acid, into selenoproteins. Twenty-five human selenoproteins have been discovered, and a majority of these serve as crucial antioxidant enzymes for redox homeostasis. Unlike other amino acids, incorporation of selenocysteine requires a distinctive UGA stop codon recoding mechanism. Although many studies correlating selenium, selenoproteins, aging, and senescence have been performed, it has not yet been explored if the upstream events regulating selenoprotein synthesis play a role in senescence-associated pathologies. The epitranscriptomic writer alkylation repair homolog 8 (ALKBH8) is critical for selenoprotein production, and its deficiency can significantly decrease levels of selenoproteins that are essential for reactive oxygen species (ROS) detoxification, and increase oxidative stress, one of the major drivers of cellular senescence. Here, we review the potential role of epitranscriptomic marks that govern selenocysteine utilization in regulating the senescence program.

The decrease of selenoprotein K induced by selenium deficiency in diet improves apoptosis and cell progression block in chicken liver via the PTEN/PI3K/AKT pathway

Selenoprotein K (SELK) is imperative for normal development of chicken. It does regulate to chicken's physiological function. However, the injury of SELK-deficiency done on chicken liver and its underlying mechanism involved has not yet been covered. Therefore, we built SELK- deficiency model by feeding diet which contained low concentration of selenium (Se) to discuss SELK's regulation mechanism. Through using TUNEL, TEM, western blot and qRT-PCR we found apoptosis occurred in chicken liver in the SELK-deficiency groups. In the meanwhile, our study showed there were differentially expressed of the PTEN/PI3K/AKT pathway, calcium homeostasis, endoplasmic reticulum healthy and cell cycle progression in SELK-deficiency chicken liver tissues. In order to claim the regulation mechanism of SELK, we set SELK-knock down model in the LMH. The results in vitro were coincided with those in vivo. In the SELK-deficiency groups, the PTEN/PI3K/AKT pathway was activated and then induced ERS which eventually resulted in apoptosis in chicken liver. As the same time, the PTEN/PI3K/AKT pathway also regulated the combined effective of MDM2-p53, which leaned liver cells to G1/S blocking. Our findings support the potential of SELK in maintain the health of chicken liver, and indicate that adding proper amount of Se on the daily dietary may alleviate the deficiency of selenium.

The protective effect of selenoprotein M on non-alcoholic fatty liver disease: the role of the AMPKα1-MFN2 pathway and Parkin mitophagy

Non-alcoholic fatty liver disease (NAFLD) is related to a dysregulation of mitophagy, a process that is not fully understood. Parkin-related mitophagy can sustain mitochondrial homeostasis and hepatocyte viability. Herein, we report that selenoprotein M (SELENOM) plays a central role in maintaining mitophagy in high-fat diet (HFD)-mediated NAFLD. We show that SELENOM was significantly downregulated in the liver of HFD-fed mice. SELENOM deletion aggravated HFD-mediated hepatic steatosis, inflammation, and fibrosis; accompanied by enhanced fatty acid oxidation and oxidative stress in the liver. Molecular analyses show that lipotoxicity was related to increased mitochondrial apoptosis as evidenced by enhanced mitochondrial ROS production, and attenuation of mitochondrial potential in the liver of HFD-fed SELENOM-/- mice. Additionally, SELENOM deletion reduced mitophagy and aggravated hepatic injury in NAFLD. Mechanistically, SELENOM overexpression activated Parkin-mediated mitophagy to reduce mitochondrial apoptosis and remove HFD-damaged mitochondria. We further found that SELENOM regulates Parkin expression via the AMPKα1-MFN2 pathway; blockade of AMPKα1 prevented SELENOM activation of Parkin-mediated mitophagy. Our work identified SELENOM downregulation as a possible explanation for the defective mitophagy in NAFLD. Thus, targeting SELENOM may be potential new therapeutic modalities for NAFLD treatment.

The Role of Selenium in Pathologies: An Updated Review

Selenium is an essential microelement required for a number of biological functions. Selenium—and more specifically the amino acid selenocysteine—is present in at least 25 human selenoproteins involved in a wide variety of essential biological functions, ranging from the regulation of reactive oxygen species (ROS) concentration to the biosynthesis of hormones. These processes also play a central role in preventing and modulating the clinical outcome of several diseases, including cancer, diabetes, Alzheimer’s disease, mental disorders, cardiovascular disorders, fertility impairments, inflammation, and infections (including SARS-CoV-2). Over the past years, a number of studies focusing on the relationship between selenium and such pathologies have been reported. Generally, an adequate selenium nutritional state—and in some cases selenium supplementation—have been related to improved prognostic outcome and reduced risk of developing several diseases. On the other hand, supra-nutritional levels might have adverse effects. The results of recent studies focusing on these topics are summarized and discussed in this review, with particular emphasis on advances achieved in the last decade.

Selenium in Endocrinology-Selenoprotein-Related Diseases, Population Studies, and Epidemiological Evidence

Selenium (Se), apart from iodine, iron, and calcium, is one of the nutrient-derived key elements strongly affecting the endocrine system. However, no specific hormonal "feedback" regulation for Se status has yet been identified, in contrast to the fine-tuned hormone network regulating Ca2+ and phosphate balance or hepcidin-related iron status. Since its discovery as an essential trace element, the effects of Se excess or deficiency on the endocrine system or components of the hypothalamic-pituitary-periphery feedback circuits, the thyroid hormone axis, glucoregulatory and adrenal hormones, male and female gonads, the musculoskeletal apparatus, and skin have been identified. Analysis of the Se status in the blood or via validated biomarkers such as the hepatically derived selenoprotein P provides valuable diagnostic insight and a rational basis for decision making on required therapeutic or preventive supplementation of risk groups or patients. Endocrine-related epidemiological and interventional evidence linking Se status to beneficial or potentially adverse actions of selected selenoproteins mediating most of the (patho-) physiological effects are discussed in this mini-review. Autoimmune thyroid disease, diabetes and obesity, male fertility, as well as osteoporosis are examples for which observational or interventional studies have indicated Se effects. The currently prevailing concept relating Se and selenoproteins to "oxidative stress," reactive oxygen species, radical hypotheses, and related strategies of pharmacological approaches based on various selenium compounds will not be the focus. The crucial biological function of several selenoproteins in cellular redox-regulation and specific enzyme reactions in endocrine pathways will be addressed and put in clinical perspective.