Effect of selenium deficiency on the development of central nervous system lesions in murine listeriosis

Nano‑selenium alleviates cadmium-induced blood-brain barrier destruction by restoring the Wnt7A/β-catenin pathway

Selenium (Se), a highly beneficial animal feed additive, exhibits remarkable antioxidant and anti-inflammatory properties. Nano‑selenium (Nano-Se) is an advanced formulation of Se featuring a specialized drug delivery vehicle, with good bioavailability, higher efficacy, and lower toxicity compared to the traditional form of Se. With the advancement of industry, cadmium (Cd) contamination occurs in different countries and regions and thereby contaminating different food crops, and the degree of pollution is degree increasing year by year. The present investigation entailed the oral administration of CdCl2 and/or Nano-Se to male chickens of the Hy-Line Variety White breed, which are one day old, subsequent to a 7-day adaptive feeding period, for a duration of 90 days. The study aimed to elucidate the potential protective impact of Nano-Se on Cd exposure. The study found that Nano-Se demonstrates potential in mitigating the blood-brain barrier (BBB) dysfunction characterized by impairment of adherens junctions (AJS) and tight junctions (TJS) by inhibiting reactive oxygen species (ROS) overproduction. In addition, the data uncovered that Nano-Se demonstrates a proficient ability in alleviating BBB impairment and inflammatory reactions caused by Cd through the modulation of the Wnt7A/β-catenin pathway, highlights its potential to maintain brain homeostasis. Hence, this research anticipates that the utilization of Nano-Se effectively mitigate the detrimental impacts associated with Cd exposure on the BBB.

Macrophage Selenoproteins Restrict Intracellular Replication of Francisella tularensis and Are Essential for Host Immunity

The essential micronutrient Selenium (Se) is co-translationally incorporated as selenocysteine into proteins. Selenoproteins contain one or more selenocysteines and are vital for optimum immunity. Interestingly, many pathogenic bacteria utilize Se for various biological processes suggesting that Se may play a role in bacterial pathogenesis. A previous study had speculated that Francisella tularensis, a facultative intracellular bacterium and the causative agent of tularemia, sequesters Se by upregulating Se-metabolism genes in type II alveolar epithelial cells. Therefore, we investigated the contribution of host vs. pathogen-associated selenoproteins in bacterial disease using F. tularensis as a model organism. We found that F. tularensis was devoid of any Se utilization traits, neither incorporated elemental Se, nor exhibited Se-dependent growth. However, 100% of Se-deficient mice (0.01 ppm Se), which express low levels of selenoproteins, succumbed to F. tularensis-live vaccine strain pulmonary challenge, whereas 50% of mice on Se-supplemented (0.4 ppm Se) and 25% of mice on Se-adequate (0.1 ppm Se) diet succumbed to infection. Median survival time for Se-deficient mice was 8 days post-infection while Se-supplemented and -adequate mice was 11.5 and >14 days post-infection, respectively. Se-deficient macrophages permitted significantly higher intracellular bacterial replication than Se-supplemented macrophages ex vivo, corroborating in vivo observations. Since Francisella replicates in alveolar macrophages during the acute phase of pneumonic infection, we hypothesized that macrophage-specific host selenoproteins may restrict replication and systemic spread of bacteria. F. tularensis infection led to an increased expression of several macrophage selenoproteins, suggesting their key role in limiting bacterial replication. Upon challenge with F. tularensis, mice lacking selenoproteins in macrophages (TrspM) displayed lower survival and increased bacterial burden in the lung and systemic tissues in comparison to WT littermate controls. Furthermore, macrophages from TrspM mice were unable to restrict bacterial replication ex vivo in comparison to macrophages from littermate controls. We herein describe a novel function of host macrophage-specific selenoproteins in restriction of intracellular bacterial replication. These data suggest that host selenoproteins may be considered as novel targets for modulating immune response to control a bacterial infection.

Role of Selenoproteins in Bacterial Pathogenesis

The trace element selenium is an essential micronutrient that plays an important role in maintaining homeostasis of several tissues including the immune system of mammals. The vast majority of the biological functions of selenium are mediated via selenoproteins, proteins which incorporate the selenium-containing amino acid selenocysteine. Several bacterial infections of humans and animals are associated with decreased levels of selenium in the blood and an adjunct therapy with selenium often leads to favorable outcomes. Many pathogenic bacteria are also capable of synthesizing selenocysteine suggesting that selenoproteins may have a role in bacterial physiology. Interestingly, the composition of host microbiota is also regulated by dietary selenium levels. Therefore, bacterial pathogens, microbiome, and host immune cells may be competing for a limited supply of selenium. Elucidating how selenium, in particular selenoproteins, may regulate pathogen virulence, microbiome diversity, and host immune response during a bacterial infection is critical for clinical management of infectious diseases.

Invasion of the central nervous system by intracellular bacteria

Infection of the central nervous system (CNS) is a severe and frequently fatal event during the course of many diseases caused by microbes with predominantly intracellular life cycles. Examples of these include the facultative intracellular bacteria Listeria monocytogenes, Mycobacterium tuberculosis, and Brucella and Salmonella spp. and obligate intracellular microbes of the Rickettsiaceae family and Tropheryma whipplei. Unfortunately, the mechanisms used by intracellular bacterial pathogens to enter the CNS are less well known than those used by bacterial pathogens with an extracellular life cycle. The goal of this review is to elaborate on the means by which intracellular bacterial pathogens establish infection within the CNS. This review encompasses the clinical and pathological findings that pertain to the CNS infection in humans and includes experimental data from animal models that illuminate how these microbes enter the CNS. Recent experimental data showing that L. monocytogenes can invade the CNS by more than one mechanism make it a useful model for discussing the various routes for neuroinvasion used by intracellular bacterial pathogens.

Identification of selenoprotein P fragments as a cell-death inhibitory factor

Megakaryoblastoma (Dami cells) cultured in a serum-free medium containing albumin, proliferated for three days but died on the fourth day. This cell death was not observed when human plasma was added, suggesting that human plasma contains a cell-death inhibitory factor. In order to identify this factor, we purified it from human plasma. N-terminal amino acid sequence analysis revealed that this factor is a mixture of C-terminal fragments of selenoprotein P, a major selenocysteine-containing protein in plasma. The specific activity (unit per pmol of selenium) of selenoprotein P fragments protein was 15-fold and 1900-fold higher than that of the full-length SeP and sodium selenite, respectively.