Inhibition of corticosteroid-binding globulin gene expression by glucocorticoids involves C/EBPβ

Understanding the podocyte immune responses in proteinuric kidney diseases: from pathogenesis to therapy

The glomerular filtration barrier, comprising the inner layer of capillary fenestrated endothelial cells, outermost podocytes, and the glomerular basement membrane between them, plays a pivotal role in kidney function. Podocytes, terminally differentiated epithelial cells, are challenging to regenerate once injured. They are essential for maintaining the integrity of the glomerular filtration barrier. Damage to podocytes, resulting from intrinsic or extrinsic factors, leads to proteinuria in the early stages and eventually progresses to chronic kidney disease (CKD). Immune-mediated podocyte injury is a primary pathogenic mechanism in proteinuric glomerular diseases, including minimal change disease, focal segmental glomerulosclerosis, membranous nephropathy, and lupus nephritis with podocyte involvement. An extensive body of evidence indicates that podocytes not only contribute significantly to the maintenance of the glomerular filtration barrier and serve as targets of immune responses but also exhibit immune cell-like characteristics, participating in both innate and adaptive immunity. They play a pivotal role in mediating glomerular injury and represent potential therapeutic targets for CKD. This review aims to systematically elucidate the mechanisms of podocyte immune injury in various podocyte lesions and provide an overview of recent advances in podocyte immunotherapy. It offers valuable insights for a deeper understanding of the role of podocytes in proteinuric glomerular diseases, and the identification of new therapeutic targets, and has significant implications for the future clinical diagnosis and treatment of podocyte-related disorders.

KLF15 cistromes reveal a hepatocyte pathway governing plasma corticosteroid transport and systemic inflammation

Circulating corticosteroids orchestrate stress adaptation, including inhibition of inflammation. While pathways governing corticosteroid biosynthesis and intracellular signaling are well understood, less is known about mechanisms controlling plasma corticosteroid transport. Here, we show that hepatocyte KLF15 (Kruppel-like factor 15) controls plasma corticosteroid transport and inflammatory responses through direct transcriptional activation of Serpina6, which encodes corticosteroid-binding globulin (CBG). Klf15-deficient mice have profoundly low CBG, reduced plasma corticosteroid binding capacity, and heightened mortality during inflammatory stress. These defects are completely rescued by reconstituting CBG, supporting that KLF15 works primarily through CBG to control plasma corticosterone homeostasis. To understand transcriptional mechanisms, we generated the first KLF15 cistromes using newly engineered Klf153xFLAG mice. Unexpectedly, liver KLF15 is predominantly promoter enriched, including Serpina6, where it binds a palindromic GC-rich motif, opens chromatin, and transactivates genes with minimal associated direct gene repression. Overall, we provide critical mechanistic insight into KLF15 function and identify a hepatocyte-intrinsic transcriptional module that potently regulates systemic corticosteroid transport and inflammation.

Sex-specific maternal programming of corticosteroid-binding globulin by predator odour

Predation is a key organizing force in ecosystems. The threat of predation may act to programme the endocrine hypothalamic-pituitary-adrenal axis during development to prepare offspring for the environment they are likely to encounter. Such effects are typically investigated through the measurement of corticosteroids (Cort). Corticosteroid-binding globulin (CBG) plays a key role in regulating the bioavailability of Cort, with only free unbound Cort being biologically active. We investigated the effects of prenatal predator odour exposure (POE) in mice on offspring CBG and its impact on Cort dynamics before, during and after restraint stress in adulthood. POE males, but not females, had significantly higher serum CBG at baseline and during restraint and lower circulating levels of Free Cort. Restraint stress was associated with reduced liver transcript abundance of SerpinA6 (CBG-encoding gene) only in control males. POE did not affect SerpinA6 promoter DNA methylation. Our results indicate that prenatal exposure to a natural stressor led to increased CBG levels, decreased per cent of Free Cort relative to total and inhibited restraint stress-induced downregulation of CBG transcription. These changes suggest an adaptive response to a high predator risk environment in males but not females that could buffer male offspring from chronic Cort exposure.

Glucocorticoid receptor-mediated alleviation of inflammation by berberine: in vitro, in silico and in vivo investigations

As a natural dietary ingredient, berberine possesses multiple biological activities including anti-inflammatory effects. In this work, glucocorticoid receptor (GR)-mediated alleviation of inflammation by berberine was investigated by a combination of in vitro, in silico, and in vivo approaches. The fluorescence polarization assay showed that berberine bound to GR with an IC₅₀ value of 9.14 ± 0.16 pM. Molecular docking and molecular dynamics simulation suggested that berberine bound stably to the active site of GR via hydrogen bonding and hydrophobic interactions. Berberine induced GR nuclear translocation but did not activate the glucocorticoid response element in HeLa cells. Furthermore, both gene and protein expressions of PEPCK were significantly attenuated by berberine in HepG2 cells. Interestingly, berberine downregulated CBG mRNA and protein levels without up-regulating TAT mRNA and protein levels in HepG2 cells, demonstrating its dissociated characteristics that could separate transrepression from transactivation. In addition, the in vitro and in vivo anti-inflammatory effects of berberine were confirmed in lipopolysaccharide-induced RAW 264.7 cells and in a mouse model of allergic contact dermatitis, respectively. In conclusion, berberine might serve as a potential selective GR modulator.

Phytochemicals from the flowers of Prunus persica (L.) Batsch: Anti-adipogenic effect of mandelamide on 3T3-L1 preadipocytes

Flowers of Prunus persica (L.) Batsch (Rosaceae), known as peach blossoms, have been reported to exert anti-obesity effects by improving hepatic lipid metabolism in obese mice. However, little is known regarding the anti-adipogenic effects of the phenolic compounds isolated from P. persica flowers. This study investigated the inhibitory effects of compounds extracted from P. persica flowers (PPF) on adipogenesis in 3T3-L1 murine preadipocytes using adipogenic differentiation assays. Additionally, we compared the anti-adipogenic effects of the phenolic compounds isolated from PPF, such as prunasin amide (1), amygdalin amide (2), prunasin acid (3), mandelamide (4), methyl caffeate (5), ferulic acid (6), chlorogenic acid (7), benzyl α-l-xylpyranosyl-(1 → 6)-β-d-glucopyranoside (8), prunin (9), naringenin (10), nicotiflorin (11), astragalin (12), afzelin (13), and uridine (14), on adipogenesis in 3T3-L1 murine preadipocytes. PPF and compounds 4-7 and 10 significantly inhibited adipogenesis. Among them, mandelamide (4) exhibited the maximum inhibitory activity with an IC₅₀ of 36.04 ± 1.82 μM. Additionally, mandelamide downregulated the expression of key adipogenic markers, such as extracellular signal-regulated kinase, c-Jun-N-terminal kinase, P38, CCAAT/enhancer-binding protein α, CCAAT/enhancer-binding protein β, peroxisome proliferator activated receptor γ, and glucocorticoid receptor. These results indicate that mandelamide is an active ingredient of PPF possessing anti-obesity properties.

GR-mediated anti-inflammation of α-boswellic acid: Insights from in vitro and in silico studies

Although multiple bioactivities of α-boswellic acid have been reported, the molecular mechanism of its anti-inflammatory action is not yet clear. Hence, glucocorticoid receptor (GR)-mediated anti-inflammation of α-boswellic acid was investigated in this work. Fluorescence polarization assay suggested that α-boswellic acid bound to GR with IC₅₀ value of 658.00 ± 0.21 μM. Upon binding to α-boswellic acid, GR translocated from cytoplasm into nucleus of HeLa cells, facilitating sequential transcriptional regulation of GR-related genes. Luciferase reporter assay suggested that α-boswellic acid lacked GR transcriptional activity, indicating its potential as a dissociative GR ligand. Interestingly, α-boswellic acid selectively modulated the anti-inflammatory gene CBG (marker for GR transrepression), while leaving the "side-effect" gene TAT (marker for GR transactivation) unaffected in HepG2 cells. Furthermore, α-boswellic acid inhibited lipopolysaccharide-stimulated cytokines production in U937 macrophages, confirming its anti-inflammation property in vitro. Molecular docking showed that both hydrogen-bonding and hydrophobic interactions helped to stabilize α-boswellic acid-GR binding. Their binding stability was further confirmed in a 70-ns dynamics simulation. In summary, α-boswellic acid could bind to and translocate GR but did not induce glucocorticoid response element-mediated transcription. Since α-boswellic acid showed the dissociated characteristic that separated transrepression from transactivation, it might be a selective GR modulator against inflammatory disorders.

Restraint Stress Alters Expression of Glucocorticoid Bioavailability Mediators, Suppresses Nrf2, and Promotes Oxidative Stress in Liver Tissue

Hepatic glutathione synthesis and antioxidant protection are critically important for efficient detoxification processes in response to metabolic challenges. However, this biosynthetic pathway, regulated by nuclear factor (erythroid-derived 2)-like 2 (Nrf2), previously demonstrated paradoxical repression following exposure to glucocorticoid stress hormones in cultured hepatic cells. Therefore, the present study used an in vivo model of sub-acute psychological stress to investigate the relationship between hepatic corticosteroid regulation and antioxidant systems. Male Wistar rats were kept under control conditions or subjected to six hours of restraint stress applied for 1 or 3 days (n = 8 per group) after which the liver was isolated for assays of oxidative/nitrosative status and expression of corticosteroid regulatory and Nrf2-antioxidant response element pathway members. A single stress exposure produced a significant increase in the expression of corticosterone reactivator, 11-beta-hydroxysteroid dehydrogenase 1 (11β-Hsd1), while the 11β-Hsd2 isozyme and corticosteroid-binding globulin were down-regulated following stress, indicative of an elevated availability of active corticosterone. Exposure to restraint significantly decreased hepatic concentrations of total cysteine thiols and the antioxidant reduced glutathione on Day 1 and increased 3-nitrotyrosinated and carbonylated proteins on Day 3, suggestive of oxidative/nitrosative stress in the liver following stress exposure. Conversely, there was a sustained down-regulation of Nrf2 mRNA and protein in addition to significant reductions in downstream glutamate-cysteine ligase catalytic subunit (Gclc), the rate-limiting enzyme in glutathione synthesis, on Day 1 and 3 of stress treatment. Interestingly, other antioxidant genes including superoxide dismutase 1 and 2, and glutathione peroxidase 4 were significantly up-regulated following an episode of restraint stress. In conclusion, the results of the present study indicate that increased expression of 11β-Hsd1, indicative of elevated tissue glucocorticoid concentrations, may impair the Nrf2-dependent antioxidant response.

Sex-specific regulation of stress-induced fetal glucocorticoid surge by the mouse placenta

Antenatal stress increases the prevalence of diseases in later life, which shows a strong sex-specific effect. However, the underlying mechanisms remain unknown. Maternal glucocorticoids can be elevated by stress and are potential candidates to mediate the effects of stress on the offspring sex-specifically. A comprehensive evaluation of dynamic maternal and placental mechanisms modulating fetal glucocorticoid exposure upon maternal stress was long overdue. Here, we addressed this gap in knowledge by investigating sex-specific responses to midgestational stress in mice. We observed increased levels of maternal corticosterone, the main glucocorticoid in rodents, along with higher corticosteroid-binding globulin levels at midgestation in C57Bl/6 dams exposed to sound stress. This resulted in elevated corticosterone in female fetuses, whereas male offspring were unaffected. We identified that increased placental expression of the glucocorticoid-inactivating enzyme 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2; Hsd11b2 gene) and ATP-binding cassette transporters, which mediate glucocorticoid efflux toward maternal circulation, protect male offspring from maternal glucocorticoid surges. We generated mice with an Hsd11b2 placental-specific disruption (Hsd11b2^PKO) and observed moderately elevated corticosterone levels in offspring, along with increased body weight. Subsequently, we assessed downstream glucocorticoid receptors and observed a sex-specific differential modulation of placental Tsc22d3 expression, which encodes the glucocorticoid-induced leucine zipper protein in response to stress. Taken together, our observations highlight the existence of unique and well-orchestrated mechanisms that control glucocorticoid transfer, exposure, and metabolism in the mouse placenta, pinpointing toward the existence of sex-specific fetal glucocorticoid exposure windows during gestation in mice.

Histone demethylase KDM5A is transactivated by the transcription factor C/EBPβ and promotes preadipocyte differentiation by inhibiting Wnt/β-catenin signaling

β-Catenin signaling is triggered by WNT proteins and is an important pathway that negatively regulates adipogenesis. However, the mechanisms controlling the expression of WNT proteins during adipogenesis remain incompletely understood. Lysine demethylase 5A (KDM5A) is a histone demethylase that removes trimethyl (me3) marks from lysine 4 of histone 3 (H3K4) and serves as a general transcriptional corepressor. Here, using the murine 3T3-L1 preadipocyte differentiation model and an array of biochemical approaches, including ChIP, immunoprecipitation, RT-qPCR, and immunoblotting assays, we show that Kdm5a is a target gene of CCAAT/enhancer-binding protein β (C/EBPβ), an important early transcription factor required for adipogenesis. We found that C/EBPβ binds to the Kdm5a gene promoter and transactivates its expression. We also found that siRNA-mediated KDM5A down-regulation inhibits 3T3-L1 preadipocyte differentiation. The KDM5A knockdown significantly up-regulates the negative regulator of adipogenesis Wnt6, having increased levels of the H3K4me3 mark on its promoter. We further observed that WNT6 knockdown significantly rescues adipogenesis inhibited by the KDM5A knockdown. Moreover, we noted that C/EBPβ negatively regulates Wnt6 expression by binding to the Wnt6 gene promoter and repressing Wnt6 transcription. Further experiments indicated that KDM5A interacts with C/EBPβ and that their interaction cooperatively inhibits Wnt6 transcription. Of note, C/EBPβ knockdown impaired the recruitment of KDM5A to the Wnt6 promoter, which had higher H3K4me3 levels. Our results suggest a mechanism involving C/EBPβ and KDM5A activities that down-regulates the Wnt/β-catenin pathway during 3T3-L1 preadipocyte differentiation.

Evaluation of physiological stress in Australian wildlife: Embracing pioneering and current knowledge as a guide to future research directions

Australia has a rich terrestrial and marine biodiversity and high species endemism. However, the oceanic continent is facing the biodiversity extinction crisis. The primary factors are anthropogenic induced environmental changes, including wildlife habitat destruction through urbanisation and predation by feral animals (e.g. red foxes and feral cats), increased severity of diseases (e.g. chytridiomycosis and chlamydia), and increased occurrence of summer heat waves and bush fires. Stress physiology is a dynamic field of science based on the studies of endocrine system functioning in animals. The primary stress regulator is the hypothalamo-pituitary adrenal (interrenal) axis and glucocorticoids (corticosterone and/or cortisol) provide stress index across vertebrate groups. This review paper focuses on physiological stress assessments in Australian wildlife using examples of amphibians, reptiles, birds and marsupials. I provide a thorough discussion of pioneering studies that have shaped the field of stress physiology in Australian wildlife species. The main findings point towards key aspects of stress endocrinology research, such as quantification of biologically active levels of glucocorticoids, development of species-specific GC assays and applications of stress physiology approaches in field ecology and wildlife conservation programs. Furthermore, I also discuss the importance of chronic stress assessment in wildlife populations. Finally, I provide a conceptual framework presenting key research questions in areas of wildlife stress physiology research. In conclusion, wildlife management programs can immensely benefit from stress physiology assessments to gauge the impact of human interventions on wildlife such as species translocation and feral species eradication.

Asn347 Glycosylation of Corticosteroid-binding Globulin Fine-tunes the Host Immune Response by Modulating Proteolysis by Pseudomonas aeruginosa and Neutrophil Elastase

Corticosteroid-binding globulin (CBG) delivers anti-inflammatory cortisol to inflamed tissues upon elastase-based proteolysis of the exposed reactive center loop (RCL). However, the molecular mechanisms that regulate the RCL proteolysis by co-existing host and bacterial elastases in inflamed/infected tissues remain unknown. We document that RCL-localized Asn(347) glycosylation fine-tunes the RCL cleavage rate by human neutrophil elastase (NE) and Pseudomonas aeruginosa elastase (PAE) by different mechanisms. NE- and PAE-generated fragments of native and exoglycosidase-treated blood-derived CBG of healthy individuals were monitored by gel electrophoresis and LC-MS/MS to determine the cleavage site(s) and Asn(347) glycosylation as a function of digestion time. The site-specific (Val(344)-Thr(345)) and rapid (seconds to minutes) NE-based RCL proteolysis was significantly antagonized by several volume-enhancing Asn(347) glycan features (i.e. occupancy, triantennary GlcNAc branching, and α1,6-fucosylation) and augmented by Asn(347) NeuAc-type sialylation (all p < 0.05). In contrast, the inefficient (minutes to hours) PAE-based RCL cleavage, which occurred equally well at Thr(345)-Leu(346) and Asn(347)-Leu(348), was abolished by the presence of Asn(347) glycosylation but was enhanced by sialoglycans on neighboring CBG N-sites. Molecular dynamics simulations of various Asn(347) glycoforms of uncleaved CBG indicated that multiple Asn(347) glycan features are modulating the RCL digestion efficiencies by NE/PAE. Finally, high concentrations of cortisol showed weak bacteriostatic effects toward virulent P. aeruginosa, which may explain the low RCL potency of the abundantly secreted PAE during host infection. In conclusion, site-specific CBG N-glycosylation regulates the bioavailability of cortisol in inflamed environments by fine-tuning the RCL proteolysis by endogenous and exogenous elastases. This study offers new molecular insight into host- and pathogen-based manipulation of the human immune system.

Altered lipid partitioning and glucocorticoid availability in CBG-deficient male mice with diet-induced obesity

OBJECTIVE

To evaluate how deficiency in corticosteroid-binding globulin (CBG), the specific carrier of glucocorticoids, affects glucocorticoid availability and adipose tissue in obesity.

METHODS

C57BL/6 (WT) and CBG-deficient (KO) male mice were fed during 12 weeks with standard or hyperlipidic diet (HL). Glucocorticoid availability and metabolic parameters were assessed.

RESULTS

Body weight and food intake were increased in KO compared with WT mice fed a standard diet and were similar when fed a HL diet. Expression of CBG was found in white adipose tissue by immunochemistry, real-time PCR, and Western blot. In obesity, the subcutaneous depot developed less in KO mice compared with WT, which was associated with a minor adipocyte area and peroxisome proliferator-activated receptor-γ expression. Conversely, the epididymal depot displayed higher weight and adipocyte area in KO than in WT mice. CBG deficiency caused a fall of hepatic 11β-hydroxysteroid dehydrogenase type 2 expression and an increase in epidymal adipose tissue, particularly in HL mice.

CONCLUSIONS

Deficiency in CBG drives lipid partitioning from subcutaneous to visceral adipose depot under a context of lipid excess and differentially modulates 11β-hydroxysteroid dehydrogenase type 2 expression.

Identification of Avian Corticosteroid-binding Globulin (SerpinA6) Reveals the Molecular Basis of Evolutionary Adaptations in SerpinA6 Structure and Function as a Steroid-binding Protein

Corticosteroid-binding globulin (CBG) was isolated from chicken serum and identified by mass spectrometry and genomic analysis. This revealed that the organization and synteny of avian and mammalian SerpinA6 genes are conserved. Recombinant zebra finch CBG steroid-binding properties reflect those of the natural protein in plasma and confirm its identity. Zebra finch and rat CBG crystal structures in complex with cortisol resemble each other, but their primary structures share only ∼40% identity, and their steroid-binding site topographies differ in several unexpected ways. Remarkably, a tryptophan that anchors ligands in mammalian CBG steroid-binding sites is replaced by an asparagine. Phylogenetic comparisons show that reptilian CBG orthologs share this unexpected property. Glycosylation of this asparagine in zebra finch CBG does not influence its steroid-binding affinity, but we present evidence that it may participate in protein folding and steroid-binding site formation. Substitutions of amino acids within zebra finch CBG that are conserved only in birds reveal how they contribute to their distinct steroid-binding properties, including their high (nanomolar) affinities for glucocorticoids, progesterone, and androgens. As in mammals, a protease secreted by Pseudomonas aeruginosa cleaves CBG in zebra finch plasma within its reactive center loop and disrupts steroid binding, suggesting an evolutionarily conserved property of CBGs. Measurements of CBG mRNA in zebra finch tissues indicate that liver is the main site of plasma CBG production, and anti-zebra finch CBG antibodies cross-react with CBGs in other birds, extending opportunities to study how CBG regulates the actions of glucocorticoids and sex steroids in these species.

Colony-Specific Differences in Endocrine and Immune Responses to an Inflammatory Challenge in Female Sprague Dawley Rats

Sprague Dawley rats from different vendor colonies display divergent responses in a variety of experimental paradigms. An adjuvant-induced arthritis (AA) model of human rheumatoid arthritis was used to examine immune and endocrine responses to inflammatory challenge in Sprague Dawley rats from Charles River and Harlan colonies. Rats were injected with either complete Freund's adjuvant or physiological saline (control), weights, and paw volumes measured over 15 days, and blood and tissue were collected 16 days post-injection. Overall, Harlan rats developed more severe AA than Charles River rats. In addition, despite comparable corticosterone levels, corticosteroid binding globulin levels were lower in Harlan compared with Charles River rats in the absence of inflammation, suggesting that a lower corticosterone reservoir in Harlan rats may underlie their greater susceptibility to inflammation. With increasing AA severity, there was an increase in plasma corticosterone (total and free) and a decrease in corticosteroid binding globulin in both Charles River and Harlan rats. However, contrasting patterns of cytokine activation were observed in the hind paw, suggesting a reliance on different cytokine networks at different stages of inflammation, with Charles River rats exhibiting increased TNF-α, monocyte chemotactic protein-1 (MCP-1), keratinocyte chemoattractant/growth-regulated oncogene (KC/GRO), and IL-1β in the absence of clinical signs of arthritis, whereas Harlan had increased TNF-α, monocyte chemotactic protein-1, and IL-6 with mild to moderate arthritis. These colony-specific differences in endocrine and immune responses to AA in Sprague Dawley rats must be considered when comparing data from different laboratories and could be exploited to provide insight into physiological changes and therapeutic outcomes in arthritis and other inflammatory disorders.

Corticosteroid-binding globulin: modulating mechanisms of bioavailability of cortisol and its clinical implications

Corticosteroid-binding globulin (CBG) is the principal transport protein of glucocorticoids. Approximately 80-90% of serum cortisol binds to CBG with high affinity and only about 5% of cortisol remain unbound and is considered biologically active. CBG seems to modulate and influence the bioavailability of cortisol to local tissues. In this review, we will discuss physicochemical properties of CBG and structure of CBG in the mechanisms of binding and release of cortisol. This review describes several factors affecting CBG functions, such as genetic factors or temperature. Furthermore, clinical implications of CBG abnormalities and the measurement of CBG and its use for assessment of free cortisol levels are described in this review.