Renal LRP2 expression in man and chicken is estrogen-responsive

Renal Endocytic Regulation of Vitamin D Metabolism during Maturation and Aging in Laying Hens

Egg-laying hens undergo a specific and dramatic calcium metabolism to lay eggs with eggshells composed of calcium carbonate. Calcium metabolism is mainly regulated by vitamin D3. Although vitamin D3 metabolism is closely related to the deterioration of eggshell quality associated with aging and heat stress, the details of the mechanisms regulating vitamin D3 metabolism are not clear. In mammals, the vitamin D3 metabolite (25(OH)D3) produced in the liver binds to the vitamin binding protein (DBP), is subsequently taken up by renal proximal tubular cells via the endocytic receptors megalin (Meg) and cubilin (CUB), and is metabolized to 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). Therefore, the present study aimed to examine the expression and localization of Meg and CUB in the kidneys of immature chicks and mature and aged laying hens to prevent eggshell quality deterioration. As a result, we showed that as circulating 1,25(OH)2D3 concentrations increased from 156.0 ± 13.5 pg/mL to 815.5 ± 61.4 pg/mL with maturation in immature chicks, relative expression levels (arbitrary units; AU) of Meg and CUB mRNA in the kidneys of mature hens significantly increased 1.92- and 2.75-fold, respectively, compared to those in immature chicks. On the other hand, the Meg mRNA expression levels of mature hens did not change with age, while CUB mRNA expression levels (1.03 ± 0.11 AU) were significantly decreased compared to mature hens (2.75 ± 0.24 AU). Immunohistochemical observations showed that Meg and CUB proteins were localized to the apical membrane of renal proximal tubular epithelial cells in immature chicks, mature hens, and aged hens, and that DBP protein was observed as granular endosomes in the cytoplasm of proximal tubular cells from the apical membrane to the cell nucleus. Especially in mature hens, the endosomes were larger and more numerous than those in immature chicks. In contrast, in aged hens, DBP-containing endosomes were smaller and limited to the apical cytoplasm. These results indicate that with maturation, the expression of Meg and CUB is promoted in the renal proximal tubules of laying hens, facilitating the uptake of the 25(OH)D3-DBP complex and its conversion to 1,25(OH)2D3, and regulating calcium metabolism in eggshell formation. On the other hand, it is suggested that the age-related decrease in CUB expression suppresses the uptake of the 25(OH)D3-DBP complex in the kidney, resulting in a deterioration of eggshell quality.

The Diverse Roles of 17β-Estradiol in Non-Gonadal Tissues and Its Consequential Impact on Reproduction in Laying and Broiler Breeder Hens

Estradiol-17β (E2) has long been studied as the primary estrogen involved in sexual maturation of hens. Due to the oviparous nature of avian species, ovarian production of E2 has been indicated as the key steroid responsible for activating the formation of the eggshell and internal egg components in hens. This involves the integration and coordination between ovarian follicular development, liver metabolism and bone physiology to produce the follicle, yolk and albumen, and shell, respectively. However, the ability of E2 to be synthesized by non-gonadal tissues such as the skin, heart, muscle, liver, brain, adipose tissue, pancreas, and adrenal glands demonstrates the capability of this hormone to influence a variety of physiological processes. Thus, in this review, we intend to re-establish the role of E2 within these tissues and identify direct and indirect integration between the control of reproduction, metabolism, and bone physiology. Specifically, the sources of E2 and its activity in these tissues via the estrogen receptors (ERα, ERβ, GPR30) is described. This is followed by an update on the role of E2 during sexual differentiation of the embryo and maturation of the hen. We then also consider the implications of the recent discovery of additional E2 elevations during an extended laying cycle. Next, the specific roles of E2 in yolk formation and skeletal development are outlined. Finally, the consequences of altered E2 production in mature hens and the associated disorders are discussed. While these areas of study have been previously independently considered, this comprehensive review intends to highlight the critical roles played by E2 to alter and coordinate physiological processes in preparation for the laying cycle.

Estrogen-enhanced apical and basolateral secretion of apolipoprotein B-100 by polarized trophoblast-derived BeWo cells

Cholesterol is an important nutrient for fetal development and transplacental transport occurs at all stages of human pregnancy. Furthermore, cholesterol is required for membrane building as well as steroid hormone synthesis. Therefore, all placental cell types require cholesterol for proper function. In human term placenta, the syncytiotrophoblast (STB) faces the maternal circulation. Uptake of maternal-derived cholesterol at the apical membrane of the STB is well understood, but the route by which cholesterol exits at the basal side for subsequent transfer across the fetal endothelial cells (FEC) or to other placental cell types remains not well characterized. Our aim was to provide evidence for basal secretion of apolipoprotein B-100 (apoB) containing lipoproteins. Furthermore, we investigated the placental localization of apolipoprotein receptors (LRP2, LDLR and LRP1) to identify cell targets of lipoprotein particles secreted in a polarized fashion by the STB. In trophoblast-derived BeWo cells grown on permeable filter supports, we demonstrate by immunoprecipitation apical as well as basolateral apoB secretion, which was significantly upregulated by estrogen-treatment for 24 or 48 h. Furthermore, we showed by immunofluorescence microscopy apoB and microsomal triglyceride transfer protein subunits localization in the STB and placental stromal cells in situ. All investigated receptors were detected by RT-qPCR and western blot in BeWo cells, but only expression of LRP2 was estrogen-inducible. In situ, the multi-ligand receptor LRP2 was expressed exclusively in the cytotrophoblast (CTB), the STB precursor cell type. LDLR and LRP1 localized to trophoblasts as well as stromal cells in situ. In summary, basal apoB secretion by BeWo cells supports the concept of basal lipoprotein particle secretion by placental STB. These lipoprotein particles may serve as cholesterol source for STB precursor cells, the CTBs, as well as all stromal cells of the chorionic villi including FECs, which were herein demonstrated to express apoB receptors, LRP2 and LDLR, respectively.

Sex Hormone Decline and Amyloid β Synthesis, Transport and Clearance in the Brain

Sex hormones (SH) are essential regulators of the central nervous system. The decline in SH levels along with ageing may contribute to compromised neuroprotection and set the grounds for neurodegeneration and cognitive impairments. In Alzheimer's disease, besides other pathological features, there is an imbalance between amyloid β (Aβ) production and clearance, leading to its accumulation in the brain of older subjects. Aβ accumulation is a primary cause for brain inflammation and degeneration, as well as concomitant cognitive decline. There is mounting evidence that SH modulate Aβ production, transport and clearance. Importantly, SH regulate most of the molecules involved in the amyloidogenic pathway, their transport across brain barriers for elimination, and their degradation in the brain interstitial fluid. This review brings together data on the regulation of Aβ production, metabolism, degradation and clearance by SH.

Xenopus embryonic epidermis as a mucociliary cellular ecosystem to assess the effect of sex hormones in a non-reproductive context

Background

How important are sexual hormones beyond their function in reproductive biology has yet to be understood. In this study, we analyzed the effects of sex steroids on the biology of the embryonic amphibian epidermis, which represents an easily amenable model of non-reproductive mucociliary epithelia (MCE). MCE are integrated systems formed by multiciliated (MC), mucus-secreting (MS) and mitochondrion-rich (MR) cell populations that are shaped by their microenvironment. Therefore, MCE could be considered as ecosystems at the cellular scale, found in a wide array of contexts from mussel gills to mammalian oviduct.

Results

We showed that the natural estrogen (estradiol, E2) and androgen (testosterone, T) as well as the synthetic estrogen (ethinyl-estradiol, EE2), all induced a significant enhancement of MC cell numbers. The effect of E2, T and EE2 extended to the MS and MR cell populations, to varying degrees. They also modified the expression profile of RNA MCE markers, and induced a range of “non-typical” cellular phenotypes, with mixed identities and aberrant morphologies, as revealed by imaging analysis through biomarker confocal detection and scanning electron microscopy. Finally, these hormones also affected tadpole pigmentation, revealing an effect on the entire cellular ecosystem of the Xenopus embryonic skin.

Conclusions

This study reveals the impact in vivo, at the molecular, cellular, tissue and organism levels, of sex steroids on non-reproductive mucociliary epithelium biogenesis, and validates the use of Xenopus as a relevant model system in this field.

The developing chicken yolk sac acquires nutrient transport competence by an orchestrated differentiation process of its endodermal epithelial cells

During chicken yolk sac (YS) growth, mesodermal cells in the area vasculosa follow the migrating endodermal epithelial cell (EEC) layer in the area vitellina. Ultimately, these cells form the vascularized YS that functions in nutrient transfer to the embryo. How and when EECs, with their apical aspect directly contacting the oocytic yolk, acquire the ability to take up yolk macromolecules during the vitellina-to-vasculosa transition has not been investigated. In addressing these questions, we found that with progressive vascularization, the expression level in EECs of the nutrient receptor triad, LRP2-cubilin-amnionless, changes significantly. The receptor complex, competent for uptake of yolk proteins, is produced by EECs in the area vasculosa but not in the area vitellina. Yolk components endocytosed by LRP2-cubilin-amnionless, preformed and newly formed lipid droplets, and yolk-derived very low density lipoprotein, shown to be efficiently endocytosed and lysosomally processed by EECs, probably provide substrates for resynthesis and secretion of nutrients, such as lipoproteins. In fact, as directly demonstrated by pulse-chase experiments, EECs in the vascularized, but not in the avascular, region efficiently produce and secrete lipoproteins containing apolipoprotein A-I (apoA-I), apoB, and/or apoA-V. In contrast, perilipin 2, a lipid droplet-stabilizing protein, is produced exclusively by the EECs of the area vitellina. These data suggest a differentiation process that orchestrates the vascularization of the developing YS with the induction of yolk uptake and lipoprotein secretion by EECs to ensure embryo nutrition.