論文の公開元へEphrin-B1 and EphB4 as novel markers for steroidogenic cells in naturally cycling mouse ovary and adrenal gland
概要
Erythropoietin-producing hepatocellular (Eph) receptors and their ligands, ephrins, are expressed in many tissues and organs, and serve as a cell–cell communication system with a variety of roles in normal development, physiology and disease pathogenesis (Pasquale, 2005, 2010). These membrane proteins typically regulate cell adhesion and migration as well as cell–cell repulsion and adhesion by regulating the organisation of the actin cytoskeleton and modulating cell adhesion properties via integrins and other adhesion molecules. In mammals, Eph receptors are divided into classes EphA (A1–A8 and A10) and EphB (B1–B4 and B6) based on amino acid sequence homology of their extracellular domains (Pasquale, 2005, 2008). Members of these two receptor classes promiscuously bind to ligands of the ephrin-A (A1–A5) and -B (B1–B3) classes, respectively. This interaction of Eph receptors with ephrins results in bidirectional signal propagation in both receptor- and ligand-expressing cells (Pasquale, 2008, 2010; Kania and Klein, 2016). The roles of Eph receptors and ephrins have been extensively characterised in developing tissues, particularly in the central nervous system and vascular system, where they regulate axon guidance, tissue border formation, cell migration, vasculogenesis and angiogenesis (Kullander and Klein, 2002; Pasquale, 2005; Klein, 2012). Recently, Eph receptors and ephrins have also been implicated in the physiology and homeostasis of normal adult tissues and organs (Pasquale, 2008; Miao and Wang, 2009). Eph/ephrin signalling has been implicated in epithelial tissue homeostasis via regulation of epithelial compartments, cell positioning, proliferation, migration, adhesion and/or differentiation in several epithelial tissues including the intestine, stomach, mammary gland and epidermis (Miao and Wang, 2009; Ishii et al., 2011; Ogawa et al., 2013; Perez White and Getsios, 2014). Specific Eph/ephrin signalling is also involved in glucose homeostasis via modulation of insulin secretion in response to glucose levels in pancreatic islets (Konstantinova et al., 2007), as well as bone maintenance and remodelling via regulation of osteoclast and osteoblast differentiation (Zhao et al., 2006).
In primary genital organs, several reports have indicated the expression and localisation of Eph receptors and ephrins in ovaries (Adu-Gyamfi et al., 2021). Buensuceso and Deroo showed that ephrin-A5 and EphA5 are localised in granulosa cells of the mouse ovary and that follicle-stimulating hormone upregulates EFNA5, EPHA3, EPHA5 and EPHA8 mRNA expression in mouse primary granulosa cells and a rat granulosa cell line (Buensuceso and Deroo, 2013). Ephrin-A5 has also been shown to be involved in folliculogenesis and ovulation, likely by mediating apoptosis, proliferation and steroidogenesis in the mouse (Buensuceso et al., 2016; Worku et al., 2018). Egawa et al. showed that ephrin-B1 is localised in theca interna cells and luteinising granulosa cells in the corpora lutea in the early luteal phase in human ovaries (Egawa et al., 2003). Moreover, certain Eph receptors and ephrins have been implicated in the progression and metastasis of ovarian carcinomas due to their upregulation or downregulation in these tumours (Adu-Gyamfi et al., 2021). On the other hand, in the testis, Gofur et al. recently showed that ephrin-B1 and EphB2/EphB4 exhibit complementary expression patterns in the epithelia along the excurrent duct system in the adult mouse testis and epididymis, and that these predominantly ephrin-B1- and EphB2/EphB4-expressing compartments are formed by two weeks of age in the mouse testis (Gofur and Ogawa, 2019; Gofur et al., 2020). They also showed that foetal Leydig cells weakly expressed ephrin-B1 and EphB4 in the mouse testis, while adult Leydig cells strongly expressed ephrin-B1. As both the adult and foetal Leydig cells commonly co-express ephrinB1 and EphB4, the author hypothesised that ephrin-B1 and EphB4 are co-expressed ubiquitously in steroidogenic cells in gonads and other steroidogenic organs. To the best of the author’s knowledge, however, the expression patterns and localisation of EphB receptors and ephrin-B ligands have not been sufficiently characterised in normal adult ovaries. In order to test this hypothesis, therefore, the author examined ephrin-B1 and EphB4 expression and localisation initially in the naturally cycling mouse ovary, especially focusing on expression in steroidogenic cells, i.e. granulosa cells, steroidogenic theca cells, luteal cells and interstitial gland cells. Accordingly, the author found out that all types of steroidogenic cells coexpressed ephrin-B1 and EphB4 in the ovary. Therefore, the author believed that the hypothesis could be likely established.
The adrenal gland is a representative steroidogenic organ in addition to the testis and ovary (Miller and Auchus, 2011). The adrenal gland parenchyma consists of the medulla and cortex and is covered by a fibrous capsule in which stem/progenitor cells for the cortical steroidogenic cells reside (Simon and Hammer, 2012). The progenitor cells located in the periphery of the cortex migrate centripetally and repopulate the inner cortical zones upon differentiation (Belloni et al., 1978; Spencer et al., 1999). The adrenal cortex is composed of three zones as zona glomerulosa (zG) of the outer layer, zona fasciculata (zF) of the middle layer, and zona reticularis (zR) of the inner layer in many mammals while the cortex of aged mice is composed of zG and zF (Pihlajoki et al., 2015). The adrenal cortex of young mice contains an ephemeral layer between the zF and medulla known as the x-zone (xZ) (Hirokawa and Ishikawa, 1974; Morohashi and Zubair, 2011) which develops after birth and regresses in the male at puberty and in the female during the first pregnancy (Holmes and Dickson, 1971; Kim and Choi, 2020). Cells in the xZ are derived from the foetal adrenal gland and are involved in progesterone catabolism (Zubair et al., 2006; Hershkovitz et al., 2007).
A few reports have indicated expressions, localisations and/or functions of ephrins and Eph receptors in the adrenal glands (Adu-Gyamfi et al., 2021). Wang and his colleagues showed that chromaffin cells in the medulla of the adrenal glands expressed ephrin-B1 and EphB6 and the ephrin-B1/EphB6 signals were involved in catecholamine synthesis and secretion in concert with the nongenomic effect of testosterone in the male mouse (Wang et al., 2018; Shi et al., 2019). Moreover, Brennan et al. showed that mRNAs of several ephrins and Eph receptors including ephrin-B1 and EphB4 mRNA expressed in the rat adrenal gland, and EphA2 and EphA3 protein were localised in zG (Brennan et al., 2008). To the best of the author's knowledge, however, the expression patterns and localisation of ephrin-B ligands and EphB receptors have not been sufficiently characterised in the adrenal glands. Thus, to test the author’s hypothesis, expression and localisation of ephrin-B1 and EphB4 were examined in the adrenal gland especially focusing on steroidogenic cells in the adrenal cortex of the male and female mice.
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