Seasonal Changes in Immunoreactivity of Vascular Endothelial Factor and its Receptors VEGFR1 and VEGFR2 in the Uterus of Wild Ground Squirrels (<i>Citellus dauricus</i> Brandt)

Abstract

Abstract. In this study, we investigated the immunoreactivity of vascular endothelial growth factor (VEGF) and its receptors flt-1 (VEGFR1) and the kinase domain receptor (KDR/Flk-1, VEGFR2) in the uteri of the wild ground squirrels during the estrous period, early pregnancy and nonbreeding period. Cellular localizations of VEGF, VEGFR1 and VEGFR2 were detected by immunohistochemistry, and total proteins were extracted from uterine tissue in the estrous period, early pregnancy and nonbreeding period for Western blotting analysis. In addition, plasma estradiol-17β and progesterone concentrations were measured by radioimmunoassay. Stronger positive staining of VEGF was found in luminal epithelial cells and glandular cells, and its receptors (VEGFR1 and VEGFR2) were observed in stromal cells in the estrous period and early pregnancy compared with the nonbreeding period. The protein levels of VEGF, VEGFR1 and VEGFR2 were significantly higher in the estrous period and early pregnancy as compared with the nonbreeding period. Besides, plasma estradiol-17β and progesterone concentrations were higher in the estrous period and early pregnancy than in the nonbreeding period, suggesting that the immunoreactivities of VEGF, VEGFR1 and VEGFR2 were correlated with changes in plasma estradiol-17β and progesterone concentrations. These results suggested that VEGF and its receptors may be involved in the regulation of seasonal changes in the uterine functions of wild female ground squirrels. Key words: Uterus, VEGF, VEGFR1, VEGFR2, Wild ground squirrel (J. Reprod. Dev. 58: [537][538][539][540][541][542][543] 2012) D uring the reproductive cycle, the uterine endometrium undergoes a precisely timed complex sequence of physiological and morphological changes in preparation for implantation. These changes are controlled primarily by the ovarian steroid hormones 17β-estradiol (E 2 ) and progesterone [1]. During pregnancy, blood flow to the uterus is increased dramatically to meet the rising demands of the growing fetus. Endocrine control of this phenomenon is complex but includes in part the action of many growth factors [2,3]. Vascular endothelial growth factor (VEGF) is a protein with angiogenic activity and a potent stimulator of microvascular permeability [4,5]. It plays an important role in physiological and pathological neovascularization via its receptors Flt1/VEGFR1 and kinase insert domain containing region (KDR)/VEGFR2, both of which have tyrosine kinase activity [6]. In reproductive organs, VEGF is required for normal ovarian angiogenesis and endometrial growth throughout the ovulatory cycle in humans [7,8] and rodents [9,10]. The expression of VEGF and its receptors has been demonstrated in the endometrium in humans and in experimental and domestic animals throughout the menstrual cycle, with an upregulation in the late proliferative and luteal phases [11][12][13][14][15], periods that correspond to angiogenesis and an increase in vascular permeability [16]. However, the expression of VEGF and its receptors VEGFR1 and V...

Seasonal expressions of androgen receptor, estrogen receptors and cytochrome P450 aromatase in the uteri of the wild Daurian ground squirrels (Spermophilus dauricus)

“… 32 , 33 Size and weight of reproductive organs were generally related to their reproductive ability. 34 The seasonality of uterine mass shown in the present study was in agreement with extensive reports in this species, 8 , 27 and the present histological results showed that the uterine gland grew bigger, including nucleus growth and gland lumen extension in the breeding season, and the gland lumen shrunk remarkably and less nuclei were observed in the non-breeding season. These findings were similar to those observations in other seasonal breeders, such as possums and dunnarts.…”

“… 36 Our previous studies have also indicated that plasma estradiol-17β and progesterone concentrations were significantly higher in the breeding season than those in the non-breeding season in this species. 8 , 18 , 27 Therefore, the present results suggested that seasonal changes of uterine morphology and histology in the wild Daurian ground squirrels might be dependent on ovarian steroid hormones cycles.…”

“…The wild Daurian ground squirrel ( Spermophilus dauricus ) is a typical seasonal breeder, which has a strict and extremely compressed breeding season from April to May and a long period of nonbreeding season from June to the following March. 8 , 20 , 21 , 27 In the wild Daurian ground squirrels, our previous studies have implicated that there were seasonal changes in the ovarian weight and follicular compositions and furthermore the circulating levels of estradiol-17β were also changed seasonally. 18 In a previous study of our group, there were statistical significant differences in the glandular nuclear numbers of endometrium between the breeding and non-breeding seasons.…”

Seasonal expressions of VEGF and its receptors VEGFR1 and VEGFR2 in the prostate of the wild ground squirrels (<em>Spermophilus dauricus</em>)

“…The specificity of VEGF, VEGFR1 and VEGFR2 antibodies has been described in our previous studies. 28 Normal goat serum was selected to replace the initial antiserum treatment in the sections of the control group. The DAB staining was evaluated using ImageJ and the integrated density of positive staining area were calculated.…”