Conditional ablation of macrophages disrupts ovarian vasculature

Abstract

Macrophages are the most abundant immune cell within the ovary. Their dynamic distribution throughout the ovarian cycle and heterogenic array of functions suggest the involvement in various ovarian processes, but their functional role has yet to be fully established. The aim was to induce conditional macrophage ablation to elucidate the putative role of macrophages in maintaining the integrity of ovarian vasculature. Using the CD11b-diphtheria toxin receptor (DTR) mouse, in which expression of human DTR is under the control of the macrophage-specific promoter sequence CD11b, ovarian macrophages were specifically ablated in adult females by injections of diphtheria toxin (DT). CD11b-DTR mice were given DT treatment or vehicle and ovaries collected at 2, 8, 16, 24 and 48 h. Histochemical stains were employed to characterise morphological changes, immunohistochemistry for F4/80 to identify macrophages and the endothelial cell marker CD31 used to quantify vascular changes. In normal ovaries, macrophages were detected in corpora lutea and in the theca layer of healthy and atretic follicles. As macrophage ablation progressed, increasing amounts of ovarian haemorrhage were observed affecting both luteal and thecal tissue associated with significant endothelial cell depletion, increased erythrocyte accumulation and increased follicular atresia by 16 h. These events were followed by necrosis and profound structural damage. Changes were limited to the ovary, as DT treatment does not disrupt the vasculature of other tissues likely reflecting the unique cyclical nature of the ovarian vasculature and heterogeneity between macrophages within different tissues. These results show that macrophages play a critical role in maintaining ovarian vascular integrity.

Ovarian phagocyte subsets and their distinct tissue distribution patterns

“…It is equally interesting to ask why IA/IE low F4/80 C macrophages, which were not capable of phagocytosis, were present in the atretic follicle. Secondly, a previous study reported that depletion of macrophages through CD11b disrupted ovarian vasculature (Turner et al 2011), suggesting a critical role of macrophages in angiogenesis. Remodeling of vasculature is dramatic during formation of a corpus luteum.…”

“…Secondly, fluctuation of the general macrophage population during the estrous cycle has been reported, although those macrophages were not further characterized (Katabuchi et al 1996, 1997, Takaya et al 1997. Involvement of macrophages in ovulation has been demonstrated by various methods (Brannstrom et al 1993, Watanabe et al 1997, Van der Hoek et al 2000, Matsuura et al 2002. It remains to be determined which types of leukocyte(s)/macrophage(s) are more critical players.…”

“…Many studies have investigated potential roles of ovarian macrophages in those ovarian events, and significant progress has been achieved during the last two decades. Macrophages have been shown to participate in ovulatory processes and in luteinization (Cohen et al 1999, Bukulmez & Arici 2000, Wu et al 2004, Turner et al 2011. Their involvement in ovarian follicular atresia has also been demonstrated in various mammalian species (Kasuya 1997, Gaytan et al 1998a, 1998b, Inoue et al 2000.…”

Ovarian Follicular Atresia

“…Macrophages secrete many of the aforementioned cytokines and growth factors, including TNF, bFGF, IGF, and EGF, which stimulate granulosa cell proliferation, suppress apoptosis, and promote follicular development. Moreover, in a number of rodent models, experimental induction of a paucity of ovarian macrophages has detrimental effects on follicle development and ovulation rate (Van der Hoek et al, 2000), ovarian vascularization (Turner et al, 2011), and fertility (Cohen et al, 1997). Others have noted there are no direct interactions between macrophages and primordial follicles during the earliest phases of follicular growth, indicating early growth of follicles occurs independently of macrophage influences (Wu et al, 2004).…”

The critical importance of ovarian angiogenesis

“…For example, neutrophils stimulate the formation of luteal endothelial cell capillary-like structures (Jiemtaweeboon et al 2011). Whilst, Turner et al (2011) recently demonstrated that macrophages play a crucial role in maintaining vascular integrity in mice. This concept is further supported by the observations that bone marrow-derived vascular progenitor cells and macrophages contribute to neovascularisation during CL formation (Kizuka et al 2012).…”