CXCL12 May Drive Inflammatory Potential in the Ovine Corpus Luteum During Implantation

Stacia Z Mcintosh,Kelsey E Quinn,Ryan L Ashley

doi:10.1007/s43032-021-00791-0

Abstract

Adequate corpus luteum (CL) function is paramount to successful pregnancy. Structural and functional CL integrity is controlled by diverse cell types that contribute and respond to the local cytokine milieu. The chemokine ligand 12 (CXCL12) and receptor, CXCR4, are modulators of inflammation and cell survival, but little is understood about CXCL12-CXCR4 axis and CL functional regulation. Corpora lutea from control nonpregnant ewes (n = 5; day 10 estrous cycle (D10C)) and pregnant ewes (n = 5/day) on days 20 (D20P) and 30 (D30P) post-breeding were analyzed for gene and protein expression of CXCL12, CXCR4, and select inflammatory cytokines. In separate cell culture studies, cytokine production was evaluated following CXCL12 treatment. Abundance of CXCL12 and CXCR4 increased (P < 0.05) in pregnant ewes compared to nonpregnant ewes, as determined by a combination of quantitative PCR, immunoblot, and immunofluorescence microscopy. CXCR4 was detected in steroidogenic and nonsteroidogenic cells in ovine CL, and select pro-inflammatory mediators were greater in CL from pregnant ewes. In vitro studies revealed greater abundance of tumor necrosis factor (TNF) following CXCL12 administration (P = 0.05), while P4 levels in cell media were unchanged. Fully functional CL of pregnant ewes is characterized by increased abundance of inflammatory cytokines which may function in a luteotropic manner. We report concurrent increases in CXCL12, CXCR4, and select inflammatory mediators in ovine CL as early pregnancy progresses. We propose CXCL12 stimulates production of select cytokines, rather than P4 in the CL to assist in CL establishment and survival.

Highlights

Progesterone (P4) synthesis and secretion during early pregnancy in mammals is the responsibility of the corpus luteum (CL), a dynamic, transient endocrine gland that develops in place of the follicle following ovulation
Protein abundance was detected by immunoblot, with elevated levels of both CXCL12 and CXCR4 on D30P (P < 0.05) compared to nonpregnant ewes on day 10 estrous cycle (D10C) (Fig. 1b and c)
Our present findings serve as the first report of concurrent increases in CXCL12, CXCR4, and inflammatory mediators in the fully functional ovine CL as early pregnancy progresses

Summary

Introduction

Progesterone (P4) synthesis and secretion during early pregnancy in mammals is the responsibility of the corpus luteum (CL), a dynamic, transient endocrine gland that develops in place of the follicle following ovulation. The ligand-receptor pair C-X-C motif chemokine ligand 12 (CXCL12) and C-X-C motif chemokine receptor 4 (CXCR4) is implicated in both implantation and placentation as reported in sheep [8, 9], humans [10, 11], baboons [12], and mice [13], and we along with others have reported that activation of CXCR4 by CXCL12 regulates inflammatory cytokine abundance at the fetal-maternal interface and in other tissues [14, 15] Potential roles for this chemokine duo have emerged in the ovary; human granulosa cells express CXCR4, and CXCL12 is found in follicular fluid [16], which may improve granulosa cell viability. We demonstrated ovine CL express CXCR4 [21], but the CXCL12-CXCR4 signaling axis has not been explored in terms of luteal function during early gestation

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