Alpha/Beta Hydrolase Domain-Containing Protein 2 regulates the rhythm of follicular maturation and estrous stages of the female reproductive cycle

Abstract

Therian female fertility is defined by a successful and strictly periodic ovarian cycle, which is under the control of gonadotropins and steroid hormones, particularly progesterone and estrogen. The latter two are produced by the ovaries that are engaged in controlled follicular growth, maturation and release of the eggs, i.e. ovulation. It is well known that steroid hormones regulate ovarian cycles via genomic signaling, by altering gene transcription and protein synthesis. However, despite this well-studied mechanism, steroid hormones can also signal via direct, non-genomic action, by binding to their membrane receptors. Here we show, that the recently discovered sperm membrane progesterone receptor α/β hydrolase domain-containing protein 2 (ABHD2) is highly expressed in mammalian ovaries where the protein plays a novel regulatory role in follicle maturation and the sexual cycle of females. Ablation of Abhd2 caused a dysregulation of the estrous cycle rhythm with females showing shortened luteal stages while remaining in the estrus stage for a longer time. Interestingly, the ovaries of Abhd2 knockout (KO) females resemble polycystic ovary morphology with a high number of atretic antral follicles that could be rescued with injection of gonadotropins. Such a procedure also allowed Abhd2 KO females to ovulate a significantly increased number of mature and fertile eggs in comparison to their wild-type littermates. These results suggest a novel regulatory role of ABHD2 as an important factor in nongenomic steroid regulation of the female reproductive cycle. Results Abhd2 expression in ovarian stromal cells and corpora luteaWhile ABHD2 has been described as an important regulator of sperm function 10 , the function of ABHD2 in female reproduction was not known. Interestingly, unlike the male reproductive tissues, we found that ABHD2 is not detected in the female gametes but is predominantly expressed in the stromal cells surrounding the developing follicles (Fig. 1a). The presence of both ABHD2 protein and mRNA was observed in pre-pubertal mouse ovaries, as shown here by immunohistochemical (IHC) staining and reverse transcriptase quantitative PCR (RT-qPCR; Fig. 1b and c). Around one month after birth, when the ovulatory cycle begins, ABHD2 expression is further found in the lutein cells of corpus luteum (Fig. 1a). In correlation with this, qPCR studies showed highest Abhd2 mRNA presence right after ovulation during the estrus stage (Fig. 1c), and the expression levels are even further increased after induction of superovulation by gonadotropin injection (Fig. 1c).

The epithelial potassium channel Kir7.1 is stimulated by progesterone

“…ABHD2 has been shown to regulate ion channel activation in human sperm cells by breaking down the endocannabinoid 2-arachidonoylglycerol in the cell membrane ( Miller et al, 2016 ). However, CPECs isolated from global Abhd2 knockout mice that were generated in our laboratory ( Björkgren et al, 2019 Preprint ) showed activation of Kir7.1 similar to that of cells from wild-type animals ( Fig. 4, E and F ), thus negating any possible effect of the receptor on Kir7.1 activation.…”

“…All experiments were performed in accordance with National Institutes of Health guidelines for animal research and approved by the University of California, Berkeley Animal Care and Use Committee (AUP 2015–07-7742), with every effort made to minimize suffering for the animals. A thorough description of how the Abhd2 full knockout mouse line was generated is provided elsewhere ( Björkgren et al, 2019 Preprint ).…”

Lipidomic QTL in Diversity Outbred mice identifies a novel function for α/β hydrolase domain 2 (Abhd2) as an enzyme that metabolizes phosphatidylcholine and cardiolipin

“…Abhd2 has been previously characterized as a monoacylglycerol lipase with potent effects on male fertility[24] and ovulation in female mice [23]. In sperm, Abhd2 is activated by progesterone, cleaves monoacylglycerols (1-arachadonoylglycerol and 2-arachadonoylglycerol) to remove the inhibition of the CatSper calcium channel thereby allowing for sperm activation.…”

“…Progesterone-induced activation of Abhd2 is required for its lipid cleavage function and regulating ovulation in females [23,24]; however, the effect of male sex hormones on Abhd2 has not been demonstrated. In a study of cerebral cortex development, a perinatal testosterone spike in male mice drove mitochondrial lipid composition and maturation [36].…”

“…To determine if Abhd2 is a key driver of liver phospholipids, we obtained a whole-body knockout of Abhd2 from Dr. Polina Lishko at UC Berkeley [23,24]. Wildtype (WT) and Abhd2 knockout (Abhd2 KO ) mice were maintained on the same Western diet (WD), high in fat and sucrose, that was provided to DO mice used for the lipidomic genetic screen [14].…”