An important mediator of progesterone's effects is its nuclear progesterone receptor (PGR). However, it has recently become evident that, at least in the uterus, many of the actions initialized by progesterone are mediated by non-genomic progesterone receptors [
1], e.g. progesterone receptor membrane component 1 (PGRMC1; [
2,
3]). PGRMC1 was first described in 1998 [
4] as a putative progesterone-binding membrane receptor of approximately 22 kDa [
2]. The protein is expressed in a variety of tissues, e.g. liver, kidney, adrenal glands, uterus and leukocytes [
2,
5,
6]. It was recently shown that PGRMC1 is part of a membrane complex that binds progesterone [
2,
3]. PGRMC1 is believed to be involved in progesterone signaling in the reproductive system and it mediates progesterone's anti-apoptotic effects on granulosa cells [
2,
5,
7,
8]. PGRMC1 binds to and positively regulates several members in the microsomal cytochrome P450 family of proteins, which are key players in intracellular sterol metabolism and steroidogenesis [
5,
6,
9,
10]. We have recently shown that reduced PGRMC1 levels are associated with premature ovarian failure (POF; [
5]). Furthermore, a PGRMC1 missense variant identified in a patient with POF shows perturbed interaction with the P450 member CYP7A1 [
5]. Recent studies have characterized the expression of PGRMC1 in uterine and placental tissues of murine origin [
8,
11]. Nothing is known about the natural variation of PGRMC1's expression throughout the human menstrual cycle or about the association of PGRMC1 levels to conditions with reduced fertility.
The aim of this study was to determine the natural expression levels of PGRMC1 in an easy accessible tissue throughout the menstrual cycle and to assess PGRMC1 levels in conditions associated with reduced fertility and anovulation. PGRMC1 is ubiquitously expressed and we selected nucleated peripheral blood cells for the analysis.