V-ATPase upregulation during early pregnancy: a possible link to establishment of an inflammatory response during preimplantation period of pregnancy

Abstract

Various mechanisms exist to prevent a potentially deleterious maternal immune response that results in compromising survival of semiallogeneic fetus. In pregnancy, there is a necessary early preimplantation inflammatory stage followed by a postimplantation antiinflammatory stage. Thus, there is a biphasic 'immune response' observed during the course of pregnancy. We provide the evidence that capacitation of sperm induced the expression of a2 isoform of V-ATPase (ATP6V0A2 referred to as a2V), leukemia inhibitory factor (Lif), Il1b, and Tnf in the sperm. Capacitated sperm also released cleaved N-terminal domain of a2V-ATPase (a2NTD), which upregulates the gene expression of Lif, Il1b, Tnf, and monocyte chemotactic protein-1 (Ccl2 (Mcp1)) in the uterus. Unfertilized eggs had low a2V expression, but after fertilization, the expression of a2V increased in zygotes. This increased level of a2V expression was maintained in preimplantation embryos. Seminal plasma was necessary for upregulation of a2V expression in preimplantation embryos, as mating with seminal vesicle-deficient males failed to elicit an increase in a2V expression in preimplantation embryos. The infiltration of macrophages into the uterus was significantly increased after insemination of both sperm and seminal plasma during the preimplantation period of pregnancy. This dynamic infiltration into the uterus corresponded with the uterine a2V expression through the induction of Ccl2 expression. Furthermore, the polarization ratio of M1:M2 (pro-inflammatory/anti-inflammatory) macrophages in the uterus fluctuated from a ratio of 1.60 (day 1) to 1.45 (day 4) when female mice were inseminated with both sperm and seminal plasma. These data provide evidence that exposure to semen may initiate an inflammatory milieu by inducing a2V and cytokine/chemokine expression, which triggers the influx of macrophages into the preimplantation uterus during the onset of pregnancy and ultimately leads to successful pregnancy outcome.

Future directions of clinical laboratory evaluation of pregnancy

“…16 The a2 subunit functions to transport H 1 into the intracellular lumen and also functions as an endosomal pH-sensor. 31 There are several lines of evidence showing that a2V-ATPase is involved in various aspects of mammalian reproduction such as spermatogenesis, 7 sperm capacitation, embryonic development, implantation 32 and placentation. 16 The a2 isoform of VATPase is located specifically in the acrosomal membrane upon capacitation of murine sperm.…”

“…Seminal fluid induces pro-inflammatory cytokines and chemokines such as GM-CSF, IL-6, IL-8, MCP-1, MIP-3a, and IL-1a in the female reproductive tract. 32,[35][36][37] Our recent study showed that exposure of sperm to seminal plasma is essential for the infiltration of macrophages in the preimplantation uterus. 32 In addition, capacitation appears to cause the release of a2NTD, which is the N-terminal portion from a2V-ATPase.…”

“…32,[35][36][37] Our recent study showed that exposure of sperm to seminal plasma is essential for the infiltration of macrophages in the preimplantation uterus. 32 In addition, capacitation appears to cause the release of a2NTD, which is the N-terminal portion from a2V-ATPase. We have also shown that a2NTD induces maternal inflammatory cytokines such as leukemia inhibitory factor, IL-1b, TNF-a, MIP-1a, and exposure of the uterus to sperm accompanied by seminal fluid enhances pregnancy success rate.…”

“…32 Infiltration of macrophage in the preimplantation uterus is essential for regulation of inflammatory milieu required for successful implantation. 32,38 Our recent studies have shown that a2V-ATPase expression in spermatozoa obtained from normal fertile men is higher than sperm obtained from infertile men. Similarly, motile spermatozoa had significantly higher a2V-ATPase expression levels than immotile spermatozoa.…”

“…32,34 Although seminal fluid has been conventionally viewed as transport media for spermatozoa traversing the female reproductive tissues, it is now known to have broader biological actions in regulating female fertility. 35,36 Seminal fluid contains a complex array of cytokines, chemokines and other bioactive molecules.…”