Pregnancy, Programming and Preeclampsia: Gap Junctions at the Nexus of Pregnancy-induced Adaptation of Endothelial Function and Endothelial Adaptive Failure in PE

Abstract

The challenge of pregnancy to the mother requires that her own metabolic and endocrine needs be met while also taking on the literally growing demands of the unborn child. While all of the mother's organs require continued support, the uterus and now added placenta must also develop substantially. One critical area of adaptation is thus the ability to provide added blood flow over and above that already serving the preexisting maternal organs. Previous reviews have covered in detail how this is achieved from an endocrine or indeed vascular physiology standpoint and we will not repeat that here. Suffice it to say in addition to new vessel growth, there is also the need to achieve reduced vascular resistance through maintenance of endothelial vasodilation, particularly through NO and PGI2 production in response to multiple agonists and their associated cell signaling systems. In this review, we continue our focus on pregnancy adaptive changes at the level of cell signaling, with a particular emphasis now on the developing story of the critical role of gap junctions. Remapping of cell signaling itself beyond changes in individual hormones and respective receptors brings about global changes in cell function, and recent studies have revealed that such post-receptor changes in cell signaling are equally if not more important in the process of pregnancy adaptation of endothelial function than the upregulated expression of vasodilator synthetic pathways themselves. The principle significance, however, of reviewing this aspect of pregnancy adaptation of endothelial cell function is that these same gap junction proteins that mediate pregnancy-adapted changes in vasodilatory signaling function may also be the focal point of failure in diseased pregnancy, and clues as to how and why are given by comparing studies of Cx43 functional suppression at wound sites with studies of preeclamptic pregnancy. If preeclamptic pregnancy is indeed a pregnancy misconstrued by the body in endocrine terms to be a wound, then the kinases so activated that correspondingly suppress Cx43 function in the vascular endothelium may also be valid pharmacologic targets for novel therapies in the near future.

Phosphorylation of Ser-279/282 and Tyr-265 positions on Cx43 as possible mediators of VEGF-165 inhibition of pregnancy-adapted Ca2+ burst function in ovine uterine artery endothelial cells

“…Furthermore, a sub-maximal dose of PMA, which gives rise to a physiologic level of inhibition of sustained ATP Ca2+ response (defined as a level of inhibition to approach the lesser function of NP-UAEC), can be completely reversed by the Src family kinase inhibitor PP2 [amino-5-(4-chlorophenyl)-7-(t-butyl) pyrazolo (3,4d) pyrimidine]. This underscores both the susceptibility of Cx43 to endocrine inhibition in P-UAEC and the reversibility of the observed loss of Ca2+ burst function (Bird et al 2013). …”

“…A failure to demonstrate a pregnancy-enhanced ability to produce vasodilators is a hallmark of the preeclamptic condition (Bird et al 2003). Recently, we (Bird, et al 2013) put forth a model of both pregnancy adaptation and disease-related failure whereby control of Cx43 function or lack thereof can be explained by the hormonal milieu and the associated endothelial cell signaling of healthy or diseased pregnancies. The model proposes that in normal pregnancy, factors known to circulate in abundance in pregnancy such as cAMP, cGMP, and estrogen, as well as mechanical signals such as shear stress, may be able to signal to the endothelium to upregulate Cx43 gap junction function.…”

“…As a consequence, there is an increase in the capacity of the endothelial tissue to produce an enhanced Ca2+ response to vasodilatory agonists, which then allows enhanced vasodilator production. Conversely, the hormonal environment of preeclampsia shares similarities with that of a wound site including abnormally high levels of growth factors and cytokines (reviewed in (Bird et al 2013)) known to signal through kinases such as PKC (protein kinase C), Src, and ERK (extracellular-signal-regulated kinase) to phosphorylate Cx43. Phosphorylation of Cx43 at multiple c-terminal amino acid residues such as Ser-279/282, Tyr-265, Ser-368, and Ser-262 are targeted by the aforementioned signaling pathways, and have been described as inhibitory phosphorylations (Lampe and Lau 2000).…”

“…Phosphorylation of Cx43 at multiple c-terminal amino acid residues such as Ser-279/282, Tyr-265, Ser-368, and Ser-262 are targeted by the aforementioned signaling pathways, and have been described as inhibitory phosphorylations (Lampe and Lau 2000). The phorbol ester, PMA (phorbol myristic acid), is commonly used as a receptor-independent inhibitor of gap junction function (Lampe 1994; Sirnes, et al 2008; van der Zandt, et al 1990) and signals through PKC, Src, and ERK in UAEC (Bird et al 2013). Indeed, when P-UAEC are exposed to PMA, sustained phase Ca2+ burst responses to ATP are dramatically reduced (Bird et al 2013; Cale and Bird 2006), and this is associated with the phosphorylation of Cx43 at both positions Ser-279/282 via the ERK-1/2 pathway and Tyr-265 via the Src pathway.…”

“…The phorbol ester, PMA (phorbol myristic acid), is commonly used as a receptor-independent inhibitor of gap junction function (Lampe 1994; Sirnes, et al 2008; van der Zandt, et al 1990) and signals through PKC, Src, and ERK in UAEC (Bird et al 2013). Indeed, when P-UAEC are exposed to PMA, sustained phase Ca2+ burst responses to ATP are dramatically reduced (Bird et al 2013; Cale and Bird 2006), and this is associated with the phosphorylation of Cx43 at both positions Ser-279/282 via the ERK-1/2 pathway and Tyr-265 via the Src pathway. Furthermore, a sub-maximal dose of PMA, which gives rise to a physiologic level of inhibition of sustained ATP Ca2+ response (defined as a level of inhibition to approach the lesser function of NP-UAEC), can be completely reversed by the Src family kinase inhibitor PP2 [amino-5-(4-chlorophenyl)-7-(t-butyl) pyrazolo (3,4d) pyrimidine].…”