Nasibyan L. Mechanism of action of Staphylococcus aureus peptidoglycan on the rat myometrial contractility

Peptidoglycan (PG) is a structural component of gram-positive and gram-negative bacteria cell wall. It surrounds the bacterial cell membrane and has pathogenic and immunogenic properties. During the growth, division or destruction of a bacterial cell, PG is released into the environment, spreaded by the bloodstream and adsorbed on tropical cells, where it eventually initiates pathological processes. The presence of PG in a woman's genital tract during pregnancy is associated with stimulation of uterine contractility and premature birth. The effect of PG on the myometrium in non-pregnants has not been well studied, despite Staphylococcus aureus is frequently detected in the genital tract of infertile women even without obvious signs of inflammation. We have hypothesized that PG may be a pathogenetic factor in infertility, due to impairment of uterine contractility in such a way that fertilization or implantation of a fertilized egg becomes impossible. Thus, the purpose of the study was to determine if PG can directly modulate contractility of myometrial cells of pregnant and non-pregnant rats, and if so what is the mechanism of its action. The effect of PG on the rat myometrial contractility and the mechanisms of its action were studied by tensometry and calcium imaging. Evaluation of the parameters of myometrial spontaneous contractions in pregnant and non-pregnant rats under the action of PG has shown the changes not only in their amplitude, but also in temporal characteristics. However, the PG-induced changes in the parameters of myometrial contractions within the groups of pregnant and nonpregnant rats were not the same. In non-pregnant rats PG exerted a stronger effect on the duration of contractions, while in the group of pregnant animals the increase in amplitude was more pronounced. In both groups of rats, the duration of the contraction's onset phase was only slightly increased by PG, whereas the relaxation phase increased by more than 50%. Under hyperestrogenia PG elicited some suppressive effect on the myometrial contractions, while progesterone stimulated the effects of PG. The COX-2 blocker, nimesulide, inhibited the PG-induced myometrial contractility in pregnant rats, but it had no effect in the group of non-pregnant animals. Inactivation of Gi/o protein by pertussis toxin abrogated stimulating properties of PG. When PG was applied to acutely isolated uterine smooth muscle myocytes, an increase in intracellular calcium content was detected. In myometrial strips from both pregnant and non-pregnant animals, application of PG after cessation of spontaneous myometrial contractions in calcium-free medium was able to activate 1-2 phasic contractions which could be inhibited by the IP3 receptor blocker 2-ARB. In the presence of voltage-gated L-type calcium channels inhibitor, nifedipine, which completely suppressed spontaneous myometrium contractility, PG could still evoke single myometrial contraction in non-pregnant animals. Nifedipine was also able to suppress stimulated uterine contractions. It is concluded that .PG of S. aureus modulates myometrial contractility of both pregnant and nonpregnant rats via intracellular calcium level increasing through Ca2+ influx as well as Ca2+ from the SR.