Peptidoglycan Recognition Proteins in the Pathogenesis of Preeclampsia and Periodontal Disease

Abstract

Background: Pre-eclampsia a potentially life threatening hypertensive disorder occurring in 3-14% of pregnancies. Its etiology is multifactorial involving the placenta. The only “cure” that currently exists is the delivery of the baby, which is often pre-term. There is no early pregnancy screening test to recognize those at risk. Recently, an altered immune-inflammatory responses at the placental level in response to infectious agents (eg., periodontal pathogens) have been proposed to be etiological for this pregnancy complication. A new class of Pattern Recognition Receptors called Peptidoglycan Recognition Proteins (PGRPs) constituting 4 distinct molecules PGRP 1-4 is emerging as a key player in modulating host responses to peptidoglycan and its breakdown products. A critical knowledge gap exists on the role of PGRPs in the innate immune responses that occur at the maternal-fetal interface in response to pathogens and their components that may be present in maternal circulation secondary to chronic infections. Aim: The aim of this pilot study is to investigate the expression PGRPs in the placenta of pre-eclamptic women. The overall goal is to better understand the association of periodontal disease and adverse pregnancy outcomes. Methods and Materials: This case control study consisted of subjects with: (1) normal term pregnancies (n=7) (2) pre-eclampsia (n=7). Preeclampsia was defined as hypertension (systolic blood pressure of ≥ 140 mm Hg or diastolic blood pressure of ≥ 90 mm Hg on at least 2 occasions, 4 hours to 1 week apart) and proteinuria (≥ 300 mg in a 24-hour urine collection or one dipstick measurement of ≥ 2+). A real time quantitative PCR array was used to analyze the relative mRNA expression of TLR2, TLR4, NOD1, NOD2, PGRP1, PGRP2, PGRP3, and PGRP4. Immunohistochemistry was performed to determine the cell type(s) expressing the PGRP proteins in the placental tissue. Summary statistics (mean, standard deviation, range, 95% confidence interval for the mean) were calculated for PGRP 1-4 expression for each group. Results and conclusions: The PCR data showed the expression of PGRPs 1, 3 and 4 in the placental samples. There was an up-regulation of PGRP-1 (1.4 fold) and down regulation of PGRP-3 (1.3 fold) and PGRP-4 (1.6 fold). TLR2, TLR4 and NOD2 mRNA were also elevated in the placental samples. Immunohistochemistry demonstrated positive staining for PGRPs 3 and 4 in the trophoblasts. The results from this novel research could lead to development of salivary and/or plasmatic biomarkers for early detection of PE and warrants further investigation.