Differential expression of Rab5 and Rab7 small GTPase proteins in placental tissues from pregnancies affected by maternal COVID-19

Abstract Purpose The majority of pregnancies affected by maternal COVID-19 do not result in fetal transmission, yet several studies have identified parenchymal changes in their placental tissues, suggesting a placental response to SARS-CoV-2 at the maternal-fetal interface. While many COVID-19 placental studies have focused on the expression of canonical SARS-CoV-2 entry proteins angiotensin-converting enzyme 2 (ACE2) and transmembrane serine protease 2 (TMPRSS2), further characterization of subcellular molecules involved in viral trafficking have not yet been investigated in these tissues. Of interest are Rab proteins, a family of small GTPase proteins that direct intracellular transport between different endocytic organelles. Rab5 and Rab7 in particular have previously been implicated in human immunodeficiency virus (HIV) and cytomegalovirus (CMV) invasion of placental trophoblast cells in vitro, but the localization of these molecules has not been fully characterized within the human maternal-fetal interface or within placental tissues from SARS-CoV-2 infected pregnancies. Methods Using fluorescent immunohistochemistry, Rab5 and Rab7 placental localization and comparative fluorescence intensity was explored in a cohort of placental tissues from pregnancies affected by maternal COVID-19 disease (“COVID”, n=15) in comparison with contemporary controls (“Control”, n=10). Fluorescence intensity was quantified using corrected total cell fluorescence (CTCF) values. Findings Within placental villi, Rab5 was consistently localized in syncytiotrophoblast cells (sTB) and cytotrophoblast cells (cTB). Rab5 had significantly higher fluorescence intensity in the COVID cohort (Control mean 1.96 +/- SEM 0.16 vs COVID mean 2.62 +/- SEM 0.09, p=0.0014). In contrast, while Rab7 was also localized within placental villous sTB and cTB, Rab7 fluorescence intensity was significantly downregulated in COVID vs Control placentas (Control mean 35.9 +/- SEM 4.1 vs mean 20.1 +/- SEM 0.52, p= 0.0001). Implications This differential expression of Rab5 and Rab7 suggests that placental endocytic pathways may be altered at the maternal-fetal interface in pregnancies affected by maternal SARS-CoV-2 infection. As key molecules governing intracellular vesicle transport including viral trafficking, RabGTPase proteins may of interest for ongoing studies examining placental responses to COVID-19 in pregnancy.