Endometrial responses to bacterial and viral infection: a scoping review

BACKGROUND

The endometrium is a highly dynamic tissue that undergoes dramatic proliferation and differentiation monthly in order to prepare the uterus for implantation and pregnancy. Intrauterine infection and inflammation are being increasingly recognized as potential causes of implantation failure and miscarriage, as well as obstetric complications later in gestation. However, the mechanisms by which the cells of the endometrium respond to infection remain understudied and recent progress is slowed in part owing to similar overlapping studies being performed in different species.

OBJECTIVE AND RATIONALE

The aim of this scoping review is to systematically summarize all published studies in humans and laboratory animals that have investigated the innate immune sensing and response of the endometrium to bacteria and viruses, and the signaling mechanisms involved. This will enable gaps in our knowledge to be identified to inform future studies.

SEARCH METHODS

The Cochrane Library, Ovid Embase/Medline, PubMed, Scopus, Google Scholar, and Web of Science databases were searched using a combination of controlled and free text terms for uterus/endometrium, infections, and fertility to March 2022. All primary research papers that have reported on endometrial responses to bacterial and viral infections in the context of reproduction were included. To focus the scope of the current review, studies in domesticated animals, included bovine, porcine, caprine, feline, and canine species were excluded.

OUTCOMES

This search identified 42 728 studies for screening and 766 full-text studies were assessed for eligibility. Data was extracted from 76 studies. The majority of studies focused on endometrial responses to Escherichia coli and Chlamydia trachomatis, with some studies of Neisseria gonorrhea, Staphylococcus aureus, and the Streptococcus family. Endometrial responses have only been studied in response to three groups of viruses thus far: HIV, Zika virus, and the herpesvirus family. For most infections, both cellular and animal models have been utilized in vitro and in vivo, focusing on endometrial production of cytokines, chemokines, and antiviral/antimicrobial factors, and the expression of innate immune signaling pathway mediators after infection. This review has identified gaps for future research in the field as well as highlighted some recent developments in organoid systems and immune cell co-cultures that offer new avenues for studying endometrial responses to infection in more physiologically relevant models that could accelerate future findings in this area.

WIDER IMPLICATIONS

This scoping review provides an overarching summary and benchmark of the current state of research on endometrial innate immune responses to bacterial and viral infection. This review also highlights some exciting recent developments that enable future studies to be designed to deepen our understanding of the mechanisms utilized by the endometrium to respond to infection and their downstream effects on uterine function.

The serotonin reuptake inhibitor fluoxetine induces human fetal membrane sterile inflammation through p38 MAPK activation

Serotonin Reuptake Inhibitors (SRIs) are often used as first line therapy for depression and other psychiatric disorders. SRI use during pregnancy is associated with preterm premature rupture of membranes (PPROM) and subsequent preterm birth. The objective of this study was to investigate the mechanism(s) responsible for SRI-associated PPROM. Putative mechanisms underlying PPROM include fetal membrane (FM) inflammation, increased apoptosis, and/or accelerated senescence, the later which may be reversed by statins. Human FM explants from normal term deliveries without labor, infection, or antidepressant use were treated with or without the SRI, fluoxetine (FLX), either alone or in the presence of a p38 MAPK inhibitor or the statins, simvastatin or rosuvastatin. FMs were also collected from women either unexposed or exposed to FLX during pregnancy. FLX significantly increased FM p38 MAPK activity and secretion of inflammatory IL-6. Inhibition of p38 MAPK reduced FM IL-6 secretion in response to FLX. Statins did not reduce the SRI-induced FM IL-6 production. FMs from women exposed to FLX during pregnancy expressed elevated levels of p38 MAPK activity compared to matched unexposed women. FMs exposed to FLX did not exhibit signs of increased apoptosis and/or accelerated senescence. These results indicate that the SRI, FLX, may induce sterile FM inflammation during pregnancy through activation of the p38 MAPK pathway, and in the absence of apoptosis and senescence. These findings may better inform clinicians and patients as they weigh the risks and benefits of SRI antidepressant treatment during pregnancy.

Retromer stabilizes transient membrane insertion of L2 capsid protein during retrograde entry of human papillomavirus

Retromer, a cellular protein trafficking complex, sorts human papillomaviruses (HPVs) into the retrograde pathway for transport of HPV to the nucleus during virus entry. Here, we conducted a protein modulation screen to isolate four artificial transmembrane proteins called traptamers that inhibit different steps of HPV entry. By analyzing cells expressing pairs of traptamers, we ordered the trafficking steps during entry into a coherent pathway. One traptamer stimulates ubiquitination of the L2 capsid protein or associated proteins and diverts incoming virus to the lysosome, whereas the others act downstream by preventing sequential passage of the virus through retrograde compartments. Complex genetic interactions between traptamers revealed that a cell-penetrating peptide (CPP) on L2 mediates transient insertion of L2 into the endosome membrane, which is stabilized by retromer-L2 binding. These results define the retrograde entry route taken by HPV and show that retromer can play a role in CPP-mediated membrane insertion.