In a recent study posted on Bio Rxiv*, Researchers investigated the pathogenic mechanisms of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) during pregnancy using digital spatial profiling of placental tissue.
Several studies have reported the development of a preeclampsia-like syndrome in pregnant women exposed to SARS-CoV-2. Vascular damage and inflammation are elevated in placental tissue from coronavirus disease 2019 (COVID-19) patients. Placental dysfunction is the underlying cause of pre-eclampsia. Pre-eclampsia is classified as early-onset (<34 weeks gestation) and late-onset (>34 weeks) depending on when symptoms are detected.
Premature preeclampsia is associated with placental malformation leading to poor placental perfusion and dysfunction, but the cause remains unknown. Maternal pathological factors that cause placental dysfunction, such as endothelial dysfunction and systemic hypertension, are thought to contribute to late-onset preeclampsia.
In the present study, researchers used whole-transcriptome digital spatial profiling of the placenta to understand the mechanisms of SARS-CoV-2 pathogenesis during pregnancy. The study involved an unvaccinated pregnant woman who had symptoms of COVID-19 in her third trimester. Archived placental tissues collected from 2016 to 2018 served as controls.
SARS-CoV-2 and controls were matched for gestational age, maternal age and comorbidities. Placental size, weight, gross changes, fetal sex and weight, and method of delivery were recorded. Placental specimens were analyzed by a trained pathologist and a tissue microarray (TMA) was created from the samples.
The investigation focused on seven samples from the SARS-CoV-2 group, as three fetuses had died. Similarly, one sample from the control was excluded due to poor quality. TMA slides were stained using fluorescent markers to characterize cell types and histological features. TMAs were hybridized using Whole Transcriptome Atlas (WTA) barcode probe sets of approximately 18,000 genes.
Raw data were normalized to 134 negative probes of the WTA probe set. Different gene expression analyzes were performed separately for villus core stromal cells and trophoblasts, including regions of interest, between the SARS-CoV-2 and control groups. Pathway enrichment analysis was performed and gene set enrichment was clustered and visualized.
Placental cores were obtained from 7 participants and 9 controls who tested positive for COVID-19 in the previous 15 days before delivery. There were no significant differences in placental weight, fetal weight, maternal age, or gestational age between SARS-CoV-2-positive subjects and controls. Three neonates from the SARS-CoV-2 group and four from the control group were delivered prematurely.
Four SARS-CoV-2-positive subjects and five controls had comorbidities such as gestational diabetes, bipolar disorder, hyperthyroidism, and hypothyroidism. Infarcts were seen in the placenta of 3 SARS-CoV-2-positive individuals. Placentas from two controls showed hypoplasia leading to premature birth.
There was no evidence of SARS-CoV-2 viral load in placental cores of COVID-19 subjects. The SARS-CoV-2 group had significantly more differentiated clusters (CD68)-positive immune cells in terminal villi than controls. Principal component analysis (PCA) revealed a separation of trophoblast and villous core stromal cells between the two groups.
In response to SARS-CoV-2, there were more differentially expressed genes (DEGs) in anchor villi than in terminal villi of villus core stromal cells and trophoblasts. Moreover, the DEGs of anchor and terminal villi were highly overlapping. However, overlap of DEGs between villous core stromal cells and trophoblasts was minimal.
Pathway enrichment analysis revealed significant activation of several preeclampsia- and oxidative stress-related pathways. Villus core stromal cells showed positive enrichment of immune-related pathways. Trophoblasts showed positive enrichment of estrogen responses, peroxisomal pathways, and E2F targets.
Overall, 1641 and 1339 genes were significantly upregulated and downregulated, respectively, in terminal and tethered villus trophoblasts in response to SARS-CoV-2. In particular, pregnancy-associated plasma protein A (PAPPA), PAPPA2, and placental alkaline phosphatase (ALPP) were upregulated. Downregulated genes included complement component C1Q, osteopontin, caveolin 1, clotting factor XII, and several collagens.
Pathways related to blood pressure and vascular tension were upregulated, and pathways related to collagen deposition, coagulation, vasoconstriction, allograft rejection, and the complement pathway were downregulated. In villous core stromal cells of tethered and terminal villi, 1026 genes were upregulated and 2697 were downregulated in response to SARS-CoV-2. Pathways related to oxidative stress, methylglyoxal levels, and nitrosative stress were enriched.
Taken together, the researchers described a unique response of villous core stromal cells and trophoblasts from the terminal and tethered villi of the placenta to SARS-CoV-2. Examination of transcriptional changes in these cells revealed an enrichment of pre-eclampsia-associated pathways. This suggests that the placenta of pregnant subjects with SARS-CoV-2 adopts a transcriptional profile consistent with that observed in pregnant women with pre-eclampsia.
bioRxiv publishes non-peer-reviewed, preliminary scientific reports and should not be considered conclusive, to guide clinical practice/health-related actions, or to be treated as established information .