Maternal and fetal thyroid dysfunction following porcine reproductive and respiratory syndrome virus2 infection

Altered structural and transporter-related gene expression patterns in the placenta play a role in fetal demise during Porcine reproductive and respiratory syndrome virus infection

BACKGROUND

Porcine reproductive and respiratory syndrome virus (PRRSV) can be transmitted across the maternal-fetal-interface from an infected gilt to her fetuses. Although fetal infection status and disease outcomes vary, the mechanisms are not completely understood. The objective was to assess targeted placental structural and transporter-related gene expression patterns. At day 85 of gestation pregnant pigs were challenged with PRRSV, and at 12 days post maternal infection sows and fetuses were sacrificed, and the placental tissue was collected. Grouping of fetuses was by preservation status and PRRS viral load (VL): control (CTRL, n = 14), viable and low VL fetus (VIA_LVF, n = 15), viable and high VL fetus (VIA_HVF, n = 21), meconium mild and low VL fetus (MECm_LVF, n = 14), meconium mild and high VL fetus (MECm_HVF, n = 14), and meconium severe and high VL fetus (MECs_HVF, n = 13). NanoString was used to evaluate the expression of 86 genes: actin cytoskeleton signaling, arachidonic acid pathway, integrin signaling, intercellular junctions, transporters, and VEGF signaling. Statistical analyses were performed using Limma with P ≤ 0.05 considered significant.

RESULTS

We identified 1, 7, 0, 29, and 39 differentially expressed genes in VIA_LVF, VIA_HVF, MECm_LVF, MECm_HVF, and MECs_HVF, respectively, contrasted to CTRL. Placental transporter genes were significantly impacted (i.e., downregulation of SLC1A3, SLC1A5, SLC2A1, SLC2A3, SLC2A5, SLC2A10, SLC2A12, SLC7A4, SLC16A5, SLC16A10, and SLC27A6; and upregulation of SLC2A2, SLC16A3, and SLC27A4), compared to CTRL. Actin cytoskeleton signaling (ARHGEF6 and ARHGEF7), arachidonic acid (PTGES3 and PTGIS), integrin signaling (FN1 and ITGB6), intercellular junctions (CDH3 and CDH11), and VEGF signaling (MAPK3 and HPSE) gene groupings were significantly impacted, compared to CTRL.

CONCLUSION

Data reported here indicate that fetal PRRSV infection levels rather than fetal demise is necessary for transcriptional dysregulation of the fetal placenta, with a tendency towards more downregulation in the target gene sets among susceptible fetuses. These results generally support that in susceptible fetuses there is altered solute transportation, placental structural integrity, and reduced angiogenesis. The data described here is associated with fetal PRRS resistance/resilience and susceptibility.

The endocannabinoid system in bovine tissues: characterization of transcript abundance in the growing Holstein steer

BACKGROUND

The endocannabinoid system (ECS) is highly integrated with seemingly all physiological and pathophysiological processes in the body. There is increasing interest in utilizing bioactive plant compounds, for promoting health and improving production in livestock. Given the established interaction between phytochemicals and the ECS, there are many opportunities for identification and development of therapies to address a range of diseases and disorders. However, the ECS has not been thoroughly characterized in cattle, especially in the gastrointestinal tract. The objective of this study was to characterize the distribution and transcriptional abundance of genes associated with the endocannabinoid system in bovine tissues.

METHODS

Tissues including brain, spleen, thyroid, lung, liver, kidney, mesenteric vein, tongue, sublingual mucosa, rumen, omasum, duodenum, jejunum, ileum and colon were collected from 10-mo old Holstein steers (n = 6). Total RNA was extracted and gene expression was measured using absolute quantification real time qPCR. Gene expression of endocannabinoid receptors CNR1 and CNR2, synthesis enzymes DAGLA, DAGLB and NAPEPLD, degradation enzymes MGLL and FAAH, and transient receptor potential vanilloids TRPV3 and TRPV6 was measured. Data were analyzed in R using a Kruskal-Wallis followed by a Wilcoxon rank-sum test. Results are reported as the median copy number/20 ng of equivalent cDNA (CN) with interquartile range (IQR).

RESULTS

The greatest expression of CNR1 and CNR2 was in the brain and spleen, respectively. Expression of either receptor was not detected in any gastrointestinal tissues, however there was a tendency (P = 0.095) for CNR2 to be expressed above background in rumen. Expression of endocannabinoid synthesis and degradation enzymes varied greatly across tissues. Brain tissue had the greatest DAGLA expression at 641 CN (IQR 52; P ≤ 0.05). DAGLB was detected in all tissues, with brain and spleen having the greatest expression (P ≤ 0.05). Expression of NAPEPLD in the gastrointestinal tract was lowest in tongue and sublingual mucosal. There was no difference in expression of NAPEPLD between hindgut tissues, however these tissues collectively had 592% greater expression than rumen and omasum (P ≤ 0.05). While MGLL was found to be expressed in all tissues, expression of FAAH was only above the limit of detection in brain, liver, kidney, jejunum and ileum. TRPV3 was expressed above background in tongue, rumen, omasum and colon. Although not different from each other, thyroid and duodenum had the greatest expression of TRPV6, with 285 (IQR 164) and 563 (IQR 467) CN compared to all other tissues (P < 0.05).

CONCLUSIONS

These data demonstrate the complex distribution and variation of the ECS in bovine tissues. Expression patterns suggest that regulatory functions of this system are tissue dependent, providing initial insight into potential target tissues for manipulation of the ECS.

Gene expression in heart, kidney, and liver identifies possible mechanisms underpinning fetal resistance and susceptibility to in utero PRRSV infection

Porcine reproductive and respiratory syndrome (PRRS) is one of the costliest diseases to pork producers worldwide. We tested samples from the pregnant gilt model (PGM) to better understand the fetal response to in-utero PRRS virus (PRRSV) infection. Our goal was to identify critical tissues and genes associated with fetal resilience or susceptibility. Pregnant gilts (N=22) were infected with PRRSV on day 86 of gestation. At 21 days post maternal infection, the gilts and fetuses were euthanized, and fetal tissues collected. Fetuses were characterized for PRRS viral load in fetal serum and thymus, and preservation status (viable or meconium stained: VIA or MEC). Fetuses (N=10 per group) were compared: uninfected (UNIF; <1 log/µL PRRSV RNA), resilient (HV_VIA, >5 log virus/µL but viable), and susceptible (HV_MEC, >5 log virus/µL with MEC). Gene expression in fetal heart, kidney, and liver was investigated using NanoString transcriptomics. Gene categories investigated were hypothesized to be involved in fetal response to PRRSV infection: renin- angiotensin-aldosterone, inflammatory, transporter and metabolic systems. Following PRRSV infection, CCL5 increased expression in heart and kidney, and ACE2 decreased expression in kidney, each associated with fetal PRRS susceptibility. Liver revealed the most significant differential gene expression: CXCL10 decreased and IL10 increased indicative of immune suppression. Increased liver gene expression indicated potential associations with fetal PRRS susceptibility on several systems including blood pressure regulation (AGTR1), energy metabolism (SLC16A1 and SLC16A7), tissue specific responses (KL) and growth modulation (TGFB1). Overall, analyses of non-lymphoid tissues provided clues to mechanisms of fetal compromise following maternal PRRSV infection.

Late gestation fetal hypothyroidism alters cell cycle regulation across multiple organ systems

BACKGROUND

Hypothyroidism is a common endocrine disruption observed in utero that adversely affects fetal growth and maturation leading to long-term impacts on health; however, the exact molecular mechanisms by which these deleterious effects occur are unknown. We hypothesize that fetal hypothyroidism during late gestation will disrupt cell cycle regulation in a tissue-specific manner. To evaluate this, eight pregnant gilts were dosed with either methimazole or an equivalent negative control during days 85-106 out of 114 days of gestation (n = 4/group). Following treatment, the gilts were humanely euthanized, and tissue samples of fetal heart, ileum, kidney, lung, liver, muscle, spleen, and thymus taken from two male and two female fetuses (n = 32) from each gilt.

RESULTS

The relative expression of three cell cycle promoters (CDK1, CDK2, and CDK4), and one cell cycle inhibitor (CDKN1A) was compared in each tissue to determine the effect of hypothyroidism on the developing fetus. All of the eight tissues examined experienced at least one significant up- or downregulation in the expression of the aforementioned genes as a result of treatment with methimazole. Substantial changes were observed in the liver and muscle, with the latter experiencing significant downregulations of CDK1, CDK2, and CDK4 as a result of treatment. In addition, all tissues were examined for changes in protein content, which further elucidated the impact of hypothyroidism on the fetal liver by the observation of a marked increase in protein content in the methimazole-treated group. Finally, the heart and liver were histologically examined for evidence of cellular hyperplasia and hypertrophy by measuring average nuclei density and size in each tissue, with the results showing a significant decrease in average nuclei size in the liver of hypothyroid fetuses.

CONCLUSIONS

Collectively, these findings indicate the occurrence of organ-specific disruptions in cell cycle progression as a result of in utero hypothyroidism, which may explain the long term and widespread effects of hypothyroidism on fetal development.

A DIO2 missense mutation and its impact on fetal response to PRRSV infection

BACKGROUND

Porcine reproductive and respiratory syndrome virus 2 (PRRSV-2) infection during late gestation substantially lowers fetal viability and survival. In a previous genome-wide association study, a single nucleotide polymorphism on chromosome 7 was significantly associated with probability of fetuses being viable in response to maternal PRRSV-2 infection at 21 days post maternal inoculation. The iodothyronine deiodinase 2 (DIO2) gene, located ~ 14 Kilobase downstream of this SNP, was selected as a priority candidate related to fetal susceptibility following maternal PRRSV-2 infection. Our objectives were to identify mutation(s) within the porcine DIO2 gene and to determine if they were associated with fetal outcomes after PRRSV-2 challenge. Sequencing of the DIO2, genotyping identified variants, and association of DIO2 genotypes with fetal phenotypes including DIO2 mRNA levels, viability, survival, viral loads, cortisol and thyroid hormone levels, and growth measurements were conducted.

RESULTS

A missense variant (p.Asn91Ser) was identified in the parental populations from two independent PRRSV-2 challenge trials. This variant was further genotyped to determine association with fetal PRRS outcomes. DIO2 mRNA levels in fetal heart and kidney differed by the genotypes of Asn91Ser substitution with significantly greater DIO2 mRNA expression in heterozygotes compared with wild-type homozygotes (P < 0.001 for heart, P = 0.002 for kidney). While Asn91Ser did not significantly alter fetal viability and growth measurements, interaction effects of the variant with fetal sex or trial were identified for fetal viability or crown rump length, respectively. However, this mutation was not related to dysregulation of the hypothalamic-pituitary-adrenal and thyroid axis, indicated by no differences in circulating cortisol, T4, and T3 levels in fetuses of the opposing genotypes following PRRSV-2 infection.

CONCLUSIONS

The present study suggests that a complex relationship among DIO2 genotype, DIO2 expression, fetal sex, and fetal viability may exist during the course of fetal PRRSV infection. Our study also proposes the increase in cortisol levels, indicative of fetal stress response, may lead to fetal complications, such as fetal compromise, fetal death, or premature farrowing, during PRRSV infection.

PRRSV-2 viral load in critical non-lymphoid tissues is associated with late gestation fetal compromise

The impact of late gestation PRRSV-2 infection is highly variable within a litter, with a subset of fetuses displaying varying degrees of compromise following infection while others remain viable despite significant systemic viral load. To understand the underlying cause of this variation, we examined the susceptibility, distribution and impact of viral infection within non-lymphoid tissues. Samples of brain, heart, kidney, liver, lung, and skeletal muscle were obtained from fetuses of pregnant gilts at gestation day 86, and the presence and distribution of CD163+ cells within each tissue evaluated via immunohistofluorescence. Equivalent samples were collected from phenotypic extremes representing resistant, resilient and susceptible fetuses at 21 days following infection of pregnant gilts with PRRSV-2 at day 86 of gestation. Viral load and its impact in each tissue was evaluated by a combination of qPCR, in vitro viral recovery, and local expression of IFNG and CD163. Resting populations of CD163+ cells were observed in all six non-lymphoid tissues from healthy day 86 fetuses, though the apparent density and the morphology of positive cells varied between tissue. Viral RNA was detected in all six tissues derived from fetuses previously classified as highly infected, and infectious viral particles successfully recovered. Significantly more viral RNA was detected in heart, brain, lung and skeletal muscle of susceptible fetuses, relative to their viable counterparts. Infection was associated with an increase in the expression of CD163 in brain, kidney and lung. In addition, the presence of virus in each tissue coincided with a significant upregulation in the expression of IFNG, but the scale of this response was not associated with fetal susceptibility. Thus, PRRSV-2 is widely distributed across these susceptible non-lymphoid fetal tissues, and fetal outcome is associated with local viral load in critical fetal organs.

Genome wide association study of thyroid hormone levels following challenge with porcine reproductive and respiratory syndrome virus

Introduction: Porcine reproductive and respiratory syndrome virus (PRRSV) causes respiratory disease in piglets and reproductive disease in sows. Piglet and fetal serum thyroid hormone (i.e., T3 and T4) levels decrease rapidly in response to Porcine reproductive and respiratory syndrome virus infection. However, the genetic control of T3 and T4 levels during infection is not completely understood. Our objective was to estimate genetic parameters and identify quantitative trait loci (QTL) for absolute T3 and/or T4 levels of piglets and fetuses challenged with Porcine reproductive and respiratory syndrome virus. Methods: Sera from 5-week-old pigs (N = 1792) at 11 days post inoculation (DPI) with Porcine reproductive and respiratory syndrome virus were assayed for T3 levels (piglet_T3). Sera from fetuses (N = 1,267) at 12 or 21 days post maternal inoculation (DPMI) with Porcine reproductive and respiratory syndrome virus of sows (N = 145) in late gestation were assayed for T3 (fetal_T3) and T4 (fetal_T4) levels. Animals were genotyped using 60 K Illumina or 650 K Affymetrix single nucleotide polymorphism (SNP) panels. Heritabilities, phenotypic correlations, and genetic correlations were estimated using ASREML; genome wide association studies were performed for each trait separately using Julia for Whole-genome Analysis Software (JWAS). Results: All three traits were low to moderately heritable (10%-16%). Phenotypic and genetic correlations of piglet_T3 levels with weight gain (0-42 DPI) were 0.26 ± 0.03 and 0.67 ± 0.14, respectively. Nine significant quantitative trait loci were identified for piglet_T3, on Sus scrofa chromosomes (SSC) 3, 4, 5, 6, 7, 14, 15, and 17, and collectively explaining 30% of the genetic variation (GV), with the largest quantitative trait loci identified on SSC5, explaining 15% of the genetic variation. Three significant quantitative trait loci were identified for fetal_T3 on SSC1 and SSC4, which collectively explained 10% of the genetic variation. Five significant quantitative trait loci were identified for fetal_T4 on SSC1, 6, 10, 13, and 15, which collectively explained 14% of the genetic variation. Several putative immune-related candidate genes were identified, including CD247, IRF8, and MAPK8. Discussion: Thyroid hormone levels following Porcine reproductive and respiratory syndrome virus infection were heritable and had positive genetic correlations with growth rate. Multiple quantitative trait loci with moderate effects were identified for T3 and T4 levels during challenge with Porcine reproductive and respiratory syndrome virus and candidate genes were identified, including several immune-related genes. These results advance our understanding of growth effects of both piglet and fetal response to Porcine reproductive and respiratory syndrome virus infection, revealing factors associated with genomic control of host resilience.

Effects of porcine reproductive and respiratory syndrome virus (PRRSV) on thyroid hormone metabolism in the late gestation fetus

Porcine reproductive and respiratory syndrome virus (PRRSV) in late gestation causes a profound suppression of circulating maternal and fetal thyroid hormone during a critical window of development. To understand this relationship, we evaluated thyroid hormone metabolism at the maternal-fetal interface and within fetal tissues, along with hormone metabolite levels in serum. Fetuses were classified using an established model based on viral load in serum and thymus, and preservation status, including uninfected (UNIF), high-viral load viable (HV-VIA), and high-viral load meconium-stained (HV-MEC), with additional controls from sham-inoculated gilts (CON). Expression of three iodothyronine deiodinases, five sulfotransferases, sulfatase, and two solute carriers known to transport thyroid hormone were evaluated in maternal endometrium and fetal placenta, liver, and kidney. Serum thyroxin (T4), reverse triiodothyronine (rT3), and diiodothyronine (T2) were evaluated via liquid chromatography tandem mass spectrometry. Significant changes in gene expression were observed in all four tissues, with the liver being the most severely impacted. We observed local and fetal specific regulation of maternal tissues through significant upregulation of DIO2 and DIO3 expression in the endometrium corresponding to infected but viable fetuses relative to uninfected and control fetuses. Expression levels of DIO2 and DIO3 were significantly higher in the resilient (HV-VIA) fetuses relative to the susceptible (HV-MEC) fetuses. A substantial decrease in serum T4 was confirmed, with no corresponding increase in rT3 or T2. Collectively, these results show that thyroid hormone metabolism is altered at the maternal-fetal interface and within the PRRSV infected fetus and is associated with fetal viability.

Effect of porcine reproductive and respiratory syndrome virus 2 on angiogenesis and cell proliferation at the maternal-fetal interface

Angiogenesis and cell proliferation in reproductive tissues are essential events for the maintenance of pregnancy, and alterations can lead to compromised fetal development and survival. Porcine reproductive and respiratory syndrome virus 2 (PRRSV-2) induces reproductive disease with negative financial and production impact on the swine industry. PRRSV-2 infection alters placental physiology through inflammatory and apoptotic pathways, yet fetal susceptibility varies. This study aimed to evaluate angiogenesis and cell proliferation in the porcine maternal-fetal interface (MFI) and determine if these physiological processes were altered by PRRSV-2 infection. Thirty-one pregnant gilts were inoculated with PRRSV-2 at gestation day 86 ± 0.4 (mean ± SD). Seven control gilts were sham-inoculated. All gilts were euthanized at 12 days postinoculation. Angiogenesis and cell proliferation were determined through the detection of vascular endothelial growth factor (VEGF) and Ki-67, respectively, using immunofluorescence of the MFI from 4 fetal resilience groups: uninfected (UNIF), high viral load–viable (HVL-VIA), and HVL-meconium-stained (MEC) from PRRSV-infected gilts, as well from sham-inoculated (CON) gilts. VEGF immunolabeling in the uterine submucosa was significantly lower in MEC compared with UNIF and HVL-VIA groups. Significantly greater Ki67 immunolabeling was detected in the trophoblasts of CON fetuses versus all other groups, and in uterine epithelium of CON and UNIF fetuses versus HVL-VIA and MEC. These results suggest that fetal resilience may be related to greater cell proliferation in uterine epithelium, and fetal compromise with reduced uterine submucosal angiogenesis, except fetuses with intrauterine growth restriction, in which inherently lower submucosal angiogenesis may be protective against PRRSV infection.

Porcine reproductive and respiratory virus 2 infection of the fetus results in multi-organ cell cycle suppression

Porcine reproductive and respiratory syndrome virus (PRRSV) infection during late gestation negatively affects fetal development. The objective of this study was to identify the fetal organs most severely impacted following infection, and evaluate the relationship between this response and fetal phenotypes. RNA was extracted from fetal heart, liver, lung, thymus, kidney, spleen, and loin muscle, collected following late gestation viral challenge of pregnant gilts. Initially, gene expression for three cell cycle promoters (CDK1, CDK2, CDK4) and one inhibitor (CDKN1A) were evaluated in biologically extreme phenotypic subsets including gestational age-matched controls (CON), uninfected (UNIF), high-viral load viable (HV-VIA), and high-viral load meconium-stained (HV-MEC) fetuses. There were no differences between CON and UNIF groups for any gene, indicating no impact of maternal infection alone. Relative to CON, high-viral load (HV-VIA, HV-MEC) fetuses showed significant downregulation of at least one CDK gene in all tissues except liver, while CDKN1A was upregulated in all tissues except muscle, with the heart and kidney most severely impacted. Subsequent evaluation of additional genes known to be upregulated following activation of P53 or TGFb/SMAD signaling cascades indicated neither pathway was responsible for the observed increase in CDKN1A. Finally, analysis of heart and kidney from a larger unselected population of infected fetuses from the same animal study showed that serum thyroxin and viral load were highly correlated with the expression of CDKN1A in both tissues. Collectively these results demonstrate the widespread suppression in cell division across all tissues in PRRSV infected fetuses and indicate a non-canonical regulatory mechanism.

Thyroid hormone suppression in feeder pigs following polymicrobial or porcine reproductive and respiratory syndrome virus-2 challenge

Thyroid hormones are powerful regulators of growth, development, and basal metabolic rate and can be dysregulated under conditions of severe stress or illness. To understand the role of these hormones in porcine disease response, serum samples were obtained from three batches of nursery-aged pigs (n = 208) exposed to a natural polymicrobial disease challenge with an array of bacterial and viral pathogens. Levels of total thyroxin (T4) and triiodothyronine (T3) assessed in sera by radioimmunoassay, decreased significantly by 14 days post-exposure (DPE). Levels of T3 partially rebounded by 48 DPE, while T4 levels remain depressed. Post-exposure T3 and T4 levels were positively correlated with acute and long-term average daily gain (ADG). Cross-sectional sampling of animals maintained at the high health source farms, showed no equivalent change in either hormone when managed under standard industrial conditions. To further elucidate the effect of porcine reproductive and respiratory syndrome virus (PRRSV)-infection on thyroid hormone levels, archived sera over 42 days post inoculation (DPI) from nursery pigs (N = 190) challenged with one of two PRRSV2 strains by the PRRS Host Genetics Consortium were similarly assessed, with animals selected in a two-by-two design, to investigate biological extremes in ADG and viral load (VL). All animals showed a similar decrease in both thyroid hormones reaching a minimum at 7 DPI and returning to near pre-challenge levels by 42 DPI. Post-challenge T3 and T4 levels were significantly greater in high ADG groups, with no significant association with VL or strain. The results of this study demonstrate porcine susceptibility to thyroid disruption in response to disease challenge and demonstrate a relationship between this response and growth performance.

Fetal hypoxia and apoptosis following maternal porcine reproductive and respiratory syndrome virus (PRRSV) infection

Background

Mechanisms of fetal death following maternal PRRSV2 infection remain uncharacterized, although hypoxia from umbilical cord lesions and/or placental detachment due to apoptosis are hypothesized. We performed two experiments examining hypoxia and apoptosis in PRRSV-infected and non-infected, third-trimester fetuses to elucidate possible associations with fetal death. Fetuses were selected based on four phenotypic infection groups: fetuses from non-challenged control gilts (CTRL); low viral load fetuses (LVL; Exp 1) or uninfected fetuses (UNINF; Exp 2) from inoculated gilts; viable high viral load fetuses (HVL-VIA); and HVL meconium-stained fetuses (HVL-MEC).

Results

In experiment 1, paraffin embedded fetal tissues collected 21 days post maternal infection (DPI) were examined for DNA fragmentation associated with apoptosis. Positively stained foci were larger and more numerous (P < 0.05) in heart, liver, and thymus of HVL-VIA and HVL-MEC compared to CTRL and LVL fetuses. In experiment 2, group differences in gene expression within the hypoxia (HIF1a, IDO1, VEGFa, LDHA, NOS2, NOX1) and apoptosis (CASP3, CASP7, CASP8, CASP9, RIPK1, RIPK3) pathways were assessed by RT-qPCR in fetal tissues collected at 12 DPI. High viral load fetuses showed differential expression relative to the CTRL and UNINF (P < 0.05 for all). Brain tissue from HVL-VIA and HVL-MEC fetuses presented increased expression of CASP7, CASP8, RIPK3, HIF1a and IDO1. Fetal heart showed increased expression of CASP8, HIF1a, IDO and NOX1 and a decrease in NOS2 expression in infected groups. CASP7, CASP9, RIPK1 and RIPK3 were only increased in the heart of HVL-VIA while VEGFa was only increased for HVL-MEC fetuses. Thymus from HVL-MEC had decreased expression of CASP9 and there was increased IDO1 in all infected fetuses.

Conclusions

There is strong evidence of apoptosis occurring in the heart, liver and thymus of highly viral load fetuses at 21 DPI. Furthermore, there was clear upregulation of apoptotic genes in the heart of high viral load infected fetuses and less prominent upregulation in the brain of PRRSV-infected fetuses, whereas thymus appears to be spared at 12 DPI. There was no strong evidence of hypoxia at 12 DPI in brain and thymus but some indication of hypoxia occurring in fetal heart.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-02883-0.

Differential responses in placenta and fetal thymus at 12 days post infection elucidate mechanisms of viral level and fetal compromise following PRRSV2 infection

BACKGROUND

A pregnant gilt infected with porcine reproductive and respiratory syndrome virus (PRRSV) can transmit the virus to her fetuses across the maternal-fetal-interface resulting in varying disease outcomes. However, the mechanisms leading to variation in fetal outcome in response to PRRSV infection are not fully understood. Our objective was to assess targeted immune-related gene expression patterns and pathways in the placenta and fetal thymus to elucidate the molecular mechanisms involved in the resistance/tolerance and susceptibility of fetuses to PRRSV2 infection. Fetuses were grouped by preservation status and PRRS viral load (VL): mock infected control (CTRL), no virus detected (UNINF), virus detected in the placenta only with viable (PLCO-VIA) or meconium-stained fetus (PLCO-MEC), low VL with viable (LVL-VIA) or meconium-stained fetus (LVL-MEC), and high VL with viable (HVL-VIA) or meconium-stained fetus (HVL-MEC).

RESULTS

The host immune response was initiated only in fetuses with detectable levels of PRRSV. No differentially expressed genes (DEG) in either the placenta or thymus were identified in UNINF, PLCO-VIA, and PLCO-MEC when compared to CTRL fetuses. Upon fetal infection, a set of core responsive IFN-inducible genes (CXCL10, IFIH1, IFIT1, IFIT3, ISG15, and MX1) were strongly upregulated in both tissues. Gene expression in the thymus is a better differentiator of fetal VL; the strong downregulation of several innate and adaptive immune pathways (e.g., B Cell Development) are indicative of HVL. Gene expression in the placenta may be a better differentiator of fetal demise than the thymus, based-on principle component analysis clustering, gene expression patterns, and dysregulation of the Apoptosis and Ubiquitination pathways.

CONCLUSION

Our data supports the concept that fetal outcome in response to PRRSV2 infection is determined by fetal, and more significantly placental response, which is initiated only after fetal infection. This conceptual model represents a significant step forward in understanding the mechanisms underpinning fetal susceptibility to the virus.