Cervical HSV-2 infection causes cervical remodeling and increases risk for ascending infection and preterm birth
Cervical HSV-2 infection causes cervical remodeling and increases risk for ascending infection and preterm birth
Devin McGee 0 1 2
Arianna Smith 0 1 2
Sharra Poncil 0 1 2
Amanda Patterson 0 1 2
Alison I. Bernstein 0 2
Karen Racicot 0 1 2
0 Kennedy Shriver National Institute of Child Health and Human Development T32HD087166 , Arianna Smith
1 Department of Obstetrics, Gynecology and Reproductive Biology, College of Human Medicine, Michigan State University , Grand Rapids, MI , United States of America, 2 Department of Translational Science and Molecular Medicine, College of Human Medicine , Grand Rapids, MI , United States of America
2 Editor: Juan C. de la Torre, The Scripps Research Institute , UNITED STATES
Preterm birth (PTB), or birth before 37 weeks gestation, is the leading cause of neonatal mortality worldwide. Cervical viral infections have been established as risk factors for PTB in women, although the mechanism leading to increased risk is unknown. Using a mouse model of pregnancy, we determined that intra-vaginal HSV2 infection caused increased rates of preterm birth following an intra-vaginal bacterial infection. HSV2 infection resulted in histological changes in the cervix mimicking cervical ripening, including significant collagen remodeling and increased hyaluronic acid synthesis. Viral infection also caused aberrant expression of estrogen and progesterone receptor in the cervical epithelium. Further analysis using human ectocervical cells demonstrated a role for Src kinase in virus-mediated changes in estrogen receptor and hyaluronic acid expression. In conclusion, HSV2 affects proteins involved in tissue hormone responsiveness, causes significant changes reminiscent of premature cervical ripening, and increases risk of preterm birth. Studies such as this improve our chances of identifying clinical interventions in the future.
Data Availability Statement: All relevant data are
within the paper and its Supporting Information
Competing interests: The authors have declared
that no competing interests exist.
Preterm birth (PTB), or birth before 37 weeks gestation, affects approximately 12% of
pregnancies in the United States[1±7] and is the leading cause of neonatal mortality worldwide[
4, 6, 8
Despite its frequency and numerous consequences, PTB rates have increased over the last 30
2, 5, 7
]. Progress in improving PTB rates has been slow due to its complexity and the
lack of understanding of the underlying causes of the condition. Indeed, PTB is better defined
as a syndrome[
], and labor is the clinical outcome that results from an accumulation of risk
factors or pathologies[
The best characterized risk factor for PTB is inflammation associated with bacterial
infection. Despite years of research, we are still largely unable to predict or prevent even these cases
]. Viruses were relatively uncharacterized in the reproductive tract during
pregnancy but, with improved technologies for detection, i.e. PCR, they have recently garnered
more attention. Specifically, cervical viral infections with herpes simplex virus-2 (HSV2) and
human papillomavirus are being established as risk factors for PTB in women[11±17]. A
mouse model of systemic viral infection during pregnancy also showed that murine
gammaherpesvirus-68 (MHV68) infection increased risk for PTB, specifically in the presence of
]. Systemic MHV68 was also found to preferentially infect the pregnant
cervix in a mouse model[
Throughout most of pregnancy, the uterine cervix serves as a structural and immune
barrier that supports and protects the developing fetus[
]. The stromal extra-cellular matrix
(ECM) consists of a dense network of highly cross-linked collagen fibers, which provide the
cervix with the mechanical strength needed to physically support the fetus. The cervical
epithelial cells synthesize a highly effective mucus barrier that protects the fetus from ascending
bacteria. At the end of gestation the cervix undergoes significant remodeling, collectively termed
ªcervical ripeningº, resulting in complete structural reorganization of the cervix in preparation
Cervical ripening is associated with the functional loss of progesterone (P4) signaling within
]. This is not a result of systemic decline in P4, but tissue-specific
enzymatic conversion of active P4 to its metabolites[
9, 22, 23
]. Although there are few studies
characterizing estradiol (E2) function at this time, it likely becomes functional within the cervix as
local P4 declines and systemic E2 is increasing. Other changes at this time include increased
hyaluronic acid (HA) synthesis, epithelial proliferation and changes in mucus
composition. It is thought that these changes are necessary, at term, to ensure the cervix is prepared for
vaginal delivery. Conversely, if these changes are premature they could result in cervical
insufficiency, which is associated with ascending infection, intra-amniotic inflammation and PTB
It is our hypothesis that viral infection affects the homeostasis of the cervix during
pregnancy, and induces changes associated with cervical ripening prematurely. We propose these
changes will, thus, reduce structural support of the developing fetus and affect the barrier to
bacterial infections. To test this, we established a mouse model of sexually transmitted HSV2
infection to best mimic the clinical scenario in women. We then used this model to determine
if viral infection induced changes associated with premature cervical ripening and determined
if these changes increased risk of PTB associated with intra-vaginal bacterial infection.
Pregnant mice and infections
Animals were maintained at Michigan State University's Animal Facility and all procedures
are approved by Michigan State University's Institutional Animal Care and Use Committee.
C57BL/6 mice were purchased from Jackson Laboratory (Bar Harbor, ME); adult female mice
(8±12 wks of age) were mated and confirmed pregnant when vaginal plug was detected. To
study cervical phenotypes following viral infection, mice received HSV2 (105), or vehicle,
intra-vaginally, on GD10.5 after sedation with isoflurane. We previously confirmed this
treatment resulted in HSV2 infection of the cervix with PCR (protocol under viral quantification)
and we noted redness and swelling of the external genitalia in HSV2- treated mice. The genital
tract was monitored daily following HSV2 infection and scored on a 5-point scale, to verify
infection and ensure humane treatment of animals. Based on previously reported work, the
scoring was as follows: 1, slight redness of the external vagina; 2, swelling and redness of the
external vagina; 3, severe swelling and redness of both vagina and surrounding tissue and hair
loss in genital area; 4, genital ulceration with severe redness, swelling, and hair loss of genital
and surrounding tissue; 5, severe genital ulceration extending to surrounding tissue, as
2 / 15
previously describe by Kaushic and associates[
]. Mice with scores of 4 or 5 were sacrificed
although scores of 4/5 did not occur in any animals with HSV2 from GD10.5-GD15.5. Mice
were humanely sacrificed on GD15.5 using CO2 followed by cervical dislocation. The cervix
was flushed with sterile 1XPBS (3x with 30μl) and fixed in 4% PFA overnight. Animal numbers
per group: Virus, n = 8; control, n = 8. To determine how HSV2 affected PTB associated with
intra-vaginal infection, pregnant mice were infected with HSV2, intra-vaginally on GD10.5,
with E. coli (serotype O55), intra-vaginally on GD16.5, or HSV2 (GD10.5) + E. coli (GD16.5).
Mice were then monitored for preterm birth (birth of non-viable pups within 48h). Animal
numbers per group: Virus only, n = 8; E. coli only, n = 6; Virus + E. coli, n = 10.
Virus production and quantification
HSV2 was passaged in Vero Cells (CL-81, ATCC, Grand Island, NY) in DMEM plus 10% FBS.
After lysis supernatants were harvested, filtered (0.45 μm pore) and titered by 10-fold serial
dilutions on confluent monolayers. To detect viral titers in mice, DNA was extracted from the
cervix using DNeasy blood and tissue kit (69504, Qiagen, Valencia, CA). 100ng total DNA was
then assayed using primers specific for HSV2 (forward primer:
5’-GCT-CGA-GTG-CGAAAA-AAC-GTT-3’, reverse primer: 5’-TGC-GGT-TGA-TAA-ACG-CGC-AGT-3’) and
compared to a standard curve. Results reported as copies/100ng DNA. MHV68 growth and
quantification was previously described[
E. coli growth and quantification
Live E. coli (serotype O55; ATCC) were grown in nutrient agar, plated, and quantified by
colony formation. Vaginal inoculation was 20 μl bacteria equal to 105 CFU, as previously
described to attain 30% preterm birth. The dose of bacteria was confirmed by using an aliquot
of leftover bacteria to plate and repeat quantification of colony-forming units after overnight
incubation, as described previously[
Cervices were harvested from mice and immediately placed into 4% paraformaldehyde
rocking at room temperature overnight. Tissues were then washed in 70% ethanol, placed into
Thermo Scientific Excelsior ES tissue processor for routine processing, and embedded in
paraffin wax. For immunohistochemical (IHC) analysis of estrogen receptor (ER)-alpha,
progesterone receptor (PR) and Ki-67 proteins, 6μm sections underwent antigen retrieval by boiling
in sodium citrate buffer and treatment with endogenous biotin inhibitor (X059030-2, Dako,
Santa Clara, CA). Tissue sections were incubated with primary antibody (ER-alpha, MC20,
Santa Cruz Biotechnology; PR, A0098, Dako; Ki-67, RB-9106-S1, ThermoScientific) in
antibody diluent (S080981-2, Dako) overnight at 4C. The following day, tissue was incubated with
secondary antibody (ab6720, 1:200, goat anti-rabbit IgG-biotinylated, Abcam, Cambridge,
ME) for 1h, treated with an inhibitor of endogenous peroxidase (S200380-2, Dako), and
developed with diaminobenzidine (DAB) substrate-chromogen (K346711-2, Dako). Negative
controls underwent the same protocol but without primary antibody. For collagen staining, 10μm
tissue sections were stained with picrosirius red (Polysciences Inc, Warrington, PA). Using a
40x objective and polarized light, a photomicrograph was taken of 3 sections, 10 micrographs
per section, at least 20μm apart, per animal. The optical density (OD) of 10 non-overlapping
sections of each photo was analyzed. Specifically, after photomicrographs were converted to
gray scale, they were inverted and OD was calculated using a calibrated threshold and the
Rodbard standard curve (NIH Image J software). In this analysis, areas of dark collagen staining
have low OD values, and areas with light staining have high OD values. To account for cell
3 / 15
density, the OD was divided by cell nuclei/area. Animal numbers per group: Virus, n = 8;
control, n = 8.
Cell culture and treatments
Immortalized human ectocervical cells (ECT1, CRL-2614, ATCC, Grand Island, NY) were
cultured in keratinocyte serum free medium (17005±042, Gibco, Grand Island, NY) with bovine
pituitary extract and hEGF supplementation as recommended by ATCC under 5% CO2 at
37ÊC. Cells were confirmed to be mycoplasma free (13100±01, Southern Biotechnology,
Birmingham, Al). Inhibitor of Src was an inhibitor cocktail, SKI-1/PP1 (ab120839, ab120859,
Abcam, Cambridge, ME) resuspended in DMSO (5μM). Cells were treated with inhibitor for
1h prior to HSV2 infection (105 PFU). Supernatants and cells were collected 24 or 48h after
HSV2 infection, as indicated. To infect ECT-1 cells with HSV2, cells were inoculated with
HSV2 (105) in 500 μl for 1h prior to addition of 2.5 mL media (protocol for 35mm plate).
Results from cell culture experiments are representative of 4 independent experiments.
RNA, cDNA synthesis and qPCR
RNA was extracted from ECT-1 cells using RNeasy RNA extraction kit (74104, Qiagen,
Valencia, CA). RNA concentration and purity was analyzed using spectrophotometric analyses of
260/280 ratios with exclusions for samples that were below 1.7. For real-time quantitative
analysis of mRNA, 1 μg of RNA was reverse transcribed for each sample using iScript cDNA
synthesis kit (170±8891, Bio-Rad, Hercules, CA). The cDNA was diluted 1:20 in nuclease free water
and 5μl was mixed with SsoAdvanced Universal SYBR green superscript (172±5270, Bio-Rad,
Hercules, CA) and gene specific primers for ER-alpha (forward primer: 5’-GGC-CCC-AGC
TCC-TCC-TCA-T-3’, reverse primer:
5’-ACG-TTC-TTG-CAC-TTC-ATG-CTG-TA3’) and GAPDH (forward primer: 5’-AGG-GCT-GCT-TTT-AAC-TCT-GGT-3’, reverse
primer: 5’-CCC-CAC-TTG-ATT-TTG-GAG-GGA-3’). Samples were evaluated with the
Applied Biosystems qPCR machine. Values were normalized to GAPDH and calculated using
delta delta Ct method; delta delta Ct = delta ct treated- delta Ct control; results expressed as fold
differences from controls.
Hyaluronic acid ELISA
Hyaluronic acid concentration was assessed using ELISA (DHYAL0, R&D systems,
Minneapolis, MN). ECT1-conditioned medium was diluted 1:40, cervical flushes were diluted 1:160,
and samples were assayed according to manufacturer's protocol. Wavelength correction was
used by subtracting 540 nm readings from all readings at 450 nm. The subtraction was used to
correct for optical imperfections in the plate as recommended by manufacturer.
Western blot analysis
Cells were lysed in M-PER Mammalian Protein Extraction Reagent buffer (78503, Pierce,
Rockford, IL), with HALT protease inhibitor. Total protein concentrations were quantified
using BCA assay (23227, Pierce, Rockford, IL). Twenty-five micrograms of total proteins were
dissolved in 1X sample buffer, boiled for 5 minutes and separated on a 5±20% SDS-PAGE gel
in 1X Tris-Glycine SDS running buffer (Novex, Carlsbad, CA) at a constant voltage of 125V
for 2h. The proteins were transferred to PVDF membranes (0.45 μm, Novex, Carlsbad, CA) in
an XCell II Blot module apparatus (Novex, Carlsbad, CA) at a constant 25 V for 2hrs. Non-fat
milk (NFM) (5%) was used to block non-specific signals and immunoblotting was performed
with a 1:1000 dilution of primary antibodies against total Src and phospho-Src-Tyr527 (2105,
4 / 15
32G6, Cell Signaling, Danvers, MA), ER-alpha (MC20, Santa Cruz Biotechnology, CA), or
1:10,000 dilution of beta-actin (ab16039, Abcam, Cambridge, ME) in 2% NFM at 4ÊC
overnight. Membranes were washed in 1X PBST and a 1:10,000 dilution of goat anti-rabbit or goat
anti-mouse IgG-horseradish peroxidase (HRP) conjugate (Cell Signaling, Danvers, Mass) was
used as appropriate. Membranes were developed using HRP substrate (Amersham ECL Prime
Detection Reagent; General Electric, Buckinghamshire, UK) and immunoreactive proteins
were visualized using the Bio-Rad ChemiDoc XRS+ and Image Lab Software (Bio-rad).
Differences were determined using analysis of variance (ANOVA) (multiple comparisons,
Tukey's test), or independent t-test functions of Graph pad inSTAT statistical software (La
Jolla, CA). A p-value of 0.05 was considered significant, different letters denote significant
differences. Data is presented as mean ± standard error of the mean (SEM).
Herpes simplex virus-2 infection increases PTB associated with E. coli infection
A primary function of the pregnant cervix is to protect the upper reproductive tract from
ascending infection. To determine if cervical HSV2 infection affected this function, we
infected mice with HSV2 (105 PFU) on gestational day (GD) 10.5, intra-vaginally, to mimic a
sexually transmitted infection. At GD16.5 virus-infected and control mice were inoculated
with pathogenic E. coli (105 CFU), intra-vaginally, and rates of preterm birth were recorded
(Fig 1A). Within 36h, 7/9 mice that received HSV2 and E. coli had PTB, 2/6 animals with E.
coli alone had PTB, and 0/8 mice with HSV2 alone had litters that were preterm (defined as
delivery of all pups within 36h of E. coli).
Cervical viral infection affects stromal tissue organization
Because ascending infections are often associated with structural changes in the cervix, like
those that occur during cervical ripening, we next determined how cervical HSV2 infection
affected the tissue organization of the cervix during pregnancy. We first determined if viral
infection affected the cellular and/or extra-cellular structure of the cervical stroma. Mice were
infected with HSV2 or vehicle, intra-vaginally, at GD10.5, and cervices were collected at
GD15.5. Tissues were fixed, stained for collagen, and examined using bright light, and
polarized light microscopy. Under bright light, it was readily apparent that infected cervices had a
looser arrangement of collagen fibers compared to controls (Fig 2A). To quantify collagen
objectively, the sections were first viewed under polarized light and converted to gray scale
(Fig 2B). Images were then inverted and OD was calculated using a calibrated threshold and
the Rodbard standard curve (NIH Image J). In this analysis, areas of dark collagen staining
(dense collagen organization) are reported as low OD values, and areas with light staining
(looser collagen organization) are reported as higher OD values, and the OD is normalized to
cell number by dividing by number of nuclei per μm2. The infected cervix tissues had higher
OD compared to the controls, indicating the collagen was less dense in infected tissue (Fig
2C), (a<b, t-test, p = .0007). The cervical stroma was also less cellular in infected animals,
which was quantified by analyzing the number of nuclei per μ m2 (Fig 2D), (a>b, t-test, p =
5 / 15
Fig 1. Herpes simplex Virus-2 infection increases PTB associated with intra-vaginal E. coli. (A) Mice
were infected with HSV2 (105 PFU) on gestational day (GD) 10.5, intra-vaginally, to mimic a sexually
transmitted infection. At GD16.5 virus-infected and control mice were inoculated with pathogenic E. coli (105
CFU), intra-vaginally, and rates of preterm birth were recorded. (B) Percentage of PTB for mice with HSV2
only, E. coli only, or HSV2 + E. coli. Number of animals depicted within graph.
Viral infection causes aberrant expression of estrogen receptor-alpha and progesterone receptor in cervical epithelial cells
Cervical remodeling is associated with tissue-specific changes in steroid hormone signaling,
characterized by a shift from progesterone to estrogen dominance[
]. Therefore, we
determined if HSV2 affected expression of progesterone receptor (PR) and estrogen
receptoralpha (ER-alpha), the primary mediators of hormone function. At GD15.5, vehicle-treated
mice had very little, if any, ER-alpha staining in the cervical epithelium while HSV-infected
mice had irregular pockets of ER-alpha staining (Fig 3A). Progesterone receptor was also
absent in the epithelium of vehicle-treated mice at GD15.5, while it was highly expressed
HSV2-infected mice (Fig 3B). There was PR staining in the cervical stroma of both vehicle and
HSV2-infected mice at GD15.5 (Fig 3B). There was no positive staining in tissues when
primary antibody was absent (Fig 3C).
Epithelial cell proliferation and hyaluronic acid are increased by HSV2 infection of the pregnant cervix
Both epithelial cell proliferation and hyaluronic acid (HA) synthesis[
] increase during
cervical ripening therefore we determined how they were affected by HSV2. At GD15.5,
6 / 15
Fig 2. Cervical viral infection affects stromal tissue organization. Histological sections from cervices of
animals infected with MHV68, HSV-2 or vehicle were stained with picrosirius red to characterize collagen
organization. (A) Representative sections from pregnant mice with vehicle (Veh) or HSV2 were imaged under
bright light microscopy (4x) and shown in gray scale. (B) Representative images from control (Veh) and
infected (HSV2) animals under polarized light and gray scale conversion (40x). (C) Collagen content and
structure was quantified by calculating the optical density (OD) using 3 non-overlapping photos from 10
sections per animal, normalized to cell nuclei/μm2. Specifically, after photomicrographs were converted to
gray scale (as shown in (B)), they were inverted and OD was calculated using a calibrated threshold and the
Rodbard standard curve. In this analysis, areas of dark collagen staining have low OD values, and areas with
light staining have high OD values (a<b, t-test, p = .0007). (D) Cell density analysis, represented as the
number of nuclei per μm2 (a>b, t-test, p = .02). Animal treatments: Vehicle, n = 8; Virus, n = 8.
HSV2-infected mice had increased epithelial cell proliferation compared to GD15.5 NT mice,
as determined by Ki-67 staining (Fig 4A). Hyaluronic acid was quantified in the cervical
flushes from GD15.5 mice with and without viral infection and was significantly increased in
flushes from the HSV2-infected mice (Fig 4B)(a<b, t-test, p = .012).
Estrogen receptor-α and HA are increased by HSV2 in the human
cervical epithelial cell line, ECT-1
Next, to investigate the mechanism of HSV2-associated changes in hormone responsiveness,
we utilized the human epithelial cell line, ECT-1. First, we determined if ECT-1 cells had a
response to HSV2 that was similar to the mouse cervical epithelium. While HSV2 did increase
ER-alpha protein (Fig 5A), infection did not change ESR1 mRNA (Fig 5B)(analysis of variance
(ANOVA), n.s.), suggesting protein stabilization as opposed to increased transcription. We
also determined that HSV2 increased HA in ECT-1, as it did in vivo. Cells were infected with
HSV2 (105 PFU) and ECT-conditioned media was collected at 24h and 48h post-infection. At
48h, HA was increased in the media of HSV2 infected cells, compared to the NT controls (Fig
5C) (24h NT vs HSV2: t-test, n.s.; 48h NT vs HSV2: a<b, t-test, p = .017).
7 / 15
Fig 3. Viral infection causes aberrant expression of estrogen receptor and progesterone receptor in
cervical epithelial cells. (A) Representative images from vehicle (VEH) and infected (HSV2) animals
analyzed for ER-alpha or (B) PR protein using immunohistochemistry. (C) There was no staining in control
assay lacking primary antibody. Animal treatments: Vehicle, n = 8; Virus, n = 8.
Herpes simplex virus-2 regulates ER-α and HA via Src kinase in ECT-1
We then used ECT-1 cells to determine how HSV2 stabilized ER-alpha protein and induced
changes in HA expression. Since herpesviruses interact with integrins on the cell surface
] we postulated integrin signaling might lead to kinase activation, which could affect
ERalpha stabilization. We tested the response of several focal adhesion kinases to HSV2
infection and determined the tyrosine kinase, Src, was affected by infection. ECT-1 cells were
infected with HSV2 (105 PFU) and Src-Tyr527 phosphorylation was quantified at multiple
time points from 30m up to 8h post-infection. This phosphorylation site is an inhibitor of
function and acts as the primary regulator of Src, therefore, loss of phosphorylation at
Tyr527 indicates Src is active. We found that viral infection reduced phosphorylation (i.e.
activated Src) at 6h and 8h post-infection (Fig 6A, S1 Fig). To determine if Src could affect
ER-alpha, ECT-1 cells were treated with Src inhibitor, SKI/PP1, which resulted in decreased
ER-alpha protein (Fig 6B, S1 Fig) (ANOVA with Tukey's multiple comparison; NT vs VEH,
n.s.; NT vs SKI/PPI, p< .02; VEH vs SKI/PPI, p< .01). Finally, to test if HSV-associated
changes in ER-alpha were mediated by Src kinase, we inhibited Src (SKI-PP1) prior to
HSV2 infection and again measured ER-alpha protein. When ECT-1 cells were treated with
the Src inhibitor, HSV2 infection no longer caused an increase in ER-alpha protein (Fig 6C,
S1 Fig) suggesting HSV2 mediates ER-alpha protein stability by activating Src kinase in
cervical epithelial cells (ANOVA with Tukey's multiple comparison; HSV2 vs VEH/HSV2, n.s.;
HSV2 vs SKI/PPI-HSV2, n.s.; VEH/HSV2 vs SKI/PPI-HSV2, p< .04). Finally, we tested if
Src mediated the HSV-associated changes in HA. When we infected ECT-1 with HSV2 in
the presence of Src inhibitors (SKI-PP1), the virus-associated increase in HA was
diminished (Fig 6D), (ANOVA; Tukey's multiple comparison; a<b, p = .012; a>c, p = .026; b>c,
p = .0003).
8 / 15
Fig 4. Epithelial cell proliferation and hyaluronic acid are increased by HSV2 infection of the pregnant
cervix. (A) Cervical epithelial cell proliferation as determined by Ki-67 staining at GD15.5 in vehicle (VEH) and
virus (HSV2) treated mice. There was no staining in control assay lacking primary antibody. (B) Hyaluronic
acid was quantified in cervical flushes from vehicle and virus-treated animals at GD15.5 using ELISA (a<b,
ttest, p = .012). Animal treatments: Vehicle, n = 8; Virus, n = 8.
For the first time, to our knowledge, we report that intra-vaginal HSV2 infection increases
rates of preterm birth following intra-vaginal bacterial infection in a mouse model of
pregnancy. Specifically, HSV2 causes significant remodeling of collagen in the cervical stroma,
increased expression of ER-alpha and PR in the cervical epithelium, increased epithelial cell
proliferation, and up-regulated HA synthesis and/or shedding. Furthermore, using ECT-1
cells, we also discovered that HSV2 activates Src kinase, which mediates the increase in
ERalpha and HA. These results demonstrate that viral infection of the cervix, specifically, can
significantly change cervical structure and function during pregnancy and these changes are
associated with reduced protection against bacterial infections and PTB.
One intriguing finding of this study was the aberrant expression of ER and PR in cervical
epithelial cells of HSV2-infected mice. Cervical ripening at term coincides with a switch from
progesterone (P4) to estrogen (E2) dominance within the cervical tissue. In rodent models,
treatment with a PR antagonist is sufficient to induce cervical ripening and in women,
intravaginal P4 can delay cervical ripening and labor. While considerably less is known about the
9 / 15
Fig 5. Estrogen receptor-alpha and HA are increased by HSV2 in the human cervical epithelial cell
line, ECT-1. ECT-1 cells were treated with vehicle or HSV2 for 24h or 48h. (A) Representative Western blot
analysis of ER-alpha, and actin loading control. (B) Quantitative PCR was used to analyze ERA mRNA
expression in ECT-1 with and without HSV2 (ANOVA, n.s.). (C) Hyaluronic acid was quantified in ECT-1
conditioned medium 24 or 48h after treatment with vehicle or HSV-2 using ELISA (24h Veh vs Virus: t-test,
n.s.; 48h Veh vs Virus: a<b, t-test, p = .017). Figures represent results of 4 independent in vitro experiments.
10 / 15
Fig 6. Herpes simplex virus-2 regulates ER-alpha and HA via Src kinase in ECT-1 cells. (A) Src kinase
activation was characterized in ECT-1 cells 4, 6, and 8h post-infection with HSV2 using Western blot analysis
with an antibody specific for Src Tyr527 phosphorylation (pSrc) or total Src (tSrc). (B) ECT-1 cells were
treated with vehicle (DMSO) or Src inhibitor (SKI/PP1). ER-alpha was quantified using densitometry following
Western blot analysis (ANOVA with Tukey's multiple comparison; NT vs VEH, n.s.; NT vs SKI/PPI, p< .02;
VEH vs SKI/PPI, p< .01). (C) ECT-1 cells were treated with HSV2, HSV2 and vehicle (DMSO), or HSV2 and
Src kinase inhibitor, and ER-alpha was quantified using densitometry following Western blot analysis (ANOVA
with Tukey's multiple comparison; HSV2 vs VEH/HSV2, n.s.; HSV2 vs SKI/PPI-HSV2, n.s.; VEH/HSV2 vs
SKI/PPI-HSV2, p< .04) (D). ECT-1 were treated with vehicle (DMSO), HSV2 and vehicle (DMSO), or HSV2
and Src kinase inhibitor, and HA was quantified in the conditioned medium using ELISA (ANOVA with Tukey's
multiple comparison; a<b, p = .012; a>c, p = .026; b>c, p = .0003). Figures represent results of 4 independent
in vitro experiments.
specific role of E2, loss of P4 following ovariectomy in rats did not induce ripening unless E2
concentrations were maintained, suggesting E2 also has an active role [
]. The shift in
hormone dominance within the cervix at term is attributed to changes in local hormone
metabolism and changes in receptor expression [
22, 23, 30
]. Therefore, it is possible that
HSV2-associated expression of ER in cervical epithelial cells increases tissue sensitivity to E2,
which could mediate the cervical changes we observe. We postulate that, in vivo, E2 ligand
binds ER and is also responsible for induction of PR in epithelial cells. Interestingly, HSV2
infection led to increased ER in ECT-1 (via protein stabilization, not transcription), but PR
mRNA and protein were not affected. It is likely PR was not up-regulated in vitro because we
did not add E2 ligand to our culture.
11 / 15
Fig 7. Model. We propose a model where virus-associated activation of Src kinase results in stabilization of
ER-alpha leading to increased expression of PR and increased HA synthesis in the epithelium. Furthermore,
we suggest these changes in hormone sensitivity affect the structure of the cervical stroma by affecting
collagen solubility and/or crosslinking.
Another phenotype associated with cervical HSV2 was a dramatic reorganization of the
cervical stroma, including reduced cell density and loosening of the collagen fiber network.
Although it is still unclear how these changes are mediated, this phenotype could be triggered
by changes in hormone signaling, or by changes in immune cell populations or local immune
]. We speculate that viral infection affects the cervix by increasing local
E2sensitivity that could affect factors that regulate collagen solubility and crosslinking. The virus
could also be affecting cervix structure by potentiating the activation of immune cells, thus
activating MMPs that degrade the collagen network[
]. These questions are the subject of
continued investigation by our laboratory and others.
We also observed an increase in cervical HA associated with HSV2 infection. Hyaluronic
acid synthesis has been associated with hormone-, and infection-, induced cervical ripening, a
result of increased expression of HA synthase-2 or -3 (Has2/3). Interestingly, Has2 is positively
regulated by estradiol in the cervix[
]. This is relevant to our study because HA synthesis was
increased in HSV2 infected cervices, which had increased expression of ER-alpha.
Unfortunately, we could not use the ECT-1 to determine the role of ER-alpha signaling in
HSVinduced HA synthesis because cervical epithelial cells do not properly respond to E2 without
the stroma. However, we did determine that ER-alpha stabilization, and HA synthesis, were
dependent on Src kinase activation following viral infection. Therefore, Src kinase could be an
important mediator of cervical changes, such as increased HA, that are associated with HSV2
infection. These changes in HA could affect the biochemical makeup of the stroma and/or
affect the mucus barrier. These functions are dependent on the form of HA that is upregulated,
long or short chain, but this was not determined in this study.
12 / 15
In conclusion, we propose a model where virus-associated activation of Src kinase results in
stabilization of ER-alpha leading to increased expression of PR, and increased HA synthesis in
the epithelium. Furthermore, we suggest these changes in hormone sensitivity affect the
structure of the cervical stroma by affecting collagen organization (Fig 7). These changes are
mediated by changes in collagen solubility and activation of local immune cells, all under the
influence of sex hormones. These changes, mimicking those of cervical ripening, affect the
structure and barrier function of the cervix, potentially leading to increased access to
ascending infections that trigger PTB. Ongoing studies are investigating the specific molecular and
structural changes in the cervical barrier associated with this phenotype. Studies like this are
necessary to understand how cervical viral infections increase the risk for PTB in women.
Based on these results, we could predict that HSV2 infection might weaken the cervix or even
induce premature cervical ripening in some women. It is our hope that understanding the
mechanism of virus-induced cervical remodeling will help us provide targets for clinical
S1 Fig. Uncut Western blots. Uncut blots associated with Fig 6A, Fig 6B and Fig 6C.
Conceptualization: Alison I. Bernstein, Karen Racicot.
Data curation: Devin McGee, Sharra Poncil.
Formal analysis: Devin McGee, Karen Racicot.
Funding acquisition: Karen Racicot.
Investigation: Devin McGee, Arianna Smith, Sharra Poncil, Amanda Patterson, Karen
Methodology: Devin McGee, Arianna Smith, Sharra Poncil, Amanda Patterson, Karen
Project administration: Karen Racicot.
Resources: Alison I. Bernstein, Karen Racicot.
Supervision: Arianna Smith, Amanda Patterson, Karen Racicot.
Validation: Arianna Smith.
Visualization: Alison I. Bernstein.
Writing ± original draft: Karen Racicot.
Writing ± review & editing: Devin McGee, Arianna Smith, Amanda Patterson, Alison I.
Bernstein, Karen Racicot.
13 / 15
14 / 15
1. Iams JD , Romero R , Culhane JF , Goldenberg RL . Primary, secondary, and tertiary interventions to reduce the morbidity and mortality of preterm birth . Lancet . 2008 ; 371 ( 9607 ): 164 ± 75 . Epub 2008/01/15. https://doi.org/10.1016/S0140- 6736 ( 08 ) 60108 - 7 PMID: 18191687 .
2. Romero R , Dey SK , Fisher SJ . Preterm labor: one syndrome, many causes . Science . 2014 ; 345 ( 6198 ): 760 ±5. https://doi.org/10.1126/science.1251816 PMID: 25124429; PubMed Central PMCID : PMC4191866 .
3. Simmons LE , Rubens CE , Darmstadt GL , Gravett MG . Preventing preterm birth and neonatal mortality: exploring the epidemiology, causes, and interventions . Seminars in perinatology. 2010 ; 34 ( 6 ): 408 ± 15 . Epub 2010/11/26. https://doi.org/10.1053/j.semperi. 2010 . 09 .005 PMID: 21094415 .
4. Rubens CE , Sadovsky Y , Muglia L , Gravett M , Lackritz E , Gravett C . Prevention of preterm birth: Harnessing science to address the global epidemic . Science translational medicine . 2014 ; 6 ( 262 ):262sr5. https://doi.org/10.1126/scitranslmed.3009871 PMID: 25391484
5. Muglia L , Katz M. The Enigma of Spontaneous Preterm Birth . New England Journal of Medicine . 2010 ; 362 : 529 ± 35 . https://doi.org/10.1056/NEJMra0904308 PMID: 20147718
6. Lawn J , Kinney M. Preterm Birth: Now the Leading Cause of Child Death Worldwide . Science translational medicine . 2014 ; 6:263ed21 . https://doi.org/10.1126/scitranslmed.aaa2563 PMID: 25411468
7. Goldenberg RL , Culhane JF , Iams JD , Romero R . Epidemiology and causes of preterm birth . The Lancet . 2008 ; 371 ( 9606 ): 75 ± 84 . https://doi.org/10.1016/s0140- 6736 ( 08 ) 60074 - 4
8. Dimes Mo , PMNCH , Children S , WHO. Born too soon: The Global Action Report . Howson C, Kinney M , Lawn J , Eds. WHO, Geneva, Switzerland, 2012 .
9. Yellon SM . Contributions to the dynamics of cervix remodeling prior to term and preterm birth . BOR . 2017 ; 96 ( 1 ): 13 ± 23 . https://doi.org/10.1095/biolreprod.116.142844 PMID: 28395330
10. Romero R , Gomez R , Chaiworapongsa T , Conoscenti G , Kim J , Kim Y. The role of infection in preterm labour and delivery . Paediatric and Perinatal Epidemiology . 2001 ; 15 ( 2 ): 41 ± 56 .
11. Gibson CS , Goldwater PN , MacLennan AH , Haan EA , Priest K , Dekker GA , et al. Fetal exposure to herpesviruses may be associated with pregnancy-induced hypertensive disorders and preterm birth in a Caucasian population . BJOG: an international journal of obstetrics and gynaecology . 2008 ; 115 ( 4 ): 492 ± 500 . https://doi.org/10.1111/j.1471- 0528 . 2007 . 01653 . x PMID : 18271886 .
12. Gibson CS , Maclennan AH , Haan EA , Priest K , Dekker GA . Fetal MBL2 haplotypes combined with viral exposure are associated with adverse pregnancy outcomes . The journal of maternal-fetal & neonatal medicine: the official journal of the European Association of Perinatal Medicine, the Federation of Asia and Oceania Perinatal Societies, the International Society of Perinatal Obstet . 2011 ; 24 ( 6 ): 847 ± 54 . https://doi.org/10.3109/14767058. 2010 .531324 PMID: 21171930 .
13. Li DK , Raebel MA , Cheetham TC , Hansen C , Avalos L , Chen H , et al. Genital Herpes and Its Treatment in Relation to Preterm Delivery . American journal of epidemiology . 2014 . https://doi.org/10.1093/aje/ kwu242 PMID: 25392064 .
14. Mosbah A , Barakat R , Nabiel Y , Barakat G . High-risk and low-risk human papilloma virus in association to spontaneous preterm labor: a case-control study in a tertiary center, Egypt. The journal of maternalfetal & neonatal medicine: the official journal of the European Association of Perinatal Medicine, the Federation of Asia and Oceania Perinatal Societies , the International Society of Perinatal Obstet . 2017 : 1±6 . https://doi.org/10.1080/14767058. 2017 .1297403 PMID: 28264621 .
15. Nakubulwa S , Kaye DK , Bwanga F , Tumwesigye NM , Nakku-Joloba E , Mirembe F . Effect of suppressive acyclovir administered to HSV-2 positive mothers from week 28 to 36 weeks of pregnancy on adverse obstetric outcomes: a double-blind randomised placebo-controlled trial . Reprod Health . 2017 ; 14 ( 1 ): 31 . https://doi.org/10.1186/s12978-017-0292-7 PMID: 28253893; PubMed Central PMCID : PMCPMC5335854 .
16. Zuo Z , Goel S , Carter JE . Association of cervical cytology and HPV DNA status during pregnancy with placental abnormalities and preterm birth . American journal of clinical pathology . 2011 ; 136 ( 2 ): 260 ±5. https://doi.org/10.1309/AJCP93JMIUEKRPIW PMID: 21757599 .
17. Subramaniam A , Lees BF , Becker DA , Tang Y , Khan MJ , Edwards RK . Evaluation of Human Papillomavirus as a Risk Factor for Preterm Birth or Pregnancy-Related Hypertension. Obstetrics and gynecology . 2016 ; 127 ( 2 ): 233 ± 40 . https://doi.org/10.1097/AOG.0000000000001247 PMID: 26942348 .
18. Cardenas I , Means RE , Aldo P , Koga K , Lang SM , Booth CJ , et al. Viral infection of the placenta leads to fetal inflammation and sensitization to bacterial products predisposing to preterm labor . Journal of immunology . 2010 ; 185 ( 2 ): 1248 ± 57 . Epub 2010/06/18. https://doi.org/10.4049/jimmunol.1000289 PMID: 20554966; PubMed Central PMCID : PMC3041595 .
19. Cardenas I , Mor G , Aldo P , Lang SM , Stabach P , Sharp A , et al. Placental viral infection sensitizes to endotoxin-induced pre-term labor: a double hit hypothesis . American journal of reproductive immunology . 2011 ; 65 ( 2 ): 110 ± 7 . Epub 2010/08/18. https://doi.org/10.1111/j.1600- 0897 . 2010 . 00908 . x PMID : 20712808 ; PubMed Central PMCID : PMC3025809 .
20. Racicot K , Cardenas I , Wunsche V , Aldo P , Guller S , Means RE , et al. Viral infection of the pregnant cervix predisposes to ascending bacterial infection . Journal of immunology . 2013 ; 191 ( 2 ): 934 ± 41 . Epub 2013/06/12. https://doi.org/10.4049/jimmunol.1300661 PMID: 23752614 .
21. Read CP , Word RA , Ruscheinsky MA , Timmons BC , Mahendroo MS . Cervical remodeling during pregnancy and parturition: molecular characterization of the softening phase in mice . Reproduction . 2007 ; 134 ( 2 ): 327 ± 40 . https://doi.org/10.1530/REP-07-0032 PMID: 17660242 .
22. Andersson S , Minjarez D , Yost NP , Word RA . Estrogen and progesterone metabolism in the cervix during pregnancy and parturition . The Journal of clinical endocrinology and metabolism . 2008 ; 93 ( 6 ): 2366 ± 74 . Epub 2008/03/28. https://doi.org/10.1210/jc.2007-2813 PMID: 18364378; PubMed Central PMCID : PMC2435631 .
23. Mahendroo M , Porter A , Russell D , Word R. The Parturition Defect in Steroid 5α-Reductase Type 1 Knockout Mice Is Due to Impaired Cervical Ripening . Molecular endocrinology . 1999 ; 13 : 981 ± 92 . https://doi.org/10.1210/mend.13.6.0307 PMID: 10379896
24. Akgul Y , Word RA , Ensign LM , Yamaguchi Y , Lydon J , Hanes J , et al. Hyaluronan in cervical epithelia protects against infection-mediated preterm birth . The Journal of clinical investigation . 2014 . https://doi. org/10.1172/JCI78765 PMID: 25384213 .
25. Lee SE , Romero R , Park CW , Jun JK , Yoon BH . The frequency and significance of intraamniotic inflammation in patients with cervical insufficiency . American journal of obstetrics and gynecology . 2008 ; 198 ( 6 ): 633 e1± 8 . Epub 2008/03/18. https://doi.org/10.1016/j.ajog. 2007 . 11 .047 PMID: 18342290 .
26. Kaushic C , Ashkar AA , Reid LA , Rosenthal KL . Progesterone Increases Susceptibility and Decreases Immune Responses to Genital Herpes Infection . Journal of virology . 2003 ; 77 ( 8 ): 4558 ± 65 . https://doi. org/10.1128/JVI.77.8. 4558 - 4565 . 2003 PMID: 12663762
27. Akgul Y , Holt R , Mummert M , Word A , Mahendroo M. Dynamic changes in cervical glycosaminoglycan composition during normal pregnancy and preterm birth . Endocrinology . 2012 ; 153 ( 7 ): 3493 ± 503 . https://doi.org/10.1210/en.2011-1950 PMID: 22529214; PubMed Central PMCID : PMCPMC3380303 .
28. Akula SM , Pramod NP , Wang FZ , Chandran B. Integrin alpha3beta1 (CD 49c/29) is a cellular receptor for Kaposi's sarcoma-associated herpesvirus (KSHV/HHV-8) entry into the target cells . Cell . 2002 ; 108 ( 3 ): 407 ± 19 . PMID: 11853674 .
29. Denison FC , Roberts KA , Barr SM , Norman JE . Obesity, pregnancy, inflammation, and vascular function . Reproduction . 2010 ; 140 ( 3 ): 373 ± 85 . Epub 2010/03/11. https://doi.org/10.1530/REP-10-0074 PMID: 20215337 .
30. Timmons B , Akins M , Mahendroo M. Cervical remodeling during pregnancy and parturition . Trends in endocrinology and metabolism: TEM . 2010 ; 21 ( 6 ): 353 ± 61 . Epub 2010/02/23. https://doi.org/10.1016/j. tem. 2010 . 01 .011 PMID: 20172738; PubMed Central PMCID : PMC2880223 .
31. Gonzalez JM , Xu H , Chai J , Ofori E , Elovitz MA . Preterm and term cervical ripening in CD1 Mice (Mus musculus): similar or divergent molecular mechanisms? Biology of reproduction . 2009 ; 81 ( 6 ): 1226 ± 32 . Epub 2009/08/18. https://doi.org/10.1095/biolreprod.108.075309 PMID: 19684330 .