Unless otherwise stated, chemicals and reagents were all purchased from Sigma-Aldrich.
Study design
The aim of the study is to determine the secretion of circulating PGE2 levels in dependence of several risk factors in mild and severe diseased COVID-19 patients compared to healthy individuals, and how PGE2 modulates the host’s immune response.
COVID-19 study: In this study of 89 patients diagnosed with COVID-19, 41 presented with mild/moderate symptoms and 48 were hospitalized with severe disease. Blood samples were also obtained from male (n=18) and female subjects (n=28) (age 18-50 years) from a healthy population established by Hannover Unified Biobank (HUB).
The local ethics committees at Hannover Medical School, Comité d’Ethique Hospitalo-Facultaire of UCLouvain, and the Ethical Committee of IEO has been obtained (IEO1271) approved this study. All patients and healthy control subjects provided written informed consent. The study conforms to the principles outlined in the Declaration of Helsinki.
Physical assessment and exercise program in healthy elderly individuals (Rebirth 60plus cohort, DRKS00013885) All subjects in the Rebirth 60plus cohort (DRKS00013885) were initially tested for maximum power output on a cycle ergometer with graded exercise test (GXT). Based on their activities, physical fitness and pathologies, each subject was given an aerobic exercise training program. Once a month, the subjects were contacted by phone to assess training progress and adjust the exercise program, if necessary. All subjects of the Rebirth 60plus study were informed about benefits and risks regarding all study procedures. Height and weight were measured using a scale (seca gmbh & co. kg, Hamburg, Germany). Body fat was measured with a medical Body Composition Analyzer mBCA (seca gmbh & co. kg, Hamburg, Germany). The physical activity was tracked using a GPS watch Forerunner 30 (Garmin Deutschland GmbH, Munich, Germany) and a daily diary where all physical activities were additionally documented. All study procedures were approved by the local ethics committee of Hannover Medical School (Vote #7617) and all subjects provided informed written consent prior to the commencement of the study procedures.
Mice study: Mice with a cardiomyocyte-restricted knockout of STAT3 (CKO: aMHC-Cretg/+; STAT3flox/flox) and wildtype mice (WT: STAT3flox/flox) were used to analyze the effect of an altered androgen receptor signaling in male mice for cardiac PGE2 secretion and modulation of the immune response. Application of the COX inhibitor ibuprofen as therapeutic strategy was tested.
Mice were housed in a specific pathogen-free barrier facility and fed standard chow. All animal studies were conducted in accordance with the German animal protection legislation and with the European Communities Council Directives 86/609/EEC and 2010/63/EU for the protection of animals used for experimental purposes. All experiments were approved by the Local Institutional Animal Care and Research Advisory Committee and permitted by the relevant local authority for animal protection “Niedersächisisches Landesamt für Verbrauerschutz und Lebensmittelsicherheit” (LAVES).
Blood sampling and blood tests
Blood samples were collected in S-Monovette® tubes containing ethylenediaminetetraacetic acid (EDTA, for plasma) or clot activator (for serum) at the time of hospitalization or at study inclusion (baseline, BL) and at the follow-up (FU) visits after 12 months for the Rebirth 60Plus male and female subjects (age >60 years). Blood samples were also obtained from young male and female subjects (age 18-50 years) from a healthy population established by Hannover Unified Biobank (HUB). Plasma or serum was separated by centrifugation at 1500 rpm for 10 min and aliquots were stored at -80 °C. Laboratory workup was performed as part of routine analysis by hospital laboratories for leukocytes, neutrophils, lymphocytes, platelets, CRP and LDH. PGE2 serum and plasma levels were measured using the prostaglandin E2 ELISA kit (abcam ab133021) according to the manufacturer's protocol. Since the PGE2 ELISA system used in the study is suitable for research use only and is not intended for diagnostic use, we showed relative PGE2 expression in %. IL-17A serum levels were measured using the IL-17A ELISA kit (abcam ab216167).
Infection of Calu-3 cells with SARS-CoV-2 and taxifolin treatment
Calu-3 cells (kindly provided by Prof. Pöhlmann, German Primate Center, Göttingen; ATCC Cat# HTB-55; RRID:CVCL_0609) were maintained in Dulbecco’s’ modified Eagle medium and Vero cells (ATCC-CCL-81; Lot 58484194) in Advanced MEM at 37°C and 5% CO2. Both media were supplemented with 10% fetal bovine serum, 2 mM glutamine, 0.1 mM non-essential amino acids and 1% Penicillin/Streptomycin. Calu-3 cells (4.5x105 cells/well) were seeded in collagen-coated 24-well plates. For infection, the SARS-CoV-2 (strain SARS-CoV-2/München-1.2/2020/984,p3) 31 kindly provided by Christian Drosten (Charité, Berlin) through the European Virus Archive – Global (EVAg) was used. The isolate was propagated and titrated in Vero cells. Calu-3 cells were pretreated with 100 µM taxifolin or DMSO (0.15 %) for 24 h. Infection with SARS-CoV-2 isolate was performed at a MOI of 2.0x10-5 for 4 h at 37°C in the presence of the compounds. Heat-inactivated virus (15 min, 70°C) served a negative control. After infection, cells were washed twice with PBS before the medium containing the respective compound was added. At 48 h post infection, culture supernatant was collected and heat-inactivated (15 min, 70°C) prior to the detection of PGE2. RNA was isolated from cell lysates using a NucleoSpin RNA kit (Macherey-Nagel) according to the manufacturer’s instructions to analyze virus genome copy numbers, COX-2 and HPGD expression.
Quantification of SARS-CoV-2 viral load in Calu-3 cells
Viral RNA was isolated from lysates by NucleoSpin RNA kit (Macherey-Nagel) and from supernatant samples by QIAamp Viral RNA Mini Kit (Qiagen) according to the manufacturer’s guidelines. RT-qPCR was performed in duplicates using a LightCycler 480 (Roche) based on a method described previously25. Viral copy numbers were determined against a standard provided by Sven Reiche (FLI, Germany). Each biological replicate consisted of an average of between two and four samples, each analyzed by RT-qPCR in duplicate Data were transformed by y=log(y).
Virus titration in Vero E6 cells for infection of lung slices with SARS-CoV-2
Vero E6 (ATCC CRL-1586) and Vero cells (ATCC CCL-81) were maintained in Eagle's Minimum Essential Medium (EMEM) (Lonza) supplemented with 25 mM of HEPES (Gibco), 1 × GlutaMAX (Gibco), 100 U/ml penicillin and 100 μg/ml streptomycin. SARS-CoV2 isolate (strain SARS-CoV-2/München-1.2/2020/984,p3) 31 was kindly provided by Christian Drosten. SARS-CoV-2 seed stocks were generated by inoculating Vero E6 (ATCC CRL-1586) at a multiplicity of infection (moi) of 0.001, collecting and aliqouting the culture supernatant at 72 h post infection (hpi), then storing at -80°C in aliquots. SARS-CoV-2 working stocks were generated by an additional passage on Vero cells (ATCC CCL-81) at a moi of 0.001. Plaque and median tissue culture infectious dose (TCID50) assays were performed to titrate the cultured virus after both passages using Vero cells. This stock was used for the ex vivo infections of human tissues.
Infections of precision-cut human lung slices (PCLS) with SARS-CoV-2
PCLS were maintained in DMEM/F12 medium (Gibco, Thermo Fisher Scientific) supplemented with 2 mM of HEPES (Gibco), 1 × GlutaMAX (Gibco), 100 U/ml penicillin and 100 μg/ml streptomycin; this media was also used for virus dilutions and post-infection incubation. On the day of infection, PCLS were rinsed with PBS (without Mg2+ and Ca2+) then inoculated with 1 × 105 PFU SARS-CoV-2 in 250 μl of media per well in 48-well plates and incubated at 37°C. After 2 h, the inoculum was removed and the PCLS were then cultured in 250 µl of DMEM/F12 medium. At 72 and 120 hpi, supernatants were collected and PCLS were fixed with fixation buffer (4% PFA, 0.1% glutaraldehyde and 200 mM HEPES in ddH2O) for 1 h at room temperature followed by 24 h at 4°C.
QRT-PCR for NSP7 to confirm SARS-CoV-2 infection
SARS-CoV-2 infections in human Calu-3 cells and human lung slices and tissue were verified by NSP7 mRNA expression using qRT-PCR (forward primer: GGG CTC AAT GTG TCC AGT TAC, reverse primer: TTG CCC TGT TGT CCA GCA TT).
Multiplex immunohistochemistry of human lung biopsies
The FFPE sections for each group (Control (Ctrl) n=3, acute COVID-19 (AC) n=6, transplant rejected (TR) n=4) were representatively stained with the manual Opal 7-Color IHC Kit (Akoya Biosciences, Marlborough, MA) as previously described 59. The primary antibodies CD4 (Cytomed SP35, 1:50), CD8 (Dako M0755, 1:600), CD68 (Dako PGM1, 1:750) and CD20 (Dako M0755, 1:1000) were combined in sequence with the opal fluorophore CD4-Opal520, CD8-Opal570, CD20-Opal540 and CD68-Opal650. The sections were scanned with the Vectra 3 System (Akoya Biosciences, Marlborough, MA). The Regions of Interest (ROIs) were selected representative for small, medium and large vessels for the entire tissue section. The number of analyzed stamps was 43 for Ctrl, 74 for AC and 56 for TR. For the detection of CD20+ B cells, the analysis was performed with the inForm Advanced Image Analysis Software Version 2.3.0 (Akoya Biosciences, Marlborough, MA) and ImageJ 1.53c (Wayne Rasband, National Institutes of Health, USA). Statistical analysis was performed using the generalized linear model with Gaussian distribution and weights adjusted according to the number of ROIs per patient.
Stimulation of human pre-B-cell lines
Human pre-B-cell lines 697 (ACC42 DSMZ collection) and SUP-B15 (ACC389 DSMZ collection) were cultivated in RPMI (Gibco) supplemented with 10 % FBS. 5x105 cells per ml were pre-incubated with either the EP1/EP2 receptor antagonist AH6809 (10 µM, Tocris) or the EP4 receptor antagonist GW627368 (10 µM, Tocris) for 2 h. PGE2 (10 µM, Sigma-Aldrich) was added and cells were harvested after 48 h in TRIzol. Control cells were incubated with dissolvents (DMSO or ethanol (ETHO), 1 µL/ml media). Alternatively, 5x105 per ml 697 and SUP-B15 cells were incubated with 10 % human serum from older individuals (>60 y) prior to the commencement of the exercise program at baseline (BL) and after 12M (12M FU) for 48 h and harvested in TRIzol SUP-B15 cells were incubated with 10 % human serum from COVID-19 patients and from healthy controls. Cells were harvested after 48 h in TRIzol
DEP characteristics
Diesel exhaust particles (DEP, SRM 2975, industrial forklift) were purchased from the National Institute of Standards and Technology (NIST, Gaithersburg, MD, USA). A list of the polycyclic aromatic hydrocarbons (PAHs) concentrations and characteristics of the particles in SRM 2975 are available on NIST website (http://www.nist.gov/srm/).
For in vitro experiments, DEP was suspended in 2mg/ml PBS, vortexed and sonicated for 2 minutes by probe sonication and filtered by 5 mm sterifix filter (Braun). Just before use, the particles were resonicated for 15 min in a bath sonicator 60.
Isolation and cultivation of adult human cardiac endothelial cells (hCECs)
hCECs were isolated from atrial appendages. Surrounding fat tissue was removed from the atrial appendage, the cardiac tissue was mechanically and subsequently enzymatically dissociated using the Neonatal Rat Heart Dissociating Kit (Miltenyi) according to the manufacturer’s instructions. Dissociated single cells were cultured in EGM-2 (Lonza). For the enrichment of hCECs, the human CD31 Microbead Kit (Miltenyi Biotec) was used according to the manufacturer’s instructions and cultivated in EGM-2. Cells were used from passage 3-6 61.
hCECs were incubated with 10 mg/ml DEP and/or 100 mM taxifolin for 24 h in EGM-2+supplements bullet kit (Lonza CC-3162) media in a humidified incubator at 37 °C and 5% CO2. hCECs control cells received equal amounts of PBS and/or DMSO.
PGE2 detection in supernatants of Calu-3, hCEC and murine adult cardiomyocytes
PGE2 levels in the supernatants of the primary hCEC (normalized to cell density), murine adult cardiomyocytes (normalized to aMHC mRNA expression), and the cell lines Calu-3 (normalized to total RNA content) were measured using the prostaglandin E2 ELISA kit (abcam ab133021) respectively, according to the manufacturer’s protocols.
Isolation of RNA and qRT-PCR
Total RNA was isolated with TRIzol (Thermo Fisher Scientific) and cDNA synthesis was performed as described previously 62. Real-time PCR with the SYBR green dye method (Brilliant SYBR Green Mastermix-Kit, Thermo Fisher Scientific) was performed with the AriaMx Real-Time PCR System (Agilent Technologies) as described 62. Expression of mRNA levels was normalized using the 2-ΔΔCT method relative to 18S, B2M and GAPDH. A list of qRT-PCR primers used in this study is provided in the supplements file Table S1, S2.
RNA Isolation from formalin fixed and paraffin embedded tissue
RNA isolation from formalin-fixed and paraffin embedded tissue was performed using the Maxwell® RSC RNA FFPE Purification Kit (Promega Corporation, Madison, WI). RNA content was measured by using the Qubit RNA IQ Assay (Thermo Fisher Scientific, Waltham, MA).
Isolation, characterization and culture of Sca-1+ cardiac progenitor cells
Mice with a cardiomyocyte-restricted knockout of STAT3 (CKO: aMHC-Cretg/+; STAT3flox/flox) and wildtype mice (WT: STAT3flox/flox) were generated and isolation and cultivation of Sca-1 cardiac progenitor cells from hearts of 3 month-old mice was performed as described 63 39. Isolated WT-CPC were incubated with PGE2 (1 µM) for 48 h and were harvested in TRIzol.
Male CKO mice at the age of 9-10 weeks were treated with ibuprofen (10 mg/kg bodyweight, ibuprofen sodium salt, Sigma-Aldrich, dissolved in drinking water) for two weeks 39. CKO control animals received drinking water.
Freshly isolated Sca-1 positive CPC were stained with CD19-PE (BD Pharmingen, 557399) for 15 min at room temperature. Flow cytometry was performed using the FACSCalibur (BD Biosciences).
Immunostaining
For immunostainings using antibodies recognizing CD19 (CD19-PE, BD Pharmingen, 557399) and Sca-1 (Sca-1-FITC microbead kit, Miltenyi Biotec), cryosections were fixed in acetone, washed 3 times with PBS and blocked with 10 % donkey serum and 0.3 % Triton in PBS for 1 h at room temperature. Cryosections were stained with the antibodies for 2 h at room temperature. Nuclei were stained with DAPI Hoechst 33342 (Sigma-Aldrich). Images were acquired with Axio Observer 7 and Zen 2.6 pro software (Carl Zeiss).
Statistical Analyses
Statistical analysis was performed using GraphPad Prism version 5.0a, 7.0 and 8.1.2 for Mac OS X (GraphPad Software, San Diego, CA, USA).
Normal distribution was tested using the D’Agostino normality test. Continuous data were expressed as mean ± SD or median and interquartile range (IQR), according to the normality of distribution. Comparison between two groups was performed using one sample t-test or unpaired two-tailed t-test for Gaussian distributed data and the Mann-Whitney-U test where at least one column was not normally distributed. When comparing more than two groups, ANOVA and Bonferroni's post hoc test or Dunnett’s post hoc test were used according to the normality of distribution. Categorical variables are presented as frequencies (percentages) and compared using Fisher’s exact test. A two-tailed P value of <0.05 was considered statistically significant. Correlation for BMI, BW, body fat content and age was analyzed via ozone correlation analysis by using Pearson correlation coefficients for Gaussian distributions or for nonparametric Spearman correlation coefficients for non-normal distribution.