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Male sex belongs to one of the major risk factors for severe COVID-19 outcome. However, underlying mechanisms that could affect sex dependent disease outcome are yet unknown. Here, we identified the CYP19A1 gene encoding for the testosterone-to-estradiol metabolizing enzyme CYP19A1 (alias aromatase) as a male abundant host factor that contributes to worsened disease outcome in SARS-CoV-2 infected male hamsters. Pulmonary CYP19A1 transcription is further elevated upon viral infection in males correlating with reduced testosterone and increased estradiol levels. Dysregulated circulating sex hormone levels in male golden hamsters are associated with reduced lung function compared to females. Treatment of SARS-CoV-2 infected hamsters with letrozole, a clinically approved CYP19A1 inhibitor, supported recovery of dysregulated plasma sex hormone levels and was associated with improved lung function and health in male but not female animals compared to placebo controls. Whole human exome sequencing data analysis using a Machine Learning approach revealed a CYP19A1 activity increasing mutation being associated with the development of severe COVID-19 for men. In human autopsy-derived lungs CYP19A1 was expressed to higher levels in men who died of COVID-19, at a time point when most viral RNA was cleared. Our findings highlight the role of the lung as a yet unrecognized but critical organ regulating metabolic responses upon respiratory virus infection. Furthermore, inhibition of CYP19A1 by the clinically approved drug letrozole may pose a new therapeutic strategy to reduce poor long-term COVID-19 outcome.

BACKGROUNDMale sex was repeatedly identified as a risk factor for death and intensive care admission. However, it is yet unclear whether sex hormones are associated with disease severity in COVID-19 patients. We sought to characterize sex differences in hormone levels and cytokine responses in critically ill COVID-19 patients.METHODSWe performed a retrospective cohort study of critically ill COVID-19 patients. Males and females were compared. Multivariate regression was performed to assess the association between sex hormones, cytokine responses and the requirement for extracorporeal membrane oxygenation (ECMO) treatment.RESULTSWe analyzed sex hormone levels (estradiol and testosterone) of n=181 male and female individuals. These consisted of n=50 critically ill COVID-19 patients (n=39 males, n=11 females), n=42 critically ill non-COVID-19 patients (n=27 males, n=15 females), n=39 non-COVID-19 patients with coronary heart diseases (CHD) (n=25 males, n=14 females) and n=50 healthy individuals (n=30 males, n=20 females). We detected highest estradiol levels in critically ill male COVID-19 patients compared to non-COVID-19 patients (p=0.0123), patients with CHD (p=0.0002) or healthy individuals (p=0.0007). Lowest testosterone levels were detected in critically ill male COVID-19 patients compared to non-COVID-19 patients (p=0.0094), patients with CHD (p=0.0068) or healthy individuals (pp=0.0301; IL-1RA, p=0.0160; IL-6, p=0.0145; MCP-1, p=0.0052; MIP-1α, p=0.0134) were significantly elevated in those with higher Sequential Organ Failure Assessment (SOFA) scores (8-11). Linear regression analysis revealed that herein IFN-γ levels correlate with estradiol levels in male and female COVID-19 patients (R2=0.216, =0.0009). Male COVID-19 patients with elevated estradiol levels were more likely to receive ECMO treatment in the course of their ICU stay (p=0.0009). CONCLUSIONS We identified high estradiol and low testosterone levels as a hallmark of critically ill male COVID-19 patients. Elevated estradiol levels in critically ill male COVID-19 patients were positively associated with IFN-γ levels and increased risk for ECMO requirement.

SARS-CoV-2 infection is associated with increased morbidities in men compared to women. Androgens are believed to play an important role in SARS-CoV-2 pathogenesis in men due to the postulated androgen-dependency of ACE2 and TMPRSS2. However, it is yet unclear whether the sex bias is mediated by SARS-CoV-2 infection itself or by other confounding factors. Here, using the golden hamster model, we show that SARS-CoV-2 infection attacks reproductive organs, causes massive dysregulation of sex hormones and induces elevated transcription of the androgen-to-estrogen converting enzyme aromatase CYP19A1 in the lung. In male hamsters, SARS-CoV-2 infection causes severely depleted testosterone and highly elevated estradiol levels. In female hamsters, SARS-CoV-2 infection causes reduced estradiol levels. Hormonal dysregulation in infected animals is followed by severe weight loss compared to control groups treated with poly(I:C) or PBS. Lungs of SARS-CoV-2 infected animals present abundant CYP19A1 expression in the endothelium and in macrophages, particularly in males. Prominent CYP19A1 expression in endothelial cells and macrophages was verified in lung sections of deceased Covid-19 males compared to females. Our results demonstrate that SARS-CoV-2 infection leads to massive dysregulation of sex hormones, which may increase the risk for sex-specific disease outcome particularly in combination with comorbidities. These findings provide insights into the complex metabolic cross talk between SARS-CoV-2 infection and sex hormones.