The number of patients with long COVID continues to rise as COVID-19 persists, yet research on its implications for female reproductive health remains scarce. Long COVID is linked to an increased risk of abnormal uterine bleeding, heavier menstrual flow, prolonged periods, and breakthrough bleeding. We therefore examined whether uterine changes occur in an animal model of long COVID. Female A/J mice were inoculated with murine hepatitis virus strain 1 (MHV-1), a murine coronavirus model used to investigate long COVID-like sequelae, and a subset of infected mice received the synthetic peptide SPIKENET (SPK). Mice infected with murine hepatitis virus strain 1 (MHV-1) showed chronic uterine inflammation and myometrial changes exhibiting fibroid-like features one year post-infection. We also observed changes in α-SMA, desmin, h-caldesmon, and vimentin staining, suggesting a myometrial origin for the lesions. Further, we found pathological changes that include hyperplastic foci in the outer layer of the myometrium, a uterus with intraluminal proteinaceous fluid, and a circumscribed, round-to-oval focus of benign hyperplastic myometrium with spindle nuclei and eosinophilic cytoplasm, with interspersed small, round lymphocytes and plasma cells, consistent with mild chronic inflammation. MHV-1-inoculated mice also showed an oviduct with several lymphocytes located toward the lumen, as well as a uterus with an ectatic lumen, inspissated intraluminal fibrinoid material, and mild-to-moderate subendometrial chronic inflammation (with scattered small lymphocytes). Additionally, immunofluorescence showed increased expression of conventional and unconventional uterine fibroid markers, including PLP1, versican, PR-A, PR-B, MSH2, TGF-β1 and 3, IGF-1, CA125, and HMGA2. Serum biomarker analysis showed increased IGF-1 levels but not increased levels of the other proteins identified by immunofluorescence. Furthermore, histopathology showed no uterine fibroid-like lesions in MHV-1-inoculated mice treated with the synthetic peptide SPK (known to prevent MHV-1 and SARS-CoV-2 infection in animals). Moreover, SPK prevented increases in the above-mentioned fibroid markers as measured by immunofluorescence and partially reduced IGF-1 expression in the serum. These findings suggest that uterine fibroids may develop during long COVID in humans.
