Abstract
BackgroundUreaplasma species (spp.) are commonly regarded as low-virulent commensals but may cause invasive diseases in immunocompromised adults and in neonates, including neonatal meningitis. The interactions of Ureaplasma spp. with host defense mechanisms are poorly understood. This study addressed Ureaplasma-driven cell death, concentrating on apoptosis as well as inflammatory cell death.MethodsHuman brain microvascular endothelial cells (HBMEC) were exposed to Ureaplasma (U.) urealyticum serovar 8 (Uu8) and U. parvum serovar 3 (Up3). Resulting numbers of dead cells as well as mRNA levels and enzyme activity of key agents in programmed cell death were assessed by flow cytometry, RNA sequencing, and qRT-PCR, respectively. xCELLigence data were used for real-time monitoring of changes in cell adhesion properties.ResultsBoth Ureaplasma isolates induced cell death (p < 0.05, vs. broth). Furthermore, Ureaplasma spp. enhanced mRNA levels for genes in apoptosis, including caspase 3 (Up3 p < 0.05, vs. broth), caspase 7 (p < 0.01), and caspase 9 (Up3 p < 0.01). Caspase 3 activity was increased upon Uu8 exposure (p < 0.01). Vice versa, Ureaplasma isolates downregulated mRNA levels for proteins involved in inflammatory cell death, namely caspase 1 (Uu8 p < 0.01, Up3 p < 0.001), caspase 4 (Uu8 p < 0.05, Up3 p < 0.01), NOD-like receptor pyrin domain-containing 3 (Uu8 p < 0.05), and receptor-interacting protein kinase 3 (p < 0.05).ConclusionsBy inducing apoptosis in HBMEC as main constituents of the blood-brain barrier, Ureaplasma spp. may provoke barrier breakdown. Simultaneous suppression of inflammatory cell death may additionally attenuate host defense strategies. Ultimate consequence could be invasive and long-term CNS infections by Ureaplasma spp.
Highlights
Ureaplasma species are commonly regarded as low-virulent commensals but may cause invasive diseases in immunocompromised adults and in neonates, including neonatal meningitis
Even in the absence of any stimulus, control cells underwent cell death over time, but exposure to Ureaplasma spp. caused a significant increase in dead cells after 24 h (Uu8 2.15-fold ± 0.4, p = 0.0133; U. parvum serovar 3 (Up3) 2.17-fold ± 0.4, p = 0.0045, vs. control) and 48 h (Uu8 1.59-fold ± 0.1, p = 0.0305; Up3 1.59-fold ± 0.1, p = 0.0273, vs. control; Fig. 2). This effect remained significant compared to broth (24 h urealyticum serovar 8 (Uu8) 1.56-fold ± 0.3, p = 0.0869; Up3 1.58-fold ± 0.3, p = 0.0178; 48 h Uu8 1.44-fold ± 0.1, p = 0.0375; Up3 1.47-fold ± 0.1, p = 0.0281, vs. broth), broth itself had a mild impact (Fig. 2)
Ureaplasma-driven apoptosis in human brain microvascular endothelial cells (HBMEC) We evaluated some of the key genes in apoptosis described in Fig. 1, correlating mRNA expression obtained by RNA sequencing and quantitative reverse transcriptase PCR (RT-PCR) (qRT-PCR) with protein levels or enzyme activity for some of the most important ones (Fig. 3a–i)
Summary
Ureaplasma species (spp.) are commonly regarded as low-virulent commensals but may cause invasive diseases in immunocompromised adults and in neonates, including neonatal meningitis. This study addressed Ureaplasma-driven cell death, concentrating on apoptosis as well as inflammatory cell death. Colonizing the adult urogenital tract, the two human Ureaplasma species (spp.) Ureaplasma (U.) urealyticum and U. parvum are generally regarded as low-virulent commensals [1]. The implications of a postnatal Ureaplasma colonization or in vitro data addressing the pro-inflammatory capacity of Ureaplasma spp. are scarce [16,17,18]. Having detected Ureaplasma-induced responses of atypical chemokine receptor 3, which may mediate BBB breakdown, we were the first to provide in vitro evidence of Ureaplasma-driven neuroinflammation [19]
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