Abstract
BackgroundAtypical chemokine receptor 3 (ACKR3, synonym CXCR7) is increasingly considered relevant in neuroinflammatory conditions, in which its upregulation contributes to compromised endothelial barrier function and may ultimately allow inflammatory brain injury. While an impact of ACKR3 has been recognized in several neurological autoimmune diseases, neuroinflammation may also result from infectious agents, including Ureaplasma species (spp.). Although commonly regarded as commensals of the adult urogenital tract, Ureaplasma spp. may cause invasive infections in immunocompromised adults as well as in neonates and appear to be relevant pathogens in neonatal meningitis. Nonetheless, clinical and in vitro data on Ureaplasma-induced inflammation are scarce.MethodsWe established a cell culture model of Ureaplasma meningitis, aiming to analyze ACKR3 variances as a possible pathomechanism in Ureaplasma-associated neuroinflammation. Non-immortalized human brain microvascular endothelial cells (HBMEC) were exposed to bacterial lipopolysaccharide (LPS) or tumor necrosis factor-α (TNF-α), and native as well as LPS-primed HBMEC were cultured with Ureaplasma urealyticum serovar 8 (Uu8) and U. parvum serovar 3 (Up3). ACKR3 responses were assessed via qRT-PCR, RNA sequencing, flow cytometry, and immunocytochemistry.ResultsLPS, TNF-α, and Ureaplasma spp. influenced ACKR3 expression in HBMEC. LPS and TNF-α significantly induced ACKR3 mRNA expression (p < 0.001, vs. control), whereas Ureaplasma spp. enhanced ACKR3 protein expression in HBMEC (p < 0.01, vs. broth control). Co-stimulation with LPS and either Ureaplasma isolate intensified ACKR3 responses (p < 0.05, vs. LPS). Furthermore, stimulation wielded a differential influence on the receptor’s ligands.ConclusionsWe introduce an in vitro model of Ureaplasma meningitis. We are able to demonstrate a pro-inflammatory capacity of Ureaplasma spp. in native and, even more so, in LPS-primed HBMEC, underlining their clinical relevance particularly in a setting of co-infection. Furthermore, our data may indicate a novel role for ACKR3, with an impact not limited to auto-inflammatory diseases, but extending to infection-related neuroinflammation as well. AKCR3-induced blood-brain barrier breakdown might constitute a potential common pathomechanism.
Highlights
Atypical chemokine receptor 3 (ACKR3, synonym CXCR7) is increasingly considered relevant in neuroinflammatory conditions, in which its upregulation contributes to compromised endothelial barrier function and may allow inflammatory brain injury
We evaluated ACKR3 responses of human brain microvascular endothelial cells (HBMEC) upon exposure to bacterial lipopolysaccharide (LPS) and tumor necrosis factor-α (TNF-α), and used ACKR3 levels to depict the interactions of Ureaplasma spp. with native and LPS-primed HBMEC
ACKR3 responses of HBMEC upon stimulation with LPS, TNF-α, and Ureaplasma isolates Via quantitative reverse transcriptase PCR (RT-PCR) (qRT-PCR), we detected a significant increase of ACKR3 mRNA in HBMEC upon stimulation with E. coli LPS at 4 h (6.4-fold ±1.5, p = 0.0004, vs. control) and 30 h (2.3-fold ±0.4, p = 0.004) (Fig. 1a)
Summary
Atypical chemokine receptor 3 (ACKR3, synonym CXCR7) is increasingly considered relevant in neuroinflammatory conditions, in which its upregulation contributes to compromised endothelial barrier function and may allow inflammatory brain injury. Commonly regarded as commensals of the adult urogenital tract, Ureaplasma spp. may cause invasive infections in immunocompromised adults as well as in neonates and appear to be relevant pathogens in neonatal meningitis. The two human Ureaplasma species (spp.) Ureaplasma (U.) urealyticum and U. parvum are among the smallest self-replicating pathogens and, unlike other bacteria, lack a cell wall [1]. They are typical commensals of the adult urogenital tract and are generally considered as being of low virulence [1]. We aimed to establish a cell culture model of Ureaplasma meningitis to assess the inflammatory pathomechanisms involved
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