C2 Fragment from Neisseria meningitidis Antigen NHBA Disassembles Adherence Junctions of Brain Microvascular Endothelial Cells
Year: 2013
Type: article
Abstract: Neisseria meningitidis is the major cause of meningitis and sepsis, two kind of diseases that can affect children and young adults within a few hours, unless a rapid antibiotic therapy is provided. The meningococcal disease dates back to the 16th century. The first description of the disease caused by this pathogen was stated by Viesseux in 1805 as 33 deaths occurred in Geneva, Switzerland [1]. \nIt took about seventy years before two Italians (Marchiafava and Celli) in 1884 identified micrococcal infiltrates within the cerebrospinal fluid [2]. \nThe worldwide presence of meningococcal serogroups may vary within regions and countries. \nWith the coming of antimicrobial agents, like sulphonamides, and with the development of an appropriate health care and prevention programme, the fatality rate cases has dropped from 14% to 9%, although 11% to 19% of patients continued to have post-infection issues such as neurological disorders, hearing or limb loss [3]. \nThe bacteria can be divided into 13 different serogroups and, among these, up to 99% of infection is ascribed to the serogroups named A, B, C, 29E, W-135 and Y (Fig. 2). All the serogroups have been listed in 20 serotypes on the presence of PorB antigen, 10 serotypes on the presence of PorA antigen, and in other immunotypes on the presence of other bacterial proteins and on the presence of a characteristic lipopolysaccharide called LOS (lipooligosaccharide) [4]. \nThe transmission from a carrier to an other person occurs by liquid droplet and the natural reservoir of Neisseria meningitidis is the human throat, in particular it usually invades the human nasopharynx where it can survive asymptomatically. \nThe reported annual incidence goes from 1 to 5 cases per 100000 inhabitants in industrialized countries, while in non developed-countries the incidence goes up to 50 cases per 100000 inhabitants. More then 50% of cases occur within children below 5 years of age, and the peak regards those under the first year of age. This fact is due to the loss of maternal antibodies by the newborn. In non-epidemic period, the percentage of healthy carriers range from 10 to 20%, and notably the condition of chronic carrier is not so uncommon [5, 6]. Only in a small percentage of cases the colonization progresses until the insurgence of the pathogenesis. This happens because in the majority of cases specific antibodies or the human complement system are able to destroy the pathogens in the blood flow allowing a powerful impairment of the dissemination. \nIn a small group of population the colonization of the upper respiratory tract is followed by a rapid invasion of the epithelial cells, and from there bacteria can reach the blood flow and invade the central nervous system (CNS), inducing the establishment of an acute inflammatory response. \nHow the balance between being an healthy carrier or a infected patient can change so rapidly it is still unknown. Some factors that can play a role in this switch could be the virulence of the bacterial strain, the responsiveness of the host immune system, the mucosal integrity, and some environmental factors [7]. \nNeisserial heparin binding antigen (NHBA) is a surface- exposed lipoprotein from Neisseria meningitidis that was originally identified by reverse vaccinology [8]. \nNHBA in Nm has a predicted molecular weight of 51 kDa. The protein contains an Arg-rich region (-RFRRSARSRRS-) located at position 296–305 that is highly conserved among different Nm strains. The protein is specific for Neisseria species, as no homologous proteins were found in non redundant prokaryotic databases. \nFull length NHBA can be cleaved by two different proteases in two different manners: NalP, a neisserial protein with serine protease activity cleaves the entire protein at its C-terminal producing a 22 kDa protein fragment (commonly named C2) which starts with Ser293 and hence comprises the highly conserved Arg-rich region. The human proteases lactoferrin (hLf) cleaves NHBA immediately downstream of the Arg-rich region releasing a shorter fragment of approximately 21 kDa (commonly named C1) [9] . \nAlthough it is known that a crucial step in the pathogenesis of bacterial meningitidis is the disturbance of cerebral microvascular endothelial function, resulting in blood-brain barrier breakdown, the bacterial factor(s) produced by Nm responsible for this alteration remains to be established. The integrity of the endothelia is controlled by the protein VE-cadherin, mainly localized at cell-to-cell adherens junctions where it promotes cell adhesion and controls endothelial permeability [10]. It has been reported that alteration in the endothelial permeability can be ascribed to phosphorylation events induced by soluble factors such as VEGF or TGF-beta[11] [12]. \nOur work demonstrates that the NHBA- derived fragment C2 (but not C1) increases the endothelial permeability of HBMEC (human brain microvasculature endothelial cells) grown as monolayer onto the membrane of a transwell system. Indeed, the exposure of the apical domain of the endothelium to C2 allows the passage of the fluorescent tracer BSA-FITC, from the apical side to the basal one, early after the treatment. Interestingly, the effect of C2 on the endothelium integrity is such to allow the passage of bacteria, E. coli but, notably, also N. meningitidis MC58, from the apical to the basolateral side of the transwell and it depends on the production of mitochondrial ROS. Remarkably, we have found that the administration of C2 to endothelia results in a ROS-dependent reduction of the total VE-cadherin content. This event requires after VE-cadherin phosphorylation, the endocytosis and the subsequent degradation of the protein. \nCollectively our data suggest the possibility that C2 might be involved in the mechanisms of invasion owned by the bacterium to cross host tissues. \n
Author: Alessandro Casellato
Language: English
Subfield: Microbiology
Field: Immunology and Microbiology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W85060308