The Neisseria meningitidis iron acquisition protein HpuA moonlights as an adhesin and inhibits host cell migration
Authors: Shortt Gabrielle A. , Ren Xiaoyun , Otto Brianna M. , MacKichan Joanna K. 
Published: February 2022

Neisseria meningitidis can cause meningococcal disease, a rapidly developing and potentially fatal infection. Despite this, it normally resides as a commensal in the nasopharynx of healthy individuals. The mechanisms by which meningococci access deeper tissues remain unknown. Epidemiological data suggest that mucosal disruptions increase the risk of meningococcal disease. We previously investigated whether meningococci inhibit host cell wound repair, enhancing invasive disease risk. Here, using genome sequencing and a collection of closely related household isolates that differ in their ability to inhibit host wound repair, we identify the responsible meningococcal factor. This protein, HpuA, has previously been characterized as part of a bipartite heme acquisition transporter. We constructed mutants to demonstrate that HpuA, but not HpuB, inhibits wound repair, acts as an adhesin for epithelial cells, and promotes cellular invasion. We showed this was not due to iron starvation resulting from the bacteria, differences in growth rate, or manipulation of host haptoglobin. Heterologous expression of HpuA in E. coli mediated adherence to 16HBE cells in an HpuA-dependent manner and conferred an aggregative phenotype onto E. coli, suggesting that HpuA may play a role in the formation of microcolonies on host cells. We also demonstrated that iron supplementation of meningococci restored the inhibition of wound repair in strains lacking HpuA (NZCM112, ΔhpuA mutant) to levels seen with the wild type. This was also seen with unrelated carriage strains previously shown not to inhibit wound repair. Iron supplementation also increased adherence and invasion of meningococci for strains lacking HpuA, while not affecting those that expressed HpuA. These findings suggest there may be a second meningococcal protein that inhibits wound repair. Together, these results suggest that HpuA is an important meningococcal virulence factor with multiple moonlighting functions, mediating adherence, invasion, inhibition of wound repair, and bacterial aggregation.

Author Summary

Neisseria meningitidis causes meningococcal disease, a potentially fatal and rapidly developing illness that most often occurs in children. Despite this, the bacteria are frequently carried harmlessly as part of the normal airway microflora in healthy people, only rarely causing invasive disease, which involves replication in the bloodstream or central nervous system. It remains unknown precisely how the bacteria reach the deeper tissues from the airways, though some epidemiological evidence suggests that wounds or disruptions to the airways may increase risk. Here, we show that a N. meningitidis protein, HpuA, moonlights from its usual job of acquiring nutrients from the host, to enable the bacteria to adhere to and invade host cells, as well as inhibiting wound closure. Furthermore, we also show that meningococci that lack HpuA acquire the ability to inhibit wound repair when they are supplemented with iron, suggesting that there are additional meningococcal proteins to be discovered that may inhibit wound repair.