NIH grant: Characterizing the impact of Hlb expression on the ability of MRSA to evade human PMN responses (1R21AI202446-01)

retained text

NIH grant 1R21AI202446-01: Characterizing the impact of Hlb expression on the ability of MRSA to evade human PMN responses
Institute: {'code': 'AI', 'abbreviation': 'NIAID', 'name': 'National Institute of Allergy and Infectious Diseases', 'admin_org_id': '12500003', 'admin_funding_url': ''}. PI: Tyler K Nygaard. Award: $217500.
Start: 2026-08-01T00:00:00.
The bacterial pathogen Staphylococcus aureus is a major cause of human morbidity and
mortality. S. aureus can colonize and infect a wide range of hosts, but the specific mechanisms this
pathogen uses to survive in humans are not completely understood. S. aureus expresses numerous
cytotoxins that destroy host cells to promote disease. In most human-associated strains of S. aureus,
expression of one of these cytotoxins, b-toxin (Hlb), is turned off by insertion of the Sa3Int prophage
into the Hlb gene. The impact of Hlb deactivation on S. aureus pathogenesis in humans is not clear.
It has been shown that Hlb inhibits hemolysis caused by a different cytotoxin expressed by S. aureus,
a-toxin. More importantly, we have also discovered that Hlb expression reduces cytotoxicity of
clinically relevant methicillin-resistant S. aureus (MRSA) against human polymorphonuclear
leukocytes (PMNs or neutrophils) by inhibiting the activity of the Panton-Valentine leukocidin (PVL)
produced by S. aureus. Other published findings suggest that the sphingomyelinase activity of Hlb
may enhance PMN function. Taken together, these findings indicate that the deactivation of Hlb
expression provides a fitness advantage to human-associated strains of S. aureus during interactions
with PMNs. Specific Aim 1 of this proposal is designed to determine how Hlb expression reduces
PVL-mediated cytotoxicity against human PMNs. To do this, Specific Aim 1A will determine if Hlb
alters the accessibility of specific PMN host cell receptors that are recognized by PVL and other
bicomponent leukocidins produced by MRSA. Specific Aim 1B will examine the influence of Hlb on
PMN lipid raft assembly that is important for the function of these host cell receptors. Specific Aim 2
of this proposal will determine the impact of Hlb on PMN motility and function. To accomplish this,
Specific Aim 2A will examine the morphology, motility, tracking to MRSA, bacterial association, and
subsequent plasma membrane permeability in real time using time-lapse confocal microscopy.
Specific Aim 2B will determine the influence of Hlb expression by MRSA on PMN bactericidal activity,
the generation of reactive oxygen species, NETosis, and degranulation. Results from experiments
described in this proposal will enhance our overall understanding of how S. aureus causes infection,
elucidate how this pathogen specifically adapts to the human host, and define a mechanism of
cytotoxin inhibition that has potential for translation into novel therapeutic strategies that minimize S.
aureus virulence.

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