Virulent bacterial pathogens disassemble the epididymal amyloid matrix to evade host defense.

Abstract

Study question: Does the functional epididymal amyloid matrix have host defense functions against the bacterial pathogens Staphylococcus aureus and Neisseria gonorrhoeae which are known to be exceedingly adept at evading host defense responses?

Summary answer: While the monomeric and preformed amyloids of cystatin-related epididymal spermatogenic (CRES), a component of the epididymal amyloid matrix, exhibited antimicrobial activity against S. aureus and N. gonorrhoeae in vitro, the epididymal amyloid matrix did not.

What is known already: The mouse epididymal amyloid matrix is an extracellular matrix-like structure with antimicrobial activity against Escherichia coli, the most common cause of human epididymal infections. The epididymal amyloid matrix exhibits distinct host defense responses depending on the bacterial strain mimicking what occurs in men and may explain why the pathogen dictates the characteristics and severity of epididymal infections.

Study design, size, duration: Control versus treatment with increasing doses of CRES amyloid and epididymal amyloid matrix.

Participants/materials, setting, methods: Increasing concentrations of recombinant mouse CRES/CRES amyloids and amyloid matrix isolated from the mouse caput and cauda epididymis were incubated with S. aureus and N. gonorrhoeae and the percentage of growth and viability measured using colony-forming unit (CFU) and live/dead assays, respectively. Transmission electron microscopy was used to assess structural changes in CRES/CRES amyloid and the epididymal amyloid matrix following incubation with bacteria while various mutant strains were used to identify the virulence factor contributing to epididymal amyloid matrix disassembly and bacterial survival.

Main results and the role of chance: Preformed CRES amyloids reduced the ability of S. aureus and N. gonorrhoeae to grow in CFU assays. In contrast, both bacterial strains disassembled the epididymal amyloid matrix effectively evading its host defense responses. Mutant S. aureus strains showed that nucleases targeting the eDNA backbone and not proteases or phenol-soluble modulins were the likely mechanisms for amyloid matrix disassembly by S. aureus.

Large scale data: N/A.

Limitations, reasons for caution: The assays were carried out in vitro using biochemically enriched populations of epididymal amyloid matrix. We cannot rule out that altered structure or disruption of the native composition and physiochemical environment of the epididymal amyloid matrix hindered its host defense functions against S. aureus and N. gonorrhoeae. We also have not established the presence of a functional amyloid matrix in the human epididymis.

Wider implications of the findings: Our studies provide insight of the interactions between mammalian and bacterial host defense mechanisms including how virulent strains can disable a first line of defense in the epididymis. Our results have direct relevance for human and suggest a possible mechanism why S. aureus and N. gonorrhoeae can cause profound inflammation, scarring, tubule blockage, and permanent infertility in cases of epididymitis. Because these strains alter a host defense structure in the epididymal lumen allowing their growth/survival, more robust immune responses from the host may be necessary to counter the loss of amyloid matrix function resulting in inflammatory responses and possible tubule scarring. Our studies also highlight the potential significance of developing functional amyloids as new antibiotics.

Funding: Funding from Texas Tech University Health Sciences Center (TTUHSC) to G.A.C.

Disclosures: The authors have nothing to disclose.