Host defense functions of the epididymal amyloid matrix

Abstract

The epididymal lumen is an immunologically distinct environment. It maintains tolerance for the naturally antigenic spermatozoa to allow their maturation into functional cells while simultaneously defending against pathogens that can ascend the male tract and cause infertility. We previously demonstrated that a nonpathological amyloid matrix that includes several CRES (cystatin-related epididymal spermatogenic) subgroup family members is distributed throughout the mouse epididymal lumen but its function was unknown. Here we reveal a role for the epididymal amyloid matrix in host defense and demonstrate that the cystatin-related epididymal spermatogenic (CRES) amyloids and CD-1 mouse epididymal amyloid matrix exhibit potent antimicrobial activity against bacterial strains that commonly cause epididymal infections in men. We show the CRES and epididymal amyloids use several defense mechanisms including bacterial trapping, disruption of bacterial membranes, and promotion of unique bacterial ghost-like structures. Remarkably, these antimicrobial actions varied depending on the bacterial strain indicating CRES amyloids and the epididymal amyloids elicit strain-specific host defense responses. We also demonstrate that the CRES monomer and immature assemblies of the epididymal amyloid transitioned into advanced structures in the presence of bacteria, suggesting their amyloid-forming/shape-shifting properties allows for a rapid reaction to a pathogen and provides an inherent plasticity in their host defense response. Together, our studies reveal new mechanistic insight into how the male reproductive tract defends against pathogens. Future studies using a mouse model for human epididymitis are needed to establish the epididymal amyloid responses to pathogens in vivo. Broadly, our studies provide an example of why nature has maintained the amyloid fold throughout evolution.

The Mouse Epididymal Amyloid Matrix: A Mammalian Counterpart of a Bacterial Biofilm

“…We used differential centrifugation to isolate fractions containing distinct populations of the epididymal amyloid matrix (pellets 2 and 4 (P2, P4)) from the mouse caput and corpus-cauda (from here on referred to as cauda) epididymis (Fig 1A, B). Our previous studies suggest the amyloid matrix is assembling in the most proximal part of the epididymis (caput) as sperm enter from the testis, forming a highly branched matrix that transitions into fibrillar arrays in the distal/cauda epididymis (7). The P2 and P4 fractions may represent precursor (early condensates) and more mature amyloid assemblies (matrix, fibrils), respectively, within each region.…”

“…Here we show that the mouse epididymal amyloid matrix contains eDNA, eRNA and complex polysaccharides, components that are critical for maintaining the extracellular epididymal amyloid matrix structure much like their functions in bacterial biofilms. Our previous work showing the epididymal amyloid matrix has host defense functions revealed a biological role similar to that of biofilms (7). Together, our studies suggest evolutionarily conserved mechanisms underlie the assembly and function of highly specialized extracellular matrices (ECMs) that protect a bacterial community and the mammalian germ line.…”

“…Whether the >10 kb forms of eDNA observed in the epididymal amyloid matrix would change following an infection or an exposure to other environmental stressors, and if, and how, these changes might contribute to a changed epididymal amyloid matrix structure and function requires further investigation. In our previous studies, we observed that the epididymal amyloid matrix formed different amyloid structures with different host defense functions depending on the bacterial strain it encountered (7). These results indicate the epididymal amyloid, like biofilms, has an inherent ability to respond to environmental cues, which in part could be mediated by eDNA.…”

“…Further, CRES3 and CRES can cross-seed suggesting interactions between subgroup members, possibly by the formation of heterooligomers, may regulate epididymal amyloid matrix assembly (6). We recently demonstrated that CRES amyloids and the epididymal amyloid matrix have host defense functions and adopt different amyloid structures (matrix, film, fibrils) with different antimicrobial functions (bacterial trapping, killing, promotion of ghost-like bacteria) depending on the pathogenicity of the bacterial strain (7). Thus, the shape-shifting properties of the amyloid matrix allow for a plasticity that is integral for its functions.…”

Immunoregulatory mechanisms between epithelial clear cells and mononuclear phagocytes in the epididymis

“…Additionally, CCs express CRES proteins that form the epididymal amyloid matrix, 5,72 which play important biological roles in host defense, including bacterial trapping and membrane disruption to protect against pathogens that commonly cause epididymal infections. 83 Furthermore, CCs express several antioxidant molecules 5 that are involved in the protection of the epididymal epithelium and spermatozoa. 84 All these pieces of evidence support the very likely involvement of CCs in immune defense.…”