Rhizopus oryzae Adheres to, Is Phagocytosed by, and Damages Endothelial Cells In Vitro

Abstract

Rhizopus oryzae is the most common cause of zygomycosis, a life-threatening infection that usually occurs in immunocompromised patients. A characteristic hallmark of zygomycosis is angioinvasion by the fungus, resulting in thrombosis and subsequent tissue necrosis. Interactions between R. oryzae and vascular endothelial cells are therefore likely of central importance to the organism's pathogenetic strategy. We studied the ability of R. oryzae to adhere to and damage human umbilical vein endothelial cells (HUVECs) in vitro. We report that R. oryzae spores and germ tubes adhere to HUVECs, whereas only spores adhere to subendothelial matrix proteins. Additionally, R. oryzae damages endothelial cells. This endothelial cell damage requires direct contact and subsequent phagocytosis of the fungus. Surprisingly, R. oryzae viability was not required for damage, but phagocytosis was required for dead R. oryzae to cause damage. These results elucidate the nature of R. oryzae-endothelial cell interactions, which are likely central to the angioinvasion and tissue necrosis seen during zygomycotic infections. The fact that dead R. oryzae damage human endothelial cells may, in part, explain the lack of efficacy of fungicidal agents during clinical disease.Rhizopus oryzae is the organism most frequently isolated from patients with zygomycosis (6, 12), a highly destructive and lethal infection in immunocompromised hosts (2, 6, 9, 13). The standard therapy for invasive zygomycosis consists of reversal of the underlying predisposing factors, widespread surgical debridement, and aggressive antifungal medication (2, 6, 13). Unfortunately, despite disfiguring surgical debridement and aggressive therapy with amphotericin B, the overall mortality of zygomycosis remains Ͼ50% (13), and it approaches 100% in patients with disseminated disease (5). Clearly, new strategies to treat zygomycosis are urgently needed.A hallmark of mucormycosis infections is the virtually uniform presence of extensive angioinvasion with resultant vessel thrombosis and tissue necrosis (2,6,9,13). This angioinvasive character is associated with the ability of the organism to spread through viable tissue and to hematogenously disseminate to other target organs. Furthermore, since antifungal agents are carried to the site of infection in the vasculature, adequate blood supply is necessary to deliver these agents to R. oryzae in vivo. Therefore, ischemic necrosis as a result of R. oryzae-mediated angioinvasion is likely an important mechanism by which the fungus survives therapy with fungicidal agents, such as amphotericin B. For these reasons, damage of and penetration through endothelial cells lining blood vessels is likely a critical step in R. oryzae's pathogenetic strategy.We therefore studied the interaction between R. oryzae and endothelial cells. We find that damage to endothelial cells from R. oryzae is dependent upon its adherence to and phagocytosis by endothelial cells. Surprisingly, R. oryzae does not need to be viable to cause endothelial cell damage. ...

CotH3 mediates fungal invasion of host cells during mucormycosis

“…Because we previously showed that endocytosis of the fungus is a prerequisite for R. oryzae to cause endothelial cell damage (14,15), we sought to determine whether blocking the function or expression of CotH3 would protect endothelial cells from R. oryzae-induced endocytosis and subsequent damage. Endothelial cell endocytosis of R. oryzae germlings was abrogated by addition of rabbit anti-CotH3 polyclonal Abs, but not preimmune serum collected from the same animal ( Figure 4A).…”

“…Thus, fungal interaction with endothelial cells lining the vasculature represents an important step in the pathogenesis of mucormycosis. Previously, we determined that R. oryzae strains adhere to human umbilical vein endothelial cells in vitro and invade these cells by induced endocytosis (14). We recently discovered glucose-regulated protein 78 (GRP78) as the endothelial cell receptor to which Mucorales bind during host cell invasion (15).…”

Human Mucormycosis

“…Pulmonary alveolar macrophages damage the invading organisms and to regulate innate immune response secrete cytokines and chemokines to destroy sporangiospores before they terminate to become hyphae. In hosts with diabetes, the monocytes/macrophages are dysfunctional and fail [5,9,10].…”

The bactericidal and fungicidal effects of salicid on pathogenic organisms involved in hospital infections

“…Auto-infection of surgical wounds by S. aureus is common, and is associated with considerable morbidity and represents an important medical and economic problem. R. oryzae is the most common cause of zygomycosis, a life-threatening infection that usually occurs in immunocompromised patients (Ibrahim et al, 2005). Infections caused by Aspergillus species have grown in importance in recent years (Pasqualotto, 2009).…”