Cell Intrinsic Galectin-3 Attenuates Neutrophil ROS-Dependent Killing of Candida by Modulating CR3 Downstream Syk Activation

Abstract

Invasive candidiasis is a leading cause of nosocomial bloodstream infection. Neutrophils are the important effector cells in host resistance to candidiasis. To investigate the modulation of neutrophil fungicidal function will advance our knowledge on the control of candidiasis. While recombinant galectin-3 enhances neutrophil phagocytosis of Candida, we found that intracellular galectin-3 downregulates neutrophil fungicidal functions. Co-immunoprecipitation and immunofluorescence staining reveal that cytosolic gal3 physically interacts with Syk in neutrophils after Candida stimulation. Gal3−/− neutrophils have higher level of Syk activation as well as greater abilities to generate reactive oxygen species (ROS) and kill Candida than gal3+/+ cells. While galectin-3 deficiency modulates neutrophil and macrophage activation and the recruitment of monocytes and dendritic cells, the deficiency does not affect the numbers of infiltrating neutrophils or macrophages. Galectin-3 deficiency ameliorates systemic candidiasis by reducing fungal burden, renal pathology, and mortality. Adoptive transfer experiments demonstrate that cell intrinsic galectin-3 negatively regulates neutrophil effector functions against candidiasis. Reducing galectin-3 expression or activity by siRNA or gal3 inhibitor TD139 enhances human neutrophil ROS production. Mice treated with TD139 have enhanced ability to clear the fungus. Our work unravels the mechanism by which galectin-3 regulates Syk-dependent neutrophil fungicidal functions and raises the possibility that blocking gal3 in neutrophils may be a promising therapeutic strategy for treating systemic candidiasis.

Whole Transcriptome Analysis Reveals That Filifactor alocis Modulates TNFα-Stimulated MAPK Activation in Human Neutrophils

“…While the minimal ROS activation at the early time points cannot be attributed to modulation of gene expression by F. alocis, generation of ROS at later time points may be inhibited by the expression of a member of the galectin family of carbohydrate-binding proteins, galectin-3. The increased expression of galectin-3 has already been associated with inhibition of ROS production when human neutrophils were challenged with Candida albicans (48). In our dataset, both the FPKM expression as well as the qPCR validation show a time-dependent increase in galectin-3 mRNA expression ( Figures 1E,F), and when tested by western blot, F. alocis induced a time dependent increase in galectin-3 protein expression (data not shown).…”

“…Although the minimal ROS induced by F. alocischallenged neutrophils was monitored between 1 and 90 min and the significant decrease in p47phox gene expression was observed at 6 h post-infection, these pathogen-induced changes in the transcript levels could leave neutrophils defective in mounting an appropriate respiratory burst response. Furthermore, cytosolic galectin-3 acts as a negative regulator of ROS production in both human and mouse neutrophils by modulating complement receptor 3 signaling pathway during C. albicans infections (48). Our results show a time-dependent increase in galectin-3 gene expression which could be one of the strategies used by F. alocis to inhibit ROS production.…”

Face/Off: The Interchangeable Side of Candida Albicans

“…However, galectin-3-deficient neutrophils had a higher level of ROS than the control strain after exposure to C. albicans. This effect is mediated via a physical interaction between galectin-3 with the CR3 downstream component Syk (Wu et al, 2017). Interestingly, additional receptors are suspected to recognize β-glucan as PBMCs have been identified to produce IL-1Ra in response to C. albicans hyphae in a Dectin-1-and CR3-independent manner (Smeekens et al, 2015).…”

Antifungal Innate Immunity: A Perspective from the Last 10 Years

“…It has also been suggested that galectin-3 can have a dual role in the regulation of neutrophil function, depending on its cellular location. While recombinant galectin-3 was shown to enhance neutrophil phagocytosis of C. albicans , it was also found that intracellular galectin-3 can downregulate neutrophil fungicidal activities by physically interacting with Syk and therefore reducing ROS-dependent killing of C. albicans [48]. …”