Gasdermin D restricts Burkholderia cenocepacia infection in vitro and in vivo

Abstract

Burkholderia cenocepacia (B. cenocepacia) is an opportunistic bacterium; causing severe life threatening systemic infections in immunocompromised individuals including cystic fibrosis patients. The lack of gasdermin D (GSDMD) protects mice against endotoxin lipopolysaccharide (LPS) shock. On the other hand, GSDMD promotes mice survival in response to certain bacterial infections. However, the role of GSDMD during B. cenocepacia infection is not yet determined. Our in vitro study shows that GSDMD restricts B. cenocepacia replication within macrophages independent of its role in cell death through promoting mitochondrial reactive oxygen species (mROS) production. mROS is known to stimulate autophagy, hence, the inhibition of mROS or the absence of GSDMD during B. cenocepacia infections reduces autophagy which plays a critical role in the restriction of the pathogen. GSDMD promotes inflammation in response to B. cenocepacia through mediating the release of inflammasome dependent cytokine (IL-1β) and an independent one (CXCL1) (KC). Additionally, different B. cenocepacia secretory systems (T3SS, T4SS, and T6SS) contribute to inflammasome activation together with bacterial survival within macrophages. In vivo study confirmed the in vitro findings and showed that GSDMD restricts B. cenocepacia infection and dissemination and stimulates autophagy in response to B. cenocepacia. Nevertheless, GSDMD promotes lung inflammation and necrosis in response to B. cenocepacia without altering mice survival. This study describes the double-edged functions of GSDMD in response to B. cenocepacia infection and shows the importance of GSDMD-mediated mROS in restriction of B. cenocepacia.

The Burkholderia cenocepacia type VI secretion system effector TecA is a virulence factor during lung infection

“…with Bc strain K65-2 and the authors reported no difference in survival as compared to WT controls (Estfanous et al 2021). These results are consistent with the idea that cleavage of GSDMD, which would occur downstream of NLRP3, caspase-11 or pyrin inflammasomes, is not essential for the virulence of Bc during lung infection as measured by a survival assay.…”

“…Results of studies with BMDMs suggest that Bc infection can trigger T6SS-1-dependent activation of the NLRP3 (Rosales- Reyes et al 2012;Valvano 2015) and non-canonical caspase-11 inflammasomes (Estfanous et al 2021;Krause et al 2018) in addition to the pyrin inflammasome. We did not detect significant amounts of IL-1b released from LPS-primed Mefv -/-BMDMs infected with BcAU1054 or BcJ2315 (Fig.…”

Host Gasdermin D restrains systemic endotoxemia by capturing Proteobacteria in the colon of high-fat diet-feeding mice

“…GSDMD is widely distributed in various cell types of the colon, including conventional intestinal epithelial cells and immune cells, such as macrophages, neutrophils, and T lymphocytes. 21 To investigate the sources of secreted GSDMD-N, we performed IF analysis to identify the source of the increased GSDMD-N levels in response to HFD feeding. As shown in Figure 2(a ), the increased protein expression of GSDMD-FL and GSDMD-N in the colons of the HFD-fed mice was mainly localized to CD4-positive T lymphocytes and to ALP-positive enterocytes, and modestly expressed in the Gr-1-positive neutrophils, but rarely accumulated in the F4/80-positive macrophages.…”

“…GSDMD is known to exert anti-bacterial function in protecting hosts from excessive infiltration of exogenous gram-negative bacteria, including E. coli, S. typhimurium , and B. cenocepacia . 16 , 20 , 21 However, the effects of GSDMD on the endogenous bacteria remain elusive. In the present study, we found that GSDMD deficiency increased the HFD-induced accumulation of the Proteobacteria phylum, suggesting that Proteobacteria serves as a potential bacterial target of GSDMD-N. On the other hand, GSDMD deficiency modestly affects DSS-disrupted gut microbiota and exacerbates DSS-induced colitis in a microbiota-independent manner.…”

“… 19 In addition, GSDMD also serves as an antibacterial peptide to protect organisms from excessive infiltration of exogenous gram-negative bacteria, including E. coli, S. typhimurium , and B. cenocepacia . 16 , 20 , 21 It should be noted that the human colon contains the most abundant and diverse assemblage of endogenous bacteria, which are disrupted in response to HFD feeding. However, the reciprocal relationship between colonic GSDMD and the endogenous gut microbiota is still unknown.…”