Trichloroethene metabolite dichloroacetyl chloride induces apoptosis and compromises phagocytosis in Kupffer Cells: Activation of inflammasome and MAPKs

Abstract

Exposure to trichloroethene (TCE), an occupational and ubiquitous environmental contaminant, is associated with the development of several autoimmune diseases, including autoimmune hepatitis (AIH). However, mechanisms contributing to TCE-mediated AIH are not known. Earlier, we have shown that dichloroacetyl chloride (DCAC), one of the reactive metabolites of TCE with strong acylating capability, can elicit an autoimmune response at much lower dose than TCE in female MRL+/+ mice. Furthermore, Kupffer cells (KCs), the liver resident macrophages, are crucial for hepatic homeostasis, but can also participate in the immunopathogenesis of AIH. However, contribution of KCs in TCE-mediated AIH and the underlying mechanisms are not understood. We hypothesized that increased apoptosis and delayed clearance of apoptotic bodies, due to compromised KC function, will result in the breakdown of self-tolerance, autoimmunity, and ultimately AIH. Therefore, using an in vitro model of immortalized mouse KCs, we investigated the contribution of DCAC in TCE-mediated AIH. KCs were treated with different concentrations of DCAC and apoptosis was measured by Annexin V and PI staining. Also, the impact of DCAC on phagocytic potential of KCs was evaluated. Furthermore, markers of inflammasome (NLRP3 and cas-pase1) were analyzed by real-time PCR and Western blot analysis. DCAC treatment resulted in significantly increased early and late-stage apoptosis, accompanied with inflammasome activation (NLRP3 increases). DCAC treatment resulted in decreased phagocytic function of KCs in a dose-dependent manner, with reduced MFG-E8 levels (phagocytotic function). Furthermore, DCAC exposure led to induction of phos-ERK and phos-AKT signaling. These findings suggest that DCAC induces apoptosis and inflammasome activation, while compromising the phagocytic function of KCs. Our data support that increased apoptosis and impaired KC function by DCAC could be contributory to TCE-mediated AIH.