Subacute ruminal acidosis induces pyroptosis via the mitophagy-mediated NLRP3 inflammasome activation in the livers of dairy cows fed a high-grain diet

Abstract

High-grain (HG) feeding can trigger subacute ruminal acidosis (SARA) and subsequent liver tissue injury. This study investigated pyroptosis and NLRP3 inflammasome activation in SARA-induced liver injury, and the role of mitophagy during this process. Twelve mid-lactating Holstein cows equipped with rumen fistulas were randomly divided into 2 groups: a low-grain (LG) diet group (grain:forage = 4:6) and a HG diet group (grain:forage = 6:4). Each group had 6 cows. The experiment lasted for 3 weeks. The ruminal fluid was collected through the rumen fistula on experimental d 20 and 21 and the pH immediately measured. At the end of the experiment, all animals were euthanized, and peripheral blood and liver tissue were collected. The ruminal pH was lower in the HG group than that in the LG group at all time points (On d 20: diet, P < 0.001; time, P = 0.02. On d 21: diet, P < 0.001; time, P = 0.002). In addition, the ruminal pH in the HG group was lower than 5.6 at 3 consecutive time points after feeding (4, 6, and 8 h on d 20; 2, 4, and 6 h on d 21), indicating that HG feeding induced SARA. The content of lipopolysaccharide (P = 0.016), interleukin 1 β (IL-1β; P < 0.01), and apoptosis-related cysteine protease 1 (caspase-1; P < 0.01) and the activity of alanine aminotransferase (P = 0.026) and aspartate aminotransferase (P = 0.002) in the blood plasma of the HG group were all significantly increased. Hepatic caspase-1 activity (P < 0.001) was increased in the livers of the HG group. The increased expression levels of pyroptosis- and NLRP3 inflammasome-related genes IL1B (P = 0.002), IL18 (P < 0.001), gasdermin D (GSDMD; P = 0.001), apoptosis-associated speck-like protein containing a card (ASC; P = 0.001), NLR family pyrin domain-containing 3 (NLRP3; P = 0.002), and caspase-1 (CASP1; P < 0.001) in liver tissue of the HG group were detected. Furthermore, Western blot analysis showed that HG feeding led to increased expression of pyroptosis- and NLRP3 inflammasome-related proteins GSDMD N-terminal (GSDMD-NT; P = 0.006), IL-1β (P < 0.001), IL-18 (P = 0.076), cleaved-caspase-1 (P = 0.001), ASC (P = 0.016), NLRP3 (P = 0.017), and cleaved-caspase-11 (P < 0.001) and upregulated expression of mitophagy-related proteins microtubule-associated protein 1 light chain 3 II (MAP1LC3-II; P = 0.001), beclin 1 (BECN1; P = 0.001), Parkin (P < 0.001), and PTEN induced kinase 1 (PINK1; P = 0.006) in liver tissue. Collectively, our results revealed that SARA caused increased mitophagy and activated the NLRP3 inflammasome, causing pyroptosis and subsequent liver injury in dairy cows fed a HG diet.