AMPK-endoplasmic reticulum stress axis contributes to lipopolysaccharide-caused mitochondrial dysfunction by regulating mitochondria-associated membrane function in bovine hepatocytes

Mitochondrial homeostasis is closely associated with cellular homeostasis process, whereas mitochondrial dysfunction contributes to Apoptosis and Mitophagy. Hence, analyzing the mechanism of lipopolysaccharide (LPS)-caused mitochondrial damage is necessary to understand how cellular homeostasis is maintained in bovine hepatocytes. Mitochondria-associated membranes (MAM), a connection between endoplasmic reticulum (ER) and mitochondria, is important to control mitochondrial function. To investigate the underlying mechanisms of the LPS-caused mitochondrial dysfunction, hepatocytes isolated from dairy cows at ∼160 d in milk (DIM) were pretreated with the specific inhibitors of adenosine 5'-monophosphate-activated protein kinase (AMPK), ER stress, RNA-activated protein kinase-like ER kinase (PERK), inositol-requiring Enzyme 1α (IRE1α), c-Jun N-terminal kinase, and Autophagy followed by a 12 μg/mL LPS treatment. The results showed that inhibiting ER stress with 4-phenylbutyric acid decreased the levels of Autophagy and mitochondrial damage with AMPK inactivation in LPS-treated hepatocytes. The AMPK Inhibitor compound C pretreatment alleviated LPS-induced ER stress, Autophagy and mitochondrial dysfunction by regulating the expression of MAM-related genes, such as mitofusin 2 (MFN2), PERK, and IRE1α. Moreover, inhibiting PERK and IRE1α mitigated Autophagy and mitochondrial dynamic disruption by regulating the MAM function. Additionally, blocking c-Jun N-terminal kinase, the downstream sensor of IRE1α, could reduce the levels of Autophagy and Apoptosis and restore the balance of mitochondrial fusion and fission by modulating the B cell leukemia 2 (Bcl-2)/Bcl-2 interacting protein 1 (Beclin1) complex in the LPS-treated bovine hepatocytes. Furthermore, Autophagy blockage with chloroquine could intervene in LPS-caused Apoptosis to restore mitochondrial function. Collectively, these findings suggest that the AMPK-ER stress axis is involved in the LPS-caused mitochondrial dysfunction by mediating the MAM activity in bovine hepatocytes.

adenosine 5′-monophosphate-activated protein kinase; bovine hepatocytes; endoplasmic reticulum stress; mitochondria-associated membranes; mitochondrial dysfunction.