Hepatic signalling disruption by pollutant Polychlorinated biphenyls in steatohepatitis

Abstract

Background: Polychlorinated biphenyl-mediated steatohepatitis has been shown to be due in part to inhibition of epidermal growth factor receptor (EGFR) signalling. EGFR signalling regulates many facets of hepatocyte function, but it is unclear which other kinases and pathways are involved in the development of toxicant-associated steatohepatitis (TASH). Methods: Comparative hepatic phosphoproteomic analysis was used to identify which kinases were affected by either PCB exposure (Aroclor 1260 mixture), high fat diet (HFD), or their interaction in a chronic exposure model of TASH. Cellular assays and western blot analysis were used to validate the phosphoproteomic findings. Results: 1760 unique phosphorylated peptides were identified and of those 588 were significantly different. PCB exposure and dietary interaction promoted a near 25% reduction of hepatic phospho-peptides. Leptin and insulin signalling were pathways highly affected by PCB exposure and liver necrosis was a pathologic ontology over represented due to interaction between PCBs and a HFD. Casein kinase 2 (CK2), Extracellular regulated kinase (ERK), Protein kinase B (AKT), and Cyclin dependent kinase (CDK) activity were demonstrated to be downregulated after PCB exposure and this downregulation was exacerbated with a HFD. PCB exposure led to a loss of hepatic CK2 subunit expression limiting CK2 kinase activity and negatively regulating caspase-3 (CASP3). PCBs promoted secondary necrosis in vitro validating the latter observation. The loss of hepatic phosphoprotein signalling appeared to be due to decreased signal transduction rather than phosphatase upregulation. Conclusions: PCBs are signal disrupting chemicals that promote secondary necrosis through affecting a myriad of liver processes including metabolism and cellular maintenance. PCB exposure, particularly with interaction with a HFD greatly down- regulates the hepatic kinome. More data are needed on signalling disruption and its impact on liver health.

Effect of Epidermal Growth Factor Treatment and Polychlorinated Biphenyl Exposure in a Dietary-Exposure Mouse Model of Steatohepatitis

“…another receptor, the EGFR, in NASH in vitro (Hardesty et al 2017(Hardesty et al , 2018 and in murine liver (Hardesty et al 2017(Hardesty et al , 2019a(Hardesty et al , 2019bJin et al 2020). Similarly, classes of EGFR inhibitors have been associated with liver injury (Qian et al 2020) in cancer patients.…”

“…Similarly, classes of EGFR inhibitors have been associated with liver injury (Qian et al 2020) in cancer patients. PCB exposures reduced EGFR signaling by inhibiting EGFR phosphorylation, thereby decreasing downstream protein kinase activity leading to indirect CAR activation in mouse liver (Hardesty et al 2017(Hardesty et al , 2019a and in vitro (Hardesty et al 2017). However, the causality of this so-called signaling disruption in PCB-associated NASH has not previously been demonstrated.…”

“…PCBs are signaling (Hardesty et al 2019a) and metabolism disrupting chemicals (Heindel et al 2017). PCBs appear to be competitive antagonists of the EGFR (Hardesty et al 2018).…”

“…PCBs are lipophilic, and hepatic steatosis markedly increased hepatic PCB levels in mice (Li et al 2020). In mice, Aroclor 1260 (20 mg=kg) increased the severity of diet-induced NAFLD (e.g., NASH vs. isolated steatosis) (Wahlang et al 2014b) and reduced hepatic protein phosphorylation by approximately 25%, consistent with profound phosphoprotein signaling disruption (Hardesty et al 2019a).…”

“…In addition to AhR activation, several modes of action affecting hepatic lipid metabolism, cell death/proliferation, inflammation, and fibrosis have been identified for PCBs. These include endocrine (Heindel et al 2017) signaling disruption (Hardesty et al 2019a), altered nuclear receptor activities (Hardesty et al 2019b), and increased oxidative stress (Wahlang et al 2019a). Aroclor 1260 is an environmentally relevant PCB mixture that was previously commercially produced.…”