Acute Endoplasmic Reticulum Stress Induces Inflammation Reaction, Complement System Activation, and Lipid Metabolism Disorder of Piglet Livers: A Proteomic Approach

Abstract

Endoplasmic reticulum stress (ERS) is closely associated with the occurrence and development of many liver diseases. ERS models mostly include experimental animals such as rats and mice. However, pigs are more similar to humans with regards to digestion and metabolism, especially liver construction, yet few reports on ERS in pigs exist. In order to explore changes in the liver under ERS, we used tunicamycin (TM), which can cause liver jaundice and damage liver function, to establish acute ERS models in piglets using a low TM dosage (LD, 0.1 mg/kg body weight (bw)), high TM dosage (HD, 0.3 mg/kg bw), or vehicle for 48 h. We found that both LD- and HD-induced ERS, as verified by the ERS-linked proteins. Furthermore, the concentrations of the proinflammatory cytokines, namely, TNF-α and IL-6 were elevated in TM-treated piglet livers, and the plasma levels of IL-6 and CRP were also higher, indicating the occurrence of inflammation in TM-treated piglets. The complement system was activated in TM-treated piglets, as indicated by increased levels of complement factors and activation products C3, C5a, and AP50. In order to gain insights into the global changes in liver proteins under ERS, we performed an isobaric tag for relative and absolute quantitation (iTRAQ)-based proteomic analysis on the livers of HD- and vehicle-treated piglets. Proteomic analysis identified 311 differentially expressed proteins (DEPs) between the two groups, and a Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis suggested that the DEPs were mainly enriched in signaling pathways such as metabolic pathways, protein processing in the endoplasmic reticulum, and complement and coagulation cascades. Many proteins involved in protein folding, lipid transport, and oxidation were upregulated. Proteins involved in lipid synthesis were downregulated to alleviate liver steatosis, and most complement factors were upregulated to protect the body, and Pearson correlation analysis found that most of the DEPs in the complement and coagulation pathway were significantly correlated with plasma CRP, IL6 and AP50. Our results revealed that TM can activate ERS, marked by liver injury and steatosis, inflammatory reactions, and complement activation in piglets.

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“…Evidence indicates that the complement cascade, as one of the primary upregulated inflammatory pathways, appears consistently in various neurodegenerative disorders, driving the degeneration progression and cognitive impairment [22]. In tunicamycintreated acute ERS models, the complement system activation product C3 was elevated [21]. Astrocytes regulated C3 secretion via the NF-κB signaling pathway, which was closely related to ERS [23,59].…”

“…Through down-regulation of C3 in vitro, LPS-induced lung cells were able to maintain viability and suppress apoptosis by decreasing ERS expression [20]. In tunicamycin-established acute ERS models of piglets, the complement system was activated, which produced higher levels of activation product C3 [21]. Within the central nervous system, astrocytes are the primary source of the secreted C3, while microglia and neurons express C3aR [22].…”

RNA-Sequencing Characterization of lncRNA and mRNA Functions in Septic Pig Liver Injury

“…Interesting, endoplasmic reticulum stress (ERS) markers were upregulated in pig livers following the LPS challenge, including the receptor protein kinase receptor-like endoplasmic reticulum kinase (PERK), eukaryotic translation initiation factor 2α (eIF2α, also known as EIF2S1 ), the transcription factor C/EBP homologous protein (CHOP), and activating transcription factor 4 (ATF4). Wang et al [ 27 ] demonstrated that acute ERS induces inflammation, complement activation, and lipid metabolism disorder, leading to liver injury in pigs. In human mesangial cells, anti-dsDNA antibodies induced the activation of NF-κB and upregulated the expression of IL-1β and TNF-α, depending on the PERK/ATF4/NF-κB pathway [ 28 ].…”

Novel molecular mechanism driving neuroprotection after soluble epoxide hydrolase inhibition: Insights for Alzheimer's disease therapeutics

“…Then, given that C3 is the central component of the complement system, which is activated by the ERS 78 and is highly expressed in AD, 79 Finally, it has been described that accumulating misfolded proteins in the ER can overwhelm the protein quality control, causing cell death in AD. 80 Then, cells can activate the UPR, which mediates cell survival by slowing protein translation 81 and being proapoptotic Bcl-2 proteins overexpressed, leading to the activation of the Caspase cascade, and generating their related breakdown products of α-spectrin such as SBDP 150 and 120.…”

“…Then, given that C3 is the central component of the complement system, which is activated by the ERS 78 and is highly expressed in AD, 79 being associated with pathological Aβ aggregation, we evaluated C3 gene expression levels in T/I/C‐activated astrocytes. C3 gene expression in activated astrocytes was about 10x more than the control cells and was completely blocked by UB‐SCG‐51 treatment.…”