Hepatic vagotomy blunts liver regeneration after hepatectomy by downregulating the expression of interleukin-22

Abstract

Background: Rapid regeneration of the residual liver is one of the key determinants of successful partial hepatectomy (PHx). At present, there is a lack of recognized safe, effective, and stable drugs to promote liver regeneration. It has been reported that vagus nerve signaling is beneficial to liver regeneration, but the potential mechanism at play here is not fully understood.

Aim: To explore the effect and mechanism of hepatic vagus nerve in liver regeneration after PHx.

Methods: A PHx plus hepatic vagotomy (Hv) mouse model was established. The effect of Hv on liver regeneration after PHx was determined by comparing the liver regeneration levels of the PHx-Hv group and the PHx-sham group mice. In order to further investigate the role of interleukin (IL)-22 in liver regeneration inhibition mediated by Hv, the levels of IL-22 in the PHx-Hv group and the PHx-sham group was measured. The degree of liver injury in the PHx-Hv group and the PHx-sham group mice was detected to determine the role of the hepatic vagus nerve in liver injury after PHx.

Results: Compared to control-group mice, Hv mice showed severe liver injury and weakened liver regeneration after PHx. Further research found that Hv downregulates the production of IL-22 induced by PHx and blocks activation of the signal transducer and activator of transcription 3 (STAT3) pathway then reduces the expression of various mitogenic and anti-apoptotic proteins after PHx. Exogenous IL-22 reverses the inhibition of liver regeneration induced by Hv and alleviates liver injury, while treatment with IL-22 binding protein (an inhibitor of IL-22 signaling) reduce the concentration of IL-22 induced by PHx, inhibits the activation of the STAT3 signaling pathway in the liver after PHx, thereby hindering liver regeneration and aggravating liver injury in PHx-sham mice.

Conclusion: Hv attenuates liver regeneration after hepatectomy, and the mechanism may be related to the fact that Hv downregulates the production of IL-22, then blocks activation of the STAT3 pathway.

Keywords: Hepatic vagotomy; Interleukin-22; Interleukin-22 binding protein; Liver regeneration; Partial hepatectomy; Signal transducer and activator of transcription 3.

Figure 1

Hepatic vagotomy inhibits liver regeneration and aggravates liver injury after partial hepatectomy. A: Representative BrdU staining pictures of liver tissue at different observation time points after partial hepatectomy (200 ×); B and C: The proportion of BrdU⁺ hepatocytes (48 h) and the liver weight/body weight ratio in each group were calculated to visually display the level of liver regeneration; D: Representative hematoxylin and eosin staining shows the area of liver injury after surgery (50 ×); E and F: Serum alanine aminotransferase and aspartate aminotransferase activities of mice in different groups were detected to determine the severity of liver injury (n = 6-10). ^aP < 0.05. PHx: Partial hepatectomy; Hv: Hepatic vagotomy; SP: Sham operation.

Figure 2

Hepatic vagotomy reduces interleukin-22 production after partial hepatectomy. A and B: A mouse interleukin (IL)-22 enzyme-linked immunosorbent assay kit was used to quantify the concentration of IL-22 in serum and liver homogenate of mice in each group; C-E: Liver tissues of different groups were obtained at 6 h after partial hepatectomy (PHx), and the expression of IL-22 protein (C and D) and IL-22 mRNA (E) in liver tissues were detected by western blotting and quantitative real-time polymerase chain reaction techniques, respectively (n = 6-10). ^aP < 0.05, ^bP < 0.01, ^cP < 0.001. PHx: Partial hepatectomy; Hv: Hepatic vagotomy; SP: Sham operation.

Figure 3

Hepatic vagotomy inhibits the activation of the hepatic signal transducer and activator of transcription 3 signaling pathway. A and B: Western blotting was used to detect the activation of the signal transducer and activator of transcription 3 pathway and the expression of its related proteins, such as CyclinD1, PCNA, and FoxM1, in liver tissues of each group at 6 h after partial hepatectomy. ^aP < 0.05, ^bP < 0.01, ^cP < 0.001. PHx: Partial hepatectomy; Hv: Hepatic vagotomy; SP: Sham operation; STAT3: Signal transducer and activator of transcription 3.

Figure 4

Administration of exogenous interleukin-22 reverses the inhibition of liver regeneration caused by hepatic vagotomy. A: Representative BrdU staining pictures of liver tissues at 48 h from the partial hepatectomy (PHx)-hepatic vagotomy (Hv) group and the PHx-Hv-interleukin-22 group (200 ×); B and C: The proportion of BrdU⁺ hepatocytes (48 h) and the liver weight/body weight ratio of these two groups were counted; D and E: Serum alanine aminotransferase and aspartate aminotransferase activities of these two groups were detected to determine the severity of liver injury; F and G: Detection of the signal transducer and activator of transcription 3 pathway and related protein expression in mouse livers by western blotting (6 h) (n = 5-7). ^aP < 0.05. PHx: Partial hepatectomy; Hv: Hepatic vagotomy; ALT: Alanine aminotransferase; AST: Aspartate aminotransferase; LW/BW: Liver weight/body weight; STAT3: Signal transducer and activator of transcription 3.

Figure 5

Treatment with interleukin-22BP can reduce the concentration of interleukin-22 and inhibit liver regeneration. A and B: The concentration of interleukin (IL)-22 in serum and liver tissue homogenate at each time point after partial hepatectomy (PHx) in the PHx-sham group and the PHx–IL-22BP group was counted; C: Representative BrdU staining pictures of liver tissue at different time points after PHx (200 ×); D: The percentage of BrdU⁺ hepatocytes (48 h) in the PHx-sham group and the PHx-IL-22BP group was calculated; E and F: We used an automatic chemical analyzer to detect the activities of serum alanine aminotransferase and aspartate aminotransferase in the PHx-sham group and the PHx–IL-22BP group (n = 4-8). ^aP < 0.05). PHx: Partial hepatectomy; Hv: Hepatic vagotomy; IL: Interleukin; ALT: Alanine aminotransferase; AST: Aspartate aminotransferase.

Figure 6

Interleukin-22BP inhibits the activation of the hepatic signal transducer and activator of transcription 3 pathway after partial hepatectomy. The expression levels of signal transducer and activator of transcription 3 (STAT3), P-STAT3, and CyclinD1 protein in liver tissue of mice in the partial hepatectomy (PHx)-sham group and the PHx-interleukin-22BP group at 6 h after PHx were detected. ^aP < 0.05, ^bP < 0.01, ^cP < 0.001. PHx: Partial hepatectomy; Hv: Hepatic vagotomy; STAT3: Signal transducer and activator of transcription 3; IL: Interleukin.