Effect of a neural relay on liver regeneration in mice: activation of serotonin release from the gastrointestinal tract

Abstract

The development of therapeutic options to promote hepatic regeneration following severe liver injury is essential. While humoral factors have been reported as mechanisms of liver regeneration, the contributions of interorgan communication to liver regeneration have not been reported. In this study, we examined the effect of a neural relay on liver regeneration via activation of serotonin release from the gastrointestinal (GI) tract. Our results demonstrated that the afferent visceral nerve from the liver activates the efferent vagus nerve from the brain, leading to activation of serotonin release from the GI tract and contributing to liver regeneration. While it is difficult to apply these results directly to human health, we believe that this study may represent a step toward developing essential therapeutics to promote liver regeneration.

Keywords: gastrointestinal tract; hormone; liver regeneration; neural relay; serotonin.

Figure 1

Animal models and protocol. (A) Four groups of animal model were established: control group (Cnt), in which peritoneum incision was performed as a sham operation; partial hepatectomy group (PH), in which partial hepatectomy was performed; partial hepatectomy following visceral nerve block group (Cap + PH); and partial hepatectomy following vagus nerve block group (HV + PH). (B) For each group, tissues were collected, and expression of serotonin in the small intestine, BrdU uptake, PCNA expression in the liver, and liver weight‐to‐body weight ratio were assessed at appropriate time points. (C) Visceral nerve block was performed by applying capsaicin (Cap) to the sympathetic nervous plexus surrounding the celiac artery. Blockade was confirmed by immunostaining of the nerves with anti‐CGRP antibody.

Figure 2

Vagus nerve activation after partial hepatectomy. (A) Representative images from a section of pancreatic islet immunohistochemically stained with anti‐insulin antibody 3 days after partial hepatectomy. The number of pancreatic islets was classified with the area and was recorded for each size category (< 10 000 μm², 10 000–30 000 μm², and > 30 000 μm²) 0, 1, and 3 days after partial hepatectomy in the Cnt (B) and PH (C) groups. (D) Time‐dependent change of the number of small islets in the pancreas in the Cnt, PH, Cap + PH, and HV + PH groups. Five different pancreatic sections from each of the five mice in all groups were immunohistochemically stained with anti‐insulin antibody, and a quantitative analysis was performed using imagej software. The values represent mean ± SD (n = 25 for each group). *P < 0.05, ***P < 0.001, and N.S., no statistical significance compared with the Cnt group. Two‐way factor repeated‐measures analysis of variance followed by Bonferroni's multiple comparison test.

Figure 3

Effect of neural relay on DNA synthesis in hepatocytes after partial hepatectomy. (A) Representative images of BrdU‐positive cells in the liver. (B) Time‐dependent change of the number of cells positively stained for BrdU in the Cnt, PH, Cap + PH, and HV + PH groups. Five different sections from each of the five mice in all groups were immunohistochemically stained with anti‐BrdU antibody, and a quantitative analysis was performed using imagej software. The values represent mean ± SD (n = 25 for each group). ***P < 0.001, and N.S., no statistical significance compared with the Cnt group. Two‐way factor repeated‐measures analysis of variance followed by Bonferroni's multiple comparison test.

Figure 4

Effect of neural relay on hepatocyte proliferation after partial hepatectomy. (A) Representative images of PCNA‐positive cells in the liver. (B) Time‐dependent change of the number of cells positively stained for PCNA in the Cnt, PH, Cap + PH, and HV + PH groups. Five different sections from each of the five mice in all groups were immunohistochemically stained with anti‐PCNA antibody, and a quantitative analysis was performed using imagej software. [Correction added after online publication on 14 February 2018: anti‐BrdU antibody changed to anti‐PCNA antibody]. The values represent mean ± SD (n = 25 for each group). *P < 0.05, **P < 0.01, ***P < 0.001, and N.S., no statistical significance compared with the Cnt group. Two‐way factor repeated‐measures analysis of variance followed by Bonferroni's multiple comparison test.

Figure 5

Effect of neural relay on liver weight‐to‐body weight ratio after partial hepatectomy. Time‐dependent changes of liver weight‐to‐body weight ratio after partial hepatectomy in the Cnt, PH, Cap + PH, and HV + PH groups. Liver weight (LW)‐to‐body weight (BW) ratio was measured in each of the five mice from the four groups at appropriate time points. The values represent mean ± SD (n = 5 for each value). **P < 0.01, ***P < 0.001, and N.S., no statistical significance compared with the PH group. Two‐way factor repeated‐measures analysis of variance followed by Bonferroni's multiple comparison test.

Figure 6

Activation of the serotonin release from the enterochromaffin cells after partial hepatectomy. (A) Representative images of serotonin‐secreting enterochromaffin cells in the small intestine of each group. Expression of the serotonin was confirmed by immunostaining of the cells with anti‐serotonin antibody. (B) Time‐dependent change of the number of cells positively stained for serotonin in the Cnt, PH, Cap + PH, and HV + PH groups. Five different sections from each of the five mice in all groups were immunohistochemically stained with anti‐serotonin antibody, and a quantitative analysis was performed using imagej software. [Correction added after online publication on 14 February 2018: anti‐insulin antibody changed to anti‐serotonin antibody]. The values represent mean ± SD (n = 25 for each group). **P < 0.01, ***P < 0.001, and N.S., no statistical significance compared with the Cnt group. Two‐way factor repeated‐measures analysis of variance followed by Bonferroni's multiple comparison test.

Figure 7

Mechanism of hepatic regeneration through neural signal. (A) The direct feedback between the liver and the brain. (B) The involvement of GI tract in liver regeneration via the neural relay.