Delayed liver regeneration in germ-free mice is normalised following colonisation with conventional mouse microbiota

Background/Aim: It has been previously reported that LPS/TLR4 signalling and/or gut microbiota may be involved in liver regeneration following partial hepatectomy (PH). Despite many investigations, the real mechanism of liver... [ view full abstract ]

Background/Aim: It has been previously reported that LPS/TLR4 signalling and/or gut microbiota may be involved in liver regeneration following partial hepatectomy (PH). Despite many investigations, the real mechanism of liver regeneration remains unclear. Liver regeneration in germ-free mice that are colonised with conventional mouse microbiota however has never been tested. Therefore, this study aims to investigate the involvement of gut microbiota and LPS/TLR4 in liver regeneration. Methods: A 70% partial hepatectomy (PH) was performed under xylazine/ketamine (i.p.) in C57BL/6 conventional (B6C), germ-free mice (GFM) and in germ-free mice following one week colonisation with conventional mouse microbiota (GFMC). PH was also performed in TLR4^-/-; in C3H/HeN; in MTS510-treated C3H/HeN; and in antibiotic-treated C3H/HeN mice. Liver regeneration was assessed by liver weight-to-body weight (LW/BW) ratio and mitotic index. Plasma IL-6 was measured using luminex assay. Results: LW/BW ratio was 20% lower in GFM compared to B6C (p<0.0001) and GFMC (p<0.001) at 0hr timepoint (sham). At 3 days after PH, LW/BW and mitotic index in GFM were significantly reduced compared to B6C (p<0.0001) and GFMC (p<0.0001). LW/BW ratio and mitotic index were not significantly different between B6C and GFMC at 3 days after PH. LW/BW ratio and mitotic index after PH were significantly reduced in MTS510- and antibiotic-treated C3H/HeN, but not in TLR4^-/- mice. There was a trend towards higher levels of plasma IL-6 secretion in GFM at 0, 3 and 6 hours following PH compared to B6C and GFMC animals.  Discussion/Conclusion: Results of the study confirms the previous findings that liver regeneration is delayed in germ-free and antibiotic-treated mice. Following colonisation with conventional mouse microbiota, delayed liver regeneration in germ-free mice is corrected to  normal. Taken together, these suggest that gut microbiota plays an important role in liver regeneration. Delayed liver regeneration in acute blockade of LPS/TLR4 signalling pathway suggests that LPS/TLR4 is involved in liver regeneration. In TLR4^-/- mice, activation of redundant signalling pathways might have occurred, leading to normal liver regeneration. IL-6 secretion does not depend on the gut microbiota and may not be directly involved in liver regeneration.