Calcium signalling from the type I inositol 1,4,5-trisphosphate receptor is required at early phase of liver regeneration

Background & Aims Liver regeneration is a multistage process that unfolds gradually, with different mediators acting at different stages of regeneration. Calcium (Ca2+) signalling is essential for liver regeneration. In hepatocytes, Ca2+ signalling results from the activation of inositol 1,4,5‐trisphosphate receptors (InsP3R) of which two of the three known isoforms are expressed (InsP3R‐I and InsP3R‐II). Here, we investigated the role of the InsP3R‐I‐dependent Ca2+ signals in hepatic proliferation during liver regeneration. Methods Partial hepatectomy (HX) in combination with knockdown of InsP3R‐I (AdsiRNA‐I) was used to evaluate the role of InsP3R‐I on liver regeneration and hepatocyte proliferation, as assessed by liver to body mass ratio, PCNA expression, immunoblots and measurements of intracellular Ca2+ signalling. Results AdsiRNA‐I efficiently infected the liver as demonstrated by the expression of β‐galactosidase throughout the liver lobules. Moreover, this construct selectively and efficiently reduced the expression of InsP3R‐I, as evaluated by immunoblots. Expression of AdsiRNA‐I in liver decreased peak Ca2+ amplitude induced by vasopressin in isolated hepatocytes 2 days after HX. Reduced InsP3R‐I expression prior to HX also delayed liver regeneration, as measured by liver to body weight ratio, and reduced hepatocyte proliferation, as evaluated by PCNA staining, at the same time point. At later stages of regeneration, control hepatocytes showed a decreased expression of InsP3R, as well as reduced InsP3R‐mediated Ca2+ signalling, events that did not affect liver growth. Conclusion Together, these results show that InsP3R‐I‐dependent Ca2+ signalling is an early triggering pathway required for liver regeneration.