Impaired liver regeneration in aged mice can be rescued by silencing Hippo core kinases MST1 and MST2

Abstract

The liver has an intrinsic capacity to regenerate in response to injury or surgical resection. Nevertheless, circumstances in which hepatocytes are unresponsive to proliferative signals result in impaired regeneration and hepatic failure. As the Hippo pathway has a canonical role in the maintenance of liver size, we investigated whether it could serve as a therapeutic target to support regeneration. Using a standard two‐thirds partial hepatectomy (PH) model in young and aged mice, we demonstrate that the Hippo pathway is modulated across the phases of liver regeneration. The activity of the core kinases MST1 and LATS1 increased during the early hypertrophic phase and returned to steady state levels in the proliferative phase, coinciding with activation of YAP1 target genes and hepatocyte proliferation. Moreover, following PH in aged mice, we demonstrate that Hippo signaling is anomalous in non‐regenerating livers. We provide pre‐clinical evidence that silencing the Hippo core kinases MST1 and MST2 with siRNA provokes hepatocyte proliferation in quiescent livers and rescues liver regeneration in aged mice following PH. Our data suggest that targeting the Hippo core kinases MST1/2 has therapeutic potential to improve regeneration in non‐regenerative disorders.

Bile canaliculi remodeling activates YAP via the actin cytoskeleton during liver regeneration

“…In addition, the BC lacked the typical smooth and regular appearance at this resolution and acquired a rough surface texture (Fig A, compare BC in PV area of untreated vs. 1.5 days post‐PH). This could reflect alterations of the acto‐myosin system, which mediates apical contractility and regulates BC geometry and bile flow (Watanabe et al , ; Meyer et al , ). Interestingly, the observed structural changes preceded the reported temporal profile of hepatocyte proliferation, which starts at 1.5 days post‐PH and peaks at 2 days (Zou et al , ).…”

“…Bile canaliculi possess a dense sub‐apical contractile actin mesh via the acto‐myosin system (Watanabe et al , ; Meyer et al , ) which contributes to BC geometry and bile flow (Meyer et al , ). To test whether the actin cytoskeleton is modified along with the changes in BC during regeneration, we quantified the levels of apical F‐actin (phalloidin, Fig A, Appendix Fig S2A) and phospho‐Myosin light chain (pMLC, Fig C, Appendix Fig S2B) at the apical area of hepatocytes at different time points after PH or sham operation.…”

“…In particular, it is unclear how cells integrate metabolic (BA levels) and/or mechanical alterations, such as changes in blood and bile pressure, to control liver size during homeostasis and regeneration. Here, we addressed these questions by applying high‐resolution microscopy and quantitative 3D image analysis (Morales‐Navarrete et al , ; Meyer et al , ) to explore tissue and cellular alterations during liver regeneration. Our results unravel a new link between liver metabolism and Hippo signaling where the signaling pathway is activated through the mechanical properties of the biliary network in a switch‐like manner.…”

Activation of Yap1/Taz signaling in ischemic heart disease and dilated cardiomyopathy

“…S2). Using YAP/TAZ antibody which can recognize both YAP1 and TAZ (Loforese et al, 2017), we found that TAZ was 5.09 (human) or 2.25 (mouse) folds over YAP1 in whole lysates of normal adult hearts by relative density in the same membrane for Western blotting (Figs. 1E and 3E).…”

“…The blot was incubated with primary antibodies for overnight at 4°. Antibodies specific for YAP1, YAP1 phosphorylated at human Ser127 (mouse Ser112), TEAD1, β tubulin and an antibody recognizing both YAP1 and TAZ (YAZ/TAZ)(Loforese et al, 2017) were purchased from Cell Signaling Technology Inc. (Danvers, MA). After 3 washes in TBST, the membrane was incubated with a peroxidase-conjugated secondary antibody (Thermo Fisher Scientific, Rockford, IL) at 1:10,000 dilution for 45 min at room temperature.…”