Upon liver injury, hepatic stellate cells (HSCs) transdifferentiate to migratory, proliferative and extracellular matrix-producing myofibroblasts (e.g., activated HSCs; aHSCs) causing liver fibrosis. HSC activation is associated with increased glycolysis and glutaminolysis. Here, we compared the contribution of glycolysis, glutaminolysis and mitochondrial oxidative phosphorylation (OXPHOS) in rat and human HSC activation. Basal levels of glycolysis (extracellular acidification rate ~3-fold higher) and particularly mitochondrial respiration (oxygen consumption rate ~5-fold higher) were significantly increased in rat aHSCs, when compared to quiescent rat HSC. This was accompanied by extensive mitochondrial fusion in rat and human aHSCs, which occurred without increasing mitochondrial DNA content and electron transport chain (ETC) components. Inhibition of glycolysis (by 2-deoxy-D-glucose) and glutaminolysis (by CB-839) did not inhibit rat aHSC proliferation, but did reduce Acta2 (encoding α-SMA) expression slightly. In contrast, inhibiting mitochondrial OXPHOS (by rotenone) significantly suppressed rat aHSC proliferation, as well as Col1a1 and Acta2 expression. Other than that observed for rat aHSCs, human aHSC proliferation and expression of fibrosis markers were significantly suppressed by inhibiting either glycolysis, glutaminolysis or mitochondrial OXPHOS (by metformin). Activation of HSCs is marked by simultaneous induction of glycolysis and mitochondrial metabolism, extending the possibilities to suppress hepatic fibrogenesis by interfering with HSC metabolism.

Sensorineural hearing loss is mainly caused by irreversible damage to sensory hair cells (HCs). A subgroup of supporting cells (SCs) in the cochlea express leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5), a marker for tissue-resident stem cells. LGR5+ SCs could be used as an endogenous source of stem cells for regeneration of HCs to treat hearing loss. Here, we report long-term presence of LGR5+ SCs in the mature adult cochlea and survival of LGR5+ SCs after severe ototoxic trauma characterized by partial loss of inner HCs and complete loss of outer HCs. Surviving LGR5+ SCs (confirmed by GFP expression) were located in the third row of Deiters’ cells. We observed a change in the intracellular localization of GFP, from the nucleus in normal-hearing to cytoplasm and membrane in deafened mice. These data suggests that the adult mammalian cochlea possesses properties essential for regeneration even after severe ototoxic trauma.

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Sensorineural hearing loss is caused by damage to sensory hair cells and/or spiral ganglion neurons. In non-mammalian species, hair cell regeneration after damage is observed, even in adulthood. Although the neonatal mammalian cochlea carries regenerative potential, the adult cochlea cannot regenerate lost hair cells. The survival of supporting cells with regenerative potential after cochlear trauma in adults is promising for promoting hair cell regeneration through therapeutic approaches. Targeting these cells by manipulating key signaling pathways that control mammalian cochlear development and non-mammalian hair cell regeneration could lead to regeneration of hair cells in the mammalian cochlea. This review discusses the pathways involved in the development of the cochlea and the impact that trauma has on the regenerative capacity of the endogenous progenitor cells. Furthermore, it discusses the effects of manipulating key signaling pathways targeting supporting cells with progenitor potential to promote hair cell regeneration and translates these findings to the human situation. To improve hearing recovery after hearing loss in adults, we propose a combined approach targeting (1) the endogenous progenitor cells by manipulating signaling pathways (Wnt, Notch, Shh, FGF and BMP/TGFβ signaling pathways), (2) by manipulating epigenetic control, and (3) by applying neurotrophic treatments to promote reinnervation.

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Background Liver regeneration is compromised in advanced fibrosis or cirrhosis, where progenitor cell therapy is being considered as a therapeutic option. Little is known about the presence and potential role of leucine-rich-repeat-containing G protein-coupled receptor 5-expressing (LGR5+) progenitor cells in chronically injured human liver. In this study, we analyzed LGR5 expression in fibrotic and cirrhotic human livers and studied the interaction between human liver organoids and hepatic stellate cells (HSC) in vitro. Methods Control and fibrotic human liver tissues were combined in a tissue microaarray and sections were stained with H&E or Sirius red, or immune-stained for LGR5 and various liver cell type markers. Adult LGR5+ progenitor cell-derived human liver organoids were co-cultured with human LX-2 HSC or exposed to LX-2 conditioned medium and analyzed by q-PCR and immuno-microscopy. Results LGR5 mRNA were significantly enhanced in fibrotic liver tissue and LGR5+ cell numbers positively correlated with the stage of fibrosis. LGR5+ cells accumulated close to the fibrotic bands and co-expressed hepatocyte markers, but not cholangiocyte markers. TGFβ1-activated LX-2 cells enhanced LGR5 expression in organoids and organoid growth, results that were replicated by exposing organoids to LX-2-conditioned medium. Blocking LX-2 activation by dimethyloxalylglycine prevented all these effects on liver organoids. Conclusion LGR5+ progenitor cells are abundantly present in human liver fibrosis. Activated HSC induce LGR5 expression and growth of human liver organoids. Treatment of advanced liver fibrosis may therefore not strongly benefit from adding exogenous progenitor cells, but rather from promoting expansion and differentiation of the endogenous LGR5+ cells.