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Because it fosters our dreams of immortality, regeneration has been for centuries a matter of fascination for countless biologists and clinicians. While in mammals regeneration is obviously less spectacular than in hydra, newt or zebrafish, it allows, in any case, repairing intestine, skin or liver. The latter organ is seen as a paradigmatic regeneration model because, as for an amputated fin's zebrafish or newt's forelimb, it is indeed possible to follow the complete restoration of a rodent liver mass after a 2/3 partial hepatectomy (PH) within a few days. The caveat is that most of our knowledge about liver regeneration is based on this specific surgical model. The amazing conclusion is that liver regeneration relies mainly on highly differentiated hepatocytes, which, while actively dividing to restore the missing part, maintain their vital functions.1 Hepatocytes are in a quiescent state (G0) in a normal adult liver. Following 2/3 PH, >95% of these parenchymal cells present in the remnant lobes divide in a rather synchronous manner, for one or two rounds of cell division. Other liver cell types, such as macrophages, cholangiocytes or endothelial cells, will divide afterwards. Schematically, one can distinguish two successive main steps allowing proper regeneration. The first phase requires the secretion of cytokines such as tumour necrosis factor-α and interleukin-6 in the very first minutes after PH, which poise hepatocytes to enter G1 phase and to become receptive to growth factors. The second step involves concomitantly metabolic changes, consisting in particular in a transient accumulation of lipid droplets, and in the activation of two growth factor pathways, epidermal growth factor receptor and c-Met. Both pathways then recruit scaffolding proteins and activate multiple intracellular intertwined networks, such as mitogen-activated protein kinases, signal transducer and activator of transcription 3 (STAT3), …
Competing interests None.
Provenance and peer review Commissioned; internally peer reviewed.