TGFβ inhibition restores a regenerative response in acute liver injury by suppressing paracrine senescence

Abstract

One Sentence Summary:Inhibiting injury-induced senescence mediated by TGFβ signaling in regenerative epithelium improves liver regeneration. Accessible Summary:The liver is a paradigm of organ regeneration, however regeneration may fail in a previously normal liver following acute severe injury such as acetaminophen poisoning. We show that, a process with prevents proliferation termed senescence, which is classically associated with aging and carcinogenesis, stops the liver's regenerative cells. This senescence can be spread from cell to cell by the signaling molecule TGFβ. When TGFβ signaling is inhibited during acetaminophen poisoning in mice, senescence is impeded, regeneration accelerates, and survival is improved. Therefore targeting senescence induced by acute tissue injury is an attractive therapeutic approach to improve regeneration. Abstract:Liver injury results in rapid regeneration through hepatocyte proliferation and hypertrophy.However, after acute severe injury, such as acetaminophen poisoning, effective regeneration may fail. We investigated how senescence may underlie this regenerative failure. In human acute liver disease, and murine models, p21-dependent hepatocellular senescence was proportionate to disease severity and was associated with impaired regeneration. In an acetaminophen injury mouse model, a transcriptional signature associated with the induction 4 of paracrine senescence was observed within twenty four hours, and was followed by one of impaired proliferation. In mouse genetic models of hepatocyte injury and senescence we observed transmission of senescence to local uninjured hepatocytes. Spread of senescence depended upon macrophage-derived TGFβ1 ligand. In acetaminophen poisoning, inhibition of TGFβ receptor 1 (TGFβR1) improved mouse survival. TGFβR1 inhibition reduced senescence and enhanced liver regeneration even when delivered after the current therapeutic window for acetaminophen poisoning. This mechanism, in which injury-induced senescence impairs liver regeneration, is an attractive therapeutic target for developing treatments for acute liver failure.

Notch signalling mediates secondary senescence

“…In this model, the presence of p53 induction through Mdm2 deletion with 15 medium levels of CDKN1A (non senescence/primary p<0.001) marks primary senescence induction (34) (Fig.4b, Supplementary Fig.4a,b). Physiological levels of p53 and high levels of CDKN1A (CDKN1A expression secondary/primary p<0.0001) marks secondary senescence in Mdm2 normal (Mdm2+) hepatocytes as described (34) (Fig. 4b).…”

“…Based on these characteristics, cells can be readily distinguished by immunohistochemistry with 23% of primary and 10% of 20 secondary senescence hepatocytes detected ( Supplementary Fig.4a). We have previously shown that both subpopulations of hepatocytes upregulate senescence markers (gH2AX, IL1A, SA-beta Galactosidase) and reduce BrdU incorporation (34).…”

“…Overall, our data identify Notch as a key mediator of secondary senescence. 10 To test the involvement of NIS in vivo, we utilised a model where primary senescence is induced in a subpopulation of hepatocytes following Mdm2 deletion (34). This model is activated by hepatocyte-targeted recombination of Mdm2 (βNF induction AhCre, Mdm2-), resulting in primary senescence in Mdm2-cells.…”

Senolytic treatment targets aberrant p21-expression to restore liver regeneration in adult mice

“…For example, in models of liver fibrosis induced by CCl4 treatment, a robust senescence response is induced primarily in the stellate cells, which serves to limit fibrosis (Krizhanovsky et al, 2008). Other models of severe liver damage such as extended hepatectomy (Lehmann et al, 2012), acetaminophen treatment (Bird et al, 2018), Mdm2-deletion (Lu et al, 2015), b1-integrin loss ( (Raven et al, 2017) or p21-overexpression (Raven et al, 2017), each induce a pronounced p21expression in hepatocytes, which results in decreased regeneration, senescence, and senescence-spreading. It will be interesting to determine if senolytic-treatment can also improve such cases of severe damage.…”

Isolation of senescent cells by iodixanol (OptiPrep) density gradient‐based separation

“…Cellular senescence has fundamental roles in organismal ageing, age‐related diseases, tumourigenesis and tissue regeneration . There are three major types of cellular senescence: (a) replicative senescence, (b) oncogene‐induced senescence and (c) DNA damage‐induced senescence.…”