ICF: Neutrophils and cellular senescence: A vicious circle promoting age-related disease.
Lead Research Organisation:
Newcastle University
Department Name: Biosciences Institute
Abstract
Chronic liver disease (CLD) is a global health care problem affecting in excess of 1.5 billion people who are at risk of developing cirrhosis and/or a primary liver cancer. Ageing and obesity are major risk factors for the development and progression of liver disease. Of particular concern is non-alcoholic steatohepatitis (NASH) which is a metabolic liver disease associated with obesity and type II diabetes. NASH incidence increases dramatically with ageing, as does the risk of progression of NASH to cirrhosis, indicating a link between ageing and NASH. Moreover, up to 25% of liver cancers that develop on the background of NASH do so in the absence of cirrhosis. NASH is characterised by fatty deposits (steatosis) in the liver, inflammation, scaring (fibrosis) and the presence of damaged (ballooned) and aged (senescent) hepatocytes (predominant liver cell).
Cellular senescence is a state in which cells lose their ability to proliferate and also secrete a soup of bioactive molecules that promote wound repair and regeneration, termed the senescence-associated secretory phenotype (SASP). In a young person senescent cells are cleared by the immune system. However, ageing is accompanied by immune decline and reduced efficiency of senescent cell clearance, leading to their accumulation and persistence of the SASP. This can lead to a pathological process where the SASP promotes spread of senescence to bystander cells and stimulates chronic inflammation and maladaptive wound repair. These pathologies being typical features of NASH alongside steatosis.
In 2014-2015 we reported in mice that a neutrophil rich persistent low-grade inflammation drives hepatocyte senescence, steatosis, fibrosis, cancer and early death. In 2021 we showed that neutrophils can directly trigger senescence in hepatocytes via oxidative DNA damage. Moreover, we discovered that neutrophils accumulate to a greater extent in the ageing liver and are attracted to senescent hepatocytes. As neutrophils are a classic histopathological characteristic of NASH this is a very significant discovery. In an earlier study, hepatocyte senescence was shown to be necessary and sufficient for steatosis. These observations suggest that neutrophilic inflammation, senescence and steatosis are mechanistically linked. We hypothesise that they combine through positive feedforward signalling pathways to promote age-related NASH, CLD and cancer.
To test our hypothesis, we will first carry out experiments that determine the bidirectional feedforward effects of interactions of senescent hepatocytes and neutrophils on the phenotype and function of these two cell types which we predict to be highly dynamic. These experiments will use a bespoke human liver slice technology and genetic experiments carried out in mouse models of induced obesity, steatosis and NASH. We expect to make discoveries that will illuminate how neutrophils and senescent hepatocytes collude to promote inflammation-driven tissue ageing and CLD. We will also include experiments that ask how acute neutrophilic inflammation associated with infections exacerbates NASH, this being relevant to Covid-19 which is reported to aggravate CLD.
Secondly, we will ask if our discovery that neutrophils are attracted to senescent cells can be exploited to stimulate the immune system to clear senescent hepatocytes. We will engineer neutrophils to express antibodies at their surface that selectively lock onto proteins expressed at the surface of senescent cells, this aimed at enhancing their physical interaction and in doing so encouraging neutrophil-mediated clearance of senescent cells.
By carrying out this 3-year project we will (1) substantially increase knowledge of how inflammation and ageing combine to promote CLD, (2) discover new mechanistic biology of broad interest to biologists and immunologists and (3) learn if neutrophils can be manipulated for immunotherapeutic purposes in ageing- and obesity-related diseases.
Cellular senescence is a state in which cells lose their ability to proliferate and also secrete a soup of bioactive molecules that promote wound repair and regeneration, termed the senescence-associated secretory phenotype (SASP). In a young person senescent cells are cleared by the immune system. However, ageing is accompanied by immune decline and reduced efficiency of senescent cell clearance, leading to their accumulation and persistence of the SASP. This can lead to a pathological process where the SASP promotes spread of senescence to bystander cells and stimulates chronic inflammation and maladaptive wound repair. These pathologies being typical features of NASH alongside steatosis.
In 2014-2015 we reported in mice that a neutrophil rich persistent low-grade inflammation drives hepatocyte senescence, steatosis, fibrosis, cancer and early death. In 2021 we showed that neutrophils can directly trigger senescence in hepatocytes via oxidative DNA damage. Moreover, we discovered that neutrophils accumulate to a greater extent in the ageing liver and are attracted to senescent hepatocytes. As neutrophils are a classic histopathological characteristic of NASH this is a very significant discovery. In an earlier study, hepatocyte senescence was shown to be necessary and sufficient for steatosis. These observations suggest that neutrophilic inflammation, senescence and steatosis are mechanistically linked. We hypothesise that they combine through positive feedforward signalling pathways to promote age-related NASH, CLD and cancer.
To test our hypothesis, we will first carry out experiments that determine the bidirectional feedforward effects of interactions of senescent hepatocytes and neutrophils on the phenotype and function of these two cell types which we predict to be highly dynamic. These experiments will use a bespoke human liver slice technology and genetic experiments carried out in mouse models of induced obesity, steatosis and NASH. We expect to make discoveries that will illuminate how neutrophils and senescent hepatocytes collude to promote inflammation-driven tissue ageing and CLD. We will also include experiments that ask how acute neutrophilic inflammation associated with infections exacerbates NASH, this being relevant to Covid-19 which is reported to aggravate CLD.
Secondly, we will ask if our discovery that neutrophils are attracted to senescent cells can be exploited to stimulate the immune system to clear senescent hepatocytes. We will engineer neutrophils to express antibodies at their surface that selectively lock onto proteins expressed at the surface of senescent cells, this aimed at enhancing their physical interaction and in doing so encouraging neutrophil-mediated clearance of senescent cells.
By carrying out this 3-year project we will (1) substantially increase knowledge of how inflammation and ageing combine to promote CLD, (2) discover new mechanistic biology of broad interest to biologists and immunologists and (3) learn if neutrophils can be manipulated for immunotherapeutic purposes in ageing- and obesity-related diseases.
Technical Summary
Due to the combination of an ageing society and the obesity epidemic there is an urgent need to improve our knowledge of the underlying biology of age- and obesity-related diseases. In the case of non-alcoholic steatohepatitis (NASH) ageing and obesity work in concert to drive chronic liver disease (CLD) and primary liver cancer, the latter now the 3rd most common cause of cancer-related deaths. There are currently no clinically effective approved treatments that can prevent progression of NASH to CLD or that suppress its associated tissue pathologies that include steatosis, inflammation, fibrosis and oncogenesis.
Our work over the past 8 years has revealed that liver inflammation, hepatocellular senescence and steatosis are all mechanistically linked such that each process appears to regulate the other. We hypothesise in this proposal that paracrine signals from physically co-located inflammatory neutrophils and senescent hepatocytes establish feedforward loops that serve to amplify senescence, sustain steatosis and drive inflammatory processes that underpin disease progression.
We will aim to understand how these paracrine signalling processes modulate the heterogeneity and biology of neutrophils and senescent hepatocytes using a combination of translational human precision cut liver technologies, genetic mouse models, transfusions of neutrophils and single cell RNA sequencing. By including experiments in mice fed a Western diet we will discover how crosstalk between neutrophils and senescent hepatocytes impacts on NASH and in doing so unlock novel therapeutic strategies. We will additionally ask if our discovery that neutrophils and senescent hepatocytes co-locate can be exploited by enhancing this interaction with the goal of stimulating immune clearance of senescent hepatocytes which could be a very novel senolytic strategy.
Our work over the past 8 years has revealed that liver inflammation, hepatocellular senescence and steatosis are all mechanistically linked such that each process appears to regulate the other. We hypothesise in this proposal that paracrine signals from physically co-located inflammatory neutrophils and senescent hepatocytes establish feedforward loops that serve to amplify senescence, sustain steatosis and drive inflammatory processes that underpin disease progression.
We will aim to understand how these paracrine signalling processes modulate the heterogeneity and biology of neutrophils and senescent hepatocytes using a combination of translational human precision cut liver technologies, genetic mouse models, transfusions of neutrophils and single cell RNA sequencing. By including experiments in mice fed a Western diet we will discover how crosstalk between neutrophils and senescent hepatocytes impacts on NASH and in doing so unlock novel therapeutic strategies. We will additionally ask if our discovery that neutrophils and senescent hepatocytes co-locate can be exploited by enhancing this interaction with the goal of stimulating immune clearance of senescent hepatocytes which could be a very novel senolytic strategy.
