Matthew Hoare

Cellular senescence and its effector programs

Cellular senescence is a stress response that accompanies stable exit from the cell cycle. Classically, senescence, particularly in human cells, involves the p53 and p16/Rb pathways, and often both of these tumor suppressor pathways need to be abrogated to bypass senescence. In parallel, a number of effector mechanisms of senescence have been identified and characterized. These studies suggest that senescence is a collective phenotype of these multiple effectors, and their intensity and combination can be different depending on triggers and cell types, conferring a complex and diverse nature to senescence. Series of studies on senescence-associated secretory phenotype (SASP) in particular have revealed various layers of functionality of senescent cells in vivo. Here we discuss some key features of senescence effectors and attempt to functionally link them when it is possible.

Functional skewing of the global CD8 T cell population in chronic hepatitis B virus infection

The inflamed liver in chronic hepatitis B virus (HBV) infection (CHB) is characterized by a large influx of non–virus-specific CD8 T cells. Little is known about the functional capacity of these lymphocytes, which could provide insights into mechanisms of failure of viral control and liver damage in this setting. We compared the effector function of total circulating and intrahepatic CD8 T cells in CHB patients and healthy donors. We demonstrated that CD8 T cells from CHB patients, regardless of their antigen specificity, were impaired in their ability to produce interleukin-2 and proliferate upon TCR-dependent stimulation. In contrast, these CD8 T cells had preserved production of the proinflammatory cytokines interferon-γ and tumor necrosis factor-α. This aberrant functional profile was partially attributable to down-regulation of the proximal T cell receptor signaling molecule CD3ζ, and could be corrected in vitro by transfection of CD3ζ or replenishment of the amino acid arginine required for its expression. We provide evidence for depletion of arginine in the inflamed hepatic microenvironment as a potential mechanism for these defects in global CD8 T cell signaling and function. These data imply that polarized CD8 T cells within the HBV-infected liver may impede proliferative antiviral effector function, while contributing to the proinflammatory cytokine environment.

Ageing, telomeres, senescence, and liver injury

Populations in developed countries continue to grow older and an understanding of the ageing process to allow healthy ageing carries important medical implications. Older individuals are more susceptible to most acquired liver disorders and more vulnerable to the consequences of liver disease. Accordingly, age is a critical determinant of outcome for hepatitis C virus infection and liver transplantation. In this review we describe changes in the ageing liver and discuss mechanisms of senescence at the cellular level. In particular, we focus on mechanisms by which inflammation, oxidative stress, and oncogenic stress accelerate cellular senescence. In the setting of chronic hepatic injury and inflammation, cellular senescence functions as an essential stress-response mechanism to limit the proliferation of damaged cells and reduce the risk of malignancy, but this benefit is achieved at the expense of senescence-related organ dysfunction. The dual role of cell senescence in chronic liver disease will make this an intriguing but challenging area for future clinical interventions.

The pattern of late mortality in liver transplant recipients in the United Kingdom.

Background. Late survival is not improving after liver transplantation. In this study, possible reasons for this were investigated. Methods. Mortality rates and causes of death were ascertained in 4483 adult primary liver allograft recipients surviving 1 year or more from engraftment, identified through the UK Transplant Database and transplanted between 1994 and 2007. Associations with death, cause of death, and retransplantation were assessed. Results. Mortality in those surviving beyond 1 year in UK liver transplant recipients was more than twice that expected in the general population and had not improved during the study period, independent of cause of liver disease, recipient age, recipient gender, and donor age. The major causes of death were malignancy (30.6%), multisystem failure (10.0%), infection (9.8%), cardiac disease (8.7%), and graft failure (9.8%). Associations with death after 1 year were pretransplant etiologies alcohol-related liver disease (hazard ratio [HR]=2.10), autoimmune hepatitis or cryptogenic (HR=1.68), hepatitis C virus (HR=2.51), and hepatocellular carcinoma (HR=4.19). Associations with retransplantation were recipient age (HR=0.95 per year), donor age (HR=1.02 per year), and hepatitis C virus (HR=2.04). Hepatocellular carcinoma and recipient age were associated with cancer-related death (odds ratio=1.87 and 1.02 per year). Recipient age was associated with cardiac death (odds ratio=1.06 per year). Conclusions. Strategies to reduce late mortality after liver transplantation are required. These may include prevention of disease recurrence, improved recipient selection, and addressing risk factors for death in late survivors of liver transplantation.

Histological changes in HCV antibody–positive, HCV RNA–negative subjects suggest persistent virus infection

It is unclear whether hepatitis C virus (HCV) has been eradicated or persists at a low level in HCV antibody–positive HCV RNA–negative individuals. The natural history and liver histology are not well characterized. One hundred seventy‐two HCV antibody–positive, serum HCV RNA–negative patients underwent diagnostic liver biopsy between 1992 and 2000 and were followed a median 7 years (range, 5–12). Patients with any possible cause of liver injury other than HCV were excluded. A single histopathologist scored sections using Ishak criteria. Characterization of the inflammatory infiltrate in selected cases used a novel semiquantitative technique and compared with HCV RNA–positive patients and healthy controls. One hundred two patients were excluded because of a risk factor for liver injury other than HCV. Seventy patients met the study criteria; four (5.7%) became HCV RNA–positive during follow‐up. Sixty‐six cases remained HCV RNA–negative; five (7.5%) had a normal liver biopsy; 54 (82%) had fibrosis (stage 2 or 3 in 16 (24%)). Nonviremic cases revealed expanded portal tracts (P < 0.05), with fewer CD4+ (P < 0.05) and more CD8+ cells (P < 0.05) than healthy controls, but were indistinguishable from HCV RNA–positive cases for these parameters. Lobular CD4 staining, absent in healthy controls, was noted in both HCV RNA–negative and –positive cases and was more marked in the latter (P < 0.05) with a sinusoidal lining cell distribution. Conclusion: Nonviremic HCV antibody–positive patients have a liver biopsy that is usually abnormal. Fibrosis was present in most with similar inflammatory infiltrate to viremic cases. The presence of a CD8+ rich inflammatory infiltrate suggests an ongoing immune response in the liver, supporting the view that HCV may persist in the liver in the majority of HCV RNA–negative cases. (HEPATOLOGY 2008;48;1737‐1745.)

Hepatocyte Expression of the Senescence Marker p21 Is Linked to Fibrosis and an Adverse Liver-Related Outcome in Alcohol-Related Liver Disease

Background and Aim Alcohol-related liver disease (ALD) remains a leading cause of liver-related morbidity and mortality. Age, fibrosis stage, MELD score and continued alcohol consumption predict outcome in everyday clinical practice. In previous studies increased hepatocyte nuclear area and hepatocyte expression of p21, both markers of senescence, were associated with increased fibrosis stage and a poor outcome in non-alcohol-related fatty liver disease, while increased hepatocyte nuclear area was related to liver dysfunction in ALD cirrhosis. This study, therefore, investigated the pattern of hepatocyte cell cycle phase distribution and hepatocyte p21 expression in relation to outcome in ALD. Methods Liver sections from two cohorts were studied. The first comprised 42 patients across the full spectrum of ALD. The second cohort comprised 77 patients with ALD cirrhosis. Immunohistochemistry assessed hepatocyte expression of cell cycle phase markers and p21. Regenerating liver (n=12) and “normal” liver sections (n=5) served as positive and negative controls, respectively. Results In the first cohort there was little cell cycle progression beyond G1/S phase and increased hepatocyte p21 expression (p<0.0001), which correlated independently with fibrosis stage (p=0.005) and an adverse liver-related outcome (p=0.03). In the second cohort, both hepatocyte p21 expression (p<0.001) and MELD score (p=0.006) were associated independently with an adverse liver-related outcome; this association was stronger with hepatocyte p21 expression (AUROC 0.74; p=0.0002) than with MELD score (AUROC 0.59; p=0.13). Further, hepatocyte p21 expression co-localised with increased hepatic stellate cell activation. Conclusions The findings are consistent with impaired cell cycle progression beyond the G1/S phase in ALD. The striking independent associations between increased hepatocyte p21 expression and both fibrosis stage and an adverse liver-related outcome in both cohorts suggests hepatocyte senescence plays an important role in ALD. Measuring hepatocyte p21 expression is simple and cheap and in this series was a useful measure of long-term prognosis in ALD.

Transmitting senescence to the cell neighbourhood

Senescence, a cell-autonomous tumour suppressor mechanism, also has pro-tumorigenic effects on neighbouring pre-malignant cells through the senescence-associated secretory phenotype (SASP). The SASP is now shown to be regulated by inflammasomes and to induce paracrine senescence in healthy cells, indicating that senescence may also represent a non-cell-autonomous tumour suppressor mechanism linked to innate immunity.

CD4+ T-lymphocyte telomere length is related to fibrosis stage, clinical outcome and treatment response in chronic hepatitis C virus infection

Background & Aims Increasing age is associated with impaired immune function and in chronic HCV infection specifically, with progressive fibrosis, liver failure, HCC and impaired responses to antiviral therapy. T-lymphocyte telomere length declines with age. We hypothesised that shorter T-lymphocyte telomere length would be associated with poor clinical outcome in HCV infection. Methods Circulating T-lymphocyte telomere length, an objective measure of immune senescence, was measured by flow-FISH in 135 HCV-RNA-positive, treatment-naïve patients and 41 healthy controls in relation to clinical outcome. Results Shorter CD4+CD45RO+ T-lymphocyte telomeres were associated with severe fibrosis (p = 0.003), independent of male sex (p = 0.04), CMV positivity (p = 0.003), previous HBV infection (p = 0.007), and age (p = ns) in viraemic patients compared to controls. There were inverse correlations between CD4+CD45RO+ telomere length and fibrosis stage (p <0.001), portal tract inflammatory grade (p = 0.035), prothrombin time (p <0.001) and bilirubin (p = 0.001). One hundred and twenty-four viraemic individuals were followed prospectively to a composite endpoint of death, hepatic decompensation or HCC. Independent of age, those with shorter CD4+CD45RO+ telomeres were less likely to be complication free after 2-years than those with longer telomeres (86% versus 96%, p = 0.009) with an age-adjusted hazard ratio of 0.93 (0.90–0.96). In addition, CD4+CD45RO+ telomere length predicted successful antiviral therapy (p = 0.001) independent of other factors. Conclusions CD4+ T-lymphocyte telomere length, independent of age, was related to inflammatory grade, fibrosis stage, laboratory indices of severity, subsequent hepatic decompensation and treatment outcome in patients with chronic HCV infection.

Autophagy in cancer: having your cake and eating it

Autophagy, one of two major intracellular degradation pathways, plays a critical role in energy homeostasis and the quality control of macromolecules and intracellular organelles. Previous work has demonstrated the importance of autophagy in maintaining cellular fitness, both in healthy and stressful conditions, revealing the complex interplay between autophagy and other stress-responsive phenotypes. The complex outcomes of stress-responsive autophagy confer on it both pro- and anti-tumourigenic roles, depending on the cellular and environmental context. Furthermore, recent findings that functionally link autophagy to the tumour suppressor mechanism, cellular senescence, have revealed a new role of autophagy in cancer biology. In this review we summarise the current evidence on the relationship between autophagy and cancer, with a focus on its role in senescence.

T-regulatory lymphocytes and chronic viral hepatitis

Both hepatitis B virus (HBV) and hepatitis C virus (HCV) can cause persistent viral infection in humans. Chronic infection is associated with a risk of cirrhosis and hepatocellular carcinoma. The cause of chronic infection is unknown. A large body of evidence suggests that a failure of the adaptive immune response is critical in the establishment of chronic infection. Recently a new group of T cells (T-regulatory cells), that express CD4+CD25+ and Foxp3, which can inhibit the cellular (CD4+/CD8+) immune response have been described. In this review the authors explore the thoughts regarding immune responses to HBV and HCV infections and the role of these T-regulatory cells in relation to the pathogenesis of chronic HBV and HCV infection and the potential for therapeutic intervention.