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

Abstract

Background and AimAlcohol-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.MethodsLiver 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.ResultsIn 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.ConclusionsThe 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.

Hepatocyte expression and prognostic importance of senescence marker p21 in liver histopathology samples from dogs with chronic hepatitis

“…In addition, whereas p21 immunopositivity was correlated with age in control dogs, there was no age correlation in dogs with CH. Similar findings have also been described in humans with liver disease and ascribed to accelerated cellular senescence in dogs with CH 17, 18…”

“…Importantly however, senescent hepatocytes are generally indistinguishable from normal cells on routine histology and their existence is therefore inevitably overlooked 16, 17, 18. Considering the high percentage of hepatocytes displaying immunopositivity in this study, it is possible that these findings reflect a state of widespread hepatocyte senescence in the livers of dogs with CH.…”

“…These findings consequently raise questions regarding the cause and effect relationship between cellular senescence and inflammatory diseases, such as CH. A positive correlation between the degree of hepatic fibrosis and p21 expression has been previously demonstrated in humans with alcohol‐related liver disease,17 however causality was not directly investigated and definitive conclusions in this regard can therefore unfortunately not be drawn.…”

“…Although further investigation of the relationship between p21 immunopositivity and liver function assays (eg, bile acid stimulation) would have been desirable, unfortunately, such results were only available for a minority of dogs due to the retrospective nature of this study. There is an association between p21 expression and serum albumin concentration and prothrombin time in humans17; however, further investigation is required to definitively elucidate the relationship between p21 immunopositivity, hepatocyte senescence, and liver dysfunction in dogs with CH.…”

“…Furthermore, p21 it also thought to play pivotal roles in inhibiting apoptosis, the regulation of transcription, and in DNA repair 12, 14, 15. Although senescent cells have been previously reported to display mild morphological changes, such as increased nuclear size,16 these features are not readily apparent using routine histological stains and their presence is inevitably likely to be overlooked.p21 is greatly upregulated in humans with alcoholic and nonalcoholic liver disease and is better correlated with survival time than histological and clinical scoring systems 17, 18. In addition to its role in determining prognosis in these cases, these findings add insight to the underlying pathophysiology of liver disease and might thereby facilitate the development of novel treatment strategies.…”