Aging-Related Expression of Twinfilin-1 Regulates Cholangiocyte Biological Response to Injury

Central role for cholangiocyte pathobiology in cholestatic liver diseases

Cholangiopathies comprise a spectrum of chronic intrahepatic and extrahepatic biliary tract disorders culminating in progressive cholestatic liver injury, fibrosis, and often cirrhosis and its sequela. Treatment for these diseases is limited, and collectively, they are one of the therapeutic "black boxes" in clinical hepatology. The etiopathogenesis of the cholangiopathies likely includes disease-specific mediators but also common cellular and molecular events driving disease progression (eg, cholestatic fibrogenesis, inflammation, and duct damage). The common pathways involve cholangiocytes, the epithelial cells lining the intrahepatic and extrahepatic bile ducts, which are central to the pathogenesis of these disorders. Current information suggests that cholangiocytes function as a signaling "hub" in biliary tract-associated injury. Herein, we review the pivotal role of cholangiocytes in cholestatic fibrogenesis, focusing on the crosstalk between cholangiocytes and portal fibroblasts and HSCs. The proclivity of these cells to undergo a senescence-associated secretory phenotype, which is proinflammatory and profibrogenic, and the intrinsic intracellular activation pathways resulting in the secretion of cytokines and chemokines are reviewed. The crosstalk between cholangiocytes and cells of the innate (neutrophils and macrophages) and adaptive (T cells and B cells) immune systems is also examined in detail. The information will help consolidate information on this topic and guide further research and potential therapeutic strategies for these diseases.

Biomarkers of aging

Aging biomarkers are a combination of biological parameters to (i) assess age-related changes, (ii) track the physiological aging process, and (iii) predict the transition into a pathological status. Although a broad spectrum of aging biomarkers has been developed, their potential uses and limitations remain poorly characterized. An immediate goal of biomarkers is to help us answer the following three fundamental questions in aging research: How old are we? Why do we get old? And how can we age slower? This review aims to address this need. Here, we summarize our current knowledge of biomarkers developed for cellular, organ, and organismal levels of aging, comprising six pillars: physiological characteristics, medical imaging, histological features, cellular alterations, molecular changes, and secretory factors. To fulfill all these requisites, we propose that aging biomarkers should qualify for being specific, systemic, and clinically relevant.

Abdominal normothermic regional perfusion in controlled donation after circulatory determination of death liver transplantation: Outcomes and risk factors for graft loss

Postmortem normothermic regional perfusion (NRP) is a rising preservation strategy in controlled donation after circulatory determination of death (cDCD). Herein, we present results for cDCD liver transplants performed in Spain 2012-2019, with outcomes evaluated through December 31, 2020. Results were analyzed retrospectively and according to recovery technique (abdominal NRP [A-NRP] or standard rapid recovery [SRR]). During the study period, 545 cDCD liver transplants were performed with A-NRP and 258 with SRR. Median donor age was 59 years (interquartile range 49-67 years). Adjusted risk estimates were improved with A-NRP for overall biliary complications (OR 0.300, 95% CI 0.197-0.459, p < .001), ischemic type biliary lesions (OR 0.112, 95% CI 0.042-0.299, p < .001), graft loss (HR 0.371, 95% CI 0.267-0.516, p < .001), and patient death (HR 0.540, 95% CI 0.373-0.781, p = .001). Cold ischemia time (HR 1.004, 95% CI 1.001-1.007, p = .021) and re-transplantation indication (HR 9.552, 95% CI 3.519-25.930, p < .001) were significant independent predictors for graft loss among cDCD livers with A-NRP. While use of A-NRP helps overcome traditional limitations in cDCD liver transplantation, opportunity for improvement remains for cases with prolonged cold ischemia and/or technically complex recipients, indicating a potential role for complimentary ex situ perfusion preservation techniques.

Cellular senescence in the cholangiopathies

PURPOSE OF REVIEW

Cellular senescence (i.e. permanent withdrawal from the cell cycle) is increasingly recognized as a pathologic feature in a variety of inflammatory liver diseases, including primary sclerosing cholangitis (PSC), primary biliary cholangitis (PBC) and additional cholangiopathies. Herein, we provide an update on the interplay between cholangiocytes, cellular senescence and the cholangiopathies.

RECENT FINDINGS

The themes covered by this review include novel models for studying the role of senescent cholangiocytes and the cholangiopathies, identification and modulation of key pathways or molecules regulating cholangiocyte senescence, and discovery of druggable targets to advance therapeutic options for the cholangiopathies. Most recent studies focused on PSC; however, the concepts and findings may be applied to additional cholangiopathies.

SUMMARY

Cholangiopathies present unique and divergent clinicopathological features, causes and genetic backgrounds, but share several common disease processes. Cholangiocyte senescence in the cholestatic cholangiopathies, primarily PSC and PBC, is regarded as a key pathogenetic process. Importantly, senescent cholangiocytes exhibit phenotypic features including the senescence-associated secretory phenotype (SASP) and resistance to apoptosis that provide new directions for basic research and new prognostic and therapeutic approaches for clinical practice.

Biliary Epithelial Senescence in Liver Disease: There Will Be SASP

Cellular senescence is a pathophysiological phenomenon in which proliferative cells enter cell cycle arrest following DNA damage and other stress signals. Natural, permanent DNA damage can occur after repetitive cell division; however, acute stress or other injuries can push cells into premature senescence and eventually a senescence-associated secretory phenotype (SASP). In recent years, there has been increased evidence for the role of premature senescence in disease progression including diabetes, cardiac diseases, and end-stage liver diseases including cholestasis. Liver size and function change with aging, and presumably with increasing cellular senescence, so it is important to understand the mechanisms by which cellular senescence affects the functional nature of the liver in health and disease. As well, cells in a SASP state secrete a multitude of inflammatory and pro-fibrogenic factors that modulate the microenvironment. Cellular SASP and the associated, secreted factors have been implicated in the progression of liver diseases, such as cholestatic injury that target the biliary epithelial cells (i.e., cholangiocytes) lining the bile ducts. Indeed, cholangiocyte senescence/SASP is proposed to be a driver of disease phenotypes in a variety of liver injuries. Within this review, we will discuss the impact of cholangiocyte senescence and SASP in the pathogenesis of cholestatic disorders.

Ginsenoside Rg1 ameliorates aging‑induced liver fibrosis by inhibiting the NOX4/NLRP3 inflammasome in SAMP8 mice

Aging is often accompanied by liver injury and fibrosis, eventually leading to the decline in liver function. However, the mechanism of aging‑induced liver injury and fibrosis is still not fully understood, to the best of our knowledge, and there are currently no effective treatment options available for liver aging. Ginsenoside Rg1 (Rg1) has been reported to exert potent anti‑aging effects due to its potential antioxidant and anti‑inflammatory activity. The present study aimed to investigate the protective effect and underlying mechanism of action of Rg1 in aging‑induced liver injury and fibrosis in senescence‑accelerated mouse prone 8 (SAMP8) mice treated for 9 weeks. The histopathological results showed that the arrangement of hepatocytes was disordered, vacuole‑like degeneration occurred in the majority of cells, and collagen IV and TGF‑β1 expression levels, that were detected via immunohistochemistry, were also significantly upregulated in the SAMP8 group. Rg1 treatment markedly improved aging‑induced liver injury and fibrosis, and significantly downregulated the expression levels of collagen IV and TGF‑β1. In addition, the dihydroethylene staining and western blotting results showed that Rg1 treatment significantly reduced the levels of reactive oxygen species (ROS) and IL‑1β, and downregulated the expression levels of NADPH oxidase 4 (NOX4), p47phox, p22phox, phosphorylated‑NF‑κB, caspase‑1, apoptosis‑associated speck‑like protein containing a C‑terminal caspase recruitment domain and the NLR family pyrin domain containing 3 (NLRP3) inflammasome, which were significantly upregulated in the liver tissues of elderly SAMP8 mice. In conclusion, the findings of the present study suggested that Rg1 may attenuate aging‑induced liver injury and fibrosis by reducing NOX4‑mediated ROS oxidative stress and inhibiting NLRP3 inflammasome activation.

Impact of Aging on Liver Cells and Liver Disease: Focus on the Biliary and Vascular Compartments

The aging process is represented by the time-dependent decay in physiologic functions of living beings. Major interest has been focused in recent years on the determinants of this progressive condition due to its correlative relationship with the onset of diseases. Several hallmark features have been observed in aging, such as genetic alterations, mitochondrial impairment, and telomere shortening. At the cellular level, a senescent phenotype has been identified in response to aging that is characterized by a flat appearance, proliferative arrest, and production of specific molecules. The net effect of these cells in the course of diseases is an argument of debate. In fact, while the onset of a senescent phenotype may prevent tumor spreading, these cells appear to support pathological processes in some conditions. Several studies are now focused on clarifying the specific molecular pathways of aging/senescence in different cells, tissues, or organs. Biliary and vascular components, within the liver, have emerged as important determinants of some form of liver disease. In this review we summarize the most recent achievements on aging/senescence, focusing on the biliary and vascular liver system. Conclusion: Several findings, in both preclinical animal models and on human liver specimens, converge in supporting the presence of specific aging hallmarks in the diseases involving these hepatic compartments.

The Dynamic Interplay Between Mast Cells, Aging/Cellular Senescence, and Liver Disease

Mast cells are key players in acute immune responses that are evidenced by degranulation leading to a heightened allergic response. Activation of mast cells can trigger a number of different pathways contributing to metabolic conditions and disease progression. Aging results in irreversible physiological changes affecting all organs, including the liver. The liver undergoes senescence, changes in protein expression, and cell signaling phenotypes during aging, which regulate disease progression. Cellular senescence contributes to the age-related changes. Unsurprisingly, mast cells also undergo age-related changes in number, localization, and activation throughout their lifetime, which adversely affects the etiology and progression of many physiological conditions including liver diseases. In this review, we discuss the role of mast cells during aging, including features of aging (e.g., senescence) in the context of biliary diseases such as primary biliary cholangitis and primary sclerosing cholangitis and nonalcoholic fatty liver disease.

Aging and the Biological Response to Liver Injury

Interest in understanding the aging process has recently risen in the scientific community. Aging, commonly defined as the functional decline in the function of organs and tissues, is indeed the major risk factor for the development of many chronic diseases, such as cardiovascular diseases, pathologies of nervous system, or cancer. To date, the influence of aging in the pathophysiology of liver and biliary diseases is not fully understood. Although liver cells have a high regenerative capacity, hepatocytes and cholangiocytes undergo extensive molecular changes in response to aging. Following time-dependent damage induced by aging, liver cells initially activate compensatory mechanisms that, if hyperstimulated, may lead to the decline of regenerative capacity and the development of pathologies. A deeper understanding of molecular aging has undoubtedly the potential to improve the clinical management of patients, possibly unveiling new pathways for selective drug treatment.

Aging-Related Molecular Pathways in Chronic Cholestatic Conditions

Aging is commonly defined as the time-dependent functional decline of organs and tissues. Average life expectancy has increased considerably over the past century and is estimated to increase even further, consequently also the interest in understanding the aging processes. Although aging is not a disease, it is the major risk factor for the development of many chronic diseases. Pathologies, such as Primary Biliary Cholangitis (PBC) and Primary Sclerosing Cholangitis (PSC) are cholestatic liver diseases characterized by chronic inflammation, biliary damage and ultimately liver fibrosis, targeting specifically cholangiocytes. To date, the influence of aging in these biliary diseases is not fully understood. Currently, liver transplantation is the only solution because of lacking in efficiently therapies. Although liver cells have a high regenerative capacity, they undergo extensive molecular changes in response to aging. Following time-dependent damage induced by aging, the cells initially activate protective compensatory processes that, if hyperstimulated, can lead to the decline of regenerative ability and the development of pathologies. Recent studies have introduced novel therapeutic tools for cholangiopathies that have showed to have promising potential as novel therapies for PSC and PBC and for the development of new drugs. The recent advancements in understanding of molecular aging have undoubtedly the potential to unveil new pathways for selective drug treatments, but further studies are needed to deepen their knowledge.