Telomere length in human liver diseases

Association of TERT (rs2736098 and rs2736100) genetic variants with elevated risk of hepatocellular carcinoma: a retrospective case-control study

Hepatocellular carcinoma (HCC) is an inflammatory problematic issue with higher mortality among different ethnic populations. The telomerase reverse transcriptase (TERT) gene has an imperative role in the proliferation of various cancerous illnesses, particularly HCC. Moreover, the TERT (rs2736098 and rs2739100) variants were correlated with the HCC susceptibility and telomere shortening, but with unconvincing outcomes. The main purpose of this outward work is to assess the correlation between these significant variants within the TERT gene and the elevated risk of HCC with the aid of various computational bioinformatics tools. This study included 233 participants [125 cancer-free controls and 108 HCC patients] from the same locality. In addition, 81.5% of HCC patients were positive for HCV autoantibodies, while 73.1% of HCC patients were positive for cirrhotic liver. Genomic DNA of the TERT (rs2736098 and rs2736100) variants were characterized utilizing the PCR-RFLP method. Interestingly, the frequencies of TERT (rs2736098*A allele) and TERT (rs2736100*T allele) conferred a significant correlation with increased risk of HCC compared to healthy controls (p-value = 0.002, and 0.016, respectively). The TERT (rs2736098*A/A) genotype indicated a definite association with positive smoking and splenomegaly (p-value < 0.05), while the TERT (rs2736100*T/T) genotype observed a significant difference with higher levels of HCV autoantibodies (p-value = 0.009). In conclusion, this significant work confirmed the contribution of the TERT (rs2736098*A and rs2736100*T) alleles with elevated risk of HCC progression and telomere shortening among Egyptian subjects.

Emerging role of aging in the progression of NAFLD to HCC

With the aging of global population, the incidence of nonalcoholic fatty liver disease (NAFLD) has surged in recent decades. NAFLD is a multifactorial disease that follows a progressive course, ranging from simple fatty liver, nonalcoholic steatohepatitis (NASH) to liver cirrhosis and hepatocellular carcinoma (HCC). It is well established that aging induces pathological changes in liver and potentiates the occurrence and progression of NAFLD, HCC and other age-related liver diseases. Studies of senescent cells also indicate a pivotal engagement in the development of NAFLD via diverse mechanisms. Moreover, nicotinamide adenine dinucleotide (NAD⁺), silence information regulator protein family (sirtuins), and mechanistic target of rapamycin (mTOR) are three vital and broadly studied targets involved in aging process and NAFLD. Nevertheless, the crucial role of these aging-associated factors in aging-related NAFLD remains underestimated. Here, we reviewed the current research on the roles of aging, cellular senescence and three aging-related factors in the evolution of NAFLD to HCC, aiming at inspiring promising therapeutic targets for aging-related NAFLD and its progression.

Pathogenesis and Current Treatment Strategies of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the most frequent liver cancer with high lethality and low five-year survival rates leading to a substantial worldwide burden for healthcare systems. HCC initiation and progression are favored by different etiological risk factors including hepatitis B virus (HBV) and hepatitis C virus (HCV) infection, non-/and alcoholic fatty liver disease (N/AFLD), and tobacco smoking. In molecular pathogenesis, endogenous alteration in genetics (TP53, TERT, CTNNB1, etc.), epigenetics (DNA-methylation, miRNA, lncRNA, etc.), and dysregulation of key signaling pathways (Wnt/β-catenin, JAK/STAT, etc.) strongly contribute to the development of HCC. The multitude and complexity of different pathomechanisms also reflect the difficulties in tailored medical therapy of HCC. Treatment options for HCC are strictly dependent on tumor staging and liver function, which are structured by the updated Barcelona Clinic Liver Cancer classification system. Surgical resection, local ablative techniques, and liver transplantation are valid and curative therapeutic options for early tumor stages. For multifocal and metastatic diseases, systemic therapy is recommended. While Sorafenib had been the standalone HCC first-line therapy for decades, recent developments had led to the approval of new treatment options as first-line as well as second-line treatment. Anti-PD-L1 directed combination therapies either with anti-VEGF directed agents or with anti-CTLA-4 active substances have been implemented as the new treatment standard in the first-line setting. However, data from clinical trials indicate different responses on specific therapeutic regimens depending on the underlying pathogenesis of hepatocellular cancer. Therefore, histopathological examinations have been re-emphasized by current international clinical guidelines in addition to the standardized radiological diagnosis using contrast-enhanced cross-sectional imaging. In this review, we emphasize the current knowledge on molecular pathogenesis of hepatocellular carcinoma. On this occasion, the treatment sequences for early and advanced tumor stages according to the recently updated Barcelona Clinic Liver Cancer classification system and the current algorithm of systemic therapy (first-, second-, and third-line treatment) are summarized. Furthermore, we discuss novel precautional and pre-therapeutic approaches including therapeutic vaccination, adoptive cell transfer, locoregional therapy enhancement, and non-coding RNA-based therapy as promising treatment options. These novel treatments may prolong overall survival rates in regard with quality of life and liver function as mainstay of HCC therapy.

Aging of Liver in Its Different Diseases

The proportion of elderly people in the world population is constantly increasing. With age, the risk of numerous chronic diseases and their complications also rises. Research on the subject of cellular senescence date back to the middle of the last century, and today we know that senescent cells have different morphology, metabolism, phenotypes and many other characteristics. Their main feature is the development of senescence-associated secretory phenotype (SASP), whose pro-inflammatory components affect tissues and organs, and increases the possibility of age-related diseases. The liver is the main metabolic organ of our body, and the results of previous research indicate that its regenerative capacity is greater and that it ages more slowly compared to other organs. With age, liver cells change under the influence of various stressors and the risk of developing chronic liver diseases such as non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH), alcoholic steatohepatitis (ASH) and hepatocellular carcinoma (HCC) increases. It has been proven that these diseases progress faster in the elderly population and in some cases lead to end-stage liver disease that requires transplantation. The treatment of elderly people with chronic liver diseases is a challenge and requires an individual approach as well as new research that will reveal other safe and effective therapeutic modalities.

Dietary Supplemental Chromium Yeast Improved the Antioxidant Capacity, Immunity and Liver Health in Broilers under High Stocking Density

This study was conducted to investigate the effects of different levels of yeast chromium on growth performance, organ index, antioxidant capacity, immune performance and liver health of broilers under high stocking density. A total of 684 1-day-old Arbor Acres broilers were selected and fed a common diet from 1 to 22 days of age. At the end of 22 days, broilers with similar weight were randomly divided into six treatments, with six replications in each treatment. The broilers in control groups were fed with a control diet and raised at low stocking density of broilers (14 broilers/m2, LSD) and high stocking density (20 broilers/m2, HSD). The broilers in treatment groups were fed with diets supplemented with 200, 400, 800 and 1600 µg Cr/kg chromium yeast (Cr-yeast) under HSD, respectively. The experimental period was 23~42 days. Compared with the LSD group, the HSD group significantly decreased the liver index (ratio of liver weight to live weight of broilers) of broilers (p < 0.05), the HSD group significantly increased the content of corticosterone (CORT) and the activities of alanine aminotransferase (ALT) and alkaline phosphatase (ALP) and decreased the prealbumin (PA) level in the serum (p < 0.05). HSD decreased the total antioxidant capacity (T-AOC) contents in the serum, liver and breast, serum glutathione peroxidase (GSH-Px) activities, breast total superoxide dismutase (T-SOD) activities and liver catalase (CAT) activities of broilers (p < 0.05). The HSD group significantly increased the total histopathological score (p < 0.05). Compared with the HSD group, adding 200, 400, and 1600 Cr-yeast significantly increased the liver index of broilers (p < 0.05), all HSD + Cr-yeast groups decreased the ALT activities (p < 0.05), and the HSD + 800 group significantly decreased the CORT contents and the ALP activities of the serum (p < 0.05); the HSD + 400, 800 and 1600 groups increased the PA contents of the serum (p < 0.05); HSD + 800 group significantly reduced the tumor necrosis factor-α (TNF-α) and Interleukin-1β (IL-1β) contents of the serum (p < 0.05); moreover, the HSD + 400 group increased the GSH-Px activities of the serum (p < 0.05), the T-AOC and the T-SOD activities of the breast (p < 0.05) and the T-AOC and CAT activities of the liver (p < 0.05). Adding 800 Cr-yeast significantly decreased the total histopathological score (degree of hepatocyte edema and inflammatory cell infiltration) under HSD (p < 0.05). In summary, Cr-yeast can improve the antioxidant capacity and immune traits, and liver health of broilers under HSD. Based on the results of the linear regression analysis, the optimal supplementation of Cr-yeast in antioxidant capacity, immunity ability and liver health were at the range of 425.00−665.00, 319.30−961.00, and 800.00−1531.60 µg Cr/kg, respectively.

Telomere length in patients with alcohol-associated liver disease: a brief report

The intact telomere structure is essential for the prevention of the chromosome end-to-end fusions and maintaining genomic integrity. The maintenance of telomere length is critical for cellular homeostasis. The shortening of telomeres has been reported in patients with chronic liver diseases. The telomere length has not been systemically studied in patients with alcohol-associated liver disease (ALD) at different stages, such as alcoholic hepatitis and alcoholic cirrhosis. In this brief report, we observed evidence of telomere shortening without changes in the telomerase activity in the liver of patients with alcoholic hepatitis and alcoholic cirrhosis when compared with controls. The alterations in the genes associated with telomere binding proteins were only observed in patients with alcoholic cirrhosis. Future studies are required to determine the mechanism of how alcohol affects the length of the telomere and if the shortening impacts the disease progression in ALD.

Liver Histology in Short Telomere Syndrome: A Case Report and Review of the Literature

Short telomere syndrome (STS) encompasses a broad family of genetically inherited conditions caused by various mutations in telomerase and other telomere maintenance genes, resulting in premature telomere shortening. STS involves a variety of clinical manifestations, including dyskeratosis congenita, premature achromotrichia, bone marrow failure, immunodeficiency, pulmonary fibrosis and liver disease. Liver histopathologic features in STS patients have not been well characterized. We report a 46-year-old male patient who presented for dyspnea. The patient had a complicated medical history significant for immune thrombocytopenic purpura and splenectomy, recurrent respiratory tract infections, pneumonia, primary immunodeficiency, and severe hepatopulmonary syndrome. He and his brother both developed gray hair by their late 20s. He had a long history of intermittently elevated liver enzymes starting at age 33. These clinical manifestations prompted an evaluation for a possible telomere biology disorder, which revealed the telomere length was critically short and fell at or below the first percentile for age, supporting the diagnosis. The liver biopsy showed marked portal inflammation with interface hepatitis, ductular reaction and frequent foci of lobular inflammation with focal hepatocyte dropout. Hepatocytes around the portal tracts demonstrated ballooning degeneration and occasional Mallory-Denk bodies. A trichrome stain highlighted bridging fibrosis. A literature review shows liver histology is available in only a small number of STS patients, demonstrating a variety of morphologic features. Our case and others suggest liver disease associated with STS exhibits a spectrum of histopathology. Being aware of these features is important for establishing the correct diagnosis of STS which is under recognized.

Cellular senescence in liver fibrosis: Implications for age-related chronic liver diseases

INTRODUCTION

New insights indicate a causative link between cellular senescence and liver fibrosis. Senescent hepatic stellate cells (HSCs) facilitate fibrosis resolution, while senescence in hepatocytes and cholangiocytes acts as a potent mechanism driving liver fibrogenesis. In many clinical studies, telomeres and mitochondrial DNA contents, which are both aging biomarkers, were reportedly associated with a degree of liver fibrosis in patients with chronic liver diseases (CLDs); this highlights their potential as biomarkers for liver fibrogenesis. A deeper understanding of mechanisms underlying multi-step progression of senescence may yield new therapeutic strategies for age-related chronic liver pathologies.

AREAS COVERED

This review examines the recent findings from preclinical and clinical studies on mechanisms of senescence in liver fibrogenesis and its involvement in liver fibrosis. A comprehensive literature search in electronic databases consisting of PubMed and Scopus from inception to 31 August 2021 was performed.

EXPERT OPINION

Cellular senescence has diagnostic, prognostic, and therapeutic potential in progressive liver complications, especially liver fibrosis. Stimulating or reinforcing the immune response against senescent cells may be a promising and forthright biotherapeutic strategy. This approach will need a deeper understanding of the immune system's ability to eliminate senescent cells and the molecular and cellular mechanisms underlying this process.

Inverse Association of Telomere Length With Liver Disease and Mortality in the US Population

Physiologic aging leads to attrition of telomeres and replicative senescence. An acceleration of this process has been hypothesized in the progression of chronic liver disease. We sought to examine the association of telomere length (TL) with liver disease and its impact on mortality risk. A cohort of 7,072 adults with leukocyte TL measurements from the National Health and Nutrition Examination Survey 1999‐2002 with mortality follow‐up through 2015 was analyzed. Liver disease was defined by aminotransferase levels and classified into etiology‐based and advanced fibrosis categories. Multivariable‐adjusted linear regression models estimated effect sizes, with 95% confidence intervals (CIs), of the presence of liver disease on TL. Cox regression models evaluated associations between TL and all‐cause mortality risk using adjusted hazard ratios (HRs). The cohort was representative of the US population with mean age 46.1 years and mean TL 5.79 kilobase pairs. No overall association between TL and liver disease was found; however, there was a significant negative association of TL and advanced liver fibrosis in individuals aged 65 and above. The liver disease cohort (HR 1.22, 95% CI 0.99‐1.51) and those with metabolic syndrome (HR 1.26, 95% CI 0.96‐1.67) had increased mortality risk with shorter TL. The relationship between TL and all‐cause mortality was stronger in women (HR 1.51, 95% CI 1.02‐2.23) and in non‐Hispanic Whites (HR 1.37, 95% CI 1.02‐1.84). Conclusion: Shortened leukocyte TL is independently associated with advanced liver disease at older ages, and with a higher risk of all‐cause mortality in those with liver disease. These associations reaffirm the need to better understand the role of telomeres in the progression of liver disease.

Telomerase: a key player in the pathogenesis of non-alcoholic fatty liver disease?

Introduction: Telomerase is a basic nuclear protein reverse transcriptase, which plays a key role in maintaining telomere stability, genome integrity, long-term cell activity, and potential continued proliferation.Area covered: This narrative review discusses key research advances involving telomerase in the development and progression of nonalcoholic fatty liver disease (NAFLD). The review evaluates 9a) whether the assessment of telomerase can be used as a noninvasive diagnostic tool; and (b) whether modification of telomerase function might be a useful potential therapeutic target for treatment of NAFLD. Furthermore, the relationship between telomerase and other chronic metabolic diseases is evaluated.Expert opinion: Several experimental and preclinical studies have suggested that telomerase plays an important role in the development of NAFLD. However, further mechanistic studies are needed to prove a causal relationship and to better elucidate whether the measurement of telomerase has utility as a diagnostic tool or whether pharmacological manipulation of telomerase has therapeutic potential in NAFLD treatment.

Short Telomeres: Cause and Consequence in Liver Disease

Short telomere syndrome is a genetically inherited syndrome resulting in premature telomere shortening. This premature shortening of telomeres can result in hematologic, pulmonary, vascular, gastrointestinal, and hepatic manifestations of disease. Identifying patients with short telomere syndrome can be a clinical challenge due to the multitude of potential manifestations and lack of widely available diagnostic tests. In this review, we will highlight hepatic manifestations of short telomere syndrome with a focus on diagnosis, testing, and potential treatments.

Telomeres and Telomerase in the Development of Liver Cancer

Liver cancer is one of the most common cancer types worldwide and the fourth leading cause of cancer-related death. Liver carcinoma is distinguished by a high heterogeneity in pathogenesis, histopathology and biological behavior. Dysregulated signaling pathways and various gene mutations are frequent in hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (iCCA), which represent the two most common types of liver tumors. Both tumor types are characterized by telomere shortening and reactivation of telomerase during carcinogenesis. Continuous cell proliferation, e.g., by oncogenic mutations, can cause extensive telomere shortening in the absence of sufficient telomerase activity, leading to dysfunctional telomeres and genome instability by breakage-fusion-bridge cycles, which induce senescence or apoptosis as a tumor suppressor mechanism. Telomerase reactivation is required to stabilize telomere functionality and for tumor cell survival, representing a genetic risk factor for the development of liver cirrhosis and liver carcinoma. Therefore, telomeres and telomerase could be useful targets in hepatocarcinogenesis. Here, we review similarities and differences between HCC and iCCA in telomere biology.

Human Telomerase Reverse Transcriptase Gene Promoter Mutation in Serum of Patients with Hepatocellular Carcinoma

BACKGROUND

Mutations in the human telomerase reverse transcriptase (hTERT) gene promoter have been reported in hepatocellular carcinoma (HCC); however, analyses of these mutations in liquid biopsies have been technically difficult because of the high GC content of the regions of interest within this promoter. We evaluated the feasibility and prognostic value of hTERT promoter mutations identified in circulating cell-free DNA (cfDNA) from the serum of patients with HCC.

OBJECTIVE

A cohort of HCC patients (n = 36) who were curatively treated by surgical resection between June 2003 and September 2014 were enrolled in this study.

METHODS

The presence of hTERT promoter mutations in cfDNA from the patients' serum was analyzed via modified droplet digital polymerase chain reaction, and associations were sought between specific promoter mutations and patients' disease-free survival (DFS).

RESULTS

The G>A hTERT mutation at -124 bp was detected in the serum of 25 patients (69%). Although no marked differences were observed between the characteristics of the serum mutation-positive and serum mutation-negative patient groups, the DFS of patients with the mutation was significantly shorter than that of the serum mutation-negative patients (p = 0.02). Among 18 clinicopathologic and background liver factors examined, the presence of the -124 bp G>A mutation was an independent and significant predictor of patients' DFS (hazard ratio = 3.01, 95% confidence interval 1.11-10.5, p = 0.03) in multivariate analyses.

CONCLUSIONS

The -124 bp G>A hTERT promoter mutation was observed in the serum of 69% of HCC patients who underwent surgical resection and was an independent predictor of disease progression in HCC.

Shortened Leukocyte Telomere Length Associates with an Increased Prevalence of Chronic Health Conditions among Survivors of Childhood Cancer: A Report from the St. Jude Lifetime Cohort

PURPOSE

We aimed to analyze and compare leukocyte telomere length (LTL) and age-dependent LTL attrition between childhood cancer survivors and noncancer controls, and to evaluate the associations of LTL with treatment exposures, chronic health conditions (CHC), and health behaviors among survivors.

EXPERIMENTAL DESIGN

We included 2,427 survivors and 293 noncancer controls of European ancestry, drawn from the participants in St. Jude Lifetime Cohort Study (SJLIFE), a retrospective hospital-based study with prospective follow-up (2007-2016). Common nonneoplastic CHCs (59 types) and subsequent malignant neoplasms (5 types) were clinically assessed. LTL was measured with whole-genome sequencing data.

RESULTS

After adjusting for age at DNA sampling, gender, genetic risk score based on 9 SNPs known to be associated with telomere length, and eigenvectors, LTL among survivors was significantly shorter both overall [adjusted mean (AM) = 6.20 kb; SE = 0.03 kb] and across diagnoses than controls (AM = 6.69 kb; SE = 0.07 kb). Among survivors, specific treatment exposures associated with shorter LTL included chest or abdominal irradiation, glucocorticoid, and vincristine chemotherapies. Significant negative associations of LTL with 14 different CHCs, and a positive association with subsequent thyroid cancer occurring out of irradiation field were identified. Health behaviors were significantly associated with LTL among survivors aged 18 to 35 years (P _trend = 0.03).

CONCLUSIONS

LTL is significantly shorter among childhood cancer survivors than noncancer controls, and is associated with CHCs and health behaviors, suggesting LTL as an aging biomarker may be a potential mechanistic target for future intervention studies designed to prevent or delay onset of CHCs in childhood cancer survivors.See related commentary by Walsh, p. 2281.

The role of telomeres and telomerase in cirrhosis and liver cancer

Telomerase is a key enzyme for cell survival that prevents telomere shortening and the subsequent cellular senescence that is observed after many rounds of cell division. In contrast, inactivation of telomerase is observed in most cells of the adult liver. Absence of telomerase activity and shortening of telomeres has been implicated in hepatocyte senescence and the development of cirrhosis, a chronic liver disease that can lead to hepatocellular carcinoma (HCC) development. During hepatocarcinogenesis, telomerase reactivation is required to enable the uncontrolled cell proliferation that leads to malignant transformation and HCC development. Part of the telomerase complex, telomerase reverse transcriptase, is encoded by TERT, and several mechanisms of telomerase reactivation have been described in HCC that include somatic TERT promoter mutations, TERT amplification, TERT translocation and viral insertion into the TERT gene. An understanding of the role of telomeres and telomerase in HCC development is important to develop future targeted therapies and improve survival of this disease. In this Review, the roles of telomeres and telomerase in liver carcinogenesis are discussed, in addition to their potential translation to clinical practice as biomarkers and therapeutic targets.

Diagnostic Performance of microRNA-122 and microRNA-224 in Hepatitis C Virus-Induced Hepatocellular Carcinoma (HCC)

Background and objectives: Hepatocellular carcinoma (HCC) is a potential health problem in Egypt because of the high prevalence of HCV infection. Using alpha-fetoprotein for diagnosis is unsatisfactory especially in early stages. Many studies showed that microRNAs (miRNA) expression may be associated with the development and progression of various types of cancer including HCC and it may serve as biomarkers for diagnosis. This study examined two miRNAs which are miRNA-122 and miRNA-224 if it could serve as biomarkers for diagnosis of HCC. Methods: This study included 20 patients with HCV-induced HCC and 20 patients with HCV-induced liver cirrhosis for comparison. As well as 20 healthy volunteers as controls. All participants were subjected to history taking, clinical examination, and determination of serum alpha-fetoprotein. Quantification of plasma miRNA-122 and miRNA-224 was done by real-time quantitative PCR. Results: Our results showed that levels of miRNA-122 were significantly lower in HCC group compared to the cirrhosis group and controls, while levels of miRNA-224 were significantly higher. The levels of both miRNAs have a correlation with tumor size. Moreover, the diagnostic accuracy of miRNA-122 (sensitivity 95%, specificity 81%, p-value <0.001) and of miRNA-224 (sensitivity 85%, specificity 79%, p-value <0.001) in discriminating patients with HCC from patients with liver cirrhosis were higher than that of alpha-fetoprotein (sensitivity 70%, specificity 70%, p-value <0.05). In addition, combining any one of these miRNAs with alpha-fetoprotein will increase the diagnostic accuracy compared to using each marker alone. Conclusion: miRNA-122 and miRNA-224 could serve as biomarkers for the diagnosis of HCC.

The Spectrum of Hepatic Involvement in Patients With Telomere Disease

Loss-of-function mutations in genes that encode for components of the telomere repair complex cause accelerated telomere shortening. Hepatic involvement has been recognized as a cause of morbidity in telomere diseases, but very few studies have characterized the nature and extent of liver involvement in affected patients. We report the prevalence and characteristics of liver involvement in a large cohort of patients with telomere disease evaluated serially at the National Institutes of Health. One hundred twenty-one patients with known or suspected telomere disease were screened; 40 patients with liver involvement were included in the current study. Median follow-up was 2.4 years. Data were collected regarding their demographic information, laboratory analysis, imaging, and histopathology. Forty patients (40% of the cohort) with a median age of 42 years were found to have liver involvement. Liver enzyme elevation was cholestatic in pattern; 8 (21%) had drug-related enzyme elevations. The most common imaging finding was increased hepatic echogenicity on ultrasound in 39% (9) of patients, followed by hepatomegaly in 26% (6). Biopsies were infrequent because of risk associated with thrombocytopenia, but in 6 patients, there were varying findings: nodular regenerative hyperplasia, steatohepatitis, hemosiderosis, cholestasis, and cirrhosis with hepatic steatosis. Almost half the cohort had pulmonary diffusion abnormalities, and 25% died during the follow-up period. Conclusion: In patients with telomere disease, hepatic involvement is common and can present in diverse ways, including elevated liver enzymes as well as histopathologic and imaging abnormalities. Liver disease has important implications for morbidity and mortality in patients with telomere disease.

Telomere Gene Therapy: Polarizing Therapeutic Goals for Treatment of Various Diseases

Modulation of telomerase maintenance by gene therapy must meet two polarizing requirements to achieve different therapeutic outcomes: Anti-aging/regenerative applications require upregulation, while anticancer applications necessitate suppression of various genes integral to telomere maintenance (e.g., telomerase, telomerase RNA components, and shelterin complex). Patients suffering from aging-associated illnesses often exhibit telomere attrition, which promotes chromosomal instability and cellular senescence, thus requiring the transfer of telomere maintenance-related genes to improve patient outcomes. However, reactivation and overexpression of telomerase are observed in 85% of cancer patients; this process is integral to cancer immortality. Thus, telomere-associated genes in the scope of cancer gene therapy must be inactivated or inhibited to induce anticancer effects. These contradicting requirements for achieving different therapeutic outcomes mean that any vector-mediated upregulation of telomere-associated genes must be accompanied by rigorous evaluation of potential oncogenesis. Thus, this review aims to discuss how telomere-associated genes are being targeted or utilized in various gene therapy applications and provides some insight into currently available safety hazard assessments.

Modulation of YrdC promotes hepatocellular carcinoma progression via MEK/ERK signaling pathway

Accumulating evidence suggested that YrdC involved in growth, telomere homeostasis, translation and the N6-threonylcarbamoylation (t6A) of tRNA was abnormally expressed in the progression of tumor. However, the role of YrdC in hepatocellular carcinoma remained elusive. Our study aimed to investigate the clinical significance and oncogenic phenotypes of YrdC in hepatocellular carcinoma, and to determine its related mechanism of this disease. With the usage of GEO datasets, we analyzed the expression of YrdC in hepatocellular carcinoma (HCC). Kaplan-Meier survival analysis was used to evaluate the prognostic significance of hepatocellular carcinoma patients in TCGA. Gain- and loss-of-function analyses in vitro of YrdC were also performed to evaluate its effects on oncogenic phenotypes and relevant signaling pathways. YrdC expression was not only dysregulated in hepatocellular carcinoma tissue but also related to the prognosis of patients with hepatocellular carcinoma. In addition, YrdC depletion suppressed the capability of proliferation, migration and invasion of huh7 cells, while there was opposite result for YrdC overexpression. Our data also unraveled that YrdC promoted the progression of HCC by activating MEK/ERK signaling pathways. Together, our findings indicated that YrdC was a potential prognosis marker for hepatocellular carcinoma, and therapeutic strategies targeting YrdC might hold promise in improving the treatment of hepatocellular carcinoma.

Telomerase reverse transcriptase germline mutations and hepatocellular carcinoma in patients with nonalcoholic fatty liver disease

In an increasing proportion of cases, hepatocellular carcinoma (HCC) develops in patients with nonalcoholic fatty liver disease (NAFLD). Mutations in telomerase reverse transcriptase (hTERT) are associated with familial liver diseases. The aim of this study was to examine telomere length and germline hTERT mutations as associated with NAFLD-HCC. In 40 patients with NAFLD-HCC, 45 with NAFLD-cirrhosis and 64 healthy controls, peripheral blood telomere length was evaluated by qRT-PCR and hTERT coding regions and intron-exon boundaries sequenced. We further analyzed 78 patients affected by primary liver cancer (NAFLD-PLC, 76 with HCC). Enrichment of rare coding mutations (allelic frequency <0.001) was evaluated by Burden test. Functional consequences were estimated in silico and by over-expressing protein variants in HEK-293 cells. We found that telomere length was reduced in individuals with NAFLD-HCC versus those with cirrhosis (P = 0.048) and healthy controls (P = 0.0006), independently of age and sex. We detected an enrichment of hTERT mutations in NAFLD-HCC, that was confirmed when we further considered a larger cohort of NAFLD-PLC, and was more marked in female patients (P = 0.03). No mutations were found in cirrhosis and local controls, and only one in 503 healthy Europeans from the 1000 Genomes Project (allelic frequency = 0.025 vs. <0.001; P = 0.0005). Mutations with predicted functional impact, including the frameshift Glu113Argfs*79 and missense Glu668Asp, cosegregated with liver disease in two families. Three patients carried missense mutations (Ala67Val in homozygosity, Pro193Leu and His296Pro in heterozygosity) in the N-terminal template-binding domain (P = 0.037 for specific enrichment). Besides Glu668Asp, the Ala67Val variant resulted in reduced intracellular protein levels. In conclusion, we detected an association between shorter telomeres in peripheral blood and rare germline hTERT mutations and NAFLD-HCC.

Telomere Length and Survival of Patients with Hepatocellular Carcinoma in the United States

BACKGROUND

Telomere shortening is an important molecular event in hepatocellular carcinoma (HCC) initiation; however, its role in HCC progression and prognosis is less clear. Our study aimed to examine the association of telomere length with survival of patients with HCC.

METHODS

We measured telomere length in tumor and adjacent non-tumor tissues from 126 persons with HCC in the United States (U.S.) who were followed for mortality outcomes. Relative telomere length (RTL) was measured by a monochrome multiplex quantitative polymerase chain reaction assay. Multivariable Cox proportional hazards modeling was used to calculate hazard ratios (HRs) and 95% CIs for the association between telomere length and all-cause mortality. We also examined associations between telomere length and patient characteristics using multiple linear regression.

RESULTS

During a mean follow-up of 6.0 years, 79 deaths occurred among 114 individuals for whom survival data were available. The ratio of RTL in tumor relative to non-tumor tissue was greater for individuals with regional or distant stage tumors (0.97) than localized stage tumors (0.77), and for individuals with grade III or IV tumors (0.95) than grade II (0.88) or grade I (0.67) tumors. An RTL ratio ≥1 was not associated with survival (HR 0.92, 95% CI 0.55, 1.55) compared to a ratio <1, after adjusting for age at diagnosis, sex, tumor stage and tumor size. Similarly, RTL in the tumor and non-tumor tissue, respectively, were not associated with survival.

CONCLUSIONS

This U.S. based study found that telomeres may be longer in more aggressive HCCs. There was no evidence, however, that telomere length was associated with survival of patients with HCC. Future investigations are warranted to clarify the role of telomere length in HCC prognosis.

Multi-OMICs and Genome Editing Perspectives on Liver Cancer Signaling Networks

The advent of the human genome sequence and the resulting ~20,000 genes provide a crucial framework for a transition from traditional biology to an integrative “OMICs” arena (Lander et al., 2001; Venter et al., 2001; Kitano, 2002). This brings in a revolution for cancer research, which now enters a big data era. In the past decade, with the facilitation by next-generation sequencing, there have been a huge number of large-scale sequencing efforts, such as The Cancer Genome Atlas (TCGA), the HapMap, and the 1000 genomes project. As a result, a deluge of genomic information becomes available from patients stricken by a variety of cancer types. The list of cancer-associated genes is ever expanding. New discoveries are made on how frequent and highly penetrant mutations, such as those in the telomerase reverse transcriptase (TERT) and TP53, function in cancer initiation, progression, and metastasis. Most genes with relatively frequent but weakly penetrant cancer mutations still remain to be characterized. In addition, genes that harbor rare but highly penetrant cancer-associated mutations continue to emerge. Here, we review recent advances related to cancer genomics, proteomics, and systems biology and suggest new perspectives in targeted therapy and precision medicine.

Telomeres, NAFLD and Chronic Liver Disease

Telomeres consist of repeat DNA sequences located at the terminal portion of chromosomes that shorten during mitosis, protecting the tips of chromosomes. During chronic degenerative conditions associated with high cell replication rate, progressive telomere attrition is accentuated, favoring senescence and genomic instability. Several lines of evidence suggest that this process is involved in liver disease progression: (a) telomere shortening and alterations in the expression of proteins protecting the telomere are associated with cirrhosis and hepatocellular carcinoma; (b) advanced liver damage is a feature of a spectrum of genetic diseases impairing telomere function, and inactivating germline mutations in the telomerase complex (including human Telomerase Reverse Transcriptase (hTERT) and human Telomerase RNA Component (hTERC)) are enriched in cirrhotic patients independently of the etiology; and (c) experimental models suggest that telomerase protects from liver fibrosis progression. Conversely, reactivation of telomerase occurs during hepatocarcinogenesis, allowing the immortalization of the neoplastic clone. The role of telomere attrition may be particularly relevant in the progression of nonalcoholic fatty liver, an emerging cause of advanced liver disease. Modulation of telomerase or shelterins may be exploited to prevent liver disease progression, and to define specific treatments for different stages of liver disease.

Dysregulated miRNA in progression of hepatocellular carcinoma: A systematic review

Hepatocellular carcinoma (HCC) is the fifth most frequent cancer and the third cause of cancer-related mortality worldwide. The primary risk factor for HCC is liver cirrhosis secondary to persistent infection with hepatitis B virus or hepatitis C virus. Although a number of cellular phenomena and molecular events have been reported to facilitate tumor initiation, progression and metastasis, the exact etiology of HCC has not yet been fully uncovered. miRNA, a class of non-coding RNA, negatively regulate post-transcriptional processes that participate in crucial biological processes, including development, differentiation, apoptosis and proliferation. In the liver, specific miRNA can be negative regulators of gene expression. Recent studies have uncovered the contribution of miRNA to cancer pathogenesis as they can function as oncogenes or tumor suppressor genes. In addition, other studies have demonstrated their potential value in the clinical management of patients with HCC as some miRNA may be used as prognostic or diagnostic markers. In this review, we summarize the current knowledge about the roles of miRNA in the carcinogenesis and progression of HCC.

Telomere Length in Peripheral Blood Leukocytes Is Associated with Severity of Biliary Atresia

Objective

The purpose of this study was to investigate the association of telomere length in peripheral blood leukocytes with the severity of biliary atresia (BA).

Methods

One hundred and fourteen BA patients and 114 age-matched healthy controls were enrolled. Relative telomere length (RTL) was assessed using a quantitative real-time polymerase chain reaction. Multivariate regression analysis was used to estimate RTL as an independent risk factor of BA. Receiver operating characteristic curve analysis was used to calculate the accuracy of biomarkers in the prediction of liver cirrhosis.

Results

BA patients had significantly shorter telomeres than healthy controls (p < 0.0001). The RTL in BA patients with jaundice was considerably lower than that of patients without jaundice (p = 0.005). Moreover, RTL was markedly shorter in patients with cirrhosis (F4), as compared to patients with mild fibrosis (F2) and non-fibrosis (F0-F1, p < 0.0001). Logistic regression analysis indicated that short RTL was associated with a higher risk of liver cirrhosis in BA. Tertile analysis showed a dose-response effect for this association (p trend < 0.0001). Additionally, RTL in BA children revealed a negative correlation with age (r = -0.50, p < 0.001). We noted an association between reduction of RTL and liver stiffness scores, adjusted for age and gender (b = -0.01, p < 0.0001). Short RTL can be employed to distinguish cirrhosis patients from non-cirrhosis patients (AUC = 0.78). Further analysis showed a linear correlation between leukocyte RTL and liver RTL in BA patients (r = 0.83, p < 0.001).

Conclusion

The findings of this study provide evidence that telomere shortening is associated with an elevated risk of liver cirrhosis in BA.

Telomere shortening as genetic risk factor of liver cirrhosis

Cirrhosis is the main complication of chronic liver disease, leads to progressive liver function impairment and is the main risk factor for the development of liver cancer. Liver failure at endstage cirrhosis is associated with increased mortality with liver transplantation as the only possible treatment at this stage. The pathogenesis of liver cirrhosis is not completely elucidated. Although the common factors leading to liver injury, such as viral hepatitis, alcohol consume or fatty liver disease can be identified in the majority of patients a small percentage of patients have no apparent risk factors. Moreover given the same risk factors, some patients progress to cirrhosis whereas others have a benign course, the reason remains unclear. In order to develop new diagnostic and therapeutic tools, it is s essential to understand the pathogenesis of cirrhosis. The identification of genetic risk factors associated with cirrhosis is one of the possible approach to achieve these goal. In the past years several studies have supported the role of telomere shortening and cirrhosis. In the recent year several studies on the relation between several single nucleotide polymorphism (SNPs) and cirrhosis have been published; it has been proposed also a cirrhosis risk score based on seven SNPs. Also epidemiological studies on identical twins and in different ethnic groups have been supporting the importance of the role of genetic risk factors. Finally in the very recent years it has been suggested that telomere shortening may represent a genetic risk factor for the development of cirrhosis.

Genome-wide transcriptional reorganization associated with senescence-to-immortality switch during human hepatocellular carcinogenesis

Senescence is a permanent proliferation arrest in response to cell stress such as DNA damage. It contributes strongly to tissue aging and serves as a major barrier against tumor development. Most tumor cells are believed to bypass the senescence barrier (become “immortal”) by inactivating growth control genes such as TP53 and CDKN2A. They also reactivate telomerase reverse transcriptase. Senescence-to-immortality transition is accompanied by major phenotypic and biochemical changes mediated by genome-wide transcriptional modifications. This appears to happen during hepatocellular carcinoma (HCC) development in patients with liver cirrhosis, however, the accompanying transcriptional changes are virtually unknown. We investigated genome-wide transcriptional changes related to the senescence-to-immortality switch during hepatocellular carcinogenesis. Initially, we performed transcriptome analysis of senescent and immortal clones of Huh7 HCC cell line, and identified genes with significant differential expression to establish a senescence-related gene list. Through the analysis of senescence-related gene expression in different liver tissues we showed that cirrhosis and HCC display expression patterns compatible with senescent and immortal phenotypes, respectively; dysplasia being a transitional state. Gene set enrichment analysis revealed that cirrhosis/senescence-associated genes were preferentially expressed in non-tumor tissues, less malignant tumors, and differentiated or senescent cells. In contrast, HCC/immortality genes were up-regulated in tumor tissues, or more malignant tumors and progenitor cells. In HCC tumors and immortal cells genes involved in DNA repair, cell cycle, telomere extension and branched chain amino acid metabolism were up-regulated, whereas genes involved in cell signaling, as well as in drug, lipid, retinoid and glycolytic metabolism were down-regulated. Based on these distinctive gene expression features we developed a 15-gene hepatocellular immortality signature test that discriminated HCC from cirrhosis with high accuracy. Our findings demonstrate that senescence bypass plays a central role in hepatocellular carcinogenesis engendering systematic changes in the transcription of genes regulating DNA repair, proliferation, differentiation and metabolism.

Mast cells and the liver aging process

It has now ascertained that the clinical manifestations of liver disease in the elderly population reflect both the cumulative effects of longevity on the liver and the generalized senescence of the organism ability to adjust to metabolic, infectious, and immunologic insults. Although liver tests are not significantly affected by age, the presentation of liver diseases such as viral hepatitis may be subtler in the elderly population than that of younger patients.

Human immunosenescence is a situation in which the immune system, particularly T lymphocyte function, deteriorates with age, while innate immunity is negligibly affected and in some cases almost up-regulated.

We here briefly review the relationships between the liver aging process and mast cells, the key effectors in a more complex range of innate immune responses than originally though.

Relative telomere length: a novel non-invasive biomarker for the risk of non-cirrhotic hepatocellular carcinoma in patients with chronic hepatitis B infection

BACKGROUND AND AIMS

Telomere length has emerged as a promising risk predictor of various cancers including hepatocellular carcinoma (HCC). However, the majority of studies in this area measured telomere length in hepatocytes and one in lymphocytes with conflicting results. Moreover, no studies have been reported on using circulating DNA telomere length as a non-invasive HCC biomarker.

METHODS

We conducted a nested case-control study to determine the relative telomere length (RTL) in serum DNA from 140 hepatitis B virus (HBV)-related HCC cases and 280 frequency-matched cancer-free HBV controls.

RESULTS

Cases had a significantly longer RTL (median, 0.31; range, 0.02-2.31) than controls (median, 0.20; range, 0.01-1.60) (P = 0.003). Consistently, longer RTLs conferred a significantly increased HCC risk compared to short RTLs in a univariate logistic regression analysis (odds ratio [OR] = 1.55, 95% confidence interval [CI] = 1.02-2.33, P = 0.038). This association attenuated after multivariate adjustment (OR = 1.40, 95% CI = 0.90-2.19, P = 0.132). In a quartile analysis, a significant dose-response relationship was noted in univariate analysis (P(trend) = 0.017) which was again attenuated in multivariate analysis (P(trend) = 0.079). Further analyses revealed that the significant association between serum RTL and HCC risk was evident in non-cirrhotic (OR = 3.54, 95% CI 1.58-7.93 P = 0.002), but not cirrhotic (OR = 0.95, 95% CI 0.55-1.64, P = 0.860) HBV patients. Moreover, the significantly increased HCC risk conferred by cirrhosis was modulated by RTL with a significant interaction effect (P(interaction) = 0.013).

CONCLUSIONS

RTL in circulating cell-free serum DNA could potentially be used as a novel non-invasive biomarker for non-cirrhotic HCC. Prospective cohort studies are warranted to validate this finding and assess its clinical significance in HCC prevention.

Molecular classification of hepatocellular carcinoma anno 2011

Hepatocellular carcinoma has an increasing incidence and high mortality. Treatment options are limited if the disease is not diagnosed in its early stage. The natural course of the disease is aggressive but not always predictable. Molecular profiling is a promising tool for classification in order to optimize prognosis prediction and treatment for an individual patient. In the last decade a large amount of studies has been conducted to better classify hepatocellular carcinomas. The focus of this review is on implications of molecular classification for prognosis and therapeutic decision making in HCC patients. Most studies used microarray technique for genome wide profiling, but other methods to detect genomic changes and microRNA are gaining interest. The whole genome profiling studies identified differences in affected signalling and tried to relate this to prognosis. Some common subgroups were identified, such as the proliferation cluster and the beta-catenin cluster. However, there is still little overlap between most studies. Better study design and bio-informatical analysis might help in this context.

Regulation of senescence in cancer and aging

Senescence is regarded as a physiological response of cells to stress, including telomere dysfunction, aberrant oncogenic activation, DNA damage, and oxidative stress. This stress response has an antagonistically pleiotropic effect to organisms: beneficial as a tumor suppressor, but detrimental by contributing to aging. The emergence of senescence as an effective tumor suppression mechanism is highlighted by recent demonstration that senescence prevents proliferation of cells at risk of neoplastic transformation. Consequently, induction of senescence is recognized as a potential treatment of cancer. Substantial evidence also suggests that senescence plays an important role in aging, particularly in aging of stem cells. In this paper, we will discuss the molecular regulation of senescence its role in cancer and aging. The potential utility of senescence in cancer therapeutics will also be discussed.

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.

Telomeres and telomerase in cancer

Myriad genetic and epigenetic alterations are required to drive normal cells toward malignant transformation. These somatic events commandeer many signaling pathways that cooperate to endow aspiring cancer cells with a full range of biological capabilities needed to grow, disseminate and ultimately kill its host. Cancer genomes are highly rearranged and are characterized by complex translocations and regional copy number alterations that target loci harboring cancer-relevant genes. Efforts to uncover the underlying mechanisms driving genome instability in cancer have revealed a prominent role for telomeres. Telomeres are nucleoprotein structures that protect the ends of eukaryotic chromosomes and are particularly vulnerable due to progressive shortening during each round of DNA replication and, thus, a lifetime of tissue renewal places the organism at risk for increasing chromosomal instability. Indeed, telomere erosion has been documented in aging tissues and hyperproliferative disease states-conditions strongly associated with increased cancer risk. Telomere dysfunction can produce the opposing pathophysiological states of degenerative aging or cancer with the specific outcome dictated by the integrity of DNA damage checkpoint responses. In most advanced cancers, telomerase is reactivated and serves to maintain telomere length and emerging data have also documented the capacity of telomerase to directly regulate cancer-promoting pathways. This review covers the role of telomeres and telomerase in the biology of normal tissue stem/progenitor cells and in the development of cancer.

Hepatocarcinoma in viral and metabolic liver disease

It is becoming increasingly evident that children, like adults, with chronic viral or metabolic liver diseases are at risk for the development of hepatocarcinoma. The aims of this article are to review the risk factors for hepatocarcinoma in chronic viral or metabolic liver disease, outline potential pathogenic mechanisms of hepatocarcinoma, and describe surveillance strategies, clinical evaluation, and management of hepatocarcinoma in children.

How stem cells age and why this makes us grow old

Recent data suggest that we age, in part, because our self-renewing stem cells grow old as a result of heritable intrinsic events, such as DNA damage, as well as extrinsic forces, such as changes in their supporting niches. Mechanisms that suppress the development of cancer, such as senescence and apoptosis, which rely on telomere shortening and the activities of p53 and p16(INK4a), may also induce an unwanted consequence: a decline in the replicative function of certain stem-cell types with advancing age. This decreased regenerative capacity appears to contribute to some aspects of mammalian ageing, with new findings pointing to a 'stem-cell hypothesis' for human age-associated conditions such as frailty, atherosclerosis and type 2 diabetes.

Hepatocellular carcinoma pathogenesis: from genes to environment

Hepatocellular carcinoma is among the most lethal and prevalent cancers in the human population. Despite its significance, there is only an elemental understanding of the molecular, cellular and environmental mechanisms that drive disease pathogenesis, and there are only limited therapeutic options, many with negligible clinical benefit. This Review summarizes the current state of knowledge of this, the most common and dreaded liver neoplasm, and highlights the principal challenges and scientific opportunities that are relevant to controlling this accelerating global health crisis.

Cooperative interactions of p53 mutation, telomere dysfunction, and chronic liver damage in hepatocellular carcinoma progression

Hepatocellular carcinoma is among the most common and lethal cancers in humans. Hepatocellular carcinoma is commonly associated with physical or functional inactivation of the p53 tumor suppressor, high levels of chromosomal instability, and disease conditions causing chronic cycles of hepatocyte death and regeneration. Mounting evidence has implicated regeneration-induced telomere erosion as a potential mechanism fueling genome instability. In mouse models of hepatocellular carcinoma, telomere dysfunction has been shown to enhance initiation of hepatic neoplasias yet constrain full malignant progression of these neoplasms possibly due to activation of a p53-dependent checkpoint and/or intolerable levels of genomic instability. Here, in a hepatocellular carcinoma-prone model brought about through toxin-induced hepatocyte injury and regeneration, we sought to determine the cooperative interactions of germ line p53 mutation and telomere dysfunction [produced by telomerase reverse transcriptase (mTERT) gene knockout]. In the setting of intact telomeres, p53 mutation had no effect on hepatocarcinogenesis, whereas in the setting of telomere dysfunction, p53 mutation enabled advanced hepatocellular carcinoma disease. Notably, there was no evidence of deletion or mutation of the wild-type p53 allele in the late generation mTert(-/-)p53(+/-) mice, suggesting that reduced levels of p53 potently enable hepatocellular carcinoma progression in the setting of telomere dysfunction. Thus, this study supports a model that, in the face of chronic liver damage, attenuated p53 function and telomere-induced chromosomal instability play critical and cooperative roles in the progression of hepatocellular carcinoma.

Molecular signaling and genetic pathways of senescence: Its role in tumorigenesis and aging

In response to progressive telomere shortening in successive cell divisions, normal somatic cells enter senescence, during which they cease to proliferate irreversibly and undergo dramatic changes in gene expression. Senescence can also be activated by various types of stressful stimuli, including aberrant oncogenic signaling, oxidative stress, and DNA damage. Because of the limited proliferative capacity imposed by senescence, as well as the ability of senescent cells to influence neighboring non-senescent cells, senescence has been proposed to play an important role in tumorigenesis and to contribute to aging. Considerable effort has been put into elucidating the molecular mechanisms of senescence, including the signals that trigger senescence, the molecular pathways by which cells enter senescence, and evidence that supports its role in tumorigenesis and aging.

Tumor size-independence of telomere length indicates an aggressive feature of HCC

Using quantitative fluorescence in situ hybridization (Q-FISH), the average telomere length of hepatoma cells was assessed by the average telomeric signal intensity of cancer cells relative to that of stromal cells. We demonstrated first the applicability of Q-FISH for tissue sections by comparing Q-FISH and Southern blotting results. Tumors less than 50mm in diameter and with a relative telomeric intensity of less than 0.6 were categorized as group A and the remainder as group B. In group A, the telomere length correlated negatively with tumor size, whereas in group B there was no correlation. Compared with the group A tumors, the group B tumors were of significantly more advanced stage, showed higher telomerase and proliferative activities, and exhibited less differentiated histology. Therefore, we considered that a lack of correlation between telomere length and tumor size, namely, size-independence of telomere length, is associated with unfavorable clinicopathological features of hepatocellular carcinomas.

Telomeres, stem cells, senescence, and cancer

Mammalian aging occurs in part because of a decline in the restorative capacity of tissue stem cells. These self-renewing cells are rendered malignant by a small number of oncogenic mutations, and overlapping tumor suppressor mechanisms (e.g., p16(INK4a)-Rb, ARF-p53, and the telomere) have evolved to ward against this possibility. These beneficial antitumor pathways, however, appear also to limit the stem cell life span, thereby contributing to aging.

Historical claims and current interpretations of replicative aging

Replicative aging is the process by which most normal human cells "count" the number of times they have divided, eventually undergoing a growth arrest termed cellular senescence. This process is dependent on the shortening of telomeres, repeated sequences at the ends of the chromosomes. The loss of telomeric sequences with each cell division eventually induces a growth arrest that has a similar phenotype to that of cells stressed by inadequate culture or other conditions. Experiments over the past several years have identified species in which replicative aging does not occur and many examples in which a failure to proliferate has been misinterpreted as replicative senescence. Insights from these studies now permit a reevaluation of much of the seemingly contradictory data concerning replicative aging. There are good theoretical reasons for believing a limited proliferative capacity contributes to declining tissue homeostasis with increasing age. Although the presence of telomere shortening provides strong circumstantial evidence that replicative aging is occurring in vivo, thus far there is only very limited direct evidence for actual physiological effects of replicative aging.

Digital image analysis of the distribution of proliferating cell nuclear antigen in hepatitis C virus-related chronic hepatitis, cirrhosis, and hepatocellular carcinoma

Viral dynamic studies in chronic hepatitis C virus (HCV) infection indicate a significantly shortened survival of virus-infected cells. Since at the steady state of chronic viral infection, the rate of infected cell elimination equals new cell regeneration, this would imply a high rate of hepatocyte turnover in chronic HCV liver disease. We estimated the fraction of regenerating hepatocytes in liver biopsy sections in chronic HCV liver disease, cirrhosis, and hepatocellular carcinoma (HCC). We used antibodies to proliferating cell nuclear antigen (PCNA) to detect proliferating cell nuclei in liver biopsy specimen from controls and patients with chronic hepatitis, cirrhosis, and HCC. We also used bis-benzimide to label fluorescently all hepatocyte nuclei simultaneously. Using digital image analysis, we calculated the area occupied by PCNA-stained hepatocyte nuclei, as a fraction of the total area occupied by fluorescently labeled hepatocyte nuclei (labeling index; LI). Antibody staining was negligible in the control specimen. The mean +/- SE PCNA LI increased from 0.21 +/- 0.1 in chronic hepatitis to 0.63 +/- 0.15 in HCC. There was no significant difference between chronic hepatitis and cirrhosis. The fraction of cells undergoing regeneration is increased in chronic HCV liver disease, HCV-related cirrhosis, and HCC. Increased hepatocyte turnover could provide the link between chronic HCV liver disease and HCC.

Hepatocyte telomere shortening and senescence are general markers of human liver cirrhosis

Telomere shortening limits the number of cell divisions of primary human cells and might affect the regenerative capacity of organ systems during aging and chronic disease. To test whether the telomere hypothesis applies to human cirrhosis, the telomere length was monitored in cirrhosis induced by a broad variety of different etiologies. Telomeres were significantly shorter in cirrhosis compared with noncirrhotic samples independent of the primary etiology and independent of the age of the patients. Quantitative fluorescence in situ hybridization showed that telomere shortening was restricted to hepatocytes whereas lymphocytes and stellate cells in areas of fibrosis had significantly longer telomere reserves. Hepatocyte-specific telomere shortening correlated with senescence-associated beta-galactosidase staining in 84% of the cirrhosis samples, specifically in hepatocytes, but not in stellate cells or lymphocytes. Hepatocyte telomere shortening and senescence correlated with progression of fibrosis in cirrhosis samples. This study demonstrates for the first time that cell type-specific telomere shortening and senescence are linked to progression of human cirrhosis. These findings give a novel explanation for the pathophysiology of cirrhosis, indicating that fibrotic scarring at the cirrhosis stage is a consequence of hepatocyte telomere shortening and senescence. The data imply that future therapies aiming to restore regenerative capacity during aging and chronic diseases will have to ensure efficient targeting of specific cell types within the affected organs.

The genetics of pancreatic adenocarcinoma: a roadmap for a mouse model

Pancreatic cancer is among the leading causes of cancer death. Although a genetic profile for pancreatic cancer is emerging, many biological aspects of this disease are poorly understood. Indeed, fundamental questions regarding progenitor cell lineages, host stromal milieu, and the role of specific genetic alterations in tumor progression remain unresolved. A mouse model engineered with signature mutations would provide a powerful ally in the study of pancreatic cancer biology and may guide improved prognostic assessment and treatment for the human disease. In this review, we discuss the molecular basis for normal pancreatic development and the genetics of human pancreatic adenocarcinoma in the hope of charting a course for the development of a faithful mouse model for this lethal cancer.

How long should telomeres be?

What began as a study of the "end-replication problem" took on a new dimension as it became clear that telomeres are a "molecular clock" of replication in human somatic cells. Here we review the biology of telomeres in vitro and in vivo, in mice and humans. We suggest that, in humans, telomeres are involved in the biology of aging and pathobiology of disorders of aging, including cancer and cardiovascular disease. We also propose that the underlying dynamics of telomere biology is in line with broad principles of evolutionary theories.