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

Potential Risks in the Paradigm of Basic to Translational Research: A Critical Evaluation of qPCR Telomere Size Techniques

Real time qPCR has become the method of choice for rapid large-scale telomere length measurements. Large samples sizes are critical for clinical trials, and epidemiological studies. QPCR has become such routine procedure that it is often used with little critical analysis. With proper controls, the mean telomere size can be derived from the data and even the size can be estimated. But there is a need for more consistent and reliable controls that will provide closer to the actual mean size can be obtained with uniform consensus controls. Although originating at the level of basic telomere research, many researchers less familiar with telomeres often misunderstand the source and significance of the qPCR metric. These include researchers and clinicians who are interested in having a rapid tool to produce exciting results in disease prognostics and diagnostics than in the multiple characteristics of telomeres that form the basis of the measurement. But other characteristics of the non-bimodal and heterogeneous telomeres as well as the complexities of telomere dynamics are not easily related to qPCR mean telomere values. The qPCR metric does not reveal the heterogeneity and dynamics of telomeres. This is a critical issue since mutations in multiple genes including telomerase can cause telomere dysfunction and a loss of repeats. The smallest cellular telomere has been shown to arrest growth of the cell carrying the dysfunction telomere. A goal for the future is a simple method that takes into account the heterogeneity by measuring the highest and lowest values as part of the scheme to compare. In the absence of this technique, Southern blots need to be performed in a subset of qPCR samples for both mean telomere size and the upper and lower extremes of the distribution. Most importantly, there is a need for greater transparency in discussing the limitations of the qPCR data. Given the potentially exciting qPCR telomere size results emerging from clinical studies that relate qPCR mean telomere size estimates to disease states, the current ambiguities have become urgent issues to validate the findings and to set the right course for future clinical investigations.

Sustained telomere length in hepatocytes and cholangiocytes with increasing age in normal liver

Telomeres, a validated biomarker of aging, comprise multiple nucleotide repeats capping chromosomes that shorten with each cell cycle until a critical length is achieved, precipitating cell senescence. Only two previous studies focused on the effect of aging in "normal" liver tissue, but these studies were compromised by small sample size, limited age range, tissue derived from individuals with an increased risk of senescence, and the use of liver homogenates. We developed a robust large-volume, four-color quantitative fluorescent in situ hybridization technique to measure telomere length in large numbers of hepatocytes, Kupffer cells, hepatic stellate cells, CD4-positive and CD8-positive lymphocytes, and cholangiocytes. Following validation against the gold standard (Southern blotting), the technique was applied to normal archived paraffin-embedded liver tissue obtained following reperfusion of implanted donor liver. We studied 73 highly selected donors aged 5-79 years with a short medical illness preceding death and no history of liver disease, reperfusion injury, or steatosis and normal graft function 1-year posttransplantation. Cholangiocytes had significantly longer telomeres compared with all other intrahepatic lineages over a wide age range (P < 0.05). Age-related telomere attrition was restricted to sinusoidal cells (i.e., Kupffer cells [P = 0.0054] and stellate cells [P = 0.0001]). Cholangiocytes and hepatocytes showed no age-related telomere shortening.

CONCLUSION

In normal liver and over a broad age range, cholangiocytes have longer telomeres than all other intrahepatic lineages. Age-related telomere length decline is restricted to Kupffer cells and stellate cells.

Nuclear size measurement is a simple method for the assessment of hepatocellular aging in non-alcoholic fatty liver disease: Comparison with telomere-specific quantitative FISH and p21 immunohistochemistry

Telomere-specific quantitative fluorescent in situ hybridization (Q-FISH) accurately evaluates hepatocellular aging on histological sections, but it requires appropriate tissue processing. To establish a more simple method for the assessment of hepatocellular aging, the usefulness of nuclear size measurement was clarified using biopsy liver samples from 64 patients with non-alcoholic fatty liver disease (NAFLD), a model for oxidative stress-associated hepatocellular aging, and 11 control individuals. Relative telomere intensity (RTI) was measured on Q-FISH, and the relative nuclear size (RNS) was calculated as the average nuclear size of the hepatocytes divided by that of lymphocytes. In normal individuals and NAFLD patients, the RTI and RNS were negatively correlated. The degree of nuclear enlargement in NAFLD patients was larger than that in normal individuals with the same telomere length, possibly reflecting telomere-independent senescence. In NAFLD patients with RNS >2.0, the regenerative responses, indicated by the ratio of Ki-67-positive index to serum alanine aminotransferase level, were significantly reduced. The RNS positively correlated with the p21 expression, another marker of senescence. This all indicates that nuclear enlargement progresses in parallel with reduced regenerative responses, telomere shortening, and p21 upregulation. Nuclear size measurement is an effective method for estimation of hepatocellular aging.

Oxidative stress may enhance the malignant potential of human hepatocellular carcinoma by telomerase activation

BACKGROUND/AIMS

Continuous oxidative stress (OS) plays an important role in the progression of chronic liver diseases and hepatocarcinogenesis through telomere shortening in hepatocytes. However, it has not been established how the OS influences the progression of human hepatocellular carcinomas (HCCs). We examined the correlations of OS with telomere length of cancer cells, telomerase activity and other clinicopathological factors in 68 HCCs.

METHODS

The level of 8-hydroxy-2'-deoxyguanosine (8-OHdG) as a marker of OS was examined immunohistochemically and OS was scored in four grades (0-3). The telomere length of cancer cells was measured by quantitative fluorescence in situ hybridization. Telomerase activity was measured by (i) immunodetection of human telomerase reverse transcriptase (hTERT) and (ii) telomere repeat amplification protocol (TRAP) assay. Telomerase related proteins, phosphatase and tensin homolog deleted on chromosome 10 (PTEN) and Akt, and other clinicopathological factors were also evaluated.

RESULTS

As the OS grade increased, the average telomere length became significantly shorter in HCCs, especially in the hTERT-negative group. In the state of high-grade OS, hTERT-positive HCC cells showed more proliferative and less apoptotic features compared with hTERT-negative HCC cells. Telomerase activity, as measured by the TRAP assay, was strongly correlated with OS grade in HCCs. Furthermore, a high OS grade was correlated with the downexpression of PTEN and the activation of Akt.

CONCLUSIONS

Oxidative stress enhanced the malignant potential of HCCs through the activation of telomerase, which raises the possibility of using OS as a marker for assessing the clinical state of HCCs.

Telomere shortening in the damaged small bile ducts in primary biliary cirrhosis reflects ongoing cellular senescence

Telomere shortening is a trigger of cellular senescence. Biliary epithelial cells in damaged small bile ducts in primary biliary cirrhosis (PBC) show senescent features such as the expression of senescence-associated beta-galactosidase and the increased expression of p16(INK4a) and p21(WAF1/Cip1). We investigated whether the telomere shortening is involved in the pathogenesis of biliary cellular senescence in PBC. We analyzed the telomere length of biliary epithelial cells using quantitative fluorescence in situ hybridization in livers taken from the patients with PBC (n = 13) and control livers (n = 13). We also assessed immunohistochemically the prevalence of DNA damage and the expression of p16(INK4a) and p21(WAF1/Cip1). The study showed a significant decrease in telomere length in biliary epithelial cells in the damaged small bile ducts and bile ductules in PBC compared with normal-looking bile ducts and bile ductules in PBC, chronic viral hepatitis, and normal livers (P < 0.01). gammaH2AX-DNA-damage-foci were detected in biliary epithelial cells in damaged small bile ducts and bile ductules in PBC but were absent in biliary epithelial cells in chronic viral hepatitis and normal livers. The expression of p16(INK4a) and p21(WAF1/Cip1) was increased corresponding to telomere shortening and gammaH2AX-DNA-damage-foci in the damaged small bile ducts in PBC.

CONCLUSION

Telomere shortening and an accumulation of DNA damage coincide with increased expression of p16(INK4a) and p21(WAF1/Cip1) in the damaged bile ducts, characterize biliary cellular senescence, and may play a role in the following progressive bile duct loss in PBC.

Induction of premature senescence in cardiomyocytes by doxorubicin as a novel mechanism of myocardial damage

Cellular senescence is an important phenomenon in decreased cellular function. Recently, it was shown that cellular senescence is induced in proliferating cells within a short period of time by oxidative stresses. This phenomenon is known as premature senescence. However, it is still unknown whether premature senescence can be also induced in cardiomyocytes. The aim of the present study was to investigate whether a senescence-like phenotype can be induced in cardiomyocytes by oxidative stress. In cardiomyocytes obtained from aged rats (24 months of age), the staining for senescence-associated beta-galactosidase increased significantly and the protein or RNA levels of cyclin-dependent kinase inhibitors increased compared to those of young rats. Decreased cardiac troponin I phosphorylation and telomerase activity were also observed in aged cardiomyocytes. Treatment of cultured neonatal rat cardiomyocytes with a low concentration of doxorubicin (DOX) (10(-7) mol L(-1)) did not induce apoptosis but did induce oxidative stress, which was confirmed by 2',7'-dichlorofluorescin diacetate staining. In DOX-treated neonatal cardiomyocytes, increased positive staining for senescence-associated beta-galactosidase, cdk-I expression, decreased cardiac troponin I phosphorylation, and decreased telomerase activity were observed, as aged cardiomyocytes. Alterations in mRNA expression typically seen in aged cells were observed in DOX-treated neonatal cardiomyocytes. We also found that promyelocytic leukemia protein and acetylated p53, key proteins involved in stress-induced premature senescence in proliferating cells, were associated with cellular alterations of senescence in DOX-treated cardiomyocytes. In conclusion, cardiomyocytes treated with DOX showed characteristic changes similar to cardiomyocytes of aged rats. promyelocytic leukemia-related p53 acetylation may be an underlying mechanism of senescence-like alterations in cardiomyocytes. These findings indicate a novel mechanism of myocardial dysfunction induced by oxidative stress.

High telomerase activity and long telomeres in advanced hepatocellular carcinomas with poor prognosis

Telomerase reactivation and telomere maintenance are crucial in carcinogenesis and tumor progression. In this study, the relationships between telomere parameters, chromosomal instability and clinicopathological features were evaluated in hepatocellular carcinomas (HCCs). Telomere length (TL), telomerase activity (TA) and human telomerase reverse transcriptase (hTERT) mRNA levels were measured in 49 hepatitis B virus (HBV)-related HCCs and corresponding non-tumorous tissues. The results were compared with clinicopathological data, including differentiation, multipolar mitosis (MM), anaphase bridge, immunohistochemical stain results for cytokeratin 19 (CK19) and patient outcome. TL of HCCs ranged from 4.7 to 13.1 kb, and 44.4% of HCCs showed telomere lengthening. hTERT mRNA levels and TA were closely related (P=0.008), and were significantly higher in HCCs than non-tumorous tissues. TL was significantly higher in HCCs with strong TA (P=0.048), high hTERT mRNA levels (P=0.001) and poor differentiation (P=0.041). Frequent MM was associated with poor differentiation (P=0.007) and advanced stage (P<0.001). TA was positively correlated with MM, anaphase bridges and advanced stage (P=0.019, P=0.017 and P=0.029). Thirteen (28.3%) HCCs were CK19+ and demonstrated longer telomeres than CK19- HCCs (P=0.046). Overall survival was poor in HCCs with MM >0.4 per field (P=0.016), high TA (P=0.009) and high TL ratio (HCC/non-HCC) >0.8 (P=0.044). Our results show that long telomeres, high TA and high mitotic instability are poor prognostic markers for HBV-related HCCs and their close association suggests that telomere maintenance may be important for the progression of HCCs with high chromosomal instability to more aggressive ones.

Role of cell-cycle turnover and oxidative stress in telomere shortening and cellular senescence in patients with chronic hepatitis C

BACKGROUND

In addition to the telomere shortening that occurs with cell division, oxidative stress can damage or shorten telomeres and induce a condition termed premature senescence, possibly before telomeres become critically short. We investigated the effects of cell-cycle turnover and oxidative stress on cellular senescence in hepatitis C virus (HCV)-related chronic liver injury.

METHOD

Using quantitative fluorescence in situ hybridization, the telomere lengths of hepatocytes in biopsy specimens from HCV-positive patients were estimated. We assessed clinicopathological parameters that reflect cell-cycle turnover, including Ki-67 positive index, serum alanine aminotransferase (ALT) level and degree of fibrosis, and also oxidative stress-related parameters, such as 8-hydroxy-2'-deoxyguanosine (8-OHdG) expression. Nuclear size and DNA content of hepatocytes were measured as morphological features of senescence.

RESULTS

Telomere shortening correlated with the degree of cell turnover, hepatic fibrosis and morphological features of aging cells. Furthermore, the rate of telomere shortening per year was positively correlated with fibrosis progression. In cases of no or mild fibrosis, telomere lengths of positive patients were generally shorter than those of 8-OHdG-negative patients, and this trend achieved statistical significance in advanced-stage fibrosis. HCV carriers with persistently normal serum ALT level (PNAL) showed significantly longer telomeres than patients with active hepatitis and mild fibrosis. There was no significant difference in telomere lengths between HCV carriers with PNAL and normal controls.

CONCLUSIONS

Cell-cycle turnover is the primary mechanism of telomere shortening, and can induce fibrosis progression and cellular senescence. However, oxidative stress can be an accelerator of senescence, especially in advanced-stage fibrosis.