Xiaojian Cao

Impartial comparative analysis of measurement of leukocyte telomere length/DNA content by Southern blots and qPCR

Telomere length/DNA content has been measured in epidemiological/clinical settings with the goal of testing a host of hypotheses related to the biology of human aging, but often the conclusions of these studies have been inconsistent. These inconsistencies may stem from various reasons, including the use of different telomere length measurement techniques. Here, we report the first impartial evaluation of measurements of leukocyte telomere length by Southern blot of the terminal restriction fragments and quantitative PCR (qPCR) of telomere DNA content, expressed as the ratio of telomeric product (T)/single copy gene (S) product. Blind measurements on the same samples from 50 donors were performed in two independent laboratories on two different occasions. Both the qPCR and Southern blots displayed highly reproducible results as shown by r values > 0.9 for the correlations between results obtained by either method on two occasions. The inter-assay CV measurement for the qPCR was 6.45%, while that of the Southern blots was 1.74%. The relation between the results generated by Southern blots versus those generated by qPCR deviated from linearity. We discuss the ramifications of these findings with regard to measurements of telomere length/DNA content in epidemiological/clinical circumstances.

Leukocyte telomere dynamics: longitudinal findings among young adults in the Bogalusa Heart Study.

Leukocyte telomere length (LTL) is ostensibly a biomarker of human aging. Cross-sectional analyses have found that LTL is relatively short in a host of aging-related diseases. These studies have also provided indirect estimates of age-dependent LTL shortening. In this paper, the authors report findings of the first comprehensive longitudinal study of 450 whites and 185 African Americans in Louisiana (aged 31.4 and 37.4 years at baseline (1995–1996) and follow-up (2001–2006) examinations, respectively) participating in the Bogalusa Heart Study. Rate of change in LTL was highly variable among individuals, with some displaying a paradoxical gain in LTL during the follow-up period. The most striking observation was that age-dependent LTL shortening was proportional to LTL at baseline examination. At both baseline and follow-up examinations, African Americans had longer LTLs than whites, and smokers had shorter LTLs than nonsmokers. The longer LTL in African Americans than in whites explained in part the faster rate of LTL shortening observed among African Americans. These findings underscore the complexity of leukocyte telomere dynamics in vivo and suggest that determinants in addition to the “end-replication problem” contribute to telomere shortening in vivo.

Measurement of telomere length by the Southern blot analysis of terminal restriction fragment lengths

In this protocol we describe a method to obtain telomere length parameters using Southern blots of terminal restriction fragments (TRFs). We use this approach primarily for epidemiological studies that examine leukocyte telomere length. However, the method can be adapted for telomere length measurements in other cells whose telomere lengths are within its detection boundaries. After extraction, DNA is inspected for integrity, digested, resolved by gel electrophoresis, transferred to a membrane, hybridized with labeled probes and exposed to X-ray film using chemiluminescence. Although precise and highly accurate, the method requires a considerable amount of DNA (3 μg per sample) and it measures both the canonical and noncanonical components of telomeres. The method also provides parameters of telomere length distribution in each DNA sample, which are useful in answering questions beyond those focusing on the mean length of telomeres in a given sample. A skilled technician can measure TRF length in ∼130 samples per week.

Genome-wide association identifies OBFC1 as a locus involved in human leukocyte telomere biology

Telomeres are engaged in a host of cellular functions, and their length is regulated by multiple genes. Telomere shortening, in the course of somatic cell replication, ultimately leads to replicative senescence. In humans, rare mutations in genes that regulate telomere length have been identified in monogenic diseases such as dyskeratosis congenita and idiopathic pulmonary fibrosis, which are associated with shortened leukocyte telomere length (LTL) and increased risk for aplastic anemia. Shortened LTL is observed in a host of aging-related complex genetic diseases and is associated with diminished survival in the elderly. We report results of a genome-wide association study of LTL in a consortium of four observational studies (n = 3,417 participants with LTL and genome-wide genotyping). SNPs in the regions of the oligonucleotide/oligosaccharide-binding folds containing one gene (OBFC1; rs4387287; P = 3.9 × 10−9) and chemokine (C-X-C motif) receptor 4 gene (CXCR4; rs4452212; P = 2.9 × 10−8) were associated with LTL at a genome-wide significance level (P < 5 × 10−8). We attempted replication of the top SNPs at these loci through de novo genotyping of 1,893 additional individuals and in silico lookup in another observational study (n = 2,876), and we confirmed the association findings for OBFC1 but not CXCR4. In addition, we confirmed the telomerase RNA component (TERC) as a gene associated with LTL (P = 1.1 × 10−5). The identification of OBFC1 through genome-wide association as a locus for interindividual variation in LTL in the general population advances the understanding of telomere biology in humans and may provide insights into aging-related disorders linked to altered LTL dynamics.

Offspring's Leukocyte Telomere Length, Paternal Age, and Telomere Elongation in Sperm

Leukocyte telomere length (LTL) is a complex genetic trait. It shortens with age and is associated with a host of aging-related disorders. Recent studies have observed that offspring of older fathers have longer LTLs. We explored the relation between paternal age and offsprings LTLs in 4 different cohorts. Moreover, we examined the potential cause of the paternal age on offsprings LTL by delineating telomere parameters in sperm donors. We measured LTL by Southern blots in Caucasian men and women (n=3365), aged 18–94 years, from the Offspring of the Framingham Heart Study (Framingham Offspring), the NHLBI Family Heart Study (NHLBI-Heart), the Longitudinal Study of Aging Danish Twins (Danish Twins), and the UK Adult Twin Registry (UK Twins). Using Southern blots, Q-FISH, and flow-FISH, we also measured telomere parameters in sperm from 46 young (<30 years) and older (>50 years) donors. Paternal age had an independent effect, expressed by a longer LTL in males of the Framingham Offspring and Danish Twins, males and females of the NHLBI-Heart, and females of UK Twins. For every additional year of paternal age, LTL in offspring increased at a magnitude ranging from half to more than twice of the annual attrition in LTL with age. Moreover, sperm telomere length analyses were compatible with the emergence in older men of a subset of sperm with elongated telomeres. Paternal age exerts a considerable effect on the offsprings LTL, a phenomenon which might relate to telomere elongation in sperm from older men. The implications of this effect deserve detailed study.

Synchrony of telomere length among hematopoietic cells

OBJECTIVE Little is known about the relationship of telomere length among leukocyte subsets and cells up the hematopoietic hierarchy. This information is relevant because telomere dynamics in granulocytes were postulated to mirror those of hematopoietic stem cells (HSCs). MATERIALS AND METHODS In newborn umbilical cord blood (UCB), we examined the relationships of telomere length in hematopoietic progenitor cells (HPCs) (CD34(+)CD45(-)) with those in T lymphocytes and granulocytes. In addition, we correlated telomere length in granulocytes with those in whole leukocyte samples of individuals ranging in age from birth to 100 years. RESULTS In the UCB, we found strong correlations of telomere length in HPCs with telomere length in T lymphocytes (r ranging from 0.882 to 0.935; p ranging from 0.0038 to 0.0007) and in granulocytes (r = 0.930; p = 0.0072). At birth, strong correlations were also observed between telomere length in granulocytes and those in all leukocytes (r = 0.979; p = 0.0003). Throughout the human lifespan, the relationship between telomere length in granulocytes and that in all leukocytes was r > 0.980 and p < 0.0001. CONCLUSIONS Robust synchrony exists among leukocyte subsets throughout the human lifespan; individuals with relatively long (or short) telomeres in one leukocyte subset have long (or short) telomeres in other leukocyte subsets. Moreover, telomere length in leukocytes reflects its length in cells up the hematopoietic hierarchy, i.e., HPCs and, by inference, HSCs. Strong links have been found by many studies between leukocyte telomere length and a host of aging-related diseases. Our findings suggest, therefore, that these links might be traced to telomere dynamics in HSCs.

Short telomeres in short-lived males: what are the molecular and evolutionary causes?

Telomere length regulation is an important aspect of cell maintenance in eukaryotes, since shortened telomeres can lead to a number of defects, including impaired cell division. Although telomere length is correlated with lifespan in some bird species, its possible role in aging and lifespan determination is still poorly understood. Here we investigate telomere dynamics (changes in telomere length and attrition rate) and telomerase activity in the ant Lasius niger, a species in which different groups of individuals have evolved extraordinarily different lifespans. We found that somatic tissues of the short‐lived males had dramatically shorter telomeres than those of the much longer‐lived queens and workers. These differences were established early during larval development, most likely through faster telomere shortening in males compared with females. Workers did not, however, have shorter telomeres than the longer‐lived queens. We discuss various molecular mechanisms that are likely to cause the observed sex‐specific telomere dynamics in ants, including cell division, oxidative stress and telomerase activity. In addition, we discuss the evolutionary causes of such patterns in ants and in other species.

Leukocyte telomere length is associated with HDL cholesterol levels: The Bogalusa heart study.

OBJECTIVE This study examined the relationships of high-density lipoprotein cholesterol (HDL-C) with LTL and the rate of its shortening. BACKGROUND Diminished levels of HDL-C are associated with an increased risk for atherosclerosis. Shortened leukocyte telomere length (LTL) also entails an increased atherosclerotic risk. METHODS We studied 472 Whites and 190 African Americans (AfAs) enrolled in the Bogalusa Heart Study. Subjects were examined serially 3-13 times for HDL-C over an average period of 27.8 years from childhood through young adulthood. LTL was measured twice during adulthood at a mean age of 31.5 years (baseline exam) and 37.8 years (follow-up exam). HDL-C trajectories with age were constructed and the area under the curve (AUC) was used as a measure of cumulative HDL-C levels. RESULTS Multivariate regression analyses showed that LTL was positively associated with HDL-C in childhood (regression coefficient (bp per mg/dL) beta=3.1, p=0.024), adulthood (beta=4.4, p=0.058) and AUC from childhood to adulthood (beta=12.2, p=0.0004) in the combined sample of AfAs and Whites. The association between LTL and HDL-C AUC was stronger in females (beta=18.5, p<0.001) than in males (beta=2.9, p=0.590) (difference in slopes p=0.037). A slower rate of LTL shortening per year was associated with higher HDL-C AUC in the total sample (p=0.033), adjusting for baseline LTL. CONCLUSIONS As HDL-C exerts anti-oxidant and anti-inflammatory effects and LTL registers the accruing burden of oxidative stress and inflammation, the association between HDL-C and LTL might be explained by the lifelong status of oxidative stress and inflammation.