Mutations in the genes encoding telomerase components can appear as familial idiopathic pulmonary fibrosis. Our findings support the idea that pathways leading to telomere shortening are involved in the pathogenesis of this disease.

Idiopathic interstitial pneumonias (IIPs) have a progressive and often fatal course, and their enigmatic etiology has complicated approaches to effective therapies. Idiopathic pulmonary fibrosis (IPF) is the most common of IIPs and shares with IIPs an increased incidence with age and unexplained scarring in the lung. Short telomeres limit tissue renewal capacity in the lung and germ-line mutations in telomerase components, hTERT and hTR, underlie inheritance in a subset of families with IPF. To examine the hypothesis that short telomeres contribute to disease risk in sporadic IIPs, we recruited patients who have no family history and examined telomere length in leukocytes and in alveolar cells. To screen for mutations, we sequenced hTERT and hTR. We also reviewed the cases for features of a telomere syndrome. IIP patients had shorter leukocyte telomeres than age-matched controls (P < 0.0001). In a subset (10%), IIP patients had telomere lengths below the first percentile for their age. Similar to familial cases with mutations, IPF patients had short telomeres in alveolar epithelial cells (P < 0.0001). Although telomerase mutations were rare, detected in 1 of 100 patients, we identified a cluster of individuals (3%) with IPF and cryptogenic liver cirrhosis, another feature of a telomere syndrome. Short telomeres are thus a signature in IIPs and likely play a role in their age-related onset. The clustering of cryptogenic liver cirrhosis with IPF suggests that the telomere shortening we identify has consequences and can contribute to what appears clinically as idiopathic progressive organ failure in the lung and the liver.interstitial lung disease ͉ liver fibrosis ͉ telomerase ͉ aplastic anemia ͉ dyskeratosis congenita

Telomeres have emerged as crucial cellular elements in aging and various diseases including cancer. To measure the average length of telomere repeats in cells, we describe our protocols that use fluorescent in situ hybridization (FISH) with labeled peptide nucleic acid (PNA) probes specific for telomere repeats in combination with fluorescence measurements by flow cytometry (flow FISH). Flow FISH analysis can be performed using commercially available flow cytometers, and has the unique advantage over other methods for measuring telomere length of providing multi-parameter information on the length of telomere repeats in thousands of individual cells. The accuracy and reproducibility of the measurements is augmented by the automation of most pipetting (aspiration and dispensing) steps, and by including an internal standard (control cells) with a known telomere length in every tube. The basic protocol for the analysis of nucleated blood cells from 22 different individuals takes about 12 h spread over 2-3 days.

Telomerase activity is readily detectable in extracts from human hematopoietic stem and progenitor cells, but appears unable to maintain telomere length with proliferation in vitro and with age in vivo. We performed a detailed study of the telomere length by flow FISH analysis in leukocytes from 835 healthy individuals and 60 individuals with reduced telomerase activity. Healthy individuals showed a broad range in average telomere length in granulocytes and lymphocytes at any given age. The average telomere length declined with age at a rate that differed between age-specific breakpoints and between cell types. Gender differences between leukocyte telomere lengths were observed for all cell subsets studied; interestingly, this trend could already be detected at birth. Heterozygous carriers for mutations in either the telomerase reverse transcriptase (hTERT) or the telomerase RNA template (hTERC) gene displayed striking and comparable telomere length deficits. Further, non-carrier relatives of such heterozygous individuals had somewhat shorter leukocyte telomere lengths than expected; this difference was most profound for granulocytes. Failure to maintain telomere homeostasis as a result of partial telomerase deficiency is thought to trigger cell senescence or cell death, eventually causing tissue failure syndromes. Our data are consistent with these statements and suggest that the likelihood of similar processes occurring in normal individuals increases with age. Our work highlights the essential role of telomerase in the hematopoietic system and supports the notion that telomerase levels in hematopoietic cells, while limiting and unable to prevent overall telomere shortening, are nevertheless crucial to maintain telomere homeostasis with age.