TRF2 rescues pathogenic phenotypes in Duchenne muscular dystrophy cardiomyocytes derived from human iPSCs

Duchenne muscular dystrophy (DMD) is a severe muscle wasting disease caused by the lack of dystrophin. Heart failure, driven by cardiomyocyte death, fibrosis, and the development of dilated cardiomyopathy, is the leading cause of death in DMD patients. Current treatments decrease the mechanical load on the heart; however, these treatments do not address the root cause of dilated cardiomyopathy: cardiomyocyte death. Previously, we showed that longer telomeres are protective against dilated cardiomyopathy. Here we investigated the role of telomeres as a target for therapy in DMD cardiomyocytes using human induced pluripotent stem cells (iPSCs) to model the disease. Compared to healthy controls, DMD cardiomyocytes exhibited reduced telomere lengths, cell size, nuclear size, and sarcomere density. The telomere-binding protein, TRF2, is a core component of the shelterin complex, which protects chromosome ends. TRF2 levels are reduced relative to healthy controls in DMD cardiomyocytes. We hypothesized that decreased TRF2 drives telomere attrition and subsequent cardiomyocyte death in the progression of dilated cardiomyopathy. Our data show that TRF2 overexpression prevented telomere attrition and also rescued deficits in cell size, nuclear size, sarcomere density, and calcium handling. These data highlight the benefits of TRF2 upregulation as a potential gene therapy to delay the onset of dilated cardiomyopathy.

Cellular Senescence in Bone

Senescence is an irreversible cell-cycle arrest process induced by environmental, genetic, and epigenetic factors. An accumulation of senescent cells in bone results in age-related disorders, and one of the common problems is osteoporosis. Deciphering the basic mechanisms contributing to the chronic ailments of aging may uncover new avenues for targeted treatment. This review focuses on the mechanisms and the most relevant research advancements in skeletal cellular senescence. To identify new options for the treatment or prevention of age-related chronic diseases, researchers have targeted hallmarks of aging, including telomere attrition, genomic instability, cellular senescence, and epigenetic alterations. First, this chapter provides an overview of the fundamentals of bone tissue, the causes of skeletal involution, and the role of cellular senescence in bone and bone diseases such as osteoporosis. Next, this review will discuss the utilization of pharmacological interventions in aging tissues and, more specifically, highlight the role of senescent cells to identify the most effective and safe strategies.

Kuakini HHP Center for Translational Research on Aging: Aims and Preliminary Findings

Kuakini Medical Center (Kuakini) is creating an interdisciplinary Hawai’i-based Center for translational research on aging. This Center will build upon Kuakini’s five-decades of NIH-funded research, its 420,000-specimen biorepository, and existing strengths in aging research, notably, the 56-year ongoing Kuakini Honolulu Heart Program cohort study (Kuakini HHP), Kuakini Honolulu-Asia Aging Study (Kuakini HAAS), and Kuakini HHP Offspring Study. The overall goal is to find practical means to enhance healthy human lifespan (healthspan). Four research project leaders (RPLs) have been selected from various disciplines for mentorship in translational aging research. The first RPL presentation will introduce a novel mouse model, enabling controlled expression of the pro-longevity gene FoxO3, and assess the impact on lifespan and healthspan phenotypes in mice. These phenotypes will be compared to similar phenotypes in humans with/without the FOXO3 longevity genotype. The second RPL presentation will assess the relation between leukocyte telomere attrition rates (from banked blood collected at three time points over 20-plus years) in older Kuakini HHP men with/without the FOXO3 longevity genotype. The third RPL presentation will assess whether FOXO3 genotype, peripheral leukocyte telomere dynamics (attrition rate, telomerase activity) and inflammatory cytokines mediate the human brain integrity and function with age. This project will utilize structural and functional MRI data from male and female Kuakini HHP Offspring Study participants. The fourth RPL presentation will assess whether APOE e2, e4, and FOXO3 longevity-associated alleles impact 34-year incidence of intracerebral hemorrhage. We will summarize the findings, address the healthspan implications and provide future directions. Supported by NIH 5P20GM125526.

Age-Related Phenotypes Linked to Aberrant Expression and Localization of a Telomeric Protein

Telomere attrition is associated with telomere biology disorders and age-related diseases. In telomere biology disorders, telomere uncapping induces a DNA damage response that evokes cell death or senescence. However, a causal mechanism for telomere attrition in age-related diseases remains elusive. Telomere capping and integrity are maintained by shelterin, a six-protein complex. Rap1 is the only shelterin member that is not required for telomere capping and is expressed at non-telomeric genomic and cytosolic regions. The objective of this study was to determine aberrant phenotypes attributed to non-telomeric Rap1. To test this, we generated a Rap1 mutant knock-in (KI) mouse model using CRISPR/Cas9 editing, in which Rap1 at telomeres is prevented, leaving only non-telomeric Rap1. Cell fractionation/western blotting of primary fibroblasts from Rap1 KI mice demonstrated decreased Rap1 expression and Rap1 re-localization off telomeres, with an altered cellular distribution. This same difference in Rap1 is also observed in human cells with telomere erosion, indicating that aberrant Rap1 in our model may recapitulate Rap1 in aging and human telomere biology disorders. Compared to wild-type control mice, Rap1 KI mice exhibited increased body weight, altered cytokine levels, behavioral deficits, and decreased lifespan. In conclusion, our results reveal a novel mechanism by which telomere shortening may contribute to age-related pathologies by disrupting Rap1 expression and cell localization.

Telomere Length and the Transition to Family Caregiving in the REGARDS Study

An increase in life expectancy and an aging population has resulted in increased risks and prevalence of age-related diseases. Previous studies have shown that factors, such as chronic stress, are associated with shorter telomere length. When telomeres become critically short, cells enter a state of senescence, which is a hallmark of aging. Several prior studies examining the relationship between caregiving and telomere length have reported mixed results. The present study utilized data from the Caregiving Transitions Study, an ancillary study to the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study. The difference in telomere length across an average ~8.6 years was compared between 235 incident caregivers and 229 controls. Telomere length was determined using the qPCR telomere-to-single copy gene (IFNB1) ratio (T/S) for each participant at both baseline and follow-up timepoints. Regression models controlling for age, sex, race, and baseline telomere length examined the association between caregiving status (exposure) and the telomere length change (□T/S). Sensitivity models adjusted for potential lifestyle and socioeconomic factors, including income, education, BMI, cigarette smoking, and alcohol use. We did not observe a significant association between □T/S and caregiving (beta=0.041, p=0.615). Adding lifestyle and socioeconomic factors did not change the null relationship (beta=0.062, p=0.455). In conclusion, this study provides evidence against an association between caregiving and the change in telomere length. Ultimately, more research to address the complex relationship between caregiving and telomere attrition is needed in order to prevent or reduce adverse outcomes and improve the well-being of caregivers and care recipients.

Hematopoiesis under telomere attrition at the single-cell resolution

The molecular mechanisms that drive hematopoietic stem cell functional decline under conditions of telomere shortening are not completely understood. In light of recent advances in single-cell technologies, we sought to redefine the transcriptional and epigenetic landscape of mouse and human hematopoietic stem cells under telomere attrition, as induced by pathogenic germline variants in telomerase complex genes. Here, we show that telomere attrition maintains hematopoietic stem cells under persistent metabolic activation and differentiation towards the megakaryocytic lineage through the cell-intrinsic upregulation of the innate immune signaling response, which directly compromises hematopoietic stem cells’ self-renewal capabilities and eventually leads to their exhaustion. Mechanistically, we demonstrate that targeting members of the Ifi20x/IFI16 family of cytosolic DNA sensors using the oligodeoxynucleotide A151, which comprises four repeats of the TTAGGG motif of the telomeric DNA, overcomes interferon signaling activation in telomere-dysfunctional hematopoietic stem cells and these cells’ skewed differentiation towards the megakaryocytic lineage. This study challenges the historical hypothesis that telomere attrition limits the proliferative potential of hematopoietic stem cells by inducing apoptosis, autophagy, or senescence, and suggests that targeting IFI16 signaling axis might prevent hematopoietic stem cell functional decline in conditions affecting telomere maintenance.

Telomere length variation does not correspond with the growth disturbances in the rainbow trout (Oncorhynchus mykiss)

Somatic growth is considered to affect pace of the telomere attrition in vertebrates. As normally developed and dwarf fish differ in the body size we have decided to compare telomere length in the rainbow trout (Oncorhynchus mykiss) with normal growth and with growth reduced due to the dwarf condition. Examined 1-year-old fish with normal and dwarf appearance were siblings originated from androgenetic fully homozygous doubled haploid (DH) line of rainbow trout. Particular dwarf individuals had body deformities such as humpback, kyphosis, and lordosis. Somatic cells of examined rainbow trout had an average telomere length between 17 and 20 kb, comparable in females and males. Dwarf rainbow trout exhibited significantly lower body length and weight than their normally developed siblings even though no differences in the telomere length were found between these fishes. Statistical analysis did not exhibit any correlation between body size and the telomere length. Equal length of telomeres observed in the studied normal and dwarf rainbow trout suggests morphological and physiological differences in fish with different growth rates do not affect dynamics of telomeric DNA. Or any variation in the telomere length might have been levelled by telomerase that in rainbow trout is active in all tissues irrespective of the individual developmental stage.

The telomere complex and the origin of the cancer stem cell

Exquisite regulation of telomere length is essential for the preservation of the lifetime function and self-renewal of stem cells. However, multiple oncogenic pathways converge on induction of telomere attrition or telomerase overexpression and these events can by themselves trigger malignant transformation. Activation of NFκB, the outcome of telomere complex damage, is present in leukemia stem cells but absent in normal stem cells and can activate DOT1L which has been linked to MLL-fusion leukemias. Tumors that arise from cells of early and late developmental stages appear to follow two different oncogenic routes in which the role of telomere and telomerase signaling might be differentially involved. In contrast, direct malignant transformation of stem cells appears to be extremely rare. This suggests an inherent resistance of stem cells to cancer transformation which could be linked to a stem cell’specific mechanism of telomere maintenance. However, tumor protection of normal stem cells could also be conferred by cell extrinsic mechanisms.