Telomere-mediated chromosomal instability triggers TLR4 induced inflammation and death in mice

The regulatory feedback of inflammatory signaling and telomere/telomerase complex dysfunction in chronic inflammatory diseases

Inflammation is believed to play a role in the progression of numerous human diseases. Research has shown that inflammation and telomeres are involved in a feedback regulatory loop: inflammation increases the rate of telomere attrition, leading to telomere dysfunction, while telomere components also participate in regulating the inflammatory response. However, the specific mechanism behind this feedback loop between inflammatory signaling and telomere/telomerase complex dysfunction has yet to be fully understood. This review presents the latest findings on this topic, with a particular focus on the detailed regulation and molecular mechanisms involved in the progression of aging, various chronic inflammatory diseases, cancers, and different stressors. Several feedback loops between inflammatory signaling and telomere/telomerase complex dysfunction, including NF-κB-TERT feedback, NF-κB-RAP1 feedback, NF-κB-TERC feedback, STAT3-TERT feedback, and p38 MAPK-shelterin complex-related gene feedback, are summarized. Understanding the latest discoveries of this feedback regulatory loop can help identify novel potential drug targets for the suppression of various inflammation-associated diseases.

Links between telomere dysfunction and hallmarks of aging

Aging is characterized by the gradual loss of physiological integrity, leading to impaired function and increased risk of death. This deterioration is the main risk factor for the great majority of chronic diseases, which account for most of the morbidity, death and medical expenses. The hallmarks of aging comprise diverse molecular mechanisms and cell systems, which are interrelated and coordinated to drive the aging process. This review focuses on telomere to analyze the interrelationships between telomere dysfunction and other aging hallmarks and their relative contributions to the initiation and progression of age-related diseases (such as neurodegeneration, cardiovascular disease, and cancer), which will contribute to determine drug targets, improve human health in the aging process with minimal side effects and provide information for the prevention and treatment of age-related diseases.

Lifelong docosahexaenoic acid intervention ameliorates aging in the telomere-DNA-mitochondria axis in telomerase-deficient mice

The health benefits of n-3 polyunsaturated fatty acids (PUFAs) in multiple age-related diseases are associated with telomere length. Telomerase is intimately related to inflammation and oxidative stress, but whether the underlying function of n-3 PUFAs on telomere maintenance is based on telomerase activation or related mechanisms remains unclear. Herein, we utilized late-generation (G4) telomerase-deficient (Terc^-/-) mice to perform a lifelong docosahexaenoic acid (DHA) intervention to determine the potential of DHA in telomere maintenance and health promotion. Unfortunately, DHA failed to prolong mouse longevity in either intrinsic or premature aging. However, intriguingly, lifelong dietary DHA intervention slowed the aging phenotypes and profoundly attenuated telomere attrition in blood leukocytes and multiple tissues, consistent with decreased β-galactosidase activity and other senescence hallmarks with no observed sex differences. Notably, DHA intervention alleviated telomere attrition-induced γ-H2AX accumulation dependent on poly (ADP-ribose) polymerase 1 (PARP1) recruitment, and further regulated mitochondrial dysfunction critically involved in the DNA damage response. Together with the improvement of mitochondria function, the blocked reactive oxygen species (ROS) accumulation and suppression of the nuclear factor-κB (NF-κB)/nucleotide-binding domain-like receptor protein 3 (NLRP3)/caspase-1 pathways partially indicated anti-oxidative and anti-inflammatory effects of DHA. These data revealed a regulatory paradigm involving DHA in the telomere-DNA-mitochondria feedback loop mediated by DNA damage response and inflammation in alleviating senescence, which may hold potential as a translatable intervention in telomere-related diseases during aging.

The relationship between n-3 polyunsaturated fatty acids and telomere: A review on proposed nutritional treatment against metabolic syndrome and potential signaling pathways

Metabolic syndrome (MetS), a cluster of metabolic abnormalities composed of central obesity, elevated blood pressure, glucose disturbances, hypercholesterolemia and dyslipidaemia, has increasingly become a public health problem in the 21st century worldwide. The dysfunction of telomeres, the repetitive DNA with highly conserved sequences (5'-TTAGGG-3'), is remarkably correlated with organismal aging, even suggesting a causal relationship with metabolic disorders. The health benefits of n-3 polyunsaturated fatty acids (PUFAs) in multiple disorders are associated with telomere length in evidence, which have recently drawn wide attention. However, functional targets and pathways for the associations of n-3 PUFAs and telomere with MetS remain scare. Few studies have summarized the role of n-3 PUFAs in DNA damage repair pathways, anti-inflammatory pathways, and redox balance, linking with telomere biology, and other potential telomere-related signaling pathways. This review aims to (i) elucidate how n-3 PUFAs ameliorate telomere attrition in the context of anti-oxidation and anti-inflammation; (ii) unravel the role of n-3 PUFAs in modulating telomere-related neuron dysfunction and regulating the neuro-endocrine-immunological network in MetS; (iii) epidemiologically implicate the associations of metabolic disorders and n-3 PUFAs with telomere length; and (iv) suggest promising biochemical approaches and advancing methodologies to overcome the inter-variation problem helpful for future research.

NF-κB signalling pathways in nucleus pulposus cell function and intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is a common clinical degenerative disease of the spine. A series of factors, such as inflammation, oxidative stress and mechanical stress, promote degradation of the extracellular matrix (ECM) of the intervertebral discs (IVD), leading to dysfunction and structural destruction of the IVD. Nuclear factor-κB (NF-κB) transcription factor has long been regarded as a pathogenic factor of IDD. Therefore, NF-κB may be an ideal therapeutic target for IDD. As NF-κB is a multifunctional functional transcription factor with roles in a variety of biological processes, a comprehensive understanding of the function and regulatory mechanism of NF-κB in IDD pathology will be useful for the development of targeted therapeutic strategies for IDD, which can prevent the progression of IDD and reduce potential risks. This review discusses the role of the NF-κB signalling pathway in the nucleus pulposus (NP) in the process of IDD to understand pathological NP degeneration further and provide potential therapeutic targets that may interfere with NF-κB signalling for IDD therapy.

Age-related response to an acute innate immune challenge in mice: proteomics reveals a telomere maintenance-related cost

Ageing is characterized by the impairment of the acute innate immune response and the upregulation of low-grade inflammation, i.e. inflammaging. At the cellular level, telomeres are considered as a marker of biological ageing as their length is progressively eroded in the absence of repair mechanisms. However, the link between telomeres and inflammaging remains underexplored. We aimed to identify proteins that are differentially expressed between age classes in response to an acute inflammatory challenge. We challenged young (two months) and old (12 months) C57BL/6 mice using bacterial lipopolysaccharide (LPS) and measured telomere length and proteomic profiles in splenocytes. In total, 233 out of the 1966 proteins we quantified differed among experimental groups. A hierarchical clustering analysis revealed that nine of those 233 proteins were differently expressed among the experimental groups. Young mice responded to LPS by increasing the expression of proteins involved in the innate immune response, and interestingly, in telomere length maintenance. However, this regulation was impaired at older ages. These results are in agreement with the assumption that the strength of selection declines with age, potentially explaining the maintenance of costly, dysregulated, immune responses at old age. We suggest that the immune response is competing with the telomere maintenance process, highlighting how telomeres reflect the ageing trade-off even in a species where telomere length is not related to lifespan.

The Telomerase Complex Directly Controls Hematopoietic Stem Cell Differentiation and Senescence in an Induced Pluripotent Stem Cell Model of Telomeropathy

Telomeropathies are rare disorders associated with impaired telomere length control mechanisms that frequently result from genetic mutations in the telomerase complex. Dyskeratosis congenita is a congenital progressive telomeropathy in which mutation in the telomerase RNA component (TERC) impairs telomere maintenance leading to accelerated cellular senescence and clinical outcomes resembling premature aging. The most severe clinical feature is perturbed hematopoiesis and bone-marrow failure, but the underlying mechanisms are not fully understood. Here, we developed a model of telomerase function imbalance using shRNA to knockdown TERC expression in human induced pluripotent stem cells (iPSCs). We then promoted in vitro hematopoiesis in these cells to analyze the effects of TERC impairment. Reduced TERC expression impaired hematopoietic stem-cell (HSC) differentiation and increased the expression of cellular senescence markers and production of reactive oxygen species. Interestingly, telomere length was unaffected in shTERC knockdown iPSCs, leading to conclusion that the phenotype is controlled by non-telomeric functions of telomerase. We then assessed the effects of TERC-depletion in THP-1 myeloid cells and again observed reduced hematopoietic and myelopoietic differentiative potential. However, these cells exhibited impaired telomerase activity as verified by accelerated telomere shortening. shTERC-depleted iPSC-derived and THP-1-derived myeloid precursors had lower phagocytic capacity and increased ROS production, indicative of senescence. These findings were confirmed using a BIBR1532 TERT inhibitor, suggesting that these phenotypes are dependent on telomerase function but not directly linked to telomere length. These data provide a better understanding of the molecular processes driving the clinical signs of telomeropathies and identify novel roles of the telomerase complex other than regulating telomere length.

Chronic Inflammation in Immune Aging: Role of Pattern Recognition Receptor Crosstalk with the Telomere Complex?

Age-related decline in immunity is characterized by stem cell exhaustion, telomere shortening, and disruption of cell-to-cell communication, leading to increased patient risk of disease. Recent data have demonstrated that chronic inflammation exerts a strong influence on immune aging and is closely correlated with telomere length in a range of major pathologies. The current review discusses the impact of inflammation on immune aging, the likely molecular mediators of this process, and the various disease states that have been linked with immunosenescence. Emerging findings implicate NF-κB, the major driver of inflammatory signaling, in several processes that regulate telomere maintenance and/or telomerase activity. While prolonged triggering of pattern recognition receptors is now known to promote immunosenescence, it remains unclear how this process is linked with the telomere complex or telomerase activity. Indeed, enzymatic control of telomere length has been studied for many decades, but alternative roles of telomerase and potential influences on inflammatory responses are only now beginning to emerge. Crosstalk between these pathways may prove to be a key molecular mechanism of immunosenescence. Understanding how components of immune aging interact and modify host protection against pathogens and tumors will be essential for the design of new vaccines and therapies for a wide range of clinical scenarios.

Prolonged inflammatory microenvironment is crucial for pro-neoplastic growth and genome instability: a detailed review

INTRODUCTION

Chronic inflammation can affect the normal cell homeostasis and metabolism by rendering the cells susceptible to genomic instability that may lead to uncontrolled cellular growth and proliferation ensuing tumorigenesis. The causal agents for inflammation may be pathogenic infections like microbial agents ranging from viruses to bacteria. These infections lead to DNA damage or disruption of normal cell metabolism and alter the genome integrity.

FINDINGS

In this review, we have highlighted the role of recurrent infections in tumor microenvironment can lead to recruitment of pro-inflammatory cells, cytokines and growth factors to the site of inflammation. This makes the environment rich in cytokines, chemokines, DNA-damaging agents (ROS, RNS) and growth factors which activate DNA damage response pathway and help in sustained proliferation of the tumor cells. In any inflammatory response, the production of cytokines and related signaling molecules is self-regulating and limiting. But in case of neoplastic risk, deregulation of these factors may lead to abnormalities and related pathogenesis.

CONCLUSION

The scope of the present review is to explore the probable mechanistic link and factors responsible for chronic inflammation. The relation between chronic inflammation and DNA damage response was further elucidated to understand the mechanism by which it makes the cells susceptible to carcinogenesis.

Telomeric repeat-containing RNA (TERRA) constitutes a nucleoprotein component of extracellular inflammatory exosomes

Telomeric repeat-containing RNA (TERRA) has been identified as a telomere-associated regulator of chromosome end protection. Here, we report that TERRA can also be found in extracellular fractions that stimulate innate immune signaling. We identified extracellular forms of TERRA in mouse tumor and embryonic brain tissue, as well as in human tissue culture cell lines using RNA in situ hybridization. RNA-seq analyses revealed TERRA to be among the most highly represented transcripts in extracellular fractions derived from both normal and cancer patient blood plasma. Cell-free TERRA (cfTERRA) could be isolated from the exosome fractions derived from human lymphoblastoid cell line (LCL) culture media. cfTERRA is a shorter form (∼200 nt) of cellular TERRA and copurifies with CD63- and CD83-positive exosome vesicles that could be visualized by cyro-electron microscopy. These fractions were also enriched for histone proteins that physically associate with TERRA in extracellular ChIP assays. Incubation of cfTERRA-containing exosomes with peripheral blood mononuclear cells stimulated transcription of several inflammatory cytokine genes, including TNFα, IL6, and C-X-C chemokine 10 (CXCL10) Exosomes engineered with elevated TERRA or liposomes with synthetic TERRA further stimulated inflammatory cytokines, suggesting that exosome-associated TERRA augments innate immune signaling. These findings imply a previously unidentified extrinsic function for TERRA and a mechanism of communication between telomeres and innate immune signals in tissue and tumor microenvironments.

Late-occurring chromosome aberrations and global DNA methylation in hematopoietic stem/progenitor cells of CBA/CaJ mice exposed to silicon ((28)Si) ions

Although myeloid leukemia (ML) is one of the major health concerns from exposure to space radiation, the risk prediction for developing ML is unsatisfactory. To increase the reliability of predicting ML risk, a much improved understanding of space radiation-induced changes in the target cells, i.e. hematopoietic stem/progenitor cells (HSPCs), is important. We focused on the in vivo induction of late-occurring damage in HSPCs of mice exposed to (28)Si ions since such damage is associated with radiation-induced genomic instability (a key event of carcinogenesis). We gave adult male CBA/CaJ mice, known to be sensitive to radiation-induced ML, a whole-body exposure (2 fractionated exposures, 15 days apart, that totaled each selected dose, delivered at the dose-rate of 1 cGy/min) to various doses of 300 MeV/n (28)Si ions, i.e. 0 (sham controls), 0.1, 0.25, or 0.5 Gy. At 6 months post-irradiation, we collected bone marrow cells from each mouse (five mice per treatment-group) for obtaining the myeloid-lineage of HSPC-derived clones for analyses. We measured the frequencies of late-occurring chromosome aberrations (CAs), using the genome-wide multicolor fluorescence in situ hybridization method. The measurement of CAs was coupled with the characterization of the global DNA methylation patterns, i.e. 5-methylcytosine (5 mC) and 5-hydroxymethylcytosine (5 hmC). A dose-dependent increase in the frequencies of CAs was detected (Analysis of Variance or ANOVA, p<0.01), indicating the induction of genomic instability after exposure of mice to 300 MeV/n (28)Si ions. Slight increases in the levels of 5 mC were observed in all treatment groups, as compared to the sham-control level. In contrast, there was a significant reduction in levels of 5 hmC (ANOVA, p<0.01). Since these endpoints were evaluated in the same mouse, our data suggested for the first time a link between a reduction in 5 hmC and genomic instability in HSPC-derived myeloid colonies of CBA/CaJ mice exposed to 300 MeV/n (28)Si ions.

Cross Cancer Genomic Investigation of Inflammation Pathway for Five Common Cancers: Lung, Ovary, Prostate, Breast, and Colorectal Cancer

BACKGROUND

Inflammation has been hypothesized to increase the risk of cancer development as an initiator or promoter, yet no large-scale study of inherited variation across cancer sites has been conducted.

METHODS

We conducted a cross-cancer genomic analysis for the inflammation pathway based on 48 genome-wide association studies within the National Cancer Institute GAME-ON Network across five common cancer sites, with a total of 64 591 cancer patients and 74 467 control patients. Subset-based meta-analysis was used to account for possible disease heterogeneity, and hierarchical modeling was employed to estimate the effect of the subcomponents within the inflammation pathway. The network was visualized by enrichment map. All statistical tests were two-sided.

RESULTS

We identified three pleiotropic loci within the inflammation pathway, including one novel locus in Ch12q24 encoding SH2B3 (rs3184504), which reached GWAS significance with a P value of 1.78 x 10(-8), and it showed an association with lung cancer (P = 2.01 x 10(-6)), colorectal cancer (GECCO P = 6.72x10(-6); CORECT P = 3.32x10(-5)), and breast cancer (P = .009). We also identified five key subpathway components with genetic variants that are relevant for the risk of these five cancer sites: inflammatory response for colorectal cancer (P = .006), inflammation related cell cycle gene for lung cancer (P = 1.35x10(-6)), and activation of immune response for ovarian cancer (P = .009). In addition, sequence variations in immune system development played a role in breast cancer etiology (P = .001) and innate immune response was involved in the risk of both colorectal (P = .022) and ovarian cancer (P = .003).

CONCLUSIONS

Genetic variations in inflammation and its related subpathway components are keys to the development of lung, colorectal, ovary, and breast cancer, including SH2B3, which is associated with lung, colorectal, and breast cancer.

The effect of environmental chemicals on the tumor microenvironment

Potentially carcinogenic compounds may cause cancer through direct DNA damage or through indirect cellular or physiological effects. To study possible carcinogens, the fields of endocrinology, genetics, epigenetics, medicine, environmental health, toxicology, pharmacology and oncology must be considered. Disruptive chemicals may also contribute to multiple stages of tumor development through effects on the tumor microenvironment. In turn, the tumor microenvironment consists of a complex interaction among blood vessels that feed the tumor, the extracellular matrix that provides structural and biochemical support, signaling molecules that send messages and soluble factors such as cytokines. The tumor microenvironment also consists of many host cellular effectors including multipotent stromal cells/mesenchymal stem cells, fibroblasts, endothelial cell precursors, antigen-presenting cells, lymphocytes and innate immune cells. Carcinogens can influence the tumor microenvironment through effects on epithelial cells, the most common origin of cancer, as well as on stromal cells, extracellular matrix components and immune cells. Here, we review how environmental exposures can perturb the tumor microenvironment. We suggest a role for disrupting chemicals such as nickel chloride, Bisphenol A, butyltins, methylmercury and paraquat as well as more traditional carcinogens, such as radiation, and pharmaceuticals, such as diabetes medications, in the disruption of the tumor microenvironment. Further studies interrogating the role of chemicals and their mixtures in dose-dependent effects on the tumor microenvironment could have important general mechanistic implications for the etiology and prevention of tumorigenesis.

Effects of four chemotherapeutic agents, bleomycin, etoposide, cisplatin, and cyclophosphamide, on DNA damage and telomeres in a mouse spermatogonial cell line

Treatment with chemotherapeutics agents may induce persistent DNA damage in male germ cells with the possibility of long-term consequences on fertility and progeny outcome. Telomeres, specialized structures at the physical ends of chromosomes, play an important role in the maintenance of genetic stability and in the response of somatic cells to anticancer drugs. Our objective was to test the hypothesis that exposure to bleomycin, etoposide, or cisplatin (the drugs used to treat testicular cancer) or cyclophosphamide (an anticancer agent and immunosuppressant) targets telomeres in the male germ line. C18-4 spermatogonial cells were exposed to bleomycin, etoposide, cisplatin, or 4-hydroperoxycyclophosphamide (4OOH-CPA, a preactivated analog of cyclophosphamide). All four anticancer drugs induced a significant increase in DNA damage in C18-4 cells, as assessed by gamma-H2AX immunofluorescence. Interestingly, the gamma-H2AX signal was localized to telomeres after treatment with bleomycin, cisplatin, and 4OOH-CPA, but not etoposide. Mean telomere lengths, the intensity of the telomere fluorescence in situ hybridization signal, telomerase activity, and the expression of the telomerase enzyme mRNA components, Tert and Terc, were reduced by exposure to cisplatin and 4OOH-CPA, but not by bleomycin or etoposide. Thus, although all four anticancer drugs induced DNA damage in this spermatogonial cell line, telomeres were not specifically affected by etoposide and only the two alkylating agents, cisplatin and 4OOH-CPA, induced telomere dysfunction. This telomere dysfunction may contribute to infertility and developmental defects in the offspring.

Deciphering the structure and function of FcεRI/mast cell axis in the regulation of allergy and anaphylaxis: a functional genomics paradigm

Allergy and anaphylaxis are inflammatory disorders caused by immune reactions mainly induced by immunoglobulin-E that signal through the high-affinity FcεRI receptor to release the inflammatory mediators from innate immune cells. The FcεRI/mast cell axis is potently involved in triggering various intracellular signaling molecules to induce calcium release from the internal stores, induction of transcription factors such as NF-kB, secretion of various cytokines as well as lipid mediators, and degranulation, resulting in the induction of allergy and anaphylaxis. In this review, we discuss various cellular and molecular mechanisms triggered through FcεRI/mast cell axis in allergy and anaphylaxis with a special emphasis on the functional genomics paradigm.

Physical activity and telomere biology: exploring the link with aging-related disease prevention

Physical activity is associated with reduced risk of several age-related diseases as well as with increased longevity in both rodents and humans. Though these associations are well established, evidence of the molecular and cellular factors associated with reduced disease risk and increased longevity resulting from physical activity is sparse. A long-standing hypothesis of aging is the telomere hypothesis: as a cell divides, telomeres shorten resulting eventually in replicative senescence and an aged phenotype. Several reports have recently associated telomeres and telomere-related proteins to diseases associated with physical inactivity and aging including cardiovascular disease, insulin resistance, and hypertension. Interestingly several reports have also shown that longer telomeres are associated with higher physical activity levels, indicating a potential mechanistic link between physical activity, reduced age-related disease risk, and longevity. The primary purpose of this review is to discuss the potential importance of physical activity in telomere biology in the context of inactivity- and age-related diseases. A secondary purpose is to explore potential mechanisms and important avenues for future research in the field of telomeres and diseases associated with physical inactivity and aging.