Telomerase and telomere biology in hematological diseases: A new therapeutic target

Telomere biology disorders: from dyskeratosis congenita and beyond

Defective telomerase function or telomere maintenance causes genomic instability. Alterations in telomere length and/or attrition are the primary features of rare diseases known as telomere biology disorders or telomeropathies. Recent advances in the molecular basis of these disorders and cutting-edge methods assessing telomere length have increased our understanding of this topic. Multiorgan manifestations and different phenotypes have been reported even in carriers within the same family. In this context, apart from dyskeratosis congenita, disorders formerly considered idiopathic (i.e. pulmonary fibrosis, liver cirrhosis) frequently correlate with underlying defective telomere maintenance mechanisms. Moreover, these patients are prone to developing specific cancer types and exhibit exceptional sensitivity and toxicity in standard chemotherapy regimens. The current review describes the diverse spectrum of clinical manifestations of telomere biology disorders in pediatric and adult patients, their correlation with pathogenic variants, and considerations during their management to increase awareness and improve a multidisciplinary approach.

Telomere biology: from disorders to hematological diseases

Variations in the length of telomeres and pathogenic variants involved in telomere length maintenance have been correlated with several human diseases. Recent breakthroughs in telomere biology knowledge have contributed to the identification of illnesses named "telomeropathies" and revealed an association between telomere length and disease outcome. This review emphasizes the biology and physiology aspects of telomeres and describes prototype diseases in which telomeres are implicated in their pathophysiology. We also provide information on the role of telomeres in hematological diseases ranging from bone marrow failure syndromes to acute and chronic leukemias.

Novel Biomarkers for Diagnosis and Monitoring of Immune Thrombocytopenia

Lower-than-normal platelet counts are a hallmark of the acquired autoimmune illness known as immune thrombocytopenia, which can affect both adults and children. Immune thrombocytopenia patients' care has evolved significantly in recent years, but the disease's diagnosis has not, and it is still only clinically achievable with the elimination of other causes of thrombocytopenia. The lack of a valid biomarker or gold-standard diagnostic test, despite ongoing efforts to find one, adds to the high rate of disease misdiagnosis. However, in recent years, several studies have helped to elucidate a number of features of the disease's etiology, highlighting how the platelet loss is not only caused by an increase in peripheral platelet destruction but also involves a number of humoral and cellular immune system effectors. This made it possible to identify the role of immune-activating substances such cytokines and chemokines, complement, non-coding genetic material, the microbiome, and gene mutations. Furthermore, platelet and megakaryocyte immaturity indices have been emphasized as new disease markers, and prognostic signs and responses to particular types of therapy have been suggested. Our review's goal was to compile information from the literature on novel immune thrombocytopenia biomarkers, markers that will help us improve the management of these patients.

Spotlight on hTERT Complex Regulation in Cutaneous T-Cell Lymphomas

As a major cancer hallmark, there is a sustained interest in understanding the telomerase contribution to carcinogenesis in order to therapeutically target this enzyme. This is particularly relevant in primary cutaneous T-cell lymphomas (CTCL), a malignancy showing telomerase dysregulation with few investigative data available. In CTCL, we examined the mechanisms involved in telomerase transcriptional activation and activity regulation. We analyzed 94 CTCL patients from a Franco-Portuguese cohort, as well as 8 cell lines, in comparison to 101 healthy controls. Our results showed that not only polymorphisms (SNPs) located at the promoter of human telomerase reverse transcriptase (hTERT) gene (rs2735940 and rs2853672) but also an SNP located within the coding region (rs2853676) could influence CTCL occurrence. Furthermore, our results sustained that the post-transcriptional regulation of hTERT contributes to CTCL lymphomagenesis. Indeed, CTCL cells present a different pattern of hTERT spliced transcripts distribution from the controls, mostly marked by an increase in the hTERT β+ variants proportion. This increase seems to be associated with CTCL development and progression. Through hTERT splicing transcriptome modulation with shRNAs, we observed that the decrease in the α-β+ transcript induced a decrease in the cell proliferation and tumorigenic capacities of T-MF cells in vitro. Taken together, our data highlight the major role of post-transcriptional mechanisms regulating telomerase non canonical functions in CTCL and suggest a new potential role for the α-β+ hTERT transcript variant.

Transcriptomic Analysis of Conserved Telomere Maintenance Component 1 (CTC1) and Its Association with Leukemia

Telomere length (TEL) regulation is important for genome stability and is governed by the coordinated role of shelterin proteins, telomerase (TERT), and CST (CTC1/OBFC1/TEN1) complex. Previous studies have shown the association of telomerase expression with the risk of acute lymphoblastic leukemia (ALL). However, no data are available for CST association with the ALL. The current pilot study was designed to evaluate the CST expression levels in ALL. In total, 350 subjects were recruited, including 250 ALL cases and 100 controls. The subjects were stratified by age and categorized into pediatrics (1–18 years) and adults (19–54 years). TEL and expression patterns of CTC1, OBFC1, and TERT genes were determined by qPCR. The univariable logistic regression analysis was performed to determine the association of gene expression with ALL, and the results were adjusted for age and sex in multivariable analyses. Pediatric and adult cases did not reflect any change in telomere lengths relative to controls. However, expression of CTC1, OBFC1, and TERT genes were induced among ALL cases. Multivariable logistic regression analyses showed association of CTC1 with ALL in pediatric [β estimate (standard error (SE)= −0.013 (0.007), p = 0.049, and adults [0.053 (0.023), p = 0.025]. The association of CTC1 remained significant when taken together with OBFC1 and TERT in a multivariable model. Furthermore, CTC1 showed significant association with B-cell ALL [−0.057(0.017), p = 0.002) and T-cell ALL [−0.050 (0.018), p = 0.008] in pediatric group while no such association was noted in adults. Together, our findings demonstrated that telomere modulating genes, particularly CTC1, are strongly associated with ALL. Therefore, CTC1 can potentially be used as a risk biomarker for the identification of ALL in both pediatrics and adults.

Telomerase-based therapies in haematological malignancies

Telomeres are specialized genetic structures present at the end of all eukaryotic linear chromosomes. They progressively get shortened after each cell division due to end replication problems. Telomere shortening (TS) and chromosomal instability cause apoptosis and massive cell death. Following oncogene activation and inactivation of tumour suppressor genes, cells acquire mechanisms such as telomerase expression and alternative lengthening of telomeres to maintain telomere length (TL) and prevent initiation of cellular senescence or apoptosis. Significant TS, telomerase activation and alteration in expression of telomere-associated proteins are frequent features of different haematological malignancies that reflect on the progression, response to therapy and recurrence of these diseases. Telomerase is a ribonucleoprotein enzyme that has a pivotal role in maintaining the TL. However, telomerase activity in most somatic cells is insufficient to prevent TS. In 85-90% of tumour cells, the critically short telomeric length is maintained by telomerase activation. Thus, overexpression of telomerase in most tumour cells is a potential target for cancer therapy. In this review, alteration of telomeres, telomerase and telomere-associated proteins in different haematological malignancies and related telomerase-based therapies are discussed.

Bone marrow-derived mesenchymal stem/stromal cells in patients with acute myeloid leukemia reveal transcriptome alterations and deficiency in cellular vitality

Background

State-of-the-art advances have indicated the pivotal characteristics of bone marrow-derived mesenchymal stem/stromal cells (BM-MSCs) in hematopoietic microenvironment as well as coordinate contribution to hematological malignancies. However, the panoramic view and detailed dissection of BM-MSCs in patients with acute myeloid leukemia (AML-MSCs) remain obscure.

Methods

For the purpose, we isolated and identified AML-MSCs together with healthy donor-derived HD-MSCs from the bone marrow mononuclear cells (BM-MNCs) by using the standard density gradient centrifugation based on clinical diagnosis and cellular phenotypic analysis. Subsequently, we systematically compared the potential similarities and discrepancy both at the cellular and molecular levels via flow cytometry, multilineage differentiation, chromosome karyotyping, cytokine quantification, and transcriptome sequencing and bioinformatic analysis including single-nucleotide polymorphism (SNP), gene ontology (GO), HeatMap, principal component analysis (PCA), Kyoto Encyclopedia of Genes and Genomes (KEGG), and gene set enrichment analysis (GSEA).

Results

On the one hand, AML-MSCs exhibited undistinguishable signatures in cytomorphology, surface biomarker expression pattern, stemness, chromosome karyotype, and chondrogenesis as HD-MSCs, whereas with impaired adipogenesis, enhanced osteogenesis, and variations in cytokine expression pattern. On the other hand, with the aid of genomic and bioinformatic analyses, we verified that AML-MSCs displayed multidimensional discrepancy with HD-MSCs both in genome-wide gene expression profiling and genetic variation spectrum. Simultaneously, the deficiency of cellular vitality including proliferation and apoptosis in AML-MSCs was largely rescued by JAK-STAT signaling inhibition.

Conclusions

Overall, our findings elucidated that AML-MSCs manifested multifaceted alterations in biological signatures and molecular genetics, and in particular, the deficiency of cellular vitality ascribed to over-activation of JAK-STAT signal, which collectively provided systematic and overwhelming new evidence for decoding the pathogenesis of AML and exploring therapeutic strategies in future.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02444-0.

Association of telomere length and telomerase methylation with n-3 fatty acids in preschool children with obesity

BACKGROUND

Telomeres play a crucial role in cellular survival and its length is a predictor for onset of chronic non-communicable diseases. Studies on association between telomeres and obesity in children have brought discrepant results and the underlying mechanisms and influential factors are to be elucidated. This study aimed to investigate changes in telomere length and telomerase reverse transcriptase (TERT) DNA methylation, and further to determine their correlation with n-3 polyunsaturated fatty acids (PUFAs) in preschool children with obesity.

METHODS

Forty-six preschool children with obesity aged 3 to 4 years were included in the study, with equal numbers of age- and gender-matched children with normal weight as control. Leukocyte telomere length was determined by the ratio of telomeric product and single copy gene obtained using real-time qPCR. DNA methylation of TERT promoter was analyzed by bisulfite sequencing. Fatty acids in erythrocytes were measured by gas chromatography with a total of 15 fatty acids analyzed. The total saturated fatty acids (SFAs), total n-6 PUFAs, total n-3 PUFAs, and the ratio of arachidonic acid (AA) to docosahexaenoic acid (DHA) were calculated. Then the correlation between leukocyte telomere length, TERT promoter methylation and fatty acids was determined.

RESULTS

In preschool children with obesity, leukocyte telomeres were shortened and had a negative association with the body mass index. The methylated fractions in 13 of 25 CpG sites in the TERT promoter were increased by approximately 3 to 35% in the children with obesity compared to the normal weight children. Erythrocyte lauric acid and total SFAs, lenoleic acid and total n-6 PUFAs were higher, and DHA was lower in the children with obesity than those in the children with normal weight. Correlative analysis showed that leukocyte telomere length had a positive association with total SFAs and DHA, and a negative association with the AA/DHA ratio. However, no association between erythrocyte DHA and the TERT promoter methylation was found.

CONCLUSION

These data indicate that the reduced body DHA content and increased AA/DHA ratio may be associated with shortened leukocyte telomeres in child obesity, which is probably not involved in the TERT promoter methylation.

Clinical Relevance of Alternative Lengthening of Telomeres in Cancer

The alternative lengthening of telomere (ALT) is a pathway responsible for cell immortalization in some kinds of tumors. Since the first description of ALT is relatively recent in the oncology field, its mechanism remains elusive, but recent works address ALT-related proteins or cellular structures as potential druggable targets for more specific and efficient antitumor therapies. Moreover, some new generation compounds for antitelomerase therapy in cancer were able to provoke acquisition of ALT phenotype in treated tumors, enhancing the importance of studies on this alternative lengthening of the telomere. However, ALT has been implicated in different - sometimes opposite - outcomes, according to the tumor type studied. Then, in order to design and develop new drugs for ALT+ cancer in an effective way, it is crucial to understand its clinical implications. In this review, we gathered works published in the last two decades to highlight the clinical relevance of ALT on oncology.

Oncolytic Viruses and Hematological Malignancies: A New Class of Immunotherapy Drugs

The use of viruses for tumour treatment has been imagined more than one hundred years ago, when it was reported that viral diseases were occasionally leading to a decrease in neoplastic lesions. Oncolytic viruses (OVs) seem to have a specific tropism for tumour cells. Previously, it was hypothesised that OVs’ antineoplastic actions were mainly due to their ability to contaminate, proliferate and destroy tumour cells and the immediate destructive effect on cells was believed to be the single mechanism of action of OVs’ action. Instead, it has been established that oncolytic viruses operate via a multiplicity of systems, including mutation of tumour milieu and a composite change of the activity of immune effectors. Oncolytic viruses redesign the tumour environment towards an antitumour milieu. The aim of our work is to evaluate the findings present in the literature about the use of OVs in the cure of haematological neoplastic pathologies such as multiple myeloma, acute and chronic myeloid leukaemia, and lymphoproliferative diseases. Further experimentations are essential to recognize the most efficient virus or treatment combinations for specific haematological diseases, and the combinations able to induce the strongest immune response.

Telomere Length and Hematological Disorders: A Review

Telomeres compose the end portions of human chromosomes, and their main function is to protect the genome. In hematological disorders, telomeres are shortened, predisposing to genetic instability that may cause DNA damage and chromosomal rearrangements, inducing a poor clinical outcome. Studies from 2010 to 2019 were compiled and experimental studies using samples of patients diagnosed with hematological malignancies that reported the size of the telomeres were described. Abnormal telomere shortening is described in cancer, but in hematological neoplasms, telomeres are still shortened even after telomerase reactivation. In this study, we compared the sizes of telomeres in leukemias, myelodysplastic syndrome and lymphomas, identifying that the smallest telomeres are present in patients at relapse. In conclusion, the experimental and clinical data analyzed in this review demonstrate that excessive telomere shortening is present in major hematological malignancies and its analysis and measurement is a crucial step in determining patient prognosis, predicting disease risk and assisting in the decision for targeted therapeutic strategies.

Heterogeneity of telomerase reverse transcriptase mutation and expression, telomerase activity and telomere length across human cancer cell lines cultured in vitro

Promoter region of the telomerase reverse transcriptase gene (TERTp) constitutes a regulatory element capable to affect TERT expression (TE), telomerase activity (TA) and telomere length (TL). TERTp mutation status, TL, TA and TE were assessed in 27 in vitro cultured human cell lines, including 11 solid tumour, 13 haematological and 3 normal cell lines. C228T and C250T TERTp mutations were detected in 5 solid tumour and none of haematological cell lines (p = 0.0100). As compared to other solid tumour cell lines, those with the presence of somatic mutations were characterized by: shorter TL, lower TA and TE. Furthermore, cell lines carrying TERTp mutations showed a linear correlation between TE and TA (R = 0.9708, p = 0.0021). Moreover, haematological cell lines exhibited higher TE compared to solid tumour cell lines (p = 0.0007). TL and TA were correlated in both solid tumour (R = 0.4875, p = 0.0169) and haematological (R = 0.4719, p = 0.0095) cell lines. Our results based on the in vitro model suggest that oncogenic processes may differ between solid tumours and haematological malignancies with regard to their TERT gene regulation mechanisms.

Short-term treatment with imetelstat sensitizes hematopoietic malignant cells to a genotoxic agent via suppression of the telomerase-mediated DNA repair process

Imetelstat is a specific and competitive inhibitor of telomerase enzymatic activity. We demonstrated that imetelstat could interfere with the DNA repair process and enhance the effect of DNA damaging agents using hematological tumor cell lines. Short-term administration of imetelstat enhanced growth suppression by anticancer agents and radiation. It also upregulated γH2AX expression induced by irradiation. Immunofluorescence staining showed that both human telomerase reverse transcriptase (hTERT) and γH2AX were upregulated and co-localized in the nucleus of peripheral blood mononuclear cells after irradiation, suggesting that hTERT was involved in the DNA-DSB repair process. Imetelstat enhanced growth inhibitory effect of cytotoxic agents in short-term culture without shortening of telomeres, indicating that this effect was attributed by telomere length independent mechanism. Our results suggest that the combination of short-term treatment with imetelstat and cytotoxic agent is a promising strategy to treat a wide variety of hematopoietic malignancies.

Nanomedicines: A Potential Treatment for Blood Disorder Diseases

Blood disorder diseases (BDDs), also known as hematologic, is one of the diseases owing to hematopoietic system disorder. Chemotherapy, bone marrow transplantation, and stem cells therapy have been used to treat BDDs. However, the cure rates are still low due to the availability of the right type of bone marrow and the likelihood of recurrence and infection. With the rapid development of nanotechnology in the field of biomedicine, artificial blood or blood substitute has shown promising features for the emergency treatment of BDDs. Herein, we surveyed recent advances in the development of artificial blood components: gas carrier components (erythrocyte substitutes), immune response components (white blood cell substitutes), and hemostasis-responsive components (platelet substitutes). Platelet-inspired nanomedicines for cancer treatment were also discussed. The challenges and prospects of these treatment options in future nanomedicine development are discussed.

Saffron inhibits the proliferation of hepatocellular carcinoma via inducing cell apoptosis

BACKGROUND

Liver cancer remains the third leading cause of cancer-related mortality worldwide. The aim of this study was to explore the effect of saffron on liver cancer cell line QGY-7703 and the underlying molecular mechanism.

METHODS

Cell growth was detected by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay and cell cycle was assessed by flow cytometry. Besides, cell apoptosis was analyzed by Annexin V/PI (Propidium Iodide) staining, and the senescent cells morphology staining of β-galactosidase was evaluated by microscopy. In addition, ELISA (enzyme-linked immunosorbent assay) Kit was used to assess the activity of telomerase. Moreover, reverse transcription-PCR (polymerase chain reaction) and Western blot analysis was applied to detect mRNA and protein expression levels, respectively.

RESULTS

Saffron treatment in QGY-7703 cells could significantly inhibit cell growth, arrest cell cycle in the G0/G1 phase, and induce cell apoptosis. Besides, the treatment of saffron could obviously decrease telomerase activity and hTERT level in QGY-7703 cells. In addition, enhanced Bax/Bcl-2 ratio and increased expression of P21 were found in saffron-treated cells. Moreover, we found that the number of senescent cells increased dramatically and the morphology of cells changed obviously after saffron treatment.

CONCLUSIONS

Saffron administration may provide some experimental evidence for the inhibitory effect of saffron on the proliferation of QGY-7703 cells, suggesting that saffron may have potential utility for the treatment of liver cancer.

Telomere shortening in breast cancer cells (MCF7) under treatment with low doses of the benzylisoquinoline alkaloid chelidonine

Telomeres, the specialized dynamic structures at chromosome ends, regularly shrink with every replication. Thus, they function as an internal molecular clock counting down the number of cell divisions. However, most cancer cells escape this limitation by activating telomerase, which can maintain telomere length. Previous studies showed that the benzylisoquinoline alkaloid chelidonine stimulates multiple modes of cell death and strongly down-regulates telomerase. It is still unknown if down-regulation of telomerase by chelidonine boosts substantial telomere shortening. The breast cancer cell line MCF7 was sequentially treated with very low concentrations of chelidonine over several cell passages. Telomere length and telomerase activity were measured by a monochrome multiplex quantitative PCR and a q-TRAP assay, respectively. Changes in population size and doubling time correlated well with telomerase inhibition and telomere shortening. MCF7 cell growth was arrested completely after three sequential treatments with 0.1 μM chelidonine, each ending after 48 h, while telomere length was reduced to almost 10% of the untreated control. However, treatment with 0.01 μM chelidonine did not have any apparent consequence. In addition to dose and time dependent telomerase inhibition, chelidonine changed the splicing pattern of hTERT towards non-enzyme coding isoforms of the transcript. In conclusion, telomere length and telomere stability are strongly affected by chelidonine in addition to microtubule formation.

Activated carbon N-acetylcysteine microcapsule protects against nonalcoholic fatty liver disease in young rats via activating telomerase and inhibiting apoptosis

Non-alcoholic fatty liver disease (NAFLD) is becoming one of the world's most common chronic liver diseases in childhood, yet no therapy is available that has been approved by the food and drug administration (FDA). Previous studies have reported that telomere and telomerase are involved the development and progression of NAFLD. This study was designed to investigate the potential beneficial effects of activated carbon N-acetylcysteine (ACNAC) microcapsules on the development of NAFLD in young rats as well as the underlying mechanism(s) involved. Three-week old male Sprague Dawley rats were given high-fat diet (HFD) with/without ACNAC treatment for 7 consecutive weeks. Liver pathologies were determined by hematoxylin and eosin (H&E) and Oil Red O staining, as well as by changes in biochemical parameters of plasma alanine transaminase (ALT) and aspartate transaminase (AST) levels, respectively. Glucose homeostasis was evaluated by the glucose tolerance test and the liver telomere length and activity were measured by real time PCR and telomeric repeat amplification protocol (TRAP). Western blot analysis was performed to determine the expression level of Bcl-2, Bax and Caspase-3. Our results demonstrated that ACNAC supplementation improved liver pathologies of rats that received long-term HFD feeding. ACNAC supplementation prevented HFD-induced telomere shortening and improved telomerase activity. Moreover, in comparison to HFD-fed rats, ACNAC supplementation markedly increased the expression of Bcl-2, but significantly decreased the expression of Bax and Caspase-3 in juvenile rats. Together, these results indicate that ACNAC may be a promising choice for preventing and treating NAFLD among children.

Dual roles of TRF1 in tethering telomeres to the nuclear envelope and protecting them from fusion during meiosis

Telomeres integrity is indispensable for chromosomal stability by preventing chromosome erosion and end-to-end fusions. During meiosis, telomeres attach to the inner nuclear envelope and cluster into a highly crowded microenvironment at the bouquet stage, which requires specific mechanisms to protect the telomeres from fusion. Here, we demonstrate that germ cell-specific knockout of a shelterin complex subunit, Trf1, results in arrest of spermatocytes at two different stages. The obliterated telomere-nuclear envelope attachment in Trf1-deficient spermatocytes impairs homologue synapsis and recombination, resulting in a pachytene-like arrest, while the meiotic division arrest might stem from chromosome end-to-end fusion due to the failure of recruiting meiosis specific telomere associated proteins. Further investigations uncovered that TRF1 could directly interact with Speedy A, and Speedy A might work as a scaffold protein to further recruit Cdk2, thus protecting telomeres from fusion at this stage. Together, our results reveal a novel mechanism of TRF1, Speedy A, and Cdk2 in protecting telomere from fusion in a highly crowded microenvironment during meiosis.