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Telomeres are terminal protective chromosome structures. Genetic variants in genes coding for proteins required for telomere maintenance cause rare, life-threatening Telomere Biology Disorders (TBDs) such as dyskeratosis congenita, aplastic anemia or pulmonary fibrosis. The more frequently used mice strains have telomeres much longer than the human ones which question their use as in vivo models for TBDs. One mice model with shorter telomeres based on the CAST/EiJ mouse strain carrying a mutation in the Terc gene, coding for the telomerase RNA component, has been studied in comparison with C57BL/6J mice, carrying the same mutation and long telomeres. The possible alterations produced in lungs and the haematopoietic system, frequently affected in TBD patients, were determined at different ages of the mice. Homozygous mutant mice presented a very shortened life span, more notorious in the short-telomeres CAST/EiJ strain. The lungs of mutant mice presented a transitory increase in fibrosis and a significant decrease in the relative amount of the alveolar epithelial type 2 cells from six months of age. This decrease was larger in mutant homozygous animals but was also observed in heterozygous animals. On the contrary the expression of the senescence-related protein P21 increased from six months of age in mutant mice of both strains. The analysis of the haematopoietic system indicated a decrease in the number of megakaryocyte-erythroid progenitors in homozygous mutants and an increase in the clonogenic potential of bone marrow and LSK cells. Bone marrow cells from homozygous mutant animals presented decreasing in vitro expansion capacity. The alterations observed are compatible with precocious ageing of lung alveolar cells and the bone marrow cells that correlate with the alterations observed in TBD patients. The alterations seem to be more related to the genotype of the animals that to the basal telomere length of the strains although they are more pronounced in the short-telomere CAST/EiJ-derived strain than in C57BL/6J animals. Therefore, both animal models, at ages over 6–8 months, could represent valuable and convenient models for the study of TBDs and for the assay of new therapeutic products.

Accumulating evidence suggests that mitogenic signaling during cell cycle arrest can lead to severe cytotoxic outcomes, such as senescence, though the underlying mechanisms remain poorly understood. Here, we explored the link between cell cycle dynamics and the formation of PML-nuclear bodies (PML-NBs), intranuclear structures known to mediate cellular stress responses. Our findings demonstrate that PML-NBs increase their number during interphase arrest. Moreover, the activation of mitogenic ERK signaling by all-trans retinoic acid (ATRA) during CDK4/6 inhibitor-induced cell cycle arrest synergistically enhances the formation of larger PML-NBs by associating with SUMO. This enlargement, triggered by the simultaneous engagement of opposing cell cycle signals, leads to potent cytotoxicity accompanied by either terminal differentiation or apoptosis, depending on the cell type, across multiple acute myeloid leukemia (AML) cell lines. Importantly, in an AML mouse model, this combination treatment significantly improved therapeutic efficacy with minimal effects on normal hematopoiesis. Our results introduce conflicting cell cycle signal-induced cytotoxicity as a promising therapeutic strategy for AML. Subject terms: PML bodies, Apoptosis

Accumulating evidence indicates that various oncogenic mutations interfere with normal myeloid differentiation of leukemogenic cells during the early process of acute myeloid leukemia (AML) development. Differentiation therapy is a therapeutic strategy capable of terminating leukemic expansion by reactivating the differentiation potential; however, the plasticity and instability of leukemia cells counteract the establishment of treatments aimed at irreversibly inducing and maintaining their differentiation states. On the basis of our previous observation that autophagy inhibitor treatment induces the accumulation of cytosolic DNA and activation of cytosolic DNA-sensor signaling selectively in leukemia cells, we herein examined the synergistic effect of cytosolic DNA-sensor signaling activation with conventional differentiation therapy on AML. The combined treatment succeeded in inducing irreversible differentiation in AML cell lines. Mechanistically, cytosolic DNA was sensed by absent in melanoma 2 (AIM2), a cytosolic DNA sensor. Activation of the AIM2 inflammasome resulted in the accumulation of p21 through the inhibition of its proteasomal degradation, thereby facilitating the myeloid differentiation. Importantly, the combined therapy dramatically reduced the total leukemia cell counts and proportion of blast cells in the spleens of AML mice. Collectively, these findings indicate that the autophagy inhibition-cytosolic DNA-sensor signaling axis can potentiate AML differentiation therapy. Clinical effects on AML therapy are closely associated with reactivating the normal myeloid differentiation potential in leukemia cells. This study shows that autophagosome formation inhibitors activate the cytosolic DNA-sensor signaling, thereby augmenting conventional differentiation therapy to induce irreversible differentiation and cell growth arrest in several types of AML cell lines.