Hematopoietic stem/progenitor cell transplantation recovers immune defects and prevents lymphomas in Atm-deficient mice.

BACKGROUND: Ataxia-telangiectasia (A-T) is a rare autosomal recessive multi-system and life-shortening disease, characterized by progressive cerebellar neurodegeneration, immunodeficiency, radiation sensitivity and cancer predisposition, with high incidence of leukemia and lymphoma. A-T is caused by mutations in the gene encoding for ATM protein that has a major role in maintaining the integrity of the genome. Because there are no cures for A-T, we aimed to tackle immunodeficiency and prevent cancer onset/progression by transplantation therapy. METHODS: Enriched hematopoietic stem/progenitor cells (HSPCs), collected from bone marrow of wild-type mice, were transplanted in the caudal vein of 1 month old conditioned Atm-/- mice. RESULTS: Genomic analyses showed that transplanted Atm positive cells were found in lymphoid organs. B cells isolated from spleen of transplanted mice were able to undergo class switching recombination. Thymocytes were capable to correctly differentiate and consequently an increase of helper T cells and TCRßhi expressing cells was observed. Protein analysis of isolated T and B cells from transplanted mice, revealed that they expressed Atm and responded to DNA damage by initiating an Atm-dependent phosphorylation cascade. Indeed, aberrant metaphases were reduced in transplanted Atm-deficient mice. Six months after transplantation, Atm-/- mice showed signs of aging, but they maintained the rescue of T cells maturation, showed DNA damage response, and prevented thymoma. CONCLUSION: We can conclude that wild-type enriched HSPCs transplantation into young Atm-deficient mice can ameliorate A-T hematopoietic phenotypes and prevent tumor of hematopoietic origin.

Absence of ATM leads to altered NK cell function in mice.

Ataxia-telangiectasia (A-T) is a rare disorder caused by genetic defects of A-T mutated (ATM) kinase, a key regulator of stress response, and characterized by neurodegeneration, immunodeficiency, and high incidence of cancer. Here we investigated NK cells in a mouse model of A-T (Atm-/-) showing that they are strongly impaired at killing tumor cells due to a block of early signaling events. On the other hand, in Atm-/- littermates with thymic lymphoma NK cell cytotoxicity is enhanced as compared with ATM-proficient mice, possibly via tumor-produced TNF-α. Results also suggest that expansion of exhausted NKG2D+ NK cells in Atm-/- mice is driven by low-level expression of stress-inducible NKG2D ligands, whereas development of thymoma expressing the high-affinity MULT1 ligand is associated with NKG2D down-regulation on NK cells. These results expand our understanding of immunodeficiency in A-T and encourage exploring NK cell biology in A-T patients in the attempt to identify cancer predictive biomarkers and novel therapeutic targets.

ATM Kinase Dead: From Ataxia Telangiectasia Syndrome to Cancer.

ATM is one of the principal players of the DNA damage response. This protein exerts its role in DNA repair during cell cycle replication, oxidative stress, and DNA damage from endogenous events or exogenous agents. When is activated, ATM phosphorylates multiple substrates that participate in DNA repair, through its phosphoinositide 3-kinase like domain at the 3'end of the protein. The absence of ATM is the cause of a rare autosomal recessive disorder called Ataxia Telangiectasia characterized by cerebellar degeneration, telangiectasia, immunodeficiency, cancer susceptibility, and radiation sensitivity. There is a correlation between the severity of the phenotype and the mutations, depending on the residual activity of the protein. The analysis of patient mutations and mouse models revealed that the presence of inactive ATM, named ATM kinase-dead, is more cancer prone and lethal than its absence. ATM mutations fall into the whole gene sequence, and it is very difficult to predict the resulting effects, except for some frequent mutations. In this regard, is necessary to characterize the mutated protein to assess if it is stable and maintains some residual kinase activity. Moreover, the whole-genome sequencing of cancer patients with somatic or germline mutations has highlighted a high percentage of ATM mutations in the phosphoinositide 3-kinase domain, mostly in cancer cells resistant to classical therapy. The relevant differences between the complete absence of ATM and the presence of the inactive form in in vitro and in vivo models need to be explored in more detail to predict cancer predisposition of A-T patients and to discover new therapies for ATM-associated cancer cells. In this review, we summarize the multiple discoveries from humans and mouse models on ATM mutations, focusing into the inactive versus null ATM.

Gene expression profiling of hypoxic response in different models of senescent endothelial cells.

Endothelial cells senescence is a physiological process affecting vascular integrity. It can contribute to heart and arterial stiffening and remodeling, impaired angiogenesis, defective vascular repair, and with an increasing prevalence of atherosclerosis. Drugs used as antineoplastic therapies, targeting tumor as well as endothelial cells, can also trigger endothelial cells senescence. We demonstrated that a short pulse of axitinib, a specific inhibitor of vascular endothelial growth factor receptors, induces cell senescence of endothelial cells. Here, we performed a high-throughput gene expression analysis to characterize the response of proliferating versus senescent endothelial cells to hypoxia, the main trigger of neo-angiogenetic phenomena in tumors. We compared the response to hypoxia of replicative senescent cells, with that of axitinib or of DNA damage-induced senescence. Overall, we enlightened common and specific responses to different senescence inducers and changes in the Senescent Associated Secretory Phenotype.

Glioblastoma Cells Do Not Affect Axitinib-Dependent Senescence of HUVECs in a Transwell Coculture Model.

Axitinib is an orally available inhibitor of tyrosine kinases, with high specificity for vascular endothelial growth factor receptors (VEGFRs) 1, 2, and 3. It is approved for the treatment of advanced renal cell carcinoma and is in phase II clinical trials for recurrent glioblastoma (GBM). GBM is a brain tumor peculiar in its ability to induce neoangiogenesis. Since both GBM tumor cells and endothelial cells of tumor vasculature express VEGFRs, Axitinib exerts its inhibitory action on both tumor and endothelial cells. We and others previously demonstrated that Axitinib triggers cellular senescence. In particular, Axitinib-dependent senescence of HUVECs (human umbilical vein endothelial cells) is accompanied by intracellular reactive oxygen species(ROS) increase and early ataxia telangiectasia mutated(ATM) activation. Here we wondered if the presence of glioblastoma tumor cells could affect the HUVEC senescence upon Axitinib exposure. To address this issue, we cocultured HUVECs together with GBM tumor cells in transwell plates. HUVEC senescence did not result in being affected by GBM cells, neither in terms of ß galactosidase activity nor of proliferation index or ATM phosphorylation. Conversely, Axitinib modulation of HUVEC gene expression was altered by cocultured GBM cells. These data demonstrate that the GBM secretome modifies HUVECs' transcriptomic profile upon Axitinib exposure, but does not prevent drug-induced senescence.