A novel defect in mitochondrial p53 accumulation following DNA damage confers apoptosis resistance in Ataxia Telangiectasia and Nijmegen Breakage Syndrome T-cells

4-(Nitrophenylsulfonyl)piperazines mitigate radiation damage to multiple tissues

Our ability to use ionizing radiation as an energy source, as a therapeutic agent, and, unfortunately, as a weapon, has evolved tremendously over the past 120 years, yet our tool box to handle the consequences of accidental and unwanted radiation exposure remains very limited. We have identified a novel group of small molecule compounds with a 4-nitrophenylsulfonamide (NPS) backbone in common that dramatically decrease mortality from the hematopoietic acute radiation syndrome (hARS). The group emerged from an in vitro high throughput screen (HTS) for inhibitors of radiation-induced apoptosis. The lead compound also mitigates against death after local abdominal irradiation and after local thoracic irradiation (LTI) in models of subacute radiation pneumonitis and late radiation fibrosis. Mitigation of hARS is through activation of radiation-induced CD11b⁺Ly6G⁺Ly6C⁺ immature myeloid cells. This is consistent with the notion that myeloerythroid-restricted progenitors protect against WBI-induced lethality and extends the possible involvement of the myeloid lineage in radiation effects. The lead compound was active if given to mice before or after WBI and had some anti-tumor action, suggesting that these compounds may find broader applications to cancer radiation therapy.

Persistent DNA damage-induced premature senescence alters the functional features of human bone marrow mesenchymal stem cells

Human mesenchymal stem cells (hMSCs) are adult multipotent stem cells located in various tissues, including the bone marrow. In contrast to terminally differentiated somatic cells, adult stem cells must persist and function throughout life to ensure tissue homeostasis and repair. For this reason, they must be equipped with DNA damage responses able to maintain genomic integrity while ensuring their lifelong persistence. Evaluation of hMSC response to genotoxic insults is of great interest considering both their therapeutic potential and their physiological functions. This study aimed to investigate the response of human bone marrow MSCs to the genotoxic agent Actinomycin D (ActD), a well-known anti-tumour drug. We report that hMSCs react by undergoing premature senescence driven by a persistent DNA damage response activation, as hallmarked by inhibition of DNA synthesis, p21 and p16 protein expression, marked Senescent Associated β-galactosidase activity and enlarged γH2AX foci co-localizing with 53BP1 protein. Senescent hMSCs overexpress several senescence-associated secretory phenotype (SASP) genes and promote motility of lung tumour and osteosarcoma cell lines in vitro. Our findings disclose a multifaceted consequence of ActD treatment on hMSCs that on the one hand helps to preserve this stem cell pool and prevents damaged cells from undergoing neoplastic transformation, and on the other hand alters their functional effects on the surrounding tissue microenvironment in a way that might worsen their tumour-promoting behaviour.

Oxidative stress and mitochondrial dysfunction across broad-ranging pathologies: toward mitochondria-targeted clinical strategies

Beyond the disorders recognized as mitochondrial diseases, abnormalities in function and/or ultrastructure of mitochondria have been reported in several unrelated pathologies. These encompass ageing, malformations, and a number of genetic or acquired diseases, as diabetes and cardiologic, haematologic, organ-specific (e.g., eye or liver), neurologic and psychiatric, autoimmune, and dermatologic disorders. The mechanistic grounds for mitochondrial dysfunction (MDF) along with the occurrence of oxidative stress (OS) have been investigated within the pathogenesis of individual disorders or in groups of interrelated disorders. We attempt to review broad-ranging pathologies that involve mitochondrial-specific deficiencies or rely on cytosol-derived prooxidant states or on autoimmune-induced mitochondrial damage. The established knowledge in these subjects warrants studies aimed at elucidating several open questions that are highlighted in the present review. The relevance of OS and MDF in different pathologies may establish the grounds for chemoprevention trials aimed at compensating OS/MDF by means of antioxidants and mitochondrial nutrients.

Damaged mitochondria in Fanconi anemia - an isolated event or a general phenomenon?

Fanconi anemia (FA) is known as an inherited bone marrow failure syndrome associated with cancer predisposition and susceptibility to a number of DNA damaging stimuli, along with a number of clinical features such as upper limb malformations, increased diabetes incidence and typical anomalies in skin pigmentation. The proteins encoded by FA-defective genes (FANC proteins) display well-established roles in DNA damage and repair pathways. Moreover, some independent studies have revealed that mitochondrial dysfunction (MDF) is also involved in FA phenotype. Unconfined to FA, we have shown that other syndromes featuring DNA damage and repair (such as ataxia-telangiectasia, AT, and Werner syndrome, WS) display MDF-related phenotypes, along with oxidative stress (OS) that, altogether, may play major roles in these diseases. Experimental and clinical studies are warranted in the prospect of future therapies to be focused on compounds scavenging reactive oxygen species (ROS) as well as protecting mitochondrial functions.

Mitochondrial dysfunction in a novel form of autosomal recessive ataxia

Defects in the recognition and/or repair of damage to DNA are responsible for a sub-group of autosomal recessive ataxias. Included in this group is a novel form of ataxia with oculomotor apraxia characterised by sensitivity to DNA damaging agents, a defect in p53 stabilisation, oxidative stress and resistance to apoptosis. We provide evidence here that the defect in this patient's cells is at the level of the mitochondrion. Mitochondrial membrane potential was markedly reduced in cells from the patient and ROS levels were elevated. This was accompanied by lipid peroxidation of mitochondrial proteins involved in electron transport and RNA synthesis. However, no gross changes or alteration in composition or activity of mitochondrial electron transport complexes was evident. Sequencing of mitochondrial DNA revealed a mutation, I349T, in the mitochondrial cytochrome b gene. These results describe a patient with an apparently novel form of AOA characterised by a defect at the level of the mitochondrion.

Pifithrin-μ increases mitochondrial COX biogenesis and MnSOD activity in skeletal muscle of middle-aged mice

We investigated the biogenesis and mitochondrial antioxidant capacity of cytochrome c oxidase (COX) within the skeletal muscle under the treatments of p53 inhibitors (pifithrin, PFTα and PFTμ). Significantly, PFTμ increased mtDNA content and COX biogenesis. These changes coincided with increases in the activity and expression of manganese superoxide dismutase (MnSOD), the key antioxidant enzyme in mitochondria. Conversely, PFTα caused muscle loss, increased oxidative damage and decreased MnSOD activity in intermyofibrillar (IMF) mitochondria. Mechanically, PFTμ inhibited p53 translocation to mitochondria and thus increased its transcriptional activity for expression of synthesis of cytochrome c oxidase 2 (SCO2), an important assembly protein for COX. This study provides in vivo evidence that PFTμ, superior to PFTα, preserves muscle mass and increases mitochondrial antioxidant activity.

Dual role of insulin-like growth factor-1 in acetyl-CoA carboxylase-alpha activity in human colon cancer cells HCT-8: downregulating its expression and phosphorylation

Insulin-like growth factor-1 (IGF-1) plays the role in cellular lipid synthesis and cell proliferation. However, the role of IGF-1 on the growth of colon cancer cell line HCT-8 is not clear. In this study, HCT-8 cells were exposed to IGF-1 at 0, 10, 50, or 100 ng/ml in serum-free medium. Fatty acid/lipid synthesis in HCT-8 cells was examined by 2-14C-acetate incorporation. HCT-8 cell growth and proliferation were determined by MTT assay and Trypan blue exclusive viable cell counting. We found that in serum starvation conditions, IGF-1 at 10-100 ng/ml induced dose-dependent down regulation of both the ACCα expression and the phosphorylation in HCT-8 cells, maintaining a balance in ACCα activity and lipid synthesis. IGF-1 reduced p-ATM, p-AMPK, and then p-ACCα protein levels in HCT-8 cells. IGF-1 increased p-Akt levels, but decreased p-ERK1/2 levels, leading to the decrease in ACCα protein and mRNA levels. Similarly, ERK1/2 inhibitor PD98059 reduced ACCα expression. IGF-1 influences neither HCT-8 cell growth nor their p53 protein levels and PARP cleavage. In a word, IGF-1 reduced ACCα phosphorylation via an ATM/AMPK signaling pathway and suppressed ACCα expression through an ERK1/2 transduction, playing a dual role in regulating ACCα activity and lipogenesis. This may render a cell with survival advantages under a serum starvation crisis, representing a novel mitogenic role of IGF-1.