Expression of the senescence marker p16INK4a in skin biopsies of acute lymphoblastic leukemia survivors: a pilot study.

BACKGROUND: Most childhood cancer survivors will develop ionizing radiation treatment-related health conditions that, in many instances, resemble age-associated pathologies. Treatment-induced premature senescence could be an underlying mechanism. FINDINGS: Here we wanted to know whether the expression of p16INK4a, a senescence/aging biomarker, is increased in skin biopsies of acute lymphoblastic leukemia survivors (ALL), previously exposed to chemotherapy and radiation therapy. Several years post-treatments, we found p16INK4a mRNA levels are 5.8 times higher in scalp skin biopsies (targeted by cranial irradiation therapy) compared to buttocks skin biopsies (n = 10, p = 0.01). CONCLUSIONS: These results demonstrate for the first time that premature senescence is induced in pediatric cancer survivors and that p16INK4a expression could be used as a potential biomarker in this population.

A soluble granulocyte colony stimulating factor decoy receptor as a novel tool to increase hematopoietic cell homing and reconstitution in mice.

The relative ineffectiveness of hematopoietic stem cells in reaching the bone marrow upon transplantation combined with the limited number of these cells available is a major reason for graft failure and delayed hematopoietic recovery. Hence, the development of strategies that could enhance homing is of high interest. Here, we provide evidence that homing is severely impaired postexposure to ionizing radiation (IR) in mice, an effect we found was time dependent and could be partially rescued using mesenchymal stromal cell (MSC) therapy. In an attempt to further increase homing, we took advantage of our observation that the granulocyte colony stimulating factor (G-CSF), a cytokine known to induce cell mobilization, is increased in the marrow of mice shortly after their exposure to IR. As such, we developed a truncated, yet functional, soluble G-CSF receptor (solG-CSFR), which we hypothesized could act as a decoy and foster homing. Using MSCs or conditioned media as delivery vehicles, we show that an engineered solG-CSFR has the potential to increase homing and hematopoietic reconstitution in mice. Altogether, our results provide novel findings at the interplay of IR and stromal cell therapy and present the regulation of endogenous G-CSF as an innovative proof-of-concept strategy to manipulate hematopoietic cell homing.

Ionizing radiation-induced long-term expression of senescence markers in mice is independent of p53 and immune status.

Exposure to IR has been shown to induce the formation of senescence markers, a phenotype that coincides with lifelong delayed repair and regeneration of irradiated tissues. We hypothesized that IR-induced senescence markers could persist long-term in vivo, possibly contributing to the permanent reduction in tissue functionality. Here, we show that mouse tissues exposed to a sublethal dose of IR display persistent (up to 45 weeks, the maximum time analyzed) DNA damage foci and increased p16(INK4a) expression, two hallmarks of cellular senescence and aging. BrdU-labeling experiments revealed that IR-induced damaged cells are preferentially eliminated, at least partially, in a tissue-dependent manner. Unexpectedly, the accumulation of damaged cells was found to occur independent from the DNA damage response modulator p53, and from an intact immune system, as their levels were similar in wild-type and Rag2(-/-) gammaC(-/-) mice, the latter being deficient in T, B, and NK cells. Together, our results provide compelling evidence that exposure to IR induces long-term expression of senescence markers in vivo, an effect that may contribute to the reduced tissue functionality observed in cancer survivors.