The role of mitochondria in the regulation of gamma rays induced mTOR-dependent senescence

The first aims of this study were to demonstrate if mitochondrial biogenesis and senescence can be induced simultaneously in cell lines upon exposure to a genotoxic stress, and if the presence of mtDNA mutations which impair the functionality of respiratory complexes can influence the ability of a cell to activate senescence. The data obtained on the oncocytic model XTC.UC1 demonstrated that the presence of mitochondrial dysfunction is involved in the maintenance of a senescent phenotype induced by γ-rays treatment. The involvement of mTORC1 in the regulation of senescence has been shown in this cell line. On the other hand, in cells which do not present mitochondrial dysfunction it has been verified that genotoxic stress determines the activation of both mitochondrial biogenesis and senescence. Further studies are necessary in order to verify if mitochondrial biogenesis sustains the activation of senescence. The second aim of this thesis was to determine the involvement of mTORC1 in the regulation of PGC-1α expression, in order to verify what is the cause of the development of oncocytoma in patients affected by two hereditary cancer syndromes; Cowden and Birt-hogg-Dubé . The study of oncocytic tumors developed by patients affected by these syndromes suggested that the double heterozigosity of the two causative genes, PTEN and FLCN respectively, induce the activation of mTORC1 and therefore the activation of PGC-1α expression. On XTC.UC1 cell line, the most suitable in vitro model, experiments of complementation of PTEN and FLCN were conducted. To date, these results demonstrated that mTORC1 is not involved in the regulation of PGC-1α expression, and PTEN and FLCN seem to have opposite effect on PGC-1α expression.

Transport Properties and Novel Sensing Applications of Organic Semiconducting Crystals

The present thesis is focused on the study of Organic Semiconducting Single Crystals (OSSCs) and crystalline thin films. In particular solution-grown OSSC, e.g. 4-hdroxycyanobenzene (4HCB) have been characterized in view of their applications as novel sensors of X-rays, gamma-rays, alpha particles radiations and chemical sensors. In the field of ionizing radiation detection, organic semiconductors have been proposed so far mainly as indirect detectors, i.e. as scintillators or as photodiodes. I first study the performance of 4HCB single crystals as direct X-ray detector i.e. the direct photon conversion into an electrical signal, assessing that they can operate at room temperature and in atmosphere, showing a stable and linear response with increasing dose rate. A dedicated study of the collecting electrodes geometry, crystal thickness and interaction volume allowed us to maximize the charge collection efficiency and sensitivity, thus assessing how OSSCs perform at low operating voltages and offer a great potential in the development of novel ionizing radiation sensors. To better understand the processes generating the observed X-ray signal, a comparative study is presented on OSSCs based on several small-molecules: 1,5-dinitronaphthalene (DNN), 1,8-naphthaleneimide (NTI), Rubrene and TIPS-pentacene. In addition, the proof of principle of gamma-rays and alpha particles has been assessed for 4HCB single crystals. I have also carried out an investigation of the electrical response of OSSCs exposed to vapour of volatile molecules, polar and non-polar. The last chapter deals with rubrene, the highest performing molecular crystals for electronic applications. We present an investigation on high quality, millimeter-sized, crystalline thin films (10 – 100 nm thick) realized by exploiting organic molecular beam epitaxy on water-soluble substrates. Space-Charge-Limited Current (SCLC) and photocurrent spectroscopy measurements have been carried out. A thin film transistor was fabricated onto a Cytop® dielectric layer. The FET mobility exceeding 2 cm2/Vs, definitely assess the quality of RUB films.

Hybrid lead-halide perovskites as novel materials for thin film direct and flexible ionizing radiation detectors

Ionizing radiations are important tools employed every day in the modern society. For example, in medicine they are routinely used for diagnostic and therapy. The large variety of applications leads to the need of novel, more efficient, low-cost ionizing radiation detectors with new functionalities. Personal dosimetry would benefit from wearable detectors able to conform to the body surfaces. Traditional semiconductors used for ionizing radiation direct detectors offer high performance but they are intrinsically stiff, brittle and require high voltages to operate. Hybrid lead-halide perovskites emerged recently as a novel class of materials for ionizing radiation detection. They combine high absorption coefficient, solution processability and high charge transport capability, enabling efficient and low-cost detection. The deposition from solution allows the fabrication of thin-film flexible devices. In this thesis, I studied the detection properties of different types of hybrid perovskites, deposited from solution in thin-film form, and tested under X-rays, gamma-rays and protons beams. I developed the first ultraflexible X-ray detector with exceptional conformability. The effect of coupling organic layers with perovskites was studied at the nanoscale giving a direct demonstration of trap passivation effect at the grain boundaries. Different perovskite formulations were deposited and tested to improve the film stability. I report about the longest aging studies on perovskite X-ray detectors showing that the addition of starch in the precursors’ solution can improve the stability in time with only a 7% decrease in sensitivity after 630 days of storage in ambient conditions. 2D perovskites were also explored as direct detector for X-rays and gamma-rays. Detection of 511 keV photons by a thin-film device is here demonstrated and was validated for monitoring a radiotracer injection. At last, a new approach has been used: a 2D/3Dmixed perovskite thin-film demonstrated to reliably detect 5 MeV protons, envisioning wearable dose monitoring during proton/hadron therapy treatments.

HIF1α regulates Mitochondrial biogenesis and Cellular senescence induced by Gamma Radiation

Cellular response to γ-rays is mediated by ATM-p53 axis. When p53 is phosphorylated, it can transactivate several genes to induce permanent cell cycle arrest (senescence) or apoptosis. Epithelial and mesenchymal cells are more resistant to radiation-induced apoptosis and respond mainly by activating senescence. Hence, tumor cells in a senescent state might remain as “dormant” malignant in fact through disruption of p53 function, cells may overcome growth arrest. Oncocytic features were acquired in the recurring neoplasia after radiation therapy in patient with colonrectal cancer. Oncocytic tumors are characterized by aberrant biogenesis and are mainly non-aggressive neoplasms. Their low proliferation degree can be explained by chronic destabilization of HIF1α, which presides to adaptation to hypoxia and also plays a pivotal role in hypoxia-related radio-resistance. The aim of the present thesis was to verify whether mitochondrial biogenesis can be induced following radiation treatment, in relation of HIF1α status and whether is predictive of a senescence response. In this study was demonstrate that mitochondrial biogenesis parameters like mitochondrial DNA copy number could be used for the prediction of hypoxic status of tissue after radiation treatment. γ-rays induce an increase of mitochondrial mass and function, in response to a genotoxic stress that pushes cells into senescence. Mitochondrial biogenesis is only indirectly regulated by p53, whose activation triggers a MDM2-mediated HIF1α degradation, leading to the release of PGC-1β inhibition by HIF1α. On the other hand, this protein blunts the mitochondrial response to γ-rays as well as the induction of p21-mediated cell senescence, indicating prevalence of the hypoxic over the genotoxic response. Finally in vivo, post-radiotherapy mtDNA copy number increase well correlates with lack of HIF1α increase in the tissue, concluding this may be a useful molecular tool to infer the trigger of a hypoxic response during radiotherapy, which may lead to failure of activation of senescence.

Real-time anomaly detection of gamma-ray bursts for the Cherenkov Telescope Array using deep learning

The Cherenkov Telescope Array (CTA) will be the next-generation ground-based observatory to study the universe in the very-high-energy domain. The observatory will rely on a Science Alert Generation (SAG) system to analyze the real-time data from the telescopes and generate science alerts. The SAG system will play a crucial role in the search and follow-up of transients from external alerts, enabling multi-wavelength and multi-messenger collaborations. It will maximize the potential for the detection of the rarest phenomena, such as gamma-ray bursts (GRBs), which are the science case for this study. This study presents an anomaly detection method based on deep learning for detecting gamma-ray burst events in real-time. The performance of the proposed method is evaluated and compared against the Li&Ma standard technique in two use cases of serendipitous discoveries and follow-up observations, using short exposure times. The method shows promising results in detecting GRBs and is flexible enough to allow real-time search for transient events on multiple time scales. The method does not assume background nor source models and doe not require a minimum number of photon counts to perform analysis, making it well-suited for real-time analysis. Future improvements involve further tests, relaxing some of the assumptions made in this study as well as post-trials correction of the detection significance. Moreover, the ability to detect other transient classes in different scenarios must be investigated for completeness. The system can be integrated within the SAG system of CTA and deployed on the onsite computing clusters. This would provide valuable insights into the method's performance in a real-world setting and be another valuable tool for discovering new transient events in real-time. Overall, this study makes a significant contribution to the field of astrophysics by demonstrating the effectiveness of deep learning-based anomaly detection techniques for real-time source detection in gamma-ray astronomy.