Studio dei fattori responsabili dell’alterazione del metabolismo osseo nella Leucemia Linfatica Cronica: specifico ruolo di HGF nel microambiente stromale.

Chronic Lymphatic Leukemia (CLL) is the most common leukemia in the Western world and is characterized by the proliferation and accumulation of mature CD5 + B lymphocytes in peripheral blood, lymph nodes and bone marrow. CLL leukemic cells in vitro don’t survive, undergoing apoptosis, preventing the availability of reliable experimental models. On the contrary, in vivo it is precisely long-term survival in the lymph node and bone marrow districts that cause disease relapses and make the disease difficult to eradicate. One of the consequences of this accumulation and disease progression is an alteration of the trabecular structure of the bone, highlighted by tomographic analyzes in patients at intermediate and advanced stages of the pathology. These premises lead to the hypothesis that the medullary microenvironment, and in particular its figurative component of the Bone Marrow Stromal Cells (BMSC), through cell-cell contacts and secreted cell signals, is able to allow and promote the survival of leukemic clones; on the other hand, leukemia cells seem to influence the surrounding environment, thus altering bone metabolism and its normal homeostasis. Thus, a cross-exchange of signals appears to occur between the leukemic cells and the cells of the medullary niche, with substantial changes in both directions. The aim of this project was to investigate the nature of this cross-talk, in particular on the one hand by investigating the role of the Hepatocyte Growth Factor (HGF) and its regulation in the survival of the CLL cell, on the other by verifying through which mechanisms and signals the leukemic clone is able to alter bone metabolism. Overall, the data collected so far lead to indicate how the bone erosion and the weakening of the trabecular structure, present in the intermediate and advanced stages of CLL, can be attributed to an alteration of the balance, present in physiological conditions, between the bone formation and reabsorption. This seems to be due to a decrease in the number of stromal cells that differentiates into osteoblasts, with a consequent decrease in the deposition of ECM, and to a simultaneous increase in the number of monocytes that differentiates into osteoclasts, with a consequent increase in the reabsorption of the bone matrix itself. Both of these phenomena seem to be in close correlation with the proximity of CLL B cells present in the bone marrow, which exert their influence on stromal cells and monocytes through the release of some cytokines, among which they seem to play a main role IL-11, IL -6 and especially TNFα. In investigating the role played by HGF in the survival of the leukemic clone, however, the studies carried out so far have identified the following possible TFs of interest on the promoter of the HGF gene: PPARγ, Ikaros, ERα and AP-2α. By then using lysate samples from cell lines having different HGF expression, it was possible to verify, through the use of Chromatin Immunoprecipitation, that TF Ikaros doesn’t seem to be involved in gene regulation.