Regulation of mast cell function and survival in health and disease

Abstract

Mast cells are sentinels of danger but they are also the major effector cells in allergic disease causing the well-known allergic symptoms caused by their mediators such as histamine and prostaglandin D2 that are released upon activation. Mastocytosis is a disease characterized by the clonal expansion of mast cells in the skin and/or other organs where the patients suffer from mediator-related symptoms and/or organ failure due to mast cell infiltration. The aim of the work presented in this thesis was to investigate mast cell function in health and disease, particularly systemic mastocytosis.

In paper I, we investigate the in vivo reactvitiy of mast cells in patients with mastocytosis. We show that though the patients with systemic mastocytosis have increased levels of circulating mast cell mediators their mast cells in skin and lung are no more reactive then those in heatlhy controls. Paper II. We analyze the reactivity of in vitro cultured mast cells from the patients investigated in paper I, and could show that systemic mastocytosis mast cells proliferate and develop normally though with increased expression of the high affinity IgE receptor. Mast cells from patients with systemic mastocytosis are more reactive to increased osmolarity by releasing more PGD2.

Investigating the genetic background of mastocytosis we discovered that they exhibit a specific miRNA profile. In the search for new therapeutical possibilities for mastocytosis we investigated the combination of ABT-737, a BH3 mimetic, and Roscovitine in paper III. By targeting expression and function of pro-survival proteins we found that even in very low doses the drugs induce apoptosis in mast cells carrying the D816V KIT mutation. Paper IV. Histone deacetylase inhibitors (HDACi) alter genetic expression. Here we show that SAHA, a class II HDACi induces mast cell apoptosis in cell lines and primary systemic mastocytosis patient cells, and that KIT is epigenetically silenced by SAHA in KIT D816V mutated cells. We have previously shown that IgE-receptor cross linking induces mast cell degranulation and activation-induced cell survival.

In paper V we further investigate the effects of the Bcl-2 family and found that Bfl-1 is vital for the cell to survive, reform and be ready to degranulate again. Patients with allergic disease or cutaneous inflammatory skin disease have increased expression of Bfl-1 in their skin mast cells suggesting that targeting Bfl-1 might be an option for treatment. Paper VI. Further investigating the function of the A1/Bfl-1 gene, we found that knockdown of A1/Bfl-1 in mice protects the animals from passive cutaneous and systemic anaphylaxis. Additionally, connective tissue mast cells depend on A1/Bfl-1 for their development and survival.