A role of mitochondria in mast cell activation and possible involvement in auto-immunity.
Abstract: Mast cells,
derived from bone marrow, are key immune effector cells that cause allergic symptoms,
regulate innate and acquired immunity, but are also involved in many autoimmune and
inflammatory diseases. Mast cells participate in immune process by secreting
granule-stored components, such as histamine, and de novo synthesized mediators, such as
IL-6, 8 and 13 in response to allergi... read morec, neuropeptide and environmental triggers. Mast
cells are well known to be activated by aggregation of high affinity receptors for the
immunoglobulin E during which most mediators are released with detrimental
pathophysiological effects. However, the regulation of secretion of granule and
non-granule stored mediators is poorly understood. We show that degranulation and
secretion of granule-stored TNF but not non-granule stored de novo synthesis and
release, of TNF from human cultured mast cells requires substantial
mitochondrial-associated energy and calcium. We further show that degranulation by
various triggers leads to rapid granule-stored TNF secretion and mitochondrial (mt)
fission and translocation to sites of exocytosis. Extracellular calcium depletion
prevents the mitochondrial translocation, while the calcium ionophore A23187 induces
translocation, indicating the necessarily of calcium influx. The calcium-dependent
calcineurin and Dynamin Related Protein1 (Drp1) which are critical for mitochondrial
dynamics, are activated rapidly after SP stimulation. Reduction of Drp1 activity by its
inhibitor MDIVI-1 and decrease of Drp1 expression using siRNA inhibit mitochondrial
translocation, TNF secretion and degranulation. In addition, gene expression of
calcineurin, Drp1 and SP is higher in skin biopsies from patients with Atopic Dermatitis
(AD) as compared to biopsies from normal control. The results presented here show that
mitochondria could be a novel regulator of mast cell activation. We also show that human
mast cell degranulation leads to mitochondrial fission into small particles and mtDNA
release extracellulary. Mitochondrial components are not normally found outside the
cells. Mitochondria purified from cultured sarcoma and LAD2 cells stimulate mast cell
degranulation and pro-inflammatory mediators' secretion. Increasing evidence indicates
that autism may be associated with some immune dysregulation, and may have a neuroimmune
component. We find that mtDNA (7s, Cytochrome B) is elevated in the serum of children
with autism. Mitochondria-based drug discovery may be used for the treatment of
inflammatory and autoimmune diseases.
Thesis (Ph.D.)--Tufts University, 2011.
Submitted to the Dept. of Biochemistry.
Advisor: Theoharis Theoharides.
Committee: Larry Feig, Louis Shuster, John Castellot, and Susan Leeman.
Keywords: Biochemistry, Pharmacology, and Immunology.read less