Alterations in arachidonic acid metabolism in mouse mast cells induced to undergo maturation in vitro in response to stem cell factor

cPLA2α knockout mice exhibit abnormalities in the architecture and synapses of cortical neurons

Cytosolic phospholipase A2α (cPLA2α) affects membrane fluidity and permeability by catalyzing the hydrolysis of membrane phospholipids. We hypothesize that cPLA2α deficiency induces rigidity and architectural changes in cell membranes, especially in large cortical neurons. These membrane changes are discernible using light and electron microscopy. Through careful comparison with wild-type counterparts, we observed significant morphological changes in cortical neurons of cPLA2α knockout mice. These changes included the following: (1) increased numbers of nucleoli and enlarged nuclei, (2) narrower spaces between the inner and outer nuclear membranes, (3) reduced numbers of nuclear pores and altered nuclear pore structure, and (4) morphological changes in synaptic clefts. These results further suggest that cPLA2α and its cleaved arachidonic acids play important roles in cortical neuronal maturation and in normal neurochemical processes.

Stem cell factor and interleukin-4 increase responsiveness of mast cells to substance P

The response of mast cells (MC) to non-IgE-mediated stimulation is critically dependent on the population of MC examined. The neuropeptide Substance P (SP) has been reported to activate connective tissue-type MC (CTMC), while mucosal MC (MMC) are not activated by SP. We examined the effect of stem cell factor (SCF) plus interleukin-4 (IL-4) on SP-initiated activation of bone marrow-derived MC (BMMC). Mouse MC, derived from a culture of BM cells with IL-3, were subsequently treated with recombinant SCF plus IL-4 for 6 days. Responsiveness to SP was monitored measuring beta-hexosaminidase and lipid mediator release. Histochemical staining, histamine analysis, and granule protease expression were achieved to characterize the cells. In contrast to IL-3 grown cells, SCF/IL-4-exposed cells showed functional responsiveness to release beta-hexosaminidase (42.25% +/- 1.46% at SP concentration of 100 microM) and produce leukotriene C(4) (LTC(4)) (7.4 +/- 1.5 ng/10(6) cells)/prostaglandin D(2) (PGD(2)) (2.0 +/- 0.3 ng/10(6) cells) upon stimulation by SP. The increase in sensitivity of the cells to SP was not due to differentiation into CTMC, as the cells remained heparin negative. Both SCF and IL-4 were needed because SCF or IL-4 alone were insufficient to keep cells viable after 3 to 4 days post coculture. SP-induced secretion from BMMC cultured in medium containing SCF plus IL-4 (25.76% +/- 1.83%) was higher in comparison with cells cultured with SCF plus IL-3 (8.85% +/- 0.68%).These findings indicate that temporal changes in cytokine expression can influence the sensitivity of MC to non-immunologic stimuli. Local cytokine production leading to an increase in MC responsiveness to SP and inducing secretion of granule content and lipid generation may, therefore, propagate and worsen inflammatory conditions.

Stem cell factor and interleukin-4 induce murine bone marrow cells to develop into mast cells with connective tissue type characteristics in vitro

In this study, we have developed a method to obtain mast cells with connective tissue type mast cell (CTMC) characteristics directly from mouse bone marrow (BM) cells. BM cells were grown for 3 weeks in presence of interleukin-4 (IL-4) plus stem cell factor (SCF). SCF alone poorly supported growth and development of mast cells. IL-4 dose-dependently enhanced the expression of c-kit and high-affinity receptor for IgE (Fc(epsilon)RI) on the cell surface of SCF-cultured BM cells. Furthermore, cytoplasmic granulation and histamine synthesis of BM-derived mast cells were increased in presence of IL-4 and SCF. Histochemical staining demonstrated that granules were safranin positive. BM-derived mast cells could be activated for granule exocytosis (beta-hexosaminidase release) and lipid mediator generation (LTC4 production) via Fc(epsilon)RI after sensitization with IgE and subsequent crosslinking with multivalent antigen. In addition, mast cells derived from BM cells cultured with SCF plus IL-4 could be activated by substance P, a nonimmunologic stimulus, to release beta-hexosaminidase. The results presented indicate that IL-4 and SCF both have a prominent role in the development of mast cells from murine BM cells in vitro. Mast cells can directly be derived from BM cells in presence of SCF and IL-4 and the cultured cells show typical hallmarks of CTMC, indicating that precursor cells for CTMC may be present in BM. The described culture procedure may be useful to investigate the molecular aspects of the development of committed mast cell lineages.