Role of PI3-kinase in the development and function of mast cells

用p85α基因缺陷小鼠检测I_A类PI3K在肥大细胞分化中的作用。我们发现，p85α缺陷小鼠选择性地缺乏胃肠道和腹膜肥大细胞，而在正常生理条件下，肥大细胞很容易在其他组织中找到，如皮肤。我们研究了为什么p85α缺陷小鼠只缺少胃肠道肥大细胞。我们首先用有限稀释法检测了骨髓、脾和肠道中肥大细胞前体细胞的频率。结果表明，与野生型小鼠相比，肠道中的前体频率低于野生型水平的10%，而骨髓和脾的前体频率未受影响。这些结果表明，在p85α缺陷小鼠中，前体细胞和/或成熟肥大细胞在肠道中的存活或前体细胞向肠道的迁移受到损害。我们发现，在p85α缺陷的肥大细胞中，以IL-3为增殖因子建立的p85α缺陷的肥大细胞中c-Kit信号严重受损，而对干细胞因子刺激的肥大细胞中的JNK活性严重受损。我们还研究了整合素的表达和功能，这些整合素在细胞迁移中起着重要的作用。我们发现α4β7整合素在P85α缺陷的肥大细胞中的表达是正常的，但α4β7与其配体MadCAM的结合明显弱于野生型肥大细胞。我们从这些观察中得出结论，p85α缺陷小鼠胃肠道肥大细胞的缺乏是由于在肠道的迁移和存活不足所致。

Role of class I_A PI3K in mast cell differentiation was examined using p85α-deficient mice. We have found that p85α-deficient mice selectively lack gastrointestinal and peritoneal mast cells whereas mast cells are readily found in other tissues such as skin under normal physiological conditions. We studied why p85α-deficient mice lack only gastrointestinal mast cells. We first examined the mast cell precursor frequency in the bone marrow, spleen and intestinal tract, by limiting dilution method. It was revealed that the precursor frequency in the intestine was less than 10% of wild type level whereas those of the bone marrow and spleen were unaffected compared to wild type mice. These results suggest that either the survival of progenitors and/or mature mast cell in the intestine or the migration of precursor cells to the intestine is impaired in p85α-deficient mice. We found that c-Kit signal is strongly impaired in p85α-deficient mast cells established from the bone marrow with IL-3 as proliferation and JNK activation in response to SCF was severely impaired in p85α-deficient cultured mast cells. We also examined the expression and function of integrins that are known to be important in cell migration. We found that expression of α4β7 integrin that is critical for cellular migration to the intestine was normal in p85α-deficient mast cells but the binding of α4β7 to its ligand, MAdCAM was significantly weaker than that of wild type mast cells. We conclude from these observations that the lack of gastrointestinal mast cells in p85α-deficient mice is due to the deficiency in both migration to and survival in the intestine.