Notch信号在胸腺上皮细胞退化中的作用机制及强力霉素对其调控机制的研究

TEC的增龄性和应激性退化导致T细胞特异性库容和输出量不可逆减少，严重影响机体免疫功能，但机制不详。Beverly发现过表达Jagged1的T细胞诱导TEC凋亡，我们也发现了相似情况。Dox具保护神经细胞抵抗凋亡作用。我们发现Dox不仅上调ERK和NF-κB促进胸腺上皮细胞系（MTEC1）增殖、分泌IL-6和GM-CSF；而且可上调BCL2，下调p53的表达，抑制Notch的活化和保护MTEC1抵抗丝裂霉素C和Jagged1诱导的凋亡。故我们提出假说："Notch信号介导了TEC的增龄性及应激性退化；Dox能下调TEC的Notch信号活化，保护胸腺上皮细胞，减缓胸腺增龄性或应激性退化和萎缩"。本研究采用Notch配体或造血干细胞移植活化TEC的Notch信号，研究Notch在胸腺退化中的作用机制，并阐明Dox对该信号的调控机制，为临床进行T细胞重建和治疗胸腺退化药物的研发奠定实验基础。

Age-associated and stress-induced involution of the thymus is accompanied by a decline in the number of thymic epithelial cells (TEC), the decrease of thymic output and a severely restricted peripheral repertoire of T-cell specificities. These events affect the immune system function seriously, but the mechanisms are unclear. Beverly and his colleagues found that T cells, overexpression of the Notch ligand Jagged1 in the transgenic mouse, induced TEC apoptosis. We also found that Jagged1 can induce the TEC apoptosis when a mouse TEC cell-line MTEC1 cells co-cultured with Jagged1 recombination protein. Doxycycline (Dox), a tetracycline antibiotic, has been shown to have neuroprotective efficiency in reduction of a variety of ischemia-reperfusion injuries as well as ischemic brain damage via inhibiting the MMPs, PKCδ and caspase. Recently, we found that Dox not only increase ERK to promote the proliferation of MTEC1 cells, but upregulate the secretion of IL-6 and GM-CSF via NF-κB and ERK. It also increases the expression of BCL2, decreases the expression of p53, inhibits the activation of Notch, and protects MTEC1 resistance to the cell apoptosis induced by mitomycin C or Jagged1 protein. Therefore, we propose a hypothesis: "The Notch signaling initiates the TEC apoptosis in thymic involution of age-associated or stress-induced; Dox downregulates the activation of Notch signal in TEC and protects them from apoptosis, then attenuates the degradation and atrophy of the thymus with aging or stress". In this study, we used the hematopoietic stem cell transplantation and Notch ligands to activated the Notch signal in TEC to investigate the mechanisms of Notch signal pathway in degradation of the thymus, and to declare the mechanism of Dox of protecting TEC. It will be beneficial to T-cell reconstitution and develop a set of new therapeutic drugs for clinical.