Role and regulation of extracellular vesicles generated in response to stimulation of CD24 on B lymphocytes

细胞外小泡(EVS)是一组从所有细胞中释放出来的异质性脂质双层结合的小泡，并根据生物发生进行分类。外体从多囊体内释放出来，而微泡从质膜上萌发出来。外切体和微囊都携带蛋白质、脂肪和核酸货物，可以从供体细胞转移到受体细胞。这种转移可以引起受体细胞功能的变化，包括我们已经发现的，可以促进受体细胞死亡的凋亡诱导受体的获得。B淋巴细胞(B细胞)是免疫系统的抗体产生细胞。B细胞在骨髓中经历了一个多阶段的发育过程。受体CD24(别名热稳定抗原)在发育早期的B细胞(前B细胞和前B细胞)上高表达，成熟后表达降低。已知CD24可诱导发育中的B细胞凋亡。我的团队是第一个证明刺激CD24诱导B细胞释放EV的人。我们发现CD24调节EVS上不同表面受体的包装。我们还发现，CD24和IgM对B细胞的刺激都会导致功能性B细胞受体(BCR)和功能性CD24通过EVS转移到受体细胞。这些数据表明，受刺激的B细胞释放的EVS可以产生对CD24诱导的细胞凋亡具有更高敏感性的受体细胞。此外，这种转移创造了表达BCR的B细胞，具有不止一种抗原结合特异性；这与B细胞只能表达一种BCR的教条直接矛盾。通过转移功能性受体诱导细胞凋亡，提示CD24可能是一种动态平衡调节剂，其中CD24的激活增加了旁观者受体上促凋亡受体的水平。这将增强受体细胞对促凋亡配体的敏感性。因此，通过EVS转移受体是调节骨髓细胞丰度的一种潜在机制。我的长期DG计划的重点是了解EVS在调节骨髓中B细胞发育方面所起的作用。未来5年，我计划实现以下3个目标。1.阐明CD24刺激EV释放的信号通路。2.确定骨髓B细胞表面CD24的共同受体。3.确定受CD24刺激的B细胞释放的EV影响的骨髓细胞。这项工作将直接影响我们对EVS是如何产生的以及EVS如何促进B细胞发育的理解。因此，增加了我们对EVS的作用和调控的全球理解，这可能会影响细胞生物学的许多领域，因为EVS是高度保守的细胞间通讯的媒介。此外，本科生和研究生将接受最先进的细胞和分子技术培训，为他们在未来的科学职业生涯中取得成功奠定基础。

Extracellular vesicles (EVs) are a group of heterogenous lipid bilayer-bound vesicles that are released from all cells and classified based on biogenesis. Exosomes are released from multivesicular bodies while microvesicles bud off the plasma membrane. Both exosomes and microvesicles carry protein, lipid, and nucleic acid cargo that can be transferred from donor to recipient cells. This transfer can cause changes to recipient cell function, including, as we have found, a gain of apoptosis-inducing receptors that can promote cell death of recipient cells. B lymphocytes (B cells) are the antibody-producing cells of the immune system. B cells undergo a multi-stage developmental process in the bone marrow. The receptor CD24 (alias heat stable antigen) is highly expressed on B cells earlier in development (pro- and pre-B cells) followed by decreased expression when they mature. CD24 is known to induce apoptosis in developing B cells. My group was the first to show that stimulation of CD24 induces the release of EVs from B cells. We found that CD24 regulates the packaging of different surface receptors on EVs. We also found that both CD24 and IgM stimulation of B cells causes transfer of a functional B cell receptor (BCR) and functional CD24 to recipient cells via EVs. These data show that EVs released by stimulated B cells can create recipient cells with increased sensitivity to CD24-induced apoptosis. In addition, this transfer creates B cells that express BCRs with more than one antigen-binding specificity; a direct contradiction to the dogma that B cells can only express one BCR. The induction of apoptosis by transfer of functional receptors suggests that CD24 may be acting as a homeostatic regulator where increased activation of CD24 increases the level of pro-apoptotic receptors on bystander recipient cells. This would enhance the sensitivity of recipient cells to pro-apoptotic ligands. Thus, transfer of receptors by EVs is a potential mechanism to regulate cell abundance in the bone marrow. My long-term DG program is focused on understanding the role that EVs play in regulating B cell development in the bone marrow. In the next 5 years, I plan to address the following 3 objectives. 1. Elucidate the signaling pathways by which CD24 stimulates EV release. 2. Identify the co-receptor for CD24 on bone marrow B cells. 3. Identify the bone marrow cells that are affected by EVs released from B cells in response to CD24. This work will directly impact our understanding of how EVs are generated and how EVs may contribute to B cell development. Thus, increasing our global understanding of the role and regulation of EVs, which may influence many areas of cell biology as EVs are highly conserved mediators of cell-cell communication. In addition, undergraduate and graduate students will be trained in state-of-the-art cellular and molecular techniques positioning them for success in their future scientific careers.