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

细胞外囊泡（Extracellular vesicles, EVs）是一组脂质双分子层结合的异质囊泡，可从所有细胞中释放出来，并根据生物发生机制进行分类。外泌体从多泡体中释放出来，而微泡从质膜中萌发。外泌体和微囊泡都携带蛋白质、脂质和核酸货物，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改变，包括，正如我们所发现的，凋亡诱导受体的增加可以促进受体细胞的死亡。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（又称热稳定抗原）在B细胞发育早期（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。我的小组是第一个证明刺激CD24诱导B细胞释放ev的小组。我们发现CD24调控着电动汽车上不同表面受体的包装。我们还发现，B细胞的CD24和IgM刺激都会导致功能性B细胞受体（BCR）和功能性CD24通过ev转移到受体细胞。这些数据表明，受刺激的B细胞释放的ev可以产生对cd24诱导的凋亡更敏感的受体细胞。此外，这种转移产生的B细胞表达具有多种抗原结合特异性的bcr；这与B细胞只能表达一种BCR的教条直接矛盾。通过功能受体的转移诱导细胞凋亡表明CD24可能作为一种稳态调节剂，其中CD24激活的增加增加了旁观受体细胞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ev转移受体是调节骨髓细胞丰度的潜在机制。我的长期DG项目的重点是了解ev在调节骨髓中B细胞发育中的作用。在未来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. 鉴定骨髓B细胞上CD24的共受体。3. 鉴定受B细胞响应CD24释放的ev影响的骨髓细胞。这项工作将直接影响我们对电动汽车如何产生以及电动汽车如何促进B细胞发育的理解。因此，增加我们对电动汽车的作用和调控的整体理解，这可能会影响细胞生物学的许多领域，因为电动汽车是细胞-细胞通讯的高度保守介质。此外，本科生和研究生将接受最先进的细胞和分子技术的培训，使他们在未来的科学事业中取得成功。

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.