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

细胞外囊泡（extracellular vesicles，EV）是一组异质性脂质双层结合的囊泡，其从所有细胞释放并基于生物发生进行分类。外泌体从多泡体释放，而微泡从质膜出芽。外泌体和微泡都携带蛋白质、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变化，包括，正如我们所发现的，可以促进受体细胞死亡的诱导凋亡受体的获得。B淋巴细胞（B细胞）是免疫系统的抗体产生细胞。B细胞在骨髓中经历多阶段发育过程。受体CD 24（别名热稳定抗原）在发育早期的B细胞（原和前B细胞）上高度表达，随后在它们成熟时表达降低。已知CD 24在发育中的B细胞中诱导凋亡。我的小组是第一个证明刺激CD 24诱导EV从B细胞释放的小组。我们发现，CD 24调节EV上不同表面受体的包装。我们还发现，CD 24和IgM刺激B细胞引起功能性B细胞受体（BCR）和功能性CD 24通过EV转移到受体细胞。这些数据表明，由刺激的B细胞释放的EV可以产生对CD 24诱导的细胞凋亡具有增加的敏感性的受体细胞。此外，这种转移产生了表达具有一种以上抗原结合特异性的BCR的B细胞;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表明，CD 24可能充当稳态调节剂，其中CD 24的活化增加会增加旁观者受体细胞上促细胞凋亡受体的水平。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中细胞丰度的潜在机制。我的长期DG计划专注于了解EV在调节骨髓B细胞发育中的作用。在未来五年，我计划实现以下三个目标。1.阐明CD 24刺激EV释放的信号通路。2.鉴定骨髓B细胞上CD 24的共受体。3.识别受B细胞响应CD 24释放EV影响的骨髓细胞。这项工作将直接影响我们对EV如何产生以及EV如何有助于B细胞发育的理解。因此，增加我们对EV的作用和调节的全球理解，这可能影响细胞生物学的许多领域，因为EV是细胞间通讯的高度保守的介质。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，使他们能够在未来的科学生涯中取得成功。

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.