NOS2

*仅供医学专业人士阅读参考众所周知，部分免疫细胞具有免疫记忆。因此，人体在遇到相同抗原刺激时，免疫系统可做出更快速和强烈的反应，这也是疫苗起效的主要机制[1]。不过，最近几年，我们对于免疫细胞记忆能力的认知，不断被刷新。4年前，匹兹堡大学和康奈尔大学的研究人员，在《科学》杂志上发表一篇研究论文，我至今记忆犹新[2]。这个研究首次发现，巨噬细胞等髓样先天免疫细胞，竟然也会形成抗原特异性的免疫记忆。我没想到的是，免疫记忆这种一直被认为是免疫细胞专属的能力，大脑里的一种非免疫细胞竟然也有。近日，由哈佛医学院Francisco J. Quintana领衔的研究团队，在《自然》杂志上发表一项重磅研究成果[3]。他们发现，中枢神经系统内的星形胶质细胞同样具有免疫记忆，而且这种免疫记忆能力受到表观遗传调控。具体来说，在受到炎症刺激后，星形胶质细胞内的一部分亚群将转变为表达组蛋白乙酰转移酶p300和ATP-柠檬酸裂解酶（ACLY）的亚群（p300+ ACLY+）。当再次受到炎症刺激时，ACLY可产生乙酰辅酶A，为组蛋白乙酰转移酶p300使组蛋白发生乙酰化提供底物，提高了炎症相关基因的染色质可及性，从而产生更快速和剧烈的炎症反应。研究人员同时通过实验证实，星形胶质细胞的这一免疫记忆很可能与中枢神经系统自身免疫性疾病，如多发性硬化症相关，且p300和ACLY基因的失活可以改善实验性自身免疫性脑脊髓炎（EAE，多发性硬化症的实验模型）小鼠的炎症反应，将来有可能针对ACLY-p300通路开发这类疾病的新疗法。论文首页截图前期已有研究表明，多发性硬化症和EAE与星形胶质细胞关系密切[4]。为了研究最初的炎症刺激是否会影响随后的星形胶质细胞反应，研究人员对两组小鼠分别脑室内注射IL-1β和TNF（两者可触发星形胶质细胞发生类似于在多发性硬化症和EAE中检测到的反应[5]）1次和2次（2次间隔1周），然后在IL-1β+TNF刺激后一天对两组小鼠脑部的星形胶质细胞进行RNA测序分析。研究结果显示，相比于1次注射IL-1β+TNF的小鼠，2次注射IL-1β+TNF小鼠脑组织中的星形胶质细胞呈现更强的促炎表型，NF-κB相关促炎通路被明显激活。同时，研究人员还通过染色体可及性测序（ATAC-seq）发现，第二次注射IL-1β+TNF后星形胶质细胞中炎症基因的染色质可及性增加，且这一现象与组蛋白乙酰转移酶p300介导的表观遗传调控相关。小鼠脑组织星形胶质细胞在第二次注射IL-1β+TNF时表现出比第一次时更强的促炎表型，并与组蛋白乙酰转移酶p300介导的表观遗传调控相关紧接着，研究人员在体外培养的小鼠脑原代星形胶质细胞中再次验证了这一点。相比于第一次受到刺激时，第二次受到IL-1β+TNF刺激的星形胶质细胞炎症相关基因表达活跃（IL6、CCL2和NOS2），并导致共培养的神经元死亡。此外，研究人员还发现，在首次IL-1β+TNF刺激后，星形胶质细胞的促炎表型在7天后恢复到基础水平。根据以上的研究结果，p300介导的表观遗传调控可能在星形胶质细胞对炎症刺激的免疫记忆中起到关键作用。为了验证这一点，研究人员使用CRISPR-Cas9技术沉默了小鼠星形胶质细胞中p300的表达，发现p300表达被沉默后，星形胶质细胞组蛋白3第27位赖氨酸（H3K27）的乙酰化及NF-κB相关促炎基因的转录受到抑制，从而减轻了星形胶质细胞的促炎反应。这一结果也在随后的染色质免疫共沉淀测序及体外原代星形胶质细胞实验中再次得到验证。p300表达被沉默后，H3K27乙酰化受到抑制，从而减轻了星形胶质细胞的促炎反应以上实验证实，p300介导的组蛋白乙酰化可通过表观遗传方式，调控星形胶质细胞的免疫记忆促炎反应，而p300使组蛋白乙酰化需要乙酰辅酶A作为底物[6]。用于组蛋白乙酰化的乙酰辅酶A主要由两种酶产生：ACLY和乙酰辅酶A合成酶2（ACSS2）[6, 7]。为了确定参与星形胶质细胞免疫记忆表观遗传调控的乙酰辅酶A的来源，研究人员测定了1次和2次IL-1β+TNF刺激后这两种酶的表达情况。结果显示，IL-1β+TNF的再次刺激仅使星形胶质细胞中ACLY的表达增加，而ACSS2表达无明显变化。紧接着，研究人员使用CRISPR-Cas9技术，分别沉默了星形胶质细胞中ACLY和ACSS2的表达，发现仅在ACLY被沉默后，H3K27乙酰化被抑制，星形胶质细胞的免疫记忆所致炎症反应减少。ACLY提供p300使组蛋白乙酰化需要的底物乙酰辅酶A，进而调控星形胶质细胞的免疫记忆接下来，研究人员在小鼠EAE模型中（由MOG诱导[8]）再次发现了星形胶质细胞中免疫记忆现象的存在，这种免疫记忆同样由ACLY和p300介导，前者提供底物乙酰辅酶A，后者使H3K27乙酰化，从而通过表观遗传方式调控再次炎症刺激时星形胶质细胞的炎症反应。研究人员还通过FIND-seq技术，对EAE小鼠和正常小鼠中ACLY-p300-、ACLY+p300-、ACLY-p300+和ACLY+p300+的星形胶质细胞亚群进行分析。实验分析表明，EAE小鼠中ACLY+p300+的星形胶质细胞亚群数量较正常小鼠增加，同时ACLY+p300+星形胶质细胞与先前实验中具有免疫记忆的星形胶质细胞的转录特征十分相似，而ACLY+p300-和ACLY-p300+亚群的转录特征，则是星形胶质细胞建立免疫记忆的一种过渡状态。最后，研究人员在培养的人胎儿星形胶质细胞中，验证了具有免疫记忆的星形胶质细胞是否与多发性硬化症的发病机制相关。在第二次受到IL-1β+TNF刺激后，人胎儿星形胶质细胞表现出增强的促炎反应，且这种增强的促炎反应可被p300抑制剂C646所拮抗。此外，17名多发性硬化症患者和12名正常对照人群的单细胞分析显示，多发性硬化症患者中ACLY+p300+星形胶质细胞亚群数目明显更多，且显示出与EAE小鼠ACLY+p300+星形胶质细胞相似的转录特征，表现出组蛋白乙酰化活跃和炎症相关基因表达增加。这些发现明确了ACLY和p300介导的表观遗传调控导致的星形胶质细胞免疫记忆在多发性硬化症发病机制中的潜在作用。具有免疫记忆的星形胶质细胞与多发性硬化症的发病机制相关总的来说，本研究发现了星形胶质细胞获得免疫记忆的表观遗传调控机制，其与ACLY和p300介导H3K27乙酰化密切相关，并可能与多发性硬化症等自身免疫性疾病的发病机制相关，具备成为潜在治疗靶点的临床价值。参考文献1.Wendeln AC, Degenhardt K, Kaurani L, Gertig M, Ulas T, Jain G, Wagner J, Hasler LM, Wild K, Skodras A et al: Innate immune memory in the brain shapes neurological disease hallmarks. Nature 2018, 556(7701):332-338.2.Dai H, Lan P, Zhao D, Abou-Daya K, Liu W, Chen W, Friday AJ, Williams AL, Sun T, Chen J et al: PIRs mediate innate myeloid cell memory to nonself MHC molecules. Science 2020, 368(6495):1122-1127.3.Lee HG, Rone JM, Li Z, Akl CF, Shin SW, Lee JH, Flausino LE, Pernin F, Chao CC, Kleemann KL et al: Disease-associated astrocyte epigenetic memory promotes CNS pathology. Nature 2024, 627(8005):865-872.4.Wheeler MA, Clark IC, Tjon EC, Li Z, Zandee SEJ, Couturier CP, Watson BR, Scalisi G, Alkwai S, Rothhammer V et al: MAFG-driven astrocytes promote CNS inflammation. Nature 2020, 578(7796):593-599.5.Rothhammer V, Borucki DM, Tjon EC, Takenaka MC, Chao CC, Ardura-Fabregat A, de Lima KA, Gutierrez-Vazquez C, Hewson P, Staszewski O et al: Microglial control of astrocytes in response to microbial metabolites. Nature 2018, 557(7707):724-728.6.Pietrocola F, Galluzzi L, Bravo-San Pedro JM, Madeo F, Kroemer G: Acetyl coenzyme A: a central metabolite and second messenger. Cell Metab 2015, 21(6):805-821.7.Wellen KE, Hatzivassiliou G, Sachdeva UM, Bui TV, Cross JR, Thompson CB: ATP-citrate lyase links cellular metabolism to histone acetylation. Science 2009, 324(5930):1076-1080.8.Chierzi S, Kacerovsky JB, Fok AHK, Lahaie S, Shibi Rosen A, Farmer WT, Murai KK: Astrocytes Transplanted during Early Postnatal Development Integrate, Mature, and Survive Long Term in Mouse Cortex. J Neurosci 2023, 43(9):1509-1529.责任编辑丨BioTalker

MXene nanoparticle scaffolds have been shown to stimulate muscle growth, making them a promising option to treat muscle loss and damage. Now, researchers explain the molecular mechanisms behind their positive influence on muscle regeneration. This discovery can advance MXene scaffolds, potentially improving muscle reconstruction surgeries and establishing them as a standard medical practice for muscle recovery. Tissue engineering, which involves the use of grafts or scaffolds to aid cell regeneration, is emerging as a key medical practice for treating volumetric muscle loss (VML), a condition where a significant amount of muscle tissue is lost beyond the body's natural regenerative capacity. To improve surgical outcomes, traditional muscle grafts are giving way to artificial scaffold materials, with MXene nanoparticles (NPs) standing out as a promising option. MXene NPs are 2D materials primarily composed of transition-metal carbides and nitride. They are highly electrically conductive, can accommodate a wide range of functional groups, and have stacked structures that promote cell interactions and muscle growth. While there have been practical demonstrations in the laboratory showcasing their ability to promote the reconstruction of skeletal muscles, the specific mechanism by which they do so remains unclear. To address this gap, Associate Professor Yun Hak Kim from the Department of Anatomy and Department of Biomedical Informatics alongside Professors Suck Won Hong, and Dong-Wook Han from the Department of Cogno-Mechatronics Engineering at Pusan National University, developed nanofibrous matrices containing MXene NPs as scaffolds. They used DNA sequencing to reveal the genes and biological pathways activated by MXene NPs to aid in muscle regeneration. These findings, published on 4 January 2024, in Volume 16 of Nano-Micro Letters, mark a significantly advancement in the use of MXene scaffolds for treating muscle damage. "This discovery posits a prospective avenue for the utilization of these materials to augment the efficacy of muscle tissue regeneration post-injury or damage," explains Professor Kim. In the initial phase, the team created a nanofibrous PCM matrix containing poly(lactide-co-ε-caprolactone) (P), reinforced with collagen (C), and Ti3C2Tx MXene nanoparticles (M). To determine the specific effect of MXene NPs on muscle growth, they prepared three controls: pristine PLCL (P), PLCL with Collagen (PC), and PLCL with MXene (PM). On testing all the scaffolds on mouse models with induced volumetric muscle loss, the researchers observed a significant increase in the overall number of muscle cells in PCM-treated mice compared to the other groups. To understand how MXene nanoparticles (NPs) impact muscle regeneration and growth at the molecular level, the researchers introduced C2C12 myoblasts, which are precursors of muscle cells, onto PC and PCM matrices. The objective was to analyze the differences in gene expression levels between the two matrices. Within the PCM matrix, a heightened production of inducible nitric oxide synthase (iNOS) and serum/glucocorticoid-regulated kinase 1 (SGK1) was identified-two proteins closely associated with calcium signaling and muscle regeneration. These results suggest that MXenes promote calcium ion (Ca2+) deposition around cells. This heightened levels of intracellular Ca2+ triggers the activation of genes that produce iNOS and SGK1 proteins. SGK1 influences the mTOR-AKT pathway, promoting cell proliferation, survival, and myogenesis-the conversion of myoblasts to muscle fibers. Simultaneously, iNOS increases the production of nitric oxide (NO), contributing to myoblast proliferation and muscle fiber fusion. The combined effects lead to the development of mature muscle tissue. The aligned PCM nanofibrous matrices offer biophysical cues for intracellular biochemical signaling, guiding myogenic behaviors. This discovery contributes to our understanding of MXene's potential to regrow muscle and holds promise for refining scaffold designs to enhance this process further. "Within 5 to 10 years, this research may yield groundbreaking treatments for muscle injuries. MXene NP-infused matrices could become a routine in medical practice for athletes, people with muscle-related ailments, and those recuperating from muscle-related traumas or surgeries," Prof. Kim optimistically states. 'These NPs might enhance muscle regeneration methods, offering improved outcomes for reconstructive surgeries and conditions like muscular dystrophy, where muscle function is compromised,' he further adds. The MXene NP-infused matrices hold potential for customization to meet diverse needs in treating muscle loss injuries. This customization may involve adjusting composition, structure, or properties to match specific patient requirements, like size, shape, or bioactivity enhancement. Tailoring these materials could offer personalized solutions for various muscle loss severities. Additionally, the observed enhanced muscle regeneration could aid in a more efficient recovery, potentially reducing post-treatment rehabilitation needs. These matrices, with controllable mechanical properties, hold promise for enhancing in vivo muscle regeneration. Further research into MXene promises expanded clinical applications, potentially benefiting human well-being.

BUSAN, South Korea, Jan. 19, 2024 /PRNewswire/ -- Tissue engineering, which involves the use of grafts or scaffolds to aid cell regeneration, is emerging as a key medical practice for treating volumetric muscle loss (VML), a condition where a significant amount of muscle tissue is lost beyond the body's natural regenerative capacity. To improve surgical outcomes, traditional muscle grafts are giving way to artificial scaffold materials, with MXene nanoparticles (NPs) standing out as a promising option. Continue Reading MXene nanoparticles (MXene NPs) promote calcium deposition around cells which triggers the upregulation of iNOS and SGK1 which contribute to muscle growth. MXene NPs are 2D materials primarily composed of transition-metal carbides and nitride. They are highly electrically conductive, can accommodate a wide range of functional groups, and have stacked structures that promote cell interactions and muscle growth. While there have been practical demonstrations in the laboratory showcasing their ability to promote the reconstruction of skeletal muscles, the specific mechanism by which they do so remains unclear. To address this gap, Associate Professor Yun Hak Kim from the Department of Anatomy and Department of Biomedical Informatics alongside Professors Suck Won Hong, and Dong-Wook Han from the Department of Cogno-Mechatronics Engineering at Pusan National University, developed nanofibrous matrices containing MXene NPs as scaffolds. They used DNA sequencing to reveal the genes and biological pathways activated by MXene NPs to aid in muscle regeneration. These findings, published on 4 January, 2024, in Volume 16 of Nano-Micro Letters, mark a significantly advancement in the use of MXene scaffolds for treating muscle damage. "This discovery posits a prospective avenue for the utilization of these materials to augment the efficacy of muscle tissue regeneration post-injury or damage," explains Professor Kim. In the initial phase, the team created a nanofibrous PCM matrix containing poly(lactide-co-ε-caprolactone) (P), reinforced with collagen (C), and Ti3C2Tx MXene nanoparticles (M). To determine the specific effect of MXene NPs on muscle growth, they prepared three controls: pristine PLCL (P), PLCL with Collagen (PC), and PLCL with MXene (PM). On testing all the scaffolds on mouse models with induced volumetric muscle loss, the researchers observed a significant increase in the overall number of muscle cells in PCM-treated mice than in other groups. Further investigations revealed that MXenes promote calcium ion (Ca2+) deposition around cells. This heightened levels of intracellular Ca2+ triggers the activation of genes that produce inducible nitric oxide synthase (iNOS) and serum/glucocorticoid-regulated kinase 1 (SGK1) proteins. SGK1 influences the mTOR-AKT pathway, promoting cell proliferation, survival, and myogenesis–the conversion of myoblasts to muscle fibers. Simultaneously, iNOS increases the production of nitric oxide (NO), contributing to myoblast proliferation and muscle fiber fusion. The combined effects lead to the development of mature muscle tissue. This discovery contributes to our understanding of MXene's potential to regrow muscle and holds promise for refining scaffold designs to enhance this process further. "Within 5 to 10 years, this research may yield groundbreaking treatments for muscle injuries," Prof. Kim optimistically states. Reference Title of original paper: Highly aligned ternary nanofiber matrices loaded with MXene expedite regeneration of volumetric muscle loss Journal: Nano-Micro Letters DOI: About the institute Pusan National University, located in Busan, South Korea, was founded in 1946, and is now the no. 1 national university of South Korea in research and educational competency. The multi-campus university also has other smaller campuses in Yangsan, Miryang, and Ami. The university prides itself on the principles of truth, freedom, and service, and has approximately 30,000 students, 1200 professors, and 750 faculty members. The university is composed of 14 colleges (schools) and one independent division, with 103 departments in all. Website: Media Contact: Jae-Eun Lee 82 51 510 7928 [email protected] SOURCE Pusan National University