肌卫星细胞研究进展

骨骼肌中的卫星细胞,长期以来就被认为是出生后骨骼肌生长、修复和维持的单能成肌干细胞。近年研究发现,卫星细胞与内皮细胞共同起源于胚胎血管祖细胞,且成年骨骼肌中存在多能干细胞,这些肌源多能干细胞在适当的微环境中具有多向分化潜能。这将为治疗包括帕金森病在内的多种临床退行性疾病提供自体干细胞的新来源。本文对肌卫星细胞的起源、增殖和成肌分化的分子调节机制,以及肌卫星细胞的多能干细胞潜能等方面的研究进展进行了综述。     

骨骼肌卫星细胞的特性及其增殖与分化的调控

成体骨骼肌细胞的数量基本保持恒定,骨骼肌的再生主要依赖肌卫星细胞的增殖与分化。骨骼肌卫星细胞是能够被激活、进而分化为肌细胞的一类成肌细胞。现对肌卫星细胞的发生、体外培养以及增殖与分化的调控进行综述,并对能否通过激活肌卫星细胞的增殖来实现肌肉组织生长的调控进行探讨。     

大鼠肌卫星细胞移植失神经骨骼肌的形态学观测

目的探讨大鼠肌卫星细胞移植能否延缓失神经骨骼肌萎缩。方法将16只成年Wistar大鼠分为实验组与对照组,两组均切断大鼠右后肢胫神经,建立腓肠肌失神经动物模型。实验组：将体外培养的同种异体肌卫星细胞悬液0．2mL缓慢注射到失神经腓肠肌内、外侧头中;对照组：则缓慢注射等量的生理盐水于相同部位。术后第4周,采用肌湿重、肌纤维横截面积形态学观测的方法,检测失神经骨骼肌的萎缩变化情况。结果成功地对成年大鼠肌卫星细胞进行了分离、纯化、鉴定、培养和移植。发现实验组与对照组相比,失神经腓肠肌湿重残存率（由手术侧与自身健侧的肌湿重测定值之比得出）：实验组为0．48±0．050,对照组为0．33±0．059,二者存在显著性差异（P〈0．01）;腓肠肌纤维横截面积残存率（由手术侧与自身健侧的肌纤维横截面积测定值之比得出）：实验组为0．58±0．011,对照组为0．50±0．018,二者存在显著性差异（P〈0．01）。结论本实验表明将肌卫星细胞异体移植到失神经骨骼肌内可明显延缓骨骼肌的萎缩进程,为再生神经到达靶器官提供较多的时间,进而为解决再生神经延伸到靶器官前,靶器官已发生不可逆性萎缩,严重制约再生神经效果的临床难题提供一个新的研究思路。     

肌卫星细胞在失重肌萎缩中的可塑性变化及机制

肌卫星细胞在骨骼肌生长发育和出生后骨骼肌损伤修复中起着重要的作用,但是有关肌萎缩中肌卫星细胞的可塑性变化、作用及其机制尚不清楚.本研究采用小鼠尾悬吊模拟失重效应诱导失重肌萎缩,动态分析了失重肌萎缩发生过程中不同类型肌纤维的肌卫星细胞数量和增殖、分化潜能可塑性的改变,发现在失重肌萎缩过程中,处于安静状态的肌卫星细胞显著增多、激活增殖的肌卫星细胞显著减少,而具有成肌分化潜能的肌卫星细胞有持续减少趋势.此外,在失重肌萎缩比目鱼肌单根肌纤维移出的体外培养中,证明了失重肌萎缩肌纤维肌卫星细胞可塑性降低的特征性变化.进一步,通过对比分析Smad3基因敲除及其同窝野生型小鼠,在失重肌萎缩中肌卫星细胞可塑性的差异性变化,揭示了Smad3在调控失重肌萎缩肌卫星细胞可塑性变化中的关键作用.     

鱼类肌肉生长分化与基因表达调控

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贮脂细胞激活的分子细胞学机制

贮脂细胞的激活是启动纤维化的关键病理事件,其激活的分子细胞学机制包括：贮脂细胞（肌成纤维细胞）分泌的ＴＧＦ－β对其自身分泌作用,是贮脂细胞激活的永久刺激因素;内皮细胞通过释放ＰＤＧＦ和ＦＧＦ刺激肌成纤维细胞增殖;Ｋｕｐｆ－ｆｅｒ细胞、单核细胞等通过释放免疫介质影响贮脂细胞增殖及改变细胞合成基质能力,而促进贮脂细胞激活;肝细胞可以通过其释放的介质和直接的膜接触而启动贮脂细胞的活化。激活的贮脂细胞产生     

成年鸡的前,后背阔肌的卫星细胞体外培养下早期发育特征的比较

用酶处理的方法分离出成年鸡前背阔肌(慢肌)和后背阔肌(快肌)中的卫星细胞,在无神经因素影响下分别进行体外培养,每天用相差显微镜观察并比较二者的发育特征。在本实验中不仅观察到一些学者已描述过的卫星细胞的体外发育过程和特征,还发现了快、慢肌的卫星细胞之间在发育上存在的时程差异,即前背阔肌的卫星细胞发育为成肌细胞所需的时间以及成肌细胞融合为肌管所需的时间均比后背阔肌的卫星细胞约少24h。支持了鸟类肌肉的卫星细胞本身带有某种发育倾向的猜想,并把快、慢肌在离体的发育过程中可鉴别出差别的时间从肌管提前到卫星细胞时期。     

肌肉卫星细胞被证实是干细胞

肌肉卫星细胞是肌肉纤维与其膜鞘之间的空间中的静止细胞，在那里它们通过形成与肌肉纤维融合的先驱细胞来对损伤作出反应。有研究报告说，它们能充当干细胞，但卫星细胞群的混合性质意味着．它们的干细胞身份难以证明。Saceo等人通过利用克隆分析证实卫星细胞的确是干细胞、能够自我更新，从而澄清了相关问题。     

激活素A调控人类滋养细胞生物学特性的分子机制及其与胎盘源性妊娠疾病关系的研究进展

在人类妊娠建立过程中,胚胎滋养外胚层细胞与子宫内膜直接接触,严密介导母胎对话,调控胚胎着床、植入宫腔,并逐渐形成维持妊娠期间物质交换、营养供应的胎盘组织。起源于滋养外胚层的一部分滋养细胞(trophoblast)侵袭、迁移进入母体蜕膜组织,重塑子宫螺旋小动脉,对于胎盘形成和母胎血液循环建立至关重要。滋养细胞侵袭、迁移、增殖、凋亡、内皮特性获得等生物学特性异常是胚胎种植失败、自然流产、妊娠滋养细胞疾病、子痫前期、胎儿生长受限等胎盘源性妊娠疾病的重要因素。激活素A(activin A)作为转化生长因子β(transforming growth factor-β,TGF-β)超家族中的一种分泌型蛋白,在妊娠期间母体循环及母胎界面表达丰富,在调控滋养细胞生物学特性以及妊娠的建立和维持中起重要作用。该文主要围绕激活素A调控人类滋养细胞生物学特性的分子机制及其在胎盘源性妊娠疾病中表达改变的研究进展进行综述。     

EGF、bFGF和PHGF对大鼠骨骼肌卫星细胞增殖的影响

用MTT、流式细胞技术、溴脱氧核甘尿嘧啶(bromodeoxyuridine,BrdU)掺入法及免疫细胞化学检测增殖细胞核抗原(proliferating cell nuclear antigen,PCNA)的方法探讨了表皮生长因子(epidermal growth factor,EGF)、碱性成纤维细胞生长因子(basic fibroblast growth factor,bFGF)及促肝细胞生长因子(hepatocyte growth-promoting factor,PHGF)对大鼠骨骼肌卫星细胞增殖的影响。结果表明bFGF、PHGF对骨骼肌卫星细胞有较强的促增殖作用,且两者之间无差别,bFGF最佳作用浓度为5μg／L,PHGF最佳作用浓度为10μg／ml。与其他生长因子相比,PHGF价格低廉易于获取,适宜推广。EGF增殖作用不明显。     

Quantitation of Satellite Cell Proliferation in Vivo Using Image Analysis

A nonisotopic, double fluorescence technique was developed to study myogenic satellite cell proliferation in posthatch turkey skeletal muscle. Labeled satellite cell nuclei were identified on enzymatically isolated myofiber segments using a mouse monoclonal antibody (anti-BrdU) followed by fluorescein-5-isothiocyanate (FITC) conjugated goat anti-mouse IgG secondary antibody. Myofiber nuclei (myonuclei + satellite cell nuclei) were counterstained with propidium iodide (PI). The myofiber segment length, myofiber segment diameter, and the number of PI and FITC labeled nuclei contained in each segment was determined using a Nikon fluorescence microscope, a SIT video camera and Image-1 software. Data collected by three different operators of the image analysis system revealed 5.0 ± 1.4 satellite cell nuclei per 1000 myofiber nuclei and 5284 ± 462 μm³ of cytoplasm surrounding each myofiber nucleus in the pectoralis thoracicus of 9-week-old tom turkeys. BrdU immunohistochemistry coupled with the new approach of PI staining of whole myofiber mounts is an effective combination to allow the use of an efficient semi-automated image analysis protocol.     

AMP-activated Protein Kinase Stimulates Warburg-like Glycolysis and Activation of Satellite Cells during Muscle Regeneration

Satellite cells are the major myogenic stem cells residing inside skeletal muscle and are indispensable for muscle regeneration. Satellite cells remain largely quiescent but are rapidly activated in response to muscle injury, and the derived myogenic cells then fuse to repair damaged muscle fibers or form new muscle fibers. However, mechanisms eliciting metabolic activation, an inseparable step for satellite cell activation following muscle injury, have not been defined. We found that a noncanonical Sonic Hedgehog (Shh) pathway is rapidly activated in response to muscle injury, which activates AMPK and induces a Warburg-like glycolysis in satellite cells. AMPKα1 is the dominant AMPKα isoform expressed in satellite cells, and AMPKα1 deficiency in satellite cells impairs their activation and myogenic differentiation during muscle regeneration. Drugs activating noncanonical Shh promote proliferation of satellite cells, which is abolished because of satellite cell-specific AMPKα1 knock-out. Taken together, AMPKα1 is a critical mediator linking noncanonical Shh pathway to Warburg-like glycolysis in satellite cells, which is required for satellite activation and muscle regeneration.     

Expression of Masticatory-specific Isoforms of Myosin Heavy-chain,Myosin-binding Protein-C and Tropomyosin in Muscle Fibers and Satellite Cell Cultures of Cat Masticatory Muscle

We test the hypothesis that cat jaw satellite cells belong to a distinct lineage preprogrammed to express masticatory-specific isoforms of myosin heavy-chain (m-MyHC), myosin-binding protein-C (m-MBP-C), and tropomyosin (m-Tm) during myogenesis in vitro. A monoclonal antibody (MAb) against m-MyHC and MAbs raised here against cat m-MBP-C and m-Tm were used to stain cryostat sections of cat masseter muscle and cultured myotubes derived from satellite cells of cat temporalis and limb muscles, using peroxidase immunohistochemistry. MAbs against m-MBP-C bound purified m-MBP-C in Western blots. MAbs against m-Tm failed to react with m-Tm in Western blots, but reacted with native m-Tm in gel electrophoresis–derived ELISA. In cat masseter sections, MAbs against m-MyHC, m-MBP-C, and m-Tm stained all masticatory fibers, but not the jaw-slow fibers. Cat jaw and limb muscle cultures mature significantly more slowly relative to rodent cultures. However, at 3 weeks, all three MAbs extensively stained temporalis myotubes, whereas they apparently stained isolated myotubes weakly in cat limb and rat jaw cultures. We conclude that satellite cells of masticatory fibers are preprogrammed to express these isoforms during myogenesis in vitro. These results consolidate the notion that masticatory and limb muscle allotypes are distinct. (J Histochem Cytochem 58:623–634, 2010)     

Molecular Control of B Cell Activation and Immunological Synapse Formation

B cells form an essential part of the adaptive immune system by producing specific antibodies that can neutralize toxins and target infected or malignant cells for destruction. During B cell activation, a fundamental role is played by a specialized intercellular structure called the immunological synapse (IS). The IS serves as a platform for B cell recognition of foreign, often pathogenic, antigens on the surface of antigen‐presenting cells (APC). This recognition is elicited by highly specific B cell receptors (BCR) that subsequently trigger carefully orchestrated intracellular signaling cascades that lead to cell activation. Furthermore, antigen internalization, essential for full B cell activation and differentiation into antibody producing effector cells or memory cells, occurs in the IS. Recent developments especially in various imaging‐based methods have considerably advanced our understanding of the molecular control of B cell activation. Interestingly, the cellular cytoskeleton is emerging as a key player at several stages of B cell activation, including the initiation of receptor signaling. Here, we discuss the functions and molecular mechanisms of the IS and highlight the multifaceted role of the actin cytoskeleton in several aspects of B cell activation.      

A Disintegrin and Metalloprotease 10 (ADAM10) Is Indispensable for Maintenance of the Muscle Satellite Cell Pool

Satellite cells (SCs) are muscle-specific stem cells that are essential for the regeneration of damaged muscles. Although SCs have a robust capacity to regenerate myofibers, the number of SCs decreases with aging, leading to insufficient recovery after muscle injury. We herein show that ADAM10 (a disintegrin and metalloprotease 10), a membrane-bound proteolytic enzyme with a critical role in Notch processing (S2 cleavage), is essential for the maintenance of SC quiescence. We generated mutant mice in which ADAM10 in SCs can be conditionally abrogated by tamoxifen injection. Tamoxifen-treated mutant mice did not show any apparent defects and grew normally under unchallenged conditions. However, these mice showed a nearly complete loss of muscle regeneration after chemically induced muscle injury. In situ hybridization and flow cytometric analyses revealed that the mutant mice had significantly less SCs compared with wild type controls. Of note, we found that inactivation of ADAM10 in SCs severely compromised Notch signaling and led to dysregulated myogenic differentiation, ultimately resulting in deprivation of the SC pool in vivo. Taken together, the present findings underscore the role of ADAM10 as an indispensable component of Notch signaling in SCs and for maintaining the SC pool.     

The Dystrophin Glycoprotein Complex Regulates the Epigenetic Activation of Muscle Stem Cell Commitment

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Cytoskeletal Control of Antigen-Dependent T Cell Activation

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