细胞外间质-整合素在牵张刺激心肌细胞肥大中的作用

应用牵张刺激培养细胞的模型 ,观察胶原、纤维连接蛋白、层粘连素对牵张刺激心肌细胞肥大的影响 ,探讨细胞外间质 -整合素受体在超负荷心肌肥大的跨膜信号传导机制中的作用。结果发现 ,胶原、纤维连接蛋白、层粘连素明显有助于培养心肌细胞的贴壁、伸展。牵张刺激后 ,胶原、纤维连接蛋白基质组心肌细胞的 3H -亮氨酸掺入率和心肌细胞表面积均显著大于对照组 ,而层粘连素组无显著变化 ;可溶性纤维连接蛋白、RGD肽均可显著抑制牵张刺激诱导的培养心肌细胞 (胶原为粘附基质 )的3H -亮氨酸掺入率升高和心肌细胞表面积增大 ,而层粘连素无明显作用。结果表明 ,特异的细胞外间质 -整合素在超负荷心肌肥大机制中发挥了跨膜信号传导作用。     

一种新的体外细胞牵张刺激装置

体外细胞机械刺激装置是研究细胞对机械牵张反应的一种研究设备。目前此类装置有多种,但是这些装置都存在一些不便之处。本文以商品化的Flexercell Strain Unit刺激装置为参照,设计一套离心力牵张装置。通过使贴壁细胞生长的培养板以一定的速度旋转,从而使心肌细胞受到固定大小的离心力的牵张作用。酶解分离3～5d SD大鼠心肌细胞,并分别给予12和24h机械刺激:传统的20%牵张刺激和180r/min的离心力刺激。以~3H-亮氨酸掺入量反映细胞的肥大指标,并测定牵张引起的血管紧张素Ⅱ的自分泌。同对照组相比,~3H-亮氨酸掺入在离心力牵张组显著升高[(1295.17±51.19)vs(1122.67± 51.63)in 12h;(1447.5±35.96)vs(1210.67±90.92)in 24h,P<0.05]。AngⅡ在离心力牵张组均比同期末牵张组均明显升高,12h为128%(P<0.05)和24h为139%(P<0.01)。经24h的牵张,培养液中乳酸脱氢酶活性在膜牵张组显著高于离心力牵张组[(14.5±8.7)U/Lvs (7.8±4.3)U/L,P<0.05]。新型改进的机械牵张装置能够有效刺激心肌细胞蛋白合成增加和AngⅡ的分泌增加,与FlexercellStrain Unit相比,离心力牵张装置对细胞的损害较轻微。     

无巨核细胞条件下促血小板生成素对骨髓基质细胞纤维形成的影响

目的：观察无巨核细胞存在的条件下促血小板生成素能否刺激骨髓基质细胞纤维形成。方法：用改良Dexter培养法进行体外不同浓度促血小板生成素（TPO）作用下的基质细胞培养,在培养过程中检测基质细胞相对增殖指数,纤维连接蛋白、层粘素和Ⅳ型胶原的表达,以及Ⅲ型前胶原蛋白的合成。结果：TPO可刺激基质细胞增殖,相对增殖指数随TPO浓度增加而增强,但不随作用时间延长而增强;纤维连接素、层粘素和Ⅳ型胶原在对照组与实验组均有阳性表达,但实验组强于对照组,但阳性强度不随培养时间的延长而增强;标记的Ⅲ型前胶原蛋白平均荧光强度实验组高于对照组,差异明显,但这种作用的强弱与TPO浓度相关性不强。结论：无巨核细胞存在的条件下,TPO可直接刺激骨髓基质细胞产生细胞外基质和胶原,促进其纤维形成。     

利用逆转录病毒RNAi载体抑制心肌成纤维细胞分泌纤维连接蛋白

心脏间质纤维化是心室重塑的最重要表现之一, 心肌细胞外基质的过度积聚在其中扮演着重要角色. 纤维连接蛋白是细胞外基质的重要成分之一, 它负责胶原之间的连接、细胞的黏附和增殖等. 纤维连接蛋白主要由心肌成纤维细胞产生. 由于导致心肌细胞外基质过度分泌的因素很多, 单独阻断某一上游途径很难完全抑制由其他途径导致的过度合成. 利用RNAi技术试图在细胞外基质合成的终末途径进行阻断以期达到更为有效的结果. 通过体外合成的双链RNA, 抑制了纤维连接蛋白在血管紧张素Ⅱ刺激下的过度表达, 进而构建带有H1启动子的逆转录病毒载体, 成功地实现了用可稳定表达的shRNA抑制纤维连接蛋白的过度分泌. 该载体也可作为今后进行基因功能快速分析和基因治疗的工具.     

蛋白激酶Cδ可能参与肥大心肌细胞转向凋亡

为了探讨肥大心肌细胞对凋亡刺激的易感性及蛋白激酶Cδ(protein kinase Cδ,PKCδ)在其中的作用,以内皮素-1 (endothelin-1,ET-1)处理原代培养的新生大鼠心肌细胞,诱导心肌细胞肥大;再用血管紧张素Ⅱ(angiotensin II,Ang II)作为细胞凋亡诱导因子,采用鬼笔环肽(phalloidin)荧光染色与细胞面积测量两种方法检测心肌肥大,Hoechst 33258荧光染色检测细胞凋亡。结果显示：(1)1与10 nmol/L ET-1作用48h,心肌细胞肌原纤维排列整齐、染色增浓,随ET-1浓度增加而愈加明显,心肌细胞表面积分别增加42．5%和67．3%,以此作为轻度和中度心肌细胞肥大模型。(2)正常、轻度肥大与中度肥大心肌细胞受1nmol/L AngⅡ处理24h后,凋亡率分别为(15．54±1．32)%、(20．65±1．40)%与(29．33±3．52)%,三组之间有显著差异(P＜0．05)。(3)受AngⅡ刺激后,PKCδ特异性抑制剂rottlerin不影响正常心肌细胞的凋亡率,却有效抑制了轻度和中度肥大心肌细胞的凋亡。肥大心肌细胞凋亡易感性明显高于正常心肌细胞,抑制PKCδ可以抑制肥大心肌细胞凋亡,提示PKCδ参与肥大心肌细胞凋亡过程。     

非诺贝特通过FoxO1 抑制心肌肥大

目的:探讨非诺贝特(fenofibrate)对血管紧张素Ⅱ(AngⅡ)诱导的肥大心肌细胞的抑制作用及对FoxO1表达的影响。方法:首先采用AngⅡ诱导心肌细胞肥大,将细胞分为三组:对照组:未给予任何干预;心肌细胞肥大组:AngⅡ(10-7mol/L)刺激细胞;治疗组:先给予fenofibrate(10-5mol/L),30min后AngⅡ(10-7mol/L)刺激细胞。应用蛋白免疫印迹法(western-blotting)和实时定量PCR法(real time PCR)检测各组细胞中转录因子FoxO1的蛋白质及mRNA含量,心肌细胞肥大的判断使用脑钠肽(brain natriuret icpepide BNP)。结果:心肌细胞肥大组的FoxO1表达较对照组明显降低,而治疗组的FoxO1表达较心肌肥大组明显升高。结论:非诺贝特可能通过上调FoxO1表达,从而抑制心肌细胞肥大。     

肥厚预刺激对苯肾上腺素诱导的心肌细胞肥大的保护作用

目的:研究不同肥厚预刺激对苯肾上腺素(Phenylephrine,PE)诱导的心肌细胞肥大的影响。方法:胶原酶联合差速贴壁法分离培养原代SD乳鼠心肌细胞后分组:(1)对照组(常规培养48 h);(2)PE组(50μM PE刺激48 h);(3)不同预刺激+PE组:A,不同浓度的PE(10、20、50μM)预刺激(12 h干预,12 h常规培养);B,PE(50μM)预刺激不同时间(period-1,6 h干预,6 h常规培养;period-2,6 h干预,6 h常规培养,再次6 h干预,6 h常规培养;period-3,8 h干预,8 h常规培养;period-4,12 h干预,12 h常规培养)。预刺激后再用PE(50μM)刺激48 h。经细胞骨架蛋白(α-actining)免疫荧光染色,利用激光共聚焦显微镜观察细胞表型,Image J软件计算心肌细胞表面积,利用实时定量PCR检测肥厚相关标志物表达水平。结果:分离的心肌细胞纯度在90%以上。PE组较对照组心肌细胞明显肥大,细胞表面积增加2.3倍,心肌肥厚标记基因心钠肽(atrial natriuretic peptide,ANP)、脑钠肽(brain natriuretic peptide,BNP)和β肌球蛋白重链(βmyosin heavy chain,βMHC)表达明显升高(P0.05);而不同预刺激+PE组心肌细胞肥大表型明显缓解,其中PE(50μM)两次6 h预刺激最为显著(P0.05)。结论:肥厚预刺激可以减轻PE诱导的心肌细胞肥大的程度,从而对心肌肥厚有保护作用。     

钙调神经磷酸酶依赖的信号通路在大鼠心肌肥大中的作用及调节

本工作在大体动物模型、细胞及分子水平上,对钙调神经磷酸酶（CaN)依赖的信号通路在大鼠豳肥大中的作用及其调节机制进行了研究。结果发现;（１）ＣaN信号通路参与血流动力学超负荷、心肌纤维化、旁／自分泌因子等诱导的心肌细胞肥大;（２）ＣaN信号通道参与血管紧张素Ⅱ(AngⅡ)及碱性成纤维细胞因子(bFGF)诱导的心肌细胞肥大和AngⅡ及bFGF刺激的心脏成纤维细胞增殖;（３）ＣaN通路与丝裂素活化蛋白激酶（ＭＡＰＫ）及蛋白激酶Ｃ（ＰＫＣ）信号途径可能存在相互关系;（４）ＣaN的活化依赖胞内Ｃa^2 浓度的持续升高,ＣaN的活化还受蛋白激酶磷酸化的调节,ＡngⅡ刺激心肌细胞ＣaNmRNA的表达显著增加,ＣaNmRNA本身的表达受Ｃa^2 信号及ＭＡＰＫ级联反应的调控。结论：Ｃa^2 -ＣaN信号通路介导心肌肥大的发生。     

Ⅰ型胶原,内皮素对肾小球内皮细胞及系膜细胞产生细胞外基…

本文观察了Ⅰ型胶原，内波素对肾小球内皮细胞、系膜细胞增殖的影响，同时探讨了Ⅰ型胶原和内皮素对培养的内皮细胞及系膜细胞产生层粘连蛋白、纤连蛋白和Ⅳ型胶原的影响。结果提示：Ⅰ型胶原可以明显促进内皮细胞的增殖，内皮素对系膜细胞的增殖有一定作用；Ⅰ型胶原可以促进内皮细胞产生层粘连蛋白和纤连蛋白，并可以促进系膜细胞产生Ⅳ型胶原；内皮素可以促进系膜细胞产生ＦＮ增多。     

诱发心肌细胞肥大过程中p53和c－myc基因表达的原位杂交研究

利用血管紧张素Ⅱ（ＡｕｇⅡ）诱发下培养的ＳＤ乳鼠心肌细胞（ＭＣ）肥大的模型,采用地高辛配体（ｄｉｇｏｘｉｇｅｎｉｎ）标记探针的原位分子杂交方法,研究了ｐ５３和ｃ－ｍｙｃ基因在血管紧张素Ⅱ促培养乳鼠心肌细胞肥大中的表达变化。实验分成二组：根据ＡｎｇⅡ持续作用心肌细胞时间,实验组分别于第一天,第三天和第七天终止培养;对照组是相同时期不加血管紧张素培养的心肌细胞。杂交信号用图象分析仪（ＭＩＡＳ３００）进行分析处理,统计结果显示：实验组ｐ５３ｍＲＮＡ的表达水平明显低于对照组,且表达水平与用药时间呈负相关。而ｃ－ｍｙｃ的ｍＲＮＡ在加药促肥大早期（第１天）,表达增高,然后逐渐衰减。结果提示：野生型ｐ５３及ｃ－ｍｙｃ基因均可能参与心肌肥大的病理过程,而ｃ－ｍｙｃ基因在心肌肥大过程中可能是一个始动因素。     

Alterations in cell surface carbohydrate composition of a human colon carcinoma cell line affect adhesion to extracellular matrix components.

The adhesion of HT29 human colon adenocarcinoma cells to different extracellular matrix components was studied. While treatment of the cells with sialidase had no detectable effect on binding to laminin and fibronectin, attachment to collagen IV was decreased. However, additional removal of beta-(1-4)-bound galactose led to significantly reduced binding to all of the substrates, including fibronectin and laminin. Tunicamycin treatment, monitored by lectin-induced aggregation, drastically diminished cell adhesion to laminin and fibronectin, whereas cell binding to collagen IV was not affected. Arg-Gly-Asp (RGD)-related peptides were used to study the adhesion to collagen IV. The results show that a serine-containing RGD-related peptide GRGDSP has virtually no effect on colon carcinoma cell adhesion to type IV collagen. In contrast, when serine was substituted for threonine (GRGDTP) adhesion to collagen IV was strongly inhibited. After incubation of sialidase-treated cells with the threonine-containing peptide adhesion was almost totally blocked. These results demonstrate the existence of both RGD-dependent and carbohydrate-based mechanisms for metastatic human HT29 cell binding to collagen IV.     

Evidence for the presence of an integrin cell adhesion receptor on the oolemma of unfertilized human oocytes.

The Arg-Gly-Asp peptide (RGD), contained in several extracellular matrix proteins such as fibronectin, laminin, vitronectin, and collagen, is a tripeptide that plays a role as a recognition sequence in many cell-to-cell and cell-to-matrix adhesion mechanisms, through its interaction with several receptors of the integrin family. We previously described the ability of the oolemma of hamster oocytes to bind GRGDTP coupled to the surface of activated immunobeads and demonstrated that RGD-containing oligopeptides inhibit the adhesion of human and hamster spermatozoa to zona-free hamster oocytes and their subsequent penetration. In the present experiments, we show, utilizing immunobeads coated with an RGD-containing peptide (PepTiteTM 2000), that the oolemma of unfertilized human eggs is also able to recognize this adhesion sequence. The binding of PepTiteTM 2000-coated immunobeads to the oolemma was inhibited by the oligopeptide GRGDTP as well as by fibronectin and laminin. When immunobeads were prepared with a PepTiteTM concentration of 10 micrograms/ml, GRGDTP 150 micrograms/ml, laminin 80 micrograms/ml, and fibronectin 60 micrograms/ml inhibited bead rosetting on the egg surface. These data suggest that a specific binding moiety for RGD is present on the human egg surface. The binding of fibronectin to the oolemma was also demonstrated by the rosetting of immunobeads coupled with antifibronectin antibody to human oocytes after their exposure to 1 mg/ml free fibronectin. Such binding of fibronectin to the oolemma could be inhibited by coincubation with a monoclonal antibody directed against the cell adhesion fragment of fibronectin.(ABSTRACT TRUNCATED AT 250 WORDS)     

肝癌细胞-胞外基质粘附性与粘附识别序列的相关性

以微管吸吮技术研究了人肝癌细胞在ＩＶ型胶原／层粘连蛋白（ＬＮ）／纤维连结蛋白（ＦＮ）裱衬表面的粘附性。进一步,用四种人工合成肽精－甘－天冬－丝（ＲＧＤＳ）、甘－精－甘－天冬－苏－脯ＧＲＧＤＴＰ）、酪－异亮－甘－丝－精（ＹＩＧＳＲ０和半胱－天冬－脯－甘－酪－异亮－甘－丝－精（ＣＤＰＧＹＩＧＳＲ）研究了肝癌细胞粘附性对两种粘附识别序列ＲＧＤ和ＹＩＧＳＲ的依赖性。为了归纳和整理实验结果,根据竞争性抑制的     

Integrin activation and focal complex formation in cardiac hypertrophy

Cardiac hypertrophy is characterized by both remodeling of the extracellular matrix (ECM) and hypertrophic growth of the cardiocytes. Here we show increased expression and cytoskeletal association of the ECM proteins fibronectin and vitronectin in pressure-overloaded feline myocardium. These changes are accompanied by cytoskeletal binding and phosphorylation of focal adhesion kinase (FAK) at Tyr-397 and Tyr-925, c-Src at Tyr-416, recruitment of the adapter proteins p130(Cas), Shc, and Nck, and activation of the extracellular-regulated kinases ERK1/2. A synthetic peptide containing the Arg-Gly-Asp (RGD) motif of fibronectin and vitronectin was used to stimulate adult feline cardiomyocytes cultured on laminin or within a type-I collagen matrix. Whereas cardiocytes under both conditions showed RGD-stimulated ERK1/2 activation, only collagen-embedded cells exhibited cytoskeletal assembly of FAK, c-Src, Nck, and Shc. In RGD-stimulated collagen-embedded cells, FAK was phosphorylated only at Tyr-397 and c-Src association occurred without Tyr-416 phosphorylation and p130(Cas) association. Therefore, c-Src activation is not required for its cytoskeletal binding but may be important for additional phosphorylation of FAK. Overall, our study suggests that multiple signaling pathways originate in pressure-overloaded heart following integrin engagement with ECM proteins, including focal complex formation and ERK1/2 activation, and many of these pathways can be activated in cardiomyocytes via RGD-stimulated integrin activation.     

RGD and YIGSR synthetic peptides facilitate cellular adhesion identical to that of laminin and fibronectin but alter the physiology of neonatal cardiac myocytes

In the mammalian heart, the extracellular matrix plays an important role in regulating cell behavior and adaptation to mechanical stress. In cell culture, a significant number of cells detach in response to mechanical stimulation, limiting the scope of such studies. We describe a method to adhere the synthetic peptides RGD (fibronectin) and YIGSR (laminin) onto silicone for culturing primary cardiac cells and studying responses to mechanical stimulation. We first examined cardiac cells on stationary surfaces and observed the same degree of cellular adhesion to the synthetic peptides as their respective native proteins. However, the number of striated myocytes on the peptide surfaces was significantly reduced. Focal adhesion kinase (FAK) protein was reduced by 50% in cardiac cells cultured on YIGSR peptide compared with laminin, even though ₁-integrin was unchanged. Connexin43 phosphorylation increased in cells adhered to RGD and YIGSR peptides. We then subjected the cardiac cells to cyclic strain at 20% maximum strain (1 Hz) for 48 h. After this period, cell attachment on laminin was reduced to 50% compared with the unstretched condition. However, in cells cultured on the synthetic peptides, there was no significant difference in cell adherence after stretch. On YIGSR peptide, myosin protein was decreased by 50% after mechanical stimulation. However, total myosin was unchanged in cells stretched on laminin. These results suggest that RGD and YIGSR peptides promote the same degree of cellular adhesion as their native proteins; however, they are unable to promote the signaling required for normal FAK expression and complete sarcomere formation in cardiac myocytes. cell adhesion; connexin43; focal adhesion kinase; surface chemistry     

Integrin-like substrate adhesion in RTG-2 cells, a fibroblastic cell line derived from rainbow trout

Fluorometric cell attachment assays together with competitive inhibitors of adhesion were used to probe for the presence of integrins, a diverse family of heterodimeric cell-surface glycoproteins involved in cell-cell and cell-extracellular matrix adhesion, in the fibroblastic rainbow trout cell line, RTG-2. The adhesive properties of this cell line were evaluated. RTG-2 cells adhered poorly to TC plastic in the absence of serum but as little as 2.5% fetal bovine serum allowed over 75% of the cells to attach after 5 h. Surfaces coated with the extracellular matrix proteins collagen I, collagen IV, fibrin, fibrinogen, or fibronectin were able to support attachment of RTG-2 cells. Adhesion of RTG-2 cells to fibronectin varied linearly with fibronectin coating densities in the range 0 to 65 ng/mm(2). Oligopeptides containing the sequence Arg-Gly-Asp (RGD) caused dose-dependent inhibition of adhesion to microtiter plates coated with fibrin, fibrinogen, and fibronectin, whereas attachment to collagen I and collagen IV was less severely affected. In all cases, peptides containing Arg-Gly-Glu (RGE) or Asp-Gly-Arg (DGR) sequences caused no reduction of cell attachment. Since many integrins mediate adhesion by binding to RGD sequences in their target ligands, these results suggest the presence of integrin-like adhesion molecules on the surface of RTG-2 cells.     

Neurite outgrowth,RGD-dependent,and RGD-independent adhesion of identified molluscan motoneurons on selected substrates

The extracellular matrix (ECM) provides structural support to cells and tissues and is involved in the regulation of various essential physiological processes, including neurite outgrowth. Most of the adhesive interactions between cells and ECM proteins are mediated by integrins. Integrins typically recognize short linear amino acid sequences in ECM proteins, one of the most common being Arginine-Glycine-Aspartate (RGD). The present study investigated neurite outgrowth and adhesion of identified molluscan neurons on a selection of substrates in vitro. Involvement of RGD binding sites in adhesion to the different substrates was investigated using soluble synthetic RGD peptides. The cells adhered to native (i.e., nondenatured) laminin and type IV collagen, but not to native plasma fibronectin. Denaturation of fibronectin dramatically enhanced cell adhesion. Only the adhesion to denatured fibronectin was inhibited by RGD peptides, indicating that denaturation uncovers a RGD binding site in the protein. Laminin as well as denatured fibronectin, but not type IV collagen, induced neurite outgrowth from a percentage of the RPA neurons. These results demonstrate that molluscan neurons can attach to various substrates using both RGD-dependent and RGD-independent adhesion mechanisms. This suggests that at least two different cell adhesion receptors, possibly belonging to the integrin family, are expressed in these neurons. Moreover, the results show that vertebrate ECM proteins can induce outgrowth from these neurons, suggesting that the mechanisms involved in adhesion as well as outgrowth promoting are evolutionarily well conserved. © 1998 John Wiley & Sons, Inc. J Neurobiol 35: 37–52, 1998     

Triflavin, an Arg-Gly-Asp-containing peptide, inhibits human cervical carcinoma (HeLa) cell-substratum adhesion through an RGD-dependent mechanism

Triflavin, a 7.5-kDa cysteine-rich polypeptide purified from Trimeresurus flavoviridis snake venom, belongs to a family of RGD-containing peptides, termed disintegrins, that have been isolated from the venoms of various vipers and shown to be potent inhibitors of platelet aggregation. The interaction of tumor cells with extracellular matrices such as fibronectin, vitronectin, and collagen has been shown to be mediated through a family of cell surface receptors that specifically recognize an arginine-glycine-aspartic acid (RGD) sequence within each adhesive protein. In this study, we show that triflavin dose-dependently inhibited adhesion of human cervical carcinoma (HeLa) cells to extracellular matrices (ECMs; i.e., fibronectin, fibrinogen, and vitronectin). On the other hand, triflavin exerted a limited inhibitory effect on cell adhesion to laminin and collagen (type I and IV). On a molar basis, triflavin is approximately 800 times more potent than Gly-Arg-Gly-Asp-Ser (GRGDS) at inhibiting cell adhesion. When immobilized on plate, triflavin significantly promoted HeLa cell adhesion, and this attachment was inhibited by GRGDS. Furthermore, FITC-conjugated triflavin bound to cells in a saturable manner and its binding was inhibited by GRGDS. In addition, triflavin did not affect [³H]thymidine uptake of HeLa cells during a 3-day incubation. These results suggest that triflavin probably binds to integrin receptors expressed on HeLa cell surface via its RGD sequence within its molecule, thereby inhibiting the adhesion of extracellular matrices to HeLa cells.     

Participation of C1q and its receptor in adherence of human diploid fibroblast

C1q binds through its collagen-like domain to specific surface receptors of fibroblasts and to adhesive elements of extracellular matrix including fibronectin, collagens, proteoglycans, and laminin. To determine whether C1q participates in fibroblast adhesion, cells in serum-free medium were plated on surfaces coated with purified C1q at physiologic ionic strength and pH. Surfaces coated with fibronectin or collagen type I served as positive controls, and those coated with BSA were negative controls. Substratum-adsorbed C1q promoted fibroblast adhesion to a maximum of 73% of available cells within 90 min at 37 degrees C. Adhesion was C1q concentration dependent, saturable, specific, and dependent on the collagen-like domain of the molecule. De novo protein synthesis plays a role in adhesion: pretreatment of fibroblasts with cycloheximide reduced adherence about 50% of controls. Addition of exogenous fibronectin, collagen type I, or C1q as soluble mediators did not affect adhesion of the cycloheximide-treated cells to C1q substrate. Adhesion could be accounted for primarily, although not completely, by the C1q receptors. Antibodies raised against the Raji cell C1q receptors (alpha C1qR Ab) specifically inhibited fibroblast adhesion to C1q substrates about 60% of controls. The binding of fibroblasts to C1q substrates could be inhibited about 24% of controls with the GRGDTP cell recognition peptide. GRGDTP and alpha C1q Ab had an additive effect on adhesion that was inhibited 77 to 80% of controls. We conclude from these data that aggregated rather than monomeric C1q may be the natural ligand of the fibroblast C1q receptor, and the biologic function of the receptor in cells of the connective tissue may be cell adhesion.