Vascular Adaptation and Mechanical Homeostasis at Tissue, Cellular, and Sub-cellular Levels

Blood vessels exhibit a remarkable ability to adapt throughout life that depends upon genetic programming and well-orchestrated biochemical processes. Findings over the past four decades demonstrate, however, that the mechanical environment experienced by these vessels similarly plays a critical role in governing their adaptive responses. This article briefly reviews, as illustrative examples, six cases of tissue level growth and remodeling, and then reviews general observations at cell-matrix, cellular, and sub-cellular levels, which collectively point to the existence of a "mechanical homeostasis" across multiple length and time scales that is mediated primarily by endothelial cells, vascular smooth muscle cells, and fibroblasts. In particular, responses to altered blood flow, blood pressure, and axial extension, disease processes such as cerebral aneurysms and vasospasm, and diverse experimental manipulations and clinical treatments suggest that arteries seek to maintain constant a preferred (homeostatic) mechanical state. Experiments on isolated microvessels, cell-seeded collagen gels, and adherent cells isolated in culture suggest that vascular cells and sub-cellular structures such as stress fibers and focal adhesions likewise seek to maintain constant a preferred mechanical state. Although much is known about mechanical homeostasis in the vasculature, there remains a pressing need for more quantitative data that will enable the formulation of an integrative mathematical theory that describes and eventually predicts vascular adaptations in response to diverse stimuli. Such a theory promises to deepen our understanding of vascular biology as well as to enable the design of improved clinical interventions and implantable medical devices.     

Cyclic tensile strain upregulates collagen synthesis in isolated tendon fascicles

Mechanical stimulation has been implicated as an important regulatory factor in tendon homeostasis. In this study, a custom-designed tensile loading system was used to apply controlled mechanical stimulation to isolated tendon fascicles, in order to examine the effects of 5% cyclic tensile strain at 1 Hz on cell proliferation and matrix synthesis. Sample viability and gross structural composition were maintained over a 24 h loading period. Data demonstrated no statistically significant differences in cell proliferation or glycosaminoglycan production, however, collagen synthesis was upregulated with the application of cyclic tensile strain over the 24 h period. Moreover, a greater proportion of the newly synthesised matrix was retained within the sample after loading. These data provide evidence of altered anabolic activity within tendon in response to mechanical stimuli, and suggest the importance of cyclic tensile loading for the maintenance of the collagen hierarchy within tendon.     

A cellular reaction to antibody in tissue culture studied with electron microscopy

The reaction of embryonic chick heart cells grown in tissue culture to specific guinea pig antiserum has been studied with electron microscopy. Heart fragments from chick embryos were cultured with a plasma clot. After being tested with antiserum or normal serum, they were fixed with buffered osmium tetroxide and embedded in butyl methacrylate before removal from the glass culture chamber. Thin cells found by phase microscopy to have reacted were sectioned in a plane parallel to the glass surface on which they had grown. The results confirm and extend observations made previously while the reactions were occurring. The plasma membrane, like that of the red cell, becomes disrupted or less resistant to trauma following the action of antiserum. The membranes of mitochondria and endoplasmic reticulum vesiculate and swell. Before nuclear shrinkage becomes prominent, the outer nuclear membrane separates over a large portion of the nuclear envelope and forms one or more large swollen blebs. Thus, the outer nuclear membrane shows a reactivity similar to endoplasmic reticulum. It is suggested that the various physical and chemical changes observed to follow the action of antibody and complement on fibroblasts may be explained by osmotic pressure differences between various cell components. Some basic similarities to the action of hemolytic agents on red cells are noted.     

肺炎链球菌培养研究

从５种肺炎链球菌液体培养基中,选择出ＢＹＧＰＰ－ｇｌｕ培养基,与国外常用的ＢＨＩ培养基相比,细菌生长良好,便于规模生产。并对肺炎链球菌生长特性作了探讨,表明维持一定的糖浓度、ｐＨ值、ＣＯ２供应量以及适宜的培养时间,是肺炎链球菌培养成功与否的主要影响因素。本文还对肺炎链球菌工作菌种的实验室保存方法进行了研究。     

A flow-through tissue culture system with fast dynamic response

A flow-through system in which monolayer cells, growing on a 50-cm² glass surface, are in contact with a film of medium with a thickness of 0.14 mm, is described. For murine B16 melanoma cells, the loading capacity is 8.10⁶ cells. The flow-through principle permits frequent off-line or on-line detection of medium constituents for a period on the order of days. The system has a fast dynamic response. With off-line radiochemical detection, the system was applied to the uptake of uridine and excretion of uracil over a period of 45 h. With on-line fluorescence detection, the interaction between the cells and two anthracycline analogs was monitored. The cells can be easily observed with a light microscope.     

Label-free biochemical imaging of heart tissue with high-speed spontaneous Raman microscopy

Label-free imaging is desirable for elucidating morphological and biochemical changes of heart tissue in vivo. Spontaneous Raman microscopy (SRM) provides high chemical contrast without labeling, but presents disadvantage in acquiring images due to low sensitivity and consequent long imaging time. Here, we report a novel technique for label-free imaging of rat heart tissues with high-speed SRM combined with resonance Raman effect of heme proteins. We found that individual cardiomyocytes were identified with resonance Raman signal arising mainly from reduced b- and c-type cytochromes, and that cardiomyocytes and blood vessels were imaged by distinguishing cytochromes from oxy- and deoxy-hemoglobin in intact hearts, while cardiomyocytes and fibrotic tissue were imaged by distinguishing cytochromes from collagen type-I in infarct hearts with principal component analysis. These results suggest the potential of SRM as a label-free high-contrast imaging technique, providing a new approach for studying biochemical changes, based on the molecular composition, in the heart.     

Biomedical advances from tissue culture

The demonstration that the “dedifferentiation” of cells commonly observed in the early days of tissue culture was due to selective overgrowth of fibroblasts led to enrichment culture techniques (alternate animal and culture passage) designed to give a selective advantage to functionally differentiated tumor cells. These experiments resulted in the derivation of a large number of functionally differentiated clonal strains of a range of cell types. These results gave rise to the hypothesis that cells in culture accurately represent cells in vivo but without the complex in vivo environment. This concept has been strengthened with the development of hormonally defined culture media in combination with functionally differentiated clonal cell lines, which have augmented the potential of tissue culture studies. The use of hormonally defined media in place of serum-supplemented media demonstrates that hormonal responses and dependencies can be discovered in culture. Discoveries of hormonal dependencies of cancer cells has led to therapies targeting intracellular signaling pathways while discoveries of hormonal responses of pluripotent cells are helping to identify the potential application of stem cells. In these and other ways tissue culture technology will continue to contribute to solving problems of human health.     

Observing growth steps of collagen self-assembly by time-lapse high-resolution atomic force microscopy

Insights into molecular mechanisms of collagen assembly are important for understanding countless biological processes and at the same time a prerequisite for many biotechnological and medical applications. In this work, the self-assembly of collagen type I molecules into fibrils could be directly observed using time-lapse atomic force microscopy (AFM). The smallest isolated fibrillar structures initiating fibril growth showed a thickness of approximately 1.5 nm corresponding to that of a single collagen molecule. Fibrils assembled in vitro established an axial D-periodicity of approximately 67 nm such as typically observed for in vivo assembled collagen fibrils from tendon. At given collagen concentrations of the buffer solution the fibrils showed constant lateral and longitudinal growth rates. Single fibrils continuously grew and fused with each other until the supporting surface was completely covered by a nanoscopically well-defined collagen matrix. Their thickness of approximately 3 nm suggests that the fibrils were build from laterally assembled collagen microfibrils. Laterally the fibrils grew in steps of approximately 4 nm, indicating microfibril formation and incorporation. Thus, we suggest collagen fibrils assembling in a two-step process. In a first step, collagen molecules assemble with each other. In the second step, these molecules then rearrange into microfibrils which form the building blocks of collagen fibrils. High-resolution AFM topographs revealed substructural details of the D-band architecture of the fibrils forming the collagen matrix. These substructures correlated well with those revealed from positively stained collagen fibers imaged by transmission electron microscopy.     

A rapid method for preparing tissue culture clones for light and electron microscopy.

Fixation and epoxy-embedment of tissue culture clones in situ were carried out in Falcon tissue culture plates. The clone of cells, retained at one end of the casting, was stained with azure II-methylene blue and then studied with the oil immersion objective. The dimensions of the epoxy casting were ideal for mouting as a block in conventional ultramicrotone chucks. The use of one epoxy casting permits a single preparation of tissue culture clones for direct light microscopic observations and subsequently for ultramicrotomy.     

A tissue culture system for different germplasms of indica rice

Agrobacterium-mediated transformation of indica rice has been manipulated in only a limited number of cultivars because the majority of indica varieties are recalcitrant to in vitro response. Establishment of a highly efficient and widely used tissue culture system for indica rice will accelerate the application of transformation technology in breeding programs and the study of the functions of indica-specific genes. By manipulating plant growth regulators, organic components and salts within the culture media, we established two media for callus induction and subculture, respectively, in tissue culture of indica rice. The modified media could guarantee the production and proliferation of a great number of embryogenic calli with high regeneration capacity from mature seeds representing different indica rice germplasms. The calli obtained from this system should be ideal material for Agrobacterium-mediated transformation. The results suggest that this optimized tissue culture system will be widely applicable for the tissue culture of indica varieties. Electronic Supplementary Material Supplementary material is available for this article at The first two authors contributed equally to this work.     

A root tissue culture system to study winter wheat-rhizobacteria interactions

Summary A tissue culture procedure was developed for growing winter wheat roots. This system was used to study bacterial-root interactions and root colonization by Pseudomonas cepacia strains R55 and R85, Azospirillum brasilense ATCC 29729 and Azotobacter chroococcum ATCC 9043. Axenic root tissue cultures were inoculated with bacteria and incubated at 25° C on a rotary shaker (150 rpm) for up to 3 weeks. At various intervals, root morphology and root hair development, bacterial colonization of root surfaces and nitrogenase activity were determined. As determined by plate counting techniques, bacterial attachment to the roots varied from 7.5 × 10⁴ to 3.2 × 10⁷ colony-forming units cm^–1. Scanning electron microscopy of inoculated roots revealed that some rhizobacteria (e.g., P. cepacia R85) significantly enhanced root hair development, and others (e.g., P. cepacia R55) specifically colonized root exudation sites. Nitrogenase activity of roots inoculated with either A. brasilense ATCC 29729 or A. chroococcum ATCC 9043 was stimulated if the inorganic nitrogen sources in the medium were replaced with 300 g glutamine ml^–1. We propose that the use of root tissue culture systems will facilitate studies on plant root-microbe interactions.Contribution no. R 626, Saskatchewan Institute of Pedology Offprint requests to: J. J. Germida     

Regulation of cell proliferation in a stratified culture system of epithelial cells from prostate tissue

Mechanisms controlling epithelial proliferation and differentiation in the prostate have been primarily investigated in mouse models. The regulation of proliferation and differentiation is poorly understood in human prostate epithelial cells. In vivo, the glandular prostate epithelium consists of a p63-positive proliferating basal cell layer and a post-mitotic p27-positive secretory cell layer. We have established an organized stratified culture system of human primary prostate epithelial cells to gain insight into mechanisms regulating proliferation and differentiation. In this system, expression of p63 is observed in the bottom layer. In addition, BrdU incorporation persists even though cells are confluent. In contrast, in the upper layer, p63 expression is greatly diminished, p27 is expressed, and the cells are growth arrested. Overexpression of cyclin D1 or knockdown of p27 does not increase proliferation. After inactivation of the nuclear phosphoprotein Rb, the cell layers remain organized and cell proliferation increases only in the bottom layer. Furthermore, the expression of p63 remains confined to the bottom layer after Rb inactivation. Altogether, this in vitro model recapitulates certain aspects of in vivo growth regulation and differentiation and suggests that the loss of Rb family proteins in human cells trigger hyperplasia but is not sufficient for transformation.This work was supported by the Departments of Pathology and Urology at Weill Medial College, by grants DAMD-17-02-1-0159, MEDC-GR-355, and P30 CA015704-30, and by grant RO1CA84069 to B.E.C.     

1,25(OH)2D3 regulates collagen quality in an osteoblastic cell culture system

The active form of vitamin D, 1,25(OH)₂D₃, has a broad range of effects on bone, however, its role in the quality of bone matrix is not well understood. In this study, using an osteoblastic cell (MC3T3-E1) culture system, the effects of 1,25(OH)₂D₃ on collagen cross-linking and related enzymes, i.e., lysyl hydroxylases (LH1-3) and lysyl oxidases (LOX, LOXL1-4), were examined and compared to controls where cells were treated with cholecalciferol or ethanol. When compared to the controls, gene expressions of LH1, LH2b and LOXL2 were significantly upregulated by 1,25(OH)₂D₃ up to 72 h of culture. In addition, hydroxylysine (Hyl), Hyl aldehyde (Hyl^ald), Hyl^ald-derived cross-links and a total number of cross-links of collagen were significantly higher and the cross-link maturation was accelerated in the 1,25(OH)₂D₃ treated group. These results demonstrate that 1,25(OH)₂D₃ directly regulates collagen cross-linking in this culture system likely by upregulating gene expression of specific LH and LOX enzymes.     

Altered response of vascular smooth muscle cells to exogenous biochemical stimulation in two- and three-dimensional culture

Removal of vascular smooth muscle cells (SMC) from their native environment alters the biochemical and mechanical signals responsible for maintaining normal cell function, causing a shift from a quiescent, contractile phenotype to a more proliferative, synthetic state. We examined the effect on SMC function of culture on two-dimensional (2D) substrates and in three-dimensional (3D) collagen Type I gels, including the effect of exogenous biochemical stimulation on gel compaction, cell proliferation, and expression of the contractile protein smooth muscle alpha-actin (SMA) in these systems. Embedding of SMC in 3D collagen matrices caused a marked decrease in both cell proliferation and expression of SMA. The presence of the extracellular matrix modulated cellular responses to platelet-derived growth factor BB, heparin, transforming growth factor-beta1, and endothelial cell-conditioned medium. Cell proliferation and SMA expression were shown to be inversely related, while gel compaction and SMA expression were not correlated. Taken together, these results show that SMC phenotype and function can be modulated using biochemical stimulation in vitro, but that the effects produced are dependent on the nature of the extracellular matrix. These findings have implications for the study of vascular biology in vitro, as well as for the development of engineered vascular tissues.     

毛脚鵟细胞体外培养体系建立及三种组织来源细胞特性分析

用组织块培养法对毛脚鵟不同组织进行原代培养,获得了3种不同组织来源的细胞,并成功对细胞进行了冷冻保存和复苏。在传代培养过程中,对比分析了3种组织来源细胞的形态学、生长曲线、贴壁率、核型等生物学特性。形态学方面,3种来源细胞均为成纤维样细胞。对于3种组织来源细胞的贴壁能力分析显示,输卵管源细胞最强,肺源细胞和气管源细胞次之。3种不同组织来源细胞的倍增时间分别为(29.91±0.39)、(33.18±0.21)和(30.67±0.28)h,群体倍增次数分别为3.54±0.01、4.52±0.02和4.38±0.03。毛脚鵟细胞的染色体数目为2n=68,性染色体为典型的ZW型。本实验为今后毛脚鵟细胞利用、遗传信息的保存及生物学特性的深入研究提供实验材料和依据。     

Absence of feedback regulation in the synthesis of COL1A1

Aim

Recent studies have emphasized the importance of the extracellular microenvironment in modulating cell growth, motility, and signalling. In this study we have evaluated the ability of a fibroblast derived-extracellular matrix (fd-ECM) to regulate type I collagen synthesis and degradation in fibroblasts.

Main methods

Fibroblasts were plated on plastic (control) or on fd-ECM and type I collagen synthesis and degradation was evaluated. MTT, western blotting, real time PCR, zymographic analysis and inhibitor assays were utilised to investigate the molecular mechanism of type I collagen regulation by the fd-ECM.

Key findings

Fibroblasts plated on fd-ECM showed significant downregulation in the production of type I collagen and COL1A2 messenger ribonucleic acid (mRNA) whilst COL1A1 mRNA remained unchanged. Cells grown on fd-ECM exhibited increased matrix metalloproteases (MMPs) and their corresponding mRNAs. The use of transforming growth factor β (TGF-β) and MMP inhibitors showed that the excess COL1A1 polypeptide chains were degraded by the combined action of MMP-1, MMP-2, MMP-9 and cathepsins.

Significance

These results show the crucial role played by proteases in regulating extracellular matrix protein levels in the feedback regulation of connective tissue gene expression.     

A bioreactor system for interfacial culture and physiological perfusion of vascularized tissue equivalents

A pivotal requirement for the generation of vascularized tissue equivalents is the development of culture systems that provide a physiological perfusion of the vasculature and tissue-specific culture conditions. Here, we present a bioreactor system that is suitable to culture vascularized tissue equivalents covered with culture media and at the air–medium interface, which is a vital stimulus for skin tissue. For the perfusion of the vascular system a new method was integrated into the bioreactor system that creates a physiological pulsatile medium flow between 80 and 120 mmHg to the arterial inflow of the equivalent's vascular system. Human dermal microvascular endothelial cells (hDMECs) were injected into the vascular system of a biological vascularized scaffold based on a decellularized porcine jejunal segment and cultured in the bioreactor system for 14 days. Histological analysis and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) staining revealed that the hDMECs were able to recolonize the perfused vascular structures and expressed endothelial cell specific markers such as platelet endothelial cell adhesion molecule and von Willebrand factor. These results indicate that our bioreactor system can serve as a platform technology to generate advanced bioartificial tissues with a functional vasculature for future clinical applications.     

Measuring the mechanical stress induced by an expanding multicellular tumor system: a case study

Rapid volumetric growth and extensive invasion into brain parenchyma are hallmarks of malignant neuroepithelial tumors in vivo. Little is known, however, about the mechanical impact of the growing brain tumor on its microenvironment. To better understand the environmental mechanical response, we used multiparticle tracking methods to probe the environment of a dynamically expanding, multicellular brain tumor spheroid that grew for 6 days in a three-dimensional Matrigel-based in vitro assay containing 1.0-microm latex beads. These beads act as reference markers for the gel, allowing us to image the spatial displacement of the tumor environment using high-resolution time-lapse video microscopy. The results show that the volumetrically expanding tumor spheroid pushes the gel outward and that this tumor-generated pressure propagates to a distance greater than the initial radius of the tumor spheroid. Intriguingly, beads near the tips of invasive cells are displaced inward, toward the advancing invasive cells. Furthermore, this localized cell traction correlates with a marked increase in total invasion area over the observation period. This case study presents evidence that an expanding microscopic tumor system exerts both significant mechanical pressure and significant traction on its microenvironment.