Growth of collagen fibrils produced by human osteosarcoma cells: high-resolution scanning electron microscopy

A Novel Antifibrotic Mechanism of Nintedanib and Pirfenidone. Inhibition of Collagen Fibril Assembly

Idiopathic pulmonary fibrosis (IPF) is characterized by excessive deposition of extracellular matrix, in particular, collagens. Two IPF therapeutics, nintedanib and pirfenidone, decelerate lung function decline, but their underlying mechanisms of action are poorly understood. In this study, we sought to analyze their effects on collagen synthesis and maturation at important regulatory levels. Primary human fibroblasts from patients with IPF and healthy donors were treated with nintedanib (0.01-1.0 μM) or pirfenidone (100-1,000 μM) in the absence or presence of transforming growth factor-β1. Effects on collagen, fibronectin, FKBP10, and HSP47 expression, and collagen I and III secretion, were analyzed by quantitative polymerase chain reaction and Western blot. The appearance of collagen fibrils was monitored by scanning electron microscopy, and the kinetics of collagen fibril assembly was assessed using a light-scattering approach. In IPF fibroblasts, nintedanib reduced the expression of collagen I and V, fibronectin, and FKBP10 and attenuated the secretion of collagen I and III. Pirfenidone also down-regulated collagen V but otherwise showed fewer and less pronounced effects. By and large, the effects were similar in donor fibroblasts. For both drugs, electron microscopy of IPF fibroblast cultures revealed fewer and thinner collagen fibrils compared with untreated controls. Finally, both drugs dose-dependently delayed fibril formation of purified collagen I. In summary, both drugs act on important regulatory levels in collagen synthesis and processing. Nintedanib was more effective in down-regulating profibrotic gene expression and collagen secretion. Importantly, both drugs inhibited collagen I fibril formation and caused a reduction in and an altered appearance of collagen fibril bundles, representing a completely novel mechanism of action for both drugs.

Observation of collagen fibrils produced by osteosarcoma cells using atomic force microscopy

The present study examined the three-dimensional process of collagen fibril formation in the human osteosarcoma cell line NOS-1 by conventional scanning electron microscopy (SEM) and atomic force microscopy (AFM). SEM images showed collagen fibril formation on the bottom of culture dishes after 1 week of culture. The collagen fibrils had diameters of 30-100 nm. The surfaces of individual fibrils had characteristic grooves and ridges with periodicities of 60-70 nm. AFM images showed that the newly formed collagen fibrils were 30-300 nm in diameter and possessed characteristic grooves and ridges with periodicities of 60-70 nm. The thicker collagen fibrils contained thinner (approximately 30 nm thick) subfibrils that ran in a helical direction along the long axis of the thicker fibrils. Furthermore, twisted structures of collagen fibrils, which possessed a characteristic rope-like structure, were also identified. The ultrastructure of the collagen fibrils was clearly imaged in liquid medium by AFM, and the process of collagen fibril assembly was successfully analyzed under conditions much closer to the physiological state than those afforded by transmission electron microscopy or SEM. AFM also provided a precise morphological measurement, particularly of the vertical distance, of collagen fibrils with nanometer-scale resolution in liquid conditions.

Designed to fail: a novel mode of collagen fibril disruption and its relevance to tissue toughness

Collagen fibrils are nanostructured biological cables essential to the structural integrity of many of our tissues. Consequently, understanding the structural basis of their robust mechanical properties is of great interest. Here we present what to our knowledge is a novel mode of collagen fibril disruption that provides new insights into both the structure and mechanics of native collagen fibrils. Using enzyme probes for denatured collagen and scanning electron microscopy, we show that mechanically overloading collagen fibrils from bovine tail tendons causes them to undergo a sequential, two-stage, selective molecular failure process. Denatured collagen molecules-meaning molecules with a reduced degree of time-averaged helicity compared to those packed in undamaged fibrils-were first created within kinks that developed at discrete, repeating locations along the length of fibrils. There, collagen denaturation within the kinks was concentrated within certain subfibrils. Additional denatured molecules were then created along the surface of some disrupted fibrils. The heterogeneity of the disruption within fibrils suggests that either mechanical load is not carried equally by a fibril's subcomponents or that the subcomponents do not possess homogenous mechanical properties. Meanwhile, the creation of denatured collagen molecules, which necessarily involves the energy intensive breaking of intramolecular hydrogen bonds, provides a physical basis for the toughness of collagen fibrils.

Some observations on the subfibrillar structure of collagen fibrils as noted during treatment with NKISK and cathepsin G with mechanical agitation

We observed the structure of collagen fibrils in rat tail tendons after treatment with NKISK and cathepsin G. NKISK is a pentapeptide that has been previously shown to bind fibronectin, while cathepsin G is a serine protease that cleaves fibronectin but not type I collagen. In tendons treated with NKISK, fibrils were seen to extensively dissociate into smaller-diameter subfibrils. These subfibrils were homogeneous in diameter with an average diameter of 26.3 ± 5.8 nm. Similar, although less extensive, dissociation into subfibrils was found in tendons treated with cathepsin G. The average diameter of these subfibrils was 24.8 ± 4.9 nm. The ability of NKISK and cathepsin G to release subfibrils at physiological pH without harsh denaturants may enhance the study of the subfibrillar structure of collagen fibrils.

Collagen fibers, reticular fibers and elastic fibers. A comprehensive understanding from a morphological viewpoint

Fibrous components of the extracellular matrix are light-microscopically classified into three types of fibers: collagen, reticular and elastic. The present study reviews the ultrastructure of these fibrous components as based on our previous studies by light, electron, and atomic force microscopy. Collagen fibers present a cord- or tape-shape 1-20 microm wide and run a wavy course in tissues. These fibers consist of closely packed thin collagen fibrils (30-100 nm thick in ordinary tissues of mammals), and exhibit splitting and joining in altering the number of the fibrils to form a three-dimensional network as a whole. Individual collagen fibrils (i.e., unit fibrils) in collagen fibers have a characteristic D-banding pattern whose length is ranges from 64 to 67 nm, depending on tissues and organs. During fibrogenesis, collagen fibrils are considered to be produced by fusing short and thin fibrils with tapered ends. Reticular fibers are usually observed as a delicate meshwork of fine fibrils stained black by the silver impregnation method. They usually underlie the epithelium and cover the surface of such cells of muscle cells, adipose cells and Schwann cells. Electronmicroscopically, reticular fibers are observed as individual collagen fibrils or a small bundle of the fibrils, although the diameter of the fibrils is thin (about 30 nm) and uniform. Reticular fibers are continuous with collagen fibers through the exchange of these collagen fibrils. In silver-impregnated specimens, individual fibrils in reticular fibers are densely coated with coarse metal particles, probably due to the high content of glycoproteins around the fibrils. Elastic fibers and laminae are composed of microfibrils and elastin components. Observations of the extracted elastin have revealed that elastin components are comprised of elastin fibrils about 0.1-0.2 microm thick. Elastic fibers and laminae are continuous with networks and/or bundles of microfibrils (or oxytalan fibers), and form an elastic network specific to individual tissues. The fibrous components of the extracellular matrix are thereby morphologically categorized into two systems: the collagen fibrillar system as a supporting framework of tissues and cells, and the microfibrilelastin system for uniformly distributing stress to maintain the resilience adapted to local tissue requirements.

The subfibrillar arrangement of corneal and scleral collagen fibrils as revealed by scanning electron and atomic force microscopy

The present study was designed to analyze the subfibrillar structure of corneal and scleral collagen fibrils by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Isolated collagen fibrils of the bovine cornea and sclera were fixed with 1% OsO4, stained with phosphotungstic acid and uranyl acetate, dehydrated in ethanol, critical point-dried, metal-coated, and observed in an in-lens type field emission SEM. Some isolated collagen fibrils were fixed with 1% OsO4, dehydrated, critical point-dried and observed without metal-coating in an AFM. Isolated collagen fibrils treated with acetic acid were also examined by SEM and AFM. SEM and AFM images revealed that corneal and scleral collagen fibrils had periodic transverse grooves and ridges on their surface; the periodicity (i.e., D-periodicity) was about 63 nm in the cornea and about 67 nm in the sclera. Both corneal and scleral collagen fibrils contained subfibrils running helicoidally in a rightward direction to the longitudinal axis of the fibril; the inclination angle was about 15 degrees in the corneal fibrils and 5 degrees in the scleral fibrils. These findings indicate that the different D-periodicity between corneal and scleral fibrils depends on the different inclinations of the subfibrils in each fibril. The present study thus showed that corneal collagen fibrils differ from scleral collagen fibrils not only in diameter but also in substructure.