The Lens As Model For Studying Fibrosis Biology Essay


The lens is a critical biological tool to look into the mechanisms involved in fibrosis. The construction of the lens is bioconvex this form helps to refract light being focused on the retina and the cornea. The lens is located in the anterior section of the oculus and is held in topographic point by fibers called the zonular. Zonular fibers attach to the lens and are connected to the cilary organic structure. See figure 1. A

Figure 1. Schematic of the lens and its cellular organisation


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Figure 1 shows the construction of lens and its distinguishable cellular parts ( 9 )

The lens can be separated into distinguishable cellular parts: the lens capsule, the lens epithelial tissue, and the lens fibers. ( 4 ) The lens capsule forms the outer bed of the lens see fig1 and the lens fibers forms most of the inside of the lens. The lens is enclosed in an elastic capsule and this is why they have a spherical form. This form is maintained by the zonular fibers. The lens capsule is a basement membrane that surrounds the whole lens. The Anterior subdivision of the lens contains the lens epithelial tissue. They are positioned between the lens capsule and the lens fibers. The cells of the lens epithelium regulate most of the homeostatic maps of the lens. ( 2 ) ( 3 ) ( 4 ) The cells in the anterior part of the epithelial tissue have been present since lens vesicle formation during embryogenesis. The cells in the peripheral epithelial tissue are capable of migration, cell division and differenating into lens fibre cells that form most of the lens. Many theoretical accounts are available to analyze fibrosis such as transgenic theoretical accounts and tissue civilization and are characterised in the lens. ( 8 )

Fibrosis is a pathological status where the tissue construction is interrupted by the

Production of inordinate extracellular matrix ( ECM ) ( 8 ) . Fibrosis is caused by homeostasis being interrupted by infection, redness and when the ocular map becomes impaired. Homeostasis of the oculus depends on the presence of normal vasculture, ECM and other cell types. Fibrosis is besides referred to the response of an hurt. The hurt can ensue in a lesion or metabolic malfunctions such as redness and degenerative diseases. Fibrosis can happen in many topographic points in the organic structure for illustration in the tegument it can take to a formation of a cicatrix. In the oculus it can do jobs with vision. Problems with vision will interrupt the ocular axis to where cellular operation is no longer possible. Fibrosis of the cornea can take to corneal opacification and loss of vision. These conditions of fibrosis in the oculus lead to vision loss in 1000000s of persons worldwide. ( 1 ) Two chief conditions to be discussed are the anterior subcapsular cataract and posterior capsule opacification.

Anterior subcapsular cataract is the physique up of hempen mass underneath the anterior capsule. It is heavy light dispersing fibrotic parts below the anterior capsule caused by fibrosis. Anterior subcapsular cataract ( ASC ) consequences from the unnatural growing and distinction of the lens epithelial cells to organize fibrotic plaques that disrupt the vision. Plaques in the ASC contain “ myofibroblast-like ” cells and accretion of collagenic matrix. Surveies on cataract utilizing a technique called immunolabelling have shown there is a presence of cytoskeltal and extracellular matrix proteins non expressed by lens cells. Proteins that have undergone immunolabelling in the fibrotic plaques of ASC are I±-smooth musculus actin, fibronection, and tenasoin. I±- smooth musculus actin is a marker for cataract. Anterior subcapsular cataracts are fibrosis opacities that occur near the Centre of the lens epithelial tissue. ( 2 ) ASC is the least prevailing signifier of cataract in the United Kingdom. A recent survey by Lee and joo has shown that transdifferentitaion of lens epithelial cells in ASC causes the production of big sums of extracellular matrix proteins such as fibronectin, collagen I and III which are non present in the lens capsule. The production and deposition of extracellular matrix is a characteristic of fibrosis. Experiments taken on stray whole rat lens civilization showed fibrotic alterations due to the transforming growing factor I? ( TGFI? ) exposure. Many fibrotic upsets are linked with TGFI? . Surveies on four ex vivo human anterior subcapsular cataracts showed folding and thickener of the anterior lens. The cells in the parts showed positive staining for alpha smooth musculus actin. ( 8 ) ( 2 )

Figure 2. A conventional diagram demoing the site of the anterior subcapsular cataract. ( 8 )

Figure 2B a conventional diagram demoing the formation of fibrotic plaque. ( 8 )

Posterior capsular opacification ( PCO ) besides known as secondary cataract is another signifier of cataract that occurs after surgery. It involves unnatural epithelial growing and the formation of fibrotic plaques. Cataract surgery involves the remotion of a section of the anterior capsule and allows visible radiation to go through through the lens once more leting vision to be restored. A lens capsular bag is produced that contains the staying anterior capsule with lens epithelial cells attached. The bag can suit an unreal intraocular lens implant. The staying lens epithelial cells quickly grow and could occupy on the ocular axis where visible radiation dispersing alterations induced by the cells can give rise to secondary ocular loss besides known as PCO. ( 5 )

Figure 3. A Image demoing the station surgical capsular bag ( B ) The growing of quickly plunging epithelial cells occupying the ocular axis giving rise to PCO. ( 8 )

PCO is the most common fibrotic status in the lens and is arisen from the lens epithelial cells that are left behind from cataract surgery. In PCO the plaques besides contain myofibroblast cells and show some of the unnatural markers found in ASC. PCO can be grouped into 4 classs: Elschnig ‘s pearls, capsular fibrosis, Soemmerring ‘s ring, and lentoid of Thiel. The most common signifiers of PCO are capsular fibrosis and Elschnig ‘s pearls. Fibrosis is normally found around the liner of the anterior capsule and the cardinal part of the posterior capsule, where it is present with capsular furrows and creases. The physique up of big sums of extracellular matrix appears to be major cause of opacification in this signifier of PCO. ( 6 )

Many characteristics are common to both PCO and ACO. Both portion similarities with the hempen opacities and in both PCO and ASC the lens epithelial cells transdifferentiate to myofibroblast-like cells. The chief characteristic in both is the transforming growing factor. ( 6 )


TGF-I? is a major system of survey. It is the major fibrotic molecule. Surveies have shown TGF- I? can originate myofibroblast formation, fibrosis and cataract formation in transgenic mice. There are different isoforms of the transforming growing factor ( 1, 2 and 3 ) and are all present in mammals. These isoforms are multifunctional cytokines that play a function in lesion healing and in tissue fix. TGF – I? exists in both a latent and active form.TGF-_2 is a major isoform within the oculus, it plays a critical function in both the short- and long-run development of PCO.It is detected in the aqueous wit and exists in the latent form.TGF_1 and TGF_3 show low degrees of look in the oculus under normal fortunes. In a surgical hurt active degrees of all TGF isoforms can be high. TGF-2 is present in the human capsular bags and besides the add-on of this growing factor to the medium can bring on the matrix and cellular alterations exhibited in vivo. Transforming growing factor is an effectual inducer of both transdifferentiation and contraction, which are critical procedures that support tissue fibrosis. There are many TGF- I? signal transduction tracts. The major intracellular signalling system identified for TGF- is through translocation of smad proteins. Smad are proteins involved in interceding intracellular signal transduction. Many experiments have been taken on animate beings to look into the function of TGF and the function it has on fibrotic upsets of the lens. A survey on a rat lens civilization theoretical account has shown TGF induces anterior subcapsular cataract. ( 7 ) ( 10 ) Studies on capsular bag following cataract surgery from a donor 1 month of surgery has shown increased degrees of TGFI?- induced fibrotic markers including the matrix contraction/wrinkling of the posterior capsule. ( 8 )


Fibrotic conditions can be both biological and cellular procedures. The mechanisms involved in fibrotic conditions are redness and how it can build the fibrotic procedure and how the factors can take to increased matrix production and deposition and the alteration finally defines fibrotic conditions in the lens. ( 8 )

To reason the conditions of fibrosis in the oculus can take to vision loss in 1000000s of persons worldwide. The belongingss of the lens lets us look into the procedures that support fibrosis. TGFI? and smad signal tracts are among the utile marks to be inhibited in the bar and intervention of fibrotic diseases in the oculus. Hyper-proliferation following hurt, matrix production deposition and contraction and the transdifferentaion to myofibroblasts can be seen utilizing the lens as a survey. Myofibroblasts are cardinal go-betweens of ECM production and deposition and in both ASC and PCO it is a common characteristic of fibrotic pathologies. Using transgenic animate beings and tissue civilization theoretical accounts in experiments have shown consequences for fibrosis and hence the lens is an first-class theoretical account to analyze fibrosis. ( 8 )