Influence of high level TGF-β1 on scleral thickness

Color Doppler Imaging, Endothelin-1, Corneal Biomechanics and Scleral Rigidity in Asymmetric Age-Related Macular Degeneration

Purpose

Age-related macular degeneration (AMD) presents a multifaceted etiopathogenesis involving ischemic, inflammatory, and genetic components. This study investigates the correlation between ocular hemodynamics, scleral rigidity (SR), and plasma endothelin-1 (ET1) levels in treatment-naive patients with asymmetrical AMD.

Patients and Methods

This study included 20 treatment-naive patients (12 females and 8 males) with an average age of 76.4 ± 3.7 years, who presented with AMD with neovascular membrane formation (nAMD) in one eye, and intermediate grade 2 AMD (iAMD) in the other eye. The control group consisted of 20 healthy subjects (13 females and 7 males) with a mean age of 74.7 ± 3.9 years. All patients and healthy controls underwent color Doppler imaging (i) of the ophthalmic artery (OA), short posterior ciliary arteries (SPCAs), and central retinal artery (CRA); Plasma ET-1 levels were measured for all patients and healthy subjects. Corneal biomechanics were assessed using an Ocular Response Analyzer and two indices were obtained: corneal hysteresis (CH) and corneal resistance factor (CRF).

Results

Results showed reduced blood flow velocities and increased resistance indices in AMD eyes, particularly affecting the short posterior ciliary arteries. According to mechanical theory, ARMD eyes exhibited elevated scleral rigidity and corneal resistance factor compared to controls, with a notable rise in SR in neovascular AMD (nAMD) eyes. As per the chronic subacute inflammation theory, plasma ET-1 levels were significantly higher in AMD patients, correlating with abnormal SPCAs blood flow and increased resistance indices.

Conclusion

Findings suggest a multifactorial etiology of AMD involving an increase of ET-1 plasma levels with biomechanic damages of corneal and scleral tissue in nAMD.

Pharmacotherapeutic candidates for myopia: A review

This review provides insights into the mechanism underlying the pathogenesis of myopia and potential targets for clinical intervention. Although the etiology of myopia involves both environmental and genetic factors, recent evidence has suggested that the prevalence and severity of myopia appears to be affected more by environmental factors. Current pharmacotherapeutics are aimed at inhibiting environmentally induced changes in visual input and subsequent changes in signaling pathways during myopia pathogenesis and progression. Recent studies on animal models of myopia have revealed specific molecules potentially involved in the regulation of eye development. Among them, the dopamine receptor plays a critical role in controlling myopia. Subsequent studies have reported pharmacotherapeutic treatments to control myopia progression. In particular, atropine treatment yielded favorable outcomes and has been extensively used; however, current studies are aimed at optimizing its efficacy and confirming its safety. Furthermore, future studies are required to assess the efficacy of combinatorial use of low-dose atropine and contact lenses or orthokeratology.

Mechanical strain affects collagen metabolism-related gene expression in scleral fibroblasts

We previously demonstrated that collagen metabolism affects scleral mechanical properties and scleral remodeling. Scleral remodeling changes the mechanical strain on sclera and scleral fibroblasts. We postulated that mechanical strain changes affect collagen metabolism in scleral fibroblasts. To understand the differences in collagen metabolism in scleral fibroblasts related to mechanical strain changes, scleral fibroblasts were isolated and cultured under different mechanical strains using the FX-4000 system or were treated with the TGF-β1 and TGFBR1 inhibitor LY364947. The collagen metabolism-related gene expression levels were detected. The results showed that the appropriate (lower) mechanical strain improved collagen synthesis and reduced collagen decomposition. In contrast, higher mechanical strain reduced collagen synthesis and enhanced collagen decomposition, especially a sustained higher strain. Furthermore, the effect of a transitory higher strain was recoverable, and collagen metabolism in scleral fibroblasts was regulated by TGF-β1. These results suggested that mechanical strain mediates TGF-β1 expression to regulate collagen metabolism in scleral fibroblasts, thereby affect scleral tissue remodeling.

Expression and role of specificity protein 1 in the sclera remodeling of experimental myopia in guinea pigs

AIM

To study the expression of collagen I and transcription factor specificity protein 1 (Sp1), a transforming growth factor-β1 (TGF-β1) downstream target, and reveal the impact of the TGF-β1-Sp1 signaling pathway on collagen remodeling in myopic sclera.

METHODS

Seventy-five 1-week-old guinea pigs were randomly divided into normal control, form deprivation myopia (FDM), and self-control groups. FDM was induced for different times using coverage with translucent latex balloons and FDM recovery was performed for 1wk after 4wk treatment; then, changes in refractive power and axial length were measured. Immunohistochemistry and reverse transcription-polymerase chain reaction were used to evaluate dynamic changes in collagen I and Sp1 expression in the sclera of guinea pigs with emmetropia and experimental myopia, and the relationship between collagen I and Sp1 levels was analyzed.

RESULTS

In the FDM group, the refractive power was gradually changed (from 2.09±0.30 D at week 0 to -1.23±0.69 D, -4.17±0.59 D, -7.07±0.56 D, and -4.30±0.58 D at weeks 2, 4, 6, and 1wk after 4wk, respectively; P<0.05), indicating deepening of myopia. The axial length was increased (from 5.92±0.39 mm at week 0 to 6.62±0.36 mm, 7.30±0.34 mm, 7.99±0.32 mm, and 7.41±0.36 mm at weeks 2, 4, 6, and 1wk after 4wk; P<0.05). The mRNA and protein expression of Sp1 and collagen I in the sclera of the FDM group was lower than that of the control groups (P<0.05), and the reduction was eye-coverage time-dependent. Furthermore, correlation between Sp1 and collagen I down-regulation in the myopic sclera was observed.

CONCLUSION

Our data indicate that transcription factor Sp1 may be involved in the regulation of type I collagen synthesis/degradation during myopic sclera remodeling, suggesting that TGF-β1 signaling plays a role in the development and progression of myopia.

Animal models in myopia research

Our current understanding of the development of refractive errors, in particular myopia, would be substantially limited had Wiesel and Raviola not discovered by accident that monkeys develop axial myopia as a result of deprivation of form vision. Similarly, if Josh Wallman and colleagues had not found that simple plastic goggles attached to the chicken eye generate large amounts of myopia, the chicken model would perhaps not have become such an important animal model. Contrary to previous assumptions about the mechanisms of myopia, these animal models suggested that eye growth is visually controlled locally by the retina, that an afferent connection to the brain is not essential and that emmetropisation uses more sophisticated cues than just the magnitude of retinal blur. While animal models have shown that the retina can determine the sign of defocus, the underlying mechanism is still not entirely clear. Animal models have also provided knowledge about the biochemical nature of the signal cascade converting the output of retinal image processing to changes in choroidal thickness and scleral growth; however, a critical question was, and still is, can the results from animal models be applied to myopia in children? While the basic findings from chickens appear applicable to monkeys, some fundamental questions remain. If eye growth is guided by visual feedback, why is myopic development not self-limiting? Why does undercorrection not arrest myopic progression even though positive lenses induce myopic defocus, which leads to the development of hyperopia in emmetropic animals? Why do some spectacle or contact lens designs reduce myopic progression and others not? It appears that some major differences exist between animals reared with imposed defocus and children treated with various optical corrections, although without the basic knowledge obtained from animal models, we would be lost in an abundance of untestable hypotheses concerning human myopia.

Genetic contributions to myopic refractive error: Insights from human studies and supporting evidence from animal models

Genetic studies of both population-based and recruited affected patient cohorts have identified a number of genomic regions and candidate genes that may contribute to myopic development. Scientists have developed animal models of myopia, as collection of affected tissues from patents is impractical. Recent advances in whole exome sequencing technology show promise for further elucidation of disease causing variants as in the recent identification of rare variants within ZNF644 segregating with pathological myopia. We present a review of the current research trends and findings on genetic contributions to myopic refraction including candidate loci for myopic development and their genomic convergence with expression studies of animal models inducing myopic development.