Study of the effects of rabbit scleral fibroblasts on cellular biomechanical properties and MMP-2 expression using two modes of riboflavin/ultraviolet A wave collagen cross-linking

Regulatory Effects of the Wnt7b/β-Catenin/MMP-2 Signaling Pathway on Scleral Stiffness in Guinea Pigs With Form-Deprivation Myopia

Purpose

The development and progression of myopia are influenced by the Wnt7b/β-catenin signaling pathway. This study investigated the specific impacts of this pathway on the biomechanical properties of the sclera by altering the expression of matrix metalloproteinase-2 (MMP-2) to regulate type I collagen (collagen I) levels.

Methods

We examined the effects of the Wnt7b/β-catenin signaling pathway and MMP-2 on human fetal scleral fibroblasts (HFSFs) and the sclera of guinea pigs with form-deprivation myopia (FDM). To explore the effects of the Wnt7b/β-catenin pathway and the role of MMP-2 in this context, we treated HFSFs and guinea pig sclera with specific agonists and inhibitors targeting Wnt7b/β-catenin and MMP-2. The expression levels of Wnt7b, MMP-2, and collagen I were subsequently analyzed quantitatively via western blot (WB) analysis, immunofluorescence, and quantitative real-time PCR (qRT-PCR) to assess protein and mRNA changes in response to pathway manipulation. Atomic force microscopy (AFM) was used to measure the elastic modulus of the treated HFSFs and guinea pig sclera to directly evaluate changes in cell and tissue stiffness. In the FDM model, essential ocular parameters such as refractive error and axial length (AL) were also assessed.

Results

In vivo and in vitro activation of the Wnt7b/β-catenin signaling pathway significantly upregulated MMP-2 expression, which was accompanied by a notable decrease in collagen I levels. This change led to a reduction in the elastic modulus of both HFSFs and the sclera of guinea pigs with FDM. These significant biomechanical changes in the scleral tissue were indicated by a reduction in stiffness. Alterations in scleral biomechanics were associated with changes in ocular parameters, including an increase in AL and a myopic shift in refraction.

Conclusions

The Wnt7b/β-catenin pathway regulates scleral biomechanics by upregulating MMP-2 expression, which leads to increased collagen I degradation and, consequently, an increase in axial elongation and a myopic shift in refractive error.

Biomechanical changes of tree shrew posterior sclera during experimental myopia, after retrobulbar vehicle injections, and crosslinking using genipin

Myopia is a common ocular condition characterized by biomechanical weakening revealed by increasing creep rate, cyclic softening scleral thinning, change of collagen fibril crimping, and excessive elongation of the posterior sclera resulting in blurred vision. Animal studies support scleral crosslinking as a potential treatment for myopia control by strengthening the weakened sclera and slowing scleral expansion. While multiple studies investigated aspects of the biomechanical weakening and strengthening effects in myopia and after scleral crosslinking, a comprehensive analysis of the underlying mechanical changes including the effect of vehicle injections is still missing. The purpose of this study was to provide a comprehensive analysis of biomechanical changes by scleral inflation testing in experimental myopia, after retrobulbar vehicle injections and scleral crosslinking using genipin in tree shrews. Our results suggest that biomechanical weakening in myopia involves an increased creep rate and higher strain levels at which collagen fibers uncrimp. Both weakening effects were reduced after scleral crosslinking using genipin at doses that were effective in slowing myopia progression. Vehicle injections increased mechanical hysteresis and had a small but significant effect on slowing myopia progression. Also, our results support scleral crosslinking as a potential treatment modality that can prevent or counteract scleral weakening effects in myopia. Furthermore, vehicle solutions may cause independent biomechanical effects, which should be considered when developing and evaluating scleral crosslinking procedures.

Effects of riboflavin/ultraviolet-A(UVA) scleral crosslinking on the mechanical behavior of the scleral fibroblasts of lens-induced myopia Guinea pigs

Myopia is becoming increasingly severe, and studies have shown that the cellular mechanics of scleral fibroblasts are altered following myopia. Scleral UVA-Riboflavin Collagen Crosslinking（sCXL） is a promising treatment for myopia prevention and control of axial growth. Understanding the mechanical properties of scleral fibroblasts is crucial, as it influences the cellular response and limits the extent of molecular deformation triggered. Thus, our study aimed to investigate the effect of mechanical properties of scleral fibroblasts in a lens-induced myopic guinea pig model following sCXL. For this purpose, we performed the 0.1% riboflavin/UVA scleral crosslinking (365 nm,3 mW/cm2,30 min) in the right eyes of guinea pigs in Group CXL. In Group LIM, the right eyes were only administrated negative lens for 6 weeks. No treatment was performed in both eyes of the guinea pigs in group Control. The scleral fibroblasts were isolated and cultured from the scleral tissue at the cross-linking area in Group CXL and the corresponding area in Group LIM and control. The curve of the length of microtubules inhaled by cells under negative pressure was measured by a microaspiration-based isolation technique, and the equilibrium Young's modulus and apparent viscosity of scleral fibroblasts were calculated by formula fitting. The equilibrium Young's modulus of scleral fibroblasts in group CXL was significantly lower than that in the LIM group (P < 0.01, two-sample t-test between pairs）, and there was no significant difference between groups CXL and control. The results show that sCXL can effectively moderate the phenomenon that scleral fibroblasts are not easy to deform after myopia. The apparent viscosity modulus in the CXL group was higher than the groups' control and LIM. Taken together, our data demonstrate the biomechanics of the scleral fibroblasts altered after Riboflavin/UVA scleral collagen cross-linking in a lens-induced myopia model.