The Dynamic Scleral Extracellular Matrix Alterations in Chronic Ocular Hypertension Model of Rats

Establishment of a novel ER-stress induced myopia model in mice

BACKGROUND

Recent studies have indicated a strong correlation between endoplasmic reticulum (ER) stress and myopia and that eyedrops containing the ER stress inducer tunicamycin (Tm) can induce myopic changes in C57BL/6 J mice. Therefore, this study aimed to create a new myopia model using Tm eyedrops and to explore the mechanism of ER stress-mediated myopia development.

METHODS

Three-week-old C57BL/6 J mice were treated with different concentrations (0, 25, 50, and 100 μg/mL) and/or number of applications (zero, one, three, and seven) of Tm eyedrops. Refraction and axial length (AL) were measured before and one week after Tm treatment. Scleral collagen alterations were evaluated under polarised light after picrosirius red staining. ER stress-related indicators, such as the expression of collagen I and cleaved collagen were detected using Western blotting.

RESULTS

Compared with the control group, mice administered eyedrops with 50 μg/mL Tm only once showed the greatest myopic shifts in refraction and AL elongation and reduced scleral expression of collagen I. Picrosirius red staining showed a lower percentage of bundled collagen in the Tm group. Expression of ER-stress indicators increased in the Tm groups. Furthermore, optimised administration of Tm induced matrix metalloproteinase-2 (MMP2) expression in the sclera, which plays a major role in collagen degradation.

CONCLUSIONS

We have demonstrated that ER stress in the sclera is involved in myopia progression. Tm eyedrops induced myopic changes, loosening of the scleral collagen and decreased expression of collagen I. This process may be associated with ER stress in the sclera, which upregulates the expression of MMP2 leading to collagen degradation.

Crocetin confers neuroprotection and is anti-inflammatory in rats with induced glaucoma

BACKGROUND

Crocetin is a bioactive ingredient in saffron, derived from the Crocus sativus stigmas of the Iridaceae family. As a chemically carotenoid derivative, crocetin exhibites effects like anti-inflammatory, antioxidant, neuroprotective, etc. However, the protective effect of crocetin on glaucoma and its mechanism remains unclear. The current study assesed the neuroprotective and anti-inflammatory effects of crocetin on retinal neurons in glaucoma rats which were induced by 0.3% carbomer injection into the anterior chamber.

METHODS AND RESULTS

The pathological structures on the retina and optic nerve were observed and examined by H&E staining and transmission electron microscopy. Immunohistochemical staining was used to detect the expression of TNF-α, IL-1β, and IL-6 of the retina and the expression of a brain-derived neurotrophic factor (BDNF) in the primary visual cortex (PVC). Western blot was carried out to detect the expression of PI3K, Akt, and NF-κB in the retina. It was found that crocetin ameliorated the pathological changes of the retina and ON and reduced the number of apoptotic retinal ganglion cells. Immunohistochemical staining showed that crocetin could decrease the contents of TNF-α, IL-1β, and IL-6 and increase the contents of BDNF. Western blot showed that crocetin was found to suppress the expression of PI3K, Akt, and NF-κB.

CONCLUSION

The results obtained in this study have indicated that crocetin showes neuroprotective effects on retinal ganglion cells in glaucoma rats and inhibits retinal dysfunction. Meanwhile, crocetin exerted an anti-inflammatory effect to protect the retina by inhibiting the expression of the PI3K/Akt/NF-κB signaling pathway. This work provides substantial evidence that crocetin may be a potential drug for the treatment of glaucoma.

HIF-1α aggravates pathologic myopia through the miR-150-5p/LAMA4/p38 MAPK signaling axis

Therapeutic inhibition of hypoxia-inducible factor-1alpha (HIF-1α) action has emerged as a potential approach for managing several diseases, including myopia. Herein, we analyzed the role of HIF-1α in the progression of pathologic myopia by regulating the miR-150-5p/LAMA4/p38 MAPK axis. Microarray-based gene expression profiling of pathologic myopia was employed to identify differentially expressed genes. Human scleral fibroblasts (HSFs) were cultured under the hypoxic conditions. Interaction among HIF-1α, miR-150-5p, and LAMA4 was identified. Gain- and loss-of-function experiments were performed in hypoxia-exposed HSFs to evaluate the effect of the HIF-1α/miR-150-5p/LAMA4/p38 MAPK axis on the extracellular matrix (ECM) degradation of HSFs and the subsequent pathologic myopia progression. Increased LAMA4 but decreased miR-150-5p was found in serum sample of pathologic myopia patients. HIF-1α and LAMA4 were abundantly expressed, and p38 MAPK was activated while miR-150-5p was weakly expressed in hypoxia-exposed HSFs. HIF-1α was enriched in the promoter region of miR-150-5p and downregulated its expression, thus repressing the ECM degradation of HSFs as shown by increased COL1A1 and TIMP-2 and reduced MMP2. In addition, LAMA4 was a downstream target of miR-150-5p and under the negative regulation by miR-150-5p. Overexpression of miR-150-5p promoted the ECM degradation of HSFs by inhibiting LAMA4 expression and p38 MAPK signaling pathway. However, upregulation of LAMA4 reversed the promoting effect of miR-150-5p on ECM degradation of HSFs. Overall, our findings suggest that HIF-1α can decline miR-150-5p expression and facilitate LAMA4-mediated p38 MAPK signaling pathway activation, thus arresting ECM degradation of HSFs and eventually inducing pathologic myopia.

Mechanical Strain Regulates Myofibroblast Differentiation of Human Scleral Fibroblasts by YAP

Scleral extracellular matrix (ECM) remodeling is thought to play a critical role in the pathogenesis of glaucoma. Mechanical strain induced by elevated intraocular pressure can promote myofibroblast differentiation of fibroblasts and result in scleral ECM remodeling; however, the underlying mechanism remains poorly understood. Yes-associated protein (YAP) is a mechanosensory protein and the key downstream transcriptional effector of the Hippo signaling pathway. Here, we investigated the role of YAP in mechanical strain-induced myofibroblast transformation during glaucoma scleral ECM remodeling. Integrative bioinformatics analyses were performed to identify the key pathways for the ECM remodeling of the sclera in glaucoma. Sprague–Dawley rats were used to establish a chronic ocular hypertension model, and the expression of collagen type I (COL1) and YAP in the sclera was analyzed by immunohistochemical analysis and Western blotting. Furthermore, human scleral fibroblasts (HSFs) were cultured and subjected to mechanical strain. In groups with or without the YAP siRNA or YAP inhibitor, cell proliferation, migration capacity, and the expression levels of YAP, COL1, and α-smooth muscle actin (α-SMA) were evaluated by Cell Counting Kit-8 assay, scratch assay, and Western blotting. The interactions between YAP and Smad3 were demonstrated by coimmunoprecipitation, and the expression levels of COL1 and α-SMA were evaluated in groups treated with or without the Smad3 inhibitor. We first revealed that the Hippo signaling pathway may be involved in mechanical strain-induced scleral ECM remodeling through bioinformatics analysis. Furthermore, the in vivo study showed upregulated YAP, COL1, and α-SMA expression in the hypertensive sclera of rats. In vitro, mechanical strain increased YAP and COL1 expression in HSFs and promoted myofibroblast differentiation. After YAP knockdown or inhibition with verteporfin, mechanical strain-induced fibrotic changes in HSFs were markedly suppressed. Additionally, YAP showed a protein interaction with Smad3, and the upregulation of a-SMA and COL1 in response to mechanical strain was also significantly downregulated following the inhibition of Smad3. In conclusion, mechanical strain activated scleral myofibroblast differentiation via YAP. The YAP pathway may play an important role in regulating scleral myofibroblast differentiation and ECM remodeling of the sclera in glaucoma.