Rac1 modulates the vitreous-induced plasticity of mesenchymal movement in retinal pigment epithelial cells

DOCK1/ELMO1/Rac1 Signaling is Essential for Vitreous-Induced Migration and Contraction of ARPE19 Cells

Purpose: To test the effects of dedicator of cytokinesis protein 1 (DOCK1) with its binding partner engulfment and cell motility protein 1 (ELMO1)-Rac1 axis on the vitreous-induced biological functions of retinal pigment epithelial (RPE) cells. Methods: Rac1 activity in RPE cells after vitreous stimulation was detected via a pull-down assay. The related protein expression levels were examined via western blot analysis. DOCK1 and ELMO1 knockdown cells were generated via CRISPR-Cas9 technology. Cytoskeletal reorganization was detected by immunofluorescent localization of F-actin. Cell proliferation, migration, invasion, and contraction ability were measured via the CCK8 assay, wound healing assay, transwell invasion assay, and collagen contraction assay. Results: Rac1 activity was significantly elevated in ARPE-19 cells stimulated with vitreous fluid for 30 min to 3 h. Depletion of either DOCK1 or ELMO1 with CRISPR/Cas9 attenuated vitreous-stimulated Rac1 activity, thus reversing the vitreous-induced cytoskeletal rearrangements. The functional cell biology results revealed that deficiencies of DOCK1 and ELMO1 significantly impeded the migration, invasion, and contraction abilities of vitreous-stimulated human RPE cells. Conclusion: This study demonstrated that the DOCK1/ELMO1-Rac1 axis plays an essential role in the pathogenesis of proliferative vitreoretinopathy (PVR), thus suggesting that interruption of this axis has potential for PVR therapy.

Leveraging AAV1-Rac1T17N to prevent experimental proliferative vitreoretinopathy

BACKGROUND

Platelet-derived growth factor receptor β (PDGFRβ) is the principal PDGFR isoform in retinal pigment epithelial (RPE) cells from the epiretinal membranes of patients with proliferative vitreoretinopathy (PVR). Ras-related C3 Botulinum toxin substrate 1 (Rac1), a member of the Rho family, is a crucial factor in the cell migration and contraction processes that are inherent to the pathogenesis of PVR. The mutants Rac1T17N and Rac1Q61L can block and promote Rac1 activation, respectively. The major objective of this research was to ascertain whether PDGFRβ mediates vitreous-induced Rac1 activation and whether Rac1T17N could be leveraged for the prevention of PVR pathogenesis in a rabbit model.

METHODS

A pull-down assay was used to examine GTP Rac1 levels, which are indicative of Rac1 activation, and western blotting was used to assess cellular protein expression. A CCK8 assay, a wound healing assay, a transwell invasion assay and a collagen contraction assay were employed to analyze cell proliferation, migration, invasion and contraction capacity, respectively. A PVR model was created by injecting platelet-rich plasma and human retinal pigment epithelial cells (ARPE-19) into the vitreous cavities of rabbits, and this model was used to evaluate the severity of PVR impacted by intravitreally injected ARPE-19 cells transduced with adeno-associated virus (AAV)1-Rac1T17N or Rac1Q61L. PVR grade was evaluated by a double-blinded investigator according to the Fastenberg classification; in addition, ultrasound and histological analyses were performed to assess PVR severity.

RESULTS

Vitreous-induced GTP Rac1 is mediated by PDGFRβ. There was a significant decrease in vitreous-induced GTP Rac1 in ARPE-19 cells transduced with AAV1-Rac1T17N compared with those transduced with AAV1-GFP. In addition, the suppression of GTP Rac1 production in human RPE cells by transduction with AAV1-Rac1T17N inhibited vitreous-induced proliferation, migration, invasion, and contractility. Importantly, the results of the animal experiments indicated that although there was a significant increase in PVR potential in rabbits intravitreally injected with ARPE-19 cells infected with AAV1-Rac1Q61L, there was a significant decrease in PVR potential in rabbits intravitreally injected with ARPE-19 cells infected with AAV1-Rac1T17N (P < 0.01).

CONCLUSIONS

AAV1-Rac1T17N has great potential for PVR therapy.

Silencing the long noncoding RNA MALAT1 inhibits vitreous-induced epithelial-mesenchymal transition in RPE cells by regulating the PDGFRs/AKT axis

PURPOSE

Epithelial-mesenchymal transition (EMT) is a crucial pathological process that contributes to proliferative vitreoretinopathy (PVR), and research indicates that factors present in the vitreous that target cells play pivotal roles in regulating EMT. Experimental studies have confirmed that rabbit vitreous (RV) promotes EMT in human retinal pigment epithelial (RPE) cells. The long noncoding RNA (lncRNA) MALAT1 has been implicated in EMT in various diseases. Thus, this study aimed to investigate the involvement of lncRNA MALAT1 in vitreous-induced EMT in RPE cells.

METHODS

MALAT1 was knocked down in ARPE-19 cells by short hairpin RNA (shRNA) transfection. Reverse transcription PCR (RT‒PCR) was used to evaluate MALAT1 expression, and Western blotting analysis was used to measure the expression of EMT-related proteins. Wound-healing, Transwell, and cell contraction assays were conducted to assess cell migration, invasion, and contraction, respectively. Additionally, cell proliferation was assessed using the CCK-8 assay, and cytoskeletal changes were examined by immunofluorescence.

RESULTS

MALAT1 expression was significantly increased in ARPE-19 cells cultured with RV. Silencing MALAT1 effectively suppressed EMT and downregulated the associated factors snail1 and E-cadherin. Furthermore, silencing MALAT1 inhibited the RV-induced migration, invasion, proliferation, and contraction of ARPE-19 cells. Silencing MALAT1 also decreased RV-induced AKT and P53 phosphorylation.

CONCLUSIONS

In conclusion, lncRNA MALAT1 participates in regulating vitreous-induced EMT in human RPE cells; these results provide new insight into the pathogenesis of PVR and offer a potential direction for the development of antiproliferative drugs.

Long noncoding RNA ERLR mediates epithelial-mesenchymal transition of retinal pigment epithelial cells and promotes experimental proliferative vitreoretinopathy

Proliferative vitreoretinopathy (PVR) is a disease that causes severe blindness and is characterized by the formation of contractile fibrotic subretinal or epiretinal membranes. The epithelial-mesenchymal transition (EMT) of retinal pigment epithelial (RPE) cells is a hallmark of PVR. This work aims to examine the role of a long noncoding RNA (lncRNA) named EMT-related lncRNA in RPE (ERLR, LINC01705-201 (ENST00000438158.1)) in PVR and to explore the underlying mechanisms. In this study, we found that ERLR is upregulated in RPE cells stimulated with transforming growth factor (TGF)-β1 as detected by lncRNA microarray and RT-PCR. Further studies characterized full-length ERLR and confirmed that it is mainly expressed in the cytoplasm. In vitro, silencing ERLR in RPE cells attenuated TGF-β1-induced EMT, whereas overexpressing ERLR directly triggered EMT in RPE cells. In vivo, inhibiting ERLR in RPE cells reduced the ability of cells to induce experimental PVR. Mechanistically, chromatin immunoprecipitation (ChIP) assays indicated that the transcription factor TCF4 directly binds to the promoter region of ERLR and promotes its transcription. ERLR mediates EMT by directly binding to MYH9 protein and increasing its stability. TCF4 and MYH9 also mediate TGF-β1-induced EMT in RPE cells. Furthermore, ERLR is also significantly increased in RPE cells incubated with vitreous PVR samples. In clinical samples of PVR membranes, ERLR was detected through fluorescent in situ hybridization (FISH) and colocalized with the RPE marker pancytokeratin (pan-CK). These results indicated that lncRNA ERLR is involved in TGF-β1-induced EMT of human RPE cells and that it is involved in PVR. This finding provides new insights into the mechanism and treatment of PVR.

The Lhx9-integrin pathway is essential for positioning of the proepicardial organ

The development of the vertebrate embryonic heart occurs by hyperplastic growth as well as the incorporation of cells from tissues outside of the initial heart field. Amongst these tissues is the epicardium, a cell structure that develops from the precursor proepicardial organ on the right side of the septum transversum caudal to the developing heart. During embryogenesis, cells of the proepicardial organ migrate, adhere and envelop the maturing heart, forming the epicardium. The cells of the epicardium then delaminate and incorporate into the heart giving rise to cardiac derivatives, including smooth muscle cells and cardiac fibroblasts. Here, we demonstrate that the LIM homeodomain protein Lhx9 is transiently expressed in Xenopus proepicardial cells and is essential for the position of the proepicardial organ on the septum transversum. Utilizing a small-molecule screen, we found that Lhx9 acts upstream of integrin-paxillin signaling and consistently demonstrate that either loss of Lhx9 or disruption of the integrin-paxillin pathway results in mis-positioning of the proepicardial organ and aberrant deposition of extracellular matrix proteins. This leads to a failure of proepicardial cell migration and adhesion to the heart, and eventual death of the embryo. Collectively, these studies establish a requirement for the Lhx9-integrin-paxillin pathway in proepicardial organ positioning and epicardial formation.

Epithelial-mesenchymal status influences how cells deposit fibrillin microfibrils

Here, we show that epithelial–mesenchymal status influences how cells deposit extracellular matrix. Retinal pigmented epithelial (RPE) cells that expressed high levels of E-cadherin and had cell–cell junctions rich in zona occludens (ZO)-1, β-catenin and heparan sulfate, required syndecan-4 but not fibronectin or protein kinase C α (PKCα) to assemble extracellular matrix (fibrillin microfibrils and perlecan). In contrast, RPE cells that strongly expressed mesenchymal smooth muscle α-actin but little ZO-1 or E-cadherin, required fibronectin (like fibroblasts) and PKCα, but not syndecan-4. Integrins α5β1 and/or α8β1 and actomyosin tension were common requirements for microfibril deposition, as was heparan sulfate biosynthesis. TGFβ, which stimulates epithelial–mesenchymal transition, altered gene expression and overcame the dependency on syndecan-4 for microfibril deposition in epithelial RPE cells, whereas blocking cadherin interactions disrupted microfibril deposition. Renal podocytes had a transitional phenotype with pericellular β-catenin but little ZO-1; they required syndecan-4 and fibronectin for efficient microfibril deposition. Thus, epithelial–mesenchymal status modulates microfibril deposition.