Combined effects of interleukin-1β and cyclic stretching on metalloproteinase expression in corneal fibroblasts in vitro

The cellular responses of corneal fibroblasts to cyclic stretching loads

Mechanical signaling plays a crucial role in maintaining extracellular matrix (ECM) homeostasis in various structures. In this study, we investigated the responses of corneal fibroblasts to cyclic stretching loads using an in vitro cell culture system. Bovine corneal fibroblasts were cultured and subjected to equibiaxial cyclic strain of 15% for 72 h at a frequency of 0.25 Hz, with bovine skin fibroblasts used as a comparison. We explored various cellular behaviors, including morphological changes, cell proliferation, and metabolism in response to mechanical stretching loads. The expression of genes, protein secretion, and enzymatic activity for several major metalloproteinases was also determined through Q-PCR, Western blot, and gel zymography. Additionally, we investigated the involvement of mitogen-activated protein kinases (MAPKs) signaling pathways in the corneal fibroblasts when subjected to mechanical stimuli. Our findings revealed that, compared to skin fibroblasts, corneal fibroblasts were reluctant to morphological changes in response to a prolonged (72 h) and high-amplitude (15% of strain) cyclic stretching load. However, cyclic stretching loads stimulated the upregulation of MMP-2 expression in corneal fibroblasts via the MAPK signaling pathways involving extracellular signal-regulated kinase and p38. Together with a lack of upregulation in type I collagen expression, our results indicate the induction of the ECM degradation process in corneal fibroblasts in response to cyclic stretching. These findings emphasize the mechanoresponsive nature of corneal fibroblasts and shed light on the potential impact of intense mechanical stress on the cornea in both normal and pathological conditions such as keratoconus, providing valuable insights for understanding corneal mechanobiology.

Unravelling the Impact of Cyclic Mechanical Stretch in Keratoconus-A Transcriptomic Profiling Study

Biomechanical and molecular stresses may contribute to the pathogenesis of keratoconus (KC). We aimed to profile the transcriptomic changes in healthy primary human corneal (HCF) and KC-derived cells (HKC) combined with TGFβ1 treatment and cyclic mechanical stretch (CMS), mimicking the pathophysiological condition in KC. HCFs (n = 4) and HKCs (n = 4) were cultured in flexible-bottom collagen-coated 6-well plates treated with 0, 5, and 10 ng/mL of TGFβ1 with or without 15% CMS (1 cycle/s, 24 h) using a computer-controlled Flexcell FX-6000T Tension system. We used stranded total RNA-Seq to profile expression changes in 48 HCF/HKC samples (100 bp PE, 70-90 million reads per sample), followed by bioinformatics analysis using an established pipeline with Partek Flow software. A multi-factor ANOVA model, including KC, TGFβ1 treatment, and CMS, was used to identify differentially expressed genes (DEGs, |fold change| ≥ 1.5, FDR ≤ 0.1, CPM ≥ 10 in ≥1 sample) in HKCs (n = 24) vs. HCFs (n = 24) and those responsive to TGFβ1 and/or CMS. PANTHER classification system and the DAVID bioinformatics resources were used to identify significantly enriched pathways (FDR ≤ 0.05). Using multi-factorial ANOVA analyses, 479 DEGs were identified in HKCs vs. HCFs including TGFβ1 treatment and CMS as cofactors. Among these DEGs, 199 KC-altered genes were responsive to TGFβ1, thirteen were responsive to CMS, and six were responsive to TGFβ1 and CMS. Pathway analyses using PANTHER and DAVID indicated the enrichment of genes involved in numerous KC-relevant functions, including but not limited to degradation of extracellular matrix, inflammatory response, apoptotic processes, WNT signaling, collagen fibril organization, and cytoskeletal structure organization. TGFβ1-responsive KC DEGs were also enriched in these. CMS-responsive KC-altered genes such as OBSCN, CLU, HDAC5, AK4, ITGA10, and F2RL1 were identified. Some KC-altered genes, such as CLU and F2RL1, were identified to be responsive to both TGFβ1 and CMS. For the first time, our multi-factorial RNA-Seq study has identified many KC-relevant genes and pathways in HKCs with TGFβ1 treatment under CMS, suggesting a potential role of TGFβ1 and biomechanical stretch in KC development.

Unraveling the mechanobiology of cornea: From bench side to the clinic

The cornea is a transparent, dome-shaped structure on the front part of the eye that serves as a major optic element and a protector from the external environment. Recent evidence shows aberrant alterations of the corneal mechano-environment in development and progression of various corneal diseases. It is, thus, critical to understand how corneal cells sense and respond to mechanical signals in physiological and pathological conditions. In this review, we summarize the corneal mechano-environment and discuss the impact of these mechanical cues on cellular functions from the bench side (in a laboratory research setting). From a clinical perspective, we comprehensively review the mechanical changes of corneal tissue in several cornea-related diseases, including keratoconus, myopia, and keratectasia, following refractive surgery. The findings from the bench side and clinic underscore the involvement of mechanical cues in corneal disorders, which may open a new avenue for development of novel therapeutic strategies by targeting corneal mechanics.

Single-cell atlas of keratoconus corneas revealed aberrant transcriptional signatures and implicated mechanical stretch as a trigger for keratoconus pathogenesis

Keratoconus is a common ectatic corneal disorder in adolescents and young adults that can lead to progressive visual impairment or even legal blindness. Despite the high prevalence, its etiology is not fully understood. In this study, we performed single-cell RNA sequencing (scRNA-Seq) analysis on 39,214 cells from central corneas of patients with keratoconus and healthy individuals, to define the involvement of each cell type during disease progression. We confirmed the central role of corneal stromal cells in this disease, where dysregulation of collagen and extracellular matrix (ECM) occurred. Differential gene expression and histological analyses revealed two potential novel markers for keratoconus stromal cells, namely CTSD and CTSK. Intriguingly, we detected elevated levels of YAP1 and TEAD1, the master regulators of biomechanical homeostasis, in keratoconus stromal cells. Cyclical mechanical experiments implicated the mechanical stretch in prompting protease production in corneal stromal cells during keratoconus progression. In the epithelial cells of keratoconus corneas, we observed reduced basal cells and abnormally differentiated superficial cells, unraveling the corneal epithelial lesions that were usually neglected in clinical diagnosis. In addition, several elevated cytokines in immune cells of keratoconus samples supported the involvement of inflammatory response in the progression of keratoconus. Finally, we revealed the dysregulated cell-cell communications in keratoconus, and found that only few ligand-receptor interactions were gained but a large fraction of interactional pairs was erased in keratoconus, especially for those related to protease inhibition and anti-inflammatory process. Taken together, this study facilitates the understanding of molecular mechanisms underlying keratoconus pathogenesis, providing insights into keratoconus diagnosis and potential interventions.

Effect of Static and Dynamic Stretching on Corneal Fibroblast Cell

A strain gradient was created by punching a hole in the center of a stretched elastic polydimethylsiloxane membrane to determine the effect of different strains on cultured human keratocytes (HK). In this study, two stretching methods were used: continuous stretching and cyclic stretching. Continuous stretching is relatively static, while acyclic stretching is relatively dynamic. These methods, respectively, represented the effects of high intraocular pressure and rubbing of the eyes on corneal cells. Image processing codes were developed to observe the effects of stress concentration, shear stress, continuous stretching, and cyclic stretching on HKs. The results demonstrate that stretching and shear stress are not conducive to the proliferation of corneal cells and instead cause cell death. A 10% strain had greater inhibitory effects than a 3% strain on cell proliferation. Cell survival rates for continuous stretching (static) were higher than those for cyclic stretching (dynamic). The stretching experiment revealed that cyclic stretching has a greater inhibitory effect on the growth and proliferation of corneal cells than continuous stretching. Accordingly, it shows that cyclic loading is more harmful than high intraocular pressure (static loading) to corneal cells.

Histological and molecular biological analysis on the reaction of absorbable thread; Polydioxanone and polycaprolactone in rat model

INTRODUCTION

One of the most frequently performed anti-aging surgical procedures is thread facelift. Since the 2010s, thread lifts using absorbable polydioxanone (PDO) thread were developed and have become increasingly popular. This research aims to identify the changes in and the mechanisms of absorbable thread-lifting components, namely, PDO (polydioxanone) and PCL (polycaprolactone), with varied absorption periods in the body.

METHODS

Four different types of threads, namely, single-stranded thread, 4-stranded thread, 12-stranded thread, and barbed Cog thread, were used for each component. Histological changes in the thread and neighboring tissue of rat model were investigated for 2-week interval, and PCR was conducted for genes related to fibroblast proliferation including type 1α1 collagen, type 3α1 collagen, transforming growth factor beta 1 (TGF-β1).

RESULTS

An increase in the collagen formation in all types of PDO and PCL groups was observed during the first 12 weeks and decreased afterward. Collagen formation decreased later in the PCL thread group significantly than the POD group. PCL thread remained logner in the tissue for over a year regarding POD requiring around 24 weeks of absorption-degradation. A larger surface area between the thread and the tissue induces a greater response in the tissue, resulting in an increase in inflammatory cells, myofibroblasts, and fibroblasts. Results showed a similar pattern of increase in type 1α1 collagen and TGF-β in the PDO thread group. This suggests that TGF-β signal transduction leads to fibroblast proliferation that stimulates collagen formation and tissue re-formation. In contrast, only type 3α1 collagen increased in the PCL thread group.

CONCLUSION

More collagen formation and tissue responses are induced by PCL thread, remaining longer in the tissue than PDO, leading to more tissue tightening effects that is one of the most important points of face lifting. Morphological comparison of threads shows that not only an increase in surface area between thread and tissue but also multi-strand increase tissue response, which in turn increases tissue maintenance effects.

Functional assistance for stress distribution in cell culture membrane under periodically stretching

Dynamic cell cultures simulate the in vivo cell environment for a regular loading system with curtain strains. However, it is difficult to obtain strains that are suitable for cells without conducting multiple trials. This study develops a device that increases the strain gradient by changing the tensile section, in order to determine the effect of various cyclic strains on cultured human keratinocytes (HK) cells. This device is used to determine the effect of 3% and 5% cyclic strain and shear strain on cell proliferation and arrangement at 1 Hz. The results show that compared with static and 3% strain, a 5% cyclic strain better inhibits the proliferation of HK cells. Compared to the initial cell attachment when there is no specific directionality, the cells are aligned in the vertical stretching direction after cyclic stretching. This equipment increases the efficiency of the experiment and more intuitively maps the cell behavior and shape to the strain field and the response to the shear strain.

Effects of Mechanical Compression on Cell Morphology and Function in Human Corneal Fibroblasts

Purpose: To explore the effect of mechanical compression (similar to that induced by eye rubbing) on cell morphology, proliferation, apoptosis, and extracellular matrix synthesis and degradation in human corneal fibroblasts.Materials and methods: Human corneal fibroblasts were isolated from corneal lenticule tissue of 10 patients after small incision lenticule extraction surgery. A system was established to mechanically compress corneal fibroblasts with pressure ranging from 0 to 524 Pa. Morphological changes, cell proliferation, apoptosis, and corneal matrix synthesis and degradation were examined using microscopy imaging, bromodeoxyuridine staining, flow cytometry, and qPCR analysis in human corneal fibroblasts after mechanical compression.Results: Human corneal fibroblasts showed short and thick cytoplasmic extensions, as well as a relatively low aspect ratio, suggesting significant morphological alterations caused by high levels of compressive stress. Mechanical compression inhibited cell proliferation and promoted cell apoptosis. Furthermore, compressive stress led to significant elevation in the expression of genes related to extracellular matrix degradation (matrix metalloproteinases MMP1 and MMP9) as early as 6 h after compression and moderate changes in the expression of tissue inhibitors of metalloproteinases. In addition, the mRNA expression levels of COL1A1, lumican, and vimentin were reduced 24 and 48 h after mechanical compression.Conclusions: Mechanical compression alters cell morphology, inhibits proliferation, induces apoptosis, upregulates genes related to extracellular matrix degradation, and downregulates corneal structural genes in human corneal fibroblasts. This study provides evidence that compressive stress significantly influences corneal keratocytes. Our findings suggest that this mechanical effect may be related to keratoconus associated with chronic eye rubbing.

Autocrine IL-1β mediates the promotion of corneal neovascularization by senescent fibroblasts

Our previous study has confirmed that senescent fibroblasts promote corneal neovascularization (CNV) partially via the enhanced secretion of matrix metalloproteases (MMPs). However, the regulation of MMP expression in senescent fibroblasts remained unclear. In this study, we identified that the expression and secretion levels of interleukin-1β (IL-1β) were significantly upregulated in senescent human corneal fibroblasts than that in normal fibroblasts. Moreover, compared with vehicle-pretreated senescent fibroblasts, IL-1β pretreatment enhanced the expression of angiogenic factors but reduced the expression of angiostatic factors in senescent fibroblasts. When cocultured with human umbilical vein endothelial cells, IL-1β-pretreated senescent fibroblasts more strongly promoted their proliferation, migration, and tube-formation capacities than the vehicle-controlled senescent fibroblasts. In addition, either interleukin-1 receptor antagonist or anti-IL-1β neutralization completely inhibited the promotion of senescent fibroblasts in vascular tube formation in vitro and CNV in vivo. Therefore, we concluded that autocrine IL-1β mediated the promotion of senescent fibroblasts on corneal neovascularization.

Pneumatically actuated cell-stretching array platform for engineering cell patterns in vitro

Cellular response to mechanical stimuli is a well-known phenomenon known as mechanotransduction. It is widely accepted that mechanotransduction plays an important role in cell alignment which is critical for cell homeostasis. Although many approaches have been developed in recent years to study the effect of external mechanical stimuli on cell behaviour, most of them have not explored the ability of mechanical stimuli to engineer cell alignment to obtain patterned cell cultures. This paper introduces a simple, yet effective pneumatically actuated 4 × 2 cell stretching array for concurrently inducing a range of cyclic normal strains onto cell cultures to achieve predefined cell alignment. We utilised a ring-shaped normal strain pattern to demonstrate the growth of in vitro patterned cell cultures with predefined circumferential cellular alignment. Furthermore, to ensure the compatibility of the developed cell stretching platform with general tools and existing protocols, the dimensions of the developed cell-stretching platform follow the standard F-bottom 96-well plate. In this study, we report the principle design, simulation and characterisation of the cell-stretching platform with preliminary observations using fibroblast cells. Our experimental results of cytoskeleton reorganisation such as perpendicular cellular alignment of the cells to the direction of normal strain are consistent with those reported in the literature. After two hours of stretching, the circumferential alignment of fibroblast cells confirms the capability of the developed system to achieve patterned cell culture. The cell-stretching platform reported is potentially a useful tool for drug screening in 2D mechanobiology experiments, tissue engineering and regenerative medicine.