Growth Differentiation Factor-15-Induced Contractile Activity and Extracellular Matrix Production in Human Trabecular Meshwork Cells

Influence of Growth Differentiation Factor 15 on Intraocular Pressure in Mice

Growth differentiation factor 15 (GDF15), a stress-sensitive cytokine, and a distant member of the transforming growth factor β superfamily, has been shown to exhibit increased levels with aging, and in various age-related pathologies. Although GDF15 levels are elevated in the aqueous humor (AH) of glaucoma (optic nerve atrophy) patients, the possible role of this cytokine in the modulation of intraocular pressure (IOP) or AH outflow is unknown. The current study addresses this question using transgenic mice expressing human GDF15 and GDF15 null mice, and by perfusing enucleated mouse eyes with recombinant human GDF15 (rhGDF15). Treatment of primary cultures of human trabecular meshwork cells with a telomerase inhibitor, an endoplasmic reticulum stress-inducing agent, hydrogen peroxide, or an autophagy inhibitor resulted in significant elevation in GDF15 levels relative to the respective control cells. rhGDF15 stimulated modest but significant increases in the expression of genes encoding the extracellular matrix, cell adhesion proteins, and chemokine receptors (C-C chemokine receptor type 2) in human trabecular meshwork cells compared with controls, as deduced from the differential transcriptional profiles using RNA-sequencing analysis. There was a significant increase in IOP in transgenic mice expressing human GDF15, but not in GDF15 null mice, compared with the respective wild-type control mice. The AH outflow facility was decreased in enucleated wild-type mouse eyes perfused with rhGDF15. Light microcopy-based histologic examination of the conventional AH outflow pathway tissues did not reveal identifiable differences between the GDF15-targeted and control mice. Taken together, these results reveal the modest elevation of IOP in mice expressing human GDF15 possibly stemming from decreased AH outflow through the trabecular pathway.

Targeting mechanics-induced trabecular meshwork dysfunction through YAP-TGFβ Ameliorates high myopia-induced ocular hypertension

High myopia is a risk factor for primary open angle glaucoma (POAG). The pathological mechanism of high myopia induced POAG occurrence is not fully understood. In this study, we successfully established the guinea pig model of ocular hypertension with high myopia, and demonstrated the susceptibility of high myopia for the occurrence of microbead-induced glaucoma compared with non-myopia group and the effect of YAP/TGF-β signaling pathway in TM pathogenesis induced by high myopia. Moreover, we performed stretching treatment on primary trabecular meshwork (TM) cells to simulate the mechanical environment of high myopia. It was found that stretching treatment disrupted the cytoskeleton, decreased phagocytic function, enhanced ECM remodeling, and promoted cell apoptosis. The experiments of mechanics-induced human TM cell lines appeared the similar trend. Mechanically, the differential expressed genes of TM cells caused by stretch treatment enriched YAP/TGF-β signaling pathway. To inhibit YAP/TGF-β signaling pathway effectively reversed mechanics-induced TM damage. Together, this study enriches mechanistic insights of high myopia induced POAG susceptibility and provides a potential target for the prevention of POAG with high myopia.

Characterization of extracellular matrix deposited by segmental trabecular meshwork cells

PURPOSE

Biophysical and biochemical attributes of the extracellular matrix are major determinants of cell fate in homeostasis and disease. Ocular hypertension and glaucoma are diseases where the trabecular meshwork tissue responsible for aqueous humor egress becomes stiffer accompanied by changes in its matrisome in a segmental manner with regions of high or low flow. Prior studies demonstrate these alterations in the matrix are dynamic in response to age and pressure changes. The underlying reason for segmentation or differential response to pressure and stiffening are unknown. This is largely due to a lack of appropriate models (in vitro or ex vivo) to study this phenomena.

METHODS

Primary trabecular meshwork cells were isolated from segmental flow regions, and cells were cultured for 4 weeks in the presence or absence or dexamethasone to obtain cell derived matrices (CDM). The biomechanical attributes of the CDM, composition of the matrisome, and incidence of crosslinks were determined by atomic force microscopy and mass spectrometry.

RESULTS

Data demonstrate that matrix deposited by cells from low flow regions are stiffer and exhibit a greater number of immature and mature crosslinks, and that these are exacerbated in the presence of steroid. We also show a differential response of high or low flow cells to steroid via changes observed in the matrix composition. However, no correlations were observed between elastic moduli and presence or absence of mature and immature crosslinks in the CDMs.

CONCLUSION

Regardless of a direct correlation between matrix stiffness and crosslinks, we observed distinct differences in the composition and mechanics of the matrices deposited by segmental flow cells. These results suggest distinct differences in cellular identify and likely a basis for mechanical memory post isolation and culture. Nevertheless, we conclude that although a mechanistic basis for matrix stiffness was undetermined in this study, it is a viable tool to study cell-matrix interactions and further our understanding of trabecular meshwork pathobiology.

Is fat the future for saving sight? Bioactive lipids and their impact on glaucoma

Glaucoma is characterized by a continuous loss of retinal ganglion cells. The cause of glaucoma is associated with an increase in intraocular pressure (IOP), but the underlying pathophysiology is diverse and, in most cases, unknown. There is an indisputable unmet need to identify new pathways involved in glaucoma pathogenesis. Increasing evidence suggests that bioactive lipids may be critical in the development and progression of glaucoma. Preclinical and clinical bioactive lipid targets exist and are being developed. In this review, we aim to shed light on the potential of bioactive lipids for the prevention, diagnosis, prognosis, and treatment of glaucoma by asking the question "is fat the future for saving sight".

Characterization of extracellular matrix deposited by segmental trabecular meshwork cells

Biophysical and biochemical attributes of the extracellular matrix are major determinants of cell fate in homeostasis and disease. Ocular hypertension and glaucoma are diseases where the trabecular meshwork tissue responsible for aqueous humor egress becomes stiffer accompanied by changes in its matrisome in a segmental manner with regions of high or low flow. Prior studies demonstrate these alterations in the matrix are dynamic in response to age and pressure changes. The underlying reason for segmentation or differential response to pressure and stiffening are unknown. This is largely due to a lack of appropriate models ( in vitro or ex vivo ) to study this phenomena. In this study, we characterize the biomechanical attributes, matrisome, and incidence of crosslinks in the matrix deposited by primary cells isolated from segmental flow regions and when treated with glucocorticosteroid. Data demonstrate that matrix deposited by cells from low flow regions are stiffer and exhibit a greater number of immature and mature crosslinks, and that these are exacerbated in the presence of steroid. We also show a differential response of high or low flow cells to steroid via changes observed in the matrix composition. We conclude that although a mechanistic basis for matrix stiffness was undetermined in this study, it is a viable tool to study cell-matrix interactions and further our understanding of trabecular meshwork pathobiology.

Increased expression and accumulation of GDF15 in IPF extracellular matrix contribute to fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic disease of unmet medical need. It is characterized by formation of scar tissue leading to a progressive and irreversible decline in lung function. IPF is associated with repeated injury, which may alter the composition of the extracellular matrix (ECM). Here, we demonstrate that IPF patient–derived pulmonary ECM drives profibrotic response in normal human lung fibroblasts (NHLF) in a 3D spheroid assay. Next, we reveal distinct alterations in composition of the diseased ECM, identifying potentially novel associations with IPF. Growth differentiation factor 15 (GDF15) was identified among the most significantly upregulated proteins in the IPF lung–derived ECM. In vivo, GDF15 neutralization in a bleomycin-induced lung fibrosis model led to significantly less fibrosis. In vitro, recombinant GDF15 (rGDF15) stimulated α smooth muscle actin (αSMA) expression in NHLF, and this was mediated by the activin receptor-like kinase 5 (ALK5) receptor. Furthermore, in the presence of rGDF15, the migration of NHLF in collagen gel was reduced. In addition, we observed a cell type–dependent effect of GDF15 on the expression of cell senescence markers. Our data suggest that GDF15 mediates lung fibrosis through fibroblast activation and differentiation, implicating a potential direct role of this matrix-associated cytokine in promoting aberrant cell responses in disease.

Elevated Levels of Growth/Differentiation Factor-15 in the Aqueous Humor and Serum of Glaucoma Patients

Dysregulated levels of growth/differentiation factor-15 (GDF15), a divergent member of the transforming growth factor-beta super family, have been found to be associated with the pathology of various diseases. In this study, we evaluated the levels of GDF15 in aqueous humor (AH) and serum samples derived from primary open-angle glaucoma (POAG) and age- and gender-matched non-glaucoma (cataract) patients to assess the plausible association between GDF15 and POAG. GDF15 levels were determined using an enzyme-linked immunosorbent assay, and data analysis was performed using the Wilcoxon rank sum test, or the Kruskal–Wallis test and linear regression. GDF15 levels in the AH (n = 105) of POAG patients were significantly elevated (by 7.4-fold) compared to cataract patients (n = 117). Serum samples obtained from a subgroup of POAG patients (n = 41) also showed a significant increase in GDF15 levels (by 50%) compared to cataract patients. GDF15 levels were elevated in male, female, African American, and Caucasian POAG patients. This study reveals a significant and marked elevation of GDF15 levels in the AH of POAG patients compared to non-glaucoma cataract control patients. Although serum GDF15 levels were also elevated in POAG patients, the magnitude of difference was much smaller relative to that found in the AH.

Roles and Regulation of Growth differentiation factor-15 in the Immune and tumor microenvironment

Growth differentiation factor-15 (GDF-15), a member of the TGF-β superfamily, plays multiple roles in a wide variety of cellular processes. It is expressed at low levels under normal conditions but is highly expressed in tumor and tumor microenvironment (TME)-related cells, such as fibroblasts and immune cells. The TME consists of the noncancerous cells present in the tumor, including immune cells, fibroblasts, blood vessel signaling molecules and extracellular matrix, which play a key role in tumor development. GDF-15 affects both stromal cells and immune cells in the TME. It also acts on immune checkpoints, such as PD-1/PDL-1 that regulate stemness of cancer cells, indicating that GDF-15 plays a prominent role in cancer, exhibiting both protumorigenic and antitumorigenic effects, although the latter are reported much less often than the former. The present review addresses novel ideas regarding communication between GDF-15 and stromal cells, immune cells, and cancer cells in the TME. In addition, it discusses the possibility of GDF-15's clinical application as a diagnostic biomarker and therapeutic target in cancer.

Role of MCP-1 and IL-8 in viral anterior uveitis, and contractility and fibrogenic activity of trabecular meshwork cells

The inflammatory chemokines, monocyte chemoattractant protein (MCP)-1 and IL-8, are produced by normal trabecular meshwork cells (TM) and elevated in the aqueous humor of primary open angle glaucoma (POAG) and hypertensive anterior uveitis associated with viral infection. However, their role in TM cells and aqueous humor outflow remains unclear. Here, we explored the possible involvement of MCP-1 and IL-8 in the physiology of TM cells in the context of aqueous outflow, and the viral anterior uveitis. We found that the stimulation of human TM cells with MCP-1 and IL-8 induced significant increase in the formation of actin stress fibers and focal adhesions, myosin light chain phosphorylation, and the contraction of TM cells. MCP-1 and IL-8 also demonstrated elevation of extracellular matrix proteins, and the migration of TM cells. When TM cells were infected with HSV-1 and CMV virus, there was a significant increase in cytoskeletal contraction and Rho-GTPase activation. Viral infection of TM cells revealed significantly increased expression of MCP-1 and IL-8. Taken together, these results indicate that MCP-1 and IL-8 induce TM cell contractibility, fibrogenic activity, and plasticity, which are presumed to increase resistance to aqueous outflow in viral anterior uveitis and POAG.

Hypothermically Stored Adipose-Derived Mesenchymal Stromal Cell Alginate Bandages Facilitate Use of Paracrine Molecules for Corneal Wound Healing

Adipose-derived mesenchymal stromal cells (Ad-MSCs) may alleviate corneal injury through the secretion of therapeutic factors delivered at the injury site. We aimed to investigate the therapeutic factors secreted from hypothermically stored, alginate-encapsulated Ad-MSCs’ bandages in in vitro and in vivo corneal wounds. Ad-MSCs were encapsulated in 1.2% w/v alginate gels to form bandages and stored at 15 °C for 72 h before assessing cell viability and co-culture with corneal scratch wounds. Genes of interest, including HGF, TSG-6, and IGF were identified by qPCR and a human cytokine array kit used to profile the therapeutic factors secreted. In vivo, bandages were applied to adult male mice corneas following epithelial debridement. Bandages were shown to maintain Ad-MSCs viability during storage and able to indirectly improve corneal wound healing in vivo. Soluble protein concentration and paracrine factors such as TSG-6, HGF, IL-8, and MCP-1 release were greatest following hypothermic storage. In vivo, Ad-MSCs bandages-treated groups reduced immune cell infiltration when compared to untreated groups. In conclusion, bandages were shown to maintain Ad-MSCs ability to produce a cocktail of key therapeutic factors following storage and that these soluble factors can improve in vitro and in vivo corneal wound healing.

Growth/Differentiation Factor-15 (GDF-15): From Biomarker to Novel Targetable Immune Checkpoint

Growth/differentiation factor-15 (GDF-15), also named macrophage inhibitory cytokine-1, is a divergent member of the transforming growth factor β superfamily. While physiological expression is barely detectable in most somatic tissues in humans, GDF-15 is abundant in placenta. Elsewhere, GDF-15 is often induced under stress conditions, seemingly to maintain cell and tissue homeostasis; however, a moderate increase in GDF-15 blood levels is observed with age. Highly elevated GDF-15 levels are mostly linked to pathological conditions including inflammation, myocardial ischemia, and notably cancer. GDF-15 has thus been widely explored as a biomarker for disease prognosis. Mechanistically, induction of anorexia via the brainstem-restricted GDF-15 receptor GFRAL (glial cell-derived neurotrophic factor [GDNF] family receptor α-like) is well-documented. GDF-15 and GFRAL have thus become attractive targets for metabolic intervention. Still, several GDF-15 mediated effects (including its physiological role in pregnancy) are difficult to explain via the described pathway. Hence, there is a clear need to better understand non-metabolic effects of GDF-15. With particular emphasis on its immunomodulatory potential this review discusses the roles of GDF-15 in pregnancy and in pathological conditions including myocardial infarction, autoimmune disease, and specifically cancer. Importantly, the strong predictive value of GDF-15 as biomarker may plausibly be linked to its immune-regulatory function. The described associations and mechanistic data support the hypothesis that GDF-15 acts as immune checkpoint and is thus an emerging target for cancer immunotherapy.

Mechanically-induced GDF15 Secretion by Periodontal Ligament Fibroblasts Regulates Osteogenic Transcription

The alveolar bone provides structural support against compressive and tensile forces generated during mastication as well as during orthodontic treatment. To avoid abnormal alveolar bone resorption and tooth loss, a balanced bone turnover by bone-degrading osteoclasts and bone-generating osteoblasts is of great relevance. Unlike its contradictory role in regulating osteoclast and osteoblast cell differentiation, the TGF-β/BMP-family member GDF15 is well known for its important functions in the regulation of cell metabolism, as well as cell fate and survival in response to cellular stress. Here, we provide first evidence for a potential role of GDF15 in translating mechanical stimuli into cellular changes in immature osteoblasts. We detected enhanced levels of GDF15 in vivo in periodontal ligament cells after the simulation of tooth movement in rat model system as well as in vitro in mechanically stressed human periodontal ligament fibroblasts. Moreover, mechanical stimulation enhanced GDF15 secretion by periodontal ligament cells and the stimulation of human primary osteoblast with GDF15 in vitro resulted in an increased transcription of osteogenic marker genes like RUNX2, osteocalcin (OCN) and alkaline phosphatase (ALP). Together, the present data emphasize for the first time a potential function of GDF15 in regulating differentiation programs of immature osteoblasts according to mechanical stimulation.

LTBP2 knockdown and oxidative stress affect glaucoma features including TGFβ pathways, ECM genes expression and apoptosis in trabecular meshwork cells

Glaucoma is the leading cause of irreversible blindness worldwide. Although the etiology of glaucoma is incompletely understood, it is known that the extracellular matrix (ECM) of the trabecular meshwork, oxidative stress, TGFβ signaling pathways, and apoptosis are important components of glaucoma pathogenesis. These components appear to be interrelated, but knowledge on their interactions remains incomplete. Relevant to this gap in knowledge, LTBP2, glaucoma causing gene, may also be related to the mentioned components of glaucoma pathogenesis because of its putative roles in TGFβ signaling and ECM functions. This background prompted us to further query interactions among some molecules and pathways thought to be important in glaucoma etiology, with emphasis on oxidative stress and LTBP2. To this end, effects of LTBP2 siRNA knockdown, oxidative stress induction, TGFβ2 and gremlin exposures on canonical TGFβ and BMP signaling pathways, expression of ECM related genes, and apoptosis were assayed in primary human trabecular meshwork cell cultures. We found that oxidative stress induction and LTBP2 knockdown both affected all the processes queried, and that their affects paralleled one another. We suggest that effects of both oxidative stress and LTBP2 knockdown on the ECM and apoptosis may be mediated by TGFβ and BMP signaling pathway activation.

Genistein inhibits the growth and regulates the migration and invasion abilities of melanoma cells via the FAK/paxillin and MAPK pathways

Genistein is one of the main components of soy-based foods, which are widely known for their many benefits, including anti-cancer, anti-inflammatory, and antioxidant effects. In this study, we investigated the anti-metastasis effects of genistein on B16F10 melanoma cells. Our results showed that genistein strongly inhibited B16F10 cell proliferation and induced apoptosis in time- and concentration-dependent manners. Genistein altered the morphology of B16F10 cells to an elongated shape with slim pseudopodia-like protrusions. Moreover, genistein inhibited the invasion and migration abilities of B16F10 cells in a dose-dependent manner. On one hand, a high concentration of genistein (100 μM) significantly inhibited cell adhesion and migration, as shown by wound healing assays and transwell-migration and invasion assays. Furthermore, the expression levels of p-FAK, p-paxillin, tensin-2, vinculin, and α-actinin were decreased by genistein. As a result, genistein is believed to strongly downregulate the migration and invasion abilities of B16F10 cells via the FAK/paxillin pathway. Moreover, p-p38, p-ERK, and p-JNK levels were also dramatically decreased by treatment with genistein. Finally, genistein significantly decreased the gene expression of FAK, paxillin, vimentin, and epithelial-to-mesenchymal transition-related transcription factor Snail, as shown by real-time PCR (qPCR) analysis. On the other hand, a lower concentration of genistein (12.5 μM) significantly promoted both invasion and migration by activating the FAK/paxillin and MAPK signaling cascades. Taken together, this study showed for the first time that genistein exerts dual functional effects on melanoma cells. Our findings suggest that genistein regulates the FAK/paxillin and MAPK signaling pathways in a highly concentration-dependent manner. Patients with melanoma should therefore be cautious of consuming soy-based foods in their diets.

Predicted protein interactions of IFITMs may shed light on mechanisms of Zika virus-induced microcephaly and host invasion

After the first reported case of Zika virus (ZIKV) in Brazil, in 2015, a significant increase in the reported cases of microcephaly was observed. Microcephaly is a neurological condition in which the infant’s head is significantly smaller with complications in brain development. Recently, two small membrane-associated interferon-inducible transmembrane proteins (IFITM1 and IFITM3) have been shown to repress members of the flaviviridae family which includes ZIKV. However, the exact mechanisms leading to the inhibition of the virus are yet unknown. Here, we assembled an interactome of IFITM1 and IFITM3 with known protein-protein interactions (PPIs) collected from publicly available databases and novel PPIs predicted using the High-confidence Protein-Protein Interaction Prediction (HiPPIP) model. We analyzed the functional and pathway associations of the interacting proteins, and found that there are several immunity pathways (toll-like receptor signaling, cd28 signaling in T-helper cells, crosstalk between dendritic cells and natural killer cells), neuronal pathways (axonal guidance signaling, neural tube closure and actin cytoskeleton signaling) and developmental pathways (neural tube closure, embryonic skeletal system development) that are associated with these interactors. Our novel PPIs associate cilia dysfunction in ependymal cells to microcephaly, and may also shed light on potential targets of ZIKV for host invasion by immunosuppression and cytoskeletal rearrangements. These results could help direct future research in elucidating the mechanisms underlying host defense to ZIKV and other flaviviruses.