TGF-beta2 inhibits growth of uveal melanocytes at physiological concentrations

Role of Decorin in the Lens and Ocular Diseases

Decorin is an archetypal member of the small leucine-rich proteoglycan gene family and is involved in various biological functions and many signaling networks, interacting with extra-cellular matrix (ECM) components, growth factors, and receptor tyrosine kinases. Decorin also modulates the growth factors, cell proliferation, migration, and angiogenesis. It has been reported to be involved in many ischemic and fibrotic eye diseases, such as congenital stromal dystrophy of the cornea, anterior subcapsular fibrosis of the lens, proliferative vitreoretinopathy, et al. Furthermore, recent evidence supports its role in secondary posterior capsule opacification (PCO) after cataract surgery. The expression of decorin mRNA in lens epithelial cells in vitro was found to decrease upon transforming growth factor (TGF)-β-2 addition and increase upon fibroblast growth factor (FGF)-2 addition. Wound healing of the injured lens in mice transgenic for lens-specific human decorin was promoted by inhibiting myofibroblastic changes. Decorin may be associated with epithelial-mesenchymal transition and PCO development in the lens. Gene therapy and decorin administration have the potential to serve as excellent therapeutic approaches for modifying impaired wound healing, PCO, and other eye diseases related to fibrosis and angiogenesis. In this review, we present findings regarding the roles of decorin in the lens and ocular diseases.

TGF-β2 upregulates tyrosinase activity via Opsin3 in human skin melanocytes in vitro

Opsin3 (OPN3) is a potential key regulator of human melanocyte melanogenesis. How OPN3-mediated regulation of melanocyte melanogenesis is triggered is largely unclear. Transforming growth factor-β (TGF-β) can inhibit the growth of human melanocytes and reduce melanin synthesis in melanocytes. However, whether TGF-β2 can modulate pigmentation in normal human primary melanocytes via OPN3 is entirely unknown. Here, we constructed a co-culture model with human epidermal melanocytes and keratinocytes. Higher OPN3, tyrosinase (TYR), tyrosinase-related protein (TRP)-1, and TRP-2 expression and higher tyrosinase activity were detected in co-cultured cells than in mono-cultured cells. Moreover, elevated levels of TGF-β2 were detected in the culture supernatant of melanocytes co-cultured with keratinocytes. OPN3 inhibition in melanocytes decreased TYR, TRP-1, and TRP-2 expression and downregulated tyrosinase activity. Our findings indicate that TGF-β2 upregulates TYR, TRP-1 and TRP-2 expression in human melanocytes via OPN3 and downstream calcium-dependent G protein-coupled signalling pathways to induce melanogenesis. Interestingly, treatment with the TGF-β2 receptor inhibitor LY2109761 (10 μM) did not inhibit TGF-β2-induced melanocyte melanogenesis via OPN3. Collectively, our data suggest that TGF-β2 upregulates tyrosinase activity via OPN3 through a TGF-β2R-independent and calcium-dependent G protein-coupled signalling pathway.

Quantitative Study of Human Scleral Melanocytes and Their Topographical Distribution

PURPOSE

While fibroblasts constitute the main cell component of the sclera, the purpose of the present study was to investigate the cell densities of melanocytes at different regions of the sclera, and to compare them with associated scleral fibroblast densities in human donor eye sections.

METHODS

. Paraffin-embedded sections of sclera from 21 human eyes were stained with hematoxylin-eosin (H&E) and immunohistochemical staining (S-100/AEC). Scleral melanocyte and fibroblast numbers were counted in different regions of the sclera. The relationship between the melanocyte density and iris pigmentation was also analyzed.

RESULTS

. Melanocytes were found in the posterior region of the sclera, especially around the vessels and nerves in emmissarial canals, whereas no or rare melanocytes were found in equatorial and anterior regions. In H&E sections, melanocyte densities in eyes with light-colored irides were significantly less than in eyes with medium or dark-colored irides (P < .05). In S-100-stained sections, more melanocytes could be detected than those in the H&E sections in light-colored eyes (P < .05), but not in medium or dark-colored eyes (P > .05). The numbers of scleral fibroblasts were relatively stable in different regions. In the posterior scleral region, the numbers of fibroblasts were slightly higher than the number of melanocytes, however, this differences were not statistically significant (P > .05).

CONCLUSION

. Notable numbers of melanocytes were present in the posterior sclera suggesting that these cells may play a role in ocular physiology and in the pathogenesis of various disorders of the sclera.

The divergent roles of growth differentiation factor-15 (GDF-15) in benign and malignant skin pathologies

GDF-15 (Growth Differentiation Factor-15) is a member of the transforming growth factor β (TGF-β) superfamily. GDF-15 is not only involved in cancer development, progression, angiogenesis and metastasis, but also controls stress responses, bone formation, hematopoietic development, adipose tissue function and cardiovascular diseases. GDF-15, which is regulated by p53, has shown antitumorigenic and proapoptotic activities in vivo and in vitro. Also, GDF-15 is involved in skin biology and histamine-induced melanogenesis; it is overexpressed in melanoma cells and is associated with depth of tumor invasion and metastasis. GDF-15 level is increased in patients with systemic sclerosis and is related with the degree of skin sclerosis and intensity of pulmonary fibrosis. In the future, GDF-15 may be a potential target for therapy in benign disorders with skin fibrosis and malignant lesions of the skin.

Histamine receptor 2-mediated growth-differentiation factor-15 expression is involved in histamine-induced melanogenesis

Vitiligo is a progressive depigmenting disorder. Histamine has been shown to induce melanogenesis via histamine receptor 2, suggesting the possibility of histamine as a repigmenting agent for the treatment of vitiligo. However, the role and signaling mechanism of histamine are still unclear in melanogenesis, especially in relation to growth-differentiation factor-15, which is a protein belonging to transforming growth factor beta and found to be overexpressed in metastatic or malignant melanoma. We found that histamine induces growth-differentiation factor-15 in melanoma cell lines such as SK-MEL-2, B16F10, and melan-a cells. Therefore, in the present study, the role of growth-differentiation factor-15 in histamine-induced melanogenesis was investigated using gene silencing or overexpression of growth-differentiation factor-15 and histamine related compounds such as histamine, amthamine, and cimetidine. Gene silencing of growth-differentiation factor-15 suppressed histamine-induced proliferation, melanin production, tyrosinase activity, and chemotactic migration of SK-MEL-2 cells. Histamine-induced expression of tyrosinase, tyrosinase-related protein 1, and tyrosinase-related protein 2 was also suppressed by growth-differentiation factor-15 gene silencing. On the other hand, overexpression of growth-differentiation factor-15 using a plasmid containing growth-differentiation factor-15 in SK-MEL-2 cells increased melanin production and chemotactic migration. Amthamine induced expression of growth-differentiation factor-15 in a time and concentration dependent manner. Amthamine-induced expression of growth-differentiation factor-15 was suppressed by cimetidine. Our results suggest that growth-differentiation factor-15 is a new player in histamine-induced melanogenesis, which can help researchers to extend the knowledge of the role of the transforming growth factor beta family in melanogenesis and in skin pigment disorders such as vitiligo.

Iris as a recipient tissue for pigment cells: organized in vivo differentiation of melanocytes and pigmented epithelium derived from embryonic stem cells in vitro

Regenerative transplantation of embryonic stem (ES) cell-derived melanocytes into adult tissues, especially skin that includes hair follicles or the hair follicle itself, generally not possible, whereas that of ES cell-derived pigmented epithelium was reported previously. We investigated the in vivo differentiation of these two pigment cell types derived from ES cells after their transfer into the iris. Melanocytes derived from ES cells efficiently integrated into the iris and expanded to fill the stromal layer of the iris, like those prepared from neonatal skin. Transplanted pigmented epithelium from either ES cells or the neonatal eye was also found to be integrated into the iris. Both types of these regenerated pigment cells showed the correct morphology. Regenerated pigment epithelium expressed its functional marker. Functional blocking of signals required for melanocyte development abolished the differentiation of transplanted melanocytes. These results indicate successful in vivo regenerative transfer of pigment cells induced from ES cells in vitro.

Local environmental influences on uveal melanoma: vitreous humor promotes uveal melanoma invasion, whereas the aqueous can be inhibitory

BACKGROUND

Uveal melanomas of the choroid and ciliary body are aggressive tumors causing the death of approximately 50% of patients. In contrast, iris melanomas only infrequently metastasize; why these differences exist is not known. The local environment can regulate cancer growth and development, and it is probable the aqueous and vitreous humors have an important role in regulating uveal melanoma behavior.

METHODS

To explore this possibility cultures of uveal melanoma were exposed to aqueous and vitreous and the effects investigated using invasion and proliferation assays. ChemiArrays (Chemicon International, Temecula, Calif) were performed to determine which regulatory factors might influence the process.

RESULTS

The vitreous universally promoted uveal melanoma invasion, whereas the aqueous mainly had no effect or was inhibitory. Tumor location, and the baseline invasion of the melanoma, affected the ability of aqueous and vitreous from different patients to regulate invasive behavior. Proliferation was not significantly altered as a result of exposure to the aqueous or vitreous. The ability of the humors to regulate uveal melanomas may involve TIMP-2, TIMP-3, and TGF-beta2, as high expression was found by ChemiArray analysis and there were differences in the levels of the regulators in the aqueous compared with the vitreous.

CONCLUSIONS

The findings suggest that in situ uveal melanoma development reflects an interaction between the tumor and the environment of the eye. Exposure to the aqueous would therefore contribute to the benign nature of iris melanomas, whereas potential interaction with the vitreous appears to promote the aggressive behavior of posterior uveal melanomas.

TGFbeta pathobiology in the eye

Transforming growth factor beta (TGFbeta), a multifunctional growth factor, is one of the most important ligands involved in the regulation of cell behavior in ocular tissues in physiological or pathological processes of development or tissue repair, although various other growth factors are also involved. Increased activity of this ligand may induce unfavorable inflammatory responses and tissue fibrosis. In mammals, three isoforms of TGFbeta, that is, beta1, beta2, and beta3, are known. Although all three TGFbeta isoforms and their receptors are present in ocular tissues, lack of TGFbeta2, but not TGFbeta1 or TGFbeta3, perturbs embryonic morphogenesis of the eyes in mice. Smads2/3 are key signaling molecules downstream of cell surface receptors for TGFbeta or activin. Upon TGF binding to the respective TGF receptor, Smads2/3 are phosphorylated by the receptor kinase at the C-terminus, form a complex with Smad4 and translocate to the nucleus for activation of TGFbeta gene targets. Moreover, mitogen-activated protein kinase, c-Jun N-terminal kinase, and p38 modulate Smad signals directly via Smad linker phosphorylation or indirectly via pathway crosstalk. Smad signals may therefore be a critical threrapeutic target in the treatment of ocular disorders related to fibrosis as in other systemic fibrotic diseases. The present paper reviews recent progress concerning the roles of TGFbeta signaling in the pathology of the eye.

Uveal Melanocytes Produce Matrix Metalloproteinases-2 and -9 In Vitro

The purpose of the present study was to investigate the expression of matrix metalloproteinase (MMP)-2 and MMP-9 by cultured human uveal melanocytes, and to test the effects of 12-O-tetradecanoyl-phorbol-13-acetate on the expression of these MMPs. Gelatin zymography of conditioned culture medium from four cultures of human uveal melanocytes (two cultures of iridal melanocytes and two cultures of choroidal melanocytes) detected MMP-2 (72 kDa) and a relatively small amount of MMP-9 (92 kDa), both in the latent form. RT-PCR analysis revealed the MMP-2 mRNA and MMP-9 mRNA in cultured uveal melanocytes. Addition of 12-O-tetradecanoyl-phorbol-13-acetate (10 ng/ml) to the culture medium caused an increase of production of MMP-2 and MMP-9 by cultured uveal melanocytes, and also stimulated the transcription of MMP-2 and MMP-9 of these cells.

Relationship between posterior capsule opacification and intraocular lens biocompatibility

The type of healing process that occurs in response to cataract surgery and intraocular lens (IOL) implantation is dependent on a complex set of variables. Their interactions determine whether or not optical clarity is restored as a result of this procedure. In this process, wound healing entails cells undergoing either epithelial-mesenchymal transition, resulting in the generation of fibroblastic cells and accumulation of extracellular matrix, or lenticular structure formation. Such desperate cellular behaviors are regulated by the localized release of different cytokines, including transforming growth factor beta and fibroblast growth factors, which can result in post-operative capsular opacification. Other factors affecting the biological and mechanical outcome of IOL implantation are its composition, surface properties and shape.

The biology of melanocytes

In veterinary medicine, our understanding of the biology and regulation of melanocytic function is mostly based on information realized from human and murine studies. Improved understanding of the biology of melanocytes is needed to develop more effective treatment regimens for malignant melanoma and other melanocytic disorders. In vertebrates, melanocytes are well known for their role in skin pigmentation, hair and feather coloration, and for their ability to produce and distribute melanin to surrounding keratinocytes. Enzymes involved in melanin synthesis are present exclusively in melanosomes. The type of melanin synthesized by melanocytes in mammals is regulated at a genetic, biochemical and environmental level. These regulatory factors affect not only the phenotypic appearance, but also the photoprotective properties of melanin. This review addresses the biology of melanocytes, melanin synthesis and the photoprotective properties of melanin.

Mechanism and clinical significance of prostaglandin-induced iris pigmentation

The new glaucoma drugs latanoprost, isopropyl unoprostone, travoprost, and bimatoprost cause increased pigmentation of the iris in some patients. The purpose of the present article is to survey the available preclinical and clinical data on prostaglandin-induced iris pigmentation and to assess the phenomenon from a clinical perspective. Most of the data have been obtained with latanoprost, and it appears that there is a predisposition to latanoprost-induced iris pigmentation in individuals with hazel or heterochromic eye color. As latanoprost and travoprost are selective agonists for the prostaglandin F(2alpha) receptor, it is likely that the phenomenon is mediated by this receptor. Several studies indicate that latanoprost stimulates melanogenesis in iridial melanocytes, and transcription of the tyrosinase gene is upregulated. The safety aspects of latanoprost-induced iris pigmentation have been addressed in histopathologic studies, and no evidence of harmful consequences of the side effect has been found. Although a final assessment of the clinical significance of prostaglandin-induced iris pigmentation currently is impossible to make, it appears that the only clear-cut disadvantage is a potential heterochromia between the eyes in unilaterally treated patients because the heterochromia is likely to be permanent, or very slowly reversible.

Transforming growth factor beta1 regulates melanocyte proliferation and differentiation in mouse neural crest cells via stem cell factor/KIT signaling

Stem cell factor is essential to the migration and differentiation of melanocytes during embryogenesis based on the observation that mutations in either the stem cell factor gene, or its ligand, KIT, result in defects in coat pigmentation in mice. Stem cell factor is also required for the survival of melanocyte precursors while they are migrating towards the skin. Transforming growth factor beta1 has been implicated in the regulation of both cellular proliferation and differentiation. NCC-melb4, an immortal cloned cell line, was cloned from a mouse neural crest cell. NCC-melb4 cells provide a model to study the specific stage of differentiation and proliferation of melanocytes. They also express KIT as a melanoblast marker. Using the NCC-melb4 cell line, we investigated the effect of transforming growth factor beta1 on the differentiation and proliferation of immature melanocyte precursors. Immunohistochemically, NCC-melb4 cells showed transforming growth factor beta1 expression. The anti-transforming growth factor beta1 antibody inhibited the cell growth, and downregulated the KIT protein and mRNA expression. To investigate further the activation of autocrine transforming growth factor beta1, NCC-melb4 cells were incubated in nonexogenous transforming growth factor beta1 culture medium. KIT protein decreased with anti-transforming growth factor beta1 antibody concentration in a concentration-dependent manner. We concluded that in NCC-melb4 cells, transforming growth factor beta1 promotes melanocyte precursor proliferation in autocrine and/or paracrine regulation. We further investigated the influence of transforming growth factor beta1 in vitro using a neural crest cell primary culture system from wild-type mice. Anti-transforming growth factor beta1 antibody decreased the number of KIT positive neural crest cell. In addition, the anti-transforming growth factor beta1 antibody supplied within the wild-type neural crest explants abolished the growth of the neural crest cell. These results indicate that transforming growth factor beta1 affect melanocyte precursor proliferation and differentiation in the presence of stem cell factor/KIT in an autocrine/paracrine manner.

Ocular phototoxicity

The human eye is constantly exposed to sunlight and artificial lighting. Therefore the eye is exposed to UV-B (295-320 nm), UV-A (320-400 nm), and visible light (400-700 nm). Light is transmitted through the eye and then signals the brain directing both sight and circadian rhythm. Therefore light absorbed by the eye must be benign. Damage to the young and adult eye by intense ambient light is avoided because the eye is protected by a very efficient antioxidant system. In addition, there are protective pigments such as the kynurenines, located in the human lens, and melanin, in the uvea and retina, which absorb ambient radiation and dissipate its energy without causing damage. After middle age there is a decrease in the production of antioxidants and antioxidant enzymes. At the same time, the protective pigments are chemically modified (lenticular 3-hydroxy kynurenine pigment is enzymatically converted into the phototoxic chromophore xanthurenic acid; melanin is altered from an antioxidant to pro-oxidant) and fluorescent chromophores (lipofuscin) accumulate to concentrations high enough to produce reactive oxygen species. We have known for some time that exposure to intense artificial light and sunlight either causes or exacerbates age-related ocular diseases. We now know many of the reasons for these effects, and with this knowledge methods are being developed to interfere with these damaging processes.

Transforming growth factor beta1 induces apoptosis in normal melanocytes but not in nevus cells grown in type I collagen gel

We used type I collagen gel cultures to compare the growth requirements of melanocytes and dermal nevus cells. Melanocytes but not nevus cells undergo apoptosis in collagen unless supplied with growth stimulators such as fibroblast growth factor 2. To characterize the mechanism of melanocyte apoptosis in collagen, we tested the effects of transforming growth factor beta1, known to be functionally active in the skin. When picomolar amounts of transforming growth factor beta1 were added to normal melanocytes grown in type I collagen gel, their apoptosis was dramatically accelerated. In contrast, the apoptotic rate of nevus cells and melanoma cells grown under similar conditions was not affected by transforming growth factor beta1. The increased apoptosis of normal melanocytes was effectively counteracted by addition of either neutralizing transforming growth factor beta1 antibodies or fibroblast growth factor 2 to the collagen gel. Interestingly, the background apoptosis of normal melanocytes was also inhibited by transforming growth factor beta1 antibodies. By Western blotting we detected transforming growth factor beta-like immunoreactivity in melanocyte, nevus cell, and melanoma cell lysates. A sensitive bioassay confirmed that their medium contained considerable amounts of heat-activatable growth inhibitory activity that could partly be neutralized by transforming growth factor beta1 antibodies. It is evident that apoptosis of melanocytes grown in type I collagen gel can be mediated by both endogenous and exogenous transforming growth factor beta. We suggest that the balance between inhibitory growth factors such as transforming growth factor beta and stimulatory growth factors like fibroblast growth factor 2 has the potential to regulate the growth, localization, and survival of normal melanocytes also in vivo. The resistance of nevus cells to transforming-growth-factor-beta-mediated apoptosis may facilitate their ability to grow in the dermal compartment of the skin.

Transforming growth factor-beta isoform proteins in cell and matrix deposits on intraocular lenses

PURPOSE

To determine whether the cells that adhere to poly(methyl methacrylate) (PMMA) posterior chamber intraocular lenses (PC IOLs) implanted in human eyes produce transforming growth factor-beta (TGF-beta) isoforms and whether the acellular proteinaceous deposits on these IOLs contain TGF-beta.

SETTING

Department of Ophthalmology, Wakayama Medical College, Japan.

METHODS

Thirty-two PMMA PC IOLs explanted from Japanese patients were immunostained for TGF-beta1, -beta2, or -beta3, and observed under light microscopy.

RESULTS

Cell deposits were observed on 12 IOLs and proteinaceous deposits on 16. Components of the cell deposits were mainly of macrophage origin. The cell and matrix deposits tested positive for each isoform of TGF-beta.

CONCLUSION

The cells that adhered to implanted PMMA PC IOLs produced TGF-beta, and the extracellular matrix that accumulated on the surface of the IOLs contained TGF-beta. Transforming growth factor-beta from the cells on IOLs may influence the healing process of residual lens capsules after cataract surgery with IOL implantation.

Effect of prostaglandins A(2), E(1), F(2 alpha)and latanoprost on cultured human iridal melanocytes

The effect of various prostaglandins on the growth, melanogenesis and dendrification of cultured iridal melanocytes were studied. Iridal melanocytes were isolated and cultured with medium supplemented with cAMP elevating agents and basic fibroblast growth factor (complete medium). The iridal melanocytes were plated into multiple well plates and cultured with complete medium, cAMP-deleted medium with or without various prostaglandins at different concentrations. After 5-7 days, the numbers of cells and dendrites were counted and melanin content was measured and compared to controls. Prostaglandin A(2)and E(1)stimulated growth, melanogenesis and dendrification of cultured iridal melanocytes in cAMP-deleted medium. Prostaglandin F(2 alpha), PhXA85 and latanoprost showed no effect under similar experimental conditions. These results indicate that prostaglandin A(2)and E(1)stimulate growth and differentiation of iridal melanocytes through the activation of cAMP system. Failure of stimulation of melanogenesis of iridal melanocytes by prostaglandin F(2 alpha)and PhXA85 in vitro may be related to a different second messenger system activated by these prostaglandins and the selective stimulating effect of these prostaglandins on iridal melanocytes from mixed-colored irides.