The role of melanocytes in the human choroidal microenvironment and inflammation: Insights from the transcriptome

An epigenome-wide association study of waist circumference in Chinese monozygotic twins

OBJECTIVES

Central obesity poses significant health risks because it increases susceptibility to multiple chronic diseases. Epigenetic features such as DNA methylation may be associated with specific obesity traits, which could help us understand how genetic and environmental factors interact to influence the development of obesity. This study aims to identify DNA methylation sites associated with the waist circumference (WC) in Northern Han Chinese population, and to elucidate potential causal relationships.

METHODS

A total of 59 pairs of WC discordant monozygotic twins (ΔWC >0) were selected from the Qingdao Twin Registry in China. Generalized estimated equation model was employed to estimate the methylation levels of CpG sites on WC. Causal relationships between methylation and WC were assessed through the examination of family confounding factors using FAmiliaL CONfounding (ICE FALCON). Additionally, the findings of the epigenome-wide analysis were corroborated in the validation stage.

RESULTS

We identified 26 CpG sites with differential methylation reached false discovery rate (FDR) < 0.05 and 22 differentially methylated regions (slk-corrected p < 0.05) strongly linked to WC. These findings provided annotations for 26 genes, with notable emphasis on MMP17, ITGA11, COL23A1, TFPI, A2ML1-AS1, MRGPRE, C2orf82, and NINJ2. ICE FALCON analysis indicated the DNA methylation of ITGA11 and TFPI had a causal effect on WC and vice versa (p < 0.05). Subsequent validation analysis successfully replicated 10 (p < 0.05) out of the 26 identified sites.

CONCLUSIONS

Our research has ascertained an association between specific epigenetic variations and WC in the Northern Han Chinese population. These DNA methylation features can offer fresh insights into the epigenetic regulation of obesity and WC as well as hints to plausible biological mechanisms.

Effects of Toll-like receptor 1 and 2 agonist Pam3CSK4 on uveal melanocytes and relevant experimental mouse model

Pam3CSK4 activates Toll-like receptors 2 and 1 (TLR1/2), which recognize mainly molecules from gram-positive pathogens. The effect of Pam3CSK4 on various cytokine and chemokine expression in cultured human uveal melanocytes (UM) has not been studied systematically. The purpose of this study was to investigate the mechanistic expressions of seven cytokines and chemokines of interleukin- (IL-) 6, IL-10, MCP-1 (CCL-2), CXCL-1 (GRO-α), CXCL-8 (IL-8), interferon-gamma (IFN-γ), and tumor necrosis factor-alpha (TNF-α) in UM. These cytokines are reported to be increased in intraocular fluids or tissues of the patients with endophthalmitis and non-infectious uveitis, as well as in various experimental animal uveitic models in the literature. Flow cytometry was used to measure the effects of Pam3CSK4 on the expression of TLR1/2 in UM. ELISA and Real-time PCR analysis were used to estimate the ability of Pam3CSK4 to elevate these cytokines and chemokines levels in conditioned media and cell lysates of UM, respectively. Flow cytometry measured and compared the phosphorylated MAPK pathway and activated NF-κB signals pathway in UM, treated with and without Pam3CSK4. ELISA analysis tested the effect of various signal inhibitors (ERK1/2, JNK1/2, p38 and NF-κB) on Pam3CSK4-induced IL-6 levels in cultured UM. The role of TLR2 in Pam3CSK4-induced acute anterior uveitis in experimental mouse model was tested in TLR2 knockout (TLR2 KO) mice and their wild-type C57Bl/6 controls. Pam3CSK4 increased the expression of TLR1/2 proteins in cultured UM. Pam3CSK4 significantly elevated the IL-6, MCP-1, CXCL-1, CXCL-8 protein, and mRNA levels in cultured UM, but not IL-10, TNF-α, or IFN-γ. Pam3CSK4 activated NF-κB, ERK, JNK, and p38 expression. Pam3CSK4-induced expression of IL-6 was decreased by NF-κB, ERK, INK, and p38 inhibitors; especially the NF-κB inhibitor, which can completely block the IL-6 stimulation. Intravitreal injection of Pam3CSK4 induced acute anterior uveitis in C57Bl/6 mice, this effect was significantly reduced in TLR2 KO mice. TLR1/2 plays an important role against invading pathogens, especially gram-positive bacteria; but an excessive reaction to molecules from gram-positive bacteria may promote non-infectious uveitis. UM can produce IL-6, MCP-1, CXCL-1, and CXCL-8, and are one of the target cells of TNF-α and IFN-γ. TLR-2 inhibitors might have a beneficial effect in the treatment of certain types of uveitis and other ocular inflammatory-related diseases and warrant further investigation.

Loss of REP1 impacts choroidal melanogenesis and vasculogenesis in choroideremia

Choroideremia (CHM) is a rare X-linked chorioretinal dystrophy affecting the photoreceptors, retinal pigment epithelium (RPE) and choroid, however, the involvement of the choroid in disease progression is not fully understood. CHM is caused by mutations in the CHM gene, encoding the ubiquitously expressed Rab escort protein 1 (REP1). REP1 plays an important role in intracellular trafficking of vesicles, including melanosomes. In this study, we examined the ultrastructure of the choroid in chmru848 fish and Chmnull/WT mouse models using transmission electron and confocal microscopy. Significant pigmentary disruptions were observed, with lack of melanosomes in the choroid of chmru848 fish from 4 days post fertilisation (4dpf), and a reduction in choroidal blood vessel diameter and interstitial pillars suggesting a defect in vasculogenesis. Total melanin and expression of melanogenesis genes tyr, tryp1a, mitf, dct and pmel were also reduced from 4dpf. In Chmnull/WT mice, choroidal melanosomes were significantly smaller at 1 month, with reduced eumelanin at 1 year. The choroid in CHM patients were also examined using spectral domain optical coherence tomography (SD-OCT) and OCT-angiography (OCT-A) and the area of preserved choriocapillaris (CC) was found to be smaller than that of overlying photoreceptors, suggesting that the choroid is degenerating at a faster rate. Histopathology of an enucleated eye from a 74-year-old CHM male patient revealed isolated areas of RPE but no associated underlying CC. Pigmentary disruptions in CHM animal models reveal an important role for REP1 in melanogenesis, and drugs that improve melanin production represent a potential novel therapeutic avenue.

Autophagy and vesicular trafficking in human uveal melanoma: A histopathological study

Uveal melanoma is an ocular tumor with a high risk of developing metastases. The endo-lysosomal system can affect the melanoma progression by accelerating and facilitating invasion or metastasis. This study aims to conduct comparative analysis of normal choroidal melanocytes and uveal melanoma cells ultrastructure with a focus on intracellular transport system, and to examine the patterns of autophagy- and vesicular trafficking-related proteins expression in a case series of uveal melanomas. Transmission electron microscopy was used to assess the ultrastructure of normal choroidal melanocytes and uveal melanoma cells. The expression levels of autophagy- and vesicular trafficking-related proteins in three histological types of uveal melanoma were analyzed by immunofluorescence staining. Electron microscopy results showed that the autophagic vacuoles were more abundant in normal choroidal melanocytes, than in uveal melanoma cells. The normal choroidal melanocytes were characterized by active intracellular vesicular trafficking; however, the proportion of caveolae was higher in uveal melanoma cells. The spindle type of tumor was characterized by a high expression levels of LC3 beta, while Rab7 and Rab11 proteins expression was significantly up-regulated in the mixed-type tumor cells. The results indicate that uveal melanoma cells probably have lower basal levels of autophagy and higher receptor-mediated endocytic trafficking-associated with caveolae than normal choroidal melanocytes. RESEARCH HIGHLIGHTS: The autophagic vacuoles are abundant in normal choroidal melanocytes. Uveal melanoma cells are characterized by a high proportion of caveolae. The high expression levels of LC3 beta were revealed in a spindle type of tumor, while Rab7 and Rab11 proteins expression was up-regulated in the mixed-type tumor cells.

Selective drug delivery to the retinal cells: Biological barriers and avenues

Retinal drug delivery is a challenging, but important task, because most retinal diseases are still without any proper therapy. Drug delivery to the retina is hampered by the anatomical and physiological barriers resulting in minimal bioavailability after topical ocular and systemic administrations. Intravitreal injections are current method-of-choice in retinal delivery, but these injections show short duration of action for small molecules and low target bioavailability for many protein, gene based drugs and nanomedicines. State-of-art delivery systems are based on prolonged retention, controlled drug release and physical features (e.g. size and charge). However, drug delivery to the retina is not cell-specific and these approaches do not facilitate intracellular delivery of modern biological drugs (e.g. intracellular proteins, RNA based medicines, gene editing). In this focused review we highlight biological factors and mechanisms that form the basis for the selective retinal drug delivery systems in the future. Therefore, we are presenting current knowledge related to retinal membrane transporters, receptors and targeting ligands in relation to nanomedicines, conjugates, extracellular vesicles, and melanin binding. These issues are discussed in the light of retinal structure and cell types as well as future prospects in the field. Unlike in some other fields of targeted drug delivery (e.g. cancer research), selective delivery technologies have been rarely studied, even though cell targeted delivery may be even more feasible after local administration into the eye.

The multifunctional human ocular melanocortin system

Immune privilege in the eye involves physical barriers, immune regulation and secreted proteins that together limit the damaging effects of intraocular immune responses and inflammation. The neuropeptide alpha-melanocyte stimulating hormone (α-MSH) normally circulates in the aqueous humour of the anterior chamber and the vitreous fluid, secreted by iris and ciliary epithelium, and retinal pigment epithelium (RPE). α-MSH plays an important role in maintaining ocular immune privilege by helping the development of suppressor immune cells and by activating regulatory T-cells. α-MSH functions by binding to and activating melanocortin receptors (MC1R to MC5R) and receptor accessory proteins (MRAPs) that work in concert with antagonists, otherwise known as the melanocortin system. As well as controlling immune responses and inflammation, a broad range of biological functions is increasingly recognised to be orchestrated by the melanocortin system within ocular tissues. This includes maintaining corneal transparency and immune privilege by limiting corneal (lymph)angiogenesis, sustaining corneal epithelial integrity, protecting corneal endothelium and potentially enhancing corneal graft survival, regulating aqueous tear secretion with implications for dry eye disease, facilitating retinal homeostasis via maintaining blood-retinal barriers, providing neuroprotection in the retina, and controlling abnormal new vessel growth in the choroid and retina. The role of melanocortin signalling in uveal melanocyte melanogenesis however remains unclear compared to its established role in skin melanogenesis. The early application of a melanocortin agonist to downregulate systemic inflammation used adrenocorticotropic hormone (ACTH)-based repository cortisone injection (RCI), but adverse side effects including hypertension, edema, and weight gain, related to increased adrenal gland corticosteroid production, impacted clinical uptake. Compared to ACTH, melanocortin peptides that target MC1R, MC3R, MC4R and/or MC5R, but not adrenal gland MC2R, induce minimal corticosteroid production with fewer amdverse systemic effects. Pharmacological advances in synthesising MCR-specific targeted peptides provide further opportunities for treating ocular (and systemic) inflammatory diseases. Following from these observations and a renewed clinical and pharmacological interest in the diverse biological roles of the melanocortin system, this review highlights the physiological and disease-related involvement of this system within human eye tissues. We also review the emerging benefits and versatility of melanocortin receptor targeted peptides as non-steroidal alternatives for inflammatory eye diseases such as non-infectious uveitis and dry eye disease, and translational applications in promoting ocular homeostasis, for example, in corneal transplantation and diabetic retinopathy.

Single-cell RNA sequencing reveals transcriptional changes of human choroidal and retinal pigment epithelium cells during fetal development, in healthy adult and intermediate age-related macular degeneration

Age-related macular degeneration (AMD) is the most prevalent cause of blindness in the developed world. Vision loss in the advanced stages of the disease is caused by atrophy of retinal photoreceptors, overlying retinal pigment epithelium (RPE) and choroidal endothelial cells. The molecular events that underline the development of these cell types from in utero to adult as well as the progression to intermediate and advanced stages AMD are not yet fully understood. We performed single-cell RNA-sequencing (RNA-Seq) of human fetal and adult RPE-choroidal tissues, profiling in detail all the cell types and elucidating cell type-specific proliferation, differentiation and immunomodulation events that occur up to midgestation. Our data demonstrate that progression from the fetal to adult state is characterized by an increase in expression of genes involved in the oxidative stress response and detoxification from heavy metals, suggesting a better defence against oxidative stress in the adult RPE-choroid tissue. Single-cell comparative transcriptional analysis between a patient with intermediate AMD and an unaffected subject revealed a reduction in the number of RPE cells and melanocytes in the macular region of the AMD patient. Together these findings may suggest a macular loss of RPE cells and melanocytes in the AMD patients, but given the complex processing of tissues required for single-cell RNA-Seq that is prone to technical artefacts, these findings need to be validated by additional techniques in a larger number of AMD patients and controls.

Proteomics of Retinal Extracellular Vesicles: A Review into an Unexplored Mechanism in Retinal Health and AMD Pathogenesis

Extracellular vesicles (EV) are nanosized delivery vehicles that participate in cell-to-cell communication through the selective transfer of molecular materials including RNA, DNA, lipids, and proteins. In the retina, the role of EV proteins is largely unclear, in part due to the lack of studies and the depth of proteomic analyses of EV cargo. This review summarizes the existing knowledge on retinal EV proteins and provides a comparative reanalysis of existing retinal EV proteomic datasets. Collective findings highlight that in homeostasis, the protein components of neural retinal and RPE-derived EV largely reflect the function of the host cells, while in disease RPE-EV protein composition becomes altered, favoring inflammatory modulation and potentially contributing to drusen formation. While these studies shed light on the potential roles of EV proteins in the neural retina and RPE, it is clear that comprehensive proteomic and molecular studies are required, in particular using in vivo models of retinal degenerations.

Identification of Therapeutic Targets and Prognostic Biomarkers Among Integrin Subunits in the Skin Cutaneous Melanoma Microenvironment

The roles of different integrin alpha/beta (ITGA/ITGB) subunits in skin cutaneous melanoma (SKCM) and their underlying mechanisms of action remain unclear. Oncomine, UALCAN, GEPIA, STRING, GeneMANIA, cBioPortal, TIMER, TRRUST, and Webgestalt analysis tools were used. The expression levels of ITGA3, ITGA4, ITGA6, ITGA10, ITGB1, ITGB2, ITGB3, ITGB4, and ITGB7 were significantly increased in SKCM tissues. The expression levels of ITGA1, ITGA4, ITGA5, ITGA8, ITGA9, ITGA10, ITGB1, ITGB2, ITGB3, ITGB5, ITGB6 and ITGB7 were closely associated with SKCM metastasis. The expression levels of ITGA1, ITGA4, ITGB1, ITGB2, ITGB6, and ITGB7 were closely associated with the pathological stage of SKCM. The expression levels of ITGA6 and ITGB7 were closely associated with disease-free survival time in SKCM, and the expression levels of ITGA6, ITGA10, ITGB2, ITGB3, ITGB6, ITGB7, and ITGB8 were markedly associated with overall survival in SKCM. We also found significant correlations between the expression of integrin subunits and the infiltration of six types of immune cells (B cells, CD8+ T cells, CD4+T cells, macrophages, neutrophils, and dendritic cells). Finally, Gene Ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were performed, and protein-protein interaction (PPI) networks were constructed. We have identified abnormally-expressed genes and gene regulatory networks associated with SKCM, improving understanding of the underlying pathogenesis of SKCM.

Choroidal melanocytes: subpopulations of different origin?

BACKGROUND

The human choroid derives from the mesectoderm, except the melanocytes originating from the neuroectoderm. To date, it is unclear whether all choroidal melanocytes share the same origin or might have different origins. The purpose of this study was to screen immunohistochemically for mesenchymal elements in the adult healthy human choroid, in the malignant melanoma of the choroid, as well as in the developing human fetal choroid.

METHODS

Human choroids were obtained from cornea donors and prepared as flat whole mounts for paraffin- and cryoembedding. Globes enucleated for choroidal melanoma and eyes from human fetuses between 11 and 20 weeks of gestation were also embedded in paraffin. Sections were processed for immunohistochemistry of the mesenchymal marker vimentin, the melanocyte marker Melan-A, and the macrophage marker CD68, followed by light-, fluorescence-, and confocal laser scanning-microscopy.

RESULTS

The normal choroid contained 499 ± 139 vimentin, 384 ± 78 Melan-A, and 129 ± 57 CD68 immunoreactive cells/mm². The vimentin immunopositive cell density was significantly higher than the density of Melan-A and CD68 immunopositive cells (p < 0.001, respectively). By confocal microscopy, 24 ± 8% of all choroidal melanocytes displayed vimentin immunoreactivity. In choroidal melanomas, numerous melanoma cells of the epithelioid and spindle cell type revealed immunopositivity for both vimentin and Melan-A. The intratumoral density of vimentin immunoreactive cells was 1758 ± 106 cells/mm², significantly higher than the density of Melan-A and CD68 immunopositive cells (p < 0.001, respectively). Comparing to healthy choroidal tissue, the choroidal melanomas revealed significantly higher densities of vimentin, Melan-A, and CD68 immunoreactive cells (p < 0.001, respectively). In the developing human fetal choroid, numerous vimentin and Melan-A immunopositive cells were detected not before the 16th week of gestation, with some of them showing colocalization of vimentin and Melan-A.

CONCLUSIONS

The adult healthy human choroid is endowed with a significant number of vimentin immunopositive mesenchymal structures, including a subpopulation of vimentin immunoreactive choroidal melanocytes. These vimentin immunopositive melanocytic cells are also present in choroidal melanomas as well as in the developing human fetal choroid. Therefore, different embryologic origins can be considered for choroidal melanocytes.