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Applied Biological Chemistry
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Jasmine tea extract enhances human retinal pigment epithelial cells survival after UVB irradiation

Applied Biological Chemistry volume 66, Article number: 22 (2023) Cite this article

Abstract

To examine the protecting effect of jasmine tea extract (JTE) against ultraviolet B (UVB) induced damage on human retinal pigment epithelial (RPE) cells, the RPE cells were subjected to UVB exposure and sequential JTE administration. The cell viability, intracellular reactive oxygen species (ROS), and apoptosis were determined by MTT, 2ʹ,7ʹ-dichlorodihydrofluorescein diacetate and flow cytometer assays, respectively. Further, the cells treated with UVB irradiation and sequential JTE administration were subjected to RNA-sequencing analysis in order to identify genes and pathways involved in the UVB-induced damage and JTE protecting mechanisms. The results showed that JTE effectively attenuated the UVB-induced cell injury by reducing the excessive intracellular ROS generation, and inhibiting the expression of apoptotic genes such as Bax, Caspase-3/9. This finding may offer a promising candidate for the prevention of UVB exposure related eye diseases.

Introduction

Solar ultraviolet B (UVB) irradiation, with wavelengths from approximately 280 to 320 nm, can penetrate the ozone layer and reach the Earth’s surface. A suitable amount of UVB exposure is essential for health benefits, but excessive exposure can lead to inflammation, oxidative stress, DNA mutations, and damage to mitochondria [1,2,3], leading to the initiation, promotion, and progression of several eye diseases, including cataracts, corneal damage, and age-related macular degeneration (AMD) [4,5,6]. Retinal pigment epithelial (RPE) cells, located in the outermost layer of the retina, are critical for maintaining neural retina function. Previous studies have shown that continuous UVB exposure can induce several signs of injury in RPE cells, such as decreased cell viability [6], redox imbalances [7], DNA fragmentation [8], and inflammatory signaling [9], all of which are associated with the development of ophthalmic disorders [10].

Jasmine tea is a popular beverage that originated in China and is widely consumed due to its fresh flavor and health benefits, including sedative effects on autonomic nerve activity and antioxidant properties [11,12,13]. The main bioactive polyphenols in jasmine tea are catechins, including ( +)-catechin (C), (−)-epicatechin (EC), (−)-epigallocatechin (EGC), (−)-epicatechin gallate (ECG), ( +)-catechin gallate (CG), ( +)-gallocatechin gallate (GCG), and (−)-epigallocatechin gallate (EGCG), which have potential anti-photoaging benefits based on their photoprotective and antioxidant activities [14, 15]. Recent studies have shown that catechins can neutralize free radicals induced by UV radiation and reduce damages caused by free radicals [16, 17]. Green tea extract that including catechins can protect against UV irradiation-induced damage in rats by preventing lipid peroxidation and DNA fragmentation [18]. Catechins have also been shown to alleviate UV-induced protein damage by increasing antioxidative capacity [19]. EGCG, the predominant catechin in teas, promotes human lens epithelial cell survival after UVB exposure by reducing the generation of free radicals and increasing the activity of antioxidant enzymes [20]. As jasmine tea extract is widely available and abundant in the tea industry [21], the utilization of jasmine tea extract (JTE) could be a promising ingredient for developing formulation with antioxidant and photo-protective activities.

To date, there is little direct evidence on the cytoprotective effect of JTE against UVB irradiation. Given the harmful effects of UVB exposure and the potential antioxidant properties of jasmine tea extract, this study aimed to evaluate the protective effect of JTE against UVB-induced injury in RPE cells by measuring cell viability and intracellular ROS levels. In addition, RNA-sequencing and quantitative real-time PCR (qPCR) analyses were also performed to investigate the underlying mechanism of UVB-induced cell damage and the protective effect of JTE. The results of this study could provide new insights into the protective effects of JTE on RPE cells after UVB exposure.

Materials and methods

Cell culture and reagents

The reagents with analytical grade were obtained from Sinopharm Chemical Company (Shanghai, China), and the ultrapure water was supplied by Milli-Q water system (Millipore Company, Bedford, USA). The RPE cells (ARPE-19, American Type Culture Collection, Manassas, VA, USA) were cultured in Dulbecco’s modified Eagle’s medium (Gibco, Rockville, MD, USA) with 10% fetal bovine serum (Gibco, Rockville, MD, USA) at 37 ℃, 5% CO2 and 100% relative humidity. The jasmine tea sample was purchased from Chunlun Ltd. Co. (Fuzhou, China), and the preparation of JTE was as follows: the dry tea sample was ground into powder and filtered through a 40-mesh sieve. Then, one gram of the tea powder was mixed with 50 mL of ultrapure water in a flask and incubated in a water-bath at 95 ℃ for 30 min. The resulting JTE supernatant was filtered using a 0.22 μm membrane and subjected to HPLC analysis. The major components of JTE are listed in Table 1.

Table 1 The concentration of catechins and caffeine in the jasmine tea extract* (mg/L)
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UVB irradiation

The UVB irradiation was conducted by using UVB lamps (FLS Inc., Foushan, Guangdong, China). These lamps emit wavelengths with the range of 290–320 nm and the intensity of UVB was examined by a UV-meter (UV-340, Optical instrument factory of Beijing Normal University, Beijing, China). RPE cells were seeded onto a 96-well plate with 1 × 105 cells per well and allowed to reach 70–80% confluence. Prior to UVB irradiation, the culture medium was replaced with serum-free Dulbecco’s modified Eagle’s medium. The cells in UVB group were exposed to irradiation with a dose of 100 mJ/cm2. For UVB-JTE sequential treated group, the cells were initially subjected to 100 mJ/cm2 UVB irradiation, then the JTE was immediately administrated into each well after UVB exposure (JTE: culture medium = 1:9, V/V). Subsequently, the cells in UVB and UVB-JTE groups were incubated at 37 ℃ for 30, 60, 120, 240 and 480 min. The cells treated without irradiated nor JTE were set as normal control.

MTT assay

The cell viability in different groups was determined by MTT assay. In brief, 20 μL of methyl thiazolyl tetrazolium solution (0.5 mg/mL) was added to each well of 96-well plate, and the plates were incubated at 37 °C for 4 h. The solution was pipetted out, and 200 μL dimethyl sulfoxide was added, then shaken at 100 rpm/min for 5 min. The formazan dye formation was measured at 540 nm using an ELISA reader (Thermo Fisher Scientific Inc., Waltham, MA, USA). The results were expressed as a percentage of viability with respect to the normal control.

Detection of intracellular reactive oxygen species (ROS)

The cells were seeded onto a culture dish (φ 3.5 cm) with a diameter of 3.5 cm at a density of 1 × 105 cells/mL.. After reaching 70–80% confluence, the cells on each dish were firstly treated with 10 μM of 2ʹ,7ʹ-dichlorodihydrofluorescein diacetate (DCF-DA), then incubated at 37 ℃ for 30 min. Subsequently the cells were washed three times with PBS. The DCF-DA loaded cells were subjected to the UVB-irradiation or UVB-JTE sequential treatment, then the fluorescence in different groups was observed using a laser confocal scanning microscope (FV1200, Olympus Corporation, Tokyo, Japan) with excitation wavelength at 488 nm and emission wavelength at 525 nm. For quantitated test, the cells were seeded on 96-well plates, then followed by the same protocol as above, the fluorescence intensity of ROS was determined by a fluorescence ELISA reader (Infinite M200 pro, Tecan Corporation, Mannedorf, Switzerland).

The apoptosis determination

The RPE cells were seeded on a culture dish with a diameter of 10 cm at a density of 1 × 105 cells/mL. When the cells reached 70–80% confluence, they were treated with either UVB irradiation or UVB-JTE sequential treatments as described earlier. Then the cells in different groups were respectively collected using the cell scrapers, and transferred into 1.5 mL centrifuge tube. The cells were rinsed by PBS for three times, then centrifuged at 2000 rpm for 5 min, followed by adding 450 μL binding buffer, 5 μL 7-amino-actinomycin D (7-AAD) and 1 μL Annexin V-PE (Keygen Biotechnonology, Nanjing, China), incubated at 37 ℃ for 15 min. Then the fluorescence of cells apoptosis was determined on a flow cytometer (EasyCyte, Merk Group, Darmstadt, Germany).

Analysis of RNA-sequencing

For each sample, three independent biological replicates were used and cells were collected separately for RNA sequencing analysis. RNA isolation was performed according to the protocol of an RNA isolation kit from Bioer Technology (Hangzhou, China), and the RNA sequencing was carried out by Novogene Bioinformatics Technology Co., Ltd (Beijing, China) using an Illumina HiSeq2500 platform and the standard Illumina RNA-Sequencing protocol. RNA integrity was assessed on 1% agarose gels, and RNA concentration was estimated using an Agilent 2100 Bioanalyzer (Agilent Technologies, Inc., Santa Clara, CA, USA). Downstream analysis of the RNA sequencing data was performed using a combination of programs including Bowtie2, Tophat2, HTseq and Cufflink. The edge R package was used to identify differentially expressed genes (DEGs) with the criterion of fold change > 2 (P < 0.05). Enrichment analysis on the DEGs using the Kyoto Encyclopedia of Genes & Genomes (KEGG) and gene ontology (GO) was implemented by GOseq R package and KOBAS.

Quantitative real-time PCR (qPCR) analysis

The PrimeScript Reagent Kit (TaKaRa, Dalian, China) was applied to the synthesis of first-strand cDNA from 1 μg of total RNA. The gene-specific primers were designed on Primer 3 software (Table 2), and the gene of reduced glyceraldehyde-phosphate dehydrogenase (GAPDH) was used as the endogenous control to normalize expression between different samples. The PCR reactions were run on a Bio-Rad CFX96 platform using the following program: 95 °C for 15 s and 40 cycles at 95 °C for 10 s, annealing at 60 °C for 30 s. Each reaction was performed in triplicate, in which the average threshold cycle was calculated to estimate the relative gene expression levels using the 2−ΔΔCt method [22].

Table 2 The primer sequences for qRT-PCR
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Statistical analysis

All the experiments were carried out in triplicates and the data was analyzed by one-way analysis of variance using the least significant difference as a multiple range test on Origin 8.0 software (OriginLab Inc., Northampton, MA, USA).

Results

JTE alleviates UVB-induced cell injury

The results of methyl thiazolyl tetrazolium (MTT) assay showed that the viability of UVB-exposed cells decreased from 51 to 8% within 480 min, indicating continuous injury after UVB irradiation (Fig. 1A). In contrast, the cell viability in the UVB-JTE group (UVB-JTE) was 78% after 30 min JTE treatment, and then decreased to 17% within 480 min, which was significantly higher than that of UVB group (Fig. 1A). These findings suggest that JTE treatment attenuated the persistent cytotoxicity in UVB-exposed RPE cells. Additionally, the cell apoptosis within 120 min after UVB exposure was determined using flow cytometer assay. The normal, early apoptotic, later apoptotic and necrotic cells were respectively distributed on lower left, lower right, upper right and upper left quadrants of two-dimensional scatter diagram (Fig. 1B). The result of flow cytometer detection showed that the proportion of apoptotic cells in UVB group clearly increased, reaching 36.01% and 49.89% at 30 and 120 min after UVB-exposure respectively, compared to 3.96% in normal cells group (NC) as showed in Fig. 1B. In contrast, the apoptotic cells in UVB-JTE group accounted for 21.15% and 31.73% at 30 and 120 min after UVB irradiation (Fig. 1B), suggesting that JTE treatment alleviated UVB-induced apoptosis, which is consistent with the results of the MTT assay in this study (Fig. 1A).

Fig.1
figure 1

The cell viability (A) and flow cytometer determination (B) of different treated cells. A RPE cells exposed to UVB irradiation then treated with or without JTE treatment for 30, 60, 120, 240, 480 min. The viability of UVB and UVB-JTE treated cells was calculated by comparing with normal cells. Statistical comparisons were performed between groups treated with same time (P < 0.05). B The flow cytometer analysis of the apoptosis of various treated RPE cells. b1: normal cell; b2: 30 min after UVB irradiation; b3: 30 min after UVB irradiation and sequential JTE treated; b4: 120 min after UVB irradiation; b5: 120 min after UVB irradiation and sequential JTE treatment

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JTE prevented UVB-induced excessive ROS generation in RPE cells

The 2ʹ,7ʹ-dichlorodihydrofluorescein diacetate (DCF-DA) stained intracellular ROS levels in different groups were presented in Fig. 2A. The fluorescence images showed that the UVB irradiation increased the intracellular ROS level in cells after exposure, and the gradually increased ROS intensity was observed within 30–120 min after UVB irradiation (Fig. 2A, a5-a6, a11-a12). Additionally, the cells after exposure became round or oval, with some irregular wrinkle on the surface (Fig. 2A, a4, a10), in contrast to the spindle-sharped cells in NC group (Fig. 2A, a1). The JTE treatment reduced the UVB-triggered intracellular ROS increase in cells, the amount of DCF-DA fluorescence intensity was clearly decreased comparing to those of UVB group (Fig. 2A, a8-a9, a14-a15), and most of the cells were similar to normal morphology after JTE-treatment (Fig. 2A, a7, a13). The quantitative determination of intracellular ROS levels in different groups revealed that UVB irradiation significantly promoted the intracellular ROS level in RPE cells comparing to that of normal cells, and the subsequent JTE treatment obviously retarded the excessive ROS generation over 120 min after UVB-exposure (Fig. 2B), demonstrating a persistent intracellular ROS scavenging capacity.

Fig. 2
figure 2

Effect of UVB irradiation and jasmine tea extract on the generation of intracellular ROS in RPE cells. A The laser confocal microscopy after DCF-DA staining on reactive oxygen species (green spots) in optical view (column 1), fluorescence view (column 2) and merged view (column 3) respectively; a1-a3: normal cell; a4-a6: 30 min after UVB exposure; a7-a9: 30 min after UVB exposure with sequential JTE treatment; a10-a12: 120 min after UVB exposure; a13-a15: 120 min after UVB exposure with sequential JTE treatment. B DCF-DA fluorescence intensity after various treatments, different letters represent significant difference (P < 0.05)

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The result of RNA-sequencing

In order to further investigate UVB-induced damage and JTE protecting mechanism in RPE cells, the RNA-sequencing analysis was performed using an Illumina High-Seq 2500 platforms. The sequencing data were blasted against human genome, the statistics on raw and filtered sequencing data were shown in Table 3. The genes with an average value of fragments per kilobase million (FPKM) higher than 1.0 were further analyzed. As a result, the RNA-seq libraries of normal cells, UVB and UVB-JTE groups obtained approximately 46.3–64.0 million clean reads, over 85% clean reads were matched to the reference genome, a total of 48,163 genes were identified and applied to the analysis on the dynamic changes of genes expression among different groups (Additional file 1: Table S1 The genes identified in RNA-sequencing).

Table 3 The statistics of RNA-sequencing results*
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The principal component analysis (PCA) of identified genes showed that the cell samples were clustered and discriminated from each other according to the RNA-seq profiles (Fig. 3A). The first two components, PC1 and PC2, accounted for nearly 75.8% of the variance, meeting the general requirements of cumulative percent variance > 70 − 85% for PCA analysis [23]. Figure 3B showed the amount of differently regulated genes (DEGs) in different paired-comparisons. The most abundant DEGs were observed in the comparison of UVB-JTE/Control, with 3941 up-regulated and 3481 down-regulated DEGs, followed by the UVB/Control (3042 up-regulated and 2343 down-regulated DEGs), the comparison of UVB-JTE/UVB had the lowest number of DEGs (1587 up-regulated and 908 down-regulated DEGs, Fig. 3B, Additional file 2: Table S2 The DEGs identified in different comparisons), suggesting the UVB-irradiation and the subsequent JTE treatment triggered the dynamic changes of gene expression compared with that of normal cells. The qPCR analysis of the ten genes related to cell apoptosis pathway was used to validate the transcriptomic profile, the result showed the qPCR dataset were in a general agreement with the transcriptomic profile, with R2 being 0.91 (Fig. 4), indicating that the transcriptomic data were able to reflect the transcript abundances in this work.

Fig. 3
figure 3

PCA analysis of identified genes (A) and The DEG numbers (B) in different groups

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Fig. 4
figure 4

The genes associated with apoptosis pathway were selected for the quantitative real-time PCR (qPCR) analysis. The genes expressions of UVB and UVB-JTE were normalized to normal control, and GAPDH gene was chosen as the endogenous control for qPCR. p53: tumor protein p53; Bax: apoptosis regulator Bax; Bcl-2: apoptosis regulator Bcl-2; Bcl-XL: apoptosis regulator Bcl-XL; COX5B: Cytochrome c oxidase subunit 5B; ERK: mitogen-activated protein kinase 1/3; SOD1: superoxide dismutase; GPx1: glutathione peroxidase

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Functional enrichment analyses of DEGs

Kyoto Encyclopedia of Genes & Genomes (KEGG) and gene ontology (GO) GO categorization were used to identified the DEGs annotated with functions. Three comparison pairs were categorized into the GO terms including biological process, molecular function, and cellular component (Fig. 5). The pair of UVB/Control had the most enriched DEGs in “binding” of molecular function and “cellular process” of biological process categories, respectively (Fig. 5A), the enrichment with similar magnitude was also observed in the comparison of UVB-JTE/Control (Fig. 5B), which is consistent with the aforementioned results in DEG amounts of different comparisons (Fig. 3B).

Fig. 5
figure 5

GO-based functional enrichment analysis of DEGs in (A) UVB/Control, (B) UVB-JTE/Control, and (C) UVB-JTE/UVB, respectively. Bar charts indicate the number of DEGs that were up- (right of X-axis) and down-regulated (left of X-axis), annotated with functions (Y-axis)

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Figure 6 showed the top ten enriched pathways in different paired-comparisons based on KEGG analysis of DEGs. The most DEGs enriched pathway in UVB/Control and UVB-JTE/Control was “Ribosome”, while the counterpart in UVB-JTE/UVB was “Lysosome” (Fig. 6). There were several shared pathways appeared in both of the UVB/Control and UVB-JTE/Control comparisons, including “Parkinson’s disease”, “Huntington’s disease”, “Alzheimer’s disease”, “Non-alcoholic fatty liver disease (NAFLD)”, “Oxidative phosphorylation” (Fig. 6A, B), suggesting a great change in genes associated with these diseases were involved in the injury of UVB-exposed RPE cells and the subsequent JTE treatment. Together with the similar changes in the GO and KEGG analyses on different treated cells, it is postulated that the same genes or pathways were involved in the UVB-mediated cytotoxicity and the JTE cyto-protection effect in this study.

Fig. 6
figure 6

The top 10 pathways enriched in KEGG-based analysis of DEGs in (A) UVB/Control, (B) UVB-JTE/Control, and (C) UVB-JTE/UVB, respectively. The adjusted P-values are annotated at the right of the bar charts

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The genes involved in the cytoprotective mechanism of JTE

To further investigate the genes involved in the cytoprotective mechanism of JTE, the 48,163 genes identified in RNA-seq dataset were filtered with the criterial of the average FPKM value higher than 1.0. As a result, a total of 13,355 genes (Additional file 3: Table S3 The filtered genes) in all samples were obtained and hierarchically clustered to provide subgrouping information using Short-Time-series Expression Miner and R package. Roughly, the cell samples from different groups were hierarchically categorized, and the genes in different groups could be classified into four subgroups according to their expression profiles (Fig. 7A). Notably, the genes enriched in subcluster2 were potentially involved in the cell damage and JTE protecting mechanism, since the expression pattern showed a resemblance with the results of cell viability and intracellular ROS level. Further, the KEGG pathway analysis on the genes enriched in subcluster2 was performed, the result demonstrated the genes enriched in subcluster2 were predominantly assigned to 15 pathways with the adjusted P-value lower than 0.05 (Fig. 7B). Then the genes associated with these 15 pathways were subjected to the co-expression analysis using R package, and the expression pattern of shared genes in the same KEGG class were presented in the heatmap, in which a total of 78 genes were obtained and clustered (Fig. 7C). The most abundant KEGG category is Human Disease (30 genes), followed by Cellular Processed (22 genes), Metabolisms (19 genes), and Genetic Information Processing (7 genes). The “Human Disease” clade enriched the Parkinson disease, Huntington disease and Alzheimer disease, showing an accordance with the result of KEGG analysis on DEGs (Fig. 6A, B). The genes involved in the pathway analysis were mainly associated with oxidative stress, including ATP synthase, cytochrome c oxidase, NADH dehydrogenase, and succinate dehydrogenase, suggesting that oxidative stress played a major part in the injury of UVB-exposed RPE cells and JTE protection effect (Fig. 8)

Fig. 7
figure 7

The RNA-sequencing analysis on RPE cells. A Heatmap of 13,355 filtered genes expression and hierarchical clustering. Each cell represents a value of log2-normalized expression of gene. The boxes at the left show the number of genes with similar expression trend in one cluster. B The KEGG-pathway based enrichment analysis of genes expression, with adjusted P-value annotated at the right of the bar. C Heatmap of 78 genes involved in UVB-mediated cell damage and JET protecting mechanism

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Fig. 8
figure 8

The schematic of photoprotective mechanism of JTE. Redrawn from the KEGG Apoptosis Reference Pathway (https://www.kegg.jp/kegg-bin/show_pathway?map04210). The bar plots represent the gene expression in normal control, UVB and UVB-JTE samples respectively from left to right. Bim: Bcl-2-like protein 11; Complex I: NADH-ubiquinone oxidoreductase; Complex II: succinate dehydrogenase; Complex III: ubiquinol-cytochrome c reductase

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Discussion

The major features of the RPE cells are their tight junctions between neighboring cells which functions to control the absorption of light irradiation and transport of metabolites between photoreceptors and choroidal capillaries [7]. The depletion of the ozone layer contributes to the greater fluxes of UVB on the earth’s surface, resulting in the increase of oxidative stress, altered apoptosis, as well as degeneration of RPE cells, which are responsible for the pathogenesis of AMD [10, 24]. The pretreatment of green tea extract on fibroblast cells could attenuate the UVB light-induced oxidative stress, increased the cell viability by 71% [25]. Our previous study also indicated that green tea extract could increase the survival of UVB stressed RPE cells via inhibiting the dysfunction in organelle [26]. As the major component of tea extra, EGCG protected against UVB‑induced human lens epithelial cell apoptosis by inhibiting the H2O2 generation [20]. In the present study, the jasmine tea extract effectively enhanced RPE cell survival after UVB exposure, and suppressed the UVB-induced apoptosis of RPE cells (Fig. 1), which is agreed with the previous studies.

The excessive UVB causes harm to living organisms mainly through injuring proteins or DNA, as well as triggering oxidative stress via the production of ROS, resulting in the apoptosis of RPE cells and retinal damage [27, 28]. It has been reported that ROS level was elevated as early as 30 min after UVB-exposure, and the apoptosis of RPE cell arrived at 30.76% within 24 h, suggesting a continuous damage to the cells [29]. The tea extract, with massive catechins, has the great efficiency in antioxidant capacity and UV protection, which could trap superfluous ROS caused by UV irradiation, arresting the persistent injury even after exposure [19, 29]. In the present study, the ROS level in UVB-treated RPE cells was dramatically higher than those in normal cells, while the ROS accumulation was reduced after sequential JTE administration (Fig. 2), this ROS scavenging effect mainly derived from the chelating ability of hydroxyl group of catechins in tea extract [30]. In addition, the results of previous studies indicated that the combination of several catechin monomers showed a synergistic effect in antioxidant activity, which suppressed H2O2-induced intracellular ROS production in RPE cells [31,32,33]. In this study, the cathine compounds in jasmine tea extract were composed of EGCG, ECG, EGC etc., these components displayed strong inhibition of ROS after UVB exposure, and the antioxidant activity of these catechins are not only highly dependent on their structure but also on the synergistic effect.

In age related disorders such as Alzheimer's disease (AD), Huntington's disease (HD), and Parkinson's disease (PD), mitochondria may play an important role, as mitochondria supplies ATP to the cell by oxidative phosphorylation, synthesizes key molecules and responds to oxidative stress as well as in apoptosis [34]. The pathway enrichment analysis in this study also showed that the genes associated with AD, HD, PD and apoptosis were significantly expressed in UVB and UVB-JTE cells respectively (Fig. 7C), implying that oxidative stress induced mitochondrial dysfunction could be a mechanism underlying the UVB-triggered RPE cells apoptosis. The mitochondrial electron transport chain is one of the important main sources of ATP in the mammalian cell and is thus essential for life. The largest amounts of ROS are produced in mitochondria by the transfer of unpaired electrons from semi-ubiquinone or from semi-reduced flavins of complex I (NADH dehydrogenase), complex II (succinate dehydrogenase), and complex III (ubiquinol-cytochrome c reductase) to ·O2¯, and the electron transport in complexes I, III which is used by the ATP synthase (complex V) to synthesize ATP from ADP and phosphate, then increased ROS level in mitochondria can ultimately lead to apoptosis [35]. The central event in the intrinsic apoptotic pathway is the mitochondrial outer membrane permeabilization, which is regulated by the pro-apoptotic proteins (Bax, Bak) and anti-apoptotic proteins (Bcl-2, Bcl-XL) [36]. Bax plays a key role in the release of mitochondrial intramembrane space proteins, such as cytochrome C, to aggravate mitochondrial outer membrane permeabilization, resulting in the activation of Caspase-induced apoptosis [37]. As we showed in Fig. 8, the gene expression of NADH dehydrogenase, succinate dehydrogenase and cytochrome c reductase remarkably enhanced after UVB-exposure in this study, in contrast to those in normal cells, indicating excessive oxidative stress were presented in the cells after UVB-exposure, potentially triggering the apoptosis process. However, the JTE treatment effectively reversed the expression levels of Bax and Bcl‑2 in RPE cells. This result is in line with the previous research, in which UVB exposure induced apoptosis of lens epithelial cells by boosting the levels of Bax, while EGCG inhibited the apoptosis by regulating the Bcl‑2/Bax ratio [20].

The levels of cytochrome c in the cytoplasm are a signal of mitochondrial injury, which results in the cell apoptosis. The catechins have been reported to suppress the release of cytochrome c from the mitochondria into the cytoplasm, contributing to the inhibition of mitochondria‑mediated apoptosis [38]. After the release from the mitochondria into the cytoplasm, the cytochrome c combined with Apaf‑1 and pro‑Caspase‑9 to form the apoptotic body, the Caspase‑9 is activated and then further cleaved downstream effector Caspases, including Caspases‑3, leading to the execution of apoptosis [39]. The catechins, were able to reduce the cell viability loss and apoptosis by eliminating ROS overproduction and overexpression of cleaved-Caspase 3, Caspase 9, cytochrome c [40, 41]. In the present study, the JTE consisted of catechins efficiently protected UVB-stressed RPE cells from apoptosis by limiting the expression of cytochrome c, Caspase‑9 and Caspase‑3, indicating that JTE could block the mitochondria‑mediated cell apoptosis pathway.

The results in this study demonstrated JTE protected RPE cells from the UVB-caused persistent damage at post-irradiation stage by reducing the intracellular ROS level and regulating the apoptotic signaling pathway, in agreement with the protective effects of polyphenols in plant extract against UV-mediated oxidative damage [42,43,44]. These results exhibit the JTE could be a feasible compound in UV-protective or after-sun injury healing preparations to prevent UVB-caused eye disease occurrence. The present study only determined the expression of genes, such as Bcl-2, Bax, cytochrome c, Caspase-9 and Caspase‑3 in vitro, however, experiments in vivo with humans are needed to validate the effects of JTE protecting against UVB irradiation and inhibiting the pathogenesis of eye diseases with desirable clinical physiological properties.

The present study investigated the protective effect of jasmine tea extract on RPE cells after UVB exposure. The results indicated that UVB irradiation induced apoptosis in RPE cells through intracellular ROS stress. However, JTE was able to scavenge the excess ROS, alleviate continuous cell damage after exposure, and significantly increase cell viability. Furthermore, JTE efficiently prevented UVB-induced apoptosis via the mitochondrial signaling pathway by regulating the expression of Bax, Bcl‑2, cytochrome c, Caspase‑9, and Caspase‑3. These findings suggest that JTE may play a protective role and have potential applications in preventing UVB-caused eye diseases.

Availability of data and materials

The raw data of RNA-sequencing has been deposited to the sequence read archive database of National Center for Biotechnology Information (NCBI) under the accession number of SRP126644.

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Acknowledgements

Not applicable.

Funding

This study was supported by the Construction Project for Technological Innovation and Service System of Tea IndustryChain (K1520005A07), the Jasmine Industry Promoting Project of Fuzhou (K15150510), China Agriculture Research System of MOF and MARA (CARS-19), and Characteristic Quality Study on Laocong Shuixian Teas (KH190365A).

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Authors and Affiliations

  1. College of Horticulture, Fujian Agriculture and Forestry University, Fuzhou, China

    Hu Shang, Yaling Guo, Liangyu Wu & Jinke Lin

Authors
  1. Hu Shang
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  2. Yaling Guo
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  3. Liangyu Wu
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  4. Jinke Lin
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Contributions

Methodology and investigation HS; project administration and writing—review and editing, YS; project administration and funding acquisition, YG; investigation and analysis, LW. All authors read and approved the final manuscript.

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Correspondence to Liangyu Wu or Jinke Lin.

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Supplementary Information

Additional file 1: Table S1.

The genes identified in RNAsequencing.

Additional file 2: Table S2.

The DEGs identified in different comparisons.

Additional file 3: Table S3.

The filtered genes.

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Shang, H., Guo, Y., Wu, L. et al. Jasmine tea extract enhances human retinal pigment epithelial cells survival after UVB irradiation. Appl Biol Chem 66, 22 (2023). https://doi.org/10.1186/s13765-023-00779-1

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