Post-doctoral Fellow, Department of Ophthalmology, Stanford University School of Medicine (2017)
Doctor of Philosophy, Taipei Medical College (2013)
Master of Science, Taipei Medical College (2008)
Bachelor of Science, Taipei Medical College (2007)
Cell type- and stage-specific expression of Otx2 is regulated by multiple transcription factors and cis-regulatory modules in the retina.
Development (Cambridge, England)
Transcription factors (TFs) are often used repeatedly during development and homeostasis to control distinct processes in the same and/or different cellular contexts. Considering the limited number of TFs in the genome and the tremendous number of events that need to be regulated, re-use of TFs is necessary. We analyzed how the expression of the homeobox TF, Orthodenticle homeobox 2 (Otx2), is regulated in a cell type- and stage-specific manner during development in the retina. We identified seven Otx2 cis-regulatory modules (CRMs), among which the O5, O7 and O9 CRMs mark three distinct cellular contexts of Otx2 expression. We discovered that Otx2, Crx and Sox2, which are well-known TFs regulating retinal development, bind to and activate the O5, O7 or O9 CRMs respectively. The chromatin status of these three CRMs was found to be distinct in vivo in different retinal cell types and at different stages. We conclude that retinal cells utilize a cohort of TFs with different expression patterns, and multiple CRMs with different chromatin configurations, to precisely regulate the expression of Otx2.
View details for DOI 10.1242/dev.187922
View details for PubMedID 32631829
Low-Luminance Blue Light-Enhanced Phototoxicity in A2E-Laden RPE Cell Cultures and Rats.
International journal of molecular sciences
2019; 20 (7)
N-retinylidene-N-retinylethanolamine (A2E) and other bisretinoids are components of lipofuscin and accumulate in retinal pigment epithelial (RPE) cells-these adducts are recognized in the pathogenesis of retinal degeneration. Further, blue light-emitting diode (LED) light (BLL)-induced retinal toxicity plays an important role in retinal degeneration. Here, we demonstrate that low-luminance BLL enhances phototoxicity in A2E-laden RPE cells and rats. RPE cells were subjected to synthetic A2E, and the effects of BLL on activation of apoptotic biomarkers were examined by measuring the levels of cleaved caspase-3. BLL modulates the protein expression of zonula-occludens 1 (ZO-1) and paracellular permeability in A2E-laden RPE cells. Early inflammatory and angiogenic genes were also screened after short-term BLL exposure. In this study, we developed a rat model for A2E treatment with or without BLL exposure for 21 days. BLL exposure caused fundus damage, decreased total retinal thickness, and caused neuron transduction injury in the retina, which were consistent with the in vitro data. We suggest that the synergistic effects of BLL and A2E accumulation in the retina increase the risk of retinal degeneration. These outcomes help elucidate the associations between BLL/A2E and angiogenic/apoptotic mechanisms, as well as furthering therapeutic strategies.
View details for PubMedID 30979028
Novel Protective Effects of Cistanche Tubulosa Extract Against Low-Luminance Blue Light-Induced Degenerative Retinopathy.
Cellular physiology and biochemistry : international journal of experimental cellular physiology, biochemistry, and pharmacology
2018; 51 (1): 63–79
Blue light-emitting diode light (BLL)-induced phototoxicity plays an important role in ocular diseases and causes retinal degeneration and apoptosis in human retinal pigment epithelial (RPE) cells. Cistanche tubulosa extract (CTE) is a traditional Chinese medicine with many beneficial protective properties; however, few studies have examined the ocular protective roles of CTE. In this study, we investigated the mechanisms underlying the effects of CTE on BLL-induced apoptosis in vitro and in vivo.RPE cells were applied in the current in vitro study and cell viability was determined by an 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Apoptosis-related protein expression was determined by western blot analysis and immunofluorescence staining. Brown Norway rats were used to examine exposure to commercially available BLL in vivo. Hematoxylin and eosin staining, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), and western blot assays were used to examine retinal morphological deformation.CTE significantly inhibited hydrogen peroxide-, tert-butyl hydroperoxide-, sodium azide-, and BLL-induced RPE damage. Further, CTE reduced the expression of apoptotic markers such as cleaved caspase-3 and TUNEL staining after BLL exposure by inactivating apoptotic pathways, as shown via immunofluorescent staining. In addition, CTE inhibited the BLL-induced phosphorylation of c-Jun N-terminal kinase, extra signal-related kinases 1/2, and p38 in RPE cells. In vivo, the oral administration of CTE rescued 60-day periodic BLL exposure-induced decrements in retinal thickness and reduced the number of TUNEL-positive cells in the brown Norway rat model.CTE is a potential prophylactic agent against BLL-induced phototoxicity.
View details for DOI 10.1159/000495162
View details for PubMedID 30439705
Editor's Highlight: Periodic Exposure to Smartphone-Mimic Low-Luminance Blue Light Induces Retina Damage Through Bcl-2/BAX-Dependent Apoptosis.
2017; 157 (1): 196-210
Blue light-induced phototoxicity plays an important role in retinal degeneration and might cause damage as a consequence of smartphone dependency. Here, we investigated the effects of periodic exposure to blue light-emitting diode in a cell model and a rat retinal damage model. Retinal pigment epithelium (RPE) cells were subjected to blue light in vitro and the effects of blue light on activation of key apoptotic pathways were examined by measuring the levels of Bcl-2, Bax, Fas ligand (FasL), Fas-associated protein with death domain (FADD), and caspase-3 protein. Blue light treatment of RPE cells increased Bax, cleaved caspase-3, FasL, and FADD expression, inhibited Bcl-2 and Bcl-xL accumulation, and inhibited Bcl-2/Bax association. A rat model of retinal damage was developed with or without continuous or periodic exposure to blue light for 28 days. In this rat model of retinal damage, periodic blue light exposure caused fundus damage, decreased total retinal thickness, caused atrophy of photoreceptors, and injured neuron transduction in the retina.
View details for DOI 10.1093/toxsci/kfx030
View details for PubMedID 28184904
Anti-inflammatory properties of shikonin contribute to improved early-stage diabetic retinopathy.
2017; 7: 44985-?
Diabetic retinopathy (DR), a major microvascular complication of diabetes, leads to retinal vascular leakage, neuronal dysfunction, and apoptosis within the retina. In this study, we combined STZ with whole-body hypoxia (10% O2) for quicker induction of early-stage retinopathy in C57BL/6 mice. We also compared the effects of a high glucose condition combined with hypoxia (1% O2) to a low glucose condition by using retinal pigment epithelial (RPE) cells, which are a crucial component of the outer blood-retinal barrier and the damage is related to retinopathy. In the retina of DM/hypoxic C57BL/6 mice, abnormal a-wave and b-wave activity, yellowish-white spots, hyperfluorescence, and reduced retinal thickness were found using electroretinography (ERG), fundus photography (FP), fundus fluorescein angiography (FFA), and optical coherence tomography (OCT). Shikonin dose-dependently (0.5-50 mg/kg, per os) prevented DM/hypoxia-induced lesions. In eye tissue, administration of shikonin also attenuated DM/hypoxia-induced pre-apoptotic protein BAX expression as well as the production of inflammatory proteins cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS). We also demonstrated that shikonin administration rescues high glucose/hypoxia (1% O2)-induced inflammation, decreased junction protein expression, and permeability in RPE cells. These results indicate that shikonin treatment may prevent the loss of vision associated with DR.
View details for DOI 10.1038/srep44985
View details for PubMedID 28322323
The natural retinoprotectant chrysophanol attenuated photoreceptor cell apoptosis in an N-methyl-N-nitrosourea-induced mouse model of retinal degenaration
Retinitis pigmentosa (RP) is an inherited photoreceptor-degenerative disease, and neuronal degeneration in RP is exacerbated by glial activation. Cassia seed (Jue-ming-zi) is a traditional herbal medicine commonly used to treat ocular diseases in Asia. In this report, we investigated the retina-protective effect of chrysophanol, an active component of Cassia seed, in an N-methyl-N-nitrosourea (MNU)-induced mouse model of RP. We determined that chrysophanol inhibited the functional and morphological features of MNU-induced retinal degeneration using scotopic electroretinography (ERG), optical coherence tomography (OCT), and immunohistochemistry analysis of R/G opsin and rhodopsin. Furthermore, TUNEL assays revealed that chrysophanol attenuated MNU-induced photoreceptor cell apoptosis and inhibited the expression of the apoptosis-associated proteins PARP, Bax, and caspase-3. In addition, chrysophanol ameliorated reactive gliosis, as demonstrated by a decrease in GFAP immunolabeling, and suppressed the activation of matrix metalloproteinase (MMP)-9-mediated gelatinolysis. In vitro studies indicated that chrysophanol inhibited lipopolysaccharide (LPS)-induced iNOS and COX-2 expression in the BV2 mouse microglia cell line and inhibited MMP-9 activation in primary microglia. Our results demonstrate that chrysophanol provided neuroprotective effects and inhibited glial activation, suggesting that chrysophanol might have therapeutic value for the treatment of human RP and other retinopathies.
View details for DOI 10.1038/srep41086
View details for PubMedID 28112220
NcoA2-Dependent Inhibition of HIF-1 alpha Activation Is Regulated via AhR
2015; 148 (2): 517-530
High endogenous levels of aryl hydrocarbon receptor (AhR) contribute to hypoxia signaling pathway inhibition following exposure to the potent AhR ligand benzo[a]pyrene (B[a]P) and could alter cellular homeostasis and disease condition. Increasing evidence indicates that AhR might compete with AhR nuclear translocator (ARNT) for complex formation with hypoxia-inducible factor-1α (HIF-1α) for transactivation, which could alter several physiological variables. Nuclear receptor coactivator 2 (NcoA2) is a transcription coactivator that regulates transcription factor activation and inhibition of basic helix-loop-helix Per (Period)-ARNT-SIM (single-minded) (bHLH-PAS) family proteins, such as HIF-1α, ARNT, and AhR, through protein-protein interactions. In this study, we demonstrated that both hypoxia and hypoxia-mimic conditions decreased NcoA2 protein expression in HEK293T cells. Hypoxia response element (HRE) and xenobiotic-responsive element (XRE) transactivation also were downregulated with NcoA2 knockdown under hypoxic conditions. In addition, B[a]P significantly decreased NcoA2 protein expression be accompanied with AhR degradation. We next evaluated whether the absence of AhR could affect NcoA2 protein function under hypoxia-mimetic conditions. NcoA2 and HIF-1α nuclear localization decreased in both B[a]P-pretreated and AhR-knockdown HepG2 cells under hypoxia-mimic conditions. Interestingly, NcoA2 overexpression downregulated HRE transactivation by competing with HIF-1α and AhR to form protein complexes with ARNT. Both NcoA2 knockdown and overexpression inhibited endothelial cell tube formation in vitro. We also demonstrated using the in vivo plug assay that NcoA2-regulated vascularization decreased in mice. Taken together, these results revealed a biphasic role of NcoA2 between AhR and hypoxic conditions, thus providing a novel mechanism underlying the cross talk between AhR and hypoxia that affects disease development and progression.
View details for DOI 10.1093/toxsci/kfv199
View details for Web of Science ID 000367195500015
View details for PubMedID 26350169
Long-term Fluorometholone Topical Use Induces Ganglion Cell Damage in Rats Analyzed With Optical Coherence Tomography
2015; 147 (2): 317-325
To determine the toxic effects of long-term topical usage of fluorometholone (FLM) on ganglion cells using a direct in vivo retinopathological Brown Norway (BN) rat model. The BN rat retinal model was investigated with a minimum of 3 rats and a maximum of 4 rats per group. Rats received vehicle and 0.02% FLM suspension via topical administration 3 times a day for 28 days. The fundus images and retinal vessels were detected on days 1, 14, and 28 using Micron III retinal imaging microscope and fundus fluorescein angiography (FFA). For retinal structures, spectral-domain optical coherence tomography (SD-OCT) images were taken after FFA on days 1, 14, and 28 using an SD-OCT Imaging System. For retinal function, electrical signal transduction of photoreceptors and bipolar cells was determined by electroretinographic (ERG) recording on days 1 and 28 and IOP detection. At the end of the experiment on day 28, immunohistochemistry and TUNEL assay were performed to investigate apoptosis in ganglion cells. Total retina and nerve fiber layer (NFL) to the inner plexiform layer (IPL) were significantly thinner following 28 days of FLM treatment. Hematoxylin and eosin stain showed that there were NFL and ganglion cell layer deformations in the FLM group. With FLM treatment, TUNEL assay showed approximately a 4.68-fold increase in apoptotic cells. Moreover, FLM decreased ERG b-wave amplitude by about 56%. Using ophthalmofundoscopy devices, after 28 days of topical administration, FLM decreased NFL-IPL and total retina thickness. This suggests that long-term FLM induces adverse effects with respect to ganglion cell apoptosis.
View details for DOI 10.1093/toxsci/kfv132
View details for Web of Science ID 000365547300005
View details for PubMedID 26141393
Minocycline accelerates hypoxia-inducible factor-1 alpha degradation and inhibits hypoxia-induced neovasculogenesis through prolyl hydroxylase, von Hippel-Lindau-dependent pathway
ARCHIVES OF TOXICOLOGY
2014; 88 (3): 659-671
Hypoxia-mediated stress responses are important in tumor progression, especially when tumor growth causes the tumor to become deprived of its blood supply. The oxygen-labile transcription factor hypoxia-inducible factor-1 alpha (HIF-1α) plays a critical role in regulating hypoxia stress-related gene expression and is considered a novel therapeutic target. Lung adenocarcinoma cell lines were exposed to minocycline, followed by incubation at hypoxic condition for 3-6 h. Here, we show that minocycline, a second-generation tetracycline, can induce HIF-1α proteasomal degradation under hypoxia by increasing the expression prolyl hydroxylase-2 and HIF-1α/von Hippel-Lindau protein interaction, thereby overcoming hypoxia-induced HIF-1α stabilization. Neither repression of hypoxia-induced phosphatidylinositol-3 kinase/Akt/mammalian target of rapamycin pathway nor inhibition of Hsp90 was required for minocycline-induced HIF-1α degradation. The HIF-1α degradation-enhancing effect of minocycline was evident in both cancerous and primary cells. Minocycline-pretreated, hypoxia-conditioned cells showed a clear reduction in hypoxia response element reporter expression and amelioration of vascular endothelial growth factor C/D (VEGF-C/D), matrix metalloproteinase 2, and glucose transporter 1 expression. By decreasing VEGF secretion of cancerous cells, minocycline could suppress endothelial cell neovasculogenesis. These findings suggest a novel application of minocycline in the treatment of tumor angiogenesis as well as hypoxia-related diseases.
View details for DOI 10.1007/s00204-013-1175-5
View details for Web of Science ID 000331653200011
View details for PubMedID 24292262
Silibinin inhibits VEGF secretion and age-related macular degeneration in a hypoxia-dependent manner through the PI-3 kinase/Akt/mTOR pathway
BRITISH JOURNAL OF PHARMACOLOGY
2013; 168 (4): 920-931
Hypoxia-mediated neovascularization plays an important role in age-related macular degeneration (AMD). There are few animal models or effective treatments for AMD. Here, we investigated the effects of the flavonoid silibinin on hypoxia-induced angiogenesis in a rat AMD model.Retinal pigmented epithelial (RPE) cells were subjected to hypoxia in vitro and the effects of silibinin on activation of key hypoxia-induced pathways were examined by elucidating the hypoxia-inducible factor-1 alpha (HIF-1α) protein level by Western blot. A rat model of AMD was developed by intravitreal injection of VEGF in Brown Norway rats, with or without concomitant exposure of animals to hypoxia. Animals were treated with oral silibinin starting at day 7 post-VEGF injection and AMD changes were followed by fluorescein angiography on days 14 and 28 post-injection.Silibinin pretreatment of RPE cells increased proline hydroxylase-2 expression, inhibited HIF-1α subunit accumulation, and inhibited VEGF secretion. Silibinin-induced HIF-1α and VEGF down-regulation required suppression of hypoxia-induced phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin (mTOR) pathway. In the rat model of AMD, silibinin administration prevented VEGF- and VEGF plus hypoxia-induced retinal oedema and neovascularization.The effects of silibinin, both in vitro and in vivo, support its potential as a therapeutic for the prevention of neovascular AMD.
View details for DOI 10.1111/j.1476-5381.2012.02227.x
View details for Web of Science ID 000314130300011
View details for PubMedID 23004355
View details for PubMedCentralID PMC3631380
Evaluation of Acute 13-Week Subchronic Toxicity and Genotoxicity of the Powdered Root of Tongkat Ali (Eurycoma longifolia Jack)
EVIDENCE-BASED COMPLEMENTARY AND ALTERNATIVE MEDICINE
Tongkat Ali (Eurycoma longifolia) is an indigenous traditional herb in Southern Asia. Its powdered root has been processed to produce health supplements, but no detailed toxicology report is available. In this study, neither mutagenicity nor clastogenicity was noted, and acute oral LD50 was more than 6 g/kg b.w. After 4-week subacute and 13-week subchronic exposure paradigms (0, 0.6, 1.2, and 2 g/kg b.w./day), adverse effects attributable to test compound were not observed with respect to body weight, hematology, serum biochemistry, urinalysis, macropathology, or histopathology. However, the treatment significantly reduced prothrombin time, partial thromboplastin time, blood urea nitrogen, creatinine, aspartate aminotransferase, creatine phosphate kinase, lactate dehydrogenase, and cholesterol levels, especially in males (P < 0.05). These changes were judged as pharmacological effects, and they are beneficial to health. The calculated acceptable daily intake (ADI) was up to 1.2 g/adult/day. This information will be useful for product development and safety management.
View details for DOI 10.1155/2013/102987
View details for Web of Science ID 000324178100001
View details for PubMedID 24062779
View details for PubMedCentralID PMC3767077
Anti-ageing effects of alpha-naphthoflavone on normal and UVB-irradiated human skin fibroblasts
2012; 21 (7): 546-548
Ageing is a complex and multifactorial process resulting in several functional and aesthetic changes to the skin. We found that α-Naphthoflavone (α-NF) concentration-dependently induced pro-collagen type I protein expression and inhibited MMP-1 protein expression, in both normal and UVB-irradiated cells. SB431542 and SIS3 - inhibitors of TGF-β and Smad3, respectively - significantly alleviate α-NF-caused response of MMP-1 and pro-collagen. LY294002 (PI3K inhibitor) can reverse α-NF-induced ERK, Akt, Smad-3 activation, pro-collagen synthesis and α-NF-suppressed AP-1 activation. PD (ERK inhibitor) was not involved in pro-collagen generation and MMP-1 inhibition. We concluded that α-NF promotes pro-collagen production and inhibits MMP-1 expression via the activation of a PI3K/Akt/Smad-3 pathway in normal and UVB-irradiated human skin fibroblasts, while TGF-β may play an important role in transducing this pathway. These results suggest that α-NF, a natural plant product, has the potential to become a novel anti-ageing skin application.
View details for DOI 10.1111/j.1600-0625.2012.01517.x
View details for Web of Science ID 000305508500014
View details for PubMedID 22716253