Visual System and the Characteristics of Human Ocular Primary Cells

Author: AcceGen R&D Team

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Visual System

The visual system is the provider of visual ability to organisms. It is also one of the main sensory systems of living organisms. The visual system is mainly composed of two parts, namely the optical system and the nervous system (Figure.1). And dysfunction or disease of components of the visual system can lead to impairment of an organism’s ability to perceive visual perception[1, 2].

The function of the visual system can be summarized as the reception, transmission, and interpretation of the visual information. The visual information is carried by light, captured by the optical system, and focused onto the retina. And then, the light signals can be converted to neural signals and carry the visual information to the nerve system. At last, the visual information reaches the visual cortex of the brain and then form visual perception[2].

Eye

The eye is one of the core organs in the visual system. The structure of the eye can be divided into two parts: the anterior segment and the posterior segment. The anterior segment is mainly the optics that capture and receive light signals, including cornea, aqueous humor, and lens. And the posterior segment is mainly the component that transmits light signals and converts light signals to nerve signals, mainly including vitreous humor, retina, and optic nerve[2]. The eyes have a certain motor ability to cooperate with the brain to maintain the accuracy of visual information. And the eye also has environmental adaptability, including chiaroscuro adaptability, circadian rhythm adaptability, etc.[3, 4]

Retina and Nerve System

The retina can be divided into an optical part and a neural part. The retina can convert the light signals into nerve signals, and the nerve signals were undergone some initial processing by several optic nerves[2]. The damage or diseases of the optic nerve may lead to blindness, and unless there is an irreversible injury or lesion, the optic nerve can regenerate[5].

Conjunctiva, Retina and Human Ocular Primary Cells

Retina and Retinal Pigment Epithelial Cells (RPEpiC)

The retina is a photosensitive element in the eye in most vertebrates, just like film or an image sensor in the camera[6, 7]. The structure of the retina can be divided into more than 10 layers, including inner limiting membrane (ILM), nerve fiber layer (NLM), ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer (INL), outer plexiform layer (OPL), outer nuclear layer (ONL), external limiting membrane (ELM), Myoid, the retinal pigmented epithelium (RPE), etc.[8] Besides, the retinal structure of vertebrates is highly conserved[9].

Human retinal pigment epithelium (H-RPE) is a layer behind photoreceptor (PR) cells[10]. Features of RPE include the conservation and storage of retinoid, phagocytosis of exfoliated tissue, absorb scattered light, material transport, and providing support for photoreceptor cells. Retinal pigment epithelial cells are hexagonal with villi on the front. This structure provides support for photoreceptor cells and increases the contact area between retinal pigment epithelial and photoreceptor cells. And the melanosome in RPE cells is an essential organelle for RPE to absorb scattered light. The operation of the culture of human retina pigment epithelial cells is normal but sometimes needs to add growth-promoting substances (such as FGF) to ensure cell RPE reproduction population numbers for primary cells, and primary cells have a longer passaging cycle and limited number of passages[11-13].

Conjunctiva and Conjunctival Epithelial Cells (ConEpiC)

Conjunctiva is a tissue inside the eyelid that covers the sclera. The functions of the conjunctiva include producing mucus to keep eyes moist and lubricated and immune surveillance[14]. Conjunctiva is rich in fibrous tissue, blood vessels and lymphatics, interspersed with goblet cells. And melanocytes, T and B cell lymphocytes are all existed in the conjunctiva[15]. About diseases, inflammation is the most common disease of the conjunctiva, and dry eye is another common disease of the conjunctiva due to lacrimal gland dysfunction[14]. [16].

Conjunctival epithelial cells (CjECs) mainly include epithelial cells (including goblet cells) and fibroblasts. And the culture of conjunctival epithelial cells is similar to retinal pigment epithelial cells but there are some differences in the composition of the medium[17]. For the culture of human conjunctival epithelial primary cells (hCEPC), EpiLife medium with human keratinocyte growth supplement and epidermal growth factor (EGF) is necessary for the growth of the cells. The cells can be digested by TrypLE. And before passage, it is necessary to pre-coat human fibronectin, collagen, and laminin on a new petri dish before plating[18].

The Last Research Related to Human Ocular Primary Cells

Retinal Pigment Epithelial Cells

How to avoid light-induced damage to retinal pigment epithelium is a common eye surgery challenge. Kassumeh, et al. use human primary retinal pigment epithelial cells (HpRPE) to evaluate the protective effect of crocin and trans-resveratrol of the retinal photodamage[19]. They isolate and culture HpRPE from donors with no history of eye disease and give the cells light exposure with the treatment of crocin and trans-resveratrol. They identified the protective effect of crocin and trans-resveratrol to the HpRPE photodamage and exclude the toxic and side effects of these two protective agents. And they found that these two protective agents can reduce glutathione consumption in irradiated HpRPE cells.

Conjunctival Epithelial Cells

In previous research, Li, et al. found that Toll-like receptors (TLRs) expression level in vitro culture conjunctival epithelial cells is significantly lower than undigested tissue. And they use human conjunctival epithelial cells to identify the factors affecting TLRs expression levels in conjunctival epithelial cells[13]. They isolate human primary conjunctival epithelial cells and treat the cells with different methods (including culture supplement, airlifted culture, cytokine stimulation, cell wounding and hypoxia stimulation), and analyze the expression level of TLRs. They found increased TLRs expression level after these treatments and airlifted culture shows the most significant increase (about 7.8 to 25.9 times than control).

Besides, human conjunctival epithelial cells are also a valuable tool for researchers to analyze the pathological mechanism of the injection of SARS-Cov-2 from the eye. Singh, et al. found that human conjunctival epithelial cells (hCEC) are susceptible to SARS-Cov-2 infection and beta variant of concern (VOC) are more infectious than parental strain[18]. The hCECs are infected with SARS-Cov-2 and VOC, genes regulating antiviral response (such as) shows a high expression level after the infection. And VOC shows a higher viral copy number and innate response than parental strain.

Conclusion

Vision is one of the most important perceptual abilities of human beings. Eye health has long been a focus of public attention, and diseases of the eye have long been the focus of research in physiology and medicine. And human ocular primary cells can be valuable tools for researchers to unravel more physiological and pathological processes of the visual system.

Where to Get Human Ocular Primary Cells for research?

AcceGen supplies plenty and the most authentic Human Retinal Pigment Epithelial Cells and Human Conjunctival Epithelial Cells. Besides, AcceGen provides different types of human ocular cells to meet various research needs. To get more information, please refer to: Human Ocular Primary Cells.

It is our pleasure to help relative researches to move forward. All the products of AcceGen are strictly comply with international standards. For more detailed information, please visit our product portfolio or contact inquiry@accegen.com.

Reference

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14. https://encyclopediathefreedictionarycom/conjunctiva. encyclopedia.

15. Goldman L: Goldman’s Cecil Medicine. Philadelphia: Elsevier Saunders; 2012.

16. Hui KPY, Cheung MC, Perera R, Ng KC, Bui CHT, Ho JCW, Ng MMT, Kuok DIT, Shih KC, Tsao SW, et al: Tropism, RPElication competence, and innate immune responses of the coronavirus SARS-CoV-2 in human respiratory tract and conjunctiva: an analysis in ex-vivo and in-vitro cultures. Lancet Respir Med 2020, 8:687-695.

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18. Singh S, Garcia G, Jr., Shah R, Kramerov AA, Wright RE, 3rd, Spektor TM, Ljubimov AV, Arumugaswami V, Kumar A: SARS-CoV-2 and its beta variant of concern infect human conjunctival epithelial cells and induce differential antiviral innate immune response. Ocul Surf 2022, 23:184-194.

19. Kassumeh S, Wertheimer CM, Ohlmann A, Priglinger SG, Wolf A: Cytoprotective effect of crocin and trans-resveratrol on photodamaged primary human retinal pigment epithelial cells. Eur J Ophthalmol 2021, 31:630-637.