Light-induced Gene Expression Research Articles

Transcriptomic Analysis of Light-Induced Genes in Nasonia vitripennis: Possible Implications for Circadian Light Entrainment Pathways.

Circadian entrainment to the environmental day-night cycle is essential for the optimal use of environmental resources. In insects, opsin-based photoreception in the compound eye and ocelli and CRYPTOCHROME1 (CRY1) in circadian clock neurons are thought to be involved in sensing photic information, but the genetic regulation of circadian light entrainment in species without light-sensitive CRY1 remains unclear. To elucidate a possible CRY1-independent light transduction cascade, we analyzed light-induced gene expression through RNA-sequencing in Nasonia vitripennis. Entrained wasps were subjected to a light pulse in the subjective night to reset the circadian clock, and light-induced changes in gene expression were characterized at four different time points in wasp heads. We used co-expression, functional annotation, and transcription factor binding motif analyses to gain insight into the molecular pathways in response to acute light stimulus and to form hypotheses about the circadian light-resetting pathway. Maximal gene induction was found after 2 h of light stimulation (1432 genes), and this included the opsin gene opblue and the core clock genes cry2 and npas2. Pathway and cluster analyses revealed light activation of glutamatergic and GABA-ergic neurotransmission, including CREB and AP-1 transcription pathway signaling. This suggests that circadian photic entrainment in Nasonia may require pathways that are similar to those in mammals. We propose a model for hymenopteran circadian light-resetting that involves opsin-based photoreception, glutamatergic neurotransmission, and gene induction of cry2 and npas2 to reset the circadian clock.

OPTO-BLUE: An Integrated Bidirectional Optogenetic Lentiviral Platform for Controlled Light-Induced Gene Expression.

Regulated systems for transgene expression are useful tools in basic research and a promising platform in biomedicine due to their regulated transgene expression by an inducer. The emergence of optogenetics expression systems enabled the construction of light-switchable systems, enhancing the spatial and temporal resolution of a transgene. The LightOn system is an optogenetic tool that regulates the expression of a gene of interest using blue light as an inducer. This system is based on a photosensitive protein (GAVPO), which dimerizes and binds to the UASG sequence in response to blue light, triggering the expression of a downstream transgene. Previously, we adapted the LightOn system to a dual lentiviral vector system for neurons. Here, we continue the optimization and assemble all components of the LightOn system into a single lentiviral plasmid, the OPTO-BLUE system. For functional validation, we used enhanced green fluorescent protein (EGFP) as an expression reporter (OPTO-BLUE-EGFP) and evaluated the efficiency of EGFP expression by transfection and transduction in HEK293-T cells exposed to continuous blue-light illumination. Altogether, these results prove that the optimized OPTO-BLUE system allows the light-controlled expression of a reporter protein according to a specific time and light intensity. Likewise, this system should provide an important molecular tool to modulate gene expression of any protein by blue light.

Enhancement of Vivid-based photo-activatable Gal4 transcription factor in mammalian cells.

The Gal4/UAS system is a versatile tool to manipulate exogenous gene expression of cells spatially and temporally in many model organisms. Many variations of light-controllable Gal4/UAS system are now available, following the development of photo-activatable (PA) molecular switches and integration of these tools. However, many PA-Gal4 transcription factors have undesired background transcription activities even in dark conditions, and this severely attenuates reliable light-controlled gene expression. Therefore, it is important to develop reliable PA-Gal4 transcription factors with robust light-induced gene expression and limited background activity. By optimization of synthetic PA-Gal4 transcription factors, we have validated configurations of Gal4 DNA biding domain, transcription activation domain and blue light-dependent dimer formation molecule Vivid (VVD), and applied types of transcription activation domains to develop a new PA-Gal4 transcription factor we have named eGAV (enhanced Gal4-VVD transcription factor). Background activity of eGAV in dark conditions was significantly lower than that of hGAVPO, a commonly used PA-Gal4 transcription factor, and maximum light-induced gene expression levels were also improved. Light-controlled gene expression was verified in cultured HEK293T cells with plasmid-transient transfections, and in mouse EpH4 cells with lentivirus vector-mediated transduction. Furthermore, light-controlled eGAV-mediated transcription was confirmed in transfected neural stem cells and progenitors in developing and adult mouse brain and chick spinal cord, and in adult mouse hepatocytes, demonstrating that eGAV can be applied to a wide range of experimental systems and model organisms.Key words: optogenetics, Gal4/UAS system, transcription, gene expression, Vivid.

Light-Induced GFP Expression in Zebrafish Embryos using the Optogenetic TAEL/C120 System.

Inducible gene expression systems are an invaluable tool for studying biological processes. Optogenetic expression systems can provide precise control over gene expression timing, location, and amplitude using light as the inducing agent. In this protocol, an optogenetic expression system is used to achieve light-inducible gene expression in zebrafish embryos. This system relies on an engineered transcription factor called TAEL based on a naturally occurring light-activated transcription factor from the bacterium E. litoralis. When illuminated with blue light, TAEL dimerizes, binds to its cognate regulatory element called C120, and activates transcription. This protocol uses transgenic zebrafish embryos that express the TAEL transcription factor under the control of the ubiquitous ubb promoter. At the same time, the C120 regulatory element drives the expression of a fluorescent reporter gene (GFP). Using a simple LED panel to deliver activating blue light, induction of GFP expression can first be detected after 30 min of illumination and reaches a peak of more than 130-fold induction after 3 h of light treatment. Expression induction can be assessed by quantitative real-time PCR (qRT-PCR) and by fluorescence microscopy. This method is a versatile and easy-to-use approach for optogenetic gene expression.

NPAS4 regulates the transcriptional response of the suprachiasmatic nucleus to light and circadian behavior

The suprachiasmatic nucleus (SCN) is the master circadian pacemaker in mammals and is entrained byenvironmental light. However, the molecular basis of the response of the SCN to light is not fully understood. We used RNA/chromatin immunoprecipitation/single-nucleus sequencing with circadian behavioral assays to identify mouse SCN cell types and explore their responses to light. We identified three peptidergic cell types that responded to light in the SCN: arginine vasopressin (AVP), vasoactive intestinal peptide (VIP), and cholecystokinin (CCK). In each cell type, light-responsive subgroups were enriched for expression of neuronal Per-Arnt-Sim (PAS) domain protein 4 (NPAS4) target genes. Further, mice lacking Npas4 had a longer circadian period under constant conditions, a damped phase response curve to light, and reduced light-induced gene expression in the SCN. Our data indicate that NPAS4 is necessary for normal transcriptional responses to light in the SCN and critical for photic phase-shifting of circadian behavior.

Reliably Engineering and Controlling Stable Optogenetic Gene Circuits in Mammalian Cells

Reliably controlling light-responsive mammalian cells requires the standardization of optogenetic methods. Toward this goal, this study outlines a pipeline of gene circuit construction, cell engineering, optogenetic equipment operation, and verification assays to standardize the study of light-induced gene expression using a negative-feedback optogenetic gene circuit as a case study.

Reliably Engineering and Controlling Stable Optogenetic Gene Circuits in Mammalian Cells.

Reliable gene expression control in mammalian cells requires tools with high fold change, low noise, and determined input-to-output transfer functions, regardless of the method used. Toward this goal, optogenetic gene expression systems have gained much attention over the past decade for spatiotemporal control of protein levels in mammalian cells. However, most existing circuits controlling light-induced gene expression vary in architecture, are expressed from plasmids, and utilize variable optogenetic equipment, creating a need to explore characterization and standardization of optogenetic components in stable cell lines. Here, the study provides an experimental pipeline of reliable gene circuit construction, integration, and characterization for controlling light-inducible gene expression in mammalian cells, using a negative feedback optogenetic circuit as a case example. The protocols also illustrate how standardizing optogenetic equipment and light regimes can reliably reveal gene circuit features such as gene expression noise and protein expression magnitude. Lastly, this paper may be of use for laboratories unfamiliar with optogenetics who wish to adopt such technology. The pipeline described here should apply for other optogenetic circuits in mammalian cells, allowing for more reliable, detailed characterization and control of gene expression at the transcriptional, proteomic, and ultimately phenotypic level in mammalian cells.

Artificial complementary chromatic acclimation gene expression system in Escherichia coli

BackgroundThe development of multiple gene expression systems, especially those based on the physical signals, such as multiple color light irradiations, is challenging. Complementary chromatic acclimation (CCA), a photoreversible process that facilitates the control of cellular expression using light of different wavelengths in cyanobacteria, is one example. In this study, an artificial CCA systems, inspired by type III CCA light-regulated gene expression, was designed by employing a single photosensor system, the CcaS/CcaR green light gene expression system derived from Synechocystis sp. PCC6803, combined with G-box (the regulator recognized by activated CcaR), the cognate cpcG2 promoter, and the constitutively transcribed promoter, the PtrcΔLacO promoter.ResultsOne G-box was inserted upstream of the cpcG2 promoter and a reporter gene, the rfp gene (green light-induced gene expression), and the other G-box was inserted between the PtrcΔLacO promoter and a reporter gene, the bfp gene (red light-induced gene expression). The Escherichia coli transformants with plasmid-encoded genes were evaluated at the transcriptional and translational levels under red or green light illumination. Under green light illumination, the transcription and translation of the rfp gene were observed, whereas the expression of the bfp gene was repressed. Under red light illumination, the transcription and translation of the bfp gene were observed, whereas the expression of the rfp gene was repressed. During the red and green light exposure cycles at every 6 h, BFP expression increased under red light exposure while RFP expression was repressed, and RFP expression increased under green light exposure while BFP expression was repressed.ConclusionAn artificial CCA system was developed to realize a multiple gene expression system, which was regulated by two colors, red and green lights, using a single photosensor system, the CcaS/CcaR system derived from Synechocystis sp. PCC6803, in E. coli. The artificial CCA system functioned repeatedly during red and green light exposure cycles. These results demonstrate the potential application of this CCA gene expression system for the production of multiple metabolites in a variety of microorganisms, such as cyanobacteria.

Phosphorylation of Serine 114 of the transcription factor ABSCISIC ACID INSENSITIVE 4 is essential for activity

The transcription factor ABA-INSENSITIVE(ABI)4 has diverse roles in regulating plant growth, including inhibiting germination and reserve mobilization in response to ABA and high salinity, inhibiting seedling growth in response to high sugars, inhibiting lateral root growth, and repressing light-induced gene expression. ABI4 activity is regulated at multiple levels, including gene expression, protein stability, and activation by phosphorylation. Although ABI4 can be phosphorylated at multiple residues by MAPKs, we found that S114 is the preferred site of MPK3. To examine the possible biological role of S114 phosphorylation, we transformed abi4-1 mutant plants with ABI4pro::ABI4 constructs encoding wild type (114S), phosphorylation-null (S114A) or phosphomimetic (S114E) forms of ABI4. Phosphorylation of S114 is necessary for the response to ABA, glucose, salt stress, and lateral root development, where the abi4 phenotype could be complemented by expressing ABI4 (114S) or ABI4 (S114E) but not ABI4 (S114A). Comparison of root transcriptomes in ABA-treated roots of abi4-1 mutant plants transformed with constructs encoding the different phosphorylation-forms of S114 of ABI4 revealed that 85 % of the ABI4-regulated genes whose expression pattern could be restored by expressing ABI4 (114S) are down-regulated by ABI4. Phosphorylation of S114 was required for regulation of 35 % of repressed genes, but only 17 % of induced genes. The genes whose repression requires the phosphorylation of S114 are mainly involved in embryo and seedling development, growth and differentiation, and regulation of gene expression.

A Blue Light-Inducible CRISPR-Cas9 System for Inhibiting Progression of Melanoma Cells

Melanoma is an aggressive skin tumor that shows a high mortality rate and level of metastasis. BRAF gene mutation (BRAF V600E) is directly related to the occurrence of melanoma. In this study, a light-inducible gene expression system was designed to control the Cas9 transcription, which could then cleave the BRAF V600E. To prove the potential utility of this system in melanoma, the physiological function of melanoma cells was tested. It illustrated that the light-induced CRISPR-Cas9 system could inhibit the progression of G361 and A375 cells. Thus, this system may provide a novel therapeutic strategy of melanoma intervention.

The characterization of Mediator 12 and 13 as conditional positive gene regulators in Arabidopsis

Mediator 12 (MED12) and MED13 are components of the Mediator multi-protein complex, that facilitates the initial steps of gene transcription. Here, in an Arabidopsis mutant screen, we identify MED12 and MED13 as positive gene regulators, both of which contribute broadly to morc1 de-repressed gene expression. Both MED12 and MED13 are preferentially required for the expression of genes depleted in active chromatin marks, a chromatin signature shared with morc1 re-activated loci. We further discover that MED12 tends to interact with genes that are responsive to environmental stimuli, including light and radiation. We demonstrate that light-induced transient gene expression depends on MED12, and is accompanied by a concomitant increase in MED12 enrichment during induction. In contrast, the steady-state expression level of these genes show little dependence on MED12, suggesting that MED12 is primarily required to aid the expression of genes in transition from less-active to more active states.

Altered light induced EGR1 expression in the SCN of PACAP deficient mice.

The brain's biological clock is located in the suprachiasmatic nucleus (SCN) of the hypothalamus and generates circadian rhythms in physiology and behavior. The circadian clock needs daily adjustment by light to stay synchronized (entrained) with the astronomical 24 h light/dark cycle. Light entrainment occurs via melanopsin expressing retinal ganglion cells (mRGCs) and two neurotransmitters of the retinohypothalamic tract (RHT), PACAP and glutamate, which transmit light information to the SCN neurons. In SCN neurons, light signaling involves the immediate-early genes Fos, Egr1 and the clock genes Per1 and Per2. In this study, we used PACAP deficient mice to evaluate PACAP's role in light induced gene expression of EGR1 in SCN neurons during early (ZT17) and late (ZT23) subjective night at high (300 lux) and low (10 lux) white light exposure. We found significantly lower levels of both EGR1 mRNA and protein in the SCN in PACAP deficient mice compared to wild type mice at early subjective night (ZT17) exposed to low but not high light intensity. No difference was found between the two genotypes at late night (ZT23) at neither light intensities. In conclusion, light mediated EGR1 induction in SCN neurons at early night at low light intensities is dependent of PACAP signaling. A role of PACAP in shaping synaptic plasticity during light stimulation at night is discussed.

Virus-Inspired Mimics: Dual-pH-Responsive Modular Nanoplatforms for Programmable Gene Delivery without DNA Damage with the Assistance of Light.

Although tremendous efforts have been made to construct gene vectors incorporating multiple functionalities and moieties, designing gene vectors integrating innovative features to successfully negotiate biological impediments, which hamper efficacious responses in gene-based therapy, is still very urgent. Herein, a light-induced virus-inspired mimic, in which a modular envelope was utilized to mask polyethylenimine/DNA (PD) polyplexes, was developed based on two pH-responsive polymers. The virus-inspired envelope, which was capable of achieving multitargeting and dual-pH-responsiveness in endo/lysosomal compartments, was composed of an internalizing arginylglycylaspartic acid-modified module and a citraconic anhydride-modified nuclear localized signal-functionalized module. The envelope conjugated with chlorin e6 (Ce6) was shielded on the surface of PD polyplexes. Dual-pH-responsive deshielding of the virus-inspired mimic in endo/lysosomes allowed generation of a nonfatal amount of reactive oxygen species (ROS) under short-time photoirradiation, leading to photochemical internalization and much more substantial enhancement in light-induced gene expression without DNA damage caused by ROS. Confocal images revealed that the virus-inspired mimic achieved successful nuclear translocation of Ce6, resulting in nucleus-targeting photodynamic therapy (PDT). Furthermore, pTRAIL-mediated gene therapy, accompanied by a fatal amount of ROS under long-time photoirradiation, additionally consolidated in vitro antitumor outcomes. This study demonstrates a novel paradigm of "one arrow, two hawks," accomplishing a combination of enhanced gene therapy and PDT.

Transcriptome analysis of the edible mushroom Lentinula edodes in response to blue light.

Lentinula edodes is one of the most popular edible mushrooms worldwide and contains important medicinal components such as lentinan, ergosterol, and eritadenine. Mushroom metabolism is regulated by the mycelia and fruit body using light; however, in mushrooms, the underlying molecular mechanisms controlling this process as well as light-induced gene expression remain unclear. Therefore, in this study, we compared morphological changes and gene expression in the fruit bodies of L. edodes cultivated under blue light and continuous darkness. Our results showed that blue light primarily induced pileus growth (diameter and thickness) compared to dark cultivation. Alternatively, stipe length development was promoted by dark cultivation. We also performed RNAseq on L. edodes under the blue light/dark cultivation conditions. A total of 12,051 genes were used for aligning the Illumina raw reads and 762 genes that showed fold change cut-offs of >|2| and significance p-values of <0.05 were selected under blue light condition. Among the genes which showed two-fold changed genes, 221 were upregulated and 541 were downregulated. In order to identify blue light induced candidate genes, differentially expressed genes (DEGs) were selected according to 4-fold changes and validated by RT-PCR. We identified 8 upregulated genes under blue light condition, such as DDR48-heat shock protein, Fasciclin-domain-containing protein and carbohydrate esterase family 4 protein, FAD NAD-binding domain-containing protein that are involved in morphological development of primordium and embryonic muscle development, cell adhesion and affect the structure of cellulosic and non-cellulosic cell walls of fruit body development, and photoreceptor of blue light signaling for fruit body and pigment development, respectively. This study provides valuable insights into the molecular mechanisms underlying the role of blue light in mushroom growth and development and can thus contribute to breeding programs to improve mushroom cultivation.

Spatiotemporal single-cell analysis of gene expression in the mouse suprachiasmatic nucleus.

Mammalian circadian behaviors are orchestrated by the suprachiasmatic nucleus (SCN) in the ventral hypothalamus, but the number of SCN cell types and their functional roles remain unclear. We have used single-cell RNA-sequencing to identify the basic cell types in the mouse SCN and to characterize their circadian and light-induced gene expression patterns. We identified eight major cell types, with each type displaying a specific pattern of circadian gene expression. Five SCN neuronal subtypes, each with specific combinations of markers, differ in their spatial distribution, circadian rhythmicity and light responsiveness. Through a complete three-dimensional reconstruction of the mouse SCN at single-cell resolution, we obtained a standardized SCN atlas containing the spatial distribution of these subtypes and gene expression. Furthermore, we observed heterogeneous circadian gene expression between SCN neuron subtypes. Such a spatiotemporal pattern of gene regulation within the SCN may have an important function in the circadian pacemaker.

Construction of a Multiwell Light-Induction Platform for Traceless Control of Gene Expression in Mammalian Cells.

Mammalian cells can be engineered to incorporate light-responsive elements that reliably sense stimulation by light and activate endogenous pathways, such as the cAMP or Ca2+ pathway, to control gene expression. Light-inducible gene expression systems offer high spatiotemporal resolution, and are also traceless, reversible, tunable, and inexpensive. Melanopsin, a well-known representative of the animal opsins, is a G-protein-coupled receptor that triggers a Gαq-dependent signaling cascade upon activation with blue light (≈470nm). Here, we describe how to rewire melanopsin activation by blue light to transgene expression in mammalian cells, with detailed instructions for constructing a 96-LED array platform with multiple tunable parameters for illumination of the engineered cells in multiwell plates.

Blue Light-Induced Gene Expression Alterations in Cultured Neurons Are the Result of Phototoxic Interactions with Neuronal Culture Media.

Blue wavelength light is used as an optical actuator in numerous optogenetic technologies employed in neuronal systems. However, the potential side effects of blue light in neurons has not been thoroughly explored, and recent reports suggest that neuronal exposure to blue light can induce transcriptional alterations in vitro and in vivo. Here, we examined the effects of blue wavelength light in cultured primary rat cortical cells. Exposure to blue light (470 nm) resulted in upregulation of several immediate early genes (IEGs) traditionally used as markers of neuronal activity, including Fos and Fosb, but did not alter the expression of circadian clock genes Bmal1, Cry1, Cry2, Clock, or Per2. IEG expression was increased following 4 h of 5% duty cycle light exposure, and IEG induction was not dependent on light pulse width. Elevated levels of blue light exposure induced a loss of cell viability in vitro, suggestive of overt phototoxicity. Induction of IEGs by blue light was maintained in cortical cultures treated with AraC to block glial proliferation, indicating that induction occurred selectively in postmitotic neurons. Importantly, changes in gene expression induced by blue wavelength light were prevented when cultures were maintained in a photoinert media supplemented with a photostable neuronal supplement instead of commonly utilized neuronal culture media and supplements. Together, these findings suggest that light-induced gene expression alterations observed in vitro stem from a phototoxic interaction between commonly used media and neurons, and offer a solution to prevent this toxicity when using photoactivatable technology in vitro.

A Controllable, Centrifugal-Based Hydrodynamic Microfluidic Chip for Cell-Pairing and Studying Long-Term Communications between Single Cells.

Investigation of cell-cell interactions between individual cells in a well-defined microenvironment is critical for the understanding of specific intercellular communications and interactions. However, most current studies in multicellular systems are often overwhelmed by additional complicated interactions. Cell-pairing based on a microfluidic chip provides a potential strategy to simplify the studies. Here, we report a robust and straightforward method, relying on a combination of hydrodynamic single-cell capture and centrifugation-assisted relocation of individual cells, which can be applied, in general, to various cell types for cell-pairing and studying cell interactions at the single-cell level. This microfluidic chip is simple to operate and easily controlled, which requires only two operational steps-capturing individual cells with hydrodynamic traps and subsequently relocating the capture cells by centrifugation. With this microfluidic chip, we demonstrated homotypic cell-pairing, heterotypic cell-pairing, and long-term cell coculture, which exhibited better or comparable performance compared with previous cell-pairing methods. Its single-cell trapping and cell-pairing efficiencies are ∼74% and ∼20%, respectively. As a proof of concept, we paired individual dHL-60 cells and HeLa cells (HeLa-IL8, HeLa-IL10, and wild-type HeLa cells) in multiple cell chambers. The HeLa-IL8 and HeLa-IL10, both engineered with a light-induced gene expression system, can secret interleukin-8 and interleukin-10, respectively, under blue light illumination. We found that these three HeLa cell lines have very different influences on the migration of dHL-60 cells. This platform demonstrates its potential applications in studies of intercellular communication (paracrine), and it can be extended to trap three or more individual cells for more complex biological systems.

Soriano award lecture: Light, circadian rhythms and sleep: Mechanisms to new therapeutics

Until recently, it seemed inconceivable to most vision researchers and ophthalmologists that there could be an unrecognised class of light sensor (photoreceptor) within the eye. However, by studying how circadian rhythms and sleep are regulated by the dawn/dusk cycle we demonstrated that there exists a “3rd class” of photoreceptor within the eye based upon a small number of photosensitive retinal ganglion cells (pRGCs) that utilise the blue light sensitive photopigment melanopsin (OPN4). The first part of the presentation will consider the discovery and clinical importance of the “third” photoreceptor system of the eye. The second part of the talk will address how these photoreceptors signal light to the molecular clockwork and by what means this pathway is modified by sleep history. There has been remarkable progress in understanding the complex intracellular mechanisms that generate circadian rhythms, the molecular pathways whereby the pRGCs entrain circadian biology and sleep has remained poorly understood. The suprachiasmatic nuclei (SCN) are the site of the primary circadian pacemakers within the mammalian brain. Until recently, the model for entrainment involved a simple linear pathway whereby glutamate release from the pRGCs resulted in Ca2+ influx and raised intracellular cAMP in SCN neurones, which in turn resulted in CREB phosphorylation leading to increased transcription of two key clock genes, Per1 and Per2. This signal then advanced or delayed the molecular clockwork. However, an important feature of entrainment is that circadian responses to light are limited – as typified by jet-lag. Full recovery from jet-lag requires a day for every time-zone crossed. We addressed this issue and have identified and characterized a key role for Salt Inducible Kinase 1 (SIK1) and the CREB-regulated transcription co-activator 1 (CRTC1) in clock re-setting. However, our most recent findings have shown that light entrainment also involves the parallel activation of a Ca2+-ERK1/2-AP-1 signalling pathway. Thus both CRE and AP-1 regulatory elements drive light-induced clock gene expression. In addition, whilst light activation of the Ca2+-ERK1/2-AP-1 signalling pathway increases Per1 and Per2 expression, sleep/wake behaviour alters the effects of light on the clock. Our proposed mechanism suggests that adenosine acts as a signalling molecule that encodes wake duration. Adenosine acts via inhibitory A1 receptors on the SCN to inhibit the Ca2+-ERK1/2-AP-1 signalling pathway, which in turn, reduces the expression of Per1 and Per2. Thus sleep/wake history, encoded by adenosine, reduces the phase shifting effects of light upon the circadian system, altering sleep/wake timing. Finally, the talk will explore how such signalling pathways provide a new target for the regulation of circadian rhythms and the “pharmacological” replacement of light for sleep/wake re-setting in individuals lacking eyes or other individuals with severe circadian rhythm disruption.

Do We Utilize Our Knowledge of the Skin Protective Effects of Carotenoids Enough?

Due to their potential health-promoting effects, carotenoids have drawn both scientific and public attention in recent years. The primary source of carotenoids in the human skin is diet, mainly fruits, vegetables, and marine product, but they may originate from supplementation and topical application, too. In the skin, they accumulate mostly in the epidermis and act as a protective barrier to various environmental influences. Namely, the skin is exposed to numerous environmental factors, including ultraviolet radiation (UVR), air pollution, and smoking, that cause oxidative stress within the skin with consequent premature (extrinsic) aging. UVR, as the most prominent environmental factor, may cause additional detrimental skin effects, such as sunburn, DNA damage, and skin cancer. Therefore, photoprotection is the first line intervention in the prevention of premature aging and skin cancer. Numerous studies have demonstrated that carotenoids, particularly β-carotene, lycopene, lutein, and astaxanthin, have photoprotective effects, not only through direct light-absorbing properties, but also through their antioxidant effects (scavenging reactive oxygen species), as well as by regulation of UV light-induced gene expression, modulation of stress-dependent signaling, and/or suppression of cellular and tissue responses like inflammation. Interventional studies in humans with carotenoid-rich diet have shown its photoprotective effects on the skin (mostly by decreasing the sensitivity to UVR-induced erythema) and its beneficial effects in prevention and improvement of skin aging (improved skin elasticity and hydration, skin texture, wrinkles, and age spots). Furthermore, carotenoids may be helpful in the prevention and treatment of some photodermatoses, including erythropoietic protoporphyria (EPP), porphyria cutanea tarda (PCT) and polymorphous light eruption (PMLE). Although UVR is recognized as the main etiopathogenetic factor in the development of non-melanoma skin cancer (NMSC) and melanoma, and the photoprotective effects of carotenoids are certain, available studies still could not undoubtedly confirm the protective role of carotenoids in skin photocarcinogenesis.