The Pineal Gland Energy Transducer
Len Wisneski in The Scientific Basis of Integrative Health, 2017
One possibility is cryptochrome, the vitamin B-based, light-absorbing protein pigment in the eye and SCN, which is sensitive to blue light (Ivanchenko et al., 2001). It is found both in the retinal ganglion and the inner retina (Sancar, 2000). Cryptochrome was discovered in plants and identified as the protein that allows plants to bend toward light. Other possible photoreceptors are the nonrod, noncone vitamin A-based opsin photopigments, such as melanopsin (Provencio et al., 1998). The retinal distribution of melanopsin cells bears a striking resemblance to the retinal cells known to connect to the SCN in rodents. The inner retina seems to be the only mammalian site at which melanopsin is expressed, suggesting a role in nonvisual photoreceptive tasks (Provencio et al., 2000). So, in the end, melanopsin and cryptochrome are viable, but unconfirmed, photoreceptor candidates of the mammalian clock.
Altitude, temperature, circadian rhythms and exercise
Adam P. Sharples, James P. Morton, Henning Wackerhage in Molecular Exercise Physiology, 2022
How is the master pacemaker in the brain synchronised to the environmental day-night cycle? The cryptochrome-encoding genes CRY1/2 are key candidates for linking the master clock to ambient light as cryptochromes are blue light-sensing proteins. However, Cry1/2 knockout mice still increase the expression of Per1 and Per2 in response to light (72), suggesting CRY1 and CRY2 proteins are not needed to synchronise the master clock with the day/night cycle. So where are the light sensors that help to entrain the master clock in the suprachiasmic nucleus? Researchers found that if they knocked out a protein in mice called melanopsin, containing intrinsically photosensitive retinal ganglion cells of the eye, the animals demonstrated normal pattern vision, yet struggled to link their circadian rhythms to the day-night cycle (73). As melanopsin responds mostly to blue light, this wavelength of visible light keeps melanopsin more active during the day and less active at night.
Photobiomodulation Therapy in Orthopedics
Kohlstadt Ingrid, Cintron Kenneth in Metabolic Therapies in Orthopedics, Second Edition, 2018
It is possible that blue light interacts with mitochondrial chromophores in the same way as red/NIR light since heme centers that are widespread in cytochromes have a significant absorption peak that coincides with the Soret band of porphyrins. However, there are several other plausible chromophores for blue light (and to a lesser extent green light). It should be noted that the term “blue light” can refer to a relatively wide range of wavelengths such as violet (390–425 nm), indigo (425–450 nm), royal blue (450–475 nm), blue green (475–500 nm). Because of the width of a typical absorption band (30 nm full width half maximum), it is theoretically possible that blue light could be absorbed by several distinct chromophores. For blue light these potential chromophores are in order of increasing wavelength: (A) tryptophan that can be photo-oxidized to form 6-formylindolo[3,2-b]carbazole (FICZ) that acts as an endogenous ligand of the aryl-hydrocarbon receptor (AhR) [30, 31]. The shortest wavelength blue light (380–400 nm) would be optimal here, as in general UV wavelengths are thought to be responsible for trytptophan photodegradation. (B) Next is the Soret band of heme groups (400 nm) where presumably similar processes are initiated as have been proposed for red/NIR light. Cytochromes b and a/a(3) were found to be responsible for the inhibitory effects of blue light on yeast [32]. (C) Wavelengths in the 440 nm range have been found to be optimal for activation of cryptochromes [33]. Cryptochromes are blue-light sensitive flavoproteins that have wide applications in plants and lower life-forms, mediating such functions as photomorphogenesis [34]. Cryptochromes are thought to play a role in entraining circadian rhythms [35] and may even be involved in sensing of magnetic fields in fruit flies [36]. Cryptochromes have recently been found to be expressed in some mammalian cells and tissues [37] and also to have activity in regulating circadian rhythms [38]. (D) The family of opsins are light-sensitive G-protein coupled receptors that rely on isomerization of cis-retinal. The wavelength maximum can range from UVA all the way to the green and red, but melanopsin (OPN4) has a λmax of 479 nm [39]. The signaling pathways differ between different opsins. Opsins signal via two main pathways depending on the type of G-protein they are coupled with [40, 41]. Those opsins (OPN1, OPN2, OPN3, OPN5) that are coupled with Go, Gi, Gt, Gs proteins, signal via a pathway involving cyclic nucleotides (cAMP and cGMP). On the other hand, OPN4 (melanopsin) is coupled to Gq and signals via the phospholipase C pathway leading to production of inositol triphosphate and di-acylglycerol. These signaling pathways are shown in Figure 6.2. It is known that activation of retinal opsins by blue light can generate ROS, which is partly responsible for ocular phototoxicity caused by violet and blue light [42].
Exploring the role of circadian clock gene and association with cancer pathophysiology
Published in Chronobiology International, 2020
Mahtab Keshvari, Mahdieh Nejadtaghi, Farnaz Hosseini-Beheshti, Ali Rastqar, Niraj Patel
Studies in animals and plants suggest that cryptochromes play a pivotal role in the generation and maintenance of circadian rhythms. Similarly, cryptochromes play a vital role in the entrainment of circadian rhythms in plants (Chaves et al. 2011). In Drosophila, cryptochrome (dCRY) acts as a blue-light photoreceptor that directly modulates light input into the circadian clock (Yoshii et al. 2016), while in mammals, cryptochromes (CRY1 and CRY2) act as transcription repressors within the circadian clockwork (Dibner et al. 2010). Some insects, including the monarch butterfly, have both a mammal-like and a Drosophila-like version of cryptochrome, providing evidence for an ancestral clock mechanism involving both light-sensing and transcriptional-repression roles for cryptochrome (Zhu et al. 2008a).
Circadian rhythmicity of body temperature and metabolism
Published in Temperature, 2020
Roberto Refinetti
It has been known for over 20 years that the molecular mechanism of the circadian clock in animals involves an auto-regulatory transcriptional feedback loop in which the proteins Clock and Bmal1 activate the transcription of the period and cryptochrome genes. The Period and Cryptochrome proteins then feed back and repress their own transcription by interaction with Clock and Bmal1 [676,677]. This is the backbone of the clock itself, but much has yet to be learned about how enzyme transcripts controlled by the clock generate circadian enzyme activity [678]. One research group has found that the circadian clock generates oscillations in mitochondrial oxidative capacity via rhythmic regulation of NAD+ biosynthesis [679], as diagrammed in Figure 9.
Magnetic fields and apoptosis: a possible mechanism
Published in Electromagnetic Biology and Medicine, 2022
Santi Tofani
There is evidence to suggest that cryptochromes can form ROS following light exposure and mammalian cryptochromes may act as a redox sensor within cells (Landler and Keays 2018). The extent to which such a mechanism is light dependent is a matter that requires further investigation, particularly given that growing evidence suggests that mammalian cryptochromes do not bind FAD (flavin adenine dinucleotide) and are not true photoreceptors (Kutta et al. 2017).
Related Knowledge Centers
- Animal
- Chlorophyll
- Circadian Rhythm
- Flavoprotein
- In Vivo
- Protein
- Magnetoreception
- Photoreceptor Protein
- Gene
- Cidnp