Cryptochromes Suppress HIF1α in Muscles

Circadian timing of satellite cell function and muscle regeneration

Recent research has highlighted an important role for the molecular circadian machinery in the regulation of tissue-specific function and stress responses. Indeed, disruption of circadian function, which is pervasive in modern society, is linked to accelerated aging, obesity, and type 2 diabetes. Furthermore, evidence supporting the importance of the circadian clock within both the mature muscle tissue and satellite cells to regulate the maintenance of muscle mass and repair capacity in response injury has recently emerged. Here, we review the discovery of circadian clocks within the satellite cell (a.k.a. adult muscle stem cell) and how they act to regulate metabolism, epigenetics, and myogenesis during both healthy and diseased states.

Interorgan rhythmicity as a feature of healthful metabolism

The finding that animals with circadian gene mutations exhibit diet-induced obesity and metabolic syndrome with hypoinsulinemia revealed a distinct role for the clock in the brain and peripheral tissues. Obesogenic diets disrupt rhythmic sleep/wake patterns, feeding behavior, and transcriptional networks, showing that metabolic signals reciprocally control the clock. Providing access to high-fat diet only during the sleep phase (light period) in mice accelerates weight gain, whereas isocaloric time-restricted feeding during the active period enhances energy expenditure due to circadian induction of adipose thermogenesis. This perspective focuses on advances and unanswered questions in understanding the interorgan circadian control of healthful metabolism.

Hypoxic Conditions Modulate Chondrogenesis through the Circadian Clock: The Role of Hypoxia-Inducible Factor-1α

Hypoxia-inducible factor-1 (HIF-1) is a heterodimer transcription factor composed of an alpha and a beta subunit. HIF-1α is a master regulator of cellular response to hypoxia by activating the transcription of genes that facilitate metabolic adaptation to hypoxia. Since chondrocytes in mature articular cartilage reside in a hypoxic environment, HIF-1α plays an important role in chondrogenesis and in the physiological lifecycle of articular cartilage. Accumulating evidence suggests interactions between the HIF pathways and the circadian clock. The circadian clock is an emerging regulator in both developing and mature chondrocytes. However, how circadian rhythm is established during the early steps of cartilage formation and through what signaling pathways it promotes the healthy chondrocyte phenotype is still not entirely known. This narrative review aims to deliver a concise analysis of the existing understanding of the dynamic interplay between HIF-1α and the molecular clock in chondrocytes, in states of both health and disease, while also incorporating creative interpretations. We explore diverse hypotheses regarding the intricate interactions among these pathways and propose relevant therapeutic strategies for cartilage disorders such as osteoarthritis.

Circadian modulation of glucose utilization via CRY1-mediated repression of Pdk1 expression

Life adapts to daily environmental changes through circadian rhythms, exhibiting spontaneous oscillations of biological processes. These daily functional oscillations must match the metabolic requirements responding to the time of the day. We focus on the molecular mechanism of how the circadian clock regulates glucose, the primary resource for energy production and other biosynthetic pathways. The complex regulation of the circadian rhythm includes many proteins that control this process at the transcriptional and translational levels and by protein-protein interactions. We have investigated the action of one of these proteins, cryptochrome (CRY), whose elevated mRNA and protein levels repress the function of an activator in the transcription-translation feedback loop, and this activator causes elevated Cry1 mRNA. We used a genome-edited cell line model to investigate downstream genes affected explicitly by the repressor CRY. We found that CRY can repress glycolytic genes, particularly that of the gatekeeper, pyruvate dehydrogenase kinase 1 (Pdk1), decreasing lactate accumulation and glucose utilization. CRY1-mediated decrease of Pdk1 expression can also be observed in a breast cancer cell line MDA-MB-231, whose glycolysis is associated with Pdk1 expression. We also found that exogenous expression of CRY1 in the MDA-MB-231 decreases glucose usage and growth rate. Furthermore, reduced CRY1 levels and the increased phosphorylation of PDK1 substrate were observed when cells were grown in suspension compared to cells grown in adhesion. Our data supports a model that the transcription-translation feedback loop can regulate the glucose metabolic pathway through Pdk1 gene expression according to the time of the day.

Regulation of protein O-GlcNAcylation by circadian, metabolic, and cellular signals

O-linked β-N-acetylglucosamine (O-GlcNAcylation) is a dynamic post-translational modification that regulates thousands of proteins and almost all cellular processes. Aberrant O-GlcNAcylation has been associated with numerous diseases, including cancer, neurodegenerative diseases, cardiovascular diseases, and type 2 diabetes. O-GlcNAcylation is highly nutrient-sensitive since it is dependent on UDP-GlcNAc, the end product of the hexosamine biosynthetic pathway (HBP). We previously observed daily rhythmicity of protein O-GlcNAcylation in a Drosophila model that is sensitive to the timing of food consumption. We showed that the circadian clock is pivotal in regulating daily O-GlcNAcylation rhythms given its control of the feeding-fasting cycle and hence nutrient availability. Interestingly, we reported that the circadian clock also modulates daily O-GlcNAcylation rhythm by regulating molecular mechanisms beyond the regulation of food consumption time. A large body of work now indicates that O-GlcNAcylation is likely a generalized cellular status effector as it responds to various cellular signals and conditions, such as ER stress, apoptosis, and infection. In this review, we summarize the metabolic regulation of protein O-GlcNAcylation through nutrient availability, HBP enzymes, and O-GlcNAc processing enzymes. We discuss the emerging roles of circadian clocks in regulating daily O-GlcNAcylation rhythm. Finally, we provide an overview of other cellular signals or conditions that impact O-GlcNAcylation. Many of these cellular pathways are themselves regulated by the clock and/or metabolism. Our review highlights the importance of maintaining optimal O-GlcNAc rhythm by restricting eating activity to the active period under physiological conditions and provides insights into potential therapeutic targets of O-GlcNAc homeostasis under pathological conditions.

Watching the clock in glioblastoma

Glioblastoma (GBM) is the most prevalent malignant primary brain tumor, accounting for 14.2% of all diagnosed tumors and 50.1% of all malignant tumors, and the median survival time is approximately 8 months irrespective of whether a patient receives treatment without significant improvement despite expansive research (Ostrom QT, Price M, Neff C, et al. CBTRUS statistical report: primary brain and other central nervous system tumors diagnosed in the United States in 2015-2019. Neurooncology. 2022; 24(suppl 5):v1-v95.). Recently, important roles for the circadian clock in GBM tumorigenesis have been reported. Positive regulators of circadian-controlled transcription, brain and muscle ARNT-like 1 (BMAL1), and circadian locomotor output cycles kaput (CLOCK), are highly expressed also in GBM and correlated with poor patient prognosis. BMAL1 and CLOCK promote the maintenance of GBM stem cells (GSCs) and the establishment of a pro-tumorigenic tumor microenvironment (TME), suggesting that targeting the core clock proteins may augment GBM treatment. Here, we review findings that highlight the critical role the circadian clock plays in GBM biology and the strategies by which the circadian clock can be leveraged for GBM treatment in the clinic moving forward.

Harmonizing Magnetic Mitohormetic Regenerative Strategies: Developmental Implications of a Calcium-Mitochondrial Axis Invoked by Magnetic Field Exposure

Mitohormesis is a process whereby mitochondrial stress responses, mediated by reactive oxygen species (ROS), act cumulatively to either instill survival adaptations (low ROS levels) or to produce cell damage (high ROS levels). The mitohormetic nature of extremely low-frequency electromagnetic field (ELF-EMF) exposure thus makes it susceptible to extraneous influences that also impinge on mitochondrial ROS production and contribute to the collective response. Consequently, magnetic stimulation paradigms are prone to experimental variability depending on diverse circumstances. The failure, or inability, to control for these factors has contributed to the existing discrepancies between published reports and in the interpretations made from the results generated therein. Confounding environmental factors include ambient magnetic fields, temperature, the mechanical environment, and the conventional use of aminoglycoside antibiotics. Biological factors include cell type and seeding density as well as the developmental, inflammatory, or senescence statuses of cells that depend on the prior handling of the experimental sample. Technological aspects include magnetic field directionality, uniformity, amplitude, and duration of exposure. All these factors will exhibit manifestations at the level of ROS production that will culminate as a unified cellular response in conjunction with magnetic exposure. Fortunately, many of these factors are under the control of the experimenter. This review will focus on delineating areas requiring technical and biological harmonization to assist in the designing of therapeutic strategies with more clearly defined and better predicted outcomes and to improve the mechanistic interpretation of the generated data, rather than on precise applications. This review will also explore the underlying mechanistic similarities between magnetic field exposure and other forms of biophysical stimuli, such as mechanical stimuli, that mutually induce elevations in intracellular calcium and ROS as a prerequisite for biological outcome. These forms of biophysical stimuli commonly invoke the activity of transient receptor potential cation channel classes, such as TRPC1.

E-box binding transcription factors in cancer

E-boxes are important regulatory elements in the eukaryotic genome. Transcription factors can bind to E-boxes through their basic helix-loop-helix or zinc finger domain to regulate gene transcription. E-box-binding transcription factors (EBTFs) are important regulators of development and essential for physiological activities of the cell. The fundamental role of EBTFs in cancer has been highlighted by studies on the canonical oncogene MYC, yet many EBTFs exhibit common features, implying the existence of shared molecular principles of how they are involved in tumorigenesis. A comprehensive analysis of TFs that share the basic function of binding to E-boxes has been lacking. Here, we review the structure of EBTFs, their common features in regulating transcription, their physiological functions, and their mutual regulation. We also discuss their converging functions in cancer biology, their potential to be targeted as a regulatory network, and recent progress in drug development targeting these factors in cancer therapy.

Cryptochrome 2 acetylation attenuates its antiproliferative effect in breast cancer

Breast cancer is the most commonly diagnosed cancer, and its global impact is increasing. Its onset and progression are influenced by multiple cues, one of which is the disruption of the internal circadian clock. Cryptochrome 2 (Cry2) genetic dysregulation may lead to the development of some diseases and even tumors. In addition, post-translational modifications can alter the Cry2 function. Here, we aimed to elucidate the post-translational regulations of Cry2 and its role in breast cancer pathogenesis. We identified p300-drived acetylation as a novel Cry2 post-translational modification, which histone deacetylase 6 (HDAC6) could reverse. Furthermore, we found that Cry2 inhibits breast cancer proliferation, but its acetylation impairs this effect. Finally, bioinformatics analysis revealed that genes repressed by Cry2 in breast cancer were mainly enriched in the NF-κB pathway, and acetylation reversed this repression. Collectively, these results indicate a novel Cry2 regulation mechanism and provide a rationale for its role in breast tumorigenesis.

Involvement of hypoxia-inducible factor activity in inevitable air-exposure treatment upon differentiation in a three-dimensional keratinocyte culture

Formation of the human skin epidermis can be reproduced by a three-dimensional (3D) keratinocyte culture system, in which air-exposure is inevitable upon initiation of differentiation. In the continuous submerged culture without air-exposure, even with a differentiation-compatible medium, several keratinocyte-specific proteins were not induced resulting in the formation of aberrant epidermal layers. To clarify the mechanism by which air-exposure promotes keratinocyte differentiation, we performed a comparative analysis on biological properties between submerged and air-liquid interphase culture systems. By transcriptomic analysis, hypoxia-inducible factor (HIF)-related genes appeared to significantly change in these cultured cells. In submerged culture, the transcriptional activity of HIF on its canonical response element was enhanced, while air-exposure treatment drastically reduced the transcriptional activity despite the high HIF protein level. Regulating HIF activity through reagents and genetic manipulation revealed that the reduced but retained HIF-transcriptional activity was essentially involved in differentiation. Furthermore, we showed, for the first time, that artificial supplementation of oxygen in the submerged culture system could restore keratinocyte differentiation as observed in the air-exposed culture. Thus, we mechanistically evaluated how HIF regulates the air-exposure-dependent differentiation of keratinocytes in a 3D culture system.

Structures of NPAS4-ARNT and NPAS4-ARNT2 heterodimers reveal new dimerization modalities in the bHLH-PAS transcription factor family

Neuronal PER-ARNT-SIM (PAS) domain protein 4 (NPAS4) is a protective transcriptional regulator whose dysfunction has been linked to a variety of neuropsychiatric and metabolic diseases. As a member of the basic helix-loop-helix PER-ARNT-SIM (bHLH-PAS) transcription factor family, NPAS4 is distinguished by an ability to form functional heterodimers with aryl hydrocarbon receptor nuclear translocator (ARNT) and ARNT2, both of which are also bHLH-PAS family members. Here, we describe the quaternary architectures of NPAS4-ARNT and NPAS4-ARNT2 heterodimers in complexes involving DNA response elements. Our crystallographic studies reveal a uniquely interconnected domain conformation for the NPAS4 protein itself, as well as its differentially configured heterodimeric arrangements with both ARNT and ARNT2. Notably, the PAS-A domains of ARNT and ARNT2 exhibit variable conformations within these two heterodimers. The ARNT PAS-A domain also forms a set of interfaces with the PAS-A and PAS-B domains of NPAS4, different from those previously noted in ARNT heterodimers formed with other class I bHLH-PAS family proteins. Our structural observations together with biochemical and cell-based interrogations of these NPAS4 heterodimers provide molecular glimpses of the NPAS4 protein architecture and extend the known repertoire of heterodimerization patterns within the bHLH-PAS family. The PAS-B domains of NPAS4, ARNT, and ARNT2 all contain ligand-accessible pockets with appropriate volumes required for small-molecule binding. Given NPAS4's linkage to human diseases, the direct visualization of these PAS domains and the further understanding of their relative positioning and interconnections within the NPAS4-ARNT and NPAS4-ARNT2 heterodimers may provide a road map for therapeutic discovery targeting these complexes.

Brief exposure to directionally-specific pulsed electromagnetic fields stimulates extracellular vesicle release and is antagonized by streptomycin: A potential regenerative medicine and food industry paradigm

Pulsing electromagnetic fields (PEMFs) have been shown to promote in vitro and in vivo myogeneses via mitohormetic survival adaptations of which secretome activation is a key component. A single 10-min exposure of donor myoblast cultures to 1.5 mT amplitude PEMFs produced a conditioned media (pCM) capable of enhancing the myogenesis of recipient cultures to a similar degree as direct magnetic exposure. Downwardly-directed magnetic fields produced greater secretome responses than upwardly-directed fields in adherent and fluid-suspended myoblasts. The suspension paradigm allowed for the rapid concentrating of secreted factors, particularly of extracellular vesicles. The brief conditioning of basal media from magnetically-stimulated myoblasts was capable of conferring myoblast survival to a greater degree than basal media supplemented with fetal bovine serum (5%). Downward-directed magnetic fields, applied directly to cells or in the form of pCM, upregulated the protein expression of TRPC channels, markers for cell cycle progression and myogenesis. Direct magnetic exposure produced mild oxidative stress, whereas pCM provision did not, providing a survival advantage on recipient cells. Streptomycin, a TRP channel antagonist, precluded the production of a myogenic pCM. We present a methodology employing a brief and non-invasive PEMF-exposure paradigm to effectively stimulate secretome production and release for commercial or clinical exploitation.

A highland-adaptation mutation of the Epas1 protein increases its stability and disrupts the circadian clock in the plateau pika

The Qinghai-Tibet Plateau (QTP) harbors hundreds of species well adapted to its extreme conditions, including its low-oxygen (hypoxic) atmosphere. Here, we show that the plateau pika-a keystone mammal of the QTP-lacks robust circadian rhythms. The major form of the plateau pika Epas1 protein includes a 24-residue insert caused by a point mutation at the 5' juncture site of Intron14 and is more stable than other mammalian orthologs. Biochemical studies reveal that an Epas1-Bmal1 complex with lower trans-activation activity occupies the E1/E2 motifs at the promoter of the core-clock gene Per2, thus explaining how an Epas1 mutation-selected in the hypoxic conditions of the QTP-disrupts the molecular clockwork. Importantly, experiments with hypoxic chambers show that mice expressing the plateau pika Epas1 ortholog in their suprachiasmatic nucleus have dysregulated central clocks, and pika Epas1 knockin mice reared in hypoxic conditions exhibit dramatically reduced heart damage compared with wild-type animals.

Daily running enhances molecular and physiological circadian rhythms in skeletal muscle

Objective

Exercise is a critical component of a healthy lifestyle and a key strategy for the prevention and management of metabolic disease. Identifying molecular mechanisms underlying adaptation in response to chronic physical activity is of critical interest in metabolic physiology. Circadian rhythms broadly modulate metabolism, including muscle substrate utilization and exercise capacity. Here, we define the molecular and physiological changes induced across the daily cycle by voluntary low intensity daily exercise.

Methods

Wildtype C57BL6/J male and female mice were housed with or without access to a running wheel for six weeks. Maximum running speed was measured at four different zeitgeber times (ZTs, hours after lights on) using either electrical or manual stimulation to motivate continued running on a motorized treadmill. RNA isolated from plantaris muscles at six ZTs was sequenced to establish the impact of daily activity on genome-wide transcription. Patterns of gene expression were analyzed using Gene Set Enrichment Analysis (GSEA) and Detection of Differential Rhythmicity (DODR). Blood glucose, lactate, and ketones, and muscle and liver glycogen were measured before and after exercise.

Results

We demonstrate that the use of mild electrical shocks to motivate running negatively impacts maximum running speed in mice, and describe a manual method to motivate running in rodent exercise studies. Using this method, we show that time of day influences the increase in exercise capacity afforded by six weeks of voluntary wheel running: when maximum running speed is measured at the beginning of the nighttime active period in mice, there is no measurable benefit from a history of daily voluntary running, while maximum increase in performance occurs at the end of the night. We show that daily voluntary exercise dramatically remodels the murine muscle circadian transcriptome. Finally, we describe daily rhythms in carbohydrate metabolism associated with the time-dependent response to moderate daily exercise in mice.

Conclusions

Collectively, these data indicate that chronic nighttime physical activity dramatically remodels daily rhythms of murine muscle gene expression, which in turn support daily fluctuations in exercise performance.

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Daily voluntary running dramatically remodels the mouse muscle circadian transcriptome.

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Daily voluntary running maximally increases mouse running speed in the late active period.

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Muscle and liver glycogen content exhibit robust daily rhythms in laboratory mice.

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Use of mild electric shocks to motivate running in mice impairs maximum running speed.

Circadian clocks' interactions with oxygen sensing and signalling

In mammals, physiology and metabolism are shaped both by immediate and anticipatory responses to environmental changes through the myriad of molecular mechanisms. Whilst the former is mostly mediated through different acute signalling pathways the latter is primarily orchestrated by the circadian clock. Oxygen is vital for life and as such mammals have evolved different mechanisms to cope with changes in oxygen levels. It is widely accepted that oxygen sensing through the HIF-1 signalling pathway is paramount for the acute response to changes in oxygen levels. Circadian clocks are molecular oscillators that control 24 hours rhythms in various aspects of physiology and behaviour. Evidence emerging in recent years points towards pervasive molecular and functional interactions between these two pathways on multiple levels. Daily oscillations in oxygen levels are circadian clock-controlled and can reset the clock through HIF-1. Furthermore, the circadian clock appears to modulate the hypoxic response. We review herein the literature related to the crosstalk between the circadian clockwork and the oxygen-signalling pathway in mammals at the molecular and physiological level both under normal and pathologic conditions.

BMAL1 drives muscle repair through control of hypoxic NAD+ regeneration in satellite cells

The process of tissue regeneration occurs in a developmentally timed manner, yet the role of circadian timing is not understood. Here, we identify a role for the adult muscle stem cell (MuSC)-autonomous clock in the control of muscle regeneration following acute ischemic injury. We observed greater muscle repair capacity following injury during the active/wake period as compared with the inactive/rest period in mice, and loss of Bmal1 within MuSCs leads to impaired muscle regeneration. We demonstrate that Bmal1 loss in MuSCs leads to reduced activated MuSC number at day 3 postinjury, indicating a failure to properly expand the myogenic precursor pool. In cultured primary myoblasts, we observed that loss of Bmal1 impairs cell proliferation in hypoxia (a condition that occurs in the first 1-3 d following tissue injury in vivo), as well as subsequent myofiber differentiation. Loss of Bmal1 in both cultured myoblasts and in vivo activated MuSCs leads to reduced glycolysis and premature activation of prodifferentiation gene transcription and epigenetic remodeling. Finally, hypoxic cell proliferation and myofiber formation in Bmal1-deficient myoblasts are restored by increasing cytosolic NAD+ Together, we identify the MuSC clock as a pivotal regulator of oxygen-dependent myoblast cell fate and muscle repair through the control of the NAD+-driven response to injury.

CRY2 missense mutations suppress P53 and enhance cell growth

Disruption of circadian rhythms increases the risk of several types of cancer. Mammalian cryptochromes (CRY1 and CRY2) are circadian transcriptional repressors that are related to DNA-repair enzymes. While CRYs lack DNA-repair activity, they modulate the transcriptional response to DNA damage, and CRY2 can promote SKP1 cullin 1-F-box (SCF)^FBXL3-mediated ubiquitination of c-MYC and other targets. Here, we characterize five mutations in CRY2 observed in human cancers in The Cancer Genome Atlas. We demonstrate that two orthologous mutations of mouse CRY2 (D325H and S510L) accelerate the growth of primary mouse fibroblasts expressing high levels of c-MYC. Neither mutant affects steady-state levels of overexpressed c-MYC, and they have divergent impacts on circadian rhythms and on the ability of CRY2 to interact with SCF^FBXL3 Unexpectedly, stable expression of either CRY2 D325H or of CRY2 S510L robustly suppresses P53 target-gene expression, suggesting that this may be a primary mechanism by which they influence cell growth.

Circadian rhythms in the tissue-specificity from metabolism to immunity; insights from omics studies

Creatures on earth have the capacity to preserve homeostasis in response to changing environments. The circadian clock enables organisms to adapt to daily predictable rhythms in surrounding conditions. In mammals, circadian clocks constitute hierarchical network, where the central pacemaker in hypothalamic suprachiasmatic nucleus (SCN) serves as a time-keeping machinery and governs peripheral clocks in every other organ through descending neural and humoral factors. The central clock in SCN is reset by light, whilst peripheral clocks are entrained by feeding-fasting rhythms, emphasizing the point that temporal patterns of nutrient availability specifies peripheral clock functions. Indeed, emerging evidence revealed various types of diets or timing of food intake reprogram circadian rhythms in a tissue specific manner. This advancement in understanding of mechanisms underlying tissue specific responsiveness of circadian oscillators to nutrients at the genomic and epigenomic levels is largely owing to employment of state-of-the-art technologies. Specifically, high-throughput transcriptome, proteome, and metabolome have provided insights into how genes, proteins, and metabolites behave over circadian cycles in a given tissue under a certain dietary condition in an unbiased fashion. Additionally, combinations with specialized types of sequencing such as nascent-seq and ribosomal profiling allow us to dissect how circadian rhythms are generated or obliterated at each step of gene regulation. Importantly, chromatin immunoprecipitation followed by deep sequencing methods provide chromatin landscape in terms of regulatory mechanisms of circadian gene expression. In this review, we outline recent discoveries on temporal genomic and epigenomic regulation of circadian rhythms, discussing entrainment of the circadian rhythms by feeding as a fundamental new comprehension of metabolism and immune response, and as a potential therapeutic strategy of metabolic and inflammatory diseases.

Circadian Biology in Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is a complex process that can lead to the dysregulation of the molecular clock, as well as 24 h rhythms of sleep and wake, blood pressure, and other associated biological processes. Previous work has demonstrated crosstalk between the circadian clock and hypoxia-responsive pathways. However, even in the absence of OSA, disrupted clocks can exacerbate OSA-associated outcomes (e.g., cardiovascular or cognitive outcomes). As we expand our understanding of circadian biology in the setting of OSA, this information could play a significant role in the diagnosis and treatment of OSA. Here, we summarize the pre-existing knowledge of circadian biology in patients with OSA and examine the utility of circadian biomarkers as alternative clinical tools.

Therapeutic Nuclear Magnetic Resonance affects the core clock mechanism and associated Hypoxia-inducible factor-1

The influence of low intensity electromagnetic fields on circadian clocks of cells and tissues has gained increasing scientific interest, either as a therapeutic tool or as a potential environmental hazard. Nuclear Magnetic Resonance (NMR) refers to the property of certain atomic nuclei to absorb the energy of radio waves under a corresponding magnetic field. NMR forms the basis for Magnetic Resonance Imaging, Magnetic Resonance Spectroscopy and, in a low-intensity form, for NMR therapy (tNMR). Since the circadian clock is bi-directionally intertwined with hypoxic signaling in vertebrates and mammals, we hypothesized that low intensity electromagnetic fields, such as tNMR, might not only affect circadian clocks but also Hypoxia-Inducible Factor-1α (HIF-1α). As master regulator of the hypoxic signaling pathway, HIF-1α is known to dampen the circadian amplitude under reduced oxygen availability, while the hypoxic response of cells and organisms, itself, is tightly clock controlled. In a first experiment, we investigated if tNMR is able to act as Zeitgeber for the core clock mechanism of unsynchronized zebrafish and mouse fibroblast cells, using direct light irradiation and treatment with the glucocorticoid Dexamethasone as references. tNMR significantly affected the cell autonomous clocks of unsynchronized mouse fibroblast cells NIH3-T3, but did not act as a Zeitgeber. Similar to light irradiation and in contrast to treatment with Dexamethasone, tNMR did not synchronize expression profiles of murine clock genes. However, irradiation with tNMR as well as light significantly altered mRNA and protein expression levels of Cryptochrome1, Cryptochrome2 and Clock1 for more than 24 h. Changes in mRNA and protein after different treatment durations, namely 6 and 12 h, appeared to be nonlinear. A nonlinear dose-response relationship is known as hallmark of electromagnetic field induced effects on biological systems. The most prominent alterations were detected in murine HIF-1α protein, again in a nonlinear dose-response. In contrast to murine cells, zebrafish fibroblasts did not respond to tNMR at all. Light, a potent Zeitgeber for the peripheral clocks of fish, led to the expected synchronized clock gene oscillations of high amplitude, as did Dexamethasone. Hence, we conclude, mammalian peripheral clocks are more susceptible to tNMR than the direct light entrainable fish fibroblasts. Although light and tNMR did not act as Zeitgebers for the circadian clocks of unsynchronized murine cells, the significant observed effects might indicate downstream cell-physiological ramifications, which are worth future investigation. However, beside the effects tNMR exerts on the core clock mechanism of mammalian cells, the technology might be the first non-pharmacological approach to modify HIF-1α protein in cells and tissues. HIF-1α and the associated circadian clock play key roles in diseases with underlying ischemic background, such as infarct, stroke, and cancer and, also infectious diseases, such as Covid-19. Hence, low intensity magnetic fields such as tNMR might be of significant medical interest.