Response to Stimulations Inducing Circadian Rhythm in Human Induced Pluripotent Stem Cells

Selenide-modified hyaluronic acid hydrogel promotes scleral remodeling during the recovery phase of form-deprivation myopia by inhibiting HIF-1α-mediated inflammation

This study investigates the molecular mechanisms by which selenide-modified hyaluronic acid hydrogel (Se-HA gel) promotes scleral remodeling during the recovery phase of form-deprivation myopia (FDM). The Se-HA gel was synthesized and characterized, exhibiting an average hydrodynamic diameter of 191.72 nm, a polydispersity index (PDI) of 0.19, and a zeta potential of -7.96 mV, indicating a monodisperse state in PBS. Both in vitro experiments and the FDM mouse model confirmed its therapeutic efficacy. At a concentration of 250 μg/mL, Se-HA gel significantly promoted fibroblast proliferation, inhibited apoptosis, and prevented transdifferentiation. A 200 mg/kg subtenon injection improved key ocular biometric parameters in FDM mice. Single-cell and transcriptomic sequencing analyses revealed that Se-HA gel facilitated scleral remodeling by downregulating Hypoxia-Inducible Factor 1 Alpha (HIF-1α) expression and regulating inflammation-related gene expression. Notably, HIF-1α overexpression reversed the beneficial effects of Se-HA gel, reinforcing its pivotal role in mediating these therapeutic outcomes. This study introduces a novel biomaterial-based strategy and identifies new molecular targets for myopia treatment. Furthermore, it addresses a critical gap in understanding how Se-HA gel promotes scleral remodeling through HIF-1α-mediated signaling pathways, with important scientific and translational potential in the field of myopia management.

Circadian rhythm defects in Prader-Willi syndrome neurons

Prader-Willi syndrome (PWS) is a neurodevelopmental disorder characterized by a spectrum of symptoms, including developmental delay, intellectual disability, and increased risk of autism. PWS is an imprinting disorder caused by the loss of paternal expression of critical genes in the 15q11.2-q13 region, including MAGEL2, SNRPN/SNURF, and SNORD116. PWS patients often suffer from various sleep disorders, including sleep-disordered breathing and central hypersomnolence. Mouse models of PWS also exhibit disruptions in circadian rhythms and sleep. In cultured cells, Magel2 was shown to regulate the expression of Bmal1 and Per2, two core clock genes involved in the circadian rhythm regulatory process. Here, we investigated the circadian clock function in neurons derived from dental pulp stem cells (DPSCs) of PWS patients and neurotypical controls. To study the circadian rhythms of PWS patients in vitro, we introduced the Per2 promoter-driven luciferase reporter (Per2:luc) to these DPSC cell lines to assess their circadian rhythm by bioluminescence. These Per2:luc cells were differentiated for 4 weeks to mature neuronal reporter cell lines, followed by kinetic measurements of luciferase activity over several days. We observed significant differences in circadian period length between PWS neurons and controls. Moreover, treatment with the small molecule longdaysin effectively lengthened the period length of PWS neurons with a shorter period length, as anticipated based on the mechanism of action of this compound. This work lays the foundation for a deeper understanding of PWS pathophysiology and represents a critical first step toward developing high-throughput assays for drug discovery targeting circadian and sleep dysfunction in PWS.

The mutual impacts of stem cells and sleep: opportunities for improved stem cell therapy

Sleep is an indispensable physiological function regulated by circadian rhythms, which influence the biological pathways and overall health of the body. Sleep is crucial for the maintenance and restoration of bodily systems, and disturbances can lead to various sleep disorders, which can impair both mental and physical health. Treatment options for these disorders encompass lifestyle modifications, psychotherapy, medications, and therapies such as light therapy and surgery. Not only sleep deprivation has a significant impact on essential organs, but it also influences various types of stem cells in the body. In this review, we explore the connection between sleep and various types of stem cells, highlighting how circadian rhythms regulate stem cell activities that are vital for tissue regeneration and homeostasis. Disruptions in sleep can hinder stem cell self-renewal, homing, proliferation, function, and differentiation, thereby affecting tissue regeneration and overall health. We also discuss how transplantation of stem cells and their products may help improve sleep disorders, how sleep quality affects stem cell behavior, and the implications for stem cell therapies. Notably, while certain stem cell transplantations can disrupt sleep, enhancing sleep quality may improve the efficacy of these therapies. Finally, stem cells can be utilized to model sleep disorders, offering valuable insights into their underlying mechanisms.

Circadian rhythms in stem cells and their therapeutic potential

Circadian rhythms are present in almost all cells, but their existence in stem cells has remains not well established. Circadian clock appears to be closely associated with differentiated mature cells and rarely detected in immature embryonic stem cells. Recent evidence reveals the presence of circadian genes and rhythmic physiologic activities in stem cells as well as stem cell-derived extracellular vesicle (EV) characteristics. The circadian clock entails diverse physiologic and pathological mechanisms underlying cell fate. Integration of circadian rhythm to clinical applications, such as chronotherapy, chrono-biomarker, and environment modification, may facilitate therapeutic outcomes of stem cell-based regenerative medicine. Understanding circadian rhythms in stem cells can optimize stem cell-based therapies by determining the best times for harvesting and administering stem cells, thereby enhancing therapeutic efficacy. Further research into the circadian properties of stem cells will refine stem cell-based therapies, contributing to advancements in regenerative medicine.

Identification of robust RT-qPCR reference genes for studying changes in gene expression in response to hypoxia in breast cancer cell lines

Hypoxia is common in breast tumours and is linked to therapy resistance and advanced disease. To understand hypoxia-driven breast cancer progression, RT-qPCR is a widely used technique to quantify transcriptional changes that occur during malignant transformation. Reference genes (RGs) are endogenous RT-qPCR controls used to normalise mRNA levels, allowing accurate assessment of transcriptional changes. However, hypoxia reprograms transcription and post-transcriptional processing of RNA such that favoured RGs including GAPDH or PGK1 are unsuitable for this purpose. To address the need for robust RGs to study hypoxic breast cancer cell lines, we identified 10 RG candidates by analysing public RNA-seq data of MCF-7 and T-47D (Luminal A), and, MDA-MB-231 and MDA-MB-468 (triple negative breast cancer (TNBC)) cells cultured in normoxia or hypoxia. We used RT-qPCR to determine RG candidate levels in normoxic breast cancer cells, removing TBP and EPAS1 from downstream analysis due to insufficient transcript abundance. Assessing primer efficiency further removed ACTB, CCSER2 and GUSB from consideration. Following culture in normoxia, acute, or chronic hypoxia, we ascertained robust non-variable RGs using RefFinder. Here we present RPLP1 and RPL27 as optimal RGs for our panel of two Luminal A and two TNBC cell lines cultured in normoxia or hypoxia. Our result enables accurate evaluation of gene expression in selected hypoxic breast cancer cell lines and provides an essential resource for assessing the impact of hypoxia on breast cancer progression.

Circadian Effects of Melatonin Receptor-Targeting Molecules In Vitro

Circadian rhythms are important for maintaining homeostasis, from regulating physiological activities (e.g., sleep-wake cycle and cognitive performance) to cellular processes (e.g., cell cycle and DNA damage repair). Melatonin is a key regulator of circadian rhythms and exerts control by binding to melatonin receptor 1 (MT1), decreasing neuronal firing in the suprachiasmatic nucleus (SCN). Previous work studying effects of melatonin on circadian rhythms utilized in vivo models. Since MT1 is also expressed outside of the brain, it is important to study impacts of melatonin on circadian gene oscillations in vitro. We evaluated the effects of melatonin and an MT1 inverse agonist, UCSF7447, in U2OS circadian reporter cell lines, which facilitate detailed assessments of oscillatory changes. We report that cellular circadian rhythms are responsive to treatment with MT1-targeting molecules; their activities are not dependent upon the SCN. Corroborating in vivo data, both melatonin and UCSF7447 lengthened the periods of BMAL1 and PER2, and while melatonin delayed circadian phases, UCSF7447 advanced them. Compounds were also dosed at two different times, however this did not yield changes. Our findings indicate the importance of utilizing in vitro models and that the direct effects of melatonin likely go beyond the SCN and should be explored further.

"Time Is out of Joint" in Pluripotent Stem Cells: How and Why

The circadian rhythm is necessary for the homeostasis and health of living organisms. Molecular clocks interconnected by transcription/translation feedback loops exist in most cells of the body. A puzzling exemption to this, otherwise, general biological hallmark is given by the cell physiology of pluripotent stem cells (PSCs) that lack circadian oscillations gradually acquired following their in vivo programmed differentiation. This process can be nicely phenocopied following in vitro commitment and reversed during the reprogramming of somatic cells to induce PSCs. The current understanding of how and why pluripotency is "time-uncoupled" is largely incomplete. A complex picture is emerging where the circadian core clockwork is negatively regulated in PSCs at the post-transcriptional/translational, epigenetic, and other-clock-interaction levels. Moreover, non-canonical functions of circadian core-work components in the balance between pluripotency identity and metabolic-driven cell reprogramming are emerging. This review selects and discusses results of relevant recent investigations providing major insights into this context.

Microfluidic models of the neurovascular unit: a translational view

The vasculature of the brain consists of specialized endothelial cells that form a blood-brain barrier (BBB). This barrier, in conjunction with supporting cell types, forms the neurovascular unit (NVU). The NVU restricts the passage of certain substances from the bloodstream while selectively permitting essential nutrients and molecules to enter the brain. This protective role is crucial for optimal brain function, but presents a significant obstacle in treating neurological conditions, necessitating chemical modifications or advanced drug delivery methods for most drugs to cross the NVU. A deeper understanding of NVU in health and disease will aid in the identification of new therapeutic targets and drug delivery strategies for improved treatment of neurological disorders.To achieve this goal, we need models that reflect the human BBB and NVU in health and disease. Although animal models of the brain's vasculature have proven valuable, they are often of limited translational relevance due to interspecies differences or inability to faithfully mimic human disease conditions. For this reason, human in vitro models are essential to improve our understanding of the brain's vasculature under healthy and diseased conditions. This review delves into the advancements in in vitro modeling of the BBB and NVU, with a particular focus on microfluidic models. After providing a historical overview of the field, we shift our focus to recent developments, offering insights into the latest achievements and their associated constraints. We briefly examine the importance of chip materials and methods to facilitate fluid flow, emphasizing their critical roles in achieving the necessary throughput for the integration of microfluidic models into routine experimentation. Subsequently, we highlight the recent strides made in enhancing the biological complexity of microfluidic NVU models and propose recommendations for elevating the biological relevance of future iterations.Importantly, the NVU is an intricate structure and it is improbable that any model will fully encompass all its aspects. Fit-for-purpose models offer a valuable compromise between physiological relevance and ease-of-use and hold the future of NVU modeling: as simple as possible, as complex as needed.

Interaction of Bmal1 and eIF2α/ATF4 pathway was involved in Shuxie compound alleviation of circadian rhythm disturbance-induced hepatic endoplasmic reticulum stress

ETHNOPHARMACOLOGICAL RELEVANCE

Shuxie Compound (SX) combines the composition and efficacy of Suanzaoren decoction and Huanglian Wendan decoction. It can soothe the liver, regulate the qi, nourish the blood and calm the mind. It is used in the clinical treatment of sleep disorder with liver stagnation. Modern studies have proved that circadian rhythm disorder (CRD) can cause sleep deprivation and liver damage, which can be effectively ameliorated by traditional Chinese medicine to soothe the liver stagnation. However, the mechanism of SX is unclear.

AIM OF THE STUDY

This study was designed to demonstrate the impact of SX on CRD in vivo, and confirm the molecular mechanisms of SX in vitro.

MATERIALS AND METHODS

The quality of SX and drug-containing serum was controlled by UPLC-Q-TOF/MS, which were used in vivo and in vitro experiments, respectively. In vivo, a light deprivation mouse model was used. In vitro, a stable knockdown Bmal1 cell line was used to explore SX mechanism.

RESULTS

Low-dose SX (SXL) could restore (1) circadian activity pattern, (2) 24-h basal metabolic pattern, (3) liver injury, and (4) Endoplasmic reticulum (ER) stress in CRD mice. CRD decreased the liver Bmal1 protein at ZT15, which was reversed by SXL treatment. Besides, SXL decreased the mRNA expression of Grp78/ATF4/Chop and the protein expression of ATF4/Chop at ZT11. In vitro experiments, SX reduced the protein expression of thapsigargin (tg)-induced p-eIF2α/ATF4 pathway and increase the viability of AML12 cells by increasing the expression of Bmal1 protein.

CONCLUSIONS

SXL relieved CRD-induced ER stress and improve cell viability by up-regulating the expression of Bmal1 protein in the liver and then inhibiting the protein expression of p-eIF2α/ATF4.

Artificial induction of circadian rhythm by combining exogenous BMAL1 expression and polycomb repressive complex 2 inhibition in human induced pluripotent stem cells

Understanding the physiology of human-induced pluripotent stem cells (iPSCs) is necessary for directed differentiation, mimicking embryonic development, and regenerative medicine applications. Pluripotent stem cells (PSCs) exhibit unique abilities such as self-renewal and pluripotency, but they lack some functions that are associated with normal somatic cells. One such function is the circadian oscillation of clock genes; however, whether or not PSCs demonstrate this capability remains unclear. In this study, the reason why circadian rhythm does not oscillate in human iPSCs was examined. This phenomenon may be due to the transcriptional repression of clock genes resulting from the hypermethylation of histone H3 at lysine 27 (H3K27), or it may be due to the low levels of brain and muscle ARNT-like 1 (BMAL1) protein. Therefore, BMAL1-overexpressing cells were generated and pre-treated with GSK126, an inhibitor of enhancer of zest homologue 2 (EZH2), which is a methyltransferase of H3K27 and a component of polycomb repressive complex 2. Consequently, a significant circadian rhythm following endogenous BMAL1, period 2 (PER2), and other clock gene expression was induced by these two factors, suggesting a candidate mechanism for the lack of rhythmicity of clock gene expression in iPSCs.

Circadian Rhythm Disruption Influenced Hepatic Lipid Metabolism, Gut Microbiota and Promoted Cholesterol Gallstone Formation in Mice

BACKGROUND

Hepatic lipid metabolism regulates biliary composition and influences the formation of cholesterol gallstones. The genes Hmgcr and Cyp7a1, which encode key liver enzymes, are regulated by circadian rhythm-related transcription factors. We aimed to investigate the effect of circadian rhythm disruption on hepatic cholesterol and bile acid metabolism and the incidence of cholesterol stone formation.

METHODS

Adult male C57BL/6J mice were fed either a lithogenic diet (LD) only during the sleep phase (time-restricted lithogenic diet feeding, TRF) or an LD ad libitum (non-time-restricted lithogenic diet feeding, nTRF) for 4 weeks. Food consumption, body mass gain, and the incidence of gallstones were assessed. Circulating metabolic parameters, lipid accumulation in the liver, the circadian expression of hepatic clock and metabolic genes, and the gut microbiota were analyzed.

RESULTS

TRF caused a dysregulation of the circadian rhythm in the mice, characterized by significant differences in the circadian expression patterns of clock-related genes. In TRF mice, the circadian rhythms in the expression of genes involved in bile acid and cholesterol metabolism were disrupted, as was the circadian rhythm of the gut microbiota. These changes were associated with high biliary cholesterol content, which promoted gallstone formation in the TRF mice.

CONCLUSION

Disordered circadian rhythm is associated with abnormal hepatic bile acid and cholesterol metabolism in mice, which promotes gallstone formation.

Circadian Synchrony: Sleep, Nutrition, and Physical Activity

The circadian clock in mammals regulates the sleep/wake cycle and many associated behavioral and physiological processes. The cellular clock mechanism involves a transcriptional negative feedback loop that gives rise to circadian rhythms in gene expression with an approximately 24-h periodicity. To maintain system robustness, clocks throughout the body must be synchronized and their functions coordinated. In mammals, the master clock is located in the suprachiasmatic nucleus (SCN) of the hypothalamus. The SCN is entrained to the light/dark cycle through photic signal transduction and subsequent induction of core clock gene expression. The SCN in turn relays the time-of-day information to clocks in peripheral tissues. While the SCN is highly responsive to photic cues, peripheral clocks are more sensitive to non-photic resetting cues such as nutrients, body temperature, and neuroendocrine hormones. For example, feeding/fasting and physical activity can entrain peripheral clocks through signaling pathways and subsequent regulation of core clock genes and proteins. As such, timing of food intake and physical activity matters. In an ideal world, the sleep/wake and feeding/fasting cycles are synchronized to the light/dark cycle. However, asynchronous environmental cues, such as those experienced by shift workers and frequent travelers, often lead to misalignment between the master and peripheral clocks. Emerging evidence suggests that the resulting circadian disruption is associated with various diseases and chronic conditions that cause further circadian desynchrony and accelerate disease progression. In this review, we discuss how sleep, nutrition, and physical activity synchronize circadian clocks and how chronomedicine may offer novel strategies for disease intervention.

Circadian Synchrony: Sleep, Nutrition, and Physical Activity

The circadian clock in mammals regulates the sleep/wake cycle and many associated behavioral and physiological processes. The cellular clock mechanism involves a transcriptional negative feedback loop that gives rise to circadian rhythms in gene expression with an approximately 24-h periodicity. To maintain system robustness, clocks throughout the body must be synchronized and their functions coordinated. In mammals, the master clock is located in the suprachiasmatic nucleus (SCN) of the hypothalamus. The SCN is entrained to the light/dark cycle through photic signal transduction and subsequent induction of core clock gene expression. The SCN in turn relays the time-of-day information to clocks in peripheral tissues. While the SCN is highly responsive to photic cues, peripheral clocks are more sensitive to non-photic resetting cues such as nutrients, body temperature, and neuroendocrine hormones. For example, feeding/fasting and physical activity can entrain peripheral clocks through signaling pathways and subsequent regulation of core clock genes and proteins. As such, timing of food intake and physical activity matters. In an ideal world, the sleep/wake and feeding/fasting cycles are synchronized to the light/dark cycle. However, asynchronous environmental cues, such as those experienced by shift workers and frequent travelers, often lead to misalignment between the master and peripheral clocks. Emerging evidence suggests that the resulting circadian disruption is associated with various diseases and chronic conditions that cause further circadian desynchrony and accelerate disease progression. In this review, we discuss how sleep, nutrition, and physical activity synchronize circadian clocks and how chronomedicine may offer novel strategies for disease intervention.

Circadian Mechanisms: Cardiac Ion Channel Remodeling and Arrhythmias

Circadian rhythms are involved in many physiological and pathological processes in different tissues, including the heart. Circadian rhythms play a critical role in adverse cardiac function with implications for heart failure and sudden cardiac death, highlighting a significant contribution of circadian mechanisms to normal sinus rhythm in health and disease. Cardiac arrhythmias are a leading cause of morbidity and mortality in patients with heart failure and likely cause ∼250,000 deaths annually in the United States alone; however, the molecular mechanisms are poorly understood. This suggests the need to improve our current understanding of the underlying molecular mechanisms that increase vulnerability to arrhythmias. Obesity and its associated pathologies, including diabetes, have emerged as dangerous disease conditions that predispose to adverse cardiac electrical remodeling leading to fatal arrhythmias. The increasing epidemic of obesity and diabetes suggests vulnerability to arrhythmias will remain high in patients. An important objective would be to identify novel and unappreciated cellular mechanisms or signaling pathways that modulate obesity and/or diabetes. In this review we discuss circadian rhythms control of metabolic and environmental cues, cardiac ion channels, and mechanisms that predispose to supraventricular and ventricular arrhythmias including hormonal signaling and the autonomic nervous system, and how understanding their functional interplay may help to inform the development and optimization of effective clinical and therapeutic interventions with implications for chronotherapy.