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

The Glucagon Receptor Is Expressed in the Frontal Cortex and Impaired Signaling Associates With Cognitive Decline

Individuals with type 2 diabetes (T2D) have an elevated risk of cognitive decline, yet the mechanisms connecting these pathologies remain unclear. Altered glucagon and insulin signaling contribute to T2D, and insulin resistance may also be associated with cognitive decline. The role of glucagon in this context is unknown. Here we aimed to characterize glucagon receptor (GCGR) expression in brain tissue and investigate the potential impact of altered GCGR signaling on dementia prevalence and cognitive function. We investigated GCGR protein expression in various human brain regions and cell types in postmortem brain samples. To explore the potential link between GCGR signaling and cognitive function, individuals with specific GCGR mutations with known or predicted impaired GCGR signaling were examined in connection to the prevalence of dementia defined by International Classification of Diseases, Tenth Revision coding and by cognitive function using population-scale cognitive tests in the UK Biobank. GCGR mRNA and protein were expressed specifically in neurons of the frontal cortex. Varying degrees of expression were observed across brain regions and with higher expression in the parietal cortex and thalamus by antibody-dependent analyses. GCGR variant carriers did not have a significantly higher prevalence of dementia, but 1 cognitive test was significantly impaired in individuals with a GCGR cAMP loss-of-function variant compared to sex- and age-matched nonvariant carrier controls. Our findings indicate GCGR expression in the human brain, particularly in neurons of the frontal cortex, and altered glucagon signaling may be associated with lower cognitive function. Further research is needed to elucidate mechanisms underlying the potential link between altered GCGR signaling and cognitive decline.

Prokineticin 2 protein is diurnally expressed in PER2-containing clock neurons in the mouse suprachiasmatic nucleus

Expression of prokineticin 2 (PK2) mRNA in the suprachiasmatic nucleus (SCN), also known as the brain's clock, exhibits circadian oscillations with peak levels midday, zeitgeber time (ZT) 4, and almost undetectable levels during night. This circadian expression profile has substantially contributed to the suggested role of PK2 as an SCN output molecule involved in transmitting circadian rhythm of behavior and physiology. Due to unreliable specificity of PK2 antibodies, the 81 amino acid protein has primarily been studied at the mRNA level and correlation between circadian oscillating mRNAs and protein products are infrequent. Hence, data on PK2 protein expression in the SCN is lacking. In this study a thorough validation of a commercial PK2 antibody for immunohistochemistry (IHC) was performed followed by fluorescence IHC on SCN mouse brain sections at six consecutive ZTs over a 24-h cycle (12:12 light-dark, ZT0 =light ON whereas ZT12 =light OFF). Data were visualized and processed using confocal microscopy. Results showed that PK2 protein expression diurnally oscillates with calculated peak expression ZT5:40 ± 1:40 h. Opposite than described for PK2 mRNA, PK2 immunoreactivity was detectable at all times during the 24-h cycle. PK2 was primarily located in neurons of the shell compartment and > 80 % of these neurons co-expressed the core clock protein PER2. In conclusion, PK2 protein expression oscillates as the mRNA, supporting the suggested role of PK2 as a SCN molecule involved in circadian rhythm regulation.

PER1 Oscillation in Rat Parathyroid Hormone and Calcitonin Producing Cells

Many endocrine glands exhibit circadian rhythmicity, but the interplay between the central circadian clock in the suprachiasmatic nucleus (SCN), the peripheral endocrine clock, and hormones is sparsely understood. We therefore studied the cellular localizations of the clock protein PER1, parathyroid hormone (PTH) and calcitonin (CT) in the parathyroid and thyroid glands, respectively. Thyroid glands, including the parathyroids, were dissected at different time-points from rats housed in 12 h:12 h light-darkness cycles, and were double-immunostained for PER1 and PTH or CT. Sera were analyzed for PTH, CT, phosphate, and calcium. In both glands, PER1 expression peaked late at night, while limited staining was seen during the daytime. High-resolution microscopy revealed cytosolic PER1 at zeitgeber time (ZT)12, and nucleic staining at ZT24 in both PTH and CT cells. PTH peaked at Z12-ZT16, while neither CT staining nor serum CT oscillated during the daily cycle. Serum PTH was significantly higher at ZT12 than ZT24, but only phosphate was found to exhibit significant diurnal oscillation. The staining of the calcium-sensitive receptor (CSR) did not demonstrate circadian oscillation. In conclusion, PER1 expression peaked late at night/early in the morning in hormone-producing cells of both the thyroid and parathyroid glands. In the parathyroids, this was preceded by a PTH peak, while neither CT nor CRS were found to oscillate.

The differential effects of blocking retinal orexin receptors on the expression of retinal c-fos and hypothalamic Vip, PACAP, Bmal1, and c-fos in Male Wistar Rats

Orexin A and B (OXA and OXB) and their receptors are expressed in the majority of retinal neurons in humans, rats, and mice. Orexins modulate signal transmission between the different layers of the retina. The suprachiasmatic nucleus (SCN) and the retina are central and peripheral components of the body's biological clocks; respectively. The SCN receives photic information from the retina through the retinohypothalamic tract (RHT) to synchronize bodily functions with environmental changes. In present study, we aimed to investigate the impact of inhibiting retinal orexin receptors on the expression of retinal Bmal1 and c-fos, as well as hypothalamic c-fos, Bmal1, Vip, and PACAP at four different time-points (Zeitgeber time; ZT 3, 6, 11, and ZT-0). The intravitreal injection (IVI) of OX1R antagonist (SB-334867) and OX2R antagonist (JNJ-10397049) significantly up-regulated c-fos expression in the retina. Additionally, compared to the control group, the combined injection of SB-334867 and JNJ-10397049 showed a greater increase in retinal expression of this gene. Moreover, the expression of hypothalamic Vip and PACAP was significantly up-regulated in both the SB-334867 and JNJ-10397049 groups. In contrast, the expression of Bmal1 was down-regulated. Furthermore, the expression of hypothalamic c-fos was down-regulated in all groups treated with SB-334867 and JNJ-10397049. Additionally, the study demonstrated that blocking these receptors in the retina resulted in alterations in circadian rhythm parameters such as mesor, amplitude, and acrophase. Finally, it affected the phase of gene expression rhythms in both the retina and hypothalamus, as identified through cosinor analysis and the zero-amplitude test. This study represents the initial exploration of how retinal orexin receptors influence expression of rhythmic genes in the retina and hypothalamus. These findings could provide new insights into how the retina regulates the circadian rhythm in both regions and illuminate the role of the orexinergic system expression within the retina.

Phenotyping of light-activated neurons in the mouse SCN based on the expression of FOS and EGR1

Light-sensitive neurons are located in the ventral and central core of the suprachiasmatic nucleus (SCN), whereas stably oscillating clock neurons are found mainly in the dorsal shell. Signals between the SCN core and shell are believed to play an important role in light entrainment. Core neurons express vasoactive intestinal polypeptide (VIP), gastrin-releasing peptide (GRP), and Neuroglobin (Ngb), whereas the shell neurons express vasopressin (AVP), prokineticin 2, and the VIP type 2 (VPAC2) receptor. In rodents, light has a phase-shifting capacity at night, which induces rapid and transient expression of the EGR1 and FOS in the SCN. Methods: The present study used immunohistochemical staining of FOS, EGR1, and phenotypical markers of SCN neurons (VIP, AVP, Ngb) to identify subtypes/populations of light-responsive neurons at early night. Results: Double immunohistochemistry and cell counting were used to evaluate the number of SCN neurons expressing FOS and EGR1 in the SCN. The number of neurons expressing either EGR1 or FOS was higher than the total number of neurons co-storing EGR1 and FOS. Of the total number of light-responsive cells, 42% expressed only EGR1, 43% expressed only FOS, and 15% expressed both EGR1 and FOS. Light-responsive VIP neurons represented only 31% of all VIP neurons, and EGR1 represents the largest group of light-responsive VIP neurons (18%). VIP neurons expressing only FOS represented 1% of the total light-responsive VIP neurons. 81% of the Ngb neurons in the mouse SCN were light-responsive, and of these neurons expressing only EGR1 after light stimulation represented 44%, whereas 24% expressed FOS. Although most light-responsive neurons are found in the core of the SCN, 29% of the AVP neurons in the shell were light-responsive, of which 8% expressed EGR1, 10% expressed FOS, and 11% co-expressed both EGR1 and FOS after light stimulation. Discussion: Our analysis revealed cell-specific differences in light responsiveness between different peptidergic and Ngb-expressing neurons in different compartments of the mouse SCN, indicating that light activates diverse neuronal networks in the SCN, some of which participate in photoentrainment.

Circadian disruption: from mouse models to molecular mechanisms and cancer therapeutic targets

The circadian clock is a timekeeping system for numerous biological rhythms that contribute to the regulation of numerous homeostatic processes in humans. Disruption of circadian rhythms influences physiology and behavior and is associated with adverse health outcomes, especially cancer. However, the underlying molecular mechanisms of circadian disruption-associated cancer initiation and development remain unclear. It is essential to construct good circadian disruption models to uncover and validate the detailed molecular clock framework of circadian disruption in cancer development and progression. Mouse models are the most widely used in circadian studies due to their relatively small size, fast reproduction cycle, easy genome manipulation, and economic practicality. Here, we reviewed the current mouse models of circadian disruption, including suprachiasmatic nuclei destruction, genetic engineering, light disruption, sleep deprivation, and other lifestyle factors in our understanding of the crosstalk between circadian rhythms and oncogenic signaling, as well as the molecular mechanisms of circadian disruption that promotes cancer growth. We focused on the discoveries made with the nocturnal mouse, diurnal human being, and cell culture and provided several circadian rhythm-based cancer therapeutic strategies.

Identifying hub circadian rhythm biomarkers and immune cell infiltration in rheumatoid arthritis

Background

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease with symptoms characterized by typical circadian rhythmic changes. This study aimed to identify the hub circadian rhythm genes (CRGs) in RA and explore their association with immune cell infiltration and pathogenesis of RA.

Methods

The differentially expressed CRGs (DECRGs) between RA and normal control samples were screened from Datasets GSE12021 and GSE55235. Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, and Gene Set Enrichment Analysis were used to explore the potential functional mechanisms of DECRGs in RA. Weighted Gene Co-expression Network Analysis and Least Absolute Shrinkage and Selection Operator regression analysis were performed to identify hub CRGs of RA. CIBERSORT was conducted to compare the infiltration level of immune cells in RA and control synovial tissue and their relationship with hub genes. In addition, the diagnostic value of hub biomarkers was evaluated by the area under the receiver operator characteristic curve. Further, a nomogram prediction model was constructed and its significance for clinical decision-making was evaluated.

Results

The green module was identified as the hub module associated with RA. Four hub CRGs (EGR1, FOSL2, GADD45B, and NFIL3) were identified and showed that they had the highest specificity and sensitivity for RA diagnosis, respectively. The expression levels and diagnostic values of these genes were externally validated in the dataset GSE55457. A nomogram prediction model based on the four hub CRGs was constructed and proved to have a certain clinical decision value. Additionally, the correlation analysis of immune cells with hub genes showed that all hub genes were significantly positively correlated with activated mast cells, resting memory CD4+ T cells, and monocytes. Whereas, all hub genes were negatively correlated with plasma cells, CD8+ T cells, and activated memory CD4+ T cells. Meanwhile, FOSL2 and GADD45B were negatively correlated with Tfh cells.

Conclusion

Four hub CRGs were identified and showed excellent diagnostic value for RA. These genes may be involved in the pathological process of RA by disrupting the rhythmic oscillations of cytokines through immune-related pathways and could be considered molecular targets for future chronotherapy against RA.

Chronic lead exposure alters photic entrainment of locomotor activity rhythm and neuronal photoactivation in the suprachiasmatic nucleus of the adult rat

Chronic lead (Pb) exposure affects the circadian physiological processes regulated by suprachiasmatic nucleus (SCN), which is synchronized (entrainment) by light. Disorders in the entrainment capacity of an organism alter its performance to interact with the environment, thus affecting its health status. The objectives of the present study were to evaluate whether chronic early Pb exposure affects the entrainment of the circadian rhythm of locomotor activity by light and to explore the possible mechanisms involved. Adult male Wistar rats, control and chronically exposed to Pb (320 ppm) in drinking water from gestation to adult age, were used. Assessment of the metal level showed a significant increase of Pb in the blood, hypothalamus and prefrontal cortex of the experimental rats. Continuous registrations of locomotor activity (12 h:12 h light-dark cycle) depicted that Pb induces important delay of this activity when the light was turned off. The Pb exposed animals entrained faster with a photoperiod delay of 6 h, (lights on at 13:00 h), and maintained the significant delay in the onset of activity at lights out. In continuous darkness, the animals were exposed to a light pulse at circadian time 23. This resulted in a significant decrease of photo-stimulated neurons (immunoreactivity to c-Fos) in the SCN of the metal-exposed animals. These results show that chronic early Pb exposure alters the photic entrainment of the rhythm of locomotor activity, which is evidenced by a significant decrease in both the number of photo-stimulated neurons and neuronal population (Nissl stain) of the SCN.

The Protective Effects of Endogenous PACAP in Oxygen-Induced Retinopathy

Pituitary adenylate cyclase–activating polypeptide (PACAP) is a neuropeptide having trophic and protective functions in neural tissues, including the retina. Previously, we have shown that intravitreal PACAP administration can maintain retinal structure in the animal model of retinopathy of prematurity (ROP). The purpose of this study is to examine the development of ROP in PACAP-deficient and wild-type mice to reveal the function of endogenous PACAP. Wild-type and PACAP-knockout (KO) mouse pups at postnatal day (PD) 7 were maintained at 75% oxygen for 5 consecutive days then returned to room air on PD12 to develop oxygen-induced retinopathy (OIR). On PD15, animals underwent electroretinography (ERG) to assess visual function. On PD16, eyes were harvested for either immunohistochemistry to determine the percentage of the central avascular retinal area or molecular analysis to assess angiogenesis proteins by array kit and anti-apoptotic protein kinase B (Akt) change by western blot. Retinas of PACAP-deficient OIR mice showed a greater central avascular area than that of the wild types. ERG revealed significantly decreased b-wave amplitude in PACAP KO compared to their controls. Several angiogenic proteins were upregulated due to OIR, and 11 different proteins markedly increased in PACAP-deficient mice, whereas western blot analysis revealed a reduction in Akt phosphorylation, suggesting an advanced cell death in the lack of PACAP. This is the first study to examine the endogenous effect of PACAP in the OIR model. Previously, we have shown the beneficial effect of exogenous local PACAP treatment in the rat OIR model. Together with the present findings, we suggest that PACAP could be a novel retinoprotective agent in ROP.