Arntl deficiency in myeloid cells reduces neutrophil recruitment and delays skeletal muscle repair.

After a muscle injury, a process comprising inflammation, repair, and regeneration must occur in a time-sensitive manner for skeletal muscle to be adequately repaired and regenerated. This complex process is assumed to be controlled by various myeloid cell types, including monocytes and macrophages, though the mechanism is not fully understood. Aryl hydrocarbon receptor nuclear translocator-like (Arntl or Bmal1) is a transcription factor that controls the circadian rhythm and has been implicated in regulating myeloid cell functions. In the present study, we generated myeloid cell-specific Arntl conditional knockout (cKO) mice to assess the role of Arntl expressed in myeloid cell populations during the repair process after muscle injury. Myeloid cell-specific Arntl deletion impaired muscle regeneration after cardiotoxin injection. Flow cytometric analyses revealed that, in cKO mice, the numbers of infiltrating neutrophils and Ly6Chi monocytes within the injured site were reduced on days 1 and 2, respectively, after muscle injury. Moreover, neutrophil migration and the numbers of circulating monocytes were significantly reduced in cKO mice, which suggests these effects may account, at least in part, for the impaired regeneration. These findings suggest that Arntl, expressed in the myeloid lineage regulates neutrophil and monocyte recruitment and is therefore required for skeletal muscle regeneration.

Adolescence as a critical period for nandrolone-induced muscular strength in relation to abuse liability, alone and in conjunction with morphine, using accumbal dopamine efflux in freely moving rats.

Nandrolone, an anabolic androgenic steroid, is included in the prohibited list of the World Anti-Doping Agency. Drugs of abuse activate brain dopamine neurons and nandrolone has been suspected of inducing dependence. Accordingly, possible critical periods for the effects of nandrolone on muscular strength and dopaminergic activity have been investigated, including the effects of chronically administered nandrolone alone and on morphine-induced increases in dopamine efflux in the nucleus accumbens. Six- or 10-week-old male Sprague-Dawley rats were used. Treatment with nandrolone was initiated in adolescent (6-week-old) and young adult (10-week-old) rats. Nandrolone (5.0 mg/kg s.c.) or sesame oil vehicle was given once daily, on six consecutive days per week, for 3 weeks and then once per day for 4 consecutive days. Nandrolone enhanced the developmental increase in grip strength of 6- but not 10-week-old rats, without altering the developmental increase in body weight of either age group. Using in vivo microdialysis in freely moving 6-week-old rats given nandrolone for 4 weeks, basal accumbal dopamine efflux was unaltered, while the increase in dopamine efflux induced by acute administration of morphine (1.0 mg/kg s.c.) was reduced. The present study provides in vivo evidence that adolescence constitutes a critical period during which repeated administration of nandrolone enhances increases in muscular strength without influencing increases in body weight. Though repeated administration of nandrolone during this period of adolescence did not stimulate in vivo mesolimbic dopaminergic activity, it disrupted stimulation by an opioid, the drug class that is most commonly coabused with nandrolone.

Inhibitory Effects of Hydrolysable Tannins on Lipid Accumulation in 3T3-L1 Cells.

Obesity is currently the most common cause of metabolic diseases including type 2 diabetes and hyperlipidemia. Obesity results from excess lipid accumulation in adipose tissue. Several studies have investigated the inhibitory effects of natural plant-derived products on adipocyte differentiation and lipid accumulation. In this study, we examined the effect of hydrolysable tannins composed of gallic acid and glucose on adipocyte differentiation in 3T3-L1 cells. 1,2,3,4,6-Penta-O-galloyl-ß-D-glucose (PGG) (1), a representative gallotannin, inhibited lipid accumulation in 3T3-L1 cells, whereas ellagitannins (tellimagrandin I, eugeniin and casuarictin) did not. The expression of adipocyte differentiation-related genes, including peroxisome proliferator activator γ2 (Pparγ2), CCAAT/enhancer binding protein α (C/EBPα) and adipocyte fatty acid binding protein (aP2), was significantly suppressed in PGG (1)-treated 3T3-L1 cells beginning at day 2 after induction of differentiation. While PGG (1) did not directly reduce Pparγ2 expression, it reduced the expression of its target genes in mature adipocytes. In addition, PGG (1) treatment inhibited mitotic clonal expansion, one of earliest events of adipocyte differentiation. These findings indicate that PGG (1) has an inhibitory effect on adipocyte differentiation through the suppression of mitotic clonal expansion.

Bmal1 Regulates Prostate Growth via Cell-Cycle Modulation.

The circadian clock system exists in most organs and regulates diverse physiological processes, including growth. Here, we used a prostate-specific Bmal1-knockout mouse model (pBmal1 KO: PbsnCre+; Bmal1fx/fx) and immortalized human prostate cells (RWPE-1 and WPMY-1) to elucidate the role of the peripheral prostate clock on prostate growth. Bmal1 KO resulted in significantly decreased ventral and dorsolateral lobes with less Ki-67-positive epithelial cells than the controls. Next, the cap analysis of gene expression revealed that genes associated with cell cycles were differentially expressed in the pBmal1 KO prostate. Cdkn1a (coding p21) was diurnally expressed in the control mouse prostate, a rhythm which was disturbed in pBmal1 KO. Meanwhile, the knockdown of BMAL1 in epithelial RWPE-1 and stromal WPMY-1 cell lines decreased proliferation. Furthermore, RWPE-1 BMAL1 knockdown increased G0/G1-phase cell numbers but reduced S-phase numbers. These findings indicate that core clock gene Bmal1 is involved in prostate growth via the modulation of the cell cycle and provide a rationale for further research to link the pathogenesis of benign prostatic hyperplasia or cancer with the circadian clock.

The Lack of Bmal1, a Core Clock Gene, in the Intestine Decreases Glucose Absorption in Mice.

The circadian clock network is an evolutionarily conserved system that regulates systemic metabolism, such as glucose homeostasis. Intestinal tissue is a pivotal organ for the regulation of glucose metabolism, mainly via glucose absorption into the circulation; however, the significance of the intestinal circadian clock network for glucose metabolism remains largely unclear. We herein utilized a mouse model in which Bmal1, a core clock gene, was deleted in an intestine-specific manner (Bmal1Int-/- mice) and demonstrated a rhythmic expression of Sglt1 with its peak at zeitgeber time (ZT) 10.7 ±â€…2.8 in control mice, whereas this was lost in Bmal1Int-/- mice. Mechanistically, chromatin immunoprecipitation analysis revealed rhythmic binding of CLOCK to the E-box elements in the Sglt1 gene in control mice; however, this was absent in Bmal1Int-/- mice. Accordingly, SGLT1 protein levels were decreased during the dark phase in Bmal1Int-/- mice and this was associated with impaired glucose absorption, leading to a decline in hepatic glycogen levels at ZT4, which was restored by ingestion of high-sucrose water. Additionally, when mice were starved from ZT0, greater expression of the lipolysis-related gene Pnpla2 was observed in adipose tissue of Bmal1Int-/- mice, and this was not noted when glycogen storage was restored by high-sucrose water prior to fasting, suggesting that higher Pnpla2 expression in Bmal1Int-/- mice was likely caused by lower glycogen storage. These results indicate that disruption of the intestinal circadian clock system impairs glucose absorption in the intestine and affects systemic glucose homeostasis.

Adiponectin regulates the circadian rhythm of glucose and lipid metabolism.

Adiponectin is a cytokine secreted from adipocytes and regulates metabolism. Although serum adiponectin levels show diurnal variations, it is not clear if the effects of adiponectin are time-dependent. Therefore, this study conducted locomotor activity analyses and various metabolic studies using the adiponectin knockout (APN (-/-)) and the APN (+/+) mice to understand whether adiponectin regulates the circadian rhythm of glucose and lipid metabolism. We observed that the adiponectin gene deficiency does not affect the rhythmicity of core circadian clock genes expression in several peripheral tissues. In contrast, the adiponectin gene deficiency alters the circadian rhythms of liver and serum lipid levels and results in the loss of the time dependency of very-low-density lipoprotein-triglyceride secretion from the liver. In addition, the whole-body glucose tolerance of the APN (-/-) mice was normal at CT10 but reduced at CT22, compared to the APN (+/+) mice. The decreased glucose tolerance at CT22 was associated with insulin hyposecretion in vivo. In contrast, the gluconeogenesis activity was higher in the APN (-/-) mice than in the APN (+/+) mice throughout the day. These results indicate that adiponectin regulates part of the circadian rhythm of metabolism in the liver.

Circadian Clock Component BMAL1 in the Paraventricular Nucleus Regulates Glucose Metabolism.

It is suggested that clock genes link the circadian rhythm to glucose and lipid metabolism. In this study, we explored the role of the clock gene Bmal1 in the hypothalamic paraventricular nucleus (PVN) in glucose metabolism. The Sim1-Cre-mediated deletion of Bmal1 markedly reduced insulin secretion, resulting in impaired glucose tolerance. The pancreatic islets' responses to glucose, sulfonylureas (SUs) and arginine vasopressin (AVP) were well maintained. To specify the PVN neuron subpopulation targeted by Bmal1, the expression of neuropeptides was examined. In these knockout (KO) mice, the mRNA expression of Avp in the PVN was selectively decreased, and the plasma AVP concentration was also decreased. However, fasting suppressed Avp expression in both KO and Cre mice. These results demonstrate that PVN BMAL1 maintains Avp expression in the PVN and release to the circulation, possibly providing islet ß-cells with more AVP. This action helps enhance insulin release and, consequently, glucose tolerance. In contrast, the circadian variation of Avp expression is regulated by feeding, but not by PVN BMAL1.

Distribution of dietary protein intake in daily meals influences skeletal muscle hypertrophy via the muscle clock.

The meal distribution of proteins throughout the day is usually skewed. However, its physiological implications and the effects of better protein distribution on muscle volume are largely unknown. Here, using the two-meals-per-day feeding model, we find that protein intake at the early active phase promotes overloading-induced muscle hypertrophy, in a manner dependent on the local muscle clock. Mice fed branched-chain amino acid (BCAA)-supplemented diets at the early active phase demonstrate skeletal muscle hypertrophy. However, distribution-dependent effects are not observed in ClockΔ19 or muscle-specific Bmal1 knockout mice. Additionally, we examined the relationship between the distribution of proteins in meals and muscle functions, such as skeletal muscle index and grip strength in humans. Higher muscle functions were observed in subjects who ingested dietary proteins mainly at breakfast than at dinner. These data suggest that protein intake at breakfast may be better for the maintenance of skeletal muscle mass.

Brown adipocyte-specific knockout of Bmal1 causes mild but significant thermogenesis impairment in mice.

OBJECTIVE: Impaired circadian clocks can cause obesity, but their pathophysiological role in brown adipose tissue (BAT), a major tissue regulating energy metabolism, remains unclear. To address this issue, we investigated the effects of complete disruption of the BAT clock on thermogenesis and energy expenditure. METHODS: Mice with brown adipocyte-specific knockout of the core clock gene Bmal1 (BA-Bmal1 KO) were generated and analyzed. RESULTS: The BA-Bmal1 KO mice maintained normal core body temperatures by increasing shivering and locomotor activity despite the elevated expression of thermogenic uncoupling protein 1 in BAT. BA-Bmal1 KO disrupted 24 h rhythmicity of fatty acid utilization in BAT and mildly reduced both BAT thermogenesis and whole-body energy expenditure. The impact of BA-Bmal1 KO on the development of obesity became obvious when the mice were fed a high-fat diet. CONCLUSIONS: These results reveal the importance of the BAT clock for maintaining energy homeostasis and preventing obesity.

Morphological characteristics of interalveolar septum and mandible in BMAL1 gene knockout mice.

PURPOSE: Circadian rhythm is associated with the pathogenesis of systemic disease and bone mineral metabolism. This study aimed to radiographically evaluate morphological characteristics of the interalveolar septum in circadian rhythm deficient animals. METHODS: Heads of 10 brain and muscle arnt-like protein-1 (BMAL1)-knockout (KO) mice and 10 wild-type mice sacrificed at 36 weeks were imaged using micro-computed tomography. The mean depth from the cementoenamel junction to the alveolar ridge (virtual bone sounding: VBS) of the interalveolar septum between the first and second molars, and the bone mineral density (BMD) of the interalveolar septum and the mandibular inferior cortex region were calculated. Tooth diameter was also measured. RESULTS: The VBS of the interalveolar septum in the BMAL1-KO mice was significantly deeper than that in wild-type mice. The BMD in the BMAL1-KO mice was significantly lower than in the wild-type mice in both regions. No significant difference was observed in tooth diameter between BMAL1-KO and wild-type mice. CONCLUSION: These results suggest that low BMD in the interalveolar septum accelerates bone resorption in the interalveolar septum in BMAL1-KO mice.

Intestinal clock system regulates skeletal homeostasis.

The circadian clock network is an evolutionarily conserved system involved in the regulation of metabolic homeostasis; however, its impacts on skeletal metabolism remain largely unknown. We herein demonstrated that the circadian clock network in the intestines plays pivotal roles in skeletal metabolism such that the lack of the Bmal1 gene in the intestines (Bmal1Int-/- mice) caused bone loss, with bone resorption being activated and bone formation suppressed. Mechanistically, Clock protein interaction with the vitamin D receptor (VDR) accelerated its binding to the VDR response element by enhancing histone acetylation in a circadian-dependent manner, and this was lost in Bmal1Int-/- mice because nuclear translocation of Clock required the presence of Bmal1. Accordingly, the rhythmic expression of VDR target genes involved in transcellular calcium (Ca) absorption was created, and this was not observed in Bmal1Int-/- mice. As a result, transcellular Ca absorption was impaired and bone resorption was activated in Bmal1Int-/- mice. Additionally, sympathetic tone, the activation of which suppresses bone formation, was elevated through afferent vagal nerves in Bmal1Int-/- mice, the blockade of which partially recovered bone loss by increasing bone formation and suppressing bone resorption in Bmal1Int-/- mice. These results demonstrate that the intestinal circadian system regulates skeletal bone homeostasis.

Deletion of Bmal1 Prevents Diet-Induced Ectopic Fat Accumulation by Controlling Oxidative Capacity in the Skeletal Muscle.

Brain and muscle arnt-like protein 1 (BMAL1), is a transcription factor known to regulate circadian rhythm. BMAL1 was originally characterized by its high expression in the skeletal muscle. Since the skeletal muscle is the dominant organ system in energy metabolism, the possible functions of BMAL1 in the skeletal muscle include the control of metabolism. Here, we established that its involvement in the regulation of oxidative capacity in the skeletal muscle. Muscle-specific Bmal1 KO mice (MKO mice) displayed several physiological hallmarks for the increase of oxidative capacity. This included increased energy expenditure and oxygen consumption, high running endurance and resistance to obesity with improved metabolic profiles. Also, the phosphorylation status of AMP-activated protein kinase and its downstream signaling substrate acetyl-CoA carboxylase in the MKO mice were substantially higher than those in the Bmal1flox/flox mice. In addition, biochemical and histological studies confirmed the substantial activation of oxidative fibers in the skeletal muscle of the MKO mice. The mechanism includes the regulation of Cacna1s expression, followed by the activation of calcium-nuclear factor of activated T cells (NFAT) axis. We thus conclude that BMAL1 is a critical regulator of the muscular fatty acid level under nutrition overloading and that the mechanism involves the control of oxidative capacity.

Micro-CT observation of in vivo temporal change in mandibular condyle morphology in BMAL1 knockout mice.

Brain and muscle Arnt-like protein-1 (BMAL1) knockout mice exhibit accelerated aging, abnormal glucose metabolism, and impaired adipocyte differentiation, among other phenotypes, which are effects associated with the BMAL1 gene. No study has investigated temporal changes in the deformation of the mandibular condyle and the presence of calcification in areas surrounding the mandibular condyle. In a study of 12 C57/BL strain mice under inhalation anesthesia, we collected images of the mandibular condyle at 6 weeks after birth and then every 5 weeks from 10 to 25 weeks after birth. At 25 weeks, deformation of the mandibular condyle was seen in 8 of 12 joints in BMAL1 knockout mice and in 2 of 12 joints in wild-type mice. At 20 and 25 weeks, deformation in areas surrounding the mandibular condyle, which are known to undergo calcification, was seen in 2 of 12 joints in BMAL1 knockout mice and in 0 of 12 joints in wild-type mice. BMAL1 knockout mice exhibited premature aging of the mandibular condyle, which suggests that circadian rhythms affect mandibular condyle morphology.

Relevance of the hippocampal endoplasmic reticulum stress response in a mouse model of chronic kidney disease.

It has been shown that the incidence of cognitive impairment increases with the severity of chronic kidney disease (CKD). A previous study has demonstrated that hippocampal oxidative stress contributes to cognitive dysfunction in CKD model mice. Endoplasmic reticulum (ER) stress is thought to contribute significantly to neuronal dysfunction, but its role in the hippocampal dysfunction seen in CKD still remains unclear. The present study examined whether the ER stress response as well as oxidative stress was activated in the hippocampus of CKD model mice. Western blotting revealed that the expression level of 4-hydroxy-2-nonenal (HNE)-protein adducts, a marker of oxidative stress, was increased in the hippocampus 8 weeks after 5/6 nephrectomy. In these mice, the expression level of glucose-regulated protein 78 (GRP78), a typical ER stress marker, also showed a pronounced increase in the hippocampus. Correlation analyses showed that the levels of these two marker proteins in the hippocampus are positively correlated with the serum concentrations of BUN and creatinine. These results suggest that ER stress as well as oxidative stress are induced in the hippocampus of CKD mice and that the levels of these stress markers in the hippocampus are correlated with the renal impairment caused by CKD.

Circadian coordination of ATP release in the urothelium via connexin43 hemichannels.

Day-night changes in the storage capacity of the urinary bladder are indispensable for sound sleep. Connexin 43 (Cx43), a major gap junction protein, forms hemichannels as a pathway of ATP in other cell types, and the urinary bladder utilizes ATP as a mechanotransduction signals to modulate its capacity. Here, we demonstrate that the circadian clock of the urothelium regulates diurnal ATP release through Cx43 hemichannels. Cx43 was expressed in human and mouse urothelium, and clock genes oscillated in the mouse urothelium accompanied by daily cycles in the expression of Cx43 and extracellular ATP release into the bladder lumen. Equivalent chronological changes in Cx43 and ATP were observed in immortalized human urothelial cells, but these diurnal changes were lost in both arrhythmic Bmal1-knockout mice and in BMAL1-knockdown urothelial cells. ATP release was increased by Cx43 overexpression and was decreased in Cx43 knockdown or in the presence of a selective Cx43 hemichannel blocker, which indicated that Cx43 hemichannels are considered part of the components regulating ATP release in the urothelium. Thus, a functional circadian rhythm exists in the urothelium, and coordinates Cx43 expression and function as hemichannels that provide a direct pathway of ATP release for mechanotransduction and signalling in the urothelium.

Bmal1-deficient mouse fibroblast cells do not provide premature cellular senescence in vitro.

Bmal1 is a core circadian clock gene. Bmal1-/- mice show disruption of the clock and premature aging phenotypes with a short lifespan. However, little is known whether disruption of Bmal1 leads to premature aging at cellular level. Here, we established primary mouse embryonic fibroblast (MEF) cells derived from Bmal1-/- mice and investigated its effects on cellular senescence. Unexpectedly, Bmal1-/- primary MEFs that showed disrupted circadian oscillation underwent neither premature replicative nor stress-induced cellular senescence. Our results therefore uncover that Bmal1 is not required for in vitro cellular senescence, suggesting that circadian clock does not control in vitro cellular senescence.

Disruption of Bmal1 Impairs Blood-Brain Barrier Integrity via Pericyte Dysfunction.

Circadian rhythm disturbances are well established in neurological diseases. However, how these disruptions cause homeostatic imbalances remains poorly understood. Brain and muscle aryl hydrocarbon receptor nuclear translocator-like protein 1 (Bmal1) is a major circadian clock transcriptional activator, and Bmal1 deficiency in male Bmal1nestin-/- mice induced marked astroglial activation without affecting the number of astrocytes in the brain and spinal cord. Bmal1 deletion caused blood-brain barrier (BBB) hyperpermeability with an age-dependent loss of pericyte coverage of blood vessels in the brain. Using Nestin-green fluorescent protein (GFP) transgenic mice, we determined that pericytes are Nestin-GFP+ in the adult brain. Bmal1 deletion caused Nestin-GFP+ pericyte dysfunction, including the downregulation of platelet-derived growth factor receptor ß (PDGFRß), a protein necessary for maintaining BBB integrity. Knockdown of Bmal1 downregulated PDGFRß transcription in the brain pericyte cell line. Thus, the circadian clock component Bmal1 maintains BBB integrity via regulating pericytes.SIGNIFICANCE STATEMENT Circadian rhythm disturbances may play a role in neurodegenerative disorders, such as Alzheimer's disease. Our results revealed that one of the circadian clock components maintains the integrity of the blood-brain barrier (BBB) by regulating vascular-embedded pericytes. These cells were recently identified as a vital component for the control of BBB permeability and cerebral blood flow. Our present study demonstrates the involvement of circadian clock component Bmal1 in BBB homeostasis and highlights the role of Bmal1 dysfunction in multiple neurological diseases.

Bmal1 regulates inflammatory responses in macrophages by modulating enhancer RNA transcription.

Bmal1 (encoded by Arntl gene) is a core circadian clock gene that regulates various genes involved in circadian rhythm. Although Bmal1 is expressed rhythmically in macrophages, the role of Bmal1 in the regulation of their cellular function remains insufficiently understood. Here, we report that Bmal1 regulates time-dependent inflammatory responses following Toll-like receptor 4 (TLR4) activation by modulating enhancer activity. Global transcriptome analysis indicated that deletion of Arntl perturbed the time-dependent inflammatory responses elicited by TLR4 activation by Kdo2-lipid A (KLA). Although the recruitment of NF-κB p65 was unaffected, the acetylation status of lysine 27 of histone 3, which correlates positively with enhancer activity, was globally increased at PU.1-containing enhancers in Arntl -/- macrophages as compared to wild-type cells. Expression of Nr1d1 and Nr1d2, encoding RevErb transcription factors, which repress enhancer RNA expression, was significantly decreased in Arntl -/- macrophages. Moreover, the level of H3K27 acetylation was increased by Arntl deletion at RevErb-dependent eRNA-expressing enhancers. These results suggest that Bmal1 controls KLA-responsive enhancers, in part by regulating RevErb-directed eRNA transcription. Taken together, the results of this study show that the clock transcription factor network containing Bmal1 controls the inflammatory responses of macrophages by regulating the epigenetic states of enhancers.

Ketogenic diet induces expression of the muscle circadian gene Slc25a25 via neural pathway that might be involved in muscle thermogenesis.

We recently found that the mRNA expression of Slc25a25, a Ca2+-sensitive ATP carrier in the inner mitochondrial membrane, fluctuates in a circadian manner in mouse skeletal muscle. We showed here that the circadian expression of muscle Slc25a25 was damped in Clock mutant, muscle-specific Bmal1-deficient, and global Bmal1-deficient mice. Furthermore, a ketogenic diet (KD) that induces time-of-day-dependent hypothermia (torpor), induced Slc25a25 mRNA expression in skeletal muscle. Hypothermia induced by KD did not affect thermogenic genes such as Sarcolipin and Pgc1a in muscles and Ucp1 in adipose tissues. Sciatic denervation abolished circadian and KD-induced Slc25a25 expression, suggesting that the circadian clock regulates muscle Slc25a25 expression via neural pathways. We measured body temperature (Tb) in sciatic denervated mice fed with KD to determine the functional role of KD-induced Slc25a25 expression. Sciatic denervation abolished Slc25a25 expression and augmented KD-induced hypothermia compared with sham-operated mice, but did not affect Tb in mice given a normal diet. These findings suggest that KD feeding induces expression of the muscle circadian gene Slc25a25 via neural pathways, and that SLC25A25 might be involved in muscle thermogenesis under KD-induced hypothermia in mammals.