Kengo Hamamura

Molecular basis for the dosing time-dependency of anti-allodynic effects of gabapentin in a mouse model of neuropathic pain

BackgroundNeuropathic pain is characterized by hypersensitivity to innocuous stimuli (tactile allodynia) that is nearly always resistant to NSAIDs or even opioids. Gabapentin, a GABA analogue, was originally developed to treat epilepsy. Accumulating clinical evidence supports the effectiveness of this drug for diverse neuropathic pain. In this study, we showed that the anti-allodynic effect of gabapentin was changed by the circadian oscillation in the expression of its target molecule, the calcium channel α2δ-1 subunit.ResultsMice were underwent partial sciatic nerve ligation (PSL) to create a model of neuropathic pain. The paw withdrawal threshold (PWT) in PSL mice significantly decreased and fluctuated with a period length about 24 h. The PWT in PSL mice was dose-dependently increased by intraperitoneal injection of gabapentin, but the anti-allodynic effects varied according to its dosing time. The protein levels of α2δ-1 subunit were up-regulated in the DRG of PSL mice, but the protein levels oscillated in a circadian time-dependent manner. The time-dependent oscillation of α2δ-1 subunit protein correlated with fluctuations in the maximal binding capacity of gabapentin. The anti-allodynic effect of gabapentin was attenuated at the times of the day when α2δ-1 subunit protein was abundant.ConclusionsThese findings suggest that the dosing time-dependent difference in the anti-allodynic effects of gabapentin is attributable to the circadian oscillation of α2δ-1 subunit expression in the DRG and indicate that the optimizing its dosing schedule helps to achieve rational pharmacotherapy for neuropathic pain.

Molecular Mechanism Regulating 24-Hour Rhythm of Dopamine D3 Receptor Expression in Mouse Ventral Striatum

The dopamine D3 receptor (DRD3) in the ventral striatum is thought to influence motivation and motor functions. Although the expression of DRD3 in the ventral striatum has been shown to exhibit 24-hour variations, the mechanisms underlying the variation remain obscure. Here, we demonstrated that molecular components of the circadian clock act as regulators that control the 24-hour variation in the expression of DRD3. The transcription of DRD3 was enhanced by the retinoic acid–related orphan receptor α (RORα), and its activation was inhibited by the orphan receptor REV-ERBα, an endogenous antagonist of RORα. The serum or dexamethasone-induced oscillation in the expression of DRD3 in cells was abrogated by the downregulation or overexpression of REV-ERBα, suggesting that REV-ERBα functions as a regulator of DRD3 oscillations in the cellular autonomous clock. Chromatin immunoprecipitation assays of the DRD3 promoter indicated that the binding of the REV-ERBα protein to the DRD3 promoter increased in the early dark phase. DRD3 protein expression varied with higher levels during the dark phase. Moreover, the effects of the DRD3 agonist 7-hydroxy-N,N-dipropyl-2-aminotetralin (7-OH-DPAT)–induced locomotor hypoactivity were significantly increased when DRD3 proteins were abundant. These results suggest that RORα and REV-ERBα consist of a reciprocating mechanism wherein RORα upregulates the expression of DRD3, whereas REV-ERBα periodically suppresses the expression at the time of day when REV-ERBα is abundant. Our present findings revealed that a molecular link between the circadian clock and the function of DRD3 in the ventral striatum acts as a modulator of the pharmacological actions of DRD3 agonists/antagonists.

24-Hour Rhythm of Aquaporin-3 Function in the Epidermis Is Regulated by Molecular Clocks

Aquaporin 3 (AQP3) is located in the basal layer of the epidermis and regulates biological functions of skin such as water content and trans-epidermal water loss. A recent study showed that the biological function of skin exhibits a 24-hour rhythm, but the molecular mechanism of the variation remains poorly understood. Here we show that mice mutated in the core clock component CLOCK (Clk/Clk) show decreased stratum corneum hydration. An extensive search for the underlying cause led us to identify AQP3 as a new regulator to control the 24-hour variation in biological functions of skin. In mouse epidermis of wild-type mice, mAqp3 exhibits circadian rhythms; however, these are significantly decreased in Clk/Clk. Luciferase reporter gene analysis revealed that transcription of mAqp3 is activated by D-site-binding protein, a clock gene. A human homolog, hAQP3, also exhibited significant oscillation in human keratinocyte (HaCaT) cells synchronized with medium containing 50% serum, and this rhythm was regulated by the endogenous CLOCK/BMAL1 heterodimer. These data indicate that although the molecular mechanisms underlying the rhythmic expression of mAqp3 and hAQP3 are different, clock genes are involved in time-dependent skin hydration. Our current findings provide a molecular link between the circadian clock and AQP3 function in mouse dorsal skin and HaCaT cells.

Time-Dependent Interaction between Differentiated Embryo Chondrocyte-2 and CCAAT/Enhancer-Binding Protein α Underlies the Circadian Expression of CYP2D6 in Serum-Shocked HepG2 Cells

Differentiated embryo chondrocyte-2 (DEC2), also known as bHLHE41 or Sharp1, is a pleiotropic transcription repressor that controls the expression of genes involved in cellular differentiation, hypoxia responses, apoptosis, and circadian rhythm regulation. Although a previous study demonstrated that DEC2 participates in the circadian control of hepatic metabolism by regulating the expression of cytochrome P450, the molecular mechanism is not fully understood. We reported previously that brief exposure of HepG2 cells to 50% serum resulted in 24-h oscillation in the expression of CYP3A4 as well as circadian clock genes. In this study, we found that the expression of CYP2D6, a major drug-metabolizing enzyme in humans, also exhibited a significant oscillation in serum-shocked HepG2 cells. DEC2 interacted with CCAAT/enhancer-binding protein (C/EBPα), accompanied by formation of a complex with histone deacetylase-1, which suppressed the transcriptional activity of C/EBPα to induce the expression of CYP2D6. The oscillation in the protein levels of DEC2 in serum-shocked HepG2 cells was nearly antiphase to that in the mRNA levels of CYP2D6. Transfection of cells with small interfering RNA against DEC2 decreased the amplitude of CYP2D6 mRNA oscillation in serum-shocked cells. These results suggest that DEC2 periodically represses the promoter activity of CYP2D6, resulting in its circadian expression in serum-shocked cells. DEC2 seems to constitute a molecular link through which output components from the circadian clock are associated with the time-dependent expression of hepatic drug-metabolizing enzyme.

Circadian Clock in a Mouse Colon Tumor Regulates Intracellular Iron Levels to Promote Tumor Progression

Iron is an important biological catalyst and is critical for DNA synthesis during cell proliferation. Cellular iron uptake is enhanced in tumor cells to support increased DNA synthesis. Circadian variations in DNA synthesis and proliferation have been identified in tumor cells, but their relationship with intracellular iron levels is unclear. In this study, we identified a 24-h rhythm in iron regulatory protein 2 (IRP2) levels in colon-26 tumors implanted in mice. Our findings suggest that IRP2 regulates the 24-h rhythm of transferrin receptor 1 (Tfr1) mRNA expression post-transcriptionally, by binding to RNA stem-loop structures known as iron-response elements. We also found that Irp2 mRNA transcription is promoted by circadian clock genes, including brain and muscle Arnt-like 1 (BMAL1) and the circadian locomotor output cycles kaput (CLOCK) heterodimer. Moreover, growth in colon-26(Δ19) tumors expressing the clock-mutant protein (CLOCKΔ19) was low compared with that in wild-type colon-26 tumor. The time-dependent variation of cellular iron levels, and the proliferation rate in wild-type colon-26 tumor was decreased by CLOCKΔ19 expression. Our findings suggest that circadian organization contributes to tumor cell proliferation by regulating iron metabolism in the tumor.

Alterations of hepatic metabolism in chronic kidney disease via D-box binding protein aggravate the renal dysfunction.

Chronic kidney disease (CKD) is associated with an increase in serum retinol; however, the underlying mechanisms of this disorder are poorly characterized. Here, we found that the alteration of hepatic metabolism induced the accumulation of serum retinol in 5/6 nephrectomy (5/6Nx) mice. The liver is the major organ responsible for retinol metabolism; accordingly, microarray analysis revealed that the hepatic expression of most CYP genes was changed in 5/6Nx mice. In addition, D-box-binding protein (DBP), which controls the expression of several CYP genes, was significantly decreased in these mice. Cyp3a11 and Cyp26a1, encoding key proteins in retinol metabolism, showed the greatest decrease in expression in 5/6Nx mice, a process mediated by the decreased expression of DBP. Furthermore, an increase of plasma transforming growth factor-β1 (TGF-β1) in 5/6Nx mice led to the decreased expression of the Dbp gene. Consistent with these findings, the alterations of retinol metabolism and renal dysfunction in 5/6Nx mice were ameliorated by administration of an anti-TGF-β1 antibody. We also show that the accumulation of serum retinol induced renal apoptosis in 5/6Nx mice fed a normal diet, whereas renal dysfunction was reduced in mice fed a retinol-free diet. These findings indicate that constitutive Dbp expression plays an important role in mediating hepatic dysfunction under CKD. Thus, the aggravation of renal dysfunction in patients with CKD might be prevented by a recovery of hepatic function, potentially through therapies targeting DBP and retinol.

Mitomycin C modulates the circadian oscillation of clock gene period 2 expression through attenuating the glucocorticoid signaling in mouse fibroblasts.

Clock gene regulates the circadian rhythm of various physiological functions. The expression of clock gene has been shown to be attenuated by certain drugs, resulting in a rhythm disorder. Mitomycin C (MMC) is often used in combination with ophthalmic surgery, especially in trabeculectomy, a glaucoma surgical procedure. The purpose of this study was to investigate the influence of MMC on clock gene expression in fibroblasts, the target cells of MMC. Following MMC treatment, Bmal1 mRNA levels was significantly decreased, whereas Dbp, Per1, and Rev-erbα mRNA levels were significantly increased in the mouse fibroblast cell line NIH3T3 cells. Microarray analysis was performed to explore of the gene(s) responsible for MMC-induced alteration of clock gene expression, and identified Nr3c1 gene encoding glucocorticoid receptor (GR) as a candidate. MMC suppressed the induction of Per1 mRNA by dexamethasone (DEX), ligand of GR, in NIH3T3 cells. MMC also modulated the DEX-driven circadian oscillations of Per2::Luciferase bioluminescence in mouse-derived ocular fibroblasts. Our results demonstrate a previously unknown effect of MMC in GR signaling and the circadian clock system. The present findings suggest that MMC combined with trabeculectomy could increase the risk for a local circadian rhythm-disorder at the ocular surface.

Administering xCT Inhibitors Based on Circadian Clock Improves Antitumor Effects

Clock genes encoding transcription factors that regulate circadian rhythms may inform chronomodulated chemotherapy, where time-dependent dose alterations might affect drug efficacy and reduce side effects. For example, inhibiting the essential cystine transporter xCT with sulfasalazine induces growth arrest in cancer cells. Although the anticancer effects of sulfasalazine have been studied extensively, its effects on transcriptional control of xCT expression have not been studied. Here, we show that sulfasalazine administration during the period of increased xCT expression improves its anticancer effects and that the Clock gene itself induces xCT expression and regulates its circadian rhythm. Our findings highlight the clinical potential of chronomodulated chemotherapy and the importance of xCT-mediated transcriptional regulation in the utility of such strategies. Cancer Res; 77(23); 6603-13. ©2017 AACR.

Inhibition of G0/G1 Switch 2 Ameliorates Renal Inflammation in Chronic Kidney Disease

Chronic kidney disease (CKD) is a global health problem, and novel therapies to treat CKD are urgently needed. Here, we show that inhibition of G0/G1 switch 2 (G0s2) ameliorates renal inflammation in a mouse model of CKD. Renal expression of chemokine (C-C motif) ligand 2 (Ccl2) was increased in response to p65 activation in the kidneys of wild-type 5/6 nephrectomy (5/6Nx) mice. Moreover, 5/6Nx Clk/Clk mice, which carry homozygous mutations in the gene encoding circadian locomotor output cycles kaput (CLOCK), did not exhibit aggravation of apoptosis or induction of F4/80-positive cells. The renal expression of G0s2 in wild-type 5/6Nx mice was important for the transactivation of Ccl2 by p65. These pathologies were ameliorated by G0s2 knockdown. Furthermore, a novel small-molecule inhibitor of G0s2 expression was identified by high-throughput chemical screening, and the inhibitor suppressed renal inflammation in 5/6Nx mice. These findings indicated that G0s2 inhibitors may have applications in the treatment of CKD.

Possible involvement of the peripheral Mu-opioid system in antinociception induced by bergamot essential oil to allodynia after peripheral nerve injury

The essential oil of bergamot (BEO) is one of the most common essential oils and is most familiar to the general public. The aims of this study were to investigate the effect of intraplantar (i.pl.) BEO on neuropathic allodynia induced by partial sciatic nerve ligation (PSNL) in mice and the opioid receptor subtypes involved in the antiallodynic effects of BEO. Our findings showed that a single dose of i.pl. administration of BEO significantly inhibited the PSNL-induced neuropathic pain using the von Frey test. The i.pl pretreatment with naloxone methiodide, a peripherally acting μ-opioid receptor preferring antagonist, β-funaltrexamine hydrochloride (β-FNA), a selective μ-opioid receptor antagonist, and β-endorphin antiserum significantly reversed the antiallodynic effect of BEO in the von Frey test, but not by naltrindole, the nonselective δ-opioid receptor antagonist and nor-binaltorphimine, the selective κ-opioid receptor antagonist. Furthermore, in the western blotting analysis, i.pl. administration of BEO resulted in a significant blockage of spinal extracellular signal-regulated protein kinase (ERK) activation induced by PSNL. Naloxone methiodide and β-FNA significantly reversed the blockage of spinal ERK activation induced by BEO. These results suggest that i.pl. injection of BEO-induced antiallodynic effect and blockage of spinal ERK activation may be triggered by activation of peripheral μ-opioid receptors.