Abstract: Synchronous oscillations of thousands of cellular clocks in the suprachiasmatic nucleus (SCN), the circadian centre, are coordinated by precisely timed cell-cell communication, the principle of which is largely unknown. Here we show that the amount of RGS16 (regulator of G protein signalling 16), a protein known to inactivate Gαi, increases at a selective circadian time to allow time-dependent activation of intracellular cyclic AMP signalling in the SCN. Gene ablation of Rgs16 leads to the loss of circadian production of cAMP and as a result lengthens circadian period of behavioural rhythm. The temporally precise regulation of the cAMP signal by clock-controlled RGS16 is needed for the dorsomedial SCN to maintain a normal phase-relationship to the ventrolateral SCN. Thus, RGS16-dependent temporal regulation of intracellular G protein signalling coordinates the intercellular synchrony of SCN pacemaker neurons and thereby defines the 24 h rhythm in behaviour.
Abstract: Spontaneous spinal epidural hematoma (SSEH) is a rare condition, and its etiology remains unclear. Spinal venous wall instability due to intravenous pressure changes and the resultant venous rupture seem to be the underlying pathophysiological mechanisms. Here, the authors report a case of posterior SSEH at the C3-5 level causing mild left hemiparesis in a previously healthy 56-year-old woman. Angiography performed at the time of admission showed left internal jugular vein (IJV) thrombotic occlusion and dilation of the surrounding venous plexus, strongly suggesting that these pathologies caused the SSEH. Furthermore, immediate MR imaging suggested severely impaired blood flow in the left IJV. The hematoma soon resolved after spontaneous IJV thrombolysis. The authors' radiological observations imply that idiopathic IJV thrombosis may cause cervical SSEH.
Abstract: Light is a powerful synchronizer of the circadian rhythms, and bright light therapy is known to improve metabolic and hormonal status of circadian rhythm sleep disorders, although its mechanism is poorly understood. In the present study, we revealed that light induces gene expression in the adrenal gland via the suprachiasmatic nucleus (SCN)-sympathetic nervous system. Moreover, this gene expression accompanies the surge of plasma and brain corticosterone levels without accompanying activation of the hypothalamo-adenohypophysial axis. The abolishment after SCN lesioning, and the day-night difference of light-induced adrenal gene expression and corticosterone release, clearly indicate that this phenomenon is closely linked to the circadian clock. The magnitude of corticostereone response is dose dependently correlated with the light intensity. The light-induced clock-dependent secretion of glucocorticoids adjusts cellular metabolisms to the new light-on environment.
Abstract: Serine/threonine kinase Akt is thought to mediate many biological actions toward anti-apoptotic responses. Screening of drugs that could interfere with the Akt signaling pathway revealed that Hsp90 inhibitors (e.g. geldanamycin, radicicol, and its analogues) induced Akt dephosphorylation, which resulted in Akt inactivation and apoptosis of the cells. Hsp90 inhibitors did not directly affect Akt kinase activity in vitro. Thus, we examined the effects of Hsp90 inhibitors on upstream Akt kinases, phosphatidylinositide-3-OH kinase (PI3K) and 3-phosphoinositide-dependent protein kinase-1 (PDK1). Hsp90 inhibitors had no effect on PI3K protein expression. In contrast, treatment of the cells with Hsp90 inhibitors decreased the amount of PDK1 without directly inhibiting PDK1 kinase activity. We found that the kinase domain of PDK1 was essential for complex formation with Hsp90 and that Hsp90 inhibitors suppressed PDK1 binding to Hsp90. PDK1 degradation mechanisms revealed that inhibition of PDK1 binding to Hsp90 caused proteasome-dependent degradation of PDK1. Treatment of proteasome inhibitors increased the amount of detergent-insoluble PDK1 in Hsp90 inhibitor-treated cells. Therefore, the association of PDK1 with Hsp90 regulates its stability, solubility, and signaling. Because Akt binding to Hsp90 is also involved in the maintenance of Akt kinase activity, Hsp90 plays an important role in PDK1-Akt survival signaling pathway.
Abstract: Vascular endothelial cells in bone are thought to have significant roles on pathological bone resorption such as bone metastasis and hypercalcemia because this resorption is often seen where blood vessels are abundant. However, the detailed mechanisms have not yet been elucidated. Here, we focused on transforming growth factor-beta (TGF-beta) and studied its effects on vascular endothelial cells because TGF-beta is abundantly stored in bone matrix and is released and activated during bone resorption. We found that TGF-beta up-regulated the expression of receptor activator of NF-kappa B ligand (RANKL) mRNA and protein in bone marrow-derived endothelial cells and in primary vascular endothelial cells but not in osteoblasts. Further analysis revealed that TGF-beta promoted phosphorylation of cAMP response element-binding protein and p38. Protein kinase A inhibitor KT5720 and p38 inhibitor SB203580 significantly reduced the TGF-beta-induced RANKL expression. Moreover, we found two CRE-like domains in murine RANKL promoter region that were critical for TGF-beta-dependent RANKL expression. Therefore, protein kinase A and p38 signaling pathways are involved in TGF-beta-induced RANKL expression by stimulating transcription factors that bind to the CRE-like domains. Our findings indicate that TGF-beta stimulates osteoclastogenesis by promoting RANKL expression in endothelial cells under pathological conditions.
