Calorie restriction (CR) extends lifespans in a wide variety of species. CR induces an increase in the NAD(+)/NADH ratio in cells and results in activation of SIRT1, an NAD(+)-dependent protein deacetylase that is thought to be a metabolic master switch linked to the modulation of lifespans. CR also affects the expression of peroxisome proliferator-activated receptors (PPARs). The three subtypes, PPARalpha, PPARgamma, and PPARbeta/delta, are expressed in multiple organs. They regulate different physiological functions such as energy metabolism, insulin action and inflammation, and apparently act as important regulators of longevity and aging. SIRT1 has been reported to repress the PPARgamma by docking with its co-factors and to promote fat mobilization. However, the correlation between SIRT1 and other PPARs is not fully understood. CR initially induces a fasting-like response. In this study, we investigated how SIRT1 and PPARalpha correlate in the fasting-induced anti-aging pathways. A 24-h fasting in mice increased mRNA and protein expression of both SIRT1 and PPARalpha in the livers, where the NAD(+) levels increased with increasing nicotinamide phosphoribosyltransferase (NAMPT) activity in the NAD(+) salvage pathway. Treatment of Hepa1-6 cells in a low glucose medium conditions with NAD(+) or NADH showed that the mRNA expression of both SIRT1 and PPARalpha can be enhanced by addition of NAD(+), and decreased by increasing NADH levels. The cell experiments using SIRT1 antagonists and a PPARalpha agonist suggested that PPARalpha is a key molecule located upstream from SIRT1, and has a role in regulating SIRT1 gene expression in fasting-induced anti-aging pathways.

Acute thrombotic events frequently occur in the early morning among hyperlipidemic patients. The activity of plasminogen activator inhibitor-1 (PAI-1), a potent inhibitor of the fibrinolytic system, oscillates daily, and this is considered one mechanism that underlies the morning onset of acute thrombotic events in hyperlipidemia. Although several studies have reported the expression of the PAI-1 gene is under the control of the circadian clock system, the molecular mechanism of the circadian transactivation of PAI-1 gene under hyperlipidemic conditions remains to be elucidated. Here, the authors investigated whether hyperlipidemia induced by a high-fat diet (HFD) enhances the daily oscillation of plasma PAI-1 activity in mice. The mRNA levels of the PAI-1 gene were increased and rhythmically fluctuated with high-oscillation amplitude in the livers of wild-type mice fed with the HFD. Circadian expression of proxisome proliferator-activated receptor-α (PPARα) mRNA was also augmented as well as that of PAI-1. Chromatin immunoprecipitation showed the HFD-induced hyperlipidemia significantly increased the binding of PPARα to the PAI-1 promoter. Luciferase reporter analysis using primary hepatocytes revealed CLOCK/BMAL1-mediated PAI-1 promoter activity was synergistically enhanced by cotransfection with PPARα/retinoid X receptor-α (RXRα), and this synergistic transactivation was repressed by negative limbs of the circadian clock, PERIOD2 and CRYPTOCHROME1. As expected, HFD-induced PAI-1 mRNA expression was significantly attenuated in PPARα-null mice. These results suggest a molecular link between the circadian clock and lipid metabolism system in the regulation of PAI-1 gene expression, and provide an aid for understanding why hyperlipidemia increases the risk of acute thrombotic events in the morning.

A functional interaction between peroxisome proliferator-activated receptor ␣ (PPAR␣) and components of the circadian clock has been suggested, but whether these transcriptional factors interact to regulate the expression of their target genes remains obscure. Here we used a PPAR␣ ligand, bezafibrate, to search for PPAR␣-regulated genes that are expressed in a CLOCK-dependent circadian manner. Microarray analyses using hepatic RNA isolated from bezafibrate treated-wild type, Clock mutant (Clk/Clk), and PPAR␣-null mice revealed that 136 genes are transcriptionally regulated by PPAR␣ in a CLOCKdependent manner. Among them, we focused on the plasminogen activator inhibitor-1 (PAI-1) gene, because its expression typically shows circadian variation, and it has transcriptional response elements for both PPAR and CLOCK. The bezafibrate-induced expression of PAI-1 mRNA was attenuated in Clk/Clk mice and in PPAR␣-null mice. The protein levels of PPAR␣ were reduced in Clk/Clk hepatocytes. However, the overexpression of PPAR␣ could not rescue bezafibrate-induced PAI-1 expression in Clk/Clk hepatocytes, suggesting that impaired bezafibrate-induced PAI-1 expression in Clk/Clk mice is not due to reduced PPAR␣ expression. Luciferase reporter and chromatin immunoprecipitation analyses using primary hepatocytes demonstrated that DNA binding of both PPAR␣ and CLOCK is essential for bezafibrate-induced PAI-1 gene expression. Pull-down assays in vitro showed that both PPAR␣ and its heterodimerized partner retinoic acid receptor-␣ can serve as potential interaction targets of CLOCK. The present findings revealed that molecular interaction between the circadian clock and the lipid metabolism regulator affects the bezafibrate-induced gene expression.

SummaryPlasminogen activator inhibitor-1 (PAI-1), a member of the ser-pin gene family, is the primary inhibitor of urokinase-type and tissue-type PA s.PA I-1 plays an important role in the process of peripheral tissue remodeling and fibrinolysis through the regulation of PA activity. This serpin is also produced in brain tissues and may regulate the neural protease sequence in the central nervous system (CNS), as it does in peripheral tissues. In fact, PA I-1 mRNA is up-regulated in mouse brain after stroke.The serpin activity of PA I-1 helps to prevent tissue-type PA -induced neuron death.However, we have previously found that PAI-1 has a novel biological function in the CNS: the contribution to survival of neurites on neurons. In neuronally differentiated rat pheochromocytoma (PC-12) cells, a deficiency of PA I-1 in vitro caused a significant reduction in Bcl-2 and Bcl-XL mRNAs and an increase in Bcl-XS and Bax mRNAs.The change in the balance between mRNA expressions of the anti- and pro-apoptotic Bcl-2 family proteins promoted the apoptotic sequence: cas-pase-3 activation, cytochrome c release from mitochondria and DNA fragmentation. Our results indicate that PA I-1 has an antiapoptotic role in neurons.PAI-1 prevented the disintegration of the formed neuronal networks by maintaining or promoting neuroprotective signaling through the MAPK/ ERK pathway, suggesting that the neuroprotective effect of PAI-1 is independent of its action as a protease inhibitor. This review discusses the neuroprotective effects of PA I-1 in vitro, together with the relevant data from other laboratories. Special emphasis is placed on its action on PC-12 cells.

3684 Poster Board III-620 Adult T-cell leukemia-lymphoma (ATL) is an aggressive peripheral T-cell neoplasm with a poor prognosis developing after long-term infection with human T-cell leukemia virus-1 (HTLV-1). HTLV-1 Tax is closely related to leukemic cell proliferation through nuclear factor-kappa B (NF-ƒÈB) activation. Recent studies have demonstrated that histone deacetylase class I/II inhibitors induce growth arrest and apoptosis of HTLV-1-infected T-cells via blockade of NF-ƒÈB signaling. SIRT1, an NAD(+)-dependent class III histone deacetylase, is widely recognized for its link to caloric restriction and longevity. SIRT1 plays a crucial role in a variety of physiological processes including metabolism, neurogenesis, cell survival, apoptosis and aging due to its ability to deacetylate numerous substrates such as histone, p53 and NF-ƒÈB. Existing reports on the role of SIRT1 in oncogenesis are controversial, with some evidence of an oncogenic role due to its increased expression in prostate cancer, acute myeloid leukemia and colon cancer, possibly mediated by inactivation of proteins involved in tumor suppression and DNA damage repair. Contrasting evidence of reduced SIRT1 expression in breast and hepatocellular carcinomas may support a tumor suppressor role, especially if the tumor is related to a p53 mutation. Such conflicting reports raise intriguing questions regarding its role in oncogenesis, and even less is known about its role in ATL in particular. We therefore set out to assess the expression of SIRT1 and the effect of its inhibition in HTLV-1 infected cell lines and ATL cells from patients. We observed SIRT1 protein and mRNA expression in ATL patient cells, an HTLV-1-infected cell line (MT-2), an ATL cell line (S1T), as well as HTLV-1 unrelated cell lines, Jurkat and HL60, as controls. SIRT1 expression in ATL patients was significantly higher than asymptomatic HTLV-1-carriers and healthy donors. The SIRT1 inhibitor, sirtinol, inhibited growth of all cell lines tested, with greater selectivity for HTLV-1 related cell lines (Figure 1) and ATL patients. Sirtinol induced apoptosis by activation of caspase-3, 8, 9 (Figure 2) and reducing IkBa phosphorylation, but did not significantly increase p53 acetylation in HTLV-1 infected cell lines. SIRT1 activation by NAD+ augmented apoptosis induction by sirtinol in MT-2 cells. These findings suggest that SIRT1 may be involved in T-cell immortalization by HTLV-1 and may be a crucial anti-apoptotic molecule in ATL cells. SIRT1 inhibition could therefore be useful in treating ATL. Figure 1 Inhibitory effects of sirtinol, SIRT1 inhibitor, on cell viability of leukemic cell lines. Cell lines were treated with sirtinol (0, 0.1, 10, 25 and 50μM) for 24hr. Each bar represents the mean ±S.D. of 3 independent experiments. Figure 1. Inhibitory effects of sirtinol, SIRT1 inhibitor, on cell viability of leukemic cell lines. Cell lines were treated with sirtinol (0, 0.1, 10, 25 and 50μM) for 24hr. Each bar represents the mean ±S.D. of 3 independent experiments. Figure 2 The activities of caspase-3, 8 and 9 in S1T and MT-2. Cell lines were treated with sirtinol (50μM) for 6 hr. Each bar represents the mean ±S.D. of 3 independent experiments. Figure 2. The activities of caspase-3, 8 and 9 in S1T and MT-2. Cell lines were treated with sirtinol (50μM) for 6 hr. Each bar represents the mean ±S.D. of 3 independent experiments. Disclosures: No relevant conflicts of interest to declare.