FoxO1 signaling plays a pivotal role in the cardia

Authors: N Makino J Oyama T Maeda M Koyanagi Y Higuchi I Shimokawa N Mori T Furuyama

Publish Date: 2015/12/26

Volume: 412, Issue: 1-2, Pages: 119-130

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Abstract

This study examined whether the forkhead transcription factors of O group 1 FoxO1 might be involved in telomere biology during calorie restriction CR We used FoxO1knockout heterozygous mice FoxO1+/− and wildtype mice WT as a control Both WT and FoxO1+/− were subjected to ad libitum AL feeding or 30  CR compared to AL for 20 weeks from 15 weeks of age The hearttobody weight ratio blood glucose and serum lipid profiles were not different among all groups of mice at the end of the study Telomere size was significantly lower in the FoxO1+/−AL than the WTAL and telomere attrition was not observed in either WTCR or FoxO1+/−CR Telomerase activity was elevated in the heart and liver of WTCR but not in those of FoxO1+/−CR The phosphorylation of Akt was inhibited and Sirt 1 was activated in heart tissues of WTCR and FoxO1+/−CR However the ratio of conjugated to cytosolic light chain 3 increased and the level of p62 decreased in WTCR but not in FoxO1+/−CR A marker of oxidative DNA damage 8OhdG was significantly lower in WTCR only The level of MnSOD and eNOS increased and the level of cleaved caspase3 decreased in WTCR but not FoxO1+/−CR Echocardiography showed that the left ventricular enddiastolic and systolic dimensions were significantly lower in WTCR or FoxO1+/−CR than WTAL or FoxO1+/−AL respectively The present studies suggest that FoxO1 plays beneficial roles by inducing genes involved in telomerase activity as well as antioxidant autophagic and antiapoptotic genes under conditions of CR and suggest that FoxO1 signaling may be an important mediator of metabolic equilibrium during CRBoth clinical and experimental studies have shown that calorie restriction CR is capable of extending life span and lowering the onset of chronic diseases as well as overall disease morbidity and mortality 1 2 CR has been shown to exert some profound cardiovascular effects such as lowering blood pressure 3 decreasing systemic inflammation 4 and improving cardiac diastolic parameters 5 The exact mechanisms by which CR exerts these cardiovascular effects remain largely elusive although the most prevalent theory points to a significant protection from DNA damage due to a reduction of metabolism 6 7Understanding the mechanisms underlying caloric restriction is of great importance as this could pinpoint new therapeutic targets for ageassociated diseases or for antiaging therapies In this regard the welldocumented association between telomere shortening and aging 8 suggests a possible role of telomere dynamics in the systemic effects of caloric restriction The length of leukocyte telomeres is inversely related to the body mass index and insulin resistance 9 and shortened leukocyte telomeres are associated with various agerelated diseases such as atherosclerosis 10 Although emerging evidence indicates that both the telomeres and telomerase activity control key cellular functions including replicative lifespan cell differentiation and cell proliferation the molecular basis of these effects and their relations to the presumed cardiac signals for the forkhead transcription factors of O group FOXO remain unknownStudies on the mechanisms of caloric restrictionrelated longevity in budding yeast have identified the silent information regulator 2 Sir2 as a survival factor that prolongs lifespan 11 12 Sirt1 a mammalian homolog of Sir2 was originally identified as an NADdependent histone deacetylase 13 Recent studies have shown that Sirt1 is involved in the regulation of a wide variety of cellular processes ranging from stress response cell cycle metabolism and apoptosis in response to the cellular energy and redox status through its deacetylase activity 14 The forkhead transcription factors of the O group FoxO are among the welldocumented targets of Sirt1 in cardiomyocytes One member of this family FoxO1 plays important roles in systemic homeostasis among other biological functions 15 In mice the loss of FoxO1 is embryonically lethal whereas FoxO3 deletion results in normal birth but the offspring are prone to cardiac hypertrophy and eventual cardiac failure 16 FoxO1 is involved in regulating various cellular processes in different tissues including the oxidative stress response cell proliferation immune homeostasis pluripotency in embryonic stem cells cell death and metabolism 15 During the oxidative stress response FoxO1 is known to increase the expression of such antioxidant genes as superoxide dismutase thereby promoting reactiveoxygenspecies ROS scavenging activity preventing DNA damage and fundamentally safeguarding cells from damage 17 FoxO1 also plays an important role in celllongevity through its collaborative activity with Sirt1 which itself turns on the transcription of antioxidant genes such as MnSOD and catalase 17Autophagy is a selfdigestion process through which cells degrade their own components thereby redirecting amino acids fatty acids and carbohydrates to energy production or synthesis of essential cellular molecules 18 The autophagic mechanism for recycling the cellular building blocks plays an important role during CR In addition autophagy is induced during increased ROS generation Indeed it has been proposed that upregulation of autophagy is a major mechanism underlying the lifespanextending properties of CR 19To investigate the potential role of FoxO1 in the cardiac effects of caloric restriction FoxO1knockout heterozygous mice FoxO1+/− in which the level of Foxo1 mRNA was reduced by 50  or more 20 were used in the present study Both wildtype WT and FoxO1+/− mice were subjected to either 30  caloric restriction CR feeding with 70  of the control diet or ad libitum feeding AL for 20 weeks We assessed the telomere biology including the telomere length and telomerase activity and the essential signaling pathways responsible for cell survival including autophagy and cardiac geometry In this way we sought to clarify whether FoxO1 signaling is an important mediator of the maintenance of telomere biology in response to CRFoxO1 mRNA expressions and body weight changes in wildtype WT and FoxO1+/− mice fed ad libitum AL or subjected to calorie restriction CR Representative data for the mRNA expressions of FoxO1 in the heart and liver tissues are shown in A and summarized results are shown in B Body weight was measured in four experimental groups in C Values are the mean ± SE n = 6 animals in each group a p  005 versus WTAL at the same age b p  005 versus FoxO1+/−AL at the same ageEach mouse was individually housed until 8 weeks of age The average caloric intake was calculated from the daily food intake over 2 weeks At 12 weeks of age the WT group and the FoxO1+/− mice group were each randomly divided into two groups an ad libitum AL group and a CR group WTAL mice were fed AL until the end of study whereas the WTCR mice were subjected to restriction of the average AL caloric intake for 3 weeks 10  restriction for acclimation followed by a 30  caloric reduction from 15 to 35 weeks of age Fig 1B The CR diet was enriched in vitamins and minerals to ensure constant daily intake of those nutrients All mice were fed AL with a Charles RiverLPF diet Oriental Yeast Co Ltd Tsukuba Japan as a standard diet for longterm studies including studies of the CR regimens in mice Body weight was monitored every week from 15 to 35 weeks of age Insulin resistance was evaluated using the value of homeostasis model assessment of insulin resistance HOMAIR as a marker 21 22 HOMAIR was determined based on both plasma glucose and serum insulin levels At 35 weeks of age the mice were decapitated and the heart and liver tissues were collected for the following analyses These tissues were immediately frozen in liquid nitrogen and stored at −80 °C until assayed

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