Downregulation of plasma insulin levels and hepatic PPARγ expression during the first week of caloric restriction in mice
Introduction
In all species studied to date, restricting caloric intake by 20–50% while still providing adequate micronutrients significantly extends mean and maximal lifespan, largely by retarding age-associated diseases, most importantly cancer (Weindruch, 1996, Weindruch et al., 1986). Not surprisingly there is intense interest in elucidating the molecular basis for the anti-aging and anti-cancer effects of calorie restriction (Ingram et al., 2006, Wolf, 2006). We have reported that 16 weeks of calorie restriction decreases protein levels in the liver of acetyl CoA carboxylase (ACC), the rate-limiting enzyme in fatty acid biosynthesis, to approximately 25% of baseline (Gonzalez et al., 2004). This observation is significant in that fatty acid biosynthesis appears to be closely linked to the timing and extent of tumor development, most notably in a subset of aggressive malignancies requiring a high rate of lipogenesis for growth (De Schrijver et al., 2003, Kuhajda, 2000, Menendez et al., 2005, Pizer et al., 1998). In fact, specific inhibition of fatty acid synthase (FAS) and lipogenesis have been used successfully to inhibit growth of malignancies (De Schrijver et al., 2003, Pizer et al., 1998). Thus calorie restriction-induced downregulation of ACC protein in the liver could be part of a general inhibition of fatty acid biosynthesis contributing to the observed decrease in spontaneous and induced tumor development in calorie restricted animals (Fu et al., 1994, Yoshida et al., 1999). Interestingly, the transcription factors PPARγ and SREBP-1c which regulate ACC and FAS expression have additional effects on processes central to aging such as cell cycling, apoptosis and inflammation (De Schrijver et al., 2003, Ettinger et al., 2004, Gonzalez et al., 2004, Kirkland et al., 2002, Picard and Guarente, 2005, Rossi et al., 2003, Semple et al., 2006). Thus any calorie restriction-induced downregulation of PPARγ, SREBP-1c, or other factors that influence fatty acid biosynthesis (i.e. insulin) could have collateral effects contributing to the anti-aging and anti-tumor phenotype of these animals.
Accordingly, our goal was to define how a calorie restricted diet affects the following regulators of fatty acid biosynthesis gene expression: PPARγ, SREBP-1c, SIRT1 and plasma insulin levels. Importantly, the caloric restriction phenotype of retarded aging and tumor development is evident within 8 weeks after initiating calorie restriction, with half of the eventual changes in hepatic gene expression already detectible at 2 weeks (Dhahbi et al., 2004). Thus the critical molecular events triggering this phenotype must occur within the first several weeks after initiating the restricted diet. Therefore, we focused on defining the early time course of caloric restriction’s effects. To accomplish this, blood, liver and adipose tissue (subcutaneous and abdominal) were collected from 6-month-old C57Bl/6 mice that had undergone 0, 1, 4 or 16 weeks of calorie restriction (60% of ad libitum calories). We focused on liver because, while the main cause of neoplastic death of aging C57bl/6 mice is lymphoma not liver cancer, CR almost eliminates the incidence of liver tumors in this strain of mice whereas it has little effect on the rate of death due to lymphoma (Blackwell et al., 1995). For comparison to liver, another highly lipogenic tissue, white adipose tissue, was chosen, which itself has been suggested to play a key role in the calorie restriction phenotype (Wolf, 2006). Adipose tissue from two distinct anatomical sites was studied so that we could test the hypothesis that abdominal (epididymal) adipose tissue, which is more closely linked to pathology than subcutaneous adipose tissue, is resistant to calorie restriction-induced changes in gene expression (Lafontan and Berlan, 2003).
Section snippets
Animals
Mice (N = 36 C57Bl/6 males) were housed singly in the specific pathogen-free Shared Aging Rodent Facility at the Madison VA Geriatric Research, Education and Clinical Center, and provided a nonpurified diet (PLI 5001 [Purina Labs, St. Louis, MO]) and acidified water ad libitum for 3 weeks following weaning. From this time until 2 months of age, all 36 mice received 12 kcal/day of a semipurified diet (TD91349 [Teklad, Madison, WI]), which is ∼10% less than the average ad libitum intake. The
Results
Plasma values for glucose, insulin and IGF-1 measured at the time of sacrifice are shown in Fig. 2. Calorie restriction did not significantly affect plasma IGF-1 concentration at any of the time points. In contrast, plasma insulin levels were significantly lowered during the first week of calorie restriction, and this low level of insulin sustained at 4 and 16 weeks of calorie restriction. This fall in insulin occurred in parallel with a decline in glucose levels which became statistically
Liver
Calorie restriction extends maximal lifespan in animals largely by decreasing the rate of tumor formation (Dhahbi et al., 2004, Weindruch, 1996, Weindruch et al., 1986). In the liver, caloric restriction dramatically lowers the incidence of both spontaneously occurring tumors as well as tumors induced by a carcinogenic agent (Fu et al., 1994, Yoshida et al., 1999). These protective effects occur within the first few weeks of initiating a calorie restricted diet (Dhahbi et al., 2004). Our
Acknowledgements
The authors thank Dr. Richard Weindruch for his invaluable assistance in conducting this study. This work was supported by National Institute on Aging Grant AG-00908, National Heart Lung and Blood Institute Grant HL-07936 and a grant from the UW Comprehensive Cancer Center.
References (34)
- et al.
Metabolism
(1995) - et al.
J. Nutr.
(2001) - et al.
Exp. Gerontol.
(2002) Nutrition
(2000)- et al.
Trends Pharmacol. Sci.
(2003) - et al.
J. Biol. Chem.
(2002) - et al.
J. Nutr.
(1986) - et al.
Horm. Metab. Res.
(2005) - et al.
Carcinogenesis
(2002) - et al.
Toxicol. Pathol.
(1995)
J. Gerontol.
Science
Obes. Rev.
Cancer Res.
Proc. Natl. Acad. Sci. USA
Cancer Res.
Carcinogenesis
Cited by (26)
Grape pomace reduces the severity of non-alcoholic hepatic steatosis and the development of steatohepatitis by improving insulin sensitivity and reducing ectopic fat deposition in mice
2021, Journal of Nutritional BiochemistryCitation Excerpt :The central roles PPARγ and lipogenic enzymes play in hepatic steatosis were demonstrated before, showing that PPARγ knockdown inhibited the expression of lipogenic enzymes and reduced HFD-induced hepatic steatosis [62,63]. In line with our data, caloric-restricted mice had an improved insulin sensitivity and reduced Pparγ, Fasn and Acaca1 expression in the liver, while the expression of lipogenic genes was preserved in adipose tissue [64]. Thus, our observations are consistent with the primary role of insulin sensitizing interventions in the treatment of hepatic steatosis.
Feed restriction alters lipogenic and adipokine gene expression in visceral and subcutaneous fat depots in lamb
2016, Livestock ScienceCitation Excerpt :The FR group plasma triglycerides, glucose and insulin levels decreased (P<0.05) after 30 d of restriction; however no significant differences were found between 30 d and 60 d. The decreased plasma triglycerides, glucose, and insulin concentration during FR has also been found in ewes and mice (Mulligan et al., 2008; Sejian et al., 2014). There were no differences in plasma cholesterol level between the FR and CON groups throughout the experiment.
The role of SIRT1 in ocular aging
2013, Experimental Eye ResearchCitation Excerpt :Sir2 shows a high level of evolutionary conservation and is an important regulator of senescence (Langley et al., 2002; van der Veer et al., 2007), cell differentiation (Takata and Ishikawa, 2003; Blander and Guarente, 2004; Anastasiou and Krek, 2006; Prozorovski et al., 2008; Wojcik et al., 2009), stress tolerance (Blander and Guarente, 2004; Anastasiou and Krek, 2006; Wojcik et al., 2009), metabolism (Blander and Guarente, 2004; Anastasiou and Krek, 2006; Wojcik et al., 2009), and cancer (Pruitt et al., 2006; Oberdoerffer et al., 2008; Han et al., 2013). Sirtuins have been suggested to have a role in aging (Gotta et al., 1997; Guarente and Kenyon, 2000), calorie restriction (Cohen et al., 2004; Nemoto et al., 2004; Rodgers et al., 2005; Nisoli et al., 2005; Corton and Brown-Borg, 2005; Civitarese et al., 2007; Milne et al., 2007; Bordone et al., 2007; Mulligan et al., 2008; Coppari et al., 2009; Satoh et al., 2010; Baur et al., 2010; Qiu et al., 2010; Gesing et al., 2011; Takemori et al., 2011; Radak et al., 2013), and inflammation (Yeung et al., 2004; Qiu et al., 2010), and apoptosis (Bhattacharya et al., 2012; Liu et al., 2012). Overexpression of Sir2 prolongs the lifespan of various organisms, whereas deletion or mutations of Sir2 leads to a shorter lifespan (Kaeberlein et al., 1999; Tissenbaum and Guarente, 2001; Rogina and Helfand, 2004).
Metabolic master regulators: Sharing information among multiple systems
2012, Trends in Endocrinology and MetabolismCitation Excerpt :A change in redox will influence different organs in important ways, either directly through ROS production, or indirectly by modifying proteins or lipids. Well-established targets of ROS and redox include transcriptional regulators, such as sirtuins, SREBPs, PPARs, and many others, that in turn regulate long-term translational components including hormones, metabolic enzymes, and adipokines [78]. This is conceptually a highly refined system that assures that after ingestion of a meal, all the metabolically important organs in the body respond appropriately in the short term: β cells secrete insulin, liver stores glucose, adipose tissue increases fat storage, and the brain signals satiety; as well as in the long term: insulin is synthesized, and adaptive metabolic enzymes are induced.
Commonly adopted caloric restriction protocols often involve malnutrition
2010, Ageing Research ReviewsThe impact of acute caloric restriction on the metabolic phenotype in male C57BL/6 and DBA/2 mice
2010, Mechanisms of Ageing and Development