Programação metabólica por superalimentação no início da vida, efeitos sobre o metabolismo e o tecido adiposo marrom : pode o exercício físico moderado ser um agente para desprogramação?

Abstract

The obesity epidemic is a priority concern, as its relationship with cardiovascular diseases and type 2 diabetes, is associated with mortality and with elevated costs for public health systems across the globe. Epidemiological data higlights the fact that the obesity epidemic is likely to increase in the near future, as younger cohorts present with, even increasing, high rates of early obesity onset and prevalence. Although there is a broadly understood adult etiology for obesity, substantial data from epidemiological and experimental studies indicate the role of the perinatal environment in promoting obesity and related metabolic syndrome. Postnatal early overfeeding, induced by maternal high fat consumption or by early exposure to overfeeding during the suckling period, lead mammals to demonstrate a precocious onset of obesity. Infants and childrens who are obese are highly susceptible to remain obese into adult life. In a previous study, our group demonstrated that postnatal early overfeeding resulted in rats becoming obese and presenting an impaired interscapular brown adipose tissue (iBAT) thermogenic function, producing less heat than the control animals both, during day and night-time periods. Brown adipose tissue (BAT) is present in adult humans and BAT thermogenesis increase energy expenditure through uncoupling-protein-1 (UCP1) activity, which disrupts the normal mitochondrial energy system, resulting in a lower production of ATP and diversion of energy as heat. Given the potential of BAT to impact upon energy balance, revert metabolic program and augment energy expenditure by BAT to reduce fat storage and counter obesity, is a desirable target. The regular practice of physical exercise is one physiological approach that results in increased BAT activity. Few studies have considered the important role of BAT on the energetic metabolism, as a mechanism to reverse the long-term programmed effects of the early overfeeding on animals. The possible effects of physical exercise upon metabolism and BAT in programmed animals have also received scant attention. In this thesis we investigated the effects of early overfeeding by maternal high fat consumption on the adipose tissue at early stages of life and tissue development, moreover, we tested the effectiveness of a moderate and lowfrequency exercise protocol on the thermogenesis function of iBAT of adult rats, which were metabolic programmed by early overnutrition. Manuscript 1: To investigate, at postnatal day 10, the morphology and gene expression in subcutaneous WAT and interscapular BAT from pups born to High Fat Fed (HFD) dams. Manuscript 2: To investigate the potential of a moderate and low-frequency exercise protocol to deprogram the function of iBAT in adult male rats made obese by exposre to overfeeding during lactation. Manuscript 1: Nine-week-old female Sprague Dawley rats were divided into 2 groups: control normal fat diet (NFD N=6), or high-fat diet (HFD N=10). Rats were kept on their respective diet for 4 weeks prior to conception, through gestation and after birth, until postnatal day 10 (PN10), when pups were weighed and euthanized. Adipose tissue was collected from subcutaneous and interscapular depots for histology and gene expression studies. Manuscript 2: Wistar rats litters were delivered normally but at PN2, litters were adjusted to 9 pups per dam (normal litters - NL) for control, or 3 pups (small litter SL) per dam to induce overfeeding during early life. At PN21, all offspring were weaned and randomly divided into exercise or sedentary groups (NL SED, NL EXE, SL SED, and SL EXE). An exercise protocol commenced at PN30. Animals were initially subjected to an effort test on a treadmill. Training sessions (45minutes) were then performed 3 times per week, at 60% of the final workload achieved in the effort test. The effort test was repeated each 15 days to adjust the training workload. At PN80, animals ceased training and at PN81, underwent surgery to implant a temperature transponder underneath interscapular BAT (iBAT). The iBAT temperature was measured during light and dark periods from PN87 to PN90. At PN91 animals were euthanized, blood samples and fat pads collected for further analysis. IBAT nerve activity was recorded from a separated set of (non operated) animals at PN90. Manuscript 1: Subcutaneous white adipose tissue (sWAT) adipocytes from HFD offspring were larger compared to controls (p<0.01). Although iBAT adipocytes did not change in size, the presence of unilocular adipocytes found within iBAT were larger in HFD pups than in NFD (p<0.05). Maternal HFD increased the expression of Leptin in sWAT (p<0.05). Reduced gene expression of LeptinR, PPAR gamma, PPAR alpha and PRDM16 were observed in iBAT of HFD offspring compared with control offspring (p<0.05). These morphological changes in WAT and BAT, points to the structural abnormalities within adipose tissue during they earliest days of postnatal life being programmed by early overnutrition. These findings are similar to those observed in the literature for adult rats that were metabolic programmed by early overnutrition, indicating that the obesity seen inadulthood may be, in fart, caused by abnormal development of these tissues. Moreover, the mRNA altered expression in BAT of transcriptor facts involved in differentiation and function of BAT, may underlie the lower thermogenesic capacity observed in adult animals. Manuscript 2: Early postnatal overfeed impaired iBAT activity during their inactive (lights-on) (p<0.0001) and inactive (lights-off) periods (p<0.01). Exercise improved iBAT function in the lights-on (p<0.0001), but not on lights-off (p=0.2236) perior. Exercise was associated with increased sympathetic iBAT nerve firing rate (p<0.05), while postnatal overfeeding was assoiated with a reduction in sympathetic nerve activity (p<0.0001) that did not respond to exercise training. In control animals, exercise resulted in a reduction of β3-AR content in iBAT (p<0.01), consistent with the increase nerve activity. Consistent with the nerve activity data, early overfeeding did not affect β3-AR content in iBAT (p=0.2172. We have presviously shown that postnatal early overfeeding induced iBAT thermogenesis hypoactivity, which was confirmed on this study. Additionally, this study shows that the exercise is able to improve the thermogenesis in lean and early obese programmed rats, which may indicate an elevation on the basal metabolical rate on these animals. Regular endurance exercise is shown to positively affect BAT in vitro differentiation and BAT activity in lean humans and control animals. This study is the first, of our knowledge, to show that a moderate intensity/low-frequency exercise protocol is a viable non-pharmacological method to deprogram the postnatal early overfeeding effects on BAT. Manuscript 1: Offspring of fat fed dams demonstrate altered morphology and gene expression in sWAT and iBAT during earliest stages of tissue development, which may have implications for long-lasting dysfunctional adipose tissue. Manuscript 2: A moderate intensity low frequency exercise protocol was able to deprogram postnatal early overfeeding effects in adult male rats, improving biometrical and metabolical parameters and reversing iBAT hypoactivity.