Effect of behavioral interventions on insulin sensitivity and atherosclerosis in the Watanabe heritable hyperlipidemic rabbit

The influence of social environment on endocrine, cardiovascular and tissue responses in the rabbit

Previous work from our lab demonstrated that social environment influences the progression of atherosclerosis in genetically hyperlipidemic rabbits. The purpose of the current study was to examine behavioral and physiological responses associated with these distinct chronic social conditions. Normolipidemic rabbits were exposed to one of three social environments for 4 hours/day over 20 weeks: 1) an Unstable Group in which animals were paired weekly with a different unfamiliar rabbit, 2) a Stable Group in which rabbits were paired with the same littermate for the entire study, and 3) an Individually Caged Group in which animals were socially isolated. It was found that the Unstable Group, characterized by increased agonistic behavior and relatively less affiliative behavior, exhibited physiological responses indicative of chronic stress (increased urinary norepinephrine, plasma cortisol, splenic weight, and decreased visceral fat and body weight compared to the other groups). These animals also had increased acute plasma oxytocin responses relative to the other groups 10 minutes into the social pairing. In contrast, the Stable Group exhibited more affiliative behavior and less stressful physiological and tissue responses. The Individually Caged Group had elevated urinary norepinephrine relative to the Stable Group, and they exhibited higher heart rates at the end of the study compared to the other groups, suggesting that this social environment is also associated with chronic sympathetic arousal. It was concluded that distinct social contexts lead to different patterns of behavioral and physiological responses, and these responses are relevant to the pathophysiology of atherosclerosis and cardiovascular disease.

Prolonged activation of S6K1 does not suppress IRS or PI-3 kinase signaling during muscle cell differentiation

BACKGROUND

Myogenesis in C2C12 cells requires the activation of the PI3K/mTOR signaling pathways. Since mTOR signaling can feedback through S6K1 to inhibit the activation of PI3K, the aim of this work was to assess whether feedback from S6K1 played a role in myogenesis and determine whether siRNA mediated knockdown of S6K1 would lead to an increased rate of myotube formation.

RESULTS

S6K1 activity increased in a linear fashion following plating and was more than 3-fold higher after Day 3 of differentiation (subconfluent = 11.09 +/- 3.05, Day 3 = 29.34 +/- 3.58). IRS-1 levels tended to increase upon serum withdrawal but decreased approximately 2-fold (subconfluent = 0.88 +/- 0.10, Day 3 = 0.42 +/- 0.06) 3 days following differentiation whereas IRS-2 protein remained stable. IRS-1 associated p85 was significantly reduced upon serum withdrawal (subconfluent = 0.86 +/- 0.07, Day 0 = 0.31 +/- 0.05), remaining low through day 1. IRS-2 associated p85 decreased following serum withdrawal (subconfluent = 0.96 +/- 0.05, Day 1 = 0.56 +/- 0.08) and remained suppressed up to Day 3 following differentiation (0.56 +/- 0.05). Phospho-tyrosine associated p85 increased significantly from subconfluent to Day 0 and remained elevated throughout differentiation. siRNA directed against S6K1 and S6K2 did not result in changes in IRS-1 levels after either 48 or 96 hrs. Furthermore, neither 48 nor 96 hrs of S6K1 knockdown caused a change in myotube formation.

CONCLUSIONS

Even though S6K1 activity increases throughout muscle cell differentiation and IRS-1 levels decrease over this period, siRNA suggests that S6K1 is not mediating the decrease in IRS-1. The decrease in IRS-1/2 associated p85 together with the increase in phospho-tyrosine associated p85 suggests that PI3K associates primarily with scaffolds other than IRS-1/2 during muscle cell differentiation.

The effect of social environment on markers of vascular oxidative stress and inflammation in the Watanabe heritable hyperlipidemic rabbit

OBJECTIVE

Previous research demonstrated that social environment can influence progression of atherosclerosis in the Watanabe Heritable Hyperlipidemic (WHHL) rabbit. This study examined the effect of social environment on markers of oxidative stress and inflammation to clarify the physiological pathways potentially responsible for the influence of social environment on disease.

METHODS AND RESULTS

WHHL rabbits were assigned to 1 of 3 social groups: an unstable group, in which unfamiliar rabbits were paired daily, with the pairing switched each week; a stable group, in which littermates were paired daily; and an individually-caged group. The stable group engaged in more affiliative social behavior than the unstable group. The unstable group showed more agonistic behavior compared with the stable group and higher C-reactive protein levels than the individually caged group. The individually caged group was behaviorally sedentary, had higher 24-hour urinary catecholamine levels than the other groups, and exhibited higher NAD(P)H-oxidase activity in the aortic arch relative to the stable group.

CONCLUSIONS

The results suggest that social environment creates distinct behavioral contexts that can affect markers of inflammation and oxidative stress early in the development of atherosclerosis. Specifically, physical inactivity associated with individual caging affects indices of oxidative stress and inflammation. These pathophysiological markers may help to explain behaviorally related differences in the extent of atherosclerosis observed in prior studies.

Type 2 Diabetes--An Introduction to the Development and Use of Animal Models

Although the epidemiology of type 2 diabetes (T2D) has been well described, there is much about the disease that remains unclear. For example, lifestyle factors-including increased body weight with visceral fat deposition and insufficient physical activity-are thought to be primary contributors to the adverse changes in the metabolism of muscle and fat cells that comprise the first stage of the disease. However, the precise mechanisms underlying these initial alterations are incompletely understood. Other, less obvious questions relate to the presence of sex differences in the development and health consequences of T2D, the etiological role of the central nervous system ("stress"), and the potential evolutionary origins of T2D susceptibility. Some of these issues can be resolved by further study of human populations. However, many questions can be answered only through the kinds of controlled prospective studies that are conducted with appropriate animal models. The use of such models can be an invaluable part of an overall strategy designed to elucidate the mechanisms underlying the development of T2D, understand the natural history of the disease, identify targets for therapy, and evaluate interventions. Current evidence indicates that no single animal model replicates the development of human T2D in all of its details. Nonetheless, the existing models (e.g., naturally occurring and genetically modified rodents, cats, pigs, and nonhuman primates) offer researchers a rich array of opportunities to investigate the myriad complexities of T2D. The individual contributions comprising this issue of ILAR Journal review the research that has been conducted on many of these animals.