Aisling C. McMahon

The Ratio of Macronutrients, Not Caloric Intake, Dictates Cardiometabolic Health, Aging, and Longevity in Ad Libitum-Fed Mice

The fundamental questions of what represents a macronutritionally balanced diet and how this maintains health and longevity remain unanswered. Here, the Geometric Framework, a state-space nutritional modeling method, was used to measure interactive effects of dietary energy, protein, fat, and carbohydrate on food intake, cardiometabolic phenotype, and longevity in mice fed one of 25 diets ad libitum. Food intake was regulated primarily by protein and carbohydrate content. Longevity and health were optimized when protein was replaced with carbohydrate to limit compensatory feeding for protein and suppress protein intake. These consequences are associated with hepatic mammalian target of rapamycin (mTOR) activation and mitochondrial function and, in turn, related to circulating branched-chain amino acids and glucose. Calorie restriction achieved by high-protein diets or dietary dilution had no beneficial effects on lifespan. The results suggest that longevity can be extended in ad libitum-fed animals by manipulating the ratio of macronutrients to inhibit mTOR activation.

Macronutrient balance, reproductive function, and lifespan in aging mice

Significance A fundamental tenet of life-history theory is that reproduction and longevity trade off against one another. Experiments on invertebrates show that, rather than competing for limiting resources, reproduction and lifespan are optimized on different dietary macronutrient compositions. In mice, studies have yet to establish the relationship between macronutrient balance, reproduction, and lifespan. We evaluated the effects of macronutrients and energy on lifespan and reproductive function. Indicators of reproductive function (uterine mass, ovarian follicle number, testes mass, epididymal sperm counts) were optimized by high protein (P), low carbohydrate (C) diets whereas lifespan was greatest on low P:C diets. Corpora lutea and estrous cycling were higher in females on lower P:C diets. Macronutrient balance has profound and opposing effects on reproduction and longevity. In invertebrates, reproductive output and lifespan are profoundly impacted by dietary macronutrient balance, with these traits achieving their maxima on different diet compositions, giving the appearance of a resource-based tradeoff between reproduction and longevity. For the first time in a mammal, to our knowledge, we evaluate the effects of dietary protein (P), carbohydrate (C), fat (F), and energy (E) on lifespan and reproductive function in aging male and female mice. We show that, as in invertebrates, the balance of macronutrients has marked and largely opposing effects on reproductive and longevity outcomes. Mice were provided ad libitum access to one of 25 diets differing in P, C, F, and E content, with reproductive outcomes assessed at 15 months. An optimal balance of macronutrients exists for reproductive function, which, for most measures, differs from the diets that optimize lifespan, and this response differs with sex. Maximal longevity was achieved on diets containing a P:C ratio of 1:13 in males and 1:11 for females. Diets that optimized testes mass and epididymal sperm counts (indicators of gamete production) contained a higher P:C ratio (1:1) than those that maximized lifespan. In females, uterine mass (an indicator of estrogenic activity) was also greatest on high P:C diets (1:1) whereas ovarian follicle number was greatest on P:C 3:1 associated with high-F intakes. By contrast, estrous cycling was more likely in mice on lower P:C (1:8), and the number of corpora lutea, indicative of recent ovulations, was greatest on P:C similar to those supporting greatest longevity (1:11).

Subfertile Female Androgen Receptor Knockout Mice Exhibit Defects in Neuroendocrine Signaling, Intraovarian Function, and Uterine Development But Not Uterine Function

Female androgen receptor (AR) knockout mice (AR(-/-)) generated by an in-frame Ar exon 3 deletion are subfertile, but the mechanism is not clearly defined. To distinguish between extra- and intraovarian defects, reciprocal ovarian transplants were undertaken. Ovariectomized AR(-/-) hosts with wild-type (AR(+/+)) ovary transplants displayed abnormal estrus cycles, with longer cycles (50%, P < 0.05), and 66% were infertile (P < 0.05), whereas AR(+/+) hosts with either AR(-/-) or surgical control AR(+/+) ovary transplants displayed normal estrus cycles and fertility. These data imply a neuroendocrine defect, which is further supported by increased FSH (P <0.05) and estradiol (P <0.05), and greater LH suppressibility by estradiol in AR(-/-) females at estrus (P <0.05). Additional intraovarian defects were observed by the finding that both experimental transplant groups exhibited significantly reduced pups per litter (P < 0.05) and corpora lutea numbers (P < 0.05) compared with surgical controls. All groups exhibited normal uterine and lactation functions. AR(-/-) uteri were morphologically different from AR(+/+) with an increase in horn length (P < 0.01) but a reduction in uterine diameter (P < 0.05), total uterine area (P < 0.05), endometrial area (P < 0.05), and myometrial area (P < 0.01) at diestrus, indicating a role for AR in uterine growth and development. Both experimental transplant groups displayed a significant reduction in uterine diameter (P < 0.01) compared with transplanted wild-type controls, indicating a role for both AR-mediated intraovarian and intrauterine influences on uterine physiology. In conclusion, these data provide direct evidence that extraovarian neuroendocrine, but not uterine effects, as well as local intraovarian AR-mediated actions are important in maintaining female fertility, and a disruption of AR signaling leads to altered uterine development.

Characterization of Reproductive, Metabolic, and Endocrine Features of Polycystic Ovary Syndrome in Female Hyperandrogenic Mouse Models

Polycystic ovary syndrome (PCOS) affects 5-10% of women of reproductive age, causing a range of reproductive, metabolic and endocrine defects including anovulation, infertility, hyperandrogenism, obesity, hyperinsulinism, and an increased risk of type 2 diabetes and cardiovascular disease. Hyperandrogenism is the most consistent feature of PCOS, but its etiology remains unknown, and ethical and logistic constraints limit definitive experimentation in humans to determine mechanisms involved. In this study, we provide the first comprehensive characterization of reproductive, endocrine, and metabolic PCOS traits in 4 distinct murine models of hyperandrogenism, comprising prenatal dihydrotestosterone (DHT, potent nonaromatizable androgen) treatment during days 16-18 of gestation, or long-term treatment (90 days from 21 days of age) with DHT, dehydroepiandrosterone (DHEA), or letrozole (aromatase inhibitor). Prenatal DHT-treated mature mice exhibited irregular estrous cycles, oligo-ovulation, reduced preantral follicle health, hepatic steatosis, and adipocyte hypertrophy, but lacked overall changes in body-fat composition. Long-term DHT treatment induced polycystic ovaries displaying unhealthy antral follicles (degenerate oocyte and/or > 10% pyknotic granulosa cells), as well as anovulation and acyclicity in mature (16-week-old) females. Long-term DHT also increased body and fat pad weights and induced adipocyte hypertrophy and hypercholesterolemia. Long-term letrozole-treated mice exhibited absent or irregular cycles, oligo-ovulation, polycystic ovaries containing hemorrhagic cysts atypical of PCOS, and displayed no metabolic features of PCOS. Long-term dehydroepiandrosterone treatment produced no PCOS features in mature mice. Our findings reveal that long-term DHT treatment replicated a breadth of ovarian, endocrine, and metabolic features of human PCOS and provides the best mouse model for experimental studies of PCOS pathogenesis.

Dietary Protein to Carbohydrate Ratio and Caloric Restriction: Comparing Metabolic Outcomes in Mice

Both caloric restriction (CR) and low-protein, high-carbohydrate (LPHC) ad-libitum-fed diets increase lifespan and improve metabolic parameters such as insulin, glucose, and blood lipids. Severe CR, however, is unsustainable for most people; therefore, it is important to determine whether manipulating macronutrient ratios in ad-libitum-fed conditions can generate similar health outcomes. We present the results of a short-term (8 week) dietary manipulation on metabolic outcomes in mice. We compared three diets varying in protein to carbohydrate ratio under both CR and ad libitum conditions. Ad libitum LPHC diets delivered similar benefits to CR in terms of levels of insulin, glucose, lipids, and HOMA, despite increased energy intake. CR on LPHC diets did not provide additional benefits relative to ad libitum LPHC. We show that LPHC diets under ad-libitum-fed conditions generate the metabolic benefits of CR without a 40% reduction in total caloric intake.

Defining the Nutritional and Metabolic Context of FGF21 Using the Geometric Framework

Fibroblast growth factor 21 (FGF21) is the first known endocrine signal activated by protein restriction. Although FGF21 is robustly elevated in low-protein environments, increased FGF21 is also seen in various other contexts such as fasting, overfeeding, ketogenic diets, and high-carbohydrate diets, leaving its nutritional context and physiological role unresolved and controversial. Here, we use the Geometric Framework, a nutritional modeling platform, to help reconcile these apparently conflicting findings in mice confined to one of 25 diets that varied in protein, carbohydrate, and fat content. We show that FGF21 was elevated under low protein intakes and maximally when low protein was coupled with high carbohydrate intakes. Our results explain how elevation of FGF21 occurs both under starvation and hyperphagia, and show that the metabolic outcomes associated with elevated FGF21 depend on the nutritional context, differing according to whether the animal is in a state of under- or overfeeding.

Rat models of myocardial infarction - Pathogenetic insights and clinical relevance

Animal models of cardiovascular pathology contribute towards understanding and treatment of a broad range of conditions. Specifically in the context of acute myocardial infarction (AMI), rat models have been commonly used in studies of pathogenesis, investigation and novel therapies, although there has often been difficulty in translating experimental findings to clinical benefit. However, recent years have seen two important changes to our clinical approaches to AMI. First, there is increasing recognition that the pathophysiology of human AMI is a process occurring at many levels, not just within the epicardial coronary artery, but also within the microvasculature and the myocardium. Second, contemporary treatments are shifting away from thrombolytic dissolution of epicardial coronary thrombus to direct mechanical approaches using angioplasty and stents. These changes in our understanding of AMI have implications for the relevance of these animal models. The following discussion therefore reviews and examines the current rat models of AMI, places them in a clinical context, discusses their advantages and limitations, and outlines likely future developments, providing an overview of the place of these important models of AMI.

Effects of dietary protein to carbohydrate balance on energy intake, fat storage, and heat production in mice.

Protein leverage plays a role in driving increased energy intakes that may promote weight gain. The influence of the protein to carbohydrate ratio (P:C) in diets of C57BL/6J mice on total energy intake, fat storage, and thermogenesis was investigated.

The response of fenestrations, actin, and caveolin-1 to vascular endothelial growth factor in SK Hep1 cells

To study the regulation of fenestrations by vascular endothelial growth factor in liver sinusoidal endothelial cells, SK Hep1 cells were transfected with green fluorescence protein (GFP)-actin and GFP-caveolin-1. SK Hep1 cells had pores; some of which appeared to be fenestrations (diameter 55 +/- 28 nm, porosity 2.0 +/- 1.4%), rudimentary sieve plates, bristle-coated micropinocytotic vesicles and expressed caveolin-1, von Willebrand factor, vascular endothelial growth factor receptor-2, endothelial nitric oxide synthase and clathrin, but not CD31. There was avid uptake of formaldehyde serum albumin, consistent with endocytosis. Vascular endothelial growth factor caused an increase in porosity to 4.8 +/- 2.6% (P < 0.01) and pore diameter to 104 +/- 59 nm (P < 0.001). GFP-actin was expressed throughout the cells, whereas GFP-caveolin-1 had a punctate appearance; both responded to vascular endothelial growth factor by contraction toward the nucleus over hours in parallel with the formation of fenestrations. SK Hep1 cells resemble liver sinusoidal endothelial cells, and the vascular endothelial growth factor-induced formation of fenestration-like pores is preceded by contraction of actin cytoskeleton and attached caveolin-1 toward the nucleus.

ICAM-1 in Acute Myocardial Infarction: A Potential Therapeutic Target

Current treatments for AMI centre on prompt restoration of epicardial coronary blood flow. Despite improvements, AMI is still associated with significant morbidity and mortality. Novel approaches are therefore keenly sought. Intercellular adhesion molecule-1 (ICAM-1, CD54) is a member of the immunoglobulin superfamily. It is implicated in neutrophil and monocyte-endothelial cell adhesion, processes contributing to myocardial neutrophil infiltration and microvascular coronary slow flow, both viewed as important to the pathophysiologic responses in AMI. ICAM-1 would therefore appear an important potential therapeutic target in this context, and is the subject of this review.