Association of adipose tisuue mediated genes in reproduction
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Adipose tissue is formed at stereotypic times and locations in a diverse array of organisms. Once formed, the tissue is dynamic, responding to homeostatic and external cues and capable of a 15-fold expansion. The formation and maintenance of adipose tissue is essential to many biological processes and when perturbed leads to significant diseases. Despite this basic and clinical significance, understanding of the developmental biology of adipose tissue has languished. In this Review, we highlight recent efforts to unveil adipose developmental cues, adipose stem cell biology and the regulators of adipose tissue homeostasis and dynamism.
Keywords: Adipose, Adipocyte, Development, Stem cells, Niche, Vascular niche
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Introduction: fat facts
Adipose tissue plays a myriad of roles; it serves as a central nexus of metabolic communication and control, an arbiter of thermoregulation, a buffer against trauma and the cold, and a regulator of reproduction and satiety. Fat is also associated with emotionally charged issues, imparting various psychosocial imprints that have changed over the centuries: from a sign of wealth in the middle ages, to a Rubenesque celebration during the Renaissance, to fear and loathing in modern Hollywood (unless of course it is injected into the lips or other ‘cosmetically desirable’ locations). Despite the current social aversion to fat, the increase in the percentage of people who are overweight has been marked and is observed in nearly all regions of the world. The global prevalence of obesity is ∼15% and in the United States more than two thirds of the population is overweight (Hossain et al., 2007). The health care system is reeling not only from an obesity epidemic, but also from a host of obesity-related negative sequelae including diabetes, cardiovascular disease, cirrhosis and even cancer. The reasons for this increase are well known - increased food consumption and decreased exercise - but this is only because the body is predisposed to fat accumulation.
What is also becoming clear is that a variety of evolutionary and developmental forces have laid the foundation for the development of obesity. Both invertebrates and vertebrates have fat-storing tissues and many aspects of the mechanistic underpinnings are conserved. These include the developmental programs, transcriptional cascades and basic proteins that regulate fat synthesis, storage and lipolysis (McKay et al., 2003; Suh et al., 2006; Suh et al., 2008; Suh et al., 2007). It appears that fat tissues evolved primarily as a safe harbor to store energy in times of plenty and to provide fuel when food sources become insufficient. However, in addition to serving as purely a storage depot, adipose tissue is now recognized as the body’s largest endocrine organ, controlling many aspects of systemic physiology by secreting hormones (adipokines), lipids, cytokines and other factors (Gesta et al., 2007; Nawrocki and Scherer, 2004; Spiegelman and Flier, 2001). Although many of the regulatory molecules are not yet identified, they control a wide variety of biological actions, including appetite, glucose homeostasis, insulin sensitivity, aging, fertility and fecundity, and body temperature.