Recent insights into body weight control: from physiology to pathology

Maternal protein restriction permanently programs adipocyte growth and development in adult male rat offspring

We previously demonstrated that maternal protein restriction (MPR) during pregnancy and lactation led to fetal growth restriction and development of increased visceral adiposity in adult male rat offspring. Here we studied the rate of proliferation and differentiation of adipocyte precursors (preadipocytes) in vitro to investigate whether MPR may permanently program adipocyte growth and development in adult male offspring. Preadipocytes were isolated from visceral adipose tissue of control and MPR offspring at 130 days of age, and cultured under standard conditions. The rate of proliferation was studied by [(3)H]-thymidine incorporation, and the rate of differentiation assessed with the use of biochemical and morphological markers. Although it did not affect the rate of differentiation, MPR increased the rate of preadipocyte proliferation by almost twofold. To ascertain if the increased proliferation was due to persisting in vivo influences or aberrations inherent in the precursor cells, we studied the rate of preadipocyte proliferation in subcultures. We found that the increased rate of proliferation of MPR preadipocytes persisted throughout the first two subcultures, indicative of an inherent abnormality. In addition, we examined the rate of preadipocyte proliferation under reduced serum conditions. We showed that MPR reduced the rate of preadipocyte proliferation to 56 and 35% of the control in the presence of 5 and 2.5% serum, respectively. Taken together, these results demonstrate that MPR permanently programs adipocyte growth and development such that adipocyte precursors derived from MPR offspring replicate excessively under standard culture conditions but exhibit markedly attenuated growth rate under reduced serum conditions.

Synthesis of a novel potent cyclic peptide MC4-ligand by ring-closing metathesis

The synthesis of a novel potent cyclic peptide MC4-ligand by ring-closing metathesis (RCM) is described. Based on the Ac-Nle-Gly-Lys-D-Phe-Arg-Trp-Gly-NH2-MC4 ligand, Ac-Nle-Alg-Lys-D-Phe-Arg-Trp-Alg-NH2 was designed and synthesized followed by cyclization using RCM. Both compounds are high affinity and selective MC4-R-agonists. The cyclic RCM-peptide was more potent in a rat-grooming assay.

Adipose tissue gene expression profiling reveals distinct molecular pathways that define visceral adiposity in offspring of maternal protein-restricted rats

There is increasing evidence that poor early growth confers an increased risk of type 2 diabetes, hypertension, and other features of the metabolic syndrome in later life. We hypothesized that this may result from poor nutrition during early life exerting permanent effects on the structure and function of key metabolic organ systems. To study the long-term impact of early-life undernutrition on susceptibility to visceral adiposity, we used a rat model of maternal protein restriction (MPR) in which dams were fed a low-protein diet (containing 8% instead of 20% protein in control diet) throughout pregnancy and lactation. MPR offspring were born smaller than controls (offspring of dams on control diet) and in adulthood developed visceral adiposity. We compared the pattern of gene expression in visceral adipose tissue (VAT) between MPR offspring and controls with Affymetrix rat expression arrays. Of the total number of genes and expressed sequence tags analyzed (15,923 probe sets), 9,790 (61.5%) were expressed in VAT. We identified 650 transcripts as differentially expressed > or =1.5-fold in the VAT of MPR offspring. Gene ontology analysis revealed a global upregulation of genes involved in carbohydrate, lipid, and protein metabolism. A number of genes involved in adipocyte differentiation, angiogenesis, and extracellular matrix remodeling were also upregulated. However, in marked contrast to other rodent models of obesity, the expression of a large number of genes associated with inflammation was reduced in this rat model. Thus visceral adiposity in this early-life programmed rat model is marked by dynamic changes in the transcriptional profile of VAT. Our data provide new insights into the molecular mechanisms that underlie the early-life programming of visceral adiposity.

The concept of allostasis in biology and biomedicine

Living organisms have regular patterns and routines that involve obtaining food and carrying out life history stages such as breeding, migrating, molting, and hibernating. The acquisition, utilization, and storage of energy reserves (and other resources) are critical to lifetime reproductive success. There are also responses to predictable changes, e.g., seasonal, and unpredictable challenges, i.e., storms and natural disasters. Social organization in many populations provides advantages through cooperation in providing basic necessities and beneficial social support. But there are disadvantages owing to conflict in social hierarchies and competition for resources. Here we discuss the concept of allostasis, maintaining stability through change, as a fundamental process through which organisms actively adjust to both predictable and unpredictable events. Allostatic load refers to the cumulative cost to the body of allostasis, with allostatic overload being a state in which serious pathophysiology can occur. Using the balance between energy input and expenditure as the basis for applying the concept of allostasis, we propose two types of allostatic overload. Type 1 allostatic overload occurs when energy demand exceeds supply, resulting in activation of the emergency life history stage. This serves to direct the animal away from normal life history stages into a survival mode that decreases allostatic load and regains positive energy balance. The normal life cycle can be resumed when the perturbation passes. Type 2 allostatic overload begins when there is sufficient or even excess energy consumption accompanied by social conflict and other types of social dysfunction. The latter is the case in human society and certain situations affecting animals in captivity. In all cases, secretion of glucocorticosteroids and activity of other mediators of allostasis such as the autonomic nervous system, CNS neurotransmitters, and inflammatory cytokines wax and wane with allostatic load. If allostatic load is chronically high, then pathologies develop. Type 2 allostatic overload does not trigger an escape response, and can only be counteracted through learning and changes in the social structure.