Cellular life histories and bow tie biology

What is normal, healthy growth? Global health, human biology, and parental perspectives

OBJECTIVES

The widespread variation seen in human growth globally stands at odds with the global health perspective that young child growth should not vary across populations if nutritional, environmental and care needs are met. This paper: (1) evaluates the idea that a single standard of "healthy" growth characterizes children under age 5, (2) discusses how variation from this standard is viewed in global health, in human biology and by parents, and (3) explores how views of "normal" growth shape biomedical and parental responses.

METHODS

This paper reviews the anthropological, public health and clinical literature on the nature of child growth and the applicability of World Health Organization Multicenter Growth Reference Study growth standards across contexts.

RESULTS

The considerable variability in child growth across contexts makes it unlikely that any one framework, with issues of sample selection and representativeness, can serve as the model of healthy growth. Global health, human biology and parents differ in the emphasis they place on heredity versus environmental context in understanding this variability, but human biologists and parents tend to view a wider range of growth as "normal." Since both biomedicine and parents base their care decisions on their perceptions of normal, healthy growth, the comparative framework used has important implications for medical treatment and feeding practices.

CONCLUSIONS

A more nuanced approach that incorporates the biology of growth and its association with health outcomes across contexts is critical to identify patterns of healthy growth and to avoid over-reliance on a single standard that may pathologize variability.

The Effect of Maternal Pulmonary Function Test Parameters on Umbilical Cord Blood Gas and the Duration of Labor

OBJECTIVE

To evaluate the relationship between the maternal pulmonary function test (PFT) and the Apgar score of the newborn, umbilical cord blood (UCB) gas values and the duration of delivery.

MATERIAL AND METHODS

The present study included 41 volunteer nulliparous pregnant women who presented to our obstetrics clinic and PFTs were performed by using spirometry.

RESULTS

A significant positive correlation was observed between 5^th-minute Apgar scores and maternal FEV1 (forced expiratory volume in the first second) (lt), FEV1%, FVC (lt), FVC% (r=0.509, p=0.003; r=0.47, p=0.007; r=0.434, p=0.013; r=0.417, p=0.017; respectively). A significant positive correlation was observed between UCB pH value and maternal FEV1 (lt), FVC (lt) (r=0.515, p=0.003; r=0.351, p=0.049; respectively).

CONCLUSION

Our results showed that FEV1 and FVC values, which indicate maternal respiratory functions, may affect Apgar scores of the newborn and UCB gas values.

Bioenergetic Evolution Explains Prevalence of Low Nephron Number at Birth: Risk Factor for CKD

There is greater than tenfold variation in nephron number of the human kidney at birth. Although low nephron number is a recognized risk factor for CKD, its determinants are poorly understood. Evolutionary medicine represents a new discipline that seeks evolutionary explanations for disease, broadening perspectives on research and public health initiatives. Evolution of the kidney, an organ rich in mitochondria, has been driven by natural selection for reproductive fitness constrained by energy availability. Over the past 2 million years, rapid growth of an energy-demanding brain in Homo sapiens enabled hominid adaptation to environmental extremes through selection for mutations in mitochondrial and nuclear DNA epigenetically regulated by allocation of energy to developing organs. Maternal undernutrition or hypoxia results in intrauterine growth restriction or preterm birth, resulting in low birth weight and low nephron number. Regulated through placental transfer, environmental oxygen and nutrients signal nephron progenitor cells to reprogram metabolism from glycolysis to oxidative phosphorylation. These processes are modulated by counterbalancing anabolic and catabolic metabolic pathways that evolved from prokaryote homologs and by hypoxia-driven and autophagy pathways that evolved in eukaryotes. Regulation of nephron differentiation by histone modifications and DNA methyltransferases provide epigenetic control of nephron number in response to energy available to the fetus. Developmental plasticity of nephrogenesis represents an evolved life history strategy that prioritizes energy to early brain growth with adequate kidney function through reproductive years, the trade-off being increasing prevalence of CKD delayed until later adulthood. The research implications of this evolutionary analysis are to identify regulatory pathways of energy allocation directing nephrogenesis while accounting for the different life history strategies of animal models such as the mouse. The clinical implications are to optimize nutrition and minimize hypoxic/toxic stressors in childbearing women and children in early postnatal development.

Relationships between neonatal weight, limb lengths, skinfold thicknesses, body breadths and circumferences in an Australian cohort

Background

Low birth weight has been consistently associated with adult chronic disease risk. The thrifty phenotype hypothesis assumes that reduced fetal growth impacts some organs more than others. However, it remains unclear how birth weight relates to different body components, such as circumferences, adiposity, body segment lengths and limb proportions. We hypothesized that these components vary in their relationship to birth weight.

Methods

We analysed the relationship between birth weight and detailed anthropometry in 1270 singleton live-born neonates (668 male) from the Mater-University of Queensland Study of Pregnancy (Brisbane, Australia). We tested adjusted anthropometry for correlations with birth weight. We then performed stepwise multiple regression on birth weight of: body lengths, breadths and circumferences; relative limb to neck-rump proportions; or skinfold thicknesses. All analyses were adjusted for sex and gestational age, and used logged data.

Results

Circumferences, especially chest, were most strongly related to birth weight, while segment lengths (neck-rump, thigh, upper arm, and especially lower arm and lower leg) were relatively weakly related to birth weight, and limb lengths relative to neck-rump length showed no relationship. Skinfolds accounted for 36% of birth weight variance, but adjusting for size (neck-rump, thigh and upper arm lengths, and head circumference), this decreased to 10%. There was no evidence that heavier babies had proportionally thicker skinfolds.

Conclusions

Neonatal body measurements vary in their association with birth weight: head and chest circumferences showed the strongest associations while limb segment lengths did not relate strongly to birth weight. After adjusting for body size, subcutaneous fatness accounted for a smaller proportion of birth weight variance than previously reported. While heavier babies had absolutely thicker skinfolds, this was proportional to their size. Relative limb to trunk length was unrelated to birth weight, suggesting that limb proportions at birth do not index factors relevant to prenatal life.

Trade-offs in relative limb length among Peruvian children: extending the thrifty phenotype hypothesis to limb proportions

Background and Methods

Both the concept of ‘brain-sparing’ growth and associations between relative lower limb length, childhood environment and adult disease risk are well established. Furthermore, tibia length is suggested to be particularly plastic under conditions of environmental stress. The mechanisms responsible are uncertain, but three hypotheses may be relevant. The ‘thrifty phenotype’ assumes that some components of growth are selectively sacrificed to preserve more critical outcomes, like the brain. The ‘distal blood flow’ hypothesis assumes that blood nutrients decline with distance from the heart, and hence may affect limbs in relation to basic body geometry. Temperature adaptation predicts a gradient of decreased size along the limbs reflecting decreasing tissue temperature/blood flow. We examined these questions by comparing the size of body segments among Peruvian children born and raised in differentially stressful environments. In a cross-sectional sample of children aged 6 months to 14 years (n = 447) we measured head circumference, head-trunk height, total upper and lower limb lengths, and zeugopod (ulna and tibia) and autopod (hand and foot) lengths.

Results

Highland children (exposed to greater stress) had significantly shorter limbs and zeugopod and autopod elements than lowland children, while differences in head-trunk height were smaller. Zeugopod elements appeared most sensitive to environmental conditions, as they were relatively shorter among highland children than their respective autopod elements.

Discussion

The results suggest that functional traits (hand, foot, and head) may be partially protected at the expense of the tibia and ulna. The results do not fit the predictions of the distal blood flow and temperature adaptation models as explanations for relative limb segment growth under stress conditions. Rather, our data support the extension of the thrifty phenotype hypothesis to limb growth, and suggest that certain elements of limb growth may be sacrificed under tough conditions to buffer more functional traits.

Reduced O2 concentration during CAM development--its effect on angiogenesis and gene expression in the broiler embryo CAM

Hypoxia during embryogenesis may induce changes in the development of some physiological regulatory systems, thereby causing permanent phenotypic changes in the embryo. Various levels of hypoxia at different time points during embryogenesis were found to affect both anatomical and physiological morphogenesis. These changes and adaptations depended on the timing, intensity, and duration of the hypoxic exposure and, moreover, were regulated by differential expression of developmentally important genes, mostly expressed in a stage- and time-dependent manner. Eggs incubated in a 17%-oxygen atmosphere for 12 h/d from E5 through E12 exhibited a clear and significant increase in the vascular area of the chorioallantoic membrane (CAM); an increase that was already significant within 12 h after the end of the 1st hypoxic exposures (E6). We used the combination of the genes, β-actin, RPLP0 and HPRT as a reference for gene expression profiling, in studying the expression levels of hypoxia-inducible factor 1-alpha (HIF1α), vascular endothelial growth factor alpha-2 (VEGF α 2), vascular endothelial growth factor receptor 2 (KDR), matrix metalloproteinase-2 (MMP2), and fibroblast growth factor 2 (FGF2), under normal and hypoxic conditions. In general, expression of all five investigated genes throughout the embryonic day of development had similar patterns of hypoxia-induced alterations. In E5.5 embryos, expression of HIF1α, MMP2, VEGFα2, and KDR was significantly higher in hypoxic embryos than in controls. In E6 embryos expression of HIF1α, VEGFα2, and FGF2 was significantly higher in hypoxic embryos than in controls. From E6.5 onward expression levels of the examined genes did not show any differences between hypoxic and control embryos. It can be concluded that in this experimental model, exposing broiler embryos to 17% O(2) from E5 to E7 induced significant angiogenesis, as expressed by the above genes. Further studies to examine whether this early exposure to hypoxic condition affects the chick's ability to withstand a post-hatch hypoxic environment is still required.

Nicotinamide, NAD(P)(H), and Methyl-Group Homeostasis Evolved and Became a Determinant of Ageing Diseases: Hypotheses and Lessons from Pellagra

Compartmentalized redox faults are common to ageing diseases. Dietary constituents are catabolized to NAD(H) donating electrons producing proton-based bioenergy in coevolved, cross-species and cross-organ networks. Nicotinamide and NAD deficiency from poor diet or high expenditure causes pellagra, an ageing and dementing disorder with lost robustness to infection and stress. Nicotinamide and stress induce Nicotinamide-N-methyltransferase (NNMT) improving choline retention but consume methyl groups. High NNMT activity is linked to Parkinson's, cancers, and diseases of affluence. Optimising nicotinamide and choline/methyl group availability is important for brain development and increased during our evolution raising metabolic and methylome ceilings through dietary/metabolic symbiotic means but strict energy constraints remain and life-history tradeoffs are the rule. An optimal energy, NAD and methyl group supply, avoiding hypo and hyper-vitaminoses nicotinamide and choline, is important to healthy ageing and avoids utilising double-edged symbionts or uncontrolled autophagy or reversions to fermentation reactions in inflammatory and cancerous tissue that all redistribute NAD(P)(H), but incur high allostatic costs.

Network, degeneracy and bow tie. Integrating paradigms and architectures to grasp the complexity of the immune system

Recently, the network paradigm, an application of graph theory to biology, has proven to be a powerful approach to gaining insights into biological complexity, and has catalyzed the advancement of systems biology. In this perspective and focusing on the immune system, we propose here a more comprehensive view to go beyond the concept of network. We start from the concept of degeneracy, one of the most prominent characteristic of biological complexity, defined as the ability of structurally different elements to perform the same function, and we show that degeneracy is highly intertwined with another recently-proposed organizational principle, i.e. 'bow tie architecture'. The simultaneous consideration of concepts such as degeneracy, bow tie architecture and network results in a powerful new interpretative tool that takes into account the constructive role of noise (stochastic fluctuations) and is able to grasp the major characteristics of biological complexity, i.e. the capacity to turn an apparently chaotic and highly dynamic set of signals into functional information.

Altered hypoxia-inducible factor-1 alpha expression levels correlate with coronary vessel anomalies

The outflow tract myocardium and other regions corresponding to the location of the major coronary vessels of the developing chicken heart, display a high level of hypoxia as assessed by the hypoxia indicator EF5. The EF5-positive tissues were also specifically positive for nuclear-localized hypoxia inducible factor-1 alpha (HIF-1alpha), the oxygen-sensitive component of the hypoxia inducible factor-1 (HIF-1) heterodimer. This led to our hypothesis that there is a "template" of hypoxic tissue that determines the stereotyped pattern of the major coronary vessels. In this study, we disturbed this template by altering ambient oxygen levels (hypoxia 15%; hyperoxia 75-40%) during the early phases of avian coronary vessel development, in order to alter tissue hypoxia, HIF-1alpha protein expression, and its downstream target genes without high mortality. We also altered HIF-1alpha gene expression in the embryonic outflow tract cardiomyocytes by injecting an adenovirus containing a constitutively active form of HIF-1alpha (AdCA5). We assayed for coronary anomalies using anti-alpha-smooth muscle actin immunohistology. When incubated under abnormal oxygen levels or injected with a low titer of the AdCA5, coronary arteries displayed deviations from their normal proximal connections to the aorta. These deviations were similar to known clinical anomalies of coronary arteries. These findings indicated that developing coronary vessels may be subject to a level of regulation that is dependent on differential oxygen levels within cardiac tissues and subsequent HIF-1 regulation of gene expression.

Hypoxia induces cardiac malformations via A1 adenosine receptor activation in chicken embryos

BACKGROUND

The current understanding of the effects of hypoxia on early embryogenesis is limited. Potential mediators of hypoxic effects include adenosine, which increases dramatically during hypoxic conditions and activates A(1) adenosine receptors (A(1)ARs).

METHODS

To examine the influences of hypoxia and adenosine signaling on cardiac development, chicken embryos were studied. Real time RT-PCR assay was used to examine the A(1)AR gene expression during embryogenesis and after siRNA- mediated knock down. Cell proliferation was determined by counting cell nuclei and PhosphoHistone H3 positive cells. Apoptosis was determined by TUNEL assay.

RESULTS

A(1)ARs were found to be expressed in chicken embryos during early embryogenesis. Treatment of Hamburger and Hamilton stage 4 embryos with the A(1)AR agonist N(6)-cyclopentyladenosine caused cardiac bifida and looping defects in 55% of embryos. Hamburger and Hamilton stage 4 embryos exposed to 10% oxygen for 6, 12, 18, and 24 h followed by recovery in room air until stage 11, exhibited cardia bifida and looping defects in 34, 45, 60, and 86% of embryos respectively. Hypoxia-induced abnormalities were reduced when A(1)AR signaling was inhibited by the A(1)AR antagonist 1,3 dipropyl-8-cyclopentylxanthine or by siRNA-targeting A(1)ARs. Hypoxia treatment did not increase apoptosis, but decreased embryonic cell proliferation.

CONCLUSIONS

These data indicate that hypoxia adversely influences cardiac malformations during development, in part by A(1)AR signaling.

Tradeoffs between oxygen and energy in tibial growth at high altitude

Some studies of high altitude populations argue that stature reduction results from caloric, rather than hypoxic, stress. However, tradeoff models of oxygen and glucose metabolism predict that in hypoxemia, glucose metabolism will be downregulated. We used tradeoff assumptions in two hypotheses: First, that hypoxia targets leg segment growth differentially, and second, that proportions of leg segments partition the impact of high altitude into hypoxemic and energetic components. A group of 113 Han and Tibetan middle school children at 3100 m aged 8 to 11 were measured for segment anthropometries, skinfolds, vital capacity, blood oxygen saturation, and percent body fat. MANOVA showed that Tibetan children were significantly larger and fatter than Han children. Independent of ethnicity or caloric status, absolute and relative tibia length was significantly reduced in children with lower blood oxygen saturation. Height, chest circumference, sitting height, tibia length, and ankle diameter were greatest in fatter children, independent of ethnicity or blood oxygen. For children of either ethnicity with the lowest blood oxygen, size as well as proportion was impacted. These results support the tradeoff model. Caloric reserves and ethnicity independently affect total skeletal size. Oxygen saturation and ethnicity affect leg proportions. In hypoxemia, body fat has less impact on growth than when ample oxygen is present. Therefore, we should qualify the claim that size in high altitude populations stems from nutritional stress. The findings also suggest that decanalization may have different meanings and outcomes depending on which body segments contribute to the effect.

Is there an elephant in the room? Addressing rival approaches to the interpretation of growth perturbations and small size

Two interpretations of growth perturbation and small size are commonly applied in human biology: an adaptationist approach in which small size is considered to be an a relatively beneficial adjustment to environmental stressors, and a biomedical approach in which small size is considered nonadaptive, a sign of dysfunction or pathology. These two interpretations conflict, but are used without acknowledging or addressing the conflict. This article reviews the strengths and weaknesses of the two. This exercise does not prove the indisputable superiority of either approach. Considerations of epistemology show that biologists will never be faced with a decisive test of either, much as they might like such clear cut evidence. Nevertheless, it is possible that a gradual decrease in the productivity of one approach will become a sufficient reason to abandon it. Alternatively, if specific areas of application can be distinguished, each approach might continue to be productive in its own domain.

Growth chart curves do not describe individual growth biology

Growth reference tables present statistical distributions of size for age of individuals within a sample or population. As summaries of phenotypic variability at the group level, they document that individuals grow by different rates during similar time frames. The data are commonly fitted by mathematical functions to produce the convex curves of percentile distributions useful for infant and childhood growth monitoring. In this form, the growth chart appears to be a frame of reference for judging how well an individual infant/child is progressing through time by comparison with peers across ages. This has led to the assumption that individuals should track in these channels during growth. The interpolated lines between the statistical distributions of size for age at the level of the population do not, however, represent how individuals grow. Growing is an individual process characterized by nonlinear episodic saltatory increments that result in shifting size relationships among similarly aged peers over short time intervals. Data from a prospective, longitudinal study of infants illustrate the poor performance of growth chart curves as representations of individual growth. Clarification of the paradigms supporting perceptions of normal growth patterns is useful both practically and theoretically: growth chart patterns have important clinical sequelae when this informs feeding recommendations. Further characterization of individual growth patterns will contribute to increased understanding of both individual growth biology and the nature of adaptability.

Maternal oxygen delivery is not related to altitude- and ancestry-associated differences in human fetal growth

Fetal growth is reduced at high altitude, but the decrease is less among long-resident populations. We hypothesized that greater maternal uteroplacental O(2) delivery would explain increased fetal growth in Andean natives versus European migrants to high altitude. O(2) delivery was measured with ultrasound, Doppler and haematological techniques. Participants (n=180) were pregnant women of self-professed European or Andean ancestry living at 3600 m or 400 m in Bolivia. Ancestry was quantified using ancestry-informative single nucleotide polymorphism. The altitude-associated decrement in birth weight was 418 g in European versus 236 g in Andean women (P<0.005). Altitude was associated with decreased uterine artery diameter, volumetric blood flow and O(2) delivery regardless of ancestry. But the hypothesis was rejected as O(2) delivery was similar between ancestry groups at their respective altitudes of residence. Instead, Andean neonates were larger and heavier per unit of O(2) delivery, regardless of altitude (P<0.001). European admixture among Andeans was negatively correlated with birth weight at both altitudes (P<0.01), but admixture was not related to any of the O(2) transport variables. Genetically mediated differences in maternal O(2) delivery are thus unlikely to explain the Andean advantage in fetal growth. Of the other independent variables, only placental weight and gestational age explained significant variation in birth weight. Thus greater placental efficiency in O(2) and nutrient transport, and/or greater fetal efficiency in substrate utilization may contribute to ancestry- and altitude-related differences in fetal growth. Uterine artery O(2) delivery in these pregnancies was 99 +/- 3 ml min(-1), approximately 5-fold greater than near-term fetal O(2) consumption. Deficits in maternal O(2) transport in third trimester normal pregnancy are unlikely to be causally associated with variation in fetal growth.

Life-long protein malnutrition in the rat (Rattus norvegicus) results in altered patterns of craniofacial growth and smaller individuals

Dietary protein is a limiting factor in mammalian growth, significantly affecting the non-linear trajectories of skeletal growth. Young females may be particularly vulnerable to protein malnutrition if the restriction is not lifted before they become reproductive. With such early malnutrition, limited amino acids would be partitioned between two physiological objectives, successful reproduction vs. continued growth. Thus, the consequences of protein malnutrition could affect more than one generation. However, few studies have quantified these cross-generational effects. Our objective was to test for differences in skeletal growth in a second generation of malnourished rats compared with rats malnourished only post-weaning, the first generation and with controls. In this longitudinal study we modelled the growth of 22 craniofacial measurements with the logistic Gompertz equation, and tested for differences in the equation's parameters among the diet groups. The female offspring of post-weaning malnourished dams did not catch up in size to the first generation or to controls, although certain aspects of their craniofacial skeleton were less affected than others. The second generation's growth trajectories resembled the longer and slower growth of the first malnourished generation. There was a complex interaction between developmental processes and early nutritional environment, which affected variation of adult size.

Growth patterns of the heart and kidney suggest inter-organ collaboration in facultative fetal growth

Maternal smoking during pregnancy has been associated with a number of negative sequelae among offspring, including elevated postnatal blood pressure. While animal studies have described organ level alterations with smoke exposure, human data have been more limited. Thirty-four healthy maternal/fetal pairs (24 nonsmokers, 10 smokers) participated in a longitudinal growth study from the thirteenth week of pregnancy to document fetal kidney and heart growth trajectories and morphology. Curve fitting followed by a mixed model for repeated measures identified significantly different growth patterns in kidney width, thickness, length, and volume growth with exposure: the smoke-exposed fetal kidney was wide and thick compared to the unexposed kidney during the second and early third trimester, declining to proportionately thin kidneys for length and width subsequently. Cardiac growth in width and volume followed a reverse pattern: a surge in cardiac volume occurred after 30 weeks with acceleration in cardiac width, resulting in a heart that was wide for length and for fetal weight. Smoke exposure altered fetal growth in size and timing of the heart and kidneys during midgestation, with changes in organ morphology suggesting compensatory growth. These are the first data providing anatomical evidence of altered renal/cardiac volume relationships that may provide a mechanism to previously reported sequelae of in utero smoke exposure. They suggest that cell-level adaptive responses to hypoxia and/or chemical insults are operative and illustrate the importance of longitudinal ultrasound to directly assess the organ-level growth response of the human fetus to a prenatal stress, in lieu of relying on birth outcome measures.

High ponderal index at birth predicts high estradiol levels in adult women

Inter-individual variation in levels of sex hormones results from differences in genetic, developmental, and environmental factors. We tested a hypothesis that programming of the fetal neuroendocrine axis may predispose some women to produce higher levels of steroid hormones during their menstrual cycles as adults. One hundred forty-five regularly menstruating 24- to 36- year-old women collected daily saliva samples for one menstrual cycle. Data on women's birth weights and birth lengths were obtained from medical records. A positive relationship was observed between ponderal index at birth (an indicator of nutritional status, calculated as birth weight/(birth length)(3)) and levels of estradiol (E2) in menstrual cycles, after controlling for potential confounding factors. Mean E2 was 16.4 pmol/l in the low ponderal index tertile, 17.3 pmol/l in the moderate ponderal index tertile, and 19.6 pmol/l in the high ponderal index tertile (the high ponderal index group had significantly higher E2 than both low and moderate ponderal index groups, P=0.0001). This study shows a positive association between ponderal index recorded for women at birth and levels of E2 measured during their menstrual cycles as adults. This suggests that conditions during fetal life influence adult production of reproductive hormones and may contribute to inter-individual variation in reproductive function. In addition, because large size at birth is one of the factors linked with an increased risk of breast cancer, our findings provide a physiological link for the observed positive relationship between indicators of energetic conditions during fetal growth and breast cancer in women.